The Origin and Function of Lung Megakaryocytes

摘要 血小板母细胞是巨核细胞（Mks）。研究历来集中在Mk衍生的血小板 在骨髓（BM）中产生（1）。最近，产生血小板的Mks被证明存在于 在肺中，我们的实验室和其他人已经描述了肺Mks的免疫调节表型（2-4）。的 最近鉴定的低倍性、免疫分化的BM Mk亚群（5）强调了 较低的Mk倍性可能与免疫分化程度更高的Mk相关。我们指的是MK的发展 免疫调节亚群作为Mk免疫分化。肺Mks的起源和机制 它们的免疫分化仍然是未知的。 在没有实验证据的情况下，假设肺Mk是从未成熟的循环BM中“接种”的 Mks. Lefrancais等显示，当mTmG肺被转染时，肺血管系统中存在GFP+ Mks。 移植到PF 4-Cre-mTmG受体。作者认为，GFP+血管内肺的存在 Mks证明是肺外来源。然而，血管内和血管外肺Mks具有 形态和可能的功能差异，并且血管外肺Mks占所有肺的约70% Mks.因此，大多数循环的Mk将不得不离开血液和组织迁移到肺 住院医生由于没有直接证据证明这种运输，血管外肺Mks的确切来源仍然存在 未知，但可能对它们的免疫分化有重大影响。我假设血管外肺 Mk来源于独立于BM巨核细胞生成的局部造血祖细胞库。我来测试一下 假设通过使用互补的方法，包括辐射和转移实验，谱系追踪， 和体外集落形成单位测定。 Mk免疫分化对血小板库的影响尚不清楚。肺Mks制造血小板，虽然 肺源性血小板的相对比例仍有争议（4，6）。研究显示， 血小板异质性开始提示血小板亚群可能具有功能意义。我 假设肺驻留Mk有助于免疫分化的血小板亚群。为了验证这一 假设，我将使用一种新的策略，通过口咽CFSE给药鉴定肺源性血小板 在生理和免疫抑制条件下，如PF 4-Cre-iDTR小鼠和非致死性鼠疟疾。 从我提出的研究结果将有助于提高对免疫分化的理解， 巨核细胞生成及其在协调免疫应答和血小板免疫表型中的作用， 应用于许多血管炎性疾病。

Abstract Platelet parent cells are megakaryocytes (Mks). Studies have historically focused on Mk derived platelet production in the bone marrow (BM) (1). More recently, platelet-producing Mks have been shown to be present in the lung, and our lab and others have described an immune modulatory phenotype of lung Mks (2-4). The recent identification of a low ploidy, immune differentiated BM Mk sub-population (5) highlights the relationship that lower Mk ploidy may correlate with a more immune differentiated Mk. We refer to the development of a Mk immune modulatory sub-population as Mk immune differentiation. The origin of lung Mks and mechanisms of their immune differentiation remain unknown. It is assumed, without experimental evidence, that lung Mks are ‘seeded’ from immature circulating BM Mks. Lefrancais et al. showed the presence of GFP+ Mks in the lung vasculature when a mTmG lung was transplanted to a PF4-Cre-mTmG recipient. The authors argued that the presence of GFP+ intravascular lung Mks demonstrated an extra-pulmonary source. However, intravascular and extravascular lung Mks have morphological and perhaps functional differences, and extravascular lung Mks make up about 70% of all lung Mks. Thus, the majority of circulating Mks would have to leave the blood and tissue migrate to become lung resident. Without direct evidence for this trafficking, the definitive origin of extravascular lung Mks remains unknown, but may have a major impact on their immune differentiation. I hypothesize that extravascular lung Mks derive from a local hematopoietic progenitor pool independent of BM megakaryopoiesis. I will test this hypothesis by using complementary methods, including irradiation and transfer experiments, lineage tracing, and in vitro colony forming unit assays. The impact of Mk immune differentiation on the platelet pool is still not clear. Lung Mks make platelets, although the relative proportion of lung derived platelets remains controversial (4, 6). Emerging evidence from studies of platelet heterogeneity are beginning to suggest that platelet subsets may have functional significance. I hypothesize that lung resident Mks contribute to an immune-differentiated platelet sub-population. To test this hypothesis, I will use a novel strategy to identify lung derived platelets using oropharyngeal CFSE administration in physiologic and thrombocytopenic conditions such as PF4-Cre-iDTR mice and nonlethal murine malaria. Results from my proposed studies will contribute to an improved understanding of immune differentiated megakaryopoiesis, and its role in coordinated immune responses and platelet immune phenotypes, with direct applications to many vascular inflammatory diseases.