This study aims to evaluate the efficacy of lysyl oxidase (LOX) inhibition in regulating rat myocardial fibrosis and chronic heart failure (CHF) and to validate the regulation of LOX by TGF-β1/Smad2/3 signaling in this process. A rat model of CHF was established by abdominal aortic coarctation. The renin-angiotensinaldosterone system (RAAS) indexes (PRA, ACE2, Ang II, and ALD), cardiac function indicators (LVEF, LVFS, SAP, DAP, and LVEDP), ventricular remodeling-and fibrosis-related indicators (hydroxyproline, collagen deposition, and MMP-2/9), and morphological changes of myocardial tissues were examined. Rat cardiac fibroblasts (RCFs) were used in vitro assays. CHF patients showed increased LOX activity, accompanied by activated RAAS and TGF-β1. Furthermore, inhibition of LOX by β-aminopropionitrile (BAPN) mitigated the RAAS activation and attenuated cardiac dysfunction, ventricular remodeling, myocardial fibrosis, and collagen deposition in CHF rats. Moreover, TGF-β1 signaling diminished the LOX inhibition-mediated antiheart failure effect. Further assays showed that TGF-β1/ Smad2/3 signaling increased expression of c-jun (AP-1 transcription factor subunit), which transcriptionally induced LOX expression. Additionally, BAPN abrogated the TGF-β1-mediated increase in cell proliferation and levels of MMP-2/9 and collagen I/III in RCFs. In conclusion, LOX can be induced by TGF-β1/Smad/AP-1 signaling and LOX inhibition attenuates rat myocardial fibrosis and CHF. K E Y W O R D S chronic heart failure, c-Jun, LOXSmadTGF-β1

Chronic heart failure (HF) is the final stage of many cardiovascular diseases and imposes a great health and economic burden on society and families due to its high morbidity and mortality [1]. Myocardial fibrosis is closely associated with almost all types of heart diseases, including HF [2]. Thus, there is an unmet need to develop novel and effective therapeutic strategies for alleviating myocardial fibrosis. The enzyme lysyl oxidase (LOX) is a copper-dependent extracellular enzyme that catalyzes lysine-derived crosslinks in collagen and elastin, contributing to remodelling the extracellular matrix (ECM) [3]. LOX upregulation and/ or overactivity are associated with myocardial fibrosis and cardiac dysfunction [3-6]. Our previous work demonstrated that inhibition of LOX by β-aminopropionitrile (BAPN) alleviated rat cardiac dysfunction, myocardial fibrosis and accumulation of fibrosis-related indicators including matrix

MicroRNA‐134‐5p (MiR‐134‐5p) has been proposed as a promising novel biomarker for the diagnosis of acute myocardial infarction (AMI). However, the biological role of miR‐134‐5p in ischemic cardiomyocytes has been little disclosed yet. Expression of miR‐134‐5p and X‐linked inhibitor of apoptosis protein (XIAP) was detected using RT‐qPCR and western blot. Oxidative stress and cell apoptosis were determined by enzyme‐linked immunosorbent assays, 3‐(4, 5‐dimethylthiazole‐2‐y1)‐2, 5‐biphenyl tetrazolium bromide assay, flow cytometry, western blot, and terminal‐deoxynucleoitidyl transferase‐mediated nick end labeling (TUNEL). The interaction between miR‐134‐5p and XIAP was confirmed by luciferase reporter assay. Expression of miR‐134‐5p was upregulated in serum of AMI patients and hypoxia/reoxygenation (H/R)‐induced cardiomyocytes (AC16 and HCM). MiR‐134‐5p downregulation could inhibit H/R‐mediated release of lactic dehydrogenase enzyme (LDH) and malondialdehyde (MDA), and promote superoxide dismutase (SOD) and glutathione peroxidase (GSH‐PX) levels. Meanwhile, cell viability was increased, while the apoptosis rate and TUNEL positive cells were inhibited by miR‐134‐5p downregulation in H/R‐treated AC16 and HCM cells. Mechanically, XIAP was downregulated and targeted by miR‐134‐5p in H/R‐induced cardiomyocytes in vitro. Overexpression of XIAP inhibited oxidative stress and cell apoptosis in H/R‐treated AC16 and HCM cells, which was similar to miR‐134‐5p knockdown. Moreover, downregulation of XIAP could partially reverse the effect of miR‐134‐5p knockdown in H/R‐induced cardiomyocytes. Knockdown of miR‐134‐5p protected cardiomyocytes from H/R‐induced oxidative stress and apoptosis in vitro through targeting XIAP.