Mechanisms of adipogenic and fibrotic degeneration of muscle

纤维化和成脂浸润是骨骼肌损伤、病变和衰老的特征。这 纤维脂肪变性(FFD)不仅导致骨骼肌功能下降，而且还导致骨骼肌功能增加。 代谢性疾病的流行。主要细胞贡献者的来源(成纤维和成脂 这种FFD的祖先)仍有待确定，但最近的证据(包括初步研究) 包括在本文中)暗示有一群间充质祖细胞被称为“成纤维脂肪祖细胞” (FAP)是主要来源。FAP位于肌肉间质中，表现出强烈的纤维化和成脂作用。 移植后的体外和体内潜力。直接检测内源性FAP的体内研究 在造成纤维化和肥胖症的背景下，损伤和疾病都受到了限制 具体的工具，以基因标签和目标的FAP。我们最近开发了这样的工具，通过利用 在肌肉单核细胞中，PDGFRα在FAP中的高度特异性表达。我们的 利用我们开发的用于基因标记或特异性标记的PDGFRαCreer菌株的初步研究 耗竭的FAP支持这样的假设，即FAP既是成纤维细胞的来源，也是成脂肪细胞的来源 与FFD相关的异常肌肉再生的设置。在初步研究中，我们还发现了一种 MicroRNA，miR-206，作为FAP成脂分化的候选调控因子和转录因子， RUNX1，作为MIR-206在这一过程中的可能目标。此外，我们已经确定了候选的microRNA 参与FAP纤维化分化的调控。 在对这一提议的研究中，我们将探索FAP成脂和致纤维化的调控。 在两个临床相关的模型中，FAP在FFD中的重要作用。在对目标1的研究中， 我们将研究miR-206/RUNX1轴在FAP体外成脂分化和脂肪细胞分化中的作用。 甘油诱导的肌肉损伤中的体内渗透。在AIM 2的研究中，我们将与我们的 他的同事Brian Feeley博士在加州大学旧金山分校探索FAP的一般作用，以及miR-206/RUNX1轴在 尤其是在肩袖损伤(RCI)的情况下发生的脂肪渗透。费利博士已经研制出 一种健壮的RCI小鼠模型，表现出人类所见的脂肪渗透和肌肉萎缩。我们 将使用我们开发的一种新的三苯氧胺模拟递送方法，仅在 RCI的区域。在目标3的研究中，我们将检测FAP纤维化分化的调节， 再次关注miRNAs在这种细胞命运决定中的关键作用。我们将确定以下功能目标 候选miRNAs使用最近开发的下拉技术与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。 士兵的创伤经历和退伍军人的治疗，容量肌肉损失(VML)。我们有 在VML小鼠模型方面有丰富的经验，我们将研究纤维化和 根据我们对FAP分化的理解进行预防纤维化的干预。 通过我们对FAP和控制其向成脂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和随后的肌肉的机制 功能障碍。我们的调查将利用新的实验工具来研究这一人群，并提供 洞察预防FFD的治疗策略。这将与退伍军人有直接关系， 经历过骨骼肌损伤，这种损伤限制了他们的功能能力，到目前为止， 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和 基于对基本干细胞生物学的透彻了解，防止肌肉退化。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 由于缺乏有效的治疗选择，其功能受到限制。

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.