β7-Integrin and MAdCAM-1 play opposing roles during the development of non-alcoholic steatohepatitis

Abstract

Non-alcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease in Western countries. It is unclear how infiltrating leukocytes affect NASH-development. Our study aims to investigate the role of the homing/receptor, pair mucosal addressin cell adhesion molecule-1 (MAdCAM-1)/β7-Integrin, on immune cell recruitment and disease progression in a steatohepatitis model. Constitutive β7-Integrin deficient (β7-/-) and MAdCAM-1 deficient (MAdCAM-1-/-) mice were fed a high fat diet (HFD) for 26weeks or methionine-choline-deficient-diet (MCD) for 4weeks. β7-/- mice displayed earlier and more progressive steatohepatitis during HFD- and MCD-treatment, while MAdCAM-1-/- mice showed less histomorphological changes. The anti-oxidative stress response was significantly weaker in β7-/- mice as reflected by a significant downregulation of the transcription factors nuclear-factor(erythroid-derived 2)-like 2 (Nrf2) and heme-oxigenase-1 (HO-1). Additionally, stronger dihydroethidium-staining revealed an increased oxidative stress response in β7-/- animals. In contrast, MAdCAM-1-/- mice showed an upregulation of the anti-oxidative stress response. β7-/- animals exhibited stronger hepatic infiltration of inflammatory cells, especially neutrophils, reflecting earlier steatohepatitis initiation. Expression of regulatory T cell (TReg) markers as well as numbers of anti-inflammatory macrophages was significantly enhanced in MAdCAM-1-/- mice. Those changes finally resulted in earlier and stronger collagen accumulation in β7-/- mice, whereas MAdCAM-1-/- mice were protected from fibrosis initiation. Adhesion molecule mediated effector cell migration contributes to the outcome of steatohepatitis in the HFD- and the MCD model. While MAdCAM-1 promotes steatohepatitis, β7-Integrin unexpectedly exerts protective effects. β7-/- mice show earlier steatohepatitis initiation and significantly stronger fibrosis progression. Accordingly, the interaction of β7-Integrins and their receptor MAdCAM-1 provide novel targets for therapeutic interventions in steatohepatitis. The mucosal addressin cell adhesion molecule 1 (MAdCAM-1) is expressed in livers upon diet-induced non-alcoholic steatohepatitis (NASH). Loss of MAdCAM-1 has beneficial effects regarding the development of NASH - manifested by reduced hepatic oxidative stress and decreased inflammation. In contrast, β7-Integrin-deficiency results in increased steatohepatitis.