Nolte C. Moeller T. Walter T. Kettenmann H [a].
Complement 5a controls motility of murine microglial cells in vitro via activation of an inhibitory G-protein and the rearrangement of the actin cytoskeleton,Neuroscience 73(4) :1091-1107, 1996.
Abstract
Microglial cells respond to most pathological events by rapid transformation from a
quiescent to an activated phenotype characterized by increased cytotoxicity and motile
activity. To investigate the regulation of microglial motility by different inflammatory
mediators, we studied cultured murine microglia by time-lapse video microscopy and a
computer-based motility assay. Microglial cells exhibited a high resting motility. The acute
application of complement 5a (C5a) immediately induced intense ruffling of microglial
membranes followed by lamellipodia extension within few seconds, while
formyl-Met-Leu-Phe-OH, bacterial endotoxin (lipopolysaccharide) or inflammatory
cytokines did not increase motility. This process was accompanied by a rapid
rearrangement of the actin cytoskeleton as demonstrated by labelling with fluorescein
isothiocyanate-phalloidin and could be inhibited by cytochalasin B. A GTP-binding protein
was involved in the signal cascade, since pertussis toxin inhibited motility and actin
assembly in response to C5a. Chemotactic migration in a gradient of C5a was also
completely blocked by pertussis toxin and cytochalasin B. The C5a-induced motility
reaction was accompanied by an increase in intracellular calcium ((Ca-2+)-i) as
measured by a Fluo-3 based imaging system. Ca-2+ transients were, however, not a
prerequisite for triggering the increase in motility; motility could be repeatedly evoked by
C5a in nominally Ca-2+-free solution, while Ca-2+ signals occurred only upon the first
simulation. Moreover, conditions mimicking intracellular Ca-2+ transients, like incubation
with thapsigargin or Ca-2+ ionophore A23187, were not able to induce any motility
reaction, suggesting that Ca-2+ transients are not necessary for, but are associated with,
microglial motility. Motile activity was shown to be restricted to a defined concentration
range of (Ca-2+)-i as revealed by lowering (Ca-2+)-i with BAPTA-AM or increasing
(Ca-2+)-i with A23187. Since complement factors are released at pathological sites, this
signal cascade could serve to increase motility and to direct microglial cells to the lesioned
or damaged area by means of a G-protein- dependent pathway and via the
rearrangement of the actin cytoskeleton.
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