Use of electron microscopy to study platelets and thrombi

Comprehensive Characterization of Surface-Bound Proteins and Measurement of Fibrin Fiber Thickness on Extracorporeal Membrane Oxygenation Circuits Collected From Patients

OBJECTIVE

To characterize surface-bound proteins and to measure the thickness of fibrin fibers bound to extracorporeal membrane oxygenation (ECMO) circuits used in children.

DESIGN

Single-center observational prospective study, April to November 2021.

SETTING

PICU, Royal Children's Hospital, Melbourne, Australia.

PATIENTS

Patients aged less than 18 years on venoarterial ECMO and without preexisting disorder.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

ECMO circuits were collected from six patients. Circuit samples were collected from five different sites, and subsequently processed for proteomic and scanning electron microscopy (SEM) studies. The concentration of proteins bound to ECMO circuit samples was measured using a bicinchoninic acid protein assay, whereas characterization of the bound proteome was performed using data-independent acquisition mass spectrometry. The Reactome Over-representation Pathway Analyses tool was used to identify functional pathways related to bound proteins. For the SEM studies, ECMO circuit samples were prepared and imaged, and the thickness of bound fibrin fibers was measured using the Fiji ImageJ software, version 1.53c (https://imagej.net/software/fiji/). Protein binding to ECMO circuit samples and fibrin networks showed significant intra-circuit and interpatient variation. The median (range) total protein concentration was 19.0 (0-76.9) μg/mL, and the median total number of proteins was 2011 (1435-2777). A total of 933 proteins were commonly bound to ECMO circuit samples from all patients and were functionally involved in 212 pathways, with signal transduction, cell cycle, and metabolism of proteins being the top three pathway categories. The median intra-circuit fibrin fiber thickness was 0.20 (0.15-0.24) μm, whereas the median interpatient fibrin fiber thickness was 0.18 (0.15-0.21) μm.

CONCLUSIONS

In this report, we have characterized proteins and fiber fibrin thickness bound to ECMO circuits in six children. The techniques and approaches may be useful for investigating interactions between blood, coagulation, and the ECMO circuit and have the potential for circuit design.

"Ultrastructural changes of platelets in COVID-19 and chronic viral hepatitis patients "

Platelet-viral interactions are evolving as a new concern. Coagulation disorder is a major consequence of the COVID-19 infection. In chronic hepatitis virus infections, defect in coagulation factors, thrombocytopenia and platelet function abnormalities are common. A SARS-CoV-2 infection on top of chronic viral hepatitis infection can be common in areas where viral hepatitis is endemic. Here, we investigate the platelet ultrastructural changes and estimate the serum platelet factor-4 (PF-4), ferritin, CRP, and D-dimer in COVID-19 patients (n = 60), COVID-19 patients with associated chronic viral hepatitis (n = 20), and healthy subjects (n = 20). Ultrastructural changes were demonstrated in all test groups, denoting platelet activation. In chronic viral hepatitis patients, Platelet ultrastrustural apoptotic changes were also seen. Significantly high levels of PF-4 were confirmed in moderate and severe COVID-19 patients (P.value <0.001), with a cut off value of 17 ng/ml for predicting disease severity. A positive correlation of PF-4 with the level of serum ferritin, CRP, and D-dimer (p value < 0.001) was noted, while negatively correlated with platelet count and platelet granule count (p value < 0.001). In our study, chronic viral hepatitis patients presented mild COVID-19 signs, and their PF-4 level was comparable with the subgroup of mild COVID-19 infection. The platelet's critical role in COVID-19 coagulopathy and chronic viral hepatitis is evidenced by the ultrastructural changes and the high levels of PF4. Moreover, a dual viral infection poses a substantial burden on the platelets, necessitating close monitoring of the patient's coagulation profile.

Enhanced coagulation cascade activation and styptic effects of Zn@SiO2 nanocomposite

Humans often have bleeding, which exerts substantial selective pressure on the coagulation system to optimize hemostasis in a variety of situations. Uncontrolled hemorrhage due to severe trauma leads to morbidity and mortality. Although nonbiological surfaces such as silicates can activate coagulation factor XII (FXII), the presence of Zn (Zinc) in the material stimulates and activates the various steps in the coagulation cascade. This results in blood clotting. The Zn@SiO2 nanocomposite has an excellent hemostatic property that establishes hemostasis by activating the factors responsible for the formation of a stable clot called fibrin mesh. This can be used as a hemostatic agent during surgeries and in any other trauma condition related to bleeding. Zn@SiO2 was synthesized and characterized with XRD, FTIR and HRTEM. It is analyzed for its RBC (Red Blood Corpuscles) aggregation and Platelet adhesion ability, fibrin formation, thrombus formation and prothrombin time (PT), Activated Partial Thromboplastin Time (aPTT), D-dimer for its ability to activate the coagulation cascade to achieve stable clotting.

Magnetic Platelets as a Platform for Drug Delivery and Cell Trapping

The possibility of using magnetically labeled blood cells as carriers is a novel approach in targeted drug-delivery systems, potentially allowing for improved bloodstream delivery strategies. Blood cells already meet the requirements of biocompatibility, safety from clotting and blockage of small vessels. It would solve the important problem of the patient's immune response to embedded foreign carriers. The high efficiency of platelet loading makes them promising research objects for the development of personalized drug-delivery systems. We are developing a new approach to use platelets decorated with magnetic nanoparticles as a targeted drug-delivery system, with a focus on bloodstream delivery. Platelets are non-nuclear blood cells and are of great importance in the pathogenesis of blood-clotting disorders. In addition, platelets are able to attach to circulating tumor cells. In this article, we studied the effect of platelets labeled with BSA-modified magnetic nanoparticles on healthy and cancer cells. This opens up broad prospects for future research based on the delivery of specific active substances by this method.

Protocol for the Investigation of Plasma and Whole Blood Clot Property of Fibrin Fiber Thickness Using Scanning Electron Microscopy

Blood clot formation represents a key component of the coagulation process for preventing excessive hemorrhage. The structural characteristics of blood clots are associated with their strength and susceptibility to fibrinolysis. Scanning electron microscopy is a technique that allows for state-of-the-art image capture of blood clots, providing visualization of topography, fibrin thickness, fibrin network density, and blood cell involvement and morphology. In this chapter, we provide a detailed protocol for characterization of plasma and whole blood clot structure using SEM, covering the spectrum from blood collection, in vitro clot formation, sample preparation for SEM, imaging, and image analysis, specifically focusing on the measurement of fibrin fiber thickness.

Landmark-based retrieval of inflamed skin vessels enabled by 3D correlative intravital light and volume electron microscopy

The nanometer spatial resolution of electron microscopy imaging remains an advantage over light microscopy, but the restricted field of view that can be inspected and the inability to visualize dynamic cellular events are definitely drawbacks of standard transmission electron microscopy (TEM). Several methods have been developed to overcome these limitations, mainly by correlating the light microscopical image to the electron microscope with correlative light and electron microscopy (CLEM) techniques. Since there is more than one method to obtain the region of interest (ROI), the workflow must be adjusted according to the research question and biological material addressed. Here, we describe in detail the development of a three-dimensional CLEM workflow for mouse skin tissue exposed to an inflammation stimulus and imaged by intravital microscopy (IVM) before fixation. Our aim is to relocate a distinct vessel in the electron microscope, addressing a complex biological question: how do cells interact with each other and the surrounding environment at the ultrastructural level? Retracing the area over several preparation steps did not involve any specific automated instruments but was entirely led by anatomical and artificially introduced landmarks, including blood vessel architecture and carbon-coated grids. Successful retrieval of the ROI by electron microscopy depended on particularly high precision during sample manipulation and extensive documentation. Further modification of the TEM sample preparation protocol for mouse skin tissue even rendered the specimen suitable for serial block-face scanning electron microscopy (SBF-SEM).

Fast, streamlined fluorescence nanoscopy resolves rearrangements of SNARE and cargo proteins in platelets co-incubated with cancer cells

BACKGROUND

Increasing evidence suggests that platelets play a central role in cancer progression, with altered storage and selective release from platelets of specific tumor-promoting proteins as a major mechanism. Fluorescence-based super-resolution microscopy (SRM) can resolve nanoscale spatial distribution patterns of such proteins, and how they are altered in platelets upon different activations. Analysing such alterations by SRM thus represents a promising, minimally invasive strategy for platelet-based diagnosis and monitoring of cancer progression. However, broader applicability beyond specialized research labs will require objective, more automated imaging procedures. Moreover, for statistically significant analyses many SRM platelet images are needed, of several different platelet proteins. Such proteins, showing alterations in their distributions upon cancer progression additionally need to be identified.

RESULTS

A fast, streamlined and objective procedure for SRM platelet image acquisition, analysis and classification was developed to overcome these limitations. By stimulated emission depletion SRM we imaged nanoscale patterns of six different platelet proteins; four different SNAREs (soluble N-ethylmaleimide factor attachment protein receptors) mediating protein secretion by membrane fusion of storage granules, and two angiogenesis regulating proteins, representing cargo proteins within these granules coupled to tumor progression. By a streamlined procedure, we recorded about 100 SRM images of platelets, for each of these six proteins, and for five different categories of platelets; incubated with cancer cells (MCF-7, MDA-MB-231, EFO-21), non-cancer cells (MCF-10A), or no cells at all. From these images, structural similarity and protein cluster parameters were determined, and probability functions of these parameters were generated for the different platelet categories. By comparing these probability functions between the categories, we could identify nanoscale alterations in the protein distributions, allowing us to classify the platelets into their correct categories, if they were co-incubated with cancer cells, non-cancer cells, or no cells at all.

CONCLUSIONS

The fast, streamlined and objective acquisition and analysis procedure established in this work confirms the role of SNAREs and angiogenesis-regulating proteins in platelet-mediated cancer progression, provides additional fundamental knowledge on the interplay between tumor cells and platelets, and represent an important step towards using tumor-platelet interactions and redistribution of nanoscale protein patterns in platelets as a basis for cancer diagnostics.

A high resolution scanning electron microscopy analysis of intracranial thrombi embedded along the stent retrievers

Endovascular treatment with stent retriever thrombectomy is a major advancement in the standard of care in acute ischemic stroke (AIS). The modalities through which thrombi embed along stent retriever following mechanical thrombectomy (MTB) have not yet been elucidated. Using scanning electron microscopy (SEM), we analyzed the appearance of thrombi retrieved by MTB from AIS patients, when embedded into the stent retriever. We observed that the organization and structural compactness vary for compositionally different thrombi. The modalities of attachment onto the stent vary according to thrombus composition and organization.

Blood Cell Analysis: From Traditional Methods to Super-Resolution Microscopy

Blood cell analysis is essential for the diagnosis and identification of hematological malignancies. The use of digital microscopy systems has been extended in clinical laboratories. Super-resolution microscopy (SRM) has attracted wide attention in the medical field due to its nanoscale spatial resolution and high sensitivity. It is considered to be a potential method of blood cell analysis that may have more advantages than traditional approaches such as conventional optical microscopy and hematology analyzers in certain examination projects. In this review, we firstly summarize several common blood cell analysis technologies in the clinic, and analyze the advantages and disadvantages of these technologies. Then, we focus on the basic principles and characteristics of three representative SRM techniques, as well as the latest advances in these techniques for blood cell analysis. Finally, we discuss the developmental trend and possible research directions of SRM, and provide some discussions on further development of technologies for blood cell analysis.

Platelet transmission electron microscopy for the assessment of poor biological response to antiplatelet agent: pilot descriptive and prospective study - ELECTROSTROKE

INTRODUCTION

Ischaemic stroke is the leading cause of adult disability. Thus, a strategy based on an efficient antiplatelet therapy has been developed. The monitoring of antiplatelet therapy is now limited to high risk and poor prognosis patients. Indeed, the biological monitoring of the antiplatelet therapy with available platelet function assays do not provide a global integrative approach. Platelet transmission electron microscopy, recently validated for assessing distinct ultrastructural abnormalities is a reliable morphological platelet structural analysis tool which could be used to collect all the ultrastructural platelet characteristics and assess the degree of activation of platelets.

METHODS AND ANALYSIS

Our pilot prospective and descriptive study will include 50 consecutive patients hospitalized for an ischaemic stroke. We expect to identify ultrastructural characteristics that will be correlated with the degree of platelet activation to guide clinicians in decision making regarding the antiplatelet therapy strategy.

ETHICS AND DISSEMINATION

The French Ethics Committee (comité de protection des personnes d'Ile-de-France VII) approved the information notice that will be given to participants and the protocol of this trial (protocol No 21-031).The results of the trial will be disseminated through scientific publications.

TRIAL REGISTRATION NUMBER

NCT05004233.

Rabbit Endothelial Progenitor Cells Derived From Peripheral Blood and Bone Marrow: An Ultrastructural Comparative Study

The present study was designed to compare the ultrastructure of early endothelial progenitor cells (EPCs) derived from rabbit peripheral blood (PB-EPCs) and bone marrow (BM-EPCs). After the cells had been isolated and cultivated up to passage 3, microphotographs obtained from transmission electron microscope were evaluated from qualitative and quantitative (unbiased stereological approaches) points of view. Our results revealed that both cell populations displayed almost identical ultrastructural characteristics represented by abundant cellular organelles dispersed in the cytoplasm. Moreover, the presence of very occasionally occurring mature endothelial-specific Weibel–Palade bodies (WPBs) confirmed their endothelial lineage origin. The more advanced stage of their differentiation was also demonstrated by the relatively low nucleus/cytoplasm (N/C) ratios (0.41 ± 0.19 in PB-EPCs; 0.37 ± 0.25 in BM-EPCs). Between PB-EPCs and BM-EPCs, no differences in proportions of cells occupied by nucleus (28.13 ± 8.97 versus 25.10 ± 11.48%), mitochondria (3.71 ± 1.33 versus 4.23 ± 1.00%), and lipid droplets (0.65 ± 1.01 versus 0.36 ± 0.40%), as well as in estimations of the organelles surface densities were found. The data provide the first quantitative evaluation of the organelles of interest in PB-EPCs and BM-EPCs, and they can serve as a research framework for understanding cellular function.

A guide to molecular and functional investigations of platelets to bridge basic and clinical sciences

Platelets have been shown to be associated with pathophysiological process beyond thrombosis, demonstrating critical additional roles in homeostatic processes, such as immune regulation, and vascular remodeling. Platelets themselves can have multiple functional states and can communicate and regulate other cells including immune cells and vascular smooth muscle cells, to serve such diverse functions. Although traditional platelet functional assays are informative and reliable, they are limited in their ability to unravel platelet phenotypic heterogeneity and interactions. Developments in methods such as electron microscopy, flow cytometry, mass spectrometry, and 'omics' studies, have led to new insights. In this Review, we focus on advances in platelet biology and function, with an emphasis on current and promising methodologies. We also discuss technical and biological challenges in platelet investigations. Using coronavirus disease 2019 (COVID-19) as an example, we further describe the translational relevance of these approaches and the possible 'bench-to-bedside' utility in patient diagnosis and care.

Erratum: Ultrastructural alterations of megakaryocytes in thrombocytopenia: A review of 43 cases

Thrombocytopenia is a frequent occurrence in a variety of hematopoietic diseases; however, the details of the mechanism leading to low platelet count remain elusive. Megakaryocytes are a series of progenitor cells responsible for the production of platelets. Alterations in megakaryocytes in the bone marrow are a causative factor resulting in thrombocytopenia in varied diseases. Based on ultrastructural analysis of incidentally encountered megakaryocytes in 43 patients with blood diseases marked by low platelet counts, electron micrographs demonstrated that aberrant megakaryocytes predominated in idiopathic thrombocytopenic purpura, aplastic anemia, and myelodysplastic syndrome; autophagy, apoptosis, and cellular damage in megakaryocytes were a prominent feature in aplastic anemia. On the other hand, poorly differentiated megakaryocytes predominated in acute megakaryoblastic leukemia (AMKL) although damaged megakaryocytes were seen in non-AMKL acute leukemia. This paper documents the ultrastructural alterations of megakaryocytes associated with thrombocytopenia and reveals distinctive features for particular blood diseases. A comment is made on future avenues of research emphasizing membrane fusion proteins.

Maternal platelets at the first trimester maternal-placental interface - Small players with great impact on placenta development

In human pregnancy, maternal platelet counts decrease with each trimester, reaching a reduction by approximately ten percent at term in uncomplicated cases and recover to the levels of the non-pregnant state a few weeks postpartum. The time when maternal platelets start to occur in the early human placenta most likely coincides with the appearance of loosely cohesive endovascular trophoblast plugs showing capillary-sized channels by mid first trimester. At that time, platelets accumulate in intercellular gaps of anchoring parts of trophoblast columns and start to adhere to the surface of placental villi and the chorionic plate. This is considered as normal process that contributes to placenta development by acting on both the extravillous- and the villous trophoblast compartment. Release of platelet cargo into intercellular gaps of anchoring cell columns may affect partial epithelial-to-mesenchymal transition and invasiveness of extravillous trophoblasts as well as deposition of fibrinoid in the basal plate. Activation of maternal platelets on the villous surface leads to perivillous fibrin-type fibrinoid deposition, contributing to the shaping of the developing placental villi and the intervillous space. In contrast, excess platelet activation at the villous surface leads to deregulation of the endocrine activity, sterile inflammation and local apoptosis of the syncytiotrophoblast. Platelets and their released cargo are adapted to pregnancy, and may be altered in high-risk pregnancies. Identification of different maternal platelet subpopulations, which show differential procoagulant ability and different response to anti-platelet therapy, are promising new future directions in deciphering the role of maternal platelets in human placenta physiology.

Venous puncture wound hemostasis results in a vaulted thrombus structured by locally nucleated platelet aggregates

Primary hemostasis results in a platelet-rich thrombus that has long been assumed to form a solid plug. Unexpectedly, our 3-dimensional (3D) electron microscopy of mouse jugular vein puncture wounds revealed that the resulting thrombi were structured about localized, nucleated platelet aggregates, pedestals and columns, that produced a vaulted thrombus capped by extravascular platelet adherence. Pedestal and column surfaces were lined by procoagulant platelets. Furthermore, early steps in thrombus assembly were sensitive to P2Y₁₂ inhibition and late steps to thrombin inhibition. Based on these results, we propose a Cap and Build, puncture wound paradigm that should have translational implications for bleeding control and hemostasis.

Rhee, Pokrovskaya et al. utilize 3D electron microscopy of mouse jugular vein puncture wounds to reveal thrombi structured around localized, nucleated platelet aggregates that produced a vaulted thrombus capped by extravascular platelet adherence. As a result, the authors propose a “Cap and Build” paradigm of primary hemostasis.

Intelligent Platelet Morphometry

Technological advances in image-based platelet analysis or platelet morphometry are critical for a better understanding of the structure and function of platelets in biological research as well as for the development of better clinical strategies in medical practice. Recently, the advent of high-throughput optical imaging and deep learning has boosted platelet morphometry to the next level by providing a new set of capabilities beyond what is achievable with traditional platelet morphometry, shedding light on the unexplored domain of platelet analysis. This Opinion article introduces emerging opportunities in 'intelligent' platelet morphometry, which are expected to pave the way for a new class of diagnostics, pharmacometrics, and therapeutics.