Mitochondrial OGG1 expression reduces age-associated neuroinflammation by regulating cytosolic mitochondrial DNA.

ABSTRACT

Aging is accompanied by a decline in DNA repair efficiency, which leads to the accumulation of different types of DNA damage. Age-associated chronic inflammation and generation of reactive oxygen species exacerbate the aging process and age-related chronic disorders. These inflammatory processes establish conditions that favor accumulation of DNA base damage, especially 8-oxo-7,8 di-hydroguanine (8-oxoG), which in turn contributes to various age associated diseases. 8-oxoG is repaired by 8-oxoG glycosylase1 (OGG1) through the base excision repair (BER) pathway. OGG1 is present in both the cell nucleus and in mitochondria. Mitochondrial OGG1 has been implicated in mitochondrial DNA repair and increased mitochondrial function. Using transgenic mouse models and cell lines that have been engineered to have enhanced expression of mitochondria-targeted OGG1 (mtOGG1), we show that elevated levels of mtOGG1 in mitochondria can reverse aging-associated inflammation and improve functions. Old male mtOGG1Tg mice show decreased inflammation response, decreased TNFα levels and multiple pro-inflammatory cytokines. Moreover, we observe that male mtOGG1Tg mice show resistance to STING activation. Interestingly, female mtOGG1Tg mice did not respond to mtOGG1 overexpression. Further, HMC3 cells expressing mtOGG1 display decreased release of mtDNA into the cytoplasm after lipopolysacchride induction and regulate inflammation through the pSTING pathway. Also, increased mtOGG1 expression reduced LPS-induced loss of mitochondrial functions. These results suggest that mtOGG1 regulates age-associated inflammation by controlling release of mtDNA into the cytoplasm.