Embryonic stem cell-derived motor neurons preserve muscle after peripheral nerve injury

BACKGROUND: The potential of motor neuron progenitor cell transplants to preserve muscle tissue after denervation was studied in in vivo and in vitro adult mammalian model of peripheral nerve injury. METHODS: Embryonic stem cells were differentiated to induce cholinergic motor neuron progenitors. Flourescent-labeled progenitor cells were injected into the gastrocnemius muscle of Sprague-Dawley rats (n = 10) after denervation by ipilateral sciatic nerve transection. Control rats received injections of either a phosphate-buffered saline solution only (n = 12), murine embryonic fibroblast (STO) cells (n= 6), or undifferentiated embryonic stem cells (n= 6). Muscles were weighed and analyzed at 7 and 21 days using histology, histomorphometry, and immunostaining. RESULTS: Seven days after progenitor cell transplant, both muscle mass and myocyte cross-sectional area were preserved, compared with control muscles, which demonstrated muscle mass reduction to 70 percent and reduction of cross-sectional area to 72 percent of normal. Fluorescent microscopy of transplanted muscles confirmed the presence of motor neuron progenitors. Presynaptic neuronal staining of the transplants overlapped with α-bungarotoxin-labeled muscle fibers, revealing the presence of new neuromuscular junctions. By 21 days, muscle atrophy in the experimental muscles was equal to that of controls and no transplanted cells were observed. Co-culture of the motor neuron progenitor cells and myocytes also demonstrated new neuromuscular junctions by immunofluorescence. CONCLUSIONS: Transplanted motor neuron progenitors prevent muscle atrophy after denervation for a brief time. These progenitor cell transplants appear to form new neuromuscular junctions with denervated muscle fibers in vivo and with myocytes in vitro.