Complex formation of APP with GABAB receptors links axonal trafficking to amyloidogenic processing

Margarita C Dinamarca,Valérie Besseyrias,Martin Gassmann,Pascal D Rem,Wolfgang Bildl,Simon Früh,Matthias Staufenbiel,Bernd Fakler,Txomin Lalanne,Adi Raveh,Bernhard Bettler,Rostislav Turecek,Thorsten Fritzius,Jochen Schwenk,Myeongjeong Choo,Andy Schneider,Detlef Bentrop,Michal Stawarski

doi:10.1038/s41467-019-09164-3

Abstract

GABAB receptors (GBRs) are key regulators of synaptic release but little is known about trafficking mechanisms that control their presynaptic abundance. We now show that sequence-related epitopes in APP, AJAP-1 and PIANP bind with nanomolar affinities to the N-terminal sushi-domain of presynaptic GBRs. Of the three interacting proteins, selectively the genetic loss of APP impaired GBR-mediated presynaptic inhibition and axonal GBR expression. Proteomic and functional analyses revealed that APP associates with JIP and calsyntenin proteins that link the APP/GBR complex in cargo vesicles to the axonal trafficking motor. Complex formation with GBRs stabilizes APP at the cell surface and reduces proteolysis of APP to Aβ, a component of senile plaques in Alzheimer’s disease patients. Thus, APP/GBR complex formation links presynaptic GBR trafficking to Aβ formation. Our findings support that dysfunctional axonal trafficking and reduced GBR expression in Alzheimer’s disease increases Aβ formation.

Highlights

GABAB receptors (GBRs) are key regulators of synaptic release but little is known about trafficking mechanisms that control their presynaptic abundance
To investigate the interdependence of protein constituents in GBR complexes we analyzed the composition of affinitypurified GBRs from GB1a−/−, amyloid precursor protein (APP)−/−, adherence-junction associated protein 1 (AJAP-1)−/−, PILRα-associated neural protein (PIANP)−/−, and APP/AJAP-1−/− double knock-out brains using quantitative mass spectrometry[15] (Fig. 1a, Source Data)
Deletion of APP or AJAP-1 increased the amount of PIANP in GBR complexes, likely because of the increased availability of sushi domains (SDs) for binding (Fig. 1a)

Summary

Introduction

GABAB receptors (GBRs) are key regulators of synaptic release but little is known about trafficking mechanisms that control their presynaptic abundance. We show that sequence-related epitopes in APP, AJAP-1 and PIANP bind with nanomolar affinities to the Nterminal sushi-domain of presynaptic GBRs. Of the three interacting proteins, selectively the genetic loss of APP impaired GBR-mediated presynaptic inhibition and axonal GBR expression. Our findings support that dysfunctional axonal trafficking and reduced GBR expression in Alzheimer’s disease increases Aβ formation. We analyzed the interaction of APP, AJAP-1, and PIANP with GB1a and addressed the role of these proteins in presynaptic GBR transport and expression. APP links GB1a/2 receptors to vesicular trafficking and, when deleted, induces a significant deficit in GBR-mediated inhibition of glutamate release. The association of presynaptic GBR expression with APP processing can explain pathological features observed in AD and suggests APP/GB1a complex stabilization as a promising therapeutic strategy

Methods

Results

Conclusion