Augmentation of Trabecular Bone by Low Magnitude Strain

描述（由申请人提供）：运动可能是公认的对骨质疏松症和肥胖症具有威慑作用的单一“干预”，但机械信号抑制其发病机制的方式尚不清楚。每天短时间的高频（30- 90hz）、低强度（<0.4g）机械信号（LMMS）对骨骼和肌肉都是合成代谢的。在一个意想不到的发现中，这些信号也抑制脂肪生成，在接受12w LMMS的小鼠中，腹部内脏脂肪总量减少29%。这些组织截然不同的反应(？骨和肌肉；？表明这些信号影响间充质干细胞（MSCs）的分化途径。对于人类来说，这将有助于解释为什么久坐的生活方式会导致骨质疏松症和肥胖症，这两种看似不同的疾病，并可能表明LMMS通过定义MSCs的命运来减少脂肪生成并加强肌肉骨骼系统，就像影响骨骼、肌肉或脂肪中的常驻细胞群一样。我们假设LMMS驱动MSCs向骨骼和肌肉表型发展，同时抑制通向肥胖的途径。为了更好地理解LMMS如何影响生长、衰老、肥胖和患病动物的身体组成，我们设计了三个具体目标：为了确定那些参与组织对LMMS反应的基因，年轻雄性B6小鼠将接受每日LMMS治疗，并将骨髓、脂肪和骨骼中96个候选基因的早期到晚期（4d， 6和12w）表达水平与骨和脂肪量的改变相关，并与基线和年龄匹配的对照组进行比较。这些基因代表了参与调节这些组织的基因。2. LMMS的长期表型影响及其影响肥胖饮食和遗传模型的能力，将在3和6个月时在喂食正常或高脂肪饮食（饮食诱导肥胖）的健康雄性B6小鼠以及易肥胖的转基因小鼠品系（瘦素缺乏的ob/ob）中确定。骨髓、脂肪和骨骼的状态，以及血清、肝脏、肌肉和脂肪组织中甘油三酯和游离脂肪酸的水平，将被量化并与对照组进行比较。3. 为了确定LMMS是否影响MSCs的分化途径，我们将C57BL/6J小鼠（B6）照射后移植GFP+供者的骨髓进行LMMS治疗，并在6和12w后，将脂肪、骨髓和骨骼中GFP+细胞的数量与年龄匹配的受体GFP+对照进行比较。为了确定MSC是否能独立受到LMMS的影响，我们将在MSC培养（C3H10T1/2）中使用一种用于传递LMMS的体外系统来评估这些信号抑制脂肪形成和促进成骨细胞形成的能力。总之，这些研究将有助于确定肌肉骨骼、脂肪和干细胞系统如何对其机械环境的细微变化作出反应，并代表着建立非药物手段抑制骨质疏松和肥胖的一步。本工作将探讨极低强度机械信号的合成代谢潜力背后的机制，以及它们如何增强骨骼和肌肉。上一阶段的研究还表明，这些信号通过影响间充质干细胞的分化途径，而不是提高动物的新陈代谢，显著抑制肥胖，表明一种以前未被认识到的调节脂肪和骨骼生成的机械手段。这项研究将为将这项工作转化为一种安全的、非药物的、控制骨质疏松和肥胖的干预措施提供基础。

DESCRIPTION (provided by applicant): Exercise is perhaps the single "intervention" recognized as a deterrent to both osteoporosis and obesity, yet the manner in which mechanical signals inhibit their pathogenesis remains unknown. Brief daily periods of high frequency (30-90 Hz), low magnitude (<0.4g) mechanical signals (LMMS) are anabolic to both bone and muscle. In an unexpected finding, these signals also suppress adipogenesis, with 29% less total visceral abdominal fat in mice subject to 12w of LMMS. The starkly distinct response of these tissues (?bone & muscle; ?fat) to LMMS suggests that these signals influence the differentiation pathway of mesenchymal stem cells (MSCs). Translated to the human, this would help explain why a sedentary lifestyle is permissive to both osteoporosis and obesity, seemingly distinct diseases, and could suggest that LMMS reduce adipogenesis and strengthen the musculoskeletal system as much by defining the fate of MSCs as influencing the resident cell population within bone, muscle, or fat. We hypothesize that LMMS drive MSCs towards a bone and muscle phenotype, simultaneously suppressing a path towards adiposity. Three specific aims are designed to better understand the means by which LMMS influences the body composition of the growing, aging, obese and diseased animal: 1. To identify those genes involved in the tissue response to LMMS, young male B6 mice will be subject to daily LMMS, and early through late (4d, 6 & 12w) expression levels of 96 candidate genes in marrow, fat and bone, representing those involved in regulating these tissues, will be correlated to alterations in bone and fat mass, and compared to baseline and age matched control. 2. The long-term phenotypic impact of LMMS, and their ability to influence dietary and genetic models of obesity, will be defined at 3 & 6 months in healthy male B6 mice fed a normal or high-fat diet (Diet Induced Obesity), as well as a transgenic strain of mice prone to adiposity (leptin-deficient ob/ob). The status of marrow, fat and bone, and level of triglycerides and free fatty acid in the serum, liver, muscle and adipose tissue, will be quantified and compared to controls. 3. To determine if LMMS influences the differentiation pathway of MSCs, irradiated C57BL/6J mice (B6) transplanted with marrow from GFP+ donors will be subject to LMMS, and following 6 & 12w, the number of GFP+ cells in fat, marrow and bone will be compared to age matched recipient GFP+ controls. To establish if MSCs can be independently influenced by LMMS, the ability of these signals to suppress adipogenesis and promote osteoblastogenesis will be evaluated in MSC cultures (C3H10T1/2) using an in vitro system used to deliver LMMS. Together, these studies will help define how the musculoskeletal, adipose and stem cell systems respond to subtle changes in their mechanical environment, and represents a step in establishing a non-drug means of inhibiting osteoporosis and obesity. PUBLIC HEALTH RELEVANCE: Augmentation of Trabecular Bone by Low Magnitude Strain This work will investigate the mechanisms behind the anabolic potential of extremely low- magnitude mechanical signals, and how they strengthen both bone and muscle. Research over the last period of funding has also shown that these signals markedly suppress adiposity, by influencing the differentiation pathway of mesenchymal stem cells rather than elevating the animal's metabolism, indicating a previously unrecognized mechanical means of the regulating fat and bone production. This research will provide the foundation to translate this work to the clinic as a safe, non-pharmacologic, intervention for the control of osteoporosis and obesity.