Identification of the ectoenzyme CD38 as a marker of committed preadipocytes

Abstract

Background/objectives: Characterisation of the adipocyte cellular lineage is required for a better understanding of white adipose tissue homoeostasis and expansion. Although several studies have focused on the phenotype of the most immature adipocyte progenitors, very few tools exist to identify committed cells. In haematopoiesis, the CD38 ectoenzyme is largely used to delineate various stages of stem cell lineage commitment. We hypothesise that this marker could be used to identify committed preadipocytes.

Methods: Complementary strategies including flow cytometry, cell-sorting approaches, immunohistochemistry and primary cultures of murine adipose progenitors isolated from different fat pads of control or high-fat diet exposed C57BL/6 J mice were used to determine the molecular expression profile, proliferative and differentiation potentials of adipose progenitors expressing the CD38 molecule.

Results: We demonstrate here that a subpopulation of CD45^- CD31^- CD34⁺ adipose progenitors express the cell surface protein CD38. Using a cell-sorting approach, we found that native CD45^- CD31^- CD34⁺ CD38⁺ (CD38⁺) adipose cells expressed lower CD34 mRNA and protein levels and higher levels of adipogenic genes such as Pparg, aP2, Lpl and Cd36 than did the CD45^- CD31^- CD34⁺ CD38^- (CD38^-) population. When cultivated, CD38⁺ cells displayed reduced proliferative potential, assessed by BrdU incorporation and colony-forming unit assays, and greater adipogenic potential. In vitro, both CD38 mRNA and protein levels were increased during adipogenesis and CD38^- cells converted into CD38⁺ cells when committed to the adipogenic differentiation programme. We also found that obesity development was associated with an increase in the number of CD38⁺ adipose progenitors, this effect being more pronounced in intra-abdominal than in subcutaneous fat, suggesting a higher rate of adipocyte commitment in visceral depots.

Conclusions: Together, these data demonstrate that CD38 represents a new marker that identifies committed preadipocytes as CD45^- CD31^- CD34^low CD38⁺ cells.