Identification of the ectoenzyme CD38 as a marker of committed preadipocytes.

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- CD34low CD38+ cells.

Human adipose derived stroma/stem cells grow in serum-free medium as floating spheres.

With the goal of obtaining clinically safe human adipose-derived stroma/stem cells (ASC) and eliminating the use of serum, we have developed a new culture system that allows the expansion of ASC as spheres in a defined medium. These spheres can be passaged several times. They are not only aggregated cells but rather originate from single cells as clonal spheres can be obtained after seeding at very low density and reform clonal spheres after dissociation. These spheres can also revert to monolayer growth when plated in medium containing human plasma and even generate fibroblast-like colonies (CFU-f). Under several differentiation-specific media, spheres-derived ASC maintain their capacity to differentiate into osteoblasts, endothelial cells and adipocytes. These results indicate that human ASC can be maintained in a serum-free 3D culture system, which is of great interest for the expansion in bioreactors of autologous ASC and their use in clinical trials.

Adult human spinal cord harbors neural precursor cells that generate neurons and glial cells in vitro.

Adult human and rodent brains contain neural stem and progenitor cells, and the presence of neural stem cells in the adult rodent spinal cord has also been described. Here, using electron microscopy, expression of neural precursor cell markers, and cell culture, we investigated whether neural precursor cells are also present in adult human spinal cord. In well-preserved nonpathological post-mortem human adult spinal cord, nestin, Sox2, GFAP, CD15, Nkx6.1, and PSA-NCAM were found to be expressed heterogeneously by cells located around the central canal. Ultrastructural analysis revealed the existence of immature cells close to the ependymal cells, which display characteristics of type B and C cells found in the adult rodent brain subventricular region, which are considered to be stem and progenitor cells, respectively. Completely dissociated spinal cord cells reproducibly formed Sox2(+) nestin(+) neurospheres containing proliferative precursor cells. On differentiation, these generate glial cells and gamma-aminobutyric acid (GABA)-ergic neurons. These results provide the first evidence for the existence in the adult human spinal cord of neural precursors with the potential to differentiate into neurons and glia. They represent a major interest for endogenous regeneration of spinal cord after trauma and in degenerative diseases.

The human NTERA2 neural cell line generates neurons on growth under neural stem cell conditions and exhibits characteristics of radial glial cells.

NTERA2 cells are a human neural cell line generating neurons after exposure to retinoic acid and, as such, are widely used as a model of neurogenesis. We report that these cells form spheres when grown in serum-free medium supplemented with basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). These spheres were found to express markers of radial glial cells such as, Pax6, glutamate transporter (GLAST), tenascin C, brain lipid-binding protein (BLBP), and the 3CB2 antigen. On plating on an adhesive substrate, NTERA2 spheres generate a large percentage of immature neurons (30-50%) together with a minority of cells of the oligodendrocyte lineage. Thus NTERA2 cells share properties with neural stem cells. However, at variance with the latter, we found that they produce their own bFGF implicated in an autocrine or paracrine proliferative loop and that they do not generate astrocytes after differentiation. These results provide an interesting model to study radial glial cells and their role in human neurogenesis.