METTL14 inhibits atherogenesis by epigenetically activating PPAR-α/γ transcription and fatty acid oxidation in VSMCs

N6-methyladenosine (m6A) RNA modification can govern cell fate by co- or post-transcriptionally regulating gene expression. VSMCs can undergo phenotypic switching, contributing to other cells within atherosclerotic plaques, including foam cell- and macrophage-like cells. However, the role of VSMC m6A in atherosclerosis development remains unclear. While PPAR-α and PPAR-γ have been extensively studied in macrophages for their roles in atherosclerosis, the epigenetic regulation of these nuclear receptors under high cholesterol conditions remains poorly understood.

We utilized murine and human atherosclerotic aortas, along with VSMC-specific Mettl3 and Mettl14 knockout mice, to evaluate the role of VSMC m6A in atherosclerosis. Lineage tracing was used to assess macrophage-like VSMCs. The epigenetic regulation of Ppara and Pparg transcription by methyltransferase-like 14 (METTL14) was investigated through a variety of methods, including histological, cellular, genomic, transcriptomic, metabolomic, lipidomic, computational, and pharmacological approaches. The therapeutic potential of VSMC Mettl14 in atherosclerosis was analysed using adenoassociated virus-mediated expression in ApoE-/- mice. We showed that the METTL3/METTL14 methyltransferase complex was reduced in both murine and human atherosclerotic VSMCs. The levels of METTL3, and consequently m6A, were regulated by METTL14, which was in turn influenced by oxidized low-density lipoprotein. Notably, while VSMC METTL3 or m6A did not contribute to atherosclerosis, VSMC-specific Mettl14 knockout mice exhibited accelerated foam cell formation, enhanced vascular inflammation, and exacerbated atherosclerosis. These effects were driven by impaired beta-oxidation and reduced mitochondrial oxidative phosphorylation (OXPHOS). Replenishment of Mettl14 significantly attenuated these adverse effects. Specifically, METTL14 regulated phenotypic switching of VSMCs and modulated the number of VSMC-derived macrophage-like cells, rather than infiltrating macrophages, within atherosclerotic plaques. Furthermore, we demonstrated that METTL14 regulates the transcription of Ppara and Pparg, master regulators of lipid metabolism that promote cholesterol efflux, by enhancing SETD1A-mediated H3K4 trimethylation in an m6A-independent manner. Activation of PPAR-γ with rosiglitazone restored impaired mitochondrial OXPHOS in Mettl14-deficient VSMCs, leading to reduced lipid accumulation. Lastly, recapitulating Mettl14 expression in atherosclerotic vessels through AAV gene therapy effectively inhibited atherosclerosis progression without compromising liver function.

We have unveiled that METTL14 promotes lipid metabolism and inhibits atherogenesis through activating PPAR-α/γ expression. These experiments highlight the therapeutic potential of the endogenous METTL14/PPAR-α/γ axis for treating atherosclerotic and metabolic diseases.