Function and Regulation of Osteonectin in Bone

描述（由申请方提供）：骨丢失随年龄增长由骨重建失衡引起，骨髓中成骨细胞数量减少、破骨细胞数量增加和脂肪细胞数量增加。间充质干细胞（MSC）产生成骨细胞和脂肪细胞，并且MSC谱系分配在衰老中改变。MSC谱系分配受多种细胞内信号、细胞-细胞相互作用和骨微环境控制。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素（富含半胱氨酸的酸性分泌蛋白，BM-40）。在骨骼中，骨粘连蛋白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，以响应PTH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，其表达降低。与此相反，骨粘连蛋白的转录水平变化不大，在成骨细胞分化，表明在翻译水平的调节。微小RNA（microRNAs，miRNAs）是一类小的非编码RNA，通过与靶mRNA的3'非翻译区（UTR）相互作用而介导翻译抑制。我们发现miR-29 a和-29c作用于骨粘连蛋白3' UTR并介导定向成骨细胞中的翻译抑制。我们假设miR-29 a和-29c调节成骨细胞分化。重要的是，骨连接素基因3' UTR中的单核苷酸多态性（SNP）与人类的骨密度相关，并且这些SNP调节3' UTR功能。由于骨粘连蛋白是至关重要的正常骨重建和骨合成代谢PTH治疗的反应，我们的工作的目标是了解转录后机制调节其在骨骼中的表达。我们将1。确定人骨粘连蛋白3' UTR SNP如何在体外成骨细胞分化期间调节蛋白质水平; 2.使用携带人UTR和3.确定miR-29在体外成骨细胞分化中的作用。这些研究将填补一个重要的空白，在知识的关键机制调节骨量。此外，我们获得的信息可以应用于骨连接素被认为在病理学中发挥作用的其他疾病，如肥胖和癌症。该提案包含基础和翻译部分，我们将获得与基础科学和临床研究相关的信息。公共卫生相关性：该项目的重点是了解对维持骨量至关重要的骨基质蛋白的调节。这种蛋白质被称为骨粘连蛋白或骨粘连蛋白，编码这种蛋白质的基因的多态性与人类的骨密度有关。从这些研究中获得的信息可用于确定骨质疏松症治疗中治疗干预的新靶点，并可用于确定有发生骨质疏松症风险的个体。

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. PUBLIC HEALTH RELEVANCE: This project focuses on understanding the regulation of a bone matrix protein that is critical for the maintenance of bone mass. This protein is called osteonectin or SPARC, and polymorphisms in the gene coding for this protein are associated with bone density in humans. Information obtained from these studies could be used to identify novel targets for therapeutic intervention in the treatment of osteoporosis, and may be used to identify individuals at risk for developing osteoporosis.