Differential ontogeny contributes to the macrophage diversity in the peripheral nervous system

周围神经是身体基本和高级功能的基本网络。虽然神经元和神经胶质细胞是神经的基本组成部分，但内皮细胞和巨噬细胞等其他常驻细胞类型在维持神经完整性方面发挥着关键作用。在这些细胞中，巨噬细胞对神经具有稳态、保护、愈合和病理功能。它们如何在生理上调整自己来协调这些不同的功能是一个活跃的研究领域，需要进一步研究它们无法解释的原位可塑性。目前的知识支持外周神经系统（PNS）中的巨噬细胞具有单一谱系，它们来源于浸润性单核细胞的终末分化。然而，我最近发表了一篇文章，在没有单核细胞贡献的情况下，巨噬细胞在PNS中自我更新和重新填充，这表明并非所有PNS中的巨噬细胞都是终末分化的单核细胞。因此，我挑战目前的范式，即PNS巨噬细胞仅浸润单核细胞。我的观点得到了早期研究的支持，即胚胎中的原始巨噬细胞甚至在单核细胞出生之前就从卵黄囊衍生祖细胞（YPCs）发育而来。我假设自我更新的PNS巨噬细胞起源于YPCs，与单核细胞相比具有不同的分子和功能特性。自我更新和浸润性巨噬细胞的混合存在和多种功能导致了与PNS巨噬细胞相关的功能分化。为了研究这一假设，并确定自我更新的巨噬细胞是否具有YPC谱系，我们将使用转基因动物系，在受控条件下用黄色荧光蛋白（YFP）不可逆地标记胚胎中YPC衍生的早期巨噬细胞。为了表征巨噬细胞亚型，这是了解其多种生理作用的核心，我们将在成年小鼠中鉴定的自我更新或浸润性巨噬细胞纯化群体中采用rna测序方法。我实验室的长期目标是了解具有复杂功能的多种细胞类型如何相互协调以执行生理任务。我在本提案中的短期目标是表征巨噬细胞亚型，并了解它们如何在空间上相互协调，以及与PNS中的其他细胞类型，以提供稳态，保护和愈合功能。为了解决这个问题，我们将在稳态条件下和神经再生过程中评估它们的分子特征、分布比例以及与PNS中的神经元、胶质细胞和内皮细胞的相互作用。这项研究是我长期研究目标的第一步，将推进巨噬细胞生物学的知识，并有助于设计这些细胞的亚型特异性操作，以用于未来的研究和治疗应用。

Peripheral nerves are essential networks for both basic and advanced functions of the body. Although neurons and glial cells are the fundamental blocks of a nerve, additional resident cell types such as endothelial cells and macrophages play critical roles in maintaining nerve integrity. Among these cells, the macrophages offer homeostatic, protective, healing and pathological functions to the nerves. How they tailor themselves to coordinate such diverse functions physiologically is an active area of investigation, and demands further investigation into their unexplained in situ plasticity. Current knowledge underpins that the macrophages in the peripheral nervous system (PNS) have a single lineage that they are derived from the terminal differentiation of infiltrating monocytes. However, I recently published that a population of macrophage self-renew and repopulate in the PNS without contribution from monocytes, suggesting that not all macrophages in the PNS are terminally differentiated monocytes. Therefore, I challenge the current paradigm that the PNS macrophages are solely infiltrating monocytes. My view is endorsed by earlier demonstrations that primitive macrophages in the embryo develop from yolk-sac derived progenitor cells (YPCs), even before a monocyte is born. I hypothesize that the self-renewing PNS macrophage originates from YPCs and has distinct molecular and functional properties compared to its monocyte counterpart. The mixed presence and diverse functions of the self-renewing and infiltrating macrophage contribute to the functional dichotomy associated with the PNS macrophages. To study this hypothesis and to identify if the self-renewing macrophage has a YPC lineage, we will use transgenic animal lines that irreversibly label YPC-derived early-born macrophages with Yellow Fluorescent Protein (YFP) in the embryo under controlled conditions. To characterize the macrophage subtypes, which is central to understand their diverse physiological roles, we will employ an RNA-sequencing approach in purified populations of either self-renewing or infiltrating macrophages identified in the adult mice. The long-term goal in my laboratory is to understand how multiple cell types with complex functions coordinate each other to perform physiological tasks. My short-term goal in this proposal is to characterize the macrophage subtypes and understand how they spatially coordinate with each other, and with other cell types in the PNS, to offer homeostatic, protective and healing functions. To address this, their molecular signature, distribution ratio, and interactions with neurons, glial cells and endothelial cells in the PNS will be assessed in the steady-state conditions and during nerve regeneration. This study is an initial upfront step for my long-term research goal and will advance the knowledge of macrophage biology, and assist in devising subtype specific manipulation of these cells for future research and therapeutic applications.