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Evidence of Improved Spinal Cord Injury using a Xenogenic model: Human Mesenchymal Stem Cells to Rats.

Cizkova D et al., Cell Mol Neurobiol 2006 (In press)
Summary by Tonye Briggs and Tom Finocchio

LAY SUMMARY

Mesenchymal stem cells (MSCs) are a specific type of stem cell that has been shown to differentiate into various types of tissues, such as bone and cartilage. Research has shown that MSCs may also differentiate into nerve cells. This suggests that MSCs may be useful in creating new nerve cells to aid in the recovery of patients with nerve damage. This study set out to test the ability of MSCs to replace damaged nerve cells in rats paralyzed with spinal cord injuries, and whether this can help the injured rats recover, improving their ability to move.

To test the hypothesis that MSC can repair spinal cord injury, the authors used rats with spinal cord injuries that have defects on movement in their hind legs. The rats were split into two groups with one group injected with MSCs and the other without MSCs. The rats’ ability to move was evaluated in both groups. The investigators found that after 3 weeks, the rats that received the MSCs were recovering at a greater rate than the rats that received no MSCs. This suggests that the MSCs, after injection, may have been able to find the injured area of the spine and form new nerve cells to replace the damaged ones.

After 4 weeks, the rats were sacrificed, and the injured areas of their spine were examined. The investigators found that despite the injection of MSCs, no new neurons had grown to replace the damaged ones. They however found that another type of nerve cell, called oligodendrocytes, had grown from the injected MSCs, but with low efficiency, or in low numbers. The few oligodendrocytes were proposed as being vital to the coating of neuronal axons of neurons with a substance called myelin, which helps the nerve impulses travel along the axons most efficiently. The investigators also found that the axons in rats that received new MSCs were growing more rapidly.

The question is why are the rats recovering faster when they received MSCs if they are not growing into new neurons? There are a couple of possibilities. The authors think that there may be other chemicals in the body that may be stimulated by the injection of MSCs. These chemicals may be responsible for the increased growth of axons in damaged tissues mentioned above, which could explain a speedier recovery. Another possibility is that the animals own MSCs are contributing to recovery, and that transplantation only speeds up the recovery process. It is unclear whether transplanting MSCs will have additional long-term benefits on total recovery. Researchers have yet to discover why all this happens, and exactly how. This study is just one small step in the road to designing new therapies against problems such as spinal cord injuries. Further research needs to be done to understand how MSCs move to the injured areas, how they affect the release of other chemical agents in the body, and what functions these chemicals will affect.

   

SCIENTIFIC SUMMARY

The differentiation potential of human mesenchymal stem cells (MSCs) into cells of the connective tissue has been well documented. In addition, MSCs can also generate cells of other tissues such as heart, skin and nervous system. The mechanisms of neural differentiation and the impact on spinal cord injury recovery are unclear. The authors’ goal was to investigate whether transplanted human MSC has an effect on spinal cord injury using an animal model. The readout of functional improvement are: the ability for the MSCs to home at the site of injury; differentiation into neural cells and stimulation of axonal growth.

Method: A xenogeneic model was established with human MSCs, injected into a spinal cord injury rat model. MSCs were established from healthy human donors and then labeled with 5-bromo-2 deoxyuridine (BrdU) as an indicator of cell proliferation. Adult male Wister rats were subjected to a spinal cord injury by a balloon-compression technique. MSCs were injected intravenously 7 days after injury. Control rats were injected with vehicle alone. In this xenogeneic transplantation, The rats were not subjected to therapeutic form of immunosuppresion. Functional motor recovery was evaluated with the Basso-Beattie-Bresnahan (BBB) scale which ranges from 0-21, where 0 represents no locomotion. The animals were sacrificed 28 days after spinal cord injury onset (21 days after transplantation). The spinal cord was harvested, sectioned and fixed for immunocytochemistry analysis. The spinal cord sections were stained with antibodies against BrdU, human specific nuclear antibody (NUMA), markers for neurons: Neu-N and MAP2, marker for oligodendrocytes: APC, and GAP-43 a marker for axonal growth. Dapi was used to stain nuclei.

Results: The results show sections positive for BrdU, indicating continuous proliferation during the period of transplantation. Homing was observed by the expression of NUMA positive nuclei in spinal cord sections as far as 3 mm rostrocaudally into the injury epicenter. There was no adverse immune response observe for the duration of the experiment. Functional recovery measured with the BBB scale indicated a statistical difference in locomotion skills in the MSC-transplanted rats as compared to control rats. Immunocytochemical staining indicated that the sections were negative for neural specific markers: Neu-N, MAP2, and GFAP. The only neural cells found in the transplanted rats were oligodendrocytes that are involved in myelination of axons. Furthermore, there was an increased staining of GAP-43, a marker for axonal growth and indicator of function recovery, compared to controls.

Discussion: Alternatives to explain the functional motor recovery in spinal cord injury transplanted with MSCs might be explained by the release of neurotrophic factors such as nerve growth factor, cytokines such as vascular endothelial growth factor and granulocyte-macrophage colony-stimulating factor. Alongside these hypotheses, it is necessary to determine whether the response might be due to endogenous MSCs. This is possible because MSCs have receptors to SDF-1 α (CXCR-4), a chemoattractant is likely to be increased at a site of injury. This hypothesis could be tested by staining sections of spinal cord with antibodies specific to rat MSCs as well as human MSCs. It is also unusual to see a xenogeneic transplant without immunosuppressive therapy. Although, allogeneic transplantation of MSCs is possible due to the immune suppressive nature of MSCs, the model needs to be further analyzed to discover the mechanism of trans-species immunosuppression.