Immunomodulation of white matter integrity after stroke

 描述(申请人提供)：白质(WM)损伤，以脱髓鞘和轴突完整性丧失为特征，是中风后长期感觉运动和认知障碍的重要原因。卒中后持续的促炎微环境被认为是阻碍少突胶质前体细胞(OPC)分化和成熟为髓鞘少突胶质细胞(OL)的潜在机制之一。越来越多的证据表明，不同功能表型的小胶质细胞/巨噬细胞在调节损伤的WM的炎症状态中起着重要作用，并最终影响WM的完整性。具体地说，“交替激活”的M2小胶质细胞对髓鞘再生和WM修复是必不可少的，因为它们可以解决局部炎症，清除破碎的髓鞘或细胞碎片，并提供促进OPC分化的营养因子。白介素4(IL-4)因此 迄今为止，它是小胶质细胞/巨噬细胞M2极化的最佳诱导因子；然而，它在西医和长期卒中预后中的小胶质细胞调节中的作用尚不清楚。我们发现IL-4是一种新型的抗WM损伤的内源性保护剂，并能促进WM的修复。我们的初步结果表明，IL-4基因敲除(KO)小鼠在tMCAO后14天表现出更严重的感觉运动障碍。值得注意的是，IL-4KO小鼠表现出加重的WM损伤。此外，IL-4 KO小鼠在tMCAO后表现出明显减少的M2小胶质细胞/巨噬细胞在WM丰富的脑区，包括胼胝体和纹状体。相反，IL-4从6小时后开始脑室内注射14天 MCAO可以减轻长期的感觉运动和认知缺陷，改善WM的完整性。除了促进M2极化外，我们还发现IL-4直接诱导分化 IL-4对OPC的这种作用是通过激活PPARγ介导的。在这项提案中，我们将重点关注IL-4在西医完整性中的新作用，并探讨其潜在的机制。我们将验证最重要的假设，即IL-4通过双重机制促进卒中后WM的完整性和长期神经功能恢复，因为它1)通过激活PPARγ促进OPC的分化/成熟，2)加强小胶质细胞/巨噬细胞向有益的M2表型的极化，这对脱髓鞘脑中的重新髓鞘形成和WM修复至关重要。测试的具体目标是：目的1：验证脑缺血后IL-4治疗增强WM完整性和卒中后长期神经功能恢复的假说。IL-4将在再灌流后通过反复鼻腔给药进入大脑。评估的终点包括神经结果和各种西医完整性的标记物。目的：验证IL-4诱导OPC分化为成熟的OPC并通过激活PPARγ促进轴突再髓鞘形成的假说。目的：验证IL-4促进小胶质细胞/巨噬细胞分化为消炎、促进组织修复的M2表型，并为有效的WM修复恢复“健康”微环境的假说。

 DESCRIPTION (provided by applicant): White matter (WM) injury, characterized by demyelination and loss of axonal integrity, is an important cause of long-term sensorimotor and cognitive deficits after stroke. A persistent pro-inflammatory microenvironment after stroke is considered one underlying mechanism that hinders oligodendrocyte precursor cell (OPCs) differentiation and maturation into myelinating oligodendrocytes (OLs). Accumulating recent evidence suggests that the different functional phenotypes of microglia/macrophages contribute considerably to the regulation of inflammatory status of injured WM and ultimately impact the WM integrity. Specifically, "alternatively activated" M2 microglia are essential for remyelination and WM repair because they resolve local inflammation, clear broken myelin sheath or cellular debris, and provide trophic factors that promote OPC differentiation. Interleukin-4 (IL-4) is thus far the best characterized inducer for M2 polarization of microglia/macrophages; however, its role in microglia regulation in WM and long term stroke outcomes is not known. We have discovered that IL-4 is a novel endogenous protectant against WM injury and that it promotes WM repair. Our preliminary results show that IL-4 knockout (KO) mice exhibit worse sensorimotor deficits over 14 days after tMCAO. Remarkably, IL-4 KO mice display deteriorated WM injury. Moreover, IL-4 KO mice show markedly reduced numbers of M2 microglia/macrophages in WM-enriched brain regions, including the corpus callosum and striatum after tMCAO. In contrast, intraventricular infusion of IL-4 for 14 days beginning 6h after MCAO attenuates long-term sensorimotor and cognitive deficits and improves WM integrity. In addition to promoting M2 polarization, we have found that IL-4 directly induces the differentiation of primary OPCs into mature OLs at nanomolar concentrations and that this effect of IL-4 on OPCs is mediated through the activation of PPARγ. In this proposal, we will focus on the novel action of IL-4 on WM integrity and explore the underlying mechanisms. We will test the overarching hypothesis that IL-4 promotes WM integrity and long-term neurological recovery after stroke by dual mechanisms, in that it 1) promotes OPC differentiation/maturation via PPARγ activation and 2) potentiates microglia/macrophage polarization toward the beneficial M2 phenotype, which is essential for remyelination and WM repair in demyelinating brains. The Specific Aims to be tested are: Aim 1: Test the hypothesis that post-ischemia IL-4 treatment enhances WM integrity and long-term neurological recovery after stroke. IL-4 will be delivered into the brain by repeated intranasal administrations after reperfusion. The endpoints for assessment include neurological outcomes and various markers for WM integrity. Aim 2: Test the hypothesis that IL-4 induces OPC differentiation into mature OLs and promotes axonal remyelination via PPARγ activation. Aim 3: Test the hypothesis that IL-4 potentiates microglia/macrophage polarization into the inflammation-resolving, tissue repair-enhancing M2 phenotype and restores a "healthy" microenvironment for efficient WM repair.