MiRNA-506 promotes primary biliary cholangitis-like features in cholangiocytes and immune activation

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease associated with autoimmune phenomena targeting intrahepatic bile duct cells (cholangiocytes). Although PBC etiopathogenesis still remains obscure, development of anti-mitochondrial auto-antibodies against pyruvate dehydrogenase complex-E2 (PDC-E2) is a common feature. MicroRNA (miR) dysregulation occurs in liver and immune cells of PBC patients, but their functional relevance is largely unknown. We previously reported that miR-506 is overexpressed in PBC cholangiocytes and directly targets both Cl–/HCO3– anion exchanger 2 (AE2) and type III inositol 1,4,5-trisphosphate receptor (InsP3R3), leading to cholestasis. Here, the regulation of miR-506 gene expression and its role in cholangiocyte pathophysiology and immune activation was studied. Several pro-inflammatory cytokines overexpressed in PBC livers [such as IL8, IL12, IL17, IL18 and TNFα] stimulated miR-506 promoter activity in human cholangiocytes, as revealed by luciferase reporter assays. Experimental overexpression of miR-506 in cholangiocytes dysregulated the cell proteomic profile (by mass spectrometry), affecting proteins involved in different biological processes including mitochondrial metabolism. In cholangiocytes, miR-506: i) induced dedifferentiation with downregulation of biliary and epithelial markers together with upregulation of mesenchymal, pro-inflammatory and pro-fibrotic markers; ii) impaired cell proliferation and adhesion; iii) increased oxidative and endoplasmic reticulum (ER) stress; iv) caused DNA damage; and v) sensitized to caspase-3-dependent apoptosis induced by cytotoxic bile acids. These events were also associated with impaired energy metabolism in mitochondria (proton leak and less ATP production) and PDC-E2 overexpression. Co-culture of miR-506 overexpressing cholangiocytes with PBC immunocytes induced activation and proliferation of PBC immunocytes. Conclusion: different pro-inflammatory cytokines enhance the expression of miR-506 in biliary epithelial cells. MiR-506 induces PBC-like features in cholangiocytes and promotes immune activation, representing a potential therapeutic target for PBC patients. This article is protected by copyright. All rights reserved.