Mitochondrial NAD ⁺ -mediated mitophagy alleviates type I interferon response to the cytosolic mitochondrial dna

Mitochondrial nicotinamide adenine dinucleotide (NAD⁺) plays a central role in energy metabolism, yet its roles and mechanisms in mitophagy and innate immunity remain poorly understood. In this study, we identify mitochondrial NAD⁺ depletion that causes mitophagy dysfunction and inflammation. We find that depletion of mitochondrial NAD⁺ owing to deficiency of the mitochondrial NAD⁺ transporter SLC25A51 impairs BNIP3-mediated mitophagy. Loss of mitochondrial NAD⁺ inhibits SIRT3-mediated deacetylation of FOXO3, leading to transcriptional downregulation of BNIP3 and subsequent disruption of MAP1LC3B/LC3B recruitment. Notably, mitochondrial NAD⁺ depletion promotes mitochondrial DNA (mtDNA) release from mitochondria to the cytosol upon oxidative stress, thereby exacerbating the type I interferon response to free cytosolic mtDNA via activation of the CGAS-STING1 signaling pathway. Our findings reveal a novel mechanistic link among mitochondrial NAD⁺, mitophagy, and mtDNA-induced inflammation by genetic manipulation of cell lines, highlighting mitochondrial NAD⁺ as a potential therapeutic target for mitigating sterile inflammation triggered by free cytosolic mtDNA. Thus, the study provides new insights into the crosstalk among mitochondrial homeostasis, inflammation, and innate immunity.