Soluble Alpha-Klotho Alleviates Cardiac Fibrosis without Altering Cardiomyocytes Renewal

Heart disease is the leading cause of death worldwide. The major cause of heart failure is the death of the myocardium caused by myocardial infarction, detrimental cardiac remodeling, and cardiac fibrosis occurring after the injury. This study aimed at discovering the role of the anti-aging protein alpha-klotho (KL), which is the co-receptor of fibroblast growth factor-23 (FGF23), in cardiac regeneration, fibrosis, and repair. We found that the anti-apoptotic function of soluble KL in isoproterenol-treated H9c2 cardiomyocytes was independent of FGF23 in vitro. In vivo, isoproterenol-induced cardiac fibrosis and cardiomyocyte and endothelial cell apoptosis were reduced by KL treatment. Moreover, the number of Ki67-positive endothelial cells and microvessel density within the isoproterenol-injured myocardium were increased upon KL treatment. However, by using genetic fate-mapping models, no evident cardiomyocyte proliferation within the injured myocardium was detected with or without KL treatment. Collectively, the cardioprotective functions of KL could be predominantly attributed to its anti-apoptotic and pro-survival activities on endothelial cells and cardiomyocytes. KL could be a potential cardioprotective therapeutic agent with anti-apoptotic and pro-survival activities on cardiomyocytes and endothelial cells.