Role of Extracellular Vesicles in Bone-Muscle Crosstalk with Aging

摘要 骨质疏松症和骨质疏松症是经常同时发生并降低生活质量的老年性疾病。 在老年人口中。有证据表明，骨骼和肌肉之间的信号串扰通过 循环和局部介质，导致了肌肉-骨骼相声可能协调年龄的概念- 相关的退行性改变。细胞间通讯中一个令人兴奋的新范例是细胞外 囊泡(EV)(外切体和微囊泡)可能提供一种新的沟通机制 细胞。也有人提出，循环中的肌源性外切体(称为“外切体”)可以 调节运动对身体的一些有益影响。EV是膜结合的颗粒物脱落 来自含有大量蛋白质、mRNAs和microRNAs(MiRNAs)的细胞。EV与目标小区对接， 运送他们的货物并改变它的功能。我们已经证明，年轻的和老年的骨细胞排出EV， 这可能为成骨细胞功能的调节提供一种新的机制。活细胞成像显示 骨细胞将EV从细胞体和树突中排出，并可能将它们排入循环。骨细胞 EV被成骨细胞和成肌细胞摄取，并对成骨细胞具有促进作用 向早期骨细胞表型分化。来自成肌细胞和肌管的EV被 并诱导β-连环蛋白信号转导。这些发现导致了我们的总体假设细胞外 囊泡(Vesicles，EV)是骨和肌肉细胞功能的重要调节因子，为人类提供了一种新的 肌肉与骨骼之间的串扰可能调节老年性骨质疏松症的机制 和骨质疏松症。这一假设将使用免费的体外和体内方法进行验证，并 在幼年和老年小鼠模型中使用带荧光记者的活体成像标记骨骼和肌肉 细胞。目的1确定EV在体外调节骨细胞-成骨细胞相互作用中的作用 在体内，以及衰老和锻炼是如何改变这一点的。这将使用来自成骨细胞的EV和 确定EV对成骨细胞系和原代细胞分化功能的相互影响 单元类型。目标2将确定EV在调节肌肉-骨骼串扰中的作用以及它是如何被 衰老和锻炼。这将使用来自成肌细胞、成骨细胞和骨细胞系的EV来完成 以确定EV对原代细胞分化功能的影响的相互细胞类型。在这两个目标中， 活细胞和活体成像将确定EV在肌肉和骨细胞中的释放和摄取的动力学 在体外和体内。年轻的和年长的老鼠模型将使用有和没有轮子跑运动的模型 在体内外测定衰老和运动对EV释放、成分和功能的影响。 这些研究可能导致对分子串扰机制的范式转换 骨骼和肌肉，将为开发肌肉和骨源性电动汽车的潜力铺平道路 循环生物标记物和作为治疗年龄相关性骨骼和肌肉损失的新疗法。

ABSTRACT Osteoporosis and sarcopenia are diseases of aging that frequently occur together and reduce quality of life in the elderly population. Evidence is emerging for signaling crosstalk between bone and muscle via circulating and local mediators, leading to the concept that muscle-bone crosstalk may coordinate age- related degenerative changes. An exciting new paradigm in cell-cell communication is that extracellular vesicles (EV) (exosomes and microvesicles) may provide a novel mechanism for communication between cells. It has also been proposed that circulating muscle-derived exosomes (termed “exersomes”) may mediate some of the beneficial effects of exercise in the body. EV are membrane-bound particles shed from cells with a cargo of proteins, mRNAs and microRNAs (miRNAs). The EV dock with a target cell, delivering their cargo and altering its function. We have shown that young and aged osteocytes shed EV, which may provide a novel mechanism for regulation of osteoblast function. Live cell imaging suggests osteocytes shed EV from their cell body and dendrites and may shed them into the circulation. Osteocyte EV are taken up by osteoblasts and myoblasts and have potent effects on osteoblasts to promote differentiation towards an early osteocyte phenotype. EV from myoblasts and myotubes are taken up by osteocytes and induce β-catenin signaling. These findings lead to our overall hypothesis that extracellular vesicles (EV) are important regulators of bone and muscle cell function and provide a novel mechanism for crosstalk between muscle and bone that may regulate age-related osteoporosis and sarcopenia. This hypothesis will be tested using complimentary in vitro and in vivo approaches and using intravital imaging in young and aged mouse models with fluorescent reporters to tag bone and muscle cells. Aim 1 will determine the role of EV in regulating osteocyte-osteoblast reciprocal interactions in vitro and in vivo and how this is altered by aging and exercise. This will be done using EV from osteoblast and osteocyte cell lines and primary cells to determine EV effects on the differentiated function of the reciprocal cell type. Aim 2 will determine the role of EV in regulating muscle-bone crosstalk and how it is altered by aging and exercise. This will be done using EV from myoblast, osteoblast and osteocyte cell lines and primary cells to determine EV effects on the differentiated function of the reciprocal cell types. In both aims, live cell and intravital imaging will determine the kinetics of EV release and uptake in muscle and bone cells in vitro and in vivo. Young and aged mouse models will be used with and without wheel running exercise to determine in vitro and in vivo the effect of aging and exercise on EV release, composition and function. These studies may result in paradigm shifting insight into the mechanisms of molecular crosstalk between bone and muscle and will pave the way for exploiting the potential of muscle and bone derived EVs as circulating biomarkers and as novel therapeutics for age related bone and muscle loss.