Non-canonical Wnt signaling and lymphostromal interactions: impact of Frizzled6/Vangl2 on stem/progenitor cell function

成人免疫系统的所有细胞都来源于少量的骨髓造血干细胞（HSC），这些造血干细胞存在于专门的口袋或壁龛中，周围环绕着被认为调节HSC功能的其他细胞。除了能够发育成不同的血细胞谱系外，HSC还具有独特的自我更新能力。它们罕见的细胞分裂是不对称的，导致产生一个与母细胞相同的子HSC和一个失去几个干细胞特征的祖细胞。这种自我更新依赖于HSC-生态位相互作用，并且对于循环血细胞的连续生成至关重要。该领域最大的技术挑战之一是开发培养HSC扩增的方法，同时限制其自我更新能力的丧失。我们相信，更好地了解生态位环境将有助于确定更好的文化条件。 通过Wnt家族信号蛋白调节HSC微生态位相互作用是我实验室的主要主题之一。特别是，我最近的研究结果已经确定了一个非传统的信号通路，参与调节小鼠骨髓中的HSC数量。其中一个涉及的分子是细胞表面受体蛋白Frizzled 6，我们最近的工作确定为应激下HSC功能的重要调节因子。已知该途径调节皮肤中的细胞取向和细胞-细胞相互作用。我们认为，同样的信号也可能参与造血干细胞与骨髓小生境细胞的相互作用，并控制造血干细胞在小生境内的方向，从而影响它们的自我更新。因此，我们的长期目标是确定参与HSC-小生境相互作用的关键膜相关Wnt信号分子，并可用于维持培养中的HSC。 目前的研究建议集中在Frizzled 6可以影响HSC-生态位相互作用，HSC在生态位内的方向以及细胞内其他相关蛋白的定位的机制。我们还将评估另一种已知与其他细胞类型中的Frizzled 6相互作用和协作的表面蛋白的作用。总之，这里提出的工作将提高我们的理解机制，调节造血干细胞在骨髓中的定位。此外，这些研究将导致识别用于培养中HSC扩增的新型生长因子和小鼠模型的开发，以促进对非传统Wnt信号传导的进一步研究。

All cells of the adult immune system are derived from a small number of bone marrow hematopoietic stem cells (HSC) that are found in specialized pockets or niches, surrounded by other cells that are believed to regulate HSC function. In addition to being able to develop into the different blood cell lineages, HSC also have the unique ability to self-renew. Their infrequent cell divisions are asymmetrical, resulting in the generation of one daughter HSC, identical to the mother cell, and one progenitor cell that has lost several stem cell characteristics. This self-renewal is dependent on HSC-niche interactions and is essential for the continuous generation of circulating blood cells. One of the greatest technical challenges in the field is to develop methods for HSC expansion in culture while limiting the loss of their self-renewal capacity. We believe that a better understanding of the niche environment would help identify better culture conditions. Regulation of HSCniche interactions by the Wnt-family of signaling proteins is one of the main overarching themes in my laboratory. In particular, my recent results have identified a non-traditional signaling pathway that is involved in the regulation of HSC numbers in mouse bone marrow. One of the molecules involved is the cell surface receptor protein Frizzled6 that our recent work identifies as an essential regulator of HSC function under stress. The pathway is known to regulate cellular orientation and cell-cell interaction in the skin. We propose that the same signals could also be involved in the interaction of HSCs with the bone marrow niche cells and control the orientation of HSCs inside the niche, thus influencing their self-renewal. Our long-term goal, therefore, is to identify the key membrane-associated Wnt signaling molecules involved in HSC-niche interactions and that could be used for maintaining HSCs in culture. The current research proposal focuses on the mechanisms by which Frizzled6 could influence HSC-niche interactions, HSC orientation inside the niche, and the localization of other associated proteins inside the cell. We will also evaluate the role of another surface protein known to interact and collaborate with Frizzled6 in other cell types. Together the work proposed here will improve our understanding of the mechanisms that regulate HSC localization in the bone marrow. Furthermore, these studies should lead to the identification of novel growth factors for HSC expansion in culture and the development of mouse models to facilitate further research on non-traditional Wnt signaling.