Investigating the Role of LRRK2 Hyperactivity in Autophagic and Synaptic Deficits

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PROJECT SUMMARY Parkinson’s disease (PD) is the second-most prevalent neurodegenerative disease and the fastest- growing. PD increases in both prevalence and severity with age, and the disease burden is projected to dramatically increase in coming decades as the population ages. Current therapies do not address the underlying neurodegeneration, and development of improved therapeutics is hindered by poor understanding of the pathogenesis. Changes in homeostatic regulation of both autophagy and synaptic transmission have been implicated in not only PD but also physiological aging. Leucine-rich repeat kinase 2 (LRRK2) is a leading candidate for a nexus bridging autophagy and PD pathogenesis. Mutations in LRRK2 are the most common genetic cause of PD, and increased LRRK2 kinase activity has also been linked to idiopathic PD. There is accumulating evidence that multiple PD-causative pathways may converge on disrupting autophagy through mechanisms dependent on LRRK2 activity. Recently, LRRK2 was shown to phosphorylate a subset of Rab GTPases, providing an important opportunity to make advances in the understanding of mechanisms downstream of LRRK2. The goal of this proposal is to elucidate the role that LRRK2 may play in autophagy and synaptic homeostasis, in the context of pathogenic mutations associated with PD. Our preliminary data suggests that the most common pathogenic mutation in LRRK2, p.G2019S, disrupts autophagic vesicle (AV) transport in the axons of rodent and iPSC-derived human neurons. We hypothesize that multiple pathogenic PD mutations disrupt autophagy and synaptic vesicle precursor (SVP) transport through mechanisms dependent on increased LRRK2 kinase activity. To test this hypothesis, we will exploit iPSC-derived neurons as a human disease model. Experiments proposed in Aim 1a will explore whether LRRK2-p.G2019S causes deficits in AV cargo degradation, as a potential mechanism of neurodegeneration. In Aim 1b, we will determine whether the VPS35-p.D620N mutation, a different pathogenic PD mutation that increases LRRK2 activity, causes similar autophagy deficits as LRRK2-p.G2019S. Finally, in Aim 2, we will explore whether SVP transport from the soma to the axon is impaired by mutations causing LRRK2 hyperactivity, with potential ramifications for synaptic homeostasis. Collectively, we expect that these Aims will help elucidate mechanisms by which multiple causes of PD can converge on a LRRK2-dependent pathway to disrupt neuronal autophagy and synaptic homeostasis. Additionally, this work may provide a foundation for future work to shed light on pathways by which physiological aging alters these processes in the absence of diseases of aging. To complement this research plan, a comprehensive training plan will help the trainee meet specific Research Goals, Professional Goals (including writing, mentoring, and presentation), and Clinical Goals (tying together an integrated physician-scientist training pathway), all in a supportive, collaborative scientific environment.