The Roles Of Platelet Endothelial Aggregation Receptor 1 In Platelets And Vascular Function

PEAR1(platelet endothelial aggregation receptor-1,also known as MEGF12 or JEDI)is a transmembrane protein of the multiple epidermal growth factor(EGF)–like domain protein family.PEAR1 is mainly expressed in platelets and endothelial cells.Studies showed that PEAR1 was believed to be a platelet-platelet contact receptor and play a significant role in platelets aggregation.Endothelial cells play critical roles in maintaining blood vessel homestasis and regulating vascular injury repair process.Platelets,as one of the direct effectors of endothelial damage have important roles in regulating the physiology and pathology functions of endothelial cells.Clinical studies have verified several PEAR1 single nucleotide polymorphisms closely correlate with platelet aggregation and vascular function.This project will study the roles and mechanisms of PEAR1 involving in function of platelets and endothelial cells.Analysis of the location of PEAR1 in platelets showed that PEAR1 increasingly expressed on the membrane of platelets when the platelets were active.The antibody against the extracellular domain of PEAR1 could act as the ligand to active the platelets.Results also showed that the PEAR1 activated the platelets through the ITAM signaling.Pulldown analysis of the platelets' lysate with the EMI domain and mass spectrometric analysis showed that the PEAR1 could interact with GPIb,?IIb?3,p-selectin on platelets.PEAR1 knockout mice were developed by the CRISPR/Cas9 gene targeting technique to investigate the function(s)of PEAR1 in platelets.Results illustrated that the platelets of PEAR1 knockout mice gave decreased respose to the low concentration of collagen and thrombin,the clot retraction and the spreading on fibrinogen were slightly affected.So,PEAR1 might influence the GPVI and TP recepters on platelets but not the ?IIb?3 outside-in signaling.PEAR1 is not only expressed in platelets,but also in endothelial cells.In the condition of adherent culture,PEAR1 was in nucleus and membrane of the HUVEC.When the HUVEC formed the tube structures on matrigels,PEAR1 mainly expressed in the membrane of the HUVEC.We incubated the PEAR1 antibody with the HUVEC and then make them culture in the Matrigel to observe the tube formation ability of the HUVEC.We found the PEAR1 antibody could suppress the tube formaton ability of HUVEC,but no effect to the proliferation of HUVEC.When we make the platelets incubate with HUVEC and culture in the Matrigel,the tube formation ability of HUVEC was inhibited as well.However,the EMI domain could rescue the inhibitory effect of the platelets to HUVEC.These results promoted that the EMI domain was the main structure of PEAR1 to interact with the ligand on platelets.Furthermore,PEAR1 antibody had no effect on the migration of HUVEC by scratch test.Thus,PEAR1 is supposed an important mediator of endothelial cell and platelet interaction.PEAR1 may play critical roles in maintaining blood vessel homestasis and vascular remodeling.