COMPLEX REGULATION OF THE microRNA-29a/b GENE BY TGF-beta SIGNALING

Background and Aims: Humans have five Notch ligands (Jagged1, Jagged2, Delta like ligand (Dll)1, Dll3 and Dll4) and four receptors (Notch1, 2, 3 and 4).Mutation of Jagged1 causes Alagille syndrome, a disease characterized by defective development of intralobular bile ducts.However, the roles of Notch ligands in liver fibrogenesis remain largely unknown, which were investigated in this study.Methods: Genechip analysis was used to investigate Notchassociated gene expression in 121 HBV-infected patients and 7 controls.Immunohistochemistry was performed to assess Notch ligands/receptors in liver specimens.Effects of Notch ligands in rat hepatic stellate cells (HSC) and cirrhotic fat storing cells (CFSC) were examined.Recombinant Dll4 (rDll4) was applied to mice challenged with carbon tetrachloride (CCl4).Results: Microarray analyses identified nine Notch signalingrelated genes that were associated with fibrotic stages in HBV patients.Immunohistochemistry co-staining and confocal microscopy analysis revealed that Dll4 and Notch1 are expressed in activated HSCs and myofibroblasts in HBV patients.Dll4 immunescore correlated with inflammatory grades and fibrotic stages in these patients.In vitro, blocking the total Notch signaling by a g-secretase inhibitor remarkably decreased expression of collagen I, a-smooth muscle actin and connective tissue growth factor whereas rDll4 protein incubation significantly decreased TGF-b-dependent expression of collagen I in HSCs.Consistent with in vitro findings, rDll4 protein injection remarkably reduced serum ALT levels, liver inflammation and fibrosis in mice after CCl4 challenge.Conclusions: Although the general Notch signaling promotes liver fibrosis, Dll4 exerts a compelling anti-fibrotic role in experimental fibrosis models, suggesting a potential therapeutic target in liver fibrosis.Elevated Dll4 expression in fibrotic liver may act as a protective mechanism to prevent the progression of liver fibrogenesis.