AUTHOR=Sui Yusheng , Mortensen Martin , Yuan Banghao , Nicholson Martin W. , Smart Trevor G. , Jovanovic Jasmina N. 

TITLE=GABAA receptors and neuroligin 2 synergize to promote synaptic adhesion and inhibitory synaptogenesis

JOURNAL=Frontiers in Cellular Neuroscience

VOLUME=18

YEAR=2024

URL=https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2024.1423471

DOI=10.3389/fncel.2024.1423471

ISSN=1662-5102

ABSTRACT=<p>GABA<sub>A</sub> receptors (γ-aminobutyric acid-gated receptors type A; GABA<sub>A</sub>Rs), the major structural and functional postsynaptic components of inhibitory synapses in the mammalian brain, belong to a family of GABA-gated Cl<sup>−</sup>/HCO<sub>3</sub><sup>−</sup> ion channels. They are assembled as heteropentamers from a family of subunits including: α (1–6), β(1–3), γ(1–3), δ, ε, π, θ and ρ(1–3). GABA<sub>A</sub>Rs together with the postsynaptic adhesion protein Neuroligin 2 (NL2) and many other pre- and post-synaptic proteins guide the initiation and functional maturation of inhibitory GABAergic synapses. This study examined how GABA<sub>A</sub>Rs and NL2 interact with each other to initiate the formation of synapses. Two functionally distinct GABA<sub>A</sub>R subtypes, the synaptic type α2β2γ2-GABA<sub>A</sub>Rs versus extrasynaptic type α4β3δ-GABA<sub>A</sub>Rs were expressed in HEK293 cells alone or together with NL2 and co-cultured with striatal GABAergic medium spiny neurons to enable innervation of HEK293 cells by GABAergic axons. When expressed alone, only the synaptic α2β2γ2-GABA<sub>A</sub>Rs induced innervation of HEK293 cells. However, when GABA<sub>A</sub>Rs were co-expressed with NL2, the effect on synapse formation exceeded the individual effects of these proteins indicating a synergistic interaction, with α2β2γ2-GABA<sub>A</sub>R/NL2 showing a significantly greater synaptogenic activity than α4β3δ-GABA<sub>A</sub>R/NL2 or NL2 alone. To investigate the molecular basis of this interaction, different combinations of GABA<sub>A</sub>R subunits and NL2 were co-expressed, and the degree of innervation and synaptic activity assessed, revealing a key role of the γ2 subunit. In biochemical assays, the interaction between NL2 and α2β2γ2-GABA<sub>A</sub>R was established and mapped to the large intracellular domain of the γ2 subunit.</p>