Functional Platelet‐derived Mitochondria Induce the Release of Neutrophil Microparticles

Abstract

INTRODUCTIONInflammation is an essential process of the host defense against infections, illness, or tissue injuries. However, unregulated inflammation has been associated with chronic inflammatory auto‐immune diseases, such as rheumatoid arthritis, multiple sclerosis and atherosclerosis. Polymorphonuclear neutrophils (PMNL) are amongst the immune cells involved in the acute inflammatory response used to fight bacterial infections. Once activated, PMNL release inflammatory mediators, enzymes and large quantities of microparticles in the extracellular milieu to recruit various immune cells required to fight the invading pathogens. Recent evidence also shows that platelets (PLTs), well known for their coagulation proprieties, are also implicated in the body’s inflammatory response. Interestingly, activated PLTs can release fully functional mitochondria in the extracellular milieu. Known as the powerhouse of the cell, the mitochondria share similar characteristics with bacteria. Therefore, we hypothesize that PLTs‐derived mitochondria present in the extracellular milieu, acting in a similar way as bacteria, induce a sterile inflammatory response that involves the PMNL.OBJECTIVESThe main objective of this study is to investigate the sterile inflammatory response of PMNL caused by the exposure of PLTs‐derived extracellular mitochondria.METHODSBlood was obtained from healthy consenting donors, then PMNL and PLTs‐derived mitochondria were isolated and purified. Following the co‐incubation of PMNL with various physiological doses of PLTs‐derived mitochondria, a characterization of the interaction between PMNL and PLTs‐derived mitochondria and an investigation of the inflammatory proprieties of PMNL was performed using flow cytometry, confocal microscopy, and high‐resolution respirometry.RESULTSOur data demonstrates that PLTs‐derived mitochondria associate with PMNL as quickly as 2 hours. This results in an increase of the PMNL intracellular calcium content and a 2.47‐fold mitochondrial‐dependent increase in oxygen consumption. Data also shows that PLTs‐derived mitochondria significantly induce, in a dose‐dependent manner, the release of PMNL microparticles.CONCLUSIONSThis study provides a new insight into the role of PLTs‐derived mitochondria in the context of sterile inflammation. Specifically, the characterization of its interaction with PMNL reveals a novel modulator in the fundamental inflammatory response. The knowledge gained from this study provides insight into the mechanism of sterile inflammation in auto‐immune diseases.Support or Funding InformationCanadian Institutes of Health Research, New Brunswick Health Research Foundation, New Brunswick Innovation Foundation