The neuromuscular junction (NMJ), a synapse formed between motoneurons and muscle fibers, has contributed greatly to understanding of the general principles of synaptogenesis, as well as of neuromuscular disorders. NMJ formation requires intimate interaction between motoneurons and muscle fibers. For example, in antegrade signaling, motoneurons release agrin that binds LRP4, a member of the LDL receptor family, in muscle cells to activate the receptor tyrosine kinase MuSK, both of which are required for NMJ formation. Downstream of MuSK was not well understood, except that AChR concentration absolutely requires the adapter protein rapsyn. However, exactly how signals are transduced from MuSK activation to AChR concentration is not well understood. On the other hand, skeletal muscles are known to be critical to the development of axon terminals of motoneurons. In contrast to antegrade regulation, much less is understood about molecular mechanisms of retrograde regulation of presynaptic differentiation by muscle fibers. In preliminary studies, we discovered that the classic adaptor protein rapsyn is an E3 ligase. Knockin mice carrying the mutation of a single residue necessary for the enzymatic activity are unable to form the NMJ. Our results suggest that rapsyn contributes to AChR clustering by promoting neddylation. These observations identify a previously unappreciated enzymatic activity of rapsyn and a role of neddylation in synapse formation. Our studies of LRP4 suggest that it could regulate developing axons by mechanisms independent of MuSK. The proposal will test two hypotheses. First, MuSK increases rapsyn enzyme activity to promote neddylation for AChR clustering and NMJ formation. Second, muscle regulates presynaptic differentiation via LRP4. Results of this proposal will provide a better understanding of cellular as well as molecular mechanisms of mammalian NMJ formation and contribute to a better understanding of pathogenic mechanisms of neuromuscular disorders.

Public Health Relevance

This study will investigate the two novel mechanisms governing the formation of the neuromuscular junction (NMJ). Results will reveal insight into NMJ assembly mechanisms and contribute to developing better diagnostic and therapeutic strategies for neuromuscular disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS082007-08
Application #
9719901
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Gubitz, Amelie
Project Start
2013-07-01
Project End
2023-06-30
Budget Start
2019-07-01
Budget End
2020-06-30
Support Year
8
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Case Western Reserve University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
077758407
City
Cleveland
State
OH
Country
United States
Zip Code
44106
Wang, Ya-Nan; Figueiredo, Dwight; Sun, Xiang-Dong et al. (2018) Controlling of glutamate release by neuregulin3 via inhibiting the assembly of the SNARE complex. Proc Natl Acad Sci U S A 115:2508-2513
Sun, Xiang-Dong; Chen, Wen-Bing; Sun, Dong et al. (2018) Neogenin in Amygdala for Neuronal Activity and Information Processing. J Neurosci 38:9600-9613
Legay, Claire; Mei, Lin (2017) Moving forward with the neuromuscular junction. J Neurochem 142 Suppl 2:59-63
Sun, Xiang-Dong; Li, Lei; Liu, Fang et al. (2016) Lrp4 in astrocytes modulates glutamatergic transmission. Nat Neurosci 19:1010-8
Li, Lei; Cao, Yu; Wu, Haitao et al. (2016) Enzymatic Activity of the Scaffold Protein Rapsyn for Synapse Formation. Neuron 92:1007-1019
Wu, Haitao; Barik, Arnab; Lu, Yisheng et al. (2015) Slit2 as a ?-catenin/Ctnnb1-dependent retrograde signal for presynaptic differentiation. Elife 4:
Shen, Chengyong; Xiong, Wen C; Mei, Lin (2014) Caspase-3, shears for synapse pruning. Dev Cell 28:604-6
Wu, Haitao; Lu, Yisheng; Shen, Chengyong et al. (2012) Distinct roles of muscle and motoneuron LRP4 in neuromuscular junction formation. Neuron 75:94-107