Biology subjects

Ahn, H. S.

Publications and source records attributed to Ahn, H. S..

3 recordsLinked to original sources

bioRxiv2024

Platelet integrin αIIbβ3 plays a key role in venous thrombogenesis in a mouse model

AbstractVenous thrombosis (VT) is a common vascular disease associated with reduced survival and a high recurrence rate. Previous studies have shown that the accumulation of platelets and neutrophils at sites of endothelial cell activation is a primary event in VT, but a role for platelet IIb{beta}3 in the initiation of venous thrombosis has not been established. This task has been complicated by the increased bleeding linked to partial agonism of current IIb{beta}3 inhibitory drugs such as tirofiban (Aggrastat(R)). Here, we show that m-tirofiban, an engineered version of tirofiban, is not a partial agonist of IIb{beta}3. This is based on its cryo-EM structure in complex with human full-length IIb{beta}3 and its inability to increase expression of an activation-sensitive epitope on platelet IIb{beta}3. m-tirofiban abolished agonist-induced platelet aggregation ex vivo at concentrations that preserved clot retraction and markedly suppressed the accumulation of platelets, neutrophils, and fibrin on thrombin-activated endothelium in real-time using intravital microscopy in a mouse model of venous thrombogenesis. Unlike tirofiban, however, m-tirofiban did not increase bleeding at the thrombosis-inhibitory dose. These findings establish a key role for IIb{beta}3 in the initiation of VT, provide a guiding principle for designing potentially safer inhibitors for other integrins, and suggest that pure antagonists of IIb{beta}3 like m-tirofiban merit further consideration as potential thromboprophylaxis agents in patients at high-risk for VT and hemorrhage.

pathology↗

bioRxiv2022

RUNX1-deficient human megakaryocytes demonstrate thrombopoietic and platelet half-life and functional defects in an in vivo murine model: Therapeutic implications

Heterozygous defects in runt-related transcription factor-1 (RUNX1) are causative of a familial platelet disorder with associated myeloid malignancy (FPDMM). Since RUNX1-deficient animal models do not mimic FPDMMs bleeding disorder or leukemic risk, establishment of a proper model system is critical to understand the underlying mechanisms of the observed phenotype and to identify therapeutic interventions. We previously reported an in vitro-megakaryopoiesis system using human CD34+-hematopoietic stem and progenitor cells that recapitulated the FPDMM quantitative megakaryocyte defect by decreasing RUNX1 expression using a lentiviral short-hairpin RNA (shRNA for RUNX1 or shRX) strategy. We now show that shRX-megakaryocytes have a marked reduction in agonist responsiveness. We then infused shRX-megakaryocytes into immunocompromised NOD-SCID gamma (NSG) mice and demonstrated that these megakaryocytes released fewer platelets than megakaryocytes transfected with a non-targeting shRNA, and these platelets had a diminished half-life. The platelets were also poorly responsive to agonists, unable to correct thrombus formation in NSG mice homozygous for a R1326H mutation in von Willebrand Factor (VWFR1326H), which switches species-binding specificity of the VWF from mouse to human glycoprotein Ib. A small-molecule inhibitor RepSox, which blocks the transforming-growth factor beta pathway, and which rescued defective megakaryopoiesis in vitro, corrected the thrombopoietic defect, platelet half-life and agonist response, and thrombus formation in NSG/VWFR1326H mice. Thus, this model recapitulates the defect in FPDMM megakaryocytes and platelets, identifies previously unrecognized defects in thrombopoiesis and platelet half-life, and demonstrates, for the first time, reversal of RUNX1 deficiencys hemostatic defects by a drug. Key PointsO_LIRUNX1-deficient megakaryocytes exhibit thrombopoietic and platelet defects in NSG/VWFR1326H mice. C_LIO_LIPre-exposure of RUNX1-deficient megakaryocytes to a TGF{beta}1-pathway inhibitor ameliorated both defects, correcting hemostasis. C_LI

cancer biology↗

bioRxiv2018

Structure-guided design of a pure orthosteric antagonist of integrin αIIbβ3 that inhibits thrombosis but not clot retraction

Platelet integrin lIb{beta}3 plays a critical role in both hemostasis and thrombosis. Current IIb{beta}3 antagonists are potent anti-thrombotic drugs, but also cause adverse outcomes, which limited their clinical use. Drug-induced serious bleeding, thrombocytopenia and paradoxical thrombosis have been linked to impaired clot retraction and to conformational changes in IIb{beta}3 that promote binding of preformed antibodies, natural ligands or both to IIb{beta}3. We have used structure-guided design to generate the orthosteric inhibitor Hr10 that acts as a pure IIb{beta}3 antagonist, i.e. it does not induce the conformational changes in IIb{beta}3. Hr10 is as effective as the partial agonist drug eptifibatide in blocking platelet aggregation and arteriolar thrombosis in mice. In contrast to eptifibatide, however, Hr10 preserved thrombin-induced clot retraction, suggesting that it may not perturb hemostasis. Our structure-based approach can find general utility in designing pure orthosteric inhibitors for other integrins, in providing vital tools for dissecting structure-activity relationships in IIb{beta}3, and potentially in offering safer alternatives for human therapy.

cell biology↗