Dysregulation of Protein Synthesis in Fragile X Syndrome and Other Developmental Disorders

人体研究按照06-M-0214， NCT00362843号协议进行。

The work on humans was conducted under the protocol 06-M-0214, NCT00362843. During the 2020 funding period, we addressed the following: 1) rCPS measured with the L-1-C-11leucine PET method in participants with FXS and healthy volunteers studied in the awake state, 2) protein synthesis rates in mouse models of other neurodevelopmental disorders, 3) mTORC1 activity as a central regulator of brain protein synthesis in some neurodevelopmental disorders, 4) sleep and neurodevelopmental disorders, 5) effects of treatment of Fmr1 KO mice with a phosphodiesterase D inhibitor on behavior and rCPS. 1) Measurement of rCPS in humans with fragile X syndrome. We used the L-1-C-11leucine PET method to measure rCPS. We have focused our efforts on trying to study individuals with fragile X syndrome without the use of sedatives. We used our modified PET protocol to enable some fragile X participants to undergo the study awake. Our preliminary results indicate that rates of cerebral protein synthesis in the awake fragile X participants are decreased compared to healthy controls. We have completed data collection and are analyzing results. 2) The genetic bases of several other neurodevelopmental disorders suggest that defects in translational control may be a core phenotype. For example, tuberous sclerosis complex (TSC) is caused by heterozygous mutations in either the TSC1 or TSC2 gene, both of which encode proteins that are negative regulators of mTOR activity. The mTOR pathway is one of the nodes regulating protein synthesis. Disruption of this control is thought to underlie some of the phenotypes observed in TSC. We have measured rCPS in a mouse model of TSC, TSC2+/-, and found that rCPS are decreased throughout the brain. We continue studies of rCPS in mouse models of other neurodevelopmental disorders such as Shank3 KO mice. We are also measuring rCPS in a conditional knockout mouse model of TSC2. These studies are ongoing in the laboratory. 3) It has been reported that the mTOR pathway is overactivated in Fmr1 KO mice. We are investigating the consequences of increased mTORC1 activation in Fmr1 KO mice. We treated Fmr1 KO mice chronically with an mTORC1 inhibitor, rapamycin, to determine if rapamycin treatment could reverse behavioral phenotypes. We found that pS6 was upregulated in Fmr1 KO mice and normalized by rapamycin treatment, but, except for an anxiogenic effect, rapamycin did not reverse any of the behavioral phenotypes examined. Moreover, rapamycin treatment had an adverse effect on sleep and social behavior in both control and Fmr1 KO mice. Studies of rCPS in rapamycin-treated Fmr1 KO mice are ongoing. We are measuring rCPS in vivo and determining behavioral phenotypes in these mice. 4) Sleep and neurodevelopmental disorders. Sleep abnormalities are one of the most prevalent concurrent disorders in patients diagnosed with neurodevelopmental syndromes. In these patients, the severity of behavioral abnormalities and the severity of sleep abnormalities are correlated. Given the importance of sleep in developmental plasticity, we continue studies on the role of sleep in neurodevelopmental disorders. We are collecting sleep data on numerous mouse models of neurodevelopmental disorders including Shank3 KO, Oxytocin receptor KO, and Tsc2+/- mice. Additionally, we are treating Fmr1 KO mice with hypnotics to determine the effects on sleep and other behavioral phenotypes. 5) Studies in humans, mice and Drosophila indicate that a deficit of FMRP in FXS influences cAMP levels. Our study investigated the possibility that targeting cAMP levels may have therapeutic value in FXS. We assessed the therapeutic and neurochemical effects of chronic administration of the phosphodiesterase-4D negative allosteric modulator, BPN14770, in Fmr1 KO mice. BPN14770 treatment had limited effects on the behavioral phenotype in Fmr1 KO mice. Some effects such as increased sleep duration and increased social behavior occurred in both genotypes. Effects on open field behavior were more striking in WT mice. BPN14770 treatment in WT mice tended to increase rCPS at the highest dose, but BPN14770 effects were less apparent in Fmr1 KO mice. Results suggest a genotype difference in the regulation of translation via a cAMP-dependent pathway.