Altered GABAA receptor subunit expression and pharmacology in human Angelman syndrome cortex

Abstract

The neurodevelopmental disorder Angelman syndrome is most frequently caused by deletion of the maternally-derived chromosome 15q11-q13 region, which includes not only the causative UBE3A gene, but also the β3-α5-γ3 GABAA receptor subunit gene cluster. GABAergic dysfunction has been hypothesized to contribute to the occurrence of epilepsy and cognitive and behavioral impairments in this condition. In the present study, analysis of GABAA receptor subunit expression and pharmacology was performed in cerebral cortex from four subjects with Angelman syndrome and compared to that from control tissue. The membrane fraction of frozen postmortem neocortical tissue was isolated and subjected to quantitative Western blot analysis. The ratios of β3/β2 and α5/α1 subunit protein expression in Angelman syndrome cortex were significantly decreased when compared with controls. An additional membrane fraction was injected into Xenopus oocytes, resulting in incorporation of the brain membrane vesicles with their associated receptors into the oocyte cellular membrane. Two-electrode voltage clamp analysis of GABAA receptor currents was then performed. Studies of GABAA receptor pharmacology in Angelman syndrome cortex revealed increased current enhancement by the α1-selective benzodiazepine site agonist zolpidem and by the barbiturate phenobarbital, while sensitivity to current inhibition by zinc was decreased. GABAA receptor affinity and modulation by neurosteroids were unchanged. This shift in GABAA receptor subunit expression and pharmacology in Angelman syndrome is consistent with impaired extrasynaptic but intact to augmented synaptic cortical GABAergic inhibition, which could contribute to the epileptic, behavioral, and cognitive phenotypes of the disorder.

Impairment of cortical GABAergic synaptic transmission in an environmental rat model of autism

“…The reduced sensitivity of VPA animals to zolpidem, which enhances GABAergic currents by preferentially binding to intra-synaptic GABA A R α subunits, suggested that VPA inhibitory synapses might have a different subunit composition compared to controls, in agreement also with the different kinetics of mIPSCs. A different sensitivity to zolpidem of GABA A R-mediated currents was also found in oocytes injected with GABA A Rs from Angelman patients (Roden et al 2010). The low sensitivity of VPA inhibitory synapses to zolpidem could be due to the insertion in the membrane of GABA A Rs from extra-synaptic or even intra-cellular origin.…”

“…ASD is often accompanied by hyperexcitable states, including aggression (Parikh et al 2008), anxiety (Spiker et al 2012), hyperactivity (Antshel et al 2011), epilepsy (Tuchman et al 2010; Tuchman and Cuccaro, 2011), as well as a plethora of sleep disorders (Goldman et al 2009; Souders et al 2009; Thatcher et al 2009; Glickman, 2010). The reliable presence of cell–cell communication abnormalities in such heterogeneous group of conditions, as in fragile X (Selby et al 2007; Bassell and Warren, 2008), Rett (Calfa et al 2011) and Angelman syndromes (Roden et al 2010) and the tuberous sclerosis complex (Curatolo et al 2008) suggests that impaired synaptic function is an important factor in the aetiology and general mechanisms of ASDs. Together, these data led to the hypothesis that an increase in the ratio between synaptic excitation and inhibition during a critical period might determine a dysfunctional development of the neural circuits causing the core symptoms of ASD (Rubenstein and Merzenich, 2003; Gogolla et al 2009).…”

Decreased Tonic Inhibition in Cerebellar Granule Cells Causes Motor Dysfunction in a Mouse Model of Angelman Syndrome

“…Although the number of GABA A benzodiazepine-binding receptors did not decrease (50), the relative expression of b3 and a5 was reduced in Angelman syndrome patients lacking these genes (51). Because b3 is a major component of extrasynaptic GABA A receptors (15) and a5 is primarily expressed extrasynaptically in the hippocampus (52), tonic inhibition may be lower in these Angelman syndrome patients in conjunction with Ube3a deficiency.…”

Loss of functional GABA A receptors in the Alzheimer diseased brain

“…The microtransplantation method is very convenient for pharmacological and biophysical experiments of human native receptors. However, previous reports mention a large variability in the amplitude of responses among microtransplanted oocytes (10,11,19). Therefore, we determined the response distribution of single brains (SI Results and Fig.…”