Autophagy and lipid metabolism coordinately modulate life span in germline-less C. elegans - PubMed (original) (raw)

Autophagy and lipid metabolism coordinately modulate life span in germline-less C. elegans

Louis R Lapierre et al. Curr Biol. 2011.

Abstract

Background: The cellular recycling process of autophagy is emerging as a key player in several longevity pathways in Caenorhabditis elegans. Here, we identify a role for autophagy in long-lived animals lacking a germline and show that autophagy and lipid metabolism work interdependently to modulate aging in this longevity model.

Results: Germline removal extends life span in C. elegans via genes such as the lipase LIPL-4; however, less is known of the cellular basis for this life-span extension. Here, we show that germline loss induces autophagy gene expression via the forkhead box A (FOXA) transcription factor PHA-4 and that autophagy is required to extend longevity. We identify a novel link between autophagy and LIPL-4, because autophagy is required to maintain high lipase activity in germline-deficient animals. Reciprocally, lipl-4 is required for autophagy induction. Coordination between autophagy and lipolysis is further supported by the finding that inhibition of TOR (target of rapamycin), a major negative regulator of autophagy, induces lipl-4 expression, and TOR levels are reduced in germline-less animals. TOR may therefore function as a common upstream regulator of both autophagy and lipl-4 expression in germline-less animals. Importantly, we find that the link between autophagy and LIPL-4 is relevant to longevity, because autophagy is induced in animals overexpressing LIPL-4 and autophagy is required for their long life span, recapitulating observations in germline-less animals.

Conclusions: Collectively, our data offer a novel mechanism by which autophagy and the lipase LIPL-4 interdependently modulate aging in germline-deficient C. elegans by maintaining lipid homeostasis to prolong life span.

Copyright © 2011 Elsevier Ltd. All rights reserved.

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Figures

Fig. 1

Fig. 1. Autophagy is Increased in glp-1 Animals Through a PHA-4-dependent Mechanism

(A) Representative electron micrograph of an intestinal cell in a 1-day old adult glp-1(e2141) animal (A: autolysosome, M: mitochondria, MV: microvilli). See Fig. S1A for more information. (B) Quantification of autophagic events detected by electron microscopy in the intestine of 1-day old N2 wild-type (WT) and glp-1(e2141) animals. The observed number of events per animal is shown as dots, and the mean is indicated by vertical line. ***, P<0.0001, _t_-test. (C) Quantification of GFP::LGG-1-positive foci in seam cells of 1-day old WT and glp-1(e2141) animals. Mean number of foci ± SEM is shown. n=100-250 cells, ***, P < 0.001, ANOVA. (D) Quantification of GFP::LGG-1-positive foci in intestinal cells of 1-day old adult WT and glp-1(e2141) animals. Cells from the proximal portion of the intestine were analyzed. Mean number of foci ± SEM is shown. n=15 worms, ***, P < 0.001, _t_-test. (E) RT-PCR analysis of mRNA levels of autophagy genes (bec-1, unc-51, and lgg-1) and of pha-4 in 1-day old adult WT and glp-1(e2141) animals. Relative mean expression ± SD is shown. *, P < 0.05, ***, P < 0.001 vs. WT, ANOVA. (F) RT-PCR analysis of mRNA levels of genes in (E) in glp-1(e2141) worms fed control bacteria or bacteria expressing pha-4 dsRNA from day 1 to day 3 of adulthood. Wild-type data is included in Fig. S2A. Relative mean expression ± SD is shown. *, P < 0.05, **, P < 0.01 vs. Control, ANOVA. In all experiments, animals were raised at the non-permissive temperature (25°C).

Fig. 2

Fig. 2. PHA-4 and Autophagy Genes are Required for glp-1 Animals to Live Long

Lifespan analysis of wild-type N2 (WT) and glp-1(e2141) animals fed control bacteria (empty-vector) or (A) bacteria expressing pha-4 dsRNA, (B) bacteria expressing bec-1, vps-34, or lgg-1 dsRNA, or (C) bacteria expressing unc-51 or atg-18 dsRNA**.** See Table S1 for details and repeats. In all experiments, animals were raised at 25°C from hatching until the first day of adulthood and were then moved to 20°C for the remainder of their life.

Fig. 3

Fig. 3. Germline-less glp-1 Animals Have Reduced TOR mRNA levels and TOR Inhibition Results in Increased Levels of lipl-4

(A) RT-PCR analysis of tor mRNA levels in wild-type (WT), glp-1(e2141), daf-16(mu86), and daf-16(mu86); glp-1(e2141) worms at day 1 of adulthood. Animals were raised at the non-permissive temperature (25°C) from hatching, and relative mean expression ± SD is shown. **, P < 0.01 vs. WT, ANOVA. (B) Lifespan analysis of WT and glp-1(e2141) animals fed control bacteria or bacteria expressing tor dsRNA. Animals were raised as described in Fig. 2. See Table S1 for details and repeats. (C) RT-PCR analysis of lipl-4 mRNA in 3-day old adult WT and daf-16(mu86) worms fed control bacteria or bacteria expressing tor dsRNA for 2 days starting from day 1. Animals were kept at 20°C throughout this experiment, and relative mean expression ± SD is shown. *, P < 0.05 vs. control, ANOVA. (D) Lipase activity measurements in 3-day old adult WT and daf-16(mu86) worms fed control bacteria or bacteria expressing tor dsRNA for 2 days starting from day 1. Animals were kept at 20°C throughout this experiment, and relative mean expression ± SD is shown. *, P < 0.05 vs. control, ANOVA.

Fig. 4

Fig. 4. Increased Lipase Activity Observed in glp-1 Animals is Dependent on Autophagy Genes and PHA-4

(A) Lipase activity was measured daily in wild-type N2 (WT, lighter line) and glp-1(e2141) animals (darker line) from day 1 to day 5 of adulthood. Animals were raised as in Fig. 2, and mean activity mean ± SD is shown. *, P < 0.05, **, P < 0.01, ***, P < 0.001 vs. WT, ANOVA. (B) Lipase activity was measured in 4-day old adult glp-1(e2141) animals fed bacteria expressing dsRNA against several autophagy genes, pha-4, lipl-4 or daf-16 for 3 days starting from day 1. Animals were raised as in Fig. 2, and relative mean activity ± SD is shown. *, P < 0.05, **, P < 0.01, ***, P < 0.001 vs. Control, ANOVA.

Fig. 5

Fig. 5. Autophagy Genes are Required for the Long Lifespan of Animals Overexpressing LIPL-4

Lifespan analysis of animals overexpressing LIPL-4 (LIPL-4 OE) and non-transgenic siblings (WT) fed control bacteria or (A) bacteria expressing bec-1 or lgg-1 dsRNA, or (B) bacteria expressing vps-34 or pha-4 dsRNA. Animals were incubated at 20°C throughout their life. See Table S2 for additional information and repeats.

Fig. 6

Fig. 6. Model for How Autophagy and LIPL-4 Coordinately Modulate Longevity in Germline-less C. elegans

TOR levels are reduced in C. elegans with an empty gonad (germline-less), which show enhanced activity of two forkhead transcription factors that modulate longevity and lipid metabolism. PHA-4/FOXA stimulates autophagy, and DAF-16/FOXO upregulates LIPL-4, thereby possibly inducing lipid hydrolysis. In turn, LIPL-4 requires autophagy to modulate lifespan, possibly through a process involving lipophagy. Novel observations made in this study are shown in red, known links are shown in black. Possible feedback and cross-talk events are not included for simplicity; see text for details.

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