Role of Secreted frizzled-related Protein 1 (Sfrp 1) in the function of the hematopoietic niche

造血干细胞(HSCs)位于骨髓中一个特定的位置，对于维持这些细胞在稳定状态和应激条件下是至关重要的。我们已经证明，HSC和基质细胞相互作用，从而刺激利基细胞产生防止HSC衰老和衰竭的因子。有趣的是，分泌的卷曲相关蛋白1(SFRP1)的敲除会导致基质细胞衰老，而基质细胞不能适当地维持HSC。有趣的是，SFRP1的下调激活了间质P53及其靶点。在这项研究中，我们将利用SFRP1表达下调的基质细胞，并通过基因编辑确定P53途径中的关键节点来确定调节HSCs的利基信号。我们进一步的目的是利用实验室建立的条件性Sfrp1 Flox/FLOX缺失模型来剖析体内HSC失调的机制。OSX-Cre驱动的SFRP1缺失突变体的初步实验表明，这些小鼠的基质细胞表达衰老的标志。因此，我们将研究在活体内P53及其靶点在肝星状细胞调节中的作用，并确定抑制P53是否能挽救SFRP1基因缺陷动物的造血缺陷。在这个项目的第二部分，将研究bcr-abl+白血病细胞的生态位依赖性。我们发现，与在WT环境中形成的细胞相比，SFRP1缺陷环境形成的白血病细胞具有不同的自我更新和细胞命运决定。在这里，我们将评估SFRP1缺陷环境中的生态位功能缺陷是否以及如何在克隆水平上决定白血病发生的变化，以及这是否影响治疗成功。因此，我们将确定参与生态位功能的关键的SFRP1和P53依赖的通路，以及这些通路如何调节HSC和白血病。

Hematopoietic stem cells (HSCs) reside in a specific niche within the bone marrow that is critical for maintaining these cells under steady state and stress conditions. We have shown that HSCs and stromal cells interact, whereby the niche is stimulated to produce factors which prevent HSC senescence and exhaustion. Interestingly, knockdown of secreted frizzled-related protein 1 (Sfrp1) causes senescence of stromal cells, which do not properly maintain HSCs. Interestingly, downregulation of Sfrp1 activates stromal p53 and its targets. In this research proposal, we will exploit stromal cells in which expression of Sfrp1 is knocked down and identify key nodes in the p53 pathway determining the niche signals regulating HSCs using gene editing. We further aim to dissect the mechanisms of HSC dysregulation in vivo using a conditional Sfrp1flox/flox deletion model generated in the lab. Preliminary experiments in Osx-Cre-driven Sfrp1 deletion mutants show that stromal cells from these mice express markers of senescence. Thus, we will investigate the role of niche senescence and the involvement of p53 and its targets in HSC regulation in vivo, and also determine whether p53 inhibition rescues the defective hematopoiesis in Sfrp1-deficient animals. In the second part of this project, the niche dependence of BCR-ABL+ leukemic cells will be investigated. We found that the Sfrp1-deficient environment forms leukemic cells with different self- renewal and cell fate decisions than those formed in a WT environment. Here, we will assess whether and how defective niche function in the Sfrp1-deficient environment determines alterations in leukemogenesis on a clonal level, and whether this affects therapeutic success. Thus, we will identify key Sfrp1- and p53-dependent pathways involved in niche function and how those regulate HSC and leukemia.