Smad信号调控血管内皮细胞生血命运的功能和机制

Embryonic origin of hematopoietic stem cells has long been hot in the field of hematopoietic development. Very recently, it has been proven that hematopoietic stem cells are derived from vascular endothelial cells. However, very little is currently known about the regulatory mechanism by which vascular endothelial cells choose the hemogenic fate during embryonic development. Transforming growth factor-β superfamily members play complicated roles in embryonic hematopoiesis. Our preliminary data showed that deletion of Smad4, the intra-cellular mediator of the transforming growth factor-β superfamily, specifically in endothelium led to increased hemogenesis in the embryo proper, implying a role of Smad signaling in the fate decision of hemogenic endothelium. In this study, we will use the conditional gene knockout strategy based on several endothelial/hematopoietic cell-specific Cre transgenic mouse models, to systematically investigate the physiological function of Smads during endothelial-hematopoietic transition. By using FACS sorting system and Cre-mediated lineage tracing strategy, we will further analyze the in vitro hemogenic capacity and the in vivo repopulating potential of Smads-deficient endothelium. In addition, we will explore the underlying mechanism by which Smads regulate endothelial-hematopoietic transition through target gene expression profiling assay and functional confirmation. Such efforts on deciphering the key signals that control the emergence of hematopoietic stem cells from vascular endothelium will have important implications in hematopoietic stem cell-related medical treatment and regeneration strategy.

造血干细胞的胚胎起源一直是造血发育领域的热点，近年来研究证实造血干细胞来源于血管内皮细胞，然而对血管内皮细胞在胚胎发育中选择生血命运的调控机制还知之甚少。转化生长因子-β超家族信号对于胚胎造血发挥复杂的调节作用。我们的初步研究显示其胞内介导分子Smad4在内皮细胞的缺失导致胚胎内皮生血增强，提示Smad信号在生血内皮细胞的命运决定中发挥调控功能。本研究中，我们将利用以多种内皮/造血细胞特异性Cre转基因小鼠为基础的条件基因敲除策略，系统研究Smads分子在内皮-造血转化过程中的生理功能。基于流式分选和谱系示踪策略，进而分析Smads缺失内皮细胞的体外生血功能和体内移植重建潜能。进一步，通过对靶分子的差异表达筛选和功能验证，探索Smad信号调节内皮-造血转化的潜在机制。上述对于调控血管内皮细胞选择造血干细胞命运关键信号的解析必将为造血干细胞相关的疾病治疗和再生策略提供理论依据和重要线索。

造血起源的研究无疑对于造血干细胞相关的疾病治疗和再生策略提供重要的理论依据。关于造血胚胎起源的精确时空、细胞类型以及调控机制仍然有许多未知。本研究中，我们利用以多种内皮/造血细胞特异性Cre 转基因小鼠为基础的条件基因敲除策略，系统研究Smad4分子在内皮-造血转化过程中的生理功能。基于流式分选和谱系示踪策略，进而分析Smad4缺失内皮细胞的体外生血功能和体内移植重建潜能。进一步，通过对靶分子的差异表达筛选和功能验证，探索Smad4信号调节内皮-造血转化的潜在机制。结果显示，内皮细胞特异性Smad4基因敲除后小鼠胚胎的血管内造血簇增加，内皮生血活性增强；造血簇细胞的增殖、凋亡和分化均未见异常；利用造血细胞特异性敲除Smad4基因，突变胚胎的造血前体细胞数量及功能均正常。上述结果提示内皮细胞Smad4特异性负向调控内皮生血过程而在造血细胞水平不发挥作用。机制研究显示，内皮细胞敲除Smad4导致血管下间质细胞的造血支持活性增强，间质Bmp4增加，并通过Smad4非依赖的Erk通路调控了内皮细胞的Kit表达，从而导致内皮造血增强。综上，我们揭示了内皮细胞的Smad4通过调节主动脉下的间质微环境而保持适度的内皮生血。Smad4缺失导致间质微环境信号的改变，从而反之改变了内皮细胞的造血命运。上述对于调控血管内皮细胞选择造血命运关键信号的解析必将为造血干细胞相关的疾病治疗和再生策略提供理论依据和重要线索。