Novel Protective Role of Endogenous Cardiac Myocyte P2X4 Receptors in Heart Failure

Abstract

Background-Heart failure (HF), despite continuing progress, remains a leading cause of mortality and morbidity. P2X4 receptors (P2X4R) have emerged as potentially important molecules in regulating cardiac function and as potential targets for HF therapy. Transgenic P2X4R overexpression can protect against HF, but this does not explain the role of native cardiac P2X4R. Our goal is to define the physiological role of endogenous cardiac myocyte P2X4R under basal conditions and during HF induced by myocardial infarction or pressure overload. Methods and Results-Mice established with conditional cardiac-specific P2X4R knockout were subjected to left anterior descending coronary artery ligation-induced postinfarct or transverse aorta constriction-induced pressure overload HF. Knockout cardiac myocytes did not show P2X4R by immunoblotting or by any response to the P2X4R-specific allosteric enhancer ivermectin. Knockout hearts showed normal basal cardiac function but depressed contractile performance in postinfarct and pressure overload models of HF by in vivo echocardiography and ex vivo isolated working heart parameters. P2X4R coimmunoprecipitated and colocalized with nitric oxide synthase 3 (eNOS) in wild-type cardiac myocytes. Mice with cardiac-specific P2X4R overexpression had increased S-nitrosylation, cyclic GMP, NO formation, and were protected from postinfarct and pressure overload HF. Inhibitor of eNOS, L-N 5 -(1-iminoethyl)ornithine hydrochloride, blocked the salutary effect of cardiac P2X4R overexpression in postinfarct and pressure overload HF as did eNOS knockout. Conclusions-This study establishes a new protective role for endogenous cardiac myocyte P2X4R in HF and is the first to demonstrate a physical interaction between the myocyte receptor and eNOS, a mediator of HF protection.(Circ Heart Fail. 2014;7:510-518.)

Antihypertrophic Effects of Small Molecules that Maintain Mitochondrial ATP Levels Under Hypoxia

“…Nifuroxazide is an anti-diarrheal agent that inhibits signal transducer and activator of transcription 3 (STAT3) ( Nelson et al, 2008 ), a transcription factor that plays well-described roles in cardiac hypertrophy and failure ( Haghikia et al, 2011 ). Although ivermectin shows anti-tumor activity ( Hashimoto et al, 2009 ; Liu et al, 2016 ; Nishio et al, 2016 ), enhances cardiomyocyte contractility ( Yang et al, 2014 ), and is neuroprotective ( Andries et al, 2007 ), few reports have addressed its effects on mitochondrial function in cardiomyocytes or cardiac hypertrophy. Therefore, we focused on ivermectin and its mechanism of action by assessing the effects of known ivermectin molecular targets on mitochondrial ATP under hypoxia.…”

Ca2+ Signaling in Cardiac Fibroblasts and Fibrosis-Associated Heart Diseases

“…In cardiac fibroblasts, P2X4 and P2X7 mRNAs have been detected in cultured human ventricular fibroblasts [46]. Furthermore, cardiac myocyte-specific overexpression of the P2X4 receptor in mice decreases fibrosis in a hypertensive heart failure mouse model [114,115], yet it is unknown whether this is due to direct cardiac myocyte protection or the interaction between cardiac myocytes and fibroblasts [116]. The function of P2X4 and P2X7 in mediating Ca 2+ entry in cardiac fibroblasts and their role in cardiac fibrosis needs further investigation.…”

ATP increases [Ca2+]iand activates a Ca2+‐dependent Cl−current in rat ventricular fibroblasts

“…Our findings, when considered in conjunction with previous work on purinergic responses in mammalian cardiac myocytes, provide new insights into the complex multifactorial purinergic signalling system in the ventricular myocardium (Vassort, ). It is well established that ATP can exhibit positive inotropic effects in the heart, both in control conditions and in the setting of experimental cardiomyopathy (Vassort, ; Yang et al., ). Although extensive electrophysiological studies have been done on a variety of different isolated single myocyte preparations, the explanation for this consistent positive inotropic effect remains to be determined.…”