Abstract The adult mammalian heart is characterized by post-mitotic polyploid cardiomyocytes (CMs). Understanding how CMs regulate cell cycle exit and polyploidy can help developing new heart regenerative therapies. Here, we uncover that the PIDDosome, a multi-protein complex activating the endopeptidase Caspase-2, helps to implement a CM-specific differentiation program that limits ploidy during postnatal heart development. DNA content analyses show that cell-autonomous PIDDosome loss causes an increase in nuclear and cellular CM ploidy. Increased ploidy does not affect cardiac structure nor function in early adulthood, but correlates with a modest reduction in cardiac performance in aged mice. PIDDosome-imposed polyploidy control commences at postnatal day 7 (P7), reaching a plateau by P14. PIDDosome activation requires ANKRD26, targeting PIDD1 to mother centrioles. Opposite to prior observations in liver development, the PIDDosome limits CM polyploidization in a p53-independent manner but reliant on induction of p21/Cdkn1a , a notion supported by nuclear RNA sequencing and genetic deletion experiments. Our results provide new insights how proliferation of polyploid CMs is restricted during postnatal heart development.
Leone et al. (2026) studied this question.