Abstract
Cytoprotective gene heme oxygenase 1 (HO-1) could be induced by nuclear factor E2-related factor 2 (Nrf2) nuclear translocation. The purpose of this study was to determine the role of Brahma-related gene 1 (Brg1), a catalytic subunit of SWI2/SNF2-like chromatin remodeling complexes, in Nrf2/HO-1 pathway activation during hepatic ischemia–reperfusion (HIR). Our results showed that hepatic Brg1 was inhibited during early HIR while Brg1 overexpression reduced oxidative injury in CMV-Brg1 mice subjected to HIR. Moreover, promoter-driven luciferase assay showed that overexpression of Brg1 by adenovirus transfection in AML12 cells selectively enhanced HO-1 gene expression after hypoxia/reoxygenation (H/R) treatment but did not affect the other Nrf2 target gene NQO1. Furthermore, inhibition of HO-1 by the selective HO-1 inhibitor zinc protoporphyria could partly reverse the hepatic protective effects of Brg1 overexpression while HO-1-Adv attenuated AML12 cells H/R damage. Further, chromatin immunoprecipitation analysis revealed that Brg1 overexpression, which could significantly increase the recruitment of Brg1 protein to HO-1 but not NQO1 promoter, was recruited by Nrf2 to the HO-1 regulatory regions in AML12 hepatocytes subjected to H/R. In conclusion, our results demonstrated that restoration of Brg1 during reperfusion could enhance Nrf2-mediated inducible expression of HO-1 during HIR to effectively increase antioxidant ability to combat against hepatocytes damage.
Highlights
Hepatic ischemia–reperfusion (HIR) injury occurs inevitably during liver transplantation, trauma, hemorrhagic shock and other systemic low-flow diseases such as sepsis, respiratory failure and congestive heart failure.[1,2,3,4] HIR features in excessive production of reactive oxygen species (ROS) from various sources, leading to disturbance of the oxidation– antioxidation balance.[5,6] Excessive free heme, which is released from heme proteins under oxidative conditions, may be a major threat because it can catalyze the overproduction of ROS.[7]
Once migrated to the nucleus, Nrf[2] forms heterodimers with small Maf proteins and subsequently binds to the cis-acting antioxidant response element (ARE) within the gene promoters including HO-1 and NQO1.14,15 The binding leads to transcriptional activation of a battery of genes that encode an array of phase II detoxifying or antioxidant enzymes, such as HO-1 and NQO1, as well as other cytoprotective proteins.[16,17,18]
We have showed that Brahma-related gene 1 (Brg1)-mediated attenuation of oxidative stress in hepatocytes subjected to H/R by enhancing Nrf[2] and HO-1, in order to determine how HO-1 promoter was regulated by Brg[1] and Nrf[2] interaction, luciferase assay was performed
Summary
Hepatic ischemia–reperfusion (HIR) injury occurs inevitably during liver transplantation, trauma, hemorrhagic shock and other systemic low-flow diseases such as sepsis, respiratory failure and congestive heart failure.[1,2,3,4] HIR features in excessive production of reactive oxygen species (ROS) from various sources, leading to disturbance of the oxidation– antioxidation balance.[5,6] Excessive free heme, which is released from heme proteins under oxidative conditions, may be a major threat because it can catalyze the overproduction of ROS.[7]. Brahma-related gene 1 (Brg1) is the core ATPase in the SWI/SNF complex, which plays a central role in the activation and transcription of genes in mammalian cells.[19] Brg[1] has been reported to participate in the transactivation of proinflammatory mediators in macrophages treated with lipopolysaccharide.[20] Interestingly, some recent studies indicated that Brg[1] upregulation could exert an antioxidative effect.[21] study showed that small interfering RNA knockdown of Brg[1] in colon cancer cell SW480 selectively decreased inducible expression of HO-1 gene after diethylmaleate treatment in vitro.[22] whether overexpression of Brg[1] could enhance Nrf2-mediated HO-1 gene transcription in hepatocyte subjected to ischemia/hypoxia and subsequent reperfusion/reoxygenation in vivo or in vitro in the epigenetic machinery remained unknown, if so, overexpression of Brg[1] maybe a potential therapy in liver diseases involving ischemia–reperfusion. We sought to determine whether or not overexpression of Brg[1] may have antioxidative effect against the hepatic damage during HIR, and if so, whether it functions via Received 19.11.16; revised 20.4.17; accepted 26.4.17; Edited by S Lavandero
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