Spinal cord injury (SCI) is uniquely devastating. Cellular transplantation strategies for SCI are showing promise. Little, however, is known about how transplanted neural precursor cells (NPCs) enhance functional recovery or the mechanisms by which they interact with the host spinal cord. Better understanding of these critical issues may lead to improved strategies to enhance recovery after SCI. Given this background, I hypothesized that NPCs mediate functional recovery by a number of mechanisms including trophin production, neuroprotection, modulation of the host inflammatory response or glial scarring, and/or remyelination. I thus endeavored to characterize trophin production by NPCs in vitro and in vivo in rats with clip compression SCI of the thoracic spinal cord, to determine if preservation of host cells and tissue contribute to functional recovery and to determine how NPC transplantation influences the host inflammatory response and glial scarring. Here I present unique and novel insights into NPC-host interactions following SCI. We show that NPCs are poised to provide trophic support to the injured spinal cord. We also show that the combination of NPCs, pharmacotherapy and trophin infusion is associated with sparing of grey and white matter, enhanced numbers of oligodendrocytes but not axons as well as an increased inflammatory response. To assess the potential impact of myelination as a mechanism underlying NPC-mediated functional recovery after SCI, experiments were undertaken using NPCs derived from shiverer mutant mice unable to produce central myelin. These experiments showed that while NPCs from wild-type mice generate myelin and mediate functional recovery after SCI; transplanted shiverer NPCs impede neurobehavioural recovery. In summary, my work provides unique insights into the functional effects of NPC transplantation after SCI. Of importance, this thesis provides novel evidence that remyelination is a key mechanism of action by which NPCs mediate recovery after SCI. Hence, this work has important implications for patients with SCI.

Spinal cord injury (SCI) is uniquely devastating. Cellular transplantation strategies for SCI are showing promise. Little, however, is known about how transplanted neural precursor cells (NPCs) enhance functional recovery or the mechanisms by which they interact with the host spinal cord. Better understanding of these critical issues may lead to improved strategies to enhance recovery after SCI. Given this background, I hypothesized that NPCs mediate functional recovery by a number of mechanisms including trophin production, neuroprotection, modulation of the host inflammatory response or glial scarring, and/or remyelination. I thus endeavored to characterize trophin production by NPCs in vitro and in vivo in rats with clip compression SCI of the thoracic spinal cord, to determine if preservation of host cells and tissue contribute to functional recovery and to determine how NPC transplantation influences the host inflammatory response and glial scarring. Here I present unique and novel insights into NPC-host interactions following SCI. We show that NPCs are poised to provide trophic support to the injured spinal cord. We also show that the combination of NPCs, pharmacotherapy and trophin infusion is associated with sparing of grey and white matter, enhanced numbers of oligodendrocytes but not axons as well as an increased inflammatory response. To assess the potential impact of myelination as a mechanism underlying NPC-mediated functional recovery after SCI, experiments were undertaken using NPCs derived from shiverer mutant mice unable to produce central myelin. These experiments showed that while NPCs from wild-type mice generate myelin and mediate functional recovery after SCI; transplanted shiverer NPCs impede neurobehavioural recovery. In summary, my work provides unique insights into the functional effects of NPC transplantation after SCI. Of importance, this thesis provides novel evidence that remyelination is a key mechanism of action by which NPCs mediate recovery after SCI. Hence, this work has important implications for patients with SCI.

Un traumatisme de la moelle épinière (TME) est une condition dévastatrice entraînant la perte permanente de fonctions neuronales. L’objectif de cette thèse est de formuler de microsupports pharmacologiquement actif (MPAs) avec une surface de fibronectine (FN), libérant le« brain-derived neurotrophic factor » (BDNF) de façon controlée. Nous voulons combiner ce système avec des cellules souches mésenchymateuses (CSMs) pour la réparation de TME. Le BDNF nanoprécipité a été encapsulé dans les FN-MPAs et le profil de libération in vitro a été évaluée. Elle a montré une libération biphasique et prolongée de BDNF bioactifs. Nous avons combinés des cellules souches humaines mésenchymateuse issues de la moelle osseuse adulte (cellules MIAMI) et FN-MPAs avec un hydrogel non-toxique silanisés-hydroxypropylméthylcellulose (Si-HPMC). Nous avons démontré que les FN-MPAs et le Si-HPMC augmentait l'expression de marqueurs neuraux/neuronaux de cellules MIAMI après 1 semaine. En outre, l'environnement 3D (hydrogel ou FN-MPAs) a augmenté le sécrétome thérapeutique de cellules MIAMI. Pour avoir un système facile à appliquer en clinique, nous avons choisi d’utiliser les cellules souches de la papille apicale (SCAP) et FN-MPAs libérant ou non du BDNF pour la thérapie du TME. Plus de 90 % du SCAP complexée avec FN-MPAs (libérant ou pas BDNF) demeurent viables pendant 7 jours et il y a augmentation de l'expression des gènes neuronaux/oligodendrogliaux in vitro. La récupération de la fonction locomotrice a été significativement améliorée après la transplantation du SCAP complexée avec FN-MPAs-BDNF avec une coordination cohérente du membre postérieur après 28 jours de traitement. / Traumatic spinal cord injury (SCI) is a devastating condition resulting in permanent loss of neural functions. The objective of this thesis is to develop pharmacologically active microcarriers (PAMs) with a fibronectin (FN) surface that deliver biologically active brain derived neurotrophic factor (BDNF) in a controlled manner. We want to combine this system with adult mesenchymal stem cells (MSCs) for SCI repair. The nanoprecipitated BDNF was encapsulated in FN-PAMs and the in vitro release profile was evaluated. It showed a prolonged, bi-phasic, release of bioactive BDNF, without burst effect. We combined human marrow-isolated adult multilineage-inducible (MIAMI) stem cells and FN-PAMs with an injectable non-toxic silanized-hydroxypropylmethylcellulose (Si-HPMC) hydrogel. We demonstrated that FN-PAMs and the Si-HPMC hydrogel increased the expression of neural/neuronal differentiation markers of MIAMI cells after 1 week. Moreover, the 3D environment (FN-PAMs or hydrogel) enhanced the therapeutic MIAMI cell secretome. To have a clinically translatable system, we chose to use stem cells of the apical papilla (SCAP) and FNPAMs releasing or not BDNF for SCI therapy. More than 90% of SCAP complexed with FN-PAMs (releasing or not BDNF) remained viable for 7 days and an increased neuronal-oligodendroglial gene expression in vitro. The recovery of locomotor function was significantly improved after transplantation of SCAP complexed with FN-PAMs-BDNF with frequent to consistent forelimb-hindlimb coordination after 28 days of treatment.