SNARE Protein Expression in Synaptic Terminals and Astrocytes in the Adult Hippocampus: A Comparative Analysis

Glia. 2011 Oct;59(10):1472-88. doi: 10.1002/glia.21190. Epub 2011 Jun 8.

Abstract

Several evidences suggest that astrocytes release small transmitter molecules, peptides, and protein factors via regulated exocytosis, implying that they function as specialized neurosecretory cells. However, very little is known about the molecular and functional properties of regulated secretion in astrocytes in the adult brain. Establishing these properties is central to the understanding of the communication mode(s) of these cells and their role(s) in the control of synaptic functions and of cerebral blood flow. In this study, we have set-up a high-resolution confocal microscopy approach to distinguish protein expression in astrocytic structures and neighboring synaptic terminals in adult brain tissue. This approach was applied to investigate the expression pattern of core SNARE proteins for vesicle fusion in the dentate gyrus and CA1 regions of the mouse hippocampus. Our comparative analysis shows that astrocytes abundantly express, in their cell body and main processes, all three protein partners necessary to form an operational SNARE complex but not in the same isoforms expressed in neighbouring synaptic terminals. Thus, SNAP25 and VAMP2 are absent from astrocytic processes and typically concentrated in terminals, while SNAP23 and VAMP3 have the opposite expression pattern. Syntaxin 1 is present in both synaptic terminals and astrocytes. These data support the view that astrocytes in the adult hippocampus can communicate via regulated exocytosis and also indicates that astrocytic exocytosis may differ in its properties from action potential-dependent exocytosis at neuronal synapses, as it relies on a distinctive set of SNARE proteins.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Astrocytes / metabolism*
  • Gene Expression Regulation / genetics
  • Gene Expression Regulation / physiology*
  • Glial Fibrillary Acidic Protein / genetics
  • Glutamate-Ammonia Ligase / metabolism
  • Glycogen Phosphorylase / metabolism
  • Green Fluorescent Proteins / genetics
  • Hippocampus / cytology*
  • In Vitro Techniques
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Microscopy, Confocal
  • Presynaptic Terminals / metabolism*
  • SNARE Proteins / classification
  • SNARE Proteins / genetics
  • SNARE Proteins / metabolism*
  • Shiga Toxin 1 / genetics
  • Shiga Toxin 1 / metabolism
  • Synaptophysin / metabolism
  • Syntaxin 1 / metabolism
  • Vesicle-Associated Membrane Protein 2 / metabolism
  • Vesicle-Associated Membrane Protein 3 / metabolism

Substances

  • Glial Fibrillary Acidic Protein
  • SNARE Proteins
  • Shiga Toxin 1
  • Synaptophysin
  • Syntaxin 1
  • Vesicle-Associated Membrane Protein 2
  • Vesicle-Associated Membrane Protein 3
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins
  • Glycogen Phosphorylase
  • Glutamate-Ammonia Ligase