Engineering the Immune and Fibrotic Response in Volumetric Muscle Loss

摘要 大面积组织缺损的创伤对普通和军事人员来说都是一个重大的临床挑战 人口数量。当这些损伤涉及体积肌肉损失（VML），目前的黄金标准手术是治疗 用肌瓣自体移植或游离组织移植。然而，这些导致显著的纤维化和脂肪浸润，受损 再生，慢性疼痛，和严重的长期功能障碍。目前基本上缺乏 了解分子和细胞过程中的恶劣环境的全厚度，临界尺寸的VML 导致纤维化和愈合不良的缺陷，无论治疗方法如何。在最近的一系列 在临床前VML模型的出版物中，我们的小组已经定义了临界尺寸阈值，超过该阈值， 观察到VML的标志：纤维化和脂肪浸润、慢性炎症和缺乏跨血管的肌纤维桥接。 缺损我们现在提出的初步证据表明，有一个独特的和失调的细胞反应，在临界大小的 纤维脂肪形成祖细胞（FAP）快速增殖的缺陷。FAPs是一种动态的间充质基质细胞 这些细胞在肌肉干细胞（也称为卫星细胞（MuSC））中起着关键的支持和协调作用， 然而，在慢性肌肉病理中，如肌营养不良症，FAP可以分化成纤维化和纤维化。 在一个过程中，脂肪形成谱系被认为是由巨噬细胞和M2巨噬细胞的特定亚群指导的。 该提案的总体目标是通过工程化免疫调节剂在VML后再生功能性肌肉。 生物材料系统引导FAP朝向促再生状态，从而创造有利于 MuSCs移植和肌肉再生。我们的中心假设是，在VML损伤后，局部FAP 经历向异常表型的转变，所述异常表型直接分化成纤维化和脂肪组织， 递送促分解脂质介质将分解这些FAP并恢复MuSC的再生潜力。我们 目的1：确定异常FAP在与肝纤维化相关的脂肪浸润和纤维化中的作用。 VML损伤。目的2：评估M2极化巨噬细胞的促纤维化信号传导增加对FAP的贡献 VML中的函数。目的3：测试促再生FAP和MuSC在PEG-4 MAL水凝胶内的共递送是否 增强VML后的肌肉再生和功能恢复。影响- VML是一个普遍的临床挑战， 即使在金标准自体移植物治疗后，功能结局也较差。我们将定义免疫和FAP的关键作用， 细胞在这一过程中，并开发新的工程免疫调节和再生治疗策略， 为VML的临床治疗提供了基础。

ABSTRACT Extremity trauma involving large tissue loss presents a significant clinical challenge for both general and military populations. When these injuries involve Volumetric Muscle Loss (VML), the current gold standard surgery is treatment with muscle flap autografts or free tissue transfer. However, these result in significant fibrosis and fatty infiltration, impaired regeneration, chronic pain, and significant long-term functional disabilities. There is currently a fundamental lack of understanding of the molecular and cellular processes in the hostile environment of a full thickness, critically sized VML defect which leads to the fibrotic and poor healing outcomes regardless of the treatment approach. In a series of recent publications in pre-clinical VML models, our group has defined the critical size threshold above which the characteristic VML hallmarks are observed: fibrosis and fatty infiltration, chronic inflammation, and lack of myofiber bridging across the defect. We now present preliminary evidence that there is a distinct and dysregulated cellular response in the critically sized defect with rapid proliferation of fibro-adipogenic progenitor cells (FAPs). FAPs are a dynamic mesenchymal stromal cells that play a critical support and coordination role for muscle stem cells, also known as satellite cells (MuSCs), during regeneration; however, in chronic muscle pathologies, like muscular dystrophies, FAPs can differentiate into fibrotic and adipogenic lineages in a process that is thought to be directed by macrophages and specific subsets of M2 macrophages. The overall objective of this proposal is to regenerate functional muscle after VML by engineering an immunomodulatory biomaterial system to direct the FAPs towards a pro-regenerative state, thus creating an environmental niche conducive to MuSCs transplantation and muscle regeneration. Our central hypothesis posits that following VML injury, local FAPs undergo a transition to an aberrant phenotype that directly differentiates into fibrotic and fatty tissue and that controlled delivery of pro-resolving lipid mediators will resolve these FAPs and restore the regenerative potential of MuSCs. We propose the following aims: Aim 1: To determine the role of aberrant FAPs in fatty infiltration and fibrosis associated with VML injuries. Aim 2: To assess the contribution of increased pro-fibrotic signaling of M2 polarized macrophages on FAPs function in VML. Aim 3: To test whether co-delivery of pro-regenerative FAPs and MuSC within PEG-4MAL hydrogel enhance muscle regeneration and functional recovery following VML. Impact – VML is a pervasive clinical challenge with poor functional outcomes even after gold standard autograft treatment. We will define the critical roles of immune and FAP cells in this process and develop newly engineered immunomodulatory and regenerative treatment strategies that will provide a foundation to translate into clinical treatments for VML.