Function and Regulation of Osteonectin in Bone

描述（由申请方提供）：骨连接素是骨中最丰富的非胶原基质成分之一，骨连接素缺失小鼠发生进行性低转换骨质减少。骨连接素缺失小鼠成骨细胞数量和骨形成率降低，因此，这种糖蛋白对于骨重建和骨量的维持至关重要。骨连接素缺失小鼠的体外细胞分析表明，骨连接素支持成骨细胞的形成、成熟和存活。此外，无骨连接素的成骨细胞更可能转分化为脂肪细胞。体外研究表明，已知指导细胞命运的Notch信号通路在无骨连接素的成骨细胞中发生改变。Notch-1转录在骨连接素缺失细胞中增加，组成性Notch信号传导抑制成骨细胞分化。此外，骨粘连蛋白支持细胞在应激条件下的存活。促凋亡信号和抗凋亡信号之间的比率在确定细胞是否将经历凋亡或能够抵抗这种命运中起作用，并且初步研究表明对照和骨连接素缺失的成骨细胞具有不同的促凋亡蛋白和抗凋亡蛋白的比率。该建议的第一个具体目的是确定骨粘连蛋白支持细胞存活的机制。这将通过定义骨连接素可以支持细胞存活的条件，并通过确定哪些细胞死亡途径在骨连接素无效细胞中被修饰，使用微阵列方法来实现。第二个具体目标是确定骨粘连蛋白支持成骨细胞形成和成熟的机制。这是我的假设，Notch信号通路的失调介导，至少部分地，骨连接素无效突变对成骨细胞分化和成熟的影响。这一假设将通过确定下调Notch-1在骨连接素无效细胞是否可以挽救成骨细胞分化的缺陷进行检验。此外，将使用微阵列方法研究影响对照和骨连接素缺失成骨细胞中细胞命运的信号通路，并且由于骨连接素调节成骨细胞中Notch-1 mRNA表达，因此将确定发生这种情况的机制。这些研究将提供骨连接素影响细胞存活和细胞命运的机制的数据，也可能提供细胞如何检测骨连接素的线索。

DESCRIPTION (provided by applicant): Osteonectin is one of the most abundant non-collagen matrix components in bone, and osteonectin-null mice develop progressive, low turnover osteopenia. Osteonectin-null mice have decreased osteoblast numbers and bone formation rate, hence, this glycoprotein is critical for bone remodeling and the maintenance of bone mass. In vitro analysis of cells from osteonectin-null mice shows that osteonectin supports osteoblast formation, maturation, and survival. In addition, osteonectin-null osteoblastic cells are more likely to transdifferentiate into adipocytes. In vitro studies indicate that the Notch signaling pathway, known to direct cell fate, is altered in osteonectin-null osteoblastic cells. Notch-1 transcripts are increased in osteonectin-null cells, and constitutive Notch signaling inhibits osteoblastic differentiation. In addition, osteonectin supports cell survival under conditions of stress. The ratio between pro- and anti-apoptotic signals plays a role in determining whether a cell will undergo apoptosis or be able to resist this fate, and preliminary studies suggest that control and osteonectin-null osteoblasts have different ratios of pro- and anti-apoptotic proteins. The first Specific Aim of this proposal is to determine the mechanisms by which osteonectin supports cell survival. This will be accomplished by defining the conditions under which osteonectin can support cell survival, and by determining which cell death pathways are modified in osteonectin-null cells, using a microarray approach. The second Specific Aim is to determine the mechanisms by which osteonectin supports osteoblast formation and maturation. It is my hypothesis that dysregulation of the Notch signaling pathway mediates, at least in part, the effect of the osteonectin-null mutation on osteoblast differentiation and maturation. This hypothesis will be tested by determining whether down-regulation of Notch-1 in osteonectin-null cells can rescue the defect in osteoblastic differentiation. In addition, the signaling pathways impacting cell fate in control and osteonectin-null osteoblasts will be investigated using a microarray approach, and because osteonectin regulates Notch-1 mRNA expression in osteoblasts, the mechanisms by which this occurs will be determined. These studies will provide data on the mechanisms by which osteonectin affects cell survival and cell fate, and may also provide clues as to how cells detect osteonectin.