Time-dependent changes in the microenvironment of injured spinal cord affects the therapeutic potential of neural stem cell transplantation for spinal cord injury

Soraya Nishimura,Masaya Nakamura,Hayao Ebise,Hiroki Iwai,Osahiko Tsuji,Morito Takano,Yoshiaki Toyama,Yoshiomi Kobayashi,Kanehiro Fujiyoshi,Hideyuki Okano,Satoshi Nori,Akimasa Yasuda

doi:10.1186/1756-6606-6-3

Abstract

BackgroundThe transplantation of neural stem/progenitor cells (NS/PCs) at the sub-acute phase of spinal cord injury, but not at the chronic phase, can promote functional recovery. However, the reasons for this difference and whether it involves the survival and/or fate of grafted cells under these two conditions remain unclear. To address this question, NS/PC transplantation was performed after contusive spinal cord injury in adult mice at the sub-acute and chronic phases.ResultsQuantitative analyses using bio-imaging, which can noninvasively detect surviving grafted cells in living animals, revealed no significant difference in the survival rate of grafted cells between the sub-acute and chronic transplantation groups. Additionally, immunohistology revealed no significant difference in the differentiation phenotypes of grafted cells between the two groups. Microarray analysis revealed no significant differences in the expression of genes encoding inflammatory cytokines or growth factors, which affect the survival and/or fate of grafted cells, in the injured spinal cord between the sub-acute and chronic phases. By contrast, the distribution of chronically grafted NS/PCs was restricted compared to NS/PCs grafted at the sub-acute phase because a more prominent glial scar located around the lesion epicenter enclosed the grafted cells. Furthermore, microarray and histological analysis revealed that the infiltration of macrophages, especially M2 macrophages, which have anti-inflammatory role, was significantly higher at the sub-acute phase than the chronic phase. Ultimately, NS/PCs that were transplanted in the sub-acute phase, but not the chronic phase, promoted functional recovery compared with the vehicle control group.ConclusionsThe extent of glial scar formation and the characteristics of inflammation is the most remarkable difference in the injured spinal cord microenvironment between the sub-acute and chronic phases. To achieve functional recovery by NS/PC transplantation in cases at the chronic phase, modification of the microenvironment of the injured spinal cord focusing on glial scar formation and inflammatory phenotype should be considered.

Highlights

The transplantation of neural stem/progenitor cells (NS/PCs) at the sub-acute phase of spinal cord injury, but not at the chronic phase, can promote functional recovery
The NS/PCs differentiated into βIII tubulin (Tuj-1)+ neurons (21.0 ± 0.5%), glial fibrillary acidic protein (GFAP)+ astrocytes (63.0 ± 1.5%), and 2’3’-cyclic nucleotide 3’-phosphodiesterase (CNPase)+ oligodendrocytes (10.4 ± 0.5%) in vitro (Figure 1D, E)
We performed sub-acute- and chronic-phase transplantations of NS/PCs derived from transgenic mice that ubiquitously express fluorescent protein-fused luciferase (ffLuc)-cp156 on a C57BL/6J background [14] to treat spinal cord injury (SCI) in adult mice. These NS/PCs showed strong bioluminescent and fluorescent signals originating from ffLuc-cp156 [14], enabling the easy detection of surviving grafted cells in living animals noninvasively by bioluminescence imaging (BLI) [4,13] and confirmation of integrated cells within the injured spinal cord by immunohistology for Green fluorescent protein (GFP) without using a lentiviral vector. Using cells from these mice, we demonstrated that the NS/PCs grafted during the chronic phase of SCI had a similar survival rate to those transplanted at the subacute phase

Summary

Introduction

The transplantation of neural stem/progenitor cells (NS/PCs) at the sub-acute phase of spinal cord injury, but not at the chronic phase, can promote functional recovery. The reasons for this difference and whether it involves the survival and/or fate of grafted cells under these two conditions remain unclear To address this question, NS/PC transplantation was performed after contusive spinal cord injury in adult mice at the sub-acute and chronic phases. Some previous reports have shown that neural stem/progenitor cells (NS/PCs) transplanted into the injured spinal cord of rodents [1,2,3,4,5,6] and non-human primates [7], 7–10 days post-injury (DPI), promote functional recovery after SCI These reports indicate that NS/PC transplantation has therapeutic potential for SCI when performed during the sub-acute phase.

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Discussion

Conclusion