Mast Cell Signaling Regulates Biliary Farnesoid X Receptor and Apical Sodium Bile Acid Transporter Expression During Cholestatic Liver Injury

Background Chronic liver diseases and cholangiopathies (targets cholangiocytes) are diagnosed at advanced stages leading to poor prognosis. Mast cells (MCs) infiltrate the liver during damage, release histamine (HA) and act via H1‐H4 HA receptors (HRs). Cholangiocytes and MCs express apical sodium bile acid transporter (ASBT); farnesoid X receptor (FXR) and H2HR. Introduction of MCs into C57BL/6 (WT) and MC deficient ( Kit W‐sh ) mice increases liver damage, biliary proliferation/liver fibrosis, and total bile acid (TBA) levels. We aimed to determine if loss of MC FXR signaling alters biliary FXR and ASBT, injury and hepatic fibrosis via HA/H2HR signaling. Methods WT or Kit W‐sh mice were subjected to tail vein injection of cultured MCs (ATCC®) pretreated with PBS (PBS‐MC) to induce liver damage or the FXR inhibitor, Z‐guggulsterone (10μM, FXR‐MC) and sacrificed after 3 days. H&E was used to determine pathological changes. Ductular reaction was determined by CK‐19 staining. Biliary proliferation and hepatic senescence were evaluated by Ki‐67 and SA‐b‐galactosidase staining. Hepatic fibrosis was determined by Sirius Red staining. Hepatic stellate cell (HSC) presence was determined by immunofluorescence (IF). Biliary senescence was determined by IF and qPCR. Cholangiocyte FXR and ASBT expression was determined by staining and qPCR in cholangiocytes. Senescence associated secretory phenotypes (SASPs) and HA secretion were measured by EIA in serum and cholangiocyte supernatants. H2HR expression was evaluated in isolated cholangiocytes. TBAs were measured in serum and liver tissues. In vitro , cultured MCs were treated with PBS or Z‐guggulsterone (10μM, 48 hr). Treated MC supernatants were placed on cholangiocytes prior to evaluating biliary ASBT and H2HR expression and secretion of HA, TGF‐b1 and IL‐1b by qPCR and EIA, respectively. In human tissue from patients with PSC or PBC, biliary ASBT, FXR and MC infiltration (marked by tryptase) was measured by IHC. Results Hepatic damage, ductular reaction, biliary senescence, ASBT expression and liver fibrosis were induced in WT and Kit W‐sh mice injected with PBS‐MC; whereas, these parameters were reversed in mice injected with FXR‐MCs. HA secretion and H2HR expression increased in serum and cholangiocytes, respectively in WT and Kit W‐sh mice injected with PBS‐MC, but were reduced in mice injected with FXR‐MC. Hepatic and serum TBA increased in WT and Kit W‐sh mice injected with PBS‐MC and were reduced in FXR‐MC groups. In vitro , stimulation with MC supernatant increased biliary ASBT, FXR, H2HR, HA, TGF‐b1 and IL‐1b expression. These parameters decreased in cholangiocytes treated with FXR‐MC supernatant. In human tissues, upregulation of MCs was coupled with increased biliary FXR and ASBT expression. Conclusions Reintroduction of MCs recapitulates cholestatic liver injury in WT and Kit W‐sh mice. Inhibition of MC FXR signaling decreases biliary ASBT expression, liver injury and hepatic fibrosis via downregulation of HA/H2HR signaling. Manipulation of BA transporters, receptors and MC mediators may be a therapeutic route for patients with cholestatic liver damage. Support or Funding Information NIH NIDDK R01s, VA Merit, IUSOM