CHROMOGRANIN-A TRIGGERS A PHENOTYPIC TRANSFORMATION AND THE GENERATION OF NITRIC-OXIDE IN BRAIN MICROGLIAL CELLS

Chromogranin A is an ubiquitous 48,000 mol, wt secretory protein store d and released from many neuroendocrine cells and neurons. In human br ain, chromogranin A is a common feature of regions that are known to b e affected by various neurodegenerative pathologies such as Alzheimer' s, Parkinson's and Pick's diseases. Brain degenerative areas are gener ally infiltrated by activated microglial cells, the resident macrophag e cell population within the central nervous system. Here, we report t hat both recombinant human chromogranin A and chromogranin A purified from bovine chromaffin granules trigger drastic morphological changes in rat microglial cells maintained in culture. Microglial cells expose d to chromogranin A adopted a flattened amoeboid shape and, this chang e was associated with an accumulation of actin in the subplasmalemmal region, as observed by immunocytochemistry and confocal laser microsco py. In single microglial cells loaded with indo-1, chromogranin A elic ited a rapid and transient increase in [Ca2+](i) which preceded the re organization of actin cytoskeleton. The activity of nitric oxide synth ase was estimated by measuring the accumulation of nitrite in the cult ure medium. Both recombinant human chromogranin A and bovine chromogra nin A triggered an important accumulation of nitrite comparable to tha t induced by lipopolysaccharide, a well-known activator of microglia. The effect of chromogranin A was dose dependent, inhibited by N omega- nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase, and by cycloheximide, an inhibitor of protein synthesis. Th ese findings suggest that chromogranin A induces an activated phenotyp e of microglia, and thus may have a role in the pathogenesis of neuron al degeneration in the brain.