Abstract
BackgroundHuman central nervous system-stem cells grown as neurospheres (hCNS-SCns) self-renew, are multipotent, and have potential therapeutic applications following trauma to the spinal cord. We have previously shown locomotor recovery in immunodeficient mice that received a moderate contusion spinal cord injury (SCI) and hCNS-SCns transplantation 9 days post-injury (dpi). Engrafted hCNS-SCns exhibited terminal differentiation to myelinating oligodendrocytes and synapse-forming neurons. Further, selective ablation of human cells using Diphtheria toxin (DT) abolished locomotor recovery in this paradigm, suggesting integration of human cells within the mouse host as a possible mechanism for the locomotor improvement. However, the hypothesis that hCNS-SCns could alter the host microenvironment as an additional or alternative mechanism of recovery remained unexplored; we tested that hypothesis in the present study.Methods and FindingsStereological quantification of human cells using a human-specific cytoplasmic marker demonstrated successful cell engraftment, survival, migration and limited proliferation in all hCNS-SCns transplanted animals. DT administration at 16 weeks post-transplant ablated 80.5% of hCNS-SCns. Stereological quantification for lesion volume, tissue sparing, descending serotonergic host fiber sprouting, chondroitin sulfate proteoglycan deposition, glial scarring, and angiogenesis demonstrated no evidence of host modification within the mouse spinal cord as a result of hCNS-SCns transplantation. Biochemical analyses supplemented stereological data supporting the absence of neural stem-cell mediated host repair. However, linear regression analysis of the number of engrafted hCNS-SCns vs. the number of errors on a horizontal ladder beam task revealed a strong correlation between these variables (r = −0.78, p<0.05), suggesting that survival and engraftment were directly related to a quantitative measure of recovery.ConclusionsAltogether, the data suggest that the locomotor improvements associated with hCNS-SCns transplantation were not due to modifications within the host microenvironment, supporting the hypothesis that human cell integration within the host circuitry mediates functional recovery following a 9 day delayed transplant.
Highlights
The endogenous capacity of the spinal cord for repair and regeneration following traumatic injury is thought to be limited
Altogether, the data suggest that the locomotor improvements associated with hCNS-SCns transplantation were not due to modifications within the host microenvironment, supporting the hypothesis that human cell integration within the host circuitry mediates functional recovery following a 9 day delayed transplant
Our results show no evidence of host modifications in association with hCNSSCns transplantation
Summary
The endogenous capacity of the spinal cord for repair and regeneration following traumatic injury is thought to be limited. Rodent- and human-derived neural/glial cell populations transplanted sub-acutely after SCI have been associated with recovery of function in several studies [1,2,3,4,5,6]. In these studies, remyelination was suggested as the primary mechanism for the observed locomotor improvement. While all the studies above suggest cell integration by means of oligodendroglial and neuronal differentiation as potential mechanisms for recovery of function after SCI, the possibility of additional mechanisms whereby engrafted cell populations contribute to endogenous repair within the host microenvironment remains unexplored. The hypothesis that hCNS-SCns could alter the host microenvironment as an additional or alternative mechanism of recovery remained unexplored; we tested that hypothesis in the present study
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