Rapamycin extends life and health in C57BL/6 mice

Abstract

Target of rapamycin inhibition by rapamycin feeding has previously been shown to extend life in genetically heterogeneous mice. To examine whether it similarly affected mouse health, we fed encapsulated rapamycin or a control diet to C57BL/6Nia mice of both sexes starting at 19 months of age. We performed a range of health assessments 6 and 12 months later. Rapamycin feeding significantly reduced mTOR activity in most but not all tissues. It also reduced total and resting metabolic rate during the light (inactive) phase of the light:dark cycle in females only but had no effect on spontaneous activity or metabolism during the dark (active) phase of either sex. Males only had less fragmented sleep when fed rapamycin, whereas stride length and rotarod performance were improved in both sexes. Survival was also improved by this late-life rapamycin feeding, and some pathological lesions were delayed. We found no adverse health consequences associated with rapamycin treatment.

Keywords: Aging; Health span; Rapamycin; Sex differences..

Figure 1.

Inhibition of mTOR signaling and proteasome activity and enhancement of autophagy in multiple tissues of rapamycin-fed mice. (A and B) Effect of rapamycin on S6 and phosphorylated S6 (pS6). Cortex = brain cortex. (C) Effect of rapamycin on autophagy and proteasome activity. N > 12 in all cases. *p < .05.

Figure 2.

Body composition and rapamycin feeding. Total body mass is lower in (A) rapamycin-fed males at 25 mo of age (rapamycin treatment for 6 mo), but the mass difference gradually disappears with increasing age; however, rapamycin-fed males appear to maintain body mass at older ages compared with controls Treatment • Age • Sex p = .001. (B) Rapamycin-fed and control females do not differ in body mass at any age although both groups’ body mass declines with age. (C and D) Rapamycin feeding does not affect percent body fat in either sex at any age.

Figure 3.

Energetics and activity. (A) Metabolic rate was significantly reduced in females only by rapamycin feeding during the light (inactive) phase of 24-h light:dark cycle and when mice were resting; however, there was no effect during the dark (active) phase. Note that metabolic rate increased with age irrespective of treatment, and females always exhibited higher metabolic rate than males. (B) Total activity showed no clear pattern with age and was not affected by rapamycin feeding. (C) Sleep was increasingly fragmented with age (greater number of sleep bouts per hour of sleep), but rapamycin-fed males had less fragmented sleep than controls.

Figure 4.

Motor and muscular function. (A) Stride length declined with age in controls but showed no change in rapamycin-fed mice. (B) Grip strength was not affected by rapamycin feeding. (C) Rotarod performance improved with rapamycin feeding with similar patterns among the sexes. (D) There were no significant differences in hind-limb muscle mass between rapamycin-fed and control animals of either sex at 25 mo of age (6 mo of rapamycin treatment). Wet weight of each individual muscle normalized to whole-body weight (n = 18–23). Gast = gastrocnemius; TA = tibialis anterior; Quad = quadriceps.

Figure 5.

Survival. (A) Male control (n = 44) control and rapamycin-fed (n = 45), (B) Female control (n = 43) and rapamycin-fed (n = 45), and (C) Both sexes combined control (n = 87) and rapamycin fed (n = 90). Controls are shown in grey and rapamycin-fed mice in black. The survival curves were compared using the Cox-Mantel log-rank test, the p-values for males, females, and the sexes combined are shown; sex • treatment interaction was not significant (p = .532). A more powerful Cox Proportional Hazards Model found a significant effect of rapamycin feeding (p = .01) and sex (p = .02). See text for details.

Figure 6.

Effect of rapamycin on pathology burden in females. (A) Neoplastic lesion burden increases with age but is significantly lower in rapamycin-fed females than controls (p = .008, false discovery rate = 4.1%). (B) Adenoma burden also increases with age but is significantly lower in rapamycin-fed females than controls (p = .04, false discovery rate = 9.7%). Box plots mean and 75% CI, whiskers 95% CI sample size within box.