Circulating mitochondrial DNA increases with age and is a familiar trait: Implications for "inflamm-aging".

Mitochondrial components, including mitochondrial DNA (mtDNA), when released extracellularly, can act as "damage-associated molecular pattern" (DAMP) agents and cause inflammation. As many elderly people are characterized by a low-grade, chronic inflammatory status defined "inflamm-aging," we evaluated if circulating mtDNA can contribute to this phenomenon. Eight hundred and thirty-one Caucasian subjects were enrolled in the study, including 429 siblings aged 90-104 (90+ siblings). mtDNA plasma levels increased gradually after the fifth decade of life. In 90+ subjects, mtDNA values of two members of the same sibling relationship were directly correlated, suggesting a role for familiar/genetic background in controlling the levels of circulating mtDNA. The subjects with the highest mtDNA plasma levels had the highest amounts of TNF-α, IL-6, RANTES, and IL-1ra; the subjects with the lowest mtDNA levels had the lowest levels of the same cytokines. In vitro stimulation of monocytes with mtDNA concentrations similar to the highest levels observed in vivo resulted in an increased production of TNF-α, suggesting that mtDNA can modulate the production of proinflammatory cytokines. Our findings therefore show that circulating mtDNA increases with age, and can significantly contribute to the maintenance of the low-grade, chronic inflammation observed in elderly people.