A Human Platelet Receptor Protein Microarray Identifies the High Affinity Immunoglobulin E Receptor Subunit (Fc epsilon R1) as an Activating Platelet Endothelium Aggregation Receptor 1 (PEAR1) Ligand

摘要

Genome-wide association studies to identify loci responsible for platelet function and cardiovascular disease susceptibility have repeatedly identified polymorphisms linked to a gene encoding Platelet endothelium aggregation receptor 1 (PEAR1), an ″orphan″ cell surface receptor that is activated to stabilize platelet aggregates. To investigate how PEAR1 signaling is initiated, we sought to identify its extracellular ligand by creating a protein microarray representing the secretome and receptor repertoire of the human platelet. Using an avid soluble recombinant PEAR1 protein and a systematic screening assay designed to detect extracellular interactions, we identified the high-affinity immunoglobulin E (IgE)-binding subunit FcϵR1α, as a PEAR1 ligand. FcϵR1α and PEAR1 directly interacted through their membrane-proximal Ig-like and 13th EGF domains with a relatively strong affinity (KD ≈ 30nM). Pre-complexing FcϵR1α with IgE potently inhibited the FcϵR1α-PEAR1 interaction and this was relieved by the anti-IgE therapeutic, omalizumab. Oligomerised FcϵR1α potentiated platelet aggregation and led to PEAR1 phosphorylation, an effect that was also inhibited by IgE. These findings demonstrate how a protein microarray resource can be used to gain important insight into the function of platelet receptors, and provide a mechanistic basis for the initiation of PEAR1 signaling in platelet aggregation.