Human mesenchymal stem cells differentiate to epithelial cells when cultured on thick collagen gel

The stem cell niche is crucial to the control of stem cell fate determination in vitro as well as in vivo, and an understanding of these niches is required for the progression of stem cell and tissue engineering. The goal of our study was to commit human mesenchymal stem cells (hMSCs) to the epithelial lineage. To do this, we cultured bone marrow-derived mesenchymal stem cells (MSCs) on plates coated with type I collagen gel with or without 10 μM all-trans retinoic acid (ATRA).We found depth-dependent differentiation of hMSCs to the epithelial lineage, with the thick collagen gel (1900 μm) generating more than 80% cytokeratin-18 (CK-18)-positive cells, whereas the thin collagen gel (100 μm) generated significantly fewer CK-18-positive cells. In addition, we found that supplementation of 10 μM ATRA enhanced CK-18 expression and induced cluster-formation in cells grown on the thick collagen gel. The effect of gel depth on hMSC differentiation appears to be caused by partial cytoskeletal disruption.These results suggest that ATRA and a collagen extracellular matrix may have a synergistic effect on differentiation of human mesenchymal stem cells to epithelial lineage.