Document text
Principal Investigator: Gary E Gilbert
Organization: VA BOSTON HEALTH CARE SYSTEM
Fiscal Year: 2024
Funding agency: Veterans Affairs
Blood coagulation enzymes function efficiently only on membranes containing phosphatidylserine.
However, phosphatidylserine is not ordinarily available because blood cells sequester it on the interior of
cell membranes. Blood platelets respond to collagen in injured tissue, exposing abundant
phosphatidylserine on bleb-like protrusions of the membrane and these platelets have been called
“procoagulant platelets” and are thought to be essential for prevention of bleeding. However, recent
clinical information from patients with platelet phosphatidylserine-exposing defects indicate that these
patients have only mild-moderate bleeding from mucous membranes. This raises the question as to
whether platelet phosphatidylserine exposure is, indeed, a critical component of blood coagulation.
Preliminary studies from our laboratory have identified several factors that may help to explain
the apparent contradiction. First, blood coagulation complexes recognize convex membrane curvature in
addition to phosphatidylserine content. A membrane with protrusions and invaginations may have
coagulation complexes highly localized to the convex protrusions. Second, platelets and endothelial cells
have modes of limited membrane phosphatidylserine exposure. In these modes, phosphatidylserine
exposure is below the threshold of detection for most phosphatidylserine assays. Thus, low level
phosphatidylserine exposure is present and can support coagulation complexes, yet goes undetected.
Third, phosphatidylserine-rich membranes also support anticoagulant proteins to a degree that can
suppress or eliminate the procoagulant potential. The net anticoagulant effect, like procoagulant support,
is dependent on both phosphatidylserine content and on membrane curvature. These insights, and the
methods used to gain them, give us the unique opportunity to study the manner in which platelet and
endothelial cell phosphatidylserine exposure localizes procoagulant enzyme activity.
We have hypothesized that blood anticoagulants ordinarily suppress the procoagulant potential of
stimulated platelets with phosphatidylserine-rich blebs. The platelets gain true procoagulant activity in
environments where anticoagulants are attenuated or bypassed by proteins in the micro-environment.
This proposal will focus on gaining insight into the anticoagulant proteins that ordinarily suppress blood
coagulation reactions on procoagulant complexes, particularly in regard to phosphatidylserine exposure
and membrane curvature. We will next probe the extent to which the anticoagulants effect is attenuated
or bypassed by the effects of plasmin in the context of mucous membranes. In addition, we will study the
manner in which conditioned endothelial support limited blood coagulation reactions on focal, highly
complex membrane projections. We will also evaluate the extent to which the endothelial procoagulant
activity may be amplified by adherent platelets and whether the endothelial generated factor Xa bypasses
anticoagulant activity on platelet blebs.
The platelet studies will provide insights relevant to treating surgical and traumatic bleeding,
relevant to hemostasis for hemophilia patients. The endothelial studies are relevant to the coagulopathy
known as disseminated intravascular coagulation and relevant to the vascular injury and inflammation of
COVID-19.
Terms: <AC Globulin><Activated Blood Coagulation Factor VII><Activated Blood Coagulation Factor X><Activated Blood Coagulation Factor XI><Activated Factor VII><Activated Factor X><Activated Factor XI><Anticoagulant Agents><Anticoagulant Drugs><Anticoagulants><Anticoagulation><Assay><Attenuated><Autoprothrombin C><Binding><Bioassay><Biological Assay><Biophysics><Bleb><Bleeding><Blister><Blood><Blood Cells><Blood Clotting><Blood Coagulation Disorders><Blood Coagulation Factor III><Blood Coagulation Factor V><Blood Plasma><Blood Platelets><Blood Reticuloendothelial System><Blood Vessels><Blood coagulation><Body Tissues><Bulla><Bullous Lesion><Bypass><CD142 Antigens><COVID-19><CV-19><Cell Body><Cell membrane><Cells><Cellular biology><Childbirth><Clinical><Clotting><Coagulation><Coagulation Disorder><Coagulation Factor III><Coagulation Factor V><Coagulation Factor VIIa><Coagulation Factor XIa><Coagulation Factor Xa><Coagulation Process><Coagulin><Coagulopathy><Cofactor Protein S><Collagen><Complex><Confocal Microscopy><Consumption Coagulopathy><Contact Activation Product><Coronavirus Infectious Disease 2019><Cytoplasmic Membrane><Defect><Detection><Disseminated Intravascular Coagulation><Endothelial Cells><Endothelium><Engineering><Environment><Enzyme Gene><Enzymes><Esteroproteases><Evaluation><Factor III><Factor Pi><Factor V><Factor VIII Deficiency><Factor VIIa><Factor XIa><Factor Xa><Fibrinolysin><Filopodia><Flow Cytofluorometries><Flow Cytofluorometry><Flow Cytometry><Flow Microfluorimetry><Flow Microfluorometry><Gene Modified><Glomerular Procoagulant Activity><Glu-Plasmin><Hemophilia><Hemophilia A><Hemorrhage><Hemostasis><Hemostatic Agents><Hemostatic function><Hemostatics><Human><Impairment><In Vitro><Individual><Inflammation><Knowledge><Laboratories><Location><Marrow platelet><Measures><Mediating><Membrane><Methodology><Methods><Mice><Mice Mammals><Microfluidics><Modeling><Modern Man><Molecular Interaction><Mucosa><Mucosal Tissue><Mucous Membrane><Multienzyme Complexes><Murine><Mus><Operative Procedures><Operative Surgical Procedures><Pathology><Pathway interactions><Patients><Peptidases><Peptide Hydrolases><Peripheral Blood Cell><Phosphatides><Phosphatidylserines><Phospholipids><Plasma><Plasma Membrane><Plasma Serum><Plasmin><Platelets><Pore Proteins><Prevention><Proaccelerin><Protease F><Protease Gene><Proteases><Protein S><Proteinases><Proteins><Proteolytic Enzymes><Prothrombinase><Reaction><Regulation><Regulatory Protein><Reticuloendothelial System, Serum, Plasma><Scott syndrome><Serine Phosphoglycerides><Spatial Distribution><Stress><Surgical><Surgical Hemostasis><Surgical Interventions><Surgical Procedure><TFPI><Tail><Testing><Therapeutic><Thrombase><Thrombin><Thrombocytes><Thrombokinase><Thromboplastin><Time><Tissue Factor><Tissue Factor Procoagulant><Tissue Thromboplastin><Tissues><Trauma><Umbilical vein><Urothromboplastin><Vesication><Vesicle><Visualization><Vitamin K-Dependent Protein S><Work><activated Protein C><attenuate><attenuates><attenuation><biophysical foundation><biophysical principles><biophysical sciences><bleeding disorder><blood loss><blood thinner><cell biology><child birth><clotting disorder><cofactor><coronavirus disease 2019><coronavirus disease-19><coronavirus infectious disease-19><enzyme activity><enzyme complex><experience><fibrinogenase><flow cytophotometry><gene modification><genetic regulatory protein><genetically modified><inhibitor><injured><injury to the vasculature><innovate><innovation><innovative><insight><labile component><labile factor><membrane structure><novel><pathway><plasmalemma><prothrombase><regulatory gene product><response><surgery><thrombopoiesis inhibitor><tissue factor pathway inhibitor><vascular><vascular inflammation><vascular injury><µfluidic>