Mitochondrial dysfunction in Fragile X: Mechanisms and treatments

摘要：脆性X综合征(FXS)是导致智力残疾和自闭症的最常见原因，由 FMR1基因功能缺失。果蝇和小鼠的FXS模型已经开发出来，这些模型基于 Fmr1、dfmr1和Fmr1同源基因的功能突变丢失。将显示这些模型 与脆性X患者症状相似的几种表型。在之前的研究中，我们和其他人 脆性X动物模型中cAMP水平降低和胰岛素/PI3K信号增强是缺陷 大脑。我们在果蝇FXS模型上的工作证明了通过治疗恢复cAMP缺陷 使用PDE4抑制剂，恢复行为和记忆。我们还证明了遗传和药理学 恢复正常胰岛素信号水平的操作可以挽救行为和记忆缺陷。我们的发现 对于这两种途径，在小鼠FXS模型中都复制了缺陷。此外，我们发现二甲双胍 对FXS果蝇模型的治疗也恢复了记忆和行为，这一发现也得到了复制 在小鼠FXS模型中。总而言之，我们的研究确定了三种看似不同的方法，例如 提高cAMP水平，减少胰岛素信号转导和二甲双胍治疗可以恢复行为和 FXS动物模型所显示的认知表型。重要的是，其中两项发现正在进行中 在临床上并产生了令人振奋的结果。一种新型的PDE4抑制剂BPN14770已经在 脆性X成人第二阶段临床试验。这项研究的结果表明，用这种化合物治疗 可以显著改善18至45岁的脆性X成年人的认知和生活技能。此外，还有几个案例研究 据报道，使用二甲双胍治疗的脆性X患者在认知和社交领域有所改善。这些 这些发现导致了二甲双胍的临床试验的启动。考虑到我们发现的临床相关性，一个 我们将在这项研究中解决的重要问题是，这三种看似不同的方法如何作用于 恢复FXS动物模型的行为和认知。我们的初步研究表明，它们汇聚在 改善线粒体功能。在最近的研究中，我们发现了线粒体的严重缺陷，表现为 果蝇FXS模型和FXS患者来源的细胞。我们还确定了线粒体主控 在果蝇模型和FXS患者来源的细胞中，调节因子PGC-1a显著减少。重要的是 我们已经确定，二甲双胍治疗可以改善线粒体缺陷和PGC-1a，并且 胰岛素信号的遗传减少。我们还证明，独立增加PGC-1a 表达可改善线粒体功能和一种行为表型。在我们提议的研究中，我们将执行 实验验证修复信号通路的缺陷，以及二甲双胍的治疗 增加果蝇FXS模型和患者来源PGC-1a的表达和线粒体功能 细胞。这些研究将有助于扩大我们对如何最有效地治疗脆性X综合征和 可能是由于类似的病理生理缺陷导致的其他神经发育障碍。

Abstract: Fragile X Syndrome (FXS), the most common cause of intellectual disability and autism, is caused by the loss of FMR1 gene function. Drosophila and mouse models of FXS have been developed that are based on loss of function mutations of their respective homologues of FMR1, dfmr1 and Fmr1. These models display several phenotypes that bear similarity to Fragile X patient symptoms. In previous studies, we and others have identified reduced cAMP levels and increased insulin/PI3K signaling as defects in the Fragile X animal model brains. Our work on a Drosophila FXS model demonstrated that restoration of the cAMP deficit, by treatment with PDE4 inhibitors, restores behavior and memory. We have also shown that genetic and pharmacological manipulations that restore normal insulin signaling levels rescue behavioral and memory deficits. Our findings for both pathway defects have been reproduced in the mouse FXS model. Further, we discovered that metformin treatment of the FXS Drosophila model also restores memory and behavior, a finding that too has been replicated in the mouse FXS model. In sum our studies have determined that three seemingly distinct approaches, e.g. increasing cAMP levels, decreasing insulin signaling and metformin treatment can restore behavioral and cognitive phenotypes displayed by the FXS animal models. Importantly two of these findings are being pursued clinically and have given rise to promising results. A novel PDE4 inhibitor, BPN14770, has been tested in a phase II clinical trial with Fragile X adults. The results of this study have shown that treatment with this compound can significantly improve cognitive and life skills in Fragile X adult aged 18 to 45. Also, several case studies of Fragile X patients treated with metformin have reported improvements in cognitive and social domains. These findings have led to the initiation of clinical trials with metformin. Given the clinical relevance of our findings, an important question that we will address in this study is how these three seemingly different approaches act to restore behavior and cognition in a FXS animal model. Our preliminary studies indicate that they converge on improving mitochondrial function. In recent studies we have identified robust mitochondrial deficits displayed by the Drosophila FXS model and FXS patient derived cells. We have also determined that the mitochondrial master regulator PGC-1a is significantly decreased in the Drosophila model and in FXS patient derived cells. Importantly we have determined that the mitochondrial defects and PGC-1a are improved by metformin treatment and the genetic reduction of insulin signaling. We have also demonstrated that independently increasing PGC-1a expression improves mitochondrial function and a behavioral phenotype. In our proposed studies we will perform experiments to verify that the restoration of the signaling pathway defects, as well as metformin treatment increase both PGC-1a expression and mitochondrial function in the Drosophila FXS model and patient derived cells. These studies will help expand our understanding of how to treat Fragile X syndrome most effectively and possibly other neurodevelopmental disorders due to similar pathophysiological defects.