Institute of Cellular Medicine, University of Newcastle upon Tyne, UK.
Cell Tissue Res. 2010 Jan;339(1):221-35. doi: 10.1007/s00441-009-0887-6. Epub 2009 Nov 14.
The joint is a discrete unit that consists of cartilage, bone, tendon and ligaments. These tissues are all composed of an extracellular matrix made of collagens, proteoglycans and specialised glycoproteins that are actively synthesised, precisely assembled and subsequently degraded by the resident connective tissue cells. A balance is maintained between matrix synthesis and degradation in healthy adult tissues. Different classes of proteinases play a part in connective tissue turnover in which active proteinases can cleave matrix protein during resorption, although the proteinase that predominates varies between different tissues and diseases. The metalloproteinases are potent enzymes that, once activated, degrade connective tissue and are inhibited by tissue inhibitors of metalloproteinases (TIMPs); the balance between active matrix metalloproteinases and TIMPs determines, in many tissues, the extent of extracellular matrix degradation. The serine proteinases are involved in the initiation of activation cascades and some, such as elastase, can directly degrade the matrix. Cysteine proteinases are responsible for the breakdown of collagen in bone following the removal of the osteoid layer and the attachment of osteoclasts to the exposed bone surface. Various growth factors increase the synthesis of matrix and proteinase inhibitors, whereas cytokines (alone or in combination) can inhibit matrix synthesis and stimulate proteinase production and matrix destruction.
关节是一个独立的单位，由软骨、骨、肌腱和韧带组成。这些组织都是由细胞外基质组成的，细胞外基质由胶原蛋白、蛋白聚糖和专门的糖蛋白组成，这些物质由驻留的结缔组织细胞主动合成、精确组装，然后降解。在健康的成年组织中，基质的合成和降解之间保持着平衡。不同类别的蛋白酶在结缔组织的更新中起作用，其中活性蛋白酶可以在吸收过程中分解基质蛋白，尽管在不同的组织和疾病中占主导地位的蛋白酶不同。金属蛋白酶是有效的酶，一旦被激活，就会降解结缔组织，并被金属蛋白酶抑制剂 (TIMPs) 抑制；在许多组织中，活性基质金属蛋白酶和 TIMPs 之间的平衡决定了细胞外基质降解的程度。丝氨酸蛋白酶参与激活级联的启动，一些蛋白酶，如弹性蛋白酶，可以直接降解基质。半胱氨酸蛋白酶负责在骨样层去除和破骨细胞附着在暴露的骨表面后分解骨胶原。各种生长因子增加基质和蛋白酶抑制剂的合成，而细胞因子（单独或联合）可以抑制基质合成并刺激蛋白酶产生和基质破坏。
