Extracellular Matrix Mediates Axonal Integrity Following Brain Trauma

描述（由申请人提供）：创伤性脑损伤（TBI）导致数百万美国人长期衰弱。该病理的一个一致特征是创伤性轴索损伤（TAI），弥漫性且具有挑战性。迄今为止，TAI的病因在大口径、有髓鞘的轴突中得到了最好的记录，这些轴突一贯表现为浆层、细胞骨架和线粒体！病理。从诊断成像可以清楚地看出，胼胝体和其他皮层下白质束易受TAI的影响。这些通路包括大的有髓鞘轴突和小的无髓鞘轴突，其中纤维类型系统地与感觉运动和联合皮层相关。鉴于脑外伤引起长期认知缺陷，以及对皮层下白质中的TAI知之甚少，我们最近发表的研究探讨了胼胝体轴突对弥漫性脑外伤的生理和形态学反应。这些结果表明TAI的进化速度快，无髓鞘纤维的易损性更大。与此同时，我们还发现胼胝体TAI上调了细胞外基质（ECM）蛋白及其调节金属蛋白酶（MMPs）。这些观察结果与这些蛋白质介导轴突生长、髓鞘形成和束状形成的事实是一致的。基于这些信息，我们建议探讨MMP/ECM通路在TAI退行性和恢复阶段的作用。我们将验证MMP/ECM蛋白影响脑外伤后白质TAI进展的假设，以及它们的激活是由纤维蛋白溶解蛋白调节的，纤维蛋白溶解蛋白通过血脑屏障的缺口渗透到神经细胞中。使用胼胝体TAI模型，我们将记录腱蛋白和磷脂的蛋白/mRNA表达，已知存在于白质中的ECM蛋白，以及已知在损伤后修饰ECM的MMPs 2、3和9。MMP活性的时间谱将与酶表达相关，并筛选这些蛋白的粘附分子结合伙伴。接下来，我们将类似地评估纤溶途径蛋白tPA和纤溶酶原对胼胝体TAI的反应。最后，我们将在药理学上操纵损伤后纤维蛋白溶解/MMP酶活性或轴突保护程度，并使用功能和形态学端点测试纤维蛋白溶解/MMP分子与轴突完整性之间的因果关系。这些研究将确定MMP/ECM蛋白在TAI中的作用，并提供新的治疗靶点。

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) results in long term debilitation for millions of Americans. A consistent feature of this pathology is traumatic axonal injury (TAI), diffuse in profile and challenging to study. To date, TAI etiology is best documented in large caliber, myelinated axons, which consistently exhibit plasmalemmal, cytoskeletal and mitochondria! pathology. From diagnostic imaging it is clear that the corpus callosum and other subcortical white matter tracts are vulnerable to TAI. These pathways contain both large myelinated and small unmyelinated axons, where fiber type is systematically associated with sensorimotor and associative cortices. Given that TBI induces long-term cognitive deficits, and that TAI in subcortical white matter is poorly understood, our recently published studies have explored the physiological and morphological response of corpus callosum axons to diffuse TBI. Those results show rapid evolution of TAI and greater vulnerability of unmyelinated fibers. In parallel, pilot studies we also find upregulation of extracellular matrix (ECM) proteins and their regulatory metalloproteinases (MMPs) with callosal TAI. Such observations are consistent with the fact that these proteins mediate axonal growth, myelination and fasciculation. Based upon this information, we propose to explore the role of MMP/ECM pathways during degenerative and recovery phases of TAI. We will test the hypothesis that MMP/ECM proteins influence the progression of white matter TAI following TBI and that their activation is regulated by fibrinolytic proteins which permeate the neuropil through breaches in the blood brain barrier. Using the callosal TAI model, we will document protein/mRNA expression of tenascin and phosphacan, ECM proteins known to be present in white matter, and MMPs 2, 3 and 9, known to modify ECM after injury. Temporal profile of MMP activity will be correlated with enzyme expression and screening for adhesion molecule binding partners of these proteins will be performed. Next, we will similarly assess the response of fibrinolytic pathway proteins tPA and plasminogen to callosal TAI. Finally, we will pharmacologically manipulate either fibrinolytic/MMP enzyme activity or degree of axonal protection after injury and test for cause/effect relationships between fibrinolytic/MMP molecules and axonal integrity using functional and morphological endpoints. These studies will establish the role of MMP/ECM proteins in TAI and provide new therapeutic targets forTBI.