NSUN2 mediated m5C modification regulates myocardial hypertrophy
Aims: Mammalian mRNA internal modification m6A has been suggested to be essential in the maintenance of cardiac homeostasis. The role of mRNA cytosine methylation (m5C) in the heart remains unexplored.Methods and results: In contrast with human normal heart, the expression of RNA cytosine methyltransferase NSun2 was found to be significantly elevated in the hypertrophied one. Consistently, NSun2 expression was increased in hypertrophic rat ventricular myocytes induced in vitro, as well as in TAC (transverse aortic constriction) developed hypertrophied murine heart. Cardiomyocyte-specific knockout of NSun2 (Myh6-CreERT2, NSun2 flox+/+) dramatically accelerated heart failure progression in TAC mice. RNA m5C immunoprecipitation followed by sequencing and MeRIP (methylation-specific RNA immunoprecipitation) revealed that NSun2 particularly methylates the mRNA of protein kinase A (PKA) catalytic subunit alpha (PRKACA). Polyribosome and dual luciferase reporter gene analysis further suggested that NSun2 promotes PRKACA translation via RNA methylation. In TAC hypertrophic cardiomyocytes, NSun2 ablation markedly dampened PKA signaling, as evidenced by reduced PKA activity and protein phosphorylation levels of PKA diverse substrates, impaired myocyte contraction and relaxation, and disturbed calcium transients. Cardiac-restricted overexpression of NSun2 via adeno-associated virus 9 (AAV9, NSun2 expression cassette driven by cTnT promoter) sensitized heart hypertrophic response, whereas administration of PKA inhibitor H89 successfully blocked this process, reiterating the importance of NSun2-PRKACA regulation in cardiac hypertrophic program.Conclusions: Our study showed that RNA methyltransferase NSun2 promotes PRKACA translation via RNA methylation, whereby achieving its modulation of PKA signaling within the cardiomyocyte. NSun2-PRKACA regulation is required for cardiac homeostasis maintenance and adaptation to hypertrophic stresses. These findings furnish us with novel understanding of heart function mediated by mRNA cytosine methylation in cardiac homeostasis. Overall design: NSUN2flox/flox and NSUN2-cKO mice were divided into the following four groups: NSUN2flox/flox group (FF), NSUN2-cKO group (cKO), NSUN2flox/flox+TAC group (FT), and NSUN2-cKO+TAC group (CT). Three weeks after TAC surgery, two mice were selected from each group, and left ventricular myocytes were isolated using the Langendorf method, followed by m5C-RIP-seq.