Amyloid-beta induced paralysis is reduced by cholecalciferol through inhibition of the steroid-signaling pathway in an Alzheimer model of Caenorhabditis elegans.

Objectives: Alzheimer's disease (AD) is a neurodegenerative disorder resulting from the accumulation of toxic ß-amyloid (Aß) aggregates in the human brain. Epidemiological studies have shown that elevated cholesterol plasma levels are associated with the development of AD and we have previously shown that cholesterol restriction reduces the Aß-induced paralysis in an Alzheimer model of the nematode Caenorhabditis elegans. In the present study we investigated the effects of the cholesterol homolog cholecalciferol, i.e. vitamin D, on Aß-induced paralysis in C. elegans and its interference with the steroid-signaling pathway. Methods: Aß-induced paralysis was assessed in the C. elegans strain CL2006, expressing human Aß1-42 under control of a muscle-specific promoter. Knockdown of members of the steroid-signaling pathway was achieved by RNA interference (RNAi). Nuclear translocation of foxo transcription factor DAF-16 was visualized using the strain TJ356, carrying a daf-16::gfp transgene. Results: Cholecalciferol at a concentration of 1 µM reduced the Aß-induced paralysis in CL2006 significantly, which was reverted by increasing the cholesterol concentration in the medium. Knockdown of nhr-8, daf-36, daf-9 or daf-12, all reduced Aß-induced paralysis to the same extent as cholecalciferol with no additional or synergistic effects under co-application. Functional DAF-16 proved to be crucial for the effects of cholecalciferol and DAF-16 nuclear translocation was increased by cholecalciferol and also RNAi versus nhr-8, daf-36, daf-9 or daf-12 with no additive or synergistic effects. Conclusions: Our results suggest, that cholecalciferol inhibits Aß-induced paralysis in C. elegans through inhibition of steroid-signaling and the concomitant nuclear translocation of DAF-16.

Amyloid-beta (Aß1-42)-induced paralysis in Caenorhabditis elegans is reduced through NHR-49/PPARalpha.

Alzheimer´s disease is a neurodegenerative disorder characterized by the misfolding and aggregation of amyloid ß (Aß). Agonists of peroxisomal proliferator-activated receptors (PPARs) are discussed as anti-amyloidogenic compounds, e.g. due to their cholesterol-lowering activities. In a previous study we have shown in Caenorhabditis elegans expressing human Aß in muscle cells, that inhibition of steroid-signaling, by RNAi of respective members of the signaling pathway or by reducing cellular cholesterol uptake, both increases the nuclear translocation of the foxo transcription factor DAF-16 and concomitantly reduces Aß-induced paralysis. Using RNAi in the present study we show that NHR-49/PPARalpha inhibits steroidal-signaling upstream of DAF-9, a cytochrome P450-dependent enzyme which generates dafachronic acids as ligands for the nuclear hormone receptor DAF-12, and upstream of DAF-12 itself. The NHR-49/PPARalpha agonist fenofibrate reduces Aß-induced paralysis in dependence on nhr-49 and nuclear translocation of DAF-16. In conclusion, activation of NHR-49/PPARalpha inhibits the steroidal-signaling pathway which increases the nuclear translocation of DAF-16 and inhibits the Aß-induced phenotype in an Alzheimer model of C. elegans.

Betaine reduces ß-amyloid-induced paralysis through activation of cystathionine-ß-synthase in an Alzheimer model of Caenorhabditis elegans.

BACKGROUND: The neurodegenerative disorder Alzheimer's disease is caused by the accumulation of toxic aggregates of ß-amyloid in the human brain. On the one hand, hyperhomocysteinemia has been shown to be a risk factor for cognitive decline in Alzheimer's disease. On the other hand, betaine has been demonstrated to attenuate Alzheimer-like pathological changes induced by homocysteine. It is reasonable to conclude that this is due to triggering the remethylation pathway mediated by betaine-homocysteine-methyltransferase. In the present study, we used the transgenic Caenorhabditis elegans strain CL2006, to test whether betaine is able to reduce ß-amyloid-induced paralysis in C. elegans. This model expresses human ß-amyloid 1-42 under control of a muscle-specific promoter that leads to progressive, age-dependent paralysis in the nematodes. RESULTS: Betaine at a concentration of 100 µM was able to reduce homocysteine levels in the presence and absence of 1 mM homocysteine. Simultaneously, betaine both reduced normal paralysis rates in the absence of homocysteine and increased paralysis rates triggered by addition of homocysteine. Knockdown of cystathionine-ß-synthase using RNA interference both increased homocysteine levels and paralysis. Additionally, it prevented the reducing effects of betaine on homocysteine levels and paralysis. CONCLUSION: Our studies show that betaine is able to reduce homocysteine levels and ß-amyloid-induced toxicity in a C. elegans model for Alzheimer's disease. This effect is independent of the remethylation pathway but requires the transsulfuration pathway mediated by cystathionine-ß-synthase.