Adipose progenitor cell dynamics

脂肪组织在调节能量平衡和全身代谢中起着核心作用。脂肪细胞从组织驻留的祖细胞发育而来，这些祖细胞响应于环境刺激而分化。由遗传疾病、衰老或肥胖引起的脂肪细胞分化障碍导致脂肪纤维化和胰岛素抵抗。相反，增强脂肪生成改善脂肪代谢障碍和肥胖相关的糖尿病。然而，目前对脂肪前体细胞在体内的身份、活性和调控知之甚少。为了以完全无偏的方式鉴定脂肪祖细胞，我们对来自白色脂肪组织的基质-血管部分进行单细胞RNA测序。来自> 12，000个细胞/研究的基因表达数据的聚类分析鉴定出许多不同的细胞群体。这包括两种不同类型的假定成脂前体细胞，我们根据它们的基因特征有条件地称之为“早期脂肪祖细胞”和“定向前脂肪细胞”。以二肽基肽酶-4（DPP4）的细胞表面表达为标志的"早期祖细胞"富集Wnt和TGF β信号传导途径中的基因表达。"定向前脂肪细胞"通过细胞间粘附分子-1（ICAM 1）的细胞表面表达来标记，并且以其选择性表达许多脂肪谱系标记物（包括Ppar β）而闻名。计算机模拟细胞轨迹分析预测早期DPP 4+祖细胞产生ICAM 1+前脂肪细胞以及另一种"新"细胞类型。与此一致，初步的移植研究表明，DPP 4+祖细胞产生ICAM 1+细胞以及体内成熟的脂肪细胞。我们的中心假设是，DPP 4+早期祖细胞在成脂条件下产生脂肪谱系定向ICAM 1+前脂肪细胞。我们还假设Wnt信号控制早期脂肪形成祖细胞的命运和增殖活性，并且这些细胞在衰老过程中失去其脂肪形成活性并采用肌成纤维细胞命运。我们将使用最先进的方法，包括细胞移植，遗传谱系追踪和单细胞转录组学分析，严格检查这些新概念和假设。Specific Aim 1使用培养中的间充质分化测定、细胞移植和遗传谱系追踪分析来检查Wnt 2/DPP 4+和ICAM 1+细胞之间的命运、增殖和等级关系。具体目标2研究了Wnt信号通路在体外和体内调节Wnt 2/DPP 4+早期祖细胞的维持和活性中的作用。总之，这些研究将确定WAT中脂肪祖细胞的层次结构，确定早期祖细胞对白色和米色脂肪细胞发育的贡献，并评估衰老对脂肪祖细胞功能的影响。

Adipose tissue plays a central role in regulating energy balance and systemic metabolism. Adipocytes develop from tissue-resident progenitor cells that differentiate in response to environmental stimuli. Impairments in adipocyte differentiation, caused by genetic disease, aging or obesity, lead to adipose fibrosis and insulin resistance. Conversely, enhancing adipogenesis ameliorates lipodystrophy- and obesity-related diabetes. However, there is relatively little known about the identity, activity and regulation of adipose precursor cells in vivo. To identify adipose progenitor cells in a completely unbiased manner, we performed single cell RNA-sequencing of the stromal-vascular fraction from white adipose tissue. Clustering analysis of the gene expression data from >12, 000 cells/study identified many distinct cell populations. This included two distinct types of putative adipogenic precursor cells, which we conditionally called “early adipose progenitors” and “committed preadipocytes” based on their gene signatures. “Early progenitors”, marked by cell surface expression of Dipeptidyl peptidase-4 (DPP4), are enriched for expression of genes in the Wnt and Tgf signaling pathways. “Committed preadipocytes” are marked by cell surface expression of Intercellular adhesion molecule-1 (ICAM1) and were noted for their selective expression of many adipose lineage markers, including Ppar. In silico cell trajectory analysis predicts that early DPP4+ progenitors give rise to ICAM1+ preadipocytes as well as another “novel” cell type. Consistent with this, preliminary transplantation studies show that DPP4+ progenitor cells produce ICAM1+ cells as well as mature adipocytes in vivo. Our central hypothesis is that DPP4+ early progenitor cells give rise to adipose-lineage committed ICAM1+ preadipocytes under adipogenic conditions. We additionally hypothesize that Wnt signaling controls the fate and proliferative activity of early adipogenic progenitors and that these cells lose their adipogenic activity and adopt a myofibroblast fate during the aging process. We will rigorously examine these new concepts and hypotheses using state-of-the-art approaches, including cell transplantation, genetic lineage tracing, and single cell transcriptomic analyses. Specific Aim 1 uses mesenchymal differentiation assays in culture, cell transplantation and genetic lineage tracing analysis to examine the fate, proliferation and hierarchical relationship between Wnt2/DPP4+ and ICAM1+ cells. Specific Aim 2 investigates the role of the Wnt signaling pathway in regulating the maintenance and activity of Wnt2/DPP4+ early progenitors in vitro and in vivo. Together, these studies will define the hierarchy of adipose progenitor cells in WAT, determine the contribution of early progenitors to white and beige adipocyte development and assess the effects of aging on adipose progenitor function.