Carbohydrate-Mediated Platelet Clearance

摘要 正常造血的维持依赖于造血干细胞的发育程序， 祖细胞（HSPC）。尽管如此，这些程序需要细胞外在机制的指导， 动态变化的血细胞需求。我们先前的工作确定了肝细胞特异性 Ashwell-Morell受体（AMR）是一种多聚体内吞受体，与老化血小板结合，诱导JAK-STAT 血小板生成素（TPO）的信号传导和产生，TPO是负责巨核细胞成熟的细胞因子， HSPC的分化、血小板产生和维持。除了规范TPO生产和 除去老化的血小板，我们发现了AMR调节红细胞生成的一种意想不到的机制。 我们的初步数据表明，肝脏AMR在调节Neuregulin 4（Nrg 4）水平中的作用， ErbB 4（也称为HER 4）的配体，受体酪氨酸激酶家族的第四个成员，包括 表皮生长因子（EGF）受体（EGFR/HER 1）、ErbB 2/HER 2和ErbB 3/HER 3。全基因组 相关性研究（GWAS）显示，NRG 4变体与血红蛋白水平的变化相关， ErbB 4信号传导有助于人类和小鼠红细胞生成。 我们的数据显示，Nrg 4的增加影响ErbB 4在骨髓间充质干细胞中的表达和信号传导。 干细胞（MSC），导致红细胞生成缺陷和S100 a8和S100 a9表达水平增加， 钙结合S100蛋白家族的成员，分别称为钙粒蛋白A和B。重组， 细胞外的S100 a8和红细胞祖细胞中增加的S100 a8表达水平诱导红系造血干细胞分化。 分化缺陷我们试图定义Nrg 4/ErbB 4如何影响HSPC稳态和红细胞生成， 包括成红细胞岛（Aim 1）。我们将探讨Nrg 4/ErbB 4影响MSC的机制， 功能、钙颗粒蛋白表达和红细胞生成（Aim 2）。我们采用了一种多管齐下的方法， 建模，抑制剂，转录组学和生物化学方法，以允许机制探索， Nrg 4/ErbB 4/钙颗粒蛋白轴参与红细胞生成。拟议的调查将 进一步推动治疗发展，以改善血液病中的红细胞生成缺陷，包括 骨髓增生性肿瘤和骨髓增生异常综合征患者。

ABSTRACT Maintenance of normal hematopoiesis depends on developmental programs for the hematopoietic stem and progenitor cell (HSPC). Still, these programs require guidance by cell-extrinsic mechanisms that correctly convey the dynamically changing needs of the blood cells. Our prior work established that the hepatocyte-specific Ashwell-Morell receptor (AMR), a multimeric endocytic receptor, binds to aged platelets, inducing JAK-STAT signaling and production of thrombopoietin (TPO), the cytokine responsible for megakaryocyte maturation and differentiation, platelet production, and maintenance of HSPCs. In addition to regulating TPO production and removing aged platelets, we uncovered an unexpected mechanism by which the AMR regulates erythropoiesis. Our preliminary data suggest a role for the hepatic AMR in regulating Neuregulin 4 (Nrg4) levels, the specific ligand for ErbB4 (also known as HER4), the fourth member of the receptor tyrosine kinase family that includes the epidermal growth factor (EGF) receptor (EGFR/HER1), ErbB2/HER2, and ErbB3/HER3. A genome-wide association study (GWAS) shows that NRG4 variants are associated with changes in hemoglobin levels, and ErbB4 signaling contributes to human and mouse erythropoiesis. Our data shows that an increase in Nrg4 affects ErbB4 expression and signaling in bone marrow mesenchymal stem cells (MSCs), leading to defective erythropoiesis and increased expression levels of S100a8 and S100a9, members of the calcium-binding S100 protein family, known as Calgranulin A and B, respectively. Recombinant, extracellular, and increased S100a8 expression levels in erythrocyte progenitors induce an erythroid differentiation defect. We seek to define how Nrg4/ErbB4 affects HSPC homeostasis and erythropoiesis, including erythroblastic islands (Aim 1). We will interrogate the mechanism by which Nrg4/ErbB4 affect MSC function, calgranulin expression, and erythropoiesis (Aim 2). We use a multipronged approach of genetic mouse modeling, inhibitors, transcriptomics, and biochemical approaches to allow mechanistic exploration into the participation of the Nrg4/ErbB4/calgranulin axis in contributing to erythropoiesis. The proposed investigation will further drive therapeutic development to ameliorate erythropoietic deficiencies in blood disease, including in patients with myeloproliferative neoplasms and myelodysplastic syndrome.