Mechanisms of amino acid-mediated lifespan extension in Caenorhabditis elegans

Abstract

BackgroundLittle is known about the role of amino acids in cellular signaling pathways, especially as it pertains to pathways that regulate the rate of aging. However, it has been shown that methionine or tryptophan restriction extends lifespan in higher eukaryotes and increased proline or tryptophan levels increase longevity in C. elegans. In addition, leucine strongly activates the TOR signaling pathway, which when inhibited increases lifespan.ResultsTherefore each of the 20 proteogenic amino acids was individually supplemented to C. elegans and the effects on lifespan were determined. All amino acids except phenylalanine and aspartate extended lifespan at least to a small extent at one or more of the 3 concentrations tested with serine and proline showing the largest effects. 11 of the amino acids were less potent at higher doses, while 5 even decreased lifespan. Serine, proline, or histidine-mediated lifespan extension was greatly inhibited in eat-2 worms, a model of dietary restriction, in daf-16/FOXO, sir-2.1, rsks-1 (ribosomal S6 kinase), gcn-2, and aak-2 (AMPK) longevity pathway mutants, and in bec-1 autophagy-defective knockdown worms. 8 of 10 longevity-promoting amino acids tested activated a SKN-1/Nrf2 reporter strain, while serine and histidine were the only amino acids from those to activate a hypoxia-inducible factor (HIF-1) reporter strain. Thermotolerance was increased by proline or tryptophan supplementation, while tryptophan-mediated lifespan extension was independent of DAF-16/FOXO and SKN-1/Nrf2 signaling, but tryptophan and several related pyridine-containing compounds induced the mitochondrial unfolded protein response and an ER stress response. High glucose levels or mutations affecting electron transport chain (ETC) function inhibited amino acid-mediated lifespan extension suggesting that metabolism plays an important role. Providing many other cellular metabolites to C. elegans also increased longevity suggesting that anaplerosis of tricarboxylic acid (TCA) cycle substrates likely plays a role in lifespan extension.ConclusionsSupplementation of C. elegans with 18 of the 20 individual amino acids extended lifespan, but lifespan often decreased with increasing concentration suggesting hormesis. Lifespan extension appears to be caused by altered mitochondrial TCA cycle metabolism and respiratory substrate utilization resulting in the activation of the DAF-16/FOXO and SKN-1/Nrf2 stress response pathways.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0167-2) contains supplementary material, which is available to authorized users.

SKN-1-independent transcriptional activation of glutathione S-transferase 4 (GST-4) by EGF signaling

“…7,11,12,15,19,20,23,[26][27][28][29][30][31][32][33] A problem arises, however, when GST-4 is used as the sole readout for SKN-1 activation, in the absence of aforementioned controls. 21,22,24,25 Based on our current observations, the interpretation of gst-4 p ::gfp fluorescence in vivo is indeed not straightforward.…”

“…3 Currently, SKN-1 transcriptional activity is often indirectly assayed via a transcriptional reporter construct of the gst-4 promotor (gst-4 p ::gfp or Pgst-4::gfp; strain CL2166) which shows increased GFP levels when transcription is activated in vivo. 7,11,12,15,[19][20][21][22][23][24][25][26][27][28][29][30] By using gst-4 transcription levels as a proxy for SKN-1 activation, the problem of a low GFP signal is mitigated. Additionally, it is possible to obtain a quantitative indication of the gene's transcription levels, instead of merely being able to discriminate between cytoplasmic or nuclear localization of a transcription factor.…”

Parsing the life-shortening effects of dietary protein: effects of individual amino acids

“…Thus, we further explored the individual role of each amino acid on the high-protein toxicity and we found that the over-representation of methionine (Met), serine (Ser), threonine (Thr) and phenylalanine (Phe) were especially harmful. These amino acids when in excess decrease growth and/or lifespan in a wide variety of life forms such as unicellular algae (Met, Thr and Ser [45]), yeasts (Met, Thr and Ser [46][47][48]), roundworms (Phe [49]), flies (Met [50,51]), rodents (Met, Thr, Ser and Phe [46,[52][53][54]), and even cancer tumour cells (Met and Phe [55]) and other human cells (Met [46]). Methionine is proposed to be related to oxidative stress processes [56].…”

Caenorhabditis elegans orthologs of human genes differentially expressed with age are enriched for determinants of longevity

“…Knockdown of tdo‐2 is thought to influence C. elegans aging by increasing TRP concentrations (van der Goot et al ., 2012). Similar to tdo‐2 ( RNAi ), adding TRP to the culture media activates DAF‐16 reporters and extends lifespan of wild‐type worms in a manner that is nonadditive with eat‐2 mutation (Edwards et al ., 2015). …”