Cardiac Fibroblasts Enhance MMP2 Activity to Suppress Gap Junction Function in Cardiomyocytes

Although it is crucial to promptly restore blood perfusion to revive the ischemic myocardium, reperfusion itself can paradoxically contribute to the electrical instability and arrhythmias of the myocardium. Several studies have revealed that cardiac fibroblasts can impact cardiac electrophysiology through various mechanisms including the deposition of extracellular matrix, release of chemical mediators, and direct electrical coupling with myocytes. Previously, we have shown that hypoxia/reoxygenation (H/R)-treated rat fibroblasts conditional medium (H/R-FCM) could decrease the spontaneous beating frequency of rat neonatal cardiomyocytes and downregulate the expression of gap junction proteins. However, the specific mechanism by which H/R-FCM affects the gap junctions requires further investigation. H/R-FCM was obtained by culturing confluent rat cardiac fibroblasts (RCF) for 4 h under hypoxic conditions. Gap junction function, hemichannel activity, and expression of Cx43 were examined upon treatment with H/R-FCM. Gelatin zymography was performed to detect matrix metalloproteinase (MMP) activity in the conditioned medium. The effect of H/R-FCM and MMP2 inhibitors on cardiac electrophysiology and arrhythmias was investigated with an isolated rat ischemia/reperfusion (I/R) model. H/R-FCM treatment impaired gap junction function, downregulated Cx43 expression, and increased hemichannel activity in rat cardiomyocytes (H9c2). The adverse effect of H/R-FCM on gap junction, which was confirmed by the cardiomyocyte H/R model, was involved in the activation of MMP2. MMP2 inhibition could partially attenuate the detrimental effects of I/R on myocardial electrophysiological indices and arrhythmia susceptibility. Our study indicates that inhibition of MMP2 may be a promising therapeutic target for the treatment of reperfusion arrhythmia.