Neuroinflammation and developmental vulnerability to manganese toxicity

描述(申请人提供)：发育中的中枢神经系统的神经毒性损伤与人类的神经疾病有关，但可能导致这种情况的机制仍然知之甚少。暴露于高水平的必需元素锰(Mn)会引起一系列神经化学和神经病理变化，最终导致皮质下和皮质结构中不可逆转的神经元损伤。儿童似乎比成年人更容易受到锰的影响，最近的流行病学证据表明，饮用水中的高锰与儿童的认知和行为障碍有关，但年轻人明显更敏感的基础尚不清楚。神经胶质细胞的持续性炎症变化可能是生命早期接触锰与神经毒性损伤和衰老过程中神经功能障碍易感性增加之间的潜在联系，因为神经炎症现在被认为是锰中毒和其他神经功能障碍进展的中心特征。这一假设的中心假设是，发育期间的锰暴露刺激了小胶质细胞和星形胶质细胞之间依赖于核因子-kB的细胞间信号转导，导致持续的神经炎症，从而增加了衰老过程中神经功能障碍的易感性。这一假说将通过三个特定的目标来检验：胶质细胞特异性的NF-kB激活在促进发育和衰老过程中锰诱导的神经毒性中的作用(特定目标1)，星形胶质细胞和小胶质细胞之间放大炎症激活和神经元损伤所必需的关键细胞与细胞之间的相互作用(特定目标2)，以及星形胶质细胞中介导依赖于NF-kB的神经炎性基因的诱导的转录调控机制(特定目标3)。我们将在我们实验室培育的NF-kB-EGFP报告小鼠和星形胶质细胞特异性NF-kB基因敲除小鼠中使用两次击打模型，从断奶前到青春期将动物暴露于锰，然后检测它们对多巴胺能神经毒剂1-甲基-4-苯基-1，2，3，6-四氢吡啶(MPTP)的敏感性。我们除了确定星形胶质细胞和小胶质细胞中核因子-kB激活的时间模式与神经炎症的发生相关，以及星形胶质细胞特有的核因子-kB活性功能丧失将减轻锰的神经毒性效应，无论是在发育中的小鼠还是在衰老过程中。我们还预计，在幼年发育期间暴露于锰将导致衰老过程中更严重的神经功能障碍，这是由于持续的神经炎症增加了神经元功能障碍，相对于没有事先暴露于锰的小鼠。总而言之，提出的具体目标将建立在我们实验室之前的工作基础上，以解决关于星形胶质细胞和小胶质细胞之间关键细胞相互作用的关键机制问题，这些细胞相互作用加强了发育过程中暴露于锰导致的神经元功能障碍。

DESCRIPTION (provided by applicant): Neurotoxic injury to the developing CNS is linked to neurological disease in humans but mechanisms that may predispose to such conditions remain very poorly understood. Exposure to elevated levels of the essential element manganese (Mn) causes a spectrum of neurochemical and neuropathologic changes that can culminate in irreversible neuronal injury in subcortical and cortical structures. Children appear to be more vulnerable to Mn than adults and recent epidemiological evidence links high Mn in drinking water to cognitive and behavioral impairment in children but the basis for the apparent greater sensitivity of young individuals is not clear. Persistent inflammatory changes in glial cells may b a potential link between exposure to Mn early in life and heightened susceptibility to neurotoxic injury and neurological dysfunction during aging because neuroinflammation is now recognized as a central feature in the progression of manganism and other neurological disorders of the basal ganglia. It is the central hypothesis of this proposal that Mn exposure during development stimulates NF-kB-dependent intercellular signaling between microglia and astrocytes, resulting in ongoing neuroinflammation that enhances susceptibility to neurological dysfunction during aging. This hypothesis will be tested by three Specific Aims that will examine: the role of glial- specific NF-kB activation in promoting Mn-induced neurotoxicity during development and aging (Specific Aim 1), critical cell-cell interactions between astrocytes and microglia necessary for amplifying inflammatory activation and neuronal injury (Specific Aim 2), and transcriptional regulatory mechanisms in astrocytes mediating NF-kB-dependent induction of neuroinflammatory genes (Specific Aim 3). We will use a two-hit model in NF-kB-EGFP reporter mice and astrocyte-specific NF-kB knockout mice generated in our laboratory that expose animals to Mn from pre-weaning through puberty and then examine their susceptibility to the dopaminergic neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We except to identify temporal patterns of NF-kB activation in astrocytes and microglia that correlate with onset of neuroinflammation and that astrocyte-specific loss of function of NF-kB activity will mitigate the neurotoxic effects of Mn, both in developing mice and during aging. We also expect that exposure to Mn during juvenile development will lead to greater neurological dysfunction during aging due to persistent neuroinflammation that increases neuronal dysfunction, relative to mice without prior exposure to Mn. Collectively, the proposed Specific Aims will build upon previous work from our laboratory to address key mechanistic questions regarding critical cellular interactions between astrocytes and microglia that potentiate neuronal dysfunction caused by developmental exposure to Mn.