ALDH2 modulates cardiac ischemic adaptation via mitochondrial DNMT1 translocation and dynamic mtDNA methylation remodeling

Abstract

Aim: Mitochondrial DNA (mtDNA) methylation is an emerging epigenetic regulator of mitochondrial function, yet the mechanisms governing its dynamic regulation under cellular stress—particularly in the heart—remain poorly understood. This study aimed to investigate whether aldehyde dehydrogenase 2 (ALDH2) regulates mtDNA methylation via the mitochondrial targeting of DNA methyltransferase 1 (DNMT1) during myocardial ischemia, and to explore the functional consequences of this regulation in Ischemic heart disease (IHD).

Methods: We identified a specific DNMT1 isoform containing a mitochondrial targeting sequence (MTS) and confirmed its localization to cardiomyocyte mitochondria. Myocardial infarction (MI) was induced in wild-type and ALDH2-knockout mice. Mitochondrial DNMT1 levels, mtDNA 5-methylcytosine (5mC) content, and MTS expression were assessed at various post-MI time points. Site-specific mtDNA methylation at ND1 and ND2 loci was analyzed. Hypoxia experiments in cardiomyocytes were performed to evaluate ALDH2-dependent DNMT1 translocation, mitochondrial gene expression, and respiratory capacity. Post-MI cardiac function was assessed by echocardiography.

Results: We confirm that a specific DNMT1 isoform localizes to cardiomyocyte mitochondria via its MTS and modulates mtDNA 5mC levels. Following MI, mitochondrial DNMT1 levels and mtDNA methylation exhibited a biphasic response: an initial increase during the early ischemic phase (1 week post-MI), followed by a decline in the later remodeling phase. Genetic deletion of ALDH2 impaired mitochondrial translocation of DNMT1, associated with downregulated MTS expression and reduced global mtDNA 5mC. Site-specific analysis revealed that ALDH2 deficiency significantly altered methylation patterns at the ND1 and ND2 loci. Functionally, hypoxia inhibited DNMT1 mitochondrial translocation in an ALDH2-dependent manner, thereby modulating the expression of these mitochondrial-encoded genes and overall mitochondrial respiratory capacity. Importantly, ALDH2 deficiency exacerbated post-MI cardiac dysfunction.

Conclusion: Our findings uncover a novel regulatory axis in which ALDH2 fine-tunes the dynamic equilibrium of mtDNA methylation by governing DNMT1-MTS expression, offering mechanistic insight into mitochondrial epigenetic adaptation in IHD and a potential therapeutic target for ALDH2-deficient populations.

Keywords

Aldehyde dehydrogenase 2 / mitochondrial DNA methylation / DNA methyltransferase 1 / myocardial ischemia / epigenetic regulation / mitochondrial function

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