BackgroundEffective treatments for degenerative and traumatic diseases of the nervous system are not currently available. The support or replacement of injured neurons with neural grafts, already an established approach in experimental therapeutics, has been recently invigorated with the addition of neural and embryonic stem-derived precursors as inexhaustible, self-propagating alternatives to fetal tissues. The adult spinal cord, i.e., the site of common devastating injuries and motor neuron disease, has been an especially challenging target for stem cell therapies. In most cases, neural stem cell (NSC) transplants have shown either poor differentiation or a preferential choice of glial lineages.Methods and FindingsIn the present investigation, we grafted NSCs from human fetal spinal cord grown in monolayer into the lumbar cord of normal or injured adult nude rats and observed large-scale differentiation of these cells into neurons that formed axons and synapses and established extensive contacts with host motor neurons. Spinal cord microenvironment appeared to influence fate choice, with centrally located cells taking on a predominant neuronal path, and cells located under the pia membrane persisting as NSCs or presenting with astrocytic phenotypes. Slightly fewer than one-tenth of grafted neurons differentiated into oligodendrocytes. The presence of lesions increased the frequency of astrocytic phenotypes in the white matter.ConclusionsNSC grafts can show substantial neuronal differentiation in the normal and injured adult spinal cord with good potential of integration into host neural circuits. In view of recent similar findings from other laboratories, the extent of neuronal differentiation observed here disputes the notion of a spinal cord that is constitutively unfavorable to neuronal repair. Restoration of spinal cord circuitry in traumatic and degenerative diseases may be more realistic than previously thought, although major challenges remain, especially with respect to the establishment of neuromuscular connections.

NSC grafts can survive well in a neurodegenerative environment and exert powerful clinical effects; at least a portion of these effects may be related to the ability of these grafts to express and release motor neuron growth factors delivered to host motor neurons via graft-host connections.

Amyotrophic lateral sclerosis (ALS) is a target for cellreplacement therapies, including therapies based on human neural stem cells (NSCs).These therapies must be first tested in the appropriate animal models, including transgenic rodents harboring superoxide dismutase (SOD1) mutations linked to familial ALS. However, these rodent subjects reject discordant xenografts. In the present investigation, we grafted NSCs from human embryonic spinal cord into the ventral lumbar cord of 2-month-old SOD1-G93A transgenic mice. Animals were immunosuppressed with FK506, FK506 plus rapamycin, FK506 plus rapamycin plus mycophenolate mofetil, or CD4 antibodies. With FK506 monotherapy, human NSC grafts were rejected within 1 week, whereas combinations of FK506 with one or two of the other agents or CD4 antibodies protected grafts into endstage illness (i.e., more than 2 months after grafting). The combination of FK506 with rapamycin appeared to be optimal with respect to efficacy and simplicity of administration. Graft protection was achieved via the blockade of CD4-and CD8-cell infiltration and attenuation of the microglial phagocytic response from the host. Surviving NSCs differentiated extensively into neurons that began to establish networks with host nerve cells, including ␣-motor neurons. Immunosuppressed animals with live cells showed later onset and a slower progression of motor neuron disease and lived longer compared with immunosuppressed control animals with dead NSC grafts. Our findings indicate that combined immunosuppression promotes the survival of human NSCs grafted in the spinal cord of SOD1-G93A mice and, in doing so, allows the differentiation of NSCs into neurons and leads to the improvement of key parameters of motor neuron disease.

The fate of exogenous neural stem cells (NSCs) in the environment of the adult nervous system continues to be a matter of debate. In the present study, we report that cells of the murine NSC clone C17.2, when grafted into the lumbar segments of the spinal cord of adult rats, survive and undergo partial differentiation. C17.2 cells migrate avidly toward axonal tracts and nerve roots and differentiate into nonmyelinating ensheathing cells. Notably, C17.2 cells induce the de novo formation of host axon tracts aiming at graft innervation. Differentiation and inductive properties of C17.2 cells are independent of the presence of lesions in the spinal cord. The tropic/trophic interactions of C17.2 NSCs with host axons, the avid C17.2 cell-host axon contacts, and the ensheathing properties of these cells are related to their complex molecular profile, which includes the expression of trophic cytokines and neurotrophins such as glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, glial growth factor receptors such as ErbB-2; and PASK, the mammalian homologue of the fray gene that is involved in axon ensheathment. These results show that NSCs might not only play a critical supportive role in repairing axonal injury in the adult spinal cord but also can be used as probes for exploring the molecular underpinnings of the regenerative potential of the mature nervous system after injury.

J. Neurochem. (2012) 120, 721–731. Abstract Nogo‐66 is a 66‐amino‐acid‐residue extracellular domain of Nogo‐A, which plays a key role in inhibition neurite outgrowth of central nervous system through binding to the Nogo‐66 receptor (NgR) expressed on the neuron. Recent studies have confirmed that NgR is also expressed on the surface of macrophages/microglia in multiple sclerosis, but its biological effects remain unknown. In the present study, our results demonstrated that Nogo‐66 triggered microglia anti‐adhesion and inhibited their migration in vitro, which was mediated by NgR. We also assessed the roles of small GTP (glycosyl phosphatidylinositol)‐binding proteins of the Rho family as the downstream signal transducers on the microglia adhesion and mobility induced by Nogo‐66. The results showed that Nogo‐66 activated RhoA and reduced the activity of Cdc42 in the meanwhile, which further triggered the anti‐adhesion and migration inhibition effects to microglia. Nogo‐66 inhibited microglia polarization and membrane protrusion formation, thus might eventually contribute to the decreasing capability of cell mobility. Taken together, the Nogo‐66/NgR pathway may modulate neuroinflammation via mediating microglia adhesion and migration in addition to its role in neurons. Better understanding the relationship between Nogo‐66/NgR and neuroinflammation may help targeting NgR for treating central nervous system diseases related with inflammation.