Molecular Mechanism And The Effect Of Prostaglandin E₂ Regulate Activation Of Mouse Peritoneal Macrophages By Staphylococcus Aureus

Staphylococcus aureus is recognized worldwide as a major gram-positive pathogen causing bacterial infections,bacteraemia and sepsis in mammals.During infection process,S.aureus activates immune cells and induces inflammatory response in the host,which induces the proinflammatory cytokines and chemokines secretion.The innate immune system plays crucial roles in the host defence against bacterial infection.In early host responses against invading pathogens,specific pathogen-associated molecular patterns(PAMPs)or damage-associated molecular patterns(DAMPs)are recognized by pattern recognition receptors(PRRs),including the toll-like receptor(TLR)and the NOD-like receptor(NLR).Among these PRRs,TLR2 has been shown to play an essential role in defence against S.aureus infection.TLR2 stimulation by S.aureus result in activation of the transcription factor NF-?B and mitogen-activated protein kinase(MAPK)signalling pathways,which are involved in many proinflammatory mediators secretion.There is a series of evidence that supports a broad role for TLR2 as a PRR for a variety of microbes and microbial structures.TLR2 has been reported recognize the peptidoglycan(PGN)and lipoteichoic acid(LTA)from S.aureus.Subsequent studies indicate that lipoproteins from S.aureus are the dominant immunobiologically active compounds that activate cells through TLR2.Stenzel et al.reported that immune response to experimental S.aureus-induced brain abscess not only dependent on TLR2,but also TLR4,a well-known lipopolysaccharide(LPS)sensor.This result suggests that TLR4 might participate in the host defence against S.aureus infections.S.aureus also activate NLRP3 inflammasome,the best characterized NLR molecules,resulting in the caspase-1 activation and the mature IL-1? secretion.All these results indicated that multiple PRRs involved in the host immune response to S.aureus infection.It is unknown the roles of S.aureus lipoproteins in other inflammatory mediator secretion in immune cells,for example Prostaglandin E2(PGE2).PGE2 is endogenous hormone that is essential to the normal physiological functions of various organs of the female reproductive,gastrointestinal,and cardiovascular systems,although in pathological conditions,PGE2 also acts as an inflammatory mediator.PGE2 production begins when phospholipases liberate arachidonic acid(AA)stored in membrane phospholipids.AA is converted into prostaglandin endoperoxide H2(PGH2)by cyclooxygenases(COXs).PGH2 is then transformed into PGE2 via PGE synthases(PGESs).Previous study indicated that in TLR4 agonist LPS activated macrophages,exogenous PGE2 induced cyclic AMP(cAMP)-dependent protein kinase(PKA)signalling pathway plays an important role in the modulation of the immune response and the inflammatory process,characterized by increased COX-2 and microsomal PGES-1(mPGES-1)expression.Granick et al.reported that granulopoiesis in S aureus-infected wounds is induced by TLR2/MyD88 activation of hematopoietic stem and progenitor cells through a mechanism that involves autocrine production and activity of PGE2.In addition,NLRP3 inflammasome mediated activation of COX-2/mPGES-1/PGE2 cascade involved in albumin-induced proximal tubule cell injury.All these results indicated that PGE2 had a tight relationship with the innate immune response triggered by PRRs.In the present study,the hypothesis has been tested that S.aureus lipoproteins are essential for induction of PGE2 secretion by immune cells,and that this process is mediated by PRRs,including TLR2,TLR4,and NLRP3.Levels of PGE2 secreted by mouse peritoneal macrophages infected with the S.aureus isogenic mutant,lgt::ermB(?lgt),which is deficient in lipoprotein maturation,were decreased compared with those from macrophages infected with wild-type S.aureus.Experiments using TLR2-deficient,TLR4-deficient,and NLRP3-deficient mice indicated that these three proteins(TLR2,TLR4,and NLRP3)are involved in PGE2 secretion by macrophages in response to S.aureus.In addition,we found that lipoproteins were essential for S.aureus internalization into and its survival within macrophages.PGE2 inhibited the process of phagocytosis for both bacterial strains,but was able to increase intracellular killing accompanied by enhanced IL-1? secretion.Our data demonstrate that S.aureus can induce macrophage TLR/MAPK/NF-?B signaling and that activation of NLRP3/caspase-1 signaling is up-regulated by PGE2 treatment.Overall,these results indicate that PGE 2 secretion by macrophages after S.aureus infection depends on bacterial lipoprotein maturation and the macrophage receptors,TLR2,TLR4 and NLRP3.Moreover,S.aureus induced activation of macrophages through TLRs and NLRP3 inflammasome signaling is regulated by exogenous PGE2.