Fluid flow induces COX-2 expression in MC3T3-E1 osteoblasts via a PKA signaling pathway

Abstract

Mechanical loading of bone generates fluid flow within the mineralized matrix which can exert fluid shear stress (FSS) at cell membranes. FSS induces new transcription of cyclooxygenase-2 (COX-2) in MC3T3-E1 osteoblasts, with peak effects at 4–5 h. Using MC3T3-E1 cells stably transfected with the COX-2 promoter fused to a luciferase reporter, we examined involvement of the protein kinase A (PKA) and protein kinase C (PKC) signaling pathways in the peak COX-2 mRNA and luciferase responses to FSS (10 dyn/cm 2). Neither inhibition nor down-regulation of the PKC pathway affected the FSS stimulation of COX-2 mRNA or luciferase activity. In contrast, inhibitors of the PKA pathway, used at doses which inhibited forskolin-stimulated luciferase activity by 70–80%, reduced FSS-stimulated COX-2 mRNA expression and luciferase activity by 50–80%. Hence, peak FSS induction of COX-2 expression in MC3T3-E1 osteoblastic cells is largely dependent on the PKA signaling pathway.