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重要网络。虽然神经元和神经胶质细胞是神经的基本块，但其他驻留细胞类型如内皮细胞和巨噬细胞在维持神经完整性方面发挥关键作用。在这些细胞中，巨噬细胞为神经提供稳态、保护、愈合和病理功能。它们如何调整自己以协调生理上的各种功能是一个活跃的研究领域，并要求进一步研究其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，它们来源于浸润单核细胞的终末分化。然而，我最近发表了一个群体的巨噬细胞自我更新和重新填充在PNS没有单核细胞的贡献，这表明不是所有的巨噬细胞在PNS终末分化的单核细胞。因此，我挑战目前的范式，即PNS巨噬细胞只是浸润单核细胞。我的观点得到了早期证据的支持，即胚胎中的原始巨噬细胞是从卵黄囊来源的祖细胞（YPC）发育而来的，甚至在单核细胞出生之前。我推测，自我更新的PNS巨噬细胞来源于YPCs，并具有不同的分子和功能特性相比，其单核细胞。自我更新和浸润性巨噬细胞的混合存在和不同功能促成了与PNS巨噬细胞相关的功能二分法。 为了研究这一假设并鉴定自我更新巨噬细胞是否具有YPC谱系，我们将使用转基因动物系，其在受控条件下在胚胎中用黄色荧光蛋白（YFP）不可逆地标记YPC衍生的早期出生的巨噬细胞。为了表征巨噬细胞亚型，这是理解其不同生理作用的核心，我们将在成年小鼠中鉴定的自我更新或浸润性巨噬细胞的纯化群体中采用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。我在这项提案中的短期目标是描述巨噬细胞亚型的特征，并了解它们如何在空间上相互协调，以及与PNS中的其他细胞类型协调，以提供稳态，保护和愈合功能。为了解决这一问题，将在稳态条件下和神经再生期间评估它们的分子特征、分布比以及与PNS中的神经元、神经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，并协助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.