STR-33, a novel G protein-coupled receptor that regulates locomotion and egg laying in Caenorhabditis elegans

Deficiency in RCAT-1 Function Causes Dopamine Metabolism Related Behavioral Disorders in Caenorhabditis elegans

When animals are faced with food depletion, food search-associated locomotion is crucial for their survival. Although food search-associated locomotion is known to be regulated by dopamine, it has yet to investigate the potential molecular mechanisms governing the regulation of genes involved in dopamine metabolism (e.g., cat-1, cat-2) and related behavioral disorders. During the studies of the pheromone ascaroside, a signal of starvation stress in C. elegans, we identified R02D3.7, renamed rcat-1 (regulator of cat genes-1), which had previously been shown to bind to regulatory sequences of both cat-1 and cat-2 genes. It was found that RCAT-1 (R02D3.7) is expressed in dopaminergic neurons and functions as a novel negative transcriptional regulator for cat-1 and cat-2 genes. When a food source becomes depleted, the null mutant, rcat-1(ok1745), exhibited an increased frequency of high-angled turns and intensified area restricted search behavior compared to the wild-type animals. Moreover, rcat-1(ok1745) also showed defects in state-dependent olfactory adaptation and basal slowing response, suggesting that the mutants are deficient in either sensing food or locomotion toward food. However, rcat-1(ok1745) has normal cuticular structures and locomotion genes. The discovery of rcat-1 not only identifies a new subtype of dopamine-related behaviors but also provides a potential therapeutic target in Parkinson’s disease.

Human amyloid beta and α-synuclein co-expression in neurons impair behavior and recapitulate features for Lewy body dementia in Caenorhabditis elegans

Amyloid β (Aβ), a product of APP, and SNCA (α-synuclein (α-syn)) are two of the key proteins found in lesions associated with the age-related neurodegenerative disorders Alzheimer's disease (AD) and Parkinson's disease (PD), respectively. Previous clinical studies uncovered Aβ and α-syn co-expression in the brains of patients, which lead to Lewy body dementia (LBD), a disease encompassing Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). To explore the pathogenesis and define the relationship between Aβ and α-syn for LBD, we established a C. elegans model which co-expresses human Aβ and α-syn with alanine 53 to threonine mutant (α-syn(A53T)) in pan-neurons. Compared to α-syn(A53T) single transgenic animals, pan-neuronal Aβ and α-syn(A53T) co-expression further enhanced the thrashing, egg laying, serotonin and cholinergic signaling deficits, and dopaminergic neuron damage in C. elegans. In addition, Aβ increased α-syn expression in transgenic animals. Transcriptome analysis of both Aβ;α-syn(A53T) strains and DLB patients showed common downregulation in lipid metabolism and lysosome function genes, suggesting that a decrease of lysosome function may reduce the clearance ability in DLB, and this may lead to the further pathogenic protein accumulation. These findings suggest that our model can recapitulate some features in LBD and provides a mechanism by which Aβ may exacerbate α-syn pathogenesis.

Metformin Attenuates Aβ Pathology Mediated Through Levamisole Sensitive Nicotinic Acetylcholine Receptors in a C. elegans Model of Alzheimer's Disease

The metabolic disease, type 2 diabetes mellitus (T2DM), is a major risk factor for Alzheimer's disease (AD). This suggests that drugs such as metformin that are used to treat T2DM may also be therapeutic toward AD and indicates an interaction between AD and energy metabolism. In this study, we have investigated the effects of metformin and another T2DM drug, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) in C. elegans expressing human Aβ₄₂. We found that Aβ expressed in muscle inhibited levamisole sensitive nicotinic acetylcholine receptors and that metformin delayed Aβ-linked paralysis and improved acetylcholine neurotransmission in these animals. Metformin also moderated the effect of neuronal expression of Aβ: decreasing hypersensitivity to serotonin, restoring normal chemotaxis, and improving fecundity. Metformin was unable to overcome the small effect of neuronal Aβ on egg viability. The protective effects of metformin were associated with a decrease in the amount of toxic, oligomeric Aβ. AICAR has a similar protective effect against Aβ toxicity. This work supports the notion that anti-diabetes drugs and metabolic modulators may be effective against AD and that the worm model can be used to identify the specific interactions between Aβ and cellular proteins.