Genetic Analysis of Hip Fragility

描述（由申请人提供）：2001年，我们小组开始研究骨脆性的遗传原因。我们选择研究大鼠，而不是小鼠，因为实验室大鼠已被证明是人类骨质疏松症等骨骼疾病的绝佳模型。由于大鼠比小鼠大，因此更容易测量股骨颈的骨骼结构和强度，股骨颈是骨骼的主要焦点部位。我们的第一项研究涉及Fischer 344 （F344）和Lewis （LEW）大鼠的杂交。我们的第二项研究重点是哥本哈根2331 （COP）和Dark Agouti （DA）大鼠，于2003年开始，是这项竞争性更新申请的主题。我们已经成功地绘制了股骨颈和股骨中轴表型的数量性状位点（qtl），这是该项目的主要和次要目标。我们过去五年的工作为我们未来五年的研究方向提供了明确的方向：我们将在qtl中识别影响骨生物学的基因。这个项目有三个目的。首先，我们将在两个效应最大的qtl中鉴定致病基因：F344和LEW大鼠的染色体（Chr） 4（13%效应）和COP和DA大鼠的染色体（Chr） 1（14%效应）。我们计划建立同源大鼠模型，进行基因表达谱分析，随后进行体内功能研究，并利用培养的成骨细胞和破骨细胞鉴定直接影响骨生物学的基因。其次，我们将与一个大型的全球研究联盟合作，在异种种群（HS）大鼠中进行基因组全关联研究（GWAS）。由Jonathan Flint领导的GWAS将提供2000多只大鼠的表型和基因型。表型将包括：行为、代谢、血液学、血液动力学、免疫学和骨骼（我们的贡献）。每只大鼠将对大约20,000个单核苷酸多态性（snp）进行基因分型。这些结果将使我们能够识别影响骨骼特征的新QTL，并将每个QTL上的候选基因数量从几十个减少到几个。最后，我们将利用基因组筛选鉴定基因表达QTLs (eQTLs)，以绘制来自COP和DA祖先的2代（F2）大鼠的转录物丰度。单个基因表达的变异将被映射到基因组上的位置，以产生相等的qtl。eQTL定位允许人们识别表达水平与所选骨表型相关的顺式eQTL，以识别和优先考虑最有可能改变骨生物学的基因。此外，我们将识别由给定QTL控制的反基因，并利用这些信息构建复杂骨性状的基因网络。eQTL定位的另一个独特特征是它能够在全基因组范围内识别基因表达的等位基因特异性调控。这些目标的完成将加速我们在确定影响骨骼脆弱的基因方面的进展。公共卫生相关性：我们的研究将确定导致骨骼脆弱的基因。我们将在实验中使用几个近交系的大鼠，并应用现代遗传学技术，如基因表达微阵列和单核苷酸多态性基因分型。我们的目标是找到骨质疏松症等骨质疏松症的遗传原因，从而开发出更好的治疗方法。

DESCRIPTION (provided by applicant): In 2001, our group began studies to determine the genetics causes of bone fragility. We chose to study rats, rather than mice, because the laboratory rat has proven to be an excellent model for human bone disorders, like osteoporosis. Because rats are larger than mice, it is easier to measure bone structure and strength at the femoral neck, which is a skeletal site of primary focus. Our first study involved a cross between Fischer 344 (F344) and Lewis (LEW) rats. Our second study focusing on Copenhagen 2331 (COP) and Dark Agouti (DA) rats began in 2003 and is the subject of this competitive renewal application. We have successfully mapped quantitative trait loci (QTLs) for femoral neck and femoral midshaft phenotypes, the primary and secondary goals of the project. Our work in the past five years has provided a clear direction for our proposed research in the next five years: we will identify genes within QTLs that affect bone biology. This project has three Aims. First, we will identify causative genes within our two QTLs with largest effect size: Chromosome (Chr) 4 for F344 and LEW rats (13% effect) and Chr 1 for COP and DA rats (14% effect). We plan to generate congenic rat models and conduct gene expression profiling followed by functional studies in vivo and using cultured osteoblasts and osteoclasts to identify genes that directly affect bone biology. Second, we will work with a large, world-wide research consortium to conduct a genome wide association study (GWAS) in heterogeneous stock (HS) rats. The GWAS led by Jonathan Flint will provide phenotypes and genotypes for over 2000 rats. Phenotypes will include: behavioral, metabolic, hematological, hemodynamic, immunological and skeletal (our contribution). Each rat will be genotyped for about 20,000 single nucleotide polymorphisms (SNPs). The results will allow us to identify new QTLs that affect bone traits and to reduce the number of candidate genes at each QTL from several dozen to a mere handful. Finally, we will identify gene expression QTLs (eQTLs) using a genome screen to map transcript abundance in 2nd filial (F2) rats derived from COP and DA progenitors. Variations in expression of individual genes will be mapped to locations on the genome to produce eQTLs. eQTL mapping allows one to identify cis-eQTLs for which expression levels can be correlated with a chosen bone phenotype to identify and prioritize genes most likely to alter bone biology. Also, we will identify trans- genes controlled by a given QTL and with this information we will construct networks of genes that underlie complex bone traits. Another unique feature of eQTL mapping is its ability to identify allele-specific regulation of gene expression on a genome-wide scale. Completion of these Aims will accelerate our progress toward identifying genes that affect bone fragility. PUBLIC HEALTH RELEVANCE: Our study will identify genes that cause bone fragility. We will use several inbred strains of rats in our experiments and apply modern genetics techniques like gene expression microarrays and single nucleotide polymorphism genotyping. Our goal is to find genetic causes for bone weakening conditions like osteoporosis so better treatments can be developed.