No abstract

Primary sclerosing cholangitis (PSC) is an incurable cholangiopathy of unknown etiopathogenesis. Here we tested the hypothesis that cholangiocyte senescence is a pathophysiologically important phenotype in PSC. We assessed markers of cellular senescence and senescence-associated secretory phenotype (SASP) in livers of patients with PSC, primary biliary cirrhosis, hepatitis C, and in normals by fluorescent in situ hybridization (FISH) and immunofluorescence microscopy (IFM). We tested whether endogenous and exogenous biliary constituents affect senescence and SASP in cultured human cholangiocytes. We determined in coculture whether senescent cholangiocytes induce senescence in bystander cholangiocytes. Finally, we explored signaling mechanisms involved in cholangiocyte senescence and SASP. In vivo, PSC cholangiocytes expressed significantly more senescence-associated p16INK4a and γH2A.x compared to the other three conditions; expression of profibroinflammatory SASP components (i.e., IL-6, IL-8, CCL2, PAI-1) was also highest in PSC cholangiocytes. In vitro, several biologically relevant endogenous (e.g., cholestane 3,5,6 oxysterol) and exogenous (e.g., lipopolysaccharide) molecules normally present in bile induced cholangiocyte senescence and SASP. Furthermore, experimentally induced senescent human cholangiocytes caused senescence in bystander cholangiocytes. N-Ras, a known inducer of senescence, was increased in PSC cholangiocytes and in experimentally induced senescent cultured cholangiocytes; inhibition of Ras abrogated experimentally induced senescence and SASP. Conclusion Cholangiocyte senescence induced by biliary constituents by way of N-Ras activation is an important pathogenic mechanism in PSC. Pharmacologic inhibition of N-Ras with a resultant reduction in cholangiocyte senescence and SASP is a new therapeutic approach for PSC.

Introduction Primary sclerosing cholangitis (PSC) is a chronic, idiopathic, fibro-inflammatory cholangiopathy. The role of the microbiota in PSC etiopathogenesis may be fundamentally important yet remains obscure. We tested the hypothesis that germ-free (GF) mdr2−/− mice develop a distinct PSC phenotype compared to conventionally-housed (CV) mdr2−/− mice. Methods Mdr2−/− mice (n=12) were re-derived as GF by embryo transfer, maintained in isolators, and sacrificed at 60 days in parallel with age-matched CV mdr2−/− mice. Serum biochemistries, gallbladder bile acids, and liver sections were examined. Histologic findings were validated morphometrically, biochemically, and by immunofluorescence microscopy (IFM). Cholangiocyte senescence was assessed by p16INK4a in situ hybridization in liver tissue and by β-galactosidase (SA-β-gal) staining in a culture-based model of insult-induced senescence. Results Serum biochemistries, including alkaline phosphatase, aspartate aminotransferase, and bilirubin, were significantly higher in GF mdr2−/− (p<0.01). Primary bile acids were similar, while secondary bile acids were absent in GF mdr2−/− mice. Fibrosis, ductular reaction, and ductopenia were significantly more severe histopathologically in GF mdr2−/− mice (p<0.01) and were confirmed by hepatic morphometry, hydroxyproline assay, and IFM. Cholangiocyte senescence was significantly increased in GF mdr2−/− mice and abrogated in vitro by ursodeoxycholic acid treatment. Conclusions GF mdr2−/− mice exhibit exacerbated biochemical and histologic features of PSC and increased cholangiocyte senescence, a characteristic and potential mediator of progressive biliary disease. Ursodeoxycholic acid, a commensal microbial metabolite, abrogates senescence in vitro. These findings demonstrate the importance of the commensal microbiota and its metabolites in protecting against biliary injury and suggest avenues for future studies of biomarkers and therapeutic interventions in PSC.

Primary sclerosing cholangitis (PSC) is an inflammatory liver disease which often progresses to liver failure. The cause of the disease is unclear and therapeutic options are limited. Therefore, we explored the role of white blood cells termed macrophages in PSC given their frequent contribution to other human inflammatory diseases. Our results implicate macrophages in PSC and PSC-like diseases in mice. More importantly, we found that pharmacologic inhibition of macrophage recruitment to the liver reduces PSC-like liver injury in the mouse. These exciting observations highlight potential new strategies to treat PSC.