Inhibition of Chlamydial Infectious Activity due to P2X7R-Dependent Phospholipase D Activation

Abstract

Chlamydia trachomatis survives within host cells by inhibiting fusion between Chlamydia vacuoles and lysosomes. We show here that treatment of infected macrophages with ATP leads to killing of chlamydiae through ligation of the purinergic receptor, P2X(7)R. Chlamydial killing required phospholipase D (PLD) activation, as PLD inhibition led to rescue of chlamydiae in ATP-treated macrophages. However, there was no PLD activation nor chlamydial killing in ATP-treated P2X(7)R-deficient macrophages. P2X(7)R ligation exerts its effects by promoting fusion between Chlamydia vacuoles and lysosomes. P2X(7)R stimulation also resulted in macrophage death, but fusion with lysosomes preceded macrophage death and PLD inhibition did not prevent macrophage death. These results suggest that P2X(7)R ligation leads to PLD activation, which is directly responsible for inhibition of infection.

P2X7 receptors regulate multiple types of membrane trafficking responses and non-classical secretion pathways

“…P2X7R activation has been shown to promote the killing of both mycobacteria [50,57,58] and Chlamydia [59,60] in two ways: enhanced maturation of the microbe-containing phagosomes and enhanced killing of the microbe-infected host cells. The first mechanism involves a P2X7R-mediated activation of phospholipase D that facilitates maturation and fusion of the mycobacteria/ chlamydia-containing phagosomes with lysosomes [50].…”

Lipid metabolism modulation by the P2X7 receptor in the immune system and during the course of infection: new insights into the old view

“…[49]). The activation of PLD by P2X7R has been described in other cell types, including lymphocytes [48], rat parotid acinar cells [36], rat brain-derived type 2 astrocyte cells [33], primary astrocytes and microglia [30,33,35], as well as macrophages [32,34,50]. In primary and macrophage cell lines, PLD has been described as part of an important killing mechanism against Mycobacterium [34] and Chlamydia [50,51], as discussed below.…”

“…Purinergic P2X receptors, especially P2X7R, are broadly distributed throughout immune cell types, such as, lymphocytes, monocytes, macrophages, neutrophils, eosinophils, and dendritic cells [71]. P2X7R plays an important role in various physiological processes in the immune system, some of which include killing pathogens [34,50,72,73], production of reactive oxygen and nitrogen species [74], maturation and release of pro-inflammatory cytokines [17][18][19]75], caspase activation [19,75], T cell maturation [76], pore-formation activity [77], and activation of phospholipases [34,50,51,72,78].…”

“…In certain bacterial infections, such as Mycobacteria and Chlamydia, activated P2X7R has been shown to be capable of controlling the infection [73,78]. Specifically, in Mycobacteria [111,112] and Chlamydia [50,73,113] infections, P2X7R activation mediates inhibition of the infection through fusion of vacuoles with lysosomes, promoting vacuole acidification, a process that requires the activation of host-cell phospholipases [50,113,114]. In macrophages infected with T. gondii, ATP mediates parasite elimination through acidification of the parasitophorous vacuole [115], which suggests a role for PLD in this infection (Fig.…”

POM-1 inhibits P2 receptors and exhibits anti-inflammatory effects in macrophages

“…P2X7R can induce cell death, cytokine release, killing of intracellular pathogens, and membrane blebbing [14][15][16][17]. The specific pathways that lead to each P2X7R-dependent response in immune cells are still poorly understood, as is the link between these functional responses and the change in membrane permeability.…”