Prostaglandin E2 receptors EP2 and EP4 are up-regulated in peritoneal macrophages and joints of pristane-treated mice and modulate TNF-α and IL-6 production

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Abstract
Prostaglandin E2 (PGE2) can have pro‐ or anti‐inflammatory effects, depending on engagement of different PGE2 receptor (EP) subtypes. The role of EPs in regulating autoimmune inflammation was studied in the murine arthritis/lupus model induced by pristane. Peritoneal macrophages were isolated (biomagnetic beads) from BALB/c, DBA/1, or C57BL/6 mice treated with pristane (intraperitoneally, 3 months earlier) or thioglycolate (3 days earlier) or with untreated controls. EPs, inducible nitric oxide synthase (iNOS), and cyclooxygenase‐2 (COX‐2) mRNA expression was examined by reverse transcriptase‐polymerase chain reaction (RT‐PCR). Cells were cultured unstimulated or stimulated with lipopolysaccharide (LPS) or LPS + interferon‐γ in combination with EP subtype‐specific agonists. Tumor necrosis factor α (TNF‐α) and interleukin (IL)‐6 production was tested by enzyme‐linked immunosorbent assay (culture supernatant) and flow cytometry. TNF‐α mRNA levels also were examined. High levels of EPs (EP4/2>EP1>EP3), iNOS, and COX‐2 mRNA were expressed in peritoneal macrophages from pristane‐treated but not untreated or thioglycolate‐treated mice (RT‐PCR). TNF‐α production was inhibited 50–70% at 2–24 h by EP4/2 agonists, whereas IL‐6 was enhanced up to ∼220%. TNF‐α inhibition is mediated partly via the protein kinase A pathway and partly via IL‐6. Intracellular TNF‐α staining was inhibited 20% by EP4/2 agonists. TNF‐α mRNA levels were inhibited 50–70% at 2–24 h, indicating that TNF‐α inhibition was partly at the level of transcription. EP1/3 agonists had little effect. Synovial cells from mice with pristane‐induced arthritis (DBA/1) also expressed EP2/4, and the EP2/4 agonist inhibited TNF‐α production. PGE2 can modulate inflammatory reactions via the EP2/4 receptor through its regulation of TNF‐α and IL‐6. Modification of EP signaling may be a new therapeutic strategy in inflammatory/autoimmune diseases.
Funding Information
  • NIH (R21-AR 056001, R01-AR44731, AI44074)