Effects of bacterial lipopolysaccharides on platelet function: inhibition of weak platelet activation

Alexey A Martyanov,Alexander A Ryabykh,Stepan P Gambaryan,Aleksandra A Filkova,Anastasia N Sveshnikova,Elena O Artemenko,Galina S Svidelskaya,Aleksandr S Maiorov,Mikhail A Panteleev

doi:10.1038/s41598-020-69173-x

Abstract

Platelets are anucleate blood cells with reported roles in hemostasis and immune responses, which possess a functional receptor for bacterial lipopolysaccharides (LPSs), the well-known inducers of inflammation. However, LPSs effects on platelets are contradictory. Here we aim to investigate mechanisms of platelet functioning in the presence of LPS and to find the cause of the discrepancy in the previously published data. Cell activity was analyzed by flow cytometry, western blotting, and aggregometry. Thrombus growth was assessed by fluorescent microscopy. LPS' activity was checked by their capability to induce PMN activation. However, LPSs did not substantially affect either thrombus growth in flow chambers, irreversible platelet aggregation, or platelet responses to strong activation. Platelet aggregation in response to 1 μM of ADP was significantly inhibited by LPSs. Flow cytometry analysis revealed that platelet activation responses to weak stimulation were also diminished by LPSs, while VASP phosphorylation was weakly increased. Additionally, LPSs were capable of inhibition of ADP-induced P2-receptor desensitization. Incubation of platelets with a pan-PDE inhibitor IBMX significantly enhanced the LPSs-induced platelet inhibition, implying cAMP/cGMP dependent mechanism. The discrepancy in the previously published data could be explained by LPS-induced weak inhibition of platelet activation and the prevention of platelet desensitization.

Highlights

Platelets are anucleate blood cells with reported roles in hemostasis and immune responses, which possess a functional receptor for bacterial lipopolysaccharides (LPSs), the well-known inducers of inflammation
A more thorough analysis of the LPS effects on platelet signalling revealed that LPSs are capable to inhibit weak platelet activation via cAMP/cGMP signalling pathways
To test the activity of LPSs, we performed flow cytometry assessment on washed PMNs ability to induce CD11b activation upon pre-incubation with LPSs of different origins (Figs. 1A, S1A,B), which in contrast to reported data was independent on the presence of albumin

Summary

Introduction

Platelets are anucleate blood cells with reported roles in hemostasis and immune responses, which possess a functional receptor for bacterial lipopolysaccharides (LPSs), the well-known inducers of inflammation. Platelet aggregation in response to 1 μM of ADP was significantly inhibited by LPSs. Flow cytometry analysis revealed that platelet activation responses to weak stimulation were diminished by LPSs, while VASP phosphorylation was weakly increased. IKκ-β involved in phosphorylation of synaptosomal-associated protein 23 (SNAP23), which controls platelet alpha-granule release[8] This was in disagreement with LPS capability to enhance aggregation of washed platelets, stimulated by thrombin, but without any effect on aggregation in platelet-rich plasma (PRP)[6]. A more thorough analysis of the LPS effects on platelet signalling revealed that LPSs are capable to inhibit weak platelet activation via cAMP/cGMP signalling pathways. This phenomenon might be the key to understanding the inconsistency in the data on LPS mediated platelet activity

Objectives

Methods

Results

Conclusion