Loss of Histamine Signaling Reduces Biliary and Hepatic Damage, Mast Cell Migration and Tumor Formation in 52 wk Old Multidrug Resistance‐2 Knockout Mice

Abstract

BackgroundPrimary sclerosing cholangitis (PSC) is characterized by biliary damage and liver fibrosis. The multidrug resistance‐2 gene knockout (Mdr2−/−) mouse (i) develops cholestasis; (ii) mimics some characteristics of human PSC; and (iii) develops hepatocellular cancer (HCC) within one year. We have demonstrated that depletion of the l‐histidine decarboxylase/histamine (HDC/HA) axis using 12 week old HDC/Mdr2 double knockout (DKO) mice results in decreased (i) hepatic damage; (ii) mast cell (MC) infiltration and activation; (iii) biliary proliferation; (iv) inflammation and (v) liver fibrosis when compared to Mdr2−/− mice. The aim of our study was to evaluate the effects of the loss of the HDC/HA axis on biliary and hepatic damage, MC infiltration/activation and tumor formation in older Mdr2−/− and DKO mice.Method52 week old homozygous DKO mice and aged matched Mdr2−/− mice were utilized. Livers were evaluated for tumor formation and lobular damage by H&E staining. In total liver we evaluated: (i) HDC/histamine receptor (HR) expression by qPCR, (ii) MC infiltration by staining for mouse mast cell protease‐1, (iii) MC activation by qPCR for chymase, tryptase and c‐Kit expression, (iv) ductular reaction by CK‐19 and Ki67 immunohistochemistry and (v) biliary senescence by SA‐β‐galactosiadse activity and staining for p16, p18, p21 and p53. Changes in liver fibrosis were evaluated by Sirius red staining in liver sections, and staining for α‐SMA and collagen‐1a. Hepatic stellate cell (HSC) activation was determined by immunofluorescence and qPCR for SYP‐9. Inflammation was evaluated by staining for IL‐6, TNF‐α and F4/80. HA serum levels were measured by EIA. In livers and tumors (when present), we evaluated angiogenesis by VEGF and vWF gene expression.ResultsLoss of the HDC/HA axis in 52 week old DKO mice resulted in little to no tumor formation compared to age‐matched Mdr2−/− mice, which displayed large HCC tumors. The HDC/HA/HR axis and MC infiltration/activation were reduced in DKO mice compared to age‐matched Mdr2−/− mice. Infiltrating MCs were found near bile ducts. Ductular reaction, biliary senescence and hepatic fibrosis were increased in Mdr2−/− mice, but were reduced in DKO mice. Furthermore, angiogenesis and inflammation were all reduced in DKO when compared to age‐matched Mdr2−/− mice.ConclusionOur data demonstrates that depletion of the HDC/HA axis blunts tumor growth and progression in Mdr2−/− mice, which is coupled with reduced biliary and hepatic damage, and MC infiltration/activation. The HDC/HA axis may be a critical therapeutic target for patients with cholestasis or liver cancer.Support or Funding InformationNIH NIDDK R01, VA MeritThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.