C. elegans: a novel pharmacogenetic model to study Parkinson's disease

Autophagy and UPS pathway contribute to nicotine-induced protection effect in Parkinson's disease

The gradual nature of age-related neurodegeneration causes Parkinson's disease (PD) and impairs movement, memory, intellectual ability, and social interaction. One of the most prevalent neurodegenerative conditions affecting the central nervous system (CNS) among the elderly is PD. PD affects both motor and cognitive functions. Degeneration of dopaminergic (DA) neurons and buildup of the protein α-synuclein (α-Syn) in the substantia nigra pars compacta (SNpc) are two major causes of this disorder. Both UPS and ALS systems serve to eliminate α-Syn. Autophagy and UPS deficits, shortened life duration, and lipofuscin buildup accelerate PD. This sickness has no cure. Innovative therapies are halting PD progression. Bioactive phytochemicals may provide older individuals with a natural substitute to help delay the onset of neurodegenerative illnesses. This study examines whether nicotine helps transgenic C. elegans PD models. According to numerous studies, nicotine enhances synaptic plasticity and dopaminergic neuronal survival. Upgrades UPS pathways, increases autophagy, and decreases oxidative stress and mitochondrial dysfunction. At 100, 150, and 200 µM nicotine levels, worms showed reduced α-Syn aggregation, repaired DA neurotoxicity after 6-OHDA intoxication, increased lifetime, and reduced lipofuscin accumulation. Furthermore, nicotine triggered autophagy and UPS. We revealed nicotine's potential as a UPS and autophagy activator to prevent PD and other neurodegenerative diseases.

Biochemical functions and structure of Caenorhabditis elegans ZK177.8 protein: Aicardi-Goutières syndrome SAMHD1 dNTPase ortholog

Mutations in sterile alpha motif domain and histidine-aspartate domain-containing protein 1 (SAMHD1) are found in a neurodevelopmental disorder, Aicardi-Goutières syndrome, and cancers, and SAMHD1, which is a deoxynucleoside triphosphate (dNTP) triphosphorylase, was identified as a myeloid-specific HIV-1 restriction factor. Here, we characterized the enzymology and structure of an SAMHD1 ortholog of Caenorhabditis elegans, ZK177.8, which also reportedly induces developmental defects upon gene knockdown. We found ZK177.8 protein is a dNTPase allosterically regulated by dGTP. The active site of ZK177.8 recognizes both 2' OH and triphosphate moieties of dNTPs but not base moiety. The dGTP activator induces the formation of the enzymatically active ZK177.8 tetramers, and ZK177.8 protein lowers cellular dNTP levels in a human monocytic cell line. Finally, ZK177.8 tetramers display very similar X-ray crystal structure with human and mouse SAMHD1s except that its lack of the canonical sterile alpha motif domain. This striking conservation in structure, function, and allosteric regulatory mechanism for the hydrolysis of the DNA building blocks supports their host developmental roles.

Effects of lanthanum nitrate on behavioral disorder, neuronal damage and gene expression in different developmental stages of Caenorhabditis elegans

Rare earth elements (REEs) are widely used in the industry, agriculture, biomedicine, aerospace, etc, and have been shown to pose toxic effects on animals, as such, studies focusing on their biomedical properties are gaining wide attention. However, environmental and population health risks of REEs are still not very clear. Also, the REEs damage to the nervous system and related molecular mechanisms needs further research. In this study, the L1 and L4 stages of the model organism Caenorhabditis elegans were used to evaluate the effects and possible neurotoxic mechanism of lanthanum(III) nitrate hexahydrate (La(NO₃)₃·6H₂O). For the L1 and L4 stage worms, the 48-h median lethal concentrations (LC₅₀s) of La(NO₃)₃·6H₂O were 93.163 and 648.0 mg/L respectively. Our results show that La(NO₃)₃·6H₂O induces growth inhibition and defects in behavior such as body length, body width, body bending frequency, head thrashing frequency and pharyngeal pumping frequency at the L1 and L4 stages in C. elegans. The L1 stage is more sensitive to the toxicity of lanthanum than the L4 stage worms. Using transgenic strains (BZ555, EG1285 and NL5901), we found that La(NO₃)₃·6H₂O caused the loss or break of soma and dendrite neurons in L1 and L4 stages; and α-synuclein aggregation in L1 stage, indicating that Lanthanum can cause toxic damage to dopaminergic and GABAergic neurons. Mechanistically, La(NO₃)₃·6H₂O exposure inhibited or activated the neurotransmitter transporters and receptors (glutamate, serotonin and dopamine) in C. elegans, which regulate behavior and movement functions. Furthermore, significant increase in the production of reactive oxygen species (ROS) was found in the L4 stage C. elegans exposed to La(NO₃)₃·6H₂O. Altogether, our data show that exposure to lanthanum can cause neuronal toxic damage and behavioral defects in C. elegans, and provide basic information for understanding the neurotoxic effect mechanism and environmental health risks of rare earth elements.

Mitochondria-affecting small molecules ameliorate proteostasis defects associated with neurodegenerative diseases

Macroautophagic recycling of dysfunctional mitochondria, known as mitophagy, is essential for mitochondrial homeostasis and cell viability. Accumulation of defective mitochondria and impaired mitophagy have been widely implicated in many neurodegenerative diseases, and loss-of-function mutations of PINK1 and Parkin, two key regulators of mitophagy, are amongst the most common causes of heritable parkinsonism. This has led to the hypothesis that pharmacological stimulation of mitophagy may be a feasible approach to combat neurodegeneration. Toward this end, we screened ~ 45,000 small molecules using a high-throughput, whole-organism, phenotypic screen that monitored accumulation of PINK-1 protein, a key event in mitophagic activation, in a Caenorhabditis elegans strain carrying a Ppink-1::PINK-1::GFP reporter. We obtained eight hits that increased mitochondrial fragmentation and autophagosome formation. Several of the compounds also reduced ATP production, oxygen consumption, mitochondrial mass, and/or mitochondrial membrane potential. Importantly, we found that treatment with two compounds, which we named PS83 and PS106 (more commonly known as sertraline) reduced neurodegenerative disease phenotypes, including delaying paralysis in a C. elegans β-amyloid aggregation model in a PINK-1-dependent manner. This report presents a promising step toward the identification of compounds that will stimulate mitochondrial turnover.

Xenobiotic metabolism and transport in Caenorhabditis elegans

Caenorhabditis elegans has emerged as a major model in biomedical and environmental toxicology. Numerous papers on toxicology and pharmacology in C. elegans have been published, and this species has now been adopted by investigators in academic toxicology, pharmacology, and drug discovery labs. C. elegans has also attracted the interest of governmental regulatory agencies charged with evaluating the safety of chemicals. However, a major, fundamental aspect of toxicological science remains underdeveloped in C. elegans: xenobiotic metabolism and transport processes that are critical to understanding toxicokinetics and toxicodynamics, and extrapolation to other species. The aim of this review was to initially briefly describe the history and trajectory of the use of C. elegans in toxicological and pharmacological studies. Subsequently, physical barriers to chemical uptake and the role of the worm microbiome in xenobiotic transformation were described. Then a review of what is and is not known regarding the classic Phase I, Phase II, and Phase III processes was performed. In addition, the following were discussed (1) regulation of xenobiotic metabolism; (2) review of published toxicokinetics for specific chemicals; and (3) genetic diversity of these processes in C. elegans. Finally, worm xenobiotic transport and metabolism was placed in an evolutionary context; key areas for future research highlighted; and implications for extrapolating C. elegans toxicity results to other species discussed.

Neuroprotective effect of damaurone D in a C. elegans model of Parkinson's disease

In this study, we evaluated the protective effects of damaurone D (DaD), a dihydropyranoaurone compound, on dopaminergic (DA) neurodegeneration in Caenorhabditis elegans. The results showed that DaD treatment could successfully increase the survival rate of the worms under MPP⁺ exposure. Additionally, DaD protected against the MPP⁺-induced neurodegeneration in all eight DA neurons of the worms. Similarly, diminished DA neuronal damage was observed in the DaD-fed transgenic mutant overexpressing tyrosine hydroxylase. In addition, the corresponding behavioral impairment induced by MPP⁺ was strongly improved in the DaD treated worms, implying DaD has protective properties for DA neuronal function. Then, we further investigated the effect of DaD on α-synuclein aggregation, a key pathogenesis of Parkinson's disease (PD). In this study, DaD reduced the fluorescence signals of transgenic mutants that carried YFP-fused α-synuclein. A similar reduction in expressions of α-synuclein was observed by Western blot. Interestingly, our result from the dot-blot assay demonstrated that the formation of oligomers was significantly attenuated by the DaD treatment. Furthermore, DaD improved the abnormal fat storage and shortened lifespan of the animals with the same genetic background which supports the beneficial action of DaD on the α-synuclein-induced DA neurodegeneration. These results demonstrate that DaD could protect against both chemical- and genetic-induced DA neurodegeneration possibly through the modulation of oxidative stress, DA metabolism, and α-synuclein toxicity. Based on our present findings, we suggest that DaD might have a potential therapeutic role in Parkinson's disease.

Novel Curcumin-Diethyl Fumarate Hybrid as a Dualistic GSK-3β Inhibitor/Nrf2 Inducer for the Treatment of Parkinson's Disease

Common copathogenic factors, including oxidative stress and neuroinflammation, are found to play a vital role in the development of neurodegenerative disorders, including Alzheimer’s disease (AD) and Parkinson’s disease (PD). Nowadays, owing to the multifactorial character of the diseases, no effective therapies are available, thus underlying the need for new strategies. Overexpression of the enzyme GSK-3β and downregulation of the Nrf2/ARE pathway are responsible for a decrease in antioxidant defense effects. These pieces of evidence underline the usefulness of dual GSK-3β inhibitors/Nrf2 inducers. In this regard, to design a dual modulator, the structures of a curcumin-based analogue, as GSK-3β inhibitor, and a diethyl fumarate fragment, as Nrf2 inducer, were combined. Among the hybrids, 5 and 6 proved to effectively inhibit GSK-3β, while 4 and 5 showed a marked ability to activate Nrf2 together to increase the neuronal resistance to oxidative stress. These last pieces of evidence translated into specific neuroprotective effects of 4 and 5 against PD pathological events including neurotoxicity elicited by α-synuclein aggregates and 6-hydroxydopamine. Hybrid 5 also showed neuroprotective effects in a C. elegans model of PD where the activation of GSK-3β is intimately involved in Nrf2 regulation. In summary, 5 emerged as an interesting multitarget derivative, valuable to be exploited in a multitarget PD perspective.

Ultrafast Detection of Peroxynitrite in Parkinson's Disease Models Using a Near-Infrared Fluorescent Probe

Parkinson's disease (PD) is a neurodegenerative disease that devastatingly affects people's lives. Numerous research studies have shown that peroxynitrite (ONOO^-) plays a pivotal role in the pathogenesis of PD. However, a suitable tool that could quickly and sensitively detect ONOO^- in various PD models is still lacking. To this end, we designed and synthesized a series of near-infrared probes that could detect ONOO^- within seconds by near-infrared fluorescent imaging in an ultrafast and highly selective manner. It is noteworthy that one of those developed probes, NIR-PN1, showed excellent sensing performance and blood-brain barrier penetrating ability. NIR-PN1 was successfully applied for imaging of ONOO^- fluxes in multiple PD models including PC12 cell, Drosophila, C. elegans, and mouse brain, indicating its great potential application not only for understanding the biological roles that ONOO^- played in PD but also for early PD diagnosis and treatment.

Guanosine Prevents against Glutamatergic Excitotoxicity in C. elegans

Glutamatergic neurotransmission is present in most mammalian excitatory synapses and plays a key role in central nervous system homeostasis. When over-activated, it can induce excitotoxicity, which is present in several neuropathologies. The nucleoside guanosine (GUO) is a guanine-based purine known to have neuroprotective effects by modulating glutamatergic system during glutamate excitotoxicity in mammals. However, GUO action in Caenorhabditis elegans, as well as on C. elegans glutamatergic excitotoxicity model, is not known. The GUO effects on behavioral parameters in Wild Type (WT) and knockouts worms for glutamate transporters (GLT-3, GLT-1), glutamate vesicular transporter (EAT-4), and NMDA and non-NMDA receptors were used to evaluate the GUO modulatory effects. The GUO tested concentrations did not alter the animals' development, but GUO reduced pharyngeal pumps in WT animals in a dose-dependent manner. The same effect was observed in pharyngeal pumps, when the animals were treated with 4 mM of GUO in glr-1, nmr-1 and eat-4, but not in glt-3 and glt-3;glt-1 knockouts. The double mutant glt-3; glt-1 for GluTs had decreased body bends and an increased number of reversions. This effect was reverted after treatment with GUO. Furthermore, GUO did not alter the sensory response in worms with altered glutamatergic signaling. Thus, GUO seems to modulate the worm's glutamatergic system in situations of exacerbated glutamatergic signaling, which are represented by knockout strains to glutamate transporters. However, in WT animals, GUO appears to reinforce glutamatergic signaling in specific neurons. Our findings indicate that C. elegans strains are useful models to study new compounds that could be used in glutamate-associated neurodegenerative diseases.

Dopamine-dependent, swimming-induced paralysis arises as a consequence of loss of function mutations in the RUNX transcription factor RNT-1

Dopamine (DA) is a neurotransmitter with actions across phylogeny that modulate core behaviors such as motor activity, reward, attention, and cognition. Perturbed DA signaling in humans is associated with multiple disorders, including addiction, ADHD, schizophrenia, and Parkinson's disease. The presynaptic DA transporter exerts powerful control on DA signaling by efficient clearance of the neurotransmitter following release. As in vertebrates, Caenorhabditis elegans DAT (DAT-1) constrains DA signaling and loss of function mutations in the dat-1 gene result in slowed crawling on solid media and swimming-induced paralysis (Swip) in water. Previously, we identified a mutant line, vt34, that exhibits robust DA-dependent Swip. vt34 exhibits biochemical and behavioral phenotypes consistent with reduced DAT-1 function though vt34; dat-1 double mutants exhibit an enhanced Swip phenotype, suggesting contributions of the vt34-associated mutation to additional mechanisms that lead to excess DA signaling. SNP mapping and whole genome sequencing of vt34 identified the site of the molecular lesion in the gene B0412.2 that encodes the Runx transcription factor ortholog RNT-1. Unlike dat-1 animals, but similar to other loss of function rnt-1 mutants, vt34 exhibits altered male tail morphology and reduced body size. Deletion mutations in both rnt-1 and the bro-1 gene, which encodes a RNT-1 binding partner also exhibit Swip. Both vt34 and rnt-1 mutations exhibit reduced levels of dat-1 mRNA as well as the tyrosine hydroxylase ortholog cat-2. Although reporter studies indicate that rnt-1 is expressed in DA neurons, its re-expression in DA neurons of vt34 animals fails to fully rescue Swip. Moreover, as shown for vt34, rnt-1 mutation exhibits additivity with dat-1 in generating Swip, as do rnt-1 and bro-1 mutations, and vt34 exhibits altered capacity for acetylcholine signaling at the neuromuscular junction. Together, these findings identify a novel role for rnt-1 in limiting DA neurotransmission and suggest that loss of RNT-1 may disrupt function of both DA neurons and body wall muscle to drive Swip.

Caenorhabditis elegans as an emerging model system in environmental epigenetics

The roundworm Caenorhabitis elegans has been an established model organism for the study of genetics and developmental biology, including studies of transcriptional regulation, since the 1970s. This model organism has continued to be used as a classical model system as the field of transcriptional regulation has expanded to include scientific advances in epigenetics and chromatin biology. In the last several decades, C. elegans has emerged as a powerful model for environmental toxicology, particularly for the study of chemical genotoxicity. Here, we outline the utility and applicability of C. elegans as a powerful model organism for mechanistic studies of environmental influences on the epigenome. Our goal in this article is to inform the field of environmental epigenetics of the strengths and limitations of the well-established C. elegans model organism as an emerging model for medium-throughput, in vivo exploration of the role of exogenous chemical stimuli in transcriptional regulation, developmental epigenetic reprogramming, and epigenetic memory and inheritance. As the field of environmental epigenetics matures, and research begins to map mechanisms underlying observed associations, new toolkits and model systems, particularly manipulable, scalable in vivo systems that accurately model human transcriptional regulatory circuits, will provide an essential experimental bridge between in vitro biochemical experiments and mammalian model systems. Environ. Mol. Mutagen. 59:560-575, 2018. © 2018 Wiley Periodicals, Inc.

Mutations in Caenorhabditis elegans neuroligin-like glit-1, the apoptosis pathway and the calcium chaperone crt-1 increase dopaminergic neurodegeneration after 6-OHDA treatment

The loss of dopaminergic neurons is a hallmark of Parkinson’s disease, the aetiology of which is associated with increased levels of oxidative stress. We used C. elegans to screen for genes that protect dopaminergic neurons against oxidative stress and isolated glit-1 (gliotactin (Drosophila neuroligin-like) homologue). Loss of the C. elegans neuroligin-like glit-1 causes increased dopaminergic neurodegeneration after treatment with 6-hydroxydopamine (6-OHDA), an oxidative-stress inducing drug that is specifically taken up into dopaminergic neurons. Furthermore, glit-1 mutants exhibit increased sensitivity to oxidative stress induced by H₂O₂ and paraquat. We provide evidence that GLIT-1 acts in the same genetic pathway as the previously identified tetraspanin TSP-17. After exposure to 6-OHDA and paraquat, glit-1 and tsp-17 mutants show almost identical, non-additive hypersensitivity phenotypes and exhibit highly increased induction of oxidative stress reporters. TSP-17 and GLIT-1 are both expressed in dopaminergic neurons. In addition, the neuroligin-like GLIT-1 is expressed in pharynx, intestine and several unidentified cells in the head. GLIT-1 is homologous, but not orthologous to neuroligins, transmembrane proteins required for the function of synapses. The Drosophila GLIT-1 homologue Gliotactin in contrast is required for epithelial junction formation. We report that GLIT-1 likely acts in multiple tissues to protect against 6-OHDA, and that the epithelial barrier of C. elegans glit-1 mutants does not appear to be compromised. We further describe that hyperactivation of the SKN-1 oxidative stress response pathway alleviates 6-OHDA-induced neurodegeneration. In addition, we find that mutations in the canonical apoptosis pathway and the calcium chaperone crt-1 cause increased 6-OHDA-induced dopaminergic neuron loss. In summary, we report that the neuroligin-like GLIT-1, the canonical apoptosis pathway and the calreticulin CRT-1 are required to prevent 6-OHDA-induced dopaminergic neurodegeneration.

Neurons use dopamine as a chemical messenger to mediate diverse behaviours. The gradual loss of dopaminergic neurons in specific brain areas is a hallmark of Parkinson’s disease. The increased occurrence of highly reactive oxygen radicals, also called oxidative stress, is assumed to contribute to the demise of dopaminergic neurons. In this study, we searched for genes that protect dopaminergic neurons against oxidative stress. We used the nematode C. elegans, a well-characterised model organism whose dopamine signalling system is very similar to that of humans. When C. elegans is exposed to 6-hydroxydopamine, an oxidative stress-inducing compound, dopaminergic neurons gradually die. Our major findings include: (i) absence of the neuroligin-like gene glit-1 causes highly increased cell death of dopaminergic neurons after 6-OHDA exposure; (ii) GLIT-1 acts in a similar manner as the previously identified tetraspanin TSP-17; (iii) GLIT-1 and TSP-17 also protect C. elegans from other types of oxidative stress; and (iv) the programmed cell death pathway and a calcium chaperone protect dopaminergic neurons as well. Collectively, this study shows that apoptosis proteins, the calcium chaperone CRT-1 and the neuroligin-like GLIT-1 protect against neurodegeneration after oxidative stress exposure.

6-OHDA-induced dopaminergic neurodegeneration in Caenorhabditis elegans is promoted by the engulfment pathway and inhibited by the transthyretin-related protein TTR-33

Oxidative stress is linked to many pathological conditions including the loss of dopaminergic neurons in Parkinson’s disease. The vast majority of disease cases appear to be caused by a combination of genetic mutations and environmental factors. We screened for genes protecting Caenorhabditis elegans dopaminergic neurons from oxidative stress induced by the neurotoxin 6-hydroxydopamine (6-OHDA) and identified the transthyretin-related gene ttr-33. The only described C. elegans transthyretin-related protein to date, TTR-52, has been shown to mediate corpse engulfment as well as axon repair. We demonstrate that TTR-52 and TTR-33 have distinct roles. TTR-33 is likely produced in the posterior arcade cells in the head of C. elegans larvae and is predicted to be a secreted protein. TTR-33 protects C. elegans from oxidative stress induced by paraquat or H₂O₂ at an organismal level. The increased oxidative stress sensitivity of ttr-33 mutants is alleviated by mutations affecting the KGB-1 MAPK kinase pathway, whereas it is enhanced by mutation of the JNK-1 MAPK kinase. Finally, we provide genetic evidence that the C. elegans cell corpse engulfment pathway is required for the degeneration of dopaminergic neurons after exposure to 6-OHDA. In summary, we describe a new neuroprotective mechanism and demonstrate that TTR-33 normally functions to protect dopaminergic neurons from oxidative stress-induced degeneration, potentially by acting as a secreted sensor or scavenger of oxidative stress.

Animals employ multiple mechanisms to prevent their cells from damage by reactive oxygen species, chemically reactive molecules containing oxygen. Oxidative stress, caused by the overabundance of reactive oxygen species or a decreased cellular defence against these chemicals, is linked to a variety of neurodegenerative conditions, including the loss of dopaminergic neurons in Parkinson’s disease. In this study, we discovered a novel protective molecule that functions to prevent dopaminergic neurodegeneration caused by oxidative stress induced by the neurotoxin 6-hydroxydopamine (6-OHDA). We used the nematode C. elegans, a well-characterised model in which mechanisms can be studied on an organismal level. When C. elegans is exposed to 6-OHDA, its dopaminergic neurons gradually die. Our major findings include (i) mutations of the transthyretin-related gene ttr-33 causes highly increased dopaminergic neurodegeneration after 6-OHDA exposure; (ii) TTR-33 is likely produced and secreted by several cells in the head of the animal; (iii) TTR-33 protects against oxidative stress induced by other compounds; (iv) mutations in the KGB-1 MAP kinase stress pathway alleviate dopaminergic neuron loss in the ttr-33 mutant; and (v) the cell corpse engulfment pathway is required for dopaminergic neurodegeneration. We hypothesise that TTR-33 protects dopaminergic neurons against 6-OHDA-induced oxidative stress by acting as an oxygen sensor or scavenger.

6-hydroxydopamine (6-OHDA) Oxidative Stress Assay for Observing Dopaminergic Neuron Loss in Caenorhabditis elegans

The nematode Caenorhabditis elegans is a powerful genetic model that can be used to investigate neuronal death. Research using C. elegans has been crucial to characterize cell death programmes that are conserved in mammals. Many neuronal signaling components, such as those mediating dopaminergic neurotransmission, are preserved as well. Dopaminergic neurons are progressively lost in Parkinson's disease and an important risk factor to develop this disease appears to be oxidative stress, the increased occurrence of highly reactive oxygen species. Oxidative stress-induced dopaminergic neurodegeneration is mimicked in animal models by treatment with 6-hydroxydopamine (6-OHDA), a dopamine analog, which is specifically taken up into dopaminergic neurons. After exposing C. elegans to 6-OHDA, the loss of fluorescently labeled dopaminergic neurons can be easily monitored. An organisms' sensitivity to oxidative stress is thought to be influenced by basal levels of intrinsic oxidative stress and the ability to counteract oxidative stress and oxidative stress-induced damage. The C. elegans '6-OHDA model' led to the discovery of novel genes that are required to protect dopaminergic neurons and it has helped to determine the effects of conserved cell death and cell engulfment pathways in dopaminergic neurodegeneration. Here, we describe a simple protocol that allows for the easy detection of dopaminergic neuron loss after 6-OHDA treatment in C. elegans.

Anti-Parkinsonian effects of β-amyrin are regulated via LGG-1 involved autophagy pathway in Caenorhabditis elegans

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disease that is associated with aging and is characterized as a movement disorder. Currently, there is still no complete therapy for PD. In recent years, the identification and characterization of medicinal plants to cure or treat PD has gained increasing scientific interest.

PURPOSE

In this study, we investigated a pentacyclic triterpenoid compound, β-amyrin, which is found in many medicinal plants for its anti-Parkinsonian effects, using Caenorhabditis elegans (C. elegans) disease models and their underlying mechanisms.

METHODS

C. elegans treated or untreated with β-amyrin were investigated for oxidative stress resistance, neurodegeneration, and α-synuclein aggregation assays. The C. elegans ortholog of Atg8/LC3, LGG-1 that is involved in the autophagy pathway was also evaluated by quantitative RT-PCR and transgenic strain experiments.

RESULTS

β-Amyrin exerted excellent antioxidant activity and reduced intracellular oxygen species in C. elegans. Using the transgenic strain BZ555, β-amyrin showed a protective effect on dopaminergic neurons reducing cell damage induced by 6-hydroxydopamine (6-OHDA). In addition, β-amyrin significantly reduced the α-synuclein aggregation in the transgenic strain NL5901. Moreover, β-amyrin up-regulated LGG-1 mRNA expression and increased the number of localized LGG-1 puncta in the transgenic strain DA2123.

CONCLUSION

The results from this study suggest that the anti-Parkinsonian effects of β-amyrin might be regulated via LGG-1 involved autophagy pathway in C. elegans. Therefore, β-amyrin may be useful for therapeutic applications or supplements to treat or slow the progression of PD.

LIN-32/Atonal Controls Oxygen Sensing Neuron Development in Caenorhabditis elegans

Development of complex nervous systems requires precisely controlled neurogenesis. The generation and specification of neurons occur through the transcriptional and post-transcriptional control of complex regulatory networks. In vertebrates and invertebrates, the proneural basic-helix-loop-helix (bHLH) family of transcription factors has multiple functions in neurogenesis. Here, we identified the LIN-32/Atonal bHLH transcription factor as a key regulator of URXL/R oxygen-sensing neuron development in Caenorhabditis elegans. When LIN-32/Atonal expression is lost, the expression of URX specification and terminal differentiation genes is abrogated. As such, lin-32 mutant animals are unable to respond to increases in environmental oxygen. The URX neurons are generated from a branch of the cell lineage that also produces the CEPDL/R and URADL/R neurons. We found development of these neurons is also defective, suggesting that LIN-32/Atonal regulates neuronal development of the entire lineage. Finally, our results show that aspects of URX neuronal fate are partially restored in lin-32 mutant animals when the apoptosis pathway is inhibited. This suggests that, as in other organisms, LIN-32/Atonal regulates neuronal apoptosis.

Behavioral deficits and neural damage of Caenorhabditis elegans induced by three rare earth elements

Rare earth elements (REEs) are widely used in industry, agriculture, medicine and daily life in recent years. However, environmental and health risks of REEs are still poorly understood. In this study, neurotoxicity of trichloride neodymium, praseodymium and scandium were evaluated using nematode Caenorhabditis elegans as the assay system. Median lethal concentrations (48 h) were 99.9, 157.2 and 106.4 mg/L for NdCl₃, PrCl₃ and ScCl₃, respectively. Sublethal dose (10-30 mg/L) of these trichloride salts significantly inhibited body length of nematodes. Three REEs resulted in significant declines in locomotor frequency of body bending, head thrashing and pharyngeal pumping. In addition, mean speed and wavelength of crawling movement were significantly reduced after chronic exposure. Using transgenic nematodes, we found NdCl₃, PrCl₃ and ScCl₃ resulted in loss of dendrite and soma of neurons, and induced down-expression of dat-1::GFP and unc-47::GFP. It indicates that REEs can lead to damage of dopaminergic and GABAergic neurons. Our data suggest that exposure to REEs may cause neurotoxicity of inducing behavioral deficits and neural damage. These findings provide useful information for understanding health risk of REE materials.

Behavioral Phenotyping and Pathological Indicators of Parkinson's Disease in C. elegans Models

Parkinson's disease (PD) is a neurodegenerative disorder with symptoms that progressively worsen with age. Pathologically, PD is characterized by the aggregation of α-synuclein in cells of the substantia nigra in the brain and loss of dopaminergic neurons. This pathology is associated with impaired movement and reduced cognitive function. The etiology of PD can be attributed to a combination of environmental and genetic factors. A popular animal model, the nematode roundworm Caenorhabditis elegans, has been frequently used to study the role of genetic and environmental factors in the molecular pathology and behavioral phenotypes associated with PD. The current review summarizes cellular markers and behavioral phenotypes in transgenic and toxin-induced PD models of C. elegans.

Chronic exposure to graphene-based nanomaterials induces behavioral deficits and neural damage in Caenorhabditis elegans

Nanomaterials of graphene and its derivatives have been widely applied in recent years, but whose impacts on the environment and health are still not well understood. In the present study, the potential adverse effects of graphite (G), graphite oxide nanoplatelets (GO) and graphene quantum dots (GQDs) on the motor nervous system were investigated using nematode Caenorhabditis elegans as the assay system. After being characterized using TEM, SEM, XPS and PLE, three nanomaterials were chronically exposed to C. elegans for 6 days. In total, 50-100 mg l^-1 GO caused a significant reduction in the survival rate, but G and GDDs showed low lethality on nematodes. After chronic exposure of sub-lethal dosages, three nanomaterials were observed to distribute primarily in the pharynx and intestine; but GQDs were widespread in nematode body. Three graphene-based nanomaterials resulted in significant declines in locomotor frequency of body bending, head thrashing and pharynx pumping. In addition, mean speed, bending angle-frequency and wavelength of the crawling movement were significantly reduced after exposure. Using transgenic nematodes, we found high concentrations of graphene-based nanomaterials induced down-expression of dat-1::GFP and eat-4::GFP, but no significant changes in unc-47::GFP. This indicates that graphene-based nanomaterials can lead to damages in the dopaminergic and glutamatergic neurons. The present data suggest that chronic exposure of graphene-based nanomaterials may cause neurotoxicity risks of inducing behavioral deficits and neural damage. These findings provide useful information to understand the toxicity and safe application of graphene-based nanomaterials. Copyright © 2017 John Wiley & Sons, Ltd.

Using C. elegans to discover therapeutic compounds for ageing-associated neurodegenerative diseases

Age-associated neurodegenerative disorders such as Alzheimer's disease are a major public health challenge, due to the demographic increase in the proportion of older individuals in society. However, the relatively few currently approved drugs for these conditions provide only symptomatic relief. A major goal of neurodegeneration research is therefore to identify potential new therapeutic compounds that can slow or even reverse disease progression, either by impacting directly on the neurodegenerative process or by activating endogenous physiological neuroprotective mechanisms that decline with ageing. This requires model systems that can recapitulate key features of human neurodegenerative diseases that are also amenable to compound screening approaches. Mammalian models are very powerful, but are prohibitively expensive for high-throughput drug screens. Given the highly conserved neurological pathways between mammals and invertebrates, Caenorhabditis elegans has emerged as a powerful tool for neuroprotective compound screening. Here we describe how C. elegans has been used to model various human ageing-associated neurodegenerative diseases and provide an extensive list of compounds that have therapeutic activity in these worm models and so may have translational potential.

Ethosuximide ameliorates neurodegenerative disease phenotypes by modulating DAF-16/FOXO target gene expression

BACKGROUND

Many neurodegenerative diseases are associated with protein misfolding/aggregation. Treatments mitigating the effects of such common pathological processes, rather than disease-specific symptoms, therefore have general therapeutic potential.

RESULTS

Here we report that the anti-epileptic drug ethosuximide rescues the short lifespan and chemosensory defects exhibited by C. elegans null mutants of dnj-14, the worm orthologue of the DNAJC5 gene mutated in autosomal-dominant adult-onset neuronal ceroid lipofuscinosis. It also ameliorates the locomotion impairment and short lifespan of worms expressing a human Tau mutant that causes frontotemporal dementia. Transcriptomic analysis revealed a highly significant up-regulation of DAF-16/FOXO target genes in response to ethosuximide; and indeed RNAi knockdown of daf-16 abolished the therapeutic effect of ethosuximide in the worm dnj-14 model. Importantly, ethosuximide also increased the expression of classical FOXO target genes and reduced protein aggregation in mammalian neuronal cells.

CONCLUSIONS

We have revealed a conserved neuroprotective mechanism of action of ethosuximide from worms to mammalian neurons. Future experiments in mouse neurodegeneration models will be important to confirm the repurposing potential of this well-established anti-epileptic drug for treatment of human neurodegenerative diseases.

Expression profile of a Caenorhabditis elegans model of adult neuronal ceroid lipofuscinosis reveals down regulation of ubiquitin E3 ligase components

Cysteine string protein (CSP) is a chaperone of the Dnaj/Hsp40 family of proteins and is essential for synaptic maintenance. Mutations in the human gene encoding CSP, DNAJC5, cause adult neuronal ceroid lipofucinosis (ANCL) which is characterised by progressive dementia, movement disorders, seizures and premature death. CSP null models in mice, flies and worms have been shown to also exhibit similar neurodegenerative phenotypes. Here we have explored the mechanisms underlying ANCL disease progression using Caenorhaditis elegans mutant strains of dnj-14, the worm orthologue of DNAJC5. Transcriptional profiling of these mutants compared to control strains revealed a broad down-regulation of ubiquitin proteasome system (UPS)-related genes, in particular, components of multimeric RING E3 ubiquitin ligases including F-Box, SKR and BTB proteins. These data were supported by the observation that dnj-14 mutant worm strains expressing a GFP-tagged ubiquitin fusion degradation substrate exhibited decreased ubiquitylated protein degradation. The results indicate that disruption of an essential synaptic chaperone leads to changes in expression levels of UPS-related proteins which has a knock-on effect on overall protein degradation in C. elegans. The specific over-representation of E3 ubiquitin ligase components revealed in our study, suggests that proteins and complexes upstream of the proteasome itself may be beneficial therapeutic targets.

Persistence of Long-Term Memory in Vitrified and Revived Caenorhabditis elegans

Can memory be retained after cryopreservation? Our research has attempted to answer this long-standing question by using the nematode worm Caenorhabditis elegans, a well-known model organism for biological research that has generated revolutionary findings but has not been tested for memory retention after cryopreservation. Our study's goal was to test C. elegans' memory recall after vitrification and reviving. Using a method of sensory imprinting in the young C. elegans, we establish that learning acquired through olfactory cues shapes the animal's behavior and the learning is retained at the adult stage after vitrification. Our research method included olfactory imprinting with the chemical benzaldehyde (C₆H₅CHO) for phase-sense olfactory imprinting at the L1 stage, the fast-cooling SafeSpeed method for vitrification at the L2 stage, reviving, and a chemotaxis assay for testing memory retention of learning at the adult stage. Our results in testing memory retention after cryopreservation show that the mechanisms that regulate the odorant imprinting (a form of long-term memory) in C. elegans have not been modified by the process of vitrification or by slow freezing.

Two novel DEG/ENaC channel subunits expressed in glia are needed for nose-touch sensitivity in Caenorhabditis elegans

Neuronal DEG/ENaC (degenerin and epithelial Na(+) channel) Na(+) channels have been implicated in touch sensation. For example, MEC-4 is expressed in touch neurons in Caenorhabditis elegans and mediates gentle-touch response. Similarly, homologous mammalian ASIC2 and ASIC3 are expressed in sensory neurons and produce touch phenotypes when knocked out in mice. Here, we show that novel DEG/ENaC subunits DELM-1 and DELM-2 (degenerin-like channel mechanosensory linked-1 and degenerin-like channel mechanosensory linked-2) are expressed in glia associated with touch neurons in C. elegans and that their knock-out causes defects in mechanosensory behaviors related to nose touch and foraging, which are mediated by OLQ and IL1 sensory neurons. Cell-specific rescue supports that DELM-1 and DELM-2 are required cell-autonomously in glia to orchestrate mechanosensory behaviors. Electron microscopy reveals that in delm-1 knock-outs, OLQ and IL1 sensory neurons and associated glia are structurally normal. Furthermore, we show that knock-out of DELM-1 and DELM-2 does not disrupt the expression or cellular localization of TRPA-1, a TRP channel needed in OLQ and IL1 neurons for touch behaviors. Rather, rescue of the delm-1 nose-touch-insensitive phenotype by expression of a K(+) channel in socket glia and of a cationic channel in OLQ neurons suggests that DELM channels set basal neuronal excitability. Together, our data show that DELM-1 and DELM-2 are expressed in glia associated with touch neurons where they are not needed for neuronal structural integrity or cellular distribution of neuronal sensory channels, but rather for their function.

Drug absorption efficiency in Caenorhbditis elegans delivered by different methods

BACKGROUND

Caenorhbditis elegans has being vigorously used as a model organism in many research fields and often accompanied by administrating with various drugs. The methods of delivering drugs to worms are varied from one study to another, which make difficult in comparing results between studies.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated the drug absorption efficiency in C. elegans using five frequently used methods with resveratrol with low aqueous solubility and water-soluble 5-Fluoro-2'-deoxyuridine (FUDR) as positive compounds. The drugs were either applied to the LB medium with bacteria OP50, before spreading onto Nematode Growth Medium (NGM) plates (LB medium method), or to the NGM with live (NGM live method) or dead bacteria (NGM dead method), or spotting the drug solution to the surface of plates directly (spot dead method), or growing the worms in liquid medium (liquid growing method). The concentration of resveratrol and FUDR increased gradually within C. elegans and reached the highest during 12 hours to one day and then decreased slowly. At the same time point, the higher the drug concentration, the higher the metabolism rate. The drug concentrations in worms fed with dead bacteria were higher than with live bacteria at the same time point. Consistently, the drug concentration in medium with live bacteria decreased much faster than in medium with dead bacteria, reach to about half of the original concentration within 12 hours.

CONCLUSION

Resveratrol with low aqueous solubility and water-soluble FUDR have the same absorption and metabolism pattern. The drug metabolism rate in worms was both dosage and time dependent. NGM dead method and liquid growing method achieved the best absorption efficiency in worms. The drug concentration within worms was comparable with that in mice, providing a bridge for dose translation from worms to mammals.

The metal transporter SMF-3/DMT-1 mediates aluminum-induced dopamine neuron degeneration

Aluminum (Al(3+)) is the most prevalent metal in the earth's crust and is a known human neurotoxicant. Al(3+) has been shown to accumulate in the substantia nigra of patients with Parkinson's disease (PD), and epidemiological studies suggest correlations between Al(3+) exposure and the propensity to develop both PD and the amyloid plaque-associated disorder Alzheimer's disease (AD). Although Al(3+) exposures have been associated with the development of the most common neurodegenerative disorders, the molecular mechanism involved in Al(3+) transport in neurons and subsequent cellular death has remained elusive. In this study, we show that a brief exposure to Al(3+) decreases mitochondrial membrane potential and cellular ATP levels, and confers dopamine (DA) neuron degeneration in the genetically tractable nematode Caenorhabditis elegans (C. elegans). Al(3+) exposure also exacerbates DA neuronal death conferred by the human PD-associated protein α-synuclein. DA neurodegeneration is dependent on SMF-3, a homologue to the human divalent metal transporter (DMT-1), as a functional null mutation partially inhibits the cell death. We also show that SMF-3 is expressed in DA neurons, Al(3+) exposure results in a significant decrease in protein levels, and the neurodegeneration is partially dependent on the PD-associated transcription factor Nrf2/SKN-1 and caspase Apaf1/CED-4. Furthermore, we provide evidence that the deletion of SMF-3 confers Al(3+) resistance due to sequestration of Al(3+) into an intracellular compartment. This study describes a novel model for Al(3+)-induced DA neurodegeneration and provides the first molecular evidence of an animal Al(3+) transporter.

Conserved role of dopamine in the modulation of behavior

Dopamine is an ancient signaling molecule. It is responsible for maintaining the adaptability of behavioral outputs and is found across taxa. The following is a summary of the role of dopamine and the mechanisms of its function and dysfunction. We discuss our recent findings on dopaminergic control of behaviors in C. elegans and discuss its potential implications for work in the fields of C. elegans and Parkinson research.

A predictable worm: application of Caenorhabditis elegans for mechanistic investigation of movement disorders

Ongoing investigations into causes and cures for human movement disorders are important toward the elucidation of diseases such as Parkinson's disease (PD) and dystonia. The use of animal model systems can provide links to susceptibility factors, as well as therapeutic interventions. In this regard, the nematode roundworm, Caenorhabditis elegans, is ideal for examining age-dependent neurodegenerative disease studies. It is genetically tractable, has a short lifespan, and a well-defined nervous system. Green fluorescent protein is readily visualized in C. elegans because it is a transparent organism, thus the nervous system and factors that alter the viability of neurons can be directly examined in vivo. Through expression of the human PD-associated protein (α-synuclein in the worm dopamine neurons), neurodegeneration is observed in an age-dependent manner. Furthermore, expression of the early-onset dystonia-related protein torsinA increases vulnerability to endoplasmic reticulum (ER) stress in C. elegans, because torsinA is located in the ER. Here we provide an overview of collaborative studies we have conducted that collectively demonstrate the usefulness of the nematode model to discern functional effectors of dopaminergic neurodegeneration and ER stress that translate to mammalian data in the fields of PD and dystonia. Taken together, the application of C. elegans toward the evaluation of genetic modifiers for movement disorders research has predictive value and serves to accelerate the path forward for therapeutic interventions.

Animal models of Parkinson's disease: a source of novel treatments and clues to the cause of the disease

Animal models of Parkinson's disease (PD) have proved highly effective in the discovery of novel treatments for motor symptoms of PD and in the search for clues to the underlying cause of the illness. Models based on specific pathogenic mechanisms may subsequently lead to the development of neuroprotective agents for PD that stop or slow disease progression. The array of available rodent models is large and ranges from acute pharmacological models, such as the reserpine- or haloperidol-treated rats that display one or more parkinsonian signs, to models exhibiting destruction of the dopaminergic nigro-striatal pathway, such as the classical 6-hydroxydopamine (6-OHDA) rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models. All of these have provided test beds in which new molecules for treating the motor symptoms of PD can be assessed. In addition, the emergence of abnormal involuntary movements (AIMs) with repeated treatment of 6-OHDA-lesioned rats with L-DOPA has allowed for examination of the mechanisms responsible for treatment-related dyskinesia in PD, and the detection of molecules able to prevent or reverse their appearance. Other toxin-based models of nigro-striatal tract degeneration include the systemic administration of the pesticides rotenone and paraquat, but whilst providing clues to disease pathogenesis, these are not so commonly used for drug development. The MPTP-treated primate model of PD, which closely mimics the clinical features of PD and in which all currently used anti-parkinsonian medications have been shown to be effective, is undoubtedly the most clinically-relevant of all available models. The MPTP-treated primate develops clear dyskinesia when repeatedly exposed to L-DOPA, and these parkinsonian animals have shown responses to novel dopaminergic agents that are highly predictive of their effect in man. Whether non-dopaminergic drugs show the same degree of predictability of response is a matter of debate. As our understanding of the pathogenesis of PD has improved, so new rodent models produced by agents mimicking these mechanisms, including proteasome inhibitors such as PSI, lactacystin and epoximycin or inflammogens like lipopolysaccharide (LPS) have been developed. A further generation of models aimed at mimicking the genetic causes of PD has also sprung up. Whilst these newer models have provided further clues to the disease pathology, they have so far been less commonly used for drug development. There is little doubt that the availability of experimental animal models of PD has dramatically altered dopaminergic drug treatment of the illness and the prevention and reversal of drug-related side effects that emerge with disease progression and chronic medication. However, so far, we have made little progress in moving into other pharmacological areas for the treatment of PD, and we have not developed models that reflect the progressive nature of the illness and its complexity in terms of the extent of pathology and biochemical change. Only when this occurs are we likely to make progress in developing agents to stop or slow the disease progression. The overarching question that draws all of these models together in the quest for better drug treatments for PD is how well do they recapitulate the human condition and how predictive are they of successful translation of drugs into the clinic? This article aims to clarify the current position and highlight the strengths and weaknesses of available models.

Big ideas for small brains: what can psychiatry learn from worms, flies, bees and fish?

While the research community has accepted the value of rodent models as informative research platforms, there is less awareness of the utility of other small vertebrate and invertebrate animal models. Neuroscience is increasingly turning to smaller, non-rodent models to understand mechanisms related to neuropsychiatric disorders. Although they can never replace clinical research, there is much to be learnt from 'small brains'. In particular, these species can offer flexible genetic 'tool kits' that can be used to explore the expression and function of candidate genes in different brain regions. Very small animals also offer efficiencies with respect to high-throughput screening programs. This review provides a concise overview of the utility of models based on worm, fruit fly, honeybee and zebrafish. Although these species may have small brains, they offer the neuropsychiatric research community opportunities to explore some of the most important research questions in our field.

Droplet microfluidics for characterizing the neurotoxin-induced responses in individual Caenorhabditis elegans

A droplet-based microfluidic device integrated with a novel floatage-based trap array and a tapered immobilization channel array was presented for characterizing the neurotoxin-induced multiple responses in individual Caenorhabditis elegans (C. elegans) continuously. The established device enabled the evaluations of movement and fluorescence imaging analysis of individual C. elegans simultaneously. The utility of this device was demonstrated by the pharmacological evaluation of neurotoxin (6-hydroxydopamine, 6-OHDA) triggered mobility defects, neuron degeneration and oxidative stress in individual worms. Exposure of living worms to 6-OHDA could cause obvious mobility defects, selective degeneration of dopaminergic (DAergic) neurons, and increased oxidative stress in a dose dependent manner. These results are important towards the understanding of mechanisms leading to DAergic toxicity by neurotoxin and will be of benefit for the screening of new therapeutics for neurodegenerative diseases. This device was simple, stable and easy to operate, with the potential to facilitate whole-animal assays and drug screening in a high throughput manner at single animal resolution.

Non-mammalian animal models of Parkinson's disease for drug discovery

IMPORTANCE OF THE FIELD

Parkinson's disease (PD) is a prevalent neurodegenerative disease affecting millions of predominantly elderly individuals worldwide. Despite intensive efforts devoted to drug discovery, the disease remains incurable. Compounding this problem is the current lack of a truly representative mammalian model of PD. However, a number of non-mammalian models of PD have been created in recent years that hold tremendous promise to accelerate our understanding of the disease as well as to transform the drug discovery process.

AREAS COVERED IN THIS REVIEW

This review provides an overview of the various Caenorhabditis elegans and Drosophila genetic models of PD that have been generated to date and discusses the utility of these model systems in the identification of molecules of potential therapeutic value for the PD patient.

WHAT THE READER WILL GAIN

Readers will appreciate the strengths (and limitations) of C. elegans and Drosophila in modeling salient features of the disease as well as their usefulness in uncovering novel gene-gene interaction and pathways relevant to PD pathogenesis. Readers will also appreciate how technological advancements have allowed the direct evaluation of novel compounds in these living models of PD in a virtually high-throughput manner.

TAKE HOME MESSAGE

Non-mammalian models of PD provide a valuable in vivo platform for drug screening. Unlike cell-based systems, these living models with an intact nervous system allow for a more meaningful evaluation of the neuroprotective properties of genetic and chemical modifiers to be conducted.

A programmable microvalve-based microfluidic array for characterization of neurotoxin-induced responses of individual C. elegans

The soil dwelling nematode Caenorhabditis elegans (C. elegans) is an excellent model organism for the study of numerous disease including neurodegenerative disease. In this study, a programmable microvalve-based microfluidic array for real-time and long-term monitoring of the neurotoxin-induced responses of the individual C. elegans was developed. The device consisted of a flow layer and a control layer, which were used for worm manipulation. By activating the programmable microvalves in the control layer, mutiple worms could be individually captured and intermittently immobilized in parallel channels. Thus the mobility behavior, together with the corresponding dopaminergic neuron features of the worms in response to neurotoxin, could be investigated simultaneously. It was found that the neurotoxin MPP+ enabled to induce mobility defects and dopaminergic neurons loss in worms. The established system is easy and fast to operate, which offers not only the controllable microenvironment for analyzing the individual worms in parallel, monitoring the same worm over time, but also the capability to characterize the mobility behavior and neuron features in response to stimuli simultaneously. In addition, the device enabled to sustain the worm culture over most of their adult lifespan without any harm to worm, providing a potential platform for lifespan and aging research.

The divalent metal transporter homologues SMF-1/2 mediate dopamine neuron sensitivity in caenorhabditis elegans models of manganism and parkinson disease

Parkinson disease (PD) and manganism are characterized by motor deficits and a loss of dopamine (DA) neurons in the substantia nigra pars compacta. Epidemiological studies indicate significant correlations between manganese exposure and the propensity to develop PD. The vertebrate divalent metal transporter-1 (DMT-1) contributes to maintaining cellular Mn(2+) homeostasis and has recently been implicated in Fe(2+)-mediated neurodegeneration in PD. In this study we describe a novel model for manganism that incorporates the genetically tractable nematode Caenorhabditis elegans. We show that a brief exposure to Mn(2+) increases reactive oxygen species and glutathione production, decreases oxygen consumption and head mitochondria membrane potential, and confers DA neuronal death. DA neurodegeneration is partially dependent on a putative homologue to DMT-1, SMF-1, as genetic knockdown or deletion partially inhibits the neuronal death. Mn(2+) also amplifies the DA neurotoxicity of the PD-associated protein alpha-synuclein. Furthermore, both SMF-1 and SMF-2 are expressed in DA neurons and contribute to PD-associated neurotoxicant-induced DA neuron death. These studies describe a C. elegans model for manganism and show that DMT-1 homologues contribute to Mn(2+)- and PD-associated DA neuron vulnerability.

Characterization of the effects of methylmercury on Caenorhabditis elegans

The rising prevalence of methylmercury (MeHg) in seafood and in the global environment provides an impetus for delineating the mechanism of the toxicity of MeHg. Deleterious effects of MeHg have been widely observed in humans and in other mammals, the most striking of which occur in the nervous system. Here we test the model organism, Caenorhabditis elegans (C. elegans), for MeHg toxicity. The simple, well-defined anatomy of the C. elegans nervous system and its ready visualization with green fluorescent protein (GFP) markers facilitated our study of the effects of methylmercuric chloride (MeHgCl) on neural development. Although MeHgCl was lethal to C. elegans, induced a developmental delay, and decreased pharyngeal pumping, other traits including lifespan, brood size, swimming rate, and nervous system morphology were not obviously perturbed in animals that survived MeHgCl exposure. Despite the limited effects of MeHgCl on C. elegans development and behavior, intracellular mercury (Hg) concentrations (<or=3 ng Hg/mg protein) in MeHgCl-treated nematodes approached levels that are highly toxic to mammals. If MeHgCl reaches these concentrations throughout the animal, this finding indicates that C. elegans cells, particularly neurons, may be less sensitive to MeHgCl toxicity than mammalian cells. We propose, therefore, that C. elegans should be a useful model for discovering intrinsic mechanisms that confer resistance to MeHgCl exposure.

Droplet-based microfluidic system for individual Caenorhabditis elegans assay

A droplet-based microfluidic system integrating a droplet generator and a droplet trap array is described for encapsulating individual Caenorhabditis elegans into a parallel series of droplets, enabling characterization of the worm behavior in response to neurotoxin at single-animal resolution.

Use of non-mammalian alternative models for neurotoxicological study

The field of neurotoxicology needs to satisfy two opposing demands: the testing of a growing list of chemicals, and resource limitations and ethical concerns associated with testing using traditional mammalian species. National and international government agencies have defined a need to reduce, refine or replace mammalian species in toxicological testing with alternative testing methods and non-mammalian models. Toxicological assays using alternative animal models may relieve some of this pressure by allowing testing of more compounds while reducing expense and using fewer mammals. Recent advances in genetic technologies and the strong conservation between human and non-mammalian genomes allow for the dissection of the molecular pathways involved in neurotoxicological responses and neurological diseases using genetically tractable organisms. In this review, applications of four non-mammalian species, zebrafish, cockroach, Drosophila, and Caenorhabditis elegans, in the investigation of neurotoxicology and neurological diseases are presented.

Whole organism approaches to chemical genomics: the promising role of zebrafish (Danio rerio)

Chemical genomics is a new and rapidly developing field. It refers to the use of cell-permeable small molecules, which are highly specific for their protein targets, in order to dissect biological pathways and to discover new drug leads. Small-molecule screening is usually limited to high-throughput approaches that use defined cell lines; however, whole organism screening is gaining increasing attention. This review addresses the latter concept and highlights the advances in whole organism-based screening, with an emphasis on the use of the zebrafish (Danio rerio).

Non-developmentally programmed cell death in Caenorhabditis elegans

The simple nematode worm Caenorhabditis elegans has played a pivotal role in deciphering the molecular mechanisms of apoptosis. Precisely 131 somatic cells undergo programmed apoptotic death during development to contour the 959-cell adult organism. In addition to developmental cell death, specific genetic manipulations and extrinsic factors can trigger non-programmed cell death that is morphologically and mechanistically distinct from apoptosis. Here, we survey paradigms of cell death that is not developmentally programmed in C. elegans and review the molecular mechanisms involved. Furthermore, we consider the potential of the nematode as a platform to investigate pathological cell death. The striking extent of conservation between apoptotic pathways in worms and higher organisms including humans, holds promise that similarly, studies of non-programmed cell death in C. elegans will yield significant new insights, highly relevant to human pathology.

Iptakalim alleviated the increase of extracellular dopamine and glutamate induced by 1-methyl-4-phenylpyridinium ion in rat striatum

The present study examined the effect of iptakalim (Ipt), a novel ATP-sensitive potassium (K(ATP)) channel opener (KCO), on 1-methyl-4-phenylpyridinium ion (MPP(+))-induced dopamine (DA) and glutamate efflux in extracellular fluid of rat striatum, using microdialysis technique. Rats were implanted guide cannula in the striatum and artificial cerebrospinal fluid was infused through a microdialysis probe to detect the level of DA and glutamate in the striatum. MPP(+) significantly enhanced the extracellular levels of DA and its metabolites, DOPAC and HVA, as well as glutamate. Application of Ipt (1, 10, 100 microM) concentration-dependently suppressed DA and its metabolites efflux induced by MPP(+). Concomitantly, Ipt reduced the increase of extracellular glutamate induced by MPP(+). These results suggest that Ipt can regulate DA and glutamate efflux induced by MPP(+) in rat striatum.

Progressive dopamine neuron loss in Parkinson's disease: the multiple hit hypothesis

Animal models have been an essential tool for researchers and clinicians in their efforts to study and treat Parkinson's disease (PD). Thus, the various ways 6-hydroxydopamine is employed, the use of MPTP in rodents and nonhuman primates, the prenatal exposure to bacterial endotoxin, the postnatal exposure to environmental toxins such as paraquat and rotenone, the assessment of dopamine (DA) neurons in genetic knockout mouse, and even the behavioral analysis of fruit flies and worms have added significantly to our knowledge base of PD--or have they? Are these animal models manifesting a true model of PD? Have the 7786 published studies (to date) on PD with animal models led to a clearer understanding of its etiology, treatment, or progression? In this review we critically assess this question. We begin with a succinct history of the major contributions, which have led to the current animal models of PD. We then evaluate the primary issue of the progressive loss of DA neurons, which, except for a few studies, has not been addressed in animal models of PD, even though this is the major pathological characteristic of the disease. Lastly, we discuss the possibility that more than one risk factor for PD may be necessary to develop an animal model that shows synergy--the progressive loss of DA neurons. Thus, the multiple hit hypothesis of PD-that is, the effect of more then one risk factor-may be the start of new era in animal models of PD that is one step closer to mimicking the pathology of PD in humans.

The Caenorhabditis elegans snf-11 gene encodes a sodium-dependent GABA transporter required for clearance of synaptic GABA

Sodium-dependent neurotransmitter transporters participate in the clearance and/or recycling of neurotransmitters from synaptic clefts. The snf-11 gene in Caenorhabditis elegans encodes a protein of high similarity to mammalian GABA transporters (GATs). We show here that snf-11 encodes a functional GABA transporter; SNF-11-mediated GABA transport is Na+ and Cl- dependent, has an EC50 value of 168 microM, and is blocked by the GAT1 inhibitor SKF89976A. The SNF-11 protein is expressed in seven GABAergic neurons, several additional neurons in the head and retrovesicular ganglion, and three groups of muscle cells. Therefore, all GABAergic synapses are associated with either presynaptic or postsynaptic (or both) expression of SNF-11. Although a snf-11 null mutation has no obvious effects on GABAergic behaviors, it leads to resistance to inhibitors of acetylcholinesterase. In vivo, a snf-11 null mutation blocks GABA uptake in at least a subset of GABAergic cells; in a cell culture system, all GABA uptake is abolished by the snf-11 mutation. We conclude that GABA transport activity is not essential for normal GABAergic function in C. elegans and that the localization of SNF-11 is consistent with a GABA clearance function rather than recycling.

Effects of iptakalim on extracellular glutamate and dopamine levels in the striatum of unilateral 6-hydroxydopamine-lesioned rats: A microdialysis study

In a previous study, we demonstrated that iptakalim (Ipt) significantly ameliorated hypolocomotion and catalepsy induced by haloperidol and rotenone in rats. In order to further understand the mechanism(s), using a rat model of Parkinson's disease (PD) established by unilateral 6-hydroxydopamine (6-OHDA) administration to the substantia nigra pars compacta (SNpc) and reverse microdialysis techniques with high performance liquid chromatography (HPLC), we investigated the effects of Ipt on extracellular levels of glutamate, dopamine (DA) and its metabolite dihydroxyphenylacetic acid (DOPAC) in the striatum of conscious and freely moving rats. The results indicated that unilateral 6-OHDA-lesioned rats have a significantly higher level of extracellular glutamate and a lower level of extracellular DOPAC in the lesioned-side of the striatum, and a lower level of extracellular DA in both sides of the striatum compared to the striatum of control rats. Ipt reduced extracellular glutamate levels in both sides of striatum of the lesioned and control rats in a concentration-dependent manner. Ipt, at lower concentrations (0.01, 0.1, 1 microM), enhanced extracellular DA levels in the lesioned-side striatum of the unilateral 6-OHDA-lesioned rats, while causing no significant changes in the intact side striatum, and even a significant decline in striatum of control rats at higher concentrations of Ipt (10, 100 microM). In addition, Ipt also caused a significant decline in the extracellular DOPAC levels in the lesioned-side striatum of unilateral 6-OHDA-lesioned rats. These data suggest that the major mechanism underlying the ameliorative effects of Ipt on the behavior in 6-OHDA-lesioned rats is the alteration of levels of extracellular neurotransmitters, such as glutamate and DA in the striatum of unilateral 6-OHDA-lesioned rats.

Iptakalim hydrochloride protects cells against neurotoxin-induced glutamate transporter dysfunction in in vitro and in vivo models

Iptakalim hydrochloride (Ipt), a novel antihypertensive drug, exhibits K(ATP) channel activation. Here, we report that Ipt remarkably protects cells against neurotoxin-induced glutamate transporter dysfunction in in vitro and in vivo models. Chronic exposure of cultured PC12 cells to neurotoxins, such as 6-OHDA, MPP+, or rotenone, decreased overall [3H]-glutamate uptake in a concentration-dependent manner. Pre-treatment using 10 microM Ipt significantly protected cells against neurotoxin-induced glutamate uptake diminishment, and this protection was abolished by the K(ATP) channel blocker glibenclamide (20 microM), suggesting that the protective mechanisms may involve the opening of K(ATP) channels. In 6-OHDA-treated rats (as an in vivo Parkinson's disease model), [3H]-glutamate uptake was significantly lower in synaptosomes isolated from the striatum and cerebral cortex, but not the hippocampus. Pre-conditioning using 10, 50, and 100 microM Ipt significantly restored glutamate uptake impairment and these protections were abolished by blockade of K(ATP) channels. It is concluded that Ipt exhibits substantial protection of cells against neurotoxicity in in vitro and in vivo models. The cellular mechanisms of this protective effect may involve the opening of K(ATP) channels. Collectively, Ipt may serve as a novel and effective drug for PD therapy.

Dopamine receptors in C. elegans

Dopamine regulates various physiological functions in the central nervous system and the periphery. Dysfunction of the dopamine system is implicated in a wide variety of disorders and behaviors including schizophrenia, addiction, and attention-deficit hyperactivity disorder. Medications that modulate dopamine signaling have therapeutic efficacy on the treatment of these disorders. However, the causes of these disorders and the role of dopamine are still unclear. Studying the dopamine system in a model organism, such as Caenorhabditis elegans, allows the genetic analysis in a simple and well-described nervous system, which may provide new insight into the molecular mechanisms of dopamine signaling. In this review, we summarize recent findings on pharmacological and biochemical properties of the C. elegans dopamine receptors and their physiological role in the control of behavior.