Mechanisms of Fibrin Action in Neuronal Functions

描述（由申请人提供）：患有中枢神经系统病变的患者，包括多发性硬化症、中风、脊髓和创伤性损伤，通常表现为认知障碍，表明神经元功能障碍。尽管血管损伤和血脑屏障（BBB）破坏（导致血蛋白渗漏到脑实质）是认知病理的标志，但血脑屏障破坏和神经元功能障碍之间的分子联系仍然知之甚少。我们已经证明，纤维蛋白原（血液凝固的关键成分）在中枢神经系统中的沉积不仅是血脑屏障破坏的标志，而且通过激活神经系统细胞中表达的整合素受体，在中枢神经系统的炎症和修复调节中起着致病作用。我们的长期目标是表征纤维蛋白原在神经系统发病机制中的作用的分子途径，这是开发治疗方案的先决条件，可以专门针对纤维蛋白原与其受体之间的相互作用，并减轻神经病理疾病的过程。我们的主要假设是纤维蛋白原激活中枢神经系统先天免疫反应，诱导脊柱改变和神经系统病理认知缺陷。我们的初步数据表明：a)向齿状回立体定向注射纤维蛋白原可诱导小胶质细胞激活并损害记忆回忆；b)注射纤维蛋白原可诱导小鼠神经元丢失、树突回缩和树突脊柱密度降低（如体内双光子显微镜所示）；c) CD11b/CD18小胶质受体基因缺失可恢复纤维蛋白原诱导的脊柱消除和树突回缩。我们的具体目标是测试我们的工作模型，其中纤维蛋白原在血脑屏障破坏和脑血管异常后沉积在大脑中，激活先天免疫反应，导致脊柱消除和认知能力下降。我们采用了尖端的实验设计，包括在Thy1启动子下表达YFP的转基因小鼠中神经元的体内双光子成像，跟踪小胶质细胞和脊髓之间随时间的动态相互作用，以及先天免疫激活的药理学和遗传抑制，包括特异性抑制纤维蛋白原与CD11b的相互作用，不影响其在血液凝固中的有益功能。确定血脑屏障破坏后纤维蛋白原、先天免疫激活和神经毒性之间的分子相互作用，可能为以脑血管异常或血脑屏障通透性增加和认知障碍为特征的各种疾病的药物干预提供特定靶点。

DESCRIPTION (provided by applicant): Patients with central nervous system pathologies, including multiple sclerosis, stroke, spinal cord and traumatic injuries, often present with cognitive impairment, indicative of neuronal dysfunction. Although vascular damage and blood-brain barrier (BBB) disruption, which results in leakage of blood proteins into the brain parenchyma, are hallmarks of cognitive pathologies, the molecular links between BBB disruption and neuronal dysfunction remain poorly understtod. We have shown that CNS deposition of fibrinogen, a critical component of blood coagulation, is not merely a marker of BBB disruption, but plays a causative role in the regulation of inflammation and repair in the CNS by activating integrin receptors expressed in nervous system cells. Our long-term goal is to characterize the molecular pathways that are responsible for the effects of fibrinogen in nervous system pathogenesis, as a prerequisite for the development of therapeutic protocols that can specifically target the interactions between fibrinogen and its receptors and attenuate neuropathological disease processes. Our major hypothesis is that fibrinogen activates the CNS innate immune response to induce spine alterations and cognitive deficits in nervous system pathology. Our preliminary data demonstrate that a) stereotactic injection of fibrinogen into the dentate gyrus induces microglial activation and impairs memory recall, b) injection of fibrinogen induces neuronal loss, dendrite retraction and dendritic spine density reduction in mice as shown with in vivo two-photon microscopy, and c) genetic depletion of the CD11b/CD18 microglial receptor rescues fibrinogen-induced spine elimination and dendritic retraction. Our specific aims are designed to test our working model, in which fibrinogen, deposited in the brain following BBB disruption and cerebrovascular abnormalities, activates the innate immune response and causes spine elimination and cognitive decline. We employ a cutting edge experimental design that includes in vivo two-photon imaging of neurons in transgenic mice expressing YFP under Thy1 promoter, following the dynamic interactions between microglial and spines over time in the living mouse, and pharmacologic and genetic inhibition of innate immune activation, including specific inhibition of fibrinogen interactions with CD11b that do not affects its beneficial functions in blood coagulation. Identifying the molecular interplay between fibrinogen following BBB disruption, activation of innate immunity, and neurotoxicity could potentially provide specific targets for pharmacological intervention in a variety of diseases characterized by cerebrovascular abnormalities or increased BBB permeability and cognitive impairment.