Platelet-Derived Chemokine CXCL7 Dimer Preferentially Exists in the Glycosaminoglycan-Bound Form: Implications for Neutrophil-Platelet Crosstalk

Proteomics data in vitiligo: a scoping review

An unbiased screening of which proteins are deregulated in vitiligo using proteomics can offer an enormous value. It could not only reveal robust biomarkers for detecting disease activity but can also identify which patients are most likely to respond to treatments. We performed a scoping review searching for all articles using proteomics in vitiligo. Eight manuscripts could be identified. Unfortunately, very limited overlap was found in the differentially expressed proteins between studies (15 out of 272; 5,51%) with variable degrees of the type of proteins and a substantial variety in the prevalence of acute phase proteins (range: 6-65%). Proteomics research has therefore brought little corroborating evidence on which proteins are differentially regulated between vitiligo patients and healthy controls or between active and stable vitiligo patients. While a limited patient size is an obvious weakness for several studies, an incomplete description of patient characteristics is an unfortunate and avoidable shortcoming. Additionally, the variations in the used methodology and analyses may further contribute to the overall observed variability. Nonetheless, more recent studies investigating the response to treatment seem to be more robust, as more differentially expressed proteins that have previously been confirmed to be involved in vitiligo were found. The further inclusion of proteomics analyses in clinical trials is recommended to increase insights into the pathogenic mechanisms in vitiligo and identify reliable biomarkers or promising drug targets. A harmonization in the study design, reporting and proteomics methodology could vastly improve the value of vitiligo proteomics research.

Cxcl1 monomer-dimer equilibrium controls neutrophil extravasation

The chemokine Cxcl1 plays a crucial role in recruiting neutrophils in response to infection. The early events in chemokine-mediated neutrophil extravasation involve a sequence of highly orchestrated steps including rolling, adhesion, arrest, and diapedesis. Cxcl1 function is determined by its properties of reversible monomer-dimer equilibrium and binding to Cxcr2 and glycosaminoglycans. Here, we characterized how these properties orchestrate extravasation using intravital microscopy of the cremaster. Compared to WT Cxcl1, which exists as both a monomer and a dimer, the trapped dimer caused faster rolling, less adhesion, and less extravasation. Whole-mount immunofluorescence of the cremaster and arrest assays confirmed these data. Moreover, the Cxcl1 dimer showed impaired LFA-1-mediated neutrophil arrest that could be attributed to impaired Cxcr2-mediated ERK signaling. We conclude that Cxcl1 monomer-dimer equilibrium and potent Cxcr2 activity of the monomer together coordinate the early events in neutrophil recruitment.

Chemokine Cxcl1-Cxcl2 heterodimer is a potent neutrophil chemoattractant

Microbial infection is characterized by release of multiple proinflammatory chemokines that direct neutrophils to the insult site. How collective function of these chemokines orchestrates neutrophil recruitment is not known. Here, we characterized the role for heterodimer and show that the Cxcl1-Cxcl2 heterodimer is a potent neutrophil chemoattractant in mice and can recruit more neutrophils than the individual chemokines. Chemokine-mediated neutrophil recruitment is determined by Cxcr2 receptor signaling, Cxcr2 endocytosis, and binding to glycosaminoglycans. We have now determined heterodimer's Cxcr2 activity using cellular assays and Cxcr2 density in blood and recruited neutrophils in heterodimer-treated mice. We have shown that the heterodimer binds glycosaminoglycans with higher affinity and more efficiently than Cxcl1 or Cxcl2. These data collectively indicate that optimal glycosaminoglycan interactions and dampened receptor activity acting in concert in a dynamic fashion promote heterodimer-mediated robust neutrophil recruitment. We propose that this could play a critical role in combating infection.

Heterodimers Are an Integral Component of Chemokine Signaling Repertoire

Chemokines are a family of signaling proteins that play a crucial role in cell-cell communication, cell migration, and cell trafficking, particularly leukocytes, under both normal and pathological conditions. The oligomerization state of chemokines influences their biological activity. The heterooligomerization occurs when multiple chemokines spatially and temporally co-localize, and it can significantly affect cellular responses. Recently, obligate heterodimers have emerged as tools to investigate the activities and molecular mechanisms of chemokine heterodimers, providing valuable insights into their functional roles. This review focuses on the latest progress in understanding the roles of chemokine heterodimers and their contribution to the functioning of the chemokine network.

Chemokine Heteromers and Their Impact on Cellular Function-A Conceptual Framework

Chemoattractant cytokines or chemokines are proteins involved in numerous biological activities. Their essential role consists of the formation of gradient and (immune) cell recruitment. Chemokine biology and its related signaling system is more complex than simple ligand-receptor interactions. Beside interactions with their cognate and/or atypical chemokine receptors, and glycosaminoglycans (GAGs), chemokines form complexes with themselves as homo-oligomers, heteromers and also with other soluble effector proteins, including the atypical chemokine MIF, carbohydrate-binding proteins (galectins), damage-associated molecular patterns (DAMPs) or with chemokine-binding proteins such as evasins. Likewise, nucleic acids have been described as binding targets for the tetrameric form of CXCL4. The dynamic balance between monomeric and dimeric structures, as well as interactions with GAGs, modulate the concentrations of free chemokines available along with the nature of the gradient. Dimerization of chemokines changes the canonical monomeric fold into two main dimeric structures, namely CC- and CXC-type dimers. Recent studies highlighted that chemokine dimer formation is a frequent event that could occur under pathophysiological conditions. The structural changes dictated by chemokine dimerization confer additional biological activities, e.g., biased signaling. The present review will provide a short overview of the known functionality of chemokines together with the consequences of the interactions engaged by the chemokines with other proteins. Finally, we will present potential therapeutic tools targeting the chemokine multimeric structures that could modulate their biological functions.

Platelets-related signature based diagnostic model in rheumatoid arthritis using WGCNA and machine learning

Background and aim

Rheumatoid arthritis (RA) is an autoinflammatory disease that may lead to severe disability. The diagnosis of RA is limited due to the need for biomarkers with both reliability and efficiency. Platelets are deeply involved in the pathogenesis of RA. Our study aims to identify the underlying mechanism and screening for related biomarkers.

Methods

We obtained two microarray datasets (GSE93272 and GSE17755) from the GEO database. We performed Weighted correlation network analysis (WGCNA) to analyze the expression modules in differentially expressed genes identified from GSE93272. We used KEGG, GO and GSEA enrichment analysis to elucidate the platelets-relating signatures (PRS). We then used the LASSO algorithm to develop a diagnostic model. We then used GSE17755 as a validation cohort to assess the diagnostic performance by operating Receiver Operating Curve (ROC).

Results

The application of WGCNA resulted in the identification of 11 distinct co-expression modules. Notably, Module 2 exhibited a prominent association with platelets among the differentially expressed genes (DEGs) analyzed. Furthermore, a predictive model consisting of six genes (MAPK3, ACTB, ACTG1, VAV2, PTPN6, and ACTN1) was constructed using LASSO coefficients. The resultant PRS model demonstrated excellent diagnostic accuracy in both cohorts, as evidenced by area under the curve (AUC) values of 0.801 and 0.979.

Conclusion

We elucidated the PRSs occurred in the pathogenesis of RA and developed a diagnostic model with excellent diagnostic potential.

Shedding Light on the Cell Biology of Platelet-Derived Extracellular Vesicles and Their Biomedical Applications

EVs are membranous subcellular structures originating from various cells, including platelets which consist of biomolecules that can modify the target cell's pathophysiological functions including inflammation, cell communication, coagulation, and metastasis. EVs, which are known to allow the transmission of a wide range of molecules between cells, are gaining popularity in the fields of subcellular treatment, regenerative medicine, and drug delivery. PEVs are the most abundant EVs in circulation, being produced by platelet activation, and are considered to have a significant role in coagulation. PEV cargo is extremely diverse, containing lipids, proteins, nucleic acids, and organelles depending on the condition that induced their release and can regulate a wide range of biological activities. PEVs, unlike platelets, can overcome tissue barriers, allowing platelet-derived contents to be transferred to target cells and organs that platelets cannot reach. Their isolation, characterization, and therapeutic efficacy, on the other hand, are poorly understood. This review summarizes the technical elements of PEV isolation and characterization methods as well as the pathophysiological role of PEVs, including therapeutic potential and translational possibility in diverse disciplines.

Neutrophil-activating Peptide 2 as a Novel Modulator of Fibrin Clot Properties in Patients with Atrial Fibrillation

Neutrophil-activating peptide 2 (NAP-2, CXCL7), a platelet-derived neutrophil chemoattractant, is involved in inflammation. We investigated associations between NAP-2 levels, neutrophil extracellular traps (NETs) formation, and fibrin clot properties in atrial fibrillation (AF). We recruited 237 consecutive patients with AF (mean age, 68 ± 11 years; median CHA₂DS₂VASc score of 3 [2-4]) and 30 apparently healthy controls. Plasma NAP-2 concentrations were measured, along with plasma fibrin clot permeability (K_s) and clot lysis time (CLT), thrombin generation, citrullinated histone H3 (citH3), as a marker of NETs formation, and 3-nitrotyrosine reflecting oxidative stress. NAP-2 levels were 89% higher in AF patients than in controls (626 [448-796] vs. 331 [226-430] ng/ml; p < 0.0001). NAP-2 levels were not associated with demographics, CHA₂DS₂-VASc score, or the AF manifestation. Patients with NAP-2 in the top quartile (> 796 ng/ml) were characterized by higher neutrophil count (+ 31.7%), fibrinogen (+ 20.8%), citH3 (+ 86%), and 3-nitrotyrosine (+ 111%) levels, along with 20.2% reduced K_s and 8.4% prolonged CLT as compared to the remaining subjects (all p < 0.05). NAP-2 levels were positively associated with fibrinogen in AF patients (r = 0.41, p = 0.0006) and controls (r = 0.65, p < 0.01), along with citH3 (r = 0.36, p < 0.0001) and 3-nitrotyrosine (r = 0.51, p < 0.0001) in the former group. After adjustment for fibrinogen, higher citH3 (per 1 ng/ml β = -0.046, 95% CI -0.029; -0.064) and NAP-2 (per 100 ng/ml β = -0.21, 95% CI -0.14; -0.28) levels were independently associated with reduced K_s. Elevated NAP-2, associated with increased oxidative stress, has been identified as a novel modulator of prothrombotic plasma fibrin clot properties in patients with AF.

Platelet-neutrophil interaction in COVID-19 and vaccine-induced thrombotic thrombocytopenia

Coronavirus disease 2019 (COVID-19) is known to commonly induce a thrombotic diathesis, particularly in severely affected individuals. So far, this COVID-19-associated coagulopathy (CAC) has been partially explained by hyperactivated platelets as well as by the prothrombotic effects of neutrophil extracellular traps (NETs) released from neutrophils. However, precise insight into the bidirectional relationship between platelets and neutrophils in the pathophysiology of CAC still lags behind. Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare autoimmune disorder caused by auto-antibody formation in response to immunization with adenoviral vector vaccines. VITT is associated with life-threatening thromboembolic events and thus, high fatality rates. Our concept of the thrombophilia observed in VITT is relatively new, hence a better understanding could help in the management of such patients with the potential to also prevent VITT. In this review we aim to summarize the current knowledge on platelet-neutrophil interplay in COVID-19 and VITT.

Platelet-Neutrophil Crosstalk in Thrombosis

Platelets are essential for the formation of a haemostatic plug to prevent bleeding, while neutrophils are the guardians of our immune defences against invading pathogens. The interplay between platelets and innate immunity, and subsequent triggering of the activation of coagulation is part of the host system to prevent systemic spread of pathogen in the blood stream. Aberrant immunothrombosis and excessive inflammation can however, contribute to the thrombotic burden observed in many cardiovascular diseases. In this review, we highlight how platelets and neutrophils interact with each other and how their crosstalk is central to both arterial and venous thrombosis and in COVID-19. While targeting platelets and coagulation enables efficient antithrombotic treatments, they are often accompanied with a bleeding risk. We also discuss how novel approaches to reduce platelet-mediated recruitment of neutrophils could represent promising therapies to treat thrombosis without affecting haemostasis.

NMR Methods for Characterization of Glycosaminoglycan-Chemokine Interactions

Humans express around 50 chemokines that play crucial roles in human pathophysiology from combating infection to immune surveillance by directing and trafficking leukocytes to the target tissue. Glycosaminoglycans (GAGs) regulate chemokine function by tuning monomer/dimer levels, chemotactic/haptotactic gradients, and how they are presented to their receptors. Knowledge of the structural features of the chemokine-GAG complexes and GAG properties that define chemokine interactions is essential not only to understand chemokine function, but also for developing drugs that disrupt chemokine-GAG crosstalk and thereby impart protection against dysregulated host defense. Nuclear magnetic resonance (NMR) spectroscopy has proven to be quite useful for providing residue-specific interactions, binding geometry and models, specificity, and affinity. Multiple NMR methods have been used including (1) chemical shift perturbation (CSP), (2) saturation transfer difference (STD), and (3) paramagnetic relaxation enhancement (PRE) techniques. In this chapter, we describe how NMR CSP, STD, and PRE can be best used for characterizing chemokine-GAG interactions.

Role of S100A8/A9 in Platelet-Neutrophil Complex Formation during Acute Inflammation

Acute respiratory distress syndrome (ARDS) due to pulmonary infections is associated with high morbidity and mortality. Upon inflammation, the alarmin S100A8/A9 is released and stimulates neutrophil recruitment mainly via binding to Toll-like receptor 4 (TLR4). TLR4 is also expressed on platelets, which modulate the immune response through direct interaction with leukocytes. In a murine model of Klebsiella pneumoniae-induced pulmonary inflammation, global S100A9 deficiency resulted in diminished neutrophil recruitment into the lung alveoli and neutrophil accumulation in the intravascular space, indicating an impaired neutrophil migration. A lack of TLR4 on platelets resulted in reduced neutrophil counts in the whole lung, emphasising the impact of TLR4-mediated platelet activity on neutrophil behaviour. Flow cytometry-based analysis indicated elevated numbers of platelet-neutrophil complexes in the blood of S100A9^-/- mice. Intravital microscopy of the murine cremaster muscle confirmed these findings and further indicated a significant increase in neutrophil-platelet complex formation in S100A9^-/- mice, which was reversed by administration of the S100A8/A9 tetramer. An in vitro bilayer assay simulated the murine alveolar capillary barrier during inflammation and validated significant differences in transmigration behaviour between wild-type and S100A9^-/- neutrophils. This study demonstrates the role of S100A8/A9 during platelet-neutrophil interactions and neutrophil recruitment during pulmonary inflammation.

Platelet-Derived Biomarkers: Potential Role in Early Pediatric Serious Bacterial Infection and Sepsis Diagnostics

Fever is the most common complaint of children who are attending a pediatric emergency department (PED). Most of the fever cases are of viral origin; however, the most common markers, such as leucocyte, neutrophil count, or C-reactive protein, are not sensitive or specific enough to distinguish the etiology of fever, especially if children present at the early phase of infection. Currently, platelets have been attributed a role as important sentinels in viral and bacterial infection pathogenesis. Thus, our aim was to analyze different platelet indices, such as PNLR (platelet-to-neutrophil/lymphocyte ratio), PNR (platelet-to-neutrophil ratio) as well as specific secreted proteins, such as sP-selectin, CXCL4, CXCL7, and serotonin. We included 68 children who were referred to PED with the early onset of fever (<12 h). All children with comorbidities, older than five years, and psychiatric diseases, who refused to participate were excluded. All the participants were divided into viral, bacterial, or serious bacterial infection (SBI) groups. All the children underwent blood sampling, and an additional sample was collected for protein analysis. Our analysis revealed statistically significant differences between leucocyte, neutrophil, and CRP levels between SBI and other groups. However, leucocyte and neutrophil counts were within the age norms. A higher PNLR value was observed in a bacterial group, PNR-in viral. As we tested CXCL7 and sP-selectin, alone and together those markers were statistically significant to discriminate SBI and sepsis from other causes of infection. Together with tachypnoe and SpO2 < 94%, it improved the prediction value of sepsis as well as SBI. CXCL4 and serotonin did not differ between the groups. Concluding, CXCL7 and sP-selectin showed promising results in early SBI and sepsis diagnosis.

Identifying platelet-derived factors as amplifiers of B. burgdorferi-induced cytokine production

Previous studies have shown that monocytes can be 'trained' or tolerized by certain stimuli to respond stronger or weaker to a secondary stimulation. Rewiring of glucose metabolism was found to be important in inducing this phenotype. As we previously found that Borrelia burgdorferi (B. burgdorferi), the causative agent of Lyme borreliosis (LB), alters glucose metabolism in monocytes, we hypothesized that this may also induce long-term changes in innate immune responses. We found that exposure to B. burgdorferi decreased cytokine production in response to the TLR4-ligand lipopolysaccharide (LPS). In addition, B. burgdorferi exposure decreased baseline levels of glycolysis, as assessed by lactate production. Using GWAS analysis, we identified a gene, microfibril-associated protein 3-like (MFAP3L) as a factor influencing lactate production after B. burgdorferi exposure. Validation experiments proved that MFAP3L affects lactate- and cytokine production following B. burgdorferi stimulation. This is mediated by functions of MFAP3L, which includes activating ERK2 and through activation of platelet degranulation. Moreover, we showed that platelets and platelet-derived factors play important roles in B. burgdorferi-induced cytokine production. Certain platelet-derived factors, such chemokine C-X-C motif ligand 7 (CXCL7) and (C-C motif) ligand 5 (CCL5), were elevated in the circulation of LB patients in comparison to healthy individuals.

Multifaceted Roles of Chemokine C-X-C Motif Ligand 7 in Inflammatory Diseases and Cancer

Over recent years, C-X-C motif ligand 7 (CXCL7) has received widespread attention as a chemokine involved in inflammatory responses. Abnormal production of the chemokine CXCL7 has been identified in different inflammatory diseases; nevertheless, the exact role of CXCL7 in the pathogenesis of inflammatory diseases is not fully understood. Persistent infection or chronic inflammation can induce tumorigenesis and progression. Previous studies have shown that the pro-inflammatory chemokine CXCL7 is also expressed by malignant tumor cells and that binding of CXCL7 to its cognate receptors C-X-C chemokine receptor 1 (CXCR1) and C-X-C chemokine receptor 2 (CXCR2) can influence tumor biological behavior (proliferation, invasion, metastasis, and tumor angiogenesis) in an autocrine and paracrine manner. CXCL7 and its receptor CXCR1/CXCR2, which are aberrantly expressed in tumors, may represent new targets for clinical tumor immunotherapy.

Platelets at the Crossroads of Pro-Inflammatory and Resolution Pathways during Inflammation

Platelets are among the most abundant cells in the mammalian circulation. Classical platelet functions in hemostasis and wound healing have been intensively explored and are generally accepted. During the past decades, the research focus broadened towards their participation in immune-modulatory events, including pro-inflammatory and, more recently, inflammatory resolution processes. Platelets are equipped with a variety of abilities enabling active participation in immunological processes. Toll-like receptors mediate the recognition of pathogens, while the release of granule contents and microvesicles promotes direct pathogen defense and an interaction with leukocytes. Platelets communicate and physically interact with neutrophils, monocytes and a subset of lymphocytes via soluble mediators and surface adhesion receptors. This interaction promotes leukocyte recruitment, migration and extravasation, as well as the initiation of effector functions, such as the release of extracellular traps by neutrophils. Platelet-derived prostaglandin E2, C-type lectin-like receptor 2 and transforming growth factor β modulate inflammatory resolution processes by promoting the synthesis of pro-resolving mediators while reducing pro-inflammatory ones. Furthermore, platelets promote the differentiation of CD4⁺ T cells in T helper and regulatory T cells, which affects macrophage polarization. These abilities make platelets key players in inflammatory diseases such as pneumonia and the acute respiratory distress syndrome, including the pandemic coronavirus disease 2019. This review focuses on recent findings in platelet-mediated immunity during acute inflammation.

An Insight into Recent Advances on Platelet Function in Health and Disease

Platelets play a variety of roles in vascular biology and are best recognized as primary hemostasis and thrombosis mediators. Platelets have a large number of receptors and secretory molecules that are required for platelet functionality. Upon activation, platelets release multiple substances that have the ability to influence both physiological and pathophysiological processes including inflammation, tissue regeneration and repair, cancer progression, and spreading. The involvement of platelets in the progression and seriousness of a variety of disorders other than thrombosis is still being discovered, especially in the areas of inflammation and the immunological response. This review represents an integrated summary of recent advances on the function of platelets in pathophysiology that connects hemostasis, inflammation, and immunological response in health and disease and suggests that antiplatelet treatment might be used for more than only thrombosis.

SWATH-MS identification of CXCL7, LBP, TGFβ1 and PDGFRβ as novel biomarkers in human systemic mastocytosis

Mastocytosis is a rare myeloproliferative disease, characterised by accumulation of neoplastic mast cells in one or several organs. It presents as cutaneous or systemic. Patients with advanced systemic mastocytosis have a median survival of 3.5 years. The aetiology of mastocytosis is poorly understood, patients present with a broad spectrum of varying clinical symptoms that lack specificity to point clearly to a definitive diagnosis. Discovery of novel blood borne biomarkers would provide a tractable method for rapid identification of mastocytosis and its sub-types. Moving towards this goal, we carried out a clinical biomarker study on blood from twenty individuals (systemic mastocytosis: n = 12, controls: n = 8), which were subjected to global proteome investigation using the novel technology SWATH-MS. This identified several putative biomarkers for systemic mastocytosis. Orthogonal validation of these putative biomarkers was achieved using ELISAs. Utilising this workflow, we identified and validated CXCL7, LBP, TGFβ1 and PDGF receptor-β as novel biomarkers for systemic mastocytosis. We demonstrate that CXCL7 correlates with neutrophil count offering a new insight into the increased prevalence of anaphylaxis in mastocytosis patients. Additionally, demonstrating the utility of SWATH-MS for the discovery of novel biomarkers in the systemic mastocytosis diagnostic sphere.

Perioperative platelet count in peripheral blood is associated with the early stage of PND after major orthopedic surgery: a prospective observational study

Background

Perioperative neurocognitive disorders (PND) are common complications of major surgery among elderly patients, remarkably decreasing patients’ life quality. Platelet count has been proved to be an essential factor in inflammation. However, as far as we know, the relationship between platelet count and PND is not clear yet in the orthopedic area. PND could be a long-term disease, which sometimes lasts for several years, and it is meaningful to find a biomarker of PND at the early stage. Thus, we designed this study to find out the association between perioperative platelet count and occurrence of PND, and determine whether preoperative platelet count could be a biomarker of the early stage of PND.

Methods

A prospective observational study was performed on the patients who would take total knee arthroplasty or total hip arthroplasty. Their peripheral platelets were counted by blood routine examination 1 day before and 3 days after the surgery. And we assessed their neurocognitive functions 1 day before and 3 days after the surgery. These data were recorded and analyzed to find out the relationship between platelet count and the occurrence of PND.

Results

Eventually, 70 patients finished the whole process, and 14 of them developed PND. The median preoperative platelet count in the PND group was significantly higher than that in the non-PND group (239 vs 168 × 10^9/L, p = 0.009). Preoperative platelet count was an independent risk factor for PND (odds ratio = 1.014, 95% confidence interval [CI] 1.000–1.027, P = 0.043) in the logistic multivariable regression, while the area under the curve of the receiver operating characteristic curve of the prediction model was 0.796 (95% CI 0.676–0.916).

Conclusions

The higher preoperative and postoperative level of platelet count in the peripheral blood were associated with the early stage of PND, and preoperative platelet count could be a potential predictor of the early stage of PND in patients undergoing major orthopedic surgeries.

Trial registration

Chinese Clinical Trial Registry: ChiCTR2000033001, registration date: 17 May 2020.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02899-7.

Solution NMR Spectroscopy for Characterizing Protein-Glycosaminoglycan Interactions

Solution nuclear magnetic resonance (NMR) spectroscopy and, in particular, chemical shift perturbation (CSP) titration experiments are ideally suited for mapping and characterizing the binding interface of macromolecular complexes. ¹H-¹⁵N-HSQC-based CSP studies have become the method of choice due to their simplicity, short-time requirements, and minimal working knowledge of NMR. CSP studies for characterizing protein-glycosaminoglycan (GAG) interactions can be challenging due to binding-induced aggregation/precipitation and/or poor quality data. In this chapter, we discuss how optimizing experimental conditions such as protein concentration, choice of buffer pH, ionic strength, and GAG size, as well as sensitivity of NMR instrumentation can overcome these roadblocks to obtain meaningful structural insights into protein-GAG interactions.

The marriage of chemokines and galectins as functional heterodimers

Trafficking of leukocytes and their local activity profile are of pivotal importance for many (patho)physiological processes. Fittingly, microenvironments are complex by nature, with multiple mediators originating from diverse cell types and playing roles in an intimately regulated manner. To dissect aspects of this complexity, effectors are initially identified and structurally characterized, thus prompting familial classification and establishing foci of research activity. In this regard, chemokines present themselves as role models to illustrate the diversification and fine-tuning of inflammatory processes. This in turn discloses the interplay among chemokines, their cell receptors and cognate glycosaminoglycans, as well as their capacity to engage in new molecular interactions that form hetero-oligomers between themselves and other classes of effector molecules. The growing realization of versatility of adhesion/growth-regulatory galectins that bind to glycans and proteins and their presence at sites of inflammation led to testing the hypothesis that chemokines and galectins can interact with each other by protein-protein interactions. In this review, we present some background on chemokines and galectins, as well as experimental validation of this chemokine-galectin heterodimer concept exemplified with CXCL12 and galectin-3 as proof-of-principle, as well as sketch out some emerging perspectives in this arena.

"Platelet-rich plasma holds promise in management of rheumatoid arthritis"-systematic review

The treatment of rheumatoid arthritis (RA) has been closely evolving with an understanding of disease pathogenesis with disease modifying anti-rheumatoid drugs (DMARDS) and Biologic DMARDS being the main stay. platelet rich plasma (PRP) has been the center of research in many specialties in the past decade. Its ability to stop and reverse inflammation have attracted researchers to try PRP in RA. A systematic review of studies on PRP in RA is lacking. The study protocol was prospectively registered in PROSPERO. Detailed search of Cochrane, Scopus, Medline, Embase, and Web of science databases were made to identify the relevant articles till Sep 2020 following Cochrane and PRISMA guidelines. Number of subjects, Animal model used, cell lines used for the study, method of induction of arthritis, PRP dose, concentration used, frequency of administration and clinical, histologic, and molecular changes from baseline following PRP use were extracted and analysed. Eight studies were included for the review. Four of these were in-vitro studies. Two were exclusive animal studies. One study analysed the effects of PRP in RA in both animal models (mice) and Hela cell lines. One study was a report of a series of patients of resistant RA treated with PRP. In the in vitro studies while platelets increase the migration and invasion of RA-FLS, they suppressed the inflammation on the whole. Available animal studies and the Human study have shown encouraging results. There has been no evidence of exacerbation of inflammation in these studies. The quantity and quality of literature on the effects of PRP in treating joint pathologies in RA is limited. Preclinical studies show decrease in disease activity with good safety profile. Invitro studies show suppression of inflammation. Thus, the available literature is encouraging towards the use of PRP in RA. Larger trials and molecular studies to understand the exact role of platelets in disease pathogenesis and treatment mechanisms are needed to decide the future course of PRP in RA.

The Chemokine CXCL7 Is Related to Angiogenesis and Associated With Poor Prognosis in Colorectal Cancer Patients

Objective

The present study was designed to investigate the role of the chemokine CXCL7 in angiogenesis and explore its prognostic value in colorectal cancer (CRC).

Methods

A total of 160 CRC patients who had undergone surgery were included in this study, and staged according to the guidelines of the AJCC, 7^th Edition. Expression of CXCL7 and VEGF was detected by immunohistochemical (IHC) staining and divided into high and low expression subgroups. The correlation between CXCL7 and VEGF expression was evaluated by Spearman’s rank-correlation coefficient. Prognosis based on CXCL7 and VEGF was evaluated using the Cox proportional hazards regression model and a nomogram of 5-year overall survival (OS) time.

Results

CXCL7 was highly expressed in tumor tissues (65.63% vs 25.00% in paracancerous tissue, P < 0.001), as was VEGF. CXCL7 and VEGF expression correlated well with N and TNM stage cancers (all P < 0.001). Importantly, CXCL7 was positively correlated with VEGF expression in CRC tissues. CXCL7 was an independent predictor of poor OS of CRC patients (HR = 2.216, 95% CI: 1.069-4.593, P = 0.032), and co-expression of CXCL7 and VEGF of predicted poor OS of 56.96 months.

Conclusion

Expression of CXCL7 correlated with VEGF and was associated with poor clinical outcomes in CRC patients.

Modulation of Early Neutrophil Granulation: The Circulating Tumor Cell-Extravesicular Connection in Pancreatic Ductal Adenocarcinoma

Simple Summary

Circulating tumor cells (CTCs) found in the blood of pancreatic cancer patients show a worse prognosis to therapy if they are seen in clusters of cells with neutrophils or platelets or with other cell types than when they are seen as singlets. We wanted to investigate if there is a secondary mode of communication between the CTCs and neutrophils that causes them to associate. We describe for the first time an extravesicular (EV) mediated communication between CTCs and neutrophils that modulates early transcriptome changes that can cause neutrophils to partially degranulate and form associations. We also identify the protein cargo carried in such EVs and how when added to naïve neutrophils, they can modulate transcriptomic changes in neutrophils partially disarming them to form clusters rather than undergo specialized cell death, which is characterized by release of condensed chromatin (NETs) and granular contents termed as NETosis.

Abstract

Tumor cells dissociate from the primary site and enter into systemic circulation (circulating tumor cells, CTCs) either alone or as tumor microemboli (clusters); the latter having an increased predisposition towards forming distal metastases than single CTCs. The formation of clusters is, in part, created by contacts between cell–cell junction proteins and/or cytokine receptor pairs with other cells such as neutrophils, platelets, fibroblasts, etc. In the present study, we provide evidence for an extravesicular (EV) mode of communication between pancreatic cancer CTCs and neutrophils. Our results suggest that the EV proteome of CTCs contain signaling proteins that can modulate degranulation and granule mobilization in neutrophils and, also, contain tissue plasminogen activator and other proteins that can regulate cluster formation. By exposing naïve neutrophils to EVs isolated from CTCs, we further show how these changes are modulated in a dynamic fashion indicating evidence for a deeper EV based remodulatory effect on companion cells in clusters.

Candidate proteomic biomarkers in systemic sclerosis discovered using mass-spectrometry: an update of a systematic review (2014-2020)

Background. Systemic sclerosis (Ssc) is an autoimmune disease characterized by graduate cutaneous and tissue fibrosis development and irreversible fibroproliferative vascular changes.The aim of the current systematic review was to update the list of proteomic candidate biomarkers identified from Ssc samples with mass spectrometry techniques.Methods. Medline and Scopus databases were searched on 1^st September 2020. Relevant articles were searched from March 2014 until September 2020. Two independent reviewers evaluated the retrieved articles.Results. From a total of 97 articles, 9 articles were included in the final analysis summarizing 539 candidate proteomic biomarkers from various samples from Ssc patients (a larger number compared to the previous systematic review). Most biomarkers were identified from cutaneous biopsies. Only 5 articles included a validation step of the findings with only 13 biomarkers being validated.Conclusions. Although many candidate biomarkers were additionally identified, independent validation studies are needed in order to evaluate the importance of these biomarkers for Ssc patients.

Proteomic discovery in sickle cell disease: Elevated neurogranin levels in children with sickle cell disease

PURPOSE

Sickle cell disease (SCD) is an inherited hemoglobinopathy that causes stroke and silent cerebral infarct (SCI). Our aim was to identify markers of brain injury in SCD.

EXPERIMENTAL DESIGN

Plasma proteomes were analyzed using a sequential separation approach of hemoglobin (Hb) and top abundant plasma protein depletion, followed by reverse phase separation of intact proteins, trypsin digestion, and tandem mass spectrometry. We compared plasma proteomes of children with SCD with and without SCI in the Silent Cerebral Infarct Multi-Center Clinical Trial (SIT Trial) to age-matched, healthy non-SCD controls.

RESULTS

From the SCD group, 1172 proteins were identified. Twenty-five percent (289/1172) were solely in the SCI group. Twenty-five proteins with enriched expression in the human brain were identified in the SCD group. Neurogranin (NRGN) was the most abundant brain-enriched protein in plasma of children with SCD. Using a NRGN sandwich immunoassay and SIT Trial samples, median NRGN levels were higher at study entry in children with SCD (0.28 ng/mL, N = 100) compared to control participants (0.12 ng/mL, N = 25, p < 0.0004).

CONCLUSIONS AND CLINICAL RELEVANCE

NRGN levels are elevated in children with SCD. NRGN and other brain-enriched plasma proteins identified in plasma of children with SCD may provide biochemical evidence of neurological injury.

Neutrophil recruitment by chemokines Cxcl1/KC and Cxcl2/MIP2: Role of Cxcr2 activation and glycosaminoglycan interactions

Chemokines play a crucial role in combating microbial infection by recruiting blood neutrophils to infected tissue. In mice, the chemokines Cxcl1/KC and Cxcl2/MIP2 fulfill this role. Cxcl1 and Cxcl2 exist as monomers and dimers, and exert their function by activating the Cxcr2 receptor and binding glycosaminoglycans (GAGs). Here, we characterized Cxcr2 G protein and β-arrestin activities, and GAG heparan sulfate (HS) interactions of Cxcl1 and Cxcl2 and of the trapped dimeric variants. To understand how Cxcr2 and GAG interactions impact in vivo function, we characterized their neutrophil recruitment activity to the peritoneum, Cxcr2 and CD11b levels on peritoneal and blood neutrophils, and transport profiles out of the peritoneum. Cxcl2 variants compared with Cxcl1 variants were more potent for Cxcr2 activity. Native Cxcl1 compared with native Cxcl2 and dimers compared with native proteins bound HS with higher affinity. Interestingly, recruitment activity between native Cxcl1 and Cxcl2, between dimers, and between the native protein and the dimer could be similar or very different depending on the dose or the time point. These data indicate that peritoneal neutrophil recruitment cannot be solely attributed to Cxcr2 or GAG interactions, and that the relationship between recruited neutrophils, Cxcr2 activation, GAG interactions, and chemokine levels is complex and highly context dependent. We propose that the ability of Cxcl1 and Cxcl2 to reversibly exist as monomers and dimers and differences in their Cxcr2 activity and GAG interactions coordinate neutrophil recruitment and activation, which play a critical role for successful resolution of inflammation.

Platelet α-granule cargo packaging and release are affected by the luminal proteoglycan, serglycin

BACKGROUND

Serglycin (SRGN) is an intragranular, sulfated proteoglycan in hematopoietic cells that affects granule composition and function.

OBJECTIVE

To understand how SRGN affects platelet granule packaging, cargo release, and extra-platelet microenvironments.

METHODS

Platelets and megakaryocytes from SRGN-/- mice were assayed for secretion kinetics, cargo levels, granule morphology upon activation, and receptor shedding.

RESULTS

Metabolic, 35 SO4 labeling identified SRGN as a major sulfated macromolecule in megakaryocytes. SRGN colocalized with α-granule markers (platelet factor 4 [PF4], von Willebrand factor [VWF], and P-selectin), but its deletion did not affect α-granule morphology or number. Platelet α-granule composition was altered, with a reduction in basic proteins (pI ≥8; e.g., PF4, SDF-1, angiogenin) and constitutive release of PF4 from SRGN-/- megakaryocytes. P-Selectin, VWF, and fibrinogen were unaffected. Serotonin (5-HT) uptake and β-hexosaminidase (HEXB) were slightly elevated. Thrombin-induced exocytosis of PF4 from platelets was defective; however, release of RANTES/CCL5 was normal and osteopontin secretion was more rapid. Release of 5-HT and HEXB (from dense granules and lysosomes, respectively) were unaffected. Ultrastructural studies showed distinct morphologies in activated platelets. The α-granule lumen of SRGN-/- platelet had a grainy staining pattern, whereas that of wild-type granules had only fibrous material remaining. α-Granule swelling and decondensation were reduced in SRGN-/- platelets. Upon stimulation of platelets, a SRGN/PF4 complex was released in a time- and agonist-dependent manner. Shedding of GPVI from SRGN-/- platelets was modestly enhanced. Shedding of GP1b was unaffected.

CONCLUSION

The polyanionic proteoglycan SRGN influences α-granule packaging, cargo release, and shedding of platelet membrane proteins.

Structural basis of a chemokine heterodimer binding to glycosaminoglycans

Chemokines Cxcl1/KC and Cxcl2/MIP2 play a crucial role in coordinating neutrophil migration to the insult site. Chemokines' recruitment activity is regulated by monomer-dimer equilibrium and binding to glycosaminoglycans (GAGs). GAG chains exist as covalently linked to core proteins of proteoglycans (PGs) and also as free chains due to cleavage by heparanases during the inflammatory response. Compared with free GAGs, binding to GAGs in a PG is influenced by their fixed directionality due to covalent linkage and restricted mobility. GAG interactions impact chemokine monomer/dimer levels, chemotactic and haptotactic gradients, life time, and presentation for receptor binding. Here, we show that Cxcl1 and Cxcl2 also form heterodimers. Using a disulfide-trapped Cxcl1-Cxcl2 heterodimer, we characterized its binding to free heparin using nuclear magnetic resonance and isothermal titration calorimetry, and to immobilized heparin and heparan sulfate using surface plasmon resonance. These data, in conjunction with molecular docking, indicate that the binding characteristics such as geometry and stoichiometry of the heterodimer are different between free and immobilized GAGs and are also distinctly different from those of the homodimers. We propose that the intrinsic asymmetry of the heterodimer structure, along with differences in its binding to PG GAGs and free GAGs, regulate chemokine function.

Multiplexed quantitative proteomics provides mechanistic cues for malaria severity and complexity

Management of severe malaria remains a critical global challenge. In this study, using a multiplexed quantitative proteomics pipeline we systematically investigated the plasma proteome alterations in non-severe and severe malaria patients. We identified a few parasite proteins in severe malaria patients, which could be promising from a diagnostic perspective. Further, from host proteome analysis we observed substantial modulations in many crucial physiological pathways, including lipid metabolism, cytokine signaling, complement, and coagulation cascades in severe malaria. We propose that severe manifestations of malaria are possibly underpinned by modulations of the host physiology and defense machinery, which is evidently reflected in the plasma proteome alterations. Importantly, we identified multiple blood markers that can effectively define different complications of severe falciparum malaria, including cerebral syndromes and severe anemia. The ability of our identified blood markers to distinguish different severe complications of malaria may aid in developing new clinical tests for monitoring malaria severity.

The Immune Nature of Platelets Revisited

Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can act as circulating sentinels by expressing Toll-like receptors (TLR) that bind pathogens and this allows platelets to effectively kill them or present them to cells of the immune system. Furthermore, activated platelets secrete and express many pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues. In addition, platelets can directly influence adaptive immune responses via secretion of, for example, CD40 and CD40L molecules. Platelets are also the source of most of the microvesicles in the circulation and these miniscule elements further enhance the platelet’s ability to communicate with the immune system. More recently, it has been demonstrated that platelets and their parent cells, the megakaryocytes (MK), can also uptake, process and present both foreign and self-antigens to CD8+ T-cells conferring on them the ability to directly alter adaptive immune responses. This review will highlight several of the non-hemostatic attributes of platelets that clearly and rightfully place them as integral players in immune reactions.

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Platelets can act as circulating sentinels by expressing pathogen-associated molecular pattern receptors that bind pathogens and induce their killing and elimination.

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Activated platelets secrete and express a multitude of pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues.

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Platelets express and secrete many critical immunoregulatory molecules that significantly affect both innate and adaptive immune responses.

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Platelets are the primary source of microparticles in the circulation and these augment the platelet’s ability to communicate with the immune system.

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Platelets and megakaryocytes can act as antigen presenting cells and present both foreign- and self-peptides to T-cells.

Role of Chemokines in the Biology of Cholangiocarcinoma

Cholangiocarcinoma (CCA), a heterogeneous tumor with poor prognosis, can arise at any level in the biliary tree. It may derive from epithelial cells in the biliary tracts and peribiliary glands and possibly from progenitor cells or even hepatocytes. Several risk factors are responsible for CCA onset, however an inflammatory milieu nearby the biliary tree represents the most common condition favoring CCA development. Chemokines play a key role in driving the immunological response upon liver injury and may sustain tumor initiation and development. Chemokine receptor-dependent pathways influence the interplay among various cellular components, resulting in remodeling of the hepatic microenvironment towards a pro-inflammatory, pro-fibrogenic, pro-angiogenic and pre-neoplastic setting. Moreover, once tumor develops, chemokine signaling may influence its progression. Here we review the role of chemokines in the regulation of CCA development and progression, and the modulation of angiogenesis, metastasis and immune control. The potential role of chemokines and their receptors as possible biomarkers and/or therapeutic targets for hepatobiliary cancer is also discussed.

Increased CCL24 and CXCL7 levels in the cerebrospinal fluid of patients with neurosyphilis

Background

Monocytes are recruited into the cerebrospinal fluid (CSF) of patients with neurosyphilis, suggesting abnormal chemokine expression. We aimed to investigate the aberrant expression of chemokines in the CSF of these patients.

Methods

CSF and serum samples were collected from patients with neurosyphilis between July 2017 and June 2019 in the Dermatology Department, Second Affiliated Hospital of Zhejiang University. Differences in the expression of 38 chemokines between patients with and without neurosyphilis were detected using RayBio^® Human Chemokine Antibody Array C1. CCL24 and CXCL7 levels in the patients’ CSF and serum were further measured using RayBio^® CCL24 and CXCL7 ELISA kits.

Results

Ninety‐three CSF and serum samples of patients with syphilis were collected. Antibody array analysis showed that the CSF levels of CCL24 (P = .0185), CXCL7 (P < .0001), CXCL13 (P < .0001), CXCL10 (P < .0001), and CXCL8 (P < .0001) were significantly higher in patients with than without neurosyphilis. ELISA confirmed significantly higher CCL24 and CXCL7 levels in the CSF of patients with than without neurosyphilis (CCL24: 6.082 ± 1.137 pg/mL vs 1.773 ± 0.4565 pg/mL, P = .0037; CXCL7: 664.3 ± 73.19 pg/mL vs 431.1 ± 90.54 pg/mL, P = .0118). Increased CCL24 and CXCL7 expression was seen throughout all neurosyphilis stages, had moderate diagnostic efficiency for neurosyphilis, and correlated poorly with CSF cell count and Venereal Disease Research Laboratory titer. CSF CCL24 levels also correlated poorly with CSF protein concentration.

Conclusion

Abnormally high CSF chemokines levels may play a role in the pathogenesis of neurosyphilis.

Structural Insights Into How Proteoglycans Determine Chemokine-CXCR1/CXCR2 Interactions: Progress and Challenges

Proteoglycans (PGs), present in diverse environments, such as the cell membrane surface, extracellular milieu, and intracellular granules, are fundamental to life. Sulfated glycosaminoglycans (GAGs) are covalently attached to the core protein of proteoglycans. PGs are complex structures, and are diverse in terms of amino acid sequence, size, shape, and in the nature and number of attached GAG chains, and this diversity is further compounded by the phenomenal diversity in GAG structures. Chemokines play vital roles in human pathophysiology, from combating infection and cancer to leukocyte trafficking, immune surveillance, and neurobiology. Chemokines mediate their function by activating receptors that belong to the GPCR class, and receptor interactions are regulated by how, when, and where chemokines bind GAGs. GAGs fine-tune chemokine function by regulating monomer/dimer levels and chemotactic/haptotactic gradients, which are also coupled to how they are presented to their receptors. Despite their small size and similar structures, chemokines show a range of GAG-binding geometries, affinities, and specificities, indicating that chemokines have evolved to exploit the repertoire of chemical and structural features of GAGs. In this review, we summarize the current status of research on how GAG interactions regulate ELR-chemokine activation of CXCR1 and CXCR2 receptors, and discuss knowledge gaps that must be overcome to establish causal relationships governing the impact of GAG interactions on chemokine function in human health and disease.

Release kinetic of pro- and anti-inflammatory biomolecules from platelet-rich plasma and functional study on osteoarthritis synovial fibroblasts

BACKGROUND AIMS

This study evaluated the release kinetics of numerous representative and less studied platelet-rich plasma (PRP) cytokines/chemokines with regard to the effects of various cellular compositions and incubation times. In addition, the biological effects of different PRPs on osteoarthritis synovial fibroblasts in vitro were tested.

METHODS

Peripheral whole blood was collected from healthy donors, and pure platelet-rich plasma (P-PRP), leukocyte-rich platelet-rich plasma (L-PRP) and platelet-poor plasma (PPP) were prepared for the analysis of the following biomolecules: IL-1β, IL-4, IL-6, IL-10, IL-17a, IL-22, MIP-1α/CCL-3, RANTES/CCL-5, MCP-3/CCL-7, Gro-α/CXCL-1, PF-4/CXCL-4, ENA-78/CXCL-5, NAP-2/CXCL-7, IL-8/CXCL-8, Fractalkine/CX3CL-1, s-CD40L P-PRP, L-PRP and PPP. Their effect on osteoarthritis synovial fibroblasts in vitro was tested by analyzing changes induced in both gene expression on a panel of representative molecules involved in physiopathology of joint environment and synthesis of IL-1β, IL-8 and hyaluronic acid.

RESULTS

This study demonstrated that among the 16 analyzed biomolecules, four were undetectable, whereas most of the detected biomolecules were more concentrated in L-PRP even when concentrations were normalized to platelet number. Despite the pro-inflammatory boost, the various PRP preparations did not alter synovial fibroblast gene expression of specific factors that play a pivotal role in joint tissue homeostasis and are able to induce anti-inflammatory (TIMP-1) biomolecules.

DISCUSSION

This study provides a set of reference data on the concentration and release kinetics of some less explored biomolecules that could represent potential specific effectors in the modulation of inflammatory processes and in tissue repair after treatment with PRP.

Platelets: emerging facilitators of cellular crosstalk in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease in which a variety of circulating pro-inflammatory cells and dysregulated molecules are involved in disease aetiology and progression. Platelets are an important cellular element in the circulation that can bind several dysregulated molecules (such as collagen, thrombin and fibrinogen) that are present both in the synovium and the circulation of patients with RA. Platelets not only respond to dysregulated molecules in their environment but also transport and express their own inflammatory mediators, and serve as regulators at the boundary between haemostasis and immunity. Activated platelets also produce microparticles, which further convey signalling molecules and receptors to the synovium and circulation, thereby positioning these platelet-derived particles as strategic regulators of inflammation. These diverse functions come together to make platelets facilitators of cellular crosstalk in RA. Thus, the receptor functions, ligand binding potential and dysregulated signalling pathways in platelets are becoming increasingly important for treatment in RA. This Review aims to highlight the role of platelets in RA and the need to closely examine platelets as health indicators when designing effective pharmaceutical targets in this disease.

Formyl peptide receptor 2 regulates monocyte recruitment to promote intestinal mucosal wound repair

Mucosal wound repair is coordinated by dynamic crosstalk between endogenous and exogenous mediators and specific receptors on epithelial cells and infiltrating immune cells. One class of such receptor-ligand pairs involves formyl peptide receptors (FPRs) that have been shown to influence inflammatory response and repair. Here we explored the role of murine Fpr2/3, an ortholog of human FPR2/receptor for lipoxin A4 (ALX), in orchestrating intestinal mucosal repair. Compared with wild-type (WT) mice, Fpr2/3-/- mice exhibited delayed recovery from acute experimental colitis and perturbed repair after biopsy-induced colonic mucosal injury. Decreased numbers of infiltrating monocytes were observed in healing wounds from Fpr2/3-/- mice compared with WT animals. Bone marrow transplant experiments revealed that Fpr2/3-/- monocytes showed a competitive disadvantage when infiltrating colonic wounds. Moreover, Fpr2/3-/- monocytes were defective in chemotactic responses to the chemokine CC chemokine ligand (CCL)20, which is up-regulated during early phases of inflammation. Analysis of Fpr2/3-/- monocytes revealed altered expression of the CCL20 receptor CC chemokine receptor (CCR)6, suggesting that Fpr2/3 regulates CCL20-CCR6-mediated monocyte chemotaxis to sites of mucosal injury in the gut. These findings demonstrate an important contribution of Fpr2/3 in facilitating monocyte recruitment to sites of mucosal injury to influence wound repair.-Birkl, D., O'Leary, M. N., Quiros, M., Azcutia, V., Schaller, M., Reed, M., Nishio, H., Keeney, J., Neish, A. S., Lukacs, N. W., Parkos, C. A., Nusrat, A. Formyl peptide receptor 2 regulates monocyte recruitment to promote intestinal mucosal wound repair.

Dysregulated IL-1β-GM-CSF Axis in Acute Rheumatic Fever That Is Limited by Hydroxychloroquine

BACKGROUND

Acute rheumatic fever (ARF) and rheumatic heart disease are autoimmune consequences of group A streptococcus infection and remain major causes of cardiovascular morbidity and mortality around the world. Improved treatment has been stymied by gaps in understanding key steps in the immunopathogenesis of ARF and rheumatic heart disease. This study aimed to identify (1) effector T cell cytokine(s) that might be dysregulated in the autoimmune response of patients with ARF by group A streptococcus, and (2) an immunomodulatory agent that suppresses this response and could be clinically translatable to high-risk patients with ARF.

METHODS

The immune response to group A streptococcus was analyzed in peripheral blood mononuclear cells from an Australian Aboriginal ARF cohort by a combination of multiplex cytokine array, flow cytometric analysis, and global gene expression analysis by RNA sequencing. The immunomodulatory drug hydroxychloroquine was tested for effects on this response.

RESULTS

We found a dysregulated interleukin-1β-granulocyte-macrophage colony-stimulating factor (GM-CSF) cytokine axis in ARF peripheral blood mononuclear cells exposed to group A streptococcus in vitro, whereby persistent interleukin-1β production is coupled to overproduction of GM-CSF and selective expansion of CXCR3⁺CCR4^-CCR6^- CD4 T cells. CXCR3⁺CCR4^-CCR6^- CD4 T cells are the major source of GM-CSF in human CD4 T cells and CXCL10, a CXCR3 ligand and potent T helper 1 chemoattractant, was elevated in sera from patients with ARF. GM-CSF has recently emerged as a key T cell-derived effector cytokine in numerous autoimmune diseases, including myocarditis, and the production of CXCL10 may explain selective trafficking of these cells to the heart. We provide evidence that interleukin-1β amplifies the expansion of GM-CSF-expressing CD4 T cells, which is effectively suppressed by hydroxychloroquine. RNA sequencing showed shifts in gene expression profiles and differentially expressed genes in peripheral blood mononuclear cells derived from patients at different clinical stages of ARF.

CONCLUSIONS

Given the safety profile of hydroxychloroquine and its clinical pedigree in treating autoimmune diseases such as rheumatoid arthritis, where GM-CSF plays a pivotal role, we propose that hydroxychloroquine could be repurposed to reduce the risk of rheumatic heart disease after ARF.

Structural basis of chemokine interactions with heparan sulfate, chondroitin sulfate, and dermatan sulfate

Chemokines play diverse roles in human pathophysiology, ranging from trafficking leukocytes and immunosurveillance to the regulation of metabolism and neural function. Chemokine function is intimately coupled to binding tissue glycosaminoglycans (GAGs), heparan sulfate (HS), chondroitin sulfate (CS), and dermatan sulfate (DS). Currently, very little is known about how the structural features and sequences of a given chemokine, the structure and sulfation pattern of a given GAG, and structural differences among GAGs and among chemokines impact binding interactions. In this study, we used solution NMR spectroscopy to characterize the binding interactions of two related neutrophil-activating chemokines, CXCL1 and CXCL5, with HS, CS, and DS. For both chemokines, the dimer bound all three GAGs with higher affinity than did the monomer, and affinities of the chemokines for CS and DS were lower than for HS. NMR-based structural models reveal diverse binding geometries and show that the binding surfaces for each of the three GAGs were different between the two chemokines. However, a given chemokine had similar binding interactions with CS and DS that were different from HS. Considering the fact that CXCL1 and CXCL5 activate the same CXCR2 receptor, we conclude that GAG interactions play a role in determining the nature of chemokine gradients, levels of free chemokine available for receptor activation, how chemokines bind their receptors, and that differences in these interactions determine chemokine-specific function.

Nox2 Regulates Platelet Activation and NET Formation in the Lung

The mortality rate of patients with critical illness has decreased significantly over the past two decades, but the rate of decline has slowed recently, with organ dysfunction as a major driver of morbidity and mortality. Among patients with the systemic inflammatory response syndrome (SIRS), acute lung injury is a common component with serious morbidity. Previous studies in our laboratory using a murine model of SIRS demonstrated a key role for NADPH oxidase 2 (Nox2)-derived reactive oxygen species in the resolution of inflammation. Nox2-deficient (gp91^phox−/y) mice develop profound lung injury secondary to SIRS and fail to resolve inflammation. Alveolar macrophages from gp91^phox−/y mice express greater levels of chemotactic and pro-inflammatory factors at baseline providing evidence that Nox2 in alveolar macrophages is critical for homeostasis. Based on the lung pathology with increased thrombosis in gp91^phox−/y mice, and the known role of platelets in the inflammatory process, we hypothesized that Nox2 represses platelet activation. In the mouse model, we found that platelet-derived chemokine (C-X-C motif) ligand 4 (CXCL4) and CXCL7 were increased in the bronchoalveolar fluid of gp91^phox−/y mice at baseline and 24 h post intraperitoneal zymosan-induced SIRS consistent with platelet activation. Activated platelets interact with leukocytes via P-selectin glycoprotein ligand 1 (PSGL-1). Within 2 h of SIRS induction, alveolar neutrophil PSGL-1 expression was higher in gp91^phox−/y mice. Platelet-neutrophil interactions were decreased in the peripheral blood of gp91^phox−/y mice consistent with movement of activated platelets to the lung of mice lacking Nox2. Based on the severe lung pathology and the role of platelets in the formation of neutrophil extracellular traps (NETs), we evaluated NET production. In contrast to previous studies demonstrating Nox2-dependent NET formation, staining of lung sections from mice 24 h post zymosan injection revealed a large number of citrullinated histone 3 (H3CIT) and myeloperoxidase positive cells consistent with NET formation in gp91^phox−/y mice that was virtually absent in WT mice. In addition, H3CIT protein expression and PAD4 activity were higher in the lung of gp91^phox−/y mice post SIRS induction. These results suggest that Nox2 plays a critical role in maintaining homeostasis by regulating platelet activation and NET formation in the lung.

Platelet-Neutrophil Interplay: Insights Into Neutrophil Extracellular Trap (NET)-Driven Coagulation in Infection

Well established for their central role in hemostasis, platelets have increasingly been appreciated as immune cells in recent years. This emerging role should not come as a surprise as the central immune cells of invertebrates, hemocytes, are able to phagocytose, secrete soluble mediators and promote coagulation of hemolymph, blurring the line between immunity and hemostasis. The undeniable evolutionary link between coagulation and immunity becomes even clearer as the role of platelets in inflammation is better understood. Platelets exert a range of immune-related functions, many of which involve an intimate interplay with leukocytes. Platelets promote leukocyte recruitment via endothelial activation and can serve as “landing pads” for leukocytes, facilitating cellular adhesion in vascular beds devoid of classic adhesion molecules. Moreover, platelets enhance leukocyte function both through direct interactions and through release of soluble mediators. Among neutrophil-platelets interactions, the modulation of neutrophil extracellular traps (NETs) is of great interest. Platelets have been shown to induce NET formation; and, in turn, NET components further regulate platelet and neutrophil function. While NETs have been shown to ensnare and kill pathogens, they also initiate coagulation via thrombin activation. In fact, increased NET formation has been associated with hypercoagulability in septic patients as well as in chronic vascular disorders. This review will delve into current knowledge of platelet-neutrophil interactions, with a focus on NET-driven coagulation, in the context of infectious diseases. A better understanding of these mechanisms will shed a light on the therapeutic potential of uncoupling immunity and coagulation through targeting of NETs.

The Role of Human Platelet Preparation for Toll-Like Receptors 2 and 4 Related Platelet Responsiveness

Background  Like immune cells, platelets express the repertoire of toll-like receptors (TLR), among them TLR2 and TLR4, which are important for the recognition of bacterial patterns. Receptor-mediated functional effects in platelets have been investigated, but reliable conclusions are tampered due to heterogeneous study designs with variable platelet preparation methods. This study compares TLR2- and TLR4-dependent platelet responsiveness in platelet-rich plasma (PRP) and in washed platelets (WPs).

Material and Methods  Fresh peripheral blood samples from healthy donors served for the preparation of PRP and WP. Basal and agonist-stimulated TLR2 and TLR4 expression levels were evaluated by flow cytometry. Light transmission aggregometry was used to investigate functional effects of TLR2 and TLR4 stimulation with Pam3CSK4 or LPS (lipopolysaccharides from Escherichia coli ) as ligands. The capacity of chemokine release was determined by immunoassays.

Results  Pam3CSK4 and LPS (in combination with thrombin) were able to induce aggregation in WP, but not in PRP, with threshold concentrations of 15 µg/mL. Basal expression levels of TLR2 and TLR4 were higher in WP than in PRP, increasing several-fold rapidly and persistently upon platelet activation with potent agonists. Pam3CSK4 (15 µg/mL) or LPS led to the submaximal release of RANTES, PF4, PDGF, NAP-2, and sCD40L from WP. In PRP, secretory effects are less pronounced for RANTES, PDGF, or PF4, and not detectable for NAP-2 or sCD40L.

Conclusion  The effects mediated by TLR2 and TLR4 stimulation are dependent on platelet preparation, an important issue for experimental designs and for manufacturing of platelet concentrates in transfusion medicine.

ELF4 facilitates innate host defenses against Plasmodium by activating transcription of Pf4 and Ppbp

Platelet factor 4 (PF4) is an anti-Plasmodium component of platelets. It is expressed in megakaryocytes and released from platelets following infection with Plasmodium Innate immunity is crucial for the host anti-Plasmodium response, in which type I interferon plays an important role. Whether there is cross-talk between innate immune signaling and the production of anti-Plasmodium defense peptides is unknown. Here we demonstrate that E74, like ETS transcription factor 4 (ELF4), a type I interferon activator, can help protect the host from Plasmodium yoelii infection. Mechanically, ELF4 binds to the promoter of genes of two C-X-C chemokines, Pf4 and pro-platelet basic protein (Ppbp), initiating the transcription of these two genes, thereby enhancing PF4-mediated killing of parasites from infected erythrocytes. Elf4 ^-/- mice are much more susceptible to Plasmodium infection than WT littermates. The expression level of Pf4 and Ppbp in megakaryocytes from Elf4 ^-/- mice is much lower than in those from control animals, resulting in increased parasitemia. In conclusion, our study uncovered a distinct role of ELF4, an innate immune molecule, in host defense against malaria.

How do chemokines navigate neutrophils to the target site: Dissecting the structural mechanisms and signaling pathways

Chemokines play crucial roles in combating microbial infection and initiating tissue repair by recruiting neutrophils in a timely and coordinated manner. In humans, no less than seven chemokines (CXCL1, CXCL2, CXCL3, CXCL5, CXCL6, CXCL7, and CXCL8) and two receptors (CXCR1 and CXCR2) mediate neutrophil functions but in a context dependent manner. Neutrophil-activating chemokines reversibly exist as monomers and dimers, and their receptor binding triggers conformational changes that are coupled to G-protein and β-arrestin signaling pathways. G-protein signaling activates a variety of effectors including Ca2+ channels and phospholipase C. β-arrestin serves as a multifunctional adaptor and is coupled to several signaling hubs including MAP kinase and tyrosine kinase pathways. Both G-protein and β-arrestin signaling pathways play important non-overlapping roles in neutrophil trafficking and activation. Functional studies have established many similarities but distinct differences for a given chemokine and between chemokines at the level of monomer vs. dimer, CXCR1 vs. CXCR2 activation, and G-protein vs. β-arrestin pathways. We propose that two forms of the ligand binding two receptors and activating two signaling pathways enables fine-tuned neutrophil function compared to a single form, a single receptor, or a single pathway. We summarize the current knowledge on the molecular mechanisms by which chemokine monomers/dimers activate CXCR1/CXCR2 and how these interactions trigger G-protein/β-arrestin-coupled signaling pathways. We also discuss current challenges and knowledge gaps, and likely advances in the near future that will lead to a better understanding of the relationship between the chemokine-CXCR1/CXCR2-G-protein/β-arrestin axis and neutrophil function.

Role of Platelets in Leukocyte Recruitment and Resolution of Inflammation

Platelets are most often recognized for their crucial role in the control of acute hemorrhage. However, current research has greatly expanded the appreciation of platelets beyond their contribution to primary hemostasis, indicating that platelets also actively participate in leukocyte recruitment and the regulation of the host defense in response to exogenous pathogens and sterile injury. Early recruitment of leukocytes, especially neutrophils, is the evolutionary stronghold of the innate immune response to successfully control exogenous infections. Platelets have been shown to physically interact with different leukocyte subsets during inflammatory processes. This interaction holds far-reaching implications for the leukocyte recruitment into peripheral tissues as well as the regulation of leukocyte cell autonomous functions, including the formation and liberation of neutrophil extracellular traps. These functions critically depend on the interaction of platelets with leukocytes. The host immune response and leukocyte recruitment must be tightly regulated to avoid excessive tissue and organ damage and to avoid chronification of inflammation. Thus, platelet-leukocyte interactions and the resulting leukocyte activation and recruitment also underlies tight regulation by several inherited feedback mechanisms to limit the extend of vascular inflammation and to protect the host from collateral damage caused by overshooting immune system activation. After the acute inflammatory phase has been overcome the host defense response must eventually be terminated to allow for resolution from inflammation and restoration of tissue and organ function. Besides their essential role for leukocyte recruitment and the initiation and propagation of vascular inflammation, platelets have lately also been implicated in the resolution process. Here, their contribution to phagocyte clearance, T cell recruitment and macrophage reprogramming is also of outmost importance. This review will focus on the role of platelets in leukocyte recruitment during the initiation of the host defense and we will also discuss the participation of platelets in the resolution process after acute inflammation.

Structural basis, stoichiometry, and thermodynamics of binding of the chemokines KC and MIP2 to the glycosaminoglycan heparin

Keratinocyte-derived chemokine (KC or mCXCL1) and macrophage inflammatory protein 2 (MIP2 or mCXCL2) play nonredundant roles in trafficking blood neutrophils to sites of infection and injury. The functional responses of KC and MIP2 are intimately coupled to their interactions with glycosaminoglycans (GAGs). GAG interactions orchestrate chemokine concentration gradients and modulate receptor activity, which together regulate neutrophil trafficking. Here, using NMR, molecular dynamics (MD) simulations, and isothermal titration calorimetry (ITC), we characterized the molecular basis of KC and MIP2 binding to the GAG heparin. Both chemokines reversibly exist as monomers and dimers, and the NMR analysis indicates that the dimer binds heparin with higher affinity. The ITC experiments indicate a stoichiometry of two GAGs per KC or MIP2 dimer and that the enthalpic and entropic contributions vary significantly between the two chemokine-heparin complexes. NMR-based structural models of heparin-KC and heparin-MIP2 complexes reveal that different combinations of residues from the N-loop, 40s turn, β₃-strand, and C-terminal helix form a binding surface within a monomer and that both conserved residues and residues unique to a particular chemokine mediate the binding interactions. MD simulations indicate significant residue-specific differences in their contribution to binding and affinity for a given chemokine and between chemokines. On the basis of our observations that KC and MIP2 bind to GAG via distinct molecular interactions, we propose that the differences in these GAG interactions lead to differences in neutrophil recruitment and play nonoverlapping roles in resolution of inflammation.

Lysines and Arginines play non-redundant roles in mediating chemokine-glycosaminoglycan interactions

Glycosaminoglycans (GAGs) bind a large array of proteins and mediate fundamental and diverse roles in human physiology. Ion pair interactions between protein lysines/arginines and GAG sulfates/carboxylates mediate binding. Neutrophil-activating chemokines (NAC) are GAG-binding proteins, and their sequences reveal high selectivity for lysines over arginines indicating they are functionally not equivalent. NAC binding to GAGs impacts gradient formation, receptor functions, and endothelial activation, which together regulate different components of neutrophil migration. We characterized the consequence of mutating lysine to arginine in NAC CXCL8, a well-characterized GAG-binding protein. We chose three lysines — two highly conserved lysines (K20 and K64) and a CXCL8-specific lysine (K67). Interestingly, the double K64R/K20R and K64R/K67R mutants are highly impaired in recruiting neutrophils in a mouse model. Further, both the mutants bind GAG heparin with higher affinity but show similar receptor activity. NMR and MD studies indicate that the structures are essentially identical to the WT, but the mutations alter the network of intramolecular ion pair interactions. These observations collectively indicate that the reduced in vivo recruitment is due to altered GAG interactions, higher GAG binding affinity can be detrimental, and specificity of lysines fine-tunes in vivo GAG interactions and function.

Glycosaminoglycan Interactions Fine-Tune Chemokine-Mediated Neutrophil Trafficking: Structural Insights and Molecular Mechanisms

Circulating neutrophils, rapidly recruited in response to microbial infection, form the first line in host defense. Humans express ~50 chemokines, of which a subset of seven chemokines, characterized by the conserved "Glu-Leu-Arg" motif, mediate neutrophil recruitment. Neutrophil-activating chemokines (NACs) share similar structures, exist as monomers and dimers, activate the CXCR2 receptor on neutrophils, and interact with tissue glycosaminoglycans (GAGs). Considering cellular assays have shown that NACs have similar CXCR2 activity, the question has been and remains, why do humans express so many NACs? In this review, we make the case that NACs are not redundant and that distinct GAG interactions determine chemokine-specific in vivo functions. Structural studies have shown that the GAG-binding interactions of NACs are distinctly different, and that conserved and specific residues in the context of structure determine geometries that could not have been predicted from sequences alone. Animal studies indicate recruitment profiles of monomers and dimers are distinctly different, monomer-dimer equilibrium regulates recruitment, and that recruitment profiles vary between chemokines and between tissues, providing evidence that GAG interactions orchestrate neutrophil recruitment. We propose in vivo GAG interactions impact several chemokine properties including gradients and lifetime, and that these interactions fine-tune and define the functional response of each chemokine that can vary between different cell and tissue types for successful resolution of inflammation.