Hepatocarcinoma–intestine–pancreas/pancreatitis-associated protein (HIP/PAP) confers protection against hepatic fibrosis through downregulation of transforming growth factor β receptor II

Hepatocarcinoma–intestine–pancreas/pancreatitis-associated protein (HIP/PAP) has antimicrobial, antioxidant, anti-inflammatory, mitogenic, and antiapoptotic effects and thus exerts important functions in the maintenance of integrity and homeostasis of several organs, such as the gastrointestinal tract, pancreas, and liver. Although the potent hepatoprotective effect of HIP/PAP has been validated, its impact on liver fibrosis has not been reported. In this study, we evaluated the role of HIP/PAP on hepatic fibrosis and explored the possible underlying mechanisms. We found that the expression of HIP/PAP and its mouse counterpart, Reg3B, was markedly upregulated in fibrotic human or mouse livers. Intraperitoneal (i.p.) interleukin (IL)-10, IL-6, and TNF-α but not TGF-β1 significantly induced hepatic overexpression of Reg3B in mice. In both CCl4 and BDL liver fibrosis models, adenovirus-mediated ectopic expression of HIP/PAP markedly alleviated liver injury, inflammation, collagen deposition, hepatic stellate cell activation, and the overexpression of profibrotic cytokines, including transforming growth factor β1 (TGF-β1), platelet-derived growth factor (PDGF)-A, B, connective tissue growth factor (CTGF), and plasminogen activator inhibitor-1 (PAI-1), in mice. In vitro experiments demonstrated that, in addition to suppressing hepatic stellate cell proliferation and accelerating hepatocyte proliferation, HIP/PAP mitigated TGF-β1-induced hepatic stellate cell activation, hepatocyte epithelial-mesenchymal transition (EMT) and upregulated expression of profibrotic cytokines in both hepatic stellate cells and hepatocytes. Moreover, HIP/PAP attenuated the overexpression of TGF-β receptor II (TGF-βRII) in fibrotic mouse livers and decreased the basal expression of TGF-βRII in nonfibrotic mouse livers as well as in cultured hepatocytes and hepatic stellate cells, which is at least partly attributable to the TGF-β1-antagonizing function of HIP/PAP. This study indicates that increased expression of hepatic HIP/PAP serves as a countermeasure against liver injury and fibrosis. Exogenous supplementation of HIP/PAP might be a promising therapeutic agent for hepatic fibrosis as well as liver injury. The expression of HIP/PAP and its mouse counterpart, Reg3B, is markedly unregulated in fibrotic livers. Ectopic HIP/PAP potently protects from CCl4- and BDL-induced liver fibrosis in mice. This study shows that downregulation of TGF-βRII expression is one of the important underlying mechanisms for HIP/PAP in suppression of hepatic fibrosis.