Cross talk between toll‐like receptor‐4 signaling and angiotensin‐II in liver fibrosis development in the rat model of non‐alcoholic steatohepatitis

Abstract

The innate immune system, including toll-like receptor-4 (TLR4) signaling cascade and angiotensin-II (AT-II) play important roles in the progression of liver fibrosis development; the cross talk between TLR4 and AT-II has not been elucidated yet. The aim of the current study was to elucidate the effect of AT-II type 1 receptor blocker (ARB), on the liver fibrosis development, especially in conjunction with the interaction of TLR4 and AT-II in the rat model of non-alcoholic steatohepatitis. Fischer 344 rats were fed a choline-deficient, L-amino-acid-defined diet for 8 weeks and the effects of losartan were elucidated in conjunction with activated hepatic stellate cells (Ac-HSC) activation, TLR4, nuclear factor-κB (NF-κB), and transforming growth factor-β (TGF-β) expressions. In vitro study was carried out to elucidate the effect of AT-II on several indices including TLR4, myeloid differentiation factor 88, NF-κB, and TGF-β expressions in the rat HSC. ARB markedly inhibited liver fibrosis development along with suppression of the number of Ac-HSC and TGF-β. These inhibitory effects of ARB were almost in parallel with suppression of the hepatic TLR4 and NF-κB expressions. This in vitro study showed that AT-II significantly augmented the TLR4 expression in a dose- and time-dependent manner via AT-II type 1 receptor in the Ac-HSC. AT-II also augmented the lipopolysaccharide-induced myeloid differentiation factor 88 (MyD88), NF-κB, and TGF-β and these increments were attenuated by treatment with ARB. These studies indicated that the cross talk between TLR4 signaling cascade and AT-II plays a pivotal role in liver fibrosis development in non-alcoholic steatohepatitis.