Time-Dependent Addition of Neuronal and Schwann Cells Increase Myotube Viability and Length in an In Vitro Tri-culture Model of the Neuromuscular Junction

The neuromuscular junction (NMJ) is a specialized chemical synapse between motor neurons and muscle fibers that enables voluntary movement of somatic muscle. Study of NMJ physiology and pathology has used various animal models and cell lines to recapitulate critical features of neuromuscular disease and increase our understanding of NMJ disruption. In vitro co-culture platforms have also been used to evaluate NMJ development using different combinations of motor neurons (MNs), glial Schwann Cells (SCs), skeletal muscle (SKM) cells, and biomaterials to advance translation of regenerative therapies. In this report, we use a compartmentalized, microfluidic platform to develop a novel, tri-culture model of the three cell types that comprise the NMJ: SKM cells, MNs, and SCs. Results illustrate the reproducible differentiation of SKM myotubes with increased viability and length following the time-dependent addition of neuronal and glial cells as introduced in vivo. The data points to Schwann Cells as key players to stabilize and maintain in vitro NMJ models that will aid development and testing of emerging therapies for neuromuscular dysfunction. Lay Summary Schwann cells (SCs) of the peripheral nervous system are essential to the development and function of the NMJ. Although recent evidence has revealed the significant roles of these glia in NMJ remodeling and regeneration, SCs have been largely overlooked in NMJ culture models. This project used a compartmentalized microfluidic platform to isolate and add each cellular component of the NMJ in a time-dependent manner to facilitate cellular interaction and stabilization. Results demonstrate that the time-dependent addition of SCs increased the viability and differentiated length of skeletal myotubes observed in vitro. Our contributions will aid the development of microfluidic, tri-culture models that utilize primary and stem-like cells to develop functional in vitro models with which to test and evaluate emerging regenerative NMJ therapies.