Senescent glia link neuronal mitochondrial dysfunction and lipid droplet accumulation with age [19082_28_MASTER]

Senescence is a cellular state linked to aging and age-onset disease across many mammalian species. Acutely, senescent cells promote wound healing and prevent tumor formation; but they are also pro-inflammatory, thus chronically exacerbate tissue decline. While senescent cells are active targets for anti-aging therapy, why these cells form in vivo, how they affect tissue aging, and the impact of their elimination remain unclear. Here we identify naturally-occurring senescent glia in aged Drosophila brains and decipher their origin and influence. Using AP1 activity to screen for senescence, we determine that senescent glia can appear in response to neuronal mitochondrial dysfunction. In turn, senescent glia promote lipid accumulation in non-senescent glia; similar effects are seen in senescent human fibroblasts in culture. Targeting AP1 activity in senescent glia mitigates senescence biomarkers, extends fly life and health span, and prevents lipid accumulation. However, these benefits come at the cost of increased oxidative damage in the brain, and neuronal mitochondrial function remains poor. Altogether, our results map the trajectory of naturally-occurring senescent glia in vivo and indicate that these cells link key aging phenomena: mitochondrial dysfunction and lipid accumulation. Through bulk-RNA-seq and a targeted RNAi screen, we determined that loss of select mitochondrial genes in neurons can trigger AP1 activity in glia. To determine if neuronal RNAi-induced AP1+ glia have features of senescence, we FACS-sorted and bulk-RNA-sequenced dsRed+ and dsRedneg cells from brains of 10d old flies with neuronal loss of inner complex genes. For this, an inducible pan-neuronal driver (elav-GeneSwitch) was used to express UAS-RNAi (UAS-ND42-RNAi or UAS-NP15.6-RNAi); cells with AP1 activity were identified using a genomic fluorescent reporter under the control of an AP1 binding motif (dsRed). Whole brains were dissected from 10d flies, dissociated into a cell suspension then dsRed+ and dsRedneg cells were FACS-isolated and bulk RNA-sequenced for downstream gene expression analysis (n=500 cells per biological replicate, 4 replicates).