Resveratrol reduces amyloid-beta (Aß1₋42)-induced paralysis through targeting proteostasis in an Alzheimer model of Caenorhabditis elegans.

PURPOSE: Resveratrol is a polyphenol present in red wine for which the capability of directly interfering with the hallmark of Alzheimer's disease (AD), i.e. toxic ß-amyloid protein (Aß) aggregation, has been shown recently. Since the stimulation of proteostasis could explain reduced Aß-aggregation, we searched for proteostasis targets of resveratrol. METHODS: The transgenic Caenorhabditis elegans strain CL2006, expressing Aß1-42 under control of a muscle-specific promoter and responding to Aß-toxicity with paralysis, was used as a model. Target identification was accomplished through specific knockdowns of proteostasis genes by RNA interference. Effects of resveratrol on protein aggregation were identified using ProteoStat(®) Detection Reagent, and activation of proteasomal degradation by resveratrol was finally proven using a specific fluorogenic peptide substrate. RESULTS: Resveratrol at a concentration of 100 µM caused a 40 % decrease in paralysis. UBL-5 involved in unfolded protein response (UPR) in mitochondria proved to be necessary for the prevention of Aß-toxicity by resveratrol. Also XBP-1, which represents an endoplasmic reticulum-resident factor involved in UPR, was identified to be necessary for the effects of resveratrol. Regarding protein degradation pathways, the inhibition of macroautophagy and chaperone-mediated autophagy prevented resveratrol from reducing paralysis as did the inhibition of proteasomal degradation. Finally, resveratrol reduced the amount of lysosomes, suggesting increased flux of proteins through the autophagy pathways and activated proteasomal degradation. CONCLUSIONS: Resveratrol reduces the Aß-induced toxicity in a C. elegans model of AD by targeting specific proteins involved in proteostasis and thereby reduces the amount of aggregated Aß.

Amyloid-beta (Aß1₋42)-induced paralysis in Caenorhabditis elegans is inhibited by the polyphenol quercetin through activation of protein degradation pathways.

SCOPE: Dietary polyphenols are suggested to play a role in the prevention of Alzheimer's disease, of which accumulation of aggregated beta amyloid (Aß) is a key histopathological hallmark. We used the transgenic Caenorhabditis elegans strain CL2006, which expresses human Aß1₋42 under control of a muscle-specific promoter and responds to Aß1₋42 aggregation with paralysis, to test effects of the polyphenol quercetin on the phenotype. METHODS AND RESULTS: Quercetin dose-dependently decreased the amount of aggregated proteins in solution and also paralysis in CL2006. The knockdown of key components of unfolded protein response in mitochondria or the endoplasmic reticulum by RNA-interference (RNAi) enhanced paralysis in CL2006 but did not prevent the paralysis reducing activities of quercetin. RNAi for essential members of proteasomal protein degradation or macroautophagy also significantly increased paralysis but prevented quercetin from being effective. Quercetin increased proteasomal activity and, moreover, enhanced the flow of proteins through the macroautophagy pathway as reflected by reduced lysosome staining. CONCLUSION: The proteostasis network, including unfolded protein response, defines the aggregation of Aß1₋42 and the associated paralysis phenotype in a nematode model for Alzheimer's disease. The polyphenol quercetin, by specifically activating macroautophagy and proteasomal degradation pathways, proved able to prevent Aß1₋42 agregation and paralysis.

Amyloid-beta (Aß1-42)-induced paralysis in Caenorhabditis elegans is reduced by restricted cholesterol supply.

Alzheimer' disease is a neurodegenerative disorder characterized by the misfolding and aggregation of amyloid ß (Aß). This process is influenced through supply of cholesterol via apolipoproteins to neurons. In the present study, we used the transgenic Caenorhabditis elegans strain CL2006, which expresses Aß1-42 under control of a muscle-specific promoter, to test the effects of the apolipoprotein B homologue vitellogenin-6 on paralysis. Knockdown of vitellogenin-6 using RNA-interference (RNAi) recently was shown to significantly reduce cholesterol absorption in C. elegans, and both, RNAi for vitellogenin-6 or lowering the cholesterol concentration in the medium was associated with reduced Aß-aggregation and paralysis in the nematodes. The effects of both interventions are mediated through the inhibition of the steroidal-signaling pathway since knockdown of its key factors DAF-9 or DAF-12 reduced paralysis independent of the cholesterol concentration and without additive effects by vitellogenin-6 RNAi. Double-RNAi for daf-12 and the downstream target of insulin-signaling, the foxo transcription factor daf-16, revealed that the paralysis-triggering effects of daf-16 RNAi were dominant over the preventive effects of daf-12 RNAi. Identical observations were made when the transcriptional co-activators of DAF-16, ftt-2 or par-5 were knocked down instead of daf-16. In conclusion, interactions between the steroidal and insulin-signaling pathways were identified in Aß1-42 expressing CL2006, where cholesterol deprivation inhibits steroidal-signaling and thereby activates DAF-16-signaling. Those effects were associated with a reduced Alzheimer phenotype in the nematodes, i.e. reduced protein aggregation and paralysis.

Vitellogenins increase stress resistance of Caenorhabditis elegans after Photorhabdus luminescens infection depending on the steroid-signaling pathway.

Resistance against environmental stress is a crucial factor in determining the lifespan of organisms. A central role herein has been recently attributed to the transport and storage of lipids with the vitellogenin family emerging as a potential key factor. Here we show that the knockdown of one out of five functional vitellogenin genes, encoding apolipoprotein B homologues, results in a reduced survival of the nematode Caenorhabditis elegans at 37 °C subsequent to infection with the bacterial pathogen Photorhabdus luminescens. An active steroid-signaling pathway, including supply of cholesterol by vitellogenins, steroid ligand formation by the cytochrome P450 dependent DAF-9, and activation of the nuclear hormone receptor DAF-12, in the presence of pathogenic bacteria was associated with reduced nuclear translocation of the forkhead transcription factor DAF-16 and increased antioxidative capacity. Taken together, the study provides functional evidence for a crucial role of vitellogenins and the steroid-signaling pathway in determination of resistance against bacteria.

Phytoestrogens genistein and daidzein affect immunity in the nematode Caenorhabditis elegans via alterations of vitellogenin expression.

SCOPE: Phytoestrogens, such as the soy isoflavones genistein and daidzein, are suggested to beneficially affect lipid metabolism in humans and thereby contribute to healthy ageing. New evidences show that phytoestrogens might slow ageing processes also by affecting immune processes. METHODS AND RESULTS: We tested in the nematode Caenorhabditis elegans the effects of 17ß-estradiol, genistein, and daidzein on resistance versus the nematode pathogen Photorhabdus luminescens with focus on vitellogenins, which are invertebrate estrogen-responsive genes that encode homologues to ApoB100 with impact on immune functions. Here, we show that the estrogen 17ß-estradiol increases the resistance of C. elegans versus P. luminescens by enhancing vitellogenin-expression at the mRNA and protein level. Knockdown of single out of five functional vits by RNA-interference blunted the life-extending effects under heat-stress of 17ß-estradiol, demonstrating a lack of redundancy for the vitellogenins. RNAi for nhr-14, a suggested nuclear hormone receptor for estrogens, displayed no influence on 17ß-estradiol effects. The soy isoflavone genistein reduced vitellogenin-expression and also resistance versus P. luminescens whereas daidzein increased resistance versus the pathogen in a vitellogenin-dependent manner. CONCLUSION: Our studies show that induction of estrogen-responsive vitellogenin(s) by the phytoestrogen daidzein potently increases resistance of C. elegans versus pathogenic bacteria and heat whereas genistein acts in an antiestrogenic manner.