Presentation Details
| IL-6-Induced Potentiation of Platelet Activity and Glycosylation in Venous Thromboembolism Michelle K.Brenner1, Karin Hoffmeister2, Brian Branchford1. 1Pediatric Hematology/Oncology/Bone Marrow Transplant, Children’s Wisconsin and Medical College of Wisconsin, Milwaukee, WI, USA.2Translational Glycomics Center, Versiti Blood Research Institute, Milwaukee, WI, USA |
Abstract
Background: Venous thromboembolism (VTE), comprising deep vein thrombosis (DVT) and pulmonary embolism (PE), affects nearly 1 of every 100 hospitalized children in the US each year and is associated with both increased mortality (up to 2%) and morbidity. While development of VTE is multifactorial, emerging data indicate that inflammatory cytokines, such as IL-6, contribute significantly to thrombosis. Thromboinflammation, the interplay of thrombosis and inflammation, causes profound alterations in vascular homeostasis. It is known that thromboinflammation leads to pathologic platelet activation and increased recruitment of immune cells in the vasculature. The full extent of platelets in inflammatory-driven VTE, however, has yet to be fully elucidated. It is well known that post-translational modification (such as glycosylation) of surface adhesion receptors affects platelet activity, localization, and adhesion. The investigation of thromboinflammation-associated glycan alterations on platelets themselves, and their role in VTE development has not been previously studied, thus representing a novel approach to exploring the mechanistic underpinnings of this pathologic event. IL-6 is a cytokine synthesized in response to inflammation, such as trauma, malignancy, or infection. IL-6 signaling requires formation of a 3-part complex including IL-6, one of two types of IL-6 receptor (membrane-bound for classical signaling or soluble for trans-signaling), and the receptor gp130 that is expressed on all cells and acts as the signal transducer. Platelets can release soluble IL-6 receptor from their granules and use IL-6 for trans-signaling. Prior data have demonstrated that stimulation of platelet rich plasma (PRP) with physiologic concentrations of IL-6 enhances agonist-induced platelet aggregation and secretion. Objective: We hypothesized that platelet activation, in the presence of IL-6, leads to specific glycoprotein changes that result in hyperreactivity, heightening the risk of pathologic thrombosis. Methods: Platelets were isolated from platelet-rich plasma, which was derived by differential centrifugation of whole blood from healthy human donors and incubated with various concentrations of human recombinant IL-6 ranging from doses comparable to patients receiving IL-6 immunotherapy (lower dose) up to those with meningococcal septic shock (higher dose). Agonist-induced platelet granule release and integrin activation, as well aggregation responses were then assessed with flow cytometry and light transmission aggregometry, respectively. Glycan changes were assessed via flow cytometry. Results: IL-6 alone does not stimulate platelet aggregation or activation. In PRP, addition of lower dose IL-6 inhibits platelet aggregation in response to collagen and TRAP (thrombin receptor activated peptide), but there is no difference with the addition of higher dose IL-6. In isolated platelets, higher dose IL-6 may increase platelet aggregation and activation with certain platelet agonists. Finally, addition of IL-6 to washed platelets induces changes in O-glycosylation both with and without platelet agonists and induces Neuraminidase-1 exposure on platelet surfaces, indicative of sialic acid loss (Figure 1). Conclusions: IL-6 modulates activation and aggregation of platelets in the presence of additional agonists. The increased presence of Neuraminidase-1 on platelets incubated with IL-6 may demonstrate desialyation of platelets that impact the role of platelets in thromboinflammation. Future studies will investigate the action of neuraminidase inhibitors, such as oseltamivir, on this process.
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