Shear stress and pathophysiological PI3K involvement in vascular malformations

Molecular characterization of vascular anomalies has revealed that affected endothelial cells (ECs) harbor gain-of-function (GOF) mutations in the gene encoding the catalytic α subunit of PI3Kα (PIK3CA). These PIK3CA mutations are known to cause solid cancers when occurring in other tissues. PIK3CA-related vascular anomalies, or “PIKopathies,” range from simple, i.e., restricted to a particular form of malformation, to complex, i.e., presenting with a range of hyperplasia phenotypes, including the PIK3CA-related overgrowth spectrum. Interestingly, development of PIKopathies is affected by fluid shear stress (FSS), a physiological stimulus caused by blood or lymph flow. These findings implicate PI3K in mediating physiological EC responses to FSS conditions characteristic of lymphatic and capillary vessel beds. Consistent with this hypothesis, increased PI3K signaling also contributes to cerebral cavernous malformations, a vascular disorder that affects low-perfused brain venous capillaries. Because the GOF activity of PI3K and its signaling partners are excellent drug targets, understanding PIK3CA’s role in the development of vascular anomalies may inform therapeutic strategies to normalize EC responses in the diseased state. This Review focuses on PIK3CA’s role in mediating EC responses to FSS and discusses current understanding of PIK3CA dysregulation in a range of vascular anomalies that particularly affect low-perfused regions of the vasculature. We also discuss recent surprising findings linking increased PI3K signaling to fast-flow arteriovenous malformations in hereditary hemorrhagic telangiectasias.

ECs are characterized by an intrinsic capacity to rapidly adapt and respond to the mechanical stimulus exerted by FSS. This response can affect their proliferation, shape, movement, and cell fate. FSS varies with respect to its magnitude, which refers to its maximal force, and its flow pattern, which can be laminar, pulsatile, or turbulent and which can diverge with respect to its direction (unidirectional or bidirectional/oscillatory) (Figure 2). Fluid flow patterns can change from laminar to turbulent based on shifts in the ratio between inertial and viscous forces. In fluid mechanics, this ratio is expressed by the Reynolds number. Large blood vessels are characterized by a high Reynolds number and are more prone to exhibit turbulent flow. Laminar flow patterns prevail at low Reynolds numbers that are characteristic of small capillaries. Importantly, the Reynolds number can also rise in small capillaries when fluid flow drops to a low magnitude. This predicts that a turbulent flow pattern can also occur in small vessels.

Figure 2

Different parameters of FSS and vascular morphology affect EC. ECs are characterized by an intrinsic capacity to rapidly adapt and respond to the mechanical stimulus exerted by FSS. (A) FSS varies with respect to the magnitude, which refers to its maximal force, and the flow pattern, which can either be pulsatile or laminar and which can diverge with respect to its direction (unidirectional or bidirectional/oscillatory). (B) Turbulent flow patterns can arise at branch points or due to shifts in the ratio between inertial and viscous forces.

Consequently, in different regions of the vasculature that are exposed to distinct FSS patterns, the responses of ECs differ and can be homeostatic, adaptive, or maladaptive. A laminar and unidirectional FSS pattern will induce EC responses that favor quiescence and vascular stability, whereas a disturbed flow pattern, arising in regions of the vasculature with branching points or curvatures, may trigger EC proliferation and a gene expression profile characteristic of inflammation and oxidative stress (41–43). A laminar flow pattern of a high magnitude will promote an elongation and alignment of ECs parallel to the direction of flow; it will also trigger their orientation and migration against flow (collectively termed axial polarity-mediated reverse migration). By contrast, in capillaries exposed to only a low magnitude of flow, ECs fail to align or to initiate polarity-induced migration (44–48). This response prevents EC regression in slowly perfused vessel beds. The response of ECs to FSS also affects vessel diameter (49–52). This capacity of ECs to respond to different levels of fluid flow has been attributed to the existence of a “FSS set point.” The FSS set point is a concept positing that ECs “memorize” an optimized FSS and that they will respond by inward or outward remodeling of the vessel diameter if transient alterations of FSS levels occur (53, 54) (reviewed in refs. 33, 55, 56). Therefore, small changes in physiological flow patterns drive adaptive and transient EC remodeling of the vascular wall until the original FSS set point is restored. It is also conceivable that a defective signal transduction triggered by FSS will result in maladapted and chronic vessel remodeling, thus contributing to vascular instability and disease.

Functional experiments in mice, zebrafish, and human ECs led to the identification of various molecular components that mediate FSS responses. Several of these studies point to a central role of PI3K signaling directly downstream of a FSS set point machinery, which assembles around EC adherens junctions and comprises PECAM-1, vascular endothelial–cadherin (VE-cadherin), and the VEGF receptors VEGFR2 and VEGFR3 (57–60) (Figure 3). Recent evidence suggests that PECAM-1 acts as a relay in the FSS cascade downstream of other mechanosensors, including GPCRs and mechanically gated ion channels, among others (61–63).

Figure 3

Interconnected signaling pathways in vascular anomalies involving PI3K signaling. Fluid shear stress (FSS) activates mechanosensitive signaling, involving, among others, a FSS set point machinery comprising VE-cadherin (cadherin 5), VEGFR2/3, and PECAM-1, which activates downstream PI3K signaling. FSS also triggers an activation of the MEKK3 pathway. In CCM, an overactivation of KLF2/4 in small venous capillaries triggers a pathological endothelial-mesenchymal transition (endMT) and overproliferation. Asterisks indicate proteins for which oncogenic GOF mutations have been identified in slow-flow vascular anomalies. Increased PI3K signaling characterizes slow-flow venous and cavernous malformations but also HHT-related fast-flow AVMs caused by LOF mutations in genes encoding ALK1, endoglin, BMP9, or SMAD4.

Another FSS mediator complex upstream of PECAM-1 involves PlexinD1, which becomes engaged in a receptor complex with Neuropilin 1 and VEGFR2; this triggers a ligand-independent activation of VEGFRs and initiates a shear stress signaling cascade involving PI3K and its central downstream mediator AKT. The activation of AKT is dependent upon the magnitude of FSS (64). BMP9 circulating in blood acts upstream of FSS to limit excessive PI3K/AKT activation (65). Yet, the precise mechanism, i.e., how activation of AKT is balanced, remains to be elucidated. In static cells, BMP9 inhibits activation of PI3K/AKT through a negative feedback loop that involves transcriptional repression of casein kinase 2–mediated (CK2-mediated) dephosphorylation of the phosphatase and tensin homolog (PTEN) (65). PTEN is a phosphatase that negatively regulates PI3K activity. Dephosphorylated PTEN binds the cell membrane and reduces the production of PIP3, thus antagonizing PI3K/AKT signaling. BMP9 also restricts the VEGFA-induced activation of PI3K/AKT, which involves PTEN as a repressive factor (66). Interestingly, laminar FSS represses PTEN levels in a time- and magnitude-dependent manner, while AKT activation follows the exact opposite trend (67). Thus, PTEN downstream of BMP9 and FSS or angiogenic stimuli restricts PI3K activity.

The activation of PI3K/AKT signaling by physiological FSS regulates EC alignment (68), and this is also important for the activation of NOS3-mediated vasodilation (69) and for cell survival (70). Thus, the alignment of ECs in response to laminar FSS is mediated by an activation of PI3K and is part of an antiinflammatory and vasodilatory adaptation program that is characteristic of healthy vessels. SMAD4 mediates many EC quiescence events, as mentioned above, and this requires a precise threshold of PI3K/AKT activity (64). Therefore, PI3K emerges as a signaling hub in several pathways that are activated in response to FSS, and accurate levels of PI3K activation ensure a correct balance between EC activation and quiescence (Figure 3).

PI3K’s key positioning in the FSS response is also linked to its paramount roles in signaling downstream of several growth or angiogenesis receptors. These include the VEGFR2 and VEGFR3 receptors that are activated during vascular growth and remodeling by FSS, hypoxic physiological conditions, or proangiogenic factors, among others (reviewed in ref. 71). PI3K also mediates TIE2 (encoded by TEK) receptor signaling upon binding of angiopoietin-1 (ANG1) (72). Signaling by ANG1/TIE2 maintains vascular quiescence in the murine adult vasculature (73–75). In part, this effect is mediated by the transcriptional regulator Krüppel-like factor 2 (KLF2), which is among the downstream targets activated by ANG1/TIE2 signaling in ECs (76), and this activation requires PI3K (72). KLF2 and KLF4 are transcriptional regulators that are activated by FSS (77–84) and trigger gene expression that promotes vascular quiescence (43, 78, 83, 85–87). TEK itself is upregulated upon laminar FSS in a KLF4-dependent manner, and TIE2 is required together with PECAM-1 for FSS-induced AKT activation (64, 88). Altogether, these studies suggest that the development and the maintenance of a mature vascular network is guided by both mechanical stimuli triggered by FSS and/or physiological conditions such as the availability of oxygen and nutrients. These factors will trigger biomechanical and biochemical signaling within ECs that both impinge upon PI3K/AKT activation. Therefore, PI3K is a key factor in the development and maintenance of vascular homeostasis in the blood and lymphatic endothelium.

In recent years, genetic studies of vascular anomalies have led to the identification of mutations that impinge upon aberrant activation of the PI3K pathway (GOF mutations in TEK, PIK3CA, or AKT and loss-of-function [LOF] mutations in PTEN) (reviewed in ref. 89). These findings underscore the crucial role of this pathway in vascular integrity and homeostasis. A recent study identified somatic LOF mutations in PIK3R1 and GOF mutations in PIK3CA that were associated with a novel vascular malformation termed capillary malformation with dilated veins (CMDV) (90).

Activating mutations in PIK3CA and AKT are predominantly somatic in nature, as germline mutations in these genes are incompatible with survival. Similar to PIK3CA, somatic mutations in AKT may also manifest as isolated lesions or within a complex syndromic phenotype, the Proteus syndrome (91). In contrast, TEK mutations can occur either somatically or in the germline. A large spectrum of LOF PTEN mutations is frequently inherited via the germline and leads to PTEN hamartoma tumor syndrome (PHTS) (92, 93).

Increasing evidence suggests that hemodynamic forces due to FSS strongly contribute to the occurrences of many types of vascular anomalies. Both the PI3K/AKT/mTOR and the RAS/MAPK pathways, together with the NO signaling pathway, become excessively activated in different types of vascular malformations (reviewed in refs. 22, 37). The same exact pathways are also stimulated by physiological laminar FSS, which transiently activates signaling via MAPK (reviewed in ref. 94), Rho family GTPase (reviewed in ref. 95), and NO signaling pathways (NOS3 and NOS), with a release of NO, an important antiinflammatory and vasodilatory signal associated with healthy vessels (96, 97). FSS can also trigger more permanent effects via ERK5, driving KLF2/4 transcription factor activation that causes an antiinflammatory phenotype (35, 80). Strikingly, disturbed flow activates the same pathways, yet also activates ROS and NF-κB proinflammatory modulators (98–100). These pathways link biomechanical signaling in response to FSS with key processes of EC biology such as cell fate determination, cell orientation and migration, and cell proliferation.

The elongation and alignment of ECs is mediated by cytoskeletal remodeling driven by the Rho GTPase family proteins RHO, RAC, and CDC42, whose activities are determined by FSS (101–104). Based on their occurrences in distinctly perfused vessel beds, a large range of vascular malformations can be categorized as either slow-flow “PIKopathies” that involve the PI3K/AKT/mTOR pathway or fast-flow “RASopathies,” involving a stimulation of the RAS/MAPK pathway (reviewed in ref. 22). This suggests critical roles of PI3K and RAS as key mediators for controlling FSS-dependent vascular biology. In alignment with such divergent physiological roles, both factors are also important fate determinants for venous versus arterial cell identities, respectively (6, 105–108). The maintenance of arterial identity also depends on FSS-mediated cell cycle arrest, regulated by the NOTCH and canonical BMP9/10 signaling pathways (64, 109). Interestingly, the class I isoform PI3Kβ binds to RAC1 and CDC42 via its RAS-binding domain, indicating that these two signaling hubs are interconnected (110).

The (patho-)physiological role of PI3K within slow-flow regions of the vasculature has been particularly well-characterized. The molecular characterization of an entire spectrum of slow-flow vascular malformations revealed the presence of well-known oncogenic driver mutations in PIK3CA that cause cancer in other tissues (111) and drive venous and lymphatic malformations in the endothelium (112–118). Therefore, vascular lesions in slowly perfused vessels beds have been linked to excessive PI3K signaling caused by either genetic GOF mutations or upon a physiological overstimulation of this pathway that converts into pathological signaling. Increased PI3K/AKT activation causes venous, lymphatic, and/or capillary ECs to lose quiescence and undergo persistent remodeling. These findings suggest that PI3K acts as a rheostat in controlling EC responses to FSS and that this pathway is particularly sensitive to slow FSS conditions.

Much of our understanding about the role of biomechanical responses in vascular malformations has come from work on CCMs. CCMs arise after a biallelic loss of one of three CCM genes encoding CCM1 (also known as KRIT1) (119), CCM2 (120), or PDCD10 (referred to herein as CCM3) (121). These mutations can cause the formation of vascular malformations that arise mainly within slowly perfused venous capillaries of the brain vasculature and result in bleeding with unpredictable consequences for patients. Molecular and genetic studies in different CCM animal models and human ECs revealed that a direct physical interaction of CCM2 with MEKK3 kinase (encoded by MAP3K3) prevents an activating phosphorylation (122, 123). MEKK3 stimulates signaling via ERK5 and the downstream transcriptional regulators KLF2 and KLF4 (123–127). The stimulation of high expression levels of KLF2/4 within brain capillary ECs contributes to CCM lesion formation (124, 127, 128). Suppression of the MEKK3/ERK5/KLF2/4 pathway prevented the formation of disease phenotypes in CCM models (124, 125, 127, 129). This research established the CCM proteins as gatekeepers of appropriate biomechanical signaling responses within slowly perfused vessel beds and established their role in suppressing an overactivation of pathological KLF2/4 signaling under conditions of low FSS (Figure 3).

Yet, the discoveries of the disease-associated CCM genes soon came with the realization that a monogenic trait was not sufficient to explain the natural disease progression in humans and that other “third hits” may be involved (reviewed in ref. 130). Such third hits involve truly genetic changes or may be nongenetic in nature. Sequencing studies of human CCM lesions revealed that, indeed, genetic third hits occur in CCM lesions. Many human CCM tissue samples harbored the same oncogenic PIK3CA GOF mutations that also occur in cancer and in other vascular anomalies (24, 131). This finding suggested a surprising genetic link between the CCM/MEKK3/KLF2/4 and the PI3K/AKT/mTOR pathways in CCM lesion formation. In further support of such a model, genetic studies in patients with spontaneous forms of CCM revealed that an overstimulation of the MEKK3/KLF2/4 pathway due to the occurrence of oncogenic MAP3K3 GOF mutations correlates with the formation of spontaneous CCM lesions (132–134). In sporadic nonfamilial forms of CCM, CCM LOF or MAP3K3 GOF mutations were frequently found together with PIK3CA GOF mutations (134). Particularly aggressive forms of CCMs arise when both oncogenic Map3k3 and Pik3ca GOF mutations co-occur within the affected murine endothelium (135). In CCM disease animal models and human CCM protein-deficient ECs, oncogenic Pik3ca^H1047R mutations synergized with loss of CCM proteins and strongly aggravated lesion formation (24). This triggered a strong mTORC1 and S6Kinase activation, and treatment with the FDA-approved drug rapamycin (sirolimus), an mTORC1 inhibitor commonly used for the treatment of venous and lymphatic malformations caused by Pik3ca GOF mutations, improved lesion outcomes. The pharmacological suppression of mTORC1 by rapamycin also suppressed lesion formation in a murine model that combined inducible Ccm LOF and Pik3ca GOF mutations (136). These discoveries suggested that a cancer-like three-hit mechanism is involved in CCM lesion formation (24). According to that model, CCM genes act as vascular “suppressor genes” and homozygous loss of these genes leads to increased vessel growth. Excessive vessel overgrowth is then fueled when affected ECs acquire an additional third oncogenic driver mutation.

Several nongenetic factors may also contribute to the occurrence of CCM lesions. The number of CCM lesions expands in patients over 50 years of age (137). In these patients, increasingly hypoxic conditions during aging apparently fuel angiogenic signaling, thus contributing to the formation of vascular lesions. Similarly, in murine EC-specific knockouts of Ccm genes, lesions form most frequently in cerebellar and retinal vessels, two vascular beds undergoing active angiogenesis at postnatal stages (138), which is mediated by hypoxic conditions. Increased angiogenesis signaling is a hallmark feature of CCMs (129, 139–144). For instance, the loss of CCM3 increased the growth and microvascular density of a glioblastoma xenograft. This was triggered by the secretion of soluble factors, including VEGF, which mediates an activation of AKT (145). Enhanced angiogenic signaling may also trigger an overactivation of PI3K signaling together with its downstream targets AKT and mTOR. In fact, AKT and mTOR activities are strongly enhanced in Ccm LOF- and Klf4 GOF-transgenic murine models (24). This study also revealed that an overstimulation of PI3K resulting from EC loss of Pten had similar effects as a genetic third hit. Therefore, PI3K not only triggers the formation of vascular anomalies when oncogenic GOF mutations render its signaling pathological, but also when there is an PI3K-independent overstimulation that turns PI3K signaling pathological (24).

The EC-specific murine knockout of Ccm3 resulted in enhanced TIE2 signaling (146), which was triggered by an increased secretion of its low-affinity ligand ANG2 (147). ANG2 secretion antagonizes the blood vessel–stabilizing ANG1 and destabilizes EC junctional integrity (148, 149). This relationship underlies molecular similarities between the small brain capillary disease CCM and slow-flow VMs caused by GOF variants of TEK (150, 151).

VMs have been associated with GOF somatic mutations in TEK (74, 77, 78), accounting for up to 60% of sporadic VMs. These mutations cause an aberrant activation of PI3K/AKT signaling in a ligand-independent manner (116, 152, 153). Consequently, their activation directly affects blood vessel stability. Overactivation of the PI3K/AKT pathway downstream of TEK GOF variants stimulates mTOR signaling (reviewed in ref. 154), which causes changes in EC morphology (116) and overgrowth phenotypes in lymphatic and venous vessel beds (114, 115, 117, 155). Somatic mutations in PIK3CA were identified in another 25% of sporadic VMs (116, 152, 153), supporting the notion that TIE2 mainly signals through PI3Kα in this context. Strikingly, driving heterozygous Pik3ca^H1047R within the murine developing vasculature using the TIE2 promoter was sufficient to cause vascular remodeling defects, likely due to an overgrowth of endothelium (156). The co-occurrence of TEK and PIK3CA mutations in VMs is rare. Yet, in a few cases, both mutations have been identified in the same patient (157, 158). Nevertheless, it remains unknown whether both mutations occur in the same cell or whether lesions are genetically heterogenous. Possibly, TEK and PIK3CA mutations may arise subsequently within the same cell, implying that VMs may also develop upon second-hit events. In fact, germline mutations in TEK result in a weak autophosphorylation of the receptor, and, strikingly, a somatic second hit in the same gene is required to cause the typical multifocal and small-sized lesions in inherited cutaneomucosal VMs (150, 151) (reviewed in ref. 89). Kobialka and colleagues recently found that active angiogenesis is required for Pik3a^H1047R-driven vascular malformations to occur (27). Thus, when mutations occur congenitally, focal lesions initially grow in size in tune with general body growth. Yet such focal lesions remain mostly quiescent with a low proliferating rate throughout adulthood. However, the presence of angiogenic stimuli can strongly stimulate proliferation in the affected vasculature and drive the growth rate of lesions. Interestingly, the levels of PI3K/AKT activation largely depend on TIE2 variants (153). Thus, it is tempting to speculate that PI3K-related vascular disease outcomes are determined by the severity of TEK mutations, which can trigger variable magnitudes of aberrant PI3K/AKT activation and abnormalities.

In contrast to venous or capillary ECs, arterial ECs apparently detain a safeguarding mechanism against PI3K-triggered lesions. However, such a model was called into question with the surprising discovery that excessive PI3K/AKT signaling also contributes to the etiopathology of fast-flow AVMs (64), which are a hallmark of the inherited vascular disorder HHT. HHT pathogenesis involves monoallelic germline LOF mutations in the genes encoding the receptors activin-like kinase 1 (ALK1) (159) and the auxiliary coreceptor endoglin (ENG) (160) or the transcriptional effector SMAD4 (161), which are components of the canonical BMP9/10 signaling pathway (Figure 3).

Studies in murine HHT disease models demonstrated that an excessive activation of the PI3K/AKT pathway in nonarterial regions of the vasculature causes AVM formation (65, 162–165). The pharmacological inhibition using pan-inhibitors for PI3K or genetic inactivation of Akt1 suppressed AVM formation in these murine HHT models. In addition, the inhibition of excessive mTOR or YAP/TAZ signaling, downstream of PI3K/AKT, suppressed or improved AVM formation (65, 162–164, 166). The pathological relevance of this finding was further substantiated by the detection of increased PI3K/AKT signaling in patients with HHT (66, 167). Currently, it is unknown which PI3K isoforms mediate such an excessive activation of AKT within AVMs. Yet, genetic studies with an heterozygous inactivation of Pik3ca prevented an Alk1-induced vascular hyperplasia within the retina (66), pointing at PI3Kα as an important player in AVM pathogenesis. Whether PI3Kα is the sole isoform involved in AVM pathogenesis remains an exciting question for future research. These findings also emphasize similarities in the molecular mechanisms that are shared in the etiology of AVMs, VMs, and CCMs.

Strikingly, a recent study with a murine EC-specific Smad4-knockout HHT model revealed that the FSS-induced KLF4/TIE2 overactivation in AVMs is upstream of PI3K/AKT signaling. These findings suggest a multifactorial regulation of PI3K/AKT by SMAD4 signaling. SMAD4 signaling restricts the activation of PI3K/AKT via a negative feedback loop involving PTEN (65, 164). In addition, SMAD4 acts upstream in defining the FSS set point, which limits the expression levels of KLF4/TIE2, which in turn affects the activation of the PI3K/AKT pathway.

These findings point to a surprising crosstalk between the HHT fast-flow and the slow-flow PI3K/AKT/mTOR pathway, hinting at the cellular origin of affected ECs in slow-flow venous and capillary beds from which these AVMs arise and in which the PI3K/AKT pathway plays a critical role during stages of AVM formation. Therefore, these fast-flow pathologies may originate within slow-flow regions of the vasculature at stages when PI3K signaling becomes excessively activated. These findings imply common cellular and molecular features of fast-flow with slow-flow vascular lesions and further support the concept that many vascular malformations arise due to excessive PI3K/AKT/mTOR activation, which leads to a permanent and chronic remodeling of nonarterial ECs.

Similar to some other vascular anomalies, including CCMs, AVM formation in HHT occurs in a characteristic spatial-temporal manner with a somatic mutation (second-hit mechanism) occurring at the second allele within the same germline-mutated gene leading to a biallelic LOF (168). The late appearance and focal distribution of AVM lesions to only selected vascular beds suggests that a loss of heterozygosity of HHT-associated genes is required but not sufficient to cause AVMs. Apparently, and similar to the disease progression in CCM and cancer, an additional third hit is required to initiate the disease progression. It has been proposed that locally high levels of VEGF, injury-mediated inflammation, or increased FSS are among the third hits contributing to AVM formation (169–172). Increasing evidence now points at an overactivation of the PI3K/AKT pathway in these instances (reviewed in refs. 71, 157, 173).

There is compelling evidence that the BMP9/10 signaling pathway and FSS act in a feedback loop to maintain EC quiescence and vascular homeostasis. Under physiological conditions, high laminar FSS potentiates the engagement of ALK1-ENG receptor complexes causing an activation of SMAD-1/5/8 signaling, which contributes to vascular stability (174, 175). Conversely, low laminar FSS potentiates BMP9-mediated SMAD-2/3 activation, which induces inward remodeling characterized by a reduction in vessel caliber (176). In turn, BMP9/SMAD4 sets the FSS set point by restricting activation of the flow-induced KLF4/TIE2/PI3K/AKT pathway, which limits EC remodeling events. This also maintains physiological FSS-mediated cell cycle arrest and arterial identity (64). Thus, exacerbated PI3K/AKT activity within AVMs is driven by both an inhibition of PTEN (65, 66, 164) and an increased activation of KLF4/TIE2 triggered by FSS (64). How BMP9 restricts FSS-mediated KLF4/TIE2/PI3K/AKT signaling to maintain ECs in a quiescent state remains unknown. The mechanism that drives an activation of KLF4 upon FSS stimulation does not involve the mechanotransduction receptor complex comprising PECAM, VE-cadherin, and VEGFRs (64). Therefore, excessive stimulation of KLF4 in AVMs may be mediated through ERK5 activation in a manner similar to KLF4 activation in CCMs (124, 125) (Figure 3), and this may increase PI3K/AKT signaling. Intriguingly, in the slow-flow vascular malformation CCM, KLF4 transcriptionally activates increased BMP6-mediated Smad2/3 pathway signaling, which causes an endothelial-mesenchymal transition (127, 177). Taken together, these studies demonstrate the surprising interconnection of various biomechanical signaling pathways that converge onto an excessive overstimulation of the PI3K/AKT pathway. Consequently, this pathway activation can contribute as a third hit in the pathogenesis of fast-flow AVMs, yet another type of vascular malformation.

Fast-flow AVMs can present with unique lesions (as in HHT) and, when occurring sporadically, can be part of a combined vascular syndrome such as the capillary malformation–AVM (CM-AVM) syndrome. Alternatively, they may present as the vascular feature of a complex syndrome of the PIK3CA-related tissue overgrowth spectrum (PROS), as in PHTS or Proteus syndrome.

The CM-AVM syndrome is caused by germline or inherited LOF variants in two genes, RAS P21 protein activator 1 (RASA1) (178, 179) and ephrin receptor B4 (EPHB4) (180), accompanied by an additional somatic variant acting as a second hit (181). Interestingly, somatic mutations in genes in the RAS/MAPK pathway leading to overactivation of this pathway were identified also in sporadic AVMs, with MAP2K1 mutations in extracranial lesions and somatic activating mutations in KRAS being prevalent in brain AVMs (bAVMs) (182–184). Activated KRAS in bAVM lesions resulted in an overactivation of the major downstream MAPK/ERK and PI3K/AKT signaling pathways. Noteworthy, only specific inhibition of MAPK ameliorated the bAVM outcome in the context of Kras mutations, suggesting that inhibition of the MAPK/ERK pathway might be a promising target for a subset of bAVMs. This finding alerts us that the term RASopathies does not encompass all fast-flow malformations and should be applied only to fast-flow lesions with a RAS pathway activation. Therefore, despite the fact that HHT-related AVMs present as fast-flow lesions, based on their molecular outcome, they should be classified as PIKopathies (see above) (Figure 3).

Approximately 30% of patients with PHTS present vascular lesions, predominantly AVMs that are localized to the extremities (185). Similar to other malformations, PHTS-related AVMs are not apparent until patients reach an older age, emphasizing the requirement for additional genetic and/or environmental hits for disease progression. Yet, it remains to be determined which pathogenic PTEN variants trigger lesion formation. During embryonic development, Pten has an antiangiogenic role in zebrafish (186). In mice, EC loss of Pten results in cardiac failure and severe hemorrhaging during early embryogenesis (187), while postnatally, PTEN is required for NOTCH-mediated cell cycle arrest in retinal stalk cells (188). In this context, both catalytic and noncatalytic activities of PTEN contribute to this function, providing evidence for dual physiological functions. PTEN is also required for BMP9/10-mediated vessel patterning (164). Therefore, PTEN is regulated by NOTCH, BMP, and FSS. Why Pten LOF mutations predominantly cause AVMs rather than VMs remains a puzzling question for future interrogations.

Recent findings demonstrate that not only slow-flow, but also some fast-flow, vascular anomalies involve an overstimulation of PI3K/AKT signaling. A number of studies have identified PI3K as a central node that integrates physiological responses of ECs to the trigger of biomechanical forces due to FSS. The present research implies that remodeling of mature vessel beds results from a pathophysiological resetting of a PI3K/AKT-dependent FSS set point. This induces a loss of EC dormancy and quiescence and causes vascular instability and disease. In agreement with such a model, levels of PI3K activation correlate with the aggressiveness and severity of lesion formation. In some vascular anomalies, PI3Kα GOF variants are the main driver of disease severity, i.e., when occurring as a third genetic hit to activate dormant CCM lesions (24). In VMs, the severity of different GOF variants of the angiogenesis receptor TIE2 leads to different outcomes (153), and this may depend on the levels of PI3K activation. Therefore, understanding this pathway in a wide range of vascular malformations comes with the opportunity of normalizing pathological signaling in affected ECs because the PI3K/AKT signaling pathway is highly druggable.

Yet, we currently lack a good understanding of how different types of FSS and patterns of blood flow impact the overactivation of PI3K signaling in vascular anomalies. Molecular studies and a systematic characterization of PI3K/AKT/mTOR activities in animal disease models and tissue culture systems with well-defined FSS conditions are urgently needed to address these fundamental questions in the future. Although vascular cells harbor the same basic machinery, different vessel beds respond to blood flow in different ways. It will be an exciting avenue for future translational endeavors to test whether targets of dysregulated PI3K/AKT signaling in diseased cells can be normalized pharmacologically by normalizing excessive signaling in response to flow. Such systematic approaches will lay the groundwork for understanding whether specific drugs can be optimized to treat particular slow- versus fast-flow regions of the vasculature and whether combinatorial drug treatments may be an option.

Currently, the standard therapy for vascular anomalies is surgical resection or sclerotherapy. However, such approaches are not feasible when the affected vasculature is too extensive in size or when malformations are located in inoperable regions of the body such as the spinal cord. Instead, pharmacological therapies of patients with GOF mutations in the TIE2/PI3K/AKT/mTOR pathway hold a great promise and have been fueled by studies using repurposed anticancer drugs. The central role of PI3K/AKT/mTOR signaling in many types of cancer has spurred research in that direction with different classes of such inhibitors currently being tested in clinical trials. These involve pan- and isoform-specific PI3K as well as dual PI3K/mTOR inhibitors (reviewed in ref. 189). The results of these studies regarding the efficacy, safety, and specificity of drugs will be of great interest also for the treatment of vascular anomalies. Several patients with PROS were treated successfully with the PI3K inhibitor alpelisib, which reduced their symptoms (25). Targeting AKT with miransertib (ARQ 092), an allosteric and selective pan-AKT inhibitor, has been used effectively in the treatment of patients with Proteus syndrome (190) and PROS (191, 192). Rapamycin is an inhibitor of the mTOR1 complex, and its efficacy in suppressing vascular anomalies has been demonstrated in a number of clinical studies (193, 194). However, rapamycin showed less efficacy in the treatment of AVMs compared with its effects on slow-flow vascular anomalies (195–197). Future pharmacological interventions will be optimized based on what has been learned about genetic causes and molecular mechanisms of these diseases in relation to the flow conditions of affected vessel beds. Such approaches will certainly help to lessen the manifestation of a plethora of vascular anomalies, including VMs, CCMs, HHT-AVMs, and others. Future endeavors will address this promising possibility.

The authors would like to apologize to colleagues whose work has not been cited in this Review. We would like to thank all members of the Abdelilah-Seyfried lab and members of the European Center of Angioscience for critical reading and valuable feedback on the manuscript. SAS is supported by Deutsche Forschungsgemeinschaft (DFG) projects SE2016/7-3, SE2016/10-1, and SE2016/13-1 and the Leducq Transatlantic Network of Excellence grant “21CVD03 - ReVAMP.” RO’s lab is supported by DFG project 394046768 - SFB1366, and start-up funding was received from Mannheim Faculty of Medicine, University of Heidelberg, and NIH grant 1R01HL169510-01 (co-PI).

Address correspondence to: Salim Abdelilah-Seyfried, Institute of Biochemistry and Biology, Potsdam University, Karl-Liebknecht-Straße 24-25, D-14476 Potsdam, Germany. Email: salim.seyfried@uni-potsdam.de. Or to: Roxana Ola, Experimental Pharmacology Mannheim (EPM), European Center for Angioscience (ECAS), Medical Faculty Mannheim, Heidelberg University, Ludolf-Krehl-Str. 13-17, 68167 Mannheim, Germany. Email: roxana.ola@medma.uni-heidelberg.de.

Conflict of interest: The authors have declared that no conflict of interest exists.

Copyright: © 2024, Abdelilah-Seyfried et al. This is an open access article published under the terms of the Creative Commons Attribution 4.0 International License.

Reference information: J Clin Invest. 2024;134(10):e172843. https://doi.org/10.1172/JCI172843.

1. Augustin HG, Koh GY. Organotypic vasculature: from descriptive heterogeneity to functional pathophysiology. Science. 2017;357(6353):eaal2379.
   View this article via: CrossRef PubMed Google Scholar
2. Nolan DJ, et al. Molecular signatures of tissue-specific microvascular endothelial cell heterogeneity in organ maintenance and regeneration. Dev Cell. 2013;26(2):204–219.
   View this article via: CrossRef PubMed Google Scholar
3. Rafii S, et al. Angiocrine functions of organ-specific endothelial cells. Nature. 2016;529(7586):316–325.
   View this article via: CrossRef PubMed Google Scholar
4. Stanczuk L, et al. cKit lineage hemogenic endothelium-derived cells contribute to mesenteric lymphatic vessels. Cell Rep. 2015;10(10):1708–1721.
   View this article via: CrossRef PubMed Google Scholar
5. Graupera M, et al. Angiogenesis selectively requires the p110alpha isoform of PI3K to control endothelial cell migration. Nature. 2008;453(7195):662–666.
   View this article via: CrossRef PubMed Google Scholar
6. Herbert SP, et al. Arterial-venous segregation by selective cell sprouting: an alternative mode of blood vessel formation. Science. 2009;326(5950):294–298.
   View this article via: CrossRef PubMed Google Scholar
7. Chen X, et al. Endothelial and cardiomyocyte PI3Kβ divergently regulate cardiac remodelling in response to ischaemic injury. Cardiovasc Res. 2019;115(8):1343–1356.
   View this article via: CrossRef PubMed Google Scholar
8. Whitehead MA, et al. Isoform-selective induction of human p110δ PI3K expression by TNFα: identification of a new and inducible PIK3CD promoter. Biochem J. 2012;443(3):857–867.
   View this article via: CrossRef PubMed Google Scholar
9. Yoshioka K, et al. Endothelial PI3K-C2α, a class II PI3K, has an essential role in angiogenesis and vascular barrier function. Nat Med. 2012;18(10):1560–1569.
   View this article via: CrossRef PubMed Google Scholar
10. Franco I, et al. PI3K class II α controls spatially restricted endosomal PtdIns3P and Rab11 activation to promote primary cilium function. Dev Cell. 2014;28(6):647–658.
    View this article via: CrossRef PubMed Google Scholar
11. Kobialka P, et al. PI3K-C2β limits mTORC1 signaling and angiogenic growth. Sci Signal. 2023;16(813):eadg1913.
    View this article via: CrossRef PubMed Google Scholar
12. Manning BD, Toker A. AKT/PKB signaling: navigating the network. Cell. 2017;169(3):381–405.
    View this article via: CrossRef PubMed Google Scholar
13. Lee MY, et al. Endothelial Akt1 mediates angiogenesis by phosphorylating multiple angiogenic substrates. Proc Natl Acad Sci U S A. 2014;111(35):12865–12870.
    View this article via: CrossRef PubMed Google Scholar
14. Chen WS, et al. Growth retardation and increased apoptosis in mice with homozygous disruption of the Akt1 gene. Genes Dev. 2001;15(17):2203–2208.
    View this article via: CrossRef PubMed Google Scholar
15. Kerr BA, et al. Stability and function of adult vasculature is sustained by Akt/Jagged1 signalling axis in endothelium. Nat Commun. 2016;7:10960.
    View this article via: CrossRef PubMed Google Scholar
16. Brunet A, et al. Akt promotes cell survival by phosphorylating and inhibiting a Forkhead transcription factor. Cell. 1999;96(6):857–868.
    View this article via: CrossRef PubMed Google Scholar
17. Wilhelm K, et al. FOXO1 couples metabolic activity and growth state in the vascular endothelium. Nature. 2016;529(7585):216–220.
    View this article via: CrossRef PubMed Google Scholar
18. Potter CJ, et al. Akt regulates growth by directly phosphorylating Tsc2. Nat Cell Biol. 2002;4(9):658–665.
    View this article via: CrossRef PubMed Google Scholar
19. Vander Haar E, et al. Insulin signalling to mTOR mediated by the Akt/PKB substrate PRAS40. Nat Cell Biol. 2007;9(3):316–323.
    View this article via: CrossRef PubMed Google Scholar
20. Angulo-Urarte A, et al. Endothelial cell rearrangements during vascular patterning require PI3-kinase-mediated inhibition of actomyosin contractility. Nat Commun. 2018;9(1):4826.
    View this article via: CrossRef PubMed Google Scholar
21. Gambardella L, et al. PI3K signaling through the dual GTPase-activating protein ARAP3 is essential for developmental angiogenesis. Sci Signal. 2010;3(145):ra76.
    View this article via: CrossRef PubMed Google Scholar
22. Van Damme A, et al. New and emerging targeted therapies for vascular malformations. Am J Clin Dermatol. 2020;21(5):657–668.
    View this article via: CrossRef PubMed Google Scholar
23. di Blasio L, et al. PI3K/mTOR inhibition promotes the regression of experimental vascular malformations driven by PIK3CA-activating mutations. Cell Death Dis. 2018;9(2):45.
    View this article via: CrossRef PubMed Google Scholar
24. Ren AA, et al. PIK3CA and CCM mutations fuel cavernomas through a cancer-like mechanism. Nature. 2021;594(7862):271–276.
    View this article via: CrossRef PubMed Google Scholar
25. Venot Q, et al. Targeted therapy in patients with PIK3CA-related overgrowth syndrome. Nature. 2018;558(7711):540–546.
    View this article via: CrossRef PubMed Google Scholar
26. Sterba M, et al. Targeted treatment of severe vascular malformations harboring PIK3CA and TEK mutations with alpelisib is highly effective with limited toxicity. Sci Rep. 2023;13(1):10499.
    View this article via: CrossRef PubMed Google Scholar
27. Kobialka P, et al. The onset of PI3K-related vascular malformations occurs during angiogenesis and is prevented by the AKT inhibitor miransertib. EMBO Mol Med. 2022;14(7):e15619.
    View this article via: CrossRef PubMed Google Scholar
28. Jiang Y-Z, et al. Endothelial epigenetics in biomechanical stress: disturbed flow-mediated epigenomic plasticity in vivo and in vitro. Arterioscler Thromb Vasc Biol. 2015;35(6):1317–1326.
    View this article via: CrossRef PubMed Google Scholar
29. Nakajima H, Mochizuki N. Flow pattern-dependent endothelial cell responses through transcriptional regulation. Cell Cycle. 2017;16(20):1893–1901.
    View this article via: CrossRef PubMed Google Scholar
30. Salvador J, Iruela-Arispe ML. Nuclear mechanosensation and mechanotransduction in vascular cells. Front Cell Dev Biol. 2022;10:905927.
    View this article via: CrossRef PubMed Google Scholar
31. Dunn J, et al. The role of epigenetics in the endothelial cell shear stress response and atherosclerosis. Int J Biochem Cell Biol. 2015;67:167–176.
    View this article via: CrossRef PubMed Google Scholar
32. Potente M, Mäkinen T. Vascular heterogeneity and specialization in development and disease. Nat Rev Mol Cell Biol. 2017;18(8):477–494.
    View this article via: CrossRef PubMed Google Scholar
33. Humphrey JD, Schwartz MA. Vascular mechanobiology: homeostasis, adaptation, and disease. Annu Rev Biomed Eng. 2021;23:1–27.
    View this article via: CrossRef PubMed Google Scholar
34. Baeyens N, et al. Endothelial fluid shear stress sensing in vascular health and disease. J Clin Invest. 2016;126(3):821–828.
    View this article via: JCI CrossRef PubMed Google Scholar
35. Parmar KM, et al. Integration of flow-dependent endothelial phenotypes by Kruppel-like factor 2. J Clin Invest. 2006;116(1):49–58.
    View this article via: JCI CrossRef PubMed Google Scholar
36. Siebel C, Lendahl U. Notch signaling in development, tissue homeostasis, and disease. Physiol Rev. 2017;97(4):1235–1294.
    View this article via: CrossRef PubMed Google Scholar
37. Abdelilah-Seyfried S, et al. Recalibrating vascular malformations and mechanotransduction by pharmacological intervention. J Clin Invest. 2022;132(8):160227.
    View this article via: JCI CrossRef PubMed Google Scholar
38. Boopathy GTK, Hong W. Role of Hippo pathway-YAP/TAZ signaling in angiogenesis. Front Cell Dev Biol. 2019;7:49.
    View this article via: CrossRef PubMed Google Scholar
39. Fu M, et al. The Hippo signalling pathway and its implications in human health and diseases. Signal Transduct Target Ther. 2022;7(1):376.
    View this article via: CrossRef PubMed Google Scholar
40. Tanaka K, et al. Early events in endothelial flow sensing. Cytoskeleton (Hoboken). 2021;78(6):217–231.
    View this article via: CrossRef PubMed Google Scholar
41. Chappell DC, et al. Oscillatory shear stress stimulates adhesion molecule expression in cultured human endothelium. Circ Res. 1998;82(5):532–539.
    View this article via: CrossRef PubMed Google Scholar
42. Garcia-Cardeña G, et al. Biomechanical activation of vascular endothelium as a determinant of its functional phenotype. Proc Natl Acad Sci U S A. 2001;98(8):4478–4485.
    View this article via: CrossRef PubMed Google Scholar
43. SenBanerjee S, et al. KLF2 Is a novel transcriptional regulator of endothelial proinflammatory activation. J Exp Med. 2004;199(10):1305–1315.
    View this article via: CrossRef PubMed Google Scholar
44. Barbacena P, et al. Competition for endothelial cell polarity drives vascular morphogenesis in the mouse retina. Dev Cell. 2022;57(19):2321–2333.
    View this article via: CrossRef PubMed Google Scholar
45. Franco CA, et al. Dynamic endothelial cell rearrangements drive developmental vessel regression. PLoS Biol. 2015;13(4):e1002125.
    View this article via: CrossRef PubMed Google Scholar
46. Franke RP, et al. Induction of human vascular endothelial stress fibres by fluid shear stress. Nature. 1984;307(5952):648–649.
    View this article via: CrossRef PubMed Google Scholar
47. Kwon H-B, et al. In vivo modulation of endothelial polarization by Apelin receptor signalling. Nat Commun. 2016;7:11805.
    View this article via: CrossRef PubMed Google Scholar
48. Tzima E, et al. Localized cdc42 activation, detected using a novel assay, mediates microtubule organizing center positioning in endothelial cells in response to fluid shear stress. J Biol Chem. 2003;278(33):31020–31023.
    View this article via: CrossRef PubMed Google Scholar
49. Tronc F, et al. Role of NO in flow-induced remodeling of the rabbit common carotid artery. Arterioscler Thromb Vasc Biol. 1996;16(10):1256–1262.
    View this article via: CrossRef PubMed Google Scholar
50. Tuttle JL, et al. Shear level influences resistance artery remodeling: wall dimensions, cell density, and eNOS expression. Am J Physiol Heart Circ Physiol. 2001;281(3):H1380–H1389.
    View this article via: CrossRef PubMed Google Scholar
51. Kamiya A, Togawa T. Adaptive regulation of wall shear stress to flow change in the canine carotid artery. Am J Physiol. 1980;239(1):H14–H21.
    View this article via: PubMed Google Scholar
52. Langille BL, O’Donnell F. Reductions in arterial diameter produced by chronic decreases in blood flow are endothelium-dependent. Science. 1986;231(4736):405–407.
    View this article via: CrossRef PubMed Google Scholar
53. Baeyens N, et al. Vascular remodeling is governed by a VEGFR3-dependent fluid shear stress set point. Elife. 2015;4:e04645.
    View this article via: CrossRef PubMed Google Scholar
54. Dajnowiec D, Langille BL. Arterial adaptations to chronic changes in haemodynamic function: coupling vasomotor tone to structural remodelling. Clin Sci (Lond). 2007;113(1):15–23.
    View this article via: CrossRef PubMed Google Scholar
55. Min E, Schwartz MA. Translocating transcription factors in fluid shear stress-mediated vascular remodeling and disease. Exp Cell Res. 2019;376(1):92–97.
    View this article via: CrossRef PubMed Google Scholar
56. Rodbard S. Vascular caliber. Cardiology. 1975;60(1):4–49.
    View this article via: CrossRef PubMed Google Scholar
57. Tzima E, et al. A mechanosensory complex that mediates the endothelial cell response to fluid shear stress. Nature. 2005;437(7057):426–431.
    View this article via: CrossRef PubMed Google Scholar
58. Conway DE, et al. Fluid shear stress on endothelial cells modulates mechanical tension across VE-cadherin and PECAM-1. Curr Biol. 2013;23(11):1024–1030.
    View this article via: CrossRef PubMed Google Scholar
59. Coon BG, et al. Intramembrane binding of VE-cadherin to VEGFR2 and VEGFR3 assembles the endothelial mechanosensory complex. J Cell Biol. 2015;208(7):975–986.
    View this article via: CrossRef PubMed Google Scholar
60. Osawa M, et al. Tyrosine phosphorylation of platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) in mechanically stimulated vascular endothelial cells. Eur J Cell Biol. 1997;72(3):229–237.
    View this article via: PubMed Google Scholar
61. Albarrán-Juárez J, et al. Piezo1 and G_q/G₁₁ promote endothelial inflammation depending on flow pattern and integrin activation. J Exp Med. 2018;215(10):2655–2672.
    View this article via: CrossRef PubMed Google Scholar
62. Ranade SS, et al. Piezo1, a mechanically activated ion channel, is required for vascular development in mice. Proc Natl Acad Sci U S A. 2014;111(28):10347–10352.
    View this article via: CrossRef PubMed Google Scholar
63. Wang S, et al. P2Y₂ and Gq/G₁₁ control blood pressure by mediating endothelial mechanotransduction. J Clin Invest. 2015;125(8):3077–3086.
    View this article via: JCI CrossRef PubMed Google Scholar
64. Banerjee K, et al. SMAD4 maintains the fluid shear stress set point to protect against arterial-venous malformations. J Clin Invest. 2023;133(18):168352.
    View this article via: JCI CrossRef PubMed Google Scholar
65. Ola R, et al. SMAD4 prevents flow induced arteriovenous malformations by inhibiting casein kinase 2. Circulation. 2018;138(21):2379–2394.
    View this article via: CrossRef PubMed Google Scholar
66. Alsina-Sanchís E, et al. ALK1 loss results in vascular hyperplasia in mice and humans through PI3K activation. Arterioscler Thromb Vasc Biol. 2018;38(5):1216–1229.
    View this article via: CrossRef PubMed Google Scholar
67. Wu S-H, et al. Shear stress triggers angiogenesis of late endothelial progenitor cells via the PTEN/Akt/GTPCH/BH4 pathway. Stem Cells Int. 2020;2020:5939530.
    View this article via: CrossRef PubMed Google Scholar
68. Mehta V, et al. The guidance receptor plexin D1 is a mechanosensor in endothelial cells. Nature. 2020;578(7794):290–295.
    View this article via: CrossRef PubMed Google Scholar
69. Wang C, et al. Endothelial cell sensing of flow direction. Arterioscler Thromb Vasc Biol. 2013;33(9):2130–2136.
    View this article via: CrossRef PubMed Google Scholar
70. Dimmeler S, et al. Fluid shear stress stimulates phosphorylation of Akt in human endothelial cells: involvement in suppression of apoptosis. Circ Res. 1998;83(3):334–341.
    View this article via: CrossRef PubMed Google Scholar
71. Graupera M, Potente M. Regulation of angiogenesis by PI3K signaling networks. Exp Cell Res. 2013;319(9):1348–1355.
    View this article via: CrossRef PubMed Google Scholar
72. Sako K, et al. Angiopoietin-1 induces Kruppel-like factor 2 expression through a phosphoinositide 3-kinase/AKT-dependent activation of myocyte enhancer factor 2. J Biol Chem. 2009;284(9):5592–5601.
    View this article via: CrossRef PubMed Google Scholar
73. Peters KG, et al. Functional significance of Tie2 signaling in the adult vasculature. Recent Prog Horm Res. 2004;59:51–71.
    View this article via: CrossRef PubMed Google Scholar
74. Wong AL, et al. Tie2 expression and phosphorylation in angiogenic and quiescent adult tissues. Circ Res. 1997;81(4):567–574.
    View this article via: CrossRef PubMed Google Scholar
75. Brindle NPJ, et al. Signaling and functions of angiopoietin-1 in vascular protection. Circ Res. 2006;98(8):1014–1023.
    View this article via: CrossRef PubMed Google Scholar
76. Fukuhara S, et al. Differential function of Tie2 at cell-cell contacts and cell-substratum contacts regulated by angiopoietin-1. Nat Cell Biol. 2008;10(5):513–526.
    View this article via: CrossRef PubMed Google Scholar
77. Dekker RJ, et al. Endothelial KLF2 links local arterial shear stress levels to the expression of vascular tone-regulating genes. Am J Pathol. 2005;167(2):609–618.
    View this article via: CrossRef PubMed Google Scholar
78. Dekker RJ, et al. Prolonged fluid shear stress induces a distinct set of endothelial cell genes, most specifically lung Krüppel-like factor (KLF2). Blood. 2002;100(5):1689–1698.
    View this article via: CrossRef PubMed Google Scholar
79. Huddleson JP, et al. Fluid shear stress induces endothelial KLF2 gene expression through a defined promoter region. Biol Chem. 2004;385(8):723–729.
    View this article via: CrossRef PubMed Google Scholar
80. Moonen J-R, et al. KLF4 recruits SWI/SNF to increase chromatin accessibility and reprogram the endothelial enhancer landscape under laminar shear stress. Nat Commun. 2022;13(1):4941.
    View this article via: CrossRef PubMed Google Scholar
81. Han Y, et al. Roles of KLF4 and AMPK in the inhibition of glycolysis by pulsatile shear stress in endothelial cells. Proc Natl Acad Sci U S A. 2021;118(21):e2103982118.
    View this article via: CrossRef PubMed Google Scholar
82. Clark PR, et al. MEK5 is activated by shear stress, activates ERK5 and induces KLF4 to modulate TNF responses in human dermal microvascular endothelial cells. Microcirculation. 2011;18(2):102–117.
    View this article via: CrossRef PubMed Google Scholar
83. Villarreal G, et al. Defining the regulation of KLF4 expression and its downstream transcriptional targets in vascular endothelial cells. Biochem Biophys Res Commun. 2010;391(1):984–989.
    View this article via: CrossRef PubMed Google Scholar
84. Methe H, et al. Vascular bed origin dictates flow pattern regulation of endothelial adhesion molecule expression. Am J Physiol Heart Circ Physiol. 2007;292(5):H2167–H2175.
    View this article via: CrossRef PubMed Google Scholar
85. Bhattacharya R, et al. Inhibition of vascular permeability factor/vascular endothelial growth factor-mediated angiogenesis by the Kruppel-like factor KLF2. J Biol Chem. 2005;280(32):28848–28851.
    View this article via: CrossRef PubMed Google Scholar
86. Lin Z, et al. Kruppel-like factor 2 inhibits protease activated receptor-1 expression and thrombin-mediated endothelial activation. Arterioscler Thromb Vasc Biol. 2006;26(5):1185–1189.
    View this article via: CrossRef PubMed Google Scholar
87. Baeyens N, et al. Syndecan 4 is required for endothelial alignment in flow and atheroprotective signaling. Proc Natl Acad Sci U S A. 2014;111(48):17308–17313.
    View this article via: CrossRef PubMed Google Scholar
88. Tai L-K, et al. Flow activates ERK1/2 and endothelial nitric oxide synthase via a pathway involving PECAM1, SHP2, and Tie2. J Biol Chem. 2005;280(33):29620–29624.
    View this article via: CrossRef PubMed Google Scholar
89. Queisser A, et al. Genetic basis and therapies for vascular anomalies. Circ Res. 2021;129(1):155–173.
    View this article via: CrossRef PubMed Google Scholar
90. De Bortoli M, et al. Somatic loss-of-function PIK3R1 and activating non-hotspot PIK3CA mutations associated with capillary malformation with dilated veins (CMDV). [published online February 29, 2024]. J Invest Dermatol. https://doi.org/10.1016/j.jid.2024.01.033.
    View this article via: PubMed Google Scholar
91. Lindhurst MJ, et al. A mosaic activating mutation in AKT1 associated with the Proteus syndrome. N Engl J Med. 2011;365(7):611–619.
    View this article via: CrossRef PubMed Google Scholar
92. Liaw D, et al. Germline mutations of the PTEN gene in Cowden disease, an inherited breast and thyroid cancer syndrome. Nat Genet. 1997;16(1):64–67.
    View this article via: CrossRef PubMed Google Scholar
93. Pilarski R. PTEN hamartoma tumor syndrome: a clinical overview. Cancers (Basel). 2019;11(6):844.
    View this article via: CrossRef PubMed Google Scholar
94. Li Y-SJ, et al. Molecular basis of the effects of shear stress on vascular endothelial cells. J Biomech. 2005;38(10):1949–1971.
    View this article via: CrossRef PubMed Google Scholar
95. Ohashi K, et al. Roles of the cytoskeleton, cell adhesion and rho signalling in mechanosensing and mechanotransduction. J Biochem. 2017;161(3):245–254.
    View this article via: PubMed Google Scholar
96. Joannides R, et al. Nitric oxide is responsible for flow-dependent dilatation of human peripheral conduit arteries in vivo. Circulation. 1995;91(5):1314–1319.
    View this article via: CrossRef PubMed Google Scholar
97. Fleming I, et al. Role of PECAM-1 in the shear-stress-induced activation of Akt and the endothelial nitric oxide synthase (eNOS) in endothelial cells. J Cell Sci. 2005;118(pt 18):4103–4111.
    View this article via: CrossRef PubMed Google Scholar
98. Mohan S, et al. Differential activation of NF-kappa B in human aortic endothelial cells conditioned to specific flow environments. Am J Physiol. 1997;273(2 pt 1):C572–C578.
    View this article via: CrossRef PubMed Google Scholar
99. Blackman BR, et al. A new in vitro model to evaluate differential responses of endothelial cells to simulated arterial shear stress waveforms. J Biomech Eng. 2002;124(4):397–407.
    View this article via: CrossRef PubMed Google Scholar
100. Hahn C, Schwartz MA. The role of cellular adaptation to mechanical forces in atherosclerosis. Arterioscler Thromb Vasc Biol. 2008;28(12):2101–2107.
     View this article via: CrossRef PubMed Google Scholar
101. Liu Y, et al. A novel pathway spatiotemporally activates Rac1 and redox signaling in response to fluid shear stress. J Cell Biol. 2013;201(6):863–873.
     View this article via: CrossRef PubMed Google Scholar
102. Wojciak-Stothard B, Ridley AJ. Shear stress-induced endothelial cell polarization is mediated by Rho and Rac but not Cdc42 or PI 3-kinases. J Cell Biol. 2003;161(2):429–439.
     View this article via: CrossRef PubMed Google Scholar
103. Tzima E, et al. Activation of integrins in endothelial cells by fluid shear stress mediates Rho-dependent cytoskeletal alignment. EMBO J. 2001;20(17):4639–4647.
     View this article via: CrossRef PubMed Google Scholar
104. Tzima E, et al. Activation of Rac1 by shear stress in endothelial cells mediates both cytoskeletal reorganization and effects on gene expression. EMBO J. 2002;21(24):6791–6800.
     View this article via: CrossRef PubMed Google Scholar
105. Bi L, et al. Proliferative defect and embryonic lethality in mice homozygous for a deletion in the p110alpha subunit of phosphoinositide 3-kinase. J Biol Chem. 1999;274(16):10963–10968.
     View this article via: CrossRef PubMed Google Scholar
106. Lelievre E, et al. Deficiency in the p110alpha subunit of PI3K results in diminished Tie2 expression and Tie2(-/-)-like vascular defects in mice. Blood. 2005;105(10):3935–3938.
     View this article via: CrossRef PubMed Google Scholar
107. Ren B, et al. ERK1/2-Akt1 crosstalk regulates arteriogenesis in mice and zebrafish. J Clin Invest. 2010;120(4):1217–1228.
     View this article via: JCI CrossRef PubMed Google Scholar
108. Ren C-G, et al. Activated N-Ras signaling regulates arterial-venous specification in zebrafish. J Hematol Oncol. 2013;6:34.
     View this article via: CrossRef PubMed Google Scholar
109. Fang JS, et al. Shear-induced Notch-Cx37-p27 axis arrests endothelial cell cycle to enable arterial specification. Nat Commun. 2017;8(1):2149.
     View this article via: CrossRef PubMed Google Scholar
110. Salamon RS, et al. Identification of the Rab5 binding site in p110β: assays for PI3Kβ binding to Rab5. Methods Mol Biol. 2015;1298:271–281.
     View this article via: CrossRef PubMed Google Scholar
111. Samuels Y, et al. Mutant PIK3CA promotes cell growth and invasion of human cancer cells. Cancer Cell. 2005;7(6):561–573.
     View this article via: CrossRef PubMed Google Scholar
112. Blesinger H, et al. PIK3CA mutations are specifically localized to lymphatic endothelial cells of lymphatic malformations. PLoS One. 2018;13(7):e0200343.
     View this article via: CrossRef PubMed Google Scholar
113. Boscolo E, et al. AKT hyper-phosphorylation associated with PI3K mutations in lymphatic endothelial cells from a patient with lymphatic malformation. Angiogenesis. 2015;18(2):151–162.
     View this article via: CrossRef PubMed Google Scholar
114. Castel P, et al. Somatic PIK3CA mutations as a driver of sporadic venous malformations. Sci Transl Med. 2016;8(332):332ra42.
     View this article via: CrossRef PubMed Google Scholar
115. Castillo SD, et al. Somatic activating mutations in Pik3ca cause sporadic venous malformations in mice and humans. Sci Transl Med. 2016;8(332):332ra43.
     View this article via: CrossRef PubMed Google Scholar
116. Limaye N, et al. Somatic activating PIK3CA mutations cause venous malformation. Am J Hum Genet. 2015;97(6):914–921.
     View this article via: CrossRef PubMed Google Scholar
117. Luks VL, et al. Lymphatic and other vascular malformative/overgrowth disorders are caused by somatic mutations in PIK3CA. J Pediatr. 2015;166(4):1048–1054.
     View this article via: CrossRef PubMed Google Scholar
118. Osborn AJ, et al. Activating PIK3CA alleles and lymphangiogenic phenotype of lymphatic endothelial cells isolated from lymphatic malformations. Hum Mol Genet. 2015;24(4):926–938.
     View this article via: CrossRef PubMed Google Scholar
119. Laberge-le Couteulx S, et al. Truncating mutations in CCM1, encoding KRIT1, cause hereditary cavernous angiomas. Nat Genet. 1999;23(2):189–193.
     View this article via: CrossRef PubMed Google Scholar
120. Liquori CL, et al. Mutations in a gene encoding a novel protein containing a phosphotyrosine-binding domain cause type 2 cerebral cavernous malformations. Am J Hum Genet. 2003;73(6):1459–1464.
     View this article via: CrossRef PubMed Google Scholar
121. Bergametti F, et al. Mutations within the programmed cell death 10 gene cause cerebral cavernous malformations. Am J Hum Genet. 2005;76(1):42–51.
     View this article via: CrossRef PubMed Google Scholar
122. Wang X, et al. Structural insights into the molecular recognition between cerebral cavernous malformation 2 and mitogen-activated protein kinase kinase kinase 3. Structure. 2015;23(6):1087–1096.
     View this article via: CrossRef PubMed Google Scholar
123. Fisher OS, et al. Structure and vascular function of MEKK3-cerebral cavernous malformations 2 complex. Nat Commun. 2015;6:7937.
     View this article via: CrossRef PubMed Google Scholar
124. Zhou Z, et al. Cerebral cavernous malformations arise from endothelial gain of MEKK3-KLF2/4 signalling. Nature. 2016;532(7597):122–126.
     View this article via: CrossRef PubMed Google Scholar
125. Zhou Z, et al. The cerebral cavernous malformation pathway controls cardiac development via regulation of endocardial MEKK3 signaling and KLF expression. Dev Cell. 2015;32(2):168–180.
     View this article via: CrossRef PubMed Google Scholar
126. Uhlik MT, et al. Rac-MEKK3-MKK3 scaffolding for p38 MAPK activation during hyperosmotic shock. Nat Cell Biol. 2003;5(12):1104–1110.
     View this article via: CrossRef PubMed Google Scholar
127. Cuttano R, et al. KLF4 is a key determinant in the development and progression of cerebral cavernous malformations. EMBO Mol Med. 2016;8(1):6–24.
     View this article via: CrossRef PubMed Google Scholar
128. Castro M, et al. CDC42 deletion elicits cerebral vascular malformations via increased MEKK3-dependent KLF4 expression. Circ Res. 2019;124(8):1240–1252.
     View this article via: CrossRef PubMed Google Scholar
129. Renz M, et al. Regulation of β1 integrin-Klf2-mediated angiogenesis by CCM proteins. Dev Cell. 2015;32(2):181–190.
     View this article via: CrossRef PubMed Google Scholar
130. Abdelilah-Seyfried S, et al. Blocking signalopathic events to treat cerebral cavernous malformations. Trends Mol Med. 2020;26(9):874–887.
     View this article via: CrossRef PubMed Google Scholar
131. Peyre M, et al. Somatic PIK3CA mutations in sporadic cerebral cavernous malformations. N Engl J Med. 2021;385(11):996–1004.
     View this article via: CrossRef PubMed Google Scholar
132. Snellings DA, et al. Developmental venous anomalies are a genetic primer for cerebral cavernous malformations. Nat Cardiovasc Res. 2022;1:246–252.
     View this article via: CrossRef PubMed Google Scholar
133. Ren J, et al. Somatic variants of MAP3K3 are sufficient to cause cerebral and spinal cord cavernous malformations. Brain. 2023;146(9):3634–3647.
     View this article via: CrossRef PubMed Google Scholar
134. Weng J, et al. Somatic MAP3K3 mutation defines a subclass of cerebral cavernous malformation. Am J Hum Genet. 2021;108(5):942–950.
     View this article via: CrossRef PubMed Google Scholar
135. Huo R, et al. Endothelial hyperactivation of mutant MAP3K3 induces cerebral cavernous malformation enhanced by PIK3CA GOF mutation. Angiogenesis. 2023;26(2):295–312.
     View this article via: CrossRef PubMed Google Scholar
136. Li L, et al. mTORC1 inhibitor rapamycin inhibits growth of cerebral cavernous malformation in adult mice. Stroke. 2023;54(11):2906–2917.
     View this article via: CrossRef PubMed Google Scholar
137. Denier C, et al. Genotype-phenotype correlations in cerebral cavernous malformations patients. Ann Neurol. 2006;60(5):550–556.
     View this article via: CrossRef PubMed Google Scholar
138. Boulday G, et al. Developmental timing of CCM2 loss influences cerebral cavernous malformations in mice. J Exp Med. 2011;208(9):1835–1847.
     View this article via: CrossRef PubMed Google Scholar
139. Wüstehube J, et al. Cerebral cavernous malformation protein CCM1 inhibits sprouting angiogenesis by activating delta-Notch signaling. Proc Natl Acad Sci U S A. 2010;107(28):12640–12645.
     View this article via: CrossRef PubMed Google Scholar
140. Koskimäki J, et al. Comprehensive transcriptome analysis of cerebral cavernous malformation across multiple species and genotypes. JCI Insight. 2019;4(3):e126167.
     View this article via: JCI Insight CrossRef PubMed Google Scholar
141. Zhu Y, et al. Differential angiogenesis function of CCM2 and CCM3 in cerebral cavernous malformations. Neurosurg Focus. 2010;29(3):E1.
     View this article via: CrossRef PubMed Google Scholar
142. You C, et al. Loss of CCM3 impairs DLL4-Notch signalling: implication in endothelial angiogenesis and in inherited cerebral cavernous malformations. J Cell Mol Med. 2013;17(3):407–418.
     View this article via: CrossRef PubMed Google Scholar
143. Zhu Y, et al. Phosphatase and tensin homolog in cerebral cavernous malformation: a potential role in pathological angiogenesis. J Neurosurg. 2009;110(3):530–539.
     View this article via: CrossRef PubMed Google Scholar
144. Otten C, et al. Systematic pharmacological screens uncover novel pathways involved in cerebral cavernous malformations. EMBO Mol Med. 2018;10(10):e9155.
     View this article via: CrossRef PubMed Google Scholar
145. Zhu Y, et al. Loss of endothelial programmed cell death 10 activates glioblastoma cells and promotes tumor growth. Neuro Oncol. 2016;18(4):538–548.
     View this article via: CrossRef PubMed Google Scholar
146. Zhou HJ, et al. Caveolae-mediated Tie2 signaling contributes to CCM pathogenesis in a brain endothelial cell-specific Pdcd10-deficient mouse model. Nat Commun. 2021;12(1):504.
     View this article via: CrossRef PubMed Google Scholar
147. Zhou HJ, et al. Endothelial exocytosis of angiopoietin-2 resulting from CCM3 deficiency contributes to cerebral cavernous malformation. Nat Med. 2016;22(9):1033–1042.
     View this article via: CrossRef PubMed Google Scholar
148. Eklund L, Olsen BR. Tie receptors and their angiopoietin ligands are context-dependent regulators of vascular remodeling. Exp Cell Res. 2006;312(5):630–641.
     View this article via: CrossRef PubMed Google Scholar
149. Maisonpierre PC, et al. Angiopoietin-2, a natural antagonist for Tie2 that disrupts in vivo angiogenesis. Science. 1997;277(5322):55–60.
     View this article via: CrossRef PubMed Google Scholar
150. Soblet J, et al. Blue rubber bleb nevus (BRBN) syndrome is caused by somatic TEK (TIE2) mutations. J Invest Dermatol. 2017;137(1):207–216.
     View this article via: CrossRef PubMed Google Scholar
151. Limaye N, et al. Somatic mutations in angiopoietin receptor gene TEK cause solitary and multiple sporadic venous malformations. Nat Genet. 2009;41(1):118–124.
     View this article via: CrossRef PubMed Google Scholar
152. Nätynki M, et al. Common and specific effects of TIE2 mutations causing venous malformations. Hum Mol Genet. 2015;24(22):6374–6389.
     View this article via: CrossRef PubMed Google Scholar
153. Uebelhoer M, et al. Venous malformation-causative TIE2 mutations mediate an AKT-dependent decrease in PDGFB. Hum Mol Genet. 2013;22(17):3438–3448.
     View this article via: CrossRef PubMed Google Scholar
154. Keppler-Noreuil KM, et al. Somatic overgrowth disorders of the PI3K/AKT/mTOR pathway & therapeutic strategies. Am J Med Genet C Semin Med Genet. 2016;172(4):402–421.
     View this article via: CrossRef PubMed Google Scholar
155. Rodriguez-Laguna L, et al. Somatic activating mutations in PIK3CA cause generalized lymphatic anomaly. J Exp Med. 2019;216(2):407–418.
     View this article via: CrossRef PubMed Google Scholar
156. Hare LM, et al. Heterozygous expression of the oncogenic Pik3ca(H1047R) mutation during murine development results in fatal embryonic and extraembryonic defects. Dev Biol. 2015;404(1):14–26.
     View this article via: CrossRef PubMed Google Scholar
157. Kobialka P, Graupera M. Revisiting PI3-kinase signalling in angiogenesis. Vasc Biol. 2019;1(1):H125–H134.
     View this article via: CrossRef PubMed Google Scholar
158. Angulo-Urarte A, Graupera M. When, where and which PIK3CA mutations are pathogenic in congenital disorders. Nat Cardiovasc Res. 2022;1:700–714.
     View this article via: CrossRef Google Scholar
159. Johnson DW, et al. Mutations in the activin receptor-like kinase 1 gene in hereditary haemorrhagic telangiectasia type 2. Nat Genet. 1996;13(2):189–195.
     View this article via: CrossRef PubMed Google Scholar
160. McAllister KA, et al. Endoglin, a TGF-beta binding protein of endothelial cells, is the gene for hereditary haemorrhagic telangiectasia type 1. Nat Genet. 1994;8(4):345–351.
     View this article via: CrossRef PubMed Google Scholar
161. Gallione CJ, et al. A combined syndrome of juvenile polyposis and hereditary haemorrhagic telangiectasia associated with mutations in MADH4 (SMAD4). Lancet. 2004;363(9412):852–859.
     View this article via: CrossRef PubMed Google Scholar
162. Ruiz S, et al. Correcting Smad1/5/8, mTOR, and VEGFR2 treats pathology in hereditary hemorrhagic telangiectasia models. J Clin Invest. 2020;130(2):942–957.
     View this article via: JCI CrossRef PubMed Google Scholar
163. Park H, et al. Defective flow-migration coupling causes arteriovenous malformations in hereditary hemorrhagic telangiectasia. Circulation. 2021;144(10):805–822.
     View this article via: CrossRef PubMed Google Scholar
164. Ola R, et al. PI3 kinase inhibition improves vascular malformations in mouse models of hereditary haemorrhagic telangiectasia. Nat Commun. 2016;7:13650.
     View this article via: CrossRef PubMed Google Scholar
165. Lee H-W, et al. Role of venous endothelial cells in developmental and pathologic angiogenesis. Circulation. 2021;144(16):1308–1322.
     View this article via: CrossRef PubMed Google Scholar
166. Jin Y, et al. Endoglin prevents vascular malformation by regulating flow-induced cell migration and specification through VEGFR2 signalling. Nat Cell Biol. 2017;19(6):639–652.
     View this article via: CrossRef PubMed Google Scholar
167. Iriarte A, et al. PI3K (phosphatidylinositol 3-kinase) activation and endothelial cell proliferation in patients with hemorrhagic hereditary telangiectasia type 1. Cells. 2019;8(9):971.
     View this article via: CrossRef PubMed Google Scholar
168. Snellings DA, et al. Somatic mutations in vascular malformations of hereditary hemorrhagic telangiectasia result in bi-allelic loss of ENG or ACVRL1. Am J Hum Genet. 2019;105(5):894–906.
     View this article via: CrossRef PubMed Google Scholar
169. Garrido-Martin EM, et al. Common and distinctive pathogenetic features of arteriovenous malformations in hereditary hemorrhagic telangiectasia 1 and hereditary hemorrhagic telangiectasia 2 animal models--brief report. Arterioscler Thromb Vasc Biol. 2014;34(10):2232–2236.
     View this article via: CrossRef PubMed Google Scholar
170. Tual-Chalot S, et al. Loss of endothelial endoglin promotes high-output heart failure through peripheral arteriovenous shunting driven by VEGF signaling. Circ Res. 2020;126(2):243–257.
     View this article via: CrossRef PubMed Google Scholar
171. Choi E-J, et al. Novel brain arteriovenous malformation mouse models for type 1 hereditary hemorrhagic telangiectasia. PLoS One. 2014;9(2):e88511.
     View this article via: CrossRef PubMed Google Scholar
172. Park SO, et al. Real-time imaging of de novo arteriovenous malformation in a mouse model of hereditary hemorrhagic telangiectasia. J Clin Invest. 2009;119(11):3487–3496.
     View this article via: JCI PubMed Google Scholar
173. Karar J, Maity A. PI3K/AKT/mTOR pathway in angiogenesis. Front Mol Neurosci. 2011;4:51.
     View this article via: CrossRef PubMed Google Scholar
174. Baeyens N, et al. Defective fluid shear stress mechanotransduction mediates hereditary hemorrhagic telangiectasia. J Cell Biol. 2016;214(7):807–816.
     View this article via: CrossRef PubMed Google Scholar
175. Corti P, et al. Interaction between alk1 and blood flow in the development of arteriovenous malformations. Development. 2011;138(8):1573–1582.
     View this article via: CrossRef PubMed Google Scholar
176. Deng H, et al. Activation of Smad2/3 signaling by low fluid shear stress mediates artery inward remodeling. Proc Natl Acad Sci U S A. 2021;118(37):e2105339118.
     View this article via: CrossRef PubMed Google Scholar
177. Maddaluno L, et al. EndMT contributes to the onset and progression of cerebral cavernous malformations. Nature. 2013;498(7455):492–496.
     View this article via: CrossRef PubMed Google Scholar
178. Eerola I, et al. Capillary malformation-arteriovenous malformation, a new clinical and genetic disorder caused by RASA1 mutations. Am J Hum Genet. 2003;73(6):1240–1249.
     View this article via: CrossRef PubMed Google Scholar
179. Wooderchak-Donahue WL, et al. Expanding the clinical and molecular findings in RASA1 capillary malformation-arteriovenous malformation. Eur J Hum Genet. 2018;26(10):1521–1536.
     View this article via: CrossRef PubMed Google Scholar
180. Amyere M, et al. Germline loss-of-function mutations in EPHB4 cause a second form of capillary malformation-arteriovenous malformation (CM-AVM2) deregulating RAS-MAPK signaling. Circulation. 2017;136(11):1037–1048.
     View this article via: CrossRef PubMed Google Scholar
181. Macmurdo CF, et al. RASA1 somatic mutation and variable expressivity in capillary malformation/arteriovenous malformation (CM/AVM) syndrome. Am J Med Genet A. 2016;170(6):1450–1454.
     View this article via: CrossRef PubMed Google Scholar
182. Couto JA, et al. Somatic MAP2K1 mutations are associated with extracranial arteriovenous malformation. Am J Hum Genet. 2017;100(3):546–554.
     View this article via: CrossRef PubMed Google Scholar
183. Nikolaev SI, et al. Somatic activating KRAS mutations in arteriovenous malformations of the brain. N Engl J Med. 2018;378(3):250–261.
     View this article via: CrossRef PubMed Google Scholar
184. Al-Olabi L, et al. Mosaic RAS/MAPK variants cause sporadic vascular malformations which respond to targeted therapy. J Clin Invest. 2018;128(4):1496–1508.
     View this article via: JCI CrossRef PubMed Google Scholar
185. Tan W-H, et al. The spectrum of vascular anomalies in patients with PTEN mutations: implications for diagnosis and management. J Med Genet. 2007;44(9):594–602.
     View this article via: CrossRef PubMed Google Scholar
186. Choorapoikayil S, et al. Loss of Pten promotes angiogenesis and enhanced vegfaa expression in zebrafish. Dis Model Mech. 2013;6(5):1159–1166.
     View this article via: PubMed Google Scholar
187. Hamada K, et al. The PTEN/PI3K pathway governs normal vascular development and tumor angiogenesis. Genes Dev. 2005;19(17):2054–2065.
     View this article via: CrossRef PubMed Google Scholar
188. Serra H, et al. PTEN mediates Notch-dependent stalk cell arrest in angiogenesis. Nat Commun. 2015;6:7935.
     View this article via: CrossRef PubMed Google Scholar
189. Mishra R, et al. PI3K inhibitors in cancer: clinical implications and adverse effects. Int J Mol Sci. 2021;22(7):3464.
     View this article via: CrossRef PubMed Google Scholar
190. Leoni C, et al. First evidence of a therapeutic effect of miransertib in a teenager with Proteus syndrome and ovarian carcinoma. Am J Med Genet A. 2019;179(7):1319–1324.
     View this article via: CrossRef PubMed Google Scholar
191. Ranieri C, et al. In vitro efficacy of ARQ 092, an allosteric AKT inhibitor, on primary fibroblast cells derived from patients with PIK3CA-related overgrowth spectrum (PROS). Neurogenetics. 2018;19(2):77–91.
     View this article via: CrossRef PubMed Google Scholar
192. Forde K, et al. Clinical experience with the AKT1 inhibitor miransertib in two children with PIK3CA-related overgrowth syndrome. Orphanet J Rare Dis. 2021;16(1):109.
     View this article via: CrossRef PubMed Google Scholar
193. Lackner H, et al. Sirolimus for the treatment of children with various complicated vascular anomalies. Eur J Pediatr. 2015;174(12):1579–1584.
     View this article via: CrossRef PubMed Google Scholar
194. Hammill AM, et al. Sirolimus for the treatment of complicated vascular anomalies in children. Pediatr Blood Cancer. 2011;57(6):1018–1024.
     View this article via: CrossRef PubMed Google Scholar
195. Gabeff R, et al. Efficacy and tolerance of sirolimus (rapamycin) for extracranial arteriovenous malformations in children and adults. Acta Derm Venereol. 2019;99(12):1105–1109.
     View this article via: PubMed Google Scholar
196. Triana P, et al. Sirolimus in the treatment of vascular anomalies. Eur J Pediatr Surg. 2017;27(1):86–90.
     View this article via: PubMed Google Scholar
197. Nadal M, et al. Efficacy and safety of mammalian target of rapamycin inhibitors in vascular anomalies: a systematic review. Acta Derm Venereol. 2016;96(4):448–452.
     View this article via: CrossRef PubMed Google Scholar
198. Glaser K, et al. Linkage of metabolic defects to activated PIK3CA alleles in endothelial cells derived from lymphatic malformation. Lymphat Res Biol. 2018;16(1):43–55.
     View this article via: CrossRef PubMed Google Scholar
199. Keppler-Noreuil KM, et al. PIK3CA-related overgrowth spectrum (PROS): diagnostic and testing eligibility criteria, differential diagnosis, and evaluation. Am J Med Genet A. 2015;167A(2):287–295.
     View this article via: CrossRef PubMed Google Scholar
200. Keppler-Noreuil KM, et al. Clinical delineation and natural history of the PIK3CA-related overgrowth spectrum. Am J Med Genet A. 2014;164A(7):1713–1733.
     View this article via: CrossRef PubMed Google Scholar
201. Kuentz P, et al. Molecular diagnosis of PIK3CA-related overgrowth spectrum (PROS) in 162 patients and recommendations for genetic testing. Genet Med. 2017;19(9):989–997.
     View this article via: CrossRef PubMed Google Scholar
202. Kurek KC, et al. Somatic mosaic activating mutations in PIK3CA cause CLOVES syndrome. Am J Hum Genet. 2012;90(6):1108–1115.
     View this article via: CrossRef PubMed Google Scholar
203. Rivière J-B, et al. De novo germline and postzygotic mutations in AKT3, PIK3R2 and PIK3CA cause a spectrum of related megalencephaly syndromes. Nat Genet. 2012;44(8):934–940.
     View this article via: CrossRef PubMed Google Scholar
204. Vikkula M, et al. Vascular dysmorphogenesis caused by an activating mutation in the receptor tyrosine kinase TIE2. Cell. 1996;87(7):1181–1190.
     View this article via: CrossRef PubMed Google Scholar
205. Wouters V, et al. Hereditary cutaneomucosal venous malformations are caused by TIE2 mutations with widely variable hyper-phosphorylating effects. Eur J Hum Genet. 2010;18(4):414–420.
     View this article via: CrossRef PubMed Google Scholar
206. Wang Q, et al. The gene dosage of class Ia PI3K dictates the development of PTEN hamartoma tumor syndrome. Cell Cycle. 2013;12(23):3589–3593.
     View this article via: CrossRef PubMed Google Scholar