Fig. 1: Enhanced mTORC1 activation in ISCs/TA cells of geriatric mice drives villus natural aging.

a–d Seventeen and half-month-old mice showed deterioration in villus and crypt structures (right panels: quantitation data) (a), decreased nutrient absorption activities (b), increased sensitivity to IR-induced decreases in the numbers of crypts and proliferating cells at day 2 post IR (c), and compromised regeneration (decreases in the height and number of villi and crypts) at day 6 (d) compared with young mice, which were partially rescued by 1.5 months of RAP treatment (3 mg/kg body weight) starting at 16 months of age. Data are expressed as mean ± SEM. N = 5 mice per group. *P < 0.05, **P < 0.01 (determined using Student’s t test). e Seventeen and half-month-old mice showed decreases in the height and number of crypts and the number of proliferating TA cells (based on (a)), which were rescued by RAP. Data are expressed as mean ± SEM. N = 5 mice per group. *P < 0.05, **P < 0.01 (determined using Student’s t test). f Representative images (proximal jejunum midline sections) showed that mTORC1 activation was increased with age in crypt cells. g Western blot results showed that mTORC1 activation was increased in the crypt samples of 17.5-month-old mice compared with 3.5-month-old mice. Isolated crypts were directly lysed and used for WB analysis. Data are expressed as mean ± SEM. N = 3 mice per group. *P < 0.05, **P < 0.01 (determined using Student’s t test). h More Lgr5⁺ ISCs isolated from 17.5-month-old mice showed mTORC1 activation than those from 3.5-month-old mice, which was suppressed by RAP treatment. Lgr5⁺ ISCs were isolated from the small intestines of Lgr5-GFP-CreERT mice with FACS sorting and stained for p-S6. Right panel: quantification data (mean ± SEM). N = 6 mice per group. **P < 0.01 (determined using Student’s t test).