Biology subjects

Bdeir, K.

Publications and source records attributed to Bdeir, K..

2 recordsLinked to original sources

bioRxiv2025

Antiphospholipid syndrome (APS) is a platelet factor 4 (PF4)-centric immunothrombotic disorder

Antiphospholipid syndrome (APS) is an immunothrombotic disorder, frequently attributed to autoantibodies that bind {beta}2-glycoprotein I ({beta}2GPI). A study showed that the platelet-specific chemokine, platelet factor 4 (PF4), binds to {beta}2GPI, enhancing recognition of {beta}2GPI by APS antibodies. APS antibodies induce the release of neutrophil extracellular traps (NETs), webs of decondensed chromatin that bind both PF4 and {beta}2GPI. We propose that PF4 bridges {beta}2GPI to NETs (and other PF4-targeted polyanions), leading to the formation of prothrombotic PF4:{beta}2GPI:NET immunotargets in APS. Dynamic light-scattering studies of isolated IgGs from four patients with triple-positive APS show formation of PF4:{beta}2GPI:NET complexes that bind APS antibodies. NETs released in a microfluidic system bound {beta}2GPI, but only in the presence of PF4, forming a multimolecular APS antigenic target. Whole blood infused through a photochemically-injured, endothelium-lined microfluidic channel formed platelet-, fibrin-, and complement-rich thrombi that bound APS antibody only in the presence of PF4. Thrombi were reduced in size if either ADAMTS13 or DNase1 was infused. In a murine APS model, wildtype and transgenic mice expressing platelet human PF4 {+/-} Fc{gamma}RIIA developed more intense neutrophil rolling along veins, and more extensive thrombus formation following laser injury to cremaster arterioles and venules, whereas mice lacking PF4 did not. Three antigenically distinct anti-hPF4 monoclonal antibodies blocked thrombosis in vitro, and neutrophil rolling and thrombosis in vivo. Our studies provide new insights into the basis of APS that has mechanistic parallels to other known PF4 immunothrombotic disorders and offer potential diagnostic and non-anticoagulant therapeutic strategies for clinical management. Key pointsO_LIPF4 enhances {beta}2GPI binding to NETs and these complexes are central to APS immunothrombosis. C_LIO_LIAnti-PF4 monoclonal antibodies block APS immunothrombosis in microfluidic and murine studies. C_LI

cell biology↗

bioRxiv2023

Packaging of supplemented urokinase into naked alpha-granules of in vitro-grown megakaryocytes for targeted therapeutic delivery

Our prior finding that uPA endogenously expressed and stored in the platelets of transgenic mice prevented thrombus formation without causing bleeding, prompted us to develop a potentially clinically relevant means of generating anti-thrombotic human platelets in vitro from CD34+ hematopoietic cell-derived megakaryocytes. CD34+-megakaryocytes internalize and store in -granules single-chain uPA (scuPA) and a uPA variant modified to be plasmin-resistant, but thrombin-activatable, (uPAT). Both uPAs co-localized with internalized factor V (FV), fibrinogen and plasminogen, low-density lipoprotein receptor-related protein 1 (LRP1), and interferon-induced transmembrane protein 3 (IFITM3), but not with endogenous von Willebrand factor (VWF). Endocytosis of uPA by CD34+-\megakaryocytes was mediated in part via LRP1 and IIb{beta}3. scuPA-containing megakaryocytes degraded endocytosed intragranular FV, but not endogenous VWF, in the presence of internalized plasminogen, whereas uPAT-megakaryocytes did not significantly degrade either protein. We used a carotid-artery injury model in NOD-scid IL2r{gamma}null (NSG) mice homozygous for VWFR1326H (a mutation switching binding VWF specificity from mouse to human glycoprotein IbmlIX) to test whether platelets derived from scuPA-MKs or uPAT-Mks would prevent thrombus formation. NSG/VWFR1326H mice exhibited a lower thrombotic burden after carotid artery injury compared to NSG mice unless infused with human platelets or MKs, whereas intravenous injection of either uPA-containing megakaryocytes into NSG/VWFR1326H generated sufficient uPA-containing human platelets to lyse nascent thrombi. These studies suggest the potential to deliver uPA or potentially other ectopic proteins within platelet -granules from in vitro-generated megakaryocytes. Key pointsO_LIUnlike platelets, in vitro-grown megakaryocytes can store exogenous uPA in its -granules. C_LIO_LIuPA uptake involves LRP1 and IIb{beta}3 receptors and is functionally available from activated platelets. C_LI

cell biology↗