A Comprehensive Analysis of Replicative Lifespan in 4,698 Single-Gene Deletion Strains Uncovers Conserved Mechanisms of Aging

Many genes that affect replicative lifespan (RLS) in the budding yeast Saccharomyces cerevisiae also affect aging in other organisms such as C. elegans and M. musculus. We performed a systematic analysis of yeast RLS in a set of 4,698 viable single-gene deletion strains. Multiple functional gene clusters were identified, and full genome-to-genome comparison demonstrated a significant conservation in longevity pathways between yeast and C. elegans. Among the mechanisms of aging identified, deletion of tRNA exporter LOS1 robustly extended lifespan. Dietary restriction (DR) and inhibition of mechanistic Target of Rapamycin (mTOR) exclude Los1 from the nucleus in a Rad53-dependent manner. Moreover, lifespan extension from deletion of LOS1 is nonadditive with DR or mTOR inhibition, and results in Gcn4 transcription factor activation. Thus, the DNA damage response and mTOR converge on Los1-mediated nuclear tRNA export to regulate Gcn4 activity and aging.

Cardiomyocyte-specific expression of lamin a improves cardiac function in Lmna-/- mice

Lmna(-/-) mice display multiple tissue defects and die by 6-8 weeks of age reportedly from dilated cardiomyopathy with associated conduction defects. We sought to determine whether restoration of lamin A in cardiomyocytes improves cardiac function and extends the survival of Lmna(-/-) mice. We observed increased total desmin protein levels and disorganization of the cytoplasmic desmin network in ~20% of Lmna(-/-) ventricular myocytes, rescued in a cell-autonomous manner in Lmna(-/-) mice expressing a cardiac-specific lamin A transgene (Lmna(-/-); Tg). Lmna(-/-); Tg mice displayed significantly increased contractility and preservation of myocardial performance compared to Lmna(-/-) mice. Lmna(-/-); Tg mice attenuated ERK1/2 phosphorylation relative to Lmna(-/-) mice, potentially underlying the improved localization of connexin43 to the intercalated disc. Electrocardiographic recordings from Lmna(-/-) mice revealed arrhythmic events and increased frequency of PR interval prolongation, which is partially rescued in Lmna(-/-); Tg mice. These findings support our observation that Lmna(-/-); Tg mice have a 12% median extension in lifespan compared to Lmna(-/-) mice. While significant, Lmna(-/-); Tg mice only have modest improvement in cardiac function and survival likely stemming from the observation that only 40% of Lmna(-/-); Tg cardiomyocytes have detectable lamin A expression. Cardiomyocyte-specific restoration of lamin A in Lmna(-/-) mice improves heart-specific pathology and extends lifespan, demonstrating that the cardiac pathology of Lmna(-/-) mice limits survival. The expression of lamin A is sufficient to rescue certain cellular defects associated with loss of A-type lamins in cardiomyocytes in a cell-autonomous fashion.

Sir2 deletion prevents lifespan extension in 32 long-lived mutants

Activation of Sir2 orthologs is proposed to increase lifespan downstream of dietary restriction. Here, we describe an examination of the effect of 32 different lifespan-extending mutations and four methods of DR on replicative lifespan (RLS) in the short-lived sir2Δ yeast strain. In every case, deletion of SIR2 prevented RLS extension; however, RLS extension was restored when both SIR2 and FOB1 were deleted in several cases, demonstrating that SIR2 is not directly required for RLS extension. These findings indicate that suppression of the sir2Δ lifespan defect is a rare phenotype among longevity interventions and suggest that sir2Δ cells senesce rapidly by a mechanism distinct from that of wild-type cells. They also demonstrate that failure to observe lifespan extension in a short-lived background, such as cells or animals lacking sirtuins, should be interpreted with caution.

Yeast life span extension by depletion of 60s ribosomal subunits is mediated by Gcn4

In nearly every organism studied, reduced caloric intake extends life span. In yeast, span extension from dietary restriction is thought to be mediated by the highly conserved, nutrient-responsive target of rapamycin (TOR), protein kinase A (PKA), and Sch9 kinases. These kinases coordinately regulate various cellular processes including stress responses, protein turnover, cell growth, and ribosome biogenesis. Here we show that a specific reduction of 60S ribosomal subunit levels slows aging in yeast. Deletion of genes encoding 60S subunit proteins or processing factors or treatment with a small molecule, which all inhibit 60S subunit biogenesis, are each sufficient to significantly increase replicative life span. One mechanism by which reduced 60S subunit levels leads to life span extension is through induction of Gcn4, a nutrient-responsive transcription factor. Genetic epistasis analyses suggest that dietary restriction, reduced 60S subunit abundance, and Gcn4 activation extend yeast life span by similar mechanisms.