Mettl3-mediated m⁶ A modification of Fgf16 restricts cardiomyocyte proliferation during heart regeneration

Cardiovascular disease is the leading cause of death worldwide due to the inability of adult heart to regenerate after injury. N⁶-methyladenosine (m⁶A) methylation catalyzed by the enzyme methyltransferase-like 3 (Mettl3) plays an important role in various physiological and patho-logical bioprocesses. However, the role of m⁶A in heart regeneration remains largely unclear. To study m⁶A function in heart regeneration, we modulated Mettl3 expression in vitro and in vivo. Knockdown of Mettl3 significantly increased the proliferation of cardiomyocytes and accelerated heart regeneration following heart injury in neonatal and adult mice. However, Mettl3 overexpres-sion decreased cardiomyocyte proliferation and suppressed heart regeneration in postnatal mice. Conjoint analysis of methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA-seq identified Fgf16 as a downstream target of Mettl3-mediated m⁶A modification during postnatal heart regeneration. RIP-qPCR and luciferase reporter assays revealed that Mettl3 negatively regulates Fgf16 mRNA expression in an m⁶A-Ythdf2-dependent manner. The silencing of Fgf16 suppressed the proliferation of cardiomyocytes. However, the overexpression of ΔFgf16, in which the m⁶A consensus sequence was mutated, significantly increased cardiomyocyte proliferation and accelerated heart regeneration in postnatal mice compared with wild-type Fgf16. Our data demonstrate that Mettl3 post-transcriptionally reduces Fgf16 mRNA levels through an m⁶A-Ythdf2-dependen pathway, thereby controlling cardiomyocyte proliferation and heart regeneration.