Systems Genetics of Osteoblast Activity

描述(申请人提供)：骨质疏松症是一种进行性骨质丢失的疾病，导致骨骼脆弱和容易骨折。这种疾病影响了大约1200万美国人，是美国社会的主要医疗和经济负担。骨质疏松症主要是一种遗传性疾病，具有骨折预测特征，如骨密度(BMD)，是最易遗传的疾病相关表型之一。到目前为止，在人类和小鼠身上，遗传学研究几乎完全集中在骨密度的分析上。然而，BMD是一个复杂的组织水平的特征，受到复杂的遗传和环境因素的影响。这阻碍了我们准确识别因果基因的能力，更重要的是，它们的作用机制，是遗传联系的基础。作为另一种选择，我们建议只专注于一种更简单的细胞水平过程的遗传学，即成骨细胞介导的骨形成。这项建议的目的是确定影响成骨细胞功能的基因。这将使用一种名为协作交叉(CC)的新颖和创新的小鼠遗传参考种群来实现。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Chr4上成骨细胞介导的骨形成的一个遗传位点，并确定Wnt4是该基因的候选基因。在目的1中，我们将在体外评价Wnt4的表达水平对成骨细胞功能的影响，以及体内缺失Wnt4对骨量和强度的影响。在目标2中，我们将定位CC中矿化结节形成的额外高分辨率数量性状基因座(QTL)，矿化结节形成是成骨细胞介导的骨形成的生理相关指标。在目标3中，我们将从QTL转移到矿化结核形成QTL候选基因的识别和验证。这将通过利用CC独特的遗传方面来从生物信息上缩小这些基因座的范围，随后进行RNA-seq/Expression QTL研究来进一步研究针点致病基因。矿化结核形成的候选基因将通过基因过表达和敲除研究进行测试。我们期望，对细胞水平过程的研究将提供更有效地从位点到基因再到机制的手段。WNT4和其他将被确定的基因将作为潜在的治疗靶点，能够在骨质疏松症的背景下增加骨形成。

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.