gms | German Medical Science

Introduction: The elucidation of adipogenesis of human adipose-derived stem cells (ASC) is not only important for the development of therapies against diseases associated with fat tissue, but also for application of ASC in adipose tissue engineering. 3-dimensional (3D) spheroids of ASC without any exogenous material provide cell-cell and cell-ECM interactions in a more in vivo-like context, as compared to conventional 2D cell culture. Such spheroids can be utilized to study adipogenesis in a 3D environment, but they may also have the potential to serve as building blocks for adipose tissue regeneration. Objectives of this study were to characterize adipogenesis a) in 3D ASC monoculture spheroids in comparison to 2D culture, and b) in 3D coculture spheroids made from ASC and microvascular endothelial cells (MVEC).

Materials and Methods: 3D monoculture (ASC) and coculture (ASC:MVEC 1:1) spheroids were produced in 96-well plates using the liquid overlay technique. Adipogenesis was induced employing a common hormonal cocktail and ananylzed in comparison to conventional 2D culture. Adipogenic differentiation was evaluated on the cellular level with regard to lipid accumulation (histology, triglyceride quantification). After ASC were harvested from the coculture spheroids using magnetic-activated cell sorting, on the molecular level mRNA gene expression was analyzed from both mono- and coculture spheroids using a TaqMan array and qRT-PCR.

Results: In 3D ASC monoculture spheroids, adipogenesis proved to be clearly less dependent on exogenous hormonal stimulation than in conventional 2D culture. Applying a short-term induction protocol, a high lipid content was observed on day 14 in 3D spheroids, whereas triglyceride synthesis was negligible in 2D culture. Gene expression of adipogenic transcription factors (PPARγ, C/EBPβ, SREBF1), adipokines, and other genes associated with lipid synthesis and transport (e.g., FASN, ACLY, FATP1) reflected these results. ASC within coculture spheroids also showed substantial adipogenesis, but accumulated less triglycerides than in corresponding monoculture spheroids. Accordingly, many adipogenic marker genes were expressed less strongly in the cocultures. Remarkably, on coculture cryosections, clusters or network-like structures of the MVEC were observed with a local inhibition of adipogenesis in ASC in the immediate vicinity of the MVEC.

Discussion: ASC in 3D spheroids exhibited strong adipogenesis, as compared to conventional 2D culture. As far as the interplay between adipogenesis and vascularization is concerned, the coculture spheroids appear suitable to investigate the molecular cross-talk of the two cell types. Furthermore, the mono- and -coculture spheroids may serve as preformed building blocks in approaches to adipose tissue engineering. Suitable hydrogel carriers for application of the spheroids will be discussed.