Proteomics of apheresis platelet supernatants during routine storage: Gender-related differences

Omics markers of platelet transfusion in trauma patients

BACKGROUND

Even in the era of the COVID-19 pandemic, trauma remains the global leading cause of mortality under the age of 49. Trauma-induced coagulopathy is a leading driver of early mortality in critically ill patients, and transfusion of platelet products is a life-saving intervention to restore hemostasis in the bleeding patient. However, despite extensive functional studies based on viscoelastic assays, limited information is available about the impact of platelet transfusion on the circulating molecular signatures in trauma patients receiving platelet transfusion.

MATERIALS AND METHODS

To bridge this gap, we leveraged metabolomics and proteomics approaches to characterize longitudinal plasma samples (n = 118; up to 11 time points; total samples: 759) from trauma patients enrolled in the Control Of Major Bleeding After Trauma (COMBAT) study. Samples were collected in the field, in the emergency department (ED), and at intervals up to 168 h (7 days) post-hospitalization. Transfusion of platelet (PLT) products was performed (n = 30; total samples: 250) in the ED through 24 h post-hospitalization. Longitudinal plasma samples were subjected to mass spectrometry-based metabolomics and proteomics workflows. Multivariate analyses were performed to determine omics markers of transfusion of one, two, three, or more PLT transfusions.

RESULTS

Higher levels of tranexamic acid (TXA), inflammatory proteins, carnitines, and polyamines were detected in patients requiring PLT transfusion. Correlation of PLT units with omics data suggested sicker patients required more units and partially overlap with the population requiring transfusion of packed red blood cell products. Furthermore, platelet activation was likely increased in the most severely injured patients. Fatty acid levels were significantly lower in PLT transfusion recipients (at time of maximal transfusion: Hour 4) compared with non-recipients, while carnitine levels were significantly higher. Fatty acid levels restore later in the time course (e.g., post-PLT transfusion).

DISCUSSION

The present study provides the first multi-omics characterization of platelet transfusion efficacy in a clinically relevant cohort of trauma patients. Physiological alterations following transfusion were detected, highlighting the efficacy of mass spectrometry-based omics techniques to improve personalized transfusion medicine. More specialized clinical research studies focused on PLT transfusion, including organized pre and post transfusion sample collection and limitation to PLT products only, are required to fully understand subsequent metabolomic and proteomic alterations.

Platelet and cryoprecipitate transfusions from female donors improve coagulopathy in vitro

BACKGROUND

Females are relatively hypercoagulable compared with males, with increased platelet aggregation and improved clot dynamics. However, sex differences in coagulation have not yet been considered in transfusion guidelines. Therefore, our objective was to evaluate hemostatic differences in sex concordant and sex discordant cryoprecipitate and platelet transfusions. We hypothesized that transfusion of blood products from female donors results in improved coagulopathy compared with male blood products.

METHODS

This was a cohort study evaluating sex dimorphisms in coagulation assays and clotting factors in healthy volunteer plasma and cryoprecipitate. Sex dimorphisms in transfusions were evaluated using an in vitro coagulopathy model. Female or male platelets or single-donor cryoprecipitate was added to "recipient" whole blood after dilution of recipient blood with citrated saline to provoke a coagulopathic profile. Citrated native thromboelastography was then performed. Liquid chromatography/mass spectroscopy was performed on single-donor cryoprecipitate to evaluate sex dimorphisms in the proteome of cryoprecipitate.

RESULTS

Females have an increased proportion of functional fibrinogen. Transfusion of female-donor platelets and cryoprecipitate induces a larger decrease in R time and greater increase in angle than male-donor platelets or cryoprecipitate. Female-donor cryoprecipitate has increased factor V and factor XIII compared with male cryoprecipitate, and comprehensive proteomics revealed sex differences in several proteins with potential immunological significance.

CONCLUSION

Platelets and cryoprecipitate from female donors improve coagulopathy more than male blood products in vitro. Increased factor V and factor XIII activity as well as increased fibrinogen activity in female donors appears to drive this disparity. Sex differences in the proteome of cryoprecipitate may influence how transfusions modulate the thromboinflammation of trauma. The differing hemostatic profiles of female and male blood products suggest the potential role of sex-specific transfusions guidelines in hemostatic resuscitation.

How I use platelet transfusions

Platelet transfusions are commonly administered for the prevention or treatment of bleeding in patients with acquired thrombocytopenia across a range of clinical contexts. Recent data, including randomized trials, have highlighted uncertainties in the risk-benefit balance of this therapy, which is the subject of this review. Hemovigilance systems report that platelets are the most frequently implicated component in transfusion reactions. There is considerable variation in platelet count increment after platelet transfusion, and limited evidence of efficacy for clinical outcomes, including prevention of bleeding. Bleeding events commonly occur despite the different policies for platelet transfusion prophylaxis. The underlying mechanisms of harm reported in randomized trials may be related to the role of platelets beyond hemostasis, including mediating inflammation. Research supports the implementation of a restrictive platelet transfusion policy. Research is needed to better understand the impact of platelet donation characteristics on outcomes, and to determine the optimal thresholds for platelet transfusion before invasive procedures or major surgery (eg, laparotomy). Platelet transfusion policies should move toward a risk-adapted approach that does not focus solely on platelet count.

Current Understanding of the Relationship between Blood Donor Variability and Blood Component Quality

While differences among donors has long challenged meeting quality standards for the production of blood components for transfusion, only recently has the molecular basis for many of these differences become understood. This review article will examine our current understanding of the molecular differences that impact the quality of red blood cells (RBC), platelets, and plasma components. Factors affecting RBC quality include cytoskeletal elements and membrane proteins associated with the oxidative response as well as known enzyme polymorphisms and hemoglobin variants. Donor age and health status may also be important. Platelet quality is impacted by variables that are less well understood, but that include platelet storage sensitive metabolic parameters, responsiveness to agonists accumulating in storage containers and factors affecting the maintenance of pH. An increased understanding of these variables can be used to improve the quality of blood components for transfusion by using donor management algorithms based on a donors individual molecular and genetic profile.

Cholesterol-Rich Microdomains Contribute to PAR1 Signaling in Platelets Despite a Weak Localization of the Receptor in These Microdomains

Platelet protease-activated receptor 1 (PAR1) is a cell surface G-protein-coupled receptor (GPCR) that acts as a thrombin receptor promoting platelet aggregation. Targeting the PAR1 pathway by vorapaxar, a PAR1 antagonist, leads to a reduction in ischemic events in cardiovascular patients with a history of myocardial infarction or with peripheral arterial disease. In platelets, specialized microdomains highly enriched in cholesterol act as modulators of the activity of several GPCRs and play a pivotal role in the signaling pathway. However, their involvement in platelet PAR1 function remains incompletely characterized. In this context, we aimed to investigate whether activation of PAR1 in human platelets requires its localization in the membrane cholesterol-rich microdomains. Using confocal microscopy, biochemical isolation, and proteomics approaches, we found that PAR1 was not localized in cholesterol-rich microdomains in resting platelets, and only a small fraction of the receptor relocated to the microdomains following its activation. Vorapaxar treatment increased the level of PAR1 at the platelet surface, possibly by reducing its endocytosis, while its colocalization with cholesterol-rich microdomains remained weak. Consistent with a cholesterol-dependent activation of Akt and p38 MAP kinase in thrombin receptor-activating peptide (TRAP)-activated platelets, the proteomic data of cholesterol-rich microdomains isolated from TRAP-activated platelets showed the recruitment of proteins contributing to these signaling pathways. In conclusion, contrary to endothelial cells, we found that PAR1 was only weakly present in cholesterol-rich microdomains in human platelets but used these microdomains for efficient activation of downstream signaling pathways following TRAP activation.

Sex- and Gender-Related Factors in Blood Product Transfusions

Blood products are indicated for a plethora of conditions in several settings, with a variety of products available for transfusion, from highly processed specific components to whole blood. Matching the donor product to the recipient is crucial in avoiding serious transfusion reactions, with the extent of matching depending on the physiological need, setting, and product. There are important factors related to sex and gender differences in donated blood products, adverse reactions to those products, interplay with underlying pathology, as well as sociocultural differences in the collection. This article will review key sex- and gender-specific research related to the use of blood products with an emphasis on the acute care setting.

Dysregulated pathways and differentially expressed proteins associated with adverse transfusion reactions in different types of platelet components

Platelet components (PCs) are occasionally associated with adverse transfusion reactions (ATRs). ATRs can occur regardless of the type of PC being transfused, whether it is a single-donor apheresis PC (SDA-PC) or a pooled PC (PPCs). The purpose of this study was to investigate the proteins and dysregulated pathways in both of the main types of PCs. The proteomic profiles of platelet pellets from SDA-PCs and PPCs involved in ATRs were analysed using the label-free LC-MS/MS method. Differentially expressed proteins with fold changes >|1.5| in clinical cases versus controls were characterised using bioinformatic tools (RStudio, GeneCodis3, and Ingenuity Pathways Analysis (IPA). The proteins were confirmed by western blotting. The common primary proteins found to be dysregulated in both types of PCs were the mitochondrial carnitine/acylcarnitine carrier protein (SLC25A20), multimerin-1 (MMRN1), and calumenin (CALU), which are associated with the important enrichment of platelet activation, platelet degranulation, and mitochondrial activity. Furthermore, this analysis revealed the involvement of commonly dysregulated canonical pathways, particularly mitochondrial dysfunction, platelet activation, and acute phase response. This proteomic analysis provided an interesting contribution to our understanding of the meticulous physiopathology of PCs associated with ATR. A larger investigation would assist in delineating the most relevant proteins to target within preventive transfusion safety strategies. BIOLOGICAL SIGNIFICANCE: Within platelet transfusion strategies, the two primary types of PCs predominantly processed in Europe, include (i) single donor apheresis PCs (SDA-PCs) from one donor and (ii) pooled PCs (PPCs). The current study used PCs from five buffy coats derived from five whole blood donations that were identical in ABO, RH1 and KEL1 groups. Both PC types were shown to be associated with the onset of an ATR in the transfused patient. Several common platelet proteins were found to be dysregulated in bags associated with ATR occurrences regardless of the type of PCs transfused and of their process. The dysregulated proteins included mitochondrial carnitine/acylcarnitine carrier protein (SLC25A20), which is involved in a fatty acid oxidation disorder; calumenin (CALU); and multimerin-1 (MMRN1), which is chiefly involved in platelet activation and degranulation. Dysregulated platelet protein pathways for ATRs that occurred with SDA-PCs and PPCs could support the dysregulated functions found in association with those three proteins. Those common platelet proteins may become candidates to define biomarkers associated with the onset of an ATR from PC transfusions, including monitoring during the quality steps of PC manufacturing, provided that the results are confirmed in larger cohorts. This study enriches our knowledge of platelet proteomics in PCs under pathological conditions.

Platelet Storage Lesions: What More Do We Know Now?

Platelet concentrate (PC) transfusions are a lifesaving adjunct to control and prevent bleeding in cancer, hematologic, surgical, and trauma patients. Platelet concentrate availability and safety are limited by the development of platelet storage lesions (PSLs) and risk of bacterial contamination. Platelet storage lesions are a series of biochemical, structural, and functional changes that occur from blood collection to transfusion. Understanding of PSLs is key for devising interventions that prolong PC shelf life to improve PC access and wastage. This article will review advancements in clinical and mechanistic PSL research. In brief, exposure to artificial surfaces and high centrifugation forces during PC preparation initiate PSLs by causing platelet activation, fragmentation, and biochemical release. During room temperature storage, enhanced glycolysis and reduced mitochondrial function lead to glucose depletion, lactate accumulation, and product acidification. Impaired adenosine triphosphate generation reduces platelet capacity to perform energetically demanding processes such as hypotonic stress responses and activation/aggregation. Storage-induced alterations in platelet surface proteins such as thrombin receptors and glycoproteins decrease platelet aggregation. During storage, there is an accumulation of immunoactive proteins such as leukocyte-derive cytokines (tumor necrosis factor α, interleukin (IL) 1α, IL-6, IL-8) and soluble CD40 ligand which can participate in transfusion-related acute lung injury and nonhemolytic transfusion reactions. Storage-induced microparticles have been linked to enhanced platelet aggregation and immune system modulation. Clinically, stored PCs have been correlated with reduced corrected count increment, posttransfusion platelet recovery, and survival across multiple meta-analyses. Fresh PC transfusions have been associated with superior platelet function in vivo; however, these differences were abrogated after a period of circulation. There is currently insufficient evidence to discern the effect of PSLs on transfusion safety. Various bag and storage media changes have been proposed to reduce glycolysis and platelet activation during room temperature storage. Moreover, cryopreservation and cold storage have been proposed as potential methods to prolong PC shelf life by reducing platelet metabolism and bacterial proliferation. However, further work is required to elucidate and manage the PSLs specific to these storage protocols before its implementation in blood banks.

Gender proteomics I. Which proteins in non-sexual organs

Differences related to gender have long been neglected but recent investigations show that they are widespread and may be recognized with all types of omics approaches, both in tissues and in biological fluids. Our review compiles evidence collected with proteomics techniques in our species, mainly focusing on baseline parameters in non-sexual organs in healthy men and women. Data from human specimens had to be replaced with information from other mammals every time invasive procedures of sample procurement were involved.

SIGNIFICANCE

As our knowledge, and the methods to build it, get refined, gender differences need to receive more and more attention, as they influence the outcome of all aspects in lifestyle, including diet, exercise and environmental factors. In turn this background modulates a differential susceptibility to some disease, or a different pathogenetic mechanism, depending on gender, and a different response to pharmacological therapy. Preparing this review we meant to raise awareness about the gender issue. We anticipate that more and more often, in the future, separate evaluations will be carried out on male and female subjects as an alternative - and an upgrade - to the current approach of reference and test groups being 'matched for age and sex'.

A roadmap for cost-of-goods planning to guide economic production of cell therapy products

Cell therapy products are frequently developed and produced without incorporating cost considerations into process development, contributing to prohibitively costly products. Herein we contextualize individual process development decisions within a broad framework for cost-efficient therapeutic manufacturing. This roadmap guides the analysis of cost of goods (COG) arising from tissue procurement, material acquisition, facility operation, production, and storage. We present the specific COG considerations related to each of these elements as identified through a 2013 International Society for Cellular Therapy COG survey, highlighting the differences between autologous and allogeneic products. Planning and accounting for COG at each step in the production process could reduce costs, allowing for more affordable market pricing to improve the long-term viability of the cell therapy product and facilitate broader patient access to novel and transformative cell therapies.

Monitoring storage induced changes in the platelet proteome employing label free quantitative mass spectrometry

Shelf life of platelet concentrates is limited to 5-7 days due to loss of platelet function during storage, commonly referred to as the platelet storage lesion (PSL). To get more insight into the development of the PSL, we used label free quantitative mass spectrometry to identify changes in the platelet proteome during storage. In total 2501 proteins were accurately quantified in 3 biological replicates on at least 1 of the 7 different time-points analyzed. Significant changes in levels of 21 proteins were observed over time. Gene ontology enrichment analysis of these proteins revealed that the majority of this set was involved in platelet degranulation, secretion and regulated exocytosis. Twelve of these proteins have been shown to reside in α-granules. Upon prolonged storage (13-16 days) elevated levels of α-2-macroglobulin, glycogenin and Ig μ chain C region were identified. Taken together this study identifies novel markers for monitoring of the PSL that may potentially also be used for the detection of "young" and "old" platelets in the circulation.

Postinjury Inflammation and Organ Dysfunction

The development of organ dysfunction (OD) is related to the intensity and balance between trauma-induced simultaneous, opposite inflammatory responses. Early proinflammation via innate immune system activation may cause early OD, whereas antiinflammation, via inhibition of the adaptive immune system and apoptosis, may induce immunoparalysis, impaired healing, infections, and late OD. Patients discharged with low-level OD may develop the persistent inflammation-immunosuppression catabolism syndrome. Although the incidence of multiple organ failure has decreased over time, it remains morbid, lethal, and resource intensive. However, single OD, especially acute lung injury, remains frequent. Treatment is limited, and prevention remains the mainstay strategy.

Hitchhiker's guide to the red cell storage galaxy: Omics technologies and the quality issue

Red blood cell storage in the blood bank makes millions of units of available for transfusion to civilian and military recipients every year. From glass bottles to plastic bags, from anticoagulants to complex additives, from whole blood to leukocyte filtered packed red blood cells: huge strides have been made in the field of blood component processing and storage in the blood bank during the last century. Still, refrigerated preservation of packed red blood cells under blood bank conditions results in the progressive accumulation of a wide series of biochemical and morphological changes to the stored erythrocytes, collectively referred to as the storage lesion(s). Approximately ten years ago, retrospective clinical evidence had suggested that such lesion(s) may be clinically relevant and mediate some of the untoward transfusion-related effects observed especially in some categories of recipients at risk (e.g. massively or chronically transfused recipients). Since then, randomized clinical trials have failed to prospectively detect any signal related to red cell storage duration and increased morbidity and mortality in several categories of recipients, at the limits of the statistical power of these studies. While a good part of the transfusion community has immediately adopted the take-home message "if it isn't broken, don't fix it" (i.e. no change to the standard of practice should be pursued), decision makers have been further questioning whether there may be room for further improvements in this field. Provocatively, we argue that consensus has yet to be unanimously reached on what makes a good quality marker of the red cell storage lesion and transfusion safety/efficacy. In other words, if it is true that "you can't manage what you can't measure", then future advancements in the field of transfusion medicine will necessarily rely on state of the art analytical omics technologies of well-defined quality parameters. Heavily borrowing from Douglas Adam's imaginary repertoire from the world famous "Hitchhiker's guide to the galaxy", we briefly summarize how some of the principles for intergalactic hitchhikers may indeed apply to inform navigation through the complex universe of red cell storage quality, safety and efficacy.

Correlation of pre-operative plasma protein concentrations in cardiac surgery patients with bleeding outcomes using a targeted quantitative proteomics approach

PURPOSE

Despite recent advancements in the use of thrombelastography (TEG) in the surgical setting, adequate technology to accurately predict bleeding phenotypes for patients undergoing cardiopulmonary bypass on the basis of non-mechanical parameters is lacking. While basic science and translational studies have provided key mechanistic insights about the protein components of coagulation cascades and regulatory mediators of hemostasis and fibrinolysis, targeted protein assays are still missing and the association of protein profiles to bleeding phenotypes and TEG readouts have yet to be discovered.

OBJECTIVE

To identify protein biomarkers of bleeding phenotypes of cardiopulmonary bypass patients in pre-operative plasma.

EXPERIMENTAL DESIGN

We applied a targeted proteomics approach to quantify 123 plasma proteins from 23 patients undergoing cardiopulmonary bypass (CPB) and sternotomy. We then correlated these measurements to bleeding outcomes and TEG parameters, associated with speed of clot formation and strength.

RESULTS

In this pilot study, we demonstrate the feasibility of protein quantitation as a viable strategy to predict low versus high bleeding phenotypes (loss of < or > than 20% of estimated blood volume, calculated as 70 mL/kg for BMI<29.9, 60 mL/kg for BMI = 30-39.9, and 50 mL/kg for BMI>40. Statistical elaborations highlighted a core set of proteins showing significant correlations to either total blood loss or TEG R/MA parameters.

CONCLUSION AND CLINICAL RELEVANCE

Though prospective verification and validation in larger cohorts will be necessary, this report suggests a potential for targeted quantitative proteomics of pre-operative plasma protein concentrations in the prediction of estimated blood loss following CPB.

Omics markers of the red cell storage lesion and metabolic linkage

The introduction of omics technologies in the field of Transfusion Medicine has significantly advanced our understanding of the red cell storage lesion. While the clinical relevance of such a lesion is still a matter of debate, quantitative and redox proteomics approaches, as well quantitative metabolic flux analysis and metabolic tracing experiments promise to revolutionise our understanding of the role of blood processing strategies, inform the design and testing of novel additives or technologies (such as pathogen reduction), and evaluate the clinical relevance of donor and recipient biological variability with respect to red cell storability and transfusion outcomes. By reviewing existing literature in this rapidly expanding research endeavour, we highlight for the first time a correlation between metabolic markers of the red cell storage age and protein markers of haemolysis. Finally, we introduce the concept of metabolic linkage, i.e. the appreciation of a network of highly correlated small molecule metabolites which results from biochemical constraints of erythrocyte metabolic enzyme activities. For the foreseeable future, red cell studies will advance Transfusion Medicine and haematology by addressing the alteration of metabolic linkage phenotypes in response to stimuli, including, but not limited to, storage additives, enzymopathies (e.g. glucose 6-phosphate dehydrogenase deficiency), hypoxia, sepsis or haemorrhage.

Platelet-functionalized three-dimensional poly-ε-caprolactone fibrous scaffold prepared using centrifugal spinning for delivery of growth factors

Bone and cartilage are tissues of a three-dimensional (3D) nature. Therefore, scaffolds for their regeneration should support cell infiltration and growth in all 3 dimensions. To fulfill such a requirement, the materials should possess large, open pores. Centrifugal spinning is a simple method for producing 3D fibrous scaffolds with large and interconnected pores. However, the process of bone regeneration is rather complex and requires additional stimulation by active molecules. In the current study, we introduced a simple composite scaffold based on platelet adhesion to poly-ε-caprolactone 3D fibers. Platelets were used as a natural source of growth factors and cytokines active in the tissue repair process. By immobilization in the fibrous scaffolds, their bioavailability was prolonged. The biological evaluation of the proposed system in the MG-63 model showed improved metabolic activity, proliferation and alkaline phosphatase activity in comparison to nonfunctionalized fibrous scaffold. In addition, the response of cells was dose dependent with improved biocompatibility with increasing platelet concentration. The results demonstrated the suitability of the system for bone tissue.

Preparation of Platelet Concentrates for Research and Transfusion Purposes

Platelets are specialized cellular elements of the blood that play central roles in physiologic and pathologic processes of hemostasis, wound healing, host defense, thrombosis, inflammation, and tumor metastasis. Activation of platelets is crucial for platelet function that includes a complex interplay of adhesion, signaling molecules, and release of bioactive factors. Transfusion of platelet concentrates is an important treatment component for thrombocytopenia and bleeding. Recent progress in high-throughput mRNA and protein profiling techniques has advanced the understanding of platelet biological functions toward identifying novel platelet-expressed and secreted proteins, analyzing functional changes between normal and pathologic states, and determining the effects of processing and storage on platelet concentrates for transfusion. It is important to understand the different standard methods of platelet preparation and how they differ from the perspective for use as research samples in clinical chemistry. Two simple methods are described here for the preparation of research-scale platelet samples from whole blood, and detailed notes are provided about the methods used for the preparation of platelet concentrates for transfusion.

Blood and Plasma Proteomics: Targeted Quantitation and Posttranslational Redox Modifications

Proteome profiling using mass spectrometry is extensively utilized to understand the physiological characteristics of cells, tissues, fluids, and many other biological matrices. From the earliest days of the proteomics era, exploratory analyses of the blood protein complement have attracted a great deal of interest, owing to the pivotal importance of blood cells and biofluids (serum, plasma) for research and biomedical purposes. Once challenged by the high dynamic range of protein concentrations, low sensitivity of mass spectrometers, and poor annotation of proteomics databases, the techniques in this field have quickly evolved in recent years, particularly in the areas of absolute quantification of proteins and in mapping of posttranslational modifications. Here we describe (a) the design and production of heavy isotope-labeled peptides used as reporter internal standards for absolute protein quantification and (b) a redox proteomics approach to optimize sample preparation and database searching to elucidate oxidative modifications to protein amino acids. The two methods achieve complimentary goals in the field of blood research and pave the way for future translation of next-generation proteomics technologies into clinical practice.

Plasma QconCATs reveal a gender-specific proteomic signature in apheresis platelet plasma supernatants

Clinical translation of proteomic technologies is often hampered by technical limitations, including inter-laboratory inconsistencies of label-free derived relative quantification, time-consuming analytical approaches and the subsequent challenge of performing proteomic analyses on large cohorts of subjects. Here we introduce plasma QconCAT-based targeted proteomics, an approach that allows the simultaneous absolute quantitation down to the picogram level of hundreds of proteins in a single liquid chromatography-selected reaction monitoring mass spectrometry run. We demonstrate the robustness of the approach by analyzing apheresis platelet concentrate supernatants at storage day 1 and the end of the shelf life for this blood-derived therapeutic, day 5. The targeted approach was repeatable and robust revealing potential gender-specific signatures across a set of three male and female donors. This technical note represents a proof-of-principle of the application of QconCAT-based MRM strategies to transfusion-medicine relevant issues, such as storage and gender-dependent proteomic signatures in blood-derived therapeutics.

BIOLOGICAL SIGNIFICANCE

Gender differences in the proteome composition of apheresis platelet supernatants have always been postulated, and might underlie a higher risk of adverse reactions when transfusing apheresis products from female donors. Preliminary proteomic studies provided an overview of gender-dependent relative compositional differences in the proteome of apheresis platelet supernatants during routine storage in the blood bank. Here we apply a proteomics approach for absolute quantitation of approximately 100 proteins in apheresis platelet supernatants from male and female donors at storage days 1 and 5. Absolute quantitative proteomic analyses allowed us to confirm and expand on previous observations about gender and storage-dependency of platelet supernatant protein profiles.

The signaling role of CD40 ligand in platelet biology and in platelet component transfusion

The CD40 ligand (CD40L) is a transmembrane molecule of crucial interest in cell signaling in innate and adaptive immunity. It is expressed by a variety of cells, but mainly by activated T-lymphocytes and platelets. CD40L may be cleaved into a soluble form (sCD40L) that has a cytokine-like activity. Both forms bind to several receptors, including CD40. This interaction is necessary for the antigen specific immune response. Furthermore, CD40L and sCD40L are involved in inflammation and a panoply of immune related and vascular pathologies. Soluble CD40L is primarily produced by platelets after activation, degranulation and cleavage, which may present a problem for transfusion. Soluble CD40L is involved in adverse transfusion events including transfusion related acute lung injury (TRALI). Although platelet storage designed for transfusion occurs in sterile conditions, platelets are activated and release sCD40L without known agonists. Recently, proteomic studies identified signaling pathways activated in platelet concentrates. Soluble CD40L is a good candidate for platelet activation in an auto-amplification loop. In this review, we describe the immunomodulatory role of CD40L in physiological and pathological conditions. We will focus on the main signaling pathways activated by CD40L after binding to its different receptors.