An Essential Role for the Tetraspanin LHFPL4 in the Cell-Type-Specific Targeting and Clustering of Synaptic GABAA Receptors

Elizabeth C Davenport,Valentina Pendolino,Georgina Kontou,Thomas P Mcgee,David F Sheehan,Guillermo López-Doménech,Mark Farrant,Josef T Kittler

doi:10.1016/j.celrep.2017.09.025

Abstract

SummaryInhibitory synaptic transmission requires the targeting and stabilization of GABAA receptors (GABAARs) at synapses. The mechanisms responsible remain poorly understood, and roles for transmembrane accessory proteins have not been established. Using molecular, imaging, and electrophysiological approaches, we identify the tetraspanin LHFPL4 as a critical regulator of postsynaptic GABAAR clustering in hippocampal pyramidal neurons. LHFPL4 interacts tightly with GABAAR subunits and is selectively enriched at inhibitory synapses. In LHFPL4 knockout mice, there is a dramatic cell-type-specific reduction in GABAAR and gephyrin clusters and an accumulation of large intracellular gephyrin aggregates in vivo. While GABAARs are still trafficked to the neuronal surface in pyramidal neurons, they are no longer localized at synapses, resulting in a profound loss of fast inhibitory postsynaptic currents. Hippocampal interneuron currents remain unaffected. Our results establish LHFPL4 as a synapse-specific tetraspanin essential for inhibitory synapse function and provide fresh insights into the molecular make-up of inhibitory synapses.

Highlights

Synaptic inhibition mediated by GABAA receptors (GABAARs) regulates the balance of excitation and inhibition in the brain and, plays a critical role in information processing
LHFPL4 Is Targeted to Inhibitory Synapses and Interacts with GABAARs recent mass spectrometry studies have identified a number of candidate GABAAR-interacting proteins (Heller et al, 2012; Nakamura et al, 2016), the biochemical validation and functional role of the majority of these putative partners remain undetermined
To determine whether LHFPL4 was present at synaptic sites, we examined the subcellular localization of LHFPL4GFP in cultured rat hippocampal neurons

Summary

Introduction

Synaptic inhibition mediated by GABAA receptors (GABAARs) regulates the balance of excitation and inhibition in the brain and, plays a critical role in information processing. Changing the number of postsynaptic GABAARs can rapidly control the strength of inhibitory synapses This is achieved by the trafficking of receptors to, and their removal from, the plasma membrane and by their surface lateral diffusion into and out of synaptically stabilized clusters (Bannai et al, 2009; Luscher et al, 2011b; Muir et al, 2010; Twelvetrees et al, 2010). In the absence of gephyrin, subsets of inhibitory synapses remain (Essrich et al, 1998; Kneussel et al, 1999; O’Sullivan et al, 2009), and genetic deletion of gephyrin in the CNS has an unexpectedly subtle effect on inhibitory synaptic transmission (Levi et al, 2004) These observations suggest the existence of as-yet-unidentified molecules important for stabilizing GABAARs at synapses

Results

Discussion

Conclusion