Mechanisms of interleukin-1β-induced Ca2+signals in mouse cortical astrocytes: roles of store- and receptor-operated Ca2+entry

Abstract

Many neurodegenerative disorders are accompanied by chronic glial activation, which is characterized by the abundant production of proinflammatory cytokines, such as IL-1β. IL-1β disrupts Ca2+homeostasis and stimulates astrocyte reactivity. The mechanisms by which IL-1β induces Ca2+dysregulation are not completely defined. Here, we examined how acute and chronic (24–48 h) treatment with IL-1β affect Ca2+homeostasis in freshly dissociated and primary cultured mouse cortical astrocytes. Cytosolic free Ca2+concentration ([Ca2+]cyt) was measured with fura-2 using digital imaging. An acute application of 10 ng/ml IL-1β induced Ca2+mobilization from intracellular stores and activated store-operated Ca2+entry (SOCE) and receptor-operated Ca2+entry (ROCE) in both freshly dissociated and cultured actrocytes. Treatment of cultured astrocytes with IL-1β for 24 and 48 h elevated resting [Ca2+]cyt, decreased Ca2+store content [associated with sarco(endo)plasmic reticulum Ca2+-ATPase 2b downregulation], and augmented ROCE. Based on evidence that receptor-operated, but not store-operated Ca2+channels are Ba2+permeable, Ba2+entry was used to distinguish receptor-operated Ca2+channels from store-operated Ca2+channels. ROCE was activated by the diacylglycerol analog, 1-oleoyl-2-acetyl- sn-glycerol (OAG). In the presence of extracellular Ba2+, OAG-induced elevations of cytosolic Ba2+(fura-2 340-to-380-nm ratio) were significantly larger in astrocytes treated with IL-1β. These changes in IL-1β-treated astrocytes correlate with augmented expression of transient receptor potential cation channel (TRPC)6 protein, which likely mediates ROCE. Knockdown of the TRPC6 gene markedly reduced ROCE. The data suggest that IL-1β-induced dysregulation of Ca2+homeostasis is the result of enhanced ROCE and TRPC6 expression. The disruption of Ca2+homeostasis appears to be an upstream component in the cascade of IL-1β-activated pathways leading to neurodegeneration.