Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States.
J Struct Biol. 2011 Jan;173(1):146-52. doi: 10.1016/j.jsb.2010.08.003. Epub 2010 Aug 7.
Bone has a complex hierarchical structure that has evolved to serve structural and metabolic roles in the body. Due to the complexity of bone structure and the number of diseases which affect the ultrastructural constituents of bone, it is important to develop quantitative methods to assess bone nanoscale properties. Autosomal dominant Osteogenesis Imperfecta results predominantly from glycine substitutions (80%) and splice site mutations (20%) in the genes encoding the α1 or α2 chains of Type I collagen. Genotype-phenotype correlations using over 830 collagen mutations have revealed that lethal mutations are located in regions crucial for collagen-ligand binding in the matrix. However, few of these correlations have been extended to collagen structure in bone. Here, an atomic force microscopy-based approach was used to image and quantitatively analyze the D-periodic spacing of Type I collagen fibrils in femora from heterozygous (Brtl/+) mice (α1(I)G349C), compared to wild type (WT) littermates. This disease system has a well-defined change in the col1α1 allele, leading to a well characterized alteration in collagen protein structure, which are directly related to altered Type I collagen nanoscale morphology, as measured by the D-periodic spacing. In Brtl/+ bone, the D-periodic spacing shows significantly greater variability on average and along the length of the bone compared to WT, although the average spacing was unchanged. Brtl/+ bone also had a significant difference in the population distribution of collagen D-period spacings. These changes may be due to the mutant collagen structure, or to the heterogeneity of collagen monomers in the Brtl/+ matrix. These observations at the nanoscale level provide insight into the structural basis for changes present in bone composition, geometry and mechanical integrity in Brtl/+ bones. Further studies are necessary to link these morphological observations to nanoscale mechanical integrity.
骨骼具有复杂的层次结构，这种结构的进化是为了在体内发挥结构和代谢作用。由于骨骼结构的复杂性和影响骨骼超微结构成分的疾病数量众多，因此开发定量方法来评估骨骼纳米尺度特性非常重要。常染色体显性遗传性骨不全症主要由编码Ⅰ型胶原α1或α2链的基因中的甘氨酸取代（80%）和剪接位点突变（20%）引起。使用超过 830 种胶原突变进行的基因型-表型相关性研究表明，致死突变位于基质中胶原配体结合的关键区域。然而，这些相关性很少扩展到骨骼中的胶原结构。在这里，使用基于原子力显微镜的方法来比较杂合子（Brtl/+）小鼠（α1（I）G349C）和野生型（WT）同窝仔鼠的股骨中Ⅰ型胶原原纤维的 D 周期间距，进行成像和定量分析。在这种疾病系统中，col1α1 等位基因发生了明确的变化，导致胶原蛋白结构发生了很好的特征性改变，这与Ⅰ型胶原纳米形态的改变直接相关，如 D 周期间距所示。在 Brtl/+骨中，D 周期间距的平均值和沿骨长度的变化明显更大，尽管平均间距没有变化。Brtl/+骨中胶原 D 周期间距的群体分布也存在显著差异。这些变化可能是由于突变胶原结构，或 Brtl/+基质中胶原单体的异质性所致。这些在纳米尺度上的观察结果为 Brtl/+骨骼中存在的骨骼成分、几何形状和机械完整性变化的结构基础提供了深入的了解。进一步的研究有必要将这些形态学观察结果与纳米尺度的机械完整性联系起来。
