Biomechanical Activation of Yap Induces Hematopoietic Stem Cell Production

摘要 首先在发育中的脊椎动物胚胎中产生的造血干细胞(HSCs)为终生提供 血液和免疫系统的基础。造血干细胞与造血干细胞移植(HSCT)一样具有治疗价值， 对免疫功能低下的受者进行供体造血干细胞的管理是许多人的标准护理。 血液病。然而，由于免疫不相容和免疫缺陷，治疗的可得性仍然存在问题。 捐赠者短缺。同样，尽管移植的造血干细胞的数量直接影响植入是众所周知的 效率方面，目前还没有建立起成功扩大供者采集的造血干细胞的临床方案， 也不能在体外将胚胎或诱导的多能干细胞(IPSCs)分化为有功能的HSCs。因此， 长期自我更新和分化的造血干细胞从头产生新修饰物的鉴定 容量是临床上未得到满足的主要需求。尽管经过了十多年的研究，目前的协议主要依赖于 关于转录因子的强制表达，以帮助引导细胞进入类似HSC的转录程序， 然而，将这些体外来源的造血干细胞移植到受辐射的小鼠体内，既显示了有限的长期 嫁接和多系潜力。这些观察表明，目前的体外分化 策略缺少关键线索，而这些线索对于释放或维持体内完整的HSC潜能是必不可少的。 在发育中的胚胎中，最终的造血干细胞来自一组独特的中胚层前体细胞。 通过一种称为内皮细胞向造血细胞转变的过程称为血源性内皮细胞(HEC) (EHT)。转录因子RUNX1在脊椎动物从头形成HSC的所有位置都有表达，是 HSC规范和EHT要求。我们先前的工作表明，RUNX1的表达强烈上调 在胚胎心跳开始后，HSC的产生与旺盛的开始相协调 循环流动和绝对应力。而壁龛的机械性能，包括纯粹的应力和 在许多情况下，周向拉伸越来越被认为是重要的干细胞信号， 机制(S)，通过机械转导驱动承诺的造血命运和造血干细胞的生产 脊椎动物的发育在很大程度上仍未被探索。这项研究的目的是描述生物力学的作用 体内和体外造血干细胞形成中血源性血管生态位的调节，总体目标是 确定连接特定生物物理力和基因调控网络的信号通路(S) 控制HSC承诺。我们的初步数据表明，周向拉伸有一个新的、但必不可少的作用-- 转录因子YAP1在调节RUNX1+HEC规范和HSC中的激活 制作。确定在体内介导高效HSC形成的分子信号通路将揭示 临床使用的成人型造血干细胞定向扩增和/或分化的新目标。

SUMMARY Hematopoietic stem cells (HSCs), first produced in the developing vertebrate embryo, supply the lifelong foundation of the blood and immune systems. HSCs are therapeutically valuable as HSC transplantation (HSCT), the administration of donor HSCs to an immunocompromised recipient, is the standard of care for many hematological diseases. However, treatment availability remains problematic due to immune incompatibility and donor shortage. Likewise, while the number of transplanted HSCs is well known to directly impact engraftment efficiency, there are currently no established clinical protocols to successfully expand donor-harvested HSCs, nor to differentiate embryonic or induced pluripotent stem cells (iPSCs) into functional HSCs in vitro. Therefore, the identification of novel modifiers of de novo production of HSCs with long-term self-renewal and differentiation capacity is a major unmet clinical need. Despite more than a decade of research, current protocols rely primarily on enforced expression of transcription factors to help steer cells into an “HSC-like” transcriptional program, however transplantation of these in vitro-derived HSCs into irradiated mice illustrates both limited long-term engraftment and multilineage potential. These observations imply that current in vitro differentiation strategies are missing critical cues which are essential to unlock or maintain full HSC potential in vivo. In the developing embryo, definitive HSCs arise from a unique population of mesodermal precursors termed hemogenic endothelium (HEC) through a process known as endothelial-to-hematopoietic transition (EHT). The transcription factor RUNX1, expressed in all sites of de novo HSC formation across vertebrates, is required for HSC specification and EHT. Our prior work revealed that Runx1 expression is strongly upregulated after initiation of the embryonic heartbeat, and HSC production is coordinated with the onset of vigorous circulatory flow and sheer stress. While mechanical properties of the niche, including sheer stress and circumferential stretch, are increasingly recognized as important stem cell cues in many contexts, the mechanism(s) by which mechanotransduction drives commitment to hemogenic fate and HSC productionduring vertebrate development remain largely unexplored. This study aims to characterize the role of biomechanical modulation of the hemogenic vascular niche in HSC formation in vivo and in vitro, with the overall goal of identifying the signaling pathway(s) connecting select biophysical forces to the gene regulatory network controlling HSC commitment. Our preliminary data indicate a novel, yet essential, role for circumferential stretch- stimulated activation of the transcription factor Yap1 in regulation of Runx1+ HEC specification and HSC production. Defining the molecular signaling pathways that mediate productive HSC formation in vivo will reveal new targets for optimizing the directed expansion and/or differentiation of adult-type HSCs for clinical use.