Reduced synaptic activity in neuronal networks derived from embryonic stem cells of murine Rett syndrome model

Abstract

Neurodevelopmental diseases such as the Rett syndrome (RTT) have received renewed attention, since the mechanisms involved may underlie a broad range of neuropsychiatric disorders such as schizophrenia and autism. In vertebrates early stages in the functional development of neurons and neuronal networks are difficult to study. Embryonic stem cell-derived neurons provide an easily accessible tool to investigate neuronal differentiation and early network formation. We used in vitro cultures of neurons derived from murine embryonic stem cells missing the methyl-CpG-binding protein 2 (MECP2) gene (MeCP2-/y) and from wild type cells of the corresponding background. Cultures were assessed using whole-cell patch-clamp electrophysiology and immunofluorescence. We studied the functional maturation of developing neurons and the activity of the synaptic connections they formed. Neurons exhibited minor differences in the developmental patterns for their intrinsic parameters, such as resting membrane potential and excitability; with the MeCP2-/y cells showing a slightly accelerated development, with shorter action potential half-widths at early stages. There was no difference in the early phase of synapse development, but as the cultures matured, significant deficits became apparent, particularly for inhibitory synaptic activity. MeCP2-/y embryonic stem cell-derived neuronal cultures show clear developmental deficits that match phenotypes observed in slice preparations and thus provide a compelling tool to further investigate the mechanisms behind RTT pathophysiology.

Synaptopathology Involved in Autism Spectrum Disorder

“…MeCP2-deficient GABAergic neurons show reduced inhibitory quantal size, consistent with a presynaptic reduction of glutamic acid decarboxylase-1 (GAD-1) and GAD-2 levels (Chao et al, 2010). The expression levels of GABA transporter 1 (GAT1) and vesicular GABA transporter (vGAT) are significantly lower in the frontal cortex of Mecp2 KO mice, implying a dysfunctional GABA recycling system (Barth et al, 2014). Loss of MeCP2 also accelerates the NMDAR subunit switch from Glu2B to 2A at excitatory synapses onto cortical PV cells, indicating an acceleration of NMDAR development, but delays this switch in pyramidal cells, suggesting a developmental delay (Mierau et al, 2016).…”