Another intervention that slows the aging process is dietary restriction (DR) — a reduction in nutrient intake without malnutrition. DR prolongs lifespan in yeast, worms, flies, rodents, and possibly primates [21, 22 and 23]. In mammals, DR also retards the onset of age-related disease. At the molecular level, the life-extending effects of DR appear to be due largely to inhibition of TOR, as suggested by the findings that TORC1 inhibition mimics starvation and DR does not further selleck chemicals llc extend lifespan in yeast and flies with defective TORC1 signaling [17 and 19]. Moreover, S6K1 knockout mice

are long-lived and display a phenotype similar to that observed upon DR [24]. The TORC1 substrate S6K (Sch9 in yeast) seems to have a pivotal role in regulating lifespan since S6K inhibition extends lifespan in yeast [17 and 25], worms [26, 27, 28 and 29], flies [19], and mice [24]. Furthermore, overexpression of a constitutively active form of S6K in D. melanogaster renders flies resistant to lifespan extension by rapamycin [ 11]. 4E-BP, the

other well-characterized UK-371804 mouse downstream target of TORC1, also mediates protective effects of DR and rapamycin treatment in flies [ 11 and 30]. Consistent with a role of the translation regulators S6K and 4E-BP in modulating lifespan, reduced protein synthesis also extends lifespan in many species [ 26, 27, 31, 32 and 33]. Thus, TORC1 appears to control aging via S6K and 4E-BP and ultimately the regulation of protein synthesis. Importantly, activation of 4E-BP also leads to activation of stress responsive 4-Aminobutyrate aminotransferase genes, such as FoxO and Nrf, and genes encoding the mitochondrial electron transport chain (mETC) [ 10•, 27, 30, 34, 35, 36 and 37]. Upregulation of stress genes exerts a positive effect on lifespan by protecting cells and tissues from age-related

damage [ 35]. Hence, TORC1 may also control aging via modulation of stress responsive genes downstream of 4E-BP. Autophagy has emerged as another downstream process via which TORC1 modulates aging [19 and 38]. Mice with a brain-specific knockout of the autophagy gene Atg5 or Atg7 have shorter lifespan and suffer from an accelerated form of age-related neuronal degeneration [ 39 and 40]. Autophagy also acts as a tumor suppressor. The oncogene BCL-2 binds beclin-1 and thereby suppresses autophagy and promotes tumorigenesis [ 41]. Thus, at least part of the lifespan extending effect of autophagy may be due to its role in cancer suppression. The role of TORC2 in aging is less clear. Extension of lifespan upon TORC2 inactivation has been demonstrated in C. elegans [ 10• and 42•]. The finding that TORC2 inhibition can increase lifespan raises an important question regarding the effects of rapamycin on aging. Is the extension of lifespan by rapamycin due to reduced TORC1, TORC2, or both? Chronic rapamycin treatment can also disrupt mTORC2 in certain cell lines [ 43].