PB0377 - Heparin and heparin proteoglycan-mimetics activate platelets via PEAR1 and PI3Kbeta

Sunday, July 10, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

CK

Caroline Kardeby

Research Fellow
University of Birmingham
Birmingham, England, United Kingdom

Co-Author(s)

AE

Alice Evans

Student
University of Birmingham
Birmingham, England, United Kingdom
JC

Joana Campos

Research Fellow
University of Birmingham
Birmingham, England, United Kingdom
CS

Christopher W. Smith

Research Fellow
University of Birmingham
Birmingham, England, United Kingdom
AS

Alexandre Slater

Research Fellow
University of Birmingham
Birmingham, England, United Kingdom
EM

Eleyna Martin

Postdoctoral Research Fellow
University of Birmingham
Birmingham, England, United Kingdom
Sonia Severin, PhD

researcher
Institute of metabolic and cardiovascular diseases
Toulouse cedex 04, Midi-Pyrenees, France
Alexander Brill, MD, PhD

Reader/Associate Professor
University of Birmingham
Birmingham, England, United Kingdom
GP

Gunnar Pejler

Professor
Uppsala University
Uppsala, Uppsala Lan, Sweden
YS

Yi Sun

Research Fellow
University of Birmingham
Birmingham, England, United Kingdom
SW

Steve Watson

Professor
University of Birmingham
Birmingham, England, United Kingdom

Background: Platelet Endothelial Aggregation Receptor 1 (PEAR1) is a single-transmembrane orphan receptor primarily expressed on platelet and endothelial cells. Genetic variants of PEAR1 have repeatedly and independently been identified as top hits associated with cardiovascular diseases. We have reported that the sulfated polysaccharide fucoidan and synthetic fucoidan-mimetics activate PEAR1 by binding to the 13th EGF-like repeat containing a BXXBB sequence (B is a positively charged amino acid), a sequence similar to known heparin-binding consensus sequences. This led us to speculate that PEAR1 may be a receptor for a heparin-based proteoglycans.

Aims: The present study aims to investigate if PEAR1 is activated by heparin proteoglycans.

Methods: A proteoglycan-mimetic was created by conjugating heparin to an albumin protein core. Nanobodies were raised against the 12-14th EGF-like repeats in PEAR1 through VIB Nanobody Core Technology, Brussels.

Results: We show that a heparin proteoglycan-mimetic causes platelet aggregation and phosphorylation of PEAR1 and Akt in washed platelets, and aggregation in platelet-rich plasma. The response to the heparin proteoglycan-mimetic was abolished by a novel anti-PEAR1 nanobody and by a selective inhibitor of PI3Kbeta, TGX 221. Unfractionated heparin stimulated full aggregation in washed platelets in 4 out of 7 donors after a delay of more than 30 minutes but not in platelet-rich plasma.

Conclusion(s): We have shown that PEAR1 is a receptor for heparin and heparin-based proteoglycan-mimetics. Suggesting that the endogenous ligand for PEAR1 may be the only heparin-containing proteoglycan expressed by mast cells, serglycin. Heparin and heparin proteoglycans, together with Fc-epsilon RI-alpha, represent three separate ligands for PEAR1; all of which are expressed by the mast cell. Further studies are required to address the significance of the mast cell–PEAR1 signalling axis in health and disease.