Preadipocytes in the human subcutaneous adipose tissue display distinct features from the adult mesenchymal and hematopoietic stem cells

The stroma-vascular fraction (SVF) of human adipose tissue has recently been described to be composed of endothelial cells identified as CD34 - /CD31 + cells, infiltrated/resident macrophages defined as CD14 + /CD31 + cells,and a new cell population characterized as CD34 + /CD31 - cells. To elucidate the cell identity of the adipocyte precursor cells, fluorescent activating cell sorter (FACS) analyses were performed on crude SVF cultured under adipogenic conditions, i.e., serum-deprived medium containing insulin, cortisol, triiodothyronine, and supplemented with a PPARy agonist for the first 3 days. The progressive accumulation of lipid droplets was associated with a selective enrichment of the CD34 + /CD31 - cell population whereas control experiments performed in medium supplemented with 10% serum showed an overall downregulation of the three cell markers without adipogenesis. Among the different cell subsets, the CD34 + /CD31 - subset was the unique cell fraction able to answer to adipogenic culture conditions. Indeed, a time-dependent expression of adipocyte markers as well as acquisition of adipocyte-typical metabolic activities were observed. In parallel, the gene expression of I ipogenic and I ipolytic enzymes increased. The ability to differentiate into adipocytes was restricted to cells that did not express the mesenchymal stem cell marker CD105. Furthermore, the CD34 + /CD31 - cells did not respond to culture conditions used for hematopoietic colony assays. Taken together, the present study demonstrates that adipocyte progenitor cells, i.e., the preadipocytes, are included in the CD34 + /CD31 - cell fraction, which displays distinct features from the adult mesenchymal and hematopoietic stem cells.