Function and Regulation of Osteonectin in Bone

描述（由申请人提供）：骨质老化导致骨重塑失衡，骨髓中成骨细胞数量减少，破骨细胞数量增加，脂肪细胞数量增加。间充质干细胞（MSCs）产生成骨细胞和脂肪细胞，MSC谱系分配随着年龄的增长而改变。MSC谱系分配受多种细胞内信号、细胞间相互作用和骨微环境的控制。骨微环境中最丰富的非胶原基质蛋白是基质细胞糖蛋白骨连接蛋白（分泌的富含半胱氨酸的酸性蛋白，SPARC; BM-40）。在骨骼中，骨连接素促进成骨细胞的承诺，抑制脂肪生成，并调节骨形成和骨吸收之间的平衡，以应对甲状旁腺激素的治疗。它在成骨细胞分化早期高度表达，但随着细胞获得成熟成骨细胞的特征，其表达减少。相反，成骨细胞分化过程中骨连接蛋白转录水平变化不大，表明在翻译水平上进行调控。MicroRNAs （miRNAs）是一种小的非编码rna，通过与靶mrna的3'非翻译区（UTR）相互作用介导翻译抑制。我们发现miR-29a和-29c作用于成骨细胞中骨连接蛋白3' UTR并介导翻译抑制。我们假设miR-29a和-29c调节成骨细胞分化。重要的是，骨连接蛋白基因3' UTR的单核苷酸多态性（snp）与人类骨密度有关，这些snp调节3' UTR功能。由于骨连接素对正常骨重塑和对骨合成代谢PTH治疗的反应至关重要，因此我们的工作目标是了解调节其在骨骼中的表达的转录后机制。我们会的。确定人骨连接蛋白3' UTR snp在体外成骨细胞分化过程中如何调节蛋白水平；2. 使用携带人类UTR和3敲入突变的小鼠，在体内测定人类骨连接蛋白3' UTR单倍型的活性。确定miR-29在体外成骨细胞分化中的作用。这些研究将填补骨量调节关键机制知识的实质性空白。此外，我们获得的信息可以应用于骨连接素被认为在病理中起作用的其他疾病，如肥胖和癌症。本提案包含基础和转化成分，我们将获得与基础科学和临床研究相关的信息。

DESCRIPTION (provided by applicant): Bone loss with aging results from imbalanced bone remodeling, with decreased osteoblast number, increased osteoclast number, and increased adipocyte number in the marrow. Mesenchymal stem cells (MSCs) give rise to both osteoblasts and adipocytes, and MSC lineage allocation is altered in aging. MSC lineage allocation is controlled by diverse intracellular signals, cell-cell interactions and the bone microenvironment. The most abundant non-collagen matrix protein in the bone microenvironment is the matricellular glycoprotein osteonectin (secreted protein acidic rich in cysteine, SPARC; BM-40). In the skeleton, osteonectin promotes osteoblast committment, suppresses adipogenesis, and regulates the balance between bone formation and resorption in response to PTH treatment. It is highly expressed early in osteoblastic differentiation, but its expression decreases as the cells acquire characteristics of mature osteoblasts. In contrast, osteonectin transcript levels change little during osteoblastic differentiation, indicating regulation at the level of translation. MicroRNAs (miRNAs) are small non-coding RNAs that mediate translational repression by interacting with the 3' untranslated region (UTR) of target mRNAs. We found that miR-29a and -29c act on the osteonectin 3' UTR and mediate translational repression in committed osteoblasts. We hypothesize that miR-29a and -29c regulate osteoblastic differentiation. Importantly, single nucleotide polymorphisms (SNPs) in the 3' UTR of osteonectin gene are associated with bone density in humans, and these SNPs modulate 3' UTR function. Since osteonectin is critical for normal bone remodeling and response to bone anabolic PTH therapy, the goal of our work is to understand post-transcriptional mechanisms regulating its expression in the skeleton. We will 1. determine how human osteonectin 3' UTR SNPs modulate protein levels during osteoblastic differentiation in vitro; 2. determine the activity of human osteonectin 3' UTR haplotypes in vivo, using mice carrying knock-in mutations of the human UTR and 3. determine the role of miR-29 in osteoblast differentiation in vitro. These studies will fill a substantial void in the knowledge of key mechanisms regulating bone mass. In addition, the information we acquire could be applied to other diseases in which osteonectin is thought to play a role in pathology, such as obesity and cancer. This proposal contains basic and translational components, and we will obtain information relevant to both basic science and clinical studies.