Human-iPSC derived neuromuscular junctions as a model for neuromuscular diseases.

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Motor neurons carry electrical signals from the brain through the spinal cord to ultimately generate muscle contraction via the neuromuscular junction (NMJ). The mechanisms involved in initiating and maintaining proper communication between the central nervous system and muscles are incredibly complex, and damage in this communication is the cause of neuromuscular diseases (NMD), such as Amyotrophic Lateral Sclerosis (ALS) and Spinal and Bulbar Muscular Atrophy (SBMA). While these disorders are among the most common NMDs, there is currently no cure or effective treatment for them. The NMD field acknowledges that a substantial number of drugs found to alleviate symptoms in animal models have failed in clinical trials. Even though this highlights the importance of the development of humanized models, a caveat of converting studies into iPSC models is the focus on single cells in detriment of the complex systems of the adult organism. In the NMD field specifically, iPSC investigations have largely focused on addressing motor neuron phenotypes that would prevent their degeneration. Unfortunately, this approach is no longer sufficient, as prolonging motor neuron survival does not assure re-innervation, nor does it guarantee prevention of denervation. Therefore, it is crucial for therapeutic advancement in the NMD field that stem cell research needs to focus not only on identifying cell-specific targets but also on testing those targets on functional NMJ systems that comprise both iPSC-derived motor neurons and skeletal muscles. To achieve this goal, we have recently developed a 2D functional human NMJ system comprised of both iPSC-derived motor neurons and skeletal muscles. Our human iPSC-NMJ model is responsive to optogenetics and we are able to quantitatively measure NMJ function in a multi-electrode array system. Hence, in this R61/R33 IGNITE Phased Innovation Award System, we propose to leverage our newly developed NMJ system to scale functional and morphological assessment (Aims 1 and 2) and validate the system by assaying NMJ-specific dysfunction using two NMDs: SBMA and ALS (Aims 3 and 4). Our lab has previously established an iPSC model for SBMA (R01NS121374-01, K01NS116119-01) and has extensive experience modeling this disease. Additionally, we selected the iPSCs harboring G4C2 hexanucleotide repeat expansion on chromosome 9 within the first intron of C9ORF72, as it represents is the most common genetic contributor to frontotemporal dementia (FTD) and ALS, accounting for ~10% of all cases of those diseases. Thus, successful completion of this R61/R33 will establish and validate a novel model system to facilitate therapeutic discovery for NMDs.