Function and Regulation of Osteonectin in Bone

随着年龄的增长，骨丢失是由于骨重建不平衡，成骨细胞数量减少， 破骨细胞数量和骨髓中脂肪细胞数量增加。骨髓间充质干细胞（MSC） 成骨细胞和脂肪细胞，并且MSC谱系分配在衰老中改变。MSC谱系分配是 由不同的细胞内信号、细胞间相互作用和骨微环境控制。最 骨微环境中丰富的非胶原基质蛋白是基质细胞糖蛋白 骨粘连蛋白（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 成骨细胞分化，抑制脂肪生成，并调节骨形成和 对PTH治疗的反应。它在成骨细胞分化早期高度表达，但其 表达随着细胞获得成熟成骨细胞的特征而降低。相反，骨粘连蛋白 在成骨细胞分化过程中，转录水平变化不大，表明在翻译水平上的调节。 微小RNA（miRNAs）是小的非编码RNA，其通过与转录因子相互作用来介导翻译抑制。 3靶mRNA的非翻译区（UTR）。我们发现miR-29 a和-29 c作用于骨粘连蛋白3 ′ UTR， 并在定向成骨细胞中介导翻译抑制。我们假设miR-29 a和-29c 调节成骨细胞分化。重要的是，在3UTR的单核苷酸多态性（SNP）， 骨粘连蛋白基因与人类骨密度相关，这些SNPs调节3UTR功能。 由于骨粘连蛋白对正常骨重建和对骨合成代谢PTH治疗的反应至关重要，因此， 我们工作的重点是了解调控其在骨骼中表达的转录后机制。我们将 1.确定人骨连接素3 <$UTR SNPs如何调节成骨细胞分化过程中的蛋白质水平 体外; 2.使用携带基因敲入的小鼠， 人UTR的突变和3.确定miR-29在体外成骨细胞分化中的作用。这些 这些研究将填补调节骨量的关键机制知识的实质性空白。此外该 我们获得的信息可以应用于其他疾病，其中骨粘连蛋白被认为在 病理学，如肥胖和癌症。该提案包含基本和翻译组成部分，我们 将获得与基础科学和临床研究相关的信息。

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 differentiation, 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.