Blockade of chloride intracellular ion channel 1 stimulates a beta phagocytosis

In amyloid-beta (A beta)-stimulated microglial cells, blockade of chloride intracellular ion channel 1 (CLIC1) reverts the increase in tumor necrosis factor-a and nitric oxide (NO) production and results in neuroprotection of cocultured neurons. This effect could be of therapeutic efficacy in Alzheimer's disease (AD), where microglial activation may contribute to neurodegeneration, but it could reduce A beta phagocytosis, which could facilitate amyloid plaque removal. Here, we analyzed the CLIC1 blockade effect on A beta-stimulated mononuclear phagocytosis. In the microglial cell line BV-2, A beta 25-35 treatment enhanced fluorescent bead phagocytosis, which persisted also in the presence of IAA-94, a CLIC1 channel blocker. The same result was obtained in rat primary microglia and in BV2 cells, where CLIC1 expression had been knocked down with a plasmid producing small interfering RNAs. To address specifically the issue of A beta phagocytosis, we treated BV-2 cells with biotinylated A beta 1-42 and measured intracellular amyloid by morphometric analysis. IAA-94-treated cells showed an increased A beta phagocytosis after 24 hr and efficient degradation of ingested material after 72 hr. In addition, we tested A beta 1-42 phagocytosis in adult rat peritoneal macrophages. Also, these cells actively phagocytosed A beta 1-42 in the presence of IAA-94. However, the increased expression of inducible NO synthase (NOS), stimulated by A beta, was reverted by IAA-94. In parallel, a decrease in NO release was detected. These results suggest that blockade of CLIC1 stimulates A beta phagocytosis in mononuclear phagocytes while inhibiting the induction of NOS and further point to CLIC1 as a possible therapeutic target in AD. (C) 2008 Wiley-Liss, Inc.