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.
The capacity to recruit and differentiate new adipocytes in adipose tissue enhances insulin sensitivity and protects against metabolic disease. Adipocytes develop from tissue-resident progenitor cells in response to environmental signals. This project uses single cell RNA profiling, progenitor transplantation and genetic lineage analysis to define the hierarchical organization and regulation of adipose progenitors. This work will improve our ability to develop new therapies aimed at promoting healthy adipose tissue remodeling.