Chang X, Yamada R, Suzuki A, Sawada T, Yoshino S, Tokuhiro S, Yamamoto K
Laboratory for Rheumatic Diseases, SNP Research Center, Institute of Physical and Chemical Research (RIKEN), 1-7-22 Suehiro, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
Rheumatology (Oxford). 2005 Jan;44(1):40-50. doi: 10.1093/rheumatology/keh414. Epub 2004 Oct 5.
Peptidylarginine deiminases (PADIs) convert peptidylarginine into citrulline via post-translational modification. Anti-citrullinated peptide antibodies are highly specific for rheumatoid arthritis (RA). Our genome-wide case-control study of single-nucleotide polymorphisms found that the PADI4 gene polymorphism is closely associated with RA. Here, we localized the expression of PADI4 and the citrullinated protein product in synovial RA tissue.
We used immunohistochemistry, double immunofluorescent labelling and western blotting.
We found that PADI4 is extensively expressed in T cells, B cells, macrophages, neutrophils, fibroblast-like cells and endothelial cells in the lining and sublining areas of the RA synovium. We also found extracellular and intracellular expression of PADI4 in fibrin deposits with loose tissue structures where apoptosis was widespread. Unlike PADI4, citrullinated protein generally appeared in fibrin deposits that were abundant in the RA synovium. The citrullinated fibrin aggregate was immunoreactive against immunoglobulin (Ig) A and IgM, but not IgG and IgE. Although a little PADI4 was expressed in osteoarthritic and normal synovial tissues, significant citrullination was undetectable.
The results showed that PADI4 is mainly distributed in cells of various haematopoietic lineages and expressed at high levels in the inflamed RA synovium. The co-localization of PADI4, citrullinated protein and apoptotic cells in fibrin deposits suggests that PADI4 is responsible for fibrin citrullination and is involved in apoptosis. The immunoreactivity of citrullinated fibrin with IgA and IgM in the RA synovium supports the notion that citrullinated fibrin is a potential antigen of RA autoimmunity.
肽基精氨酸脱亚氨酶（PADIs）通过翻译后修饰将肽基精氨酸转化为瓜氨酸。抗瓜氨酸化肽抗体对类风湿关节炎（RA）具有高度特异性。我们对单核苷酸多态性进行的全基因组病例对照研究发现，PADI4基因多态性与RA密切相关。在此，我们定位了RA滑膜组织中PADI4的表达及瓜氨酸化蛋白产物。
我们采用了免疫组织化学、双重免疫荧光标记和蛋白质印迹法。
我们发现PADI4在RA滑膜衬里和衬里下层区域的T细胞、B细胞、巨噬细胞、中性粒细胞、成纤维样细胞和内皮细胞中广泛表达。我们还在组织结构疏松且凋亡广泛存在的纤维蛋白沉积物中发现了PADI4的细胞外和细胞内表达。与PADI4不同，瓜氨酸化蛋白通常出现在RA滑膜中丰富的纤维蛋白沉积物中。瓜氨酸化纤维蛋白聚集体对免疫球蛋白（Ig）A和IgM具有免疫反应性，但对IgG和IgE无反应。虽然在骨关节炎和正常滑膜组织中表达了少量PADI4，但未检测到明显的瓜氨酸化。
结果表明，PADI4主要分布于各种造血谱系的细胞中，并在炎症性RA滑膜中高水平表达。PADI4、瓜氨酸化蛋白和凋亡细胞在纤维蛋白沉积物中的共定位表明，PADI4负责纤维蛋白瓜氨酸化并参与凋亡。RA滑膜中瓜氨酸化纤维蛋白与IgA和IgM的免疫反应性支持了瓜氨酸化纤维蛋白是RA自身免疫潜在抗原的观点。
