Elevated Trehalose Levels in C. elegans daf-2 Mutants Increase Stress Resistance, Not Lifespan

Abstract

The C. elegans insulin/IGF-1 (insulin-like growth factor 1) signaling mutant daf-2 recapitulates the dauer metabolic signature-a shift towards lipid and carbohydrate accumulation-which may be linked to its longevity and stress resistance phenotypes. Trehalose, a disaccharide of glucose, is highly upregulated in daf‑2 mutants and it has been linked to proteome stabilization and protection against heat, cold, desiccation, and hypoxia. Earlier studies suggested that elevated trehalose levels can explain up to 43% of the lifespan extension observed in daf-2 mutants. Here we demonstrate that trehalose accumulation is responsible for increased osmotolerance, and to some degree thermotolerance, rather than longevity in daf-2 mutants. This indicates that particular stress resistance phenotypes can be uncoupled from longevity.

Keywords: Caenorhabditis elegans; glucose; glycogen; lifespan; maltose; trehalose; trehalose 6-phosphate synthase.

Figure 1

Expression patterns for tps-1 and tps-2: (A) tps expression based on transcriptional profiling data from [35]. Note that scales of tps-1 and tps-2 bar graphs differ tenfold. (B) Transcriptional tps-1p::gfp reporter strain fed with E. coli HT115 expressing empty vector (a–c) and daf-2 RNAi (d,e). (C) Transcriptional tps-2p::gfp reporter strain fed with E. coli HT115 expressing empty vector (a–c) and daf-2 RNAi (d–f). HN, head neuron; CAN, Canal-associated neuron; SIM, stomatointestinal muscle; AD, anal depressor muscle; INT, intestine; GS, gonadal sheath; CN, ciliated neuron; BWM, body wall muscle; HYP, hypodermis. Scale bars are 25 µm.

Figure 2

The effect of trehalose synthesis capacity on daf-2(e1370) longevity: (A–E) Tissue-specific RNAi of tps genes, (A) systemic RNAi, (B) intestine-specific RNAi, (C) muscle-specific RNAi, (D) hypodermis-specific RNAi, (E) germline-specific RNAi. Tissue-specific RNAi strains used are listed in Table S1. (F) Lifespan of the double tps deletion mutant tps-1(ok373);tps-2(ok526) in a wild-type and daf-2(e1370) background. All data are summarized in Table S2.

Figure 3

The role of tps-1 and tps-2 in worm carbohydrate levels: (A) tps-1 and/or tps-2 RNAi in wild-type N2 and daf-2(e1370) mutants—EV is empty vector control; (B) carbohydrates levels in OP50-fed daf-2(e1370) and daf-2(e1370);tps-1(ok373);tps-2(ok526). All error bars indicate SEM of three independent replicates. * p ≤ 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. Data of all replicates are summarized in Table S3.

Figure 4

The role of double tps deletion tps-1(ok373);tps-2(ok526) in stress resistance of wild-type N2 and daf-2(e1370): Stress survival measured with the LFASS method [44] (A) oxidative stress, 0.28% tert-butyl hydroperoxide (TBHP); (B) heat stress, 40 °C; (C) osmotic stress survival 500 mM NaCl. Error bars in (A,B) indicate SEM of three independent replicates. ns: p > 0.05, * p ≤ 0.05. Survival data of all replicates are summarized in Table S4.