Mast Cell (MC)‐Induced Cholestasis is Dependent on Apical Sodium Bile Acid Transporter (ASBT) Expression

Abstract

BackgroundImpaired bile flow is a characteristic of primary sclerosing cholangitis (PSC). Up to 80% of PSC patients present with irritable bowel disease (IBD). Mast cell (MC) injection into normal or MC‐deficient mice increases ductular reaction (DR), biliary senescence, liver fibrosis and total bile acid (TBA) levels in liver and serum. MCs infiltrate the liver, activating cholangiocytes and hepatic stellate cells (HSCs), and in the intestine, MCs increase intestinal permeability in PSC and IBD patients, respectively. Bacterial translocation and leaky gut have been proposed to initiate cholestatic injury. BA circulation is dependent on apical sodium BA transporter (ASBT) expression in ileum and cholangiocytes, and inhibition of ASBT by Vivo‐Morpholino blocks cholehepatic and enterohepatic BA circulation and reduces hepatic and ileal MC infiltration in cholestatic mice.AimWe aimed to investigate the role of ASBT and disruption of BA circulation in a model of MC‐induced cholestasis.MethodsWT and ASBT knockout (KO) mice, 14‐16 wks of age, received sterile 1X PBS or 5x106 MCs (MC/9 ATCC CRL8306) via tail vein injection. Three days after injection we collected liver, colon, and isolated hepatocytes and cholangiocytes and supernatants from all mice. Hepatic damage was determined by H&E staining and liver TBA content. DR was determined with CK‐19 immunohistochemistry (marker of cholangiocytes) and semi‐quantification. Hepatic inflammation was assessed by immunohistochemistry, and semi‐quantification of F4/80. Hepatic fibrosis was determined by fast green‐Sirius red staining and semi‐quantification of collagen deposition. Cholehepatic shunting was determined by TBA levels in isolated cholangiocyte and hepatocyte supernatant. Intestinal permeability was determined by colon ZO‐1 immunostaining and hepatic bacterial translocation by quantification of colony forming units (CFUs) from liver homogenates.ResultsMC injection increased liver damage, DR, hepatic inflammation, and fibrosis in WT mice that was reduced in ASBT KO + MC mice. Cholehepatic shunting increased in WT + MC mice demonstrated by enhanced TBA content in isolated hepatocyte and cholangiocyte supernatants compared to WT mice that was reduced in ASBT KO + MC mice. MC injection lowered colonic ZO‐1 expression in WT mice, but no change was noted in ASBT KO + MC mice. MC injection increased bacterial translocation in WT mice, yet ASBT KO + MC mice had reduced bacterial translocation similar to WT and ASBT KO mice.ConclusionMC injection increases PSC phenotypes in WT mice that are reduced when BA circulation is disrupted by KO of ASBT. Regulation of ASBT is a potential therapeutic strategy for PSC and PSC‐IBD patients.