A Potential Biochemical Mechanism Underlying the Influence of Sterol Deprivation Stress on Caenorhabditis elegans Longevity

Abstract

To investigate the biochemical mechanism underlying the effect of sterol deprivation on longevity in Caenorhabditis elegans, we treated parent worms (P0) with 25-azacoprostane (Aza), which inhibits sitosterol-to-cholesterol conversion, and measured mean lifespan (MLS) in F2 worms. At 25 M (ϳEC 50 ), Aza reduced total body sterol by 82.5%, confirming sterol depletion. Aza (25 M) treatment of wild-type (N2) C. elegans grown in sitosterol (5 g/ml) reduced MLS by 35%. Similar results were obtained for the stress-related mutants daf-16(mu86) and gas-1(fc21). Unexpectedly, Aza had essentially no effect on MLS in the stress-resistant daf-2(e1370) or mitochondrial complex II mutant mev-1(kn1) strains, indicating that Aza may target both insulin/IGF-1 signaling (IIS) and mitochondrial complex II. Aza increased reactive oxygen species (ROS) levels 2.7-fold in N2 worms, but did not affect ROS production by mev-1(kn1), suggesting a direct link between Aza treatment and mitochondrial ROS production. Moreover, expression of the stress-response transcription factor SKN-1 was decreased in amphid neurons by Aza and that of DAF-28 was increased when DAF-6 was involved, contributing to lifespan reduction.Sterols are important molecules involved in membrane organization, hormone production, and signal processing. Because Caenorhabditis elegans lacks a de novo sterol biosynthesis pathway, it requires dietary cholesterol or plant sterols (e.g. sitosterol) that can be converted to cholesterol or its most abundant sterol, 7-dehydrocholesterol (1, 2) (Fig. 1A). Sterol depletion experiments have revealed that a restriction in the sterol supply caused by inadequate nutrition produces serious defects in development and reduces the longevity of C. elegans (3-7). For example, sterol starvation leads to an increase in embryonic lethality (7) and a decrease in lifespan (ϳ40%) in wild-type N2 worms (6). Most of the sterol depletion phenotype also occurs when worms are grown in the presence of sitosterol as a sterol nutrient and 25-azacoprostane (Aza), 2 an inhibitor of sterol C24-reductase and dealkylation of desmosterol during its conversion to cholesterol (8). Using proteomic approaches, our laboratory has previously shown that defects in development and growth in C. elegans caused by Aza treatment are associated with changes in the abundance of many proteins (3). The major proteins influenced by Aza treatment were the lipoproteins VIT-2 and VIT-6 and their putative receptors RME-2 and LRP-1, which were previously known to respond to sterols (3). Recently, the endogenous ligands of DAF-12 have been discovered to be 3-keto bile acid-like steroids, called ⌬ 4 -and ⌬ 7 -dafachronic acids (9). Dafachronic acids and related metabolites regulate longevity and stress resistance (9 -11). DAF-36, a Rieske-like oxygenase, and DAF-9, a cytochrome P450 enzyme, produce dafachronic acid ligands that activate the DAF-12 nuclear receptor (9). It was also reported that methyltransferase STRM-1 modifies sterol substrates for the synthesis of dafachronic acid (...

NSBP-1 mediates the effects of cholesterol on insulin/IGF-1 signaling in Caenorhabditis elegans

“…Although C. elegans lack de novo cholesterol biosynthesis, they require cholesterol for germ cell development, growth, stress resistance, dauer formation, fat storage, cuticle formation, and modulation of other lipids [7, 9, 10, 48–50]. Changes in exogenous or endogenous cholesterol profoundly affect C. elegans cellular function and cholesterol cannot be replaced by other lipid molecules.…”

“…For instance, SREBP and LXR are transcription factors that regulate the expression of genes involved in cholesterol homeostasis [1, 2], lipoproteins and NPCs are transporters of cholesterol, and caveolin located in the membrane regulates both cholesterol transport and signal transduction [3–5]. As in mammals, cholesterol in Caenorhabditis elegans has diverse functions [6–9] including an interaction with the insulin signaling pathway [10, 11]. A key difference between worms and mammals, however, is that worms require only a very small amount of cholesterol, suggesting that cholesterol primarily functions in signaling.…”

High glucose diets shorten lifespan ofCaenorhabditis elegansvia ectopic apoptosis induction

“…It was also found that glucose diet reduces the lifespan of C. elegans through repressing the activity of transcription factors involved in extending lifespan [ 18 ]. Such transcription factors are inactivated by insulin signaling executed by DAF-16 and HSF-1 [ 22 , 23 ]. The level of insulin in the blood increases quickly after intake of high glucose foods and then decreases soon thereafter, making insulin a potent mediator of the effects of high glucose diets on aging in humans.…”

Transcriptional feedback in the insulin signalling pathway modulates ageing in both Caenorhabditis elegans and Drosophila melanogaster

“…Several of the paths examined intersect on the transcription factor skn-1 , shown to inhibit one of insulin-like peptides ( ins-7 ) 33,61 and skn-1 suppression coupled with a daf-28 induction has been suggested as a negative transcriptional feedback. 62 Furthermore, both ins-7 and daf-28 were found to be up-regulated in 2 of the experiments, i.e. rheb-1 i and let-363 i.…”