Participation of bile ductular cells in the pathological progression of non-alcoholic fatty liver disease

Abstract

Aims: Non-alcoholic fatty liver disease (NAFLD) represents a spectrum of pathological conditions, ranging from simple steatosis to hepatic fibrosis with progression to cirrhosis. While activated hepatic stellate cells (HSC) are known to be involved in intralobular, perisinuosidal fibrosis, the mechanisms of portal and bridging fibrosis remain speculative. This study investigated the roles of bile ductules in portal and septal fibrosis.

Methods: 48 liver biopsies were obtained from NAFLD patients. These cases were divided into four stages according to the Brunt classification.

Results: Bile ductules positive for CK19 were increased along with the progression of staging and fibrosis of NAFLD, and the increased bile ductules were associated with portal inflammation and fibrosis. The cellular senescence marker; p16(INK4a) and p21(WAF1/Cip1)-positive bile ductular cells were increased in stages 3 and 4. Such senescent bile ductules frequently express chemotactic protein, CCL2 (MCP-1), which may be responsible for chemoattraction of activated HSC around the bile ductules in portal and septal fibrosis and for portal inflammation. The migration of cultured mouse HSC was significantly facilitated in the presence of cultured senescent mouse biliary epithelial cells (BEC), and this migration was mediated by CCL2 secreted from senescent cultured BEC. Small spindle-like cells positive for CK7 alone in the hepatic parenchyma in the advanced stage seem to differentiate to periportal bile ductular cells positive for CK19 and CK7.

Conclusions: It seems possible that increased bile ductules expressing cellular senescence markers and chemokines are at least partly involved in the progressive portal and bridging fibrosis in NAFLD.