Metabotropic Glutamate Receptor Regulation in MeCP2-Related Disorders

描述（由申请人提供）：Rett综合征是一种毁灭性的神经系统疾病，其特征是自闭症、语言技能丧失、刻板行为、运动迟缓、认知缺陷、癫痫发作和呼吸异常。大多数病例是由于MeCP2蛋白的突变或缺失造成的，MeCP2是一种结合DNA甲基化CpG区域的转录因子。在小鼠中敲除MeCP2重现了许多Rett表型，而在成年小鼠神经元中重新表达MeCP2纠正了表型缺陷，这表明在疾病发展后给予的治疗可能是可行的。然而，患有MeCP2重复综合征的儿童也表现出明显的ret样症状，这表明精确水平的MeCP2对于维持正常的神经元功能至关重要。我们发现代谢性谷氨酸受体7 （GRM7/mGlu7）是一种调节谷氨酸和GABA释放的受体，在体外和体内MeCP2敲除小鼠模型中都受到MeCP2的正调控。重要的是，我们发现Mecp2 KO小鼠的多个脑区mGlu7 mRNA和蛋白水平显著降低。这些结果表明GRM7基因可能是MeCP2的真实和新的靶点。如果正确，我们预测mGlu7水平将在MeCP2过表达的小鼠中升高，这代表了MeCP2重复综合征的模型。由于mGlu7激活的一个功能是减少突触前末端的谷氨酸释放，我们假设Mecp2 KO小鼠中mGlu7水平的异常降低可以增强谷氨酸能张力。在Mecp2 KO、敲入和过表达小鼠中，Schaffer侧侧ca1 （SC-CA1）突触的突触传递和长时程增强被改变。有趣的是，每种情况下的损伤似乎都部分由突触前机制介导，缺乏Mecp2的小鼠表现出配对脉冲促进减少，这与突触前末端谷氨酸释放增加一致。相反，过表达Mecp2的小鼠显示成对脉冲比增加，提示谷氨酸释放减少。由于mGlu7是成年动物SC-CA1突触中主要存在的mGlu，这些神经传递缺陷，加上我们在Mecp2 KO小鼠中mGlu7水平降低的发现，与突触前mGlu7作为SC-CA1突触谷氨酸释放的主要控制器的作用一致，可能导致这些动物的认知缺陷。我们已经证实了先前的结果，表明Mecp2-/y小鼠的突触可塑性和长时程增强发生了改变，重要的是，mGlu7活性的增强可以挽救这些缺陷。我们提出在MeCP2复制小鼠模型中验证mGlu7水平相反增加的假设，进一步证实MeCP2在mGlu7基因调控中的作用。此外，我们将验证使用药理学工具调节mGlu7活性将使MeCP2蛋白过表达和过表达小鼠的突触可塑性和行为缺陷正常化的假设。

DESCRIPTION (provided by applicant): Rett syndrome is a devastating neurological disorder characterized by autism, language skill loss, stereotyped behaviors, motor delays, cognitive deficits, seizures, and breathing abnormalities. Most cases result from mutations in or loss of the protein MeCP2, a transcription factor that binds to methylated CpG regions of DNA. Knockout of MeCP2 in mice recapitulates many Rett phenotypes and re-expression of MeCP2 in adult mouse neurons corrects phenotypic deficits, suggesting that treatments given after disease development may be therapeutically viable. However, children with MeCP2 Duplication syndrome also exhibit significant Rett-like symptoms, indicating that a precise level of MeCP2 is critical for maintaining normal neuronal function. We have found that the gene encoding metabotropic glutamate receptor 7 (GRM7/mGlu7), a receptor which modulates glutamate and GABA release, is positively regulated by MeCP2 both in vitro and in an in vivo Mecp2 knockout mouse model. Importantly, we have found that mGlu7 mRNA and protein levels are significantly decreased in multiple brain areas in Mecp2 KO mice. These results suggest that the GRM7 gene appears to be true and novel target of MeCP2. If correct, we predict that mGlu7 levels will be elevated in mice overexpressing MeCP2, which represent a model for MeCP2 Duplication syndrome. As one function of mGlu7 activation is to decrease glutamate release from presynaptic terminals, we hypothesized that aberrantly decreased levels of mGlu7 in Mecp2 KO mice enhances glutamatergic tone. It has been demonstrated in Mecp2 KO, knock-in, and overexpressing mice that synaptic transmission, as well as long term potentiation, at Schaffer Collateral-CA1 (SC-CA1) synapses is altered. Interestingly, the impairment in each case appears to be mediated, in part, by a presynaptic mechanism, with mice lacking Mecp2 exhibiting reduced paired pulse facilitation, an observation consistent with increased glutamate release from presynaptic terminals. In contrast, mice overexpressing Mecp2 show increases in paired pulse ratios, suggestive of decreased glutamate release. As mGlu7 is the predominant mGlu present at the SC-CA1 synapse in adult animals, these defects in neurotransmission, coupled with our findings that mGlu7 levels are reduced in Mecp2 KO mice, are consistent with a role for presynaptic mGlu7 as a major controller of glutamate release at SC-CA1 synapses, potentially resulting in cognitive deficits seen in these animals. We have confirmed previous results showing that synaptic plasticity and long term potentiation are altered in Mecp2-/y mice and show, importantly, that potentiation of mGlu7 activity can rescue these defects. We propose to test the hypotheses that mGlu7 levels are conversely increased in an MeCP2 Duplication mouse model, further substantiating a role for MeCP2 in mGlu7 gene regulation. Additionally, we will test the hypotheses that modulation of mGlu7 activity using pharmacological tools will normalize synaptic plasticity and behavioral deficits in mice under- and overexpressing the MeCP2 protein.