Changes in glycans on platelet microparticles released during storage of apheresis platelets are associated with phosphatidylserine externalization and phagocytosis

BACKGROUND

Platelets shed platelet microparticles (PMP) when activated or stored. As the removal of sialic acid (desialylation) promotes platelet uptake and clearance from the circulation, similar mechanisms for PMP uptake were hypothesized. The aim of the study was to investigate the role of surface glycans in the in vitro uptake of PMP from stored platelet components.

STUDY DESIGN AND METHODS

Apheresis platelet components were stored in 40% plasma/60% SSP+ and sampled on day 1, 5, and 7 post-collection. PMP were characterized by staining with annexin-V (AnV) for phosphatidylserine (PS)-exposure, CD41 antibody, and fluorescently labeled glycan-binding lectins using flow cytometry. The procoagulant function of PMP following desialylation by neuraminidase treatment was assessed by AnV binding and a procoagulant phospholipid assay. PMP were isolated and stained with Deep Red, and phagocytosis by HepG2 cells was measured. Isolated PMP were deglycosylated with neuraminidase and galactosidase to assess the involvement of glycans in mediating phagocytosis.

RESULTS

While the overall platelet surface glycan profile was unchanged during storage, PS⁺ platelets were sialylated, indicating different glycoproteins were changed. In contrast, sialic acid was removed from PS⁺ and CD41⁺ PMP, which specifically lost α-2,3-linked sialic acid during platelet storage. PMP were phagocytized by HepG2 cells, and PMP from platelets stored for 7 days were phagocytized to a lesser extent than on day 1. Desialylation by neuraminidase induced PS-exposure on PMP, decreased PPL clotting time, and increased PMP phagocytosis.

CONCLUSION

PMP glycans change during platelet storage. Desialylation influences the procoagulant function of PMP and phagocytosis by HepG2 cells.

Circulating platelets as liquid biopsy sources for cancer detection

Nucleic acids and proteins are shed into the bloodstream by tumor cells and can be exploited as biomarkers for the detection of cancer. In addition, cancer detection biomarkers can also be nontumor‐derived, having their origin in other organs and cell types. Hence, liquid biopsies provide a source of direct tumor cell‐derived biomolecules and indirect nontumor‐derived surrogate markers that circulate in body fluids or are taken up by circulating peripheral blood cells. The capacity of platelets to take up proteins and nucleic acids and alter their megakaryocyte‐derived transcripts and proteins in response to external signals makes them one of the richest liquid biopsy biosources. Platelets are the second most abundant cell type in peripheral blood and are routinely isolated through well‐established and fast methods in clinical diagnostics but their value as a source of cancer biomarkers is relatively recent. Platelets do not have a nucleus but have a functional spliceosome and protein translation machinery, to process RNA transcripts. Platelets emerge as important repositories of potential cancer biomarkers, including several types of RNAs (mRNA, miRNA, circRNA, lncRNA, and mitochondrial RNA) and proteins, and several preclinical studies have highlighted their potential as a liquid biopsy source for detecting various types and stages of cancer. Here, we address the usability of platelets as a liquid biopsy for the detection of cancer. We describe several studies that support the use of platelet biomarkers in cancer diagnostics and discuss what is still lacking for their implementation into the clinic.

Clinical-grade cryopreserved doxorubicin-loaded platelets: role of cancer cells and platelet extracellular vesicles activation loop

Background

Human platelets (PLT) and PLT-extracellular vesicles (PEV) released upon thrombin activation express receptors that interact with tumour cells and, thus, can serve as a delivery platform of anti-cancer agents. Drug-loaded nanoparticles coated with PLT membranes were demonstrated to have improved targeting efficiency to tumours, but remain impractical for clinical translation. PLT and PEV targeted drug delivery vehicles should facilitate clinical developments if clinical-grade procedures can be developed.

Methods

PLT from therapeutic-grade PLT concentrate (PC; N > 50) were loaded with doxorubicin (DOX) and stored at − 80 °C (DOX-loaded PLT) with 6% dimethyl sulfoxide (cryopreserved DOX-loaded PLT). Surface markers and function of cryopreserved DOX-loaded PLT was confirmed by Western blot and thromboelastography, respectively. The morphology of fresh and cryopreserved naïve and DOX-loaded PLT was observed by scanning electron microscopy. The content of tissue factor-expressing cancer-derived extracellular vesicles (TF-EV) present in conditioned medium (CM) of breast cancer cells cultures was measured. The drug release by fresh and cryopreserved DOX-loaded PLT triggered by various pH and CM was determined by high performance liquid chromatography. The thrombin activated PEV was analyzed by nanoparticle tracking analysis. The cellular uptake of DOX from PLT was observed by deconvolution microscopy. The cytotoxicities of DOX-loaded PLT, cryopreserved DOX-loaded PLT, DOX and liposomal DOX on breast, lung and colon cancer cells were analyzed by CCK-8 assay.

Results

15~36 × 10⁶ molecules of DOX could be loaded in each PLT within 3 to 9 days after collection. The characterization and bioreactivity of cryopreserved DOX-loaded PLT were preserved, as evidenced by (a) microscopic observations, (b) preservation of important PLT membrane markers CD41, CD61, protease activated receptor-1, (c) functional activity, (d) reactivity to TF-EV, and (e) efficient generation of PEV upon thrombin activation. The transfer of DOX from cryopreserved PLT to cancer cells was achieved within 90 min, and stimulated by TF-EV and low pH. The cryopreserved DOX-loaded PLT formulation was 7~23-times more toxic to three cancer cells than liposomal DOX.

Conclusions

Cryopreserved DOX-loaded PLT can be prepared under clinically compliant conditions preserving the membrane functionality for anti-cancer therapy. These findings open perspectives for translational applications of PLT-based drug delivery systems.

Internalization of microparticles by platelets is partially mediated by toll-like receptor 4 and enhances platelet thrombogenicity

BACKGROUND AND AIMS

Circulating platelet microparticles (PMP) are the most abundant in bloodstream, are highly procoagulant and contribute to cross-talk with inflammatory cells. The aim of the present study was to investigate the interactions of PMP with platelets and explore the involvement of toll-like receptor 4 (TLR-4).

METHODS

PMP were separated by ultracentrifugation of expired platelet concentrates and added to: i) washed platelets, to confirm uptake, by flow cytometry and confocal and transmission electron microscopy, ii) platelet rich plasma (PRP), to assess changes in platelet function due to uptake by aggregometry in response to ADP; and iii) whole blood, to evaluate heterotypic aggregate (HA) formation by flow cytometry. Moreover, whole blood previously enriched with platelets with internalized PMP was used to explore modifications in thromboelastometry parameters (ROTEM). The inhibitory action of anti-TLR-4 was investigated.

RESULTS

Confocal and ultrastructural microscopy studies revealed PMP internalization by platelets. Flow cytometry showed PMP-platelet association (p < 0.01 vs controls, at different PMP dilutions). PMP, at 1/20 dilution, increased HA (p < 0.05 vs controls), the percentage of maximal platelet aggregation to ADP (p < 0.05 vs controls), and accelerated clotting and clot formation times (p < 0.05 vs controls). Incubation of platelets with anti-TLR-4 prior to exposure to PMP reduced PMP-platelet association (p < 0.05 vs absence of the antibody), prevented HA formation, reduced maximal platelet aggregation and normalized ROTEM parameters.

CONCLUSIONS

Platelets exhibit internalization ability towards their own PMP, a process that potentiates their thrombogenicity and is partially mediated by the innate immunity receptor TLR-4.

Inhibitory Effects of Ginsenoside Ro on Clot Retraction through Suppressing PI3K/Akt Signaling Pathway in Human Platelets

Glycoprotein IIb/IIIa (αIIb/β₃) is the most abundant integrin on platelet surfaces, which is involved in interaction between platelets, and triggers an intracellular signaling cascade, platelet shape changes, granule secretion, and clot retraction. In this study, we evaluated the effect of ginsenoside Ro (G-Ro) on the binding of fibronectin and fibrinogen to αIIb/β₃ and clot retraction. We found that G-Ro inhibited thrombin-induced platelet aggregation dose-dependently and attenuated the fibronectin-, and fibrinogen-binding to αIIb/β₃ through the dephosphorylation of phosphoinositide 3-kinase p85 and Akt, which influence clot retraction, reflecting the intensification of thrombus. We observed that G-Ro is involved in αIIb/β₃ in human platelets. These results suggest that G-Ro is beneficial, inhibiting fibronectin adhesion, fibrinogen binding, and clot retraction. Therefore, G-Ro in Panax ginseng may prevent platelet aggregation-mediated thrombotic disease.

Alterations in vascular function by syncytiotrophoblast extracellular vesicles via lectin-like oxidized low-density lipoprotein receptor-1 in mouse uterine arteries

Syncytiotrophoblast extracellular vesicles (STBEVs), released into the maternal circulation during pregnancy, have been shown to affect vascular function; however, the mechanism remains unknown. In rats, STBEVs were shown to reduce endothelium-mediated vasodilation via lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), a multi-ligand scavenger receptor that has been associated with vascular dysfunction. Recently, LOX-1 was shown to interact with the angiotensin II type 1 receptor (AT-1). We hypothesized that, in pregnant mice, STBEVs would impair vascular function via LOX-1 and would specifically affect angiotensin II responses. Uterine arteries from pregnant control (C57BL/6) and LOX-1 knockout (LOX-1KO) mice were isolated on gestational day (GD) 18.5. Endothelium-dependent (methylcholine (MCh); ± N(G)-Nitro-L-arginine methyl ester to assess nitric oxide (NO) contribution), and -independent (sodium nitroprusside) vasodilation, and vasoconstriction (angiotensin II; ± AT-1 [candesartan] or angiotensin II type 2 receptor (AT-2) [PD123.319] receptor antagonists; high potassium salt solution) responses were assessed using wire myography. AT-1 and AT-2 expression was analyzed using fluorescence microscopy. Human umbilical vein endothelial cells (HUVECs) were stimulated with STBEVs ± LOX-1 blocking antibody, and superoxide and peroxynitrite production were analyzed. Although MCh-induced vasodilation was decreased (P=0.0012), NO contribution to vasodilation was greater in LOX-1KO mice (P=0.0055). STBEVs delayed angiotensin II tachyphylaxis in arteries from control but not LOX-1KO mice (P<0.0001), while AT-1 and AT-2 expression was unchanged. STBEVs increased peroxynitrite production in HUVECs via LOX-1 (P=0.0091). In summary, LOX-1 deletion altered endothelium-mediated vasodilation, suggesting that LOX-1 contributes to vascular adaptations in pregnancy. STBEVs increased angiotensin II responsiveness and oxidative stress levels via LOX-1, suggesting that increased LOX-1 expression/activation or STBEVs could adversely affect vascular function and contribute to vascular complications of pregnancy.

The Platelet Releasate is Altered in Human Pregnancy

PURPOSE

Healthy pregnancy is characterized by an increase in platelet activation and a decrease in the number of circulating platelets with gestation. Despite this recognized importance, proteomic studies investigating platelets in healthy pregnancy have not been performed. As platelet cargo can be altered in different conditions, it is hypothesized that platelets may store a relevant and bespoke collection of molecules during pregnancy.

EXPERIMENTAL DESIGN

Comparative label-free quantitative proteomic profiling of platelet releasates (PRs) is performed from 18 healthy pregnant and 13 non-pregnant women using an MS/MS approach.

RESULTS

Of the 723 proteins identified, 69 PR proteins are found to be differentially released from platelets in pregnancy, including proteins only expressed during pregnancy such as pregnancy-specific glycoproteins and human placental lactogen. Moreover, the population of exosomal vesicles present in the PR is also modified in pregnancy. Receiver operating characteristic analysis shows the predictive ability of 11 PR proteins to distinctly classify pregnant and nonpregnant women with an area under the curve of 0.876, a sensitivity of 88.9%, and a specificity of 84.6%.

CONCLUSIONS AND CLINICAL RELEVANCE

Taken together this demonstrates that platelets and their released cargo are 'educated' in physiologic stressful conditions such as pregnancy and may represent a promising platform to study pregnancy complications.

Platelet Releasate Proteome Profiling Reveals a Core Set of Proteins with Low Variance between Healthy Adults

Upon activation, platelets release a powerful cocktail of soluble and vesicular signals, collectively termed the "platelet releasate" (PR). Although several studies have used qualitative/quantitative proteomic approaches to characterize PR; with debated content and significant inter-individual variability reported, confident, and reliable insights have been hindered. Using label-free quantitative (LFQ)-proteomics analysis, a reproducible, quantifiable investigation of the 1U mL^-1 thrombin-induced PR from 32 healthy adults was conducted. MS proteomics data are available via ProteomeXchange, identifier PXD009310. Of the 894 proteins identified, 277 proteins were quantified across all donors and form a "core" PR. Bioinformatics and further LFQ-proteomic analysis revealed that the majority (84%) of "core" PR proteins overlapped with the protein composition of human platelet-derived exosomes. Vesicles in the exosomal-size range were confirmed in healthy-human PR and reduced numbers of similar-sized vesicles were observed in the PR of a mouse model of gray platelet syndrome, known to be deficient in platelet alpha-granules. Lastly, the variability of proteins in the PR was assessed, and reproducible secretion levels were found across all 32 healthy donors. Taken together, the PR contains valuable soluble and vesicular cargo and has low-population variance among healthy adults, rendering it a potentially useful platform for diagnostic fingerprinting of platelet-related disease.

Podocyte-derived microparticles promote proximal tubule fibrotic signaling via p38 MAPK and CD36

Tubulointerstitial fibrosis is a hallmark of advanced diabetic kidney disease that is linked to a decline in renal function, however the pathogenic mechanisms are poorly understood. Microparticles (MPs) are 100–1000 nm vesicles shed from injured cells that are implicated in intercellular signalling. Our lab recently observed the formation of MPs from podocytes and their release into urine of animal models of type 1 and 2 diabetes and in humans with type 1 diabetes. The purpose of the present study was to examine the role of podocyte MPs in tubular epithelial cell fibrotic responses. MPs were isolated from the media of differentiated, untreated human podocytes (hPODs) and administered to cultured human proximal tubule epithelial cells (PTECs). Treatment with podocyte MPs increased p38 and Smad3 phosphorylation and expression of the extracellular matrix (ECM) proteins fibronectin and collagen type IV. MP-induced responses were attenuated by co-treatment with the p38 inhibitor SB202190. A transforming growth factor beta (TGF-β) receptor inhibitor (LY2109761) blocked MP-induced Smad3 phosphorylation and ECM protein expression but not p38 phosphorylation suggesting that these responses occurred downstream of p38. Finally, blockade of the class B scavenger receptor CD36 completely abrogated MP-mediated p38 phosphorylation, downstream Smad3 activation and fibronectin/collagen type IV induction. Taken together our results suggest that podocyte MPs interact with proximal tubule cells and induce pro-fibrotic responses. Such interactions may contribute to the development of tubular fibrosis in glomerular disease.

The role of RNA uptake in platelet heterogeneity

The role of platelets in regulating vascular homeostasis has expanded beyond mediation of haemostasis and thrombosis. The discovery of platelet RNA and the presence of subpopulations of platelets containing varying amounts of RNA suggest a role for platelet transcripts in vascular function. As the RNA in anucleated platelets is biologically functional and may transfer to other vascular cells, we hypothesised that platelet RNA diminishes over the lifespan of the platelet with diminishing platelet size due to horizontal cellular transfer. The purpose of this study is to determine if platelet RNA variance is the result of horizontal cellular transfer between platelets and other vascular cells. Utilising platelet sorting and RNA sequencing, we found that smaller platelets contained a more diverse set of transcripts than larger platelets. Further investigation using fluorescence imaging, gene expression analyses and in vitro and in vivo modelling revealed that platelets take up RNA from other vascular cells in a complex manner, revealing a dynamic role for platelets in modulating vascular homeostasis through bidirectional RNA transfer. The resultant RNA profile heterogeneity suggests unique functional roles for platelets dependent on size and complexity. This study expands our basic understanding of platelet function and heterogeneity and is the first to evaluate endogenous vascular RNA uptake and its relation to platelet processes. Our findings describe a novel endogenous phenomenon that can help elucidate the platelet’s role in these non-thrombotic and haemostatic fields, as well as present potential for diagnostic and therapeutic development.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Extracellular vesicles: how they interact with endothelium, potentially contributing to metastatic cancer cell implants

Extracellular vesicles (EV) are blebs of cellular membranes, which entrap small portions of subjacent cytosol. They are released from a variety of cells, circulate in the blood for an unknown length of time and come to rest on endothelial surfaces. They contribute to an array of physiologic pathways, the complexity of which is still being investigated. They contribute to metastatic malignant cell implants and tumor-related angiogenesis, possibly abetted by the tissue factor that they carry. It is thought that the adherence of the EV to endothelium is dependent upon a combination of their P-selectin glycoprotein ligand-1 and exposed phosphatidylserine, the latter of which is normally hidden on the inner bilayer of the intact cellular membrane. This manuscript reviews what is known about EV origins, their clearance from the circulation and how they contribute to malignant cell implants upon endothelium surfaces and subsequent tumor growth.

Platelet microvesicles in health and disease

Interest in cell-derived extracellular vesicles and their physiological and pathological implications is constantly growing. Microvesicles, also known as microparticles, are small extracellular vesicles released by cells in response to activation or apoptosis. Among the different microvesicles present in the blood of healthy individuals, platelet-derived microvesicles (PMVs) are the most abundant. Their characterization has revealed a heterogeneous cargo that includes a set of adhesion molecules. Similarly to platelets, PMVs are also involved in thrombosis through support of the coagulation cascade. The levels of circulatory PMVs are altered during several disease manifestations such as coagulation disorders, rheumatoid arthritis, systemic lupus erythematosus, cancers, cardiovascular diseases, and infections, pointing to their potential contribution to disease and their development as a biomarker. This review highlights recent findings in the field of PMV research and addresses their contribution to both healthy and diseased states.

Microparticles in sickle cell anaemia: promise and pitfalls

Blood from patients with sickle cell disease contains microparticles (MP) derived from multiple cell sources, including red cells, platelets, monocytes and endothelial cells. MPs are of great interest because of their disease associations, their status as promising biomarkers, and the intercellular communications they mediate. To illustrate the likelihood of their relevance in sickle cell disease, we discuss the nature of MP, their profiling in sickle disease, some caveats relevant to their detection, their roles in supporting coagulation and the disparate influences they may exert upon the pathobiology of sickle cell disease.