METTL3-m6A-MALAT1 axis exacerbates the autophagy impairment and lipid accumulation in NAFLD by regulating miR-690

Non-alcoholic fatty liver disease (NAFLD) has become the fastest-growing etiology of cirrhosis and hepatocellular carcinoma. No Food and Drug Administration (FDA)-approved pharmacotherapy currently exists, underscoring the urgent need for novel regulatory circuits that can be translated into druggable targets. Here we demonstrate that autophagic flux is severely impaired and lipid accumulation markedly exacerbated in livers of NAFLD mouse models and in hepatocytes challenged with free fatty acid (FFA). Knock-down of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) elevated miR-690 abundance, restored autophagic flux, and attenuated intracellular lipid deposition. Consistently, silencing methyltransferase-like 3 (METTL3) decreased MALAT1, thereby increasing miR-690 and producing the same protective phenotype, whereas METTL3 over-expression elicited the opposite effects. Mechanistically, METTL3 directly bound MALAT1 and installed N6-methyladenosine (m6A) modifications that enhanced MALAT1 stability and expression. Up-regulated MALAT1 subsequently sponged miR-690, leading to its functional depletion, autophagosome-lysosome fusion blockade, and aggravated lipid retention. Collectively, the METTL3-m6A/MALAT1/miR-690 axis orchestrates autophagy and lipid homeostasis, operationalizing an "m6A-long non-coding RNA (lncRNA)-microRNA (miRNA)" regulatory paradigm in NAFLD and offering an epitranscriptomic perspective on disease pathogenesis.