Silencing of the SR gene induces a decrease in the basal proliferative capacity of large cholangiocytes compared with large

mock-transfected cholangiocytes. In our evaluation of SR expression, we found a time-dependent increase in the expression of SR in large cholangiocytes during BDL compared with normal large cholangiocytes. This finding was consistent with previous studies showing that: (1) in the rodent liver SR is only expressed by large cholangiocytes,1, 4, 5, 9, 12 (2) SR expression is up-regulated following BDL ligation in large cholangiocytes,14, 17 and (3) the extent of secretin effects on cholangiocyte functions parallel with the duration of BDL.16 This finding parallels recent findings that mouse cholangiocytes share a similar heterogeneous Protease Inhibitor Library profile

as rat cholangiocytes5 and freshly isolated and immortalized large mouse cholangiocytes are the only cell types to express the SR.5, 8, 14 In human, SR expression is present in the biliary tract in click here normal bile ducts and ductules and the majority of cholangiocarcinomas, but is not present in hepatocytes or hepatocellular carcinoma.26, 27 Consistent with animal models of cholestasis, SR expression was up-regulated in ductular reactions in liver cirrhosis.27 In our in vivo model, the level of the reduction of cholangiocyte proliferation is consistent with the paradigm that cholangiocyte proliferation is regulated in autocrine and paracrine mechanisms by a number of stimulatory neurohormonal factors.18, 20, 28 In a knockout mouse model for α-calcitonin gene-related peptide, the lack of circulating α-calcitonin gene-related peptide also reduces biliary proliferation during BDL to a similar degree as the lack of SR,20 which indicates that the regulation of biliary

proliferation during extrahepatic cholestasis is multifactorial and a complex regulatory system.18, 20, 28 The trophic effects of secretin were dependent upon the activation of the cAMP/PKA/ERK1/2 signaling. The second messenger system, cAMP, is a key factor for the function of large cholangiocytes.1, 4, 7, 9, 13 Secretin stimulates bicarbonate secretion of large bile ducts through activation of cAMP-dependent CFTRCl−/HCO3− anion exchanger 2.1, 4, 7, 9, 13 Also, the activation of the cAMP/PKA/ERK1/2 Farnesyltransferase pathway modulates cholangiocyte proliferation.12, 15, 18, 29 In fact, the direct stimulation of adenylyl cyclase activity by the chronic administration of forskolin stimulates normal cholangiocyte proliferation both in vivo and in vitro, which is associated with activation of the PKA/Src/MEK/ERK1/2 pathway.29 Maintenance of cAMP levels by forskolin administration prevents the impairment of cholangiocyte proliferation and enhancement of biliary apoptosis induced by vagotomy.30 Furthermore, Banales et al. have shown31 that cAMP stimulates cholangiocyte proliferation through two downstream effectors (i.e., PKA and Epacs) in an animal model of autosomal recessive polycystic kidney disease.