Hypoxia‐induced apoptosis is linked to the pathogenesis of myocardial infarction (MI) and heart failure. Ubiquitin‐specific peptidase 7 (USP7) is related to catabolic/pro‐apoptotic signaling. However, its role in cardiomyocyte injury is unclear. In this study, we aimed to investigate the role and the underlying regulatory mechanism of USP7 in MI. H9c2 cardiomyocytes were cultured in hypoxia to establish an in vitro model of myocardial hypoxic/ischemic injury. Sprague‐Dawley (SD) rats were used to establish animal models with MI. Quantitative real‐time polymerase chain reaction (qRT‐PCR) and Western blot assays were performed to evaluate the expression levels of miR‐409‐5p, USP7, and p53, respectively. After USP7 and miR‐409‐5p were selectively regulated in H9c2 cells, the inflammatory response, apoptosis, and cell viability were detected by ELISA, flow cytometry, and MTT assay, respectively. The interaction between USP7 and miR‐409‐5p was determined by bioinformatics analysis, qRT‐PCR, Western blot, and dual‐luciferase reporter assay. LVEF, LVIDd, and LVIDs of rats after MI were also measured. USP7 expression was markedly elevated while miR‐409‐5p expression was significantly down‐regulated in H9c2 cells under hypoxic culture. Augmentation of USP7 expression led to a dramatic promotion of hypoxia‐induced apoptosis of cardiomyocytes, accompanied by an increase in the secretion of the cytokines IL‐1β, TNF‐α, and IL‐6. Myocardial injury markers LDH, cTnI, and CK‐MB expressions were also increased. Besides, overexpression of USP7 aggravated left ventricular remodeling and decreased left ventricular function of the rats. Conversely, the up‐regulation of miR‐409‐5p expression protected H9c2 cells from apoptosis and inhibited the release of cytokines and myocardial injury. Left ventricular remodeling and left ventricular function were also improved by miR‐409‐5p overexpression. Furthermore, USP7 was identified as a target of miR‐409‐5p and the overexpression of miR‐409‐5p reversed the effects of USP7 on H9c2 cells. USP7 exacerbates myocardial ischemic injury by promoting inflammation and apoptosis of cardiomyocytes, and the up‐regulation of its expression is partly caused by the down‐regulation of miR‐409‐5p expression.

中文翻译：

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受miR-409-5p负调控的USP7加重了缺氧引起的心肌细胞损伤

低氧诱导的细胞凋亡与心肌梗死（MI）和心力衰竭的发病机理有关。泛素特异性肽酶7（USP7）与分解代谢/促凋亡信号有关。但是，其在心肌细胞损伤中的作用尚不清楚。在这项研究中，我们旨在调查USP7在MI中的作用和潜在的调控机制。在缺氧条件下培养H9c2心肌细胞以建立体外心肌缺氧/缺血性损伤模型。使用Sprague-Dawley（SD）大鼠建立MI的动物模型。进行实时定量聚合酶链反应（qRT-PCR）和Western印迹分析以分别评估miR-409-5p，USP7和p53的表达水平。在H9c2细胞中选择性调节USP7和miR-409-5p后，分别通过ELISA，流式细胞仪和MTT分析检测了炎症反应，凋亡和细胞活力。USP7和miR-409-5p之间的相互作用通过生物信息学分析，qRT-PCR，Western印迹和双荧光素酶报告基因测定来确定。还测量了MI后大鼠的LVEF，LVIDd和LVID。在低氧培养下，H9c2细胞中USP7表达显着升高，而miR-409-5p表达显着下调。USP7表达的增强导致缺氧诱导的心肌细胞凋亡的显着促进，伴随着细胞因子IL-1β，TNF-α和IL-6分泌的增加。心肌损伤标志物LDH，cTnI和CK-MB的表达也增加了。此外，USP7的过表达加剧了大鼠的左心室重构，降低了其左心室功能。相反，miR-409-5p表达的上调保护H9c2细胞免于凋亡，并抑制细胞因子的释放和心肌损伤。miR‐409‐5p过表达还改善了左心室重构和左心室功能。此外，USP7被确定为miR-409-5p的靶标，miR-409-5p的过表达逆转了USP7对H9c2细胞的作用。