Possible involvement of PPARγ in the regulation of basal channel opening of P2X7 receptor in cultured mouse astrocytes

Recently, we demonstrated that cultured mouse astrocytes exhibited basal channel opening of P2X7 receptor (P2X7R) in the absence of any exogenous ligand, but the regulatory mechanism involved was not elucidated. Since our preliminary experiments suggested possible involvement of peroxisome proliferator-activated receptor (PPAR) γ in the regulation, we examined whether PPARγ regulated P2X7R basal channel opening in mouse astrocytes. P2X7R channel opening was assessed as to the uptake of a marker dye, YO-PRO-1 ® (YP), in the presence or absence of agonists and antagonists for PPARγ under a fluorescence microscope. Expression of PPARγ was evaluated by Western blotting and immunocytochemistry. NSAIDs such as flufenamic acid (FFA) and indomethacin, which are a cyclooxygenase inhibitor and a PPARγ agonist, showed enhancing and inhibiting effects on YP uptake at low and high concentrations, respectively, and the enhanced uptake was abolished by periodate-oxidized ATP (oxATP), a selective P2X7R antagonist. The PPARγ agonists 15-deoxy- Δ 12,14-prostaglandin J 2 and ciglitazone decreased the basal and FFA-enhanced YP uptake, while the antagonist GW9662 increased YP uptake, this effect being blocked by the agonists and also by oxATP. PPARγ was distributed in the nucleus and cytosolic/membrane fraction of cultured mouse astrocytes. These findings indicate that basal channel opening of P2X7R in mouse astrocytes is at least in part regulated by PPARγ.