Abstract
Osteoarthritis (OA) was recently identified as being regulated by the induction of cyclooxygenase-2 (COX-2) in response to high fluid shear stress. Although the metabolic products of COX-2, including prostaglandin (PG)E2, 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2), and PGF2α, have been reported to be effective in regulating the occurrence and development of OA by activating matrix metalloproteinases (MMPs), the roles of PGF2α in OA are largely overlooked. Thus, we showed that high fluid shear stress induced the mRNA expression of MMP-12 via cyclic (c)AMP- and PGF2α-dependent signaling pathways. Specifically, we found that high fluid shear stress (20 dyn/cm2) significantly increased the expression of MMP-12 at 6 h ( > fivefold), which then slightly decreased until 48 h ( > threefold). In addition, shear stress enhanced the rapid synthesis of PGE2 and PGF2α, which generated synergistic effects on the expression of MMP-12 via EP2/EP3-, PGF2α receptor (FPR)-, cAMP- and insulin growth factor-2 (IGF-2)-dependent phosphatidylinositide 3-kinase (PI3-K)/protein kinase B (AKT), c-Jun N-terminal kinase (JNK)/c-Jun, and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-activating pathways. Prolonged shear stress induced the synthesis of 15d-PGJ2, which is responsible for suppressing the high levels of MMP-12 at 48 h. These in vitro observations were further validated by in vivo experiments to evaluate the mechanisms of MMP-12 upregulation during the onset of OA by high fluid shear stress. By delineating this signaling pathway, our data provide a targeted therapeutic basis for combating OA.
Highlights
Recent studies have changed the traditional concept of osteoarthritis (OA) from a prototypical noninflammatory arthropathy to an inflammatory component.[1]
The results demonstrated that the treatment of T/C-28a2 chondrocytes with different inhibitors abolished forskolininduced or insulin growth factor-2 (IGF-2)-induced AKT, NF-κB, and c-Jun phosphorylation and the matrix metalloproteinases (MMPs)-12 mRNA and protein levels (Fig. 5c, d)
Deciphering the mechanisms of MMP-12 upregulation by shear stress in the COX-2 and PGs-dependent pathways potentially provide the therapeutic targets for treating OA Using in vitro techniques of high fluid shear stress, we show that high fluid shear stress elevated the expression of COX-231 and the synthesis of PGE2, PGF2α, and 15d-PGJ2
Summary
Recent studies have changed the traditional concept of osteoarthritis (OA) from a prototypical noninflammatory arthropathy to an inflammatory component.[1]. In light of the critical roles of COX-2 in regulating the expression of MMP-12, we subsequently determined the effects of PGE2 and PGF2α on the expression of MMP-12 in sheared-activated T/C-28a2 cells. To verify this hypothesis, experiments were carried out to determined using an ELISA kit following the manufacturer’s instructions. The inductions of PGE2 and PGF2α were attenuated by the transfection of T/C28a2 cells with mPGES-1 or PGFS siRNA (Fig. 2e, f) Both mPGES-1 extraction was used as the loading control, and the results were and PGFS knockdown inhibited the shear-induced MMP-12 expressed as IGF-2, PGE2, PGF2α, cAMP, or 15d-PGJ2 /total protein. Our analysis indicates that high fluid shear stress rapidly stimulated the production of cAMP, which was sustained above basal level until 48 h of shear stress exposure
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