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-1beta. IL-1beta disrupts Ca(2+) homeostasis and stimulates astrocyte reactivity. The mechanisms by which IL-1beta induces Ca(2+) dysregulation are not completely defined. Here, we examined how acute and chronic (24-48 h) treatment with IL-1beta affect Ca(2+) homeostasis in freshly dissociated and primary cultured mouse cortical astrocytes. Cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) was measured with fura-2 using digital imaging. An acute application of 10 ng/ml IL-1beta induced Ca(2+) mobilization from intracellular stores and activated store-operated Ca(2+) entry (SOCE) and receptor-operated Ca(2+) entry (ROCE) in both freshly dissociated and cultured actrocytes. Treatment of cultured astrocytes with IL-1beta for 24 and 48 h elevated resting [Ca(2+)](cyt), decreased Ca(2+) store content [associated with sarco(endo)plasmic reticulum Ca(2+)-ATPase 2b downregulation], and augmented ROCE. Based on evidence that receptor-operated, but not store-operated Ca(2+) channels are Ba(2+) permeable, Ba(2+) entry was used to distinguish receptor-operated Ca(2+) channels from store-operated Ca(2+) channels. ROCE was activated by the diacylglycerol analog, 1-oleoyl-2-acetyl-sn-glycerol (OAG). In the presence of extracellular Ba(2+), OAG-induced elevations of cytosolic Ba(2+) (fura-2 340-to-380-nm ratio) were significantly larger in astrocytes treated with IL-1beta. These changes in IL-1beta-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-1beta-induced dysregulation of Ca(2+) homeostasis is the result of enhanced ROCE and TRPC6 expression. The disruption of Ca(2+) homeostasis appears to be an upstream component in the cascade of IL-1beta-activated pathways leading to neurodegeneration.