Long‐lived Snell dwarf mice display increased proteostatic mechanisms that are not dependent on decreased mTORC1 activity

Abstract

Maintaining proteostasis is thought to be a key factor in slowed aging. In several growth-restricted models of long-life, we have shown evidence of increased proteostatic mechanisms, suggesting that proteostasis may be a shared characteristic of slowed aging. The Snell dwarf mouse is generated through the mutation of the Pit-1 locus causing reductions in multiple hormonal growth factors and mTORC1 signaling. Snell dwarfs are one of the longest lived rodent models of slowed aging. We hypothesized that proteostatic mechanisms would be increased in Snell compared to control (Con) as in other models of slowed aging. Using D2O, we simultaneously assessed protein synthesis in multiple subcellular fractions along with DNA synthesis in skeletal muscle, heart, and liver over 2 weeks in both sexes. We also assessed mTORC1-substrate phosphorylation. Skeletal muscle protein synthesis was decreased in all protein fractions of Snell compared to Con, varied by fraction in heart, and was not different between groups in liver. DNA synthesis was lower in Snell skeletal muscle and heart but not in liver when compared to Con. The new protein to new DNA synthesis ratio was increased threefold in Snell skeletal muscle and heart compared to Con. Snell mTORC1-substrate phosphorylation was decreased only in heart and liver. No effect of sex was seen in this study. Together with our previous investigations in long-lived models, we provide evidence further supporting proteostasis as a shared characteristic of slowed aging and show that increased proteostatic mechanisms may not necessarily require a decrease in mTORC1.

Enhanced skeletal muscle regrowth and remodelling in massaged and contralateral non‐massaged hindlimb

“…For analysis of protein, tissues were fractionated according to our previously published procedures (Drake et al . , , ). Skeletal muscle tissue was homogenized 1:10 in isolation buffer (100 m m KCl, 40 m m Tris–HCl, 10 m m Tris base, 5 m m MgCl 2 , 1 m m EDTA, 1 m m ATP, pH 7.5) with phosphatase and protease inhibitors (Halt, Thermo Fisher Scientific, Waltham, MA, USA) using a bead homogenizer (Next Advance Inc., Averill Park, NY, USA).…”

“…After homogenization, subcellular fractions were isolated via differential centrifugation as previously described (Drake et al . , , ). Once protein pellets were isolated and purified, 250 μl 1 m NaOH was added and pellets were incubated for 15 min at 50°C while slowly mixing.…”

Mitochondrial proteostasis as a shared characteristic of slowed aging: the importance of considering cell proliferation

“…; Drake et al . , , ). Further, DNA synthesis decreases to a greater degree than protein synthesis thus indicating that a greater proportion of protein synthesis is directed toward maintaining existing cellular structures (somatic maintenance) and less toward proliferation (growth).…”

“…Since our study in calorically restricted mice, we have made similar assessments in multiple long‐lived models (Drake et al . , , ; Miller et al . , ).…”

Mechanisms of protein balance in skeletal muscle

“…Current evidence suggests that dietary restriction or reductions in insulin/IGF-I signaling improves proteostasis in association with increased life span [20,109–111]. However, these life span benefits can associate with reduced fertility and/or increased development time [112,113].…”