Acute psychological stress increases serum circulating cell-free mitochondrial DNA

•Circulating cell-free mitochondrial DNA (ccf-mtDNA) is released from mitochondria.•Ccf-mtDNA is a pro-inflammatory molecule elevated with aging and inflammatory diseases.•Psychological stress rapidly and selectively increases serum ccf-mtDNA, not ccf-nDNA.•The effect size for stress-induced elevation in serum ccf-mtDNA is larger in men.•Neuroendocrine signaling triggers mtDNA extrusion in primary human fibroblasts. Intrinsic biological mechanisms transduce psychological stress into physiological adaptation that requires energy, but the role of mitochondria and mitochondrial DNA (mtDNA) in this process has not been defined in humans. Here, we show that similar to physical injury, exposure to psychological stress increases serum circulating cell-free mtDNA (ccf-mtDNA) levels. Healthy midlife adults exposed on two separate occasions to a brief psychological challenge exhibited a 2-3-fold increase in ccf-mtDNA, with no change in ccf-nuclear DNA levels, establishing the magnitude and specificity for ccf-mtDNA reactivity. In cell-based studies, we show that glucocorticoid signaling – a consequence of psychological stress in humans – is sufficient to induce mtDNA extrusion in a time frame consistent with stress-induced ccf-mtDNA increase. Collectively, these findings provide evidence that acute psychological stress induces ccf-mtDNA and implicate neuroendocrine signaling as a potential trigger for ccf-mtDNA release. Further controlled work is needed to confirm that observed increases in ccf-mtDNA result from stress exposure and to determine the functional significance of this effect.