Calpain of Synovia and synovial fluid in arthritis

钙蛋白酶，又称钙活化中性蛋白酶（CAMP），是一种钙离子依赖性的中性半胱氨酸蛋白酶。存在两种形式的calpain，它们对Ca^<2+>的激活要求不同：mu-calpain，或calpain I需要低浓度（微摩尔）和m-calpain，或calpain II需要高浓度（毫摩尔）。已知还存在特异性抑制剂蛋白calpastatin。已知钙蛋白酶是细胞内蛋白酶。近年来的研究揭示了钙蛋白酶作为基质蛋白酶的一个新方面，即其对软骨蛋白多糖具有强大的蛋白酶活性。骨关节炎的滑膜液含有mu-calpain、m-calpain和calpastatin，并在细胞外发挥蛋白聚糖活性（Arthritis Rheum, 1990）。本研究的目的是阐明钙蛋白酶分泌到滑膜液中的负责细胞，并阐明钙蛋白酶在关节炎中的作用。用抗钙蛋白酶抗体对类风湿关节炎（RA）和骨关节炎（OA）的滑膜组织进行免疫组化染色。滑膜衬里细胞、内皮细胞和间质成纤维细胞显示钙蛋白酶免疫反应性。免疫印迹法对滑膜组织、滑膜液、培养的滑膜成纤维细胞、培养基均可见特异性钙蛋白酶条带。测定RA和OA患者滑液中钙蛋白酶活性。结果表明，该化合物具有降解钙蛋白酶的活性和抑制钙pastatin的活性。总降解活性高于抑制活性。这些数据有力地表明，钙蛋白酶从滑膜细胞分泌到滑膜液中，钙蛋白酶有助于骨关节炎中软骨基质和其他已知基质蛋白酶的降解。

Calpain, also called Calcium-activated neutral proteinase (CAMP) , is a calcium ion-dependent neutral cysteine proteinase. Two forms of calpain are present, and they differ in their Ca^<2+> requirements for activation : mu-calpain, or calpain I requires low concentrations (micromolar) and m-calpain, or calpain II requires high concentrations (millimolar) . Specific inhibitor protein, calpastatin, is also known to exist. Calpains have been known to be intracellular proteinases. Recent studies elucidated a new aspect of calpain as a matrix proteinase with its potent proteinase activities against cartilage proteoglycan. Osteoarthritic synovial fluid contains mu-calpain, m-calpain and calpastatin and exerting proteoglycanse activities extracellularly (Arthritis Rheum 1990) . The present study was performed with the object of elucidating responsible cells for secretion of calpain into synovial fluid and to clarify function of calpain in arthritis. Synovial tissues from rheumatoid arthritis (RA) and Osteoarthritis (OA) was stained immunohistochemically using anti-calpain antibody. Calpain immunoreactivity was demonstrated in synovial lining cell, endothelial cells, and interstitial fibroblast. Immunoblot of synovial tissues, synovial fluid, cultured synovial fibroblast, culture medium showed specific band of calpain. Calpain activity was assayd in synovial fluids of RA and OA.The results showed both degrading activity of calpain and inhibitory activity of calpastatin. Total degrading activity was higher than inhibitory activity. These data strongly suggest that calpain is secreted from synovial cells into synovial fluid and that calpain contributes to degradation of cartilage matrix as well as other known matrix proteinases in osteoarthritis.