Objective 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. Methods 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. Results 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. Conclusion Collectively, our data suggest that Ab that specifically inhibit sdc4 dimerisation may support anti-IL-1 strategies in diseases such as inflammatory arthritis.

中文翻译：

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抗体介导的对 syndecan-4 二聚化的抑制减少了白细胞介素 (IL)-1 受体的运输和信号传导

目的 Syndecan-4 (sdc4) 是一种细胞锚定蛋白聚糖，由跨膜核心蛋白和葡糖胺聚糖 (GAG) 侧链组成。可溶性因子与 sdc4 的 GAG 链的结合可能导致 sdc4 的二聚化和下游信号级联的启动。然而，sdc4 二聚化和信号传导如何影响细胞对炎症刺激的反应的问题尚不清楚。方法对类风湿性关节炎（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 的产生。使用免疫沉淀研究了 IL-1 与 sdc4 的结合。IL-1 受体 (IL1R1) 在野生型上染色，sdc4 和 IL1R1 敲除成纤维细胞在荧光激活细胞分选分析中进行。使用阻断 sdc4 抗体研究人肿瘤坏死因子-α 转基因小鼠中的 sdc4 二聚化、IL1R1 表达和组织学爪破坏。结果我们表明，在成纤维细胞中，sdc4 的缺失或抗体介导的 sdc4 二聚化抑制降低了 IL-1R 的细胞表面表达，并调节了成纤维细胞对 IL-1 的敏感性。我们证明 IL-1 直接与 sdc4 结合，并以不依赖 IL-1R 的方式导致其二聚化。IL-1 诱导的 sdc4 二聚化调节小窝蛋白囊泡介导的 IL1R1 运输，这反过来决定了对 IL-1 的反应。施用针对 sdc4 二聚化结构域的抗体 (Ab)，因此，在体外和人类 RA 的动物模型中，强烈降低关节炎成纤维细胞上 IL1R1 的表达。结论 总的来说，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中的抗 IL-1 策略。