Amyloid-β Oligomers Interact with Neurexin and Diminish Neurexin-mediated Excitatory Presynaptic Organization

Abstract

Alzheimer’s disease (AD) is characterized by excessive production and deposition of amyloid-beta (Aβ) proteins as well as synapse dysfunction and loss. While soluble Aβ oligomers (AβOs) have deleterious effects on synapse function and reduce synapse number, the underlying molecular mechanisms are not well understood. Here we screened synaptic organizer proteins for cell-surface interaction with AβOs and identified a novel interaction between neurexins (NRXs) and AβOs. AβOs bind to NRXs via the N-terminal histidine-rich domain (HRD) of β-NRX1/2/3 and alternatively-spliced inserts at splicing site 4 of NRX1/2. In artificial synapse-formation assays, AβOs diminish excitatory presynaptic differentiation induced by NRX-interacting proteins including neuroligin1/2 (NLG1/2) and the leucine-rich repeat transmembrane protein LRRTM2. Although AβOs do not interfere with the binding of NRX1β to NLG1 or LRRTM2, time-lapse imaging revealed that AβO treatment reduces surface expression of NRX1β on axons and that this reduction depends on the NRX1β HRD. In transgenic mice expressing mutated human amyloid precursor protein, synaptic expression of β-NRXs, but not α-NRXs, decreases. Thus our data indicate that AβOs interact with NRXs and that this interaction inhibits NRX-mediated presynaptic differentiation by reducing surface expression of axonal β-NRXs, providing molecular and mechanistic insights into how AβOs lead to synaptic pathology in AD.

IgSF21 promotes differentiation of inhibitory synapses via binding to neurexin2α

“…IgSF21 deletion constructs were generated by inverse PCR using mouse IgSF21-HA as the template to delete the regions encoding aa 31–141 (IgSF21ΔIg1) or aa 348–431 (IgSF21ΔIg2). A series of extracellularly HA-tagged neurexin (HA-NRX) constructs, HA-CD4 and HA-NLG2 were previously described 29 , 56 . For the pDisplay-NRX2α constructs, the following coding regions of NRX2αS1–S4(+) were subcloned into pDisplay (Invitrogen): aa 29-199 (LNS1), aa 29-309 (LNS1-EGF1), aa 29-499 (LNS1-LNS2) and aa 29-680 (LNS1-LNS3).…”

Synaptic Organizers in Alzheimer’s Disease: A Classification Based on Amyloid-β Sensitivity

“…At the synapse level, NLGN1 and NLGN2 are mostly localized at excitatory and inhibitory synapses, respectively, whereas NLGN3 is localized at both excitatory and inhibitory synapses (Song et al, 1999 ; Varoqueaux et al, 2004 ; Budreck and Scheiffele, 2007 ). Artificial synapse formation assays have shown that NLGNs have a synaptogenic activity to induce presynaptic organization of excitatory and inhibitory synapses (Scheiffele et al, 2000 ; Graf et al, 2004 ; Chubykin et al, 2005 ; Craig et al, 2006 ; Naito et al, 2017b ) through their trans-interaction with presynaptic NRXs (Ko et al, 2009b ; Gokce and Südhof, 2013 ). Further, a recent study using NLGN1-4 conditional KO mouse brain slices with rescue experiments has shown that the NLGN1 extracellular domain, particularly its trans-interaction with presynaptic NRXs, is crucial for LTP (Wu et al, 2019 ).…”

“…LRRTM3/4 are highly expressed in the hippocampal DG, the cerebral cortex layer 2 and moderately expressed in the cerebral cortex layers 3–6 (Laurén et al, 2003 ). LRRTMs can promote the presynaptic organization of excitatory, but not inhibitory, synapses (Ko et al, 2009a ; Linhoff et al, 2009 ; de Wit et al, 2013 ; Naito et al, 2017b ). Interestingly, LRRTM1/2 bind to SS4-negative NRX [NRX SS4(−)], but not SS4-positive NRX [NRX SS4(+)], regardless of α- and β-NRX isoforms (Ko et al, 2009a ; Siddiqui et al, 2010 ).…”

“…Given the evidence of synaptic impairments in AD, recent studies have been trying to test whether and how Aβ interferes with synaptic organizers because of their pivotal roles in synapse physiology and cognitive function. Interestingly, our recent study has identified NRXs as a direct binding protein of AβOs (Naito et al, 2017b ). Other groups have further uncovered the binding of Aβ with NLGN1 (Dinamarca et al, 2011 ; Brito-Moreira et al, 2017 ).…”

“…We then review the emerging evidence of how synaptic organizers are involved in AD pathology, mainly focusing on Aβ pathology. Furthermore, considering their capability of Aβ binding (Dinamarca et al, 2011 ; Brito-Moreira et al, 2017 ; Naito et al, 2017b ), we propose a new classification of synaptic organizers divided into two groups: Aβ-sensitive and Aβ-insensitive organizers, and discuss their implications in Aβ vulnerability and tolerance of synapses in AD. This would be essential to better understand the mechanisms involved in AD progression and give some insights into the development of novel therapeutic approaches for AD.…”