Investigating mitochondrial dysfunction in human astrocytes with RTT-causing MECP2 mutations - Summary Mutations in the X-linked gene, methyl-CpG binding protein 2 (MECP2), underlie a wide range of neuropsychiatric disorders, most commonly Rett syndrome (RTT), a severe neurodevelopmental disorder. Despite numerous studies, why the loss of MeCP2 function results in RTT remains largely obscure, and it represents a major challenge from both basic biological and therapeutic standpoints. Our previous studies, based on mouse models, advanced the knowledge of the disease and the specific cell types involved in RTT neuropathology. We showed that mutant glia, specifically astrocytes, are an integral part of RTT and that healthy astrocytes can rescue many aspects of the disease. However, mouse models do not faithfully represent human RTT, which is known to be more severe than in mouse models. Importantly, human astrocytes are significantly different from mouse astrocytes in their structure, gene expression landscape, mitochondrial physiology, energy metabolism, and susceptibility to oxidative stress and hypoxia. For this reason, we have recently established human stem cell-based models for RTT to investigate the cellular and molecular features of human astrocytes bearing RTT-causing mutations in MECP2. Our studies revealed significant aberrations in mutant human astrocytes, including aberrant gene expression landscape, impaired structural complexity, and impaired metabolic homeostasis. Importantly, we showed significant aberrations in mitochondrial morphology and function in mutant astrocytes, suggesting that dysfunctional mitochondria likely lie at the heart of the impaired metabolic homeostasis in mutant astrocytes. Furthermore, our preliminary data show the presence of senescence markers in mutant astrocytes, suggesting that mitochondrial dysfunction likely leads to cellular senescence in mutant astrocytes. Thus, we propose to build on our recent findings and identify the common aberrations in gene expression in human astrocytes bearing different MECP2 mutations with a focus on genes involved in mitochondrial function (Aim 1), investigate whether mitochondrial dysfunction is a common and specific feature of mutant human astrocytes bearing different MECP2 mutations and whether mitochondrial dysfunction leads to a specific type of cellular senescence in all mutant astrocytes (Aim 2). Importantly, we will examine whether rescuing mitochondrial dysfunction and/or cellular senescence could ameliorate the structural and functional abnormalities we identified in mutant astrocytes and thereby their ability to properly support neurons (Aim 3). Understanding the molecular mechanisms that underlie mitochondrial dysfunction and its downstream effects on MECP2 mutant human astrocytes, and whether rescuing mitochondrial dysfunction and/or senescence could ameliorate the structural and functional aberrations of mutant astrocytes and consequently restore their support to neurons, is highly important for developing therapeutic strategies for RTT.
