In vivo and in silico mapping of cell-cell interactions in the haematopoietic stem cell niche

成年人的每一秒钟都会产生大约200万个红细胞；在一天的过程中，健康个体总共产生10^12个新的血细胞。产生如此数量惊人的细胞的过程始于骨髓，骨髓中存在一组特定的干细胞，即造血干细胞（hsc）。这些细胞产生各种不同的细胞，构成我们的血液和免疫系统。理解这一过程至关重要，合理影响造血系统动力学的能力也将对衰老研究、再生医学和临床血液学产生重大影响。为了正常发挥功能，造血干细胞依赖于骨髓内其他细胞的支持，但这些支持尚不确定。在拟议的研究中，我们将使用小鼠实验来确定哪些细胞允许造血干细胞正常发挥作用。我们将进行的实验使用一种非常强大的显微镜，使我们能够看到活小鼠骨髓内的造血干细胞。随着时间的推移，我们将获得高分辨率的3D图像，显示造血干细胞的位置及其邻近细胞的身份。我们将使用计算方法对这些图像进行多次测量，所得数据将进行统计分析，并为开发细胞及其在骨髓内相互作用的计算机模型提供基础。我们可以运行这些计算机模型来模拟体内发生的事件，通过将模拟输出与实验数据进行比较，我们将能够测试、改进和验证我们对负责支持骨髓干细胞的细胞相互作用的理解。这里的数学模型概括了我们对骨髓内作用机制的理解；模拟和观测数据之间的任何分歧都表明我们的理解存在差距，并将激发进一步的分析。在初步分析和建模的基础上，我们将研究缺乏某些细胞类型的小鼠。这反过来将为我们提供关于这些细胞对造血干细胞命运的影响的更详细的见解。除了测量不同类型骨骼中细胞的空间分布外，我们还将确定其他类型细胞缺失导致造血干细胞中基因表达的差异。最后，我们计划使用新的基于显微镜的技术，使我们能够直接杀死造血干细胞附近的单个细胞，并研究造血干细胞对这种扰动的反应。如果我们能够成功地预测造血干细胞会向与被删除细胞相同类型的其他细胞迁移，那么这将大大增加我们对模型的信心。HSC生态位内细胞种群动态的计算机模型将用于系统地探索我们的理解；但在未来，它们也可以用来代替小鼠实验。

Every second of our adult lives we produce some 2 million red blood cells; over the course of a day in total 10^12 new blood cells are generated in healthy individuals. The process which produces this extraordinary number of cells begins in the bone marrow where a specific set of stem cells, so called haematopoietic stem cells (HSCs), reside. These cells give rise to all the different cells that make up our blood and the immune system. Understanding of this process is of fundamental importance, and the ability to rationally affect the dynamics of the haematopoietic system will also have major consequences for ageing research, regenerative medicine and clinical haematology.In order to function properly, HSCs rely on the support of other cells inside the bone marrow, but these are as yet not known with certainty. In the proposed research we will use experiments in mice to determine which cells allow HSCs to function properly. The experiments we will conduct use a very powerful type of microscopy allowing us to visualise the HSCs inside the bone marrow of living mice. We will obtain high-resolution 3D images over time showing the location of HSCs and the identity of their neighbouring cells. We will use computational method to perform several measurements on these images and the resulting data will be analysed statistically and provide the basis for the development of computer models of the cells and their interactions inside the bone marrow. We can run these computer models to simulate the events happening in vivo and by comparing the simulation output with the experimental data we will be able to test, improve and validate our understanding of the cellular interactions responsible to support the stem cells in the bone marrow. The mathematical model here serves as a summary of our understanding of the mechanisms acting within the bone marrow; any disagreement between the simulations and the observed data points to gaps in our understanding and will motivate further analysis.Based on preliminary analyses and modelling we will then study mice that lack certain cell-types. This in turn will provide us with more detailed insights about the effect that these cells have on the fate of HSCs. In addition to measuring the spatial distributions of cells in different types of bones, we will also determine the differences in gene expression in HSCs that result from deletion of other cell types.Finally, we plan to use new microscopy-based techniques which allow us to directly kill individual cells in the neighbourhood of HSCs and study the response of HSCs to such perturbations. If we can successfully predict that HSCs migrate towards other cells of the same type as the deleted cell then this would substantially increase our confidence in our models.Computer models of the cell population dynamics inside the HSC niche will be used to systematically probe our understanding; but they can also be used in the future to replace experiments in mice.