Inhibitory Signaling to Ion Channels in Hippocampal Neurons Is Differentially Regulated by Alternative Macromolecular Complexes of RGS7

Abstract

The neuromodulatory effects of GABA on pyramidal neurons are mediated by GABA B receptors (GABA B Rs) that signal via a conserved G-protein-coupled pathway. Two prominent effectors regulated by GABA B Rs include G-protein inwardly rectifying K ϩ (GIRK) and P/Q/N type voltage-gated Ca 2ϩ (Ca V 2) ion channels that control excitability and synaptic output of these neurons, respectively. Regulator of G-protein signaling 7 (RGS7) has been shown to control GABA B effects, yet the specificity of its impacts on effector channels and underlying molecular mechanisms is poorly understood. In this study, we show that hippocampal RGS7 forms two distinct complexes with alternative subunit configuration bound to either membrane protein R7BP (RGS7 binding protein) or orphan receptor GPR158. Quantitative biochemical experiments show that both complexes account for targeting nearly the entire pool of RGS7 to the plasma membrane. We analyzed the effect of genetic elimination in mice of both sexes and overexpression of various components of RGS7 complex by patch-clamp electrophysiology in cultured neurons and brain slices. We report that RGS7 prominently regulates GABA B R signaling to Ca V 2, in addition to its known involvement in modulating GIRK. Strikingly, only complexes containing R7BP, but not GPR158, accelerated the kinetics of both GIRK and Ca V 2 modulation by GABA B Rs. In contrast, GPR158 overexpression exerted the opposite effect and inhibited RGS7-assisted temporal modulation of GIRK and Ca V 2 by GABA. Collectively, our data reveal mechanisms by which distinctly composed macromolecular complexes modulate the activity of key ion channels that mediate the inhibitory effects of GABA on hippocampal CA1 pyramidal neurons.

Gpr158 deficiency impacts hippocampal CA1 neuronal excitability, dendritic architecture, and affects spatial learning

“…Basal synaptic transmission onto CA1 pyramidal cells appears unaffected in Gpr158 KO hippocampus, with no notable changes in either spontaneous excitatory or inhibitory frequency and amplitude observed, in line with recent observations for evoked IPSCs (Ostrovskaya et al, 2018). This is in contrast the reductions observed in sEPSC frequency and amplitude in Gpr158 KO CA3 (Condomitti et al, 2018).…”

GPCR-dependent biasing of GIRK channel signaling dynamics by RGS6 in mouse sinoatrial nodal cells

“…The increase in A 1 R-GIRK channel signaling seen with Rgs6 ablation, however, suggests that this is not the main influence of RGS6 in SAN cells. Other work has called attention to the role of adaptor proteins, including R7BP and GPR158, in fine-tuning the influence of RGS proteins (21,(43)(44)(45). While R7BP or GPR158 expression has not been observed in the heart (46,47), an unknown adaptor protein(s) may influence the impact of RGS6/Gβ5 on GIRK-dependent signaling in cardiomyocytes.…”

Gpr158 Deficiency Impacts Hippocampal CA1 Neuronal Excitability, Dendritic Architecture, and Affects Spatial Learning

“…Given the significant hippocampal expression of Gpr158 (Allen brain atlas probe RP_051121_01_A10; Khrimian et al, 2017), not only in CA3 but also in the CA1 region (Ostrovskaya et al, 2018) (Supplementary Figure 1), we tested Gpr158 KO mice and WT littermates in an array of hippocampal-dependent behavioral paradigms (Supplementary Figure 2). First, we performed MWM training with male Bl6/J Gpr158 KO mice (Figures 1A,B and Supplementary Figure 2) and a probe test to assess long-term memory retainment of hidden platform location based on distal cues.…”

“…Given the considerable CA1 expression from post-weaning onward (Condomitti et al, 2018; Ostrovskaya et al, 2018), as well as the role of Gpr158 in neuronal signaling and cognition (Khrimian et al, 2017; Sutton et al, 2018), we investigated the effect of Gpr158 deficiency on both electrophysiological properties and neuronal architecture in the hippocampus CA1 with in vitro and ex vivo approaches. We took specific advantage of measuring hippocampus-dependent behavior and performing electrophysiological recordings with cellular reconstructions in the same set of animals, allowing us to create insightful correlations between the behavior and underlying neuronal architecture observed.…”