Regulation of monocyte lineage development in systemic and vascular inflammation and the influence of Notch signaling

单核-吞噬系统和血管不断地相互作用以维持体内平衡。内皮细胞(EC)提供特定的信号，引导经典(Ly6chi)单核细胞分化为巡逻(Ly6Clo)单核细胞、MHC-II+单核细胞、巨噬细胞(MF)和树突状细胞(DC)。另一方面，成熟的吞噬细胞与炎症反应和血管或组织监测有关。这种多功能的EC到单核细胞的串扰受到慢性环境应激的损害，这会导致低度炎症和单核细胞发育程序的失调。这会导致炎症细胞的扩张和激活，血管的渗透和随后的损伤，以及心血管疾病的发展。当失调的吞噬细胞暴露在额外的微生物应激下时，炎症和血管病理进一步增强。Ly6chi单核细胞具有发育可塑性，可分化为表型和功能不同的成熟细胞，包括Ly6Clo、MHC-II+单核细胞、MF和DC。这一单核细胞生成的后期步骤受到EC到髓系Notch信号的严格控制。然而，单核细胞形成的早期步骤、单核细胞的前体细胞和分化途径却知之甚少，它们定义了单核细胞的异质性、发育可塑性和影响炎症。我们假设并在初步结果中表明，单核细胞至少来自两个独立的祖细胞谱系，即依赖于MDP2和cMoP的途径，这一过程受Notch控制。我们开发了一种新的小鼠模型，其中Notch2在早期依赖MDP2的单核细胞生成中被特异性删除，而另一种依赖cMoP的单核细胞生成保持不变。Notch2缺失导致稳定状态下Ly6Clo-减少，MHC-II+单核细胞和DC扩张。当受到炎症刺激时，这些小鼠会出现严重的炎症，血液中的MF样细胞和MHC-II+单核细胞异常扩张，MF渗入主要血管。在体外，Notch配体DLL1诱导Ly6Clo单核细胞的特异性扩增，而DLL4支持MHC-II+单核细胞的发育。在体内，血管中DLL1的下调和DLL4的上调以及MHC-II+单核细胞、DC和MF的同时扩张证实了单核细胞命运的配体特异性调节。因此，Notch控制单核细胞的异质性、分化、功能和影响炎症。在这里，我们建议研究单核细胞生成的途径，并解决单核细胞异质性的机制。我们打算定义控制单核细胞生成的信号机制，单核细胞的功能以及与炎症的关系。这些知识对于理解炎症和血管损伤的病理生理学可能是至关重要的，并有助于设计有效的治疗策略和预防措施。

Mononuclear-phagocytic system and blood vessels constantly interact with each other to maintain homeostasis. Endothelial cells (EC) provide specific signals and guide classical (Ly6Chi) monocyte differentiation into patrolling (Ly6Clo) monocytes, MHC-II+ monocytes, or macrophages (MF) and dendritic cells (DC). On the other hand, mature phagocytes are implicated in inflammatory reactions and vascular or tissue monitoring. Such versatile EC-to-monocyte cross-talk is impaired by chronic environmental stress, which induces low-grade inflammation and dysregulates monocyte developmental program. This leads to expansion and activation of inflammatory cells, infiltration and subsequent damage of blood vessels and development of cardiovascular disease. Inflammation and vascular pathology is further enhanced when dysregulated phagocytes are exposed to the additional microbial stressors.Ly6Chi monocytes have developmental plasticity for a spectrum of phagocytes as they differentiate into phenotypically and functionally distinct mature cells including Ly6Clo, MHC-II+ monocytes, MF and DCs. This late step of monopoiesis is tightly controlled by EC-to-myeloid Notch signaling. Yet little is known about early steps of monopoiesis, monocyte progenitors and differentiation pathways which define monocyte heterogeneity, developmental plasticity and influence inflammation.We have hypothesized and show in preliminary results that monocytes are derived from at least two independent progenitor lineages, i.e. MDP2- and cMoP-dependent pathways, and this process is controlled by Notch. We developed a new mouse model where Notch2 is specifically deleted in early MDP2-dependent monopoiesis, while the alternative, cMoP-dependent monopoiesis remains intact. Notch2 deletion causes reduction of Ly6Clo- and expansion of MHC-II+ monocytes and DCs in steady state. When subjected to inflammatory stimuli, these mice develop severe inflammation with aberrant expansion of MF-like cells and MHC-II+ monocytes in the blood and MF infiltration of major blood vessels. In vitro Notch ligand DLL1 induced specific expansion of Ly6Clo monocytes, while DLL4 supported MHC-II+ monocyte development. In vivo, downregulation of Dll1 and upregulation of Dll4 in blood vessels with simultaneous expansion of MHC-II+ monocytes, DC and MF during vascular inflammation confirmed ligand-specific regulation of monocyte cell fate. Thus, Notch controls monocyte heterogeneity, differentiation, function and influences inflammation.Here we propose to study pathways of monopoiesis and address the mechanisms of monocyte heterogeneity. We intend to define signaling mechanisms controlling monopoiesis, the function of monocytes and implication for inflammation. This knowledge might be crucial for understanding of the pathophysiology of inflammation and vascular damage and significantly contribute to the design of efficient treatment strategies and preventive measures.