Glial mechanisms governing the removal and repair of degenerating myelin

项目总结 髓磷脂的进化是为了加快、微调和提高电信号传输的代谢效率 在大脑里。然而，在许多人类疾病中，髓鞘退化，最终导致毁灭性的 运动和认知障碍。重要的是，为了在髓鞘损伤后进行组织修复 发生时，构成髓鞘的多层致密细胞膜必须迅速和 被大脑中常驻的吞噬细胞有效地清除。这些碎片的清除是有缺陷的 与许多退行性疾病有关，包括但不限于多发性硬化症和衰老 我们对这些过程的细胞动力学和分子机制知之甚少。为了 研究这些关键的细胞事件，并回答围绕涉及哪些细胞群体和 这些不同的细胞类型扮演着什么角色，我们已经开发了先进的成像和操作技术 这些在活体动物中的离散事件发生在从几秒到几个月的广泛的时间尺度上。这些 技术包括基于荧光团的多色转基因标记的新组合的活体成像 不同的神经元和神经胶质细胞群，以及致密髓鞘特有的无标记成像方式。 除了这些强大的标记和光学成像策略外，我们还开发了一种新技术 对于单细胞死亡的定向诱导，我们最近建立了一个按需和 可滴定的小鼠皮质灰质脱髓鞘。结合使用这些技术，现在可以实现动态 靶向基因操作和动物研究中的脱髓鞘和重新髓鞘形成 人类疾病的模型。使用这些强大的工具，该项目将调查三个主要目标。首先，在那里 越来越多的证据表明，除了小胶质细胞，大脑的初级吞噬细胞，其他常驻的胶质细胞 星形胶质细胞和NG2胶质细胞也参与其中，并在吞噬和修复过程中发挥重要作用。 进程。我们将确定每种神经胶质细胞类型在动态检测和清除中的确切贡献 退化的髓鞘碎片。接下来，我们和其他人展示了磷脂酰丝氨酸受体的重要性 在有效检测和清除死亡神经元和不同器官中的其他细胞方面。我们将决定 吞噬细胞受体缺陷和碎片消化信号在动态过程中的作用和后果 NG2神经胶质细胞对皮质脱髓鞘的反应，以及由此导致的重新髓鞘形成和髓鞘模式。 最后，有证据表明，神经元活动和/或感觉体验可以改变髓鞘再生，但影响较小。 在脱髓鞘的背景下，已知神经元活动对吞噬细胞功能的作用。我们会 确定双向神经元活动改变对吞噬细胞对 单细胞脱髓鞘。最终，这些研究将揭示哪些细胞参与了髓鞘碎片的清除， 主要细胞碎片识别通路在成功清除和修复中的作用，以及神经元的活动 而感觉体验改变了吞噬细胞胶质细胞对脱髓鞘事件的反应。

PROJECT SUMMARY Myelin has evolved to speed up, finely tune, and increase the metabolic efficiency of electrical signal transmission in the brain. In numerous human diseases however, myelin degenerates, ultimately resulting in devastating motor and cognitive impairment. Importantly, in order for tissue repair to proceed after myelin damage has occurred, the many layers of compacted cell membrane that constitute the myelin sheath must be rapidly and efficiently removed by resident phagocytic cells in the brain. Defective removal of these debris has been implicated in a number of degenerative conditions, including but not limited to, multiple sclerosis and aging, yet we know little about the cellular dynamics and molecular mechanisms governing these processes. In order to study these critical cellular events and answer questions centered on which cell populations are involved and what roles these different cell types play, we have developed advanced techniques for imaging and manipulating these discrete events in the live animal over a wide range of temporal scales from seconds to months. These techniques include intravital imaging of new combinations of fluorophore-based multicolor transgenic labels of distinct populations of neurons and glia together with label-free imaging modalities specific for compact myelin. In addition to these powerful labeling and optical imaging strategies, we have also developed a new technique for targeted induction of single-cell death, which we have recently established as a model of on-demand and titratable demyelination in the mouse cortical gray matter. Combining these techniques now allows dynamic investigation of demyelination and remyelination in the context of targeted genetic manipulations and animal models of human disease. Using these powerful tools this project will investigate three central aims. First, there is increasing evidence that in addition to microglia, the primary phagocytes of the brain, other resident glial cell types, namely astrocytes and NG2 glia, are also involved and play important roles in the phagocytosis and repair process. We will determine the precise contribution of each glial cell type in the dynamic detection and clearance of degenerating myelin debris. Next, we and others have shown the importance of phosphatidylserine receptors in the efficient detection and clearance of dying neurons and other cells in different organs. We will determine the role and consequences of both defective phagocytic receptors and debris digestion signaling on the dynamic response by NG2 glia to cortical demyelination and the resulting remyelination success and myelin patterning. Finally, there is evidence that neuronal activity and/or sensory experience can modify remyelination, but less is known about the roles of neuronal activity on phagocytic function in the context of demyelination. We will determine the consequences of bidirectional neuronal activity changes on the response by phagocytic cells to single-cell demyelination. Ultimately, these studies will reveal which cells are involved in myelin debris clearance, the role of major cell debris recognition pathways in successful clearance and repair, and how neuronal activity and sensory experience modify the response of phagocytic glia to a demyelinating event.