Alterations of gene expression and glutamate clearance in astrocytes derived from an MeCP2-null mouse model of Rett syndrome

Rett syndrome (RTT) is a neurodevelopmetal disorder associated with mutations in the methyl-CpG-binding protein 2 (MeCP2) gene. MeCP2-deficient mice recapitulate the neurological degeneration observed in RTT patients. Recent studies indicated a role of not only neurons but also glial cells in neuronal dysfunction in RTT. We cultured astrocytes from MeCP2-null mouse brain and examined astroglial gene expression, growth rate, cytotoxic effects, and glutamate (Glu) clearance. Semi-quantitative RT-PCR analysis revealed that expression of astroglial marker genes, including GFAP and S100β, was significantly higher in MeCP2-null astrocytes than in control astrocytes. Loss of MeCP2 did not affect astroglial cell morphology, growth, or cytotoxic effects, but did alter Glu clearance in astrocytes. When high extracellular Glu was added to the astrocyte cultures and incubated, a time-dependent decrease of extracellular Glu concentration occurred due to Glu clearance by astrocytes. Although the shapes of the profiles of Glu concentration versus time for each strain of astrocytes were grossly similar, Glu concentration in the medium of MeCP2-null astrocytes were lower than those of control astrocytes at 12 and 18 h. In addition, MeCP2 deficiency impaired downregulation of excitatory amino acid transporter 1 and 2 (EAAT1/2) transcripts, but not induction of glutamine synthetase (GS) transcripts, upon high Glu exposure. In contrast, GS protein was significantly higher in MeCP2-null astrocytes than in control astrocytes. These findings suggest that MeCP2 affects astroglial genes expression in cultured astrocytes, and that abnormal Glu clearance in MeCP2-deficient astrocytes may influence the onset and progression of RTT.

Disturbance of cardiac gene expression and cardiomyocyte structure predisposes Mecp2-null mice to arrhythmias

Methyl-CpG-binding protein 2 (MeCP2) is an epigenetic regulator of gene expression that is essential for normal brain development. Mutations in MeCP2 lead to disrupted neuronal function and can cause Rett syndrome (RTT), a neurodevelopmental disorder. Previous studies reported cardiac dysfunction, including arrhythmias in both RTT patients and animal models of RTT. In addition, recent studies indicate that MeCP2 may be involved in cardiac development and dysfunction, but its role in the developing and adult heart remains unknown. In this study, we found that Mecp2-null ESCs could differentiate into cardiomyocytes, but the development and further differentiation of cardiovascular progenitors were significantly affected in MeCP2 deficiency. In addition, we revealed that loss of MeCP2 led to dysregulation of endogenous cardiac genes and myocardial structural alterations, although Mecp2-null mice did not exhibit obvious cardiac functional abnormalities. Furthermore, we detected methylation of the CpG islands in the Tbx5 locus, and showed that MeCP2 could target these sequences. Taken together, these results suggest that MeCP2 is an important regulator of the gene-expression program responsible for maintaining normal cardiac development and cardiomyocyte structure.

Neural development of methyl-CpG-binding protein 2 null embryonic stem cells: a system for studying Rett syndrome

Mutations in methyl-CpG-binding protein 2 (MeCP2) gene cause the neurodevelopmental disorder Rett syndrome (RTT). Here, we describe a new experimental system that efficiently elucidates the role of MeCP2 in neural development. MeCP2-null and control ES cells were generated by adenoviral conditional targeting and examined for maintenance of the undifferentiated ES cell state, neurogenesis, and gliogenesis during in vitro differentiation. In addition, dopamine release and electrophysiological features of neurons differentiated from these ES cells were examined. Loss of MeCP2 did not affect undifferentiated ES cell colony morphology and growth, or the timing or efficiency of neural stem cell differentiation into Nestin-, TuJ- or TH-positive neurons. In contrast, gliogenesis was drastically accelerated by MeCP2 deficiency. Dopamine production and release in response to a depolarizing stimulus in MeCP2-null ES-derived dopaminergic neurons was intact. However, MeCP2-null differentiated neurons showed significantly smaller voltage-dependent Na(+) currents and A-type K(+) currents, suggesting incomplete maturation. Thus, MeCP2 is not essential for maintenance of the undifferentiated ES cell state, neurogenesis, or dopaminergic function; rather, it is principally involved in inhibiting gliogenesis. Altered neuronal maturity may indirectly result from abnormal glial development and may underlie the pathogenesis of RTT. These data contribute to a better understanding of the developmental roles of MeCP2 and the pathogenesis of RTT.