Mouse Models to Delineate a Unique Metabolic and Skeletal Network

描述（由申请人提供）：本提案的主要目标是利用我们实验室创建的小鼠模型，表征小鼠染色体（Chr） 6中部两个相邻基因多态性的骨骼和代谢影响。我们最初在两个自交系（C3H/HeJ[C3H]和C57BL/6[B6]）的杂交中发现了一个强烈影响骨获取峰值和IGF-I的数量性状位点（QTL）。我们随后创造了一只基因小鼠B6。C3H-6T（即6T），该基因座位于B6背景上。6T雌性小鼠具有显著的骨骼和代谢表型，包括非常低的峰值骨量，骨形成减少，低血清IGF-I，抑制瘦素浓度，显著的骨髓和肝脏肥胖，以及对高脂肪喂养的胰岛素敏感性。此外，我们能够通过增加膳食脂肪摄入量来挽救6T的小梁表型。我们发现Chr 6 QTL在一个非常小的基因组区域内携带至少6个基因，这些基因参与脂肪细胞和成骨细胞的分化，我们发现其中两个基因，Alox5和Pparg，不仅在6T骨髓基质细胞（MSCs）中被抑制，而且还携带多态性，影响它们的转录。此外，我们还发现了一个染色体反转，其断点位于Alox5的远端，位于基质分化因子-1 （SDF-1）基因高度保守的区域5'附近。因此，我们假设6T同源基因具有一个功能调控子，即在另一个调控基因的控制下，由一组不相邻的基因组成的遗传单元，并参与多效性功能。为了验证这一假设，我们提出了两个具体目标：1 .高脂肪饮食和Pparg激动剂治疗后6T， Alox5-/-和B6小鼠的综合代谢和骨骼表型；2 .利用高脂肪饮食和parg激动剂对6T、Alox5-/-和B6小鼠的MSCs、脂肪细胞和破骨细胞的体外研究，描述该调控如何影响Wnt/ b -连环蛋白和IGF-I网络。在第二个目标中，我们还将使用TOPGAL 6T和B6报告小鼠来确定Wnt/ b -连环蛋白系统的体内活性。

DESCRIPTION (provided by applicant): The primary goal of this proposal is to characterize the skeletal and metabolic effects of polymorphisms in two adjacent genes in the mid-region of mouse chromosome (Chr) 6, using mouse models created in our laboratory. We initially found a quantitative trait locus (QTL) that strongly influenced peak bone acquisition and IGF-I in a cross between two inbred strains (C3H/HeJ[C3H], and C57BL/6[B6]). We subsequently created a congenic mouse B6.C3H-6T (i.e. 6T) in which this locus was placed on a B6 background. 6T female mice had a remarkable skeletal and metabolic phenotype including very low peak bone mass, reduced bone formation, low serum IGF-I, suppressed leptin concentrations, significant marrow and hepatic adiposity, and insulin sensitivity in response to high fat feeding. In addition, we were able to rescue the trabecular phenotype of 6T by increasing dietary fat intake. We found that the Chr 6 QTL carried at least 6 genes within a very small genomic region that were involved in both adipocyte and osteoblast differentiation, and we showed two of these, Alox5 and Pparg, not only were suppressed in 6T marrow stromal cells (MSCs) but also carried polymorphisms which affected their transcription. Furthermore, we discovered a chromosomal inversion with a break point just distal to Alox5, in the vicinity of a highly conserved region 5' to the stromal differentiation factor-1 (SDF-1) gene. Hence we postulate that the 6T congenic has a functioning regulon, i.e. a genetic unit composed of a non-contiguous group of genes under the control of another regulatory gene, and which is involved in pleiotropic functions. To test that hypothesis, we propose two specific aims: 1-comprehensive metabolic and skeletal phenotyping of 6T, Alox5-/- and B6 mice on high fat diets and after treatment with Pparg agonists; 2-delineation of how this regulon influences the Wnt/B-catenin and IGF-I networks utilizing in vitro studies of MSCs, adipocytes and osteoclasts from 6T, Alox5-/- and B6 mice on high fat diets and Pparg agonists. In this 2nd aim we will also determine the in vivo activity of the Wnt/B-catenin system using TOPGAL 6T and B6 reporter mice. Relevance to Public Health Successful completion of this proposal will shed new light on a unique metabolic and skeletal network, and will also provide important insight into the relationship of dietary fat and marrow adiposity to bone acquisition. More importantly, this work could lead to a sea change in our general approach to identifying osteoporosis genes in mice and humans.