The effect of glucocorticoid excess on the osteohematopoietic niche

糖皮质激素(GCs)是一种有效的免疫抑制药物，通过对循环免疫细胞和组织特异性细胞的复杂作用而发挥抗炎作用。然而，长期的GC治疗会导致严重的副作用，如GC引起的骨质疏松症，这是由于GCs在间充质组织中的不良反应造成的。糖皮质激素主要通过调节基因表达的糖皮质激素受体发挥作用。尽管已知GC对免疫细胞的抑制作用，但GC在骨造血生态位中的作用仍不明确。因此，我们旨在探讨长期GC治疗对造血干细胞(HSC)功能的影响。在GC治疗GR缺陷小鼠的初步研究中，我们发现GR充足小鼠的骨髓细胞数量减少，而GR缺陷小鼠的HSCs减少。此外，长期的GC治疗削弱了骨髓来源的HSCs分化为不同造血系的潜力。因此，我们假设长期GC暴露以GR依赖的方式影响HSC的数量、活性和功能。因此，我们旨在探讨GC治疗对骨造血龛细胞成分的影响及其分子机制。我们的目标是通过骨髓移植研究和流式细胞仪分析，彻底评估GC对HSC功能和壁龛细胞室的影响。此外，我们将使用转基因GR-小鼠模型，通过免疫学和组织学研究、基因表达分析和体外方法来描绘骨髓间室内GCs的细胞靶点。最后，我们将在基因组和蛋白质水平上以无偏见的组学方法描述GCs在靶细胞中影响的分子通路。我们的结果将为GCs对HSCs的分子效应提供重要的见解。剖析其中涉及的机制可能会导致制定策略，以减轻GCs对骨造血细胞生态位的有害影响。

Glucocorticoids (GCs) are potent immunosuppressive drugs exerting anti-inflammatory effects through complex actions on circulating immune cells as well as tissue-specific cells. However, long-term GC treatment causes severe side effects such as GC-induced osteoporosis due to adverse actions of GCs in mesenchymal tissues. GCs exert their effects mainly via the glucocorticoid receptor (GR) that regulates gene expression. Despite the known suppressive impact of GCs on immune cells, GC actions in the osteohematopoietic niche remain ill-defined. Thus, we aim to explore the effects of long-term GC treatment on hematopoietic stem cell (HSC) function. In preliminary investigations of GC-treated GR deficient mice, we found a reduced cell number in the bone marrow as well as a reduction of HSCs in GR-sufficient mice but not in GR-deficient mice. Furthermore, the potential of HSCs derived from bone marrow to differentiate into the various hematopoietic lineages was impaired upon long-term GC treatment. Thus, we hypothesize that long-term GC exposure affects HSC numbers, viability and function in a GR-dependent manner. Therefore, we aim to explore the effects and molecular mechanisms of GC treatment on the cellular constituents of the osteohematopoietic niche. We aim to thoroughly assess GC effects on HSC function and the cellular compartments of the niche by bone marrow transplantation studies and flow cytometric analysis. In addition, we will use genetically modified GR-mouse models to delineate the cellular targets of GCs within the bone marrow compartment utilizing immuno- and histologic investigations, gene expression analyses and ex vivo approaches. Finally we will characterize molecular pathways affected by GCs within target cells in an unbiased omics-approach on genome and protein level. Our results will provide significant insights to the molecular effects of GCs on HSCs. Dissecting the mechanisms involved could lead to the development of strategies to alleviate the deleterious effects of GCs on the osteohematopoietic niche.