Abstract
Myeloperoxidase (MPO), an oxidant-producing enzyme, stored in azurophilic granules of neutrophils has been recently shown to influence red blood cell (RBC) deformability leading to abnormalities in blood microcirculation. Native MPO is a homodimer, consisting of two identical protomers (monomeric MPO) connected by a single disulfide bond but in inflammatory foci as a result of disulfide cleavage monomeric MPO (hemi-MPO) can also be produced. This study investigated if two MPO isoforms have distinct effects on biophysical properties of RBCs. We have found that hemi-MPO, as well as the dimeric form, bind to the glycophorins A/B and band 3protein on RBC's plasma membrane, that lead to reduced cell resistance to osmotic and acidic hemolysis, reduction in cell elasticity, significant changes in cell volume, morphology, and the conductance of RBC plasma membrane ion channels. Furthermore, we have shown for the first time that both dimeric and hemi-MPO lead to phosphatidylserine (PS) exposure on the outer leaflet of RBC membrane. However, the effects of hemi-MPO on the structural and functional properties of RBCs were lower compared to those of dimeric MPO. These findings suggest that the ability of MPO protein to influence RBC's biophysical properties depends on its conformation (dimeric or monomeric isoform). It is intriguing to speculate that hemi-MPO appearance in blood during inflammation can serve as a regulatory mechanism addressed to reduce abnormalities on RBC response, induced by dimeric MPO.
Highlights
Myeloperoxidase (MPO) is a cationic protein, which is most abundantly expressed in azurophilic granules of neutrophils (2–5% of the total cellular protein)
We have shown that hemi-MPO, as well as the dimeric form, bind to the glycophorins A/B and band 3 protein on red blood cell (RBC)’s plasma membrane, that led to changes in transmembrane potential, RBC morphology, reduced RBC deformability and reduced resistance to hemolysis
To check if hemi-MPO binds to the same targets on RBC surface, RBC ghosts (RBCGs) proteins were separated by SDS-PAGE
Summary
Myeloperoxidase (MPO) is a cationic protein, which is most abundantly expressed in azurophilic granules of neutrophils (2–5% of the total cellular protein). It is a heme-containing glycosylated oxidoreductase, which in addition to its peroxidase activity, catalyzes the production of (pseudo)hypohalous acids (halogenating activity), mainly hypochlorous (HOCl), hypothiocyanous (HOSCN) and hypobromous (HOBr) acids [1,2,3,4]. Being strong oxidants and halogenating agents, hypohalous acids interact with many biologically important molecules: nucleic acids, proteins, lipids, carbohydrates, etc. Excessive production of reactive halogen-containing compounds (reactive halogen species) can lead to host cell and tissue damage, initiating the development of oxidative/halogenative stress and triggering a number of diseases associated with inlammation [6,7,8]
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