Bile Acids and Deregulated Cholangiocyte Autophagy in Primary Biliary Cholangitis.

BACKGROUND

Primary biliary cholangitis (PBC) is characterized by a high prevalence of serum anti-mitochondrial antibodies against the E2 subunit of the pyruvate dehydrogenase complex and bile duct lesions called chronic non-suppurative destructive cholangitis (CNSDC) in small bile ducts, eventually followed by extensive bile duct loss and biliary cirrhosis. Macroautophagy (a major type of autophagy) is a process of cellular self-digestion that plays a critical role in energy homeostasis and in the cytoprotection to various stresses. Deregulated autophagy is thought to be associated with various human diseases. Key Messages: Accumulating evidences suggest that deregulated autophagy may be a central player in the pathogenesis of PBC. Damaged cholangiocytes involved in CNSDC show vesicular expression of autophagy marker LC3 and accumulation of p62/sequestosome-1, suggesting deregulated autophagy. Deregulated autophagy may be involved in the autoimmune process via the abnormal expression of mitochondrial antigens and also in cholangiocyte senescence in bile duct lesions in PBC. In vitro study showed that hydrophobic bile acids, such as glycochenodeoxycholic acid (GCDC), as well as serum deprivation and oxidative stress, cause autophagy, deregulated autophagy and abnormal expression of mitochondrial antigens followed by cellular senescence in cholangiocytes. Although exact mechanisms of deregulated autophagy remain to be clarified, endoplasmic reticulum (ER) stress may be a plausible cause of deregulated autophagy induced by GCDC in cholangiocytes. Impaired 'biliary bicarbonate umbrella' may further exacerbate the toxicity of GCDC to cholangiocytes. Interestingly, pretreatment with ursodeoxycholic acid (UDCA) and tauro-UDCA, which is a chemical chaperone enhancing the adaptive capacity of the ER, significantly suppressed ER stress, deregulated autophagy and cellular senescence induced by GCDC and other stresses in cholangiocytes.

CONCLUSIONS

GCDC may play a role in the occurrence of deregulated autophagy and cellular senescence at least partly through the induction of ER stress in PBC. Deregulated autophagy and cellular senescence can be a promising therapeutic target in PBC.