The endocannabinoid 2-arachidonoylglycerol is released and transported on demand via extracellular microvesicles
While it is known that endocannabinoids (eCB) modulate multiple neuronal functions, the molecular mechanism governing their release and transport remains elusive. Here, we propose an 'on-demand release' model, wherein the formation of microvesicles, a specific group of extracellular vesicles (EVs) containing the eCB, 2-arachidonoylglycerol (2-AG), is the rate-limiting step. A co-culture model system that combines a reporter cell line expressing the fluorescent eCB sensor, GRABeCB2.0, and neuronal cells revealed that neurons release EVs containing 2-AG, but not anandamide, in a stimulus-dependent process regulated by PKC, DAGL, Arf6, and which was sensitive to inhibitors of eCB facilitated diffusion. A vesicle contained approximately 2000 2-AG molecules. Accordingly, hippocampal eCB-mediated synaptic plasticity was modulated by Arf6 and transport inhibitors. This 'on demand release' model, supported by mathematical analysis, offers a cohesive framework for understanding eCB signaling at the molecular level and suggests that microvesicles carrying signaling lipids regulate neuronal functions in parallel to canonical synaptic vesicles.