Perspectives on Caenorhabditis elegans models of human Parkinson’s Disease

Caenorhabditis elegans is a 1 mm long nematode comprised of 959 cells in the adult hermaphrodite. Through transgenic injection, neurotoxin treatment, or isolation of mutants, this roundworm has been used as an animal model for studies of human Parkinson’s disease (PD). The ability to genetically manipulate this animal, its short reproductive cycle and transparent body type have allowed it to be treated pharmacologically and toxicologically and interrogated for features of PD including loss of dopaminergic neurons, aggregation of α-synuclein protein, basal slowing responses to food, and lifespan. This short review aims to capture some of the recent studies on Caenorhabditis elegans PD models and highlight some aspects of absorption, distribution, metabolism, and excretion that make the worm a useful organism for studies in neurodegeneration

RNA-Seq Reveals Acute Manganese Exposure Increases Endoplasmic Reticulum Related and Lipocalin mRNAs in Caenorhabditis elegans

Manganese (Mn) is an essential nutrient; nonetheless, excessive amounts can accumulate in brain tissues causing manganism, a severe neurological condition. Previous studies have suggested oxidative stress, mitochondria dysfunction, and impaired metabolism pathways as routes for Mn toxicity. Here, we used the nematode Caenorhabditis elegans to analyze gene expression changes after acute Mn exposure using RNA-Seq. L1 stage animals were exposed to 50 mM MnCl2 for 30 min and analyzed at L4. We identified 746 up- and 1828 downregulated genes (FDR corrected p < 0.05; two-fold change) that included endoplasmic reticulum related abu and fkb family genes, as well as six of seven lipocalin-related (lpr) family members. These were also verified by qRT-PCR. RNA interference of lpr-5 showed a dramatic increase in whole body vulnerability to Mn exposure. Our studies demonstrate that Mn exposure alters gene transcriptional levels in different cell stress pathways that may ultimately contribute to its toxic effects

Methylmercury exposure increases lipocalin related (lpr) and decreases activated in blocked unfolded protein response (abu) genes and specific miRNAs in Caenorhabditis elegans

Methylmercury (MeHg) is a persistent environmental and dietary contaminant that causes serious adverse developmental and physiologic effects at multiple cellular levels. In order to understand more fully the consequences of MeHg exposure at the molecular level, we profiled gene and miRNA transcripts from the model organism Caenorhabditis elegans. Animals were exposed to MeHg (10µM) from embryo to larval 4 (L4) stage and RNAs were isolated. RNA-seq analysis on the Illumina platform revealed 541 genes up- and 261 genes down-regulated at a cutoff of 2-fold change and false discovery rate-corrected significance q < 0.05. Among the up-regulated genes were those previously shown to increase under oxidative stress conditions including hsp-16.11 (2.5-fold), gst-35 (10.1-fold), and fmo-2(58.5-fold). In addition, we observed up-regulation of 6 out of 7 lipocalin related (lpr) family genes and down regulation of 7 out of 15 activated in blocked unfolded protein response (abu) genes. Gene Ontology enrichment analysis highlighted the effect of genes related to development and organism growth. miRNA-seq analysis revealed 6–8 fold down regulation of mir-37-3p, mir-41-5p, mir-70-3p, and mir-75-3p. Our results demonstrate the effects of MeHg on specific transcripts encoding proteins in oxidative stress responses and in ER stress pathways. Pending confirmation of these transcript changes at protein levels, their association and dissocation characteristics with interaction partners, and integration of these signals, these findings indicate broad and dynamic mechanisms by which MeHg exerts its harmful effects

Inhibition of Excessive Oxidative Protein Folding Is Protective in MPP+ Toxicity-Induced Parkinson's Disease Models

Aims: Protein misfolding occurs in neurodegenerative diseases, including Parkinson's disease (PD). In endoplasmic reticulum (ER), an overload of misfolded proteins, particularly alpha-synuclein (alpha Syn) in PD, may cause stress and activate the unfolded protein response (UPR). This UPR includes activation of chaperones, such as protein disulphide isomerase (PDI), which assists refolding and contributes to removal of unfolded proteins. Although up-regulation of PDI is considered a protective response, its activation is coupled with increased activity of ER oxidoreductin 1 (Ero1), producing harmful hydroperoxide. The objective of this study was to assess whether inhibition of excessive oxidative folding protects against neuronal death in well-established 1-methyl-4-phenylpyridinium (MPP+) models of PD. Results: We found that the MPP+ neurotoxicity and accumulation of aSyn in the ER are prevented by inhibition of PDI or Ero1 alpha. The MPP+ neurotoxicity was associated with a reductive shift in the ER, an increase in the reduced form of PDI, an increase in intracellular Ca2+, and an increase in Ca2+-sensitive calpain activity. All these MPP+-induced changes were abolished by inhibiting PDI. Importantly, inhibition of PDI resulted in increased autophagy, and it prevented MPP+-induced death of dopaminergic neurons in Caenorhabditis elegans. Innovation and Conclusion: Our data indicate that although inhibition of PDI suppresses excessive protein folding and ER stress, it induces clearance of aggregated aSyn by autophagy as an alternative degradation pathway. These findings suggest a novel model explaining the contribution of ER dysfunction to MPP+-induced neurodegeneration and highlight PDI inhibitors as potential treatment in diseases involving protein misfolding