Parkinson's disease (PD) affects at least 1 million individuals in the US alone. Although much is known about its pathophysiology and information is emerging about its cause, there are no pharmacological treatments shown to have a significant, sustained impact on the prevention of PD or on attenuation of its progress. However, clinical evidence suggests that physical exercise is such a treatment, and this is supported by studies of animal models of the dopamine (DA) deficiency associated with the motor symptoms of PD. Moreover, exercise is a practical and sustainable therapeutic intervention likely to act simultaneously on most if not all of the cellular events capable of protecting DA neurons and restoring DA function. This proposal is designed test the hypothesis that exercise increases DA function and protects DA neurons against toxic insult due in part to increased neurotrophic factor (NTF) signaling, protection of mitochondrial respiration, and stimulation of angiogenesis. An MPTP mouse model will be used to test this hypothesis.
Aim 1. To determine the effects of exercise on the impact of MPTP on dopaminergic function (1a) the optimal temporal relationship between exercise and toxin exposure will first be established, thus exploring both protection (exercise before toxin) and rescue (exercise after toxin). (1b) The impact of the optimal exercise paradigm on DA cell loss and on changes in pre- and post-synaptic DA receptors will then be assessed. (1c) Levels of DA and metabolites in striatal tissue and extracellular fluid will be measured in MPTP animals treated with exercise as dictated by Aim 1a. (1d) Mitochondrial respiration will be assessed after MPTP exercise.
Aim 2. To assess the role of NTFs in exercise-induced protection members of four distinct NTF families known to protect DA neurons will be examined: GDNF, BDNF, MANF, and VEGF. (2a) The temporal and anatomical profile of NTF changes will be determined after exercise, MPTP, and the optimal combination of MPTP and exercise. (b) The ability of exogenous NTF to mimic the effects of exercise identified in Aim 1 will then be assessed. (2c) The NTFs and/or their receptors suggested by Aim 2a and 2b will be conditionally knocked out to determine if this increases the toxin impact of MPTP and reduces the protective impact of exercise, thereby strengthening the hypothesis of a causal relationship between NTF and exercise-induced protection.
Aim 3. To examine the role of angiogenesis in exercise- and NTF-induced neuroprotection, (a) vasculature be assessed in substantia nigra, striatum, and cortex using BrdU to measure new cells and PECAM-1 (CD31), to mark blood vessels. (3b) FITC-conjugated tomato lectin will be used to detect patent blood vessels. (3c) A 3-dimensional analysis of vascular density will be performed. (3d) Finally, expression of angiogenesis-promoting proteins, including angiopoetins 1 and 2, will be measured. These results will provide the basis for the next iteration of a research program focusing on additional mechanisms underlying exercise-induced protection, provide stronger evidence for exercise-induced protection in PD, and establish targets for pharmacological treatment of the condition.
Parkinson's disease affects well over a million individuals in the US alone. Although we know a good deal about how the brain is affected by the disease, there are no pharmacological treatments shown to have a significant and sustained impact on the prevention of the disease or on the attenuation of its progress. Such treatments are urgently needed. Clinical evidence suggests that physical exercise is just such a treatment, and studies of animal models of the dopamine loss associated with the motor symptoms of the condition further support this hypothesis. This study is designed to test that hypothesis. Such a demonstration would not only strengthen the case for advising individuals to engage in exercise, but may also provide insights into drug development for the condition.
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