Inhibition of P2X Receptors Protects Human Monocytes against Damage by Leukotoxin from Aggregatibacter actinomycetemcomitans and α-Hemolysin from Escherichia coli

• Published in: Infection and immunity Vol. 84; no. 11; pp. 3114 - 3130
• Main Authors: Fagerberg, Steen K, Jakobsen, Martin R, Skals, Marianne, Praetorius, Helle A
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.11.2016
• Subjects: Aggregatibacter actinomycetemcomitans - metabolism; Bacterial Toxins - metabolism; Bacterial Toxins - toxicity; Cell Death - drug effects; Cellular Microbiology: Pathogen-Host Cell Molecular Interactions; Cytoplasm - metabolism; Cytotoxins - metabolism; Erythrocytes - metabolism; Escherichia coli; Escherichia coli - metabolism; Escherichia coli Proteins - metabolism; Escherichia coli Proteins - toxicity; Exotoxins - metabolism; Exotoxins - toxicity; Hemolysin Proteins - metabolism; Hemolysin Proteins - toxicity; Hemolysis - physiology; Humans; Monocytes - drug effects; Monocytes - metabolism; Receptors, Purinergic P2X - physiology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00674-16

α-Hemolysin (HlyA) from Escherichia coli and leukotoxin A (LtxA) from Aggregatibacter actinomycetemcomitans are important virulence factors in ascending urinary tract infections and aggressive periodontitis, respectively. The extracellular signaling molecule ATP is released immediately after insertion of the toxins into plasma membranes and, via P2X receptors, is essential for the erythrocyte damage inflicted by these toxins. Moreover, ATP signaling is required for the ensuing recognition and phagocytosis of damaged erythrocytes by the monocytic cell line THP-1. Here, we investigate how these toxins affect THP-1 monocyte function. We demonstrate that both toxins trigger early ATP release and a following increase in the intracellular Ca concentration ([Ca ] ) in THP-1 monocytes. The HlyA- and LtxA-induced [Ca ] response is diminished by the P2 receptor antagonist in a pattern that fits the functional P2 receptor expression in these cells. Both toxins are capable of lysing THP-1 cells, with LtxA being more aggressive. Either desensitization or blockage of P2X , P2X , or P2X receptors markedly reduces toxin-induced cytolysis. This pattern is paralleled in freshly isolated human monocytes from healthy volunteers. Interestingly, only a minor fraction of the toxin-damaged THP-1 monocytes eventually lyse. P2X receptor inhibition generally prevents cell damage, except from a distinct cell shrinkage that prevails in response to the toxins. Moreover, we find that preexposure to HlyA preserves the capacity of THP-1 monocytes to phagocytose damaged erythrocytes and may induce readiness to discriminate between damaged and healthy erythrocytes. These findings suggest a new pharmacological target for protecting monocytes during exposure to pore-forming cytolysins during infection or injury.