Neonatal Stroke: the Role of Microglia

描述(申请人提供)：动脉缺血性中风在足月婴儿和老年人中发生的频率一样高，但不成熟影响缺血性损伤和恢复的机制。新生儿脑更易发生缺氧缺血、单纯缺血和兴奋性毒性损伤，并伴有广泛的神经细胞凋亡。与调控细胞凋亡的分子事件的广泛知识相比，人们对负责清除凋亡神经元和降解细胞碎片的过程知之甚少。巨噬细胞不能迅速清除凋亡的神经元，导致死亡的细胞发生凋亡后的坏死，导致损伤加剧。小胶质细胞可以通过清除濒临死亡的细胞来保护大脑，但也可以在正常的出生后大脑发育过程中造成损伤，甚至引发神经元凋亡。在幼年啮齿动物大脑中动脉(MCA)局灶性短暂性闭塞的动物模型中，小胶质细胞激活迅速，这些细胞产生大量有毒物种但吞噬能力较差的凋亡神经元。利用我们的体内模型和体外培养小胶质细胞与凋亡神经元的模型，我们将确定清道夫受体CD36在介导新生儿中风后凋亡神经元移除中的作用，并评估CD36介导的小胶质细胞识别、吞噬和吞噬凋亡神经元的信号机制。将使用药理学方法和CD36和caspase-3缺失的小鼠以及来自缺陷小鼠的细胞。我们将验证这一假设，即小胶质细胞通过对凋亡神经元的清除不足而加剧对新生儿大脑的急性缺血再灌注损伤。我们将确定去除小胶质细胞是否保护新生儿大脑免受中风(目标1)，如果新生儿中风后小胶质细胞对凋亡神经元的有限吞噬受到清道夫受体CD36的调节(目标2)，炎性细胞因子是否对依赖于caspase-3的死亡神经元的CD36介导的吞噬产生不利影响(目标3)，以及是否通过CD36移除凋亡神经元取决于caspase-3的激活(目标4)。与公共卫生相关：新生儿中风是一种存在的严重和频繁的疾病。了解新生儿脑损伤的机制是确定保护新生儿免受中风终身后果的治疗靶点的重要一步。

DESCRIPTION (provided by applicant): Arterial ischemic stroke occurs as frequently in term babies as in the elderly but immaturity affects mechanisms of ischemic injury and recovery. The neonatal brain is preferentially susceptible to hypoxic-ischemic, pure ischemic and excitotoxic injury with widespread neuronal apoptosis. Compared to the extensive knowledge of the molecular events regulating apoptosis, relatively little is known about the processes responsible for clearance of apoptotic neurons and degradation of cellular debris. Failure to rapidly remove apoptotic neurons by macrophages allows dying cells to undergo post-apoptotic necrosis and leads to injury exacerbation. Microglial cells can protect the brain by removing dying cells but can also contribute to injury or even provoke neuronal apoptosis during normal postnatal brain development. In an animal model of neonatal stroke, focal transient middle cerebral artery (MCA) occlusion in immature rodents, microglial activation is rapid, these cells produce a number of toxic species but poorly phagocytose apoptotic neurons. Using our in vivo model and in vitro models of primary microglial cells cultured with apoptotic neurons, we will determine the effects of the scavenger receptor CD36 in mediating removal of apoptotic neurons after neonatal stroke and evaluate signaling mechanisms involved in CD36-mediated recognition, engulfment and phagocytosis of apoptotic neurons by microglial cells. Pharmacological approaches and mice with deleted CD36 and caspase-3 and cells derived from deficient mice will be used. We will test the hypothesis that microglial cells exacerbate acute ischemia-reperfusion injury to the neonatal brain by insufficient clearance of apoptotic neurons. We will determine if ablation of microglia protects the neonatal brain from stroke (Aim 1), if limited phagocytosis of apoptotic neurons by microglial cells after neonatal stroke is modulated by the scavenger receptor CD36 (Aim 2), if inflammatory cytokines adversely affect CD36-medated phagocytosis of neurons dying in a caspase-3 dependent manner (Aim 3), and if removal of apoptotic neurons via CD36 depends on caspase-3 activation (Aim 4). RELEVANCE TO PUBLIC HEALTH: Neonatal stroke is an existing serious and frequent disorder. Understanding the mechanisms of brain injury in the neonatal brain is an important step in the identification of therapeutic targets that protect the newborn from the lifelong consequences of stroke.