Exocytotic properties of astrocytic vesicles

An important mode of intercellular communication involves the release of molecules from cells by exocytosis. Exocytotic transmitter release is most likely regulated by the SNARE complex, which contains a vesicular protein, synaptobrevin2 (Sb2). By using super-resolution stimulated emission depletion (STED) microscopy and structured illumination microscopy (SIM), we showed that in astrocytes smaller vesicles contain amino acid and peptidergic transmitters and larger vesicles contain ATP (1). We determined that an average astrocytic vesicle contains 15–25 endogenous Sb2 molecules (2). Then we monitored the interaction of a single vesicle with the plasma membrane by a high-resolution membrane capacitance approach. Astrocyte stimulation increases the frequency of predominantly transient fusion exocytotic events in smaller vesicles, whereas larger vesicles proceed more likely to full fusion exocytosis. Treatment of astrocytes with botulinum neurotoxins D and E, and dnSNARE peptide (coding the cytoplasmic domain of Sb2) stabilized the fusion-pore diameter to narrow, release-unproductive diameters in both vesicle types, regardless of vesicle diameter (1). Astrocytes also exhibit strong vesicle related phenotype in certain disorders, like X-linked non-syndromic intellectual disability (XLID), that have traditionally been linked to neurons. (1) Guček A, Jorgačevski J, Singh P, Geisler C, Lisjak M, Vardjan N, Kreft M, Egner A, Zorec R. Dominant negative SNARE peptides stabilize the fusion pore in a narrow, release-unproductive state. Cellular and molecular life sciences. 2016;73: 3719-3731. (2) Singh P, Jorgačevski J, Kreft M, Grubišić V, Stout RF, Potokar M, Parpura V, Zorec R. Single-vesicle architecture of synaptobrevin2 in astrocytes. Nature communications. 2014;5: 1-12. Financing: Research Agency of Slovenia (Grant Numbers P3 0310, J3 4051, J3 4146, J3 7605 and J3 3632) and CipKeBip