Recent developments in in situ microscopy have enabled unparalleled resolution of the architecture of the bone marrow (BM) niche for murine hematopoietic stem and progenitor cells (HSPCs). However, the extent to which these observations can be extrapolated to human BM remains unknown. In humans, adipose tissue occupies a significant portion of the BM medullary cavity, making quantitative immunofluorescent analysis difficult due to lipid-mediated light scattering. In this study, we employed optical clearing, confocal microscopy and the nearest neighbor analysis to determine the spatial distribution of CD34+ HSPCs in the BM in a translationally relevant rhesus macaque model. Immunofluorescent analysis revealed that femoral BM adipocytes are associated with the branches of vascular sinusoids, with half of HSPCs localizing in close proximity of the nearest BM adipocyte. Immunofluorescent microscopy and flow cytometry analysis demonstrate that BM adipose tissue exists as a multicellular niche consisted of adipocytes, endothelial cells, granulocytes, and macrophages. Analysis of the BM adipose tissue conditioned media using liquid chromatography-tandem mass spectrometry revealed the presence of multiple bioactive proteins involved in regulation of hematopoiesis, inflammation and bone development with many predicted to reside inside microvesicles. Pretreatment of purified HSPCs with BM adipose tissue-conditioned media, comprising soluble and exosomal/microvesicle-derived factors, led to enhanced proliferation and an increase in granulocyte-monocyte differentiation potential ex vivo. Our work translationally extends extensive studies in murine models, indicating that BM adipose tissue is a central paracrine regulator of hematopoiesis and in nonhuman primates and possibly in humans.

中文翻译：

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恒河猴骨髓脂肪组织与造血干细胞和祖细胞之间的空间和生化相互作用

原位显微镜的最新发展使小鼠造血干细胞和祖细胞 (HSPC) 的骨髓 (BM) 生态位结构具有无与伦比的分辨率。然而，这些观察结果可以在多大程度上外推到人类 BM 仍然未知。在人类中，脂肪组织占据了 BM 髓腔的很大一部分，由于脂质介导的光散射，使得定量免疫荧光分析变得困难。在这项研究中，我们采用光学透明化、共聚焦显微镜和最近邻分析来确定 CD34+ HSPC 在翻译相关的恒河猴模型中 BM 中的空间分布。免疫荧光分析显示股骨 BM 脂肪细胞与血管窦的分支有关，一半的 HSPCs 定位在最近的 BM 脂肪细胞附近。免疫荧光显微镜和流式细胞术分析表明，BM 脂肪组织作为由脂肪细胞、内皮细胞、粒细胞和巨噬细胞组成的多细胞生态位存在。使用液相色谱-串联质谱法对 BM 脂肪组织条件培养基的分析表明，存在多种参与调节造血、炎症和骨骼发育的生物活性蛋白，其中许多预计存在于微泡内。用包含可溶性和外泌体/微泡衍生因子的 BM 脂肪组织条件培养基预处理纯化的 HSPC，导致体外增殖增强和粒细胞-单核细胞分化潜能增加。