Dissecting the heterogeneity of bone marrow mesenchymal lineage progenitors

项目摘要 骨质疏松症、骨量减少以及骨折等相关问题是主要的公共卫生问题 给我们的医疗保健系统带来了巨大的经济负担。骨骼是一种动态组织。在健康的骨骼中，它是 普遍认为间充质祖细胞，包括它们最原始的形式间充质干细胞 (MSCs)，通过序贯的、单向的、 和分枝分化步骤。几乎所有类型的骨质疏松症都与骨质减少有关。 形成和增加骨髓肥胖症。因此，鉴定真正的MSCs并阐明它们的区别 向成骨细胞和脂肪细胞的转化是理解骨质疏松症发病机制的关键。 骨质疏松。然而，我们目前对骨髓间充质干细胞及其后代的了解主要是获得的 通过体外研究。这些细胞在体内的性质在很大程度上仍不清楚。在过去，由于缺乏 适当的活体研究工具，我们故意忽略了异质性和可塑性特征 间充质祖细胞，简单地将所有祖细胞称为MSCs或间充质祖细胞 并搜索了一个或一组标记(S)来覆盖所有这些标记。最近，我们发现在Col2-Cre玫瑰中- Td番茄(Col2/td)小鼠，td信号标记所有骨内(干干端)间充质细胞，但不标记其他细胞 细胞类型，从而为全面分析间充质细胞亚群提供了一个完美的系统 骨髓间充质干细胞向成熟细胞分化。最重要的是，在过去的两年里，大规模的单细胞RNA 测序(scrna-seq)技术发展如此之快，现在它可以解决复杂的细胞异质性。 以其他传统方法无法实现的方式进行器官移植。在将这项技术应用于前1%的人之后 从1月龄Col2/TD小鼠新鲜分离的TD+骨内膜骨髓细胞，我们鉴定了8种间充质细胞 并在伪时间线轨迹中对它们进行排序，这说明了分化的分化 从真正的MSCs到成骨细胞/骨细胞、脂肪细胞和软骨细胞的过程。拥有这种令人敬畏的力量， 我们认为现在是检验我们的中心假设的正确时机，即间充质系细胞中的祖细胞 是由状态连续体中的子群体组成的，这些子群体保持在 一种动态的方式，可以对内在和外在的暗示做出快速反应，例如衰老和治疗。这个 将实现以下目标：1)描述和表征异质祖细胞亚群 2)观察衰老及甲状旁腺素对小鼠骨髓间充质系细胞的影响。 新发现的间充质系细胞亚群。我们的目标是勾勒出整个体内的 从真正的MSCs到成熟细胞的分化过程以及解开促进新骨的新靶点 队形。该项目的成功完成不仅将揭示MSCS的关键特征及其 子代祖细胞也为了解糖尿病的发病机制提供了新的方向 骨质疏松症和开发新的治疗方法。

Project Summary Osteoporosis, low bone mass, and related problems such as fractures, are major public health problems with a substantial economic burden on our health care system. Bone is a dynamic tissue. In healthy bone, it is commonly believed that mesenchymal progenitors, including their most primitive form mesenchymal stem cells (MSCs), constantly generate bone surface osteoblasts and marrow adipocytes via sequential, unidirectional, and branched differentiation steps. Almost all types of osteoporosis are associated with diminished bone formation and increased marrow adiposity. Therefore, identifying true MSCs and illustrating their differentiation processes into osteoblasts and adipocytes are essential for understanding the disease mechanisms of osteoporosis. However, our current knowledge of MSCs and their descendant progenitors is mostly obtained by in vitro studies. The in vivo nature of these cells is still largely unknown. In the past, owing to a lack of proper in vivo investigative tools, we deliberately ignored the heterogeneity and plasticity features of mesenchymal lineage progenitors by simply referring to all progenitors as MSCs or mesenchymal progenitors and searched for one or a set of marker(s) to cover all of them. Recently, we discovered that in Col2-Cre Rosa- tdTomato (Col2/Td) mice, Td signal labels all endosteal (metaphyseal) mesenchymal lineage cells but no other cell types, thus providing a perfect system to comprehensively analyze the subpopulations of mesenchymal lineage cells from MSCs to mature cells. Most importantly, in the past two years, large scale single-cell RNA sequencing (scRNA-seq) technique has evolved so quickly that now it can solve cell heterogeneity in complex organs in a way that no other conventional approaches can achieve. After applying this technique to the top 1% Td+ endosteal bone marrow cells freshly isolated from 1-month-old Col2/Td mice, we identified 8 mesenchymal cell clusters and ordered them in a pseudotimeline trajectory that illustrates the divergent differentiation processes from true MSCs to osteoblasts/osteocytes, adipocytes, and chondrocytes. With this awesome power, we believe now is the right time to test our central hypothesis that progenitors in mesenchymal lineage cells are made of subpopulations in a continuum of states and that those subpopulations are maintained in a dynamic way for quick responses to intrinsic and extrinsic cues, such as aging and therapies. The following aims will be performed: 1) delineate and characterize the heterogeneous progenitor subpopulations of mouse bone marrow mesenchymal lineage cells; 2) investigate the effects of aging and PTH treatment on newly identified subpopulations of mesenchymal lineage cells. Our objectives are to delineate the entire in vivo differentiation process from true MSCs to mature cells and to unravel novel targets that promote new bone formation. Successful completion of this project will not only reveal critical features of MSCs and their descendant progenitors but also shed light on new directions to understand the disease mechanisms of osteoporosis and develop novel treatments.