Selective cardiomyocyte loss triggers myocardial regeneration via miR221 driven activation of cardiac stem cells and p57 suppression

Abstract Introduction The adult mammalian heart exhibits a limited yet measurable regenerative capacity, with cardiomyocyte (CM) turnover occurring throughout life. However, it remains unclear whether this capacity can be amplify in response to acute CM loss. Methods To investigate this, we used Tg-Myh6MCM:R26stop-DTA mice to induce controlled, CM-restricted ablation via tamoxifen (TAM)-dependent activation of Diphtheria Toxin A (DTA). Mice were implanted with osmotic mini-pumps to systemically release BrdU over 28 days to track newly generated cells. Results DTA activation triggered dose-dependent CM death, with a single TAM dose leading to ~20% ventricular CM loss, associated with acute systolic dysfunction and chamber dilation. Remarkably, surviving mice underwent complete anatomical and functional recovery within 28 days. This recovery was driven by robust CM renewal, as demonstrated by BrdU labeling of newly formed mononucleated CMs at rates matching the extent of initial loss. Mechanistically, this regenerative response was sustained by activation of endogenous resident cardiac stem cells (CSCs), which rapidly exited quiescence, proliferated, and committed to cardiomyogenic differentiation both in vitro and in vivo. Ablation of proliferating cells with 5-Fluorouracil blocked regeneration, confirming CSCs are necessary for CM renewal. Conversely, CSC transplantation rescued cardiac structure and function, demonstrating sufficiency. Molecularly, CSC activation was orchestrated by repression of the quiescence-enforcing kinase inhibitor p57 through upregulation of miR-221. miR-221 was both necessary and sufficient to drive CSC cell cycle entry and cardiomyogenic commitment, and its overexpression in quiescent CSCs recapitulated the regenerative effects of injury-activated CSCs in vivo. Conclusions This study demonstrates that, under conditions of selective genetic CM ablation, the adult heart can regenerate nearly one-fifth of its ventricular CM content within one month. This regeneration is mediated by endogenous CSCs and regulated by a miR-221/p57 axis, offering a therapeutic framework to enhance cardiac repair.