Sestrins orchestrate cellular metabolism to attenuate aging

Abstract

The Sestrins constitute a family of evolutionarily conserved stress-inducible proteins that suppress oxidative stress and regulate AMP-dependent protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling. By virtue of these activities, the Sestrins serve as important regulators of metabolic homeostasis. Accordingly, inactivation of Sestrin genes in invertebrates resulted in diverse metabolic pathologies, including oxidative damage, fat accumulation, mitochondrial dysfunction, and muscle degeneration, that resemble accelerated tissue aging. Likewise, Sestrin deficiencies in mice led to accelerated diabetic progression upon obesity. Further investigation of Sestrin function and regulation should provide new insights into age-associated metabolic diseases, such as diabetes, myopathies, and cancer.

Figure 1. Regulation of Oxidative Metabolism by Sestrin-Family Proteins

(A) Regulation of Sestrin expression by oxidative stress. Although p53 is essential for Sestrin1 expression after oxidative stress, it is dispensable for induction of Sestrin2 and Sestrin3. While Nrf2 and AP-1 are required for Sestrin2 induction, FoxO1 and FoxO3 are required for Sestrin3 induction upon oxidative stress. (B) Signaling pathways through which Sestrins control oxidative stress. Sestrins can recycle peroxiredoxin (Prx) as a part of an oxidoreductase enzyme complex that includes sulfiredoxin (Srx). Alternatively, Sestrins activate an antioxidant transcriptional program by stabilizing Nrf2 through removal of its inhibitor Keap1. Sestrin-induced AMPK activation can lead to activation of PPARγ coactivator 1α (PGC1α) resulting in increased mitochondrial biogenesis, whereas Sestrin-mediated AMPK activation can lead to upregulation of autophagy that removes dysfunctional mitochondria (mitophagy). Through these activities Sestrins decrease ROS accumulation and stimulate anti-oxidant defenses.

Figure 2. Regulation of Nutrient-Sensing Signaling Pathways by Sestrins

Sestrins control metabolism through AMPK and mTORC1. Sestrins potentiate AMPK activation and thereby suppress mTORC1 activity, leading to inhibition of cellular anabolism and augmentation of catabolic processes such as beta-oxidation and autophagy. Abbreviations: TBC1D1, TBC1 domain family member 1; GS, glycogen synthase; CRTC2, CREB regulated transcription coactivator 2; PKFB, fructose-6-phosphate kinase; ACC2, acetyl-coA carboxylase 2; HMGCR, HMG-CoA reductase; CAD, carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase.

Figure 3. Regulation of Insulin Signaling by Sestrins

Sestrin-enhanced activation of AMPK liberates insulin signaling from mTORC1-mediated inhibitory effects. Abbreviations: CR, caloric restriction; InR, insulin receptor; IRS, insulin receptor substrate, PDK, phosphoinositide-dependent kinase; Grb10, Growth factor receptor-bound protein 10.