The cytokine IL-1β transiently enhances P2X₇ receptor expression and function in human astrocytes

Extracellular nucleotide di- and triphosphates such as ATP and ADP mediate their effects through purinergic P2 receptors belonging to either the metabotropic P2Y or the ionotropic P2X receptor family. The P2X₇R is a unique member of the P2X family, which forms a pore in response to ligand stimulation, regulating cell permeability, cytokine release, and/or apoptosis. This receptor is also unique in that its affinity for the ligand benzoyl-benzoyl ATP (BzATP) is at least 10-fold greater than that of ATP. Primary human fetal astrocytes in culture express low-levels of P2X₇R mRNA and protein, and BzATP induces only a slight influx in intracellular calcium [Ca ²⁺]_i, with little demonstrable effect on gene expression or pore formation in these cells. We now show that, following treatment with the proinflammatory cytokine IL-1β, BzATP induces a robust rise in [Ca ²⁺]_i with agonist and antagonist profiles indicative of the P2X₇R. IL-1β also induced the formation of membrane pores as evidenced by the uptake of YO-PRO-1 (375 Da). Quantitative real-time PCR demonstrated transient upregulation of P2X₇R mRNA in IL-1β-treated cells, while FACS analysis indicated a similar upregulation of P2X₇R protein at the cell membrane. In multiple sclerosis lesions, immunoreactivity for the P2X₇R was demonstrated on reactive astrocytes in autopsy brain tissues. In turn, P2X₇R stimulation increased the production of IL-1-induced nitric oxide synthase activity by astrocytes in culture. These studies suggest that signaling via the P2X ₇R may modulate the astrocytic response to inflammation in the human central nervous system.