Systems Genetics of Osteoblast Activity

描述（由申请人提供）：骨质疏松症是一种进行性骨质流失的疾病，导致骨骼脆弱和易骨折。这种疾病影响了约1200万美国人，是美国社会的主要医疗和经济负担。骨质疏松主要是一种具有骨折预测特征的遗传性疾病，如骨密度（BMD），是最具遗传性的疾病相关表型之一。迄今为止，对人类和小鼠的基因研究几乎完全集中在骨密度分析上。然而，骨密度是一种复杂的生物水平性状，受遗传和环境因素的复杂影响。这阻碍了我们精确识别因果基因的能力，更重要的是，它们的作用机制，是遗传关联的基础。作为替代方案，我们建议专注于更“简单”的细胞水平过程的遗传学，成骨细胞介导的骨形成。本研究的目的是鉴定影响成骨细胞功能的基因。这将完成使用一种新的和创新的小鼠遗传参考群体称为协作交叉（CC）。在一项初步研究中，我们利用全基因组关联图谱确定了小鼠Chr 4上一个与成骨细胞介导的骨形成有关的遗传位点，并确定Wnt4是该位点的候选基因。在Aim 1中，我们将在体外评估调节Wnt4表达水平对成骨细胞功能的影响，以及在体内剔除Wnt4对骨量和强度的影响。在目标2中，我们将绘制矿化结节形成的额外高分辨率定量性状位点（QTL），这是成骨细胞介导的骨形成的生理相关测量，在CC中。在目标3中，我们将从QTL转移到矿化结节形成QTL的候选基因的鉴定和验证。这将通过利用CC独特的遗传方面来生物信息学地缩小这些位点，然后通过RNA-seq/表达QTL研究来进一步确定致病基因来实现。矿化结核形成QTL的候选基因将通过基因过表达和敲低研究进行检测。我们期望对细胞水平过程的研究将为更有效地从位点到基因再到机制提供手段。Wnt4和其他将被鉴定的基因将作为潜在的治疗靶点，能够在骨质疏松症的情况下增加骨形成。

DESCRIPTION (provided by applicant): Osteoporosis is a disease of progressive bone loss, leading to weak and fracture prone bones. This disease affects ~12 million Americans and is a major medical and economic burden on American society. Osteoporosis is primarily a genetic disorder with fracture predicting traits, such as bone mineral density (BMD), being among the most highly heritable disease associated phenotypes. In humans and mice, genetic studies to date have almost exclusively focused on the analysis of BMD. However, BMD is a complex organismal- level trait that is influenced by a complicated milieu of genetic and environmental factors. This has hampered our ability to precisely identify the causal genes, and more importantly, their mechanisms of action, that underlie genetic associations. As an alternative, we propose to focus exclusively on the genetics of a more 'simple' cell-level process, osteoblast-mediated bone formation. The objective of this proposal is to identify genes affecting osteoblast function. This will be accomplished using a novel and innovative mouse genetic reference population termed the Collaborative Cross (CC). In a pilot study, we identified a genetic locus on mouse Chr 4 for osteoblast-mediated bone formation using genome-wide association mapping and determined that Wnt4 was the candidate gene for this locus. In Aim 1, we will evaluate the effect of modulating expression levels of Wnt4 on osteoblast function in vitro and the effects of deleting Wnt4 on bone mass and strength in vivo. In Aim 2, we will map additional high-resolution quantitative trait loci (QTL) for mineralized nodule formation, a physiologically relevant measure of osteoblast-mediated bone formation, in the CC. In Aim 3, we will move from QTL to the identification of and validation of candidate genes for mineralized nodule formation QTL. This will be accomplished by exploiting the unique genetic aspects of the CC to bioinformatically narrow these loci, followed by RNA-seq/expression QTL studies to further pin point causative genes. Candidate genes for mineralized nodule formation QTL will be tested by gene overexpression and knockdown studies. We expect that the study of a cell-level process will provide the means to more efficiently go from locus to gene to mechanism. Wnt4 and additional genes that will be identified will serve as potential therapeutic targets capable of increasing bone formation in the setting of osteoporosis.