CD200/CD200R信号转导通路和小胶质细胞激活对急性缺血性脑卒中病理的调节研究

Stroke is currently the number one cause of death and disability in China; however to date we still lack protective agents for this devastating disease. New effective therapeutic strategies are urgently needed. There is considerable evidence that inflammation plays a major role in outcomes from clinical and experimental stroke. Inflammatory processes have a fundamental role in the pathophysiology of acute ischemic stroke. A key initial event is the rapid activation of resident immune cells, primarily the microglia. This cell population is an important target for new therapeutic approaches to limit stroke damage. Activation of microglia is normally held in check by strictly controlled mechanisms involving neuronal-glial communication. Uncontrolled microglial activation can injure healthy neurons as well as decrease the survival of injured neurons. CD200 is an important, but understudied regulator of microglial activation. CD200 is expressed on a variety of cell types, including endothelia and neurons. Neuronal CD200 induces an inhibitory signal by interacting with CD200 receptors (CD200Rs) on microglia reducing injury-induced inflammation. Disruption of CD200/CD200R signaling aggravates injury in models of neuroinflammation but this signaling pathway has not been well investigated in stroke. Aging is associated with an increase in the number and activation state of microglia. Recent work demonstrates that the molecular response to stroke differs in the aging brain. Aged animals have an altered inflammatory and cytokine response after stroke compared to young cohorts. Behavioral outcomes were significantly worse in aged animals, and mortality was significantly higher; both of which were independent of infarct size. We hypothesize that acute ischemic stroke decreases the normal inhibitory constraints of neuronal CD200 on microglia and that this is further exacerbated in the aged brain. We will utilize a well-established experimental model of stroke, middle cerebral artery occlusion (MCAO), to determine if CD200 signaling is activated after an ischemic insult and manipulate this signaling pathway to determine the effects on stroke-induced inflammatory responses and stroke outcomes. The main goal of this proposal is to determine if CD200 signaling is altered in experimental models of stroke, the time-course of this activation, and if it differs in the aged brain. As stroke is now exerting an increasing burden on our economy and public health, new treatments targeting microglial regulation should be explored.

炎性反应对急性缺血性脑卒中的病理发展起重要作用，启动该反应的关键是小胶质细胞的迅速激活。因此小胶质细胞是治疗卒中、减轻病损的一个重要的新靶标。神经元表达的CD200与小胶质细胞上的CD200受体（CD200R）相互作用，可抑制小胶质细胞激活，并减轻脑损伤后的炎性反应。破坏CD200/CD200R信号转导通路会加重神经性炎症，但是此信号通路在卒中病理中研究很少。年龄老化伴有小胶质细胞的激活数量增多。我们设想卒中刺激将减弱CD200对小胶质细胞的激活抑制而加剧炎性反应，且这种效应在老年脑组织中更加显著。我们将采用大脑中动脉阻断（MCAO）模型来研究CD200/CD200R信号转导通路在卒中后的活动规律；本项目的主要目标是确定该通路在急性脑卒中后是否改变、激活的时程规律，以及这些变化在老年脑组织中有何异同，并确定干预CD200/CD200R信号传导对卒中诱导的炎性反应和卒中结果的效应。

炎性反应对急性缺血性脑卒中的病理发展起重要作用，启动该反应的关键是小胶质细胞 (MG) 的迅速激活。因此小胶质细胞是治疗卒中、减轻病损的一个重要的新靶标。神经元表达的CD200与小胶质细胞上的CD200受体（CD200R）相互作用，可抑制小胶质细胞激活，并减轻脑损伤后的炎性反应。破坏CD200/CD200R信号转导通路会加重神经性炎症，但是此信号通路在卒中病理中研究很少。随着年龄的增长，大脑内小胶质细胞数量增多且易于激活。因此老年大脑即使没有缺血性损伤也呈现出较高的细胞因子基线水平。我们的科研假设是小胶质细胞激活是加重脑卒中损伤的关键因素，并呈现年龄差异；对小胶质细胞激活通路的调控可改变卒中结果。我们采用大脑中动脉阻断（MCAO）模型来研究CD200/CD200R信号转导通路在年轻、老年小鼠卒中后的活动规律。实验数据表明随着年龄老化，小胶质细胞的激活数量增多，尤其在脑缺血早期激活为主，而且以M1表型激活占优势，从而促进炎症反应的发生；而M2表型激活处于劣势，保护缺血组织损伤能力减弱，说明老年卒中症状重，预后差。CD200在脑缺血后表达逐步降低，而CD200R1在脑缺血早期表达逐步升高。同时，M1表型炎性标志因子早期表达较高；但是随着CD200R1表达升高，M2型炎症因子表达也升高。经CD200Fc干预后，CD200R1表达明显升高，M2型炎症因子表达增强。故在卒中早期，卒中刺激将减弱CD200对小胶质细胞的激活抑制而加剧炎性反应，且这种效应在老年脑组织中更加显著。