The Mechanism Of Endothelial NADPH Oxidase 4 In Regulation Of Atherosclerosis

Atherosclerosis seriously threatens human health and attracts worldwide attention.Physiological reactive oxygen species(ROS)are important signaling molecules that regulate the structure and function of blood vessels.However,pathologically induced ROS cause cell oxidative stress and participate in the process of atherosclerosis.Nicotinamide adenine dinucleotide phosphate(NADPH)oxidases are the major source of ROS in blood vessels.There is a preliminary progress in the relationship between different subtypes of NADPH oxidase and atherosclerosis.Nox4 as the most abundant subtypes of NADPH oxidase in blood vessels,its relationship to atherosclerosis and the potential mechanism involved remains to be clarified.We found that in the atherosclerosis-prone area,the expression of endothelial Nox4 was significantly decreased while smooth muscle Nox4 was significantly increased,implying that Nox4 plays opposite roles in regulation of atherosclerosis between endothelium and smooth muscle.Using Nox4 mutant mice to inhibit the function of Nox4 in vascular smooth muscle,our previous study indicates that the pathological increased Nox4 in smooth muscle accelerates the process of atherosclerosis by upregulating its downstream target soluble epoxide hydrolase 2(sEH,coding gene EPHX2).The aim of this study is to investigate whether sEH mediates the reguation of endothelial Nox4 in atherosclerosis.Type I diabetes accelerates atherosclerosis mainly through inflammation.We found that type I diabetes downregulated the expression of Nox4 and upregulated the expression of sEH and vascular cell adhesion molecule 1(VCAM1)in the aortic endothelium,suggesting that downregulation of endothelial Nox4 promotes atherosclerosis by upregulation of both sEH and VCAM1.Using endothelial Nox4 mutant mice to mimic the downregulation of endothelial Nox4 in atherosclerosis-prone vessel area,we found that inhibition of endothelial Nox4 significantly accelerated the process of atherosclerosis and type I diabetes further worsened it.In isolated endothelial cells,inhibition of Nox4 upregulated the expression of sEH and VCAM1,increased the promoter activity of nuclear factor kappa B(NF-?B),and promoted the adhesion of macrophages to endothelial cells,indicating that endothelial Nox4 regulates inflammation through sEH.In endothelial cells from Nox4 mutant mice,sEH inhibitor TPPU reduced the activity of NF-?B promoter and decreased the expression of VCAM1,inhibited the adhesion of macrophages to endothelial cells.In endothelial cells,overexpression of Nox4 wild type inhibited sEH expression,while overexpression of Nox4 mutant increased sEH expression,indicating that endothelial Nox4 inversely regulate the expression of sEH.We hypothesize that downregulation of endothelial Nox4 can upregulate the expression of its downstream target sEH to promote the inflammatory response and to accelerate the process of atherosclerosis in atherosclerosis-prone conditions.