Abstract
Mitral valve prolapse (MVP) is a common human phenotype, yet little is known about the pathogenesis of this condition. MVP can occur in the context of genetic syndromes, including Marfan syndrome (MFS), an autosomal-dominant connective tissue disorder caused by mutations in fibrillin-1. Fibrillin-1 contributes to the regulated activation of the cytokine TGF-β, and enhanced signaling is a consequence of fibrillin-1 deficiency. We thus hypothesized that increased TGF-β signaling may contribute to the multisystem pathogenesis of MFS, including the development of myxomatous changes of the atrioventricular valves. Mitral valves from fibrillin-1–deficient mice exhibited postnatally acquired alterations in architecture that correlated both temporally and spatially with increased cell proliferation, decreased apoptosis, and excess TGF-β activation and signaling. In addition, TGF-β antagonism in vivo rescued the valve phenotype, suggesting a cause and effect relationship. Expression analyses identified increased expression of numerous TGF-β–related genes that regulate cell proliferation and survival and plausibly contribute to myxomatous valve disease. These studies validate a novel, genetically engineered murine model of myxomatous changes of the mitral valve and provide critical insight into the pathogenetic mechanism of such changes in MFS and perhaps more common nonsyndromic variants of mitral valve disease.
Authors
Connie M. Ng, Alan Cheng, Loretha A. Myers, Francisco Martinez-Murillo, Chunfa Jie, Djahida Bedja, Kathleen L. Gabrielson, Jennifer M.W. Hausladen, Robert P. Mecham, Daniel P. Judge, Harry C. Dietz
Abstract
Homozygosity for mutations in ABC transporter A1 (ABCA1) causes Tangier disease, a rare HDL-deficiency syndrome. Whether heterozygosity for genetic variation in ABCA1 also contributes to HDL cholesterol (HDL-C) levels in the general population is presently unclear. We determined whether mutations or single-nucleotide polymorphisms (SNPs) in ABCA1 were overrepresented in individuals with the lowest 1% (n = 95) or highest 1% (n = 95) HDL-C levels in the general population by screening the core promoter and coding region of ABCA1. For all nonsynonymous SNPs identified, we determined the effect of genotype on lipid traits in 9,259 individuals from the general population. Heterozygosity for ABCA1 mutations was identified in 10% of individuals with low HDL-C only. Three of 6 nonsynonymous SNPs (V771M, V825I, and R1587K) were associated with increases or decreases in HDL-C in women in the general population and some with consistent trends in men, determined as isolated single-site effects varying only at the relevant SNP. Finally, these results were consistent over time. In conclusion, we show that at least 10% of individuals with low HDL-C in the general population are heterozygous for mutations in ABCA1 and that both mutations and SNPs in ABCA1 contribute to HDL-C levels in the general population.
Authors
Ruth Frikke-Schmidt, Børge G. Nordestgaard, Gorm B. Jensen, Anne Tybjærg-Hansen
Abstract
Calcineurin, which binds to the Z-disc in cardiomyocytes via α-actinin, promotes cardiac hypertrophy in response to numerous pathologic stimuli. However, the endogenous mechanisms regulating calcineurin activity in cardiac muscle are not well understood. We demonstrate that a muscle-specific F-box protein called atrogin-1, or muscle atrophy F-box, directly interacts with calcineurin A and α-actinin-2 at the Z-disc of cardiomyocytes. Atrogin-1 associates with Skp1, Cul1, and Roc1 to assemble an SCFatrogin-1 complex with ubiquitin ligase activity. Expression of atrogin-1 decreases levels of calcineurin A and promotes its ubiquitination. Moreover, atrogin-1 attenuates agonist-induced calcineurin activity and represses calcineurin-dependent transactivation and NFATc4 translocation. Conversely, downregulation of atrogin-1 using adenoviral small interfering RNA (siRNA) expression enhances agonist-induced calcineurin activity and cardiomyocyte hypertrophy. Consistent with these cellular observations, overexpression of atrogin-1 in hearts of transgenic mice reduces calcineurin protein levels and blunts cardiac hypertrophy after banding of the thoracic aorta. These studies indicate that the SCFatrogin-1 ubiquitin ligase complex interacts with and represses calcineurin by targeting calcineurin for ubiquitin-mediated proteolysis, leading to inhibition of cardiac hypertrophy in response to pathologic stimuli.
Authors
Hui-Hua Li, Vishram Kedar, Chunlian Zhang, Holly McDonough, Ranjana Arya, Da-Zhi Wang, Cam Patterson
Abstract
The Raf/MEK/extracellular signal–regulated kinase (ERK) signaling pathway regulates diverse cellular processes such as proliferation, differentiation, and apoptosis and is implicated as an important contributor to the pathogenesis of cardiac hypertrophy and heart failure. To examine the in vivo role of Raf-1 in the heart, we generated cardiac muscle–specific Raf-1–knockout (Raf CKO) mice with Cre-loxP–mediated recombination. The mice demonstrated left ventricular systolic dysfunction and heart dilatation without cardiac hypertrophy or lethality. The Raf CKO mice showed a significant increase in the number of apoptotic cardiomyocytes. The expression level and activation of MEK1/2 or ERK showed no difference, but the kinase activity of apoptosis signal–regulating kinase 1 (ASK1), JNK, or p38 increased significantly compared with that in controls. The ablation of ASK1 rescued heart dysfunction and dilatation as well as cardiac fibrosis. These results indicate that Raf-1 promotes cardiomyocyte survival through a MEK/ERK–independent mechanism.
Authors
Osamu Yamaguchi, Tetsuya Watanabe, Kazuhiko Nishida, Kazunori Kashiwase, Yoshiharu Higuchi, Toshihiro Takeda, Shungo Hikoso, Shinichi Hirotani, Michio Asahi, Masayuki Taniike, Atsuko Nakai, Ikuko Tsujimoto, Yasushi Matsumura, Jun-ichi Miyazaki, Kenneth R. Chien, Atsushi Matsuzawa, Chiharu Sadamitsu, Hidenori Ichijo, Manuela Baccarini, Masatsugu Hori, Kinya Otsu
Abstract
Skeletal myoblast transplantation is a potential treatment for congestive heart failure. To study the functional activity of both donor and host myocytes following transplantation, skeletal myoblasts expressing an enhanced green fluorescent protein (EGFP) transgene were transplanted into hearts of nontransgenic recipients, and changes in intracellular calcium concentration ([Ca2+]i) were monitored in donor and host cells. While the vast majority of donor-derived myocytes were observed to be functionally isolated from the host myocardium, a small population of donor myocytes exhibited action potential–induced calcium transients in synchrony with adjacent host cardiomyocytes. In many cases, the durations of these [Ca2+]i transients were heterogeneous compared with those in neighboring host cardiomyocytes. In other studies, EGFP-expressing donor myoblasts were transplanted into the hearts of adult transgenic recipient mice expressing a cardiomyocyte-restricted β-gal reporter gene. A small population of myocytes was observed to express both reporter transgenes, indicating that the transplanted myoblasts fused with host cardiomyocytes at a very low frequency. These cells also expressed connexin43, a component of gap junctions. Thus engraftment of skeletal myoblasts generated spatial heterogeneity of [Ca2+]i signaling at the myocardial/skeletal muscle interface, most likely as a consequence of fusion events between donor myoblasts and host cardiomyocytes.
Authors
Michael Rubart, Mark H. Soonpaa, Hidehiro Nakajima, Loren J. Field
Abstract
Production of thromboxane (TX) A2 and PG I2/prostacyclin (PGI2) is increased in patients with atherosclerosis. However, their roles in atherogenesis have not been critically defined. To examine this issue, we cross-bred atherosclerosis-prone apoE-deficient mice with mice deficient in either the TXA receptor (TP) or the PGI receptor (IP). Although they showed levels of serum cholesterol and triglyceride similar to those of apoE-deficient mice, apoE–/–TP–/– mice exhibited a significant delay in atherogenesis, and apoE–/–IP–/– mice exhibited a significant acceleration in atherogenesis compared with mice deficient in apoE alone. The plaques in apoE–/–IP–/– mice showed partial endothelial disruption and exhibited enhanced expression of ICAM-1 and decreased expression of platelet endothelial cell adhesion molecule 1 (PECAM-1) in the overlying endothelial cells compared with those of apoE–/–TP–/– mice. Platelet activation with thrombin ex vivo revealed higher and lower sensitivity for surface P-selectin expression in platelets of apoE–/–IP–/– and apoE–/–TP–/– mice, respectively, than in those of apoE–/– mice. Intravital microscopy of the common carotid artery revealed a significantly greater number of leukocytes rolling on the vessel walls in apoE–/–IP–/– mice than in either apoE–/–TP–/– or apoE–/– mice. We conclude that TXA2 promotes and PGI2 prevents the initiation and progression of atherogenesis through control of platelet activation and leukocyte-endothelial cell interaction.
Authors
Takuya Kobayashi, Yoshio Tahara, Mayumi Matsumoto, Masako Iguchi, Hideto Sano, Toshinori Murayama, Hidenori Arai, Hiroji Oida, Takami Yurugi-Kobayashi, Jun K. Yamashita, Hiroyuki Katagiri, Masataka Majima, Masayuki Yokode, Toru Kita, Shuh Narumiya
Abstract
Persistent reduction of renal perfusion pressure induces renovascular hypertension by activating the renin-angiotensin-aldosterone system; however, the sensing mechanism remains elusive. Here we investigated the role of PGI2 in renovascular hypertension in vivo, employing mice lacking the PGI2 receptor (IP–/– mice). In WT mice with a two-kidney, one-clip model of renovascular hypertension, the BP was significantly elevated. The increase in BP in IP–/– mice, however, was significantly lower than that in WT mice. Similarly, the increases in plasma renin activity, renal renin mRNA, and plasma aldosterone in response to renal artery stenosis were all significantly lower in IP–/– mice than in WT mice. All these parameters were measured in mice lacking the four PGE2 receptor subtypes individually, and we found that these mice had similar responses to WT mice. PGI2 is produced by COX-2 and a selective inhibitor of this enzyme, SC-58125, also significantly reduced the increases in plasma renin activity and renin mRNA expression in WT mice with renal artery stenosis, but these effects were absent in IP–/– mice. When the renin-angiotensin-aldosterone system was activated by salt depletion, SC-58125 blunted the response in WT mice but not in IP–/– mice. These results indicate that PGI2 derived from COX-2 plays a critical role in regulating the release of renin and consequently renovascular hypertension in vivo.
Authors
Takayuki Fujino, Naoki Nakagawa, Koh-ichi Yuhki, Akiyoshi Hara, Takehiro Yamada, Koji Takayama, Shuhko Kuriyama, Yayoi Hosoki, Osamu Takahata, Takanobu Taniguchi, Jun Fukuzawa, Naoyuki Hasebe, Kenjiro Kikuchi, Shuh Narumiya, Fumitaka Ushikubi
Abstract
Allograft vascular dysfunction predisposes to arteriosclerosis and graft loss. We examined how dysfunction develops in transplanted human arteries in response to circulating allogeneic T cells in vivo using immunodeficient murine hosts. Within 7–9 days, transplanted arteries developed endothelial cell (EC) dysfunction but remained sensitive to exogenous NO. By 2 weeks, the grafts developed impaired contractility and desensitization to NO, both signs of VSMC dysfunction. These T cell–dependent changes correlated with loss of eNOS and expression of iNOS — the latter predominantly within infiltrating T cells. Neutralizing IFN-γ completely prevented both vascular dysfunction and changes in NOS expression; neutralizing TNF reduced IFN-γ production and partially prevented dysfunction. Inhibiting iNOS partially preserved responses to NO at 2 weeks and reduced graft intimal expansion after 4 weeks in vivo. In vitro, memory CD4+ T cells acted on allogeneic cultured ECs to reduce eNOS activity and expression of protein and mRNA. These effects required T cell activation by class II MHC antigens and costimulators (principally lymphocyte function-associated antigen–3, or LFA-3) on the ECs and were mediated by production of soluble mediators including IFN-γ and TNF. We conclude that IFN-γ is a central mediator of vascular dysfunction and, through dysregulation of NOS expression, links early dysfunction with late arteriosclerosis.
Authors
Kian Peng Koh, Yinong Wang, Tai Yi, Stephen L. Shiao, Marc I. Lorber, William C. Sessa, George Tellides, Jordan S. Pober
Abstract
The action of insulin in the central nervous system produces sympathetic nervous system activation (also called sympathoactivation), although the neuronal intracellular mechanisms that mediate this are unclear. We hypothesized that PI3K and MAPK, the major pathways involved in insulin receptor signaling, mediate sympathetic nerve responses to insulin. Intracerebroventricular administration of insulin in rat increased multifiber sympathetic nerve activity to the hindlimb, brown adipose tissue (BAT), adrenal gland, and kidney. Ex vivo biochemical studies of mediobasal hypothalamic tissue revealed that insulin stimulated the association of insulin receptor substrate–1 with the p85α subunit of PI3K and also tyrosine phosphorylation of p42 and p44 subunits of MAPK in the hypothalamus. In order to determine whether PI3K and/or MAPK were involved in insulin-mediated sympathoactivation, we tested the effect of specific inhibitors of PI3K (LY294002 and wortmannin) and MAPK (PD98059 and U0126) on regional sympathetic responses to insulin. Interestingly, regional sympathoactivation to insulin was differentially affected by blockade of PI3K and MAPK. Inhibition of PI3K specifically blocked insulin-induced sympathoactivation to the hindlimb, while inhibition of MAPK specifically blocked insulin-induced sympathoactivation to BAT. Sympathoactivation to corticotrophin-releasing factor, however, was not affected by inhibition of PI3K and MAPK. These data demonstrate that PI3K and MAPK are specific and regionally selective mediators of the action of insulin on the sympathetic nervous system.
Authors
Kamal Rahmouni, Donald A. Morgan, Gina M. Morgan, Xuebo Liu, Curt D. Sigmund, Allyn L. Mark, William G. Haynes
Abstract
Authors
Koichi Shimizu, Masayoshi Shichiri, Peter Libby, Richard T. Lee, Richard N. Mitchell
Copyright © 2026 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)