Light-Activated ROS Production Induces Synaptic Autophagy

Abstract

The regulated turnover of synaptic vesicle (SV) proteins is thought to involve the ubiquitin-dependent tagging and degradation through endo-lysosomal and autophagy pathways. Yet, it remains unclear which of these pathways are used, when they become activated, and whether SVs are cleared en masse together with SV proteins or whether both are degraded selectively. Equally puzzling is how quickly these systems can be activated and whether they function in real-time to support synaptic health. To address these questions, we have developed an imaging-based system that simultaneously tags presynaptic proteins while monitoring autophagy. Moreover, by tagging SV proteins with a light-activated ROS generator, Supernova, it was possible to temporally control the damage to specific SV proteins and assess their consequence to autophagy-mediated clearance mechanisms and synaptic function. Our results show that, in mouse hippocampal neurons of either sex, presynaptic autophagy can be induced in as little as 5-10 min and eliminates primarily the damaged protein rather than the SV en masse. Importantly, we also find that autophagy is essential for synaptic function, as light-activated damage to, for example, Synaptophysin only compromises synaptic function when autophagy is simultaneously blocked. These data support the concept that presynaptic boutons have a robust highly regulated clearance system to maintain not only synapse integrity, but also synaptic function.

A CRHR1 antagonist prevents synaptic loss and memory deficits in a trauma-induced delirium-like syndrome

“…Indeed, we observed in our experimental setup that BCN-1, LC3, and Lamp-2 were significantly upregulated by elevated CRH levels in neurons (in vitro and in vivo) and that signs of autophagy induction, especially in the presynaptic compartment, appeared. Interestingly, recent evidence of fine-tuned protein homeostasis regulated by autophagy at synapses, especially in the presynaptic compartment, was reported [71][72][73]. We found that CRHR1 activation was correlated with the rapid downregulation of (presynaptic) BDNF and that BDNF degradation was rescued by CRHR1 blockage as well as NF-κB pathway inhibition.…”

Neuronal Autophagy Regulates Presynaptic Neurotransmission by Controlling the Axonal Endoplasmic Reticulum

“…Distally formed autophagosomes mature during their retrograde axonal transport (Guedes-Dias and Holzbaur, 2019; Stavoe and Holzbaur, 2019) prior to their fusion with degradative lysosomes enriched in proximal axons and in neuronal somata (Hill and Coló n-Ramos, 2020;Maday and Holzbaur, 2014;Maday et al, 2012). In addition to this largely constitutive process of neuronal autophagy (Maday and Holzbaur, 2016), formation of autophagosomes has been suggested to be facilitated by mitochondrial damage (Ashrafi et al, 2014), neuronal activity (Shehata et al, 2012;Wang et al, 2015), overexpression of aggregation-prone proteins (Corrochano et al, 2012), reactive oxygen species (ROS)-induced protein oxidation (Hoffmann et al, 2019), or genetic depletion of key AZ proteins (Okerlund et al, 2017). We demonstrate, using knockout mice conditionally lacking the essential autophagy protein ATG5 and quantitative proteomics, that loss of neuronal autophagy causes selective accumulation of tubular ER in axons, resulting in increased excitatory neurotransmission because of elevated calcium release from ER stores via ryanodine receptors.…”

Emerging Role of the Autophagy/Lysosomal Degradative Pathway in Neurodevelopmental Disorders With Epilepsy

“…Whether SV cycling and synaptic autophagy are reciprocally regulated and how they crosstalk with somatic autophagy is a matter of investigation. In a recent article, selective induction of autophagy at the presynaptic site has been shown to specifically target damaged proteins, thus maintaining synapse integrity and function (Hoffmann et al, 2019). The discovery that neuronal autophagy and formation of APs at synapses are activity dependent (Shehata et al, 2018) suggests that synaptic autophagy may be regulated by long-term synaptic plasticity underlying learning and memory formation.…”