Mechanisms of adipogenic and fibrotic degeneration of muscle

纤维化和脂肪形成浸润是骨骼肌损伤、病变和老化的标志。这 纤维脂肪变性（“FFD”）不仅导致骨骼肌的功能下降，而且还导致骨骼肌中纤维脂肪的增加。 代谢紊乱的患病率。主要细胞贡献者（纤维化和脂肪形成）的起源 这种FFD的祖细胞）仍有待确定，但最近的证据（包括初步研究） 包括在本文中）提出了称为“纤维脂肪生成祖细胞”的间充质祖细胞群 （FAP）是主要来源。FAP存在于肌肉结缔组织中，并显示出强大的纤维形成和脂肪形成 在体外和体内移植后的潜力。直接测试内源性FAP是否 在损伤和疾病的情况下导致纤维化和肥胖， 基因标记和靶向FAP的特定工具。我们最近开发了这样的工具， PDGFRα在FAP中的高度特异性表达在肌肉单核细胞中。我们 使用PDGFRαCreER菌株进行的初步研究，我们开发该菌株用于遗传标记或特异性 耗尽的FAP支持了FAP是纤维化和脂肪形成细胞来源的假设。 与FFD相关的异常肌肉再生的设置。在初步研究中，我们还确定了一个 microRNA，miR-206，作为FAP成脂分化的候选调节因子，和转录因子， Runx 1，作为mIR-206在此过程中的可能目标。此外，我们还鉴定了候选的microRNA， 参与FAP纤维化分化的调节。 在本课题的研究中，我们将探讨FAP对成脂和成纤维的调控作用， 分化，以及FAP在两个临床相关模型中FFD中的重要作用。在目标1的研究中， 我们将研究miR-206/Runx 1轴在体外FAP成脂分化中的作用以及在脂肪细胞中的作用。 体内甘油诱导的肌肉损伤中的浸润。在目标2的研究中，我们将与 我的同事，Brian Feeley博士，在加州大学旧金山分校，探索FAPs的作用，以及miR-206/Runx 1轴， 特别是在肩袖损伤（RCI）的情况下发生的脂肪浸润中。费利博士开发了 RCI的一种稳健的鼠模型，其表现出在人类中看到的那种脂肪浸润和肌肉萎缩。我们 将使用一种新的他莫昔芬类似物输送方法，我们已经开发，允许消耗FAP只在 RCI的区域。在目的3的研究中，我们将检查FAP纤维化分化的调节， 再次关注miRNA在细胞命运决定中的关键作用。我们将确定功能目标， 使用最近开发的下拉技术联合收割机与RNA测序（LAMP- seq）。此外，我们还将探讨FAP在常见肢体广泛纤维化中的作用。 创伤性损伤经验的士兵和治疗的退伍军人，体积肌肉损失（VML）。我们有 在VML小鼠模型的广泛经验中，我们将研究纤维化的发展， 基于我们对FAP分化的理解，进行干预以预防纤维化。 通过我们对FAPs和控制其向成脂细胞分化的调控过程的研究， 和纤维化细胞，我们的目标是了解引起FFD和随后的肌肉损伤的机制。 功能障碍我们的研究将利用新的实验工具来研究这一人群， 深入了解预防FFD的治疗策略。这将直接关系到退伍军人谁有 经历过骨骼肌损伤，这些损伤限制了他们的功能能力，并且迄今为止， 功能恢复的希望渺茫我们的目标是开发治疗方法来增强肌肉修复， 预防肌肉退化的基础上，彻底了解基本的干细胞生物学。这些 目标是基于对改善退伍军人健康和生活质量的使命的坚定承诺 其功能由于缺乏有效的治疗选择而受到限制。

Fibrotic and adipogenic infiltration are hallmarks of injured, diseased, and aged skeletal muscle. This fibrofatty degeneration (“FFD”) results not only in functional decline of skeletal muscle but also to the increased prevalence of metabolic disorders. The origins of the major cellular contributors (fibrogenic and adipogenic progenitors) of this FFD remain to be definitively identified, but recent evidence (including Preliminary Studies included herein) suggest a population of mesenchymal progenitors termed “fibroadipogenic progenitors” (FAPs) are major sources. FAPs reside in the muscle interstitium and display robust fibrogenic and adipogenic potential in vitro and in vivo following transplantation. Studies in vivo to directly test whether endogenous FAPs are responsible for fibrosis and adiposity in the setting of injury and disease have been limited by the lack of specific tools to genetically label and target FAPs. We have recently developed such tools by taking advantage of the highly specific expression of PDGFRα in FAPs among the mononucleated cells of muscle. Our Preliminary Studies using a PDGFRαCreER strain that we developed to either genetically label or specifically deplete FAPs support the hypothesis that FAPs are sources of both fibrogenic and adipogenic cells in the setting of aberrant muscle regeneration associated with FFD. In Preliminary Studies, we also identified a microRNA, miR-206, as a candidate regulator of FAP adipogenic differentiation, and a transcription factor, Runx1, as a likely target of mIR-206 in this process. We have, in addition, identified candidate microRNAs involved in the regulation of FAP fibrogenic differentiation. In the studies of this proposal, we will explore the regulation of FAP adipogenic and fibrogenic differentiation, and the essential role of FAPs in FFD in two clinically relevant models. In the studies of Aim 1, we will examine the role of the miR-206/Runx1 axis in FAP adipogenic differentiation in vitro and in fatty infiltration in glycerol-induced muscle injury in vivo. In the studies of Aim 2, we will work collaboratively with our colleague, Dr. Brian Feeley, at UCSF to explore the role of FAPs in general, and of the miR-206/Runx1 axis in particular, in the fatty infiltration that occurs in the setting of rotator cuff injury (RCI). Dr. Feeley has developed a robust murine model of RCI that exhibits the kind of fatty infiltration and muscle atrophy seen in humans. We will use a novel tamoxifen analog delivery method we have developed to allow for the depletion of FAPs only in the region of the RCI. In the studies of Aim 3, we will examine the regulation of FAP fibrogenic differentiation, again focusing on the key role of miRNAs in such cell fate decisions. We will identify functional targets of candidate miRNAs using a recently developed pull-down technology combine with RNA sequencing (LAMP- seq). Furthermore, we will address the role of FAPs in the extensive fibrosis seen in the common extremity traumatic injury experience by soldiers and treated in Veterans, volumetric muscle loss (VML). We have extensive experience with a murine model of VML, and we will examine both the development of fibrosis and interventions to prevent fibrosis based on our understanding of FAP differentiation. Through our studies of FAPs and the regulatory processes that control their differentiation to adipogenic and fibrogenic cells, we aim to understand the mechanisms that give rise to FFD and the subsequent muscle dysfunction. Our investigation will both capitalize on new experimental tools to study this population and lend insight into therapeutic strategies to prevent FFD. This will have direct relevance to Veterans who have experienced skeletal muscle injuries, injuries that have limited their functional capacity and that, to date, have little hope of functional recovery. Our goal is to develop therapeutic approaches to enhance muscle repair and prevent muscle degeneration based upon a thorough understanding of the basic stem cell biology. These goals are based upon a firm commitment to a mission to improve the health and quality of life of Veterans whose function is limited by the lack of effective therapeutic options.