Embryonic Stem Cell-Derived Motor Neurons Form Neuromuscular Junctions In Vitro and Enhance Motor Functional Recovery In Vivo

Background: Transplantation of embryonic stem cell-derived motor neurons may support the biological integrity of denervated muscle by forming new neuromuscular junctions and up-regulating specific growth factors. The authors examined the functional properties of embryonic stem cell-derived motor neurons in vitro and the effect of these cells transplanted in vivo. Methods: Murine GFP/HB9 embryonic stem cells were differentiated into motor neurons. Co-cultures of motor neurons and myotubes were prepared to confirm the formation of neuromuscular junctions with synaptic markers. Athymic mice (n = 59) were assigned randomly to one of three experimental groups. A tibial nerve transection was performed without nerve repair, and motor neurons were transplanted into the gastrocnemius muscles immediately after transection (n = 24) or 3 weeks after denervation (n = 24). Quantitative and histologic assessments of gastrocnemius muscle were performed at days 7 and 21 after cell transplantation. Additional experimental groups (n = 11), where the tibial nerve underwent repair after transplantation, were formed. The effect of the transplants on motor recovery following nerve repair was investigated. Results: Co-culture experiments showed the formation of neuromuscular junctions. In the experiment with nerve transection without nerve repair, the muscles transplanted with motor neurons were less atrophied than control phosphate-buffered saline-injected muscles at days 7 and 21. Those muscles receiving cells transplanted 3 weeks after denervation were not preserved. The motor recovery after nerve repair with cell transplantation was significantly enhanced compared with the control group. Conclusions: Transplantation of motor neurons prevented denervation atrophy but was not capable of rescuing already atrophied muscle. After nerve repair, motor neuron transplantation improved functional recovery. (Plast. Reconstr. Surg. 123 (Suppl.): 139S, 2009.)