The neurotransmitter dopamine (DA) plays a critical role in regulating cognition, behavior and physiology in humans. Imbalances in DA or damage to the dopaminergic (DAnergic) system can be consequential to neurological health and lead to the progression of psychiatric and neurodegenerative disorders that include but are not limited to schizophrenia and Parkinson’s disease (PD). PD, in particular, is associated with debilitating motor symptoms that result following a considerable loss of midbrain DAnergic neurons. This loss is likely correlated to a combinatory insult of environmental exposures and genetic predisposition, as the majority of cases are idiopathic in nature. To date there remains to be a curative treatment, thus much research has been done to generate models of sporadic PD through the use of neurotoxic exposures in addition to the search for plant-derived chemicals that confer neuroprotection prior to the onset of symptoms to improve the quality of life for those at risk.
Here, we established a model to mimic pathologies observed in sporadic PD using both larval and adult zebrafish. The larval model examined the neurotoxic impact of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenyl-pyridinium (MPP+), 6-hydroxydopamine (6-OHDA), rotenone, and paraquat to delineate the optimal compound that exerts the largest degree of diencephalic DAnergic cell death and motor perturbance using Tg(dat:eGFP) transgenic zebrafish. Using this model, we also showed that between ascorbic acid (AA), ferulic acid (FA) and vanillic acid (VA), pretreatment of FA elicits that largest neuroprotective effect against MPTP-induced oxidative stress and neurodegeneration. The optimization of a reliable adult model to investigate mitochondrial impacts in vivo was then addressed through introducing MPTP into the cerebroventricular fluid of Tg(dat:tom20 MLS:mCherry) transgenic zebrafish. Gene expression and immunostaining data suggest that MPTP induces DAnergic mitochondrial fragmentation through mitophagy activation.
Moreover, we sought to examine the genetic influence over DAnergic production and disorders by targeting nr4a2 paralogs for CRISPR-Cas9 mediated mutagenesis. Despite a similar deleterious effect observed in DAnergic populations, nr4a2a and nr4a2b mutants each possess variable effects on neurotrophins, metabolism, other neurotransmitters and behavior. nr4a2a mutants more closely resemble PD pathologies, whereas nr4a2b mutants exhibit phenotypes reminiscent of psychiatric disorders. Throughout DAnergic regeneration, nr4a2a was also shown to mimic shha expression patterns suggestive of a predominant role over nr4a2b in differentiation. Further gene expression data may also indicate that notch1a drives the proliferative stages of DAnergic progenitors prior to the shift to shha signaling for differentiation.
In sum, we believe the sporadic and genetic models of DA deficiencies offer an opportunistic tool to study molecular mechanisms of DAnergic regeneration, potential therapeutics and to gain a better understanding of mitochondrial influence in neurological pathologies.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/44453 |
| Date | 03 January 2023 |
| Creators | Kalyn, Michael |
| Contributors | Ekker, Marc |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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