Overexpression of Nicotinamide phosphoribosyltransferase in mouse cells confers protective effect against oxidative and ER stress-induced premature senescence.

A main feature of aged organisms is the accumulation of senescent cells. Accumulated senescent cells, especially stress-induced premature senescent cells, in aged organisms lead to the decline of the regenerative potential and function of tissues. We recently reported that the over-expression of NAMPT, which is the rate-limiting enzyme in mammalian NAD(+)salvage pathway, delays replicative senescence in vitro. However, whetherNampt-overexpressing cells are tolerant of stress-induced premature senescence remains unknown. Here, we show that primary mouse embryonic fibroblasts derived fromNampt-overexpressing transgenic mice (NamptTg-MEF cells) possess resistance against stress-induced premature senescence in vitro. We found that higher oxidative or endoplasmic reticulum (ER) stress is required to induce premature senescence inNamptTg-MEF cells compared to wild-type cells. Moreover, we found thatNamptTg-MEF cells show acute expression of unfolded protein response (UPR)-related genes, which in turn would have helped to restore proteostasis and avoid cellular senescence. Our results demonstrate that NAMPT/NAD(+)axis functions to protect cells not only from replicative senescence, but also from stress-induced premature senescence in vitro. We anticipate that in vivo activation of NAMPT activity or increment of NAD(+)would protect tissues from the accumulation of premature senescent cells, thereby maintaining healthy aging.