Platelet Formation Research Articles

Liquid-Crystallization-Driven Self-Assembly toward Uniform Multi-Morphology Fried-Egg-Like Nanostructures.

Liquid-crystallization-driven self-assembly (LCDSA) has recently emerged as an efficient strategy to create uniform one-dimensional (1-D), 2-D and 3-D nanostructures in a controlled manner. However, the examples of generation of uniform multi-morphology nanostructures from solution self-assembly of one single polymer sample are rare. Herein, we report the first example of preparation of multi-morphology fried-egg-like nanostructures consisting of an inner spherical/bowl-like core of uniform size and platelets protruded from the core by LCDSA of PAMAM-Azo6 (PAMAM = polyamidoamine, Azo = azobenzene) in methanol. It is disclosed that the different aggregation rates for PAMAM-Azo6 with varying contents of Azo units spontaneously separated nucleation and growth stages, which led to the formation of inner spherical/bowl-like cores ("seeds") firstly, followed by the formation of platelets protruded from the edges of inner core to give "imperfect" fried-egg-like nanostructures. Additional annealing of initially formed "imperfect" fried-egg-like micelles will promote the rearrangement of Azo units to give thermodynamically-favored "perfect" fried-egg-shaped micelles with a uniform dimension both in the core and whole structure. This work not only provides an efficient strategy to create uniform multi-morphology fried-egg-shaped nanostructures, but also reveals the essential impact of aggregation kinetics of liquid-crystalline-coil BCPs in the formation of multi-morphology nanostructures.

A modern overview of the process of platelet formation (thrombocytopoiesis) and its dependence on several factors.

Structural and functional alterations in platelets are an actual problem that requires more attention. The treatment of these illnesses proves challenging, inefficient and heavily relies on platelet donations. A difficult task confronting science is producing platelets in vitro, which calls for meticulous examination of factors affecting platelet generation. It is known that megakaryocytes produce platelets in vitro and in vivo differently: in the laboratory we can get a smaller number of platelets compared to the human body. This review primarily examines the stages of megakaryocyte maturation and the processes involved in platelet formation. The article reflects the results of both fundamental research on the problem and the new results obtained over the past decade. Currently, most scientists accept the pro-platelets theory of platelet formation. This review aims to explore in detail each stage of pro-platelet formation and the platelet formation process. It explains on the processes of polyploidization, endomitosis, and apoptosis, as well as the functions of structural cell components (microtubules, mitochondria, T- and α-granules) and pro-platelet migration. The microenvironment influence is acknowledged for the osteoblastic and vascular niches that affect thrombocytopoiesis. The additional aspect is the contribution of specific proteins to thrombocytopoiesis such as RhoA, β1-tubulin, cytokines IL-6, IL-8, Toll-like receptors, etc.

Sparse inference of the human haematopoietic system from heterogeneous and partially observed genomic data

Abstract Haematopoiesis is the process of blood cells’ formation, with progenitor stem cells differentiating into mature forms such as white and red blood cells or platelets. While progenitor cells share regulatory pathways involving common nuclear factors, specific networks shape their fate towards particular lineages. This paper analyses the complex regulatory network that drives the formation of mature red blood cells and platelets from their common precursors. Using the latest reverse transcription quantitative real-time PCR genomic data, we develop a dedicated graphical model that incorporates the effect of external genomic data and allows inference of regulatory networks from the high-dimensional and partially observed data.

Hemin-induced platelet activation is regulated by the ACKR3 chemokine surface receptor and has implications for passivation of vulnerable atherosclerotic plaques.

In vulnerable atherosclerotic plaques, intraplaque hemorrhages (IPH) result in hemolysis of red blood cells and release of hemoglobin and free hemin. Hemin activates platelets and leads to thrombosis. Agonism of the inhibitory platelet receptor ACKR3 inhibits hemin-dependent platelet activation and thrombus formation. To characterize the effect of hemin and ACKR3 agonism on isolated human platelets, multi-color flow cytometry and classical experimental setup such as light transmission aggregometry and a flow chamber assay were used. Hemin induces platelet aggregation and ex vivo platelet-dependent thrombus formation on immobilized collagen under a low shear rate of 500 s-1, indicating that free hemin is a strong activator of platelet-dependent thrombosis. Recently, we described that ACKR3 is a prominent inhibitory receptor of platelet activation. Specific ACKR3 agonists but not conventional antiplatelet compounds such as COX-1 inhibitor (indometacin), ADP-receptor blocker (cangrelor), or PAR1 inhibitor (ML161) inhibit both hemin-dependent aggregation and thrombus formation. To further characterize the effect of hemin on platelet subpopulations, we established a multi-color flow cytometry assay. We found that hemin induces procoagulant (CD42bpos/PAC-1neg/AnnexinVpos), aggregatory (CD42bpos/PAC-1pos/AnnexinVneg), and inflammatory (CD42bpos/CXCR4pos/ACKR3pos/AnnexinVpos) platelet subpopulations. Treatment with ACKR3 agonists significantly decreased the formation of procoagulant and ACKR3pos platelets in response to hemin. We conclude that hemin is a strong activator for the formation of procoagulant platelets and thrombus formation which is dependent on the function of ACKR3. Activation of ACKR3 using specific agonists may offer a therapeutic strategy to regulate the vulnerability of atherosclerotic plaques in areas of IPH.

ACKR3 agonism induces heterodimerization with chemokine receptor CXCR4 and attenuates platelet function.

Platelet receptors ACKR3 and CXCR4 play a crucial role in a variety of cardiovascular diseases. Like most chemokine receptors, CXCR4 is a G protein coupled receptor that induces platelet activation. In contrast, the atypical chemokine receptor 3 (ACKR3) lacks the ability to activate heterotrimeric G proteins and its activation leads to platelet inhibition and attenuates thrombus formation. In nucleated cells, heterodimerization of ACKR3 with CXCR4 regulates CXCL12-dependent signalling. The aim of our study was to investigate the formation of ACKR3/CXCR4 heterodimers in platelets and the subsequent consequences for platelet function. Using a proximity ligation assay (PLA, Duolink®) to screen for CXCR4/ACKR3 heterodimerization inducing compounds, we found that ACKR3 agonism but not conventional platelet agonists or endogen ligands lead to heterodimer formation. To further characterize the formation of ACKR3/CXCR4 heterodimers, we studied the CXCL12-dependent platelet activation via CXCR4. Both, CXCL12-dependent platelet aggregation and collagen-dependent exvivo thrombus formation were significantly downregulated by ACKR3 agonism. Moreover, platelet intracellular calcium and Akt signalling were increased by CXCL12 and again suppressed by ACKR3-specific agonists. Previously, CXCL12 was shown to decrease platelet cAMP levels via CXCR4. Treatment with a specific ACKR3 agonist counteracted this CXCL12/CXCR4-dependent cAMP decrease. Our results reveal that the formation of platelet ACKR3/CXCR4 heterodimers is dependent on ACKR3 rather than CXCR4. Furthermore, ACKR3 agonism induced heterodimerization is associated with mitigating CXCL12/CXCR4-dependent platelet activation possibly by modulating CXCR4-dependent G protein signalling. Our results indicate possible ACKR3 agonist functions and reinforce the potential therapeutic applications of ACKR3 agonists.

Cardiovascular Disease May Be Triggered by Gut Microbiota, Microbial Metabolites, Gut Wall Reactions, and Inflammation

Cardiovascular disease (CVD) may be inherited, as recently shown with the identification of single nucleotide polymorphisms (SNPs or “snips”) on a 250 kb DNA fragment that encodes 92 proteins associated with CVD. CVD is also triggered by microbial dysbiosis, microbial metabolites, metabolic disorders, and inflammatory intestinal epithelial cells (IECs). The epithelial cellular adhesion molecule (Ep-CAM) and trefoil factor 3 (TFF3) peptide keeps the gut wall intact and healthy. Variations in Ep-CAM levels are directly linked to changes in the gut microbiome. Leptin, plasminogen activator inhibitor 1 (PAI1), and alpha-1 acid glycoprotein 1 (AGP1) are associated with obesity and may be used as biomarkers. Although contactin 1 (CNTN1) is also associated with obesity and adiposity, it regulates the bacterial metabolism of tryptophan (Trp) and thus appetite. A decrease in CNTN1 may serve as an early warning of CVD. Short-chain fatty acids (SCFAs) produced by gut microbiota inhibit pro-inflammatory cytokines and damage vascular integrity. Trimethylamine N-oxide (TMAO), produced by gut microbiota, activates inflammatory Nod-like receptors (NLRs) such as Nod-like receptor protein 3 (NLRP3), which increase platelet formation. Mutations in the elastin gene (ELN) cause supra valvular aortic stenosis (SVAS), defined as the thickening of the arterial wall. Many of the genes expressed by human cells are regulated by gut microbiota. The identification of new molecular markers is crucial for the prevention of CVD and the development of new therapeutic strategies. This review summarizes the causes of CVD and identifies possible CVD markers.

Influence of applied tensile/compressive stress on He-irradiated SiC: Examining defect evolution through experimental investigation and DFT simulations

This study investigates the effects of applied tensile and compressive stresses on the evolution of defects in He-irradiated silicon carbide (SiC) materials. By combining experimental studies with density-functional theory (DFT) simulations, we systematically analyzed the microstructural changes and defect formation mechanisms in SiC under stress. The research focused on He irradiation of SiC at 750 °C, with a fluence of 1 × 101⁷ He/cm2. The results revealed that the strain resulting from radiation damage depends on the applied stress during irradiation. Moreover, the formation of platelets is influenced by this applied stress: tensile stress promotes platelet growth, while compressive stress inhibits it. DFT simulations further supported these experimental findings by showing that under tensile strain, both carbon vacancies (Cv) and He atoms exhibit low energy barriers for migration. This phenomenon facilitates platelet growth, aligning well with the observations made in the experiments. However, when considering applications like semiconductor thin film transfer, such as the Smart-cut technique, He implantation under tensile stress can actually be advantageous. This approach enables the use of lower He fluence, which in turn reduces the overall cost of the operation. By strategically leveraging the effects of tensile stress on He implantation, it becomes possible to optimize processes like Smart-cut for more efficient and cost-effective thin film transfer in semiconductor manufacturing.

Paclitaxel improves thrombopoiesis in the absence of thrombopoietin receptor (Mpl)

BackgroundPlatelets are critical for thrombosis and hemostasis. The THPO-MPL pathway is the primary pathway for generating thrombocytes. Dysregulation of thrombopoiesis results in platelet formation and/or function-related disorders, such as thrombocytopenia. Paclitaxel is an extensively utilized chemotherapeutic agent and its activity may be related to platelets, but the effect of paclitaxel on thrombocytopoiesis warrants comprehensive exploration. ObjectivesWe focused on identifying factors that regulate thrombocyte production and elucidating paclitaxel’s regulatory mechanisms on thrombocytopoiesis, with a particular emphasis on discovering mechanisms that bypass THPO-MPL pathways. MethodsWe performed drug screenings using the Tg(mpl:eGFP) zebrafish model in vivo to identify Food and Drug Administration–approved compounds capable of boosting thrombocyte production. An injury experiment was used to evaluate thrombocyte function. Bromodeoxyuridine assays, terminal deoxynucleotidyl transferase dUTP nick-end labeling, and RNA sequencing analyses were performed to explore cytological and molecular mechanisms. Routine blood testing and flow cytometry were used to analyze mouse phenotypes. ResultsWe found that paclitaxel expands thrombocytes by accelerating the proliferation of thrombocytic lineage cells in zebrafish and elevates platelet levels in mice. This effect occurs by bypassing the thrombopoietin receptor (Mpl). We found that paclitaxel promotes thrombopoiesis, potentially involving the JAK2-ERK1/2 MAPK signaling cascade, a pathway integral to MPL and other regulators. Our results further demonstrate that ERK1/2 is at least partially downstream of JAK2 in paclitaxel-induced thrombopoiesis. ConclusionPaclitaxel could promote thrombopoiesis by bypassing Mpl but presumably via the JAK2-ERK1/2 MAPK pathways. It will aid in understanding the relationship between paclitaxel and platelets clinically, and paclitaxel may have potential value for safeguarding platelets and improving thrombocytosis in related diseases.

Exploring defect behavior in helium-irradiated single-crystal and nanocrystalline 3C-SiC at 800°C: A synergy of experimental and simulation techniques

In this study, single crystal (sc) and nanocrystalline (nc) 3C-SiC samples were subjected to 30 keV He ion irradiation across various doses while maintaining a temperature of 800 °C. Employing techniques including Raman spectroscopy, transmission electron microscopy (TEM), and nanoindentation, the alterations in microstructure and hardness resulting from He irradiation with various fluences were examined.In sc-SiC, irradiation prompted the formation of He platelets, resulting in a hardness increase of 7 GPa. In contrast, nc-SiC, characterized by a higher stacking fault density, exhibited the formation of bubbles, primarily at grain boundaries (GBs), with fewer occurrences within the grain interior, leading to a hardness increase of 1 GPa. Notably, in both sc- and nc-SiC, hardness reached saturation and subsequently stabilized or declined with increasing He fluence.Through molecular dynamics (MD) cascade simulations, we discerned that various planar defects do not uniformly contribute to enhancing radiation resistance. For example, intrinsic stacking faults (ISF) and twins in SiC played a substantial role in altering defect density and configurations, thereby facilitating point defect annihilation. Conversely, extrinsic stacking faults (ESF) and Σ3 GBs had a limited impact on defect production during a cascade.Furthermore, calculations of cluster diffusivity revealed an accelerated movement of He-vacancy towards GBs compared to bulk material and other planar defects. Moreover, the scarcity of point defects and constrained mobility of He atoms towards stacking faults in nc-SiC elucidated the marked tendency of He to form platelets in sc-SiC.Additionally, our findings established a correlation between the calculated indentation hardness and the geometry of He defects, consistent with experimental results from nanoindentation. These results significantly contribute to ongoing efforts to design SiC materials with heightened radiation tolerance.

Exchange bias behavior in cobalt ferrite-cobalt oxide CoFe2O4/CoO nanocomposites for data storage applications

In this study cobalt ferrite-cobalt oxide CFO/CoO nanoparticles were synthesized using hydrothermal chemical method for studying the exchange bias (EB) phenomena, a key parameter for data storage applications. The structural analysis was carried out by Scanning electron microscopy (SEM), x-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS), which confirm formation of platelets like CFO/CoO nanoparticles with appropriate chemical composition of different elements with an average crystallite size of 15 nm. Magnetic study revealed the ferromagnetic behaviour of nanoparticles from (5 K–360 K) and blocking temperature has found to be above 360 K, which decreases nonmonotonically with increasing the applied field HFC. The field cool (FC) magnetic hystersis (MH) loop studies have revealed that the samples exhibit very large exchange bias effect. The values of exchange bias (HEB) is found to be maximum at low temperature and decreases with increasing temperature before vanishing at the blocking temperature. The aim of the study is to determine role of cooling field strength for the exchange bias in magnetically contrasted CFO/CoO nanoparticles suitable for data storage applications.

Plasmacytoid dendritic cells control homeostasis of megakaryopoiesis

Platelet homeostasis is essential for vascular integrity and immune defence1,2. Although the process of platelet formation by fragmenting megakaryocytes (MKs; thrombopoiesis) has been extensively studied, the cellular and molecular mechanisms required to constantly replenish the pool of MKs by their progenitor cells (megakaryopoiesis) remains unclear3,4. Here we use intravital imaging to track the cellular dynamics of megakaryopoiesis over days. We identify plasmacytoid dendritic cells (pDCs) as homeostatic sensors that monitor the bone marrow for apoptotic MKs and deliver IFNα to the MK niche triggering local on-demand proliferation and maturation of MK progenitors. This pDC-dependent feedback loop is crucial for MK and platelet homeostasis at steady state and under stress. pDCs are best known for their ability to function as vigilant detectors of viral infection5. We show that virus-induced activation of pDCs interferes with their function as homeostatic sensors of megakaryopoiesis. Consequently, activation of pDCs by SARS-CoV-2 leads to excessive megakaryopoiesis. Together, we identify a pDC-dependent homeostatic circuit that involves innate immune sensing and demand-adapted release of inflammatory mediators to maintain homeostasis of the megakaryocytic lineage.

Epigenetic regulation of megakaryopoiesis and platelet formation.

Platelets, produced by megakaryocytes, play unique roles in physiological processes, such as hemostasis, coagulation, and immune regulation, while also contributing to various clinical diseases. During megakaryocyte differentiation, the morphology and function of cells undergo significant changes due to the programmed expression of a series of genes. Epigenetic changes modify gene expression without altering the DNA base sequence, effectively affecting the inner workings of the cell at different stages of growth, proliferation, differentiation, and apoptosis. These modifications also play important roles in megakaryocyte development and platelet biogenesis. However, the specific mechanisms underlying epigenetic processes and the vast epigenetic regulatory network formed by their interactions remain unclear. In this review, we systematically summarize the key roles played by epigenetics in megakaryocyte development and platelet formation, including DNA methylation, histone modification, and non-coding RNA regulation. We expect our review to provide a deeper understanding of the biological processes underlying megakaryocyte development and platelet formation and to inform the development of new clinical interventions aimed at addressing platelet-related diseases and improving patients' prognoses.

Inducible CXCL12/CXCR4–dependent extramedullary hematopoietic niches in the adrenal gland

AbstractAdult hematopoietic stem and progenitor cells (HSPCs) reside in the bone marrow (BM) hematopoietic niche, which regulates HSPC quiescence, self-renewal, and commitment in a demand-adapted manner. Although the complex BM niche is responsible for adult hematopoiesis, evidence exists for simpler, albeit functional and more accessible, extramedullary hematopoietic niches. Inspired by the anecdotal description of retroperitoneal hematopoietic masses occurring at higher frequency upon hormonal dysregulation within the adrenal gland, we hypothesized that the adult adrenal gland could be induced into a hematopoietic-supportive environment in a systematic manner, thus revealing mechanisms underlying de novo niche formation in the adult. Here, we show that upon splenectomy and hormonal stimulation, the adult adrenal gland of mice can be induced to recruit and host functional HSPCs, capable of serial transplantation, and that this phenomenon is associated with de novo formation of platelet-derived growth factor receptor α/leptin receptor (PDGFRα+/LEPR+/–)–expressing stromal nodules. We further show in CXCL12–green fluorescent protein reporter mice that adrenal glands contain a stromal population reminiscent of the CXCL12-abundant reticular cells, which compose the BM HSPC niche. Mechanistically, HSPC homing to hormonally induced adrenal glands was found dependent on the CXCR4–CXCL12 axis. Mirroring our findings in mice, we found reticular CXCL12+ cells coexpressing master niche regulator FOXC1 in primary samples from human adrenal myelolipomas, a benign tumor composed of adipose and hematopoietic tissue. Our findings reignite long-standing questions regarding hormonal regulation of hematopoiesis and provide a novel model to facilitate the study of adult-specific inducible hematopoietic niches, which may pave the way to therapeutic applications.

Antiplatelet Effects of Flavonoid Aglycones Are Mediated by Activation of Cyclic Nucleotide-Dependent Protein Kinases.

Flavonoid aglycones are secondary plant metabolites that exhibit a broad spectrum of pharmacological activities, including anti-inflammatory, antioxidant, anticancer, and antiplatelet effects. However, the precise molecular mechanisms underlying their inhibitory effect on platelet activation remain poorly understood. In this study, we applied flow cytometry to analyze the effects of six flavonoid aglycones (luteolin, myricetin, quercetin, eriodictyol, kaempferol, and apigenin) on platelet activation, phosphatidylserine externalization, formation of reactive oxygen species, and intracellular esterase activity. We found that these compounds significantly inhibit thrombin-induced platelet activation and decrease formation of reactive oxygen species in activated platelets. The tested aglycones did not affect platelet viability, apoptosis induction, or procoagulant platelet formation. Notably, luteolin, myricetin, quercetin, and apigenin increased thrombin-induced thromboxane synthase activity, which was analyzed by a spectrofluorimetric method. Our results obtained from Western blot analysis and liquid chromatography-tandem mass spectrometry demonstrated that the antiplatelet properties of the studied phytochemicals are mediated by activation of cyclic nucleotide-dependent signaling pathways. Specifically, we established by using Förster resonance energy transfer that the molecular mechanisms are, at least partly, associated with the inhibition of phosphodiesterases 2 and/or 5. These findings underscore the therapeutic potential of flavonoid aglycones for clinical application as antiplatelet agents.

Activating SRC/MAPK signaling via 5-HT1A receptor contributes to the effect of vilazodone on improving thrombocytopenia.

Thrombocytopenia caused by long-term radiotherapy and chemotherapy exists in cancer treatment. Previous research demonstrates that 5-Hydroxtrayptamine (5-HT) and its receptors induce the formation of megakaryocytes (MKs) and platelets. However, the relationships between 5-HT1A receptor (5-HTR1A) and MKs is unclear so far. We screened and investigated the mechanism of vilazodone as a 5-HTR1A partial agonist in promoting MK differentiation and evaluated its therapeutic effect in thrombocytopenia. We employed a drug screening model based on machine learning (ML) to screen the megakaryocytopoiesis activity of Vilazodone (VLZ). The effects of VLZ on megakaryocytopoiesis were verified in HEL and Meg-01 cells. Tg (itga2b: eGFP) zebrafish was performed to analyze the alterations in thrombopoiesis. Moreover, we established a thrombocytopenia mice model to investigate how VLZ administration accelerates platelet recovery and function. We carried out network pharmacology, Western blot, and immunofluorescence to demonstrate the potential targets and pathway of VLZ. VLZ has been predicted to have a potential biological action. Meanwhile, VLZ administration promotes MK differentiation and thrombopoiesis in cells and zebrafish models. Progressive experiments showed that VLZ has a potential therapeutic effect on radiation-induced thrombocytopenia in vivo. The network pharmacology and associated mechanism study indicated that SRC and MAPK signaling are both involved in the processes of megakaryopoiesis facilitated by VLZ. Furthermore, the expression of 5-HTR1A during megakaryocyte differentiation is closely related to the activation of SRC and MAPK. Our findings demonstrated that the expression of 5-HTR1A on MK, VLZ could bind to the 5-HTR1A receptor and further regulate the SRC/MAPK signaling pathway to facilitate megakaryocyte differentiation and platelet production, which provides new insights into the alternative therapeutic options for thrombocytopenia.

Activating SRC/MAPK signaling via 5-HT1A receptor contributes to the effect of vilazodone on improving thrombocytopenia

Thrombocytopenia caused by long-term radiotherapy and chemotherapy exists in cancer treatment. Previous research demonstrates that 5-Hydroxtrayptamine (5-HT) and its receptors induce the formation of megakaryocytes (MKs) and platelets. However, the relationships between 5-HT1A receptor (5-HTR1A) and MKs is unclear so far. We screened and investigated the mechanism of vilazodone as a 5-HTR1A partial agonist in promoting MK differentiation and evaluated its therapeutic effect in thrombocytopenia. We employed a drug screening model based on machine learning (ML) to screen the megakaryocytopoiesis activity of Vilazodone (VLZ). The effects of VLZ on megakaryocytopoiesis were verified in HEL and Meg-01 cells. Tg (itga2b: eGFP) zebrafish was performed to analyze the alterations in thrombopoiesis. Moreover, we established a thrombocytopenia mice model to investigate how VLZ administration accelerates platelet recovery and function. We carried out network pharmacology, Western blot, and immunofluorescence to demonstrate the potential targets and pathway of VLZ. VLZ has been predicted to have a potential biological action. Meanwhile, VLZ administration promotes MK differentiation and thrombopoiesis in cells and zebrafish models. Progressive experiments showed that VLZ has a potential therapeutic effect on radiation-induced thrombocytopenia in vivo. The network pharmacology and associated mechanism study indicated that SRC and MAPK signaling are both involved in the processes of megakaryopoiesis facilitated by VLZ. Furthermore, the expression of 5-HTR1A during megakaryocyte differentiation is closely related to the activation of SRC and MAPK. Our findings demonstrated that the expression of 5-HTR1A on MK, VLZ could bind to the 5-HTR1A receptor and further regulate the SRC/MAPK signaling pathway to facilitate megakaryocyte differentiation and platelet production, which provides new insights into the alternative therapeutic options for thrombocytopenia.

Bioprinting Soft 3D Models of Hematopoiesis using Natural Silk Fibroin-Based Bioink Efficiently Supports Platelet Differentiation.

Hematopoietic stem and progenitor cells (HSPCs) continuously generate platelets throughout one's life. Inherited Platelet Disorders affect ≈ 3 million individuals worldwide and are characterized by defects in platelet formation or function. A critical challenge in the identification of these diseases lies in the absence of models that facilitate the study of hematopoiesis ex vivo. Here, a silk fibroin-based bioink is developed and designed for 3D bioprinting. This bioink replicates a soft and biomimetic environment, enabling the controlled differentiation of HSPCs into platelets. The formulation consisting of silk fibroin, gelatin, and alginate is fine-tuned to obtain a viscoelastic, shear-thinning, thixotropic bioink with the remarkable ability to rapidly recover after bioprinting and provide structural integrity and mechanical stability over long-term culture. Optical transparency allowed for high-resolution imaging of platelet generation, while the incorporation of enzymatic sensors allowed quantitative analysis of glycolytic metabolism during differentiation that is represented through measurable color changes. Bioprinting patient samples revealed a decrease in metabolic activity and platelet production in Inherited Platelet Disorders. These discoveries are instrumental in establishing reference ranges for classification and automating the assessment of treatment responses. This model has far-reaching implications for application in the research of blood-related diseases, prioritizing drug development strategies, and tailoring personalized therapies.

The Therapeutic Action of the Leech Hirudo medicinalis

The article under discussion examines the mechanism of the therapeutic effect of the medicinal leech Hirudo medicinalis. Today, studying the composition of the saliva of medicinal leeches is of the greatest relevance. The secretion of leech saliva contains a whole complex of biologically active substances — it contains more than a hundred medicinal components, enzymes, hormones, vitamins and amino acids, as well as a special substance hirudin, which makes the blood more fluid, which prevents the formation of unnecessary platelets. This is an indispensable way to prevent heart attacks, strokes and thrombosis. The author of the article believes that proof of the medicinal properties of specific components of saliva can lead to the development of new drugs or therapeutic methods.

Influence of Hematocrit Level and Integrin αIIbβIII Function on vWF-Mediated Platelet Adhesion and Shear-Induced Platelet Aggregation in a Sudden Expansion.

Shear-mediated thrombosis is a clinically relevant phenomenon that underlies excessive arterial thrombosis and device-induced thrombosis. Red blood cells are known to mechanically contribute to physiological hemostasis through margination of platelets and vWF, facilitating the unfurling of vWF multimers, and increasing the fraction of thrombus-contacting platelets. Shear also plays a role in this phenomenon, increasing both the degree of margination and the near-wall forces experienced by vWF and platelets leading to unfurling and activation. Despite this, the contribution of red blood cells in shear-induced platelet aggregation has not been fully investigated-specifically the effect of elevated hematocrit has not yet been demonstrated. Here, a microfluidic model of a sudden expansion is presented as a platform for investigating platelet adhesion at hematocrits ranging from 0 to 60% and shear rates ranging from 1000 to 10,000 s-1. The sudden expansion geometry models nonphysiological flow separation characteristic to mechanical circulatory support devices, and the validatory framework of the FDA benchmark nozzle. PDMS microchannels were fabricated and coated with human collagen. Platelets were fluorescently tagged, and blood was reconstituted at variable hematocrit prior to perfusion experiments. Integrin function of selected blood samples was inhibited by a blocking antibody, and platelet adhesion and aggregation over the course of perfusion was monitored. Increasing shear rates at physiological and elevated hematocrit levels facilitate robust platelet adhesion and formation of large aggregates. Shear-induced platelet aggregation is demonstrated to be dependent on both αIIbβIII function and the presence of red blood cells. Inhibition of αIIbβIII results in an 86.4% reduction in overall platelet adhesion and an 85.7% reduction in thrombus size at 20-60% hematocrit. Hematocrit levels of 20% are inadequate for effective platelet margination and subsequent vWF tethering, resulting in notable decreases in platelet adhesion at 5000 and 10,000 s-1 compared to 40% and 60%. Inhibition of αIIbβIII triggered dramatic reductions in overall thrombus coverage and large aggregate formation. Stability of platelets tethered by vWF are demonstrated to be αIIbβIII-dependent, as adhesion of single platelets treated with A2A9, an anti-αIIbβIII blocking antibody, is transient and did not lead to sustained thrombus formation. This study highlights driving factors in vWF-mediated platelet adhesion that are relevant to clinical suppression of shear-induced thrombosis and in vitro assays of platelet adhesion. Primarily, increasing hematocrit promotes platelet margination, permitting shear-induced platelet aggregation through αIIbβIII-mediated adhesion at supraphysiological shear rates. The online version contains supplementary material available at 10.1007/s12195-024-00796-0.

Newly identified roles for PIEZO1 mechanosensor in controlling normal megakaryocyte development and in primary myelofibrosis.

Mechanisms through which mature megakaryocytes (Mks) and their progenitors sense the bone marrow extracellular matrix to promote lineage differentiation in health and disease are still partially understood. We found PIEZO1, a mechanosensitive cation channel, to be expressed in mouse and human Mks. Human mutations in PIEZO1 have been described to be associated with blood cell disorders. Yet, a role for PIEZO1 in megakaryopoiesis and proplatelet formation has never been investigated. Here, we show that activation of PIEZO1 increases the number of immature Mks in mice, while the number of mature Mks and Mk ploidy level are reduced. Piezo1/2 knockout mice show an increase in Mk size and platelet count, both at basal state and upon marrow regeneration. Similarly, in human samples, PIEZO1 is expressed during megakaryopoiesis. Its activation reduces Mk size, ploidy, maturation, and proplatelet extension. Resulting effects of PIEZO1 activation on Mks resemble the profile in Primary Myelofibrosis (PMF). Intriguingly, Mks derived from Jak2V617F PMF mice show significantly elevated PIEZO1 expression, compared to wild-type controls. Accordingly, Mks isolated from bone marrow aspirates of JAK2V617F PMF patients show increased PIEZO1 expression compared to Essential Thrombocythemia. Most importantly, PIEZO1 expression in bone marrow Mks is inversely correlated with patient platelet count. The ploidy, maturation, and proplatelet formation of Mks from JAK2V617F PMF patients are rescued upon PIEZO1 inhibition. Together, our data suggest that PIEZO1 places a brake on Mk maturation and platelet formation in physiology, and its upregulation in PMF Mks might contribute to aggravating some hallmarks of the disease.