Multinucleated polyploid cardiomyocytes undergo an enhanced adaptability to hypoxia via mitophagy

There is a large subpopulation of multinucleated polyploid cardiomyocytes (M*Pc CMs) in the adult mammalian heart. However, the pathophysiological significance of increased M*Pc CMs in heart disease is poorly understood. We sought to determine the pathophysiological significance of increased M*Pc CMs during hypoxia adaptation.

A model of hypoxia-induced cardiomyocyte (CM) multinucleation and polyploidization was established and found to be associated with less apoptosis and less reactive oxygen species (ROS) production. Compared to mononucleated diploid CMs (1*2c CMs), tetraploid CMs (4c CMs) exhibited better mitochondria quality control via increased mitochondrial autophagy (mitophagy). RNA-seq revealed Prkaa2, the gene for AMPKα2, was the most obviously up-regulated autophagy-related gene. Knockdown of AMPKα2 increased apoptosis and ROS production and suppressed mitophagy in 4c CMs compared to 1*2c CMs. Rapamycin, an autophagy activator, alleviated the adverse effect of AMPKα2 knockdown. Furthermore, silencing PINK1 also increased apoptosis and ROS in 4c CMs and weakened the adaptive superiority of 4c CMs. Finally, AMPKα2^-/- mutant mice exhibited exacerbation of apoptosis and ROS production via decreases in AMPKα2-mediated mitophagy in 4c CMs compared to 1*2c CMs during hypoxia.

Compared to 1*2c CMs, hypoxia-induced 4c CMs exhibited enhanced mitochondria quality control and less apoptosis via AMPKα2-mediated mitophagy. These results suggest that multinucleation and polyploidization allow CM to better adapt to stress via enhanced mitophagy. In addition, activation of AMPKα2 may be a promising target for myocardial hypoxia-related diseases.