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ALS is a devastating disease resulting in degeneration of motor neurons (MNs) in the brain and spinal cord. The survival of MNs strongly depends on surrounding glial cells and neurotrophic support from muscles. We previously demonstrated that boundary cap neural crest stem cells (bNCSCs) can give rise to neurons and glial cells in vitro and in vivo and have multiple beneficial effects on co-cultured and co-implanted cells, including neural cells. In this paper, we investigate if bNCSCs may improve survival of MNs harboring a mutant form of human SOD1 (SOD1(G93A)) in vitro under normal conditions and oxidative stress and in vivo after implantation to the spinal cord. We found that survival of SOD1(G93A) MNs in vitro was increased in the presence of bNCSCs under normal conditions as well as under oxidative stress. In addition, when SOD1(G93A) MN precursors were implanted to the spinal cord of adult mice, their survival was increased when they were co-implanted with bNCSCs. These findings show that bNCSCs support survival of SOD1(G93A) MNs in normal conditions and under oxidative stress in vitro and improve their survival in vivo, suggesting that bNCSCs have a potential for the development of novel stem cell-based therapeutic approaches in ALS models.

Aim: Stem cell-derived motor neurons (MNs) are utilized to develop replacement strategies for spinal cord disorders. Differentiation of embryonic stem cells into MN precursors involves factors and their repeated administration. We investigated if delivery of factors loaded into mesoporous nanoparticles could be effective for stem cell differentiation in vitro.

Materials & methods: We used a mouse embryonic stem cell line expressing green fluorescent protein under the promoter for the MN-specific gene Hb9 to visualize the level of MN differentiation. The differentiation of stem cells was evaluated by expression of MN-specific transcription factors monitored by quantitative real-time PCR reactions and immunocytochemistry.

Results: Mesoporous nanoparticles have strong affiliation to the embryoid bodies, penetrate inside the embryoid bodies and come in contact with differentiating cells.

Conclusion: Repeated administration of soluble factors into a culture medium can be avoided due to a sustained release effect using mesoporous silica.

Context: Neural crest stem cells (NCSCs) are capable of substantially improving murine islet function by promoting beta-cell proliferation. Objective: The present study aimed to investigate the potential of NCSCs to stimulate human beta-cell proliferation, and improve neural and vascular engraftment of human islets. Design, Setting, and Subjects: Human pancreatic islets from 18 brain-dead cadaveric donors (age range, 19-78 y) were obtained through the Nordic Network for Clinical Islet Transplantation. beta-cell proliferation and graft function was investigated at our experimental laboratory. Intervention and Main Outcome Measures: Human islets were transplanted, either alone or together with spheres of NCSCs. beta-cell proliferation, as well as islet neuralandvascular densities, were assessed by immunohistochemistry. Graft blood perfusion and oxygen tension were measured using laser-Doppler flowmetry and Clark microelectrodes, respectively. Results: Two days posttransplantation, the number of Ki67-positive beta-cells was doubled in human islets that had been exposed to NCSCs. Similar findings were obtained in vitro, as well as with EdU as proliferation marker. Four weeks posttransplantation, NCSC-exposed human islet grafts had much higher neural and vascular densities. The newly formed blood vessels were also functional, given that these human islets had a substantially higher blood perfusion and oxygen tension when compared with control transplants. Conclusion: We conclude that exposure to NCSCs stimulates human beta-cell proliferation, andthat these cells improve both the neural and vascular engraftment of transplanted human islets. NCSCs are a promising cellular therapy for translation into clinical use.

Injury and neurodegenerative conditions of the spinal cord can lead to paralysis and loss of sensation. Cell therapeutic approaches can restore sensory innervation of the spinal cord following injury and protect spinal cord cells from degeneration. This thesis primarily focuses on the restoration of deaffarented sensory fibres following injury to the dorsal root and spinal cord. These injuries lead to the formation of a non-permissive glial scar that prevents sensory axons from reinnervating spinal cord targets. It takes advantage of a dorsal root injury model that closely mimics spinal root avulsion injuries occurring in humans. In the first part of the thesis, three different neural progenitor types from human or murine sources are tested for their regenerative properties following their transplantation to the site of dorsal root avulsion injury. In the second part, the ability of murine neural progenitors to protect spinal motor neurons from a neurodegenerative process is tested.

In the first original research article, I show that human embryonic stem cell derived neural progenitors are able to restore sensorimotor functions, mediated by the formation of a tissue bridge that allows ingrowth of sensory axons into the spinal cord. In the second research article, I present that murine boundary cap neural crest stem cells, a special type of neural progenitor that governs the entry of sensory axons into the spinal cord during development, are unable to form a permissive tissue bridge. This is possibly caused by the contribution of transplant derived ingrowth non-permissive glial cells. In the third research article, I show that human neural progenitors derived from foetal sources are capable of stimulating sensory ingrowth and that they ameliorate the glial scar. When this approach is combined with the delivery of sensory outgrowth stimulating neurotrophic factors, these cells fail to form a permissive tissue bridge and fail to modify the glial scar. In the final research article, murine boundary cap neural crest stem cells are shown to protect motor neurons, which harbor an amyotrophic lateral sclerosis causing mutation, from oxidative stress. Oxidative stress is a pathological component of amyotrophic lateral sclerosis in human patients.

Taken together, this thesis provides first evidence that sensory regeneration following a spinal root avulsion injury can be achieved by transplantation of human neural progenitors. In addition, it introduces murine boundary cap neural crest stem cells as interesting candidates for the cell therapeutic treatment of amyotrophic lateral sclerosis.

Spinal root injuries result in newly formed glial scar formation, which prevents regeneration of sensory axons causing permanent sensory loss. Previous studies showed that delivery of trophic factors or implantation of human neural progenitor cells supports sensory axon regeneration and partly restores sensory functions. In this study, we elucidate mechanisms underlying stem cell-mediated ingrowth of sensory axons after dorsal root avulsion (DRA). We show that human spinal cord neural stem/progenitor cells (hscNSPC), and also, mesoporous silica particles loaded with growth factor mimetics (MesoMIM), supported sensory axon regeneration. However, when hscNSPC and MesoMIM were combined, sensory axon regeneration failed. Morphological and tracing analysis showed that sensory axons grow through the newly established glial scar along "bridges" formed by migrating stem cells. Coimplantation of MesoMIM prevented stem cell migration, "bridges" were not formed, and sensory axons failed to enter the spinal cord. MesoMIM applied alone supported sensory axons ingrowth, but without affecting glial scar formation. In vitro, the presence of MesoMIM significantly impaired migration of hscNSPC without affecting their level of differentiation. Our data show that (1) the ability of stem cells to migrate into the spinal cord and organize cellular "bridges" in the newly formed interface is crucial for successful sensory axon regeneration, (2) trophic factor mimetics delivered by mesoporous silica may be a convenient alternative way to induce sensory axon regeneration, and (3) a combinatorial approach of individually beneficial components is not necessarily additive, but can be counterproductive for axonal growth.

Dorsal root avulsion results in permanent impairment of sensory functions due to disconnection between the peripheral and central nervous system. Improved strategies are therefore needed to reconnect injured sensory neurons with their spinal cord targets in order to achieve functional repair after brachial and lumbosacral plexus avulsion injuries. Here, we show that sensory functions can be restored in the adult mouse if avulsed sensory fibers are bridged with the spinal cord by human neural progenitor (hNP) transplants. Responses to peripheral mechanical sensory stimulation were significantly improved in transplanted animals. Transganglionic tracing showed host sensory axons only in the spinal cord dorsal horn of treated animals. Immunohistochemical analysis confirmed that sensory fibers had grown through the bridge and showed robust survival and differentiation of the transplants. Section of the repaired dorsal roots distal to the transplant completely abolished the behavioral improvement. This demonstrates that hNP transplants promote recovery of sensorimotor functions after dorsal root avulsion, and that these effects are mediated by spinal ingrowth of host sensory axons. These results provide a rationale for the development of novel stem cell-based strategies for functionally useful bridging of the peripheral and central nervous system.