CD44 MEDIATED CATABOLISM OF HYALURONAN BY CHONDROCYTES

CD44 介导软骨细胞对透明质酸的分解代谢

• 批准号: 7119261
• 负责人: Warren Knudson
• 金额: $ 27.55万
• 依托单位: EAST CAROLINA UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-09-30 至 2010-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7119261
• 关键词: CD44 molecule; animal tissue; antigen receptors; articular cartilage; biotransformation; cell membrane; chondrocytes; chondroitin sulfates; clinical research; endocytosis; enzyme activity; fatty acylation; human tissue; hyaluronate; immunoprecipitation; metalloendopeptidases; osteoarthritis; palmitates; protein degradation; protein isoforms; proteoglycan; proteolysis; receptor binding; receptor expression

DESCRIPTION (provided by applicant): The underlying new hypothesis of this proposal is that CD44 receptor-mediated endocytosis of hyaluronan (HA) provides a mechanism for chondrocytes to regulate local proteolytic events in the turnover of aggrecan proteoglycan (PG). During the current funding period we have determined that the local turnover of HA in cartilage occurs by CD44-mediated endocytosis, as there is no contribution of membrane-associated hyaluronidases to extracellular HA degradation. In addition we have determined that the ITEGE and DIPEN-containing aggrecan G1 domains-domains that remain bound to HA following proteolytic cleavage of PG, are co-internalized with HA by the same CD44-mediated mechanism. Furthermore, we have also shown that when metabolism is altered, and chondrocytes become more "catabolic" due to IL-1 treatment, there is an increase in CD44 expression by 6-8 fold at the protein level -- a change that increases the internalization of HA by 3 fold above control. Another critical observation that we made was that HA decorated with intact proteoglycan monomers cannot be internalized. Thus, for HA turnover to proceed, cleavage of PG within or near the G1-G2 domains is a prerequisite event. We propose that the presence of intact, highly-sulfated PG bound to HA establishes a resistance that inhibits CD44-mediated HA endocytosis. However the active cell-mediated processes that drive endocytosis also generate a focal clustering of PG aggregates, setting the stage for targeted PG degradation. Our new exciting data demonstrates that chondrocyte CD44 clusters into lipid raft microdomains as a prerequisite for endocytosis. We can now selectively manipulate CD44-mediated endocytosis of HA and determine the resultant effect on the rate of PG degradation. We will also determine whether CD44 serves as a raft-anchoring platform for MMP and ADAMTS proteinases- proteinases that recently have been shown to be present as active membrane-bound enzymes. Thus, the focus of this proposal is to determine the mechanistic link between HA endocytosis and PG degradation.

描述（由申请方提供）：该提议的潜在新假设是，CD 44受体介导的透明质酸（HA）内吞作用为软骨细胞提供了一种机制，以调节聚集蛋白聚糖（PG）周转中的局部蛋白水解事件。在目前的资助期间，我们已经确定，局部营业额的HA在软骨中发生的CD 44介导的内吞作用，因为没有贡献的膜相关的透明质酸酶的细胞外HA降解。此外，我们已经确定，含有ITEGE和DIPEN的聚集蛋白聚糖G1结构域-在PG的蛋白水解裂解后保持与HA结合的结构域通过相同的CD 44介导的机制与HA共内化。此外，我们还表明，当代谢改变时，软骨细胞由于IL-1处理而变得更加“分解代谢”，在蛋白质水平上CD 44表达增加6-8倍--这种变化使HA的内化增加3倍，高于对照。我们的另一个关键观察是，用完整的蛋白聚糖单体修饰的HA不能被内化。因此，为了进行HA周转，G1-G2结构域内或附近的PG裂解是先决条件。我们认为，完整的，高度硫酸化的PG结合HA的存在下建立了一个阻力，抑制CD 44介导的HA内吞作用。然而，驱动内吞作用的活性细胞介导的过程也产生PG聚集体的焦点聚集，为靶向PG降解奠定基础。我们的新的令人兴奋的数据表明，软骨细胞CD 44簇成脂筏微结构域作为内吞作用的先决条件。我们现在可以选择性地操纵CD 44介导的HA内吞作用，并确定对PG降解速率的影响。我们还将确定CD 44是否作为MMP和ADAMTS蛋白酶的筏锚定平台，这些蛋白酶最近已被证明是活性膜结合酶。因此，该建议的重点是确定HA内吞作用和PG降解之间的机制联系。