CD44 MEDIATED CATABOLISM OF HYALURONAN BY CHONDROCYTES

描述：（改编自申请人的摘要）：骨关节炎是一种 以关节退化为表现的严重衰弱性疾病 软骨衬里关节腔。 维护健康的软骨 取决于平衡所涉及的合成和降解过程 软骨细胞外基质的周转。 软骨细胞外 基质主要由胶原蛋白和蛋白聚糖组成 到另一种基质大分子透明质酸（HA）的单丝。 这个 反过来，HA 通过以下方式直接结合或锚定到软骨细胞膜上： 与 HA 受体蛋白（最近被鉴定为 CD44）相互作用。 大多数 软骨分解代谢的研究集中在细胞外 通过蛋白酶和蛋白酶抑制剂处理基质成分。 然而，参与软骨细胞外降解的酶 HA 从未被记录，HA 的其他细胞机制也没有记录 分解代谢。 尽管 HA 发挥着重要作用，但我们仍然缺乏这方面的知识。 在软骨细胞外基质的组织中发挥核心作用。 初步研究表明CD44受体介导内吞作用 HA 的细胞内降解。 HA的结合和内化 被 HA 六糖（HA 结合的竞争性抑制剂）阻断，如 以及抗CD44抗体。 HA 的小降解片段也 在细胞内检测到并且这些片段的产生被抑制 由溶酶体药物氯喹引起。 分解代谢细胞介质 上调 CD44 表达，导致软骨细胞容量增加 积累细胞内HA。 因此，第一次建立了一种机制 软骨细胞对 HA 的分解代谢正在不断发展。 具体目标 该提案旨在：(i) 确定 HA 内吞作用的确切速率， 包括各种大小的HA和用蛋白多糖片段“修饰”的HA 和连接蛋白； (ii) 确定 CD44 的表达水平如何影响 HA 内吞作用的速率。 第二个目标将涉及使用 软骨细胞培养物和培养物中 CD44 的反义抑制 完整的软骨组织切片； (iii) 表征 CD44 的变化和 衰老和疾病期间发生的人类软骨中同种型的表达。

DESCRIPTION: (Adapted from the Applicant's Abstract): Osteoarthritis is a severe debilitating disease manifested by degeneration of articular cartilage-lining joint cavities. The maintenance of healthy cartilage depends on balancing the synthetic and degradative processes involved in turnover of cartilage extracellular matrix. Cartilage extracellular matrices are composed predominately of collagen and proteoglycans tethered to single filaments of another matrix macromolecule, hyaluronan (HA). This HA, in turn, is bound or anchored directly to the chondrocyte membrane via interaction with an HA receptor protein, recently identified as CD44. Most studies of cartilage catabolism have centered on the extracellular processing of matrix components via proteases and protease inhibitors. However, enzymes(s) involved in the extracellular degradation of cartilage HA have never been documented, nor have other cellular mechanisms for HA catabolism. This knowledge is lacking despite the fact that HA plays a central role in the organization of cartilage extracellular matrix. Preliminary studies have shown that CD44 receptors mediate the endocytosis of HA for intracellular degradation. The binding and internalization of HA is blocked by HA hexasaccharides (competitive inhibitors of HA binding), as well as anti-CD44 antibodies. Small degradation fragments of HA are also detected intracellularly and the generation of these fragments is inhibited by the lysosomotropic agent, chloroquine. Catabolic cell mediators up-regulate CD44 expression, resulting in increased capacity of chondrocytes to accumulate intracellular HA. Thus for the first time, a mechanism for the catabolism of HA by the chondrocyte is evolving. The Specific Aims of this proposal are to: (i) determine the exact rates of HA endocytosis, including HA of various sizes and HA "decorated" with proteoglycan fragments and link protein; (ii) determine how the level of expression of CD44 affects the rate of HA endocytosis. This second aim will involve the use of antisense inhibition of CD44 in both chondrocyte cultures, and cultures of intact cartilage tissue slices; and (iii) characterize changes in CD44 and isoform expression in human cartilage that occur during aging and disease.