Bad to the Bone: Age-related Increases in Serum SDF-1 Leads to Bone Loss with Age

骨质疏松症在男性中报告不足，可能存在于高达31%的男性VA患者中。进一步应 其中最令女性衰弱的疾病-谁弥补了越来越大的份额，我们的退伍军人 人口髋部和椎骨骨折，骨质疏松症的主要风险，导致失去独立性，疼痛，甚至 潜在的严重心脏和脑部疾病，以及死亡率增加。我们的主要假设是 细胞因子基质衍生因子1（SDF-1，又名CXCL 12）在外周循环中随年龄增加而增加， 会导致与年龄相关的骨质流失在外周血中，SDF-1迅速转化为N-末端 循环二肽基肽酶CD26（二肽基肽酶4，DPP 4）的内肽酶裂解形式。的 SDF-1的切割形式结合并阻断SDF-1受体CXCR4，但不激活它。 抑制剂的作用。由于DPP 4对SDF-1的快速改变，但其总分解较慢， 我们的研究表明，血液和骨髓中的大部分SDF-1是由 无活性/抑制形式。我们的部分假设是，如果不活跃形式的水平缓慢上升， 随着年龄的增长，CXCR4信号长期减少，这将对骨骼产生负面影响， 骨髓间充质干细胞的数量和减少骨形成。越来越多的证据表明，CXCR4信号是 骨髓间充质干细胞（BMSC）需要维持祖细胞群，并启动和 支持骨生成。重要的是，我们实验室的临床前小鼠研究表明， 总SDF-1水平，包括DPP 4裂解形式，随着小鼠年龄的增长而增加， 增加年轻小鼠中DPP 4裂解的SDF-1的血浆水平降低骨形成血清标志物 并显著降低骨小梁体积和骨密度。这导致了NIH PO1资助， 确定SDF-1亚型在调节鼠骨形成中的作用。有关研究调查可能 这里提出的是看看我们在小鼠中的假设和观察是否适用于人类：我们建议测试 新的假说认为，在人类中，增加的DPP 4切割的SDF-1亚型是年龄和 疾病相关的骨质流失。我们建议评估循环和骨髓中SDF-1的水平 （DPP4切割的和未切割的）水平、DPP4活性和这些同种型对人BMSC的作用 体外成骨活性和体内骨形成和质量/密度。我们将测量SDF-1亚型 沿着DPP4在不同年龄患者的血清和骨髓中的表达，并将其与他们的骨相关联 密度和体积，以及骨形成或分解的血清标志物。我们还将确定是否有 这些SDF-1和DPP4参数在骨质疏松症患者中的变化相对于年龄匹配的 对照我们进一步建议确定FDA批准的用于治疗骨质疏松症的药物对骨形成的影响。 糖尿病治疗，其通过调节DPP4活性起作用（例如西格列汀）。我们将确定糖尿病患者 与对照相比，接受这些DPP4抑制剂治疗的患者显示出改善的骨形成。最后， 我们将使用分离的人患者BMSC来确定DPP 4切割的SDF-1是否降低BMSC细胞存活， 增殖和成骨潜能。此外，将评估这些人BMSC以确定是否存在 是靶向SDF-1轴和成骨基因的miRNA的年龄相关变化。我们将确定 如果这种miRNAs影响BMSC细胞命运，这项工作可能会迅速导致临床试验， FDA批准DPP4抑制剂作为骨质疏松症的新型促骨重塑治疗替代品， 或增强目前有问题的抗重塑疗法。在后续研究中， DPP4还可能具有通过增加SDF-1的活性形式以增加骨修复率的价值。 骨折或其他创伤性骨损伤后干细胞归巢和成骨诱导， 为退伍军人事务部和国防部工作长期而言，这项工作开启了利用特定miRNA调控来调节 随着年龄的增长，BMSCs的成骨环境和预防骨质疏松症。

Osteoporosis is under-reported in men and may be present in up to 31% of male VA patients. Further, it is among the most debilitating disorders for women - who make up an increasingly larger share of our veteran population. Hip and vertebral fractures, major risks with osteoporosis, lead to loss of independence, pain, even potentially serious cardiac and brain morbidities, as well as increased mortality. Our main hypothesis is that the cytokine stromal-derived factor 1 (SDF-1, aka CXCL12) is increased in the peripheral circulation with age and contributes to age-associated bone loss. In the peripheral blood SDF-1 is rapidly converted to an N-terminal endopeptidase-cleaved form by the circulating dipetidlylpeptidase CD26 (dipetidlylpeptidase 4, DPP4). The cleaved form of SDF-1 binds to and blocks the SDF-1 receptor CXCR4, but does not activate it. It becomes in effect an inhibitor. Because of the quick alteration of SDF-1 by DPP4, but its slower total breakdown and removal, our research suggests the majority of the SDF-1 in the blood and bone marrow is of the inactive/inhibitory form. Part of our hypothesis is that if the level of the inactive form rises slowly, and stays up with aging, then CXCR4 signaling is reduced long-term and this will have a negative impact on bone, reducing the number of BMSCs and reducing bone formation. There is increasing evidence that CXCR4 signaling is needed for BM mesenchymal stem cells (BMSCs) to maintain a progenitor cell population and to initiate and support osteogenesis. Importantly, preclinical murine studies from our laboratory have shown that circulating levels of total SDF-1, including the DPP4-cleaved form, increase with age in mice and that experimentally increasing the plasma level of DPP4-cleaved SDF-1 in young mice reduces bone formation serum markers and significantly decreases trabecular bone volume and bone density. This led to a funded NIH PO1 grant to determine the role of SDF-1 isoforms in the regulation of murine bone formation with age. The research studies proposed here are to see if our hypotheses and observations in mice are true in humans: We propose to test the novel hypothesis that in humans increased DPP4-cleaved SDF-1 isoforms are important factors in age-and disease-associated bone loss. We propose to assess the levels of circulating, and bone marrow, SDF-1 (DPP4-cleaved and non-cleaved) levels, DPP4 activity, and the effects of these isoforms on human BMSC's osteogenic activity in vitro and bone formation and quality/density in vivo. We will measure SDF-1 isoforms along with DPP4 in the serum and bone marrow of patients of different ages, and correlate this with their bone density and volume, as well as serum markers of bone formation or breakdown. We will also determine if there are changes in these SDF-1 and DPP4 parameters in patients with osteoporosis relative to age-matched controls. We further propose to determine the effects on bone formation of FDA-approved drugs in use for diabetic therapy, which act by regulating DPP4 activity (e.g. sitaglitin). We will determine if diabetic patients receiving treatment with these DPP4 inhibitors show improved bone formation compared to controls. Finally, we will use isolated human patient BMSCs to determine if DPP4 cleaved SDF-1 reduces BMSC cell survival, proliferation, and osteogenic potential. Additionally, these human BMSCs will be assessed to determine if there are age-associated changes in miRNAs targeting the SDF-1 axis and osteogenic genes. We will deteremine experimentally if such miRNAs effect BMSC cell fate. This work could rapidly lead to clinical trials of already FDA approved DPP4 inhibitors as a novel pro-bone remodeling treatment for osteoporosis as a replacement, or enhancement, of current problematic anti-remodeling therapies. In follow up studies, acute inhibition of DPP4 may also have value in increasing bone repair rates via increasing the active form of SDF-1 to increase stem cell homing and osteogenic induction following fracture, or other truamatic injury to bone, a critical need for the VA and DoD. Longer-term this work opens the potential to use regulation of specific miRNAs to regulate the osteogenic environment for BMSCs with age and to prevent osteoporosis.