Metabolic shift from glycogen to trehalose promotes lifespan and healthspan in Caenorhabditis elegans

Abstract

As Western diets continue to include an ever-increasing amount of sugar, there has been a rise in obesity and type 2 diabetes. To avoid metabolic diseases, the body must maintain proper metabolism, even on a high-sugar diet. In both humans and Caenorhabditis elegans, excess sugar (glucose) is stored as glycogen. Here, we find that animals increased stored glycogen as they aged, whereas even young adult animals had increased stored glycogen on a high-sugar diet. Decreasing the amount of glycogen storage by modulating the C. elegans glycogen synthase, gsy-1, a key enzyme in glycogen synthesis, can extend lifespan, prolong healthspan, and limit the detrimental effects of a high-sugar diet. Importantly, limiting glycogen storage leads to a metabolic shift whereby glucose is now stored as trehalose. Two additional means to increase trehalose show similar longevity extension. Increased trehalose is entirely dependent on a functional FOXO transcription factor DAF-16 and autophagy to promote lifespan and healthspan extension. Our results reveal that when glucose is stored as glycogen, it is detrimental, whereas, when stored as trehalose, animals live a longer, healthier life if DAF-16 is functional. Taken together, these results demonstrate that trehalose modulation may be an avenue for combatting high-sugar-diet pathology.

Keywords: daf-16; glycogen; gsy-1; lifespan; trehalose.

Fig. 1.

A high-glucose diet decreases lifespan and healthspan and increases glycogen storage. (A) Lifespan of wild type grown on NGM with 0%, 1%, 2%, or 4% glucose, 200 µM FUdR, and UV-killed OP50 E. coli. (B) Locomotion in liquid measured by number of body bends per minute, wild type grown for 1, 5, 10, and 15 d on NGM with 0% or 2% glucose, 200 µM FUdR, and OP50 E. coli. (C) Locomotion on solid media measured by track length traveled per 30 s, wild type grown for 1, 5, 10, and 15 d on NGM with 0% or 2% glucose, 200 µM FUdR, and OP50 E. coli. (D) AGEs of wild type grown on NGM with 0% or 2% glucose for 3 d, OP50 E. coli. AGEs standardized to protein content. (E and F) Glycogen stores of wild type grown on NGM with 0% or 2% glucose for 1 d, OP50 E. coli. (E) Iodine staining. (F) Total glycogen assay-glycogen content standardized to protein concentration. (G and H) Glycogen stores of aging wild type on NGM at 1, 3, 6, 9, and 12 d of adulthood, OP50 E. coli. (G) Iodine staining. (H) Total glycogen assay-glycogen content standardized to protein concentration (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, NS, not significant).

Fig. 2.

Disruption of glycogen synthesis extends lifespan and promotes healthspan. (A) Iodine staining of wild type and gsy-1(tm6196) mutants, day 3 adults. (B) Lifespan of wild type and gsy-1 mutants. (C) AGEs of wild type and gsy-1 mutants, day 3 adults, standardized to protein content. (D) Locomotion measured by number of body bends per minute in liquid, wild type and gsy-1 mutants grown for 1, 5, 10, and 15 d. (E) Locomotion measured by track length traveled per 30 s on solid media, wild type and gsy-1 mutants grown for 1, 5, 10, and 15 d. (F) Resistance to oxidative stress, wild type and gsy-1 mutants grown for 1, 5, 10, and 15 d. (G) Resistance to heat stress, wild type and gsy-1 mutants grown for 1, 5, 10, and 15 d (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001). All animals were grown on NGM with 200 µM FUdR, OP50 E. coli.

Fig. 3.

Modulating glycogen storage, but not other glucose-processing pathways, attenuates the effects of a high-glucose diet on longevity. (A) Lifespan of wild type on 0% or 2% glucose, 200 µM FUdR, empty vector or gsy-1 RNAi. (B) AGEs of day 3 adults on 0% or 2% glucose, on empty vector or gsy-1 RNAi. AGEs results standardized to protein content. (C) Model of glucose metabolic pathways in C. elegans, f6p, fructose-6-phosphate; g1p, glucose-1-phosphate; g6p, glucose-6-phosphate; HP, hexosamine pathway; PPP, pentose phosphate pathway; UDP-G, uridine diphosphate glucose. (D–G) Lifespan of wild type on 0% or 2% glucose, 200 µM FUdR, with either empty vector, gspd-1, gfat-1, gfat-2, or pfk-1.2 RNAi. (H and I) Lifespan of wild type, tre-1(ok327), and tre-3(ok394) mutants on 0% or 2% glucose, 200 µM FUdR, fed UV-killed OP50 E. coli (**P ≤ 0.01).

Fig. 4.

Animals with increased internal trehalose exhibit lifespan extension. (A) Internal trehalose levels of wild type on 0% or 2% glucose, with either empty vector, gspd-1, gfat-1, gfat-2, or pfk-1.2 RNAi; and gsy-1, tre-1, and tre-3 mutants on 0% or 2% glucose, UV-killed OP50 E. coli. (B) Internal trehalose levels of day 1 adults, on 0 mM or 5 mM trehalose, UV-killed OP50 E. coli, internal trehalose levels standardized to protein content. (C) RT-qPCR of trehalose synthesis genes in wild-type day 1 adults and gsy-1 mutants day 1 adults, OP50 E. coli. (D) RT-qPCR of trehalose synthesis genes in wild-type day 1 adults on 0 mM or 5 mM trehalose, UV-killed OP50 E. coli. (E) RT-qPCR of trehalose synthesis genes in wild-type, tre-1, and tre-3 mutants day 1 adults, OP50 E. coli. (F) Lifespan of wild type and gsy-1 mutants, 200 µM FUdR, with either empty vector or tps-1 RNAi (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).

Fig. 5.

Positive benefits of increased internal trehalose requires functional DAF-16. (A) Lifespan of wild type and daf-16(mgDf50) on 0 mM or 5 mM trehalose, 200 µM FUdR, UV-killed OP50 E. coli. (B) RT-qPCR of DAF-16 targets of day 1 adults on 0 mM or 5 mM trehalose, UV-killed OP50 E. coli. (C) Lifespan of daf-16 mutant with either vector or gsy-1 RNAi, 200 µM FUdR. (D) RT-qPCR of DAF-16 targets in wild-type day 1 adults with either vector or gsy-1 RNAi. (E) Internal trehalose concentration of wild type and daf-16 mutants on 0 mM and 5 mM trehalose, UV-killed OP50 E. coli, day 3 adults, internal trehalose concentration standardized to protein content. (F) RT-qPCR of trehalose synthesis genes in wild type and daf-16 mutants on 0 mM and 5 mM trehalose, UV-killed OP50 E. coli, day 3 adults (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).

Fig. 6.

Positive benefits of increased internal trehalose requires autophagy. (A) RT-qPCR of autophagy-related genes in wild type and daf-16 mutants on 0 mM and 5 mM trehalose, UV-killed OP50 E. coli, day 3 adults. (B) RT-qPCR of autophagy-related genes in wild type and gsy-1 mutants, OP50 E. coli, day 1 adults. (C) Lifespan of wild type and gsy-1 mutants, 200 µM FUdR, with either empty vector, pha-4, lgg-1, or bec-1 RNAi. (D) Photographs and quantification of wild-type control and sqst-1::GFP on 0 mM or 5 mM trehalose, UV-killed OP50 E. coli, day 3 adult pharynx. Red arrows denote GFP positive puncta, which were quantified. (E) Photographs and quantification of sqst-1::GFP on either empty vector, gsy-1, or gfp(control) RNAi, day 3 adult pharynx. Red arrows denote GFP positive puncta, which were quantified (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).