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

Adult Neural Progenitor Cells Transplanted into Spinal Cord Injury Differentiate into Oligodendrocytes, Enhance Myelination, and Contribute to Recovery

Summary: Long-term survival and integration of neural progenitor cells (NPCs) transplanted following spinal cord injury (SCI) have been observed. However, questions concerning the differentiation choice, the mechanism of action, and the contribution of NPCs to functional recovery remains unanswered. Therefore, we investigated the differentiation of NPCs, global transcriptomal changes in transplanted NPCs, the effect of NPCs on neuroinflammation, and the causality between NPC transplantation and functional recovery. We found that NPCs transplanted following SCI differentiate mainly into oligodendrocytes and enhance myelination, upregulate genes related to synaptic signaling and mitochondrial activity, and downregulate genes related to cytokine production and immune system response. NPCs suppress the expression of pro-inflammatory cytokines/chemokines; moreover, NPC ablation confirm that NPCs were responsible for enhanced recovery in hindlimb locomotor function. Understanding the reaction of transplanted NPCs is important for exploiting their full potential. Existence of causality implies that NPCs are useful in the treatment of SCI. : In this article, Brundin and colleagues show that NPCs transplanted following SCI differentiated mainly into oligodendrocytes and enhanced myelination, upregulated genes related to synaptic signaling and mitochondrial activity, suppressed pro-inflammation, and were responsible for enhanced recovery in hindlimb function. Understanding the reaction of transplanted NPCs is important for exploiting their full potential. Existence of causality implies that NPCs are useful in the treatment of SCI. Keywords: spinal cord injury, neural progenitor cells, global transcriptomal changes, neuroinflammation, oligodendrocyte, myelination, regeneration, hindlimb locomotor function, transplantatio

Sex-Specific Effects of Microglia-Like Cell Engraftment during Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic neuroinflammatory disorder of the central nervous system (CNS) that usually presents in young adults and predominantly in females. Microglia, a major resident immune cell in the CNS, are critical players in both CNS homeostasis and disease. We have previously demonstrated that microglia can be efficiently depleted by the administration of tamoxifen in Cx3cr1CreER/+Rosa26DTA/+ mice, with ensuing repopulation deriving from both the proliferation of residual CNS resident microglia and the engraftment of peripheral monocyte-derived microglia-like cells. In this study, tamoxifen was administered to Cx3cr1CreER/+Rosa26DTA/+ and Cx3cr1CreER/+ female and male mice. Experimental autoimmune encephalomyelitis (EAE), a widely used animal model of MS, was induced by active immunization with myelin oligodendrocyte glycoprotein (MOG) one month after tamoxifen injections in Cx3cr1CreER/+Rosa26DTA/+ mice and Cx3cr1CreER/+ mice, a time point when the CNS niche was colonized by microglia derived from both CNS microglia and peripherally-derived macrophages. We demonstrate that engraftment of microglia-like cells following microglial depletion exacerbated EAE in Cx3cr1CreER/+Rosa26DTA/+ female mice as assessed by clinical symptoms and the expression of CNS inflammatory factors, but these findings were not evident in male mice. Higher major histocompatibility complex class II expression and cytokine production in the female CNS contributed to the sex-dependent EAE severity in mice following engraftment of microglia-like cells. An underestimated yet marked sex-dependent microglial activation pattern may exist in the injured CNS during EAE