The objective of this proposal is to elucidate the molecular mechanisms that cause denervation of aged neuromuscular junctions (NMJs) and how exercise ameliorates NMJ denervation in aging. In the elderly, progressive denervation of NMJs decreases neuromuscular function, decreases quality of life from frailty, and increases the risk of falling and fractures. However, there are knowledge gaps about the molecular mechanisms that underlie NMJ denervation in aging and how exercise ameliorates this condition. Our long-term goal is to elucidate these mechanisms and to identify new intervention strategies to improve neuromuscular function in the elderly. Here, we hypothesize that an age-related loss of synaptic vesicle release sites - active zones - causes NMJ denervation, and that exercise ameliorates this denervation by restoring active zones at the aged NMJs. This hypothesis has been formulated on the basis of our published and preliminary data that strongly suggest that age-related loss of active zone organizer laminin ?2 causes active zone depletion and NMJ denervation, and that exercise restores active zones and NMJ innervations by increasing laminin ?2 protein expression. Furthermore, these data are firmly supported by our published studies showing the molecular mechanism that organizes NMJ active zones involves interactions between laminin ?2, a specific receptor for laminin ?2 (presynaptic P/Q-type voltage-dependent calcium channels, VDCC), and the active zone protein Bassoon.
The specific aims for testing the hypothesis are as follows: (1) Elucidate molecular defects that cause denervation of aged NMJs and how exercise ameliorates the defects. Aged and exercised aged rodents will be analyzed using confocal + super resolution microscopy; (2) Test the hypothesis that exercise maintains aged NMJs by increasing laminin ?2 expression level using transgenic mice; and (3) Evaluate systemic effects of a novel calcium channel agonist on neuromuscular function of aged mice using electrophysiology, electromyography, and behavior tests. This project is innovative because it is based on a novel, untested concept, namely the causality of active zone integrity in NMJ denervation. It is thus distinct from current aging research approaches. Another innovation is the testing of a novel calcium channel agonist specific for the P/Q-type VDCC that was invented by the Co-PI. The significance of this project is that it will yield: (i) the molecular mechanisms of NMJ denervation in aging, (ii) the exercise activated mechanism that ameliorates NMJ denervation in aging, and (iii) a VDCC agonist that may function as an intervention for age-related neuromuscular dysfunction and potentially as an exercise mimetic. Cross-disciplinary investigators from developmental and aging neurobiology, electrophysiology, gerontology, imaging, nephrology, and physiology fields have been assembled for this project.
The project is relevant for human health because the discovery of molecular mechanisms that ameliorate aged NMJ denervation will provide mechanism-based target(s) for a novel mode of intervention to treat the elderly. Thus, the proposed research is relevant to National Institute on Aging's mission to understand the nature of aging in order to promote the health and well-being of older adults.
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