How do synaptic connections change in demyelinating disease?

作者：Dorothy P. 项目摘要 多发性硬化（MS）是中枢神经系统（CNS）的炎性脱髓鞘疾病， 有一个深刻的，目前棘手的，神经退行性成分-一个大的，未满足的临床需求。在许多 在神经退行性疾病中，最早的退行性事件之一是突触功能障碍和丧失。有 MS中的突触丢失，但潜在的分子机制仍然是一个悬而未决的问题。整体 该建议的假设是补体依赖性信号传导是突触丢失的基础， 脆弱神经元亚群的脱髓鞘疾病。这在很大程度上是基于我们在 发展视网膜神经回路，证明经典补体级联蛋白C1 q和C3 定位于突触，吞噬性小胶质细胞通过C3受体吞噬和消除突触， 补体受体3（CR 3）。引人注目的是，我们有新的证据表明，视网膜神经突触的一个子集是 在MS和多种MS相关动物模型中， 脱髓鞘疾病（例如非人灵长类动物和小鼠实验性自身免疫性脑脊髓炎（EAE）） 模型）。我们进一步确定，这种突触丢失可以发生在脱髓鞘、轴突变性， 或细胞死亡，但与外周免疫细胞浸润，反应性小胶质细胞增生和水平增加一致， 补体C1 q和C3。然而，与发育不同的是，C3而不是C1 q定位于突触。最后， 在小鼠EAE中特异性抑制视网膜小神经突触处的C3防止小胶质细胞突触吞噬， 突触丧失和视觉功能障碍这些实验确立了C3和小胶质细胞作为细胞增殖的关键调节因子。 MS相关脱髓鞘疾病中的突触丢失，并提出了我们将探讨的几个新问题：1） 脱髓鞘疾病中哪些细胞产生突触消除所必需的补体？2)并 小胶质细胞补体受体CR 3调节脱髓鞘疾病中的突触丢失（Aim 2）？3)哪些RGC 是最容易受到补体介导的突触消除和后来的退化（目标3）？解决 这些问题，我们将继续使用视网膜神经回路。这是一个非常容易处理和强大的 它是用于研究突触变化的系统，并且与MS高度相关，其中视神经的炎症（即， 视神经炎）发生在超过50%的患者中，并导致长期的、通常是永久性的视觉功能障碍。 我们现在将结合细胞特异性分子遗传学和视网膜小神经节的高分辨率成像技术， 突触在小鼠EAE模型的分子解剖突触损失的炎性脱髓鞘疾病。 研究结果可以发现旨在减缓或预防MS神经退行性变的新靶点， 广泛适用于具有突触丧失和神经炎症其它神经变性疾病（阿尔茨海默氏病 疾病、额颞叶痴呆等）。

Schafer, Dorothy P. Project Summary Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS), which has a profound, currently intractable, neurodegenerative component--a large, unmet clinical need. In many neurodegenerative diseases, one of the earliest degenerative events is synapse dysfunction and loss. There is also synapse loss in MS, but the underlying molecular mechanism(s) remains an open question. The overall hypothesis of this proposal is that complement-dependent signaling underlies synapse loss in demyelinating disease in a subset of vulnerable neurons. This is largely based on our initial findings in the developing retinogeniculate circuit demonstrating that classical complement cascade proteins C1q and C3 localize to synapses and that phagocytic microglia engulf and eliminate synapses via the C3 receptor, complement receptor 3 (CR3). Strikingly, we have new evidence that a subset of retinogeniculate synapses are also engulfed by microglia, leading to synapse loss, in MS and in multiple MS-relevant animal models of demyelinating disease (e.g. non-human primate and mouse experimental autoimmune encephalomyelitis (EAE) models). We further identified that this synapse loss can occur early prior to demyelination, axon degeneration, or cell death, but is coincident with peripheral immune cell infiltration, reactive microgliosis, and increased levels of complement C1q and C3. However, unlike development, C3, but not C1q, is localized to synapses. Finally, inhibiting C3 specifically at retinogeniculate synapses in mouse EAE prevents microglial synapse engulfment, synapse loss, and visual dysfunction. These experiments establish C3 and microglia as key regulators of synapse loss in MS-relevant demyelinating disease and open up several new questions that we will explore: 1) What cells produce complement necessary for synapse elimination in demyelinating disease (Aim 1)? 2) Does microglial complement receptor CR3 regulate synapse loss in demyelinating disease (Aim 2)? 3) Which RGCs are most vulnerable to complement-mediated synapse elimination and later degeneration (Aim 3)? To address these questions, we will continue to use the retinogeniculate circuit. This is a highly tractable and powerful system for studying synaptic changes and it is highly relevant to MS, where inflammation of the optic nerve (i.e. optic neuritis) occurs in upwards of 50% of patients and results in prolonged, often permanent, visual dysfunction. We will now use a combination of cell-specific molecular genetics and high-resolution imaging of retinogeniculate synapses in the mouse EAE model to molecularly dissect synapse loss in inflammatory demyelinating disease. Results could uncover novel targets aimed at slowing or preventing neurodegeneration in MS, which could be broadly applicable to other neurodegenerative disease with synapse loss and neuroinflammation (Alzheimer’s disease, frontotemporal dementia, etc.).