Central nervous system-infiltrated immune cells alter calcium dynamics in astrocytes

Abstract

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS), characterized by focal neurodegenerative and demyelinating lesions. A major contributor to the pathogenic process of MS is the complex interaction between astrocytes and the CNS-infiltrating immune cells (CNS-IIC). The aim of our study is to explore how naïve astrocytes respond to the autoreactive immune cells that invade the CNS. For this reason, CNS-IICs were isolated and purified from spinal cords of rats with experimental autoimmune encephalomyelitis. Ca2+ dynamics was monitored in Fluo-4 labeled naïve astrocytes, isolated from spinal cords of wild type rat pups, following brief bath application of CNS-IIC or peripheral immune cells, with different pharmacological agents. CNS-IICs, and not peripheral immune cells, induced robust elevation of intracellular Ca2+ in naïve astrocytes. We demonstrated that this CNS IIC-induced increase in astrocyte Ca2+ does not depend on the metabotropic glutamate receptors, metabotropic purinergic P2Y1 receptors or TRPA1 channels. Remarkably, further research showed that Ca2+ elevation in astrocytes upon exposure to CNS IICs is due to the activation of ionotropic purinergic P2X7 receptors. Bioluminescence assay showed that immune cell-derived ATP is not a cause of astrocytic P2X7 receptor activation. In fact, we showed that CNS-IICs promoted P2X7 receptor activation and increase in cytosolic Ca2+ in astrocytes by astrocytic hemichannel-dependent ATP release mechanism. Our data suggest that direct contact between astrocytes and CNS IICs induce ATP-dependent Ca2+ changes in astrocytes and points to the new aspect of cell-cell interactions in propagation of neuroinflammatory response in CNS autoimmunity.