Background and objectives: Recent findings suggest that therapeutic potential of mesenchymal stem cells (MSCs) could be increased through aggregation into three-dimensional (3D) bodies, and different culture methods have been employed to obtain 3D spheroids of MSCs. In the current study we report accidentally encountered spontaneous formation of adipose-derived stem cell (ASC) bodies in standard ASC culture of a single donor.
Methods and results: Human ASCs from passages 1 to 3, cultured in a medium containing 5% autologous serum (AS), spontaneously clustered and formed floating 3D bodies. After a transfer of floating ASC bodies onto new adherent plastic dish, they attached to the surface and gradual migration of spindle-shaped ASCs out of the bodies was detected. A substitution of AS with allogeneic sera did not hinder this ability, but commercial medium containing fetal bovine serum delayed the process. Substantial part of ASCs surrounding transferred ASC bodies showed alkaline phosphatase (AP) activity, while ASC aggregates were AP negative. Similar 3D bodies formed when ASCs were grown on an uncoated glass surface. These ASC aggregates as well as clusters of ASCs, where formation of the 3D bodies is initiated, expressed pluripotency marker NANOG, but the expression of OCT4A was not detected.
Conclusions: Obtained results suggest that spontaneously formed ASC aggregates may represent a more primitive cell subpopulation within the individual ASC culture. The ability to form 3D aggregates, the expression of NANOG, and the lack of the AP activity may be used to enrich ASC cultures with potentially more primitive cells serving as an excellent basis for therapeutic applications.
Keywords: Alkaline phosphatase; Human adipose-derived stem cells; NANOG; Pluripotency markers; Spontaneous clustering; Three-dimensional cell aggregates.