Investigation of mouse amniotic fluid for stimulating ability of keratinocyte differentiation depending on the fetal stage.

During fetal development, the barrier function of the fetal skin is developed under specific conditions for epidermis formation. In keratinocyte differentiation, the well-orchestrated production and modification of various structural proteins are induced. We assessed the epidermal barrier function in different fetal stages by evaluating the enzymatic activity of cross-linking proteins, transglutaminases, and the permeation of fluorescence dye in the stained epidermal sections. During days 15.5-17.5 in gestation, the enzymatic activities in the epidermis appeared to increase significantly; meanwhile, dye permeation was substantially decreased, suggesting the formation of a protective barrier. For the fetal epidermis formation in the earlier stage, unclarified stimulating factors in the amniotic fluid (AF) are possible to promote barrier function by stimulating keratinocyte differentiation. Thus, we performed proteomic spectrometric (MS) analysis on the components in the AF at different fetal stages. Also, we investigated the promotive ability of the components using a cultured keratinocyte differentiation system. According to the MS analysis, the AF components appeared to exhibit stage-specific variations, where possible unique functions have been identified. We also found that adding the AF from each stage to the medium for cultured keratinocytes specifically enhanced the levels of the differentiation markers. These results provide information on the possible role of AF that contains regulatory factors on keratinocyte differentiation.

Studies on differentiation-dependent expression and activity of distinct transglutaminases by specific substrate peptides using three-dimensional reconstituted epidermis.

During skin formation, particularly during differentiation of keratinocytes, unique post-translational modifications play a role in forming a proteinaceous supermolecule called the cornified envelope (CE), which is necessary for barrier function. Transglutaminases (TGs) are essential enzymes involved in the cross-linking of various keratinocyte structural proteins to complete CE formation. The TG family consists of eight isozymes, with two members, TG1 and TG3, located mainly in the epidermis. In an in vitro three-dimensional (3D) culture system, reconstruction of the epidermis allows cornification of the terminally differentiated keratinocytes. In this study, using isozyme-specific substrate peptides that enable detection of TG activity, we investigated the expression and the activation pattern of each isozyme during differentiation in this culture system. In the differentiating cells, the protein levels, enzymatic activities, as well as localization of TG1 and TG3 exhibited distinct patterns. Specific knockdown of these enzymes by siRNA revealed less cornification, suggesting that each TG contributes to the epidermal formation. In conclusion, we demonstrate the efficiency of the 3D system for studying differentiation-dependent expression and activity of distinct TGs by specific substrate peptides. ENZYME: Transglutaminase, EC2.3.2.13.