A Novel Role of Claudin-5 in Prevention of Mitochondrial Fission Against Ischemic/Hypoxic Stress in Cardiomyocytes

Downregulation of claudin-5 in the heart is associated with the end-stage heart failure. However, the underlying mechanism ofclaudin-5 is unclear. Here we investigated the molecular actions of claudin-5 in perspective of mitochondria in cardiomyocytes to better understand the role of claudin-5 in cardioprotection during ischemia. Myocardial ischemia/reperfusion (I/R; 30 min/24 h) and hypoxia/reoxygenation (H/R; 24 h/4 h) were used in this study. Confocal microscopy and transmission electron microscope (TEM) were used to observe mitochondrial morphology. Claudin-5 was detected in murine heart tissue and neonatal rat cardiomyocytes (NRCM). Its protein level was severely decreased after myocardial I/R or H/R. Confocal microscopy showedclaudin-5 presented in the mitochondria of NRCM. H/R-induced claudin-5 downregulation was accompanied by mitochondrial fragmentation. The mitofusin 2 (Mfn2) expressionwas dramatically decreased while the dynamin-related protein (Drp) 1 expression was significantly increased after H/R. The TEM indicatedH/R-induced mitochondrial swelling and fission. Adenoviral claudin-5 overexpression reversed these structural disintegration of mitochondria. The mitochondria-centered intrinsic pathway of apoptosis triggered by H/R and indicated by the cytochrome c and cleaved caspase 3 in the cytoplasm of NRCMs was also reduced by overexpressing claudin-5. Claudin-5 overexpression in mouse heart also significantly decreased cleaved caspase 3 and the infarct size in ischemic heart with improved systolic function. We demonstrated for the first time the presence of claudin-5 in the mitochondria in cardiomyocytes and provided the firm evidence for the cardioprotective role of claudin-5 in the preservation of mitochondrial dynamics and cell fate against hypoxia- or ischemia-induced stress. Une régulation négative de la claudine-5 dans le cœur est associée à l'insuffisance cardiaque au stade terminal. Cependant, le mécanisme sous-jacent de la claudine-5 n'est pas clair. Nous avons étudié les mécanismes d'actions moléculaires de la claudine-5 dans les mitochondries des cardiomyocytes afin de mieux comprendre le rôle de la claudine-5 dans la cardioprotection pendant l'ischémie. L'ischémie/reperfusion (I/R; 30 min/24 h) du myocarde et l'hypoxie/régénération (H/R; 24 h/4 h) ont été appliquées lors de cette étude. La microscopie confocale et la microscopie électronique en transmission (MET) ont été utilisées pour l'observation de la morphologie des mitochon