Activation of Endogenous Cardiac Stem Cells by Apelin-13 in Infarcted Rat Heart

Our previous study demonstrated that the apelin–APJ pathway contributed to myocardial regeneration and functional recovery after bone marrow-derived mesenchymal stem cell (BM-MSC) transplantation during the differentiation of BM-MSCs into cardiomyogenic cells in acute myocardial infarction (AMI) rat models. However, the underlying mechanisms by which apelin promotes cardiac repair and functional recovery have not been completely clarified. In the present study, we investigated whether apelin could mobilize and activate endogenous cardiac stem cells and progenitors, thereby mediating regeneration and repair of the myocardium after AMI in rat models. Six-week-old male Sprague–Dawley rats underwent AMI and received apelin-13 (200 ng, n = 10) or an equivalent volume of saline by intramyocardial injection (n = 10); there was also a sham operation group (n = 8). Proliferation of endogenous cardiac stem cells was analyzed by immunofluorescence staining in rat infarcted myocardium, and heart function was evaluated by echocardiography at 28 days after apelin-13 injection. Treatment with apelin-13 led to a significant increase of Ki-67+-c-kit+/Sca-1+/Flk-1+ endogenous cardiac stem or progenitor cells in the border zone and infarct zone of rat hearts at 28 days after myocardial infarction (MI). Significant increases in the expression of c-kit, Sca-1, and Flk-1 on both levels of transcription and translation were confirmed by real-time polymerase chain reaction (RT-PCR) and Western blot. Treatment of apelin-13 also resulted in a significant reduction of infarct size and improvement of cardiac function post-MI. We conclude that apelin-13 is able to enhance mobilization, survival, and proliferation of endogenous myocardial stem cells in the injured heart, providing a novel mechanistic explanation for how apelin-13 might repair the heart and improve cardiac function. Thus, apelin-13 or pharmacological agonists of the APJ receptor could act as novel therapies for heart regeneration.