Osteogenic differentiation of human adipose-derived stem cells in 3D conditions – comparison of spheroids and polystyrene scaffolds

Expansion and differentiation of adipose-derived stem cells (ADSCs) in vitro are routinely performed in two-dimensional (2D) environments. The study hypothesis was that the utilisation of three-dimensional (3D) culture conditions, mimicking the natural stem cell niche, might increase the osteogenic commitment of ADSCs. Therefore, human ADSCs were seeded in 3D culture systems lacking bioactive material components: spheroids and polystyrene scaffolds. ALP activity, a marker of early osteogenesis, was higher in ADSC spheroids and ADSC seeded on polystyrene scaffolds as compared to 2D cultures. Furthermore, the expression of the osteoblast marker genes Runt-related transcription factor 2 (RUNX2), osterix and integrin binding sialoprotein (IBSP) was significantly up-regulated in spheroids as compared to polystyrene scaffolds and 2D culture. Elevated levels of RUNX2 and IBSP in spheroids were confirmed at the protein level by Western blot and immunofluorescence, respectively. Bone mineral production was lower in spheroids than in polystyrene scaffolds and 2D culture at day 14. Curiously, adipocyte differentiation was downregulated in spheroids as compared to 2D-culture. Finally, to induce late differentiation events, cells were dissociated from spheroids after a 7 d osteogenic pre-differentiation culture and replated in 2D culture in osteoblast maturation medium. After a subsequent 14 d of maturation, cells produced bone mineral and osteocalcin proteins, which are late osteoblast markers. The present work showed that the 3D environment may provide additional stimuli for the commitment of ADSCs to the osteogenic lineage. Furthermore, the presented data may be valuable when designing protocols to prepare ADSCs for use in bone regeneration clinical studies