Amyotrophic lateral sclerosis (ALS) is a lethal disease, characterized by progressive death of motor neurons with unknown etiology. Evidence from animal models indicates that neuronal dysfunction precedes the clinical phase of the disease. However, in parallel extensive nerve sprouting and synaptic remodeling as part of a compensatory reinnervation processes and possibly also of motor neurons pathology was demonstrated. Therefore, the weakness in muscle groups will not be clinically apparent until a large proportion of motor units are lost. This motor unit loss and associated muscle function which precedes the death of motor neurons may resemble the "die-back" phenomena. Studies indicated that in the early stages the nerve terminals and motor neuron junctions are partially degraded while the cell bodies in the spinal cord are mostly intact. Treatments to rescue motor neurons according to "dying-forward" model of motor neuron pathology in ALS have shown only limited success in SOD1(G93A) transgenic mice as well as in humans. If cell body degeneration is late compared with axonal degeneration, early intervention could potentially prevent loss of motor neurons. Therefore, it should be considered, according to the dying back hypothesis, to focus on motor neurons terminals in order to delay or prevent the progressive degradation.

Sciatic nerve injury is common and may cause neurological deficits. Previous studies showed that administration of neurotrophic factors (NTFs), naturally occurring proteins that support the development and survival of neurons, preserved and protected damaged motor neuron in the injured sciatic nerve. We have been successful in converting bone marrow-derived mesenchymal stem cells into astrocyte-like cells that produce and secrete NTFs (NTF(+) cells). These cells demonstrate typical astrocyte morphology, express characteristic astrocyte markers and secrete high levels of NTFs. We have already shown that these cells and their conditioned media can protect neurons in culture and in animal models of neurodegenerative diseases. In the current study we examined whether NTF(+) cells are capable of rescuing motor neurons in a rat sciatic nerve injury model, where the right hind limb sciatic nerve was crushed. Rats were transplanted with NTF(+) cells, MSCs or PBS into the lesion site. In rats injected with the NTF(+) cells motor function was markedly preserved. Moreover, NTF(+) cells significantly inhibited the degeneration of the neuromuscular junctions and preserved the myelinated motor axons. Our findings suggest that autologous therapeutic approach can alleviate signs of sciatic nerve injury and probably other neurological disorders.

Although further research is still needed, this therapeutic approach will probably become a routine treatment technique in the coming years, especially with bone marrow mesenchymal stem cells. We believe that the most promising results were noted for the use of stem cells of this origin in the treatment of sciatic nerve injury.

Human oral mucosa stem cells (hOMSC) are a recently described neural crest-derived stem cell population. Therapeutic quantities of potent hOMSC can be generated from small biopsies obtained by minimally invasive procedures. Our objective was to evaluate the potential of hOMSC to differentiate into astrocyte-like cells and provide peripheral neuroprotection. We induced hOMSC differentiation into cells showing an astrocyte-like morphology that expressed characteristic astrocyte markers as glial fibrillary acidic protein, S100β, and the excitatory amino acid transporter 1 and secreted neurotrophic factors (NTF) such as brain-derived neurotrophic factor, vascular endothelial growth factor, glial cell line-derived neurotrophic factor, and insulin-like growth factor 1. Conditioned medium of the induced cells rescued motor neurons from hypoxia or oxidative stress in vitro, suggesting a neuroprotective effect mediated by soluble factors. Given the neuronal support (NS) ability of the cells, the differentiated cells were termed hOMSC-NS. Rats subjected to sciatic nerve injury and transplanted with hOMSC-NS showed improved motor function after transplantation. At the graft site we found the transplanted cells, increased levels of NTF, and a significant preservation of functional neuromuscular junctions, as evidenced by colocalization of α-bungarotoxin and synaptophysin. Our findings show for the first time that hOMSC-NS generated from oral mucosa exhibit neuroprotective effects in vitro and in vivo and point to their future therapeutic use in neural disorders.