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The Journal of Membrane Biology Dec 2022Blood coagulation is an intricate process, and it requires precise control of the activities of pro- and anticoagulant factors and sensitive signaling systems to monitor... (Review)
Review
Blood coagulation is an intricate process, and it requires precise control of the activities of pro- and anticoagulant factors and sensitive signaling systems to monitor and respond to blood vessel insults. These requirements are fulfilled by phosphatidylserine, a relatively miniscule-sized lipid molecule amid the myriad of large coagulation proteins. This review limelight the role of platelet membrane phosphatidylserine (PS) in regulating a key enzymatic reaction of blood coagulation; conversion of factor X to factor Xa by the enzyme factor IXa and its cofactor factor VIIIa. PS is normally located on the inner leaflet of the resting platelet membrane but appears on the outer leaflet surface of the membrane surface after an injury happens. Human platelet activation leads to exposure of buried PS molecules on the surface of the platelet-derived membranes and the exposed PS binds to discrete and specific sites on factors IXa and VIIIa. PS binding to these sites allosterically regulates both factors IXa and VIIIa. The exposure of PS and its binding to factors IXa/VIIIa is a vital step during clotting. Insufficient exposure or a defective binding of PS to these clotting proteins is responsible for various hematologic diseases which are discussed in this review.
Topics: Humans; Factor VIIIa; Factor IXa; Phosphatidylserines; Factor X; Factor Xa; Kinetics; Binding Sites
PubMed: 36098799
DOI: 10.1007/s00232-022-00265-7 -
Proceedings of the National Academy of... Jun 2023Phagocytic clearance of degenerating neurons is triggered by "eat-me" signals exposed on the neuronal surface. The conserved neuronal eat-me signal phosphatidylserine...
Phagocytic clearance of degenerating neurons is triggered by "eat-me" signals exposed on the neuronal surface. The conserved neuronal eat-me signal phosphatidylserine (PS) and the engulfment receptor Draper (Drpr) mediate phagocytosis of degenerating neurons in . However, how PS is recognized by Drpr-expressing phagocytes in vivo remains poorly understood. Using multiple models of dendrite degeneration, we show that the chemokine-like protein Orion can bind to PS and is responsible for detecting PS exposure on neurons; it is supplied cell-non-autonomously to coat PS-exposing dendrites and to mediate interactions between PS and Drpr, thus enabling phagocytosis. As a result, the accumulation of Orion on neurons and on phagocytes produces opposite outcomes by potentiating and suppressing phagocytosis, respectively. Moreover, the Orion dosage is a key determinant of the sensitivity of phagocytes to PS exposed on neurons. Lastly, mutagenesis analyses show that the sequence motifs shared between Orion and human immunomodulatory proteins are important for Orion function. Thus, our results uncover a missing link in PS-mediated phagocytosis in and imply conserved mechanisms of phagocytosis of neurons.
Topics: Animals; Humans; Apoptosis; Chemokines; Drosophila; Drosophila Proteins; Neurons; Phagocytosis; Phosphatidylserines
PubMed: 37276397
DOI: 10.1073/pnas.2303392120 -
The Journal of Experimental Medicine Apr 2022New neurons, continuously added in the adult olfactory bulb (OB) and hippocampus, are involved in information processing in neural circuits. Here, we show that synaptic...
New neurons, continuously added in the adult olfactory bulb (OB) and hippocampus, are involved in information processing in neural circuits. Here, we show that synaptic pruning of adult-born neurons by microglia depends on phosphatidylserine (PS), whose exposure on dendritic spines is inversely correlated with their input activity. To study the role of PS in spine pruning by microglia in vivo, we developed an inducible transgenic mouse line, in which the exposed PS is masked by a dominant-negative form of milk fat globule-EGF-factor 8 (MFG-E8), MFG-E8D89E. In this transgenic mouse, the spine pruning of adult-born neurons by microglia is impaired in the OB and hippocampus. Furthermore, the electrophysiological properties of these adult-born neurons are altered in MFG-E8D89E mice. These data suggest that PS is involved in the microglial spine pruning and the functional maturation of adult-born neurons. The MFG-E8D89E-based genetic approach shown in this study has broad applications for understanding the biology of PS-mediated phagocytosis in vivo.
Topics: Animals; Antigens, Surface; Mice; Mice, Transgenic; Microglia; Neuronal Plasticity; Neurons; Phosphatidylserines
PubMed: 35297954
DOI: 10.1084/jem.20202304 -
International Journal of Molecular... Mar 2022Human red blood cells (RBCs), senescent or damaged due to particular stress, can be removed by programmed suicidal death, a process called eryptosis. There are various... (Review)
Review
Human red blood cells (RBCs), senescent or damaged due to particular stress, can be removed by programmed suicidal death, a process called eryptosis. There are various molecular mechanisms underlying eryptosis. The most frequent is the increase in the cytoplasmic concentration of Ca ions, later exposure of erythrocytes to oxidative stress, hyperosmotic shock, ceramide formation, stimulation of caspases, and energy depletion. Phosphatidylserine (PS) exposed by eryptotic RBCs due to interaction with endothelial CXC-Motiv-Chemokin-16/Scavenger-receptor, causes the RBCs to adhere to vascular wall with consequent damage to the microcirculation. Eryptosis can be triggered by various xenobiotics and endogenous molecules, such as high cholesterol levels. The possible diseases associated with eryptosis are various, including anemia, chronic kidney disease, liver failure, diabetes, hypertension, heart failure, thrombosis, obesity, metabolic syndrome, arthritis, and lupus. This review addresses and collates the existing ex vivo and animal studies on the inhibition of eryptosis by food-derived phytochemicals and natural compounds including phenolic compounds (PC), alkaloids, and other substances that could be a therapeutic and/or co-adjuvant option in eryptotic-driven disorders, especially if they are introduced through the diet.
Topics: Anemia; Animals; Calcium; Eryptosis; Erythrocytes; Humans; Oxidative Stress; Phosphatidylserines; Phytochemicals
PubMed: 35328440
DOI: 10.3390/ijms23063019 -
Biochemical and Biophysical Research... May 2020Proteolytic processing of membrane proteins by A disintegrin and metalloprotease-17 (ADAM17) is a key regulatory step in many physiological and pathophysiological...
Proteolytic processing of membrane proteins by A disintegrin and metalloprotease-17 (ADAM17) is a key regulatory step in many physiological and pathophysiological processes. This so-called shedding is essential for development, regeneration and immune defense. An uncontrolled ADAM17 activity promotes cancer development, chronic inflammation and autoimmune diseases. Consequently, the ADAM17 activity is tightly regulated. As a final trigger for the shedding event a phosphatidylserine (PS) flip to the outer leaflet of the cell membrane was recently described. PS interacts with the extracellular part of ADAM17, which results in the shedding event by shifting the catalytic domain towards the membrane close to the cleavage sites within ADAM17 substrates. Our data indicate that the intrinsic proteolytic activity of the catalytic domain is prerequisite for the shedding activity and constantly present. However, the accessibility for substrate cleavage sites is controlled on several levels. In this report, we demonstrate that the positioning of the catalytic domain towards the cleavage sites is a crucial part of the shedding process. This finding contributes to the understanding of the complex and multilayered regulation of ADAM17 at the cell surface.
Topics: ADAM17 Protein; Amino Acid Sequence; Catalytic Domain; HEK293 Cells; Humans; Mutation; Phosphatidylserines; Proteolysis; Receptors, Interleukin-6
PubMed: 32222277
DOI: 10.1016/j.bbrc.2020.03.093 -
The International Journal of... Sep 2022Membrane phospholipids are critical components of several signaling pathways. Maintained in a variety of asymmetric distributions, their trafficking across the membrane... (Review)
Review
Membrane phospholipids are critical components of several signaling pathways. Maintained in a variety of asymmetric distributions, their trafficking across the membrane can be induced by intra-, extra-, and intercellular events. A familiar example is the externalization of phosphatidylserine from the inner leaflet to the outer leaflet in apoptosis, inducing phagocytosis of the soma. Recently, it has been recognized that phospholipids in the axonal membrane may be a signal for axonal degeneration, regeneration, or other processes. This review focuses on key recent developments and areas for ongoing investigations. KEY FACTS: Phosphatidylserine externalization propagates along an axon after axonal injury and is delayed in the Wallerian degeneration slow (Wld) mutant. The ATP8A2 flippase mutant has spontaneous axonal degeneration. Microdomains of axonal degeneration in spheroid bodies have differential externalization of phosphatidylserine and phosphatidylethanolamine. Phospholipid trafficking could represent a mechanism for coordinated axonal degeneration and elimination, i.e. axoptosis, analogous to apoptosis of the cell body.
Topics: Axons; Humans; Neurons; Phosphatidylserines; Phospholipids; Wallerian Degeneration
PubMed: 35868612
DOI: 10.1016/j.biocel.2022.106264 -
The EMBO Journal Aug 2021Glia contribute to synapse elimination through phagocytosis in the central nervous system. Despite the important roles of this process in development and neurological...
Glia contribute to synapse elimination through phagocytosis in the central nervous system. Despite the important roles of this process in development and neurological disorders, the identity and regulation of the "eat-me" signal that initiates glia-mediated phagocytosis of synapses has remained incompletely understood. Here, we generated conditional knockout mice with neuronal-specific deletion of the flippase chaperone Cdc50a, to induce stable exposure of phosphatidylserine, a well-known "eat-me" signal for apoptotic cells, on the neuronal outer membrane. Surprisingly, acute Cdc50a deletion in mature neurons causes preferential phosphatidylserine exposure in neuronal somas and specific loss of inhibitory post-synapses without effects on other synapses, resulting in abnormal excitability and seizures. Ablation of microglia or the deletion of microglial phagocytic receptor Mertk prevents the loss of inhibitory post-synapses and the seizure phenotype, indicating that microglial phagocytosis is responsible for inhibitory post-synapse elimination. Moreover, we found that phosphatidylserine is used for microglia-mediated pruning of inhibitory post-synapses in normal brains, suggesting that phosphatidylserine serves as a general "eat-me" signal for inhibitory post-synapse elimination.
Topics: Animals; Brain; Membrane Proteins; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Microglia; Phagocytosis; Phosphatidylserines; Seizures; Synapses; c-Mer Tyrosine Kinase; Mice
PubMed: 34013588
DOI: 10.15252/embj.2020107121 -
Theranostics 2020Cancer is a leading cause of mortality and morbidity worldwide. Despite major improvements in current therapeutic methods, ideal therapeutic strategies for improved... (Review)
Review
Cancer is a leading cause of mortality and morbidity worldwide. Despite major improvements in current therapeutic methods, ideal therapeutic strategies for improved tumor elimination are still lacking. Recently, immunotherapy has attracted much attention, and many immune-active agents have been approved for clinical use alone or in combination with other cancer drugs. However, some patients have a poor response to these agents. New agents and strategies are needed to overcome such deficiencies. Phosphatidylserine (PS) is an essential component of bilayer cell membranes and is normally present in the inner leaflet. In the physiological state, PS exposure on the external leaflet not only acts as an engulfment signal for phagocytosis in apoptotic cells but also participates in blood coagulation, myoblast fusion and immune regulation in nonapoptotic cells. In the tumor microenvironment, PS exposure is significantly increased on the surface of tumor cells or tumor cell-derived microvesicles, which have innate immunosuppressive properties and facilitate tumor growth and metastasis. To date, agents targeting PS have been developed, some of which are under investigation in clinical trials as combination drugs for various cancers. However, controversial results are emerging in laboratory research as well as in clinical trials, and the efficiency of PS-targeting agents remains uncertain. In this review, we summarize recent progress in our understanding of the physiological and pathological roles of PS, with a focus on immune suppressive features. In addition, we discuss current drug developments that are based on PS-targeting strategies in both experimental and clinical studies. We hope to provide a future research direction for the development of new agents for cancer therapy.
Topics: Animals; Apoptosis; Cell Membrane; Humans; Immunotherapy; Neoplasms; Phosphatidylserines; Tumor Microenvironment
PubMed: 32802188
DOI: 10.7150/thno.45125 -
Haematologica Oct 2023Heparin-induced thrombocytopenia (HIT) is a severe immune-mediated prothrombotic disorder caused by antibodies (Ab) reactive to complexes of platelet factor 4 and...
Heparin-induced thrombocytopenia (HIT) is a severe immune-mediated prothrombotic disorder caused by antibodies (Ab) reactive to complexes of platelet factor 4 and heparin. Platelets (PLT) and their interaction with different immune cells contribute to prothrombotic conditions in HIT. However, the exact mechanisms and the role of different PLT subpopulations in this prothrombotic environment remain poorly understood. In this study, we observed that HIT patient Ab induce a new PLT population that is characterized by increased P-selectin expression and phosphatidylserine (PS) externalization. Formation of this procoagulant PLT subpopulation was dependent on engagement of PLT Fc-γ-RIIA by HIT Ab and resulted in a significant increase of thrombin generation on the PLT surface. Using an ex vivo thrombosis model and multi-parameter assessment of thrombus formation, we observed that HIT Ab-induced procoagulant PLT propagated formation of large PLT aggregates, leukocyte recruitment and most importantly, fibrin network generation. These prothrombotic conditions were prevented via the upregulation of PLT intracellular cAMP with Iloprost, a clinically approved prostacyclin analogue. Additionally, the functional relevance of P-selectin and PS was dissected. While inhibition of P-selectin did not affect thrombus formation, the specific blockade of PS prevented HIT Ab-mediated thrombin generation and most importantly procoagulant PLT-mediated thrombus formation ex vivo. Taken together, our findings indicate that procoagulant PLT are critical mediators of prothrombotic conditions in HIT. Specific PS targeting could be a promising therapeutic approach to prevent thromboembolic events in HIT patients.
Topics: Humans; Phosphatidylserines; P-Selectin; Thrombin; Thrombocytopenia; Heparin; Thrombosis; Antibodies; Platelet Factor 4
PubMed: 37102605
DOI: 10.3324/haematol.2022.282275 -
Proceedings of the National Academy of... Aug 2023The membrane contact site ER/PM junctions are hubs for signaling pathways, including Ca signaling. Phosphatidylserine (PtdSer) mediates various physiological functions;...
The membrane contact site ER/PM junctions are hubs for signaling pathways, including Ca signaling. Phosphatidylserine (PtdSer) mediates various physiological functions; however, junctional PtdSer composition and the role of PtdSer in Ca signaling and Ca-dependent gene regulation are not understood. Here, we show that STIM1-formed junctions are required for PI(4)P/PtdSer exchange by ORP5 and ORP8, which have reciprocal lipid exchange modes and function as a rheostat that sets the junctional PtdSer/PI(4)P ratio. Targeting the ORP5 and ORP8 and their lipid transfer ORD domains to PM subdomains revealed that ORP5 sets low and ORP8 high junctional PI(4)P/PtdSer ratio that controls STIM1-STIM1 and STIM1-Orai1 interaction and the activity of the SERCA pump to determine the pattern of receptor-evoked Ca oscillations, and consequently translocation of NFAT to the nucleus. Significantly, targeting the ORP5 and ORP8 ORDs to the STIM1 ER subdomain reversed their function. Notably, changing PI(4)P/PtdSer ratio by hydrolysis of PM or ER PtdSer with targeted PtdSer-specific PLA1a1 reproduced the ORPs function. The function of the ORPs is determined both by their differential lipid exchange modes and by privileged localization at the ER/PM subdomains. These findings reveal a role of PtdSer as a signaling lipid that controls the available PM PI(4)P, the unappreciated role of ER PtdSer in cell function, and the diversity of the ER/PM junctions. The effect of PtdSer on the junctional PI(4)P level should have multiple implications in cellular signaling and functions.
Topics: Phosphatidylserines; Signal Transduction; Cell Nucleus; Hydrolysis; Mitochondrial Membranes
PubMed: 37607230
DOI: 10.1073/pnas.2301410120