Retrograde Synaptic Inhibition Is Mediated by α-Neurexin Binding to the α2δ Subunits of N-Type Calcium Channels

Abstract

Summary The synaptic adhesion molecules Neurexin and Neuroligin alter the development and function of synapses and are linked to autism in humans. In C. elegans, post-synaptic Neurexin (NRX-1) and pre-synaptic Neuroligin (NLG-1) mediate a retrograde synaptic signal that inhibits acetylcholine (ACh) release at neuromuscular junctions. Here we show that the retrograde signal decreases ACh release by inhibiting the function of pre-synaptic UNC-2/CaV2 calcium channels. Post-synaptic NRX-1 binds to an auxiliary subunit of pre-synaptic UNC-2/CaV2 channels (UNC-36/α2δ) decreasing UNC-36 abundance at pre-synaptic elements. Retrograde inhibition is mediated by a soluble form of NRX-1’s ectodomain, which is released from the post-synaptic membrane by the SUP-17/ADAM10 protease. Mammalian Neurexin-1α binds α2δ–3 and decreases CaV2.2 current in transfected cells whereas Neurexin-1α has no effect on CaV2.2 reconstituted with α2δ1 and α2δ2. Collectively, these results suggest that α-Neurexin binding to α2δ is a conserved mechanism for regulating synaptic transmission.

Transcellular Nanoalignment of Synaptic Function

“…Additional evidence for instructive roles of trans-synaptic organizers in synapse development comes from studies of another class of postsynaptic neurexin ligands called LRRTM proteins (de Wit and Ghosh, 2016), LAR phosphotyrosine phosphatases that signal on the presynaptic side (Takahashi and Craig, 2013), and SynCAM 1, which is preferentially postsynaptic and required and sufficient to control the number of excitatory synapses in vivo (Park et al, 2016; Korber and Stein, 2016; Robbins et al, 2010). The subsynaptic functions of these and other adhesion molecules could include localization or retention of pre- and post-synaptic nanodomains at developing and mature synapses, altering the geometry of the cleft and hence the diffusion of neurotransmitters, or modulating presynaptic Ca channel function (Freche et al, 2011; Glebov et al, 2016; Tong et al, 2017; Wahl et al, 1996). Adhesion molecules also provide candidate mechanisms for the trans-synaptic alignment of nanocolumns, as discussed later.…”

“…A recent study also observed loss of both Ca 2+ channels and AMPARs/PSD-95 co-localization upon α2δ loss in auditory ribbon synapses, implicating a role in organizing this synapse (Fell et al, 2016). Intriguingly, the C. elegans α2δ protein participates in retrograde signaling via neurexin-neuroligin interactions (Tong et al, 2017). Overall, diverse protein interactions with glutamate receptors and Ca 2+ channels in the synaptic cleft may cooperate to establish subsynaptic functional alignment along with or independent of trans-synaptic adhesion.…”

Subsynaptic spatial organization as a regulator of synaptic strength and plasticity

“…In C. elegans neuromuscular junction, postsynaptic neurexin1 plays a key role in mediating a retrograde inhibition of presynaptic transmitter release [57**]. Emerging evidence suggests that this kind of retrograde coordination could happen structurally at the nanoscale level.…”

Outside‐in regulation of the readily releasable pool of synaptic vesicles by α2δ‐1

“…39 Radioligand binding assays showed that the recombinant extracellular region of rat NRX1α bound α2δ-1 with an estimated IC 50 of 140 nmol/L ( Figure 6A). 39 Radioligand binding assays showed that the recombinant extracellular region of rat NRX1α bound α2δ-1 with an estimated IC 50 of 140 nmol/L ( Figure 6A).…”

“…The effect was not observed when 65 nmol/L NRX1α(Leu31-Thr1431) was applied concomitantly with 650 nmol/L l-isoleucine ( Figure 6C) thus resembling pregabalin action (see Figure 1D). Taking into account that the ectodomain of NRX1α binds to α2δ1-3 subunits 39 and gabapentinoids interact with α2δ1-2, 40 we investigated whether other α2δ isoforms could be mediating the described effects. Pregabalin was unable to reduce synaptic strength if NRX1α(Leu31-Thr1431) was previously applied.…”