Examining the effect of mitochondrial function manipulation in the development of cellular senescence

Abstract

Mitochondrial dysfunction and cellular senescence are key drivers of ageing and agerelated disease, and are linked by several processes. The mitochondria are essential for the induction of senescence, and oxidative stress from mitochondrial respiratory dysfunction is one of the known triggers of senescence. Senescent cells accumulate with age and secrete pro-inflammatory cytokines and chemokines termed the SenescenceAssociated Secretory Phenotype (SASP), which contributes to tissue dysfunction and disease. However, because cell cycle arrest of damaged cells is a beneficial tumour suppressor mechanism, this study aimed remove the harmful SASP while maintaining cell cycle arrest. To do this I screened inhibitors of the mitochondrial electron transport chain (ETC) to manipulate mitochondrial function at different respiratory complexes and examine the effects on SASP factor production. I found that interrupting electron flow at multiple points in the ETC reduced SASP factor secretion in vitro. Data suggests that this reduction was a result of respiratory inhibition, as SASP factor reduction correlated with oxygen consumption rates. Additional markers of senescence including DNA damage foci, nuclear enlargement and SA-β-Gal activity were reduced following inhibition at respiratory complex I by the biguanide metformin, but cells remained arrested. Finally, I found that long-term treatment of an established senescent phenotype with senostatic drugs metformin and rapamycin, and CIII inhibitor myxothiazol, was sufficient to alleviate the SASP, but not other markers of senescence. Similarly, shorter treatments with myxothiazol or rapamycin after irradiation successfully inhibited secretion of some key SASP factors, but other markers remained unchanged. Overall, this study shows that manipulation of mitochondrial electron transport rescues harmful aspects of the senescent phenotype without allowing cell-cycle re-entry. Moreover, I have provided evidence that treatment timing is key to effectiveness, and that the SASP appears more receptive to reversal than other senescent markers, offering a promising avenue of investigation in age-related disease treatment.