A novel bioengineered functional motor unit platform to study neuromuscular interaction

BACKGROUND: In many neurodegenerative and muscular disorders, and loss of innervation in sarcopenia, improper reinnervation of muscle and dysfunction of the motor unit (MU) are key pathogenic features. In vivo studies of MUs are constrained due to difficulties isolating and extracting functional MUs, so there is a need for a simplified and reproducible system of engineered in vitro MUs. OBJECTIVE: to develop and characterise a functional MU model in vitro, permitting the analysis of MU development and function. METHODS: an immortalised human myoblast cell line was co-cultured with rat embryo spinal cord explants in a serum-free/growth fact media. MUs developed and the morphology of their components (neuromuscular junction (NMJ), myotubes and motor neurons) were characterised using immunocytochemistry, phase contrast and confocal microscopy. The function of the MU was evaluated through live observations and videography of spontaneous myotube contractions after challenge with cholinergic antagonists and glutamatergic agonists. RESULTS: blocking acetylcholine receptors with α-bungarotoxin resulted in complete, cessation of myotube contractions, which was reversible with tubocurarine. Furthermore, myotube activity was significantly higher with the application of L-glutamic acid. All these observations indicate the formed MU are functional. CONCLUSION: a functional nerve-muscle co-culture model was established that has potential for drug screening and pathophysiological studies of neuromuscular interactions.