SESSION TITLE: Biomarkers in Severe Sepsis and Septic Shock
SESSION TYPE: Original Investigation Slide
PRESENTED ON: Wednesday, October 28, 2015 at 02:45 PM - 04:15 PM
PURPOSE: Annexin A2 (A2) is a calcium-dependent, functionally diverse protein that exists in both soluble cytosolic and phospholipid-bound forms. On the endothelial surface, A2 forms a heterotetramer with S100A10 and serves as the co-receptor for tissue plasminogen activator (tPA) and plasminogen, facilitating plasmin generation, and mitigating fibrin deposition on the vascular surface. In sepsis, fibrin deposition coincides with increased systemic inflammation and immune dysregulation. Our preliminary data show markedly decreased cell surface tPA-dependent fibrinolytic activity of human peripheral blood mononuclear cells (PBMCs) isolated from septic patients. Thus, we sought to understand the regulation and clinical relevance of A2 in human sepsis.
METHODS: Whole blood from healthy volunteers and patients in the medical intensive care unit with a confirmed or suspected diagnosis of sepsis was collected within twenty-four hours of diagnosis. PBMCs were isolated with Ficoll-Paque density gradient centrifugation, their cell lysates were prepared and resolved via sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and transferred to polyvinylidene difluoride membranes. A2 was probed with various antibodies recognizing specific epitopes.
RESULTS: Immunoblot analysis revealed that total A2 was reduced in PBMC cell lysates of septic patients in comparison to those of healthy controls. Lower levels of A2 correlate with increased sepsis severity. There was no significant decrease in A2-encoding mRNA as assessed by quantitative polymerase chain reaction. By utilizing a monoclonal antibody directed against a carboxy-terminal epitope of A2, we observed multiple lower molecular weight bands in septic PBMC samples, suggesting that A2 is proteolyzed in septic PBMCs. Furthermore, an identical pattern of proteolytic A2 fragments was observed after incubating purified recombinant A2 with septic mononuclear cell lysate, but not lysates of PBMCs from healthy donors.
CONCLUSIONS: These results demonstrate that A2 is proteolyzed in PBMCs from septic subjects, correlating with observed reductions in tPA-dependent cell surface fibrinolytic activity. Loss of cellular A2 may represent an adaptive response to systemic inflammation and immune dysregulation, which characterize sepsis syndromes.
CLINICAL IMPLICATIONS: Annexin A2 may serve an important role in the interaction between inflammation and coagulation in sepsis. Understanding the pathophysiologic role of A2 in sepsis could help identify novel therapies.
DISCLOSURE: The following authors have nothing to disclose: Frances West, Julio Lanfranco, Huigen Chen, Dena Almeida, David Berlin, Katherine Hajjar
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