Contribution of TRPV1 to microglia-derived IL-6 and NFκB translocation with elevated hydrostatic pressure

PURPOSE. The authors investigated the contributions of the transient receptor potential vanilloid-1 receptor (TRPV1) and Ca2+ to microglial IL-6 and nuclear factor kappa B (NF kappa B) translocation with elevated hydrostatic pressure. METHODS. The authors first examined IL-6 colocalization with the microglia marker Iba-1 in the DBA/2 mouse model of glaucoma to establish relevance. They isolated microglia from rat retina and maintained them at ambient or elevated (+ 70 mm Hg) hydrostatic pressure in vitro and used ELISA and immunocytochemistry to measure changes in the IL-6 concentration and NF kappa B translocation induced by the Ca2+ chelator EGTA, the broad-spectrum Ca2+ channel inhibitor ruthenium red, and the TRPV1 antagonist iodo-resiniferatoxin (I-RTX). They applied the Ca2+ dye Fluo-4 AM to measure changes in intracellular Ca2+ at elevated pressure induced by I-RTX and confirmed TRPV1 expression in microglia using PCR and immunocytochemistry. RESULTS. In DBA/2 retina, elevated intraocular pressure increased microglial IL-6 in the ganglion cell layer. Elevated hydrostatic pressure (24 hours) increased microglial IL-6 release, cytosolic NF kappa B, and NF kappa B translocation in vitro. These effects were reduced substantially by EGTA and ruthenium red. Antagonism of TRPV1 in microglia partially inhibited pressure-induced increases in IL-6 release and NF kappa B translocation. Brief elevated pressure (1 hour) induced a significant increase in microglial intracellular Ca2+ that was partially attenuated by TRPV1 antagonism. CONCLUSIONS. Elevated pressure induces an influx of extracellular Ca2+ in retinal microglia that precedes the activation of NF kappa B and the subsequent production and release of IL-6 and is at least partially dependent on the activation of TRPV1 and other ruthenium red-sensitive channels.