Engineering the Immune and Fibrotic Response in Volumetric Muscle Loss

摘要 涉及大面积组织丢失的四肢创伤对普通和军事都是一个重大的临床挑战。 人口。当这些损伤涉及到容量肌肉丢失(VML)时，目前的黄金标准手术是治疗 采用自体肌瓣移植或游离组织移植。然而，这些导致了显著的纤维化和脂肪渗透，损害了 再生、慢性疼痛和严重的长期功能残疾。目前根本上缺乏 了解在全厚、临界大小的VML恶劣环境中的分子和细胞过程 导致纤维化和愈合不良的缺陷，无论采用何种治疗方法。在最近的一系列 在临床前VML模型的发表中，我们小组定义了临界大小阈值，超过该阈值的特征 观察到VML的特征：纤维化和脂肪渗透，慢性炎症，以及缺乏横跨 叛逃。我们现在提出的初步证据表明，在临界大小的 成纤维脂肪前体细胞(FAP)快速增殖的缺陷。FAP是一种动态的间充质基质细胞 对肌肉干细胞，也称为卫星细胞(MuSCs)起着关键的支持和协调作用 再生；然而，在慢性肌肉病理中，如肌营养不良，FAP可分化为纤维性和 成脂血统在一个被认为是由巨噬细胞和M2巨噬细胞的特定亚群指导的过程中。 这项建议的总体目标是通过设计一种免疫调节剂来再生VML后的功能性肌肉 生物材料系统将FAP引向促进再生的状态，从而创造有利于 间充质干细胞移植与肌肉再生。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，直接分化为纤维化和脂肪组织，并控制 提供促进分解的脂质介体将分解这些FAP并恢复MUSCs的再生潜力。我们 提出以下目标：目标1：确定异常的FAP在脂肪渗透和纤维化中的作用 VML损伤。目的2：评估M2极化巨噬细胞促纤维化信号增强对FAP的作用 函数在VML中执行。目的3：检测促再生因子FAP和MUSC在聚乙二醇4MAL水凝胶中的联合传递 促进VML后肌肉再生和功能恢复。Impact-VML是一项普遍的临床挑战， 即使在黄金标准的自体移植治疗后，功能结果也很差。我们将定义免疫和FAP的关键作用 细胞参与这一过程，并开发新的工程免疫调节和再生治疗策略， 为将VML转化为临床治疗提供基础。

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.