Burn Injury-Induced Extracellular Vesicle Production and Characteristics

Abstract

Extracellular vesicles (EVs) are nano-sized membrane-bound particles containing biologically active cargo molecules. The production and molecular composition of EVs reflect the physiological state of parent cells, and once released into the circulation, they exert pleiotropic functions via transferring cargo contents. Thus, circulating EVs not only serve as biomarkers, but also mediators in disease processes or injury responses. In the present study, we performed a comprehensive analysis of plasma EVs from burn patients and healthy subjects, characterizing their size distribution, concentration, temporal changes, cell origins, and cargo protein contents. Our results indicated that burn injury induced a significant increase in circulating EVs, the response peaked at the time of admission and declined over the course of recovery. Importantly, EV production correlated with injury severity, as indicated by the total body surface area and depth of burn, requirement for critical care/ICU stay, hospitalization length, wound infection, and concurrence of sepsis. Burn patients with inhalation injury showed a higher level of EVs than those without inhalation injury. We also evaluated patient demographics (age and sex) and pre-existing conditions (hypertension, obesity, and smoking) and found no significant correlation between these conditions and overall EV production. At the molecular level, flow cytometric analysis showed that the burn-induced EVs were largely derived from leukocytes and endothelial cells (ECs), which are known to be activated postburn. Additionally, a high level of zona-occludens-1 (ZO-1), a major constituent of tight junctions, was identified in burn EV cargos, indicative of injury in tissues that form barriers via tight junctions. Moreover, when applied to endothelial cell monolayers, burn EVs caused significant barrier dysfunction, characterized by decreased transcellular barrier resistance and disrupted cell–cell junction continuity. Taken together, these data suggest that burn injury promotes the production of EVs containing unique cargo proteins in a time-dependent manner; the response correlates with injury severity and worsened clinical outcomes. Functionally, burn EVs serve as a potent mediator capable of reducing endothelial barrier resistance and impairing junction integrity, a pathophysiological process underlying burn-associated tissue dysfunction. Thus, further in-depth characterization of circulating EVs will contribute to the development of new prognostic tools or therapeutic targets for advanced burn care.

Extracellular Vesicles as Regulators of Immune Function in Traumatic Injuries and Sepsis

“…We and others have found that circulating EV levels change after burn injury and participate in burn pathology. After a severe burn injury, there are increased numbers of circulating plasma EVs ( 6 , 15 , 16 ). Furthermore, there is a positive correlation between the level of circulating EVs and severity of burn injury, with increased EV concentrations corresponding to increases in percentage of total body surface area burn, and these concentrations correlate with postburn sepsis, wound infection, and admission to intensive care units ( 15 , 16 ).…”

“…After a severe burn injury, there are increased numbers of circulating plasma EVs ( 6 , 15 , 16 ). Furthermore, there is a positive correlation between the level of circulating EVs and severity of burn injury, with increased EV concentrations corresponding to increases in percentage of total body surface area burn, and these concentrations correlate with postburn sepsis, wound infection, and admission to intensive care units ( 15 , 16 ). Inhalation injury due to smoke or chemical fume inhalation often occurs at the time of burn injury and increases morbidity and mortality for patients ( 14 ).…”

“…Inhalation injury due to smoke or chemical fume inhalation often occurs at the time of burn injury and increases morbidity and mortality for patients ( 14 ). Patients with a combined burn and inhalation injury were found to have a substantially higher number of circulating EVs ( 16 ). Thus, plasma EV numbers are increased after burn injury and can predict disease course and severity.…”

“…In addition to immune responses, EVs promote burn-induced endothelial barrier dysfunction. Extracellular vesicles isolated after burn impaired the barrier function of endothelial cells as measured by a transendothelial electrical resistance assay ( 16 ). Based on these studies, the alterations in the cargo of EVs could be an adjuvant or a driver of pathologic responses after severe burn injury.…”

“…In severe burn injury, both plasma EV contents and concentrations could serve as predictive markers. After severe burn injury, EV concentrations were positively correlated with burn size ( 12 , 16 ). liquid chromatography tandem mass spectrometry proteomic assessment of plasma EVs from 50 burn patients found increased levels of both serum amyloid A1 (SAA1) and CRP in EVs 72 hours after injury, which correlated with length of hospital stay in females ( 12 ).…”