Yamaguchi Ryosuke, Kamiya Nobuhiro, Adapala Naga Suresh, Drissi Hicham, Kim Harry K W
Center for Excellence in Hip Disorders, Texas Scottish Rite Hospital for Children, Dallas, Texas Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, Texas.
Faculty of Budo and Sport Studies, Tenri University, Tenri, Nara, Japan.
J Bone Joint Surg Am. 2016 Jul 6;98(13):1122-31. doi: 10.2106/JBJS.15.01209.
Ischemic osteonecrosis of the femoral head in children is associated with chronic hip synovitis and increased levels of the pro-inflammatory cytokine interleukin-6 (IL-6) in the synovial fluid due to unknown mechanisms. The purpose of this study was to investigate hypoxia-inducible factor-1 (HIF-1) activation as a molecular mechanism linking the induction of ischemic osteonecrosis to IL-6 production and the initiation of hip synovitis.
Ischemic osteonecrosis was surgically induced in the right femoral head of 6 piglets. A histologic score, synovial fluid volume, and IL-6 level were used to assess hip synovitis. IL-6 immunostaining of articular cartilage and synovial tissue was performed as well. To study the role of HIF-1 in IL-6 activation, in vitro experiments using an HIF-1α activator (deferoxamine) and inhibitor (HIF-1 small interfering-RNA [siRNA]) were carried out. Synovial cell responses to hypoxic chondrocyte-conditioned media with and without an IL-6 receptor blocker (tocilizumab) were assessed on the basis of IL-1β and tumor necrosis factor-alpha (TNF-α) gene expressions and with a synovial cell-proliferation assay.
Induction of ischemic osteonecrosis produced hip synovitis and increased IL-6 levels in the synovial fluid. Immunostaining and protein analysis demonstrated articular chondrocytes as a source of increased IL-6 production. When articular chondrocytes were cultured under hypoxic conditions, significantly increased HIF-1α and IL-6 expressions were observed. Under hypoxic culture conditions, IL-6 gene expression was significantly increased by HIF-1α activation using deferoxamine and inhibited by HIF-1α inhibition using HIF-1 siRNA. Synovial cells exposed to hypoxic chondrocyte-conditioned medium showed significant increases in IL-1β and TNF-α gene expressions and cell proliferation, which were inhibited by the IL-6 receptor blocker tocilizumab.
Induction of ischemic osteonecrosis results in IL-6 production in the articular cartilage through an HIF-1-dependent pathway. IL-6 produced by hypoxic articular chondrocytes stimulates inflammatory cytokine responses in synovial cells, which were significantly decreased by tocilizumab.
This study provides new insight into the inherent relationship between the induction of ischemia and the initiation of hip synovitis following ischemic osteonecrosis and suggests a potential therapeutic target in the treatment of the synovitis.
儿童股骨头缺血性坏死与慢性髋关节滑膜炎相关，且由于未知机制，滑液中促炎细胞因子白细胞介素-6（IL-6）水平升高。本研究的目的是探究缺氧诱导因子-1（HIF-1）激活作为一种分子机制，将缺血性坏死的诱导与IL-6产生及髋关节滑膜炎的起始联系起来。
通过手术诱导6只仔猪右侧股骨头发生缺血性坏死。采用组织学评分、滑液体积和IL-6水平来评估髋关节滑膜炎。还对关节软骨和滑膜组织进行了IL-6免疫染色。为研究HIF-1在IL-6激活中的作用，进行了使用HIF-1α激活剂（去铁胺）和抑制剂（HIF-1小干扰RNA [siRNA]）的体外实验。根据IL-1β和肿瘤坏死因子-α（TNF-α）基因表达以及滑膜细胞增殖试验，评估滑膜细胞对含和不含IL-6受体阻滞剂（托珠单抗）的缺氧软骨细胞条件培养基的反应。
缺血性坏死的诱导导致髋关节滑膜炎，并使滑液中IL-6水平升高。免疫染色和蛋白质分析表明关节软骨细胞是IL-6产生增加的来源。当关节软骨细胞在缺氧条件下培养时，观察到HIF-1α和IL-6表达显著增加。在缺氧培养条件下，使用去铁胺激活HIF-1α可显著增加IL-6基因表达，而使用HIF-1 siRNA抑制HIF-1α则可抑制该表达。暴露于缺氧软骨细胞条件培养基的滑膜细胞显示IL-1β和TNF-α基因表达及细胞增殖显著增加，而IL-6受体阻滞剂托珠单抗可抑制这些增加。
缺血性坏死的诱导通过HIF-1依赖途径导致关节软骨中产生IL-6。缺氧关节软骨细胞产生的IL-6刺激滑膜细胞中的炎性细胞因子反应，而托珠单抗可显著降低这些反应。
本研究为缺血性坏死诱导与缺血性坏死后髋关节滑膜炎起始之间的内在关系提供了新见解，并提示了滑膜炎治疗中的潜在治疗靶点。
