Genetic and functional analyses demonstrate a role for abnormal glycinergic signaling in autism

Abstract

Autism spectrum disorder (ASD) is a common neurodevelopmental condition characterized by marked genetic heterogeneity. Recent studies of rare structural and sequence variants have identified hundreds of loci involved in ASD, but our knowledge of the overall genetic architecture and the underlying pathophysiological mechanisms remains incomplete. Glycine receptors (GlyRs) are ligand-gated chloride channels that mediate inhibitory neurotransmission in the adult nervous system but exert an excitatory action in immature neurons. GlyRs containing the α2 subunit are highly expressed in the embryonic brain, where they promote cortical interneuron migration and the generation of excitatory projection neurons. We previously identified a rare microdeletion of the X-linked gene GLRA2, encoding the GlyR α2 subunit, in a boy with autism. The microdeletion removes the terminal exons of the gene (GLRA2(Δex8-9)). Here, we sequenced 400 males with ASD and identified one de novo missense mutation, p.R153Q, absent from controls. In vitro functional analysis demonstrated that the GLRA2(Δex8)(-)(9) protein failed to localize to the cell membrane, while the R153Q mutation impaired surface expression and markedly reduced sensitivity to glycine. Very recently, an additional de novo missense mutation (p.N136S) was reported in a boy with ASD, and we show that this mutation also reduced cell-surface expression and glycine sensitivity. Targeted glra2 knockdown in zebrafish induced severe axon-branching defects, rescued by injection of wild type but not GLRA2(Δex8-9) or R153Q transcripts, providing further evidence for their loss-of-function effect. Glra2 knockout mice exhibited deficits in object recognition memory and impaired long-term potentiation in the prefrontal cortex. Taken together, these results implicate GLRA2 in non-syndromic ASD, unveil a novel role for GLRA2 in synaptic plasticity and learning and memory, and link altered glycinergic signaling to social and cognitive impairments.

α2‐glycine receptors modulate adult hippocampal neurogenesis and spatial memory

“…During the training phase, the performance of glr2 −/y and control mice were found to be similar, indicating equivalent spatial learning between genotypes. This result is consistent with a previous report (Pilorge et al, ). However, in the probe test, while littermate control animals spent more time in the target quadrant vs nontarget quadrants, glra2 −/y mice spent similar amounts of time in the target and nontarget quadrants.…”

“…Moreover, the distance that glra2 −/y mice traveled in the target quadrant was decreased. These results appear to disagree with those of the recent study of Pilorge and colleagues, which found intact performance of glra2 −/y mice in the probe trial, although these authors did report short‐ and long‐term memory impairment in these animals (Pilorge et al, ). This may be explained by differences in the age of the mice used in these studies, since the results obtained in this behavioral test are known to be affected by age (Chouinard et al, ; Geinisman et al, ).…”

Effects of prenatal alcohol exposure (PAE): insights into FASD using mouse models of PAE

“…Whole brain tissue qPCR studies revealed a down-regulation of Glra1 and Grin2c , involved in the glycine receptor complex and glutamate NMDA receptor complexes, respectively (Kleiber et al 2011). Interestingly, GRIN and GLRA gene family subunits are down-regulated in individuals with schizophrenia and autism, respectively (Marín 2012; Pilorge et al 2016). These findings provide further evidence for a possible link between PAE and neurodevelopmental/psychiatric disorders.…”

RNA Editing—Systemic Relevance and Clue to Disease Mechanisms?

“…Like GABA type A receptors the neurotransmitter receptors for glycine (GlyRs) belong to the ligand-gated ion channel gene superfamily and are glycine-gated chloride channels which were involved in TLE, inflammatory pain sensitization, autism spectrum disorder and glioblastoma (Harvey et al, 2004; Eichler et al, 2008; Förstera et al, 2014; Pilorge et al, 2016). GlyRs are C-to-U RNA edited although the mooring sequence recognized by ACF is not very well conserved (Meier et al, 2005).…”