Peptidomic Analyses of Mouse Astrocytic Cell Lines and Rat Primary Cultured Astrocytes

Astrocytes play an active role in the modulation of synaptic transmission by releasing cell–cell signaling molecules in response to various stimuli that evoke a Ca<sup>2+</sup> increase. We expand on recent studies of astrocyte intracellular and secreted proteins by examining the astrocyte peptidome in mouse astrocytic cell lines and rat primary cultured astrocytes, as well as those peptides secreted from mouse astrocytic cell lines in response to Ca<sup>2+</sup>-dependent stimulations. We identified 57 peptides derived from 24 proteins with LC–MS/MS and CE–MS/MS in the astrocytes. Among the secreted peptides, four peptides derived from elongation factor 1, macrophage migration inhibitory factor, peroxiredoxin-5, and galectin-1 were putatively identified by mass-matching to peptides confirmed to be found in astrocytes. Other peptides in the secretion study were mass-matched to those found in prior peptidomics analyses on mouse brain tissue. Complex peptide profiles were observed after stimulation, suggesting that astrocytes are actively involved in peptide secretion. Twenty-six peptides were observed in multiple stimulation experiments but not in controls and thus appear to be released in a Ca<sup>2+</sup>-dependent manner. These results can be used in future investigations to better understand stimulus-dependent mechanisms of astrocyte peptide secretion.