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A modified clot-based assay to measure negatively charged procoagulant phospholipids.

ABSTRACT: Growing evidence supports a role for extracellular vesicles (EVs) in haemostasis and thrombosis due to exposure of negatively charged procoagulant phospholipids (PPL). Current commercial PPL-dependent clotting assays use chemically phospholipid depleted plasma to measure PPL activity. The purpose of our study was to modify the PPL assay by substituting the chemically phospholipid depleted plasma with PPL depleted plasma obtained by ultracentrifugation This in order to get readily access to a sensitive and reliable assay to measure PPL activity in human plasma and cell supernatants. The performance of the assay was tested, including the influence of individual coagulation factors and postprandial lipoproteins and compared to a commercial PPL assay (STA-Procoag-PPL). The two PPL assays displayed similar sensitivity to exogenously added standardized phospholipids. The PPL activity measured by the modified assay strongly correlates with the results from the commercial assay. The intraday- and between-days coefficients of variation ranged from 2-4% depending on the PPL activity in the sample. The modified PPL assay was insensitive to postprandial lipoprotein levels in plasma, as well as to tissue factor (TF) positive EVs from stimulated whole blood. Our findings showed that the modified assay performed equal to the comparator, and was insensitive to postprandial lipoproteins and TF⁺ EVs.

SUBMITTER: Ramberg C

PROVIDER: S-EPMC8085201 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Macrophage reprogramming by negatively-charged membrane phospholipids controls infection

Project description:Extracellular vesicles (ECV) are heterogeneous membrane-enclosed structures containing proteins, nucleic acids and lipids that participate in intercellular communication by transferring their content to recipient cells. Although most of the attention has been directed at the biological effect of proteins and microRNA, the contribution of phospholipids present in ECV on cellular activation has not been extensively addressed. Here we investigated the biological effect of phosphatidylserine (PS) and phosphatidylcholine (PC), two phospholipids highly abundant in ECV. A transcriptomic analysis revealed that about 4,700 genes were specifically modified by exposing peritoneal macrophages to PS or PC liposomes in vivo. Among them, the expression of several chemokines and cytokines was highly upregulated by PS liposome treatment, translating into a massive neutrophil infiltration into the peritoneum capable of neutralizing a septic polymicrobial insult. Both the L and D stereoisomers of PS induced the same response, suggesting that the effect was related to the negative charge of the phospholipid head. We concluded that an increase in the internal negative charge of the cell triggers a signaling cascade activating an innate immune response capable of controlling infection.

2018-11-02 | GSE115489 | GEO

Macrophage reprogramming by negatively charged membrane phospholipids controls infection.

Project description:Extracellular vesicles (ECVs) are heterogeneous membrane-enclosed structures containing proteins, nucleic acids, and lipids that participate in intercellular communication by transferring their contents to recipient cells. Although most of the attention has been directed at the biologic effect of proteins and microRNA, the contribution of phospholipids present in ECVs on cellular activation has not been extensively addressed. We investigated the biologic effect of phosphatidylserine (PS) and phosphatidylcholine (PC), 2 phospholipids highly abundant in ECVs. A transcriptomic analysis revealed that ∼4700 genes were specifically modified by exposing peritoneal macrophages to PS or PC liposomes in vivo. Among them, the expression of several chemokines and cytokines was highly upregulated by PS liposome treatment, translating into a massive neutrophil infiltration of the peritoneum capable of neutralizing a septic polymicrobial insult. Both the l and d stereoisomers of PS induced the same response, suggesting that the effect was related to the negative charge of the phospholipid head. We concluded that an increase in the internal negative charge of the cell triggers a signaling cascade activating an innate immune response capable of controlling infection.-Cauvi, D. M., Hawisher, D., Dores-Silva, P. R., Lizardo, R. E., De Maio, A. Macrophage reprogramming by negatively charged membrane phospholipids controls infection.

| S-EPMC6338646 | biostudies-literature

Modulation of toxin stability by 4-phenylbutyric acid and negatively charged phospholipids.

Project description:AB toxins such as ricin and cholera toxin (CT) consist of an enzymatic A domain and a receptor-binding B domain. After endocytosis of the surface-bound toxin, both ricin and CT are transported by vesicle carriers to the endoplasmic reticulum (ER). The A subunit then dissociates from its holotoxin, unfolds, and crosses the ER membrane to reach its cytosolic target. Since protein unfolding at physiological temperature and neutral pH allows the dissociated A chain to attain a translocation-competent state for export to the cytosol, the underlying regulatory mechanisms of toxin unfolding are of paramount biological interest. Here we report a biophysical analysis of the effects of anionic phospholipid membranes and two chemical chaperones, 4-phenylbutyric acid (PBA) and glycerol, on the thermal stabilities and the toxic potencies of ricin toxin A chain (RTA) and CT A1 chain (CTA1). Phospholipid vesicles that mimic the ER membrane dramatically decreased the thermal stability of RTA but not CTA1. PBA and glycerol both inhibited the thermal disordering of RTA, but only glycerol could reverse the destabilizing effect of anionic phospholipids. In contrast, PBA was able to increase the thermal stability of CTA1 in the presence of anionic phospholipids. PBA inhibits cellular intoxication by CT but not ricin, which is explained by its ability to stabilize CTA1 and its inability to reverse the destabilizing effect of membranes on RTA. Our data highlight the toxin-specific intracellular events underlying ER-to-cytosol translocation of the toxin A chain and identify a potential means to supplement the long-term stabilization of toxin vaccines.

| S-EPMC3161752 | biostudies-literature

Macrophage reprogramming by negatively-charged membrane phospholipids controls infection

Project description:Macrophage reprogramming by negatively-charged membrane phospholipids controls infection

| PRJNA475156 | ENA

Regulation of DGK? Activity and Substrate Acyl Chain Specificity by Negatively Charged Phospholipids.

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| S-EPMC7036746 | biostudies-literature

Segregation of negatively charged phospholipids by the polycationic and farnesylated membrane anchor of Kras.

Project description:The Kras protein, a member of the Ras family of bio-switches that are frequently mutated in cancer and developmental disorders, becomes functional when anchored to the inner surface of the plasma membrane. It is well known that membrane attachment involves the farnesylated and poylcationic C-terminus of the protein. However, little is known about the structure of the complex and the specific protein-lipid interactions that are responsible for the binding. On the basis of data from extensive (>0.55 ?s) molecular dynamics simulations of multiple Kras anchors in bilayers of POPC/POPG lipids (4:1 ratio), we show that, as expected, Kras is tethered to the bilayer surface by specific lysine-POPG salt bridges and by nonspecific farnesyl-phospholipid van der Waals interactions. Unexpectedly, however, only the C-terminal five of the eight Kras Lys side chains were found to directly interact with the bilayer, with the N-terminal ones staying in water. Furthermore, the positively charged Kras anchors pull the negatively charged POPG lipids together, leading to the clustering of the POPG lipids around the proteins. This selective Kras-POPG interaction is directly related to the specific geometry of the backbone, which exists in two major conformational states: 1), a stable native-like ensemble of structures characterized by an extended geometry with a pseudohelical turn; and 2), less stable nonnative ensembles of conformers characterized by severely bent geometries. Finally, although the interface-bound anchor has little effect on the overall structure of the bilayer, it induces local thinning within a persistence length of ?12 Å. Our results thus go beyond documenting how Kras attaches to a mixed bilayer of charged and neutral lipids; they highlight a fascinating process of protein-induced lipid sorting coupled with the (re)shaping of a surface-bound protein by the host lipids.

| S-EPMC2998625 | biostudies-literature

SARS-CoV-2 Protein S Fusion Peptide Is Capable of Wrapping Negatively-Charged Phospholipids.

Project description:COVID-19, caused by SARS-CoV-2, which is a positive-sense, single-stranded RNA enveloped virus, emerged in late 2019 and was declared a worldwide pandemic in early 2020 causing more than 600 million infections so far and more than 6 million deaths in the world. Although new vaccines have been implemented, the pandemic continues to impact world health dramatically. Membrane fusion, critical for the viral entry into the host cell, is one of the main targets for the development of novel antiviral therapies to combat COVID-19. The S2 subunit of the viral S protein, a class I membrane fusion protein, contains the fusion domain which is directly implicated in the fusion mechanism. The knowledge of the membrane fusion mechanism at the molecular level will undoubtedly result in the development of effective antiviral strategies. We have used all-atom molecular dynamics to analyse the binding of the SARS-CoV-2 fusion peptide to specific phospholipids in model membranes composed of only one phospholipid plus cholesterol in the presence of either Na+ or Ca2+. Our results show that the fusion peptide is capable of binding to the membrane, that its secondary structure does not change significantly upon binding, that it tends to preferentially bind electronegatively charged phospholipids, and that it does not bind cholesterol at all. Understanding the intricacies of the membrane fusion mechanism and the molecular interactions involved will lead us to the development of antiviral molecules that will allow a more efficient battle against these viruses.

| S-EPMC10057416 | biostudies-literature

Performance Evaluation and Clinical Associations of Immunoassays That Detect Antibodies to Negatively Charged Phospholipids Other Than Cardiolipin.

Project description:Objectives:We evaluate the performance characteristics of antiphosphatidylserine (anti-PS), antiphosphatidylinositol (anti-PI), and antiphospholipid mixture (APhL) enzyme-linked immunosorbent assays (ELISAs) compared with anticardiolipin (aCL) and anti-?2 glycoprotein I (anti-?2GPI) in a large group of patients with antiphospholipid (aPL)-related diseases. Methods:Serum samples from 548 patients from the Hopkins and Jamaican systemic lupus erythematosus cohorts, the PROMISSE cohort, and the Antiphospholipid Standardization Laboratory were examined for immunoglobulin G (IgG)/immunoglobulin M (IgM) positivity in aCL, anti-?2GPI, anti-PS, anti-PI, and APhL ELISA assays. Results:All IgG assays were associated with one or more thrombotic and/or obstetric manifestations, with an increased risk associated with higher antibody titers. Analytical performance was similar among assays, but IgG assays performed better than IgM counterparts. Conclusions:Increasing titers of APhL, anti-PS, and anti-PI antibodies could indicate an increased risk of thrombotic and/or obstetric aPL-related manifestations. These assays may be promising biomarkers for particular APS manifestations.

| S-EPMC5889035 | biostudies-literature

Bid binding to negatively charged phospholipids may not be required for its pro-apoptotic activity in vivo.

Project description:Bid is a ubiquitous pro-apoptotic member of the Bcl-2 family that has been involved in a variety of pathways of cell death. Unique among pro-apoptotic proteins, Bid is activated after cleavage by the apical caspases of the extrinsic pathway; subsequently it moves to mitochondria, where it promotes the release of apoptogenic proteins in concert with other Bcl-2 family proteins like Bak. Diverse factors appear to modulate the pro-apoptotic action of Bid, from its avid binding to mitochondrial lipids (in particular, cardiolipin) to multiple phosphorylations at sites that can modulate its caspase cleavage. This work addresses the question of how the lipid interactions of Bid that are evident in vitro actually impact on its pro-apoptotic action within cells. Using site-directed mutagenesis, we identified mutations that reduced mouse Bid lipid binding in vitro. Mutation of the conserved residue Lys157 specifically decreased the binding to negatively charged lipids related to cardiolipin and additionally affected the rate of caspase cleavage. However, this lipid-binding mutant had no discernable effect on Bid pro-apoptotic function in vivo. The results are interpreted in relation to an underlying interaction of Bid with lysophosphatidylcholine, which is not disrupted in any mutant retaining pro-apoptotic function both in vitro and in vivo.

| S-EPMC2822702 | biostudies-literature

Dasatinib Inhibits Procoagulant and Clot Retracting Activities of Human Platelets.

Project description:Tyrosine kinase inhibitors (TKI) such as the BCR-ABL inhibitor dasatinib and nilotinib are highly effective therapies for chronic myeloid leukemia (CML). However, several lines of evidence suggest that dasatinib can induce bleeding which may be due to impaired collagen-induced platelet adhesion, aggregation, and secretion. Sarcoma family kinases (SFK) play central role in the GPVI-induced signaling pathway. We aimed to investigate whether and how dasatinib can modulate SFK-mediated platelet procoagulant activity in a purified system and in dasatinib/nilotinib treated CML patients. In platelet rich plasmas of healthy volunteers, dasatinib dose-dependently reduced convulxin-induced phosphatidylserine exposure and attenuated thrombin formation. Similarly to these changes, integrin activation and clot retraction were also significantly inhibited by 100 nM dasatinib. Platelets isolated from dasatinib treated patients showed a significantly lower phosphatidylserine expression upon convulxin activation compared to premedication levels. In these samples, thrombin generation was significantly slower, and the quantity of formed thrombin was less compared to the trough sample. Western blot analyses showed decreased phosphorylation levels of the C-terminal tail and the activation loop of SFKs upon dasatinib administration. Taken together, these results suggest that dasatinib inhibits the formation of procoagulant platelets via the GPVI receptor by inhibiting phosphorylation of SFKs.

| S-EPMC6862041 | biostudies-literature

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