Phosphatidylserine Exposure Research Articles

Phosphatidylserine-blocking nanoparticles inhibit thrombosis without increased bleeding in mice.

Phosphatidylserine (PS) is a procoagulant phospholipid enriched on surfaces of activated vascular cells including platelets, endothelium, monocytes, and microvesicles. As a molecular driver of thrombosis accessible to drug blockade, PS is an attractive pharmacological target for modulating thrombogenesis, with potentially reduced bleeding risk compared to anticoagulant and antiplatelet therapies. Test antithrombotic capabilities of a liposomal formulation, Zn-dipicolylamine cyanine-3[22,22]/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine POPC(molar ratio 3:97), designated as DPAL, which we previously described binds selectively to PS-enriched cell surfaces, compared with effects on bleeding, in mouse models. PS-dependent DPAL binding to human and murine platelets was tested in vitro. Thrombosis and bleeding after DPAL intravenous administration were tested in C57Bl/6J mice following FeCl3 carotid arterial injury and tail tip amputation, respectively. Incorporation in hemostatic clots was investigated in the cremaster muscle laser injury model. Toxicity was tested by direct exposure to human endothelial cell cultures. DPAL bound agonist-stimulated, PS-positive human and murine platelets, blocked by Annexin V or Ano6 deletion which ablate PS exposure. DPAL prolonged prothrombin time, but did not prevent thrombin-induced fibrinogen receptor activation or aggregation, nor alter blood cell counts including platelets. Following arteriolar laser injury, DPAL bound wound surfaces and edges without destabilizing plugs. DPAL dose-dependently blocked FeCl3-induced arterial thrombosis, but did not substantially increase bleeding, or induce endothelial cell death. DPAL reduces thrombogenesis with minimal effects on bleeding in mouse models via selective binding to PS. DPAL may support novel approaches to modulate pathogenic thrombin generation with improved safety profiles in multiple contexts.

Flow cytometry for RBC damage and complement activation

Abstract Introduction Red blood cells (RBCs) express anionic phospholipids such as phosphatidylserine (PS) in their inner cell membrane layer. As RBCs age, physiochemical changes in their cell membranes, particularly exposure of PS on the outer membrane layer, lead to phagocytosis and clearance from circulation. PS in RBCs induces activation of the complement system, increasing binding of C3 to RBCs. Thus, quantifying PS-expressing (PS+) RBCs and complement deposition on RBCs (C3+) is a potential measure of RBC injury and may improve transfusion quality when used for predicting post-transfusion RBC recovery. Our goal was to develop a flow cytometry assay that quantifies PS+ and C3+RBCs and to assess how this assay correlates with the direct antiglobulin test for C3 (C3-DAT). Methods Using the Cytoflex S flow cytometer, we measured PS+ and C3+ RBCs using anti-annexin-PE (PS+RBC) and biotin-labeled anti-C3 with streptravidin-PE-Cy5 (C3+RBC). RBCs from healthy donors (NL-RBCs) with negative direct antiglobulin tests for C3 (C3-DAT) (n = 4) were analyzed. To assess the sensitivity of the assay and correlation with C3-DATs, complement control cells (CCC; Immucor) were used as a positive control for both PS+RBCs and C3+RBCs and diluted to different concentrations by mixing CCCs with NL-RBCs. Aliquots of diluted RBCs were analyzed blinded for C3-DAT. Differences between means for PS+RBC and C3+RBC were compared using two-sample t-test, and one-way ANOVA and Tukey’s HSD test were used to determine differences in C3+RBCs among a C3-DAT range of reactivities (0+ to 3+) in diluted CCC samples. P values less than 0.05 were statistically significant. Results In healthy, DAT-negative individuals, the mean positivity for PS+RBCs was 0.28% and for C3+RBCs was 0.34%, indicating that healthy individuals have very low percentages of RBCs with PS and C3 on their cell membrane surface. In CCC diluted samples, the mean C3+RBC percentage was 1.4% in negative C3-DAT samples, 5.9% in weak+ C3-DAT samples, 28.1% in 1+ C3-DAT samples, 67.2% in 2+ C3-DAT samples, and 99.0% in 3+ C3-DAT samples. One-way ANOVA revealed a statistically significant difference in C3+RBCs amongst all C3-DAT reactivities in diluted CCC samples (P<0.001), and Tukey’s HSD test found a mean difference in C3+RBCs percentage of 26.7% between 0+ and 1+ samples (P<0.001), 39.2% between 1+ and 2+ samples (P<0.001), and 31.8% between 2+ and 3+ samples (P<0.01). Undiluted CCC samples had a mean PS+RBC percentage of 7.0% and was statistically different from the PS+RBC percentage in NL-RBCs (P<0.01). Conclusion We describe a feasible assay to measure both PS+RBCs and C3+RBCs using flow cytometry in which CCC can be used as a positive control for PS+RBCs. This assay could serve to evaluate the quality of transfused RBC units and provide insights into the role of phosphatidylserine expression and complement deposition for RBC clearance.

Suppressed ORAI1-STIM1-dependent Ca2+ entry by protein kinase C isoforms regulating platelet procoagulant activity

Agonist-induced rises in cytosolic Ca2+ control most platelet responses in thrombosis and hemostasis. In human platelets we earlier demonstrated that the ORAI1-STIM1 pathway is a major component of extracellular Ca2+ entry, in particular when induced via the ITAM-linked collagen receptor, glycoprotein VI (GPVI). In the present paper, using functionally defective platelets from patients with a loss-of-function mutation in ORAI1 or STIM1, we show that Ca2+ entry induced by the endoplasmic reticulum ATPase inhibitor, thapsigargin, fully relies on this pathway. We demonstrate that both the GPVI-induced and thapsigargin-induced Ca2+ entry is strongly suppressed by protein kinase C (PKC) activation, while leaving intracellular Ca2+ mobilization unchanged. Comparing effects of a PKC inhibitory panel pointed to redundant roles of beta and theta PKC isoforms in Ca2+-entry suppression. In contrast, tyrosine kinases positively regulated GPVI-induced Ca2+ entry and mobilization. Label-free and stable isotope phosphoproteome analysis of GPVI-stimulated platelets suggested a regulatory role of bridging integrator-2 (BIN2), known as important mediator of the ORAI1-STIM1 pathway in mouse platelets. Identified were 25-45 regulated phospho- sites in BIN2 and 16-18 in STIM1. Five of these were characterized as direct substrates of the expressed PKC isoforms alpha, beta delta and theta. Functional platelet testing indicated that the downregulation of Ca2+ entry by PKC resulted in suppressed phosphatidylserine exposure and plasmatic thrombin generation. Conclusively, our results indicate that in platelets multiple PKC isoforms constrain the store-regulated Ca2+ entry via ORAI1-BIN2-STIM1, and hence downregulate platelet-dependent coagulation.

Reduced platelet activation in triple-negative essential thrombocythemia compared with JAK2V617F-mutated essential thrombocythemia.

Triple-negative (TN) essential thrombocytopenia (ET) is characterized by the absence of driver mutations while retaining histological and phenotypic characteristics sufficient for an ET diagnosis. Our understanding of TN-ET and its platelet activation remains incomplete. We carried out a large-scale multi-center clinical analysis to analyze the clinical and molecular characteristics, thrombotic complications of TN-ET. We also related the above characteristics to platelet activation to further explore the thrombosis mechanism of TN-ET. A retrospective multicenter study was conducted on 138 TN-ET and 759 ET patients with driver mutations from 1 March 2012 to 1 December 2021. The clinical and molecular characteristics of the TN-ET were summarized. Additionally, platelet activation, apoptosis, and reactive oxygen species (ROS) levels were analyzed in 73 TN-ET patients from this cohort and compared to 41 age- and sex-matched healthy donors. Compared to patients with the JAK2V617F mutation, those with triple-negative mutation were younger (P < 0.001) and exhibited fewer thrombotic events before diagnosis (P < 0.001) and during follow-up (P = 0.039). Patients with triple-negative mutation also presented with significantly reduced CD62P expression in platelets (P = 0.031), slightly reduced calcium concentration in platelets (P = 0.063), increased mitochondrial membrane potential (P = 0.011), reduced phosphatidylserine exposure (P = 0.015), reduced levels of ROS (P = 0.043) and MitoSOX in platelets (P = 0.047). In comparison to JAK2V617F-mutated ET, TN-ET is associated with lower platelet ROS levels, which leads to reduced platelet activation and consequently a lower risk of thrombosis.

Circulating extracellular vesicles as novel biomarkers for pulmonary arterial hypertension in patients with systemic lupus erythematosus.

Pulmonary arterial hypertension (PAH) is a serious complication of systemic lupus erythematosus (SLE) with increased mortality. A prothrombotic state may contribute to pathogenesis of SLE-PAH. Extracellular vesicles (EVs) are known to be associated with thrombosis. Here, we investigated circulating EVs and their associations with SLE-PAH. Eighteen SLE-PAH patients, 36 SLE-non-PAH patients, and 36 healthy controls (HCs) were enrolled. Flow cytometry was used to analyze circulating EVs from leukocytes (LEVs), red blood cells (REVs), platelets (PEVs), endothelial cells (EEVs), and Annexin V+ EVs with membrane phosphatidylserine (PS) exposure. Plasma levels of all EV subgroups were elevated in SLE patients with or without PAH compared to HCs. Furthermore, plasma Annexin V+ EVs, LEVs, PEVs, REVs, EEVs, and Annexin V+ REVs were significantly elevated in SLE-PAH patients compared to SLE-non-PAH patients. Additionally, PAH patients with moderate/high SLE showed a significant increase in LEVs, PEVs, REVs, Annexin V+ EVs, and Annexin V+ REVs compared to SLE-non-PAH patients. However, PAH patients with inactive/mild SLE only exhibited elevations in Annexin V+ EVs, REVs, and Annexin V+ REVs. In the SLE-PAH patients, EEVs were positively correlated with pulmonary arterial systolic pressure, while PEVs and EEVs were positively correlated with right ventricular diameter. Moreover, the receiver operating characteristic curve indicated that Annexin V+ EVs, LEVs, PEVs, REVs, EEVs and Annexin V+ REVs could predict the presence of PAH in SLE patients. Importantly, multivariate logistic regression analysis showed that circulating levels of LEVs or REVs, anti-nRNP antibody, and serositis were independent risk factors for PAH in SLE patients. Findings reveal that specific subgroups of circulating EVs contribute to the hypercoagulation state and the severity of SLE-PAH. Higher plasma levels of LEVs or REVs may serve as biomarkers for SLE-PAH.

NADPH oxidase 1/4 dual inhibitor setanaxib suppresses platelet activation and thrombus formation

AimsThe production of reactive oxygen species (ROS) by NADPH oxidase (NOX) is able to induce platelet activation, making NOX a promising target for antiplatelet therapy. In this study, we examined the effects of setanaxib, a dual NOX1/4 inhibitor, on human platelet function and ROS-related signaling pathways. Materials and methodsIn collagen-stimulated human platelets, aggregometry, assessment of ROS and Ca2+, immunoblotting, ELISA, flow cytometry, platelet adhesion assay, and assessment of mouse arterial thrombosis were performed in this study. Key findingsSetanaxib inhibited both intracellular and extracellular ROS production in collagen-activated platelets. Additionally, setanaxib significantly inhibited collagen-induced platelet aggregation, P-selectin exposure from α-granule release, and ATP release from dense granules. Setanaxib blocked the specific tyrosine phosphorylation-mediated activation of Syk, LAT, Vav1, and Btk within collagen receptor signaling pathways, leading to reduced activation of PLCγ2, PKC, and Ca2+ mobilization. Setanaxib also inhibited collagen-induced activation of integrin αIIbβ3, which is linked to increased cGMP levels and VASP phosphorylation. Furthermore, setanaxib suppressed collagen-induced p38 MAPK activation, resulting in decreased phosphorylation of cytosolic PLA2 and reduced TXA2 generation. Setanaxib also inhibited ERK5 activation, affecting the exposure of procoagulant phosphatidylserine. Setanaxib reduced thrombus formation under shear conditions by preventing platelet adhesion to collagen. Finally, in vivo administration of setanaxib in animal models led to the inhibition of arterial thrombosis. SignificanceThis study is the first to show that setanaxib suppresses ROS generation, platelet activation, and collagen-induced thrombus formation, suggesting its potential use in treating thrombotic or cardiovascular diseases.

The effects of complement-independent, autoantibody-induced apoptosis of platelets in immune thrombocytopenia (ITP).

Autoantibodies that cause platelet apoptosis may play a role in the development of immune thrombocytopenia (ITP), specifically antibodies that target GPIIbIIIa and GPIbα. Our research aims to compare the impact of the antigen specificity of antiplatelet antibodies on normal platelets under conditions that do not rely on complement. Using a modified monoclonal antibody-specific immobilization of platelet antigen (MAIPA) assay, we detected the levels of autoantibodies against specific platelet membrane glycoproteins (GPIIb/IIIa, GPIb/IX) in the plasma of 36 patients diagnosed with chronic ITP. IgG was isolated and purified using a protein A agarose affinity chromatography column, and their concentrations were measured using spectrophotometry. We obtained normal platelets and treated them with the purified IgG anti-GPIIb/IIIa and/or anti-GPIb/IX antibodies, as well as an IgG-free buffer and healthy control IgG. Flow cytometry was used to analyze markers of apoptosis, including phosphatidylserine (PS) exposure, mitochondrial inner membrane potential (ΔΨm), and platelet particle formation. Our results indicate that ITP patients with GPIb/IX-specific autoantibodies can induce platelet apoptosis and platelet particle formation through complement-independent pathways, which are not associated with platelet activation, while GPIIb/IIIa-specific autoantibodies did not have this effect. This suggests that specific autoantibodies may serve as a valuable predictive tool to identify patients who could potentially benefit from complement-inhibiting therapy in the future.

Exposed Phosphatidylserine as a Biomarker for Clear Identification of Breast Cancer Brain Metastases in Mouse Models.

Brain metastasis is the most common intracranial malignancy in adults. The prognosis is extremely poor, partly because most patients have more than one brain lesion, and the currently available therapies are nonspecific or inaccessible to those occult metastases due to an impermeable blood-tumor barrier (BTB). Phosphatidylserine (PS) is externalized on the surface of viable endothelial cells (ECs) in tumor blood vessels. In this study, we have applied a PS-targeting antibody to assess brain metastases in mouse models. Fluorescence microscopic imaging revealed that extensive PS exposure was found exclusively on vascular ECs of brain metastases. The highly sensitive and specific binding of the PS antibody enables individual metastases, even micrometastases containing an intact BTB, to be clearly delineated. Furthermore, the conjugation of the PS antibody with a fluorescence dye, IRDye 800CW, or a radioisotope, 125I, allowed the clear visualization of individual brain metastases by optical imaging and autoradiography, respectively. In conclusion, we demonstrated a novel strategy for targeting brain metastases based on our finding that abundant PS exposure occurs on blood vessels of brain metastases but not on normal brain, which may be useful for the development of imaging and targeted therapeutics for brain metastases.

A novel role for thioredoxin-related transmembrane protein TMX4 in platelet activation and thrombus formation

BackgroundThe functions of critical platelet proteins are controlled by thiol-disulfide exchanges, which are mediated by the protein disulfide isomerase (PDI) family. It has been shown that some PDI family members are important in platelet activation and thrombosis with distinct functions. TMX4, a membrane-type PDI family member, is expressed in platelets, but whether it has a role in platelet activation remains unknown. ObjectivesTo determine the role of TMX4 in platelet activation and thrombosis. MethodsThe phenotypes of TMX4-deficient mice were evaluated in tail bleeding time assay and laser-induced and FeCl3-induced arterial injury models. The functions of TMX4 in platelets were assessed in vitro using TMX4-null platelets, recombinant TMX4 protein, and anti-TMX4 antibody. ResultsCompared with the control mice, Tie2-Cre/TMX4fl/fl mice deficient of hematopoietic and endothelial TMX4 exhibited prolonged tail bleeding times and reduced platelet thrombus formation. Pf4-Cre/TMX4fl/fl mice deficient of platelet TMX4 also had prolonged tail bleeding times and decreased thrombus formation, which was rescued by injection of recombinant TMX4 protein. Consistently, TMX4 deficiency inhibited platelet aggregation, integrin αIIbβ3 activation, P-selectin expression, phosphatidylserine exposure, and thrombin generation, without affecting tyrosine phosphorylation of intracellular signaling molecules Syk, LAT, PLCγ2 and calcium mobilization. Recombinant TMX4 protein enhanced platelet aggregation and reduced integrin αIIbβ3 disulfide bonds, and TMX4 deficiency decreased free thiols of integrin αIIbβ3, consistent with a potent reductase activity of TMX4. In contrast, an inactive TMX4 protein and a specific anti-TMX4 antibody inhibited platelet aggregation. ConclusionTMX4 is a novel PDI family member that enhances platelet activation and thrombosis.

Effect of a thiohydantoin salt derived from l-Arginine on Leishmania amazonensis and infected cells: Insights from biological effects to molecular docking interactions

Leishmaniasis is a neglected tropical disease caused by parasites of the genus Leishmania and is responsible for more than 1 million new cases and 70,000 deaths annually worldwide. Treatment has high costs, toxicity, complex and long administration time, several adverse effects, and drug-resistant strains, therefore new therapies are urgently needed. Synthetic compounds have been highlighted in the medicinal chemistry field as a strong option for drug development against different diseases. Organic salts (OS) have multiple biological activities, including activity against protozoa such as Leishmania spp. This study aimed to investigate the in vitro leishmanicidal activity and death mechanisms of a thiohydantoin salt derived from l-arginine (ThS) against Leishmania amazonensis. We observed that ThS treatment inhibited promastigote proliferation, increased ROS production, phosphatidylserine exposure and plasma membrane permeabilization, loss of mitochondrial membrane potential, lipid body accumulation, autophagic vacuole formation, cell cycle alteration, and morphological and ultrastructural changes, showing parasites death. Additionally, ThS presents low cytotoxicity in murine macrophages (J774A.1), human monocytes (THP-1), and sheep erythrocytes. ThS in vitro cell treatment reduced the percentage of infected macrophages and the number of amastigotes per macrophage by increasing ROS production and reducing TNF-α levels. These results highlight the potential of ThS among thiohydantoins, mainly related to the arginine portion, as a leishmanicidal drug for future drug strategies for leishmaniasis treatment. Notably, in silico investigation of key targets from L. amazonensis, revealed that a ThS compound from the l-arginine amino acid strongly interacts with arginase (ARG) and TNF-α converting enzyme (TACE), suggesting its potential as a Leishmania inhibitor.

Role of Piezo1 in Terminal Density Reversal of Red Blood Cells.

Density reversal of senescent red blood cells has been known for a long time, yet the identity of the candidate ion transporter(s) causing the senescent cells to swell is still elusive. While performing fractionation of RBCs from healthy individuals in Percoll density gradient and characterization of the separated fractions, we identified a subpopulation of cells in low-density fraction (1.02% ± 0.47) showing signs of senescence such as loss of membrane surface area associated with a reduction in band 3 protein abundance, and Phosphatidylserine (PS) exposure to the outer membrane. In addition, we found that these cells are overloaded with Na+ and Ca2+. Using a combination of blockers and activators of ion pumps and channels, we revealed reduced activity of Plasma membrane Ca2+ ATPase and an increase in Ca2+ and Na+ leaks through ion channels in senescent-like cells. Our data revealed that Ca2+ overload in these cells is a result of reduced PMCA activity and facilitated Ca2+ uptake via a hyperactive Piezo1 channel. However, we could not exclude the contribution of other Ca2+-permeable ion channels in this scenario. In addition, we found, as a universal mechanism, that an increase in intracellular Ca2+ reduced the initially high selectivity of Piezo1 channel for Ca2+ and allowed higher Na+ uptake, Na+ accumulation, and swelling.

Carbamylation Is Instrumental in End-Stage Kidney Disease Coagulopathies: The Impact on von Willebrand Factor and Platelet Functionality.

Chronic kidney disease (CKD) is a progressive, irreversible, and incurable condition characterized by high morbidity and mortality, affecting approximately one-tenth of the global population. Rise of urea-derived cyanate levels in CKD patients, severalfold higher in comparison to those found in healthy individuals, leads to an increased rate of carbamylation of lysine residues of proteins and peptides. This posttranslational modification plays an important role in the progression of kidney failure but also in the onset of CKD-related complications, including previously reported coagulopathies. In this study, we have explored the impact of carbamylation on the functionality of von Willebrand factor (vWF), a pivotal player in hemostasis, and its implications for platelet adhesion. We have explored carbamylated vWF's interactions with its partner proteins via ELISA. Mass spectrometry was employed to identify modified lysine residues. Blood platelets isolated from healthy donors were carbamylated, and their activation, binding to endothelium and thromboxane release were evaluated using flow cytometry, adhesion assays and ELISA, respectively. Using mass spectrometry we detected the vWF's lysine residue smost susceptible to carbamylation. This modification has in turn affected vWF's interactions with its key binding partners: decreased binding to collagen types I/III but increased the affinity to factor FVIII, while its binding to fibrinogen remained unchanged. Carbamylation of vWF impeded vWF-blood platelet binding, but carbamylation of platelets led to their increased thrombin-dependent activation as observed by enhanced phosphatidylserine exposure, improved their binding to vascular endothelium, at the same time decreasing the production of the prothrombotic mediator, thromboxane A2. Our findings highlight the multifaceted impact of carbamylation on vWF and platelets, disturbing the delicate balance of coagulation cascade. These alterations could contribute to the complex hemostatic imbalance in ESKD, underscoring the need for further research to fully understand these mechanisms and their clinical implications.

Biomedical application of TiO2NPs can cause arterial thrombotic risks through triggering procoagulant activity, activation and aggregation of platelets.

Titanium dioxide nanoparticles (TiO2NPs) are widely used in medical application. However, the relevant health risk has not been completely assessed, the potential of inducing arterial thrombosis (AT) in particular. Alterations in platelet function and susceptibility to arterial thrombosis induced by TiO2NPs were examined using peripheral blood samples from healthy adult males and an in vivo mouse model, respectively. Here, using human platelets (hPLTs) freshly isolated from health volunteers, we demonstrated TiO2NP treatment triggered the procoagulant activity of hPLTs through phosphatidylserine exposure and microvesicles generation. In addition, TiO2NP treatment increased the levels of glycoprotein IIb/IIIa and P-selectin leading to aggregation and activation of hPLTs, which were exacerbated by providing physiology-mimicking conditions, including introduction of thrombin, collagen, and high shear stress. Interestingly, intracellular calcium levels in hPLTs were increased upon TiO2NP treatment, which were crucial in TiO2NP-induced hPLT procoagulant activity, activation and aggregation. Moreover, using mice in vivo models, we further confirmed that TiO2NP treatment a reduction in mouse platelet (mPLT) counts, disrupted blood flow, and exacerbated carotid arterial thrombosis with enhanced deposition of mPLT. Together, our study provides evidence for an ignored health risk caused by TiO2NPs, specifically TiO2NP treatment augments procoagulant activity, activation and aggregation of PLTs via calcium-dependent mechanism and thus increases the risk of AT.

Immunization of recombinant NS3 protein (protease region) of dengue virus induces high levels of CTLA-4 and apoptosis in splenocytes of BALB/c mice.

DENV infection outcomes depend on the host's variable expression of immune receptors and mediators, leading to either resolution or exacerbation. While the NS3 protein is known to induce robust immune responses, the specific impact of its protease region epitopes remains unclear. This study investigated the effect of recombinant NS3 protease region proteins from all four DENV serotypes on splenocyte activation in BALB/c mice (n = 5/group). Mice were immunized with each protein, and their splenocytes were subsequently stimulated with homologous antigens. We measured the expression of costimulatory molecules (CD28, CD80, CD86, CD152) by flow cytometry, along with IL-2 production, CD25 expression, and examined the antigen-specific activation of CD4 + and CD8 + T cells. Additionally, the expression of IL-1, IL-10, and TGF-β1 in splenocytes from immunized animals was assessed. Apoptosis was evaluated using Annexin V/PI staining and DNA fragmentation analysis. Stimulation of splenocytes from immunized mice triggered apoptosis (phosphatidylserine exposure and caspase 3/7 activation) and increased costimulatory molecule expression, particularly CD152. Low IL-2 production and low CD25 expression, as well as sustained expression of the IL-10 gene. These results suggest that these molecules might be involved in mechanisms by which the NS3 protein contributes to viral persistence and disease pathogenesis.

RNF135 Promotes Human Osteosarcoma Cell Growth and Inhibits Apoptosis by Upregulating the PI3K/AKT Pathway.

Ring finger protein 135 (RNF135) is an E3 ubiquitin ligase that has been implicated in the tumorigenesis of multiple human malignancies. However, whether RNF135 plays a role in the development of human osteosarcoma (OS) remains unknown. RNF135 expression in 20 human OS and 20 human osteochondroma specimens were evaluated by means of immunohistochemistry staining. The effects of shRNA-mediated RNF135 knockdown on human OS cell growth and apoptosis were evaluated through a panel of in vitro studies on cell proliferation, colony formation, exposure of phosphatidylserine on the cell surface, and caspase 3/7 activation. The protein levels of PI3K, AKT, and p-AKT were determined by western blot analysis. We detected significantly higher RNF135 levels in human OS tissues than human osteochondroma tissues. In in vitro studies, shRNA-mediated RNF135 knockdown in human OS cells inhibited proliferation and induced apoptosis. In addition, RNF135 knockdown reduced PI3K and p-AKT protein levels and activated caspase 3 and 7. These results supported that RNF135 contributes to human OS development through PI3K/AKT-dependent mechanisms. Targeting RNF135 may provide a new therapeutic approach for treating this human malignancy.

Neutrophil extracellular traps induce intrahepatic thrombotic tendency and liver damage in cholestatic liver disease.

Cholestatic liver diseases induce local and systemic hypercoagulation, with neutrophil extracellular traps (NETs) serving as major drivers. These NETs have been linked to decreased liver function in patients with obstructive jaundice. However, the impact of NETs on liver hypercoagulation in cholestatic liver disease remains unknown. We utilized bile duct ligation to create experimental mice and analyzed NETs formation in the liver. Fibrin deposition, tissue factor expression, and inflammation in the liver were visualized through western blot and immunohistochemical techniques. LSECs were incubated with isolated NETs, and we detected endothelial procoagulant activity using coagulation protein production assays and measuring endothelial permeability. In both in vivo and in vitro settings, DNase I was applied to clarify the effect of NETs on intrahepatic hypercoagulability, hepatotoxicity, LSEC, and macrophage activation or injury. Bile duct ligation mice exhibited significantly increased levels of NETs in liver tissue, accompanied by neutrophil infiltration, tissue necrosis, fibrin deposition, and thrombophilia compared to sham mice. Notably, NETs resulted in phosphatidylserine and tissue factor exposure on LSEC, enhancing coagulation Factor Xa and thrombin production. The enhanced procoagulant activity could be reversed by degrading NETs with DNase I. Additionally, NETs-induced permeability changes in LSECs, characterized by increased VE-cadherin expression and F-actin retraction, which could be rescued by DNase I. Meanwhile, NET formation is associated with KC activation and the formation of inflammatory factors. NETs promote intrahepatic activation of coagulation and inflammation, leading to liver tissue injury. Strategies targeting NET formation may offer a potential therapeutic approach for treating cholestatic liver disease.

Unexpected bleeding with platelet phosphatidylserine exposure defect: new kindred motivates rethinking Scott syndrome

Unexpected bleeding with platelet phosphatidylserine exposure defect: new kindred motivates rethinking Scott syndrome

Caspase-8 promotes scramblase-mediated phosphatidylserine exposure and fusion of osteoclast precursors

Efficient cellular fusion of mononuclear precursors is the prerequisite for the generation of fully functional multinucleated bone-resorbing osteoclasts. However, the exact molecular factors and mechanisms controlling osteoclast fusion remain incompletely understood. Here we identify RANKL-mediated activation of caspase-8 as early key event during osteoclast fusion. Single cell RNA sequencing-based analyses suggested that activation of parts of the apoptotic machinery accompanied the differentiation of osteoclast precursors into mature multinucleated osteoclasts. A subsequent characterization of osteoclast precursors confirmed that RANKL-mediated activation of caspase-8 promoted the non-apoptotic cleavage and activation of downstream effector caspases that translocated to the plasma membrane where they triggered activation of the phospholipid scramblase Xkr8. Xkr8-mediated exposure of phosphatidylserine, in turn, aided cellular fusion of osteoclast precursors and thereby allowed generation of functional multinucleated osteoclast syncytia and initiation of bone resorption. Pharmacological blockage or genetic deletion of caspase-8 accordingly interfered with fusion of osteoclasts and bone resorption resulting in increased bone mass in mice carrying a conditional deletion of caspase-8 in mononuclear osteoclast precursors. These data identify a novel pathway controlling osteoclast biology and bone turnover with the potential to serve as target for therapeutic intervention during diseases characterized by pathologic osteoclast-mediated bone loss.Proposed model of osteoclast fusion regulated by caspase-8 activation and PS exposure. RANK/RANK-L interaction. Activation of procaspase-8 into caspase-8. Caspase-8 activates caspase-3. Active capase-3 cleaves Xkr8. Local PS exposure is induced. Exposed PS is recognized by the fusion partner. FUSION. PS is re-internalized.

Red cell exchange modulates neutrophil degranulation responses in sickle cell disease.

Neutrophils in sickle cell disease (SCD) are activated, contributing to disease. Red cell exchange (RCE), with the goal of lowering hemoglobin S (HbS), is an important part of therapy for many SCD patients. Whether RCE impacts neutrophil reactivity is unknown. To determine the effect of RCE on neutrophil activation, SCD patients undergoing RCE in steady-state were enrolled. Neutrophil degranulation responses were examined before/after RCE. Kinetic studies were completed to determine the duration of the effect of RCE on neutrophil function. Degranulation results were examined in relation to white blood cell count, neutrophil count, and HbS levels. The effect of RCE on RBC phosphatidylserine (PS) exposure was examined as a possible contributor to modulation of neutrophil function by RCE. Twenty-two patients with SCD, genotype SS, who underwent RCE (average pre-RCE HbS 33 ± 14%) were included for the study. RCE significantly decreased neutrophil degranulation responses. The effect of RCE on neutrophil activation was unrelated to cell count and instead directly correlated with HbS. The effect of RCE on neutrophil activation was sustained over several days post-apheresis. Furthermore, while increased RBC PS exposure results in increased neutrophil degranulation, RCE decreases RBC PS exposure. To our knowledge, this is the first study demonstrating that RCE significantly decreases neutrophil activation in a sustained HbS-dependent manner. Modulation of PS exposure by RCE may be a contributing mechanism by which RCE modulates neutrophil activation. These studies raise the possibility that modulation of neutrophil activation contributes significantly to the therapeutic effect of RCE.

Red Cell Damage During Extracorporeal Life Support.

Sublethal damage to red blood cells (RBCs) during extracorporeal life support (ECLS) may lead to RBC loss. Using flow cytometry, phosphatidylserine-positive (PhS+) RBCs and RBC extracellular vesicles were quantified as measures of sublethal RBC injury in 41 pediatric ECLS runs, stored RBC units, and normal adult subjects. We estimated the clearance half-life of PhS+ RBCs and compared the rates of RBC loss during pediatric ECLS due to phlebotomy, intravascular hemolysis, and extravascular clearance of PhS+ RBCs. Extracorporeal life support patients had 0.9% PhS+ RBCs, sixfold higher than normal subjects (p < 0.0001). Phosphatidylserine-positive RBCs were increased in stored RBC units (twofold in whole blood derived units, p = 0.0013; 12-fold in apheresis RBC units, p < 0.0001). Phosphatidylserine-positive RBCs were cleared with an average half-life of 15 hours. During ECLS, PhS+ RBC clearance accounted for 7% of RBC loss (1-60%), phlebotomy 12%, and intravascular hemolysis 12%. Increasing PhS+ RBCs occurred in 40% of patients that died on ECLS. Red blood cell extracellular vesicles, another marker of red cell injury/activation, were elevated fivefold during ECLS. Phosphatidylserine exposure on RBCs is increased during ECLS, marking these cells for extravascular clearance with a half-life of ~15 hours and accounting for ~7% of RBC loss.