The importance of choosing a preclinical model that reflects what happens in Parkinson's disease

Modelling Parkinson's Disease in C. elegans: Strengths and Limitations

Parkinson's disease (PD) is a common neurodegenerative disease that affects the motor system and progressively worsens with age. Current treatment options for PD mainly target symptoms, due to our limited understanding of the etiology and pathophysiology of PD. A variety of preclinical models have been developed to study different aspects of the disease. The models have been used to elucidate the pathogenesis and for testing new treatments. These models include cell models, non-mammalian models, rodent models, and non-human primate models. Over the past few decades, Caenorhabditis elegans (C. elegans) has been widely adopted as a model system due to its small size, transparent body, short generation time and life cycle, fully sequenced genome, the tractability of genetic manipulation and suitability for large scale screening for disease modifiers. Here, we review studies using C. elegans as a model for PD and highlight the strengths and limitations of the C. elegans model. Various C. elegans PD models, including neurotoxin-induced models and genetic models, are described in detail. Moreover, met.

Neonatal 6-OHDA lesion of the SNc induces striatal compensatory sprouting from surviving SNc dopaminergic neurons without VTA contribution

Dopamine (DA) neurons of the substantia nigra pars compacta (SNc) are uniquely vulnerable to neurodegeneration in Parkinson's disease (PD). We hypothesize that their large axonal arbor is a key factor underlying their vulnerability, due to increased bioenergetic, proteostatic and oxidative stress. In keeping with this model, other DAergic populations with smaller axonal arbors are mostly spared during the course of PD and are more resistant to experimental lesions in animal models. Aiming to improve mouse PD models, we examined if neonatal partial SNc lesions could lead to adult mice with fewer SNc DA neurons that are endowed with larger axonal arbors because of compensatory mechanisms. We injected 6-hydroxydopamine (6-OHDA) unilaterally in the SNc at an early postnatal stage at a dose selected to induce loss of approximately 50% of SNc DA neurons. We find that at 10 and 90 days after the lesion, the axons of SNc DA neurons show massive compensatory sprouting, as revealed by the proportionally smaller decrease in tyrosine hydroxylase (TH) in the striatum compared with the loss of SNc DA neuron cell bodies. The extent and origin of this axonal sprouting was further investigated by AAV-mediated expression of eYFP in SNc or ventral tegmental area (VTA) DA neurons of adult mice. Our results reveal that SNc DA neurons have the capacity to substantially increase their axonal arbor size and suggest that mice designed to have reduced numbers of SNc DA neurons could potentially be used to develop better mouse models of PD, with elevated neuronal vulnerability.