IL-1 b differentially regulates calcium wave propagation between primary human fetal astrocytes via pathways involving P2 receptors and gap junction channels

In mammalian astrocytes, calcium waves are transmitted between cells via both a gap junction-mediated pathway and an extracellular, P2 receptor-mediated pathway, which link the cells into a syncytium. Calcium waves in astrocytes have also been shown to evoke calcium transients in neurons, and activity in neurons can elicit calcium waves in astrocytes. In this study, we show that in primary human fetal astrocytes, the P2 receptor-mediated and gap junction-mediated pathways are differentially regulated by the cytokine IL-1 b . Confocal microscopy of astrocytes loaded with Indo-1 demonstrated that intercellular calcium wave transmission in IL-1 b -treated cultures was potentiated compared with controls. However, transmission of calcium waves via the gap junction-mediated pathway was strikingly reduced. The major component of functional gap junctions in human fetal astrocytes was demonstrated to be connexin43 (Cx43), and there was a marked reduction of junctional conductance, loss of dye coupling, loss of Cx43 protein, and down-regulation of Cx43 mRNA expression after IL-1 b treatment of cultures. Con-versely, transmission of calcium waves via the P2 receptor-mediated pathway was potentiated in IL-1 b -treated cultures compared with controls. This potentiation was associated with an increase in the number our results demonstrate that the potentiation of calcium wave transmission induced by IL-1 b is accompanied by an increase in mRNA expression of at least one P2Y receptor. In this context, we have noted with interest the recent observation that in the mouse macrophage cell line J774, binding of UTP to pyrimidinoceptors potentiates the activation of the induc-ible form of nitric oxide synthase (36). We suggest that the selective potentiation of pathways activated by specific nucleotides may alter the repertoire of responses that the cell can make to changes in the extracellular environment. Because a number of studies have also demonstrated interaction of glia and neuronal circuits, modulation of the ability of astrocytes to respond to changes in the extracellular environment may in turn alter the data transmitted from such glial networks to neuronal circuits in the CNS. In the normal CNS, ATP is a neurotransmitter and as such its release and breakdown in the extracellular space is tightly regulated. Similarly, IL-1 is expressed at very low levels in the normal CNS but can be readily detected in a number of different inflammatory and degenerative conditions. For example, in tissues from patients with multiple sclerosis, a strong signal for IL-1 is detected in both acute and chronic-active lesions, with particularly prominent expression at the lesion edge (37). In Alzheimer’s disease, IL-1 b is expressed by activated microglial cells associated with senile plaques (38). In HIV, associated encephalitis immunoreactivity for IL-1 b co-localizes with HIV to microglial nodules (39), and in stroke, IL-1 b is expressed in the ischemic tissue (17). These studies indicate that IL-1 b is both by resident glia and macrophages early in the of a number of pathological and animal models have also for IL-1 in in many of these Although there has been debate surrounding the relative contribution of the two pathways to calcium wave transmission between mammalian cells, our data indicate that in primary human astrocytes, a single proinflammatory stimulus differentially regulates wave trans- mission via the P2 receptor-mediated pathway versus the gap junction-mediated pathway. Because in inflammatory condi- tions of the human CNS IL-1 b is produced both by resident glia and by invading cells of the immune system, our data would suggest that inflammatory events may have significant effects on the coordination of astrocytic function and on information processing in the human CNS.