Function and Regulation of Osteonectin in Bone

随着年龄的增长，骨丢失是由于不平衡的骨重建，随着成骨细胞数量的减少而增加 骨髓中破骨细胞数量增加，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，随着年龄的增长，MSC的谱系分配发生了变化。MSC谱系分配是 受不同的细胞内信号、细胞-细胞相互作用和骨骼微环境控制。最多的 骨微环境中丰富的非胶原基质蛋白是基质糖蛋白。 骨联素(富含半胱氨酸的酸性分泌蛋白，SPARC；BM-40)。在骨骼中，骨连蛋白促进 成骨细胞分化，抑制脂肪生成，调节骨形成和骨形成之间的平衡 甲状旁腺素治疗后的吸收反应。它在成骨细胞分化早期高度表达，但其 随着细胞获得成熟成骨细胞的特征，其表达减少。相比之下，骨连蛋白 在成骨细胞分化过程中，转录水平变化不大，表明在翻译水平上存在调控。 MicroRNAs(MiRNAs)是一种小的非编码RNA，通过与 3.靶基因的非翻译区。我们发现miR-29a和-29c作用于骨连接蛋白3？UTR 并在承诺的成骨细胞中调节翻译抑制。我们假设miR-29a和-29c 调节成骨细胞分化。重要的是，3‘非编码区的单核苷酸多态(SNPs) 在人类中，骨连接蛋白基因与骨密度相关，这些单核苷酸多态调控着3‘非编码区功能。 由于骨连接蛋白对正常的骨重建和对骨合成代谢甲状旁腺素治疗的反应是至关重要的，目标是 我们的工作之一是了解转录后调节其在骨骼中表达的机制。我们会 1.确定在成骨细胞分化过程中，人骨连接蛋白3非编码区SNPs如何调节蛋白质水平。 在体外；2.利用携带敲入基因的小鼠在体内测定人骨连接蛋白3？非编码区单倍型的活性。 3.决定miR-29在体外成骨细胞分化中的作用。这些 研究将填补在调节骨量的关键机制方面的知识的重大空白。此外， 我们获得的信息可以应用于其他疾病，在这些疾病中，骨连接蛋白被认为在 病理学，如肥胖和癌症。该提案包含基本和翻译部分，我们 将获得与基础科学和临床研究有关的信息。

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.