OC 51.4 - Spleen Tyrosine Kinase Activation Drives Platelet Procoagulation in Antiphospholipid Syndrome During Pregnancy

Tuesday, July 12, 2022

11:30 AM – 11:45 AM

Location: ExCel Center, S11A

Presentation Format: In-Person

Presenting Author(s)

Ejaife O. Agbani, BPharm, MSc, PhD

Assistant Professor
University of Calgary
Calgary, Alberta, Canada

Co-Author(s)

SC

Shruti Chaturvedi

Associate Professor
Johns Hopkins University
Baltimore, Maryland, United States
AL

Adrienne Lee

Physician
Division of Hematology & Hematological Malignancies, Department of Medicine, Cumming School of Medicine, University of Calgary, Alberta, Canada.
Calgary, Alberta, Canada
PS

Prism Skeith, MD, PhD, FRCSC

Orthopaedic Trauma Surgeon & Associate Professor
University of Calgary
Calgary, Alberta, Canada
MB

Megan RW Barber

Clinical Assistant Professor
University of Calgary
Calgary, Alberta, Canada
Lisa Yamaura, MKin

Graduate Student
University of Calgary
Calgary, Alberta, Canada
KM

Kimberly Main

General Associate, Physiology & Pharmacology
University of Calgary
Calgary, Alberta, Canada
YE

Yekta Eslambolchi

General Associate, Physiology & Pharmacology
University of Calgary
Calgary, Alberta, Canada
AG

Alexandra Garven

Research Coordinator
Department of Medicine, University of Calgary, Calgary, AB, Canada
Calgary, Alberta, Canada
EM

Etienne Mahe

Clinical Associate Professor
University of Calgary
University of Calgary, Alberta, Canada
AD

Antoine Dufour

Assistant Professor
University of Calgary
Calgary, Alberta, Canada
AC

Ann E. Clarke

Professor
University of Calgary
Calgary, Alberta, Canada
MC

May Y. Choi

Assistant Professor
University of Calgary
Calgary, Alberta, Canada
MP

Man-Chiu Poon

Clinical Professor; Professor Emeritus of Medicine - Paediatrics and Oncology
Division of Hematology and Hematological Malignancies, Department of Medicine, University of Calgary, Calgary, AB, Canada
Calgary, Alberta, Canada
AP

Alastair W. Poole

Principal Investigator
School of Physiology, Pharmacology and Neuroscience/University of Bristol
Bristol, England, United Kingdom
Leslie Skeith, MD

Associate Professor
University of Calgary
Calgary, Alberta, Canada

Background: Pregnant patients with antiphospholipid syndrome (APS) develop thrombotic and obstetric complications despite therapy with low-molecular-weight heparin (LMWH) and aspirin. Platelets are known to play a role in thrombosis, but platelet characteristics in pregnant patients with APS are poorly understood. Elucidating platelet procoagulant mechanisms may allow us to identify novel drug targets to improve thrombotic or obstetric outcomes.

Aims: To elucidate platelet characteristics and procoagulant mechanisms in pregnant patients with APS.

Methods: Two pregnant patients with systemic lupus erythematosus and high-titre triple positive antiphospholipid syndrome (APS/SLE) on LMWH/aspirin, and two pregnant control (PC) participants were followed at matched time points during pregnancy (REB19-1447). We utilized a high-resolution fluorescence imaging suite to visualise platelets in plasma, followed by a systematic analysis of procoagulant membrane dynamics and biochemical study.

Results: Circulating ballooned platelets typified all three trimesters of pregnancy in APS/SLE participants. Platelet activation and P-selectin expression increased as pregnancy progressed and peaked during gestational week 24-28. Expectedly, phosphatidylserine (PS) externalisation (indicated by platelet membrane annexin-V binding) and thrombin generation followed a similar temporal pattern. Additionally, PC platelets treated with plasma from APS/SLE participants (PC+) phenocopied the ballooning and procoagulation characteristics of APS/SLE platelets. Compared to PC platelets, APS/SLE platelets during the early 3rd trimester showed a four- to six-fold increase in Spleen tyrosine kinase (Syk) phosphorylation (Tyr-525/Tyr-526) and a three-fold increase in αIIbβ3 integrin activation. PC+ platelets also showed increased Syk phosphorylation but not integrin αIIbβ3 activation. Treatment of APS/SLE or PC+ platelets with the Syk inhibitor PRT-060318 (10 µM) significantly attenuated Syk phosphorylation, P-selectin expression, and PS exposure. Notably, PRT-060318 reduced αIIbβ3 integrin activation in APS/SLE platelets only, and inhibited membrane ballooning in PC+ but not APS/SLE platelets.

Conclusion(s): We provide evidence that Syk-driven platelet activation and procoagulation characterise pregnancy in APS/SLE patients. We are currently evaluating the mechanisms of antiphospholipid-driven platelet activation and procoagulation.