Abstract
The pore-forming exotoxin α-hemolysin from E. coli causes a significant volume reduction of human erythrocytes that precedes the ultimate swelling and lysis. This shrinkage results from activation of Ca2+-sensitive K+ (KCa3.1) and Cl− channels (TMEM16A) and reduced functions of either of these channels potentiate the HlyA-induced hemolysis. This means that Ca2+-dependent activation of KCa3.1 and TMEM16A protects the cells against early hemolysis. Simultaneous to the HlyA-induced shrinkage, the erythrocytes show increased exposure of phosphatidylserine (PS) in the outer plasma membrane leaflet, which is known to be a keen trigger for phagocytosis. We hypothesize that exposure to HlyA elicits removal of the damaged erythrocytes by phagocytic cells. Cultured THP-1 cells as a model for erythrocytal phagocytosis was verified by a variety of methods, including live cell imaging. We consistently found the HlyA to very potently trigger phagocytosis of erythrocytes by THP-1 cells. The HlyA-induced phagocytosis was prevented by inhibition of KCa3.1, which is known to reduce PS-exposure in human erythrocytes subjected to both ionomycin and HlyA. Moreover, we show that P2X receptor inhibition, which prevents the cell damages caused by HlyA, also reduced that HlyA-induced PS-exposure and phagocytosis. Based on these results, we propose that erythrocytes, damaged by HlyA-insertion, are effectively cleared from the blood stream. This mechanism will potentially reduce the risk of intravascular hemolysis.
Highlights
The limited lifespan of mammalian erythrocytes indirectly results from the lack of nuclei in this cell type
Our first question was whether the erythrocytes are phagocytosed or if they just stay attached to the plasma membrane of Tamm-Horsefall protein 1 (THP-1) cells
We generated z-stacks from a plane where the erythrocyte was in focus and this plane was used as the reference plane for both the fluorescence and z-stacks of transmitted light images in differential interference contrast (DIC)
Summary
The limited lifespan of mammalian erythrocytes indirectly results from the lack of nuclei in this cell type. Erythrocytes have an innate inability to renew cellular proteins, and maintain a normal cell homeostasis on a long-term basis. Another consequence of the absence of nuclei is that they cannot undergo regular apoptosis and, the normal pathway of clearing old or damaged cells does not immediately apply for mammalian erythrocytes. The toxin inflicts distinct biphasic volume changes, where the volume increase that leads to lysis is preceded by marked erythrocyte shrinkage. This shrinkage is triggered by the influx of Ca2+, which happens very quickly after insertion of HlyA into the membrane.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
