Opposing functions for retromer and Rab11 in extracellular vesicle cargo traffic at presynaptic terminals

Abstract

Neuronal extracellular vesicles (EVs) play critical roles in intercellular communication and in propagation of pathogenic proteins in neurological disease. However, little is known about how cargoes are selectively packaged into neuronal EVs. Here, we examined the intracellular traffic and release of the EV cargoes Amyloid Precursor Protein (APP) and Synaptotagmin-4 (Syt4) at presynaptic nerve terminals of Drosophila motor neurons. We found that loss of the endosomal retromer complex leads to increased EV cargo levels both presynaptically and in EVs, and that this function is separable from previously identified roles of neuronal retromer. Conversely, EV cargo levels are reduced in rab11 mutants, and EV cargo sorting depends on a balance between Rab11-mediated recycling and retromer-dependent removal from the EV pathway. Rab11 and retromer have previously been implicated in Alzheimer's Disease, suggesting that these competing pathways may serve as therapeutic targets for limiting accumulation and release of toxic EV cargoes.

Retromer subunit, VPS29, regulates synaptic transmission and is required for endolysosomal function in the aging brain

“…To explore the requirement of retromer at synapses, we next turned to the larval neuromuscular junction (NMJ). Based on previous work, Vps35 is present at both the NMJ pre-and post-synapse, and loss of Vps35 causes synaptic terminal overgrowth and altered neurophysiology suggestive of synaptic vesicle recycling defects (Inoshita et al, 2017;Korolchuk et al, 2007;Malik et al, 2015;Walsh et al, 2019). We therefore examined whether Vps29 mutants show similar phenotypes.…”

Function of Drosophila Synaptotagmins in membrane trafficking at synapses

“…Drosophila SYT4 is homologous to mammalian SYT4 and SYT11 and is transferred to the postsynaptic compartment from exosomes (Fig. 3b), where it functions in retrograde signaling [97,100,[104][105][106][107]. Mutations in Drosophila Syt4 and Syt7 are viable and fertile as adults [82,97,104,105], though no studies to date have examined potential roles in synaptic plasticity and learning in adult animals.…”

“…Indeed, endogenously CRISPR-tagged SYT4-GFP expression is eliminated from the postsynaptic compartment following RNAi knockdown of the Syt4 gene presynaptically but not postsynaptically. SYT4 is one of the several proteins that undergo trans -synaptic delivery in extracellular vesicles through a pathway regulated by presynaptic Rab11 [ 107 , 310 , 311 ]. This finding parallels trans-synaptic delivery of Drosophila and mammalian ARC proteins that regulate synaptic plasticity [ 312 – 315 ].…”