Life-span extension from hypoxia in Caenorhabditis elegans requires both HIF-1 and DAF-16 and is antagonized by SKN-1

Abstract

Stabilization of the hypoxia-inducible factor (HIF-1) protein extends longevity in Caenorhabditis elegans. However, stabilization of mammalian HIF-1α has been implicated in tumor growth and cancer development. Consequently, for the hypoxic response to benefit mammalian health, we must determine the components of the response that contribute to longevity, and separate them from those that cause harm in mammals. Here, we subject adult worms to low oxygen environments. We find that growth in hypoxia increases longevity in wild-type worms but not in animals lacking HIF-1 or DAF-16. Conversely, hypoxia shortens life span in combination with overexpression of the antioxidant stress response protein SKN-1. When combined with mutations in other longevity pathways or dietary restriction, hypoxia extends life span but to varying extents. Collectively, our results show that hypoxia modulates longevity in a complex manner, likely involving components in addition to HIF-1.

Keywords: Caenorhabditis elegans.; DAF-16; HIF-1; Hypoxia; Longevity.

Figure 1.

Life-span extension by hypoxia requires HIF-1. This figure shows life spans of Caenorhabditis elegans cultured at 20°C on UV-killed OP50 bacteria in both normoxia (21% O₂) and hypoxia (0.5% O₂) throughout adulthood. (A) N2 (wild-type) worms have increased longevity in hypoxia (median life-span increase of 12.5%, p value 2.3E-4). (B) hif-1 mutant worm life span is unaffected by hypoxia (−4.3% decrease in median life span, p value .18). (C) vhl-1 mutant worm (stabilized HIF-1) life span is decreased by hypoxia (median life-span decrease of −6.9%, p value 1.2E-4). Composite of all trials are shown. Significance: *p < .01, **p < .001.

Figure 2.

DAF-16 is required for life-span extension in hypoxia. (A) daf-16 mutant worm life span is not extended by hypoxia (change in median life span is 0%). Composite of all four trials are shown. (B) Hypoxic conditions cause DAF-16 to localize to the nucleus, approximately to the frequency of daf-2 (RNAi), as visualized by DAF-16::GFP transgenic worms with nuclear puncta when imaged. (C) Quantification of the fraction of animals with nuclear puncta. (D) Quantification of DAF-16 target mRNA levels by qPCR.

Figure 3.

Dietary restriction (DR) and hypoxia do not interact to extend life span. Worms under DR (bacterial deprivation [BD] after Day 4 of adulthood) have extended longevity in hypoxia (20.0% median life-span increase, p value 1.5E-31). Composite of all trials are shown. Significance: **p < .001.

Figure 4.

SKN-1 and the hypoxic response. This figure shows life spans of Caenorhabditis elegans cultured at 20°C on UV-killed OP50 bacteria in both normoxia (21% O₂) and hypoxia (0.5% O₂) throughout adulthood. (A) In hypoxic conditions, skn-1(zu-67) mutants increase median life span 14.3% and (B) skn-1(zu135) mutant worms increase median life span by 22.2% (p values 9.0E-13 and 5.8E-16, respectively). (C) ls007 (skn-1b/c::gfp) worms (overexpressing SKN-1) have a median life-span decrease of −21.7% (p value 8.0E-6). Composite of all trials are shown. Significance: **p < .001.

Figure 5.

Summary of hypoxia’s effect upon median life span. The percentage of change in median life span of worms in hypoxia compared with their normoxic counterparts. Composite of all trials are shown. Significance: *p < .01, **p < .001.

Figure 6.

Genes independent of the HIF-1 pathway. This figure shows life spans of Caenorhabditis elegans cultured at 20°C on UV-killed OP50 bacteria in both normoxia (21% O₂) and hypoxia (0.5% O₂) throughout adulthood. (A) sir-2.1, (B) aak-2, and (C) cep-1 worms in hypoxia have increased longevity (median life-span increases of 8.3%, p value 9.6E-6; 9.5%, p value 4.6E-8; and 3.7%, p value 5.1E-3, respectively). Composite of all trials are shown. Significance: *p < .01, **p < .001.