Background/Purpose:

Microsomal prostaglandin E synthase-1 (mPGES-1) is an essential player in inflammation and has an indispensible role in the generation and maintenance of autoimmune disease such as rheumatoid arthritis (RA). It is an inducible terminal synthase that generates PGE₂. Pharmacological inhibition and genetic deletion of mPGES-1 has been proven to be protective in experimental models of inflammation. Platelets play a vital role in homeostasis and modulation of inflammatory processes by releasing a diversity of cytokines, chemokines and other lipid mediators. It has been recognized that activated platelets and formation of platelet-derived microparticles (PMPs) play a major role in RA pathogenesis. We hypothesize that mPGES-1/PGE₂ pathway may contribute to platelet activation and mPGES-1 inhibition might have beneficial effects on platelet-mediated functions during inflammation. The aim of the study was to investigate the outcome of mPGES-1 deletion on platelet function in mice stimulated with LPS. 

Methods:

mPGES-1 wild type (WT) and knockout (KO) DBA mice were injected with 2μg LPS i.p, for 24h. Mice were anesthetized and blood was slowly drawn from the heart by a syringe containing 100μl 3.8% sodium citrate and was transferred to tubes.  The numbers and activation of platelets and PMPs were measured in whole blood by flow cytometry. Briefly, blood samples were labeled with CD61-Alexa 488 together with CD62P-PE and CD154-APC. The platelet and PMP numbers where defined by their size characteristics and CD61 expression. The platelets were then investigated for co- expression of CD62P or CD154 respectively. In addition, platelet-leukocyte interaction was also measured in the leukocyte gate. To investigate platelet aggregation, a flow cytometry–based platelet aggregation assay (FCA) was used. Briefly, whole blood is divided into two tubes and labeled with either CD61-Alexa 488 or CD61-PE. After incubation, the tubes were combined and platelets were activated with ADP (6.5μM). Platelets expressing both markers were considered as platelet aggregates. 

Results:

Upon LPS stimulation the number of platelets in WT mice was significantly reduced compared to KO mice (p<0.001). Platelet activation (assessed by CD62P and CD154 expression) was significantly higher in WT mice compared to KO mice upon treatment with LPS (p<0.01 for both). Moreover, the levels of platelet-leukocyte interaction were higher in WT mice (p<0.05). PMP numbers were also higher in WT mice compared to KO (p<0.01). In addition, platelet aggregation measured with the FCA assay, yielded significantly higher numbers of platelet aggregates in WT compared to KO mice (p<0.001). 

Conclusion:

mPGES-1 deletion affects platelet concentration and activation as well as PMP formation in LPS stimulated WT mice. The data suggest possible role of mPGES-1 in platelets function in inflammation.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-effect-of-mpges-1-deletion-on-platelet-function-in-mice/