The cytokine IL-1beta modulates calcium signaling in human fetal astrocytes
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Inflammation is a causative or contributory process in a spectrum of central nervous system (CNS) disorders, from acute events like trauma to chronic conditions like multiple sclerosis (MS). Astrocytes and microglia are major contributors to the CNS inflammatory process, and astrocytes are particularly important immune effectors. The goal of this thesis was to examine the effect of inflammation upon calcium signaling components in human astrocytes.;We hypothesized that the inflammatory cytokine IL-1beta would modulate expression and function of P2X7 in human fetal astrocytes. Intracellular calcium imaging measurements demonstrated that resting astrocytes responded to the selective P2X agonist Benzoyl-benzoyl ATP (BzATP) with a slight increase in intracellular calcium. However, in IL-1beta treated astrocytes BzATP induced a robust rise in intracellular calcium, abolished by removal of extracellular calcium, application of an inhibitory P2X7 monoclonal antibody, or preincubation with the P2X7 selective antagonist, KN-62. Untreated astrocytes were relatively impermeable, whereas IL-1beta treated cells readily took up the dye, indicative of functional P2X7 membrane pores. Thus IL-1beta controls astrocytic expression of P2X7 receptors, suggesting a change in the functionality of this receptor at sites of CNS inflammation.;Elevation of cytosolic calcium results either from extracellular influx, or intracellular release from the endoplasmic reticulum (ER). Once emptied, ER stores are replenished through the activation of sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA) pumps. It is thought that, upon store depletion, members of the mammalian transient receptor potential (TRP) family mediate capacitative calcium entry (CCE) across the plasma membrane, functioning as store-operated channels (SOC). The TRPC subfamily has been the most intensely studied in the search for SOC's. Seven mammalian genes, TRPC 1--7 are currently known. Given the described changes in astrocytic calcium signaling, we hypothesized that IL-1beta would also modulate CCE in these cells. We have characterized SOC mediated calcium entry in astrocytes using the SERCA inhibitor thapsigargin. SOC activity presents as prolonged elevation of intracellular calcium after thapsigargin treatment, attenuated by removal of extracellular calcium or treatment with an SOC inhibitor, 2-aminoethoxydiphenylborane (2-APB). IL-1beta treatment dramatically increased both the rate and magnitude of astrocytic calcium influx, in a 2-APB sensitive manner. (Abstract shortened by UMI.).
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