Role of anion exchanger 2 (ae2) in primary biliary cirrhosisstudy of hepatic and immunologic alterations in the ae2a,b-/- mouse model

Resumo

Background & Aims: Cl−/HCO3− anion exchanger 2 (AE2) is involved in intracellular pH (pHi) regulation and transepithelial acid-base transport, including secretin-stimulated biliary bicarbonate excretion. AE2 gene expression was found to be reduced in liver biopsies and blood mononuclear cells from patients with primary biliary cirrhosis (PBC), a disease characterized by chronic nonsuppurative cholangitis associated with antimitochondrial antibodies (AMA) and other autoimmune phenomena. Here we analyzed the hepatobiliary and immunologic changes in Ae2a,b-deficient mice. Methods: We studied the splenocytes for the pHi and T-cell populations using flow cytometry. CD3-stimulated cytokine secretion was analyzed with cytokine arrays. AMA were evaluated by immunoblotting and proteomics. Hepatobiliary changes were assessed by immunohistopathogy, flow cytometry and serum biochemistry. Cholangiocyte gene expression profiles were analyzed by PCR. Results: Ae2a,b-/- mice exhibit splenomegaly, elevated pHi in splenocytes, increased production of IL12p70 and IFN-γ, and expanded CD8+ T cells with under represented Tregs. Most Ae2a,b-/- mice developed AMA, and had increased serum levels of IgM and IgG and alkaline phosphatase (liver-specific isoform). About one third of Ae2a,b-/- mice had extensive portal inflammation with CD8+ and CD4+ T lymphocytes surrounding damaged bile ducts. Cholangiocytes isolated from Ae2a,b-/- mice showed gene expression changes compatible with oxidative stress and increased antigen presentation. Conclusions: Ae2 deficiency alters pHi homeostasis in immunocytes and gene expression profile in cholangiocytes, leading to immunologic and hepatobiliary changes that resemble PBC.