Glial chemosensitivity and control of breathing in Rett syndrome

 描述(申请人提供)：Rett综合征(RTT)是一种神经发育障碍，由编码甲基CpG结合蛋白2(MECP2)的基因功能丧失突变引起。RTT的症状包括智力残疾、自闭症行为和癫痫发作。此外，严重的呼吸功能障碍极大地导致了生活质量的下降，并与该人群的高死亡率有关。来自RTT小鼠模型的证据表明，RTT中的呼吸障碍可能是由于中枢化学感受器(对CO2/H+反应而调节呼吸的神经元)的破坏所致，但MeCP2依赖的呼吸控制的细胞和分子基础在很大程度上仍不清楚。MeCP2在神经系统中高度表达，最近的证据表明，星形胶质细胞中MeCP2的缺失与RTT的症状有关，包括呼吸紊乱。位于脑干区的星形胶质细胞被称为后梯形核(RTN)，通过抑制内向整流钾通道(Kir4.1)和释放ATP来刺激附近的化疗敏感神经元，通过感知CO2/H+来控制呼吸。初步数据显示，在MeCP2缺陷小鼠的多个脑区，Kir4.1的表达显著降低，这表明该通道的表达受到MeCP2的调控。因此，我们推测在RTN星形胶质细胞中，Kir4.1的表达需要MeCP2，而星形胶质细胞中MeCP2的缺失破坏了RTN化学感受器的功能，并导致RTT呼吸障碍。在这项建议中，我们使用已建立的RTT小鼠模型和新开发的可诱导的星形胶质细胞特异性Kir4.1基因敲除，结合分子、遗传学、切片电生理学和全动物体积描记来确定星形胶质细胞中的MeCP2和Kir4.1是否对呼吸控制是必要的。该项目的三个具体目标是：1)确定在RTN星形胶质细胞中是否需要MeCP2来表达Kir4.1；2)确定MeCP2的缺失是否影响对化疗敏感的RTN神经元的兴奋性；3)确定Kir4.1在RTN星形胶质细胞中控制呼吸的重要作用。通过了解星形胶质细胞中MeCP2和Kir4.1在体外和体内对RTN生理学的贡献，我们将深入了解RTT中呼吸障碍的细胞和分子基础，从而为治疗这种疾病威胁生命的症状创造新的途径。

 DESCRIPTION (provided by applicant): Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function mutations in the gene encoding methyl-CpG-binding protein 2 (MECP2). Symptoms of RTT include mental disability, autistic behavior, and seizures. In addition, severe respiratory dysfunction contributes significantly to poor quality of life and is associated with high mortality rate in this population. Evidence from RTT mouse models suggest that disordered breathing in RTT may result from disruption of central chemoreceptors (neurons that regulate breathing in response to CO2/H+), yet the cellular and molecular basis of MeCP2-dependent control of breathing remains largely unknown. MeCP2 is highly expressed throughout the nervous system and recent evidence shows that loss of MeCP2 from astrocytes contributes to symptoms of RTT including disordered breathing. Astrocytes in a brainstem region called the retrotrapezoid nucleus (RTN) are known to control breathing by sensing CO2/H+ by inhibition of inward rectifying K+ channels (Kir4.1) and releasing ATP to stimulate nearby chemosensitive neurons. Preliminary data presented here demonstrates Kir4.1 expression is significantly decreased in multiple brain regions in MeCP2 deficient mice, suggesting expression of this channel is regulated by MeCP2. Therefore, we hypothesize that MeCP2 is required for expression of Kir4.1 in RTN astrocytes and loss of MeCP2 from astrocytes disrupts RTN chemoreceptor function and contributes to disordered breathing in RTT. In this proposal, we use an established mouse model of RTT and the newly developed inducible astrocyte specific Kir4.1 knockouts in conjunction with molecular, genetics, slice electrophysiology, and whole-animal plethysmography to determine if MeCP2 and Kir4.1 in astrocytes are essential for control of breathing. The three Specific Aims of this project are: 1) determine whether MeCP2 is required for expression of Kir4.1 in RTN astrocytes; 2) determine if loss of MeCP2 affects excitability chemosensitive RTN neurons; 3) determine the essential roles of Kir4.1 in RTN astrocytes for control of breathing. By understanding contributions of MeCP2 and Kir4.1 in astrocytes to RTN physiology in vitro and in vivo, we will provide insight into the cellular and molecular basis of disordered breathing in RTT and in doing so create new avenues for treatment of life-threatening symptoms of this disease.