Extracellular Histones Induced Eryptotic Death in Human Erythrocytes

Area of Science:

• Cell Biology
• Immunology
• Toxicology

Background:

• Extracellular histones (EHs) are damage-associated molecular patterns (DAMPs) implicated in diseases like sepsis.
• The mechanism by which EHs affect human erythrocytes (red blood cells) remains unclear.
• This study investigates the hypothesis that EHs induce eryptosis, a form of programmed red blood cell death.

Purpose of the Study:

• To elucidate the mechanistic relationship between extracellular histones and human erythrocyte cytotoxicity.
• To determine if extracellular histones induce eryptosis in red blood cells.
• To identify potential blocking agents for EH-induced eryptosis.

Main Methods:

• Human red blood cells (RBCs) were incubated with EHs or positive controls.
• Flow cytometry was used to assess phosphatidylserine (PS) exposure, cell shrinkage (FSC), intracellular calcium (Ca2+), reactive oxygen species (ROS), and caspase-3 activation.
• Hemolysis and membrane permeabilization were measured via hemoglobin and calcein release, respectively.

Main Results:

• EHs induced hallmarks of eryptosis within 3 hours, including PS exposure, cell shrinkage, increased ROS, Ca2+ influx, and caspase-3 activation.
• No significant hemolysis or membrane permeabilization was observed after 24 hours of EH treatment.
• EH-induced ROS production and PS externalization occurred independently of external Ca2+.
• Heparin and an antibody against Toll-like receptor 2 (TLR2) partially inhibited EH-induced eryptosis.

Conclusions:

• Extracellular histones act as DAMPs that induce rapid eryptosis in human red blood cells.
• Key eryptosis markers manifest within 3 hours in a dose-dependent manner.
• Heparin and anti-TLR2 antibodies demonstrate potential as therapeutic agents to mitigate EH-induced red blood cell death.