Rivenprost

This study aimed to re-examine the receptor subtype that mediates the fever-producing effects of prostaglandin E₂ (PGE₂) in the rostral ventromedial preoptic area (rvmPOA) of the hypothalamus. Among the four subtypes of PGE₂ receptors (EP₁, EP₂, EP₃, and EP₄), EP₃ receptor is crucially involved in the febrile effects of PGE₂. However, it is possible for other subtypes of PGE₂ receptor to contribute in the central mechanism of fever generation. Accordingly, effects of microinjection of PGE₂ receptor subtype-specific agonists or antagonists were examined at the locus where a microinjection of a small amount (420 fmol) of PGE₂ elicited prompt increases in the O₂ consumption rate (VO₂), heart rate, and colonic temperature (T_c) in the rvmPOA of urethane-chloralose-anesthetized rats. The EP₃ agonist sulprostone mimicked, whereas its antagonist L-798,106 reduced, the febrile effects of PGE₂ microinjected into the same site. Similarly, the EP₄ agonist rivenprost mimicked, whereas its antagonist ONO-AE3-208 reduced, the effects of PGE₂ microinjected into the same site. In contrast, microinjection of the EP₁ agonist iloprost induced a very small increase in VO₂ but did not have significant influences on the heart rate and T_c, whereas its antagonist, AH6809, did not affect the PGE₂-induced responses. Microinjection of the EP₂ agonist butaprost had no effects on the VO₂, heart rate, and T_c. The results suggest that the EP₃ and EP₄ receptor subtypes are both involved in the fever generated by PGE₂ in the rvmPOA.

Our previous study showed that chronic treatment with tumor necrosis factor-α (TNF-α) decreased cAMP concentration in fibroblast-like synoviocytes (FLSs) of collagen-induced arthritis (CIA) rats. In this study we investigated how TNF-α impairs cAMP homeostasis, particularly clarifying the potential downstream molecules of TNF-α and prostaglandin receptor 4 (EP4) signaling that would interact with each other. Using a cAMP FRET biosensor PM-ICUE3, we demonstrated that TNF-α (20 ng/mL) blocked ONO-4819-triggered EP4 signaling, but not Butaprost-triggered EP2 signaling in normal rat FLSs. We showed that TNF-α (0.02-20 ng/mL) dose-dependently reduced EP4 membrane distribution in normal rat FLS. TNF-α significantly increased TNF receptor 2 (TNFR2) expression and stimulated proliferation in human FLS (hFLS) via ecruiting TNF receptor-associated factor 2 (TRAF2) to cell membrane. More interestingly, we revealed that TRAF2 interacted with G protein-coupled receptor kinase (GRK2) in the cytoplasm of primary hFLS and helped to bring GRK2 to cell membrane in response of TNF-α stimulation, the complex of TRAF2 and GRK2 then separated on the membrane, and translocated GRK2 induced the desensitization and internalization of EP4, leading to reduced production of intracellular cAMP. Silencing of TRAF2 by siRNA substantially diminished TRAF2-GRK2 interaction, blocked the translocation of GRK2, and resulted in upregulated expression of membrane EP4 and intracellular cAMP. In CIA rats, administration of paroxetine to inhibit GRK2 effectively improved the symptoms and clinic parameters with significantly reduced joint synovium inflammation and bone destruction. These results elucidate a novel form of cross-talk between TNFR (a cytokine receptor) and EP4 (a typical G protein-coupled receptor) signaling pathways. The interaction between TRAF2 and GRK2 may become a potential new drug target for the treatment of inflammatory diseases.