Reversible Inhibition of Chlamydia trachomatis Infection in Epithelial Cells Due to Stimulation of P2X ₄ Receptors

Abstract

Bacterial infections of the mucosal epithelium are a major cause of human disease. The prolonged presence of microbial pathogens stimulates inflammation of the local tissues, which leads to changes in the molecular composition of the extracellular milieu. A well-characterized molecule that is released to the extracellular milieu by stressed or infected cells is extracellular ATP and its ecto-enzymatic degradation products, which function as signaling molecules through ligation of purinergic receptors. There has been little information, however, on the effects of the extracellular metabolites on bacterial growth in inflamed tissues. Millimolar concentrations of ATP have been previously shown to inhibit irreversibly bacterial infection through ligation of P2X 7 receptors. We show here that the proinflammatory mediator, ATP, is released from Chlamydia trachomatis-infected epithelial cells. Moreover, further stimulation of the infected cells with micromolar extracellular ADP or ATP significantly impairs the growth of the bacteria, with a profile characteristic of the involvement of P2X 4 receptors. A specific role for P2X 4 was confirmed using cells overexpressing P2X 4 . The chlamydiae remain viable and return to normal growth kinetics after removal of the extracellular stimulus, similar to responses previously described for persistence of chlamydial infection. Danger signals comprise a varied group of extracellular molecules which indicate a potentially harmful physiological state and for which specific sensory mechanisms exist (38,40,51,55,56). Well-known danger signals include extracellular ATP, adenosine, uric acid crystals, the chromatin component HMGB1, and heat shock proteins. However, the level of danger posed elicits different cellular responses. For example, ATP is released from resting cells (nanomolar range) (5, 37), stressed and dying cells (micromolar range) (23), and physically compromised cells (millimolar range), although actual concentrations depend heavily on cell type and environment. Cells in the adjacent tissue must then decide whether to modify their own behavior in response to the extracellular signal, and whether to amplify the response by secreting other signaling molecules such as cytokines.The cells sense extracellular ATP and other nucleotides and nucleosides via a family of membrane receptors called purinergic receptors. These receptors are subdivided by function and homology into three classes: P2X are ligand-gated ion channels sensitive to ATP, P2Y are G-protein-coupled receptors stimulated by adenine and uracil nucleotides, and P1 receptors are also G protein coupled but are sensitive to adenosine (11,45). The tissue distribution and sensitivity to the ligands vary significantly within each family (12), such that slightly different concentrations of ligand can have different effects at a single cell type, and the same concentration of ligand can have contrasting effects on different cell types.While purinergic receptors have been best characterized in the central nervous system, the...

A1 adenosine receptor signaling reducesStreptococcus pneumoniaeadherence to pulmonary epithelial cells by targeting expression of platelet‐activating factor receptor

“…Similar to other studies, despite differences at the mRNA levels, we could detect protein expression for all four adenosine receptors (Giacomelli et al, 2018). Lung epithelial cells are also known to express P2 purinergic receptors that respond to ADP and/or ATP (Burnstock et al, 2012) and ATP and/or ADP impaired replication of Chlamydia trachomatis in cervical epithelial cells (Pettengill et al, 2012). However, addition of ATP did not alter S. pneumoniae binding to the lung epithelial cells in vitro while AMP significantly decreased bacterial binding.…”

“…We found that consistent with previous studies with A549 cells, a type II pneumocyte cell line (Roman et al, 2006) as well as primary bronchial epithelial cells (Zhong et al, 2006), H292 cells expressed mRNA for A2B, A1, A2A, and A3 in decreasing levels. Lung epithelial cells are also known to express P2 purinergic receptors that respond to ADP and/or ATP (Burnstock et al, 2012) and ATP and/or ADP impaired replication of Chlamydia trachomatis in cervical epithelial cells (Pettengill et al, 2012). Lung epithelial cells are also known to express P2 purinergic receptors that respond to ADP and/or ATP (Burnstock et al, 2012) and ATP and/or ADP impaired replication of Chlamydia trachomatis in cervical epithelial cells (Pettengill et al, 2012).…”

Macrophage P2X4 receptors augment bacterial killing and protect against sepsis

“…Although not the subject of the current study, it is also possible that P2X4Rs can also increase, at least under some circumstances, the killing of obligate intracellular bacteria. In fact, Pettengill et al reported that P2X4Rs augmented the killing of Chlamidia trachomatis (C. trachomatis) in epithelial cells (45). However, based on .…”

Leukotriene B4 Modulates P2X7 Receptor–MediatedLeishmania amazonensisElimination in Murine Macrophages

“…These results suggest a key role for this receptor in the elimination process. Previous studies have shown the ability of infecting pathogens to cause ATP release in a physiological form (22,23). Thus, we measured the ATP release during infection with L. amazonensis at different time points.…”