Microparticles stimulate the synthesis of prostaglandin E(2) via induction of cyclooxygenase 2 and microsomal prostaglandin E synthase 1.
OBJECTIVE
Microparticles are small vesicles that are released from activated or dying cells and that occur abundantly in the synovial fluid of patients with rheumatoid arthritis (RA). The goal of these studies was to elucidate the mechanisms by which microparticles activate synovial fibroblasts to express a proinflammatory phenotype.


METHODS
Microparticles from monocytes and T cells were isolated by differential centrifugation. Synovial fibroblasts were cocultured with increasing numbers of microparticles. Gene expression was analyzed by real-time polymerase chain reaction and confirmed by Western blotting and enzyme immunoassay. Arachidonic acid labeled with tritium was used to study the transport of biologically active lipids by microparticles. The roles of NF-kappaB and activator protein 1 (AP-1) signaling were analyzed with electrophoretic mobility shift assay and transfection with small interfering RNA and IkappaB expression vectors.


RESULTS
Microparticles strongly induced the synthesis of cyclooxygenase 2 (COX-2), microsomal prostaglandin E synthase 1 (mPGES-1), and prostaglandin E(2) (PGE(2)). In contrast, no up-regulation of COX-1, mPGES-2, cytosolic PGES, or phospholipase A(2) was observed. The induction of PGE(2) was blocked by selective inhibition of COX-2. Microparticles activated NF-kappaB, AP-1, p38, and JNK signaling in synovial fibroblasts. Inhibition of NF-kappaB, AP-1, and JNK signaling reduced the stimulatory effects. Arachidonic acid was transported from leukocytes to fibroblasts by microparticles. Arachidonic acid derived from microparticles was converted to PGE(2) by synovial fibroblasts.


CONCLUSIONS
These results demonstrate that microparticles up-regulate the production of PGE(2) in synovial fibroblasts by inducing COX-2 and mPGES-1. These data provide evidence for a novel mechanism by which microparticles may contribute to inflammation and pain in RA.
Jüngel
Astrid
A
Zurich Center of Integrative Human Physiology, and University Hospital Zurich, Zurich, Switzerland.
Distler
Oliver
O
Schulze-Horsel
Ursula
U
Huber
Lars C
LC
Ha
Huy Riem
HR
Simmen
Beat
B
Kalden
Joachim R
JR
Pisetsky
David S
DS
Gay
Steffen
S
Distler
Jörg H W
JH
D001095:Arachidonic Acids / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000235:genetics* / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000378:metabolism*; D005347:Fibroblasts / Q000201:enzymology* / Q000276:immunology / Q000473:pathology; D006801:Humans; D019746:Intramolecular Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008861:Microsomes / Q000201:enzymology; D009000:Monocytes / Q000378:metabolism / Q000648:ultrastructure; D016328:NF-kappa B / Q000378:metabolism; D009578:Nitrobenzenes / Q000494:pharmacology; D010003:Osteoarthritis / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D010316:Particle Size; D000071876:Prostaglandin-E Synthases; D015398:Signal Transduction / Q000276:immunology; D013449:Sulfonamides / Q000494:pharmacology; D013582:Synovial Fluid / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism / Q000648:ultrastructure; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015854:Up-Regulation / Q000276:immunology
D001095:Arachidonic Acids; D016861:Cyclooxygenase Inhibitors; D016328:NF-kappa B; D009578:Nitrobenzenes; D013449:Sulfonamides; D018808:Transcription Factor AP-1; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D051546:Cyclooxygenase 2; D048031:JNK Mitogen-Activated Protein Kinases; D019746:Intramolecular Oxidoreductases; C000605862:PTGES protein, human; C000605863:PTGES2 protein, human; D000071876:Prostaglandin-E Synthases; D015232:Dinoprostone