GENETIC REGULATION OF IGF-I IN PEAK BONE DENSITY OF MICE

描述(由申请人提供)：胰岛素样生长因子I(IGF-I)是峰值骨获取的关键决定因素，IGF-I基因多态和骨密度(BMD)的相关性研究以及显著影响骨生长和维持的实验性基因组操作证明了这一点。我们最近的工作集中在一个工作假设上，即血清IGF-I表型是一种复杂的可遗传性状，由对骨获得至关重要的多个遗传因素决定，并可通过QTL(数量性状基因座)策略识别。我们先前定位了4个QTL，解释了两个近交系之间循环IGF-I差异的近一半：C3H/HeJ(C3H)和C57BL/6J(B6)。然后，我们在染色体(Chr)6上发现了一个主要的IGF-I QTL，该QTL与低血清IGF-I相关，特别是当与Chr 11中部区域的一个位点相互作用时。通过在B6背景(Igf1s1：6T)上导入C3H等位基因而产生该QTL的N10F2同源小鼠后，我们发现血清IGF-I与B6相比有显著差异，并显著降低了皮质和小梁BMD，并改变了脂肪分布。6T小鼠在肝脏、脂肪、肌肉和骨骼中的IGF-I mRNA转录也受到抑制，这反映在骨髓基质细胞的功能研究中，发现成骨细胞谱系的分配发生了重大变化。随后的实验使我们能够绕过遗传障碍(即在C3H中CHR 6上的倒位)，并将Igf1s1 QTL精细地定位到脂氧合酶过氧化物酶体增殖物-激活剂受体伽马(PPARGamma)途径中的两个基因。我们现在提出两个特定的目标来检验这一假设，即在Chr6和11上的QTL对IGF-I和BMD都有很强的交互作用：1-确定Chr 6上的Igf1s1基因并精细定位减少IGF-I表达和生产的Chr 11基因座；2-定义Igf1s1基因和Chr 11互作基因如何影响峰值骨获取。在这项提案中，我们将结合功能基因组学的专业知识与分子和基质细胞生物学的合作者来确定其交互伙伴IGF-I的主要调控基因，以及这些基因在成骨细胞和脂肪细胞谱系分配中的作用。

DESCRIPTION (provided by applicant): Insulin-like growth factor I (IGF-I) is a critical determinant of peak bone acquisition as demonstrated by association studies of IGF-I gene polymorphisms and bone mineral density (BMD), and experimental genomic manipulations that dramatically impact bone growth and maintenance. Our recent work has focused on the working hypothesis that the serum IGF-I phenotype is a complex heritable trait determined by multiple genetic factors critical for bone acquisition, and identifiable through a QTL (quantitative trait locus) strategy. We previously mapped 4 QTL accounting for nearly half the difference in circulating IGF-I between two inbred strains: C3H/HeJ (C3H) and C57BL/6J (B6). We then identified a major Igf-I QTL on chromosome (Chr) 6 which was associated with low serum IGF-I particularly when there was interaction with a locus on the mid region of Chr 11. After generating N10F2 congenic mice for this QTL by introgressing C3H alleles onto a B6 background (Igf1s1:6T), we found significant differences in serum IGF-I compared to B6 as well as markedly reduced cortical and trabecular BMD, and altered fat distribution. 6T mice also demonstrated suppression in hepatic, fat, muscle and skeletal IGF-I mRNA transcripts, which were reflected in functional studies of bone marrow stromal cells that revealed a major alteration in osteoblast lineage allocation. Subsequent experiments allowed us to bypass a genetic roadblock (i.e. an inversion on chr 6 in C3H) and fine map the Igf1s1 QTL to two genes in the lipoxygenase peroxisome proliferators-activator receptor gamma (Ppargamma) pathway. We now propose two specific aims to test the hypothesis that there is a strong interactive effect for the QTL on Chr 6 and 11 that influences both IGF-I and BMD: 1-Identify the Igf1s1 gene on chr 6 and fine map the Chr 11 locus that reduce IGF-I expression and production; 2- Define how the Igf1s1 gene and the Chr 11 interactive locus impact peak bone acquisition. In this proposal we will combine expertise in functional genomics with collaborators in molecular and stromal cell biology to identify a major regulatory gene for IGF-I, its interactive partner, and the role of these genes in osteoblast and adipocyte lineage allocation.