Fig. 8
cAMP, IGF-2, PGE2, PGF2α, and 15d-PGJ2 upregulated the mRNA expression of MMP-12 in mice. a 8-Br-cAMP (2 μg/5 μl), (b) IGF-2 (10 ng/5 μl), (c) PGE2 (1 μg/5 μl) or PGF2α (1 μg/5 μl) was injected into the cavity of articular cartilage of WT mice. d In select experiments, 15d-PGJ2 (1 μg/5 μl) was injected into the cavity of articular cartilage of COX-2 Tg mice. MMP-12 mRNA and protein levels were determined by qRT-PCR and western blots, respectively. GAPDH and MMP-11 served as internal controls in qRT-PCR and western blots, respectively. e Knee joint samples were dissected from 3-month-old mice, and alcian blue/hematoxylin and eosin and safranin O-fast green staining was performed. Data represent the mean ± SE of at least three independent experiments. *p < 0.05 with respect to PBS (-)-treated control. f Proposed cascade of signaling events regulates the progressive synthesis of MMP-12 in human chondrocytes with high fluid shear stress. High fluid shear stress induces the rapid and sustained expression of COX-2 and synthesis of PGE2 and PGF2α. The accumulation of PGE2 and PGF2α proceeds via an EP2/EP3- and FPR-dependent cAMP and IGF-2 induction mechanism to increase the expression of MMP-12 at 6 h of shear stress exposure. In contrast, 15d-PGJ2 was produced after prolonged exposure to high fluid shear stress. The production of 15d-PGJ2 suppressed the expression of MMP-12 at 48 h of shear stress exposure. The roles of metabolic products of shear-induced COX-2 in regulating the mRNA and protein expressions of MMP-12 were finally verified in mice
