Stem cells in inflammation and regeneration : focusing on animal models of multiple sclerosis and spinal cord injury

The main objective of regenerative medicine is to replace or restore injured cells and tissues in the body. Stem cells are identified playing a key role in the regeneration but action of inflammatory mediators in disease is not well understood. In this work, stem cells from bone marrow, adult brain and spinal cord were studied with regards to regenerative possibilities.

Paper I, Cell fusion has been observed during development and adult regeneration processes such as in heart, muscle and liver. Scientists have reported BMDC fusion with Purkinje neurons in cerebellum and that the BMDC nucleus can be reprogrammed to express Purkinje neuronal genes. Here we described in finding that, cell fusion between bone marrow derived cells and motor neurons in the spinal cord can take place. This is the first report demonstrating that motor neurons in spinal cord are able to fuse with hematopoietic cells during inflammation. We also identified the fusion phenomenon in spinal interneurons and in the olfactory bulb. In order to identify fusion event outside cerebellum, we used mice bone marrow transplantations and the EAE animal model. We identified fused motor neurons in the ventral horn expressing NeuN,and ChAT. Motor neuron identity was confirmed by tracing with axons in the sciatic nerve fibers to the cell body location in the spinal cord. We also observed that these fused neurons often are bi-nucleated. Yet, not all fused motor neurons were bi-nucleated, this might be due to technical difficulties or that other mechanisms might playing a role during fusion.

Paper II, Is focused on how inflammation affects endogenous neural stem cells distant from EAE lesions in spinal cord. We isolated NSC from different levels of the EAE affected spinal cord and we report that inflammation during EAE can affect NSC that are distant from lesion site. NSC from normal appearing spinal cord showed increased proliferation, altered gene expression and differentiation profile in-vitro. We detected that, NSC in normal appearing spinal cord displayed increased neurogenesis and reduced oligodendrocyte differentiation after the inflammatory event.

Paper III, We asked whether transplantation of NSC from subventricular zone improves hind limb function in spinal cord injured rats. For this, we isolated SVZ-NSC expressing eGFP and transplanted into immune compatible rats after SCI. We observed that transplanted NSC survived until 12weeks of post injury, filled the cyst and differentiated predominantly into oligodendrocytes (CC1), astrocytes (GFAP) and few neurons (ß-III tubulin). We observed that the animals received NSC improved hind limb function, decreased pro-inflammatory profile in cerebrospinal fluid and altered gene expression in the grafted cells. Further, ablation of the transplanted NSC using diphtheria receptor transfection, confirmed that, recovery of animal was due to the influence of the transplanted NSC.

Conclusion: BMDC fuses with motor neuron and interneurons in entire neuroaxis and these events increases during inflammation. Inflammatory lesions can affect differentiation and proliferation of NSC that are present in the normal appearing spinal cord distant from the site of inflammation. Finally, transplantation of NSC after spinal cord injury improves hindlimb recovery in rats.

List of scientific papers

I. Sankavaram SR, Svensson MA, Olsson T, Brundin L, Johansson CB. Cell Fusion along the Anterior-Posterior Neuroaxis in Mice with Experimental Autoimmune Encephalomyelitis. PLoS One. 2015 Jul 24;10(7):0133903.
https://doi.org/10.1371/journal.pone.0133903

II. Arvidsson L, Covacu R, Estrada CP, Sankavaram SR, Svensson M, Brundin L. Long-distance effects of inflammation on differentiation of adult spinal cord neural stem/progenitor cells. J Neuroimmunol. 2015 Nov 15;288:47-55.
https://doi.org/10.1016/j.jneuroim.2015.09.001

III. Sankavaram SR, Ramil Hakim, Arvid Frostell, Ruxandra Covacu, Susanne Neumann, Mikael Svensson, Lou Brundin. Analysis of possible mechanisms behind functional recovery following neural progenitor cell transplantation into spinal cord injury. [Submitted]