CXCL8 and CXCR1 Remodel the Vascular Niche to Promote Hematopoietic Stem and Progenitor Cell Colonization and Engraftment [wt vs kdrl:cxcr1]

The microenvironment is an important regulator of hematopoietic stem and progenitor cell (HSPC) biology. Interactions between the niche and stem cells have been difficult to track, but recent advances marking fluorescent HSPCs have allowed exquisite visualization in the caudal hematopoietic tissue (CHT) of the developing zebrafish. Sinusoidal endothelial cells interact closely with HSPCs as they colonize this niche. Here we show that the chemokine cxcl8 and its receptor, cxcr1, are abundantly expressed by zebrafish endothelial cells and we identify cxcl8/cxcr1 signaling as a positive regulator of HSPC colonization using genetic gain- and loss-of-function techniques. Single-cell tracking experiments demonstrated that this effect is due to an increase in HSPC “cuddling” by endothelial cells, thereby increasing CHT residency time and allowing more HSPC cell divisions to occur. Enhanced cxcl8/cxcr1 signaling was associated with an increase in the volume of the CHT and induction of cxcl12a expression, favoring HSPC colonization. Finally, using parabiotic zebrafish, we show that cxcr1 acts stem cell non-autonomously to improve the efficiency of donor HSPC engraftment. This work identifies a mechanism by which the hematopoietic niche remodels to promote HSPC engraftment and suggests that cxcl8/cxcr1 signaling is a potential therapeutic target in patients undergoing hematopoietic stem cell transplantation. Kdrl:mcherry and kdrl:mcherry;kdrl:cxcr1 zebrafish were dissociated and endothelial cells purified by FACS. RNA-seq libraries were prepared from endothelial cells purified from two independent clutches of fish (four libraries total).

造血干细胞与祖细胞（hematopoietic stem and progenitor cell, HSPC）的生物学功能受其微环境的重要调控。造血龛与干细胞之间的相互作用长期以来难以追踪，但近期荧光标记HSPC的技术进展，已实现对发育中斑马鱼尾部造血组织（caudal hematopoietic tissue, CHT）的精细可视化观测。当HSPC定植于该造血龛时，血窦内皮细胞会与其发生紧密相互作用。
本研究证实，趋化因子cxcl8及其受体cxcr1在斑马鱼内皮细胞中大量表达，并通过功能获得性与功能缺失性遗传学实验手段，确定cxcl8/cxcr1信号轴为HSPC定植的正向调控因子。单细胞追踪实验表明，该调控效应源于内皮细胞对HSPC的“依偎”行为增强，进而延长了HSPC在CHT中的驻留时间，使其能够进行更多次细胞分裂。增强的cxcl8/cxcr1信号轴与CHT体积增大及cxcl12a表达诱导相关，可促进HSPC定植。
最后，通过连体共生斑马鱼模型，本研究发现cxcr1以干细胞非细胞自主性的方式发挥作用，提升供体HSPC的嵌合效率。本研究阐明了造血龛重塑以促进HSPC嵌合的分子机制，并提示cxcl8/cxcr1信号轴可作为造血干细胞移植患者潜在的治疗靶点。
研究人员对Kdrl:mcherry及kdrl:mcherry;kdrl:cxcr1转基因斑马鱼进行组织解离，并通过荧光激活细胞分选（fluorescence-activated cell sorting, FACS）纯化内皮细胞。从两批独立的鱼卵批次中纯化得到的内皮细胞被用于构建RNA测序文库，总计4个文库。