Secretory autophagy - a new paradigm regulating synaptic plasticity

When exposed to new experiences or changes in the environment, neurons rapidly remodel their synaptic structure and function in a process called activity-induced synaptic remodeling. This process is necessary for transforming transient experiences into stable, lasting memories. The molecular mechanisms underlying acute, activity-dependent synaptic changes are not well understood, partly because processes regulating synaptic plasticity and neurodevelopment are intricately linked. By using an RNAi screen in Drosophila targeting genes associated with human nervous system function, we found that while macroautophagy (referred to as autophagy) is fundamental for both synapse development and synaptic plasticity, activity-induced synaptic remodeling does not rely on genes associated with lysosomal degradation. These findings suggest a requirement for the unconventional secretory autophagy pathway in regulating synaptic plasticity, wherein autophagosomes, instead of fusing with lysosomes for degradation, fuse with the plasma membrane to release their contents extracellularly. To test this hypothesis, we knocked down Sec22, Snap29, and Rab8, molecular components required for secretory autophagy, all of which disrupted structural and functional plasticity. Additionally, by monitoring autophagy, we demonstrated that neuronal activity suppresses degradative autophagy to shift the pathway toward secretory autophagy release. Our work unveils secretory autophagy as a novel trans-synaptic signaling mechanism crucial for activity-induced synaptic remodeling.