Adipose tissue is a highly plastic organ that plays a central role in regulating whole-body energy metabolism. The capacity for adipocytes to store chemical energy in lipid droplets protects other organs against the toxic effects of ectopic lipid deposition. In the setting of chronic nutritional excess, such as obesity, adipose tissue expands through increases in fat cell size (hypertrophy) and/or fat cell number (hyperplasia). Adipocyte hypertrophy causes fibrosis and inflammation, thereby promoting metabolic disease. Conversely, hyperplastic growth, mediated by the differentiation of progenitor cells into new adipocytes, is critical for preserving adipose tissue function and protecting against metabolic disease. However, the precise cell types, lineage dynamics, and mechanisms governing the development of adipocytes are incompletely understood.

Adipose mesenchymal progenitors constitute a heterogeneous pool of diverse cell types. Previous attempts to characterize these cells have relied on nonspecific mesenchymal markers and candidate lineage marker genes. We used single-cell RNA sequencing to identify distinct types of progenitor cells in murine and human adipose tissues and to predict lineage relationships in an unbiased manner. Functional assessments of these cell types in vitro and in vivo define a mesenchymal cell hierarchy involved in adipocyte formation.

Single-cell RNA sequencing and cell trajectory analyses identified a lineage hierarchy consisting of several distinct mesenchymal cell types in murine and human adipose. Dipeptidyl peptidase–4–expressing (DPP4+) cells are highly proliferative and multipotent progenitors that are relatively resistant to differentiation into adipocytes. Intercellular adhesion molecule–1–expressing (ICAM1+) cells are committed preadipocytes that express Pparg and are poised to differentiate into mature adipocytes with minimal stimulation. CD142+/Clec11a+ cells represent a distinct adipogenic population in murine subcutaneous adipose that shares many properties with ICAM1+ preadipocytes. In vivo cell transplantation studies showed that DPP4+ progenitors give rise to both ICAM1+ and CD142+ preadipocytes before differentiation into mature adipocytes. DPP4+ cells depend on transforming growth factor–β (TGFβ) signaling to maintain their progenitor identity, whereas ICAM1+ preadipocytes are refractory to the proliferative and anti-adipogenic actions of the TGFβ pathway. Obesity and insulin resistance lead to a depletion of DPP4+ mesenchymal progenitors and a reduction in the adipogenic differentiation competency of preadipocytes, specifically in visceral white adipose tissue. Single-cell analysis of human subcutaneous adipose tissue revealed distinct DPP4+ and ICAM1+ populations that displayed functional properties similar to those of the analogous mouse populations. Histological examination of murine subcutaneous adipose tissue showed that ICAM1+ preadipocytes are intercalated between mature adipocytes, occupying a perivascular niche. The DPP4+ progenitor cells are localized in an anatomically distinct niche surrounding the adipose depot, which we term the reticular interstitium.

Our studies define a developmental hierarchy of adipose progenitors consisting of DPP4+ interstitial progenitors that give rise to committed ICAM1+ and CD142+ preadipocytes, which are poised to differentiate into mature adipocytes. Targeting one or more of these cell populations may be beneficial for promoting adaptive hyperplastic adipose growth to ameliorate metabolic disease. A key finding from this work is that adipose progenitor cells reside …