Aging-associated mitochondrial circular RNAs

During mammalian aging, there are changes in abundance of noncoding RNAs including microRNAs, long noncoding RNAs, and circular RNAs. Although global profiles of the human transcriptome and epitranscriptome during the aging process are available, the existence and function of mitochondrial circular RNAs originating from the mitochondrial genome are poorly studied. Here, we report profiles of circular RNAs annotated to mitochondrial chromosome, chrM, in young and old cohorts. The most abundant circular RNA junctions are found in MT-RNR2, whose level is depleted in old cohorts and senescent fibroblast. The mitochondria-localized RNA-binding protein GRSF1 binds various mitochondrial transcripts, including linear and circular MT-RNR2, with a distinct RNA motif. Linear and circular MT-RNR2 bind a subset of TCA cycle enzymes, suggesting their possible function in regulating glucose metabolism in mitochondria to preserve proliferating status in young cohorts. In human fibroblasts, depletion of GRSF1 reduced levels of circMT-RNR2 and fumarate/succinate, concomitantly accelerating cellular senescence and mitochondrial dysfunction. Taken together, our findings demonstrate the existence and possible function of circular MT-RNR2 during human aging and senescence, implicating its role in promoting the TCA cycle.