Platelet secretory behaviour: as diverse as the granules … or not?

Cord blood platelet-rich plasma: proteomics analysis for ophthalmic applications

Our objective is to determine the protein and complements constituents of Cord blood Platelet-rich plasma (CB-PRP), based on the hypothesis that it contains beneficial components capable of arresting or potentially decelerating the advancement of atrophic age-related macular degeneration (dry-AMD), with the support of radiomics. Two distinct pools of CB-PRP were assessed, each pool obtained from a total of 15 umbilical cord-blood donors. One aliquot of each pool respectively was subjected to proteomic analysis in order to enhance the significance of our findings, by identifying proteins that are shared between the two sample pools and gaining insights into the pathways they are associated with. The bioinformatics analysis was developed using Reactome software. Three-hundred-seven (307) distinct proteins were found. Two hundred fifteen (215) of the elements mentioned above are shared by both pools. Seventy (70) elements are exclusive to pool S1, while pool S2 contains 22. We detected 109 representative and statistically significant pathways out of 549. We found proteins related to the immune system, signal transduction, vesicle-mediated transport, cell-cell communication, hemostasis, cellular responses to stimuli, cell cycle, and developmental biology. The analysis showed the presence of P15692-12, representing VEGF factor A, long form. With over 200 proteins, the CB-PRP can increase the immune response, including BCR, CD-22, FCGR, phospholipids, IL-10, FCGR-3A, and others. Discovering crucial trophic and complement-regulating variables is highly significant for potential applications in dry AMD. Our future research will examine the effects of intravitreal CB-PRP on dry-AMD eyes.

Comparative analysis of cold-stored apheresis platelet units in additive solution with or without pathogen reduction: Implications of cytochrome c supplementation

BACKGROUND

Platelets are limited in supply, and the preservation of platelet function during storage remains challenging. Novel storage approaches are being explored to improve platelet quality, extend shelf life, and reduce risk of infection. This study sought to elucidate platelet function in cold-stored apheresis units in additive solution (platelet additive solution [PAS]) and subjected to pathogen reduction (PR) as well as the impact of cytochrome c (cyt c) supplementation. We hypothesized that the PR would decrease stored platelet function, regardless of cyt c supplementation.

METHODS

Platelet apheresis units (PAS) were collected (N = 5 volunteers) and divided into PR or no PR (PAS) and supplemented with vehicle or cyt c (100 μM). Units were stored at 4°C for 15 days, sequential aliquots were removed, and platelet/mitochondrial respiratory function and biochemical parameters were analyzed.

RESULTS

There was no difference in platelet aggregation in response to adenosine diphosphate between PAS and PR platelets. Aggregation function in response to arachidonic acid was higher in PR versus PAS platelets. Maximum clot strength was not different between PAS and PR from Day 0 to Day 5 but declined in PR platelets on Days 10 and 15. Oxygen consumption declined at the same rate in PAS and PR platelets, while rate of lactate and TCO2 decrease was greater in PR platelets than in PAS platelets. Supplementation with cyt c did not alter platelet function or biochemical parameters in PAS or PR platelets.

CONCLUSION

Platelet additive solution and PR platelets show similar declines in respiratory capacity, and biochemical parameters during cold storage, but PR platelets demonstrated significantly increased arachidonic acid-induced aggregation across all time points. Further understanding this mechanism may provide a means to prolong platelet shelf life.

GSDME-mediated pyroptosis contributes to chemotherapy-induced platelet hyperactivity and thrombotic potential

ABSTRACT

Thrombotic complications due to platelet hyperreactivity are a major cause of death in patients undergoing chemotherapy. However, the underlying mechanisms are not fully understood. Herein, using human platelets and platelets from mice lacking gasdermin E (GSDME), we show that GSDME is functionally expressed in anucleate platelets, and that GSDME-mediated pyroptosis, a newly identified form of cell death in mammalian nucleated cells, contributes to platelet hyperactivity in cisplatin-based chemotherapy. Cisplatin or etoposide activates caspase-3 to cleave GSDME, thereby releasing the N-terminal fragment of GSDME (GSDME-N) toward the platelet plasma membrane, subsequently forming membrane pores and facilitating platelet granule release. This eventually promotes platelet hyperactivity and thrombotic potential. We identified flotillin-2, a scaffold protein, as a GSDME-N interactor that recruits GSDME-N to the platelet membrane. Loss of GSDME protects mice from cisplatin-induced platelet hyperactivity. Our results provide evidence that targeting GSDME-mediated pyroptosis could reduce thrombotic potential in chemotherapy.

Reciprocal tumor-platelet interaction through the EPHB1-EFNB1 axis in the liver metastatic niche promotes metastatic tumor outgrowth in pancreatic ductal adenocarcinoma

BACKGROUND

The interaction between the metastatic microenvironment and tumor cells plays an important role in metastatic tumor formation. Platelets play pivotal roles in hematogenous cancer metastasis through tumor cell-platelet interaction in blood vessels. Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy distinguished by its notable tendency to metastasize to the liver. However, the role of platelet in the liver metastatic niche of PDAC remains elusive. This study aimed to elucidate the role of platelets and their interactions with tumor cells in the liver metastatic niche of PDAC.

METHODS

An mCherry niche-labeling system was established to identify cells in the liver metastatic niche of PDAC. Platelet depletion in a liver metastasis mouse model was used to observe the function of platelets in PDAC liver metastasis. Gain-of-function and loss-of-function of erythropoietin-producing hepatocellular receptor B1 (Ephb1), tumor cell-platelet adhesion, recombinant protein, and tryptophan hydroxylase 1 (Tph1)-knockout mice were used to study the crosstalk between platelets and tumor cells in the liver metastatic niche.

RESULTS

The mCherry metastatic niche-labeling system revealed the presence of activated platelets in the liver metastatic niche of PDAC patients. Platelet depletion decreased liver metastatic tumor growth in mice. Mechanistically, tumor cell-expressed EPHB1 and platelet-expressed Ephrin B1 (EFNB1) mediated contact-dependent activation of platelets via reverse signaling-mediated AKT signaling activation, and in turn, activated platelet-released 5-HT, further enhancing tumor growth.

CONCLUSION

We revealed the crosstalk between platelets and tumor cells in the liver metastatic niche of PDAC. Reciprocal tumor-platelet interaction mediated by the EPHB1-EFNB1 reverse signaling promoted metastatic PDAC outgrowth via 5-HT in the liver. Interfering the tumor-platelet interaction by targeting the EPHB1-EFNB1 axis may represent a promising therapeutic intervention for PDAC liver metastasis.

High-Dimensional Single-Cell Mass Cytometry Demonstrates Differential Platelet Functional Phenotypes in Infants With Congenital Heart Disease

BACKGROUND

Congenital heart disease (CHD) is a group of complex heart defects associated with hematologic abnormalities, including increased risk of thrombotic and bleeding events. Past studies have observed evidence of platelet hyperreactivity, while other studies showed decreased platelet activation in patients with CHD. The goal of this study was to develop a mass spectrometry approach to characterize single platelets in infants with CHD and identify potential etiology for such discrepant results.

METHODS

We enrolled 19 infants with CHD along with 21 non-CHD controls at Yale New Haven Children's Heart Center. A single-cell high-dimensional mass cytometry method was developed to quantitatively interrogate platelet surface markers in whole blood. Additionally, plasma cytokine analysis was performed through a multiplexed panel of 52 vascular and inflammatory markers to assess for platelet releasates.

RESULTS

We found that infants with CHD had significant differences in platelet activation and functional markers by mass cytometry compared with non-CHD controls. Based on cell surface markers, we classified the platelets into 8 subpopulations (P0 to P7). Distinct subpopulations of platelets (P1, P4, and P5) exhibiting decreased aggregatory phenotype but altered secretory phenotypes were also identified and found to be more abundant in the blood of infants with CHD. Electron microscopy identified increased proportion of hypogranular platelets in CHD. Moreover, cytokine analysis demonstrated an overall increase in plasma cytokines and biomarkers in CHD, including IL (interleukin)-6, IL-8, IL-27, RANTES (regulated upon activation, normal T cell expressed and secreted), and VWF (von Willebrand factor), which are expressed in platelet granules and can be released upon activation.

CONCLUSIONS

We developed a robust mass cytometry approach to identify platelet phenotypic heterogeneity. Infants with CHD had alterations in distinct subpopulations of platelets with overall reduced aggregatory phenotype and secretory dysfunction. These findings suggest that platelets in infants with CHD may be exhausted due to persistent stimulation and may explain both bleeding and thrombotic vascular complications associated with CHD.

Platelet interaction and performance of antibacterial bioinspired nanostructures passivated with human plasma

The ever-increasing ageing of the world population is demanding superior orthopedic devices. Issues such as implant infection, poor osseointegration, or chronic inflammation remain problematic to the lifespan and long-term efficacy of implants. Fabrication of materials with bioinspired nanostructures is one emerging antibacterial strategy to prevent implant infection, however their interactions with blood components, and whether they retain their bactericidal properties in an environment displaying a complex protein corona, remains largely unexplored. In the present study, titanium alloy, commercially pure and plasma-sprayed titania were hydrothermally etched, passivated with human native plasma to develop a protein corona, and then incubated with either Staphylococcus aureus, Pseudomonas aeruginosa or human platelets. Surface analysis was first used to characterize the topography, chemical composition or crystallinity of each material. Fluorescence staining and SEM were performed to evaluate the nanostructure bactericidal properties, as well as to study platelet attachment and morphology. Composition of platelet supernatant was studied using ELISA and flow cytometry. Overall, our study showed that the bioinspired nanostructured surfaces displayed both impressive antibacterial properties in a complex environment, and a superior blood biocompatibility profile in terms of platelet activation (particularly for titanium alloy). Additionally, the amount of pro-inflammatory cytokines released by platelets was found to be no different to that found in native plasma (background levels) and, in some cases, presented a more pro-healing profile with an increased secretion of factors such as TGF-β, PDGF-BB or BMP-2. The nanostructured surfaces performed equally, or better, than hydroxyapatite-coated titanium which is one of the current gold standards in orthopedics. Although further in vivo studies are required to validate these results, such bioinspired nanostructured surfaces certainly show promise to be safely applied to medical device surfaces used in orthopedics and other areas.

Targeting cargo to an unconventional secretory system within megakaryocytes allows the release of transgenic proteins from platelets

BACKGROUND

Platelets are essential for hemostasis and thrombosis and play vital roles during metastatic cancer progression and infection. Hallmarks of platelet function are activation, cytoskeletal rearrangements, and the degranulation of their cellular contents upon stimulation. While α-granules and dense granules are the most studied platelet secretory granules, the dense tubular system (DTS) also functions as a secretory system for vascular thiol isomerases. However, how DTS cargo is packaged and transported from megakaryocytes (MKs) to platelets is poorly understood.

OBJECTIVES

To underpin the mechanisms responsible for DTS cargo transport and leverage those for therapeutic protein packaging into platelets.

METHODS

A retroviral expression system combined with immunofluorescence confocal microscopy was employed to track protein DTS cargo protein disulfide isomerase fused to enhanced green fluorescent protein (eGFP-PDI) during platelet production. Murine bone marrow transplantation models were used to determine the release of therapeutic proteins from platelets.

RESULTS

We demonstrated that the endoplasmic reticulum retrieval motif Lys-Asp-Glu-Leu (KDEL) located at the C-terminus of protein disulfide isomerase was essential for the regular transport of eGFP-PDI-containing granules. eGFP-PDIΔKDEL, in which the retrieval signal was deleted, was aberrantly packaged, and its expression was upregulated within clathrin-coated endosomes. Finally, we found that ectopic transgenic proteins, such as tissue factor pathway inhibitor and interleukin 2, can be packaged into MKs and proplatelets by adding a KDEL retrieval sequence.

CONCLUSION

Our data corroborate the DTS as a noncanonical secretory system in platelets and demonstrate that in vitro-generated MKs and platelets may be used as a delivery system for transgenic proteins during cellular therapy.

The Well-Forgotten Old: Platelet-Rich Plasma in Modern Anti-Aging Therapy

Currently, approaches to personalized medicine are actively developing. For example, the use of platelet-rich plasma (PRP) is actively growing every year. As a result of activation, platelets release a wide range of growth factors, cytokines, chemokines, and angiogenic factors, after which these molecules regulate chemotaxis, inflammation, and vasomotor function and play a crucial role in restoring the integrity of damaged vascular walls, angiogenesis, and tissue regeneration. Due to these characteristics, PRP has a wide potential in regenerative medicine and gerontology. PRP products are actively used not only in esthetic medicine but also to stimulate tissue regeneration and relieve chronic inflammation. PRP therapy has a number of advantages, but the controversial results of clinical studies, a lack of standardization of the sample preparation of the material, and insufficient objective data on the evaluation of efficacy do not allow us to unambiguously look at the use of PRP for therapeutic purposes. In this review, we will examine the current clinical efficacy of PRP-based products and analyze the contribution of PRP in the therapy of diseases associated with aging.

Thrombocytopenia in dengue infection: mechanisms and a potential application

Thrombocytopenia is a common symptom and one of the warning signs of dengue virus (DENV) infection. Platelet depletion is critical as it may lead to other severe dengue symptoms. Understanding the molecular events of this condition during dengue infection is challenging because of the multifaceted factors involved in DENV infection and the dynamics of the disease progression. Platelet levels depend on the balance between platelet production and platelet consumption or clearance. Megakaryopoiesis and thrombopoiesis, two interdependent processes in platelet production, are hampered during dengue infection. Conversely, platelet elimination via platelet activation, apoptosis and clearance processes are elevated. Together, these anomalies contribute to thrombocytopenia in dengue patients. Targeting the molecular events of dengue-mediated thrombocytopenia shows great potential but still requires further investigation. Nonetheless, the application of new knowledge in this field, such as immature platelet fraction analysis, may facilitate physicians in monitoring the progression of the disease.

Unlocking the intricacies: Exploring the complex interplay between platelets and ovarian cancer

Ovarian cancer, an aggressive malignancy of the female reproductive tract, is frequently linked to an elevated risk of thrombotic events. This association is manifested by a pronounced rise in platelet counts and activation levels. Current research firmly supports the pivotal role of platelets in the oncogenic processes of ovarian cancer, influencing tumor cell proliferation and metastasis. Platelets influence these processes through direct interactions with tumor cells or by secreting cytokines and growth factors that enhance tumor growth, angiogenesis, and metastasis. This review aims to thoroughly dissect the interactions between platelets and ovarian cancer cells, emphasizing their combined role in tumor progression and associated thrombotic events. Additionally, it summarizes therapeutic strategies targeting platelet-cancer interface which show significant promise. Such approaches could not only be effective in managing the primary ovarian tumor but also play a pivotal role in preventing metastasis and attenuating thrombotic complications associated with ovarian cancer.

Platelets at the intersection of inflammation and coagulation in the APC-mediated response to myocardial ischemia/reperfusion injury

Thromboinflammation is a complex pathology associated with inflammation and coagulation. In cases of cardiovascular disease, in particular ischemia-reperfusion injury, thromboinflammation is a common complication. Increased understanding of thromboinflammation depends on an improved concept of the mechanisms of cells and proteins at the axis of coagulation and inflammation. Among these elements are activated protein C and platelets. This review summarizes the complex interactions of activated protein C and platelets regulating thromboinflammation in cardiovascular disease. By unraveling the pathways of platelets and APC in the inflammatory and coagulation cascades, this review summarizes the role of these vital mediators in the development and perpetuation of heart disease and the thromboinflammation-driven complications of cardiovascular disease. Furthermore, this review emphasizes the significance of the counteracting effects of platelets and APC and their combined role in disease states.

Skin Telocytes Could Fundament the Cellular Mechanisms of Wound Healing in Platelet-Rich Plasma Administration

For more than 40 years, autologous platelet concentrates have been used in clinical medicine. Since the first formula used, namely platelet-rich plasma (PRP), other platelet concentrates have been experimented with, including platelet-rich fibrin and concentrated growth factor. Platelet concentrates have three standard characteristics: they act as scaffolds, they serve as a source of growth factors and cytokines, and they contain live cells. PRP has become extensively used in regenerative medicine for the successful treatment of a variety of clinical (non-)dermatological conditions like alopecies, acne scars, skin burns, skin ulcers, muscle, cartilage, and bone repair, and as an adjuvant in post-surgery wound healing, with obvious benefits in terms of functionality and aesthetic recovery of affected tissues/organs. These indications were well documented, and a large amount of evidence has already been published supporting the efficacy of this method. The primordial principle behind minimally invasive PRP treatments is the usage of the patient's own platelets. The benefits of the autologous transplantation of thrombocytes are significant, representing a fast and economic method that requires only basic equipment and training, and it is biocompatible, thus being a low risk for the patient (infection and immunological reactions can be virtually disregarded). Usually, the structural benefits of applying PRP are attributed to fibroblasts only, as they are considered the most numerous cell population within the interstitium. However, this apparent simplistic explanation is still eluding those different types of interstitial cells (distinct from fibroblasts) that are residing within stromal tissue, e.g., telocytes (TCs). Moreover, dermal TCs have an already documented potential in angiogenesis (extra-cutaneous, but also within skin), and their implication in skin recovery in a few dermatological conditions was attested and described ultrastructurally and immunophenotypically. Interestingly, PRP biochemically consists of a series of growth factors, cytokines, and other molecules, to which TCs have also proven to have a positive expression. Thus, it is attractive to hypothesize and to document any tissular collaboration between cutaneous administered PRP and local dermal TCs in skin recovery/repair/regeneration. Therefore, TCs could be perceived as the missing link necessary to provide a solid explanation of the good results achieved by administering PRP in skin-repairing processes.

Biofilm-dispersed pneumococci induce elevated leukocyte and platelet activation

Introduction

Streptococcus pneumoniae (the pneumococcus) effectively colonizes the human nasopharynx, but can migrate to other host sites, causing infections such as pneumonia and sepsis. Previous studies indicate that pneumococci grown as biofilms have phenotypes of bacteria associated with colonization whereas bacteria released from biofilms in response to changes in the local environment (i.e., dispersed bacteria) represent populations with phenotypes associated with disease. How these niche-adapted populations interact with immune cells upon reaching the vascular compartment has not previously been studied. Here, we investigated neutrophil, monocyte, and platelet activation using ex vivo stimulation of whole blood and platelet-rich plasma with pneumococcal populations representing distinct stages of the infectious process (biofilm bacteria and dispersed bacteria) as well as conventional broth-grown culture (planktonic bacteria).

Methods

Flow cytometry and ELISA were used to assess surface and soluble activation markers for neutrophil and monocyte activation, platelet-neutrophil complex and platelet-monocyte complex formation, and platelet activation and responsiveness.

Results

Overall, we found that biofilm-derived bacteria (biofilm bacteria and dispersed bacteria) induced significant activation of neutrophils, monocytes, and platelets. In contrast, little to no activation was induced by planktonic bacteria. Platelets remained functional after stimulation with bacterial populations and the degree of responsiveness was inversely related to initial activation. Bacterial association with immune cells followed a similar pattern as activation.

Discussion

Differences in activation of and association with immune cells by biofilm-derived populations could be an important consideration for other pathogens that have a biofilm state. Gaining insight into how these bacterial populations interact with the host immune response may reveal immunomodulatory targets to interfere with disease development.

Acidification of α-granules in megakaryocytes by vacuolar-type adenosine triphosphatase is essential for organelle biogenesis

BACKGROUND

Platelets coordinate blood coagulation at sites of vascular injury and play fundamental roles in a wide variety of (patho)physiological processes. Key to many platelet functions is the transport and secretion of proteins packaged within α-granules, organelles produced by platelet precursor megakaryocytes. Prominent among α-granule cargo are fibrinogen endocytosed from plasma and endogenously synthesized von Willebrand factor. These and other proteins are known to require acidic pH for stable packaging. Luminal acidity has been confirmed for mature α-granules isolated from platelets, but direct measurement of megakaryocyte granule acidity has not been reported.

OBJECTIVES

To determine the luminal pH of α-granules and their precursors in megakaryocytes and assess the requirement of vacuolar-type adenosine triphosphatase (V-ATPase) activity to establish and maintain the luminal acidity and integrity of these organelles.

METHODS

Cresyl violet staining was used to detect acidic granules in megakaryocytes. Endocytosis of fibrinogen tagged with the pH-sensitive fluorescent dye fluorescein isothiocyanate was used to load a subset of these organelles. Ratiometric fluorescence analysis was used to determine their luminal pH.

RESULTS

We show that most of the acidic granules detected in megakaryocytes appear to be α-granules/precursors, for which we established a median luminal pH of 5.2 (IQR, 5.0-5.5). Inhibition of megakaryocyte V-ATPase activity led to enlargement of cargo-containing compartments detected by fluorescence microscopy and electron microscopy.

CONCLUSION

These observations reveal that V-ATPase activity is required to establish and maintain a luminal acidic pH in megakaryocyte α-granules/precursors, confirming its importance for stable packaging of cargo proteins such as von Willebrand factor.

Fibrinogen binding to activated platelets and its biomimetic thrombus-targeted thrombolytic strategies

Thrombosis is associated with various fatal arteriovenous syndromes including ischemic stroke, myocardial infarction, and pulmonary embolism. However, current clinical thrombolytic treatment strategies still have many problems in targeting and safety to meet the thrombolytic therapy needs. Understanding the molecular mechanism that underlies thrombosis is critical in developing effective thrombolytic strategies. It is well known that platelets play a central role in thrombosis and the binding of fibrinogen to activated platelets is a common pathway in the process of clot formation. Based on this, a concept of biomimetic thrombus-targeted thrombolytic strategy inspired from fibrinogen binding to activated platelets in thrombosis was proposed, which could selectively bind to activated platelets at a thrombus site, thus enabling targeted delivery and local release of thrombolytic agents for effective thrombolysis. In this review, we first summarized the main characteristics of platelets and fibrinogen, and then introduced the classical molecular mechanisms of thrombosis, including platelet adhesion, platelet activation and platelet aggregation through the interactions of activated platelets with fibrinogen. In addition, we highlighted the recent advances in biomimetic thrombus-targeted thrombolytic strategies which inspired from fibrinogen binding to activated platelets in thrombosis. The possible future directions and perspectives in this emerging area are briefly discussed.

Profound Properties of Protein-Rich, Platelet-Rich Plasma Matrices as Novel, Multi-Purpose Biological Platforms in Tissue Repair, Regeneration, and Wound Healing

Autologous platelet-rich plasma (PRP) preparations are prepared at the point of care. Centrifugation cellular density separation sequesters a fresh unit of blood into three main fractions: a platelet-poor plasma (PPP) fraction, a stratum rich in platelets (platelet concentrate), and variable leukocyte bioformulation and erythrocyte fractions. The employment of autologous platelet concentrates facilitates the biological potential to accelerate and support numerous cellular activities that can lead to tissue repair, tissue regeneration, wound healing, and, ultimately, functional and structural repair. Normally, after PRP preparation, the PPP fraction is discarded. One of the less well-known but equally important features of PPP is that particular growth factors (GFs) are not abundantly present in PRP, as they reside outside of the platelet alpha granules. Precisely, insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF) are mainly present in the PPP fraction. In addition to their roles as angiogenesis activators, these plasma-based GFs are also known to inhibit inflammation and fibrosis, and they promote keratinocyte migration and support tissue repair and wound healing. Additionally, PPP is known for the presence of exosomes and other macrovesicles, exerting cell-cell communication and cell signaling. Newly developed ultrafiltration technologies incorporate PPP processing methods by eliminating, in a fast and efficient manner, plasma water, cytokines, molecules, and plasma proteins with a molecular mass (weight) less than the pore size of the fibers. Consequently, a viable and viscous protein concentrate of functional total proteins, like fibrinogen, albumin, and alpha-2-macroglobulin is created. Consolidating a small volume of high platelet concentrate with a small volume of highly concentrated protein-rich PPP creates a protein-rich, platelet-rich plasma (PR-PRP) biological preparation. After the activation of proteins, mainly fibrinogen, the PR-PRP matrix retains and facilitates interactions between invading resident cells, like macrophages, fibroblast, and mesenchymal stem cells (MSCs), as well as the embedded concentrated PRP cells and molecules. The administered PR-PRP biologic will ultimately undergo fibrinolysis, leading to a sustained release of concentrated cells and molecules that have been retained in the PR-PRP matrix until the matrix is dissolved. We will discuss the unique biological and tissue reparative and regenerative properties of the PR-PRP matrix.

The Implications of Brain-Derived Neurotrophic Factor in the Biological Activities of Platelet-Rich Plasma

Platelet-rich plasma (PRP) is a biological blood-derived therapeutic obtained from whole blood that contains higher levels of platelets. PRP has been primarily used to mitigate joint degeneration and chronic pain in osteoarthritis (OA). This clinical applicability is based mechanistically on the release of several proteins by platelets that can restore joint homeostasis. Platelets are the primary source of brain-derived neurotrophic factor (BDNF) outside the central nervous system. Interestingly, BDNF and PRP share key biological activities with clinical applicability for OA management, such as anti-inflammatory, anti-apoptotic, and antioxidant. However, the role of BDNF in PRP therapeutic activities is still unknown. Thus, this work aimed to investigate the implications of BDNF in therapeutic outcomes provided by PRP therapy in vitro and in-vivo, using the MIA-OA animal model in male Wistar rats. Initially, the PRP was characterized, obtaining a leukocyte-poor-platelet-rich plasma (LP-PRP). Our assays indicated that platelets activated by Calcium release BDNF, and suppression of M1 macrophage polarization induced by LP-PRP depends on BDNF full-length receptor, Tropomyosin Kinase-B (TrkB). OA animals were given LP-PRP intra-articular and showed functional recovery in gait, joint pain, inflammation, and tissue damage caused by MIA. Immunohistochemistry for activating transcriptional factor-3 (ATF-3) on L4/L5 dorsal root ganglia showed the LP-PRP decreased the nerve injury induced by MIA. All these LP-PRP therapeutic activities were reversed in the presence of TrkB receptor antagonist. Our results suggest that the therapeutic effects of LP-PRP in alleviating OA symptoms in rats depend on BDNF/TrkB activity.

Immunological role of Gas6/TAM signaling in hemostasis and thrombosis

The immune system is an emerging regulator of hemostasis and thrombosis. The concept of immunothrombosis redefines the relationship between coagulation and immunomodulation, and the Gas6/Tyro3-Axl-MerTK (TAM) signaling pathway builds the bridge across them. During coagulation, Gas6/TAM signaling pathway not only activates platelets, but also promotes thrombosis through endothelial cells and vascular smooth muscle cells involved in inflammatory responses. Thrombosis appears to be a common result of a Gas6/TAM signaling pathway-mediated immune dysregulation. TAM TK and its ligands have been found to be involved in coagulation through the PI3K/AKT or JAK/STAT pathway in various systemic diseases, providing new perspectives in the understanding of immunothrombosis. Gas6/TAM signaling pathway serves as a breakthrough target for novel therapeutic strategies to improve disease management. Many preclinical and clinical studies of TAM receptor inhibitors are in process, confirming the pivotal role of Gas6/TAM signaling pathway in immunothrombosis. Therapeutics targeting the TAM receptor show potential both in anticoagulation management and immunotherapy. Here, we review the immunological functions of the Gas6/TAM signaling pathway in coagulation and its multiple mechanisms in diseases identified to date, and discuss the new clinical strategies that may generated by these roles.

Platelet, Antiplatelet Therapy and Metabolic Dysfunction-Associated Steatotic Liver Disease: A Narrative Review

Metabolic dysfunction-associated steatotic liver disease (MASLD) is not only related to traditional cardiovascular risk factors like type 2 diabetes mellitus and obesity, but it is also an independent risk factor for the development of cardiovascular disease. MASLD has been shown to be independently related to endothelial dysfunction and atherosclerosis. MASLD is characterized by a chronic proinflammatory response that, in turn, may induce a prothrombotic state. Several mechanisms such as endothelial and platelet dysfunction, changes in the coagulative factors, lower fibrinolytic activity can contribute to induce the prothrombotic state. Platelets are players and addresses of metabolic dysregulation; obesity and insulin resistance are related to platelet hyperactivation. Furthermore, platelets can exert a direct effect on liver cells, particularly through the release of mediators from granules. Growing data in literature support the use of antiplatelet agent as a treatment for MASLD. The use of antiplatelets drugs seems to exert beneficial effects on hepatocellular carcinoma prevention in patients with MASLD, since platelets contribute to fibrosis progression and cancer development. This review aims to summarize the main data on the role of platelets in the pathogenesis of MASLD and its main complications such as cardiovascular events and the development of liver fibrosis. Furthermore, we will examine the role of antiplatelet therapy not only in the prevention and treatment of cardiovascular events but also as a possible anti-fibrotic and anti-tumor agent.

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.

The subtilisin-like protease furin regulates hemin-induced CD63 surface expression on platelets

Accumulation of free heme B in the plasma can be the result of severe hemolytic events, when the scavenger system for free hemoglobin and heme B is overwhelmed. Free heme B can be oxidized into toxic hemin, which has been proven to activate platelet degranulation and aggregation and promote thrombosis. In the present study we analyzed the effect of hemin on the activation-mediated lysosomal degranulation and CD63 surface expression on platelets using classic flow cytometry and fluorescence microscopy techniques. Classical platelet activators were used as control to distinguish the novel effects of hemin from known activation pathways. CD63 is a tetraspanin protein, also known as lysosomal-associated membrane protein 3 or LAMP-3. In resting platelets CD63 is located within the membrane of delta granules and lysosomes of platelet, from where it is integrated into the platelet outer membrane upon stimulation. We were able to show that hemin like the endogenous platelet activators ADP, collagen or thrombin does provoke CD63 re-localization. Interestingly, only hemin-induced CD63 externalization is dependent on the subtilisin-like pro-protein convertase furin as shown by inhibitor experiments. Furthermore, we were able to demonstrate that hemin induces lysosome secretion, a source of the hemin-mediated CD63 presentation. Again, only the hemin-induced lysosome degranulation is furin dependent. In summary we have shown that the pro-protein convertase furin plays an important role in hemin-mediated lysosomal degranulation and CD63 externalization.

Fibroblasts and platelets: a face-to-face dialogue at the heart of cardiac fibrosis

Myocardial fibrosis is a feature found in most cardiac diseases and a key element contributing to heart failure and its progression. It has therefore become a subject of particular interest in cardiac research. Mechanisms leading to pathological cardiac remodeling and heart failure are diverse, including effects on cardiac fibroblasts, the main players in cardiac extracellular matrix synthesis, but also on cardiomyocytes, immune cells, endothelial cells, and more recently, platelets. Although transforming growth factor-β (TGF-β) is a primary regulator of fibrosis development, the cellular and molecular mechanisms that trigger its activation after cardiac injury remain poorly understood. Different types of anti-TGF-β drugs have been tested for the treatment of cardiac fibrosis and have been associated with side effects. Therefore, a better understanding of these mechanisms is of great clinical relevance and could allow us to identify new therapeutic targets. Interestingly, it has been shown that platelets infiltrate the myocardium at an early stage after cardiac injury, producing large amounts of cytokines and growth factors. These molecules can directly or indirectly regulate cells involved in the fibrotic response, including cardiac fibroblasts and immune cells. In particular, platelets are known to be a major source of TGF-β1. In this review, we have provided an overview of the classical cellular effectors involved in the pathogenesis of cardiac fibrosis, focusing on the emergent role of platelets, while discussing opportunities for novel therapeutic interventions.

The Interplay between Liver Sinusoidal Endothelial Cells, Platelets, and Neutrophil Extracellular Traps in the Development and Progression of Metabolic Dysfunction-Associated Steatotic Liver Disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) represents a societal burden due to the lack of effective treatment and incomplete pathophysiology understanding. This review explores the intricate connections among liver sinusoidal endothelial cells (LSECs), platelets, neutrophil extracellular traps (NETs), and coagulation disruptions in MASLD pathogenesis. In MASLD's early stages, LSECs undergo capillarization and dysfunction due to excessive dietary macronutrients and gut-derived products. Capillarization leads to ischemic changes in hepatocytes, triggering pro-inflammatory responses in Kupffer cells (KCs) and activating hepatic stellate cells (HSCs). Capillarized LSECs show a pro-inflammatory phenotype through adhesion molecule overexpression, autophagy loss, and increased cytokines production. Platelet interaction favors leucocyte recruitment, NETs formation, and liver inflammatory foci. Liver fibrosis is facilitated by reduced nitric oxide, HSC activation, profibrogenic mediators, and increased angiogenesis. Moreover, platelet attachment, activation, α-granule cargo release, and NETs formation contribute to MASLD progression. Platelets foster fibrosis and microthrombosis, leading to parenchymal extinction and fibrotic healing. Additionally, platelets promote tumor growth, epithelial-mesenchymal transition, and tumor cell metastasis. MASLD's prothrombotic features are exacerbated by insulin resistance, diabetes, and obesity, manifesting as increased von Willebrand factor, platelet hyperaggregability, hypo-fibrinolysis, and a prothrombotic fibrin clot structure. Improving LSEC health and using antiplatelet treatment appear promising for preventing MASLD development and progression.

The role of platelet P2Y12 receptors in inflammation

Inflammation is a complex pathophysiological process underlying many clinical conditions. Platelets contribute to the thrombo-inflammatory response. Platelet P2Y12 receptors amplify platelet activation, potentiating platelet aggregation, degranulation and shape change. The contents of platelet alpha granules, in particular, act directly on leucocytes, including mediating platelet-leucocyte aggregation and activation via platelet P-selectin. Much evidence for the role of platelet P2Y12 receptors in inflammation comes from studies using antagonists of these receptors, such as the thienopyridines clopidogrel and prasugrel, and the cyclopentyltriazolopyrimidine ticagrelor, in animal and human experimental models. These suggest that antagonism of P2Y12 receptors decreases markers of inflammation with some evidence that this reduces incidence of adverse clinical sequelae during inflammatory conditions. Interpretation is complicated by pleiotropic effects such as those of the thienopyridines on circulating leucocyte numbers and of ticagrelor on adenosine reuptake. The available evidence suggests that P2Y12 receptors are prominent mediators of inflammation and P2Y12 receptor antagonism as a potentially powerful strategy in a broad range of inflammatory conditions. LINKED ARTICLES: This article is part of a themed issue on Platelet purinergic receptor and non-thrombotic disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.4/issuetoc.

Analysis of the Healthy Platelet Proteome Identifies a New Form of Domain-Specific O-Fucosylation

Platelet activation induces the secretion of proteins that promote platelet aggregation and inflammation. However, detailed analysis of the released platelet proteome is hampered by platelets' tendency to preactivate during their isolation and a lack of sensitive protocols for low abundance releasate analysis. Here, we detail the most sensitive analysis to date of the platelet releasate proteome with the detection of >1300 proteins. Unbiased scanning for posttranslational modifications within releasate proteins highlighted O-glycosylation as being a major component. For the first time, we detected O-fucosylation on previously uncharacterized sites including multimerin-1 (MMRN1), a major alpha granule protein that supports platelet adhesion to collagen and is a carrier for platelet factor V. The N-terminal elastin microfibril interface (EMI) domain of MMRN1, a key site for protein-protein interaction, was O-fucosylated at a conserved threonine within a new domain context. Our data suggest that either protein O-fucosyltransferase 1, or a novel protein O-fucosyltransferase, may be responsible for this modification. Mutating this O-fucose site on the EMI domain led to a >50% reduction of MMRN1 secretion, supporting a key role of EMI O-fucosylation in MMRN1 secretion. By comparing releasates from resting and thrombin-treated platelets, 202 proteins were found to be significantly released after high-dose thrombin stimulation. Complementary quantification of the platelet lysates identified >3800 proteins, which confirmed the platelet origin of releasate proteins by anticorrelation analysis. Low-dose thrombin treatment yielded a smaller subset of significantly regulated proteins with fewer secretory pathway enzymes. The extensive platelet proteome resource provided here (larancelab.com/platelet-proteome) allows identification of novel regulatory mechanisms for drug targeting to address platelet dysfunction and thrombosis.

Liver fibrosis in NAFLD/NASH: from pathophysiology towards diagnostic and therapeutic strategies

Liver fibrosis, as an excess deposition of extracellular matrix (ECM) components, results from chronic liver injury as well as persistent activation of inflammatory response and of fibrogenesis. Liver fibrosis is a major determinant for chronic liver disease (CLD) progression and in the last two decades our understanding on the major molecular and cellular mechanisms underlying the fibrogenic progression of CLD has dramatically improved, boosting pre-clinical studies and clinical trials designed to find novel therapeutic approaches. From these studies several critical concepts have emerged, starting to reveal the complexity of the pro-fibrotic microenvironment which involves very complex, dynamic and interrelated interactions between different hepatic and extrahepatic cell populations. This review will offer first a recapitulation of established and novel pathophysiological basic principles and concepts by intentionally focus the attention on NAFLD/NASH, a metabolic-related form of CLD with a high impact on the general population and emerging as a leading cause of CLD worldwide. NAFLD/NASH-related pro-inflammatory and profibrogenic mechanisms will be analysed as well as novel information on cells, mediators and signalling pathways which have taken advantage from novel methodological approaches and techniques (single cell genomics, imaging mass cytometry, novel in vitro two- and three-dimensional models, etc.). We will next offer an overview on recent advancement in diagnostic and prognostic tools, including serum biomarkers and polygenic scores, to support the analysis of liver biopsies. Finally, this review will provide an analysis of current and emerging therapies for the treatment of NAFLD/NASH patients.

Biomarkers for Serious Bacterial Infections in Febrile Children

Febrile infections in children are a common cause of presentation to the emergency department (ED). While viral infections are usually self-limiting, sometimes bacterial illnesses may lead to sepsis and severe complications. Inflammatory biomarkers such as C reactive protein (CRP) and procalcitonin are usually the first blood exams performed in the ED to differentiate bacterial and viral infections; nowadays, a better understanding of immunochemical pathways has led to the discovery of new and more specific biomarkers that could play a role in the emergency setting. The aim of this narrative review is to provide the most recent evidence on biomarkers and predictor models, combining them for serious bacterial infection (SBI) diagnosis in febrile children. Literature analysis shows that inflammatory response is a complex mechanism in which many biochemical and immunological factors contribute to the host response in SBI. CRP and procalcitonin still represent the most used biomarkers in the pediatric ED for the diagnosis of SBI. Their sensibility and sensitivity increase when combined, and for this reason, it is reasonable to take them both into consideration in the evaluation of febrile children. The potential of machine learning tools, which represent a real novelty in medical practice, in conjunction with routine clinical and biological information, may improve the accuracy of diagnosis and target therapeutic options in SBI. However, studies on this matter are not yet validated in younger populations, making their relevance in pediatric precision medicine still uncertain. More data from further research are needed to improve clinical practice and decision making using these new technologies.

New insights of platelet endocytosis and its implication for platelet function

Endocytosis constitutes a cellular process in which cells selectively encapsulate surface substances into endocytic vesicles, also known as endosomes, thereby modulating their interaction with the environment. Platelets, as pivotal hematologic elements, play a crucial role not only in regulating coagulation and thrombus formation but also in facilitating tumor invasion and metastasis. Functioning as critical components in the circulatory system, platelets can internalize various endosomal compartments, such as surface receptors, extracellular proteins, small molecules, and pathogens, from the extracellular environment through diverse endocytic pathways, including pinocytosis, phagocytosis, and receptor-mediated endocytosis. We summarize recent advancements in platelet endocytosis, encompassing the catalog of cargoes, regulatory mechanisms, and internal trafficking routes. Furthermore, we describe the influence of endocytosis on platelet regulatory functions and related physiological and pathological processes, aiming to offer foundational insights for future research into platelet endocytosis.

Platelet-targeted gene therapy induces immune tolerance in hemophilia and beyond

Blood platelets have unique storage and delivery capabilities. Platelets play fundamental roles in hemostasis, inflammatory reactions, and immune responses. Beyond their functions, platelets have been used as a target for gene therapy. Platelet-targeted gene therapy aims to deliver a sustained expression of neo-protein in vivo by genetically modifying the target cells, resulting in a cure for the disease. Even though there has been substantial progress in the field of gene therapy, the potential development of immune responses to transgene products or vectors remains a significant concern. Of note, multiple preclinical studies using platelet-specific lentiviral gene delivery to hematopoietic stem cells in hemophilia have demonstrated promising results with therapeutic levels of neo-protein that rescue the hemorrhagic bleeding phenotype and induce antigen-specific immune tolerance. Further studies using ovalbumin as a surrogate protein for platelet gene therapy have shown robust antigen-specific immune tolerance induced via peripheral clonal deletions of antigen-specific CD4- and CD8-T effector cells and induction of antigen-specific regulatory T (Treg) cells. This review discusses platelet-targeted gene therapy, focusing on immune tolerance induction.

Tumor-educated platelets

Beyond traditional roles in homeostasis and coagulation, growing evidence suggests that platelets also reflect malignant transformation in cancer. Platelets are present in the tumor microenvironment where they interact with cancer cells. This interaction results in direct and indirect "education" as evident by platelet alterations in adhesion molecules, glycoproteins, nucleic acids, proteins and various receptors. Subsequently, these tumor-educated platelets (TEPs) circulate throughout the body and play pivotal roles in promotion of tumor growth and dissemination. Accordingly, platelet status can be considered a unique blood-based biomarker that can potentially predict prognosis and therapeutic success. Recently, liquid biopsies including TEPs have received much attention as safe, minimally invasive and sensitive alternatives for patient management. Herein, we provide an overview of TEPs and explore their benefits and limitations in cancer.

The Role of the Complement System in the Pathogenesis of Infectious Forms of Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) is an acute disease and the most common cause of childhood acute renal failure. HUS is characterized by a triad of symptoms: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. In most of the cases, HUS occurs as a result of infection caused by Shiga toxin-producing microbes: hemorrhagic Escherichia coli and Shigella dysenteriae type 1. They account for up to 90% of all cases of HUS. The remaining 10% of cases grouped under the general term atypical HUS represent a heterogeneous group of diseases with similar clinical signs. Emerging evidence suggests that in addition to E. coli and S. dysenteriae type 1, a variety of bacterial and viral infections can cause the development of HUS. In particular, infectious diseases act as the main cause of aHUS recurrence. The pathogenesis of most cases of atypical HUS is based on congenital or acquired defects of complement system. This review presents summarized data from recent studies, suggesting that complement dysregulation is a key pathogenetic factor in various types of infection-induced HUS. Separate links in the complement system are considered, the damage of which during bacterial and viral infections can lead to complement hyperactivation following by microvascular endothelial injury and development of acute renal failure.

Platelet-Rich Plasma (PRP) in Dermatology: Cellular and Molecular Mechanisms of Action

Platelet-rich plasma (PRP) therapy has gained attention in the scientific field due to its potential regenerative effects and great benefit-risk ratio. This review extensively explores the most studied mechanisms of this therapy according to the etiopathogenesis of skin diseases: cellular proliferation, matrix formation, regulation of inflammation, angiogenesis, collagen synthesis, and the remodeling of new tissue. Moreover, it draws on newly reported and lesser-known effects of PRP: its anti-apoptotic effects, immunological suppression, decrease in melanin synthesis, anti-microbial effects, overexpression of miR-155, antioxidant effects, and their involved pathways. This work aims to provide a complete update for understanding PRP's benefits and clinical relevance in wound healing, alopecia, pigmentary disorders, scars, rejuvenation, lichen sclerosus, and other inflammatory dermatoses, based on the current evidence. Furthermore, recent reports with novel indications for PRP therapy are highlighted, and new potential pathways correlated with the pathogenesis of skin diseases are explored.

Sodium bicarbonate as a local adjunctive agent for limiting platelet activation, aggregation, and adhesion within cardiovascular therapeutic devices

Cardiovascular therapeutic devices (CTDs) remain limited by thrombotic adverse events. Current antithrombotic agents limit thrombosis partially, often adding to bleeding. The Impella® blood pump utilizes heparin in 5% dextrose (D5W) as an internal purge to limit thrombosis. While effective, exogenous heparin often complicates overall anticoagulation management, increasing bleeding tendency. Recent clinical studies suggest sodium bicarbonate (bicarb) may be an effective alternative to heparin for local anti-thrombosis. We examined the effect of sodium bicarbonate on human platelet morphology and function to better understand its translational utility. Human platelets were incubated (60:40) with D5W + 25 mEq/L, 50 mEq/L, or 100 mEq/L sodium bicarbonate versus D5W or D5W + Heparin 50 U/mL as controls. pH of platelet-bicarbonate solutions mixtures was measured. Platelet morphology was examined via transmission electron microscopy; activation assessed via P-selectin expression, phosphatidylserine exposure and thrombin generation; and aggregation with TRAP-6, calcium ionophore, ADP and collagen quantified; adhesion to glass measured via fluorescence microscopy. Sodium bicarbonate did not alter platelet morphology but did significantly inhibit activation, aggregation, and adhesion. Phosphatidylserine exposure and thrombin generation were both reduced in a concentration-dependent manner-between 26.6 ± 8.2% (p = 0.01) and 70.7 ± 5.6% (p < 0.0001); and 14.0 ± 6.2% (p = 0.15) and 41.7 ± 6.8% (p = 0.03), respectively, compared to D5W control. Platelet aggregation via all agonists was also reduced, particularly at higher concentrations of bicarb. Platelet adhesion to glass was similarly reduced, between 0.04 ± 0.03% (p = 0.61) and 0.11 ± 0.04% (p = 0.05). Sodium bicarbonate has direct, local, dose-dependent effects limiting platelet activation and adhesion. Our results highlight the potential utility of sodium bicarbonate as a locally acting agent to limit device thrombosis.

The critical role of platelet in cancer progression and metastasis

Platelets play a crucial role in cancer blood metastasis. Various cancer-related factors such as Toll-like receptors (TLRs), adenosine diphosphate (ADP) or extracellular matrix (ECM) can activate these small particles that function in hemostasis and thrombosis. Moreover, platelets induce Epithelial Mesenchymal Transition (EMT) to promote cancer progression and invasiveness. The activated platelets protect circulating tumor cells from immune surveillance and anoikis. They also mediate tumor cell arrest, extravasation and angiogenesis in distant organs through direct or indirect modulation, creating a metastatic microenvironment. This review summarizes the recent advances and progress of mechanisms in platelet activation and its interaction with cancer cells in metastasis.

The WASH-complex subunit Strumpellin regulates integrin αIIbβ3 trafficking in murine platelets

The platelet specific integrin αIIbβ3 mediates platelet adhesion, aggregation and plays a central role in thrombosis and hemostasis. In resting platelets, αIIbβ3 is expressed on the membrane surface and in intracellular compartments. Upon activation, the number of surface-expressed αIIbβ3 is increased by the translocation of internal granule pools to the plasma membrane. The WASH complex is the major endosomal actin polymerization-promoting complex and has been implicated in the generation of actin networks involved in endocytic trafficking of integrins in other cell types. The role of the WASH complex and its subunit Strumpellin in platelet function is still unknown. Here, we report that Strumpellin-deficient murine platelets display an approximately 20% reduction in integrin αIIbβ3 surface expression. While exposure of the internal αIIbβ3 pool after platelet activation was unaffected, the uptake of the αIIbβ3 ligand fibrinogen was delayed. The number of platelet α-granules was slightly but significantly increased in Strumpellin-deficient platelets. Quantitative proteome analysis of isolated αIIbβ3-positive vesicular structures revealed an enrichment of protein markers, which are associated with the endoplasmic reticulum, Golgi complex and early endosomes in Strumpellin-deficient platelets. These results point to a so far unidentified role of the WASH complex subunit Strumpellin in integrin αIIbβ3 trafficking in murine platelets.

Loss of zinc transporters ZIP1 and ZIP3 augments platelet reactivity in response to thrombin and accelerates thrombus formation in vivo

Zinc (Zn2+) is considered as important mediator of immune cell function, thrombosis and haemostasis. However, our understanding of the transport mechanisms that regulate Zn2+ homeostasis in platelets is limited. Zn2+ transporters, ZIPs and ZnTs, are widely expressed in eukaryotic cells. Using mice globally lacking ZIP1 and ZIP3 (ZIP1/3 DKO), our aim was to explore the potential role of these Zn2+ transporters in maintaining platelet Zn2+ homeostasis and in the regulation of platelet function. While ICP-MS measurements indicated unaltered overall Zn2+ concentrations in platelets of ZIP1/3 DKO mice, we observed a significantly increased content of FluoZin3-stainable free Zn2+, which, however, appears to be released less efficiently upon thrombin-stimulated platelet activation. On the functional level, ZIP1/3 DKO platelets exhibited a hyperactive response towards threshold concentrations of G protein-coupled receptor (GPCR) agonists, while immunoreceptor tyrosine-based activation motif (ITAM)-coupled receptor agonist signalling was unaffected. This resulted in enhanced platelet aggregation towards thrombin, bigger thrombus volume under flow ex vivo and faster in vivo thrombus formation in ZIP1/3 DKO mice. Molecularly, augmented GPCR responses were accompanied by enhanced Ca2+ and PKC, CamKII and ERK1/2 signalling. The current study thereby identifies ZIP1 and ZIP3 as important regulators for the maintenance of platelet Zn2+ homeostasis and function.

Adiponectin receptor agonist AdipoRon modulates human and mouse platelet function

Adiponectin, an adipokine secreted by adipocytes, has anti-atherosclerotic and antithrombotic activities. AdipoRon is synthetic small molecule adiponectin receptor agonist. In this study, we investigated the effect of AdipoRon on platelet activation and thrombus formation. Washed human platelets were prepared from the peripheral blood of healthy donors. In a series of in vitro platelet functional assays, pre-treatment with AdipoRon (10, 20, 40 µg/mL) dose-dependently inhibited the aggregation, granule secretion and spreading of washed human platelets. We showed that AdipoRon (20, 40 µg/mL) significantly inhibited AMPK, Syk, PLCγ2, PI3K, Akt, p38-MAPK and ERK1/2 signalling pathways in washed human platelets. In addition, we demonstrated that the phosphorylation of CKII at Tyr255 was an important mechanism of the integrin αIIbβ3-mediated platelet activation. Meanwhile, AdipoR1 deficiency impaired the inhibitory effect of AdipoRon on mouse platelets. In ferric chloride-induced carotid injury model, injection of AdipoRon (5 or 12.5 mg/kg, iv) significantly attenuated arterial thrombosis. In conclusion, AdipoRon attenuates platelet function via the AdipoR1/AMPK/CKII/PI3K/AKT signalling pathways, while exerting a protective effect against arterial thrombosis. This study offers new insights into the fields of cardiovascular disease and antiplatelet drug discovery.Schematic model of AdipoRon regulating platelet activation. (BioRender.com).

Inflammatory processes involved in NASH-related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related death worldwide. In the recent years nonalcoholic fatty liver disease (NAFLD) is becoming a growing cause of HCCs and the incidence of NAFLD-related HCCs is expected to further dramatically increase by the next decade. Chronic inflammation is regarded as the driving force of NAFLD progression and a key factor in hepatic carcinogenesis. Hepatic inflammation in NAFLD results from the persistent stimulation of innate immunity in response to hepatocellular injury and gut dysbiosis as well as by the activation of adaptive immunity. However, the relative roles of innate and adaptive immunity in the processes leading to HCC are still incompletely characterized. This is due to the complex interplay between different liver cell populations, which is also strongly influenced by gut-derived bacterial products, metabolic/nutritional signals. Furthermore, carcinogenic mechanisms in NAFLD/NASH appear to involve the activation of signals mediated by hypoxia inducible factors. This review discusses recent data regarding the contribution of different inflammatory cells to NAFLD-related HCC and their possible impact on patient response to current treatments.

Evaluation of Platelet-Rich Plasma by means of PRGF®-Endoret® protocol in leukemia cats: PDGF-BB and TGF-ß1 valuation

Introduction

Feline leukemia virus (FeLV) is a chronic disease that leads to the weakening of a cat's immune system. Platelet-rich plasma (PRP) offers therapeutic effects for multiple diseases, the use of PRP and growth factors (GFs) determination could be an alternative treatment to improve the quality of life in these patients. The objectives of this study were to determine and compare the concentration of platelets (PLTs), red blood cells (RBCs) and white blood cells (WBCs) between samples of whole blood (WB), PRP and platelet-poor plasma (PPP) fractions, and to evaluate the concentration of platelet-derived growth factor BB (PDGF-BB) and transforming growth factor β1 (TGF-β1) in both fractions in FeLV cats using a PRGF^®-Endoret^® protocol previously standardized in this species.

Methods

WB was collected from 11 asymptomatic FeLV-positive cats. PRP and PPP was obtained following PRGF^®-Endoret^® technology according to centrifugation at 265 g for 10 min. Cellular components, RBCs, WBCs, PLTs, and the PDGF-BB and TGF-β1 concentrations in PRP and PPP fractions were determined.

Results

PLT in the PRP fraction was statistically higher than WB and PPP fraction, with no statistical differences between WB and PPP. PLT concentration increased 1.4 times in PRP fraction compared to WB. Mean platelet volume (MPV) did not differ significantly between the WB, PRP, and PPP fractions. Compared to WB, the absolute numbers of RBCs and WBCs were decreased by 99% and more than 95% in the PRP and PPP fractions, respectively. TGF-ß1 concentrations increased in PRP vs. PPP, with no changes in PDGF-BB.

Discussion

Based on the degree of PLT enrichment and the absence of RBCs and WBCs, this blood product could be classified as a Pure Platelet-Rich Plasma (P-PRP). The presence of GFs in PRP and PPP samples suggests that the PRGF^®-Endoret^® methodology is suitable for obtaining PRP in FeLV cats, despite future studies are necessary to optimize the technique, standardize the results and assess clinical efficacy.

Repeated platelet activation and the potential of previously activated platelets to contribute to thrombus formation

BACKGROUND

Especially in disease conditions, platelets can encounter activating agents in circulation.

OBJECTIVES

To investigate the extent to which previously activated platelets can be reactivated and whether in-and reactivation applies to different aspects of platelet activation and thrombus formation.

METHODS

Short-and long-term effects of glycoprotein VI (GPVI) and G protein-coupled receptor (GPCR) stimulation on platelet activation and aggregation potential were compared via flow cytometry and plate-based aggregation. Using fluorescence and electron microscopy, we assessed platelet morphology and content, as well as thrombus formation.

RESULTS

After 30 minutes of stimulation with thrombin receptor activator peptide 6 (TRAP6) or adenosine diphosphate (ADP), platelets secondarily decreased in PAC-1 binding and were less able to aggregate. The reversibility of platelets after thrombin stimulation was concentration dependent. Reactivation was possible via another receptor. In contrast, cross-linked collagen-related peptide (CRP-XL) or high thrombin stimulation evoked persistent effects in α_IIbβ₃ activation and platelet aggregation. However, after 60 minutes of CRP-XL or high thrombin stimulation, when α_IIbβ₃ activation slightly decreased, restimulation with ADP or CRP-XL, respectively, increased integrin activation again. Compatible with decreased integrin activation, platelet morphology was reversed. Interestingly, reactivation of reversed platelets again resulted in shape change and if not fully degranulated, additional secretion. Moreover, platelets that were previously activated with TRAP6 or ADP regained their potential to contribute to thrombus formation under flow. On the contrary, prior platelet triggering with CRP-XL was accompanied by prolonged platelet activity, leading to a decreased secondary platelet adhesion under flow.

CONCLUSION

This work emphasizes that prior platelet activation can be reversed, whereafter platelets can be reactivated through a different receptor. Reversed, previously activated platelets can contribute to thrombus formation.

Platelets and (Lymph)angiogenesis

The formation of new blood and lymphatic vessels is essential for both the development of multicellular organisms and (patho)physiological processes like wound repair and tumor growth. In the 1990s, circulating blood platelets were first postulated to regulate tumor angiogenesis by interacting with the endothelium and releasing angiogenic regulators from specialized α granules. Since then, many studies have validated the contributions of platelets to tumor angiogenesis, while uncovering novel roles for platelets in other angiogenic processes like wound resolution and retinal vascular disease. Although the majority of (lymph)angiogenesis occurs during development, platelets appear necessary for lymphatic but not vascular growth, implying their particular importance in pathological cases of adult angiogenesis. Future work is required to determine whether drugs targeting platelet production or function offer a clinically relevant tool to limit detrimental angiogenesis.

Filamin A in platelets: Bridging the (signaling) gap between the plasma membrane and the actin cytoskeleton

Platelets are anucleate cells that are essential for hemostasis and wound healing. Upon activation of the cell surface receptors by their corresponding extracellular ligands, platelets undergo rapid shape change driven by the actin cytoskeleton; this shape change reaction is modulated by a diverse array of actin-binding proteins. One actin-binding protein, filamin A (FLNA), cross-links and stabilizes subcortical actin filaments thus providing stability to the cell membrane. In addition, FLNA binds the intracellular portion of multiple cell surface receptors and acts as a critical intracellular signaling scaffold that integrates signals between the platelet's plasma membrane and the actin cytoskeleton. This mini-review summarizes how FLNA transduces critical cell signals to the platelet cytoskeleton.

Regulatory Effects of Curcumin on Platelets: An Update and Future Directions

The rhizomatous plant turmeric, which is frequently used as a spice and coloring ingredient, yields curcumin, a bioactive compound. Curcumin inhibits platelet activation and aggregation and improves platelet count. Platelets dysfunction results in several disorders, including inflammation, atherothrombosis, and thromboembolism. Several studies have proved the beneficial role of curcumin on platelets and hence proved it is an important candidate for the treatment of the aforementioned diseases. Moreover, curcumin is also frequently employed as an anti-inflammatory agent in conventional medicine. In arthritic patients, it has been shown to reduce the generation of pro-inflammatory eicosanoids and to reduce edema, morning stiffness, and other symptoms. Curcumin taken orally also reduced rats' acute inflammation brought on by carrageenan. Curcumin has also been proven to prevent atherosclerosis and platelet aggregation, as well as to reduce angiogenesis in adipose tissue. In the cerebral microcirculation, curcumin significantly lowered platelet and leukocyte adhesion. It largely modulated the endothelium to reduce platelet adhesion. Additionally, P-selectin expression and mice survival after cecal ligation and puncture were improved by curcumin, which also altered platelet and leukocyte adhesion and blood-brain barrier dysfunction. Through regulating many processes involved in platelet aggregation, curcuminoids collectively demonstrated detectable antiplatelet activity. Curcuminoids may therefore be able to prevent disorders linked to platelet activation as possible therapeutic agents. This review article proposes to highlight and discuss the regulatory effects of curcumin on platelets.

Features of platelet and plasma hemostasis in premature infants with hemorrhagic disorders

The research revealed features of platelet and plasma hemostasis indicators in children born before 32 weeks with hemorrhagic disorders in the early neonatal period, a method for predicting the development of intraventricular hemorrhage was developed.

Material and methods. 132 premature newborns were examined, a detailed clinical blood test, a coagulogram with the determination of: activated partial thromboplastin time, prothrombin time, thrombin time, prothrombin index, fibrinogen content, D-dimer were performed on 1–3 days of life. The main group consisted of 58 children with hemorrhagic disorders, the comparison group included 74 children without hemorrhagic disorders.

Results. Risk factors for the formation of hemorrhagic disorders in the early neonatal period were established: a lower gestational age of the child, lower Apgar scores at the end of the first and fifth minutes of life, the need for the introduction of an exogenous surfactant, and the use of higher concentrations of oxygen-air mixture during respiratory therapy. The features of hemostasis indicators in deep-premature newborns with hemorrhagic disorders in the early neonatal period were revealed: a lower number of platelets in the blood and higher platelet granularity, higher activated partial thromboplastin time, and a decrease in the prothrombin index. Based on the data obtained, a new method for predicting the formation of intraventricular hemorrhage in deeply premature newborns is proposed based on determining the concentration of total Ca2+ in the blood and the average concentration of platelet components. The results of this study can be used in intensive care units for newborns. Conclusion. The implementation of the obtained results in practice will help timely assess the state of hemostasis in deeply premature newborns to predict the development of intraventricular hemorrhages in the early neonatal period. 

Modifying Orthobiological PRP Therapies Are Imperative for the Advancement of Treatment Outcomes in Musculoskeletal Pathologies

Autologous biological cellular preparations have materialized as a growing area of medical advancement in interventional (orthopedic) practices and surgical interventions to provide an optimal tissue healing environment, particularly in tissues where standard healing is disrupted and repair and ultimately restoration of function is at risk. These cellular therapies are often referred to as orthobiologics and are derived from patient's own tissues to prepare point of care platelet-rich plasma (PRP), bone marrow concentrate (BMC), and adipose tissue concentrate (ATC). Orthobiological preparations are biological materials comprised of a wide variety of cell populations, cytokines, growth factors, molecules, and signaling cells. They can modulate and influence many other resident cells after they have been administered in specific diseased microenvironments. Jointly, the various orthobiological cell preparations are proficient to counteract persistent inflammation, respond to catabolic reactions, and reinstate tissue homeostasis. Ultimately, precisely delivered orthobiologics with a proper dose and bioformulation will contribute to tissue repair. Progress has been made in understanding orthobiological technologies where the safety and relatively easy manipulation of orthobiological treatment tools has been demonstrated in clinical applications. Although more positive than negative patient outcome results have been registered in the literature, definitive and accepted standards to prepare specific cellular orthobiologics are still lacking. To promote significant and consistent clinical outcomes, we will present a review of methods for implementing dosing strategies, using bioformulations tailored to the pathoanatomic process of the tissue, and adopting variable preparation and injection volume policies. By optimizing the dose and specificity of orthobiologics, local cellular synergistic behavior will increase, potentially leading to better pain killing effects, effective immunomodulation, control of inflammation, and (neo) angiogenesis, ultimately contributing to functionally restored body movement patterns.

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.

Effect of stimulated platelets in COVID-19 thrombosis: Role of alpha7 nicotinic acetylcholine receptor

Since early 2020, SARS-CoV-2-induced infection resulted in global pandemics with high morbidity, especially in the adult population. COVID-19 is a highly prothrombotic condition associated with subsequent multiorgan failure and lethal outcomes. The exact mechanism of the prothrombotic state is not well understood and might be multifactorial. Nevertheless, platelets are attributed to play a crucial role in COVID-19-associated thrombosis. To date, platelets' role was defined primarily in thrombosis and homeostasis. Currently, more focus has been set on their part in inflammation and immunity. Moreover, their ability to release various soluble factors under activation as well as internalize and degrade specific pathogens has been highly addressed in viral research. This review article will discuss platelet role in COVID-19-associated thrombosis and their role in the cholinergic anti-inflammatory pathway. Multiple studies confirmed that platelets display a hyperactivated phenotype in COVID-19 patients. Critically ill patients demonstrate increased platelet activation markers such as P-selectin, PF4, or serotonin. In addition, platelets contain acetylcholine and express α7 nicotinic acetylcholine receptors (α7nAchR). Thus, acetylcholine can be released under activation, and α7nAchR can be stimulated in an autocrine manner and support platelet function. α7 receptor is one of the most important mediators of the anti-inflammatory properties as it is associated with humoral and intrinsic immunity and was demonstrated to contribute to better outcomes in COVID-19 patients when under stimulation. Hematopoietic α7nAchR deficiency increases platelet activation and, in experimental studies, α7nAchR stimulation can diminish the pro-inflammatory state and modulate platelet reactiveness via increased levels of NO. NO has been described to inhibit platelet adhesion, activation, and aggregation. In addition, acetylcholine has been demonstrated to decrease platelet aggregation possibly by blocking the e p-38 pathway. SARS-CoV-2 proteins have been found to be similar to neurotoxins which can bind to nAChR and prevent the action of acetylcholine. Concluding, the platelet role in COVID-19 thrombotic events could be explained by their active function in the cholinergic anti-inflammatory pathway.

Platelet-rich plasma: a comparative and economical therapy for wound healing and tissue regeneration

Rise in the incidences of chronic degenerative diseases with aging makes wound care a socio-economic burden and unceasingly necessitates a novel, economical, and efficient wound healing treatment. Platelets have a crucial role in hemostasis and thrombosis by modulating distinct mechanistic phases of wound healing, such as promoting and stabilizing the clot. Platelet-rich plasma (PRP) contains a high concentration of platelets than naïve plasma and has an autologous origin with no immunogenic adverse reactions. As a consequence, PRP has gained significant attention as a therapeutic to augment the healing process. Since the past few decades, a robust volume of research and clinical trials have been performed to exploit extensive role of PRP in wound healing/tissue regeneration. Despite these rigorous studies and their application in diversified medical fields, efficacy of PRP-based therapies is continuously questioned owing to the paucity of large samplesizes, controlled clinical trials, and standard protocols. This review systematically delineates the process of wound healing and involvement of platelets in tissue repair mechanisms. Additionally, emphasis is laid on PRP, its preparation methods, handling, classification,application in wound healing, and PRP as regenerative therapeutics combined with biomaterials and mesenchymal stem cells (MSCs).

Coagulation and complement: Key innate defense participants in a seamless web

In 1969, Dr. Oscar Ratnoff, a pioneer in delineating the mechanisms by which coagulation is activated and complement is regulated, wrote, “In the study of biological processes, the accumulation of information is often accelerated by a narrow point of view. The fastest way to investigate the body’s defenses against injury is to look individually at such isolated questions as how the blood clots or how complement works. We must constantly remind ourselves that such distinctions are man-made. In life, as in the legal cliché, the devices through which the body protects itself form a seamless web, unwrinkled by our artificialities.” Our aim in this review, is to highlight the critical molecular and cellular interactions between coagulation and complement, and how these two major component proteolytic pathways contribute to the seamless web of innate mechanisms that the body uses to protect itself from injury, invading pathogens and foreign surfaces.