miR-199a-3p suppresses Vldlr expression to promote cardiomyocyte proliferation.

The proliferative capacity of cardiomyocytes is limited in adult mammals, and replacing lost tissue following acute ischemic injury is challenging. Previous studies have demonstrated that miR-199a-3p can promote cardiomyocyte proliferation, but the exact mechanism by which this occurs remains unclear, although multiple targets of miR-199a-3p have been identified. We recently showed that very-low-density-lipoprotein receptor (Vldlr) inhibits cardiomyocyte proliferation, and in this study we aim to test whether Vldlr is a functional target gene of miR-199a-3p. 3'UTR reporter assays demonstrate that miR-199a-3p directly binds to the 3'UTR of Vldlr and inhibits its translation. Overexpressing Vldlr blunts the pro-proliferative effect of miR-199a-3p on cardiomyocytes, suggesting that Vldlr is indeed a functional target of miR-199a-3p. Mechanistically, Vldlr reduces S807/811 phosphorylation of RB1, and inhibiting CDK4/6 to prevent RB1 phosphorylation can block the pro-proliferative effect of both Vldlr knockdown and miR-199a-3p, suggesting that RB1 phosphorylation is required for the cardiomyocyte proliferation induced by miR-199a-3p and Vldlr knockdown. The findings of this study reveal Vldlr as a novel functional target of miR-199a-3p in cardiomyocytes and identify RB1 as a downstream effector of cardiomyocyte proliferation. The identification of the role of the miR-199a-3p- Vldlr-RB1 axis in cardiomyocyte proliferation may provide potential therapeutic targets for cardiac regenerative medicine.