Characterization of mTOR Pathway and Reduced Neuronal Size Phenotype in Rett Syndrome Model

Rett syndrome is a genetically based, X-linked neurodevelopmental disorder that affects 1 in 10,000 live female births. Approximately 95-97% of Rett syndrome cases are attributed to a mutation in the MECP2 gene. In the laboratory setting, key neuropathological phenotypes of Rett syndrome include small neuronal soma and nuclear size, increased cell packing density, and abnormal dendritic branching. Our lab previously created and characterized the A140V mouse model of atypical Rett syndrome in which the males are viable. Hippocampal and cerebellar granule neurons in A140V male mice have reduced soma and nuclear size compared to wild type. We also found that components of the mTOR pathway including rictor, 4E-BP-1, and mTOR, were reduced in A140V mutant mice. Quantitative PCR analysis also showed reduced IGFPB2 expression in A140V mice along with an upward trend in AKT levels that did not meet statistical significance. The objective of this study is i) to characterize the down regulation of AKT-mTOR pathway, and ii) to examine the effect of a genetic strategy to rescue mTOR pathway deficiencies in Mecp2 mutant mouse model. Genetic rescue of the mTOR pathway downregulation was done by crossing heterozygous female A140V mice with heterozygous male Tsc2 mice. Quantitative PCR analysis of A140V_Tsc2 RNA expression supported genetic rescue of mTOR pathway components, however, more testing is needed to fully characterize the rescue effect. Western blot analysis also showed reduction in phosphorylated AKT in Mecp2 A140V and T158A mutant mice, however, more testing is still needed to characterize the mTOR pathway in A140V_Tsc2 mice. Finally, other methods, such as a pharmacological approach, or transfection to increase mTOR pathway activity in cell lines, will be tested to determine if rescue of mTOR pathway activity ameliorate the Rett syndrome phenotype.