BackgroundHydrogen peroxide (H2O2) is a critical molecular signal in the development of abdominal aortic aneurysm (AAA) formation. Vascular peroxidase 1 (VPO1) catalyzes the production of hypochlorous acid (HOCl) from H2O2 and significantly enhances oxidative stress. The switch from a contractile phenotype to a synthetic one in vascular smooth muscle cells (VSMCs) is driven by reactive oxygen species and is recognized as an early and important event in AAA formation. This study aims to determine if VPO1 plays a critical role in the development of AAA by regulating VSMC phenotypic switch.Methods and Results VPO1 is upregulated in human and elastase‐induced mouse aneurysmal tissues compared with healthy control tissues. Additionally, KLF4, a nuclear transcriptional factor, is upregulated in aneurysmatic tissues along with a concomitant downregulation of differentiated smooth muscle cell markers and an increase of synthetic phenotypic markers, indicating VSMC phenotypic switch in these diseased tissues. In cultured VSMCs from rat abdominal aorta, H2O2 treatment significantly increases VPO1 expression and HOCl levels as well as VSMC phenotypic switch. In support of these findings, depletion of VPO1 significantly attenuates the effects of H2O2 and HOCl treatment. Furthermore, HOCl treatment promotes VSMC phenotypic switch and ERK1/2 phosphorylation. Pretreatment with U0126 (a specific inhibitor of ERK1/2) significantly attenuates HOCl‐induced VSMC phenotypic switch.ConclusionsOur results demonstrate that VPO1 modulates VSMC phenotypic switch through the H2O2/VPO1/HOCl/ERK1/2 signaling pathway and plays a key role in the development of AAA. Our findings also implicate VPO1 as a novel signaling node that mediates VSMC phenotypic switch and plays a key role in the development of AAA.Clinical Trial Registration URL: http://www.chictr.org.cn. Unique identifier: ChiCTR1800016922.

Collectively, these results demonstrate that VPO1 promotes hypoxia-induced proliferation, apoptosis resistance, and migration in PASMCs via the NOX4/VPO1/HOCl/NF-κB signalling pathway.

Cardiac fibrosis is the most important mechanism contributing to cardiac remodeling after myocardial infarction (MI). VPO1 is a heme enzyme that uses hydrogen peroxide (H 2 O 2 ) to produce hypochlorous acid (HOCl). Our previous study has demonstrated that VPO1 regulates myocardial ischemic reperfusion and renal fibrosis. We investigated the role of VPO1 in cardiac fibrosis after MI. The results showed that VPO1 expression was robustly upregulated in the failing human heart with ischemic cardiomyopathy and in a murine model of MI accompanied by severe cardiac fibrosis. Most importantly, knockdown of VPO1 by tail vein injection of VPO1 siRNA significantly reduced cardiac fibrosis and improved cardiac function and survival rate. In VPO1 knockdown mouse model and cardiac fibroblasts cultured with TGF-β1, VPO1 contributes to cardiac fibroblasts differentiation, migration, collagen I synthesis and proliferation. Mechanistically, the fibrotic effects following MI of VPO1 manifested partially through HOCl formation to activate Smad2/3 and ERK1/2. Thus, we conclude that VPO1 is a crucial regulator of cardiac fibrosis after MI by mediating HOCl/Smad2/3 and ERK1/2 signaling pathways, implying a promising therapeutic target in ischemic cardiomyopathy.

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