Cartilage Mechanics in Small Animal Models of OA

描述（由申请人提供）：Xl型胶原蛋白在控制关节软骨的微观结构组织和组成中起重要作用。该项目的长期目标是确定Xl型胶原蛋白基因突变如何导致骨关节炎（OA）的关节软骨破坏。Col11a1基因突变序列杂合的小鼠发育正常，但会出现早发性OA。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下降和相关的OA局部表达。因此，我们假设在该模型中，机械因素通过使软骨细胞外基质暴露于加载时改变的应力和应变的功能变化而引发OA。我们提出了在这种转基因小鼠模型中机械诱导OA的机制，其中突变型Xl胶原基因产物的表达导致：(1)软骨拉伸性能的改变与胶原纤维组织的改变有关；(2)与改性蛋白聚糖含量相关的软骨压缩性能的变化。我们进一步提出，Xl型胶原蛋白基因突变影响小鼠关节软骨更高度组织的区域，即浅表区。在1月龄时对膝关节和髋关节软骨进行研究，以量化可能使关节易患OA的早期变化。软骨拉伸性能将使用渗透加载法进行量化，胶原纤维取向将使用光学双折射测量。软骨压缩性能将通过压痕测试和负固定电荷密度来量化，从红花素- o染色的密度测量中，作为组织S-GAG含量的测量。软骨将比较具有高度组织的浅表区（即股髁和股骨头）和具有更随机定向的胶原网络（即胫骨平台）的部位。为了描述野生型和突变型关节软骨破坏的时间过程，我们将量化9个月大的小鼠的组织形态学等级、软骨蛋白和/或相关蛋白酶、细胞因子和炎症介质前体的mRNA水平。这项研究的完成可能会揭示胶原突变导致OA的机制，并将阐明机械刺激、蛋白水解和炎症之间的时间相互作用。

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.