Extra-nigral Neurodegeneration in Experimental Parkinson's Disease

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DESCRIPTION (provided by applicant): Parkinson's disease (PD), a progressive degenerative movement disorder associated with loss of dopaminergic neurons in substantia nigra (SN), leads to dysfunction. The current therapy, L-dopa, does not block disease progression; therefore, new therapies must be developed. Thus, the aim is to investigate inflammatory events in brain and spinal cord (SC) and their degeneration in PD and characterize whether SC integrity and neurons are lost in PD, contributing to dysfunction. Understanding the mechanisms of damage may help develop new therapeutic strategies. While the etiology of PD is not fully understood, neurotoxins have been im- plicated in PD pathogenesis. Toxic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been extensively used as an experimental model. Since 1-methyl-4-phenylpyridinium ion (MPP+), the active toxic metabolite of MPTP, increases intracellular-free Ca2+ level and promotes mitochondrial dysfunction, a Ca2+-mediated pathology in PD has been hypothesized. Increased Ca2+ levels will promote calpain activation, increase inflammatory responses, and damage brain/SC neurons, axons, and myelin, ultimately leading to functional deficit. Our preliminary findings of direct detection of MPP+ in PD mouse SC, activation of astrocytes and microglia, and increased calpain activity and expression in neurons indicate that SC is also affected. These findings were corroborated by preliminary data showing motoneurons from SC of PD patients are also damaged. MPP+ treatment of ventral SC motor neuron cells (VSC4.1) showed increased intracellular [Ca2+] and calpain activity with loss of membrane potential and death while calpain inhibitors (calpeptin, SJA6017) protected and restored cell function. From these findings, we hypothesize that, since SC coordinates movement and sensation of the body, damage to SC neurons, axons, and myelin, in addition to SN, may be an important factor in PD, and calpain plays a crucial role in this dysfunction by promoting inflammation and cell death and may be a target for therapy. Three specific aims will test the hypotheses. Specific Aim 1 will investigate whether MPTP is directly converted into MPP+ in SC, enters through the degenerating axons from brain, or a combination of both; examine the effects of MPTP (MPP+) on SN and SC neurons and white matter in acute and chronic parkinsonism; assess calpain expression and activity and subsequent inflammation and cell damage; and examine the status of neurons, axons, and myelin in SC of postmortem PD patients. Specific Aim 2 will explore the effects of neurotoxic MPP+ in differentiated VSC4.1 cells and test the neuroprotective efficacy of calpain inhibitors in vitro employing electrophysiological technique. Specific Aim 3 will examine whether calpain inhibitor treatment will attenuate inflammation, prevent apoptosis of brain and SC neurons, protect cells, preserve axons and myelin, and improve function in MPTP-induced PD mice. These studies will delineate the role of calpain in inflammation and neurodegeneration in MPTP-induced PD and the probable neuroprotective efficacy of calpain inhibitors in PD as therapeutic agents. PUBLIC HEALTH RELEVANCE: Since the spinal cord coordinates movement and sensation of the body, damage to spinal cord neurons, in addition to the substantia nigra (brain), and alteration in white matter integrity (i.e., axonal and myelin degeneration) as well as loss of myelin-forming cells may be important factors in Parkinson's disease (PD), and calpain could play a crucial role in this dysfunction. This study will examine the role of calpain in cell and axon damage in the progression of disease in an animal model, the efficacy of calpain inhibitor as a therapeutic agent in vivo and in vitro, and the status of neurons in post-mortem PD tissue. Delineating a role for calpain in the progression of disease could potentially lead to new therapeutic targets since the most potent therapy, L-dopa, does not block the progression of Parkinson's disease.