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Objective: It is unclear why activated platelets and platelet-derived microparticles (MPs) accumulate in the blood of patients with systemic sclerosis (SSc). This study was undertaken to investigate whether defective phagocytosis might contribute to MP accumulation in the blood of patients with SSc., Methods: Blood samples were obtained from a total of 81 subjects, including 25 patients with SSc and 26 patients with stable coronary artery disease (CAD). Thirty sex- and age-matched healthy volunteers served as controls. Studies were also conducted in NSG mice, in which the tail vein of the mice was injected with MPs, and samples of the lung parenchyma were obtained for analysis of the pulmonary microvasculature. Tissue samples from human subjects and from mice were assessed by flow cytometry and immunochemical analyses for determination of platelet-neutrophil interactions, phagocytosis, levels and distribution of P-selectin, P-selectin glycoprotein ligand 1 (PSGL-1), and HMGB1 on platelets and MPs, and concentration of byproducts of neutrophil extracellular trap (NET) generation/catabolism., Results: Activated P-selectin+ platelets and platelet-derived HMGB1+ MPs accumulated in the blood of SSc patients but not in the blood of healthy controls. Patients with CAD, a vasculopathy independent of systemic inflammation, had fewer P-selectin+ platelets and a negligible number of MPs. The expression of the receptor for P-selectin, PSGL-1, in neutrophils from SSc patients was significantly decreased, raising the possibility that phagocytes in SSc do not recognize activated platelets, leading to a failure of phagocytosis and continued neutrophil release of MPs. As evidence of this process, activated platelets were not detected in the neutrophils from SSc patients, whereas they were consistently present in the neutrophils from patients with CAD. HMGB1+ MPs elicited generation of NETs, which were only detected in the plasma of SSc patients. In mice, P-selectin-PSGL-1 interaction resulted in platelet phagocytosis in vitro and influenced the ability of MPs to elicit NETs, endothelial activation, and migration of leukocytes through the pulmonary microvasculature., Conclusion: The clearance of activated platelets via PSGL-1 limits the undesirable effects of MP-elicited neutrophil activation. This balance is disrupted in patients with SSc. Its reconstitution might curb vascular inflammation and prevent fibrosis., (© 2021, American College of Rheumatology.)

Endothelial cell damage and platelet activation contribute to sustained vasculopathy, which is a key clinical characteristic of systemic sclerosis (SSc), also known as scleroderma. Microparticles released from activated platelets in the blood of SSc patients (SSc-microparticles) are abundant and express the damage-associated molecular pattern (DAMP) HMGB1. SSc-microparticles interacted with neutrophils in vitro and in immunocompromised mice and promoted neutrophil autophagy, which was characterized by mobilization of their granule content, enhanced proteolytic activity, prolonged survival, and generation of neutrophil extracellular traps (NETs). Neutrophils migrated within the mouse lung, with collagen accumulation in the interstitial space and the release of soluble E-selectin by the vascular endothelium. Microparticle-neutrophil interaction, neutrophil autophagy and survival, and generation of NETs abated in the presence of BoxA, a competitive inhibitor of HMGB1. Consistent with these results, neutrophils in the blood of SSc patients were autophagic and NET by-products were abundant. Our findings implicate neutrophils in SSc vasculopathy and suggest that platelet-derived, microparticle-associated HMGB1 may be a potential indicator of disease and target for novel therapeutics., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The link between platelet activation and vascular injury in Systemic Sclerosis (SSc) is poorly characterized. Here we report that platelet activation results in i) the translocation from the cytoplasm to the surface of HMGB1, a prototypical DAMP signal associated with tissue regeneration and ii) the release of platelet derived microparticles (PDμP) expressing HMGB1. Decreased HMGB1 content (334.6 ± 21.2 vs 587.1 ± 11.1 AUF, P < 0.001) and HMGB1 translocation to the outer leaflet of the plasma membrane (17.8 ± 3.5 vs 4.5 ± 0.5%, P < 0.001) characterize circulating platelets of SSc patients (n = 29) when compared with age-matched healthy controls (HC, n = 20). Conversely, a significantly higher fraction of PDμP in the blood of SSc patients, but not of HC, consistently expose (HMGB1 (MFI 62.8 ± 3.95 vs 4.3 ± 0.7). Platelet HMGB1 depletion is significantly associated in SSc patients with degranulation and with expression of P-selectin and of tissue factor as well as with fibrinogen binding to their plasma membrane. These findings indicate that platelets represent a source of HMGB1, an ancestral signal of necrosis, in the vasculature of SSc patients, possible contributing to persistent microvascular injury and endothelial cell activation.

Objective: Systemic sclerosis (SSc; scleroderma) is characterized by a unique widespread vascular involvement that can lead to severe digital ischemia, pulmonary arterial hypertension (PAH), or other organ dysfunction. Microthrombotic events and procoagulation factors such as anti-beta2-glycoprotein I (anti-beta2GPI) or anticardiolipin antibodies (aCL) may be implicated in the development of these manifestations. This study was undertaken to investigate whether anti-beta2GPI and aCL are correlated with macrovascular disease, including ischemic digital loss and PAH, in SSc patients., Methods: Seventy-five SSc patients with a history of ischemic digital loss and 75 matched SSc controls were evaluated. Anticentromere antibodies (ACAs), anti-beta2GPI, and aCL were measured, and clinical associations were determined using conditional and simple logistic regression models., Results: Positivity for anti-beta2GPI was significantly more frequent in SSc patients with digital loss than in patients without digital loss (P=0.017), with the IgA isotype of anti-beta2GPI showing the strongest association (odds ratio [OR] 4.0). There was no significant difference in aCL frequency between patients with digital loss and control patients. After adjustment for demographic characteristics, disease type, smoking, and ACA, anti-beta2GPI positivity was significantly associated with active digital ischemia (OR 9.4), echocardiographically evident PAH (OR 4.8), and mortality (OR 2.9). ACA positivity was associated with history of digital loss (OR 3.28), but not with PAH or mortality. History of digital loss was strongly associated with increased mortality (OR 12.5)., Conclusion: Anti-beta2GPI is significantly associated with macrovascular disease in SSc and independently predicts mortality. It is unclear whether it has a pathogenetic role or simply reveals the presence of underlying endothelial injury. The use of anti-beta2GPI as a biomarker of vascular disease in SSc should be further explored.