In vitro regulation of adipogenesis: tunable engineered tissues

A major clinical challenge in creating a tissue-engineered medical implant is the ability to expand cells biopsied from the patient to obtain a clinically relevant cell volume. A common tissue engineering strategy involves the culture of autologous progenitor cells on biomaterials to form an implantable cellular device. However, autologous progenitor cells often lose their differentiation potential during the expansion process. The acute regulation of mammary tissue expansion in vivo through local modulation of connective tissue suggests that the parenchymal-stromal interactions are crucial to develop tissue ex vivo. To better understand cellular behaviour in co-culture in two-dimensional systems, mesenchymal stem cells were treated with mammary epithelial cell conditioned medium and assessed for cell proliferation, lipid production and morphological changes over a 17 day culture period. The results showed that bovine epithelial cells (MAC-T) are able to inhibit mouse mesenchymal stem cell differentiation (D1), even in the presence of adipogenic cocktails. The inhibitory effect is reversible, thus potentially providing a mechanism for 'tuning' a cell-based device prior to implantation. Further studies found that there were significantly higher levels of urokinase plasminogen activator (uPA) and plasminogen activator inhibitor 1 (PAI-1) in the MAC-T-conditioned medium than in the murine mammary epithelial cell (NMuMG)-conditioned medium, which was not able to inhibit adipogenesis of D1 cells. D1 cells are able to proliferate and maintain their differentiation potential in MAC-T-conditioned medium. The long-term implication is that new culture media may be developed that allow the rapid, clinical expansion and differentiation or dedifferentiation of cells for regenerative medicine applications.