Coordinated resident macrophage-tenocyte signaling in tendon formation

总结 尽管成熟肌腱的结构和机械功能有着丰富的知识， 在发育过程中的tenogenic细胞分化，以及来自非tenogenic起源的细胞类型，如 巨噬细胞，影响肌腱生成是有限的。组织驻留巨噬细胞在发育中起关键作用 集落刺激因子1受体（CSF 1 R）信号传导对它们的分化至关重要 和生存作用于CSF 1 R（CSF 1是最常见的）的配体的来源通常源自 相邻的居民小区。除了作用于巨噬细胞的CSF 1 R信号传导外，巨噬细胞通常产生 作用于邻近驻留细胞以调节组织发育方面的营养因子。在令人兴奋的新 数据，我们证明了表达CSF 1 R的常驻巨噬细胞位于表达CSF 1的巨噬细胞附近， 从最初形成（E15.5）到成年，肌腱束中线性阵列内的肌腱细胞，这些驻留 在出生后早期，巨噬细胞在肌腱内迅速积累到总细胞群的近10 生长，并且由腱生成细胞产生的CSF 1是其存活所必需的。此外，这些巨噬细胞 原位内化胶原，这可能表明在生长过程中基质重塑中的潜在作用， 发展尽管它们相对丰富，并假定与邻近的腱细胞沟通，我们的研究表明， 对驻留巨噬细胞在肌腱生长和发育中的作用和潜力的了解有限 腱细胞的营养信号传导是知识上的重大空白。因为巨噬细胞对于 和修复的许多组织，确定其在肌腱发育中的作用将提供深入了解信号 在未来的治疗中可以利用这些机制来改善修复结局，这是一个未满足的临床需求。 需要的为了解决这些知识差距，本提案将定义个体发育，分布和表型 常驻巨噬细胞的概况，并建立其与肌腱细胞的串扰，以调节肌腱形成， 增长和发展。我们的中心假设是存在稳定的巨噬细胞-腱细胞串扰， 沟通是肌腱形成所必需的。目标1将定义个体发育、丰度和分布 与表达Csf 1的腱细胞相关的常驻巨噬细胞的数量以及这些细胞在 生长和发育的多个阶段。然后，目标2将建立巨噬细胞和 邻近的腱细胞及其在腱形成和生长中的作用。在这份提案中，我们将阐明 稳定的巨噬细胞-腱细胞串扰促进细胞分化和肌腱形成的生长， 发展，从而为肌腱细胞生物学提供新的和关键的见解，这将为未来的再生 战略布局

Summary Despite the vast knowledge of the structure and mechanical function of mature tendons, the understanding of tenogenic cell differentiation during development and how cell types from non-tenogenic origins, such as macrophages, influence tenogenesis is limited. Tissue resident macrophages play key roles in the development of several tissues and colony stimulating factor 1 receptor (CSF1R) signaling is essential for their differentiation and survival. The source of ligands that act on CSF1R (CSF1 being the most common) often originate from adjacent resident cells. In addition to CSF1R signaling acting on the macrophages, macrophages often produce trophic factors that act on the adjacent resident cells to regulate aspects of tissue development. In exciting new data, we demonstrate that CSF1R-expressing resident macrophages are situated adjacent to CSF1-expressing tenocytes within linear arrays in the tendon fascicle from initial formation (E15.5) into adulthood, these resident macrophages rapidly accumulate to nearly 10% of the total cell population within tendons during early postnatal growth, and CSF1 produced by tenogenic cells is required for their survival. Additionally, these macrophages internalize collagen in situ, which may indicate a potential role in matrix remodeling during growth and development. Despite their relative abundance and presumed communication with adjacent tenocytes, our limited understanding of the role of resident macrophages in tendon growth and development and potential trophic signaling to tenocytes are significant gaps in knowledge. As macrophages are critical to the development and repair of numerous tissues, defining their role in tendon development will provide insight into signaling mechanisms that could be leveraged in future therapies to improve repair outcomes, which is an unmet clinical need. To address these gaps in knowledge, this proposal will define the ontogeny, distribution, and phenotypic profile of resident macrophages and establish their cross-talk with tenocytes to regulate tendon formation during growth and development. Our central hypothesis is that stable macrophage-tenocyte cross-talk exists and this communication is necessary for tendon formation. Aim 1 will define the ontogeny, abundance, and distribution of resident macrophages with respect to Csf1-expressing tenocytes and the phenotypic profile of these cells at multiple stages of growth and development. Aim 2 will then establish the cross-talk between macrophages and adjacent tenocytes and its role in tendon formation and growth. In this proposal, we will elucidate the importance of stable macrophage-tenocyte cross-talk in promoting cell differentiation and tendon formation in growth and development, thus providing new and critical insight to tendon cell biology that will inform future regenerative strategies.