Proteomics-wise, how similar are mouse and human platelets?

The field of proteomics and its application to platelet biology, is rapidly and promisingly developing. Platelets (and megakaryocytes) are postulated as biosensors of health and disease, and their proteome poses as a tool to identify the specific health-disease hallmarks. Furthermore, the clinical management of certain pathologies where platelets are active players demands the development of alternative treatments, such is the case in patients where the balance thrombosis-bleeding is compromised, and a proteomics approach might aid at the identification of novel targets. Hereby, the mouse and human platelet proteomes and secretomes from public databases are compared, which shows that human and mouse platelets share a highly conserved proteome, considering identified proteins, and most importantly, their relative abundance. These supports, also interspecies wise, the use of the proteomics tool in the field, substantiated by a growing number of clinically relevant studies in humans or preclinical models. While the study of platelets through proteomics seems accessible and direct (i.e. noninvasive blood sampling, enucleated), there are some points of concern regarding the quality control of samples for such proteomics studies. Importantly, the quality of the generated data is improving over the years, which will allow cross-study comparisons. In parallel, the application of proteomics to the megakaryocyte compartment has a promising but long journey ahead. We foresee and encourage the application of platelet proteomics for diagnostic/prognostic purposes even beyond hematopoiesis and transfusion medicine, and as a tool that will procure the improvement of current therapies and the development of alternative treatment options.

The unbiased identification and quantitation of the protein profile (the so-called proteome) of cells, tissues, or organs, has gained attention from different fields because it gives additional valuable information to research questions. Understanding the protein building blocks of a biological system in normal physiological processes and how this may be altered in disease, may allow the discovery of biomarkers that could be used in diagnosis (early diagnosis), prognosis of disease or response to treatment. Furthermore, it may allow the identification of novel targets to develop personalized treatment options. Platelets, the anucleate cell components of the blood in charge of maintaining the body hemostasis, are postulated as biosensors of health and disease, and their proteome poses as a tool to identify health-disease hallmarks. Since platelets are in the circulation, a noninvasive blood sample is sufficient to obtain platelets from donors or patients in order to acquire information of the platelet proteome. Still, some research questions might require the use of animal preclinical models, where researchers may phenocopy human disorders, pathologies or diseases, to better understand the mechanisms behind these traits and to test potential novel treatments. How meaningful the studies in preclinical models are depends on how similar the biological systems of study are, interspecies wise. Hereby, the mouse and human platelet proteomes from available databases obtained by different research groups are compared, which shows that human and mouse platelets share a highly conserved proteome, considering identified proteins, and most importantly, their relative abundance. These supports, also interspecies wise, the use of the proteomics tool in the field, an approach with growing clinical relevance, as discussed.

Platelet number and function alterations in preclinical models of sterile inflammation and sepsis patients: implications in the pathophysiology and treatment of inflammation.

Platelets are the blood cells in charge of maintaining the body hemostasis, recognising the damaged vessel wall, and providing the appropriate cellular surface for the coagulation cascade to act locally. Additionally, platelets are active immunomodulators. At the crossroads of hemostasis and inflammation, platelets may exert either beneficial actions or participate in pathological manifestations, and have been associated with the prothrombotic nature of multi-organ failure in systemic inflammation. Platelet number alterations have been reported in septis, and platelet transfusions are given to thrombocytopenic patients. However, the risk to develop transfusion related acute lung injury (TRALI) is higher in sepsis patients. In this manuscript we show that platelets produced during inflammation in preclinical mouse models of sterile inflammation display lower aggregation capacity when stimulating certain receptors, while responses through other receptors remain intact, and we name them "inflammation-conditioned" platelets. In a cohort of sepsis patients, we observed, as previously reported, alterations in the number of platelets and platelet hyperreactivity. Furthermore, we identified a receptor-wise platelet aggregation response disbalance in these patients, although not similar to platelets from preclinical models of sterile inflammation. Interestingly, we generated evidence supporting the notion that platelet aggregation capacity disbalance was partially triggered by plasma components from sepsis patients. Our findings have implications in the indication of platelet transfusions in sepsis patients: Are fully functional platelets suitable for transfusion in sepsis patients? Current Clinical Trials (RESCUE) will answer whether platelet production stimulation with thrombopoietin receptor agonists (TPO-RAs) could be a substitute of platelet transfusions.

In vitro platelet production for transfusion purposes: Where are we now?

Over the last decade there has been a worldwide increase in the demand of platelet concentrates (PCs) for transfusion. This is, to a great extent, due to a growing and aging population with the concomitant increase in the incidence of onco-hematological diseases, which require frequent platelet (PLT) transfusions. Currently, PLTs are sourced uniquely from donations, and their storage time is limited only to a few days. The necessity to store PCs at room temperature (to minimize loss of PLT functional integrity), poses a major risk for bacterial contamination. While the implementation of pathogen reduction treatments (PRTs) and new-generation PLT additive solutions have allowed the extension of the shelf life and a safer PLT transfusion product, the concern of PCs shortage still pressures the scientific community to find alternative solutions with the aim of meeting the PLT transfusion increasing demand. In this concise report, we will focus on the efforts made to produce, in in vitro culture, high yields of viable and functional PLTs for transfusion purposes in a cost-effective manner, meeting not only current Good Manufacturing Practices (cGMPs), but also transfusion safety standards.

On the Quest for In Vitro Platelet Production by Re-Tailoring the Concepts of Megakaryocyte Differentiation.

The demand of platelet transfusions is steadily growing worldwide, inter-donor variation, donor dependency, or storability/viability being the main contributing factors to the current global, donor-dependent platelet concentrate shortage concern. In vitro platelet production has been proposed as a plausible alternative to cover, at least partially, the increasing demand. However, in practice, such a logical production strategy does not lack complexity, and hence, efforts are focused internationally on developing large scale industrial methods and technologies to provide efficient, viable, and functional platelet production. This would allow obtaining not only sufficient numbers of platelets but also functional ones fit for all clinical purposes and civil scenarios. In this review, we cover the evolution around the in vitro culture and differentiation of megakaryocytes into platelets, the progress made thus far to bring the culture concept from basic research towards good manufacturing practices certified production, and subsequent clinical trial studies. However, little is known about how these in vitro products should be stored or whether any safety measure should be implemented (e.g., pathogen reduction technology), as well as their quality assessment (how to isolate platelets from the rest of the culture cells, debris, microvesicles, or what their molecular and functional profile is). Importantly, we highlight how the scientific community has overcome the old dogmas and how the new perspectives influence the future of platelet-based therapy for transfusion purposes.

Characterization of the molecular composition and in vitro regenerative capacity of platelet-based bioproducts and related subfractions.

The use and demand of platelet-based bioproducts in regenerative medicine is steadily increasing. However, it is very difficult to establish the real clinical benefits of these therapies, as the lack of characterization and detailed production methods of platelet-based bioproducts persists in the literature and precludes cross-study comparisons. We characterized the molecular composition and in vitro regenerative capacity of platelet-rich plasma (PRP) produced in a closed-system. Furthermore, we performed a parallel characterization on different PRP subfractions (plasma and plasma-free platelet lysate), identifying that the fractions containing platelet-derived cargo exert the most potent regenerative capacity. This observation led us to develop a method to obtain a platelet secretome highly enriched in growth factors, free of plasma and cellular components (PCT/IB2022/057936), with the aim of establishing a superior bioproduct. The molecular characterization of secretomes revealed agonist-dependent differences, which correlates with beneficial grades of regenerative capacity. Importantly, secretomes showed general superiority to PRP in vitro. We discuss the variables influencing the bioproduct quality (inter-donor variation, platelet source and processing methods). Finally, we propose that the characteristics of secretomes circumvents certain limitations of PRP (autologous vs allogeneic), and envision that optimizing post-processing protocols (nanoencapsulation, lyophilization), would allow their clinical application even beyond regenerative medicine. STATEMENT OF SIGNIFICANCE: The use and demand of platelet-based bioproducts in regenerative medicine is steadily increasing. However, it is very difficult to establish the real clinical benefits of these therapies, or to improve/personalize them, as the lack of characterization of the bioproducts and their production methods is a constant in the literature, reason that precludes cross-study comparisons. In the present manuscript, we provide a comprehensive molecular and functional characterization of platelet-based bioproducts and subfractions, including platelet rich plasma, plasma fractions and platelet secretomes produced with a methodology developed by our group. Our results show that the molecular composition of each fraction correlates with its regenerative capacity in vitro. Thus, a rigorous characterization of platelet-derived bioproducts will potentially allow universal use, customizing and new applications.

Analyzing Protein Interactions by MAC-Tag Approaches.

Proteomics methods such as affinity purification (AP) and proximity-dependent labeling (PL) coupled with mass spectrometry (MS) are currently commonly utilized to define interaction landscapes. BioID is one of the PL approaches, and it employs the expression of bait proteins fused to a nonspecific biotin ligase (BirA*), to induce in vivo biotinylation of proximal proteins. We developed the multiple approaches combined (MAC)-tag workflow, which allows for both AP and BioID analysis with a single construct and with almost identical protein purification and MS identification procedures. MAC-tag is a well-established method and has been widely used. Recent developed PL tags such as BioID2 and UltraID are smaller versions of BirA* with faster labeling efficiency. We therefore incorporate these tags into our system to develop MAC2-tag (containing BioID2) and MAC3-tag (containing UltraID) to overcome potential limitations of the original MAC-tag system and broaden the spectrum of applications for MAC-tags. Here, we describe a detailed procedure for the MAC-tag system workflow including cell line generation for the MAC/MAC2/MAC3-tagged protein of interest (POI), sample preparation for AP and PL protein purification, and MS analysis.

Platelet and white blood-cell-based ratios: Differential inflammatory markers of severe mental disorders?

INTRODUCTION: Neutrophil/lymphocyte (NLR), monocyte/lymphocyte (MLR), and platelet/lymphocyte (PLR) ratios, and systemic inflammatory index (SII) represent peripheral markers of inflammation associated with different severe mental disorders. MATERIAL AND METHODS: In this study, these parameters were analyzed in a sample of 622 participants [197 patients with major depressive disorder (MDD), 154 with bipolar disorder (BD), 176 with schizophrenia (SCH), and 95 healthy controls (HC)]. Sociodemographic and clinical data of patients were recorded. RESULTS: Differences in age and sex were detected among groups (p<0.001), with SCH patients being younger and MDD patients being older. After stratifying by sex, these ratios were compared using the nonparametric ANCOVA (Quade's test) using age as a covariate. In males, no significant statistical differences were found between groups. However, differences were observed in MLR in the subgroup of females [MDD: 0.23 (SD=0.09); BD: 0.23 (SD=0.11); SCH: 0.24 (SD=0.11); HC: 0.29 (SD=0.13); F=5.376, p=0.001]. Post hoc testing revealed that there are MLR differences between HC versus MDD and between HC versus BD, with higher values in HC versus the other two groups. On the other hand, no differences were found in either males or females for any of the studied ratios, among the three diagnostic groups. CONCLUSIONS: MLR is reduced in MDD and BD patients versus HC, but exclusively in the female group. However, based on the analyzed indices, it is not possible to differentiate among the three diagnostic groups of patients. As a limitation of this study, note that the effects of psychopharmacological treatments and smoking have not been controlled for.

Dissecting platelet proteomics to understand the pathophysiology of immune thrombocytopenia: studies in mouse models.

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by enhanced platelet clearance and defective platelet production. Diagnosis by exclusion and trial-and-error treatment strategies is common practice, and despite the advancement in treatment options, many patients remain refractory. Although the existence of different pathophysiological entities is acknowledged, we are still far from stratifying and understanding ITP. To investigate, we sought to dissect the platelet proteome dynamics in so-called passive and active preclinical ITP mouse models, with which we propose to phenocopy respectively acute/newly diagnosed and persistent/chronic stages of ITP in humans. We obtained the platelet proteome at the thrombocytopenic stage and after platelet count recovery (reached naturally or by IVIg-treatment, depending on the model). Although most of the proteomic alterations were common to both ITP models, there were model-specific protein dynamics that accompanied and explained alterations in platelet aggregation responses, as measured in the passive ITP model. The expression dynamics observed in Syk may explain, extrapolated to humans and pending validation, the increased bleeding tendency of patients with ITP when treated with fostamatinib as third or later- as opposed to second line of treatment. We propose that the platelet proteome may give diagnostic and prognostic insights into ITP and that such studies should be pursued in humans.

Clinical Management of Hypertension, Inflammation and Thrombosis in Hospitalized COVID-19 Patients: Impact on Survival and Concerns.

The most severe clinical manifestations of the Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are due to an unbalanced immune response and a pro-thrombotic hemostatic disturbance, with arterial hypertension or diabetes as acknowledged risk factors. While waiting for a specific treatment, the clinical management of hospitalized patients is still a matter of debate, and the effectiveness of treatments to manage clinical manifestations and comorbidities has been questioned. In this study, we aim to assess the impact of the clinical management of arterial hypertension, inflammation and thrombosis on the survival of COVID-19 patients. The Spanish cohorts included in this observational retrospective study are from HM Hospitales (2035 patients) and from Hospital Universitario Central de Asturias (72 patients). Kaplan Meier survival curves, Cox regression and propensity score matching analyses were employed, considering demographic variables, comorbidities and treatment arms (when opportune) as covariates. The management of arterial hypertension with angiotensin-converting enzyme 2 (ACE2) inhibitors or angiotensin receptor blockers is not detrimental, as was initially reported, and neither was the use of non-steroidal anti-inflammatory drugs (NSAIDs). On the contrary, our analysis shows that the use on itself of corticosteroids is not beneficial. Importantly, the management of COVID-19 patients with low molecular weight heparin (LMWH) as an anticoagulant significantly improves the survival of hospitalized patients. These results delineate the current treatment options under debate, supporting the effectiveness of thrombosis prophylaxis on COVID-19 patients as a first-line treatment without the need for compromising the treatment of comorbidities, while suggesting cautiousness when administering corticosteroids.

Immunophenotyping and Cell Sorting of Human MKs from Human Primary Sources or Differentiated In Vitro from Hematopoietic Progenitors.

Megakaryocyte (MK) differentiation encompasses a number of endomitotic cycles that result in a highly polyploid (reaching even >64N) and extremely large cell (40-60 µm). As opposed to the fast-increasing knowledge in megakaryopoiesis at the cell biology and molecular level, the characterization of megakaryopoiesis by flow cytometry is limited to the identification of mature MKs using lineage-specific surface markers, while earlier MK differentiation stages remain unexplored. Here, we present an immunophenotyping strategy that allows the identification of successive MK differentiation stages, with increasing ploidy status, in human primary sources or in vitro cultures with a panel integrating MK specific and non-specific surface markers. Despite its size and fragility, MKs can be immunophenotyped using the above-mentioned panel and enriched by fluorescence-activated cell sorting under specific conditions of pressure and nozzle diameter. This approach facilitates multi-Omics studies, with the aim to better understand the complexity of megakaryopoiesis and platelet production in humans. A better characterization of megakaryopoiesis may pose fundamental in the diagnosis or prognosis of lineage-related pathologies and malignancy.

Sex-dependent grades of haematopoietic modulation in patients with major depressive episodes are associated with suicide attempts.

Suicide is the leading cause of non-natural death worldwide, and major depressive disorder (MDD) is the mood disorder with the highest prevalence among individuals with suicidal behaviour (SB). The role of inflammation and immunomodulation in mood disorders has raised interest in recent years, as inflammation biomarkers have been reported to be increased in mood disorder patients, suggesting a role of inflammation in their pathogenesis. The influence of inflammation on the haematopoietic production is well known; however, a comprehensive study of the haematopoietic production in patients with major depressive episodes (MDE) is lacking. We examined global haematopoietic parameters from complete blood counts (CBC) of patients with MDE, in search of prognostic patterns. MDE patients presented differences in several CBC parameters, differences that were clearly pronounced and/or significant in concurrence with suicide attempts (SA). Red and white blood cell lineage parameters were affected, suggesting general haematopoietic modulation or imbalance. We observed distinct haematological parameter changes in women versus men, with men presenting milder alterations than women. Interestingly, we found that the List of Threatening Experiences (LTE) score, but not the Childhood Trauma Questionnaire (CTQ), was associated with the haematopoietic alterations observed exclusively in women and, more importantly, served as a parameter to stratify female MDE patients based on concurrence or non-concurrence with SA. In conclusion, grades of haematopoietic modulation in MDE patients are associated with absence or presence of SA. Haematopoietic manifestations differ between men and women and, in the latter, are markedly influenced by late, and not early, traumatic events.

Comparison of the PU.1 transcriptional regulome and interactome in human and mouse inflammatory dendritic cells.

Dendritic cells (DCs) are key immune modulators and are able to mount immune responses or tolerance. DC differentiation and activation imply a plethora of molecular and cellular responses, including transcriptional changes. PU.1 is a highly expressed transcription factor in DCs and coordinates relevant aspects of DC biology. Due to their role as immune regulators, DCs pose as a promising immunotherapy tool. However, some of their functional features, such as survival, activation, or migration, are compromised due to the limitations to simulate in vitro the physiologic DC differentiation process. A better knowledge of transcriptional programs would allow the identification of potential targets for manipulation with the aim of obtaining "qualified" DCs for immunotherapy purposes. Most of the current knowledge regarding DC biology derives from studies using mouse models, which not always find a parallel in human. In the present study, we dissect the PU.1 transcriptional regulome and interactome in mouse and human DCs, in the steady state or LPS activated. The PU.1 transcriptional regulome was identified by performing PU.1 chromatin immunoprecipitation followed by high-throughput sequencing and pairing these data with RNAsequencing data. The PU.1 interactome was identified by performing PU.1 immunoprecipitation followed by mass spectrometry analysis. Our results portray PU.1 as a pivotal factor that plays an important role in the regulation of genes required for proper DC activation and function, and assures the repression of nonlineage genes. The interspecies differences between human and mouse DCs are surprisingly substantial, highlighting the need to study the biology of human DCs.