Recruitment of large peritoneal macrophages to capsular fibrosis developed on the liver surface.

Upon injury to Glisson's capsule, mesothelial cells covering the liver surface differentiate into myofibroblasts and participate in capsular fibrosis. In the fibrotic area, infiltrating macrophages are present, but their origin and role in capsular fibrosis remain elusive. In the present study, we examined whether macrophages in the peritoneal cavity migrate to the liver and participate in capsular fibrosis. Capsular fibrosis was induced by intraperitoneal injection of chlorhexidine gluconate. Chlorhexidine gluconate treatment induced disappearance of CD11bHigh F4/80High large peritoneal macrophages from the peritoneal cavity. Transplantation of TIMD4+ large peritoneal macrophages to the mouse peritoneal cavity resulted in their recruitment to the fibrotic area of the liver. Bone marrow-derived monocytes were also recruited to the chlorhexidine gluconate-induced fibrotic area upon their transplantation to the peritoneal cavity. However, bone marrow-derived macrophages, Kupffer cells, peritoneal B cells, and small peritoneal macrophages prepared from chlorhexidine gluconate-treated mice did not exhibit such potential. In the hepatic fibrotic area, peritoneal macrophages lost expression of unique markers (Gata6, Timd4) and increased expression of genes involved in inflammation (Il1b, Il6, Tnf) and extracellular matrix remodeling (Mmp13, Timp1). Depletion of peritoneal macrophages by clodronate liposomes reduced capsular fibrosis. Our data indicate that large peritoneal macrophages are recruited to the injured liver surface and promote capsular fibrosis by inducing inflammation and extracellular matrix remodeling. Modulating the function of peritoneal macrophages might be a new approach for suppressing capsular fibrosis.

TWEAK/FN14 promotes profibrogenic pathway activation in Prominin-1-expressing hepatic progenitor cells in biliary atresia.

BACKGROUND AND AIMS: Biliary atresia (BA), a congenital cholestatic liver disease, commonly culminates in end-stage liver disease. We previously demonstrated in BA that Prominin-1 ( Prom1 )-expressing hepatic progenitor cells (HPCs) expand within regions of developing fibrosis, giving rise to cholangiocytes within biliary ductular reactions. Null mutation of Prom1 or ablation of cells expressing Prom1 significantly diminishes fibrogenesis. FN14, the receptor for TNF-like weak inducer of apoptosis (TWEAK), is expressed by HPCs. TWEAK/FN14 signaling promotes fibrosis in multiple organ systems. Therefore, we hypothesized that TWEAK/FN14 signaling mediates Prom1 -expressing HPC proliferation leading to profibrogenic ductular reactions in BA. APPROACH AND RESULTS: The experimental mouse model of BA mediated by perinatal rhesus rotavirus (RRV) infection resulted in increased co-expression of Fn14 in Prom1 -expressing HPCs within regions of ductular reactions. FN14 antagonist L524-0366 decreased ductular reactions, biliary fibrosis and periportal fibroblast activation in RRV injury. L524-0366 inhibition also demonstrated loss of downstream noncanonical NF-kB signaling expression in RRV injury. Murine HPC organoids demonstrated accelerated organoid growth and proliferation when treated with recombinant TWEAK. Increased organoid proliferation with recombinant TWEAK was lost when also treated with L524-0366. Analysis of a large publicly available RNA sequencing database of BA and normal control patients revealed significant increases in expression of PROM1 , FN14 , and genes downstream of TNF signaling and noncanonical NF-κB signaling pathways in BA infants. Infants who failed to achieve bile drainage after hepatoportoenterostomy had higher relative levels of FN14 expression. CONCLUSION: TWEAK/FN14 signaling activation in Prom1 -expressing HPCs contributes to proliferation of profibrogenic ductular reactions in BA.

Emergence of highly profibrotic and proinflammatory Lrat+Fbln2+ HSC subpopulation in alcoholic hepatitis.

BACKGROUND AND AIMS: Relative roles of HSCs and portal fibroblasts in alcoholic hepatitis (AH) are unknown. We aimed to identify subpopulations of collagen type 1 alpha 1 (Col1a1)-expressing cells in a mouse AH model by single-cell RNA sequencing (scRNA-seq) and filtering the cells with the HSC (lecithin retinol acyltransferase [Lrat]) and portal fibroblast (Thy-1 cell surface antigen [Thy1] and fibulin 2 [Fbln2]) markers and vitamin A (VitA) storage. APPROACH AND RESULTS: Col1a1-green fluorescent protein (GFP) mice underwent AH, CCl 4 , and bile duct ligation (BDL) procedures to have comparable F1-F2 liver fibrosis. Col1a1-expressing cells were sorted via FACS by VitA autofluorescence and GFP for single-cell RNA sequencing. In AH, approximately 80% of Lrat+Thy1-Fbln2- activated HSCs were VitA-depleted (vs. ~13% in BDL and CCl 4 ). Supervised clustering identified a subset co-expressing Lrat and Fbln2 (Lrat+Fbln2+), which expanded 44-fold, 17-fold, and 1.3-fold in AH, BDL, and CCl 4 . Lrat+Fbln2+ cells had 3-15-times inductions of profibrotic, myofibroblastic, and immunoregulatory genes versus Lrat+Fbln2- cells, but 2-4-times repressed HSC-selective genes. AH activated HSCs had up-regulated inflammatory (chemokine [C-X-C motif] ligand 2 [Cxcl2], chemokine [C-C motif] ligand 2), antimicrobial (Il-33, Zc3h12a), and antigen presentation (H2-Q6, H2-T23) genes versus BDL and CCl 4 . Computational deconvolution of AH versus normal human bulk-liver RNA-sequencing data supported an expansion of LRAT+FBLN2+ cells in AH; AH patient liver immunohistochemistry showed FBLN2 staining along fibrotic septa enriched with LRAT+ cells; and in situ hybridization confirmed co-expression of FBLN2 with CXCL2 and/or human leukocyte antigen E in patient AH. Finally, HSC tracing in Lrat-Cre;Rosa26mTmG mice detected GFP+FBLN2+ cells in AH. CONCLUSION: A highly profibrotic, inflammatory, and immunoregulatory Lrat+Fbln2+ subpopulation emerges from HSCs in AH and may contribute to the inflammatory and immunoreactive nature of AH.

Heterozygous midnolin knockout attenuates severity of nonalcoholic fatty liver disease in mice fed a Western-style diet high in fat, cholesterol, and fructose.

Although midnolin has been studied for over 20 years, its biological roles in vivo remain largely unknown, especially due to the lack of a functional animal model. Indeed, given our recent discovery that the knockdown of midnolin suppresses liver cancer cell tumorigenicity and that this antitumorigenic effect is associated with modulation of lipid metabolism, we hypothesized that knockout of midnolin in vivo could potentially protect from nonalcoholic fatty liver disease (NAFLD) which has become the most common cause of chronic liver disease in the Western world. Accordingly, in the present study, we have developed and now report on the first functional global midnolin knockout mouse model. Although the overwhelming majority of global homozygous midnolin knockout mice demonstrated embryonic lethality, heterozygous knockout mice were observed to be similar to wild-type mice in their viability and were used to determine the effect of reduced midnolin expression on NAFLD. We found that global heterozygous midnolin knockout attenuated the severity of NAFLD in mice fed a Western-style diet, high in fat, cholesterol, and fructose, and this attenuation in disease was associated with significantly reduced levels of large lipid droplets, hepatic free cholesterol, and serum LDL, with significantly differential gene expression involved in cholesterol/lipid metabolism. Collectively, our results support a role for midnolin in regulating cholesterol/lipid metabolism in the liver. Thus, midnolin may represent a novel therapeutic target for NAFLD. Finally, our observation that midnolin was essential for survival underscores the broad importance of this gene beyond its role in liver biology.NEW & NOTEWORTHY We have developed and now report on the first functional global midnolin knockout mouse model. We found that global heterozygous midnolin knockout attenuated the severity of nonalcoholic fatty liver disease (NAFLD) in mice fed a Western-style diet, high in fat, cholesterol, and fructose, and this attenuation in disease was associated with significantly reduced levels of large lipid droplets, hepatic free cholesterol, and serum LDL, with significantly differential gene expression involved in cholesterol/lipid metabolism.

TAZ/WWTR1 mediates liver mesothelial-mesenchymal transition induced by stiff extracellular environment, TGF-ß1, and lysophosphatidic acid.

Mesothelial cells cover the surface of the internal organs and the walls of body cavities, facilitating the movement between organs by secretion of a lubricating fluid. Upon injury, mesothelial cells undergo a mesothelial-mesenchymal transition (MMT) and give rise to myofibroblasts during organ fibrosis, including in the liver. Although transforming growth factor-ß1 (TGF-ß1) was shown to induce MMT, molecular and cellular mechanisms underlying MMT remain to be clarified. In the present study, we examined how the extracellular environment, soluble factors, and cell density control the phenotype of liver mesothelial cells by culturing them at different cell densities or on hydrogels of different stiffness. We found that TGF-ß1 does not fully induce MMT in mesothelial cells cultured at high cell density or in the absence of fetal bovine serum. Extracellular lysophosphatidic acid (LPA) synergistically induced MMT in the presence of TGF-ß1 in mesothelial cells. LPA induced nuclear localization of WW domain-containing transcription regulator1 (WWTR1/TAZ) and knockdown of Taz, which suppressed LPA-induced MMT. Mesothelial cells cultured on stiff hydrogels upregulated nuclear localization of TAZ and myofibroblastic differentiation. Knockdown of Taz suppressed MMT of mesothelial cells cultured on stiff hydrogels, but inhibition of TGF-ß1 signaling failed to suppress MMT. Our data indicate that TAZ mediates MMT induced by TGF-ß1, LPA, and a stiff matrix. The microenvironment of a stiff extracellular matrix is a strong inducer of MMT.

Development of Capsular Fibrosis Beneath the Liver Surface in Humans and Mice.

Glisson's capsule is the connective tissue present in the portal triad as well as beneath the liver surface. Little is known about how Glisson's capsule changes its structure in capsular fibrosis (CF), which is characterized by fibrogenesis beneath the liver surface. In this study, we found that the human liver surface exhibits multilayered capsular fibroblasts and that the bile duct is present beneath the mesothelium, whereas capsular fibroblasts are scarce and no bile ducts are present beneath the mouse liver surface. Patients with cirrhosis caused by alcohol abuse or hepatitis C virus infection show development of massive CF. To examine the effect of alcohol on CF in mice, we first injected chlorhexidine gluconate (CG) intraperitoneally and then fed alcohol for 1 month. The CG injection induces CF consisting of myofibroblasts beneath the mesothelium. One month after CG injection, the fibrotic area returns to the normal structure. In contrast, additional alcohol feeding sustains the presence of myofibroblasts in CF. Cell lineage tracing revealed that mesothelial cells give rise to myofibroblasts in CF, but these myofibroblasts disappear 1 month after recovery with or without alcohol feeding. Capsular fibroblasts isolated from the mouse liver spontaneously differentiated into myofibroblasts and their differentiation was induced by transforming growth factor beta 1 (TGF-ß1) or acetaldehyde in culture. In alcohol-fed mice, infiltrating CD11b+ Ly-6CLow/- monocytes had reduced mRNA expression of matrix metalloproteinase 13 and matrix metalloproteinase 9 and increased expression of tissue inhibitor of matrix metalloproteinase 1, Tgfb1, and interleukin-10 during resolution of CF. Conclusion: The present study revealed that the structure of Glisson's capsule is different between human and mouse livers and that alcohol impairs the resolution of CF by changing the phenotype of Ly-6CLow/- monocytes.

Loss of lysophosphatidic acid receptor 1 in hepatocytes reduces steatosis via down-regulation of CD36.

Nonalcoholic steatohepatitis is a major public health concern and is characterized by the accumulation of triglyceride in hepatocytes and inflammation in the liver. Steatosis is caused by dysregulation of the influx and efflux of lipids, lipogenesis, and mitochondrial ß-oxidation. Extracellular lysophosphatidic acid (LPA) regulates a broad range of cellular processes in development, tissue injury, and cancer. In the present study, we examined the roles of LPA in steatohepatitis induced by a methionine-choline-deficient (MCD) diet in mice. Hepatocytes express LPA receptor (Lpar) 1-3 mRNAs. Steatosis developed in mice fed the MCD diet was reduced by treatment with inhibitors for pan-LPAR or LPAR1. Hepatocyte-specific deletion of the Lpar1 gene also reduced the steatosis in the MCD model. Deletion of the Lpar1 gene in hepatocytes reduced expression of Cd36, a gene encoding a fatty acid transporter. Although LPA/LPAR1 signaling induces expression of Srebp1 mRNA in hepatocytes, LPA does not fully induce expression of SREBP1-target genes involved in lipogenesis. Human hepatocytes repopulated in chimeric mice are known to develop steatosis and treatment with an LPAR1 inhibitor reduces expression of CD36 mRNA and steatosis. Our data indicate that antagonism of LPAR1 reduces steatosis in mouse and human hepatocytes by down-regulation of Cd36.

Moderate alcohol intake promotes pancreatic ductal adenocarcinoma development in mice expressing oncogenic Kras.

Kras mutations are associated with pancreatic ductal adenocarcinoma (PDAC). Although tobacco smoking, pancreatitis, and obesity are known environmental risk factors for PDAC, the contribution of moderate alcohol intake to PDAC remains elusive. In the present study, we tested whether a combination of risk factors or moderate alcohol intake induces PDAC development in mice. Control Pdx1Cre and Pdx1Cre;LSL-KrasG12D mutant mice were fed a Western alcohol diet containing high levels of cholesterol and saturated fat, 3.5% alcohol, and lipopolysaccharide for 5 mo. In addition, mice were treated with cerulein, for induction of pancreatitis, and nicotine every month. Treatment with all of these risk factors promoted development of advanced pancreatic neoplasia and PDAC in the Pdx1Cre;LSL-KrasG12D mice but not in the control Pdx1Cre mice. Moderate alcohol intake or Western diet feeding also significantly promoted advanced neoplasia and PDAC development in Pdx1Cre;LSL-KrasG12D mice compared with mice fed a regular chow. Alcohol, but not Western diet, increased tumor development in the liver in the Pdx1Cre;LSL-KrasG12D mice, but its origin remained elusive due to leakiness of Pdx1Cre in hepatocytes. RNA-seq analysis revealed that alcohol feeding increases expression of markers for tumors (Epcam, Krt19, Prom1, Wt1, and Wwtr1), stroma (Dcn, Fn1, and Tnc), and cytokines (Tgfb1 and Tnf) and decreases expression of Fgf21 and Il6 in the pancreatic tumor tissues. Immunostaining showed heterogeneous expression of nephronectin, S100 calcium-binding protein A6, and vascular cell adhesion molecule 1 in pancreatic tumors surrounded by podoplanin-positive stromal cells. Our data indicate that moderate alcohol drinking is a risk factor for development of PDAC.NEW & NOTEWORTHY Heavy alcohol intake has been suspected to be a risk factor of pancreatic ductal adenocarcinoma (PDAC) in humans. However, the contribution of moderate alcohol intake to PDAC development remains elusive. In the present study, we experimentally show that moderate alcohol feeding significantly induces advanced stages of pancreatic intraepithelial neoplasia development and invasive PDAC in Pdx1Cre;LSL-KrasG12D mutant mice. Our data indicate that moderate alcohol drinking is a risk factor for PDAC.

Isolation of a unique hepatic stellate cell population expressing integrin α8 from embryonic mouse livers.

BACKGROUND: Hepatic stellate cells (HSCs) play an important role in liver fibrogenesis. However, little is known about their phenotype and role in liver development. The aim of this study is to identify specific markers for embryonic HSCs. RESULTS: Using antibodies against ALCAM and PDPN, we separated mesothelial cells (MCs) and HSCs from developing livers and identified integrin α8 (ITGA8) as a marker for embryonic desmin+ HSCs that are preferentially localized near the developing liver surface and α-smooth muscle actin+ perivascular mesenchymal cells around the vein. A cell lineage-tracing study revealed that upon differentiation, MC-derived HSCs or perivascular mesenchymal cells express ITGA8 during liver development. Using anti-ITGA8 antibodies, we succeeded in isolating MC-derived HSCs and perivascular mesenchymal cells from embryonic livers. In direct co-culture, ITGA8+ mesenchymal cells promoted the expression of hepatocyte and cholangiocyte markers in hepatoblasts. In the normal adult liver, expression of ITGA8 was restricted to portal fibroblasts in the portal triad. Upon liver injury, myofibroblasts increased the expression of ITGA8. CONCLUSIONS: ITGA8 is a specific cell surface marker of MC-derived HSCs and perivascular mesenchymal cells in the developing liver. Our data suggest that ITGA8+ mesenchymal cells maintain the phenotype of hepatoblast in liver development. Developmental Dynamics 247:867-881, 2018. © 2018 Wiley Periodicals, Inc.

Characterization of hepatic stellate cells, portal fibroblasts, and mesothelial cells in normal and fibrotic livers.

BACKGROUND & AIMS: Contribution of hepatic stellate cells (HSCs), portal fibroblasts (PFs), and mesothelial cells (MCs) to myofibroblasts is not fully understood due to insufficient availability of markers and isolation methods. The present study aimed to isolate these cells, characterize their phenotypes, and examine their contribution to myofibroblasts in liver fibrosis. METHODS: Liver fibrosis was induced in Collagen1a1-green fluorescent protein (Col1a1(GFP)) mice by bile duct ligation (BDL), 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet, or CCl4 injections. Combining vitamin A (VitA) lipid autofluorescence and expression of GFP and glycoprotein M6a (GPM6A), we separated HSCs, PFs, and MCs from normal and fibrotic livers by fluorescence-activated cell sorting (FACS). RESULTS: Normal Col1a1(GFP) livers broadly expressed GFP in HSCs, PFs, and MCs. Isolated VitA+ HSCs expressed reelin, whereas VitA-GFP+GPM6A- PFs expressed ectonucleoside triphosphate diphosphohydrolase-2 and elastin. VitA-GFP+GPM6A+ MCs expressed keratin 19, mesothelin, and uroplakin 1b. Transforming growth factor (TGF)-ß1 treatment induced the transformation of HSCs, PFs, and MCs into myofibroblasts in culture. TGF-ß1 suppressed cyclin D1 mRNA expression in PFs but not in HSCs and MCs. In biliary fibrosis, PFs adjacent to the bile duct expressed α-smooth muscle actin. FACS analysis revealed that HSCs are the major source of GFP+ myofibroblasts in the injured Col1a1(GFP) mice after DDC or CCl4 treatment. Although PFs partly contributed to GFP+ myofibroblasts in the BDL model, HSCs were still dominant source of myofibroblasts. CONCLUSION: HSCs, PFs, and MCs have distinct phenotypes, and PFs partly contribute to myofibroblasts in the portal triad in biliary fibrosis.

Role of TGF-ß signaling in differentiation of mesothelial cells to vitamin A-poor hepatic stellate cells in liver fibrosis.

Mesothelial cells (MCs) form a single layer of the mesothelium and cover the liver surface. A previous study demonstrated that, upon liver injury, MCs migrate inward from the liver surface and give rise to hepatic stellate cells (HSCs) in biliary fibrosis induced by bile duct ligation (BDL) or myofibroblasts in CCl4-induced fibrosis. The present study analyzed the role of transforming growth factor-ß (TGF-ß) signaling in mesothelial-mesenchymal transition (MMT) and the fate of MCs during liver fibrosis and its regression. Deletion of TGF-ß type II receptor (Tgfbr2) gene in cultured MCs suppressed TGF-ß-mediated myofibroblastic conversion. Conditional deletion of Tgfbr2 gene in MCs reduced the differentiation of MCs to HSCs and myofibroblasts in the BDL and CCl4 models, respectively, indicating that the direct TGF-ß signaling in MCs is responsible to MMT. After BDL and CCl4 treatment, MC-derived HSCs and myofibroblasts were distributed near the liver surface and the thickness of collagen was increased in Glisson's capsule beneath the liver surface. Fluorescence-activated cell sorting analysis revealed that MC-derived HSCs and myofibroblasts store little vitamin A lipids and have fibrogenic phenotype in the fibrotic livers. MCs contributed to 1.4 and 2.0% of activated HSCs in the BDL and CCl4 models, respectively. During regression of CCl4-induced fibrosis, 20% of MC-derived myofibroblasts survived in the liver and deactivated to vitamin A-poor HSCs. Our data indicate that MCs participate in capsular fibrosis by supplying vitamin A-poor HSCs during a process of liver fibrosis and regression.

Myofibroblastic Conversion and Regeneration of Mesothelial Cells in Peritoneal and Liver Fibrosis.

Mesothelial cells (MCs) form a single epithelial layer and line the surface of body cavities and internal organs. Patients who undergo peritoneal dialysis often develop peritoneal fibrosis that is characterized by the accumulation of myofibroblasts in connective tissue. Although MCs are believed to be the source of myofibroblasts, their contribution has remained obscure. We determined the contribution of peritoneal MCs to myofibroblasts in chlorhexidine gluconate (CG)-induced fibrosis compared with that of phenotypic changes of liver MCs. CG injections resulted in disappearance of MCs from the body wall and the accumulation of myofibroblasts in the connective tissue. Conditional linage tracing with Wilms tumor 1 (Wt1)-CreERT2 and Rosa26 reporter mice found that 17% of myofibroblasts were derived from MCs in peritoneal fibrosis. Conditional deletion of transforming growth factor-ß type II receptor in Wt1(+) MCs substantially reduced peritoneal fibrosis. The CG treatment also induced myofibroblastic conversion of MCs in the liver. Lineage tracing with Mesp1-Cre mice revealed that Mesp1(+) mesoderm gave rise to liver MCs but not peritoneal MCs. During recovery from peritoneal fibrosis, peritoneal MCs, but not liver MCs, contribute to the regeneration of the peritoneal mesothelium, indicating an inherent difference between parietal and visceral MCs. In conclusion, MCs partially contribute to myofibroblasts in peritoneal and liver fibrosis, and protection of the MC layer leads to reduced development of fibrous tissue.

Mesothelial cells give rise to hepatic stellate cells and myofibroblasts via mesothelial-mesenchymal transition in liver injury.

In many organs, myofibroblasts play a major role in the scarring process in response to injury. In liver fibrogenesis, hepatic stellate cells (HSCs) are thought to transdifferentiate into myofibroblasts, but the origins of both HSCs and myofibroblasts remain elusive. In the developing liver, lung, and intestine, mesothelial cells (MCs) differentiate into specific mesenchymal cell types; however, the contribution of this differentiation to organ injury is unknown. In the present study, using mouse models, conditional cell lineage analysis has demonstrated that MCs expressing Wilms tumor 1 give rise to HSCs and myofibroblasts during liver fibrogenesis. Primary MCs, isolated from adult mouse liver using antibodies against glycoprotein M6a, undergo myofibroblastic transdifferentiation. Antagonism of TGF-ß signaling suppresses transition of MCs to mesenchymal cells both in vitro and in vivo. These results indicate that MCs undergo mesothelial-mesenchymal transition and participate in liver injury via differentiation to HSCs and myofibroblasts.

Mesodermal mesenchymal cells give rise to myofibroblasts, but not epithelial cells, in mouse liver injury.

UNLABELLED: Hepatic stellate cells (HSCs) and portal fibroblasts (PFs) are believed to be the major source of myofibroblasts that participate in fibrogenesis by way of synthesis of proinflammatory cytokines and extracellular matrices. Previous lineage tracing studies using MesP1(Cre) and Rosa26lacZ(flox) mice demonstrated that MesP1+ mesoderm gives rise to mesothelial cells (MCs), which differentiate into HSCs and PFs during liver development. In contrast, several in vivo and in vitro studies reported that HSCs can differentiate into other cell types, including hepatocytes, cholangiocytes, and progenitor cell types known as oval cells, thereby acting as stem cells in the liver. To test whether HSCs give rise to epithelial cells in adult liver, we determined the hepatic lineages of HSCs and PFs using MesP1(Cre) and Rosa26mTmG(flox) mice. Genetic cell lineage tracing revealed that the MesP1+ mesoderm gives rise to MCs, HSCs, and PFs, but not to hepatocytes or cholangiocytes, in the adult liver. Upon carbon tetrachloride injection or bile duct ligation surgery-mediated liver injury, mesodermal mesenchymal cells, including HSCs and PFs, differentiate into myofibroblasts but not into hepatocytes or cholangiocytes. Furthermore, differentiation of the mesodermal mesenchymal cells into oval cells was not observed. These results indicate that HSCs are not sufficiently multipotent to produce hepatocytes, cholangiocytes, or oval cells by way of mesenchymal-epithelial transition in vivo. CONCLUSION: Cell lineage tracing demonstrated that mesodermal mesenchymal cells including HSCs are the major source of myofibroblasts but do not differentiate into epithelial cell types such as hepatocytes, cholangiocytes, and oval cells.

Expansion of prominin-1-expressing cells in association with fibrosis of biliary atresia.

UNLABELLED: Biliary atresia (BA), the most common cause of end-stage liver disease and the leading indication for pediatric liver transplantation, is associated with intrahepatic ductular reactions within regions of rapidly expanding periportal biliary fibrosis. Whereas the extent of such biliary fibrosis is a negative predictor of long-term transplant-free survival, the cellular phenotypes involved in the fibrosis are not well established. Using a rhesus rotavirus-induced mouse model of BA, we demonstrate significant expansion of a cell population expressing the putative stem/progenitor cell marker, PROMININ-1 (PROM1), adjacent to ductular reactions within regions of periportal fibrosis. PROM1positive (pos) cells express Collagen-1α1. Subsets of PROM1pos cells coexpress progenitor cell marker CD49f, epithelial marker E-CADHERIN, biliary marker CYTOKERATIN-19, and mesenchymal markers VIMENTIN and alpha-SMOOTH MUSCLE ACTIN (αSMA). Expansion of the PROM1pos cell population is associated with activation of Fibroblast Growth Factor (FGF) and Transforming Growth Factor-beta (TGFß) signaling. In vitro cotreatment of PROM1-expressing Mat1a-/- hepatic progenitor cells with recombinant human FGF10 and TGFß1 promotes morphologic transformation toward a myofibroblastic cell phenotype with increased expression of myofibroblastic genes Collagen-1α1, Fibronectin, and α-Sma. Infants with BA demonstrate similar expansion of periportal PROM1pos cells with activated Mothers Against Decapentaplegic Homolog 3 (SMAD3) signaling in association with increased hepatic expression of FGF10, FGFR1, and FGFR2 as well as mesenchymal genes SLUG and SNAIL. Infants with perinatal subtype of BA have higher tissue levels of PROM1 expression than those with embryonic subtype. CONCLUSION: Expansion of collagen-producing PROM1pos cells within regions of periportal fibrosis is associated with activated FGF and TGFß pathways in both experimental and human BA. PROM1pos cells may therefore play an important role in the biliary fibrosis of BA.

Hepatic stellate cell-derived delta-like homolog 1 (DLK1) protein in liver regeneration.

Hepatic stellate cells (HSCs) undergo myofibroblastic activation in liver fibrosis and regeneration. This phenotypic switch is mechanistically similar to dedifferentiation of adipocytes as such the necdin-Wnt pathway causes epigenetic repression of the master adipogenic gene Pparγ, to activate HSCs. Now we report that delta-like 1 homolog (DLK1) is expressed selectively in HSCs in the adult rodent liver and induced in liver fibrosis and regeneration. Dlk1 knockdown in activated HSCs, causes suppression of necdin and Wnt, epigenetic derepression of Pparγ, and morphologic and functional reversal to quiescent cells. Hepatic Dlk1 expression is induced 40-fold at 24 h after partial hepatectomy (PH) in mice. HSCs and hepatocytes (HCs) isolated from the regenerating liver show Dlk1 induction in both cell types. In HC and HSC co-culture, increased proliferation and Dlk1 expression by HCs from PH are abrogated with anti-DLK1 antibody (Ab). Dlk1 and Wnt10b expression by Sham HCs are increased by co-culture with PH HSCs, and these effects are abolished with anti-DLK Ab. A tail vein injection of anti-DLK1 Ab at 6 h after PH reduces early HC proliferation and liver growth, accompanied by decreased Wnt10b, nonphosphorylated ß-catenin, p-ß-catenin (Ser-552), cyclins (cyclin D and cyclin A), cyclin-dependent kinases (CDK4, and CDK1/2), p-ERK1/2, and p-AKT. In the mouse developing liver, HSC precursors and HSCs express high levels of Dlk1, concomitant with Dlk1 expression by hepatoblasts. These results suggest novel roles of HSC-derived DLK1 in activating HSCs via epigenetic Pparγ repression and participating in liver regeneration and development in a manner involving the mesenchymal-epithelial interaction.

Rosmarinic acid and baicalin epigenetically derepress peroxisomal proliferator-activated receptor γ in hepatic stellate cells for their antifibrotic effect.

UNLABELLED: Hepatic stellate cells (HSCs) undergo myofibroblastic transdifferentiation (activation) to participate in liver fibrosis and identification of molecular targets for this cell fate regulation is essential for development of efficacious therapeutic modalities for the disease. Peroxisomal proliferator-activated receptor γ (PPARγ) is required for differentiation of HSCs and its epigenetic repression underlies HSC activation. The herbal prescription Yang-Gan-Wan (YGW) prevents liver fibrosis, but its active ingredients and molecular mechanisms are unknown. Here we demonstrate YGW prevents and reverses HSC activation by way of epigenetic derepression of Pparγ involving reductions in MeCP2 expression and its recruitment to Pparγ promoter, suppressed expression of PRC2 methyltransferase EZH2, and consequent reduction of H2K27di-methylation at the 3' exon. High-performance liquid chromatography / mass spectrometry (HPLC/MS) and nuclear magnetic resonance (NMR) analyses identify polyphenolic rosmarinic acid (RA) and baicalin (BC) as active phytocompounds. RA and BC suppress the expression and signaling by canonical Wnts, which are implicated in the aforementioned Pparγ epigenetic repression. RA treatment in mice with existing cholestatic liver fibrosis inhibits HSC activation and progression of liver fibrosis. CONCLUSION: These results demonstrate a therapeutic potential of YGW and its active component RA and BC for liver fibrosis by way of Pparγ derepression mediated by suppression of canonical Wnt signaling in HSCs.

Prominin-1 promotes restitution of the murine extrahepatic biliary luminal epithelium following cholestatic liver injury.

BACKGROUND AND AIMS: Restitution of the extrahepatic biliary luminal epithelium in cholangiopathies is poorly understood. Prominin-1 (Prom1) is a key component of epithelial ciliary body of stem/progenitor cells. Given that intrahepatic Prom1-expressing progenitor cells undergo cholangiocyte differentiation, we hypothesized that Prom1 may promote restitution of the extrahepatic bile duct (EHBD) epithelium following injury. APPROACH AND RESULTS: Utilizing various murine biliary injury models, we identified Prom1-expressing cells in the peribiliary glands of the EHBD. These Prom1-expressing cells are progenitor cells which give rise to cholangiocytes as part of the normal maintenance of the EHBD epithelium. Following injury, these cells proliferate significantly more rapidly to re-populate the biliary luminal epithelium. Null mutation of Prom1 leads to significantly >10-fold dilated peribiliary glands following rhesus rotavirus-mediated biliary injury. Cultured organoids derived from Prom1 knockout mice are comprised of biliary progenitor cells with altered apical-basal cellular polarity, significantly fewer and shorter cilia, and decreased organoid proliferation dynamics consistent with impaired cell motility. CONCLUSIONS: We, therefore, conclude that Prom1 is involved in biliary epithelial restitution following biliary injury in part through its role in supporting cell polarity.

Septum transversum-derived mesothelium gives rise to hepatic stellate cells and perivascular mesenchymal cells in developing mouse liver.

UNLABELLED: The septum transversum mesenchyme (STM) signals to induce hepatogenesis from the foregut endoderm. Hepatic stellate cells (HSCs) are sinusoidal pericytes assumed to originate from the STM and participate in mesenchymal-epithelial interaction in embryonic and adult livers. However, the developmental origin of HSCs remains elusive due to the lack of markers for STM and HSCs. We previously identified submesothelial cells (SubMCs) beneath mesothelial cells (MCs) as a potential precursor for HSCs in developing livers. In the present study, we reveal that both STM in embryonic day (E) 9.5 and MC/SubMCs in E12.5 share the expression of activated leukocyte cell adhesion molecule (Alcam), desmin, and Wilms tumor 1 homolog (Wt1). A cell lineage analysis using MesP1(Cre) /Rosa26lacZ(flox) mice identifies the mesodermal origin of the STM, HSCs, and perivascular mesenchymal cells (PMCs). A conditional cell lineage analysis using the Wt1(CreERT2) mice demonstrates that Wt1(+) STM gives rise to MCs, SubMCs, HSCs, and PMCs during liver development. Furthermore, we find that Wt1(+) MC/SubMCs migrate inward from the liver surface to generate HSCs and PMCs including portal fibroblasts, smooth muscle cells, and fibroblasts around the central veins. On the other hand, the Wt1(+) STM and MC/SubMCs do not contribute to sinusoidal endothelial cells, Kupffer cells, and hepatoblasts. CONCLUSION: our results demonstrate that HSCs and PMCs are derived from MC/SubMCs, which are traced back to mesodermal STM during liver development.

Hepatic stellate cell progenitor cells.

Hepatic stellate cells (HSCs) are recognized as a major player in liver fibrogenesis. Upon liver injury, HSCs differentiate into myofibroblasts and participate in progression of fibrosis and cirrhosis. Additional cell types such as resident liver fibroblasts/myofibroblasts or bone marrow cells are also known to generate myofibroblasts. One of the major obstacles to understanding the mechanism of liver fibrogenesis is the lack of knowledge regarding the developmental origin of HSCs and other liver mesenchymal cells. Recent cell lineage analyses demonstrate that HSCs are derived from mesoderm during liver development. MesP1-expressing mesoderm gives rise to the septum transversum mesenchyme before liver formation and then to the liver mesothelium and mesenchymal cells, including HSCs and perivascular mesenchymal cells around the veins during liver development. During the growth of embryonic liver, the mesothelium, consisting of mesothelial cells and submesothelial cells, migrates inward from the liver surface and gives rise to HSCs and perivascular mesenchymal cells, including portal fibroblasts, smooth muscle cells around the portal vein, and fibroblasts around the central vein. Cell lineage analyses indicate that mesothelial cells are HSC progenitor cells capable of differentiating into HSCs and other liver mesenchymal cells during liver development.