Mechanisms Of Hepassocin-regulated Cell Growth, Liver Development And Lipid Metabolism

Hepassocin (HPS), also called fibrinogen-like1(FGL1) and HFREP-1(hepatocyte-derived fibrinogen-related protein), overwhelmingly expressed in liverand up-regulated during liver regeneration. It was identified as a specific hepatokinethrough an autocrine mechanism to stimulate DNA synthesis activities in primaryhepatocytes and other hepatic cell lines，but currently the molecular mechanisms ofHPS-induced cell proliferation are still unclear. On the other hands, recombinanthuman HPS effectively improved survival rate of rats with fulminant hepatic failure,suggesting an important role of HPS for the treatment of liver injure. In addition, HPSdeficient mice showed a global metabolic defect phenotype, and nonalcoholic fattyliver disease (NAFLD) patients had a significantly higher serum HPS level, indicatingthat the biological roles of HPS were more complicated and need further investigationand confirmation.Our previous results showed that HPS stimulates normal hepatic cellsproliferation in ERK dependent way, and there has unknown HPS receptor exsting onthe surface of cell lines derived from liver tissues. However, the way that HPSstimulates ERK activation and cell proliferation via HPS receptor is still unknown. Inthis thesis, at the cell level, we found that EGFR transactivation plays an importantrole in mediating HPS-induced ERK activation and cell proliferation. In addition,inhibiting the activity of Src or knocking down the endogeouse Src could effectivelyattenuate HPS-stimulated EGFR/ERK pathway activation and cell proliferation.Furthermore, HPS could stimulate the activation of FAK, which is responsible for theoccurance of autophagy and subsequently the protein turnover of caveolin-1andfinally leads to the G1/S phase cell cycle progression in L02cells. In this thesis wecontinue to investigate the novel biological roles of HPS at the aninmal level. Wefound HPS possesses high evolutional conservation between zebrafish and otherspecies, koncking down endogenous zebrafish HPS with specific Morpholino couldeffectively inhibit liver proliferation stage development, suggesting that HPS wasinvolved in the liver development of zebrafish. In addition, when treated withmetabolism stresses such as fasting, free fatty acids in mouse was up-regulated andstimulated HPS expression via the activation of PPAR. Furthermore, HPS injectioninto mouse could down regulate the triglyceride content in plasma. Continuedmechanism investigation found that HPS could up-regulate the expression and activityof LPL, which are response for the hydrolysis of serum lipid, indicating that HPS plays an important role in regulating lipid metabolism. We also screened the bindingprotein of HPS via two-yeast hybrid, phage display and MS-IP methods, whichprovide molecular basis for the further function studies. Overall, our results reveal thenovel mechanism of HPS-stimuated cell proliferation and G1/S phase cell cycleprogression. Furthermore, we also found the novel biological roles of HPS on liverdevelopment and lipid metabolism, and explored the related mechanisms, which willprovide molecular basis and theritical evidences for the future clinical application ofHPS on the prevention and treatment of diseases.