Central nervous system (CNS) injury transforms naive astrocytes into reactive astrocytes, which eventually become scar-forming astrocytes that can impair axonal regeneration and functional recovery. This sequential phenotypic change, known as reactive astrogliosis, has long been considered unidirectional and irreversible. However, we report here that reactive astrocytes isolated from injured spinal cord reverted in retrograde to naive astrocytes when transplanted into a naive spinal cord, whereas they formed astrocytic scars when transplanted into injured spinal cord, indicating the environment-dependent plasticity of reactive astrogliosis. We also found that type I collagen was highly expressed in the spinal cord during the scar-forming phase and induced astrocytic scar formation via the integrin-N-cadherin pathway. In a mouse model of spinal cord injury, pharmacological blockade of reactive astrocyte-type I collagen interaction prevented astrocytic scar formation, thereby leading to improved axonal regrowth and better functional outcomes. Our findings reveal environmental cues regulating astrocytic fate decisions, thereby providing a potential therapeutic target for CNS injury.

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Spinal cord injury (SCI) is a devastating disorder for which the identification of exacerbating factors is urgently needed. We demonstrate that transient hyperglycemia during acute SCI is a detrimental factor that impairs functional improvement in mice and human patients after acute SCI. Under hyperglycemic conditions, both in vivo and in vitro, inflammation was enhanced through promotion of the nuclear translocation of the nuclear factor κB (NF-κB) transcription factor in microglial cells. During acute SCI, hyperglycemic mice exhibited progressive neural damage, with more severe motor deficits than those observed in normoglycemic mice. Consistent with the animal study findings, a Pearson χ(2) analysis of data for 528 patients with SCI indicated that hyperglycemia on admission (glucose concentration ≥126 mg/dl) was a significant risk predictor of poor functional outcome. Moreover, a multiple linear regression analysis showed hyperglycemia at admission to be a powerful independent risk factor for a poor motor outcome, even after excluding patients with diabetes mellitus with chronic hyperglycemia (regression coefficient, -1.37; 95% confidence interval, -2.65 to -0.10; P < 0.05). Manipulating blood glucose during acute SCI in hyperglycemic mice rescued the exacerbation of pathophysiology and improved motor functional outcomes. Our findings suggest that hyperglycemia during acute SCI may be a useful prognostic factor with a negative impact on motor function, highlighting the importance of achieving tight glycemic control after central nervous system injury.

neural stem/progenitor cell (nsPC) transplantation is a promising treatment for various neurodegenerative disorders including spinal cord injury, however, no direct analysis has ever been performed on their in vivo profile after transplantation. Here we combined bioimaging, flow-cytometric isolation and ultra-high-throughput RnA sequencing to evaluate the cellular properties of engrafted nsPCs. The acutely transplanted nsPCs had beneficial effects on spinal cord injury, particularly neuroprotection and neurohumoral secretion, whereas their in situ secretory activity differed significantly from that predicted in vitro. The RnA-sequencing of engrafted nsPCs revealed dynamic expression/splicing changes in various genes involved in cellular functions and tumour development depending on graft environments. notably, in the pathological environment, overall transcriptional activity, external signal transduction and neural differentiation of engrafted nsPCs were significantly suppressed. These results highlight the vulnerability of engrafted nsPCs to environmental force, while emphasizing the importance of in situ analysis in advancing the efficacy and safety of stem cell-based therapies.

Acute inflammation is a prominent feature of central nervous system (CNS) insult and is detrimental to the CNS tissue. Although this reaction spontaneously diminishes within a short period of time, the mechanism underlying this inflammatory resolution remains largely unknown. In this study, we demonstrated that an initial infiltration of Ly6C + Ly6G À immature monocyte fraction exhibited the same characteristics as myeloid-derived suppressor cells (MDSCs), and played a critical role in the resolution of acute inflammation and in the subsequent tissue repair by using mice spinal cord injury (SCI) model. Complete depletion of Ly6C + Ly6G À fraction prior to injury by anti-Gr-1 antibody (clone: RB6-8C5) treatment significantly exacerbated tissue edema, vessel permeability, and hemorrhage, causing impaired neurological outcomes.Functional recovery was barely impaired when infiltration was allowed for the initial 24 h after injury, suggesting that MDSC infiltration at an early phase is critical to improve the neurological outcome. Moreover, intraspinal transplantation of ex vivo-generated MDSCs at sites of SCI significantly reduced inflammation and promoted tissue regeneration, resulting in better functional recovery. Our findings reveal the crucial role of an Ly6C + Ly6G À fraction as MDSCs in regulating inflammation and tissue repair after SCI, and also suggests an MDSC-based strategy that can be applied to acute inflammatory diseases.

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The transplantation of neural stem/precursor cells (NSPCs) is a promising therapeutic strategy for many neurodegenerative disorders including spinal cord injury (SCI) because it provides for neural replacement or trophic support. This strategy is now being extended to the treatment of chronic SCI patients. However, understanding of biological properties of chronically transplanted NSPCs and their surrounding environments is limited. Here, we performed temporal analysis of injured spinal cords and demonstrated their multiphasic cellular and molecular responses. In particular, chronically injured spinal cords were growth factorenriched environments, whereas acutely injured spinal cords were enriched by neurotrophic and inflammatory factors. To determine how these environmental differences affect engrafted cells, NSPCs transplanted into acutely, subacutely, and chronically injured spinal cords were selectively isolated by flow cytometry, and their whole transcriptomes were compared by RNA sequencing. This analysis revealed that NSPCs produced many regenerative/ neurotrophic molecules irrespective of transplantation timing, and these activities were prominent in chronically transplanted NSPCs. Furthermore, chronically injured spinal cords permitted engrafted NSPCs to differentiate into neurons/oligodendrocytes and provided more neurogenic environment for NSPCs than other environments. Despite these results demonstrate that transplanted NSPCs have adequate capacity in generating neurons/oligodendrocytes and producing therapeutic molecules in chronic SCI microenvironments, they did not improve locomotor function. Our results indicate that failure in chronic transplantation is not due to the lack of therapeutic activities of engrafted NSPCs but the refractory state of chronically injured spinal cords. Environmental modulation, rather modification of transplanting cells, will be significant for successful translation of stem cell-based therapies into chronic SCI patients.

SummaryNeural stem/progenitor cell (NSPC) transplantation is a promising therapeutic strategy for spinal cord injury (SCI). However, the efficacy of NSPC transplantation on severe SCI is poorly understood. We herein show that NSPC transplantation promotes functional recovery after mild and moderate SCI, but not after severe SCI. In severe SCI mice, there were few remaining host neurons within the range of NSPC engraftment; thus, we examined whether the co-distribution of transplant and host is a contributory factor for functional improvement. A cellular selective analysis using laser microdissection revealed that drug-induced host neuronal ablation considerably decreased the synaptogenic potential of the engrafted NSPCs. Furthermore, following host neuronal ablation, neuronal retrograde tracing showed less propriospinal relay connections bridging the lesion after NSPC transplantation. Our findings suggest that the interactive synaptic reorganization between engrafted NSPCs and spared host neurons is crucial for functional recovery, providing significant insight for establishing therapeutic strategies for severe SCI.