Calpain of Synovia and synovial fluid in arthritis

钙蛋白酶（Calpain）又称钙激活中性蛋白酶（Calcium-activated neutral proteinase，CAMP），是一种钙离子依赖性中性半胱氨酸蛋白酶。钙蛋白酶有两种形式，它们激活所需的Ca^2+不同：μ-钙蛋白酶或钙蛋白酶I需要低浓度（微摩尔），而m-钙蛋白酶或钙蛋白酶II需要高浓度（毫摩尔）。特异性抑制蛋白，钙蛋白酶抑制蛋白，也已知存在。钙蛋白酶是细胞内的蛋白酶。最近的研究阐明了钙蛋白酶作为一种基质蛋白酶的一个新的方面，其强大的蛋白酶活性对软骨蛋白多糖。骨关节炎滑液含有μ-钙蛋白酶、m-钙蛋白酶和钙蛋白酶抑制剂，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液中的负责细胞，并阐明钙蛋白酶在关节炎中的功能。用抗钙蛋白酶抗体对类风湿性关节炎（RA）和骨关节炎（OA）的滑膜组织进行免疫组化染色。Calpain在滑膜衬里层细胞、内皮细胞和间质成纤维细胞中表达。滑膜组织、滑膜液、培养的滑膜成纤维细胞、培养液免疫印迹显示钙蛋白酶特异性条带。测定了RA和OA关节液中钙蛋白酶活性，结果显示钙蛋白酶既有降解活性，又有抑制活性。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液中，并且钙蛋白酶有助于软骨基质的降解以及骨关节炎中的其他已知基质蛋白酶。

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.