Signaling pathways regulated by GSK3 in hematopoietic stem cell

首席调查员/项目主任(最后、第一、中间)：黄健 GSK3调控的造血干细胞信号转导途径 摘要 造血干细胞(HSCs)具有两个明显的特征：自我更新和分化为 成熟的血细胞。调节HSC自我更新和分化的信号通路不是很好 明白了。糖原合成酶激酶-3(GSK3)，一个典型的Wnt信号的负调控因子和一个 通过JAK/STAT和PI3信号传导的造血生长因子信号通路的下游靶点 激酶/Akt依赖的通路参与了HSC活性的调节。规范的Wnt信号 已被认为与HSC的自我更新有关，但该途径的作用仍存在争议。最近， PTEN-PI3K-mTOR通路在HSC的维持中起重要作用。我们的 假设GSK3是Wnt和PI3K下游的关键效应器，在HSCs中调节 HSC人群。为了支持这一假设，我们的初步数据显示：1)锂和其他 选择性GSK3抑制剂显著增加小鼠HSCs数量，2)RNAi介导的HSCs耗竭 小鼠HSCs中的GSK3最初扩大了骨髓移植中的HSC数量，但长期抑制 GSK3会耗尽HSC。3)抑制GSK3对HSCs的增殖作用是通过β-连环蛋白介导的 HSCs的耗竭在很大程度上依赖于mTOR信号。这些观察结果支持这一假说 GSK3是一种重要的造血调节因子。在这项建议中，我们会把研究扩展至探讨 GSK3磷酸化在肝星状细胞中的作用我们还将讨论Gsk3a的异构体特定功能 新构建的条件性基因敲除小鼠的造血细胞中Gsk3b的比较。非单元格- GSK3抑制对HSCs的自主作用也将通过有条件地敲除GSK3在 成骨细胞的利基。此外，我们还将测试调节GSK3和mTOR的活性是否可以扩大 肝星状细胞体外培养。体外培养中鉴定HSCs自我更新新调控因子的功能筛选 将会被执行。这个项目的总体目标是检查WNT和WNT各自的贡献 PTEN-PI3K-mTOR信号通路在GSK3抑制反应中的作用 在造血系统中调节这些途径。从这些研究中学到的知识 将为HSC自我更新和分化的调控机制提供新的见解 并可能提高造血系统疾病的治疗水平。 1

Principal Investigator/Program Director (Last, First, Middle): Huang, Jian Signaling pathways regulated by GSK3 in hematopoietic stem cells Abstract Hematopoietic stem cells (HSCs) possess two distinct features: the ability to self-renew and to differentiate into mature blood cells. The signaling pathways that regulate HSC self-renewal and differentiation are not well understood. Glycogen synthase kinase-3 (GSK3), a negative regulator of canonical Wnt signaling and a downstream target of hematopoietic growth factor signaling pathways that signal through Jak/Stat and PI3 kinase/Akt dependent pathways, has been implicated in the regulation of HSC activity. Canonical Wnt signaling has been implicated in HSC self-renewal, but the role of this pathway remains controversial. Recently, the PTEN-PI3K-mTOR pathway has been demonstrated to play an essential role in HSC maintenance. Our hypothesis is that GSK3 is a critical effector downstream of Wnt and PI3K within HSCs that regulates the HSC population. In support of this hypothesis, our preliminary data show that: 1) lithium and other selective GSK3 inhibitors significantly increase the number of HSCs in mice, 2) RNAi mediated depletion of Gsk3 in murine HSCs initially expands the HSC population in bone marrow transplants, but long-term inhibition of GSK3 exhausts HSC. 3) The expansion of HSCs by inhibition of GSK3 is mediated through ¿-catenin while the depletion of HSCs is largely dependent on mTOR signaling. These observations support the hypothesis that GSK3 is an important regulator of hematopoiesis. In this proposal, we will extend our study to explore the functional role of GSK3 phosphorylation in HSCs. We will also address the isoform specific functions of Gsk3a vs Gsk3b in hematopoietic cells with newly constructed conditional knockouts in mice. The non cell- autonomous effect of GSK3 inhibition on HSCs will also be explored with the conditional knockout of Gsk3 in the osteoblast niche. Furthermore, we will test whether modulating the activity of GSK3 and mTOR can expand HSCs in ex vivo culture. A functional screen to identify new regulators of HSCs self-renewal in ex vivo culture will be carried out. The overall goal of this project is to examine the respective contributions of Wnt and PTEN-PI3K-mTOR signaling in the response to GSK3 inhibition and to define the role of GSK3 in regulating these pathways within the hematopoietic system. The knowledge learned from these studies will provide new insights into the mechanisms of the regulation of HSC self-renewal and differentiation and may improve the therapy of hematopoietic disorders. 1