Mechanisms of lung macrophage programming by MUC5B during health and disease

项目摘要 粘液和巨噬细胞保护健康的肺部，但它们也可能导致肺部疾病， 损伤它们的保护功能与病理功能是如何校准的，人们对此知之甚少。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，粘蛋白糖蛋白MUC5B是必不可少的。在小鼠中，Muc5b的缺失导致颗粒和 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是人类肺纤维化的重要危险因素，在细支气管俱乐部中错误表达 细胞和2型肺泡上皮细胞。小鼠中这些细胞类型中Muc5b的过表达增强纤维化 博来霉素引起的肺损伤这些数据表明，MUC5B/Muc5b-1的水平和位置可能与MUC5B/Muc5b-1的表达有关。 表达是肺纤维化发病机制中的重要因素。然而，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 最近的研究表明，气道粘液的防御和病理作用受到相互作用的调节， Muc5b与肺泡巨噬细胞（AM）之间的关系。常驻AM按规定出席， 非炎症性防御作为对损伤的反应，AM池通过募集血液而增加 单核细胞成熟为巨噬细胞。这些被招募的AM比常驻AM更具煽动性， 它们也是短暂的，导致AM池的瞬时膨胀然后收缩。机制 区分驻留型和募集型AM类型的急性和消退性炎症也影响纤维化。 修复. MUC5B/Muc5b和AM在远端气隙中的存在，沿着我们先前的观察， Muc5b基因敲除小鼠AM功能障碍，提示MUC5B/Muc5b与AM功能之间存在联系。 我们确定了一个潜在的机制介导的粘蛋白聚糖和AM聚糖受体。MUC5B/Muc5b是 被通过α 2，3-键连接到半乳糖上的唾液酸（SA）严重包被。它也是唾液酸的配体 酸结合免疫球蛋白样凝集素-F（Siglec-F），一种抑制性信号分子， 对健康肺部的AM我们发现Muc5b-SA-Siglec-F轴对于解决炎症是至关重要的， 在缺乏每种成分的小鼠中，增加的AM蓄积时间延长。我们现在还表明， 博来霉素诱导的肺纤维化在Muc5b-SA-Siglec-F轴破坏的小鼠中被抑制。因此，虽然 这种机制虽然对细菌炎症有保护作用，但在促纤维化中似乎是有害的 伤害设置。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。这将在三个目标中得到检验，这些目标将检验：1）促进 Muc5b引起的肺纤维化需要α 2，3-唾液酸化; 2）唾液酸化的Muc5b连接Siglec-F介导纤维化; 和3）Muc5b-SA-Siglec-F轴调节驻留AM与募集AM的纤维化编程。

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.