Extracellular Matrix Mediates Axonal Integrity Following Brain Injury

描述(由申请者提供)：创伤性脑损伤(TBI)是美国一个重要的健康问题，每年有超过170万新病例。大脑回路的丧失是患者持续认知缺陷的基础，轴突损伤是主要原因。本研究以损伤的胼胝体(CC)为模型，发现损伤后基质金属蛋白酶(MMPs)的变化与不同的有髓和无髓纤维病理改变有关。MMPs是脑细胞外基质(ECM)的重要调节剂，影响轴突的完整性。我们发现CC明胶酶MMP2和MMP9在损伤后不同的时间段活性最高，以反应性胶质反应为标志。我们还观察到，这种基质金属蛋白酶活性与无髓鞘轴突病理有时间上的相关性。用神经保护化合物FK-506和米诺环素处理后，这种明胶酶活性选择性地、时间依赖性地降低，CC复合动作电位(CAPS)的缺陷减少。初步的基因芯片研究显示，骨桥蛋白(OPN)是一种分泌到ECM并与基质金属蛋白酶功能相互关联的细胞因子，在受损的CC中显著上调。根据这些数据，我们假设明胶酶对创伤性轴突损伤的反应是通过反应性胶质细胞内OPN的急性激活来介导的。我们还假设无髓纤维和有髓纤维在这一途径中的时间进程和神经胶质的作用是不同的。为了验证这些假说，我们将在颅脑损伤的液体打击模型中探索下列目标：1)记录OPN/MMP2，9在富含无髓(On，嗅神经)和有髓纤维(IC，内囊)的纤维环境中的轴突损伤过程，并确定OPN KO和MMP9KO是否改变这些变化；2)使用原代CC和胶质细胞培养来研究OPN/MMP2，9)体外细胞特异性相互作用；3)测试OPNKO或MMPKO是否改变轴索神经保护药物FK-506和米诺环素的疗效，然后确定OPN/MMP9与OPN/MMP9联合使用是否会改变FPTBI大鼠模型的功能或结构结局。这些研究可能为脑外伤后轴突损伤患者的局部和纤维靶向治疗确定新的选择。

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is a significant U.S. health concern, with over 1.7 million new cases each year. Loss of brain circuitry underlies persistent cognitive deficits suffered by its victims, with axonal damage as a major contributor. Using the injured corpus callosum (CC) as a model, we have shown that postinjury change in matrix metalloproteinases (MMPs) is correlated with distinct myelinated and unmyelinated fiber pathology. MMPs are critical modulators of brain extracellular matrix (ECM) which affect axonal integrity. We found that CC gelatinases MMP2 and 9 peak in activity at different postinjury intervals which are marked by reactive glial response. We also observed that this MMP activity was temporally correlated with unmyelinated axon pathology. Treatment with neuroprotective compounds FK-506 and minocycline resulted in selective, time- dependent reduction of this gelatinase activity and reduced deficits in CC compound action potentials(CAPs). Pilot microarray studies revealed that osteopontin (OPN), a cytokine secreted into the ECM and reciprocally linked to MMP function, was significantly upregulated in injured CC. From these data we hypothesize that gelatinase response to traumatic axonal injury is mediated through acute activation of OPN within reactive glia. We also posit that the time course and glial role in this pathway will differ between unmyelinated and myelinated fibers. To test these hypotheses, the following aims will be explored in the fluid percussion model of TBI : 1) to document OPN/MMP2,9 during axonal injury within fiber environments enriched in unmyelinated (ON, olfactory nerve) and myelinated fibers (IC, internal capsule), and determine if OPN KO and MMP9KO alters these changes, 2) to dissect cell specific OPN/MMP2,9 interaction in vitro using primary CC and ON glial cultures, and 3) to test whether OPNKO or MMPKO alters efficacy of axonal neuroprotective drugs FK-506 and minocycline, then determine if combining optimal drug and OPN/MMP9 manipulation alters functional or structural outcome in the rat model of FPTBI. These studies are likely to identify novel options for regional and fiber targeted therapy in patients suffering from axonal damage after TBI.