Institute of Musculoskeletal Medicine (IMM), University Muenster, Muenster, Germany.
Department of Orthopaedic Surgery, Otto-von-Guericke University, Magdeburg, Germany.
Ann Rheum Dis. 2020 Apr;79(4):481-489. doi: 10.1136/annrheumdis-2019-216847. Epub 2020 Feb 24.
Syndecan-4 (sdc4) is a cell-anchored proteoglycan that consists of a transmembrane core protein and glucosaminoglycan (GAG) side chains. Binding of soluble factors to the GAG chains of sdc4 may result in the dimerisation of sdc4 and the initiation of downstream signalling cascades. However, the question of how sdc4 dimerisation and signalling affects the response of cells to inflammatory stimuli is unknown.
Sdc4 immunostaining was performed on rheumatoid arthritis (RA) tissue sections. Interleukin (IL)-1 induced extracellular signal-regulated kinases (ERK) phosphorylation and matrix metalloproteinase-3 production was investigated. Il-1 binding to sdc4 was investigated using immunoprecipitation. IL-1 receptor (IL1R1) staining on wild-type, sdc4 and IL1R1 knockout fibroblasts was performed in fluorescence-activated cell sorting analyses. A blocking sdc4 antibody was used to investigate sdc4 dimerisation, IL1R1 expression and the histological paw destruction in the human tumour necrosis factor-alpha transgenic mouse.
We show that in fibroblasts, the loss of sdc4 or the antibody-mediated inhibition of sdc4 dimerisation reduces the cell surface expression of the IL-1R and regulates the sensitivity of fibroblasts to IL-1. We demonstrate that IL-1 directly binds to sdc4 and in an IL-1R-independent manner leads to its dimerisation. IL-1-induced dimerisation of sdc4 regulates caveolin vesicle-mediated trafficking of the IL1R1, which in turn determines the responsiveness to IL-1. Administration of antibodies (Ab) against the dimerisation domain of sdc4, thus, strongly reduces the expression IL1R1 on arthritic fibroblasts both in vitro and an animal model of human RA.
Collectively, our data suggest that Ab that specifically inhibit sdc4 dimerisation may support anti-IL-1 strategies in diseases such as inflammatory arthritis.
连接蛋白-4（sdc4）是一种细胞锚定蛋白聚糖，由跨膜核心蛋白和糖胺聚糖（GAG）侧链组成。可溶性因子与 sdc4 的 GAG 链结合，可能导致 sdc4 二聚化，并启动下游信号级联反应。然而，sdc4 二聚化和信号转导如何影响细胞对炎症刺激的反应尚不清楚。
对类风湿关节炎（RA）组织切片进行 sdc4 免疫染色。研究了白细胞介素（IL）-1 诱导的细胞外信号调节激酶（ERK）磷酸化和基质金属蛋白酶-3 产生。采用免疫沉淀法研究 IL-1 与 sdc4 的结合。采用流式细胞术分析野生型、sdc4 和 IL1R1 敲除成纤维细胞上的 IL1R1 染色。用阻断 sdc4 的抗体研究 sdc4 二聚化、IL1R1 表达以及在人肿瘤坏死因子-α转基因小鼠中的组织学爪破坏。
我们表明，在成纤维细胞中，sdc4 的缺失或 sdc4 二聚化的抗体抑制降低了 IL-1R 的细胞表面表达，并调节成纤维细胞对 IL-1 的敏感性。我们证明 IL-1 直接与 sdc4 结合，并以 IL-1R 非依赖性的方式导致其二聚化。IL-1 诱导的 sdc4 二聚化调节了 IL1R1 的小窝蛋白囊泡介导的转运，进而决定了对 IL-1 的反应性。因此，在体外和人类 RA 动物模型中，针对 sdc4 二聚化结构域的 Ab 的给药强烈降低了关节炎成纤维细胞上的 IL1R1 表达。
总之，我们的数据表明，特异性抑制 sdc4 二聚化的 Ab 可能支持炎症性关节炎等疾病的抗 IL-1 策略。
