ErbB4 reduces synaptic GABA _A currents independent of its receptor tyrosine kinase activity

Abstract

ErbB4 signaling in the central nervous system is implicated in neuropsychiatric disorders and epilepsy. In cortical tissue, ErbB4 associates with excitatory synapses located on inhibitory interneurons. However, biochemical and histological data described herein demonstrate that the vast majority of ErbB4 is extrasynaptic and detergent-soluble. To explore the function of this receptor population, we used unbiased proteomics, in combination with electrophysiological, biochemical, and cell biological techniques, to identify a clinically relevant ErbB4-interacting protein, the GABA A receptor α1 subunit (GABAR α1). We show that ErbB4 and GABAR α1 are robustly coexpressed in hippocampal interneurons, and that ErbB4-null mice have diminished cortical GABAR α1 expression. Moreover, we characterize a Neuregulin-mediated ErbB4 signaling modality, independent of receptor tyrosine kinase activity, that couples ErbB4 to decreased postsynaptic GABAR currents on inhibitory interneurons. Consistent with an evolving understanding of GABAR trafficking, this pathway requires both clathrin-mediated endocytosis and protein kinase C to reduce GABAR inhibitory currents, surface GABAR α1 expression, and colocalization with the inhibitory postsynaptic protein gephyrin. Our results reveal a function of ErbB4, independent of its tyrosine kinase activity, that modulates postsynaptic inhibitory control of hippocampal interneurons and may provide a novel pharmacological target in the treatment of neuropsychiatric disorders and epilepsy.PKC | schizophrenia | hippocampus | parvalbumin | mIPSCs E rbB4 signaling regulates neuronal excitability (1, 2) and synaptic plasticity (3, 4) in the adult brain, and has been implicated in psychiatric disorders (5, 6) and epilepsy (2, 7). In the neocortex and hippocampus of rodents, monkeys, and humans, ErbB4 expression is restricted to GABAergic interneurons, and its expression is particularly high in parvalbumin-positive fastspiking (PV+) interneurons (8, 9). Of note, targeted ablation of ErbB4 specifically in PV+ interneurons recapitulates behavioral abnormalities of full ErbB4-null mice, highlighting the importance of ErbB4 signaling in this GABAergic interneuron subclass (10). Moreover, gamma oscillations, a type of high-frequency network activity that depends on synchronization of local circuits by PV+ interneurons, are augmented by Neuregulin (NRG)1 in vitro in an ErbB4-dependent manner (11).In the hippocampus, the GABA A receptor α1 subunit (GABAR α1), which imparts rapid decay kinetics (12), is also selectively expressed in subsets of inhibitory interneurons, especially in PV+ neurons (13,14). Furthermore, a mutation in GABRA1 has been linked to absence seizures (15), and heterozygous Gabra1-null mice show cortical absence epileptiform activity (16). Additionally, genome-wide linkage analyses have repeatedly identified a cluster of GABAR subunits, which includes GABRA1, as a schizophrenia (SCZ) susceptibility locus (17). Therefore, identifying mechanisms that acutely regulate α1-containing GABARs o...

A negative feedback loop controls NMDA receptor function in cortical interneurons via neuregulin 2/ErbB4 signalling

“…Our finding differs from previous reports that interpreted NRG/ErbB4 effects on NMDAR function or on morphology (i.e. dendritic spines) as occurring directly in pyramidal neurons (see 23, 41, 42 ), and is consistent with a growing consensus that ErbB4 is not expressed by hippocampal and neocortical pyramidal neurons 7, 8, 15, 16, 18, 43 . Moreover, morphological and functional studies in mice with targeted receptor ablation in distinct neuron subtypes indicate that changes in pyramidal neurons are mediated indirectly via ErbB4 in inhibitory interneurons 43 .…”

“…Metabolizing rat brain synaptosomes were treated for 10 min with 10 nM recombinant NRG2-ECD (hereafter referred to as NRG2), and ErbB4-interacting proteins were coimmunoprecipitated following Triton X-100-solubilization using the ErbB4 antibody mAB10 as described previously 16 . Coomassie-stained protein bands designated for mass spectrometry were selected based on Western blots run in parallel to reveal NRG2-augmented phosphotyrosine signals ( Fig.…”

Neuregulin-ERBB Signaling in the Nervous System and Neuropsychiatric Diseases

“…As for Type III, it is still unclear whether the proteolytic processing is essential for biological activity, or whether pro-Nrg1 can stimulate Schwann cells to some extent. Additional complexity of Nrg1 processing emerged with the finding that the metalloprotease TACE1 (‘tumor necrosis factor-alpha converting enzyme’/ADAM17) also digests membrane-bound Nrg1 (Montero et al, 2000), but closer to the EGF-like domain and presumably antagonizing the role of BACE1 as a myelination-promoting factor (La Marca et al, 2011). At least in the PNS, the β1 splice variant of Nrg1 (Falls, 2003) is by far the most abundant one.…”

Neurodevelopment, GABA System Dysfunction, and Schizophrenia

“…NRG1/ErbB4 signaling also appears to have distinct functions in development and maintenance of cortical circuitry. ErbB4 associates with GABA A a1 subunit-containing GABA receptors expressed on interneurons and NRG1/ErbB4 signaling reduces their surface expression (Mitchell et al, 2013), which likely contributes to increased excitability of interneurons by NRG1 and partially explains the mechanism behind increased GABA release and decreased pyramidal cell activity after NRG1 application (Wen et al, 2010). Fastspiking PV þ interneurons are necessary for the generation of gamma oscillations and it is possible that these pathways underlie deficient oscillatory activity in schizophrenia (Hou et al, 2013;Lewis et al, 2012;Uhlhaas and Singer, 2010).…”

“…Kim et al, 2012) and NRG1 regulates the expression and activity of GABA receptors and interneuron activity Mitchell et al, 2013;Wen et al, 2010). Therefore, any environmental exposure affecting GAD1, DISC1, or NRG1 might have opposite effects depending on the developmental time point of its introduction.…”