Optimization of seeding cell density for differentiation of adipose-derived stem cells into epithelial-like cells on bioengineered composite scaffolds.

This study investigates the biological factors influencing the epithelial differentiation of adipose-derived stem cells (ASC) to develop an engineered upper airway construct. One fraction of ASC was seeded onto a fibrin sealant (Tisseel) matrix encompassing an additional equal fraction of ASC that has been integrated into a porous polyethylene scaffold (Medpor®). Constructs with ASC seeded at total densities of 5 × 10, 1 × 10, 2.5 × 10, and 5 × 10 cells cm-2 were cultured under submerged conditions for 11 days to achieve partial epithelial differentiation (PD). To simulate post-transplantation exposure to air and interaction with host epithelial cells, PD constructs with ASC at 5 × 10 cells cm-2 were transitioned to air-liquid interface (ALI) conditions for additional 10 days (PD/ALI-21d) or 21 days (PD/ALI-32d). The latter cultures were either maintained alone or co-cultured with bronchial epithelial cells (PD/ALI-32d + BEAS). Gene expressions of mesenchymal and epithelial basal, secretory, and ciliated cell markers were assessed and validated via immunohistochemistry. ASC seeded at 5 × 10 cells cm-2 achieved the highest partial epithelial differentiation, supporting the use of this density for further experiments. In PD/ALI-21d, basal and secretory epithelial marker gene expression significantly increased, while ciliated cell markers remained unchanged. In PD/ALI-32d, expression of basal and goblet cell markers and several mesenchymal stem cell markers decreased, but co-culturing with BEAS maintained the levels of their expression. These results indicate that long-term ALI cultures cannot sustain terminal differentiation of ASC into secretory phenotypes without co-culture with primary epithelial cells. In conclusion, partially differentiated ASC on constructs maintain a stem cell phenotype and may promote differentiation into basal/secretory phenotypes, but not ciliated cells. Enhancing ciliogenesis and ensuring ASC commitment to the epithelial lineage, require modifications to the study design.