Mechanisms of lung macrophage programming by MUC5B during health and disease

项目总结 黏液和巨噬细胞在健康中保护肺部，但它们也可能导致肺部疾病。 受伤。它们的保护功能和病理功能是如何校准的，目前还知之甚少。我们寻求 确定在肺损伤反应过程中控制它们相互作用的机制。对于粘液介导的 防御方面，粘蛋白糖蛋白MUC5B是必不可少的。在小鼠中，缺乏MUC5B会导致颗粒和 细菌在肺部积聚，最终导致早期死亡。尽管它对健康有要求， MUC5B是人类肺纤维化的一个重要危险因素，它在细支气管球中错误表达 细胞和2型肺泡上皮细胞。MUC5B在小鼠这些细胞类型中的过度表达加剧了纤维化 博莱霉素性肺损伤后。这些数据表明，MUC5B/MUC5B的水平和位置- 表达是肺纤维化发病机制中的重要因素。尽管如此，我们还没有完全 了解解释MUC5B/MUC5B如何促进肺纤维化的细胞和分子机制。我们的 最近的工作表明，呼吸道粘液的防御和病理作用是由相互作用调节的。 在MUC5B和空域巨噬细胞(AM)之间。常驻AM是符合宪法的，并且是必需的 用于非炎症性防御。作为对伤害的反应，AM池通过补充血液来增加 成熟为巨噬细胞的单核细胞。这些招募的AM比常驻AM更具煽动性，但 它们也是短暂的，导致AM池的瞬时扩张和收缩。机制： 区分常驻和招募AM类型的急性和消退性炎症也影响纤维化 修理。MUC5B/MUC5B和AM在远端空间的存在，以及我们先前观察到的 MUC5B基因敲除小鼠的AM功能障碍，暗示MUC5B/MUC5B与AM功能之间存在联系。 我们发现了一种由粘蛋白多糖和AM多糖受体介导的潜在机制。MUC5B/MUC5B是 涂有大量唾液酸(SA)，通过α2，3-键连接到半乳糖上。它也是唾液酸的配体 酸结合免疫球蛋白，如凝集素-F(Siglec-F)，一种几乎仅存在的抑制性信号分子 在健康的肺中使用AM。我们发现，MUC5B-SA-Siglec-F轴对于消退炎症至关重要，因为 表现为在缺乏每种成分的小鼠中长时间的招募AM积累。我们现在还展示了 博莱霉素诱导的肺纤维化在MUC5B-SA-Siglec-F轴被破坏的小鼠中受到抑制。因此，虽然 作为对细菌炎症的保护性反应，这一机制似乎对促纤维化有害。 伤情设置。我们假设肺组织的纤维化修复是由MUC5B-SA-Siglec-F介导的 依赖AM编程机制。这将在三个目标中进行测试，这三个目标测试1)推广 MUC5B引起的肺纤维化需要α2，3-唾液酸化，2)唾液酸化MUC5B结扎Siglec-F介导纤维化； 3)MUC5B-SA-Siglec-F轴调节常驻AM与招募AM的纤维性编程。

PROJECT SUMMARY Mucus and macrophages protect the lungs in health, but they can also contribute to disease following lung injury. How their protective vs. pathological functions are calibrated is poorly understood. We seek to determine mechanisms that control their interactions during responses to lung injury. For mucus-mediated defense, the mucin glycoprotein MUC5B is essential. In mice, absence of Muc5b causes particles and bacteria to accumulate in the lungs, ultimately resulting in early mortality. Despite its requirement for health, MUC5B is an important risk factor in human pulmonary fibrosis, where it is misexpressed in bronchiolar club cells and type 2 alveolar epithelia. Overexpression of Muc5b in these cell types in mice potentiates fibrosis following bleomycin-induced lung injury. These data suggest that the levels and locations of MUC5B/Muc5b- expression are significant factors in the pathogenesis of pulmonary fibrosis. Nonetheless, we do not yet fully understand cellular and molecular mechanisms that explain how MUC5B/Muc5b promotes lung fibrosis. Our recent work suggests that defensive and pathologic effects of airway mucus are regulated by interactions between Muc5b and airspace macrophages (AMs). Resident AMs are present constitutively and are required for non-inflammatory defense. In response to injury, AM pools increase through recruitment of blood monocytes that mature into macrophages. These recruited AMs are more inflammatory than resident AMs, but they are also short-lived, resulting in transient expansion and then contraction of the AM pools. Mechanisms of acute and resolving inflammation that distinguish resident and recruited AM types also impinge on fibrotic repair. The presence of both MUC5B/Muc5b and AMs in distal airspaces, along with our prior observation of AM dysfunction in Muc5b knockout mice, implicate a connection between MUC5B/Muc5b and AM functions. We identified a potential mechanism mediated by mucin glycans and AM glycan receptors. MUC5B/Muc5b is heavily coated with sialic acid (SA) that is attached to galactose via an α2,3-linkage. It is also a ligand for sialic acid binding immunoglobulin like lectin-F (Siglec-F), an inhibitory signaling molecule found almost exclusively on AMs in healthy lungs. We found that a Muc5b-SA-Siglec-F axis is critical for resolving inflammation, as shown by prolonged recruited AM accumulation in mice lacking each component. We now also show that bleomycin-induced lung fibrosis is suppressed in Muc5b-SA-Siglec-F axis disrupted mice. Thus, while protective in response to bacterial inflammation, this mechanism appears to be detrimental in a pro-fibrotic injury setting. We hypothesize that fibrotic repair of lung tissues is mediated by a Muc5b-SA-Siglec-F dependent AM programming mechanism. This will be tested in three aims that test whether 1) promotion of lung fibrosis by Muc5b requires α2,3-sialylation; 2) ligation of Siglec-F by sialylated Muc5b mediates fibrosis; and 3) the Muc5b-SA-Siglec-F axis regulates fibrotic programming of resident vs. recruited AMs.