Organotypic Cocultures with Genetically Modified Mouse Fibroblasts as a Tool to Dissect Molecular Mechanisms Regulating Keratinocyte Growth and Differentiation

Abstract

Organotypic cocultures of keratinocytes and fibroblasts generate a normal epidermis irrespective of the species and tissue origin of fibroblasts. The use of mouse fibroblasts and human keratinocytes facilitates the identification of the origin of compounds involved in epidermal tissue reconstitution and growth regulation. Moreover, the functional significance for the keratinocyte phenotype of genetically modified fibroblasts from transgenic or knockout mice, even those exhibiting an embryonic lethal phenotype, can be studied in such heterologous in vitro tissue equivalents. Here we communicate results of such studies revealing the antagonistic function of mouse fibroblasts defective in the AP-1 constituents c-Jun and JunB, respectively, on human keratinocyte growth and differentiation. Furthermore, the hematopoietic growth factor granulocyte macrophage-colony stimulating factor has been identified as a novel regulator of keratinocyte growth and differentiation. As will be reported in detail elsewhere both granulocyte macrophage-colony stimulating factor and keratinocyte growth factor have been identified as major mediators of fibroblast-keratinocyte interactions and their expression is induced via AP-1 by interleukin-1 released by the epithelial cells. Thus, these heterologous cocultures provide a novel promising tool for elucidating molecular mechanisms of epithelial-mesenchymal interactions and their consequences on epithelial cell proliferation and differentiation.

Development and Validation of Human Psoriatic Skin Equivalents

“…20 -22 Fibroblasts, which are included in these models, 20 -22 promote keratinocyte proliferation and differentiation via the secretion of factors such as KGF and GM-CSF. 29,30 In our model, we showed that addition of fibroblast-derived KGF to the skin equivalents in combination with EGF results in the correct morphological and molecular characteristics of normal human skin, including the absence of the psoriasis-associated proteins SKALP, hBD-2, and cytokeratin 16. It should be noted that the cytokines used in our model might have different effects, both qualitatively and quantitatively, in skin equivalent models containing fibroblasts.…”

Recapitulation of oral mucosal tissues in long‐term organotypic culture

“…It was assumed that fibroblasts influence keratinocytes through diffusible factors that act in a paracrine fashion to regulate keratinocyte growth and differentiation (Tuan et al, 1994;Luger and Schwarz, 1995;Garner, 1998;Smola et al, 1998). More recently it has been shown that fibroblasts and keratinocytes interact through a double paracrine regulatory pathway that involves upregulation of interleukin-1 in keratinocytes, which then stimulates keratinocyte growth factor expression in cocultured fibroblasts (Maas-Szabowski et al, 2001). This correlates with our finding that skin keratinocytes upregulate K19 expression only in combination with alveolar or sulcular gingival fibroblasts, and upregulate K4 and K13 only in combination with alveolar fibroblasts.…”

Proliferation and cornification during development of the mammalian epidermis

“…Keratinocytes from mice in which c-Jun has been conditionally inactivated in the epidermis show decreased expression of epidermal growth factor receptor (EGFR) and its ligand HB-EGF, proliferate poorly, and differentiate at a faster rate (Zenz et al, 2003). In addition, AP-1 is involved in a paracrine loop whereby IL-1 in keratinocytes induces c-Jun in fibroblasts to produce keratinocyte growth factor (KGF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), both of which feed back on keratinocytes to promote cell growth and differentiation (Szabowski et al, 2000;Maas-Szabowski et al, 2001). AP-1 is also involved in the expression of cornified envelope precursors, including loricrin (DiSepio et al, 1995) and involucrin (Takahashi and Iizuka, 1993;Welter and Eckert, 1995), as well as TGase1 (Liew and Yamanishi, 1992;Yamada et al, 1994).…”