Impairment of mitochondrial unfolded protein response contribute to resistance declination of H O -induced injury in senescent MRC-5 cell model.

Accumulation of oxidative proteins within mitochondria leads to loss of mitochondrial function, which may lead to age-related degenerative diseases. Mitochondrial antioxidant defense capacity reflects the expression of mitochondrial unfolded protein response (mtUPR)-related proteins. Senescent cells are considered to be less resistant to cellular stress stimuli than exponentially growing cells. In this study, we aimed to investigate the ability of mitochondrial stress response in senescent cells to cope with the accumulation of mitochondrial unfolded proteins induced by hydrogen peroxide (H O ) and to understand the relevant molecular mechanisms. We report here that senescence-associated β-galactosidase (SA-β-gal) and senescence marker protein-30 (SMP-30), commonly used replicative senescence biomarkers, changed remarkably between population doubling (PD) 25 (exponentially growing cells) and PD50 (senescent cells) of MRC-5 fibroblasts. Mitochondrial unfolded proteins were significantly accumulated in H O -treated senescent cells, whereas mtUPR-related molecular chaperones (heat shock protein Hsp60 and Hsp10) and proteases (caseinolytic Clp protease) were not concomitantly elevated in senescent cells. In addition, decreased expression of stromal interacting molecule 1-Orai1-mediated store-operated Ca entry following an declined intracellular calcium level after 2 mM calcium treatment together with H O addition, implying impairment of calcium influx in senescent MRC-5 during H O -induced injury. These findings suggest that senescent fibroblasts expressed higher vulnerability to H O -induced injury involving the imbalance of calcium homeostasis and impaired mitochondrial nuclear communication. This may provide useful information for the future development of therapeutic agents to prevent the adverse effects of aging on cells and the potential for treatment of proteinopathies in the elderly.