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Claire H. Mitchell, Sonia Guha, Jason C. Lim, Alan M. Laties; Autophagy and Cytokine Release from RPE Cells. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3703.
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Cytokines can be released through a variety of mechanisms. In addition to the classical release pathways, recent evidence suggests a role for autophagy in cytokine release. As autophagy may be perturbed in aging RPE cells, this could alter the signaling dependent release of cytokines. Release of IL-6 may be particularly important in this regard as it may impact macrophage activity. This study probes the relationship between autophagy, lysosomal pH and IL-6 release from RPE cells.
IL-6 release from fresh mouse RPE and ARPE-19 cells was measured with Elisa assays. Ca2+ was determined using Fura-2 and lysosomal pH using Lysosensor Yellow/Blue.
Fresh and cultured RPE cells released baseline levels of the cytokine IL-6. The vHATPase inhibitor bafilomycin reduced baseline secretion of IL-6 from RPE cells. Tamoxifen, which like bafilomycin can raise lysosomal pH, also reduced secretion of IL-6, suggesting that lysosomal alkalinization can decrease cytokine release. The P2X7 receptor agonist BzATP also raised lysosomal pH and increased LC3BII levels, consistent with impaired autophagy. In contrast, however, it triggered an increased release of IL-6 release from cultured and fresh mouse RPE. This BzATP-stimulated release was even greater for ABCA4-/-mice than control. BzATP also raised intracellular Ca2+; the ability to simultaneously raise Ca2+ may be critical in triggering the cytokine release as the release of IL-6 by BzATP was prevented by the removal of extracellular Ca2+.
The interplay between autophagy and cytokine release is complex. While decreased autophagy levels and/or elevated lysosomal pH can decrease secretion of IL-6, simultaneously raising intracellular Ca2+ leads to a net rise in IL-6 release. The increased release of IL-6 in ABCA4-/- mice suggests the process may contribute to the pathology in AMD.
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