MFN2 interacts with phosphorylated AMPK to mediate mitophagy in MCF-7 cells

Mitofusin 2 (MFN2) has been reported to play an important role in mitophagy, but how MFN2 mediates mitophagy remains incompletely understood. Here, we establish that MFN2 upregulation is a key driver of mitophagy in MCF-7 cells. MFN2 overexpression triggers mitochondrial degradation, as verified by multiple mitophagy markers, whereas MFN2 knockdown abolishes the mitophagic response induced by Leflunomide (Lef), a compound that promotes mitophagy by upregulating MFN2. To elucidate the underlying mechanism, fluorescence imaging and subcellular fractionation reveal that MFN2 promotes AMP-activated protein kinase (AMPK) phosphorylation at Thr172 and facilitates translocation of AMPK from the cytoplasm to mitochondria. Quantitative Förster resonance energy transfer (FRET) analysis supports phosphorylation-dependent formation of an MFN2-AMPK complex in cells, and site-directed mutagenesis supports Thr172 phosphorylation dependence, as the phosphomimetic AMPK (T172D) mutant exhibits enhanced complex formation with MFN2, while the phosphodeficient AMPK (T172A) mutant shows little or no complex formation with MFN2. Co-immunoprecipitation further supports an MFN2-AMPK complex in cells. The MFN2-AMPK complex is essential for mitophagy: Compound C, a pharmacological inhibitor of AMPK, prevents both MFN2-AMPK complex formation and mitophagy, even in cells overexpressing MFN2. Notably, AMPK activation through Acadesine (AICAR) treatment is insufficient to induce mitophagy, but it markedly enhances mitophagy markers when combined with MFN2 overexpression. In conclusion, MFN2 mediates efficient mitophagy by recruiting Thr172-phosphorylated AMPK to mitochondria through a phosphorylation-dependent MFN2-AMPK complex.