Intermediate filaments attenuate stimulation‐dependent mobility of endosomes/lysosomes in astrocytes

AbstractIntermediate filament (IF) proteins upregulation is a hallmark of astrocyte activation and reactive gliosis, but its pathophysiological implications remain incompletely understood. A recently reported association between IFs and directional mobility of peptidergic vesicles allows us to hypothesize that IFs affect vesicle dynamics and exocytosis‐mediated astrocyte communication with neighboring cells. Here, we ask whether the trafficking of recycling vesicles (i.e., those fused to and then retrieved from the plasma membrane) and endosomes/lysosomes depends on IFs. Recycling vesicles were labeled by antibodies against vesicle glutamate transporter 1 (VGLUT1) and atrial natriuretic peptide (ANP), respectively, and by lysotracker, which labels endosomes/lysosomes. Quantitative fluorescence microscopy was used to monitor the mobility of labeled vesicles in astrocytes, derived from either wild‐type (WT) mice or mice deficient in glial fibrillary acidic protein and vimentin (GFAP−/−Vim−/−), the latter lacking astrocyte IFs. Stimulation with ionomycin or ATP enhanced the mobility of VGLUT1‐positive vesicles and reduced the mobility of ANP‐positive vesicles in WT astrocytes. In GFAP−/−Vim−/− astrocytes, both vesicle types responded to stimulation, but the relative increase in mobility of VGLUT1‐positive vesicles was more prominent compared with nonstimulated cells, whereas the stimulation‐dependent attenuation of ANP‐positive vesicles mobility was reduced compared with nonstimulated cells. The mobility of endosomes/lysosomes decreased following stimulation in WT astrocytes. However, in GFAP−/−Vim−/− astrocytes, a small increase in the mobility of endosomes/lysosomes was observed. These findings show that astrocyte IFs differentially affect the stimulation‐dependent mobility of vesicles. We propose that upregulation of IFs in pathologic states may alter the function of astrocytes by deregulating vesicle trafficking. © 2010 Wiley‐Liss, Inc.