Myofibroblastic cells function as progenitors to regenerate murine livers after partial hepatectomy

Abstract

Objective Smoothened (SMO), a co-receptor of the Hedgehog (Hh) pathway, promotes fibrogenic repair of chronic liver injury. We investigated the roles of SMO+ myofibroblasts (MF) in liver regeneration by conditional deletion of SMO in αSMA+ cells after partial hepatectomy (PH). Design αSMA-Cre-ERT2×SMO/flox mice were treated with vehicle (Veh) or tamoxifen (TMX), and sacrificed 24 to 96 hrs post-PH. Regenerating livers were analyzed for proliferation, progenitors, and fibrosis by qRT-PCR and quantitative-IHC. Results were normalized to liver-segments resected at PH. For lineage-tracing studies, αSMA-Cre-ERT2×ROSA-Stop-flox-YFP mice were treated with Veh or TMX; livers were stained for YFP, and hepatocytes isolated 48 and 72 hrs post-PH were analysed for YFP by FACS. Results Post-PH, Veh-αSMA-SMO mice increased expression of Hh-genes, transiently accumulated MF, fibrosis, and liver progenitors, and ultimately exhibited proliferation of hepatocytes and cholangiocytes. In contrast, TMX-αSMA-SMO mice showed loss of whole liver SMO expression, repression of Hh-genes, enhanced accumulation of quiescent HSC but reduced accumulation of MF, fibrosis, and progenitors, as well as inhibition of hepatocyte and cholangiocyte proliferation, and reduced recovery of liver weight. In TMX-αSMA-YFP mice, many progenitors, cholangiocytes, and up to 25% of hepatocytes were YFP+ by 48-72 h after PH, indicating that liver epithelial cells were derived from αSMA-YFP+cells. Conclusion Hedgehog signaling promotes transition of quiescent hepatic stellate cells to fibrogenic MF, some of which become progenitors that regenerate the liver epithelial compartment after PH. Hence, scarring is a component of successful liver regeneration.

Hepatic stellate cells contribute to progenitor cells and liver regeneration

“…Future research should address whether MSC populations are connected to stem cell niches within the canals of Hering and contribute to progenitor cell formation. Monitoring of hepatic differentiation of MSC populations and mesodermal proteins in epithelial cells in ductular reactions, as demonstrated in this study, as well as recent lineage-tracing experiments with the Acta2 promoter (18,19), support this possibility.…”

“…Quiescent stellate cells are typically located between sinusoidal endothelial cells and hepatocytes in the space of Disse, which has characteristics of stem cell niches (14,15). Moreover, activated stellate cells can develop into hepatocyte-like cells in vitro (14,16), and fate-mapping experiments using Gfap and Acta2 promoters indicate that they contribute to liver regeneration in vivo (17)(18)(19). In contrast to this, lineage-tracing experiments with lecithin retinol acyltransferase (LRAT) and mesoderm posterior 1 homolog (MESP1) failed to demonstrate a differentiation of HSCs into epithelial cells during regeneration of the injured mouse liver (20,21).…”

Elaboration of tubules with active hedgehog drives parenchymal fibrogenesis in gestational alloimmune liver disease

“…Nevertheless, the possibility exists that Hh regulates SPP1 expression in tubules both via GLI1 and SOX9 pathways. Furthermore, Hh signal may directly influence myofibroblastic transformation of HSCs [37,38], and excessive SOX9 expression in fetal hepatocytes may mediate ectopic extracellular matrix deposition characteristic of fibrosis by way of HSC transformation [39]. Thus, there appear to be multiple tubule-associated signal pathways in GALD that could contribute to fibrosis associated with expanded numbers of parenchymal tubules: Hh-driven SPP1 production, SOX9-driven SPP1 production, Hh-driven myofibroblastic transformation of HSCs, and SOX9-driven ectopic extracellular matrix deposition via HSC transformation.…”

Bile Acids and Stellate Cells

“…This finding indicated the potential of stellate cells to contribute to liver regeneration. Indeed, cell lineage-tracing and transplantation studies confirmed that stellate cells can differentiate into epithelial liver cells such as hepatocytes and bile duct cells also in vivo [31,32,33,34,35]. …”