Figure 4.

Dose-response and involvement of GPCR in the PGE₂ production by S1P. A) Dose-response: OA chondrocytes were stimulated in vitro with S1P (0.1, 1 or 10 μM) for 24 h. Top: Levels of PGE₂ in the culture supernatants were assayed using ELISA in triplicate (N = 3 each). Bottom: A representative result of western blot of COX-2 expression is shown. B): PTX inhibition: OA chondrocytes were stimulated in vitro with S1P (10 μM) with or without pertussis toxin (PTX, 10 ng/ml) for 24 h, and levels of PGE₂ were analyzed using ELISA (N = 3 each, in triplicate).