Project 3 - Role of SDF-1 in Age-Related changes in BMSC miRNA and Bone Loss

细胞因子SDF-1(CXCL12)在骨髓间充质干细胞中的作用 功能和骨骼动态平衡是我们在PO1项目3中之前工作的重点。 这些研究的结果正在推动这场竞争更新的当前目标。其作用机制 然而，我们小组最近的研究表明，与衰老相关的骨质疏松症的定义仍然不明确。 其他人则认为这是一种干细胞疾病。一个关键的问题是，衰老会导致本地化受损， 骨髓中成骨祖细胞群体的增殖、存活和分化； 尤其是骨髓间充质干细胞。防止这些变化的一个关键障碍是确定关键的监管途径，以及 能够改变或纠正它们。我们的目标是使用从我们最初的PO1生成的信息，在那里我们 已经确定了BMSCs中miRNAs子集的表观遗传学变化，并针对这些miRNAs进行限制，或 反之，骨质流失。SDF-1的年龄相关变化系统性地改变了表观遗传调控系统， 特别是骨髓间充质干细胞中的miRNAs，它反过来直接并通过营养信号通路影响细胞存活， 成骨和骨形成。SDF-1在翻译、转录和转录后受到严格调控 从转录上讲。我们已经确定了SDF-1轴的年龄相关变化。这里我们展示了SDF-1是 不仅是新的年龄相关miRNA表观遗传调控的靶点，而且它本身也改变miRNAs的表达 在BMSCs中，这种情况随着年龄的变化而变化，并以SDF-1轴为靶点。值得注意的是，我们发现了一个关键的miRNA BMSCs随年龄增长(miR-29b-1-5p)属于miR29家族的miRNAs，已被证明 在细胞外基质动态平衡和成骨方面起关键作用。什么是新奇的，是对现有的挑战 范例是miR29b-1-5p是“乘客链”，通常认为它会被降解，离开 互补miR-29b-1-3p作为功能miRNA的“引导链”。了解这一机制 推动这种以前未知的与年龄相关的乘客链增加是一个关键目标，因为我们 已经证明miR29b-1-5p调节SDF-1的表达并抑制BMSC的成骨和 生存之路。我们建议检验这一假设，即循环中SDF-1水平的升高与年龄相关 而降低的骨髓间隔室水平和活性调节miR-29b-1-1的表达增加 5P及其下游对骨稳态的影响。我们的目标是测试从 通过操纵我们确定的随年龄变化的miRNAs在人/鼠中发现原始PO1 骨髓间充质干细胞在体内及分子水平对骨形成和骨转换的影响 成骨功能。我们将测试减少这些miRNAs表达的新方法，包括改变 营养途径通过利用特定形式的膳食氨基酸和输送合成的 抗miRNAs来抑制它们。该项目的影响将展示与年龄相关的 骨髓间充质干细胞miRNAs的变化和寻找减少或逆转与年龄相关的骨丢失的新靶点。

The role of the cytokine SDF-1 (CXCL12) in bone marrow mesenchymal stem/progenitor cells (BMSCs) function and bone homeostasis was the focus of our previous work in the original PO1 Project 3. The novel outcomes from those studies are driving the current goals in this competitive renewal. The mechanisms involved in aging-related osteoporosis remain poorly defined, however, recent studies from our group, and others, suggest that it is a stem cell disease. A critical problem is that aging triggers impaired localization, proliferation, survival, and differentiation of the osteogenic progenitor cell population in the bone marrow (BM), specifically BMSCs. A critical barrier to preventing these changes is identifying key regulatory pathways, and being able to alter or correct them. Our goal is to use information generated from our original PO1, where we have identified epigenetic changes in a subset of miRNAs in BMSCs, and to target these miRNAs to limit, or reverse, bone loss. Age-associated changes in SDF-1 systemically alter epigenetic regulatory systems, specifically miRNAs, in BMSCs, which in turn directly, and via nutrient signaling pathways, affect cell survival, osteogenesis and bone formation. SDF-1 is tightly regulated translationally, transcriptionally, and post- transcriptionally. We have identified age-associated changes in the SDF-1 axis. Here we show that SDF-1 is not only a target of novel age-associated miRNA epigenetic regulation, but itself alters expression of miRNAs that change with age in BMSCs and target the SDF-1 axis. Significantly, a key miRNA that we identified to increase with age in BMSCs (miR-29b-1-5p) belongs to the miR29 family of miRNAs that have been shown to be critical in extracellular matrix homeostasis and osteogenesis. What is novel, and a challenge to the existing paradigm, is that miR29b-1-5p is the “passenger strand”, which is normally thought to be degraded leaving the complementary miR-29b-1-3p “guide strand” as the functional miRNA. Understanding the mechanism that drives this previously unknown age-associated increase in the passenger strand is a critical goal because we have demonstrated that miR29b-1-5p regulates SDF-1 expression and suppresses BMSC osteogenesis and survival pathways. We propose to test the hypothesis that the elevated age-related levels of circulating SDF-1 and decreased bone marrow compartment levels and activity regulate the increased expression of miR-29b-1- 5p and downstream effects on bone homeostasis. Our objectives are to test new hypotheses derived from the findings of the original PO1 by manipulating the miRNAs we identified as changing with age in human/murine BMSCs to determine their effects on bone formation and turnover in vivo and at the molecular level on BMSC osteogenic function. We will test novel methods to reduce expression of these miRNAs, including altering nutritional pathways leading to bone loss by using specific forms of dietary amino acid and delivering synthetic anti-miRNAs to inhibit them. The impact of this project will be demonstrating the role of age-associated changes of BMSC miRNAs and identifying novel targets for reducing, or reversing, age related bone loss.