With these results we provide evidence that

With these results, we provide evidence that the transplantation of iPSC-derived NSCs could have a beneficial role in modifying the course of SMARD1. Regarding the translational safety of iPSC-derived cells, one major finding of this study is that adverse events such as tumorigenesis or abnormal growth were not observed, even if our observational time is limited. Although NSC transplantation was not sufficient to fully rescue the nmd phenotype, the behavioral improvements and enhanced survival were significant. The neurological phenotypic improvement correlated with a significant modification in spinal cord pathology, and the motor neuron count in NSC-transplanted relative to vehicle-treated and fibroblasts-treated mice confirmed a significant reduction in neural cell degeneration. We observed the generation of a low proportion of donor-derived motor neurons, as evaluated by immunopathological characterization, which were correctly located in the anterior horns. In addition, we detected an increased number of endogenous motor neurons as well as myelinated ci-1033 in iPSC-transplanted nmd mice compared with vehicle-treated controls. Overall, the functional improvement in the SMARD1 mouse models was supported by the results of our neuromuscular function tests and by the improved survival of transplanted mice. NSC transplantation increased survival by 30% compared with the vehicle-treated group. The extended survival time resulting from stem cell transplantation, although limited, is a significant finding. Similarly, the neuromuscular function test results in this study must be considered in the context of decreased disease severity; treated animals could perform the rotarod task, even if with lower performance respect to the wild-type, whereas untreated animals would never be able to execute the task. Therefore, although the amelioration was not complete, it was relatively substantial. In addition, human iPSC-derived NSCs produce neurotrophic factors that may be neuroprotective of murine and human motor neurons by paracrine signaling, as our coculture results suggest. This neurotrophic benefit of NSCs indicates that they can lessen some of the effects of SMARD1 pathogenesis. Particularly promising is the finding that NSCs exert this protection in motor neurons derived from reprogrammed SMARD1 fibroblasts. We also showed that iPSCs from SMARD1 patients are a suitable model for evaluating cellular features of motor neuron disease degeneration. Overall, NSC coculture improved motor neuron survival, increased neurite length, and boosted growth cone size of SMARD1 iPSC-derived motor neurons. Our mechanistic studies of NSC protective effects of human SMARD1 motor neurons showed that NSC coculture increased GSK3β phosphorylation, which would be expected to elicit decreased kinase activity, a feature associated with motor neuron survival (Yang et al., 2013). In keeping with this finding, our results also demonstrated that NSC coculture inhibits the JNK/c-JUN-mediated cell death signaling cascade in motor neurons that HGK kinase controls. Overall, these findings indicate that NSC treatment inhibits GSK-3 and HGK kinase activation in our motor neuron cultures and suggest an important therapeutic target for SMARD1.
Experimental Procedures
Author Contributions
Acknowledgments
Introduction Neural stem cells (NSCs) remain in specialized niches of the brain over the lifespan and give rise to new neurons that integrate neural circuits. They are proposed to enable regeneration of injured tissue. The subependymal zone (SEZ), one of the main neurogenic niches in the adult mammalian brain, is comprised of astrocyte-like NSCs corresponding to a heterogeneous cell population. Among the identified subpopulations, active NSCs (aNSCs) expressing the epidermal growth factor receptor (EGFR) give rise to transit amplifying progenitors (TAPs). Most of these cells generate neuroblasts, migrating along the rostral migratory stream (RMS) and differentiating into granule and periglomerular interneurons in the olfactory bulb (OB). Quiescent NSCs (qNSCs) do not express the EGFR and are resistant to antimitotic drugs or irradiation. They are implicated in SEZ neurogenesis replenishment through aNSCs and TAPs (Costa et al., 2011; Pastrana et al., 2011; Ponti et al., 2013). Establishing the identity and lineage of SEZ stem cells is under intense studies, but the regulatory mechanisms involved in their self-renewal and differentiation still need more investigation. Only a few signals determining these distinct behaviors have been discovered. For instance, bone morphogenetic protein signals and EGFR-mediated inactivation of NOTCH signaling in NSCs are required for progression of the NSC progeny toward the neurogenic lineage (Aguirre et al., 2010; Colak et al., 2008), whereas the pigment epithelium-derived factor was proposed to regulate the NSC expansion (Karpowicz et al., 2009).