Involvement of the intracellular ion channel CLIC1 in microglia-mediatedbeta-amyloid-induced neurotoxicity.

It is widely believed that the inflammatory events mediated by microglialactivation contribute to several neurodegenerative processes. Alzheimer'sdisease, for example, is characterized by an accumulation of beta-amyloidprotein (Abeta) in neuritic plaques that are infiltrated by reactive microgliaand astrocytes. Although Abeta and its fragment 25-35 exert a direct toxiceffect on neurons, they also activate microglia. Microglial activation isaccompanied by morphological changes, cell proliferation, and release of variouscytokines and growth factors. A number of scientific reports suggest that theincreased proliferation of microglial cells is dependent on ionic membranecurrents and in particular on chloride conductances. An unusual chloride ionchannel known to be associated with macrophage activation is the chlorideintracellular channel-1 (CLIC1). Here we show that Abeta stimulation of neonatalrat microglia specifically leads to the increase in CLIC1 protein and to thefunctional expression of CLIC1 chloride conductance, both barely detectable onthe plasma membrane of quiescent cells. CLIC1 protein expression in microgliaincreases after 24 hr of incubation with Abeta, simultaneously with theproduction of reactive nitrogen intermediates and of tumor necrosis factor-alpha(TNF-alpha). We demonstrate that reducing CLIC1 chloride conductance by aspecific blocker [IAA-94(R(+)-[(6,7-dichloro-2-cyclopentyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5yl)-oxy]acetic acid)] prevents neuronal apoptosis in neurons cocultured withAbeta-treated microglia. Furthermore, we show that small interfering RNAs usedto knock down CLIC1 expression prevent TNF-alpha release induced by Abetastimulation. These results provide a direct link between Abeta-inducedmicroglial activation and CLIC1 functional expression.