Hypoxic preconditioning enhances the differentiation of bone marrow stromal cells into mature oligodendrocytes via the mTOR/HIF‐1α/VEGF pathway in traumatic brain injury

Xiaoyu Yuan,Guohua Wang,Yechao Sun,Lihua Shen,Lingzhi Ding,Jin Chen,Deqiang Gan,Qianqian Luo

doi:10.1002/brb3.1675

Abstract

ObjectiveTraumatic brain injury (TBI) results not only in gray matter damage, but also in severe white matter injury (WMI). Previous findings support hypoxic preconditioning (HP) could augment the efficacy of bone marrow stromal cell (BMSC) transplantation in a TBI mouse model. However, whether HP‐treated BMSCs (H‐BMSCs) could overcome remyelination failure after WMI is unclear, and the molecular mechanisms remain to be explored. Here, we focused on the therapeutic benefits of H‐BMSC transplantation for treating WMI, as well as its underlying mechanisms.MethodsIn vitro, BMSCs were incubated at passage 4 in the hypoxic preconditioning (1.0% oxygen) for 8 hr. In vivo, a TBI mouse model was established, and DMEM cell culture medium (control), normal cultured BMSCs (N‐BMSCs), or H‐BMSCs were transplanted to mice 24 hr afterward. Neurobehavioral function, histopathological changes, and oligodendrogenesis were assessed for up to 35 days post‐TBI.ResultsCompared with the control group, improvement of cognitive functions and smaller lesion volumes was observed in the two BMSC‐transplanted groups, especially the H‐BMSC group. H‐BMSC transplantation resulted in a greater number of neural/glial antigen 2 (NG2)–positive and adenomatous polyposis coli (APC)–positive cells than N‐BMSC transplantation in both the corpus callosum and the striatum. In addition, we observed that the expression levels of hypoxia‐inducible factor‐1a (HIF‐1α), phosphorylated mechanistic target of rapamycin (p‐mTOR), and vascular endothelial growth factor (VEGF) were all increased in H‐BMSC–transplanted mice. Furthermore, the mTOR pathway inhibitor rapamycin attenuated the impact of HP both in vivo and in vitro.ConclusionThe results provided mechanistic evidences suggesting that HP‐treated BMSCs promoted remyelination partly by modulating the pro‐survival mTOR/HIF‐1α/VEGF signaling pathway.

Highlights

Bone marrow stromal cells (BMSCs), known as mesenchymal stem cells, are multipotent nonhematopoietic stem cells (Javazon, Colter, Schwarz, & Prockop, 2001; Li, Ghazanfari, Zacharaki, Lim, & Scheding, 2016)
Enhanced regeneration was observed in the HP-treated BMSCs (H-BMSCs)–treated group compared with that in the normal cultured BMSCs (N-BMSCs)– treated group both in the corpus callosum (CC) and the STR (Figures 5 and 6), indicating that the protection induced by H-BMSCs was mediated through the induction of the differentiation of oligodendrocyte progenitor cells (OPCs) from BMSCs
DMSO alone was used as a diluent control in the N-BMSC and H-BMSC groups. (b–e) phosphorylated mechanistic target of rapamycin (p-mTOR), mTOR, HIF-1α, and vascular endothelial growth factor (VEGF) intensity levels were measured and calculated as fold changes over sham. (f) The CC and STR in the brain 35 days after Traumatic brain injury (TBI) were double-labeled with antibodies against adenomatous polyposis coli (APC) and BrdU

Summary

| INTRODUCTION

Bone marrow stromal cells (BMSCs), known as mesenchymal stem cells, are multipotent nonhematopoietic stem cells (Javazon, Colter, Schwarz, & Prockop, 2001; Li, Ghazanfari, Zacharaki, Lim, & Scheding, 2016). Hypoxic preconditioning (HP) has been reported to increase ischemic tolerance, reduce apoptosis, and cause gene expression alterations (Feng & Bhatt, 2015; Huang et al, 2013) It has been reported in studies on ischemic and hemorrhagic stroke that HP promotes the regenerative capability of the transplanted cells and increases their therapeutic benefits (Chen et al, 2017; Huang et al, 2013). TBI results in gray matter damage, and in severe white matter injury (WMI), thereby disrupting signal transmission and eliciting poor functional outcomes (Wang, Shi, et al, 2015). There are no satisfactory therapies to protect TBI patients against either gray matter injury or WMI (Shein & Shohami, 2011; Wang, Shi, et al, 2015). This study aimed to investigate the potential mechanisms involved in this process, potentially providing critical evidence supporting the use of H-BMSC transplantation for TBI therapy in future clinical trials

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