P2X7 receptor-mediated phosphatidic acid production delays ATP-induced pore opening and cytolysis of RAW 264.7 macrophages

Abstract

In macrophages, extracellular ATP (ATPe) stimulation of P2X7 receptors (P2X7R) results in cation channel opening, non-specific pore formation, secretion of cytokines, killing of intracellular bacteria and cytolysis. Signaling pathways controlling these diverse responses are currently under investigation. Among these pathways, phospholipase D (PLD) has been implicated in P2X7R-activated macrophages killing of intracellular pathogenic bacteria. Here we present evidence that early P2X7R-mediated PLD activation reduces pore opening and delays cytolysis of RAW 267.4 macrophages induced by ATPe. Use of inhibitors of PA metabolic enzymes suggests that PA, and not one of its metabolites, is the bioactive lipid. This is strengthened by the observation that addition of exogenous PA also reduces pore formation and cytolysis of RAW 264.7 macrophages. However, the beneficial effects of PA are only transient, due to its conversion into diacylglycerol through PA phosphatase-1 activity during prolonged P2X7R stimulation. Revealing that the PLD/PA pathway mediates survival of macrophages provides a potent strategy to inhibit P2X7R-mediated cytolysis by controlling PA metabolism. This will be important in the case of P2X7R-induced killing of intracellular bacteria which is lately associated with macrophage death, limiting the potency of ATPe to eliminate pathogenic bacteria.