Investigation of Collagen as a Smart Engineering Material

描述（由申请人提供）：仅骨关节炎就使10%的60岁以上的美国人残疾，据估计，美国经济每年损失超过600亿美元。关节炎只是严重影响患者生活质量的一系列胶原蛋白相关疾病中的一个例子。胶原蛋白是动物体内最主要的拉伸承重分子，它负责我们与周围机械世界相互作用的能力。第一批后生动物是近8亿年前胶原蛋白进化的直接结果。在此之前，生命被限制在单个细胞的范围内。胶原蛋白是一种由gly-x-y序列组成的三螺旋分子（其中x和y分别代表脯氨酸和羟基脯氨酸），是将动物结合在一起的物质。与这一观点一致的事实是，纤维状胶原（I、II、III、V和XI）几乎总是处于张力状态。即使在软骨中，施加的压缩载荷是由糖胺聚糖上的固定电荷携带的，II型胶原原纤维也处于张力状态。纤维胶原具有显著的纵向和径向自组装能力。它们还具有很高的机械强度。然而，在本提案中，我们认为纤维胶原蛋白最重要的特征是它们构成了“智能”工程材料的基本构建块。具体来说，回顾文献和我们自己的初步数据表明，在机械拉伸载荷下的纤维胶原比未载荷的胶原更能抵抗高温变性和细菌胶原酶降解。如果基质金属蛋白酶（MMP）降解也是如此，那么胶原/MMP酶动力学将是菌株的函数。简而言之，当暴露于MMP中时，装载或“使用”的胶原蛋白不太可能降解。因此，在分解代谢分子和合成代谢分子存在的情况下，对施加机械负荷的基质适应性可以进行。这样就不需要成纤维细胞“选择”要去除的分子。菌株的状态将决定可用酶的有效性。为了验证这一假设，具有高度各向异性组织和单分子的脱细胞胶原基质将在不同的机械负荷下受到MMPs。纤维在大块组织中的降解模式和单个分子的裂解速率将被记录下来。如果胶原蛋白的分裂是应变的作用，那么对胶原蛋白的生成、体内平衡和疾病的影响是显而易见的。

DESCRIPTION (provided by applicant): Osteoarthritis alone disables 10% of Americans older than 60 and is estimated to cost the US economy more than $60 billion annually. Arthritis is just one example of a constellation of collagen-related diseases that severely affect the quality of life of patients. As the principle tensile load-bearing molecule in animals, collagen is responsible for our ability to interact with the mechanical world around us. The first metazoans were a direct result of the evolution of collagen nearly 800 million years ago. Prior to this time, life was restricted to the confines of a single cell. Collagen, a triple helical molecule comprising the sequence gly-x-y (where x and y are typically proline and hydroxyproline respectively), is the material that binds animals together. Consistent with this idea is the fact that fibrillar collagens (I, II, III, V and XI) are virtually always found in tension. Even in cartilage, where the applied compressive load is carried by the fixed charges on glycosaminoglycans, the type II collagen fibrils are loaded in tension. Fibrillar collagens have the remarkable ability to self-assemble both longitudinally and radially. They also possess high mechanical strength. However, in this proposal we suggest that the most important feature of fibrillar collagens is that they comprise the basic building blocks of a "smart" engineering material. Specifically, review of literature and our own preliminary data show that fibrillar collagen under a mechanical tensile load is more resistant than unloaded collagen to both high temperature denaturation and to bacterial collagenase degradation. If this is also true for matrix metalloproteinase (MMP) degradation, then collagen/MMP enzyme kinetics would be a function of strain. In short, collagen that is loaded or "in use" would be less likely to degrade when exposed to MMP. Thus, matrix adaptation to applied mechanical load could proceed in the presence of both catabolic and anabolic molecules. Fibroblasts would not then be required to "select" molecules for removal. The state of strain would determine the effectiveness of available enzymes. To test this hypothesis, acellular collagenous matrices with highly anisotropic organization and single molecules will be subjected to MMPs in the presence of varying mechanical loads. The pattern of fibrillar degradation in the bulk tissue and the rate of cleavage of the single molecules will be recorded. If collagen cleavage is a function of strain, then the implications for collagen genesis, homeostasis and disease are apparent.