NAD Deficiency Triggers a Fake Viral Alarm Via Mitochondrial DNA Leakage

NAD is a critical coenzyme underpinning energy metabolism, DNA repair, and cell signaling, and its levels decline with aging and in numerous diseases. While acute NAD depletion (typically via pharmacological inhibition of NAMPT) has been studied extensively, the cellular consequences of slow, chronic NAD deficiency — more representative of aging and nutritional deficiency — were poorly understood.

To model chronic NAD depletion, researchers at Mayo Clinic cultured NIH3T3 mouse fibroblasts in media stripped of nicotinamide (NAM), the primary NAD precursor, using dialyzed fetal bovine serum to eliminate residual NAM from the medium. Within two days, intracellular NAD+ fell to roughly 10% of control levels, and by day 12 it was nearly undetectable. Broader NAD-related metabolites — including NMN, NR, NAM, and ADPR — were all substantially reduced. Critically, cells survived up to 28 days under these conditions without significant apoptosis, necrosis, or senescence, though their proliferation rate declined progressively. ATP levels dropped to about 60% of controls, indicating partial metabolic compensation.

The most striking finding was that chronic NAD depletion triggered a robust interferon-dependent inflammatory gene expression program resembling a viral infection response. Transcriptomic analysis revealed strong upregulation of interferon-stimulated genes (ISGs) and type I interferon signaling pathways. Mechanistically, NAD depletion caused mitochondrial dysfunction — including reduced spare respiratory capacity and maximal mitochondrial respiration, along with impaired glycolysis — and increased mitochondrial mass. This mitochondrial stress led to cytosolic leakage of mitochondrial DNA (mtDNA) through oligomerized VDAC1 channels. The escaped mtDNA was detected as a danger signal by cytosolic cGAS, activating STING and downstream interferon gene expression. Blocking VDAC1 oligomerization with VBIT-4, inhibiting STING with H-151, or depleting cellular mtDNA all abolished the interferon response induced by NAM depletion, confirming the causal chain: NAD depletion → mitochondrial stress → VDAC1-mediated mtDNA release → cGAS-STING activation → interferon response.

These results were reproduced in IMR90 human lung fibroblasts and HS5 human stromal cells, indicating the phenomenon is not species- or cell-type-specific. The authors also observed compensatory upregulation of NAD synthesis enzymes (NAMPT, NMNAT3) and the nucleoside transporter ENT2, while NAD-consuming enzymes CD38, CD157, and SIRT3 were downregulated. Metabolomic profiling confirmed broad metabolic reprogramming under chronic NAD depletion.

These findings are significant because NAD decline is a well-documented feature of aging and chronic disease, and the cGAS-STING-interferon axis is increasingly recognized as a driver of inflammaging. The study provides a direct mechanistic link between NAD deficiency and sterile inflammation, and identifies VDAC1, cGAS, and STING as potential therapeutic targets for conditions where NAD decline contributes to pathology.