Age-Related Kynurenine Accumulation Impairs miRNA and Hdac Epigenetic Regulation of the SDF-1 Axis Resulting in Bone Loss

与年龄相关的骨质疏松症的机制仍然不清楚，然而，最近的研究，从我们的研究， 研究小组和其他人认为这是一种干细胞疾病。我们一直在研究细胞因子SDF-1在 CXCL12和Hdac3在骨髓间充质干/基质细胞（BMSC）功能和骨稳态中的作用。 一个关键的问题是，老化触发受损的定位，增殖，存活和分化的细胞， 骨髓（BM）中的成骨祖细胞群，特别是BMSC。一个关键的障碍， 防止这些变化的方法是确定关键的调节途径，并能够改变或纠正它们。我们 已经确定了BMSC在microRNA miR-29b-1 - 5p中的表观遗传变化，这似乎与组蛋白相互作用 脱乙酰酶3（Hdac3），第二表观遗传调节系统。此外，我们已经确定， 色氨酸（TRP）代谢物犬尿氨酸（KYN）改变BMSC中的这些特异性表观遗传调节分子， 进而直接并通过SDF-1信号通路影响细胞存活、骨生成、成骨细胞脂质 储存和骨形成。值得注意的是，miR-29b-1 - 5p在BMSCs中随着衰老而增加，属于 miR29家族的miRNAs已被证明在细胞外基质稳态中起关键作用， 成骨一个新的方面是miR29b-1 - 5p是"乘客链"，通常认为其是 降解，留下互补的miR-29b-1 - 3p "引导链"作为功能性miRNA;然而，随着衰老， 我们的数据提示该过客链是BMSC功能障碍的重要效应物。重要的是，miR-29b- 靶向SDF-1的1 - 5p被KYN上调，而Hdac3被下调，导致脂质增加 BM骨祖细胞和OB的储存和功能障碍。 驱动这些先前未知的miR-29b-1 - 5p和Hdac 3的年龄相关变化是一个关键目标， 我们已经证明这两个相互作用的系统调节SDF-1表达并抑制BMSC 骨生成和生存途径，同时增加BM脂肪储存。我们建议检验这个假设， 与年龄相关的KYN水平升高驱动miR-29b-1 - 5p表达增加和Hdac3抑制， 表达，通过SDF-1及其受体CXCR4对骨稳态产生下游作用，或直接通过 我们的目标是在BMSCS和OBs中靶向额外的成骨基因。我们的目标是测试新的假设 通过操纵我们确定为随年龄变化的miRNAs和Hdacs， 人/鼠BMSC，以确定其在体内和分子水平对骨形成和转换的影响。 水平对BMSC成骨功能的影响。我们将测试新的方法来减少这些分子的表达， 包括抑制KYN产生、抑制KYN信号通路或递送合成的抗miRNA， 抑制miR29b-1 - 5p。这个项目的影响将是澄清年龄相关的表观遗传变化的作用 在BMSC miRNA和HISTORY系统的交叉对话中，目的是鉴定新的靶点， 逆转与年龄相关的骨丢失和骨质疏松症。

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. We have been studying the role of the cytokine SDF-1 (CXCL12) and Hdac3 in bone marrow mesenchymal stem/stromal cell (BMSC) function and bone homeostasis. 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. We have identified BMSC epigenetic changes in the microRNA miR-29b-1-5p, that appears to cross-talk with histone deacetylase 3 (Hdac3), a second epigenetic regulatory system. Further, we have identified that the oxidized tryptophan (TRP) metabolite kynurenine (KYN) alters these specific epigenetic regulatory molecules in BMSCs, which in turn directly, and via SDF-1 signaling pathways, affect cell survival, osteogenesis, osteoblastic lipid storage, and bone formation. Significantly, miR-29b-1-5p, which increases with aging in BMSCs, belongs to the miR29 family of miRNAs that have been shown to be critical in extracellular matrix homeostasis and osteogenesis. One novel aspect 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; with aging, however, our data suggest that this passenger strand is an important effector of BMSC dysfunction. Importantly, miR-29b- 1-5p, which targets SDF-1, is upregulated by KYN while Hdac3 is down regulated leading to increased lipid storage and dysfunction in BM osteoprogenitor cells and OBs. Understanding the upstream mechanisms that drive these previously unknown age-associated changes in miR-29b-1-5p and Hdac3 is a critical goal because we have demonstrated that these two interacting systems regulate SDF-1 expression and suppress BMSC osteogenesis and survival pathways while increasing BM fat storage. We propose to test the hypothesis that the elevated, age-related levels of KYN drive the increased expression of miR-29b-1-5p and inhibition of Hdac3 expression, with downstream effects on bone homeostasis via SDF-1 and its receptor CXCR4, or directly by targeting additional osteogenic genes both in BMSCS and OBs. Our objectives are to test new hypotheses derived from our findings by manipulating the miRNAs and Hdacs 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 molecules, including inhibiting KYN generation, inhibiting KYN signaling pathways, or delivering synthetic anti-miRNAs to inhibit miR29b-1-5p. The impact of this project will be to clarify the roles of age-associated epigenetic changes in cross-talking BMSC miRNA and Hdac systems with the goal of identifying novel targets for reducing, or reversing, age-related bone loss and osteoporosis.