Muscle Atrophy and Bone Anabolism

描述(由申请人提供)：这个项目将探索一个新的假说，这个假说来自我们意外的观察，即在外源性的骨机械负荷上叠加肌肉麻痹，极大地增强了对负荷的成骨反应。这些数据直接挑战了该领域的一个中心范式，该范式反映了从组织到分子水平上的共识，即肌肉和骨骼的萎缩和肥大并行。我们的初步研究进一步证明，瘫痪肌肉相对于负荷骨的位置不会改变这种反应，证实了循环因子负责调节增强的合成代谢。我们随后的研究揭示了一个耦合肌肉萎缩和骨合成代谢的候选基因，microRNA206(mir-206)。与迅速发展的关于通过外体microRNA进行细胞间信号传递的文献相一致，以及mir-206抑制组蛋白脱乙酰酶4(HDAC4)的能力，进而促进成骨细胞分化，我们假设：肌肉瘫痪瞬时上调外体mir-206，后者通过抑制HDAC4，促进成骨细胞的分化和功能。我们将通过四个密切相关的S.目标来推进这一论题，每个目标 以及相应的子假说。S.AIMS#1和#2的体内实验旨在证明，肌肉瘫痪诱导的细胞信号通过血清中的外切体瞬时增强正在进行的成骨细胞分化和功能，所观察到的合成代谢增强可以独立于负荷诱导的成骨细胞激活实现，并且这种反应可以在小梁骨和皮质骨中诱导。我们将使用体外方法证实外体mir-206通过抑制HDAC4的翻译来增强成骨细胞的分化和功能(S.Aim#3)，我们将证明在体内靶向该途径的下游(通过抑制HDAC4)能够复制增强的骨合成代谢，而不需要诱导肌肉瘫痪(S.Aim#4)。如果该项目成功，我们相信这些数据将从根本上改变我们对肌肉和骨骼如何在分子、细胞和组织水平上相互作用的概念化，并将使这一途径成为最终能够改善骨骼形态的临床干预的新靶点。

DESCRIPTION (provided by applicant): This project will explore a novel hypothesis that arose from our unexpected observation that superimposing muscle paralysis upon exogenous mechanical loading of bone greatly augments the osteogenic response to loading. These data directly challenge a central paradigm in the field, which reflects the consensus that, from the tissue to molecular levels, muscle and bone atrophy and hypertrophy in parallel. Our preliminary studies further demonstrated that the location of the paralyzed muscle relative to the loaded bone did not alter this response, confirming that a circulating factor was responsible for mediating the enhanced anabolism. Our subsequent studies have revealed a candidate for coupling muscle atrophy and bone anabolism, microRNA 206 (mir-206). Consistent with the rapidly expanding literature regarding cell-to-cell signaling via exosomal microRNA and the demonstrated ability of mir-206 to suppress histone deacetylase 4 (HDAC4) which, in turn, enhances osteoblast differentiation, we hypothesize that: muscle paralysis transiently upregulates exosomal mir-206 which, via suppression of HDAC4, enhances osteoblast differentiation and function. We will pursue this thesis through four closely related S. Aims, each with a corresponding sub- hypothesis. The in vivo experiments of S. Aims #1 and #2 are designed to demonstrate that cellular signaling induced by muscle paralysis transiently enhances ongoing osteoblast differentiation and function via exosomes within the serum, that the observed anabolic augmentation can be achieved independently of loading induced osteoblast activation, and that the response can be induced in both trabecular and cortical bone. We will use in vitro approaches to confirm that exosomal mir-206 serves to enhance osteoblast differentiation and function by suppressing translation of HDAC4 (S. Aim #3) and we will demonstrate that downstream in vivo targeting of this pathway (via HDAC4 inhibition) is able to replicate enhanced bone anabolism without the necessity of inducing muscle paralysis (S. Aim #4). If the project is successful, we believe these data would fundamentally alter our conceptualization of how muscle and bone interact at the molecular, cellular, and tissue levels and would enable novel targeting of this pathway as an eventual clinical intervention capable of enhancing bone morphology.