Rapamycin is an antibiotic inhibiting eukaryotic cell growth and proliferation by acting on target of rapamycin (TOR) kinase. Mammalian TOR (mTOR) is thought to work through 2 independent complexes to regulate cell size and cell replication, and these 2 complexes show differential sensitivity to rapamycin. Here we combine functional genetics and pharmacological treatments to analyze rapamycin-sensitive mTOR substrates that are involved in cell proliferation and tissue regeneration after partial hepatectomy in mice. After hepatectomy, hepatocytes proliferated rapidly, correlating with increased S6 kinase phosphorylation, while treatment with rapamycin derivatives impaired regeneration and blocked S6 kinase activation. In addition, genetic deletion of S6 kinase 1 (S6K1) caused a delay in S phase entry in hepatocytes after hepatectomy. The proliferative defect of S6K1-deficient hepatocytes was cell autonomous, as it was also observed in primary cultures and hepatic overexpression of S6K1-rescued proliferation. We found that S6K1 controlled steady-state levels of cyclin D1 (Ccnd1) mRNA in liver, and cyclin D1 expression was required to promote hepatocyte cell cycle. Notably, in vivo overexpression of cyclin D1 was sufficient to restore the proliferative capacity of S6K-null livers. The identification of an S6K1-dependent mechanism participating in cell proliferation in vivo may be relevant for cancer cells displaying high mTOR complex 1 activity and cyclin D1 accumulation.
Catherine Espeillac, Claudia Mitchell, Séverine Celton-Morizur, Céline Chauvin, Vonda Koka, Cynthia Gillet, Jeffrey H. Albrecht, Chantal Desdouets, Mario Pende
α1-Antitrypsin deficiency is an inherited condition that causes liver disease and emphysema. The normal function of this protein, which is synthesized by the liver, is to inhibit neutrophil elastase, a protease that degrades connective tissue of the lung. In the classical form of the disease, inefficient secretion of a mutant α1-antitrypsin protein (AAT-Z) results in its accumulation within hepatocytes and reduced protease inhibitor activity, resulting in liver injury and pulmonary emphysema. Because mutant protein accumulation increases hepatocyte cell stress, we investigated whether transplanted hepatocytes expressing wild-type AAT might have a competitive advantage relative to AAT-Z–expressing hepatocytes, using transgenic mice expressing human AAT-Z. Wild-type donor hepatocytes replaced 20%–98% of mutant host hepatocytes, and repopulation was accelerated by injection of an adenovector expressing hepatocyte growth factor. Spontaneous hepatic repopulation with engrafted hepatocytes occurred in the AAT-Z–expressing mice even in the absence of severe liver injury. Donor cells replaced both globule-containing and globule-devoid cells, indicating that both types of host hepatocytes display impaired proliferation relative to wild-type hepatocytes. These results suggest that wild-type hepatocyte transplantation may be therapeutic for AAT-Z liver disease and may provide an alternative to protein replacement for treating emphysema in AAT-ZZ individuals.
Jianqiang Ding, Govardhana R. Yannam, Namita Roy-Chowdhury, Tunda Hidvegi, Hesham Basma, Stephen I. Rennard, Ronald J. Wong, Yesim Avsar, Chandan Guha, David H. Perlmutter, Ira J. Fox, Jayanta Roy-Chowdhury
Systemic iron homeostasis is mainly controlled by the liver through synthesis of the peptide hormone hepcidin (encoded by Hamp), the key regulator of duodenal iron absorption and macrophage iron release. Here we show that the liver-specific microRNA miR-122 is important for regulating Hamp mRNA expression and tissue iron levels. Efficient and specific depletion of miR-122 by injection of a locked-nucleic-acid–modified (LNA-modified) anti-miR into WT mice caused systemic iron deficiency, characterized by reduced plasma and liver iron levels, mildly impaired hematopoiesis, and increased extramedullary erythropoiesis in the spleen. Moreover, miR-122 inhibition increased the amount of mRNA transcribed by genes that control systemic iron levels, such as hemochromatosis (Hfe), hemojuvelin (Hjv), bone morphogenetic protein receptor type 1A (Bmpr1a), and Hamp. Importantly, miR-122 directly targeted the 3′ untranslated region of 2 mRNAs that encode activators of hepcidin expression, Hfe and Hjv. These data help to explain the increased Hamp mRNA levels and subsequent iron deficiency in mice with reduced miR-122 levels and establish a direct mechanistic link between miR-122 and the regulation of systemic iron metabolism.
Mirco Castoldi, Maja Vujic Spasic, Sandro Altamura, Joacim Elmén, Morten Lindow, Judit Kiss, Jens Stolte, Richard Sparla, Lorenza A. D’Alessandro, Ursula Klingmüller, Robert E. Fleming, Thomas Longerich, Hermann J. Gröne, Vladimir Benes, Sakari Kauppinen, Matthias W. Hentze, Martina U. Muckenthaler
Wilson disease (WD) is a rare hereditary condition that is caused by a genetic defect in the copper-transporting ATPase ATP7B that results in hepatic copper accumulation and lethal liver failure. The present study focuses on the structural mitochondrial alterations that precede clinical symptoms in the livers of rats lacking Atp7b, an animal model for WD. Liver mitochondria from these Atp7b–/– rats contained enlarged cristae and widened intermembrane spaces, which coincided with a massive mitochondrial accumulation of copper. These changes, however, preceded detectable deficits in oxidative phosphorylation and biochemical signs of oxidative damage, suggesting that the ultrastructural modifications were not the result of oxidative stress imposed by copper-dependent Fenton chemistry. In a cell-free system containing a reducing dithiol agent, isolated mitochondria exposed to copper underwent modifications that were closely related to those observed in vivo. In this cell-free system, copper induced thiol modifications of three abundant mitochondrial membrane proteins, and this correlated with reversible intramitochondrial membrane crosslinking, which was also observed in liver mitochondria from Atp7b–/– rats. In vivo, copper-chelating agents reversed mitochondrial accumulation of copper, as well as signs of intra-mitochondrial membrane crosslinking, thereby preserving the functional and structural integrity of mitochondria. Together, these findings suggest that the mitochondrion constitutes a pivotal target of copper in WD.
Hans Zischka, Josef Lichtmannegger, Sabine Schmitt, Nora Jägemann, Sabine Schulz, Daniela Wartini, Luise Jennen, Christian Rust, Nathanael Larochette, Lorenzo Galluzzi, Veronique Chajes, Nathan Bandow, Valérie S. Gilles, Alan A. DiSpirito, Irene Esposito, Martin Goettlicher, Karl H. Summer, Guido Kroemer
Tissue homeostasis and remodeling are processes that involve high turnover of biological macromolecules. Many of the waste molecules that are by-products or degradation intermediates of biological macromolecule turnover enter the circulation and are subsequently cleared by liver sinusoidal endothelial cells (LSEC). Besides the mannose receptor, stabilin-1 and stabilin-2 are the major scavenger receptors expressed by LSEC. To more clearly elucidate the functions of stabilin-1 and -2, we have generated mice lacking stabilin-1, stabilin-2, or both stabilin-1 and -2 (Stab1–/–Stab2–/– mice). Mice lacking either stabilin-1 or stabilin-2 were phenotypically normal; however, Stab1–/–Stab2–/– mice exhibited premature mortality and developed severe glomerular fibrosis, while the liver showed only mild perisinusoidal fibrosis without dysfunction. Upon kidney transplantation into WT mice, progression of glomerular fibrosis was halted, indicating the presence of profibrotic factors in the circulation of Stab1–/–Stab2–/– mice. While plasma levels of known profibrotic cytokines were unaltered, clearance of the TGF-β family member growth differentiation factor 15 (GDF-15) was markedly impaired in Stab1–/–Stab2–/– mice but not in either Stab1–/– or Stab2–/– mice, indicating that it is a common ligand of both stabilin-1 and stabilin-2. These data lead us to conclude that stabilin-1 and -2 together guarantee proper hepatic clearance of potentially noxious agents in the blood and maintain tissue homeostasis not only in the liver but also distant organs.
Kai Schledzewski, Cyrill Géraud, Bernd Arnold, Shijun Wang, Hermann-Josef Gröne, Tibor Kempf, Kai C. Wollert, Beate K. Straub, Peter Schirmacher, Alexandra Demory, Hiltrud Schönhaber, Alexei Gratchev, Lisa Dietz, Hermann-Josef Thierse, Julia Kzhyshkowska, Sergij Goerdt
E3 ubiquitin ligase complexes of the SCF type consist of ring-box 1 (Rbx1), cullin 1 (Cul1), S-phase kinase-associated protein 1 (Skp1), and a member of the F-box family of proteins. The identity of the F-box protein determines the substrate specificity of the complex. The F-box family member F-box– and WD repeat domain–containing 7 (Fbxw7; also known as Fbw7, SEL-10, hCdc4, and hAgo) targets for degradation proteins with wide-ranging functions, and uncovering its in vivo role has been difficult, because Fbxw7–/– embryos die in utero. Using two different Cre-loxP systems (Mx1-Cre and Alb-Cre), we generated mice with liver-specific null mutations of Fbxw7. Hepatic ablation of Fbxw7 resulted in hepatomegaly and steatohepatitis, with massive deposition of triglyceride, a phenotype similar to that observed in humans with nonalcoholic steatohepatitis. Both cell proliferation and the abundance of Fbxw7 substrates were increased in the Fbxw7-deficient liver. Long-term Fbxw7 deficiency resulted in marked proliferation of the biliary system and the development of hamartomas. Fbxw7 deficiency also skewed the differentiation of liver stem cells toward the cholangiocyte lineage rather than the hepatocyte lineage in vitro. This bias was corrected by additional loss of the Notch cofactor RBP-J, suggesting that Notch accumulation triggered the abnormal proliferation of the biliary system. Together, our results suggest that Fbxw7 plays key roles, regulating lipogenesis and cell proliferation and differentiation in the liver.
Ichiro Onoyama, Atsushi Suzuki, Akinobu Matsumoto, Kengo Tomita, Hideki Katagiri, Yuichi Oike, Keiko Nakayama, Keiichi I. Nakayama
Bile acid homeostasis is tightly regulated via a feedback loop operated by the nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP). Contrary to current models, which place FXR upstream of SHP in a linear regulatory pathway, here we show that the phenotypic consequences in mice of the combined loss of both receptors are much more severe than the relatively modest impact of the loss of either Fxr or Shp alone. Fxr–/–Shp–/– mice exhibited cholestasis and liver injury as early as 3 weeks of age, and this was linked to the dysregulation of bile acid homeostatic genes, particularly cytochrome P450, family 7, subfamily a, polypeptide 1 (Cyp7a1). In addition, double-knockout mice showed misregulation of genes in the C21 steroid biosynthesis pathway, with strong induction of cytochrome P450, family 17, subfamily a, polypeptide 1 (Cyp17a1), resulting in elevated serum levels of its enzymatic product 17-hydroxyprogesterone (17-OHP). Treatment of WT mice with 17-OHP was sufficient to induce liver injury that reproduced many of the histopathological features observed in the double-knockout mice. Therefore, our data indicate a pathologic role for increased production of 17-hydroxy steroid metabolites in liver injury and suggest that Fxr–/–Shp–/– mice could provide a model for juvenile onset cholestasis.
Sayeepriyadarshini Anakk, Mitsuhiro Watanabe, Scott A. Ochsner, Neil J. McKenna, Milton J. Finegold, David D. Moore
Activation of hepatic stellate cells in response to chronic inflammation represents a crucial step in the development of liver fibrosis. However, the molecules involved in the interaction between immune cells and stellate cells remain obscure. Herein, we identify the chemokine CCL5 (also known as RANTES), which is induced in murine and human liver after injury, as a central mediator of this interaction. First, we showed in patients with liver fibrosis that CCL5 haplotypes and intrahepatic CCL5 mRNA expression were associated with severe liver fibrosis. Consistent with this, we detected Ccl5 mRNA and CCL5 protein in 2 mouse models of liver fibrosis, induced by either injection of carbon tetrachloride (CCl4) or feeding on a methionine and choline–deficient (MCD) diet. In these models, Ccl5–/– mice exhibited decreased hepatic fibrosis, with reduced stellate cell activation and immune cell infiltration. Transplantation of Ccl5-deficient bone marrow into WT recipients attenuated liver fibrosis, identifying infiltrating hematopoietic cells as the main source of Ccl5. We then showed that treatment with the CCL5 receptor antagonist Met-CCL5 inhibited cultured stellate cell migration, proliferation, and chemokine and collagen secretion. Importantly, in vivo administration of Met-CCL5 greatly ameliorated liver fibrosis in mice and was able to accelerate fibrosis regression. Our results define a successful therapeutic approach to reduce experimental liver fibrosis by antagonizing Ccl5 receptors.
Marie-Luise Berres, Rory R. Koenen, Anna Rueland, Mirko Moreno Zaldivar, Daniel Heinrichs, Hacer Sahin, Petra Schmitz, Konrad L. Streetz, Thomas Berg, Nikolaus Gassler, Ralf Weiskirchen, Amanda Proudfoot, Christian Weber, Christian Trautwein, Hermann E. Wasmuth
The cell death receptor Fas plays a role in the establishment of fulminant hepatitis, a major cause of drug-induced liver failure. Fas activation elicits extrinsic apoptotic and hepatoprotective signals; however, the mechanisms by which these signals are integrated during disease are unknown. Tissue inhibitor of metalloproteinases 3 (TIMP3) controls the critical sheddase a disintegrin and metalloproteinase 17 (ADAM17) and may dictate stress signaling. Using mice and cells lacking TIMP3, ADAM17, and ADAM17-regulated cell surface molecules, we have found that ADAM17-mediated ectodomain shedding of TNF receptors and EGF family ligands controls activation of multiple signaling cascades in Fas-induced hepatitis. We demonstrated that TNF signaling promoted hepatotoxicity, while excessive TNF receptor 1 (TNFR1) shedding in Timp3–/– mice was protective. Compound Timp3–/–Tnf–/– and Timp3–/–Tnfr1–/– knockout conferred complete resistance to Fas-induced toxicity. Loss of Timp3 enhanced metalloproteinase-dependent EGFR signaling due to increased release of the EGFR ligands TGF-α, amphiregulin, and HB-EGF, while depletion of shed amphiregulin resensitized Timp3–/– hepatocytes to apoptosis. Finally, adenoviral delivery of Adam17 prevented acetaminophen-induced liver failure in a clinically relevant model of Fas-dependent fulminant hepatitis. These findings demonstrate that TIMP3 and ADAM17 cooperatively dictate cytokine signaling during death receptor activation and indicate that regulated metalloproteinase activity integrates survival and death signals during acute hepatotoxic stress.
Aditya Murthy, Virginie Defamie, David S. Smookler, Marco A. Di Grappa, Keisuke Horiuchi, Massimo Federici, Maria Sibilia, Carl P. Blobel, Rama Khokha
Organic anion transporting polypeptides (OATPs) are uptake transporters for a broad range of endogenous compounds and xenobiotics. To investigate the physiologic and pharmacologic roles of OATPs of the 1A and 1B subfamilies, we generated mice lacking all established and predicted mouse Oatp1a/1b transporters (referred to as Slco1a/1b–/– mice, as SLCO genes encode OATPs). Slco1a/1b–/– mice were viable and fertile but exhibited markedly increased plasma levels of bilirubin conjugated to glucuronide and increased plasma levels of unconjugated bile acids. The unexpected conjugated hyperbilirubinemia indicates that Oatp1a/1b transporters normally mediate extensive hepatic reuptake of glucuronidated bilirubin. We therefore hypothesized that substantial sinusoidal secretion and subsequent Oatp1a/1b-mediated reuptake of glucuronidated compounds can occur in hepatocytes under physiologic conditions. This alters our perspective on normal liver functioning. Slco1a/1b–/– mice also showed drastically decreased hepatic uptake and consequently increased systemic exposure following i.v. or oral administration of the OATP substrate drugs methotrexate and fexofenadine. Importantly, intestinal absorption of oral methotrexate or fexofenadine was not affected in Slco1a/1b–/– mice. Further analysis showed that rifampicin was an effective and specific Oatp1a/1b inhibitor in controlling methotrexate pharmacokinetics. These data indicate that Oatp1a/1b transporters play an essential role in hepatic reuptake of conjugated bilirubin and uptake of unconjugated bile acids and drugs. Slco1a/1b–/– mice will provide excellent tools to study further the role of Oatp1a/1b transporters in physiology and drug disposition.
Evita van de Steeg, Els Wagenaar, Cornelia M.M. van der Kruijssen, Johanna E.C. Burggraaff, Dirk R. de Waart, Ronald P.J. Oude Elferink, Kathryn E. Kenworthy, Alfred H. Schinkel
PDGF-dependent hepatic stellate cell (HSC) recruitment is an essential step in liver fibrosis and the sinusoidal vascular changes that accompany this process. However, the mechanisms that regulate PDGF signaling remain incompletely defined. Here, we found that in two rat models of liver fibrosis, the axonal guidance molecule neuropilin-1 (NRP-1) was upregulated in activated HSCs, which exhibit the highly motile myofibroblast phenotype. Additionally, NRP-1 colocalized with PDGF-receptor β (PDGFRβ) in HSCs both in the injury models and in human and rat HSC cell lines. In human HSCs, siRNA-mediated knockdown of NRP-1 attenuated PDGF-induced chemotaxis, while NRP-1 overexpression increased cell motility and TGF-β–dependent collagen production. Similarly, mouse HSCs genetically modified to lack NRP-1 displayed reduced motility in response to PDGF treatment. Immunoprecipitation and biochemical binding studies revealed that NRP-1 increased PDGF binding affinity for PDGFRβ-expressing cells and promoted downstream signaling. An NRP-1 neutralizing Ab ameliorated recruitment of HSCs, blocked liver fibrosis in a rat model of liver injury, and also attenuated VEGF responses in cultured liver endothelial cells. In addition, NRP-1 overexpression was observed in human specimens of liver cirrhosis caused by both hepatitis C and steatohepatitis. These studies reveal a role for NRP-1 as a modulator of multiple growth factor targets that regulate liver fibrosis and the vascular changes that accompany it and may have broad implications for liver cirrhosis and myofibroblast biology in a variety of other organ systems and disease conditions.
Sheng Cao, Usman Yaqoob, Amitava Das, Uday Shergill, Kumaravelu Jagavelu, Robert C. Huebert, Chittaranjan Routray, Soha Abdelmoneim, Meher Vasdev, Edward Leof, Michael Charlton, Ryan J. Watts, Debabrata Mukhopadhyay, Vijay H. Shah
Hepatic fibrosis occurs during most chronic liver diseases and is driven by inflammatory responses to injured tissue. Because DCs are central to modulating liver immunity, we postulated that altered DC function contributes to immunologic changes in hepatic fibrosis and affects the pathologic inflammatory milieu within the fibrotic liver. Using mouse models, we determined the contribution of DCs to altered hepatic immunity in fibrosis and investigated the role of DCs in modulating the inflammatory environment within the fibrotic liver. We found that DC depletion completely abrogated the elevated levels of many inflammatory mediators that are produced in the fibrotic liver. DCs represented approximately 25% of the fibrotic hepatic leukocytes and showed an elevated CD11b+CD8– fraction, a lower B220+ plasmacytoid fraction, and increased expression of MHC II and CD40. Moreover, after liver injury, DCs gained a marked capacity to induce hepatic stellate cells, NK cells, and T cells to mediate inflammation, proliferation, and production of potent immune responses. The proinflammatory and immunogenic effects of fibrotic DCs were contingent on their production of TNF-α. Therefore, modulating DC function may be an attractive approach to experimental therapeutics in fibro-inflammatory liver disease.
Michael K. Connolly, Andrea S. Bedrosian, Jon Mallen-St. Clair, Aaron P. Mitchell, Junaid Ibrahim, Andrea Stroud, H. Leon Pachter, Dafna Bar-Sagi, Alan B. Frey, George Miller
Massive liver resection and small-for-size liver transplantation pose a therapeutic challenge, due to increased susceptibility of the remnant/graft to ischemia reperfusion injury (IRI) and impaired regeneration. We investigated the dual role of complement in IRI versus regeneration in mice. Complement component 3 (C3) deficiency and complement inhibition with complement receptor 2–complement receptor 1–related protein y (CR2-Crry, an inhibitor of C3 activation) provided protection from hepatic IRI, and while C3 deficiency also impaired liver regeneration following partial hepatectomy (PHx), the effect of CR2-Crry in this context was dose dependent. In a combined model of IRI and PHx, either C3 deficiency or high-dose CR2-Crry resulted in steatosis, severe hepatic injury, and high mortality, whereas low-dose CR2-Crry was protective and actually increased hepatic proliferative responses relative to control mice. Reconstitution experiments revealed an important role for the C3a degradation product acylation-stimulating protein (ASP) in the balance between inflammation/injury versus regeneration. Furthermore, liver regeneration was dependent on the putative ASP receptor, C5L2. Several potential mechanisms of hepatoprotection and recovery were identified in mice treated with low-dose CR2-Crry, including enhanced IL-6 expression and STAT3 activation, reduced hepatic ATP depletion, and attenuated oxidative stress. These data indicate that a threshold of complement activation, involving ASP and C5L2, promotes liver regeneration and suggest a balance between complement-dependent injury and regeneration.
Songqing He, Carl Atkinson, Fei Qiao, Katherine Cianflone, Xiaoping Chen, Stephen Tomlinson
Biliary atresia is a neonatal obstructive cholangiopathy that progresses to end-stage liver disease. Although the etiology is unknown, a neonatal adaptive immune signature has been mechanistically linked to obstruction of the extrahepatic bile ducts. Here, we investigated the role of the innate immune response in the pathogenesis of biliary atresia. Analysis of livers of infants at diagnosis revealed that NK cells populate the vicinity of intrahepatic bile ducts and overexpress several genes involved in cytotoxicity. Using a model of rotavirus-induced biliary atresia in newborn mice, we found that activated NK cells also populated murine livers and were the most abundant cells in extrahepatic bile ducts at the time of obstruction. Rotavirus-primed hepatic NK cells lysed cholangiocytes in a contact- and Nkg2d-dependent fashion. Depletion of NK cells and blockade of Nkg2d each prevented injury of the duct epithelium after rotavirus infection, maintained continuity of duct lumen between the liver and duodenum, and enabled bile flow, despite the presence of virus in the tissue and the overexpression of proinflammatory cytokines. These findings identify NK cells as key initiators of cholangiocyte injury via Nkg2d and demonstrate that injury to the duct epithelium drives the phenotype of experimental biliary atresia.
Pranavkumar Shivakumar, Gregg E. Sabla, Peter Whitington, Claire A. Chougnet, Jorge A. Bezerra
Hepatic fibrosis develops as a response to chronic liver injury and almost exclusively occurs in a proinflammatory environment. However, the role of inflammatory mediators in fibrogenic responses of the liver is only poorly understood. We therefore investigated the role of CC chemokines and their receptors in hepatic fibrogenesis. The CC chemokines MIP-1α, MIP-1β, and RANTES and their receptors CCR1 and CCR5 were strongly upregulated in 2 experimental mouse models of fibrogenesis. Neutralization of CC chemokines by the broad-spectrum CC chemokine inhibitor 35k efficiently reduced hepatic fibrosis, and CCR1- and CCR5-deficient mice displayed substantially reduced hepatic fibrosis and macrophage infiltration. Analysis of fibrogenesis in CCR1- and CCR5-chimeric mice revealed that CCR1 mediates its profibrogenic effects in BM-derived cells, whereas CCR5 mediates its profibrogenic effects in resident liver cells. CCR5 promoted hepatic stellate cell (HSC) migration through a redox-sensitive, PI3K-dependent pathway. Both CCR5-deficient HSCs and CCR1- and CCR5-deficient Kupffer cells displayed strong suppression of CC chemokine–induced migration. Finally, we detected marked upregulation of RANTES, CCR1, and CCR5 in patients with hepatic cirrhosis, confirming activation of the CC chemokine system in human fibrogenesis. Our data therefore support a role for the CC chemokine system in hepatic fibrogenesis and suggest distinct roles for CCR1 and CCR5 in Kupffer cells and HSCs.
Ekihiro Seki, Samuele De Minicis, Geum-Youn Gwak, Johannes Kluwe, Sayaka Inokuchi, Christina A. Bursill, Josep M. Llovet, David A. Brenner, Robert F. Schwabe
The formation of polyploid cells is part of the developmental program of several tissues. During postnatal development, binucleated tetraploid cells arise in the liver, caused by failure in cytokinesis. In this report, we have shown that the initiation of cytokinesis failure events and the subsequent appearance of binucleated tetraploid cells are strictly controlled by the suckling-to-weaning transition in rodents. We found that daily light/dark rhythms and carbohydrate intake did not affect liver tetraploidy. In contrast, impairment of insulin signaling drastically reduced the formation of binucleated tetraploid cells, whereas repeated insulin injections promoted the generation of these liver cells. Furthermore, inhibition of Akt activity decreased the number of cytokinesis failure events, possibly through the mammalian target of rapamycin signaling complex 2 (mTORC2), which indicates that the PI3K/Akt pathway lies downstream of the insulin signal to regulate the tetraploidization process. To our knowledge, these results are the first demonstration in a physiological context that insulin signaling through Akt controls a specific cell division program and leads to the physiologic generation of binucleated tetraploid liver cells.
Séverine Celton-Morizur, Grégory Merlen, Dominique Couton, Germain Margall-Ducos, Chantal Desdouets
The forkhead box proteins A1 and A2 (Foxa1 and Foxa2) are transcription factors with critical roles in establishing the developmental competence of the foregut endoderm and in initiating liver specification. Using conditional gene ablation during a later phase of liver development, we show here that deletion of both Foxa1 and Foxa2 (Foxa1/2) in the embryonic liver caused hyperplasia of the biliary tree. Abnormal bile duct formation in Foxa1/2-deficient liver was due, at least in part, to activation of IL-6 expression, a proliferative signal for cholangiocytes. The glucocorticoid receptor is a negative regulator of IL-6 transcription; in the absence of Foxa1/2, the glucocorticoid receptor failed to bind to the IL-6 promoter, causing enhanced IL-6 expression. Thus, after liver specification, Foxa1/2 are required for normal bile duct development through prevention of excess cholangiocyte proliferation. Our data suggest that Foxa1/2 function as terminators of bile duct expansion in the adult liver through inhibition of IL-6 expression.
Zhaoyu Li, Peter White, Geetu Tuteja, Nir Rubins, Sara Sackett, Klaus H. Kaestner
Hepatitis C virus (HCV) is a common RNA virus that causes hepatitis and liver cancer. Infection is treated with IFN-α and ribavirin, but this expensive and physically demanding therapy fails in half of patients. The genomic sequences of independent HCV isolates differ by approximately 10%, but the effects of this variation on the response to therapy are unknown. To address this question, we analyzed amino acid covariance within the full viral coding region of pretherapy HCV sequences from 94 participants in the Viral Resistance to Antiviral Therapy of Chronic Hepatitis C (Virahep-C) clinical study. Covarying positions were common and linked together into networks that differed by response to therapy. There were 3-fold more hydrophobic amino acid pairs in HCV from nonresponding patients, and these hydrophobic interactions were predicted to contribute to failure of therapy by stabilizing viral protein complexes. Using our analysis to detect patterns within the networks, we could predict the outcome of therapy with greater than 95% coverage and 100% accuracy, raising the possibility of a prognostic test to reduce therapeutic failures. Furthermore, the hub positions in the networks are attractive antiviral targets because of their genetic linkage with many other positions that we predict would suppress evolution of resistant variants. Finally, covariance network analysis could be applicable to any virus with sufficient genetic variation, including most human RNA viruses.
Rajeev Aurora, Maureen J. Donlin, Nathan A. Cannon, John E. Tavis
Environmental arsenic exposure, through drinking contaminated water, is a significant risk factor for developing vascular diseases and is associated with liver portal hypertension, vascular shunting, and portal fibrosis through unknown mechanisms. We found that the addition of low doses of arsenite to the drinking water of mice resulted in marked pathologic remodeling in liver sinusoidal endothelial cells (SECs), including SEC defenestration, capillarization, increased junctional PECAM-1 expression, protein nitration, and decreased liver clearance of modified albumin. Furthermore, the pathologic changes observed after in vivo exposure were recapitulated in isolated mouse SECs exposed to arsenic in culture. To investigate the role of NADPH oxidase–generated ROS in this remodeling, we examined the effect of arsenite in the drinking water of mice deficient for the p47 subunit of the NADPH oxidase and found that knockout mice were protected from arsenite-induced capillarization and protein nitration. Furthermore, ex vivo arsenic exposure increased SEC superoxide generation, and this effect was inhibited by addition of a Nox2 inhibitor and quenched by the cell-permeant superoxide scavenger. In addition, inhibiting either oxidant generation or Rac1-GTPase blocked ex vivo arsenic-stimulated SEC differentiation and dysfunction. Our data indicate that a Nox2-based oxidase is required for SEC capillarization and that it may play a central role in vessel remodeling following environmentally relevant arsenic exposures.
Adam C. Straub, Katherine A. Clark, Mark A. Ross, Ashwin G. Chandra, Song Li, Xiang Gao, Patrick J. Pagano, Donna B. Stolz, Aaron Barchowsky
Hyperproliferation of bile duct epithelial cells due to cell-cycle dysregulation is a key feature of cystogenesis in polycystic liver diseases (PCLDs). Recent evidence suggests a regulatory role for microRNAs (miRNAs) in a variety of biological processes, including cell proliferation. We therefore hypothesized that miRNAs may be involved in the regulation of selected components of the cell cycle and might contribute to hepatic cystogenesis. We found that the cholangiocyte cell line PCK-CCL, which is derived from the PCK rat, a model of autosomal recessive polycystic kidney disease (ARPKD), displayed global changes in miRNA expression compared with normal rat cholangiocytes (NRCs). More specific analysis revealed decreased levels of 1 miRNA, miR15a, both in PCK-CCL cells and in liver tissue from PCK rats and patients with a PCLD. The decrease in miR15a expression was associated with upregulation of its target, the cell-cycle regulator cell division cycle 25A (Cdc25A). Overexpression of miR15a in PCK-CCL cells decreased Cdc25A levels, inhibited cell proliferation, and reduced cyst growth. In contrast, suppression of miR15a in NRCs accelerated cell proliferation, increased Cdc25A expression, and promoted cyst growth. Taken together, these results suggest that suppression of miR15a contributes to hepatic cystogenesis through dysregulation of Cdc25A.
Seung-Ok Lee, Tatyana Masyuk, Patrick Splinter, Jesús M. Banales, Anatoliy Masyuk, Angela Stroope, Nicholas LaRusso