Quiescence, Stemness and Adipogenic Differentiation Capacity in Human DLK1-/CD34+/CD24+ Adipose Stem/Progenitor Cells

Abstract

We explore the status of quiescence, stemness and adipogenic differentiation capacity in adipose stem/progenitor cells (ASCs) ex vivo, immediately after isolation from human subcutaneous white adipose tissue, by sorting the stromal vascular fraction into cell-surface DLK1⁺/CD34^-, DLK1⁺/CD34^dim and DLK1^-/CD34⁺ cells. We demonstrate that DLK1^-/CD34⁺ cells, the only population exhibiting proliferative and adipogenic capacity, express ex vivo the bonafide quiescence markers p21^Cip1, p27^Kip1 and p57^Kip2 but neither proliferation markers nor the senescence marker p16^Ink4a. The pluripotency markers NANOG, SOX2 and OCT4 are barely detectable in ex vivo ASCs while the somatic stemness factors, c-MYC and KLF4 and the early adipogenic factor C/EBPβ are highly expressed. Further sorting of ASCs into DLK1^-/CD34⁺/CD24^- and DLK1^-/CD34⁺/CD24⁺ fractions shows that KLF4 and c-MYC are higher expressed in DLK1^-/CD34⁺/CD24⁺ cells correlating with higher colony formation capacity and considerably lower adipogenic activity. Proliferation capacity is similar in both populations. Next, we show that ASCs routinely isolated by plastic-adherence are DLK1^-/CD34⁺/CD24⁺. Intriguingly, CD24 knock-down in these cells reduces proliferation and adipogenesis. In conclusion, DLK1^-/CD34⁺ ASCs in human sWAT exist in a quiescent state, express high levels of somatic stemness factors and the early adipogenic transcription factor C/EBPβ but senescence and pluripotency markers are barely detectable. Moreover, our data indicate that CD24 is necessary for adequate ASC proliferation and adipogenesis and that stemness is higher and adipogenic capacity lower in DLK1^-/CD34⁺/CD24⁺ relative to DLK1^-/CD34⁺/CD24^- subpopulations.

Keywords: adipogenesis; ex vivo; human adipose stem/progenitor cells; proliferation; quiescence; senescence; stemness.