Elevation of lysosomal pH leads to the release of Ca2+, ATP and cytokines from RPE cells

Abstract

The modulation of lysosomal pH can influence the degradation of cellular material delivered through autophagic or phagocytotic pathways. In retinal pigmented epithelial (RPE) cells, lysosomal alkalinization impairs both pathways, while drugs identified to reacidify lysosomes can enhance the clearance of this material. In addition to aiding in degradation, however, lysosomes also serve as a storage site for signaling molecules such as Ca2+, ATP and cytokines. We thus asked whether lysosomal alkalinization led to the release of these compounds in RPE cells. Lysosomal pH was elevated by bafilomycin, chloroquine or the P2X7 receptor agonist BzATP. Cytoplasmic Ca2+ was increased by bafilomycin or chloroquine, but was this rise was lessened by treatment to reacidify lysosomes. Bafilomycin or chloroquine also led to a rapid rise in extracellular levels of ATP, consistent with vesicular release of ATP. While release of cytokine IL‐6 was triggered by bafilomycin or chloroquine, BzATP was more effective than either. IL‐6 release following BzATP stimulation was rapid, sustained, dependent on extracellular Ca2+ and blocked by P2X7R antagonists. In conclusion, elevation of lysosomal pH in RPE cells influences both the degradation of waste material and the release of Ca2+, ATP and cytokines. Whether these release pathways are compromised by chronic elevation of lysosomal pH remains unknown.