How Does Actin Disassembly Drive Myelin Wrapping?

项目总结/摘要 髓磷脂--神经元轴突周围的电绝缘体--在脊椎动物中是快速神经信号传递所必需的， 而在多发性硬化症等疾病中以及随后的损伤中，它的缺失会导致患者严重残疾。在 在中枢神经系统中，少突胶质细胞首先通过延伸它们的膜突起来构建髓鞘， 包裹轴突，然后在轴突周围包裹纤维，同时压缩它们的膜， 电绝缘。在慢性多发性硬化症病变中，少突胶质细胞包裹轴突但不能包裹， 这表明包裹是髓鞘再生的限速步骤。为了最终理解为什么髓鞘再生 在多发性硬化症中失败，我们首先旨在了解髓鞘正常包裹的机制。这是 长期假设，肌动蛋白丝的组装提供了驱动包裹所需的力，就像 运动细胞的板状伪足或神经生长锥。然而，我们和其他人最近发现， 包裹需要少突胶质细胞肌动蛋白细胞骨架的剧烈分解。该结果 这是完全出乎意料的，并提出了两种包装模式。肌动蛋白分解和重组的循环 可能需要“棘轮”少突胶质细胞膜向前。根据我们初步的 数据，我们建议肌动蛋白拆卸作为一个“触发器”，启动肌动蛋白独立包装， 肌动蛋白分解的主要作用是使髓鞘致密化。为了测试这些模型，我们使用了一套 创新的方法，包括一流的遗传工具，我们创造了实验诱导肌动蛋白 在体内包裹过程中， 先进的显微镜技术，以解决髓鞘在体内，和活细胞成像的少突胶质细胞在文化。 我们的初步数据表明：（1）在少突胶质细胞中，肌动蛋白丝在缠绕之前会发生分解，（2） 在体内实验性地诱导特异性地在少突胶质细胞中的肌动蛋白分解增加了髓鞘包裹， 和（3）实验性阻断肌动蛋白分解会损害髓鞘膜的致密化， 髓鞘形成这些数据支持髓鞘包裹的“触发”模型，为将来的研究奠定了基础。 翻译研究，以测试这种基于肌动蛋白分解的机制是重演还是扰动 在髓鞘再生过程中。通过定义肌动蛋白分解在髓鞘包裹和压实中的作用， 将开辟新的研究方向，以了解髓鞘的形成，可塑性和疾病， 中枢神经系统

PROJECT SUMMARY/ABSTRACT Myelin—the electrical insulator around neuronal axons—is essential in vertebrates for rapid nerve signaling, and its loss in diseases like multiple sclerosis and following injury causes severe disability in patients. In the central nervous system, oligodendrocytes build myelin by first extending their membrane processes to ensheath axons, then wrapping spirally around the axon while compacting their membranes to become electrically insulating. In chronic multiple sclerosis lesions, oligodendrocytes ensheath axons but fail to wrap, suggesting that wrapping is a rate-limiting step for remyelination. To ultimately understand why remyelination fails in multiple sclerosis, we first aim to understand the mechanism by which myelin wraps normally. It was long hypothesized that the assembly of actin filaments provides the force required to drive wrapping, like the lamellipodium of a motile cell or a neuronal growth cone. However, we and others recently discovered that the dramatic disassembly of the oligodendrocyte actin cytoskeleton is required for wrapping. This finding was completely unexpected and suggests two models for wrapping. Cycles of actin disassembly and reassembly could be required to “ratchet” the oligodendrocyte membrane forward. In contrast, based on our preliminary data, we propose that actin disassembly acts as a “trigger” to initiate actin-independent wrapping and that the major role of actin disassembly is to allow myelin to compact. To test these models, we are using a suite of innovative approaches including first-in-class genetic tools we created to experimentally induce actin disassembly (DeActs) or block actin disassembly (StablActs) in oligodendrocytes during wrapping in vivo, advanced microscopy techniques to resolve myelin in vivo, and live cell imaging of oligodendrocytes in culture. Our preliminary data demonstrate: (1) actin filaments disassemble in oligodendrocytes prior to wrapping, (2) experimentally inducing actin disassembly specifically in oligodendrocytes in vivo increases myelin wrapping, and (3) experimentally blocking actin disassembly impairs myelin membrane compaction in a culture model of myelination. These data support the “trigger” model of myelin wrapping, laying the foundation for future translational studies to test whether this actin disassembly-based mechanism is recapitulated or perturbed during remyelination. By defining the role of actin disassembly in myelin wrapping and compaction, this project will open up new research directions towards understanding myelin formation, plasticity, and disease in the central nervous system.