脂氧酶抑制劑在TNF-α誘導之類風濕關節炎滑囊纖維母細胞抗發炎作用之探討

Abstract

類風濕性關節炎為一種慢性自體免疫疾病，具有全身或局部的關節滑囊發炎，軟硬骨侵蝕之特性。在開發中地區，每百人就有約一人受此疾病影響，且每十萬人就有5到50人罹患此疾病，其中又以老年婦女居多。致病原因目前尚未完全明瞭，但造成疾病加重的原因之一可能為關節囊中過度增生之關節滑囊纖維母細胞 所產生過多的細胞激素以及化學趨素所導致，關節滑囊纖維母細胞過去即被認為具有軟硬骨侵蝕以及分泌細胞激素以及化學趨素的能力，在疾病發生過程中扮演一重要的角色。腫瘤壞死因子α，為最顯著影響疾病進程的發炎性細胞激素之一，在發炎細胞生理中，具有誘發其他細胞激素釋放的能力包括介白素第一及第六因子，進而放大身體中的免疫反應包括白血球浸潤堆積，破骨及軟骨細胞活化，以及釋放更多的發炎因子，其中包括了脂氧酶代謝物，白三烯素以及二十碳四烯酸。 脂氧酶，包括第五及第十五型，為一群非血紅素鐵二氧化酶，可催化內生性的花生油酸產生各種白三烯素以及二十碳四烯酸。過去文獻指出，人類類風濕性關節滑膜組織中有過度表現的第五及第十五型脂氧酶。脂氧酶代謝物，包括白三烯素以及15-羥基二十碳四烯酸亦具有誘發發炎因子包括介白素第六因子以及單核細胞趨化蛋白-1的能力，被認為與疾病的進程具有密切的關係。因為腫瘤壞死因子能夠促進脂氧酶及其代謝物的表現，又脂氧酶及其代謝物本身也有增加發炎因子包括介白素以及單核細胞趨化蛋白-1的能力，因此本篇的目的即為探討細胞及活體中脂氧酶路徑在腫瘤壞死因子所誘發的細胞激素及化學趨素過度分泌所扮演的角色。 在本篇的研究中，我們發現腫瘤壞死因子可以誘發人類關節滑囊纖維母細胞釋放介白素-1β及介白素-6的mRNA 及蛋白的表現，接著我們探討第五及第十五型脂氧酶抑制劑在腫瘤壞死因子之人類關節滑囊纖維母細胞所扮演的角色，發現到預處理第五或第十五型脂氧酶抑制劑可以拮抗腫瘤壞死因子誘導之人類關節滑囊纖維母細胞的介白素-1β及介白素-6 mRNA 以及蛋白的表現，然而，外給予第五或第十五型脂氧酶代謝物包括白三烯素B4或15-羥基二十碳四烯酸可以增加介白素-6的mRNA或蛋白的表現。 我們接著探討第五或第十五型脂氧酶抑制劑拮抗腫瘤壞死因子誘導之人類關節滑囊纖維母細胞的介白素-1β及介白素-6表現的訊息傳遞機制，我們發現外給予腫瘤壞死因子可以活化人類關節滑囊纖維母細胞中IKKα/β的活性，促進IκBα磷酸化，以及增加IκBα的降解，然而在預處理第五或第十五型脂氧酶抑制劑後可以拮抗此現象。進一步的我們利用西方墨點法及螢光染色分析核內蛋白也發現預處理第五或第十五型脂氧酶抑制劑可以拮抗腫瘤壞死因子誘發的NF-κB次單元體p65及p50的入核現象。當我們轉殖一段具有專一性拮抗第五或第十五型脂氧酶mRNA的shRNA，使人類關節滑囊纖維母細胞內第五或第十五型脂氧酶的表現量降低，進而發現腫瘤壞死因子誘導之介白素-6以及單核細胞趨化蛋白-1表現明顯下降。 我們最後更進一步地去探討第五或第十五型脂氧酶在腫瘤壞死因子誘導發炎的動物模式上所扮演的角色。我們發現腫瘤壞死因子可以誘導單核細胞趨化蛋白-1在動物血清中的表現增加，然後同時給予第五型脂氧酶抑制劑NDGA可以拮抗此現象。另外，我們也發現在腫瘤壞死因子誘導下，在第十五型脂氧酶基因剔除鼠血清中的單核細胞趨化蛋白-1明顯的比正常老鼠來的低。 總結本篇的研究結果，我們發現第五及第十五型脂氧酶抑制劑可以拮抗腫瘤壞死因子誘導之人類關節滑囊纖維母細胞的介白素-1β及介白素-6表現。此外我們也證實了人類關節滑囊纖維母細胞在腫瘤壞死因子誘導下第五及第十五型脂氧酶與細胞激素以及化學趨素的關係。在腫瘤壞死因子誘導下，第五及第十五型脂氧酶可能會藉由NF-κB訊息傳遞路徑去調控細胞激素以及化學趨素的表現。此外，第五及第十五型脂氧酶在腫瘤壞死因子所誘導的發炎現象，在活體中亦扮演了一個重要的角色。我們的實驗結果更進一步的確立第五及第十五型脂氧酶路徑與類風濕性關節炎病理的功能性關係，未來或許可以成為類風濕性關節炎新治療方式之標的。

Rheumatoid arthritis is a chronic progressive autoimmune disease characterized by synovium inflammation, cartilage destruction, and bone erosion. There are about 0.5~1% of adults affected by this disease and the incidence ranges from 5 to 50 per 100000 adults in developed region, especially in elders and women. TNF-α, one of the remarkable pro-inflammatory cytokines, is perceived to be important in the pathogenesis of RA including its abilities to induce the production of pro-inflammatory cytokines, such as IL-1 and IL-6. In addition, it also enable to amplify the immune response such as leukocyte accumulation and pro-inflammatory mediators release, such as leukotriene or 15-hydroxyeicosatetraenoic acid (15-HETE), metabolites of 5- or 15-lipoxygenase. It has been reported that lipoxygenase isoforms, including both 5- and 15-lipoxygenase (LOX), which can catalyze the endogenous arachidonic acid to leukotrienes or 15-HETE, are overexpressed in human RA synovium tissue. Its metabolism products, leukotrienes and 15-Hydroxyeicosatetraenoic acid (15-HETE), are involved in the pathogenesis of RA that promote release of pro-inflammatory mediators, including interleukin-6 and monocyte chemo-attractant protein-1 (MCP-1). Since TNF-α can enhance the expression of lipoxygenase and its downstream metabolites, which further promote the release of pro-inflammatory mediators such as IL-1, IL-6, and MCP-1. Therefore, the aim of this study was to investigate whether lipoxygenase pathways mediated TNF-α-induced production of cytokines and chemokines in vitro and in vivo. In the present study, we found that exposure of human synovial fibroblasts to TNF-α (10ng/ml) led to increase of IL-1β and IL-6 mRNA and protein expression. We thus further investigated the role of 5- and 15-LOX inhibitor in human synovial fibroblasts in TNF-α-induced cytokines and chemokines production. Treatment with 5- or 15-LOX inhibitor decreased the TNF-α-induced mRNA and protein upregulation of IL-6 and MCP-1 in human synovial fibroblasts. On the other hand, treatment with 5- or 15-LOX downstream metabolites, LTB4 or 15-(S)-HETE enhanced the expression of IL-6. We then investigated the signaling mechanism by which 5- or 15-LOX inhibitor antagonized TNF-α-induced cytokines and chemokines expression. The results showed that TNF-α increased IKKα/B activation, IκBα phosphorylation and degradation while pretreatment with 5- or 15-LOX inhibitor antagonized such response in human synovial fibroblasts. Furthermore, pretreatment with 5- or 15-LOX inhibitor antagonized the TNF-α-induced nuclear translocation of NF-κB subunits, p65 and p50, in Western blotting analysis and immunofluorescent staining. Transfection with the specific 5- or 15-LOX small hairpin RNA (shRNA) in human synovial fibroblasts found that knockdown of 5- or 15-LOX significantly inhibited TNF-α-induced IL-6 and MCP-1 protein expression. We finally explored the role of 5- or 15-LOX in TNF-α-induced inflammation in the animal model. TNF-α injection increased MCP-1 protein expression in mice serum while co-treatment with 5-LOX inhibitor NDGA antagonized such response. In addition, MCP-1 protein expression in 15-LOX knockout mice serum was significantly reduced comparing with wild-type mice following TNF-α treatment. In conclusion, TNF-α enhanced cytokine and chemokine mRNA and protein expression in human RA synovial fibroblasts, which could be antagonized by pretreatment of 5- or 15-LOX inhibitor. The inhibition of TNF-α-induced cytokines and chemokines expression by 5- or 15-LOX inhibitor may be due to the inhibition of NF-κB signaling. Moreover, 5- or 15-LOX plays an important role in TNF-α-induced inflammation in vivo. Our results demonstrate the involvement of 5- or 15-LOX in the pathophysiology of RA and may provide a new target for RA therapy.