Effect of peptidoglycans on erythrocyte survival

Peptidoglycans (PGNs) from bacterial cell walls belong to 'pathogen-associated molecular patterns' (PAMP), which modify the course of an infection with bacterial pathogens. Bacterial infections may lead to anaemia, which at least partially could result from accelerated erythrocyte death. The present study explored the effect of PGNs on eryptosis, a stress-induced suicidal death of erythrocytes, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptotic cells are phagocytosed and thus rapidly cleared from circulating blood. Eryptosis is triggered by an increase in the cytosolic Ca(2+) concentration and by formation of ceramide. Erythrocyte Ca(2+) activity was estimated from Fluo3 fluorescence, ceramide formation by fluorescent antibodies, phosphatidylserine exposure from annexin V-binding, and erythrocyte volume from forward scatter in fluorescence activated cell sorting (FACS) analysis. Exposure of erythrocytes to PGNs increased cytosolic Ca(2+) concentration, increased ceramide formation, enhanced the percentage of annexin V-binding erythrocytes, decreased erythrocyte forward scatter, and lowered the intracellular ATP concentration. The effect of peptidoglycans was significantly blunted in the absence of extracellular Ca(2+). The clearance of erythrocytes exposed to PGNs was significantly enhanced in vivo. In conclusion, peptidoglycans induce eryptosis at least partially through an increase in the cytosolic Ca(2+) concentration, an effect presumably contributing to the development of anaemia during bacterial infections.