| The spinal cord injury (SCI) is at present the nerve domain common vigorous trouble around the world, its incidence rate presents the tendency which rises gradually year by year. The patient clinical manifestation is mainly serious damage symptom of the central nervous system. The main pathology change is divided into the primary damage and the sequential damage, the primary damage is because of neuron and blood vessel's direct damage caused by injuries, such as the natural disaster, the traffic accident, the movement and so on; A series of physiological, the biochemistry responses based on above changes cause sequential damage of spinal cord, and form secondary damage. Once the SCI occurs, a large number of neurons will die, the scar and the cavity will form at the necrotic location which affect the axon growth, hinder the conduction function and cause the patient movement and the feeling function disturbance finally. It is extremely difficult to treat SCI with high expense and the high disability rate, which has brought the enormous economic burden for the family and the society. Therefore, it has become a hot spot in SCI research to seek for good curative effect, the long response time, the safe effective method of treatment.The cell transplantation therapy is one of effective curative pathways, bone marrow mesenchymal stem cells already become the ideal seed cells for the treatment of nerve diseases because they have some unique biology characteristics. At present, massive researches confirm mesenchymal stem cells (MSCs) transplantation could improve movement function and the nerve conduction function of SCI model animal in vivo, and MSCs have the effect of protection, repair and improvement of growth through the pathology examination after marrow mesenchymal stem cell were transplanted into SCI animal models. But the mechanism of SCI treatment by the bone marrow mesenchymal stem cell transplantation has not yet been identified, specially the report about mechanism of direction migration of MSCs to damage location is rare.The purpose of this research is to explore the mechanism of migration the MSCs to spincal cord injury and repair of spinal cord injury using the marrow mesenchymal stem cell by different transplantation pathway, and provide experimental basis and theory basis for seeking for highly effective, the safe therapy fro SCI.This research first performed the BMSCs biology characteristic identificaiton, isolation and purification of BMSCs according to BMSCs adherence and found the cultured cells originated from rat bone marrow had the BMSCs biology characteristic, simultaneously expressed CD44, the CD 105 stem cell mark, but they didn't express the CD34, which showed that the isolated and cultured cells in this research weew multipotent BMSCs, and it confirmed the rat BMSCs as stem cells origin was feasibilable.In order to confirm that BMSCs have a therapeutic effect on the spinal cord injury and the possible mechanism, in vitro experiment the interaction between BMSCs and the spinal cord damage was observed through the effect of supernatant of injuried spinal cord on nerve trophic factors secreted by BMSCs, the effect of BMSCs on growth and survival on neuron in damaged spinal cord and the effect of the nerve trophic factors gene transfection on survival and differentiation of cultured spinal cord neurons. The results showed that normal and the damaged spinal cord refining supernate could induce differentiation of BMSCs into neuron expressing NSE, but the promoting differentiation effect of damaged spinal cord refining supernate was stronger that that of normal one. After BMSCs and the spinal cord neuron were cocultured,, the rate neuron growth increased, the cell body became larger and the number of neuron stretched out the pseudopod increased, the network architecture became more compact, and neuron activity increased. According to the above the results, it is extrapolated that BMSCs could promote the growth of neuron possibly through secreted one kind or several kinds of factors to bind the membrane acceptor or intracellular receptor. In order to further confirm therapeutic effect of SCI using the nerve trophic factors alone or their combination application, in the experiment the effect of the nerve trophic factors on spinal cord neuron survival was compared, which showed that BDNF and NT3 had a certain protective effect on the spinal cord neuron, and combination application of two trophic factors transfection produced stronger effect, indicated that two factors have the superimposed effect on the spinal cord neuron survival, and it was extrapolated that they produced the effect possibly through the different nerve growth regulation pathways.On the basis of in vitro experiment, in vivo the rat model of traumatic spinal cord injury (SCI) by Allen's weight dropping were prepared and the BMSCs were transplanted at injuried location and the waist shinbone sheath ways. The nerve conduction function, the movement function and the morphology examination results showed that nerve function, the movement function's restoration and the morphology changes by the waist shinbone sheath transplantation were better than those by local transplantation. In the experiment, the location and quantitative analysis of chemotatic factor, CXCL12 and its receptor, CXCR4 in spinal cord injury location and distal end were detected by;immunofluorescence, Real Time PCR and Western Blot. The results showed that the expression of CXCL12 in the injury location was stronger after SCI for 7 days, a larger number of red transplanted BMSCs were seen in the spinal cord injury location, green CXCL12 were observed around the injury location, which was concentrated on the cortical location of spinal cord injury location, CXCL12 expression didn't not seen in the spinal cord tissue 1 cm from the injury site. The expression of CXCR4 protein had not time effect. The results of CXCL12 mRNA transcriptional level confirmed that CXCL12 mRNA transcriptional level in cell transplantation group was significantly more than that in sham operation group and model group. On 14 days after injury, CXCL12 mRNA transcriptional level in injury location was highese. On 21 days after injury, it decreased. The CXCL12 mRNA transcriptional level in injury location was obviously higher than that at dital end. The chemotatic factors CXCR4 was expressed in the injury location, but its expression didn't appear time-course differentce. The CXCR4 transcriptional level in injury location was slightly higher than that in distal end, but there was not statistical difference.At present, a large number of researches confirmed that the BMSCs transplantation could treat SCI, but the mechanism is unclear, therefore, this research focused on the exploration the treatment mechanism of SCI by BMSCs transplantation and their cytotaxis to the damage spinal cord, which will provide theory and the experiment basis for the therapy of SCI using BMSCs in clinical.Conclusion:1. The BMSCs may conduct the experimental study as the stem cell origin.2. Both Normal and the injury spinal cord refining supernate may induce BMSCs to differentiate into nerve cells expressing NSE, but the effect of refining supernate of the injury spinal cord was stronger.3. The micro environment change after spinal cord damage is a main inducing factor which promotes BMSCs to further differentiated into the neuron, release trophic factors, expresses certain specificity gene.4. BDNFand NT3 have a protective effect on spinal cord neuron, and combination of two Neurotrophic factors had an additive effect of survival of spinal cord neuron.5. The CM-Dil tracer used in this studv does not have阿influence on the marrow mesenchymal stem cell proliferation.6. BMSCs by scabbard lumbosacral transplantion in spinal cord injury model animals can effective improved neural function and sports function than those by local transplants. CXCL12 and CXCR4 expression in BMSCS in vitro.7. CXCL12/CXCR4 biologic strand played a the guiding role in the migration of the BMSCs.
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