LAUSR

Background Persistent oxidative stress and unrelenting vascular inflammation are hallmarks of Systemic Sclerosis (SSc). Platelet-derived microparticles (PD-uP) that express a bioactive redox-dependent moiety, HMGB1 accumulate in the peripheral blood of patients with SSc. Objectives To verify whether PD-uP might represent a biomarker of SSc clinical involvement and whether their biological actions is regulated by environmental redox. Methods Fifty-four patients with SSc were enrolled so far. Twenty healthy controls (HC) matched for sex and age were studied in parallel. PD-uP were characterized and quantified by flow cytometry. Leukocyte features, including expression and distribution of myeloperoxidase (MPO), were assessed by flow cytometry and confocal microscopy. PD-uP ability to regulate neutrophil activation and proteolytic action was assessed in vitro in defined redox conditions and in vivo upon intravenous (i.v.) injection in immunocompromised NSG mice, and traced at various times based on recognition of the human platelet antigen CD61. Action on fibroblasts derived from SSc patients and HC are being assessed using biochemical and functional assays. Results PD-uP are present in the blood of SSc patients. Their concentration is significantly higher than in the blood of HC (p<0.0001). A substantially higher fraction of SSc PD-uP express the prototypic DAMP, HMGB1 (70% SSc vs 5% HC). Among SSc patients, those with pulmonary hypertension had a significantly higher concentration of HMGB1+ PDuP (p=0.002). In contrast other disease-associated variables, including the extent of fibrosis and the presence of active SSc pattern at the NVC, were not apparently influent. Neutrophils of SSc patients were activated, as demonstrated by the MPO redistribution from the primary granules to the plasma membrane. Moreover, they had a substantially higher ability to degrade fibrin in vitro, suggesting that enzymes at the plasma membrane are bioactive. Circulating neutrophils appeared to be viable and the fraction of cells undergoing apoptosis was similar in SSc patients and HC. The extent of neutrophil activation was associated with the concentration of HMGB1+ PDuP (p<0.001). SSc PDuP but not HC PDuP induced MPO redistribution in vitro. The effect was dependent on HMGB1 and increased by oxidizing moieties. Injection in immunocompromised mice resulted in time-dependent association of SSc PDuP to mouse neutrophils, which contextually redistributed MPO at the plasma membrane. Conclusions HMGB1 expression on PD-up of SSc patients could help identify functionally relevant population of microparticles, involved in neutrophil activation/function and possibly valuable as a novel biomarker of vascular remodeling. References Sabbadini MG et al, Lupus, 1999. Filippi et al., Lancet Neurol 2013. Rocca MA et al., Brain Struct Funct, 2016. Disclosure of Interest None declared