Activated Platelets Induce Endothelial Cell Activation via an Interleukin-1β Pathway in Systemic Lupus Erythematosus

Autoimmune diseases and atherosclerotic cardiovascular disease

Autoimmune diseases are associated with a dramatically increased risk of atherosclerotic cardiovascular disease and its clinical manifestations. The increased risk is consistent with the notion that atherogenesis is modulated by both protective and disease-promoting immune mechanisms. Notably, traditional cardiovascular risk factors such as dyslipidaemia and hypertension alone do not explain the increased risk of cardiovascular disease associated with autoimmune diseases. Several mechanisms have been implicated in mediating the autoimmunity-associated cardiovascular risk, either directly or by modulating the effect of other risk factors in a complex interplay. Aberrant leukocyte function and pro-inflammatory cytokines are central to both disease entities, resulting in vascular dysfunction, impaired resolution of inflammation and promotion of chronic inflammation. Similarly, loss of tolerance to self-antigens and the generation of autoantibodies are key features of autoimmunity but are also implicated in the maladaptive inflammatory response during atherosclerotic cardiovascular disease. Therefore, immunomodulatory therapies are potential efficacious interventions to directly reduce the risk of cardiovascular disease, and biomarkers of autoimmune disease activity could be relevant tools to stratify patients with autoimmunity according to their cardiovascular risk. In this Review, we discuss the pathophysiological aspects of the increased cardiovascular risk associated with autoimmunity and highlight the many open questions that need to be answered to develop novel therapies that specifically address this unmet clinical need.

Vascular damage in systemic lupus erythematosus

Vascular disease is a major cause of morbidity and mortality in patients with systemic autoimmune diseases, particularly systemic lupus erythematosus (SLE). Although comorbid cardiovascular risk factors are frequently present in patients with SLE, they do not explain the high burden of premature vascular disease. Profound innate and adaptive immune dysregulation seems to be the primary driver of accelerated vascular damage in SLE. In particular, evidence suggests that dysregulation of type 1 interferon (IFN-I) and aberrant neutrophils have key roles in the pathogenesis of vascular damage. IFN-I promotes endothelial dysfunction directly via effects on endothelial cells and indirectly via priming of immune cells that contribute to vascular damage. SLE neutrophils are vasculopathic in part because of their increased ability to form immunostimulatory neutrophil extracellular traps. Despite improvements in clinical care, cardiovascular disease remains the leading cause of mortality among patients with SLE, and treatments that improve vascular outcomes are urgently needed. Improved understanding of the mechanisms of vascular injury in inflammatory conditions such as SLE could also have implications for common cardiovascular diseases, such as atherosclerosis and hypertension, and may ultimately lead to personalized therapeutic approaches to the prevention and treatment of this potentially fatal complication.

Platelets are a major player and represent a therapeutic opportunity in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune dysregulation and organ injury with a premature mortality due to cardiovascular diseases. Platelets, that are primarily known for their role in hemostasis, have been shown to play an active role in the pathogenesis and in the progression of immune-mediated inflammatory diseases. Here we summarize the evidence of their roles in SLE pathogenesis which supports the development of targeted treatments. Platelets and their precursors, the megakaryocytes, are intrinsically different in SLE patients compared with healthy controls. Different triggers related to innate and adaptive immunity activate platelets which release extracellular vesicles, soluble factors and interact with immune cells, thereby perpetuating inflammation. Platelets are involved in organ damage in SLE, especially in lupus nephritis and participate in the heightened cardiovascular mortality. They also play a clear role in antiphospholipid syndrome which can be associated with both thrombocytopenia and thrombosis. To tackle platelet activation and their interactions with immune cells now constitute promising therapeutic strategies in SLE.

Platelet activation: a promoter for psoriasis and its comorbidity, cardiovascular disease

Psoriasis is a chronic inflammatory skin disease with a prevalence of 0.14% to 1.99%. The underlying pathology is mainly driven by the abnormal immune responses including activation of Th1, Th17, Th22 cells and secretion of cytokines. Patients with psoriasis are more likely to develop cardiovascular disease (CVD) which has been well recognized as a comorbidity of psoriasis. As mediators of hemostasis and thromboinflammation, platelets play an important part in CVD. However, less is known about their pathophysiological contribution to psoriasis and psoriasis-associated CVD. A comprehensive understanding of the role of platelet activation in psoriasis might pave the path for more accurate prediction of cardiovascular (CV) risk and provide new strategies for psoriasis management, which alleviates the increased CV burden associated with psoriasis. Here we review the available evidence about the biomarkers and mechanisms of platelet activation in psoriasis and the role of platelet activation in intriguing the common comorbidity, CVD. We further discussed the implications and efficacy of antiplatelet therapies in the treatment of psoriasis and prevention of psoriasis-associated CVD.

Circulating extracellular vesicles from patients with traumatic brain injury induce cerebrovascular endothelial dysfunction

Endothelial dysfunction is a key proponent of pathophysiological process of traumatic brain injury (TBI). We previously demonstrated that extracellular vesicles (EVs) released from injured brains led to endothelial barrier disruption and vascular leakage. However, the molecular mechanisms of this EV-induced endothelial dysfunction (endotheliopathy) remain unclear. Here, we enriched plasma EVs from TBI patients (TEVs), and detected high mobility group box 1 (HMGB1) exposure to 50.33 ± 10.17% of TEVs and the number of HMGB1⁺TEVs correlated with injury severity. We then investigated for the first time the impact of TEVs on endothelial function using adoptive transfer models. We found that TEVs induced dysfunction of cultured human umbilical vein endothelial cells and mediated endothelial dysfunction in both normal and TBI mice, which were propagated through the HMGB1-activated receptor for advanced glycation end products (RAGE)/Cathepsin B signaling, and the resultant NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation and canonical caspase-1/gasdermin D (GSDMD)-dependent pyroptosis. Finally, von Willebrand factor (VWF) was detected on the surface of 77.01 ± 7.51% of HMGB1⁺TEVs. The TEV-mediated endotheliopathy was reversed by a polyclonal VWF antibody, indicating that VWF might serve a coupling factor that tethered TEVs to ECs, thus facilitating HMGB1-induced endotheliopathy. These results suggest that circulating EVs isolated from patients with TBI alone are sufficient to induce endothelial dysfunction and contribute to secondary brain injury that are dependent on immunologically active HMGB1 exposed on their surface. This finding provided new insight for the development of potential therapeutic targets and diagnostic biomarkers for TBI.

Platelet LGALS3BP as a Mediator of Myeloid Inflammation in Systemic Lupus Erythematosus

OBJECTIVE

Platelets are mediators of inflammation with immune effector cell properties and have been implicated in the pathogenesis of systemic lupus erythematosus (SLE). This study investigated the role of platelet-associated lectin, galactoside-binding, soluble 3 binding protein (LGALS3BP) as a mediator of inflammation in SLE and as a potential biomarker associated with clinical phenotypes.

METHODS

We performed RNA sequencing on platelets from patients with SLE (n = 54) and on platelets from age-, sex-, and race/ethnicity-matched healthy controls (n = 18) and measured LGALS3BP levels in platelet releasate and in circulating serum. We investigated the association between LGALS3BP levels and the prevalence, disease severity, and clinical phenotypes of SLE and studied platelet-mediated effects on myeloid inflammation.

RESULTS

Platelets from patients with SLE exhibited increased expression of LGALS3BP (fold change 4.0, adjusted P = 6.02 × 10-11 ). Platelet-released LGALS3BP levels were highly correlated with circulating LGALS3BP (R = 0.69, P < 0.0001), and circulating LGALS3BP levels were correlated with the severity of disease according to the SLE Disease Activity Index (r = 0.32, P = 0.0006). Specifically, circulating LGALS3BP levels were higher in SLE patients with lupus nephritis than in patients with inactive disease (4.0 μg/ml versus 2.3 μg/ml; P < 0.001). Interferon-α induced LGALS3BP transcription and translation in a megakaryoblastic cell line (MEG-01) in a dose-dependent manner. Recombinant LGALS3BP and platelet releasates from SLE patients enhanced proinflammatory cytokine production by macrophages.

CONCLUSIONS

Our results support that platelets act as potent effector cells that contribute to the pathogenesis of SLE by secreting proinflammatory LGALS3BP, which also represents a novel biomarker of SLE clinical activity.

Modeling of clinical phenotypes in systemic lupus erythematosus based on the platelet transcriptome and FCGR2a genotype

BACKGROUND

The clinical heterogeneity of SLE with its complex pathogenesis remains challenging as we strive to provide optimal management. The contribution of platelets to endovascular homeostasis, inflammation and immune regulation highlights their potential importance in SLE. Prior work from our group showed that the Fcγ receptor type IIa (FcγRIIa)-R/H131 biallelic polymorphism is associated with increased platelet activity and cardiovascular risk in SLE. The study was initiated to investigate the platelet transcriptome in patients with SLE and evaluate its association across FcγRIIa genotypes and distinct clinical features.

METHODS

Fifty-one patients fulfilling established criteria for SLE (mean age = 41.1 ± 12.3, 100% female, 45% Hispanic, 24% black, 22% Asian, 51% white, mean SLEDAI = 4.4 ± 4.2 at baseline) were enrolled and compared with 18 demographically matched control samples. The FCGR2a receptor was genotyped for each sample, and RNA-seq was performed on isolated, leukocyte-depleted platelets. Transcriptomic data were used to create a modular landscape to explore the differences between SLE patients and controls and various clinical parameters in the context of FCGR2a genotypes.

RESULTS

There were 2290 differentially expressed genes enriched for pathways involved in interferon signaling, immune activation, and coagulation when comparing SLE samples vs controls. When analyzing patients with proteinuria, modules associated with oxidative phosphorylation and platelet activity were unexpectedly decreased. Furthermore, genes that were increased in SLE and in patients with proteinuria were enriched for immune effector processes, while genes increased in SLE but decreased in proteinuria were enriched for coagulation and cell adhesion. A low-binding FCG2Ra allele (R131) was associated with decreases in FCR activation, which further correlated with increases in platelet and immune activation pathways. Finally, we were able to create a transcriptomic signature of clinically active disease that performed significantly well in discerning SLE patients with active clinical disease form those with inactive clinical disease.

CONCLUSIONS

In aggregate, these data demonstrate the platelet transcriptome provides insight into lupus pathogenesis and disease activity, and shows potential use as means of assessing this complex disease using a liquid biopsy.

Development of systemic lupus erythematosus in patients with immune thrombocytopenic purpura: A systematic meta-analysis

BACKGROUND

Recent population-based cohort studies suggest that the incidence of systemic lupus erythematosus (SLE) is increased in patients with immune thrombocytopenic purpura (ITP). We performed a systematic review and meta-analysis to evaluate the development of SLE in patients with ITP.

METHODS

Literature search was performed in PubMed, Web of Science and Cochrane Library for studies published prior to October 2022. Studies were included that reported development of SLE in ITP patients. Forest plot was used to detect overall SLE frequency in ITP and compare risk ratios for SLE development in different ITP subgroups. Study heterogeneity was assessed by using I2 statistics.

RESULTS

26 eligible studies comprising 14867 ITP patients were included in analysis. 311 ITP patients developed SLE during the follow-up period (range: 1.1-14 years) (2.09%, 95%CI: 1.87-2.33). Relative risk (RR) for developing SLE was significantly higher in female ITP patients (RR: 4.23, 95%CI: 2.52-7.12, p < 0.0001). Anti-nuclear antibody (ANA) was reported in 23 studies, there were 766/4377 ANA positive patients with ITP (17.5%). The risk of SLE development in ANA positive ITP patients was significant (RR: 26.29, 95%CI: 14.45-47.81, p < 0.0001).

CONCLUSIONS

Our study suggests ITP patients are at high risk of developing SLE in future. Pooled data revealed that females and patients with a positive ANA titer are at a significantly high risk of developing SLE.

The role of platelets in immune-mediated inflammatory diseases

Immune-mediated inflammatory diseases (IMIDs) are characterized by excessive and uncontrolled inflammation and thrombosis, both of which are responsible for organ damage, morbidity and death. Platelets have long been known for their role in primary haemostasis, but they are now also considered to be components of the immune system and to have a central role in the pathogenesis of IMIDs. In patients with IMIDs, platelets are activated by disease-specific factors, and their activation often reflects disease activity. Here we summarize the evidence showing that activated platelets have an active role in the pathogenesis and the progression of IMIDs. Activated platelets produce soluble factors and directly interact with immune cells, thereby promoting an inflammatory phenotype. Furthermore, platelets participate in tissue injury and promote abnormal tissue healing, leading to fibrosis. Targeting platelet activation and targeting the interaction of platelets with the immune system are novel and promising therapeutic strategies in IMIDs.

α1-Adrenergic Stimulation Increases Platelet Adhesion to Endothelial Cells Mediated by TRPC6

Stimulation of a1-adrenergic nervous system is increased during systemic inflammation and other pathological conditions with the consequent adrenergic receptors (ARs) activation. It has been reported that a1-stimulation contributes to coagulation since a1-AR blockers inhibit coagulation and its organic consequences. Also, coagulation induced by a1-AR stimulation can be greatly decreased using a1-AR blockers. In health, endothelial cells (ECs) perform anticoagulant actions at cellular and molecular level. However, during inflammation, ECs turn dysfunctional promoting a procoagulant state. Endothelium-dependent coagulation progresses at cellular and molecular levels, promoting endothelial acquisition of procoagulant properties to potentiate coagulation by means of prothrombotic and antifibrinolytic proteins expression increase in ECs releasing them to circulation, the thrombus formation is strengthened. Calcium signaling is a main feature of coagulation. Inhibition of ion channels involved in Ca²⁺ entry severely decreases coagulation. The transient receptor potential canonical 6 (TRPC6) is a non-selective Ca²⁺-permeable ion channel. TRPC6 activity is induced by diacylglycerol, suggesting that is regulated by a1-ARs. Furthermore, a1-ARs stimulation elicits a TRPC-like current in rat mesenteric artery smooth muscle and mesangial cells. However, whether TRPC6 could promote an ECs-mediated platelet adhesion induced by a1-adrenergic stimulation is currently not known. Therefore, the aim of this study was to examine if the TRPC6 calcium channel mediates platelet adhesion induced by a1-adrenergic stimulation. Our results suggest that platelet adhesion to ECs is enhanced by the a1-adrenergic stimulation evoked by phenylephrine mediated by TRPC6 activity. We conclude that TRPC6 is a molecular determinant in platelet adhesion to ECs with implications in systemic inflammatory diseases treatment.

Non-Traditional Pro-Inflammatory and Pro-Atherosclerotic Risk Factors Related to Systemic Lupus Erythematosus

Cardiovascular diseases (CVD) are one of the leading causes of high mortality in patients with systemic lupus erythematosus (SLE). The Framingham risk score and other traditional risk factors do not fully reflect the CVD risk in SLE patients. Therefore, in order to stratify these high-risk patients, additional biomarkers for subclinical CVD are needed. The mechanisms of atherogenesis in SLE are still being investigated. During the past decades, many reports recognized that inflammation plays a crucial role in the development of atherosclerosis. The aim of this report is to present novel proinflammatory and pro-atherosclerotic risk factors that are closely related to SLE inflammation and which determine an increased risk for the occurrence of early cardiovascular events.

Antiplatelet Effects of Clopidogrel Vs Aspirin in Virologically Controlled HIV: A Randomized Controlled Trial

Patients with HIV exhibit platelet activation and increased risk of cardiovascular disease, the prevention of which is not fully known. Fifty-five HIV-positive patients were randomized to clopidogrel, aspirin, or no-treatment for 14 days, and the platelet phenotype and ability to induce endothelial inflammation assessed. Clopidogrel as opposed to aspirin and no-treatment reduced platelet activation (P-selectin and PAC-1 expression). Compared with baseline, platelet-induced proinflammatory transcript expression of cultured endothelial cells were reduced in those assigned to clopidogrel, with no change in the aspirin and no-treatment arms. In HIV, clinical trials of clopidogrel to prevent cardiovascular disease are warranted. (Antiplatelet Therapy in HIV; NCT02559414).

Splice factor polypyrimidine tract-binding protein 1 (Ptbp1) primes endothelial inflammation in atherogenic disturbed flow conditions

Plaque forms in low and disturbed flow regions of the vasculature, where platelets adhere and endothelial cells are “primed” to respond to cytokines (e.g., tumor necrosis factor-α) with elevated levels of cell adhesion molecules via the NF-κB signaling pathway. We show that the splice factor polypyrimidine tract binding protein (Ptbp1; purple) mediates priming. Ptbp1 is induced in endothelial cells by platelet recruitment, promoting priming and subsequent myeloid cell infiltration into plaque. Mechanistically, Ptbp1 regulates splicing of genes (e.g., Ripk1) involved in the NF-κB signaling pathway and is required for efficient nuclear translocation of NF-κB in endothelial cells. This provides new insight into the molecular mechanisms underlying an endothelial priming process that reinforces vascular inflammation.

NF-κB–mediated endothelial activation drives leukocyte recruitment and atherosclerosis, in part through adhesion molecules Icam1 and Vcam1. The endothelium is primed for cytokine activation of NF-κB by exposure to low and disturbed blood flow (LDF)but the molecular underpinnings are not fully understood. In an experimental in vivo model of LDF, platelets were required for the increased expression of several RNA-binding splice factors, including polypyrimidine tract binding protein (Ptbp1). This was coordinated with changes in RNA splicing in the NF-κB pathway in primed cells, leading us to examine splice factors as mediators of priming. Using Icam1 and Vcam1 induction by tumor necrosis factor (TNF)-α stimulation as a readout, we performed a CRISPR Cas9 knockout screen and identified a requirement for Ptbp1 in priming. Deletion of Ptbp1 had no effect on cell growth or response to apoptotic stimuli, but reversed LDF splicing patterns and inhibited NF-κB nuclear translocation and transcriptional activation of downstream targets, including Icam1 and Vcam1. In human coronary arteries, elevated PTBP1 correlates with expression of TNF pathway genes and plaque. In vivo, endothelial-specific deletion of Ptbp1 reduced Icam1 expression and myeloid cell infiltration at regions of LDF in atherosclerotic mice, limiting atherosclerosis. This may be mediated, in part, by allowing inclusion of a conserved alternative exon in Ripk1 leading to a reduction in Ripk1 protein. Our data show that Ptbp1, which is induced in a subset of the endothelium by platelet recruitment at regions of LDF, is required for priming of the endothelium for subsequent NF-κB activation, myeloid cell recruitment and atherosclerosis.

Pregnancy-related complications in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune inflammatory disease that predominantly affects women of childbearing age and results in various adverse pregnancy outcomes (APOs). Pregnancy was formerly discouraged in patients with SLE because of unstable disease activity during the gestation period, increased thrombosis risk, severe organ damage, and inevitable side effects of immunosuppressive agents. Currently, most patients with SLE have successful pregnancies due to preconception counselling, strict monitoring, and improved therapy with minimised complications for both the mother and foetus. Hydroxychloroquine (HCQ) is extensively used and is beneficial for improving pregnancy outcomes. However, pregnant women with SLE have a high-risk of APOs, such as disease flare, preterm birth, intrauterine growth restriction (IUGR), preeclampsia, and pregnancy loss. Better understanding of the changes in maternal immunity and serum biomarkers, as well as their relationships with SLE-related APOs progression, would facilitate the investigation of molecular mechanisms for triggering and ameliorating APOs. Furthermore, it would enable us to explore and develop novel and effective therapeutic strategies to prevent disease activation. Therefore, this review briefly introduces the interaction between pregnancy outcomes and SLE, elucidates pathophysiological and immunological changes during SLE pregnancy. Furthermore, this review systematically expounds on the effective predictors of APOs and the molecular mechanisms underlying the SLE-related APOs to provide a solid foundation for the advanced management of lupus pregnancy.

Mechanistic insight into premature atherosclerosis and cardiovascular complications in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is associated with a significant risk of cardiovascular disease (CVD), which substantially increases disease mortality and morbidity. The overall mechanisms associated with the development of premature atherosclerosis and CVD in SLE remain unclear, but has been considered as a result of an intricate interplay between the profound immune dysregulation and traditional CVD risk factors. Aberrant systemic inflammation in SLE may lead to an abnormal lipid profile and dysfunction, which can further fuel the pro-atherosclerotic environment. The existence of a strong imbalance between endothelial damage and vascular repair/angiogenesis promotes vascular injury, which is the early step in the progression of atherosclerotic CVD. Profound innate and adaptive immune dysregulation, characterized by excessive type I interferon burden, aberrant macrophage, platelet and complements activation, neutrophil dysregulation and neutrophil extracellular traps formation, uncontrolled T cell activation, and excessive autoantibody production and immune complex formation, have been proposed to promote accelerated CVD in SLE. While designing targeted therapies to correct the dysregulated immune activation may be beneficial in the treatment of SLE-related CVD, much additional work is needed to determine how to translate these findings into clinical practice. Additionally, a number of biomarkers display diagnostic potentials in improving CVD risk stratification in SLE, further prospective studies will help understand which biomarker(s) will be the most impactful one(s) in assessing SLE-linked CVD. Continued efforts to identify novel mechanisms and to establish criteria for assessing CVD risk as well as predicting CVD progression are in great need to improve CVD outcomes in SLE.

The phosphatase PTEN links platelets with immune regulatory functions of mouse T follicular helper cells

Beyond a function in hemostasis and thrombosis, platelets can regulate innate and adaptive immune responses. Hyperactive platelets are frequently associated with multiple human autoimmune diseases, yet their pathogenic functions in these diseases have not been fully established. Emerging studies show an essential function of the phosphatase and tensin homolog (PTEN) in maintenance of immune homeostasis. Here, we show that mice with platelet-specific deletion of Pten, develop age-related lymphoproliferative diseases and humoral autoimmunity not seen in wildtype animals. Platelet-specific Pten-deficient mice have aberrant T cell activation, excessive T follicular helper (Tfh) cell responses and accumulation of platelet aggregates in lymph nodes. Transferred Pten-deficient platelets are able to infiltrate into the peripheral lymphoid tissues and form more aggregates. Moreover, Pten-deficient platelets are hyperactive and overproduce multiple Tfh-promoting cytokines via activation of the PDK1/mTORC2-AKT-SNAP23 pathway. Pten-deficient platelets show enhanced interaction with CD4⁺ T cells and promote conversion of CD4⁺ T cells into Tfh cells. Our results implicate PTEN in platelet-mediated immune homeostasis, and provide evidence that hyperactive platelets function as an important mediator in autoimmune diseases using mouse models.

Cardiovascular disease risk and pathogenesis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) often features extensive cardiovascular (CV) comorbidity and patients with SLE are at significantly increased risk of CV event occurrence and CV-related mortality. While the specific mechanisms leading to this increased cardiovascular disease (CVD) risk remain to be fully characterized, this heightened risk cannot be fully explained by traditional CV risk factors and is likely driven by immunologic and inflammatory features of SLE. Widespread innate and adaptive immune dysregulation characterize SLE, and factors including excessive type I interferon burden, inappropriate formation and ineffective clearance of neutrophil extracellular traps, and autoantibody formation have been linked to clinical and metabolic features impacting CV risk in SLE and may represent pathogenic drivers of SLE-related CVD. Indeed, functional and phenotypic aberrations in almost every immune cell type are present in SLE and may impact CVD progression. As understanding of the contribution of SLE-specific factors to CVD in SLE improves, improved screening and monitoring of CV risk alongside development of therapeutic treatments aimed at prevention of CVD in SLE patients are required and remain the focus of several ongoing studies and lines of inquiry.

Enrichment of complement, immunoglobulins and autoantibody targets in the proteome of platelets from patients with Systemic Lupus Erythematosus (SLE)

Background  Systemic lupus erythematosus (SLE) is a complex disease characterized by autoimmunity toward apoptotic cells, excessive amounts of circulating immune complexes, and complement activation. A decreased platelet size has been observed in SLE and their nonhemostatic functions may play an active role in the disease. The main objective of this study was to find clues that could explain their decreased size and functional role, analyzing the entire platelet proteome.

Methods  Platelets were isolated from 23 patients with SLE. The five individuals with the highest and lowest average platelet forward scatter were selected for further analysis. Platelet protein content was analyzed using liquid chromatography with tandem mass spectrometry (LC-MS/MS) and compared with platelets from five healthy controls. Data are available via ProteomeXchange with identifier PXD031202.

Results  Out of 2,572 proteins identified, 396 had significantly different levels (ANOVA q -value ≤ 0.01). Forty proteins, including immunoglobulin-, complement- and phosphatidylserine-binding proteins had higher abundance in platelets from SLE patients, largely independent of size (fold difference of ≥1.5 and a t -test p -value of ≤0.05 as cut-off). Functional characterization revealed increased degranulation and skewed hemostatic balance in platelets from SLE patients. In the SLE proteome, immunoglobulin proteins were negatively correlated to serum complement C3 and C4 and the highest relative levels were detected in platelets of normal size.

Conclusion  Platelets from SLE patients shared a specific protein profile, including immunoglobulins, complement proteins, and autoantigens, largely independent of the platelet size and in agreement with an integrated role for platelets in SLE.

Cardiovascular disease risk and pathogenesis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) often features extensive cardiovascular (CV) comorbidity and patients with SLE are at significantly increased risk of CV event occurrence and CV-related mortality. While the specific mechanisms leading to this increased cardiovascular disease (CVD) risk remain to be fully characterized, this heightened risk cannot be fully explained by traditional CV risk factors and is likely driven by immunologic and inflammatory features of SLE. Widespread innate and adaptive immune dysregulation characterize SLE, and factors including excessive type I interferon burden, inappropriate formation and ineffective clearance of neutrophil extracellular traps, and autoantibody formation have been linked to clinical and metabolic features impacting CV risk in SLE and may represent pathogenic drivers of SLE-related CVD. Indeed, functional and phenotypic aberrations in almost every immune cell type are present in SLE and may impact CVD progression. As understanding of the contribution of SLE-specific factors to CVD in SLE improves, improved screening and monitoring of CV risk alongside development of therapeutic treatments aimed at prevention of CVD in SLE patients are required and remain the focus of several ongoing studies and lines of inquiry.

A guide to molecular and functional investigations of platelets to bridge basic and clinical sciences

Platelets have been shown to be associated with pathophysiological process beyond thrombosis, demonstrating critical additional roles in homeostatic processes, such as immune regulation, and vascular remodeling. Platelets themselves can have multiple functional states and can communicate and regulate other cells including immune cells and vascular smooth muscle cells, to serve such diverse functions. Although traditional platelet functional assays are informative and reliable, they are limited in their ability to unravel platelet phenotypic heterogeneity and interactions. Developments in methods such as electron microscopy, flow cytometry, mass spectrometry, and 'omics' studies, have led to new insights. In this Review, we focus on advances in platelet biology and function, with an emphasis on current and promising methodologies. We also discuss technical and biological challenges in platelet investigations. Using coronavirus disease 2019 (COVID-19) as an example, we further describe the translational relevance of these approaches and the possible 'bench-to-bedside' utility in patient diagnosis and care.

A new decade awaits sticky platelet syndrome: where are we now, how do we manage and what are the complications?

INTRODUCTION

Sticky platelet syndrome is a less known platelet function disorder with a familiar occurrence and likely genetic background. Clinically, it is characterized by an increased risk of venous and arterial thromboembolic events and obstetric placenta-mediated complications. The increased aggregation after low-dose ADP and/or epinephrine is its distinctive laboratory feature. Though described for almost 40 years, several issues regarding its etiology, involved pathomechanisms, genetic background, optimal diagnostic and treatment approach remain controversial.

AREAS COVERED

The work aims to summarize published studies, the actual definition of the syndrome, and point out its drawbacks. A literature search on Medline, Embase, and archives from EHA congresses was performed (terms: 'sticky platelet syndrome' - 'platelet hyperreactivity' - 'platelet hyperaggregability'). The authors added in their unpublished data. The introductory overview of the present understanding is followed by the discussion of the pathophysiologic, diagnostic, and therapeutic problems.

EXPERT OPINION

Despite the growing evidence provided by case reports and series, the lack of robust studies limits the decision-making on diagnostics and management. The diagnostic issues, particularly the standardization of light transmission aggregometry, represent the crucial problem for the broader acceptance of the syndrome.

Platelets contribute to disease severity in COVID-19

OBJECTIVE

Heightened inflammation, dysregulated immunity, and thrombotic events are characteristic of hospitalized COVID-19 patients. Given that platelets are key regulators of thrombosis, inflammation, and immunity they represent prime candidates as mediators of COVID-19-associated pathogenesis. The objective of this study was to understand the contribution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to the platelet phenotype via phenotypic (activation, aggregation) and transcriptomic characterization.

APPROACH AND RESULTS

In a cohort of 3915 hospitalized COVID-19 patients, we analyzed blood platelet indices collected at hospital admission. Following adjustment for demographics, clinical risk factors, medication, and biomarkers of inflammation and thrombosis, we find platelet count, size, and immaturity are associated with increased critical illness and all-cause mortality. Bone marrow, lung tissue, and blood from COVID-19 patients revealed the presence of SARS-CoV-2 virions in megakaryocytes and platelets. Characterization of COVID-19 platelets found them to be hyperreactive (increased aggregation, and expression of P-selectin and CD40) and to have a distinct transcriptomic profile characteristic of prothrombotic large and immature platelets. In vitro mechanistic studies highlight that the interaction of SARS-CoV-2 with megakaryocytes alters the platelet transcriptome, and its effects are distinct from the coronavirus responsible for the common cold (CoV-OC43).

CONCLUSIONS

Platelet count, size, and maturity associate with increased critical illness and all-cause mortality among hospitalized COVID-19 patients. Profiling tissues and blood from COVID-19 patients revealed that SARS-CoV-2 virions enter megakaryocytes and platelets and associate with alterations to the platelet transcriptome and activation profile.

Ultrastructural Study of Platelet Behavior and Interrelationship in Sprouting and Intussusceptive Angiogenesis during Arterial Intimal Thickening Formation

Platelets in atherosclerosis, bypass stenosis, and restenosis have been extensively assessed. However, a sequential ultrastructural study of platelets in angiogenesis during the early phases of these lesions has received less attention. Our objective was the study of platelets in angiogenesis and vessel regression during intimal thickening (IT) formation, a precursor process of these occlusive vascular diseases. For this purpose, we used an experimental model of rat occluded arteries and procedures for ultrastructural observation. The results show (a) the absence of platelet adhesion in the de-endothelialized occluded arterial segment isolated from the circulation, (b) that intraarterial myriad platelets contributed from neovessels originated by sprouting angiogenesis from the periarterial microvasculature, (c) the association of platelets with blood components (fibrin, neutrophils, macrophages, and eosinophils) and non-polarized endothelial cells (ECs) forming aggregates (spheroids) in the arterial lumen, (d) the establishment of peg-and-socket junctions between platelets and polarized Ecs during intussusceptive angiogenesis originated from the EC aggregates, with the initial formation of IT, and (e) the aggregation of platelets in regressing neovessels (‘transitory paracrine organoid’) and IT increases. In conclusion, in sprouting and intussusceptive angiogenesis and vessel regression during IT formation, we contribute sequential ultrastructural findings on platelet behavior and relationships, which can be the basis for further studies using other procedures.

Pathogenic mechanisms contributing to thrombocytopenia in patients with systemic lupus erythematosus

SummarySystemic lupus erythematosus (SLE) is an autoimmune condition developing thrombocytopenia in about 10-15% of cases, however, mechanisms leading to low platelet count were not deeply investigated in this illness. Here we studied possible causes of thrombocytopenia, including different mechanisms of platelet clearance and impairment in platelet production. Twenty-five SLE patients with and without thrombocytopenia were included. Platelet apoptosis, assessed by measurement of loss of mitochondrial membrane potential, active caspase 3 and phosphatidylserine exposure, was found to increase in thrombocytopenic patients. Plasma from 67% SLE patients (thrombocytopenic and non-thrombocytopenic) induced loss of sialic acid (Ricinus communis agglutinin I and/or Peanut agglutinin binding) from normal platelet glycoproteins. Concerning platelet production, SLE plasma increased megakaryopoiesis (evaluated using normal human cord blood CD34+ hematopoietic progenitors), but inhibited thrombopoiesis (proplatelet count). Anti-platelet autoantibody depletion from SLE plasma reverted this inhibition. Overall, abnormalities were more frequently observed in thrombocytopenic than non-thrombocytopenic SLE patients and in those with active disease (SLEDAI≥5). In conclusion, platelet clearance due to apoptosis and desialylation, and impaired platelet production mainly due to inhibition of thrombopoiesis, could be relevant mechanisms leading to thrombocytopenia in SLE. These findings could provide a rational basis for the choice of proper therapies to correct platelet counts in these patients.[Figure: see text].

Platelets amplify endotheliopathy in COVID-19

Given the evidence for a hyperactive platelet phenotype in COVID-19, we investigated effector cell properties of COVID-19 platelets on endothelial cells (ECs). Integration of EC and platelet RNA sequencing revealed that platelet-released factors in COVID-19 promote an inflammatory hypercoagulable endotheliopathy. We identified S100A8 and S100A9 as transcripts enriched in COVID-19 platelets and were induced by megakaryocyte infection with SARS-CoV-2. Consistent with increased gene expression, the heterodimer protein product of S100A8/A9, myeloid-related protein (MRP) 8/14, was released to a greater extent by platelets from COVID-19 patients relative to controls. We demonstrate that platelet-derived MRP8/14 activates ECs, promotes an inflammatory hypercoagulable phenotype, and is a significant contributor to poor clinical outcomes in COVID-19 patients. Last, we present evidence that targeting platelet P2Y12 represents a promising candidate to reduce proinflammatory platelet-endothelial interactions. Together, these findings demonstrate a previously unappreciated role for platelets and their activation-induced endotheliopathy in COVID-19.

Activation of Platelet NLRP3 Inflammasome in Crohn's Disease

Patients with Crohn’s disease (CD) are inclined to have platelet hyperactivity and an increased risk of intestinal micro-thrombosis. However, the mechanisms underlying platelet hyperactivity in CD are not well understood. We investigated the assembly of platelet NLRP3 inflammasome in patients with active CD and its correlation with platelet hyperactivity. In this study, Real-time PCR and western blotting analyses uncovered that ASC, NLRP3, and active caspase-1 were significantly upregulated in platelets from patients with active CD compared with healthy subjects. As revealed by flow cytometry (FCM) and ELISA analyses, the levels of interleukin-1β in both serum and isolated platelets were elevated in patients with active CD. Co-immunoprecipitation and immunofluorescence experiments revealed an increased assembly of NLRP3 inflammasome in platelets from patients with active CD. In addition, higher levels of intracellular reactive oxygen species (ROS) were observed in these platelets by FCM. Furthermore, elevated levels of platelet P-selectin exposure and fibrinogen binding were demonstrated in patients with active CD by FCM. They were positively correlated with the protein levels of NLRP3 inflammasome components. Collectively, our results indicate that the ROS-NLRP3 inflammasome-interleukin-1β axis may contribute to platelet hyperactivity in active CD.

Rapid Release of Interleukin-1β from Human Platelets Is Independent of NLRP3 and Caspase

OBJECTIVE

 Platelets are critical in mediating both rapid responses to injury and the development and progression of coronary disease. Several studies have shown that, after prolonged exposure to agonists, they produce and release inflammatory mediators including interleukin-1β (IL-1β), via the classical pathway (NLRP3 inflammasome and caspase-1 cleavage to release active IL-1β) as described for leukocytes. This study aimed to determine whether there is rapid release of IL-1β in response to soluble platelet agonists and whether such rapid release is NLRP3- and caspase-1-dependent.

METHODS AND RESULTS

 Using flow cytometry to detect platelet activation (and release of α and dense granule contents) and the combination of Western blotting, enzyme-linked-immunosorbent assay, and immunogold labeling transmission electron and immunofluorescence microscopy, we identified that resting human platelets contain mature IL-1β. Platelets release IL-1β within minutes in response to adenosine diphosphate (ADP), collagen, and thrombin receptor agonists, but not in response to conventional NLRP3 inflammasome agonists-lipopolysaccharide and adenosine triphosphate. The rapid release of IL-1β in response to ADP and thrombin receptor agonists was independent of caspases (including caspase-1) and NLRP3. Immature and mature IL-1β were identified as low-abundance proteins on transmission electron microscopy of human platelets, and were localized to the platelet cytosol, open canalicular system, and the periphery of α granules.

CONCLUSION

 Unlike monocytes and neutrophils, human platelets are capable of rapid agonist- and time-dependent release of IL-1β by a mechanism which is independent of caspase-1 and NLRP3.

Platelet bound complement split product (PC4d) is a marker of platelet activation and arterial vascular events in Systemic Lupus Erythematosus

Platelet-bound complement activation products (PC4d) are associated with thrombosis in Systemic Lupus Erythematosus (SLE). This study investigated the effect of PC4d on platelet function, as a mechanistic link to arterial thrombosis. In a cohort of 150 SLE patients, 13 events had occurred within five years of enrollment. Patients with arterial events had higher PC4d levels (13.6 [4.4-24.0] vs. 4.0 [2.5-8.3] net MFI), with PC4d 10 being the optimal cutoff for event detection. The association of arterial events with PC4d remained significant after adjusting for antiphospholipid status, smoking, and prednisone use (p = 0.045). PC4d levels correlated with lower platelet counts (r = -0.26, p = 0.002), larger platelet volumes (r = 0.22, p = 0.009) and increased platelet aggregation: the adenosine diphosphate (ADP) concentration to achieve 50% maximal aggregation (EC₅₀) was lower in patients with PC4d 10 compared with PC4d < 10 (1.6 vs. 3.7, p = 0.038, respectively). These results suggest that PC4d may be a mechanistic marker for vascular disease in SLE.

Understanding Accelerated Atherosclerosis in Systemic Lupus Erythematosus: Toward Better Treatment and Prevention

Systemic lupus erythematosus (SLE) carries a significant risk of cardiovascular disease (CVD). The prevalence of premature CVD is especially noteworthy because it occurs in premenopausal women with SLE who would otherwise have very low rates of CVD. While traditional risk factors likely play a role in development of CVD in the setting of SLE, they do not fully explain the excess risk. The pathogenesis of CVD in SLE is not fully understood, but the inflammatory nature of SLE is believed to be a key factor in accelerating atherosclerosis. Systemic inflammation may lead to an abnormal lipid profile with elevated triglycerides, total cholesterol, and low-density lipoprotein cholesterol and dysfunctional high-density lipoprotein cholesterol. Additionally, the inflammatory milieu of SLE plasma promotes endothelial dysfunction and vascular injury, early steps in the progression of atherosclerotic CVD. Despite the overall headway that has been achieved in treating lupus, innovative therapeutics specifically targeting the progression of atherosclerosis within the lupus population are currently lacking. However, there have been advancements in the development of promising modalities for diagnosis of subclinical atherosclerosis and detection of high CVD risk patients. Due to the significant impact of CVD on morbidity and mortality, research addressing prevention and treatment of CVD in SLE needs to be prioritized. This review explores the intricate interplay of SLE-specific properties that contribute to atherosclerosis and CVD within this population, as well as screening methods and possible therapies.

The Dual Role of Platelets in the Cardiovascular Risk of Chronic Inflammation

Patients with chronic inflammatory diseases often exhibit cardiovascular risk. This risk is associated with the systemic inflammation that persists in these patients, causing a sustained endothelial activation. Different mechanisms have been considered responsible for this systemic inflammation, among which activated platelets have been regarded as a major player. However, in recent years, the role of platelets has become controversial. Not only can this subcellular component release pro- and anti-inflammatory mediators, but it can also bind to different subsets of circulating lymphocytes, monocytes and neutrophils modulating their function in either direction. How platelets exert this dual role is not yet fully understood.

The latest in systemic lupus erythematosus-accelerated atherosclerosis: related mechanisms inform assessment and therapy

PURPOSE OF REVIEW

Accelerated atherosclerosis is a significant comorbidity and the leading cause of death for patients with systemic lupus erythematosus (SLE). It is now apparent that SLE-accelerated atherosclerosis is not driven solely by traditional cardiovascular risk factors, adding complexity to disease characterization and mechanistic understanding. In this review, we will summarize new insights into SLE-accelerated atherosclerosis evaluation, treatment, and mechanism.

RECENT FINDINGS

Recent work highlights the need to incorporate inflammatory biomarkers into cardiovascular disease (CVD) risk assessments. This is especially true for SLE patients, in which mechanisms of immune dysfunction likely drive CVD progression. There is new evidence that commonly prescribed SLE therapeutics hinder atherosclerosis development. This effect is achieved both by reducing SLE-associated inflammation and by directly improving measures of atherosclerosis, emphasizing the interconnected mechanisms of the two conditions.

SUMMARY

SLE-accelerated atherosclerosis is most likely the consequence of chronic autoimmune inflammation. Therefore, diligent management of atherosclerosis requires assessment of SLE disease activity as well as traditional cardiovascular risk factors. This supports why many of the therapeutics classically used to control SLE also modulate atherosclerosis development. Greater understanding of the mechanisms underlying this condition will allow for the development of more targeted therapeutics and improved outcomes for SLE patients.

Platelet Proteomes, Pathways, and Phenotypes as Informants of Vascular Wellness and Disease

Platelets rapidly undergo responsive transitions in form and function to repair vascular endothelium and mediate hemostasis. In contrast, heterogeneous platelet subpopulations with a range of primed or refractory phenotypes gradually arise in chronic inflammatory and other conditions in a manner that may indicate or support disease. Qualitatively distinguishable platelet phenotypes are increasingly associated with a variety of physiological and pathological circumstances; however, the origins and significance of platelet phenotypic variation remain unclear and conceptually vague. As changes in platelet function in disease exhibit many similarities to platelets following the activation of platelet agonist receptors, the intracellular responses of platelets common to hemostasis and inflammation may provide insights to the molecular basis of platelet phenotype. Here, we review concepts around how protein-level relations-from platelet receptors through intracellular signaling events-may help to define platelet phenotypes in inflammation, immune responses, aging, and other conditions. We further discuss how representing systems-wide platelet proteomics data profiles as circuit-like networks of causally related intracellular events, or, pathway maps, may inform molecular definitions of platelet phenotype. In addition to offering insights into platelets as druggable targets, maps of causally arranged intracellular relations underlying platelet function can also advance precision and interceptive medicine efforts by leveraging platelets as accessible, dynamic, endogenous, circulating biomarkers of vascular wellness and disease. Graphic Abstract: A graphic abstract is available for this article.

Vascular Inflammation and Dysfunction in Lupus-Prone Mice-IL-6 as Mediator of Disease Initiation

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disease and patients are under an increased risk for cardiovascular (CV) events and mortality. The increased CV risk for patients with SLE seems to be caused by a premature and accelerated atherosclerosis, attributable to lupus-specific risk factors (i.e., increased systemic inflammation, altered immune status), apart from traditional CV risk factors. To date, there is no established experimental model to explore the pathogenesis of this increased CV risk in SLE patients.

METHODS

Here we investigated whether MRL-Fas^lpr mice, which develop an SLE-like phenotype, may serve as a model to study lupus-mediated vascular disease. Therefore, MRL-Fas^lpr, MRL-++, and previously generated Il6^-/- MRL-Fas^lpr mice were used to evaluate vascular changes and possible mechanisms of vascular dysfunction and damage.

RESULTS

Contrary to MRL-++ control mice, lupus-prone MRL-Faslpr mice exhibited a pronounced vascular and perivascular leukocytic infiltration in various organs; expression of pro-inflammatory cytokines in the aorta and kidney was augmented; and intima-media thickness of the aorta was increased. IL-6 deficiency reversed these changes and restored aortic relaxation.

CONCLUSION

Our findings demonstrate that the MRL-Fas^lpr mouse model is an excellent tool to investigate vascular damage in SLE mice. Moreover, IL-6 promotes vascular inflammation and damage and could potentially be a therapeutic target for the treatment of accelerated arteriosclerosis in SLE.

Impairment of platelet NO signalling in coronary artery spasm: role of hydrogen sulphide

BACKGROUND AND PURPOSE

The pathophysiology of coronary artery spasm (CAS), with its associated ischaemic crises, is currently poorly understood and treatment is frequently ineffective. In view of increasing evidence that platelet-based defects may occur in CAS patients, we investigated platelet reactivity in CAS patients and whether symptomatic crises reflect activation of platelet-endothelial interactions.

EXPERIMENTAL APPROACH

CAS patients were evaluated during acute and/or chronic symptomatic phases and compared with healthy control subjects. Inhibition of ADP-induced platelet aggregation by the NO donor sodium nitroprusside (SNP) and plasma concentrations of syndecan 1 (glycocalyx shedding marker), tryptase (mast cell activation marker) and platelet microparticles were measured.

KEY RESULTS

Inhibition of platelet aggregation by SNP was diminished in chronic CAS, with further (non-significant) deterioration during symptomatic crises, whereas plasma concentrations of syndecan 1, tryptase and platelet microparticles increased. Treatment of patients with high-dose N-acetylcysteine (NAC) plus glyceryl trinitrate rapidly increased platelet responsiveness to SNP and decreased plasma syndecan 1 concentrations. The effect of NAC on platelet responsiveness to SNP was confirmed in vitro and mimicked by the H₂ S donor NaHS. Conversely, inhibition of enzymatic production of H₂ S attenuated NAC effect.

CONCLUSION AND IMPLICATIONS

CAS is associated with substantial impairment of platelet NO signalling. During acute symptomatic exacerbations, platelet resistance to NO is aggravated, together with mast cell activation and damage to both vasculature and platelets. NAC, via release of H₂ S, reverses platelet resistance to NO and terminates glycocalyx shedding during symptomatic crises: This suggests that H₂ S donors may correct the pathophysiological anomalies underlying CAS.

Association of systemic lupus erythematosus with peripheral arterial disease: a meta-analysis of literature studies

OBJECTIVE

SLE patients have an increased cardiovascular morbidity and mortality. Contrasting data are available about the association between peripheral arterial disease (PAD) and SLE. We aimed to perform a meta-analysis of studies evaluating the association between SLE and PAD.

METHODS

Studies were systematically searched in the PubMed, Web of Science, Scopus and EMBASE databases according to preferred reporting items for systematic reviews and meta-analyses guidelines.

RESULTS

Eight studies reporting on 263 258 SLE patients and 768 487 controls showed that the prevalence of PAD was 15.8% (95% CI: 10.5%, 23.2%) in SLE patients and 3.9% (95% CI: 1.8%, 7.9%) in controls with a corresponding odds ratio of 4.1 (95% CI: 1.5, 11.6; P <0.001). In addition, five studies reporting on ankle-brachial index showed significantly lower values in 280 SLE patients as compared with 201 controls (mean difference: -0.018; 95% CI: -0.034, -0.001; P =0.033). Meta-regression models showed that age, hypertension and diabetes were inversely associated with the difference in the prevalence of PAD between SLE patients and non-SLE controls, whereas no effect for all the other clinical and demographic variables on the evaluated outcome was found.

CONCLUSION

SLE patients exhibit an increased prevalence of PAD and lower ankle-brachial index values as compared with non-SLE controls. This should be considered when planning prevention, interventional and rehabilitation strategies for these chronic patients with functional disability and poor long-term outcomes.

FcγRIIA expression accelerates nephritis and increases platelet activation in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease characterized by deposits of immune complexes (ICs) in organs and tissues. The expression of FcγRIIA by human platelets, which is their unique receptor for immunoglobulin G antibodies, positions them to ideally respond to circulating ICs. Whereas chronic platelet activation and thrombosis are well-recognized features of human SLE, the exact mechanisms underlying platelet activation in SLE remain unknown. Here, we evaluated the involvement of FcγRIIA in the course of SLE and platelet activation. In patients with SLE, levels of ICs are associated with platelet activation. Because FcγRIIA is absent in mice, and murine platelets do not respond to ICs in any existing mouse model of SLE, we introduced the FcγRIIA (FCGR2A) transgene into the NZB/NZWF1 mouse model of SLE. In mice, FcγRIIA expression by bone marrow cells severely aggravated lupus nephritis and accelerated death. Lupus onset initiated major changes to the platelet transcriptome, both in FcγRIIA-expressing and nonexpressing mice, but enrichment for type I interferon response gene changes was specifically observed in the FcγRIIA mice. Moreover, circulating platelets were degranulated and were found to interact with neutrophils in FcγRIIA-expressing lupus mice. FcγRIIA expression in lupus mice also led to thrombosis in lungs and kidneys. The model recapitulates hallmarks of human SLE and can be used to identify contributions of different cellular lineages in the manifestations of SLE. The study further reveals a role for FcγRIIA in nephritis and in platelet activation in SLE.

Insights into the Procoagulant Profile of Patients with Systemic Lupus Erythematosus without Antiphospholipid Antibodies

We aimed to identify the key players in the prothrombotic profile of patients with systemic lupus erythematosus (SLE) not mediated by antiphospholipid antibodies, as well as the potential utility of global coagulation tests to characterize hemostasis in these patients. Patients with SLE without antiphospholipid antibodies and without signs of thrombosis were included. The kinetics of clot formation were determined by ROTEM^®. Platelet activation markers were determined by flow cytometry. Thrombin generation associated with Neutrophil Extracellular Traps (NETs) and microparticles (MPs) was measured by calibrated automated thrombogram (CAT). The plasma levels of PAI-1 were also determined. ROTEM^® showed a procoagulant profile in SLE patients. SLE patients had activated platelets and more leukocyte/platelet aggregates at basal conditions. The plasma PAI-1 and platelet aggregates correlated with several ROTEM^® parameters. The thrombin generation associated withthe tissue factor (TF) content of MPs and with NETs was increased. Our results suggest the utility of global tests for studying hemostasis in SLE patients because they detect their procoagulant profile, despite having had neither antiphospholipid antibodies nor any previous thrombotic event. A global appraisal of hemostasis should, if possible, be incorporated into clinical practice to detect the risk of a thrombotic event in patients with SLE and to consequently act to prevent its occurrence.

Platelet regulation of myeloid suppressor of cytokine signaling 3 accelerates atherosclerosis

Platelets are best known as mediators of hemostasis and thrombosis; however, their inflammatory effector properties are increasingly recognized. Atherosclerosis, a chronic vascular inflammatory disease, represents the interplay between lipid deposition in the artery wall and unresolved inflammation. Here, we reveal that platelets induce monocyte migration and recruitment into atherosclerotic plaques, resulting in plaque platelet-macrophage aggregates. In Ldlr ^-/- mice fed a Western diet, platelet depletion decreased plaque size and necrotic area and attenuated macrophage accumulation. Platelets drive atherogenesis by skewing plaque macrophages to an inflammatory phenotype, increasing myeloid suppressor of cytokine signaling 3 (SOCS3) expression and reducing the Socs1:Socs3 ratio. Platelet-induced Socs3 expression regulates plaque macrophage reprogramming by promoting inflammatory cytokine production (Il6, Il1b, and Tnfa) and impairing phagocytic capacity, dysfunctions that contribute to unresolved inflammation and sustained plaque growth. Translating our data to humans with cardiovascular disease, we found that women with, versus without, myocardial infarction have up-regulation of SOCS3, lower SOCS1:SOCS3, and increased monocyte-platelet aggregate. A second cohort of patients with lower extremity atherosclerosis demonstrated that SOCS3 and the SOCS1:SOCS3 ratio correlated with platelet activity and inflammation. Collectively, these data provide a causative link between platelet-mediated myeloid inflammation and dysfunction, SOCS3, and cardiovascular disease. Our findings define an atherogenic role of platelets and highlight how, in the absence of thrombosis, platelets contribute to inflammation.

Impact of change in bedtime variability on body composition and inflammation: secondary findings from the Go Red for Women Strategically Focused Research Network

Variability in daily sleep patterns is an emerging factor linked to metabolic syndrome. However, whether reducing bedtime variability improves markers of disease risk has not been tested. Here, we assessed whether body composition and inflammation were impacted by changes in bedtime variability over a 6-week period, during which, women were instructed to maintain healthy, habitual sleep (HS) patterns (one arm of a randomized trial). Data were available for 37 women (age 34.9 ± 12.4 years, BMI 24.7 ± 2.9 kg/m2, sleep duration 7.58 ± 0.49 h/night). Body composition and leukocyte platelet aggregates (LPA) were measured at baseline and endpoint using magnetic resonance imaging and flow cytometry, respectively. Sleep data were collected daily using wrist actigraphy. Change in bedtime variability was calculated as the difference in the standard deviation (SD) of bedtimes measured during the 2-week screening period and the 6-week intervention period. Results showed that women who reduced their bedtime variability (n = 29) during the intervention had reductions in total (P < 0.001) and subcutaneous adipose tissue (P < 0.001) relative to women who increased/maintained (n = 8) bedtime variability. Similar effects were observed for LPA levels between women who reduced vs increased/maintained bedtime variability (P = 0.011). Thus, reducing bedtime variability, without changing sleep duration, could improve cardiometabolic health by reducing adiposity and inflammation.

Platelet disturbances correlate with endothelial cell activation in uncomplicated Plasmodium vivax malaria

Platelets drive endothelial cell activation in many diseases. However, if this occurs in Plasmodium vivax malaria is unclear. As platelets have been reported to be activated and to play a role in inflammatory response during malaria, we hypothesized that this would correlate with endothelial alterations during acute illness. We performed platelet flow cytometry of PAC-1 and P-selectin. We measured platelet markers (CXCL4, CD40L, P-selectin, Thrombopoietin, IL-11) and endothelial activation markers (ICAM-1, von Willebrand Factor and E-selectin) in plasma with a multiplex-based assay. The values of each mediator were used to generate heatmaps, K-means clustering and Principal Component analysis. In addition, we determined pair-wise Pearson’s correlation coefficients to generate correlation networks. Platelet counts were reduced, and mean platelet volume increased in malaria patients. The activation of circulating platelets in flow cytometry did not differ between patients and controls. CD40L levels (Median [IQ]: 517 [406–651] vs. 1029 [732–1267] pg/mL, P = 0.0001) were significantly higher in patients, while P-selectin and CXCL4 showed a nonsignificant trend towards higher levels in patients. The network correlation approach demonstrated the correlation between markers of platelet and endothelial activation, and the heatmaps revealed a distinct pattern of activation in two subsets of P. vivax patients when compared to controls. Although absolute platelet activation was not strong in uncomplicated vivax malaria, markers of platelet activity and production were correlated with higher endothelial cell activation, especially in a specific subset of patients.

Endothelial cell activation is a key process in the pathogenesis of Plasmodium vivax malaria. Platelets are classically involved in endothelial cell activation in several diseases, but their role in the context of vivax malaria remains unclear. Thrombocytopenia is the most common hematological disturbance in P. vivax-infected patients, and platelets have been implicated in parasitemia control. In this work, we studied the activation of platelets in association with endothelial cell activation in vivax malaria. Platelets retrieved from infected peripheral blood were non-activated when analyzed by flow cytometry; however, they displayed higher mean volume and significantly reduced counts. We also found higher levels of circulating factors associated with platelet activation (especially soluble CD40L), thrombopoiesis and endothelial cell activation in infected patients. Further, through pair-wise correlation and clustering analysis, we found a subgroup of patients showing significant associations between markers of platelet and endothelial activation in a pattern different from that of endemic controls. Collectively, our findings indicate a role of platelets in endothelial cell activation in vivax malaria and indicate a heterogeneous host response in the setting of uncomplicated disease, a finding to be further explored in future studies.

Targeting the Immune System for Pulmonary Inflammation and Cardiovascular Complications in COVID-19 Patients

In December 2019, following a cluster of pneumonia cases in China caused by a novel coronavirus (CoV), named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the infection disseminated worldwide and, on March 11th, 2020, the World Health Organization officially declared the pandemic of the relevant disease named coronavirus disease 2019 (COVID-19). In Europe, Italy was the first country facing a true health policy emergency, and, as at 6.00 p.m. on May 2nd, 2020, there have been more than 209,300 confirmed cases of COVID-19. Due to the increasing number of patients experiencing a severe outcome, global scientific efforts are ongoing to find the most appropriate treatment. The usefulness of specific anti-rheumatic drugs came out as a promising treatment option together with antiviral drugs, anticoagulants, and symptomatic and respiratory support. For this reason, we feel a duty to share our experience and our knowledge on the use of these drugs in the immune-rheumatologic field, providing in this review the rationale for their use in the COVID-19 pandemic.

Risk of systemic lupus erythematosus in patients with idiopathic thrombocytopenic purpura: a population-based cohort study

BACKGROUND

Idiopathic thrombocytopenic purpura (ITP) may play a role in early-stage systemic lupus erythematosus (SLE). The incidence of SLE in patients with ITP and the potential relationship between them is still unclear. This study was performed to provide epidemiological evidence regarding the relationship between ITP and SLE occurrence.

METHODS

In this population-based retrospective cohort study, the risk of SLE was analysed in a cohort of patients newly diagnosed with ITP between 2000 and 2013. Controls were selected at a 1:2 ratio through propensity score matching (PSM) using the greedy algorithm. The Cox proportional hazard model was used to analyse the association between ITP and SLE incidence. There were four different Cox regression models, and the sensitivity analyses were implemented to evaluate the HR of SLE after exposure with ITP.

RESULTS

In the age-matched and sex-matched ITP and non-ITP cohort, the average follow-up time was about 80 months in this study. There were 34 (4.70%) and 27 (0.19%) incident cases of SLE in ITP and non-ITP group. The incidence rates were 62.0 (95% CI 44.3 to 86.8) and 2.10 (95% CI 1.44 to 3.06), respectively. The adjusted HR of incidental SLE in the ITP group was 25.1 (95% CI 13.7 to 46.0). The other risk factors for SLE were female sex and Sjogren's syndrome. After PSM, the incidence rate and Kaplan-Meir curves of SLE were consistent with the results for the age-matched and sex-matched population, the HR 17.4 (95% CI 5.28 to 57.4) was estimated by conditional Cox model.

CONCLUSION

This cohort study demonstrated that patients with ITP have a higher risk of SLE. Clinically, patients with ITP should be monitored for incidental lupus.

Activated Platelets Induce Endothelial Cell Inflammatory Response in Psoriasis via COX-1

OBJECTIVE

Patients with psoriasis have impaired vascular health and increased cardiovascular disease (CVD). Platelets are key players in the pathogenesis of vascular dysfunction in cardiovascular disease and represent therapeutic targets in cardiovascular prevention. The object of this study was to define the platelet phenotype and effector cell properties on vascular health in psoriasis and evaluate whether aspirin modulates the platelet-induced phenotype. Approach and Results: Platelets from psoriasis patients (n=45) exhibited increased platelet activation (relative to age- and gender-matched controls, n=18), which correlated with psoriasis skin severity. Isolated platelets from psoriasis patients demonstrated a 2- to 3-fold (P<0.01) increased adhesion to human aortic endothelial cells and induced proinflammatory transcriptional changes, including upregulation of IL 8 (interleukin 8), IL1β, and Cox (cyclooxygenase)-2 Platelet RNA sequencing revealed an interferon signature and elevated expression of COX-1, which correlated with psoriasis disease severity (r=0.83, P=0.01). In a randomized trial of patients with psoriasis, 2 weeks of 81 mg low-dose aspirin, a COX-1 inhibitor, reduced serum thromboxane (Tx) B2 and reduced brachial vein endothelial proinflammatory transcript expression >70% compared with the no-treatment group (P<0.01). Improvement in brachial vein endothelial cell inflammation significantly correlated with change in serum TxB2 (r=0.48, P=0.02).

CONCLUSIONS

In patients with psoriasis, platelets are activated and induce endothelial cell inflammation. Low-dose aspirin improved endothelial cell health in psoriasis via platelet COX-1 inhibition. These data demonstrate a previously unappreciated role of platelets in psoriasis and endothelial cell inflammation and suggests that aspirin may be effective in improving vascular health in patients with psoriasis. Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT03228017.

Common innate pathways to autoimmune disease

Until recently, autoimmune disease research has primarily been focused on elucidating the role of the adaptive immune system. In the past decade or so, the role of the innate immune system in the pathogenesis of autoimmunity has increasingly been realized. Recent findings have elucidated paradigm-shifting concepts, for example, the implications of "trained immunity" and a dysbiotic microbiome in the susceptibility of predisposed individuals to clinical autoimmunity. In addition, the application of modern technologies such as the quantum dot (Qdot) system and 'Omics' (e.g., genomics, proteomics, and metabolomics) data-processing tools has proven fruitful in revisiting mechanisms underlying autoimmune pathogenesis and in identifying novel therapeutic targets. This review highlights recent findings discussed at the American Autoimmune Related Disease Association (AARDA) 2019 colloquium. The findings covering autoimmune diseases and autoinflammatory diseases illustrate how new developments in common innate immune pathways can contribute to the better understanding and management of these immune-mediated disorders.

In systemic lupus erythematosus anti-dsDNA antibodies can promote thrombosis through direct platelet activation

Systemic lupus erythematosus (SLE) is associated with a high risk of venous and arterial thrombosis, not necessarily associated with prothrombotic antiphospholipid antibodies (Abs). Alternatively, thrombosis may be due to an increased titer of anti-dsDNA Abs that presumably promote thrombosis via direct platelet activation. Here, we investigated effects of purified anti-dsDNA Abs from the blood of SLE patients, alone or in a complex with dsDNA, on isolated normal human platelets. We showed that anti-dsDNA Abs and anti-dsDNA Ab/dsDNA complexes induced strong platelet activation assessed by enhanced P-selectin expression and dramatic morphological and ultrastructural changes. Electron microscopy revealed a significantly higher percentage of platelets that lost their discoid shape, formed multiple filopodia and had a shrunken body when treated with anti-dsDNA Abs or anti-dsDNA Ab/dsDNA complexes compared with control samples. In addition, these platelets activated with anti-dsDNA Ab/dsDNA complexes typically contained a reduced number of secretory α-granules that grouped in the middle and often merged into a solid electron dense area. Many activated platelets released plasma membrane-derived microvesicles and/or fell apart into subcellular cytoplasmic fragments. Confocal microscopy revealed that platelets treated with anti-dsDNA Ab/dsDNA complex had a heterogeneous distribution of septin2 compared with the homogeneous distribution in control platelets. Structural perturbations were concomitant with mitochondrial depolarization and a decreased content of platelet ATP, indicating energetic exhaustion. Most of the biochemical and morphological changes in platelets induced by anti-dsDNA Abs and anti-dsDNA Ab/dsDNA complexes were prevented by pre-treatment with a monoclonal mAb against FcγRIIA. The aggregate of data indicates that anti-dsDNA Abs alone or in a complex with dsDNA strongly affect platelets via the FcγRIIA receptor. The immune activation of platelets with antinuclear Abs may comprise a prothrombotic mechanism underlying a high risk of thrombotic complications in patients with SLE.

Aspirin inhibits platelets from reprogramming breast tumor cells and promoting metastasis

It is now recognized that compounds released from tumor cells can activate platelets, causing the release of platelet-derived factors into the tumor microenvironment. Several of these factors have been shown to directly promote neovascularization and metastasis, yet how the feedback between platelet releasate and the tumor cell affects metastatic phenotype remains largely unstudied. Here, we identify that breast tumor cells secrete high levels of interleukin 8 (IL-8, CXCL8) in response to platelet releasate, which promotes their invasive capacity. Furthermore, we found that platelets activate the Akt pathway in breast tumor cells, and inhibition of this pathway eliminated IL-8 production. We therefore hypothesized inhibiting platelets with aspirin could reverse the prometastatic effects of platelets on tumor cell signaling. Platelets treated with aspirin did not activate the Akt pathway, resulting in reduced IL-8 secretion and impaired tumor cell invasion. Of note, patients with breast cancer receiving aspirin had lower circulating IL-8, and their platelets did not increase tumor cell invasion compared with patients not receiving aspirin. Our data suggest platelets support breast tumor metastasis by inducing tumor cells to secrete IL-8. Our data further support that aspirin acts as an anticancer agent by disrupting the communication between platelets and breast tumor cells.

Metabolic Biomarkers In Midtrimester Maternal Plasma Can Accurately Predict Adverse Pregnancy Outcome in Patients with SLE

Patients with systemic lupus erythematosus (SLE) are at increased risk for adverse pregnancy outcome (APO). Accurate prediction of APO is critical to identify, counsel, and manage these high-risk patients. We undertook this study to identify novel biomarkers in mid-trimester maternal plasma to identify pregnant patients with SLE at increased risk of APOs. The study population consisted of pregnant women whose plasma was taken in mid-trimester and available for metabolic signature: (1) SLE and normal pregnancy outcome (Group 1, n = 21); (2) SLE with APO (Group 2, n = 12); and (3) healthy pregnant controls (Group 3, n = 10). Mid-trimester maternal plasma was analyzed for integrative profiles of primary metabolite and phospholipid using gas chromatography time-of-flight mass spectrometry (GC-TOF MS) and liquid chromatography Orbitrap mass spectrometry (LC-Orbitrap MS). For performance comparison and validation, plasma samples were analyzed for sFlt-1/PlGF ratio. In the study population, APO developed in 12 of 33 women with SLE (36%). Metabolite profiling of mid-trimester maternal plasma samples identified a total of 327 metabolites using GC-TOF MS and LC-Orbitrap MS. Partial least squares discriminant analysis (PLS-DA) showed clear discrimination among the profiles of SLE groups and healthy pregnant controls (Groups 1/2 vs. 3). Moreover, direct comparison between Groups 1 and 2 demonstrated that 4 primary metabolites and 13 lipid molecules were significantly different. Binary logistic regression analysis suggested a potential metabolic biomarker model that could discriminate Groups 1 and 2. Receiver operating characteristic (ROC) analysis revealed the best predictability for APO with the combination model of two metabolites (LysoPC C22:5 and tryptophan) with AUC of 0.944, comparable to the AUC of sFlt-1/PlGF (AUC 0.857). In conclusion, metabolic biomarkers in mid-trimester maternal plasma can accurately predict APO in patients with SLE.