The polyphenol quercetin protects from glucotoxicity depending on the aggresome in Caenorhabditis elegans.

PURPOSE: Impaired proteostasis, i.e., protein homeostasis, is considered as a consequence of high-glucose exposure and is associated with reduced survival. The previous studies demonstrated that the polyphenol quercetin can protect from glucotoxicity. The aim of the present study was to unravel the contribution of the aggresome, sequestering potentially cytotoxic aggregates and also acting as a staging center for eventual autophagic clearance from the cell. METHODS: Knockdown of the aggresome-relevant genes dnc-1 and ubql-1 was achieved in stress-sensitive mev-1 mutants of the nematode Caenorhabditis elegans by RNA interference (RNAi). Survival assay was conducted under heat stress at 37 °C, protein aggregation using ProteoStat® and chymotrypsin-like proteasomal activity according to the cleavage of a fluorogenic peptide substrate. RESULTS: Survival was reduced by knockdown of ubql-1 and even more by knockdown of dnc-1 which both were not further reduced by addition of glucose. The rescue of survival due to quercetin in glucose-exposed nematodes was completely prevented under RNAi versus ubql-1 or dnc-1. Both knockdowns caused an increase of aggregated protein and prevented the reduction of aggregated protein caused by quercetin in glucose-exposed animals. Finally, the knockdown of ubql-1 and dnc-1 blocked the increase of proteasomal activity achieved by quercetin in glucose-treated nematodes. CONCLUSIONS: The study provides evidence that quercetin protects C. elegans from glucotoxicity through the activation of the aggresome, thereby, quercetin prevents the aggregation and functional loss of proteins, which is typically caused by enhanced glucose concentrations.

Betaine-rich sugar beet molasses protects from homocysteine-induced reduction of survival in Caenorhabditis elegans.

PURPOSE: Homocysteine (Hcy) in humans represents a blood-borne biomarker which predicts the risk of age-related diseases and mortality. Using the nematode Caenorhabditis elegans, we tested whether feeding betaine-rich sugar beet molasses affects the survival under heat stress in the presence of Hcy, in spite of a gene loss in betaine-homocysteine methyltransferase. METHODS: Knockdown of the genes relevant for remethylation or transsulfuration of Hcy was achieved by RNA interference (RNAi). Survival assay was conducted under heat stress at 37 °C and Hcy levels were determined by enzyme-linked immunosorbent assay. RESULTS: Addition of 500 mg/l betaine-rich sugar beet molasses (SBM) prevented the survival reduction that was caused by exposure to Hcy at 37 °C. Although SBM was no longer capable of reducing Hcy levels under RNAi versus homologues for 5, 10-methylenetetrahydrofolate reductase or cystathionine-ß-synthase, it still enabled the survival extension by SBM under exposure to Hcy. In contrast, RNAi for the small heat shock protein hsp-16.2 or the foxo transcription factor daf-16 both prevented the extension of survival by betaine-rich molasses in the presence of Hcy. CONCLUSIONS: Our studies demonstrate that betaine-rich SBM is able to prevent survival reduction caused by Hcy in C. elegans in dependence on hsp-16.2 and daf-16 but independent of the remethylation pathway.