METTL3 improves cardiomyocyte proliferation upon myocardial infarction via upregulating miR-17-3p in a DGCR8-dependent manner

Abstract

Myocardial infarction (MI), one of the most severe types of heart attack, exerts a strong negative effect on heart muscle by causing a massive and rapid loss of cardiomyocytes. However, the existing therapies do little to improve cardiac regeneration. Due to the role of methyltransferase-like 3 (METTL3) in the physiological proliferation of cardiomyocytes, we aimed to determine whether METTL3 could also promote cardiomyocyte proliferation under pathological conditions and to elucidate the underlying mechanism. The effects of METTL3 on cardiomyocyte proliferation and apoptosis were investigated in an in vivo rat model of MI and in an in vitro model of neonatal rat cardiomyocytes (NRCMs) exposed to hypoxia. We found that METTL3 expression was downregulated in hypoxia-exposed NRCMs and MI-induced rats. Furthermore, METTL3 pretreatment enhanced cardiomyocyte proliferation and inhibited cardiomyocyte apoptosis under hypoxic or MI conditions, and silencing METTL3 had the opposite effects. Additionally, METTL3 overexpression upregulated miR-17-3p expression. The miR-17-3p agomir mimicked the pro-proliferative and antiapoptotic effects of METTL3 in hypoxia-exposed cells or rats with MI, while the miR-17-3p antagomir blocked these effects. Additionally, pretreatment with the RNA-binding protein DGCR8 also hampered the protective role of METTL3 in hypoxia-exposed cells. Overall, the current study indicated that METTL3 could improve cardiomyocyte proliferation and subsequently ameliorate MI in rats by upregulating proliferation-related miR-17-3p in a DGCR8-dependent pri-miRNA-processing manner.

METTL3 mediates Ang-II-induced cardiac hypertrophy through accelerating pri-miR-221/222 maturation in an m6A-dependent manner

“…In fact, similar contradictory results regarding the role of METTL3 have been observed in other cardiovascular diseases. For example, a recent study discovered that METTL3 knockdown could promote CM proliferation [31], while in another METTL3 was proven to activate the proliferation of CMs [32], which highly suggested that the biological function of m6A modification is extremely complex in the cardiac system. Our results were based on Ang-II stimulation, which mainly exerts its function through the angiotensin type 1 receptor (AT1R), while phenylephrine compound predominantly acts as α(1) adrenergic receptor agonist [33,34].…”

Emerging roles of the RNA modifications N6-methyladenosine and adenosine-to-inosine in cardiovascular diseases

“… 55 In line with this, METTL3 overexpression has recently been unveiled to also promote neonatal rat cardiomyocyte proliferation after hypoxia and to ameliorate ischemic myocardial damage in adult rats by promoting pri-miR-17-3p maturation in a m 6 A-DGCR8 microprocessor complex subunit-(DGCR8)-dependent manner. 147 …”

“…55 In line with this, METTL3 overexpression has recently been unveiled to also promote neonatal rat cardiomyocyte proliferation after hypoxia and to ameliorate ischemic myocardial damage in adult rats by promoting pri-miR-17-3p maturation in a m 6 A-DGCR8 microprocessor complex subunit-(DGCR8)-dependent manner. 147 On the other hand, in mice, global METTL3 knockout has been described to enhance regeneration-related markers and enhance cardiac function after MI via m 6 A-dependently inhibited pri-miR-143-3p maturation. 140 The muscle-specific cardiac miRNA, miR-133a, was found to harbor a complementary motif CCUG for the DR-m 6 A-CH m 6 A consensus sequence within its seed sequence, thus making it exquisitely prone to bind m 6 A-modified mRNAs.…”

“…While METTL3 knockout decreases RNA m 6 A content and promotes regenerative cardiac healing in mice, similar to eraser overexpression, 140 the role in rats appears to be the opposite. 55,147 It is clear that these findings stress the need for species-specific considerations, but further efforts to identifying downstream responsive molecular pathways for potential therapeutic intervention to promote cardiac regeneration are also warranted.…”

“…344,345 Such postulation is strengthened by the findings that (1) METTL3 knockout before mice MI preserves cardiac function and structure afterward, 140 and (2) METTL3 promotes cardiomyocyte pyroptosis and myocardial I/R injury in rats via an m 6 A-dependent DGCR8-mediated pri-miR-143-3p maturation to yield miR-143-3p to finally suppress protein kinase C epsilon type (PRKCE). 142 However, myocardial METTL3 overexpression has also been implicated with cardioprotective ability by (1) inducing therapeutic myocardial angiogenesis in mice shortly after MI, 56 (2) lessening post-MI damage in rats by promoting cardiomyocyte proliferation via stimulated pri-miR-17-3p maturation, 147 and (3) its non-catalytic METTL14 subunit protecting mice heart from extensive I/R injury by activating Wnt1/b-catenin signal pathway via an m 6 Adependent enhanced Wnt family member 1 (Wnt1) mRNA translation. 143 Hence, it can be postulated that the resulting final effect on the cardiac phenotype depends considerably on the relative weights of METTL3 activity within the distinct cardiac cell types, ischemic models, as well as the expression profile of the m 6 A readers and transcribed transcriptome available for methylation at a given time, as discussed above (see section "cardiac hypertrophy and failure").…”