Selective deletion of hepatocyte platelet-derived growth factor receptor and development of liver fibrosis in mice

BackgroundPlatelet-derived growth factor receptor (PDGFR) expression is increased in activated hepatic stellate cells (HSCs) in cirrhotic liver, while normal hepatocytes express PDGFR at a negligible level. However, cancerous hepatocytes may show upregulation of PDGFR, and hepatocellular carcinoma is preceded by chronic liver injury. The role of PDGFR in non-cancerous hepatocytes and liver fibrosis is unclear. We hypothesized that upon liver injury, PDGFR in insulted hepatocytes contributes to liver fibrosis by facilitating intercellular crosstalk between hepatocytes and HSCs.MethodsHepatocytes were isolated from normal and thioacetamide (TAA)-induced cirrhotic livers for assessment of PDGFR expression. Conditional knock-out (KO) C57BL/6 mice, in which PDGFR was selectively deleted in hepatocytes, were generated. Liver fibrosis was induced by injecting TAA for 8weeks. Hep3B cells were transfected with a small interfering RNA (siRNA) (PDGFR or control) and co-cultured with LX2 cells.ResultsPDGFR expression was increased in hepatocytes from fibrotic livers compared to normal livers. Conditional PDGFR KO mice had attenuated TAA-induced liver fibrosis with decreased HSC activation and proliferation. Immunoblot analyses revealed decreased expression of phospho-p44/42 MAPK in TAA-treated KO mice; these mice also showed almost complete suppression of the upregulation of mouse double minute 2. Although KO mice exhibited increased expression of transforming growth factor (TGF)- and Smad2/3, this was compensated for by increased expression of inhibitory Smad7. LX2 cells co-cultured with PDGFR siRNA-infected Hep3B cells showed decreased PDGFR, smooth muscle actin, collagen 1(I), TGF, and Smad2/3 expression. LX2/PDGFR-deleted hepatocyte co-culture medium showed decreased PDGF-BB and PDGF-CC levels.ConclusionsDeletion of PDGFR in hepatocytes attenuated the upregulation of PDGFR in HSCs after TAA treatment, resulting in decreased liver fibrosis and HSC activation. This suggests that in the event of chronic liver injury, PDGFR in hepatocytes plays an important role in liver fibrosis by affecting PDGFR expression in HSCs.