Cartilage Mechanics in Small Animal Models of OA

描述(申请人提供)：XL型胶原在控制关节软骨的微结构组织和组成方面起着重要作用。该项目的长期目标是确定XL型胶原基因突变如何在骨关节炎(OA)的关节软骨破坏中起作用。COL11A1基因突变序列杂合子的小鼠看起来发育正常，但会发生早发性骨性关节炎。我们的初步研究表明，这种胶原蛋白缺陷会导致局部软骨硬度降低，并伴随着局部骨关节炎的表达。因此，我们假设，在这个模型中，机械因素通过使软骨细胞外基质在加载时暴露于改变的应力和应变的功能变化来启动骨关节炎。我们提出了在这个转基因小鼠模型中机械诱导骨关节炎的机制，其中突变的XL型胶原基因产物的表达导致：(1)与胶原纤维组织的改变相关的软骨拉伸性能的改变；(2)与蛋白多糖含量改变相关的软骨压缩性能的改变。我们进一步提出，XL型胶原基因突变影响小鼠关节软骨组织更紧密的区域，即浅表区。对膝关节和髋关节软骨的研究将在1个月龄时进行，以量化可能使关节易患骨性关节炎的早期变化。软骨的拉伸性能将使用渗透加载方法进行量化，胶原纤维的取向将使用光学双折射进行测量。软骨的压缩性能将通过压痕试验和藏红花-O染色密度测量的负电荷密度来量化，作为组织S-GAG含量的测量。软骨将在具有高度组织的浅层(即股骨髁和股骨头)和那些具有更随机定向的胶原网络的位置(即胫骨平台)之间进行比较。为了描述野生型和突变型关节软骨破坏的时间过程，我们将对9月龄以下小鼠的组织形态计量学分级、软骨蛋白和/或相关的蛋白酶、细胞因子和炎症介质前体的mRNA水平进行量化。这项研究的完成可能会揭示这种胶原突变对骨性关节炎的作用机制，并将阐明机械刺激、蛋白分解和炎症在骨性关节炎发生中的时间相互作用。

DESCRIPTION (provided by applicant): Type Xl collagen plays important roles in controlling the microstructural organization and composition of articular cartilage. The long-term objective of this project is to determine how a type Xl collagen gene mutation contributes to articular cartilage destruction in osteoarthritis (OA). Mice heterozygous for a mutated sequence in the Col11a1 gene appear developmentally normal, but develop premature onset of OA. Our preliminary studies demonstrate that this collagen defect gives rise to local decreased cartilage stiffness and associated local expression of OA. Thus, we hypothesize that mechanical factors initiate OA in this model, through functional changes that expose the cartilage extracellular matrix to altered stresses and strains upon loading. We propose a mechanism for the mechanical induction of OA in this transgenic mouse model, whereby expression of the mutated type Xl collagen gene product leads to: (1) changes in cartilage tensile properties associated with modifications in collagen fiber organization; and (2) changes in cartilage compressive properties associated with modified proteoglycan content. We further propose that the type Xl collagen gene mutation affects the more highly organized regions of mouse articular cartilage, i.e., superficial zone. Studies of knee and hip joint cartilage will be performed at 1 month of age to quantify early changes that may predispose the joints to OA. Cartilage tensile properties will be quantified using an osmotic loading method, and collagen fiber orientation will be measured using optical birefringence. Cartilage compressive properties will be quantified with indentation tests and negative fixed charge density from densitometric measures of Safranin-O staining, as a measure of tissue S-GAG content. Cartilage will be compared between sites with a highly organized superficial zone (i.e., femoral condyle and femoral head), and those with a more randomly oriented collagen network (i.e., tibial plateau). To characterize the time course of cartilage destruction in wild-type and mutant joints, we will quantify histomorphometric grade, cartilage protein and/or mRNA levels of relevant proteinases, cytokines and precursors to inflammatory mediators in mice up to 9 months of age. Completion of this study may reveal the mechanism by which this collagen mutation contributes to OA and will illustrate the temporal interplay between mechanical stimuli, proteolysis and inflammation involved in OA development.