Hardy Rowan, Juarez Maria, Naylor Amy, Tu Jinwen, Rabbitt Elizabeth H, Filer Andrew, Stewart Paul M, Buckley Christopher D, Raza Karim, Cooper Mark S
Arthritis Res Ther. 2012 Oct 18;14(5):R226. doi: 10.1186/ar4065.
Inflammatory arthritis is associated with increased bone resorption and suppressed bone formation. The Wnt antagonist dickkopf-1 (DKK1) is secreted by synovial fibroblasts in response to inflammation and this protein has been proposed to be a master regulator of bone remodelling in inflammatory arthritis. Local glucocorticoid production is also significantly increased during joint inflammation. Therefore, we investigated how locally derived glucocorticoids and inflammatory cytokines regulate DKK1 synthesis in synovial fibroblasts during inflammatory arthritis.
We examined expression and regulation of DKK1 in primary cultures of human synovial fibroblasts isolated from patients with inflammatory arthritis. The effect of TNFα, IL-1β and glucocorticoids on DKK1 mRNA and protein expression was examined by real-time PCR and ELISA. The ability of inflammatory cytokine-induced expression of the glucocorticoid-activating enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11β-HSD1) to sensitise fibroblasts to endogenous glucocorticoids was explored. Global expression of Wnt signalling and target genes in response to TNFα and glucocorticoids was assessed using a custom array.
DKK1 expression in human synovial fibroblasts was directly regulated by glucocorticoids but not proinflammatory cytokines. Glucocorticoids, but not TNFα, regulated expression of multiple Wnt agonists and antagonists in favour of inhibition of Wnt signalling. However, TNFα and IL-1β indirectly stimulated DKK1 production through increased expression of 11β-HSD1.
These results demonstrate that in rheumatoid arthritis synovial fibroblasts, DKK1 expression is directly regulated by glucocorticoids rather than TNFα. Consequently, the links between synovial inflammation, altered Wnt signalling and bone remodelling are not direct but are dependent on local activation of endogenous glucocorticoids.
炎症性关节炎与骨吸收增加和骨形成受抑制有关。Wnt拮抗剂Dickkopf-1（DKK1）由滑膜成纤维细胞在炎症反应时分泌，该蛋白被认为是炎症性关节炎中骨重塑的主要调节因子。在关节炎症期间，局部糖皮质激素的产生也显著增加。因此，我们研究了在炎症性关节炎期间，局部产生的糖皮质激素和炎性细胞因子如何调节滑膜成纤维细胞中DKK1的合成。
我们检测了从炎症性关节炎患者分离的人滑膜成纤维细胞原代培养物中DKK1的表达和调控。通过实时PCR和ELISA检测肿瘤坏死因子α（TNFα）、白细胞介素-1β（IL-1β）和糖皮质激素对DKK1 mRNA和蛋白表达的影响。探讨了炎性细胞因子诱导的糖皮质激素激活酶11β-羟基类固醇脱氢酶1型（11β-HSD1）表达使成纤维细胞对内源性糖皮质激素敏感的能力。使用定制阵列评估Wnt信号通路及其靶基因在TNFα和糖皮质激素作用下的整体表达。
人滑膜成纤维细胞中DKK1的表达直接受糖皮质激素调节，而非促炎细胞因子。糖皮质激素而非TNFα调节多种Wnt激动剂和拮抗剂的表达，有利于抑制Wnt信号通路。然而，TNFα和IL-1β通过增加11β-HSD1的表达间接刺激DKK1的产生。
这些结果表明，在类风湿性关节炎滑膜成纤维细胞中，DKK1的表达直接受糖皮质激素而非TNFα调节。因此，滑膜炎症、Wnt信号通路改变与骨重塑之间的联系不是直接的，而是依赖于内源性糖皮质激素的局部激活。
