The slow channel syndrome (SCS) is a disorder congenital and progressive weakness due to mutations in the muscle acetylcholine receptor (AChR) that cause Ca2+ overload and degeneration of the neuromuscular junction (NMJ). The long-range goal of this project is to define the pathways and explore therapies for the progressive synaptic dysfunction seen in SCS. Detailed in vitro and in vivo expression studies in this laboratory and elsewhere have identified several consequences of mutations in the SCS that may contribute to disease pathogenesis, with Ca2+ overload of the junctional sarcoplasm being the most critical. Recently we have recognized the combined participation of two separate, but interrelated protease pathways that impair neuromuscular transmission at pre and post-synaptic levels. Our goals are to:
Aim 1. Test and compare strategies for NMJ protection in SCS by eliminating Ca2+ overload in intact synapses. We will test the hypothesis that elimination of sources of Ca2+ overload through pharmacological blockade of mutant AChRs or IP3Rs will reduce activation of proteases and correct the functional deficit and pathological changes of SCS mice. Second, we will attempt to identify new potential long duration AChR ion channel blockers for treating SCS by screening a panel of candidate channel blockers to identify those that normalize mutant SCS AChR channel openings, shorten synaptic currents recorded in vitro and block endplate Ca2+ overload in muscle from transgenic mice expressing diverse set of SCS mutations.
Aim 2. Characterize the basis for the postsynaptic impairment and the role of caspase activation in SCS. We test the hypothesis that the defect in AChR density is due to a metabolic or synthetic defect in AChRs. Furthermore, we will use direct expression of recombinant caspase inhibitors to test the hypothesis that inhibition of caspases in muscle will increase in AChR density and improve synaptic function.
Aim 3. Characterize the role of calpain in the presynaptic impairment of neuromuscular transmission in SCS. We test the hypothesis that muscle calpain, acts through a Cdk5 pathway to cause reduced ACh vesicle release and impaired synaptic strength, to increase nNOS enzymatic activity and synaptic NO production. We will test this hypothesis using transfection and transgenic expression of recombinant Cdk5 and nNOS proteins and testing the effect on presynaptic function and the activity of these pathways.
These studies will lead to practical strategies for therapeutic intervention with long-term benefit for myasthenic syndromes. They may also provide new insights into modulation of both pre and post synaptic impairment of neuromuscular transmission that are relevant to both synaptic plasticity and synaptic diseases.
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|Tsou, Wei-Ling; Hosking, Ryan R; Burr, Aaron A et al. (2015) DnaJ-1 and karyopherin ?3 suppress degeneration in a new Drosophila model of Spinocerebellar Ataxia Type 6. Hum Mol Genet 24:4385-96|
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|Zhu, Haipeng; Bhattacharyya, Bula; Lin, Hong et al. (2013) Skeletal muscle calpain acts through nitric oxide and neural miRNAs to regulate acetylcholine release in motor nerve terminals. J Neurosci 33:7308-7324|
|Du, Xiaofei; Wang, Jun; Zhu, Haipeng et al. (2013) Second cistron in CACNA1A gene encodes a transcription factor mediating cerebellar development and SCA6. Cell 154:118-33|
|Grajales-Reyes, G E; Báez-Pagán, C A; Zhu, H et al. (2013) Transgenic mouse model reveals an unsuspected role of the acetylcholine receptor in statin-induced neuromuscular adverse drug reactions. Pharmacogenomics J 13:362-8|
|Zhu, Haipeng; Gomez, Christopher M (2012) Further evidence for the role of IP 3R 1 in regulating subsynaptic gene expression and neuromuscular transmission. Channels (Austin) 6:65-8|
|Zhu, Haipeng; Bhattacharyya, Bula J; Lin, Hong et al. (2011) Skeletal muscle IP3R1 receptors amplify physiological and pathological synaptic calcium signals. J Neurosci 31:15269-83|
|Otero-Cruz, José David; Báez-Pagán, Carlos Alberto; Dorna-Pérez, Luisamari et al. (2010) Decoding pathogenesis of slow-channel congenital myasthenic syndromes using recombinant expression and mice models. P R Health Sci J 29:4-17|
|Nieves-Cintron, Madeline; Caballero-Rivera, Daniel; Silva, Walter I et al. (2008) Functional contribution of alpha3L8'to the neuronal nicotinic alpha3 receptor. J Neurosci Res 86:2884-94|
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