This proposal is aimed at determining the role of neurotrophins that signal through Trk receptors in modulating synapse structure and function in the developing and adult nervous system. Mouse neuromuscular synapses will be used as a model system. The cell types that comprise neuromuscular junctions, the perisynaptic Schwann cells, presynaptic motor neuron terminals, and postsynaptic muscle fibers, each express a complement of neurotrophins and Trks, suggesting that neurotrophin signaling at this synapse is multi-directional and involves all three cell types. Similarly, CNS neurons express several neurotrophins and Trks, but the relative roles of each signaling pathway in synaptic maturation and maintenance are unclear. Previous work and preliminary results from our lab showed that TrkB isoforms (which bind the neurotrophins BDNF and NT4/5) are expressed primarily postsynaptically, in the muscle fiber membrane in and around acetylcholine receptor (AChR) rich regions, while TrkC isoforms are localized to perisynaptic Schwann cells and TrkA is not localized to neuromuscular junctions. Down-regulation of TrkB signaling in muscle fibers, via adenovirus-mediated over-expression of a truncated, non-signaling form of TrkB (TrkB.t1), induced the dismantling of postsynaptic AChR rich regions. In contrast, preliminary results show that TrkC modulates the extension of processes by these cells that play important roles in axon sprouting and reinnervation. These observations lead to the hypothesis that exchange of ligands that signal through TrkB or TrkC receptors play functionally distinct roles in synaptic maturation and maintenance. While adenoviral methods are useful, and are the supported by another grant, to determine the role of these signaling molecules at synapses, it will be essential to selectively delete neurotrophin or Trk genes from one of the cell types at neuromuscular synapses. Because many of the relevant mutations in mice result in perinatal lethality, we will use cre-mediated recombination to delete neurotrophins or Trks from cells of interest in a spatially and temporally controlled fashion. The effect of neurotrophin (BDNF, NT3) or TrkB deletion on neuromuscular synaptic structure and function will be analyzed with in vivo imaging, immunostaining, confocal microscopy and electrophysiological characterization of synaptic strength. The results of these experiments will provide new insights into the functional role(s) of neurotrophin and Trk-mediated signaling at developing and adult synapses, and extend our understanding of the relative roles of antero- and retrograde synaptic signaling in the peripheral as well as central nervous system.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS046490-04
Application #
7058714
Study Section
Molecular, Cellular and Developmental Neurosciences 2 (MDCN)
Program Officer
Mamounas, Laura
Project Start
2003-06-01
Project End
2008-04-30
Budget Start
2006-05-01
Budget End
2008-04-30
Support Year
4
Fiscal Year
2006
Total Cost
$326,527
Indirect Cost
Name
University of Pennsylvania
Department
Neurosciences
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Peng, Xiaoyu; Parsons, Thomas D; Balice-Gordon, Rita J (2012) Determinants of synaptic strength vary across an axon arbor. J Neurophysiol 107:2430-41
Dorsey, Susan G; Lovering, Richard M; Renn, Cynthia L et al. (2012) Genetic deletion of trkB.T1 increases neuromuscular function. Am J Physiol Cell Physiol 302:C141-53
Hughes, Ethan G; Elmariah, Sarina B; Balice-Gordon, Rita J (2010) Astrocyte secreted proteins selectively increase hippocampal GABAergic axon length, branching, and synaptogenesis. Mol Cell Neurosci 43:136-45
Hughes, Ethan G; Peng, Xiaoyu; Gleichman, Amy J et al. (2010) Cellular and synaptic mechanisms of anti-NMDA receptor encephalitis. J Neurosci 30:5866-75
Hess, Darren M; Scott, Marion O; Potluri, Srilatha et al. (2007) Localization of TrkC to Schwann cells and effects of neurotrophin-3 signaling at neuromuscular synapses. J Comp Neurol 501:465-82
Song, Yuanquan; Panzer, Jessica A; Wyatt, Ryan M et al. (2006) Formation and plasticity of neuromuscular synaptic connections. Int Anesthesiol Clin 44:145-78
Pitts, Elizabeth Vernon; Potluri, Srilatha; Hess, Darren M et al. (2006) Neurotrophin and Trk-mediated signaling in the neuromuscular system. Int Anesthesiol Clin 44:21-76
Elmariah, Sarina B; Hughes, Ethan G; Oh, Eun Joo et al. (2005) Neurotrophin signaling among neurons and glia during formation of tripartite synapses. Neuron Glia Biol 1:1-11