Mechanism of manganese-induced impairment of astrocytic glutamate transporters

 描述(申请人提供)：帕金森病(PD)是一种神经退行性疾病，只有10%-20%的病例可归因于遗传学。流行病学证据表明，帕金森病在农村地区更为常见，其患病率的增加与使用杀虫剂、除草剂和包括锰(Mn)在内的重金属有关。长期暴露于高水平的锰可引起锰中毒，它与帕金森病有许多共同的特点，但锰引起神经毒性的机制尚未完全确定。锰降低谷氨酸转运体GLT-1的表达，GLT-1调节突触谷氨酸水平，防止兴奋性毒性神经元损伤。我们的初步研究表明，转录因子阴阳1(YY1)在锰对GLT-1的影响中起着关键作用。因此，阐明锰诱导GLT-1表达失调的确切机制对于促进我们对锰神经毒性的理解是至关重要的。此外，确定锰诱导的GLT-1功能障碍的分子靶点将具有广泛的适用性，因为大量的神经退行性疾病，如帕金森病、阿尔茨海默病和肌萎缩侧索硬化症与继发于GLT-1功能障碍的谷氨酸平衡紊乱有关。因此，我们的长期目标是了解与兴奋性毒性神经变性相关的GLT-1表达调节机制。我们的近期目标是确定YY1如何调节锰诱导的GLT-1的抑制。在这里，我们提供了初步的数据，描述了YY1在锰诱导的GLT-1抑制中所扮演的未知角色。此外，表观遗传修饰剂组蛋白脱乙酰酶(HDACs)是YY1的共同抑制因子，而组蛋白脱乙酰酶抑制剂(HDACi)可逆转锰诱导的κ-1启动子活性的抑制。鉴于这些观察，我们假设，锰通过依赖于NF-κB的YY1激活而诱导GLT-1抑制，而HDAC作为辅助抑制物，介导了锰诱导的神经毒性。我们的工作首次在转录水平上探讨了锰通过YY1对GLT-1表达的影响。我们的假设将在以下特定目标进行检验：1)利用星形胶质细胞特异的YY1条件基因敲除小鼠，确定星形胶质细胞YY1是否通过损害GLT-1的表达和功能来介导锰诱导的神经毒性；2)利用原代星形胶质细胞来描述锰诱导YY1激活的分子机制及其在体外调节GLT-1功能中的作用；以及3)测试是否通过HDAC表观遗传修饰来调节锰增强的Y1表达和随后的GLT-1抑制。我们的研究将对YY1通路在锰诱导的GLT-1功能抑制和锰诱导的神经毒性中的作用机制(S)提供新的见解。此外，这项研究的结果将为与GLT-1功能受损和兴奋性毒性相关的神经退行性疾病提供新的治疗策略。

 DESCRIPTION (provided by applicant): Parkinson's disease (PD) is a neurodegenerative disease which can be ascribed in only 10-20% of cases to genetics. Epidemiological evidence suggests that PD is more common in rural areas, where its increased prevalence is associated with the use of pesticides, herbicides and heavy metals, including manganese (Mn). Chronic exposure to high Mn levels causes manganism, which has multiple shared features with PD, but the mechanisms by which Mn induces neurotoxicity have yet to be fully established. Mn decreases expression of glutamate transporter GLT-1, which regulates synaptic glutamate levels and prevents excitotoxic neuronal injury. Our preliminary studies indicate that the transcription factor yin yang 1 (YY1) plays a critical role in the effect of Mn on GLT-1. Accordingly, delineating the precise mechanism of Mn-induced dysregulation of GLT-1 expression is critical in advancing our understanding of Mn neurotoxicity. Moreover, identifying molecular targets of Mn-induced GLT-1 dysfunction will have broad applicability, since a plethora of neurodegenerative diseases, such as PD, Alzheimer's disease and amyotrophic lateral sclerosis are associated with perturbed glutamate homeostasis secondary to GLT-1 dysfunction. Thus, our long-term goal is to understand the mechanisms involved in the regulation of GLT-1 expression in relation to the excitotoxic neurodegeneration. Our immediate objective is to determine how YY1 regulates Mn-induced repression of GLT-1. Here, we present preliminary data characterizing a previously unknown role of YY1 in Mn-induced repression of GLT-1. Among our findings, we determined that Mn increases YY1 expression via NF-κB. In addition, epigenetic modifier histone deacetylases (HDACs) serve as co-repressors of YY1, and HDAC inhibitors (HDACi) reverse Mn-induced repression of GLT-1 promoter activity. Given these observations, we hypothesize that Mn-induced GLT-1 repression by NF-κB-dependent YY1 activation, with HDACs acting as co-repressors, mediates Mn-induced neurotoxicity. Our proposed work is the first in the field to explore the effect of Mn on GLT-1 expression via YY1 at the transcriptional level. Our hypothesis will be tested in the following specific aims: 1) Determine if astrocytic YY1 mediates Mn-induced neurotoxicity by impairing GLT-1 expression and function using astrocyte-specific YY1 conditional knockout mice, 2) Delineate the molecular mechanisms of Mn-induced activation of YY1 and its role in regulating GLT-1 function in vitro using primary astrocytes, and 3) Test if Mn- enhanced YY1 expression and the ensuing GLT-1 repression are regulated by HDAC epigenetic modification. Our studies will provide novel insights into the mechanism(s) underlying the role of the YY1 pathway in Mn-induced repression of GLT-1 function and Mn-induced neurotoxicity. Moreover, the outcome of this study will offer novel therapeutic strategies for neurodegenerative diseases associated with impairment in GLT-1 function and excitotoxicity.