FGF信号通路在少突胶质细胞的发育以及脊髓损伤后髓鞘再生机制中的调控作用

Spinal cord injury (SCI) is a devastating and debilitating condition that affects an estimated 400,000 to 800,000 persons in the People’s Republic of China with approximately 10,000 new cases occurring each year. SCI irreversibly damages axons, which is always accompanied by loss of glia and de-myelination of spared neuronal tracts. Successful functional recovery following SCI involves the production of specialized glial cells by transplanting exogenous stem cells, or activating endogenous multipotent stem/progenitor cell populations. Among these cells are the myelin-producing oligodendrocytes (OLs) that are generated from oligodendrocyte progenitor cells (OPCs) that are located in the adult spinal cord. It has been shown that FGF signaling is involved in the OL generation and axonal remyelination processes in the forebrain, but so far prior investigation has failed to establish this mechanism in the spinal cord. For this reason, we generated Nestin::Cre driven Fgfr2 conditional knockout, Fgfr3 null knockout, and their double mutant mice. . We have now obtained preliminary data that reveals a similar, broad requirement for FGF signaling in generating OLs in the developing spinal cord. Specifically, analysis of conditional Fgfr2;Fgfr3 double mutant embryos clearly shows a drastic decrease of the OPC proliferation which causes the significant reduction on the expression of OL markers in both the grey matter and white matter. Taken together, these data provide the first evidence that the FGF signaling is required for generating the majority of OLs in the spinal cord. It raises the likely possibility that FGF signaling is also involved in producing OLs in adults after SCI. Three aims of this proposal will address this issue. First, we will define the requirement of embryonic FGF signaling to produce ventral spinal cord OLs by extending our preliminary analysis. Next, we will address how the deficiency of FGF signaling will affect axonal myelination during postnatal stages. These studies together will provide important mechanistic insights into FGF signaling directed OL formation that will be readily applicable to our adult SCI studies. Thus, we will eventually determine whether FGF signaling is required for adult OL formation and axonal remyelination following SCI. The overall goal of these experiments is to test whether FGF signaling is required in reactive cells to generate glial progeny after SCI. Thus, these experiments will establish a definitive role for FGF signaling in the specification and differentiation of embryonic and adult spinal cord OPCs under normal and lesioned conditions, respectively. Results from our studies will provide important information on the molecular sequence of events that occurs in OL progenitors following SCI that could be used to improve treatment and recovery from this devastating problem.

在我国当下，脊髓损伤是困扰数以百万计国民的顽疾，至今尚无治愈方案，如何有效修复脊髓损伤更是一个重大的全球性课题。最具前景的治疗方案即是干细胞参与的脊髓组织再生，而其重中之重便是激活髓鞘再生，及时准确地实现少突胶质细胞形成是髓鞘再生技术成功与否的关键。本项目预数据及其他已发表数据均显示FGF信号与髓鞘生成有诸多关联。为此我们已经培育了一系列特异性的Fgfr2/3单及双突变小鼠，并系统分析了FGF信号在胚胎脊髓少突胶质细胞形成初期有关其分裂、迁移和细胞命运决定过程中所起到的关键性作用。继而，本项目旨在全面阐明胚胎期、胎后期、成熟期、以及脊髓损伤后FGF信号通路如何影响少突胶质细胞的发育和再生，从而明确揭示其对髓鞘形成与再生的调控机制。本项目的全部数据采集于动物模型，因此其最终实验结果将对脊髓损伤治愈方案的预临床和一期临床提供直接可信的依据。相信其必将促进最前沿的脊髓损伤治愈科技实现新的突破。

当下，针对脊髓损伤的治疗与研究已经成为医学临床和生命科学的一个全球性的重大课题。理清发育阶段细胞初生的机制并将其应用于损伤后细胞再生的调控是治愈脊髓损伤最具前景的方案。其中，系统精准的研究关键信号通路对少突胶质细胞发育的作用及其对损伤后髓鞘再生的调控尤为关键。为此，本课题全面深入的分析了胚胎期、成熟期以及脊髓损伤后Fgf信号通路对少突胶质细胞的发育全过程和再生进程的重要作用。本课题首先构建了Nestin::Cre;Fgfr2flox/flox;Fgfr3-/-复合突变小鼠模型，其可在脊髓发育的不同阶段实现Fgf信号通路的有效阻断。对该系小鼠自胚胎期至胎后成年不同发育阶段的脊髓组织进行研究发现，Fgf信号通路在脊髓少突胶质细胞发育的全过程，包括胚胎期少突胶质细胞的命运决定、迁移、分裂与分化以及胎后少突胶质细胞的成熟与髓鞘的形成，均扮演着特异且不可或缺的重要角色。为深入分析Fgf信号通路对脊髓祖细胞层腹、背部不同来源的少突胶质细胞发育的调控，本课题进一步培育了Nkx2.2CRM::Cre；Fgfr2flox/flox；Fgfr3-/-；RosAeyfp/eyfp荧光标记复合突变小鼠模型，其不仅可有效区分标记不同族群来源的少突胶质细胞，并可针对腹部来源的细胞族群实现Fgf信号通路的阻断。由此，本课题更深入精准的研究了不同族群来源少突胶质细胞发育进程的差异，以及Fgf信号在其中特异且关键的调控。在阐明Fgf信号通路对少突胶质细胞发育作用的基础之上，本课题对所构建的复合突变小鼠模型实施了“脊髓Lysophosphatidylcholine（LPC）诱发局灶性脱髓鞘手术”，并揭示了Fgf 信号通路在脊髓脱髓鞘损伤后对少突胶质细胞再生以及髓鞘修复进程所起到的重要作用。本课题不仅系统且深入的阐述了Fgf关键信号通路在少突胶质细胞发育全过程所扮演的关键角色，更探索性发现了其对脊髓损伤后髓鞘再生的调控作用。所收获的动物模型科研成果，对后继的少突胶质细胞的相关课题研究及脊髓损伤医疗的预临床方案积累了直接可靠的活体依据。