Mast Cell (MC) Activation and Histamine (HA) Signaling Promotes Atypical Ductular Reaction, Biliary Senescence and Liver Fibrosis During Advanced Stage Primary Biliary Cholangitis (PBC)
Authors: Kennedy Lindsey , Meadows Vik , Kundu Debjyoti , Yang Zhihong , Invernizzi Pietro , Carbone Marco , Liangpunsakul Suthat , Alpini Gianfranco , Francis Heather 
Published: April 2020

BackgroundAdvanced stage PBC is characterized by immune response, portal inflammation and liver fibrosis, and can be attributed to enhanced atypical ductular reaction (DR) and biliary senescence. Dominant‐negative transforming growth factor beta receptor II (dnTGFβRII) mice phenotypically mimic some features of late stage PBC at 34 wks of age. MCs infiltrate the liver of humans and murine models of cholestasis, and reside adjacent to bile ducts. Activated MCs release large amounts of tryptase, as well as histamine (HA) that that can act through its specific receptors, H1‐H4 HRs on bile ducts. In models of cholestasis, we have found that blocking MC activation and HR signaling reduces biliary senescence and liver fibrosis. However, the role of MCs and HA signaling during PBC are unknown. The aim of our study was to determine changes in MC and HA signaling during advanced stage PBC, and the therapeutic potential of blocking MCs in our model of advanced stage PBC.MethodsFemale human control and advanced stage PBC samples were analyzed for: (i) MC presence by immunostaining for tryptase and MC‐specific markers by qPCR, (ii) H2HR expression by IHC and qPCR, and (iii) tryptase serum levels by EIA. H2HR expression was evaluated in senescent bile ducts by co‐staining. For in vivo studies we utilized female (i) wild‐type (WT), (ii) dnTGFβRII and (iii) dnTGFβRII treated with cromolyn sodium (24 mg/kg/BW) for 1 wk by intraperitoneally implanted osmotic minipump mice at 34 wks of age. MC presence was determined by staining for chymase and tryptase. MC activation was determined by serum tryptase and HA levels by EIA. H2HR expression was evaluated by immunostaining. Liver damage was evaluated by H&E, and serum levels of ALP and AMA. Atypical DR was visualized by CK‐19 staining and correlated with liver inflammation shown by F4/80 staining. Biliary senescence was determined by qPCR and staining for SA‐β‐Galactosidase, p18 and IL‐1β. Liver fibrosis and hepatic stellate cell activation was assessed by Sirius Red staining and quantification, desmin staining and serum TGF‐β1 levels by EIA.ResultsHuman advanced stage PBC samples showed enhanced hepatic MC number and activation, and activated MCs were found near senescent bile ducts. There was increased hepatic H2 HR expression, which was was upregulated in senescent bile ducts in human advanced stage PBC. dnTGFβRII mice at 34 wks of age had increased MC number/activation, H2HR expression, atypical DR, inflammation, biliary senescence and liver fibrosis; however, all of these parameters were reduced in dnTGFβRII mice treated with cromolyn sodium.ConclusionIncreased MC activation and biliary H2HR expression may drive PBC progression through enhanced biliary senescence that promotes liver fibrosis in a paracrine manner. Inhibition of MC activation via cromolyn sodium treatment may be a therapeutic option for advanced stage PBC patients.Support or Funding InformationNIH NIDDK R01s, VA Merit, Indiana University School of Medicine