Roiz-Valle, D.; Folgueira, C.; Moledo-Nodar, L.; Tartiere, A. G.; Cicuendez, B.; Romero-Becerra, R.; Rodriguez, F.; He, Y.-W.; Freije, J. M. P.; Sabio, G.; Lopez-Otin, C.; Caravia, X. M.; P. Ugalde, A.

Aging is the main risk factor for cardiovascular diseases, underscoring the need to identify the molecular regulators that sustain cardiac function during aging. The microRNA miR-29 is a well-established aging-associated regulator as its expression increases with age, and its overexpression promotes premature aging. Here, we define the cardiomyocyte-autonomous role of miR-29 in the adult heart by generating an inducible, cardiomyocyte-specific miR-29-deficient mouse model (Heart-iKO). We show that Heart-iKO mice develop dilated cardiomyopathy (DCM) with reduced ejection fraction that ultimately leads to premature death. Mechanistically, Heart-iKO cardiomyocytes exhibit alterations in mitochondrial structure and function. Transcriptomic profiling of bulk heart tissue and isolated cardiomyocytes revealed a consistent downregulation of genes involved in oxidative phosphorylation and the electron transport chain. We further observed a similar pattern of mitochondrial impairment in miR-29-deficient human cardiomyocytes derived from induced pluripotent stem cells (CM-iPSCs). Together, these findings highlight the context-dependent role of miR-29 in cardiac physiology and aging: although its upregulation promotes premature aging, its basal expression is required to maintain mitochondrial homeostasis and prevent heart failure in the adult myocardium.