Characterization of global gene expression during assurance of lifespan extension by caloric restriction in budding yeast

Caloric restriction (CR) is the best-studied intervention known to delay aging and extend lifespan in evolutionarily distant organisms ranging from yeast to mammals in the laboratory. Although the effect of CR on lifespan extension has been investigated for nearly 80 years, the molecular mechanisms of CR are still elusive. Consequently, it is important to understand the fundamental mechanisms of when and how lifespan is affected by CR. In this study, we first identified the time-windows during which CR assured cellular longevity by switching cells from culture media containing 2% or 0.5% glucose to water, which allows us to observe CR and non-calorically-restricted cells under the same conditions. We also constructed time-dependent gene expression profiles and selected 646 genes that showed significant changes and correlations with the lifespan-extending effect of CR. The positively correlated genes participated in transcriptional regulation, ribosomal RNA processing and nuclear genome stability, while the negatively correlated genes were involved in the regulation of several metabolic pathways, endoplasmic reticulum function, stress response and cell cycle progression. Furthermore, we discovered major upstream regulators of those significantly changed genes, including AZF1 (YOR113W), HSF1 (YGL073W) and XBP1 (YIL101C). Deletions of two genes, AZF1 and XBP1 (HSF1 is essential and was thus not tested), were confirmed to lessen the lifespan extension mediated by CR. The absence of these genes in the tor1Δ and ras2Δ backgrounds did show non-overlapping effects with regard to CLS, suggesting differences between the CR mechanism for Tor and Ras signaling.