不同程度激活的β-catenin信号对造血干细胞的自我更新调控作用

The self-renewal of hematopoietic stem cells (HSCs) is strictly controlled by a collaboration of multiple cellular signals. Among those cellular signals, some of them need to be activated constitutively for maintaining the quantity of HSCs, while some others are only required to be activated transiently in order to induce the activation and expansion of HSCs. The timely controlled activities of later group of signals is critical for HSCs self-renewal, constitutive activation of such signals will impairs the self-renewal and repopulation capacity of HSCs. We believed that Wnt-β-catenin is a representative of such signals. .β-catenin signaling has been implicated in the regulation of HSCs' self-renewal; however, the experimental results yielded by different laboratories are controversial or even contradictory. We speculated that such inconsistences are due to the constitutive gain- or loss-of function approaches used in previous studies. A most recent study indicated the importance of activity levels of β-catenin in HSCs self-renewal. Constitutively activation of β-catenin at low levels (2 times of normal levels) can enhance the self-renewal of HSCs, while constitutively activation of β-catenin at higher levels induce HSCs differentiation or apoptosis. We propose that, in addition to its levels, the time period of β-catenin activation is also critical for HSCs self-renewal. We predict that a appropriate rhythm of β-catenin activation might stimulate HSCs self-renewal, even at a high level of activity. We intend to use an 4OHT-inducible transgeneic approach to investigate our hypothesis by comparing the effects of weekly-induced β-catenin activation to that of consistently induced β-catenin activation on HSCs activity. The levels of β-catenin activity will be carefully controlled by controlling the dosage of 4OHT applied.

造血干细胞（HSCs）自我更新受多种信号调控，某些信号需要持续活化维持HSCs数量，某些信号则只有在需要时瞬间激活诱导HSCs扩增。那些只需瞬间激活信号的持续活化不但不利于HSCs自我更新，反而损伤HSCs功能。β-catenin信号可能属于后一类。资料显示，β-catenin 信号参与调节HSCs自我更新,但相关研究结果不相一致甚至相互矛盾。以往研究均采用基因敲除或转基因等持续抑制或持续活化手段。持续低水平β-catenin 信号活化可促进HSCs自我更新；过高水平将诱导HSCs分化或凋亡，严重影响HSCs自我更新。我们推测，节律性适当水平的β-catenin 信号可能是调节HSCs自我更新的关键，不合时宜的β-catenin 信号的活化可损伤HSCs自我更新。本项目将用先进的可调控型转基因技术，通过调控β-catenin信号的活化时间和强度研究该信号对HSCs自我更新和造血重建的影响。

本项目采用先进的可调控型转基因技术，通过调控Wnt/β-catenin信号通路的活化时间和强度研究了该信号通路对HSC自我更新和扩增的影响。研究基本达到预期目标，结果发现瞬时或持续低水平激活Wnt/β-catenin信号通路对HSC自我更新和扩增没有作用；过高水平Wnt/β-catenin将诱导HSC死亡，严重影响HSC的自我更新；只有持续的恰当水平的Wnt/β-catenin可调节HSC的自我更新，促进HSC的体外扩增。在我们的体系中，最佳的β-catenin信号的激活时间周期和浓度剂量为每隔3天加药（1µM 4-OHT），持续加到第9天，HSC扩增最为明显。我们的研究初步揭示了Wnt/β-catenin信号通路对HSC自我更新的调控机制，同时为HSC的体外扩增提供新的方案。下一步工作我们将探索其他Wnt/β-catenin通路相关信号分子对HSC体外扩增的影响，同时研究骨髓微环境中其他Niche分子与Wnt/β-catenin通路协同对HSC的体外扩增影响，从而构建体外HSC扩增体系的最佳策略，解决临床治疗中HSC来源严重短缺的困难。

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