P2X₇ receptor stimulation raises lysosomal pH and triggers cytokine release from RPE cells

Abstract

Accumulation of lipofuscin in retinal pigmented epithelial (RPE) cell, results from incomplete degradation of phagocytic and autophagic material by lysosomes. Both increased lipofuscin and enhanced cytokine release are associated with macular degeneration in these cells, although the link between the two is unclear. Since stimulation of the P2X7 receptor (P2X7R) activates IL‐1β release in some cell types, and triggers lysosomal exocytosis in others, we investigated the effect of P2X7R activation on lysosomal pH in, and cytokine release from, RPE cells. Surprisingly, stimulation of the P2X7R with agonist BzATP did not lead to a release of IL‐1β but did trigger release of both IL‐6 and MCP‐1. BzATP led to a rise in intracellular Ca2+, and extracellular Ca2+ was necessary for IL‐6 release. Lysosomal pH was elevated by BzATP and this alkalinization was inhibited by P2X7R antagoinsts A438079 and Brilliant Blue G. BzATP on its own did not significantly increase expression of IL‐6, MCP‐1 or the ectoATPase NTPDase1, but did increase expression of all three genes in cells concurrently exposed to oxidized photoreceptor outer segments. In conclusion, stimulation of the P2X7R on RPE cells elevated lysosomal pH and enhanced cytokine release. P2X7R stimulation also upregulated cytokine gene expression in cells subjected to an oxidative challenge.Grant: EY013434