Control of bone physiology by a novel type of adipose cells

项目摘要 骨质疏松症和低骨量是常见的慢性疾病， 大量的医疗费用。骨是一种动态的组织，它不断地经历耦合重塑， 成骨细胞和破骨细胞。骨髓（BM）脂肪细胞，由相同的间充质干细胞产生 骨髓间充质干细胞（MSC）作为成骨细胞，在骨稳态中也起着至关重要的作用。因此，提高我们对 了解它们的功能将揭示新的靶点， 对骨骼疾病的改进治疗的未满足的临床需求。通过进行大规模的单细胞 转录组分析，我们最近计算定义了BM间充质谱系细胞的层次结构， 并通过多个中间亚群描述了MSCs的体内分化过程。 有趣的是，我们发现了一个新的亚群，位于增殖的间充质祖细胞之后， 沿着成脂分化途径，在经典的载脂脂肪细胞（LiLA）之前， 细胞骨髓成脂谱系前体（MALPs）。这些非增殖细胞表达成熟的脂肪细胞 标志物，包括脂联素（Adipoq），但不积累脂质。在年轻的小鼠中，MALPs，遗传上 由Adipoq-Cre（ER）标记，以BM基质细胞和毛细血管周细胞的形式大量存在。从形态学上讲， 显示出许多长的细胞突起，这些突起在它们之间以及与周围的细胞进行接触， 骨表面，以在BM腔内建立无处不在的3D网络。细胞消融显示，这些 Adipoq+细胞在维持BM脉管系统和抑制骨形成中起关键作用。引人注目的是， MALP在局灶性辐射后迅速短暂扩张，这意味着在损伤期间具有修复作用 反应MALP的一个重要特征是它们高度表达许多分泌因子，如VEGFa， RANKL（Tnfsf 11）、CSF 1、Cxcl 12等，表明对周围细胞的调节作用。这些数据导致我们 中心假设，MALP代表一种新的脂肪细胞类型，在调节其BM中具有关键作用 在骨骼发育、稳态、衰老和损伤修复过程中的环境。骨髓脂肪组织 (MAT)通常指的是LiLA，目前的MAT研究集中在其能量和脂质相关的作用。这 这项提案将扩大MAT的概念，包括MALP，一个更丰富的细胞群，及其 非脂质相关作用。我们的目标是：1）确定MALP的体内命运和性质; 2） 阐明MALPs在调节骨髓血管系统中的作用; 3）确定MALPs的调节作用。 骨吸收的MALP。创新方法，如单核RNA测序（snRNA-seq）， 共聚焦3D成像，RNA FISH，转基因和报告动物模型，将在整个研究中使用。 提议我们的项目将全面表征一种新的间充质亚群及其 在骨骼中的多方面调节作用。我们在这里收集的数据将为骨骼、脂肪和 血管生物学并确定骨质疏松症和骨修复干预的新目标。

Project Summary Osteoporosis and low bone mass are common chronic disorders associated with significant morbidity and substantial healthcare costs. Bone is a dynamic tissue that constantly undergoes coupled remodeling by osteoblasts and osteoclasts. Bone marrow (BM) adipocytes, arising from the same mesenchymal stem cells (MSCs) as osteoblasts, also play a crucial role in bone homeostasis. Therefore, advancing our knowledge on mesenchymal populations in bone and understanding their functions will reveal novel targets that address the unmet clinical need for improved treatments for skeletal diseases. By carrying out large scale single cell transcriptome analysis, we recently computationally defined the hierarchy of BM mesenchymal lineage cells and delineated the in vivo differentiation process of MSCs through multiple intermediate subpopulations. Interestingly, we identified a new subpopulation situated after proliferative mesenchymal progenitors and before classic lipid-laden adipocytes (LiLAs) along the adipogenic differentiation route, and thus named those cells marrow adipogenic lineage precursors (MALPs). These non-proliferative cells express mature adipocyte markers, including Adiponectin (Adipoq), but do not accumulate lipid. In young mice, MALPs, genetically labelled by Adipoq-Cre(ER), exist abundantly as BM stromal cells and capillary pericytes. Morphologically, they display many long cell processes that make contacts among themselves and with surrounding cells, as well as the bone surface, to establish a ubiquitous 3D network inside BM cavity. Cell ablation revealed that these Adipoq+ cells play critical roles in maintaining BM vasculature and in suppressing bone formation. Strikingly, MALPs are rapidly and transiently expanded after focal radiation, implying a reparative role during injury response. One important feature of MALPs is that they highly express many secreted factors, such as VEGFa, RANKL (Tnfsf11), CSF1, Cxcl12 etc, indicating regulatory actions on surrounding cells. These data lead to our central hypothesis that MALPs represent a novel adipose cell type with pivotal roles in regulating their BM environment during skeletal development, homeostasis, aging, and injury repair. Bone marrow adipose tissue (MAT) normally refers to LiLAs, and current MAT research centers on their energy and lipid-related roles. This proposal will expand the concept of MAT to include MALPs, a much more abundant cell population, and its non-lipid-associated actions. Our aims are to: 1) determine the in vivo fate and properties of MALPs; 2) elucidate the role of MALPs in regulating bone marrow vasculature; 3) determine the regulatory actions of MALPs on bone resorption. Innovative approaches, such as single nucleus RNA-sequencing (snRNA-seq), confocal 3D imaging, RNA FISH, genetically modified and reporter animal models, will be used throughout the proposal. Our project will comprehensively characterize a novel mesenchymal subpopulation and its multifaceted regulatory roles in bone. The data we gather here will shed new light on bone, adipose, and vascular biology and identify new targets of intervention on osteoporosis and bone repair.