Studies of Mitochondrial Dysfunction in Models of Rett Syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder affecting primarily females that is predominantly caused by mutations in the MECP2 gene. RTT is characterized by a loss of previously acquired skills, ambulatory deficits, respiratory problems and overall retarded growth. Mitochondrial dysfunction and oxidative stress identified in MeCP2-deficient tissues raised the possibility that mitochondrial impairments may play role in the pathogenesis of RTT. To further investigate the role of mitochondrial dysfunction in the absence of MeCP2, I analyzed mitochondrial function and morphology in Mecp2-deficient mouse adult skin fibroblasts (ASF) and in Mecp2-null mouse ESC derived neurons using an array of fluorescent dyes coupled with flow cytometry and confocal microscopy. The heterogeneity of cellular responses in ASF prevented identification of consistent changes in mitochondrial function, making them an unsuitable model for studying mitochondrial dysfunctions. Mecp2-null mouse ESC were differentiated into enriched population of neurons. Mecp2-null neurons displayed hyperpolarized mitochondria, high levels of ROS, low ATP and impaired mitochondrial trafficking. Resveratrol and mitochondrial cocktail that target expression of mitochondrial genes and mitochondrial metabolism, but not simple ROS scavengers, were successful at ameliorating ROS levels and normalizing mitochondrial membrane potential. Since oxidative stress was reported in RTT mice, I tested whether resveratrol and mitochondrial cocktail could reverse or improve behavioral phenotype in RTT mice. Mitochondrial cocktail but not resveratrol improved exploratory, locomotor and social behavior deficits in RTT mice. Taken together these results suggest that both mitochondrial deficits and oxidative stress are not only the consequences of dysfunctional MeCP2, but are likely the causes of the RTT phenotype. Further, I determined that over-expression of mitochondrial Sirt3, known for its multifaceted effects on mitochondrial metabolism, is sufficient to protect neurons form various cytotoxic insults including oxidative stress. Overall, this study paves the way for potential new therapeutic strategies aimed at improving quality of life in RTT patients.Ph.D