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，与显著的发病率和 高额的医疗费用。骨是一种动态组织，它不断经历偶联重塑，通过 成骨细胞和破骨细胞。骨髓(BM)脂肪细胞，来源于相同的间充质干细胞 骨髓间充质干细胞(MSCs)作为成骨细胞，在骨稳态中也起着至关重要的作用。因此，推进我们对 骨骼中的间充质细胞群体及其功能的了解将揭示解决 改善骨骼疾病治疗的临床需求尚未得到满足。通过开展大规模的单电池 转录组分析，我们最近通过计算定义了骨髓间充质系细胞的层级 并通过多个中间亚群描绘了MSCs在体内的分化过程。 有趣的是，我们发现了一个新的亚群，位于增殖性间充质祖细胞和 在成脂分化途径的经典载脂脂肪细胞(LILAs)之前，因此将这些细胞命名为 骨髓成脂前体细胞(MALPs)。这些非增殖性细胞表达成熟的脂肪细胞 标记物，包括脂联素(ADIPOQ)，但不积累脂肪。在年轻的小鼠身上，MALP，从基因上讲 以ADIPOQ-Cre(ER)标记的BM基质细胞和毛细血管周细胞大量存在。从形态上看，它们 显示许多长的细胞突起，这些细胞突起在它们之间和周围的细胞之间以及 骨表面，在BM腔内建立无处不在的3D网络。细胞消融显示这些 ADIPOQ细胞在维持骨髓血管形成和抑制骨形成方面起着关键作用。令人惊讶的是， MALP在焦点照射后迅速和瞬时扩张，意味着在损伤过程中起到修复作用。 回应。MALP的一个重要特征是高度表达许多分泌因子，如VEGFA， RANKL(Tnfsf11)、CSF1、CXCL12等，表明对周围细胞的调节作用。这些数据导致我们的 中心假设MALP代表一种新的脂肪细胞类型，在调节其BM方面起着关键作用 骨骼发育、动态平衡、衰老和损伤修复过程中的环境。骨髓脂肪组织 (MAT)通常指LILAS，目前MAT的研究集中在它们的能量和脂质相关的作用上。这 提案将扩大MAT的概念，以包括MALP，更丰富的细胞群体，以及其 非脂质相关的作用。我们的目标是：1)确定MALP在体内的去向和性质；2) 阐明MALP在调节骨髓血管中的作用；3)确定MALP的调节作用 MALP对骨吸收的影响。创新的方法，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 求婚。我们的项目将全面描述一种新的间充质亚群及其 在骨骼中发挥多方面的调节作用。我们在这里收集的数据将为骨骼、脂肪和 血管生物学，确定骨质疏松症和骨修复干预的新靶点。

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.