Project description:Background: Heart failure with reduced ejection fraction (HFrEF) is characterized by impaired contractility and high mortality. Dysregulation of intracellular ion cycling underlies the decline in cardiac contractility. Modulation of cardiac Na+/H+ and Ca2+ handling is considered a valuable approach for restoring cardiac function; thus, an in-depth understanding of the molecular regulation is timely for the discovery of new strategies to treat HFrEF.Methods: Cardiac tissues from HFrEF patients and mice subjected to transverse aortic constriction (TAC) were analyzed for sterol regulatory element-binding protein 1 (SREBP1)  transactivation of Sodium-hydrogen exchanger 3 (NHE3).Cardiomyocyte-specific SREBP1 transgenic (Srebp1a-Tg) and knockdown (Cre-Srebp1f/f) mice were generated. AAV9 vectors carrying Slc9a3 (encoding NHE3), Srebf1 or shRNA against Slc9a3, driven by the cardiomyocyte-specific cTnT promoter, were used to validate the role of the SREBP1-NHE3 in HFrEF. Results: SREBP1 was activated in human hearts with HFrEF (dilated cardiomyopathy without diabetes or hyperlipidemia) and in mouse hearts with TAC-induced HFrEF. Srebp1a-Tg mice exhibited impaired cardiac contractilitywith dysregulated calcium handling in cardiomyocytes without apparent lipid accumulation. Transcriptomics analysis, ChIP-seq, ChIP assay, and promoter activity assessment showed that Slc9a3 (encoding NHE3) is a transcriptional target of SREBP1. Consistently, NHE3 was upregulated in Srebp1a-Tg mouse hearts, hearts under TAC surgery, and human failing hearts. Cardiomyocyte-specific knockdown of Srebp1 or Slc9a3 restored calcium handling and improved cardiac function in TAC hearts. In Srebp1a-Tg mice, NHE3 knockdown alleviated Na+ and Ca2+ overload and rescued cardiac systolic dysfunction. Conversely, NHE3 overexpression caused contractile impairment in both Cre-Srebp1f/f mice and controls, which offset the protective effect due to SREBP1 loss in the context of Na+ and Ca2+ overload. These resultsdemonstrate that SREBP1 upregulation of NHE3 caused cardiac dysfunction. Notably, empagliflozin downregulated NHE3 via AMP-activated protein kinase activation and inhibition of SREBP1, which ameliorated calcium overload and restored cardiac systolic function.Conclusions: SREBP1 transactivates cardiac NHE3 expression during the progression of HFrEF, leading to dysregulatedcalcium handling and impaired contractility, suggesting a non-canonical role of SREBP1 in heart failure. Empagliflozin mitigates these detrimental effects by inhibiting the cardiac SREBP1-NHE3 axis, thus revealing a new pharmacological mechanism by which SGLT2i alleviates HF.

Project description:Intracellular calcium (Ca2+) overload is known to play a critical role in the development of cardiac dysfunction. Despite the remarkable improvement in managing the progression of heart disease, developing effective therapies for heart failure (HF) remains a challenge. A better understanding of molecular mechanisms that maintain proper Ca2+ levels and contractility in the injured heart could be of therapeutic value. Here, we report that the transcription factor Zinc finger E-box-binding homeobox2 (ZEB2) is induced by Hypoxia-inducible factor 1-alpha (HIF1a) in hypoxic cardiomyocytes and regulates a network of genes involved in Ca2+-handling and contractility during ischemic heart disease. Gain- and loss-of-function studies in genetic mouse models revealed ZEB2 in cardiomyocytes to be necessary and sufficient to protect the heart against ischemia-induced diastolic dysfunction and structural remodeling. Moreover, RNA sequencing (RNA-seq) of ZEB2-overexpressing (Zeb2 cTg) hearts post-injury implicated ZEB2 in regulating numerous Ca2+-handling and contractility-related genes. Mechanistically, ZEB2 overexpression increased the phosphorylation of phospholamban (PLN) at both serine-16 and threonine-17, implying enhanced activity of sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), thereby augmenting SR Ca2+ uptake and contractility. Furthermore, we observed a decrease in the activity of Ca2+-dependent calcineurin/NFAT signaling in Zeb2 cTg hearts, which is the main driver of pathological cardiac remodeling. On a post-transcriptional level, we showed that ZEB2 expression can be regulated by the cardiomyocyte-specific microRNA-208a (miR-208a). Blocking the function of miR-208a with antimiR-208a increased ZEB2 expression in the heart and effectively protected from the development of pathological cardiac hypertrophy. Together, we present ZEB2 as a central regulator of contractility and Ca2+-handling components in the mammalian heart. Further mechanistic understanding of the role of ZEB2 in regulating Ca2+ homeostasis in cardiomyocytes is an essential step towards the development of improved therapies for HF.

Project description:Background: Pathological cardiac overload triggers maladaptive myocardial remodeling that predisposes to the development of heart failure. The contribution of long non-coding RNAs (lncRNAs) to intercellular signaling during cardiac remodeling is largely unknown. Methods: We analyzed the expression of Gadlor 1 and Gadlor2 lncRNAs in mouse hearts, mouse cardiac cells, extracellular vesicles (EVs), human failing hearts as well as patient serum. Gadlor knock-out (KO) mice were generated and analyzed. The effect of Gadlor knock-out and Gadlor overexpression during cardiac pressure overload induced by transverse aortic constriction (TAC) was analyzed by echocardiography, histological analyses and RNA sequencing in isolated cardiac cells. Gadlor1/2 interaction partners were identified by RNA antisense purification coupled with mass-spectrometry (RAP-MS). Results: In the heart, the related lncRNAs Gadlor1 and 2 are mainly expressed in endothelial cells and to a lesser extent in fibroblasts. Gadlor1/2 are upregulated in failing mouse hearts as well as in the myocardium and in serum of heart failure patients. Interestingly, Gadlor1 and 2 are secreted from endothelial cells within EVs, which are taken up by cardiomyocytes. Gadlor-KO mice exerted reduced cardiomyocyte hypertrophy, diminished myocardial fibrosis and improved cardiac function, but paradoxically suffered from sudden death during prolonged overload. Gadlor overexpression, in turn, triggered hypertrophy, fibrosis and cardiac dysfunction. Mechanistically, Gadlor1 and Gadlor2 inhibit angiogenic gene expression in endothelial cells, while promoting the expression of pro-fibrotic genes in cardiac fibroblasts. In cardiomyocytes, Gadlor1/2 upregulate mitochondrial genes, but downregulate angiogenesis genes, while interacting with the transcriptional regulator Glyr1 and the calcium/calmodulin-dependent protein kinase type II (CaMKII), entailing cardiomyocyte hypertrophy and perturbed cardiomyocyte calcium dynamics. Conclusions: We describe that Gadlor1 and 2, two related, novel lncRNAs, are upregulated in cardiac pathological overload and are secreted from endothelial cells within EVs. Gadlor1/2 induce cardiac dysfunction, cardiomyocyte hypertrophy and myocardial fibrosis by exerting heterocellular effects on cardiac cellular gene-expression and by affecting calcium dynamics in cardiomyocytes, which take up the Gadlor1/2 by EV mediated transfer from endothelial cells. Targeted inhibition of Gadlor lncRNAs in endothelial cells or fibroblasts might serve as therapeutic strategy in the future.

Project description:Ventricular arrhythmogenesis is a key cause of sudden cardiac death following myocardial infarction (MI). Accumulating data show that ischemia, sympathetic activation, and inflammation contribute to arrhythmogenesis. However, the role and mechanisms of abnormal mechanical stress in ventricular arrhythmia following MI remain undefined. We aimed to examine the impact of increased mechanical stress and identify the role of the key sensor Piezo1 in ventricular arrhythmogenesis in MI. Concomitant with increased ventricular pressure, Piezo1, as a newly recognized mechano-sensitive cation channel, was the most up-regulated mechanosensor in the myocardium of patients with advanced heart failure. Piezo1 was mainly located at the intercalated discs and T-tubules of cardiomyocytes, which are responsible for intracellular calcium homeostasis and intercellular communication. Cardiomyocyte-conditional Piezo1 knockout mice (Piezo1Cko) exhibited preserved cardiac function after MI. Piezo1Cko mice also displayed a dramatically decreased mortality in response to the programmed electrical stimulation after MI with a markedly reduced incidence of ventricular tachycardia. In contrast, activation of Piezo1 in mouse myocardium increased the electrical instability as indicated by prolonged QT interval and sagging ST segment. Mechanistically, Piezo1 impaired intracellular calcium cycling dynamics by mediating the intracellular Ca2+overload and increasing the activation of Ca2+-modulated signaling, CaMKII, and calpain, which led to the enhancement of phosphorylation of RyR2 and further increment of Ca2+leaking, finally provoking cardiac arrhythmias. Furthermore, in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), Piezo1 activation remarkably triggered cellular arrhythmogenic remodeling by significantly shortening the duration of the action potential, inducing early afterdepolarization, and enhancing triggered activity.This study uncovered a proarrhythmic role of Piezo1 during cardiac remodeling, which is achieved by regulating Ca2+handling, implying a promising therapeutic target in sudden cardiac death and heart failure.

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Cardiac untargeted lipidomics in cardiomyocyte-specific Srebp1a-Tg mice

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