involucrin and Skin-Abnormalities

A defective epidermal permeability barrier (EPB) in premature birth remains a leading cause of neonatal death as a result of its associated complications, which include poor temperature stability, infection by micro-organisms through the skin, and the outflow of water. Despite its importance in survival, the mechanisms involved in the formation and maintenance of the EPB are not well understood. To address the possibility that claudins, a new superfamily of tight junctional molecules, are involved, we engineered transgenic mice with claudin 6 (Cldn6) overexpressed via the involucrin (Inv) promoter. Interestingly, the Inv-Cldn6 transgenic animals die within 2 days of birth, apparently due to the lack of an intact EPB as evidenced by increased water loss and the penetration of X-gal through the skin. Barrier dysfunction was manifested biochemically by the aberrant expression of late epidermal differentiation markers, including K1, filaggrin, loricrin, transglutaminase 3, involucrin, repetin, members of the SPRR family and the transcriptional regulator Klf4. The overall claudin profile of the epidermis was also modified. Our data suggest that repetin and SPRR1A and 2A are downregulated in response to the downregulation of Klf4 in the transgenic animals, which would contribute to decreased protein crossbridging leading to fragile, defective cornified envelopes. These results provide new insights into the role of claudin 6 in epithelial differentiation and EPB formation. In addition, the epidermal phenotype of these transgenic mice, which is very reminiscent of that in pre-term infant skin, suggest that they will be an important and novel model for studies on human premature EPB-related morbidity.

Topics: Animals; Animals, Newborn; Claudins; Epidermis; Filaggrin Proteins; Gene Expression; Kruppel-Like Factor 4; Membrane Proteins; Mice; Mice, Transgenic; Permeability; Promoter Regions, Genetic; Protein Precursors; Skin Abnormalities; Tight Junctions

Nude mice are characterized by the absence of visible hair, epidermal defects, and the failure to develop a thymus. This phenotype results from loss-of-function mutations in Whn (Hfh11), a winged-helix transcription factor. In murine epidermis and hair follicles, endogenous whn expression is induced as epithelial cells initiate terminal differentiation. Using the promoter for the differentiation marker involucrin, transgenic mice that ectopically express whn in stratified squamous epithelia, hair follicles, and the transitional epithelium of the urinary tract were generated. Transgenic epidermis and hair follicles displayed impaired terminal differentiation and a subset of hair defects, such as delayed growth, a waved coat, and curly whiskers, correlated with decreased transforming growth factor (TGF)-alpha expression. The exogenous Whn protein also stimulated epithelial cell multiplication. In the epidermis, basal keratinocytes exhibited hyperproliferation, though transgene expression was restricted to suprabasal, postmitotic cells. Hair follicles failed to enter telogen (a resting period) and remained continuously in an abnormal anagen (the growth phase of the hair cycle). Ureter epithelium developed severe hyperplasia, leading to the obstruction of urine outflow and death from hydronephrosis. Though an immune infiltrate was present occasionally in transgenic skin, the infiltrate was not the primary cause of the epithelial hyperproliferation, as the immune reaction was not observed in all affected transgenics, and the transgene induced identical skin and urinary tract abnormalities in immunodeficient Rag1-null mice. Given the effects of the transgene on cell proliferation and TGFalpha expression, the results suggest that Whn modulates growth factor production by differentiating epithelial cells, thereby regulating the balance between proliferative and postmitotic populations in self-renewing epithelia.

Topics: Animals; Calcium; Cell Culture Techniques; Cell Differentiation; Cell Division; DNA-Binding Proteins; Dose-Response Relationship, Drug; Epithelium; Eye Abnormalities; Forkhead Transcription Factors; Humans; Keratinocytes; Mice; Mice, Nude; Mice, Transgenic; Phenotype; Protein Precursors; Skin; Skin Abnormalities; Skin Transplantation; Time Factors; Transcription Factors; Transforming Growth Factor alpha; Urogenital System; Vibrissae

Integrin expression is normally confined to the basal layer of the epidermis, but when epidermal homeostasis is perturbed, the receptors are also expressed by suprabasal, differentiating keratinocytes. We have used the involucrin promoter to express functional human integrin subunits alpha 2, alpha 5, and beta 1 in the suprabasal epidermal layers of transgenic mice. In mice expressing alpha 5 or beta 1 alone or alpha 2 beta 1 or alpha 5 beta 1 heterodimers, there were hair and whisker abnormalities and a failure of eyelid fusion. In addition, mice expressing beta 1 alone or in combination with alpha 2 or alpha 5 exhibited epidermal hyper-proliferation, perturbed keratinocyte differentiation, and skin inflammation, all of which are features of a common human skin disease, psoriasis.

Topics: Animals; Cell Adhesion; Cell Differentiation; Cell Division; Crosses, Genetic; Embryonic and Fetal Development; Epidermis; Eyelids; Hair; Homeostasis; Humans; Integrins; Keratinocytes; Mice; Mice, Transgenic; Promoter Regions, Genetic; Protein Precursors; Psoriasis; Skin; Skin Abnormalities; Vibrissae