PDGF-BB and TGFβ-mediated Cellular Crosstalk during Hepatic Injury Activates Hepatic Stellate Cells.

Apoptotic hepatocytes release factors that activate hepatic stellate cells (HSCs), thereby inducing hepatic fibrosis. In the present study, in vivo and in vitro injury models were established using acetaminophen, ethanol, carbon tetrachloride, or thioacetamide. Histology of hepatotoxicant-induced diseased hepatic tissue correlated with differential expression of fibrosisrelated genes. A marked increase in co-staining of transforming growth factor beta receptor type II (TGFRII beta) - desmin or alpha-smooth muscle actin -platelet-derived growth factor receptor beta (PDGFR beta), markers of activated HSCs, in liver sections of these hepatotoxicant-treated mice also depicted an increase in Annexin V - cytokeratin expressing hepatocytes. To understand the molecular mechanisms of disease pathology, in vitro experiments were designed using the conditioned medium (CM) of hepatotoxicant-treated HepG2 cells supplemented to HSCs. A significant increase in HSC proliferation, migration, and expression of fibrosis-related genes and protein was observed, thereby suggesting the characteristics of an activated phenotype. Treating HepG2 cells with hepatotoxicants resulted in a significant increase in mRNA expression of platelet-derived growth factor BB (PDGF-BB) and transforming growth factor beta (TGF beta). CM supplemented to HSCs resulted in increased phosphorylation of PDGFR beta and TGFRII beta along with its downstream effectors, extracellular signal-related kinase 1/ 2 and focal adhesion kinase. Neutralizing antibodies against PDGF-BB and TGF beta effectively perturbed the hepatotoxicant-treated HepG2 cell CM-induced activation of HSCs. This study suggests PDGF-BB and TGF beta as potential molecular targets for developing anti-fibrotic therapeutics.