How do synaptic connections change in demyelinating disease?

作者：Schafer，Dorothy P. 项目摘要 多发性硬化症(MS)是一种中枢神经系统(CNS)炎症性脱髓鞘疾病， 有一个深刻的，目前难以解决的神经退行性成分--一个巨大的，未得到满足的临床需求。在许多 神经退行性疾病，最早的退行性事件之一是突触功能障碍和丢失。的确有 MS中也有突触丢失，但其潜在的分子机制(S)仍然是一个悬而未决的问题。整体而言 这一提议的假设是补体依赖的信号转导是突触丢失的基础 脆弱神经元亚群中的脱髓鞘疾病。这很大程度上是基于我们在 显示经典补体级联蛋白C1q和C3的视网膜原生循环 定位于突触和吞噬小胶质细胞通过C3受体吞噬和消除突触， 补体受体3(CR3)。引人注目的是，我们有新的证据表明，视黄素生成的突触的一个子集 在MS和多种MS相关动物模型中，也被小胶质细胞吞噬，导致突触丢失 脱髓鞘疾病(如非人灵长类和小鼠实验性自身免疫性脑脊髓炎) 模特)。我们进一步证实，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多症和水平升高相一致 补体C1q和C3。然而，与发育不同的是，C3而不是C1q定位于突触。最后， 在小鼠EAE中特异性抑制视黄素原性突触的C3可防止小胶质突触被吞噬， 突触丢失和视觉功能障碍。这些实验确定C3和小胶质细胞是 MS相关脱髓鞘疾病中的突触丢失，并开辟了我们将探索的几个新问题：1) 在脱髓鞘疾病中，哪些细胞产生消除突触所必需的补体(目标1)？2) 小胶质细胞补体受体CR3调节脱髓鞘疾病的突触丢失(目标2)？3) 最容易受到补体介导的突触消除和后来的变性的影响(目标3)？致信地址 对于这些问题，我们将继续使用视网膜原化回路。这是一个非常容易驯服和强大的 研究突触变化的系统，它与MS高度相关，在MS中，视神经的炎症(即， 视神经炎)在50%以上的患者中发生，并导致长期的、往往是永久性的视觉功能障碍。 我们现在将结合细胞特有的分子遗传学和高分辨率的视黄醇原酸盐成像 小鼠EAE模型中突触的分子解剖炎性脱髓鞘疾病中突触丢失。 结果可能会发现旨在减缓或防止多发性硬化症神经变性的新靶点，这可能是 广泛适用于其他伴有突触丢失和神经炎症(阿尔茨海默氏症)的神经退行性疾病 疾病、额颞部痴呆等)。

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.).