| In vitro models of the neuromuscular junction (NMJ) are emerging as a valuable tool to study synaptogenesis, synaptic maintenance, and pathogenesis of neurodegenerative diseases. Many models have previously been developed using a variety of cell sources for muscle and motoneurons, but the models can be further improved by integrating beneficial features to better mimic the native milieu of NMJ development. We created a functional in vitro model of NMJ by bioreactor cultivation of C2C12 myoblasts, transdifferentiated myocytes and stem cell-derived motoneurons with electrical stimulation. Proper coculture medium and electrical stimulation led to improved functional coupling between the emerging motoneurons and myocytes, as evidenced by mature cellular structures, increased expression of neuronal and muscular genes, clusterization of acetylcholine receptors (AChRs) in the vicinity of motoneurons, and the response of the coculture to glutamate stimulation. To validate the models and demonstrate utility for pharmacological testing, we analyzed the potency of the drugs that affect key pathways during NMJ signal transduction, including acetylcholine (ACh) synthesis, ACh vesicular storage, ACh synaptic release, AChR activation, and ACh inactivation in the synaptic cleft. The models properly responded to the drugs in a concentration-dependent manner. The proposed in vitro NMJ model could thus be used in pharmacological screening and controlled studies of neuromuscular diseases. |
