Autophagy Impairment Induces Premature Senescence in Primary Human Fibroblasts

Abstract

BackgroundRecent studies have demonstrated that activation of autophagy increases the lifespan of organisms from yeast to flies. In contrast to the lifespan extension effect in lower organisms, it has been reported that overexpression of unc-51-like kinase 3 (ULK3), the mammalian homolog of autophagy-specific gene 1 (ATG1), induces premature senescence in human fibroblasts. Therefore, we assessed whether the activation of autophagy would genuinely induce premature senescence in human cells.Methodology/Principal FindingsDepletion of ATG7, ATG12, or lysosomal-associated membrane protein 2 (Lamp2) by transfecting siRNA or infecting cells with a virus containing gene-specific shRNA resulted in a senescence-like state in two strains of primary human fibroblasts. Prematurely senescent cells induced by autophagy impairment exhibited the senescent phenotypes, similar to the replicatively senescent cells, such as increased senescence associated β-galactosidase (SA-β-gal) activity, reactive oxygen species (ROS) generation, and accumulation of lipofuscin. In addition, expression levels of ribosomal protein S6 kinase1 (S6K1), p-S6K1, p-S6, and eukaryotic translation initiation factor 4E (eIF4E) binding protein 1 (4E-BP1) in the mammalian target of rapamycin (mTOR) pathway and beclin-1, ATG7, ATG12-ATG5 conjugate, and the sequestosome 1 (SQSTM1/p62) monomer in the autophagy pathway were decreased in both the replicatively and the autophagy impairment-induced prematurely senescent cells. Furthermore, it was found that ROS scavenging by N-acetylcysteine (NAC) and inhibition of p53 activation by pifithrin-α or knockdown of p53 using siRNA, respectively, delayed autophagy impairment-induced premature senescence and restored the expression levels of components in the mTOR and autophagy pathways.ConclusionTaken together, we concluded that autophagy impairment induces premature senescence through a ROS- and p53-dependent manner in primary human fibroblasts.

Chronic stress induces ageing-associated degeneration in rat Leydig cells

“…37,38 In the present study, Leydig cells from either the young control or the stressed rats stained blue after 5 h of SA-bgal staining; similar results were obtained with the aged Leydig cells (data not shown). Therefore, SA-bgal staining was not an appropriate method to distinguish between young and senescent Leydig cells.…”

Senescence associated secretory phenotype profile from primary lung mice fibroblasts depends on the senescence induction stimuli

“…Various pathways have been proposed to explain senescence induction; the most studied is replicative senescence due to telomere shortening (Cristofalo et al 2004;Rodier et al 2009Rodier et al , 2010, along with other prematureinduced senescence provoked by diverse stimuli such as oxidative stress and radiation exposure (Toussaint et al 2000;López-Diazguerrero et al 2006;Lee et al 2011), autophagy impairment (Kang et al 2011;Fujii et al 2012), proteasome inhibition (Torres et al 2006;Bitto et al 2010), and oncogenic stress (Bartkova et al 2006). Fig.…”

“…al. 2000), along with oncogenic stress (Bartkova et al 2006), proteasome inhibition (Torres et al 2006;Bitto et al 2010), or mitophagy impairment (Kang et al 2011;Fujii et al 2012).…”

p62/SQSTM1 at the interface of aging, autophagy, and disease

“…p16 INK4A is a marker of cellular senescence (Alcorta et al 1996), a terminal proliferative arrest triggered by a series of insults, including oxidative stress. Interestingly, autophagy impairment causes cellular senescence and accumulation of p16 INK4A in human fibroblasts, because of increased oxidative stress from the mitochondria (Kang et al 2011). Thus, loss of p62/SQSTM1 in the elderly may further reduce the production of insulin by promoting cellular senescence in β cells and thus diminishing their regenerative capacity.…”

“…In addition, autophagy is required for chronological lifespan extension in yeast (Alvers et al 2009), and for the longevity response to DR and reduced TOR and insulin signaling in C. elegans, even though its induction alone is not sufficient to extend lifespan (Hansen et al 2008). Inhibiting autophagy triggers premature cellular senescence in human fibroblasts (Kang et al 2011), but it is also required for the senescence transition in response to oncogenic signaling (Young et al 2009), suggesting that autophagy could have pleiotropic effects. Indeed, excessive activation of autophagy can be deleterious and cause cell death independently of apoptosis (Pattingre et al 2005).…”