Adipose progenitor cell dynamics

脂肪组织在调节能量平衡和系统代谢方面起着核心作用。脂肪细胞由组织驻留的祖细胞发育而来，这些祖细胞对环境刺激做出反应而分化。由遗传病、衰老或肥胖引起的脂肪细胞分化障碍会导致脂肪纤维化和胰岛素抵抗。相反，促进脂肪生成可以改善脂肪营养不良和肥胖相关的糖尿病。然而，关于脂肪前体细胞在体内的识别、活性和调控，目前还知之甚少。为了以完全公正的方式鉴定脂肪前体细胞，我们对白色脂肪组织中的间质血管部分进行了单细胞RNA测序。对来自12,000个细胞/研究的基因表达数据进行的聚类分析确定了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，根据它们的基因特征，我们有条件地将其称为“早期脂肪前体细胞”和“承诺前脂肪细胞”。以细胞表面二肽基肽酶-4(DPP4)的表达为标志的“早期祖细胞”，富含Wnt和转化生长因子信号通路中的基因表达。“前脂肪细胞”以细胞表面细胞间黏附分子-1(ICAM-1)的表达为标志，并以选择性表达许多脂肪谱系标记物而闻名，包括PPAR。在硅胶细胞轨迹分析中预测，早期的DPP4前体细胞产生ICAM1前体脂肪细胞以及另一种“新的”细胞类型。与此一致，初步的移植研究表明，DPP4前体细胞在体内既能产生ICAM1细胞，也能产生成熟的脂肪细胞。我们的中心假设是，在成脂条件下，DPP4早期前体细胞可以产生脂肪谱系承诺的ICAM1前体脂肪细胞。我们还假设，Wnt信号控制着早期成脂前体细胞的命运和增殖活性，这些细胞在衰老过程中失去成脂活性，并采用肌成纤维细胞的命运。我们将使用最先进的方法严格检验这些新的概念和假设，包括细胞移植、遗传谱系追踪和单细胞转录分析。特异性目的1在培养、细胞移植和遗传谱系分析中使用间充质分化分析来检测WNT2/DPP4和ICAM1细胞的命运、增殖和等级关系。特定目的2研究Wnt信号通路在体内外调节Wnt2/DPP4早期祖细胞维持和活性中的作用。总之，这些研究将确定WAT中脂肪前体细胞的等级，确定早期前体细胞对白色和米色脂肪细胞发育的贡献，并评估衰老对脂肪前体细胞功能的影响。

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.