NADPH oxidase signal transduces angiotensin II in hepatic stellate cells and is critical in hepatic fibrosis

Abstract

Angiotensin II (Ang II) is a pro-oxidant and fibrogenic cytokine. We investigated the role of NADPH oxidase in Ang II-induced effects in hepatic stellate cells (HSCs), a fibrogenic cell type. Human HSCs express mRNAs of key components of nonphagocytic NADPH oxidase. Ang II phosphorylated p47 phox , a regulatory subunit of NADPH oxidase, and induced reactive oxygen species formation via NADPH oxidase activity. Ang II phosphorylated AKT and MAPKs and increased AP-1 DNA binding in a redox-sensitive manner. Ang II stimulated DNA synthesis, cell migration, procollagen α1(I) mRNA expression, and secretion of TGF-β1 and inflammatory cytokines. These effects were attenuated by N-acetylcysteine and diphenylene iodonium, an NADPH oxidase inhibitor. Moreover, Ang II induced upregulation of genes potentially involved in hepatic wound-healing response in a redoxsensitive manner, as assessed by microarray analysis. HSCs isolated from p47 phox-/-mice displayed a blunted response to Ang II compared with WT cells. We also assessed the role of NADPH oxidase in experimental liver fibrosis. After bile duct ligation, p47 phox-/-mice showed attenuated liver injury and fibrosis compared with WT counterparts. Moreover, expression of smooth muscle α-actin and expression of TGF-β1 were reduced in p47 phox-/-mice. Thus, NADPH oxidase mediates the actions of Ang II on HSCs and plays a critical role in liver fibrogenesis.

Aliskiren in combination with valsartan exerts synergistic protective effects against ventricular remodeling after myocardial infarction in mice

“…Angiotensin II stimulates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase expression that induces the production of reactive oxygen species, and triggers inflammatory response. [25][26][27][28] In this study, we found that aliskiren reduced oxidative stress and IL-6 expression in non-infarcted area similarly to valsartan with our tested doses. In addition, the combination of valsartan and aliskiren further suppressed oxidative stress and IL-6 expression in non-infarcted area than either monotherapy.…”

Lipid-induced oxidative stress causes steatohepatitis in mice fed an atherogenic diet

“…The hydroxyproline content in liver samples was quantified colorimetrically according to a published method. 19 Briefly, a 0.2-g liver sample was homogenized in 6 N HCl and hydrolyzed at 110°C for 16 hours. The hydrolysate was filtered, aliquots were evaporated under a vacuum, and the sediment was redissolved in 50% isopropanol.…”

Role of free radicals in liver diseases

“…ROS are involved in necrosis and apoptosis of hepatocytes and HSC activation [24,25]. Several major classes of free radical scavengers, such as catalase, superoxide SOD, and glutathione peroxidase (GSH-P), were investigated in various types of liver damage, and they afforded effective protection against the oxidative insults to hepatic parenchyma [26].…”

“…High levels of ROS, from phagocytic cells, such as Kupffer cells (KC), protect the organism from external pathogens; however, lower amounts of ROS mainly from HSC actively participate in the regulation of intracellular signaling [25,27]. Platelet-derived growth factor (PDGF) is the most potent mitogen of HSC and is, therefore, likely to be an important mediator during liver fibrogenesis [28].…”