Carbohydrate-Mediated Platelet Clearance

摘要 正常造血的维持依赖于造血干细胞和 祖细胞(HSPC)。尽管如此，这些程序仍然需要细胞--正确传递信息的外部机制--的指导 动态变化的血细胞需求。我们之前的工作确定了肝细胞特异性 Ashwell-Morell受体(AMR)是一种多聚体内源性受体，与衰老的血小板结合，诱导JAK状态 血小板生成素(TPO)的信号和产生，TPO是负责巨核细胞成熟和释放的细胞因子 HSPC的分化、血小板生成和维持。除了监管TPO的生产和 去除老化的血小板，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NeuRegin 4(NRG4)水平方面发挥了作用，NRG4是特异性的 ErbB4(也称为HER4)的配体，是受体酪氨酸激酶家族的第四个成员，包括 表皮生长因子受体(EGFR/HER1)、ErbB2/HER2和ErbB3/HER3。一个全基因组的 协会研究表明，NRG4变异与血红蛋白水平的变化有关，并且 ERBB4信号与人和小鼠的红细胞生成有关。 我们的数据显示，NRG4的增加影响了骨髓间充质中ErbB4的表达和信号转导 干细胞(MSCs)，导致红细胞生成缺陷和S100A8和S100a9表达水平增加， 钙结合蛋白S100家族的成员，分别称为钙粒蛋白A和B。重组， 细胞外，并增加红细胞祖细胞S100A8的表达水平诱导红系 分化缺陷。我们试图定义NRG4/ErbB4如何影响HSPC动态平衡和红细胞生成， 包括红细胞岛(目标1)。我们将询问NRG4/ErbB4影响MSC的机制 功能、钙颗粒蛋白表达和红细胞生成(目标2)。我们使用了一种多管齐下的方法来遗传小鼠 建模、抑制物、转录学和生化方法，以允许对 NRG4/ErbB4/钙颗粒蛋白轴参与促进红细胞生成。拟议的调查将 进一步推动治疗开发，以改善血液疾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.