A functional human motor unit platform engineered from human embryonic stem cells and immortalized skeletal myoblasts

Marwah Abd Al Samid,1 Jamie S McPhee,2 Jasdeep Saini,1 Tristan R McKay,1 Lorna M Fitzpatrick,1 Kamel Mamchaoui,3 Anne Bigot,3 Vincent Mouly,3 Gillian Butler-Browne,3 Nasser Al-Shanti1 1Healthcare Science Research Institute, School of Healthcare Science, Manchester Metropolitan University, Manchester, UK; 2Department of Sport and Exercise Science, Manchester Metropolitan University, Manchester, UK; 3Center for Research in Myology, Sorbonne Université-INSERM, Paris, France Background: Although considerable research on neuromuscular junctions (NMJs) has been conducted, the prospect of in vivo NMJ studies is limited and these studies are challenging to implement. Therefore, there is a clear unmet need to develop a feasible, robust, and physiologically relevant in vitro NMJ model. Objective: We aimed to establish a novel functional human NMJs platform, which is serum and neural complex media/neural growth factor-free, using human immortalized myoblasts and human embryonic stem cells (hESCs)-derived neural progenitor cells (NPCs) that can be used to understand the mechanisms of NMJ development and degeneration. Methods: Immortalized human myoblasts were co-cultured with hESCs derived committed NPCs. Over the course of the 7 days myoblasts differentiated into myotubes and NPCs differentiated into motor neurons. Results: Neuronal axon sprouting branched to form multiple NMJ innervation sites along the myotubes and the myotubes showed extensive, spontaneous contractile activity. Choline acetyltransferase and βIII-tubulin immunostaining confirmed that the NPCs had matured into cholinergic motor neurons. Postsynaptic site of NMJs was further characterized by staining dihydropyridine receptors, ryanodine receptors, and acetylcholine receptors by α-bungarotoxin. Conclusion: We established a functional human motor unit platform for in vitro investigations. Thus, this co-culture system can be used as a novel platform for 1) drug discovery in the treatment of neuromuscular disorders, 2) deciphering vital features of NMJ formation, regulation, maintenance, and repair, and 3) exploring neuromuscular diseases, age-associated degeneration of the NMJ, muscle aging, and diabetic neuropathy and myopathy. Keywords: motor unit, neuromuscular junctions, human embryonic stem cells, neuronal progenitor cells, human myoblast