Dermal Fibroblast-Derived Growth Factors Restore the Ability of β1 Integrin-Deficient Embryonal Stem Cells to Differentiate into Keratinocytes

AbstractEmbryonal stem (ES) cells that are homozygous null for the β1 integrin subunit fail to differentiate into keratinocytes in vitro but do differentiate in teratomas and wild-type/β1-null chimeric mice. The failure of β1-null ES cells to differentiate in culture might be the result of defective extracellular matrix assembly or reduced sensitivity to soluble inducing factors. By culturing embryoid bodies on dead, deepidermized human dermis (DED) we showed that epidermal basement membrane did not induce β1-null ES cells to undergo keratinocyte differentiation and did not stimulate the differentiation of wild-type ES cells. Coculture with epidermal keratinocytes also had no effect. However, when human dermal fibroblasts were incorporated into DED, the number of epidermal cysts formed by wild-type ES cells increased dramatically, and small groups of keratin 14-positive cells differentiated from β1-null ES cells. Fibroblast-conditioned medium stimulated differentiation of K14-positive cells in wild-type and β1-null embryoid bodies. Of a range of growth factors tested, KGF, FGF10, and TGFα all stimulated differentiation of keratin 14-positive β1-null cells, and KGF and FGF10 were shown to be produced by the fibroblasts used in coculture experiments. The effects of the growth factors on wild-type ES cells were much less pronounced, suggesting that the concentrations of inducing factors already present in the medium were not limiting for wild-type cells. We conclude that the lack of β1 integrins decreases the sensitivity of ES cells to soluble factors that induce keratinocyte differentiation