Retinal microglial cells increase expression and release of IL-1β when exposed to ATP

Abstract

AbstractCytokine IL-1β is an early component of inflammatory cascades, with both priming and activation steps required before IL-1β release. Here, the P2X7 receptor (P2X7R) for ATP was shown to both prime and release IL-1β from retinal microglial cells. Isolated retinal microglial cells increased expression ofIl1bwhen stimulated with endogenous receptor agonist extracellular ATP; ATP also rapidly downregulated expression of microglial markersTmem119andCd206.Changes to all three genes were reduced by specific P2X7R antagonist A839977, implicating the P2X7R. Microglial cells expressed the P2X7R on ramifications and responded to receptor agonist BzATP with robust and rapid rises in intracellular Ca2+. BzATP increased expression of IL-1β protein colocalizing with CX3CR1-GFP in retinal wholemounts consistent with microglial cells. ATP also triggered release of IL-1β from isolated retinal microglia into the bath; release was inhibited by A839977 and induced by BzATP, supporting a role for the P2X7R in release as well as priming. The IL-1β release triggered by ATP was substantially greater from microglial cells compared to astrocytes from the optic nerve head region.Il1bexpression was increased by a transient rise in intraocular pressure andIl1blevels remained elevated 10 days after a single IOP elevation. In summary, this study suggests the P2X7 receptor can both prime IL-1β levels in microglial cells and trigger its release. The P2Y12R was previously identified as a chemoattractant for retinal microglia, suggesting the recruitment of the cells towards the source of released extracellular ATP could position microglia for P2X7R receptor, enabling both priming and release of IL-1β.