Neuronal Autophagy Regulates Presynaptic Neurotransmission by Controlling the Axonal Endoplasmic Reticulum

Marijn Kuijpers,Gaga Kochlamazashvili,Alexander Stumpf,Dmytro Puchkov,Aarti Swaminathan,Max Thomas Lucht,Eberhard Krause,Tanja Maritzen,Dietmar Schmitz,Volker Haucke

doi:10.1016/j.neuron.2020.10.005

Abstract

SummaryNeurons are known to rely on autophagy for removal of defective proteins or organelles to maintain synaptic neurotransmission and counteract neurodegeneration. In spite of its importance for neuronal health, the physiological substrates of neuronal autophagy in the absence of proteotoxic challenge have remained largely elusive. We use knockout mice conditionally lacking the essential autophagy protein ATG5 and quantitative proteomics to demonstrate that loss of neuronal autophagy causes selective accumulation of tubular endoplasmic reticulum (ER) in axons, resulting in increased excitatory neurotransmission and compromised postnatal viability in vivo. The gain in excitatory neurotransmission is shown to be a consequence of elevated calcium release from ER stores via ryanodine receptors accumulated in axons and at presynaptic sites. We propose a model where neuronal autophagy controls axonal ER calcium stores to regulate neurotransmission in healthy neurons and in the brain.

Highlights

Information processing in the brain critically relies on the relay of information from a presynaptic neuron to the postsynapse via regulated neurotransmitter release
We demonstrate, using knockout mice conditionally lacking the essential autophagy protein autophagy-related protein 5 (ATG5) and quantitative proteomics, that loss of neuronal autophagy causes selective accumulation of tubular endoplasmic reticulum (ER) in axons, resulting in increased excitatory neurotransmission because of elevated calcium release from ER stores via ryanodine receptors
Analysis by immunoblotting revealed profound loss of ATG5 protein mainly in the cerebral cortex and in the hippocampus (Figure 1B). This was accompanied by accumulation of the autophagy adaptor and substrate protein p62, consistent with prior observations in ATG5flox/flox; nestinCre KO mice lacking ATG5 throughout the brain (Hara et al, 2006)

Summary

Introduction

Information processing in the brain critically relies on the relay of information from a presynaptic neuron to the postsynapse via regulated neurotransmitter release This process is triggered by the action potential (AP)-triggered, calcium-driven exocytic fusion of neurotransmitter-containing synaptic vesicles (SVs) at active zone (AZ) release sites (Jahn and Fasshauer, 2012; Su€dhof, 2013). To prevent neuronal and synaptic dysfunction, neurons have evolved mechanisms for removal of toxic or defective proteins and organelles to maintain regulated neurotransmission and the integrity of their functional proteome Among these mechanisms are lysosomal turnover of membrane proteins and autophagy, a cellular process by which defective proteins and organelles are degraded through sequestration in autophagosomes and delivery to lysosomes (Hill and Colon-Ramos, 2020; Nikoletopoulou and Tavernarakis, 2018; Vijayan and Verstreken, 2017). Induction of autophagy counteracts neurodegeneration in disease models (Moreau et al, 2014; Nixon, 2013; Ravikumar et al, 2004, 2010; Williams et al, 2006)

Methods

Results

Discussion

Conclusion