Increased p16INK4a-expressing senescent bile ductular cells are associated with inadequate response to ursodeoxycholic acid in primary biliary cholangitis

Senescent biliary epithelial cells (BECs) may be involved in the pathophysiology of primary biliary cholangitis (PBC) by secreting senescence-associated secretory phenotypes. We examined an association of the extent of cellular senescence in BECs with clinicopathological features including response to ursodeoxycholic acid (UDCA) and a possibility of senolytic therapy in PBC. The expression of senescent markers (p21WAF1/Cip1, p16INK4a) and B-cell lymphoma–extra large (Bcl-xL), a key regulator of senescent cell anti-apoptotic pathway, was immunohistochemically examined in livers from patients with PBC (n = 145) and 103 control livers. Senolytic effect of Bcl-xL inhibitors (A-1331852 and Navitoclax) was examined in senescent murine BECs. Senescent BECs were increased in small bile ducts in PBC, compared with control livers (p < 0.01). Senescent BECs were increased in ductular reactions in PBC, stage 3–4, compared with PBC, stage 1–2 and control livers (p < 0.01). The extent of senescent BECs in bile ductules was significantly correlated with stage and hepatitis activity (p < 0.01) and the expression of p16INK4a in bile ductules was significantly correlated to inadequate response to UDCA in PBC (p < 0.01). Double immunofluorescence revealed an increased expression of Bcl-xL in p16INK4a-positive senescent BECs in PBC. Bcl-xL inhibitors selectively induced apoptosis in senescent murine BECs (p < 0.01). The extent of senescent BECs in small bile ducts and bile ductules was closely related to stage and activity of PBC and the increased expression of p16 INK4a in bile ductules was correlated with inadequate response to UDCA.