Age-dependent spatial segregation of synaptobrevin 2-containing vesicles in astrocytes.

Astrocytes possess much of the same exocytotic protein machinery as neurons do and can release various gliotransmitters stored in their secretory vesicles. An essential component of this exocytotic machinery is the vesicle-associated membrane protein synaptobrevin 2 (Sb2). In order to assess whether vesicular age plays a role in determining the intracellular location of vesicles in astrocytes, we generated a fluorescent chimeric form of Sb2. We appended the Sb2 cytosolic N-terminus with the fluorescent 'timer' protein DsRedE5, which changes its fluorescence emission from green to red as it ages. We found that Sb2-containing vesicles in astrocytes segregate and localize intracellularly in an age dependent manner. Younger vesicles predominately localize at the periphery of cell somata and processes, while older vesicles predominately locate at the central portion of the cell body. These findings raise the notion that there might be differential astrocyte-neuron signaling at sites away or at the tripartite synapse that could be modulated by the age of vesicles and/or their cargo.