Keratinocytes In Mouse Epidermis Research Articles

Dynamically Regulated CFTR Expression and Its Functional Role in Cutaneous Wound Healing.

The physiological role of cystic fibrosis transmembrane conductance regulator (CFTR) in keratinocytes and skin wound healing is completely unknown. The present study shows that CFTR is expressed in the multiple layers of keratinocytes in mouse epidermis and exhibits a dynamic expression pattern in a dorsal skin wound healing model, with diminishing levels observed from day 3 to day 5 and re-appearing from day 7 to day 10 after wounding. Knockdown of CFTR in cultured human keratinocytes promotes cell migration but inhibits differentiation, while overexpression of CFTR suppresses migration but enhances differentiation, indicating an important role of CFTR in regulating keratinocyte behavior. In addition, we have demonstrated a direct association of CFTR with epithelial junction formation as knockdown of CFTR downregulates the expression of adhesion molecules, such as E-cadherin, ZO-1 and β-catenin, and disrupts the formation of cell junction, while overexpression of CFTR enhances cell junction formation. More importantly, we have shown that ΔF508cftr-/- mice with defective CFTR exhibit delayed wound healing as compared to wild type mice, indicating that normal function of CFTR is critical for wound repair. Taken together, the present study has revealed a previously undefined role of CFTR in regulating skin wound healing processes, which may have implications in injury repair of other epithelial tissues.

Genetic and pharmacological evidence that a retinoic acid cannot be the RXR-activating ligand in mouse epidermis keratinocytes

Using genetic and pharmacological approaches, we demonstrate that both RARgamma/RXRalpha heterodimers involved in repression events, as well as PPARbeta(delta)/RXRalpha heterodimers involved in activation events, are cell-autonomously required in suprabasal keratinocytes for the generation of lamellar granules (LG), the organelles instrumental to the formation of the skin permeability barrier. In activating PPARbeta(delta)/RXRalpha heterodimers, RXRalpha is transcriptionally active as its AF-2 activation function is required and can be inhibited by an RXR-selective antagonist. Within repressing RARgamma/RXRalpha heterodimers, induction of the transcriptional activity of RXRalpha is subordinated to the addition of an agonistic ligand for RARgamma. Thus, the ligand that possibly binds and activates RXRalpha heterodimerized with PPARbeta(delta) cannot be a retinoic acid, as it would also bind RARgamma and relieve the RARgamma-mediated repression, thereby yielding abnormal LGs. Our data also demonstrate for the first time that subordination of RXR transcriptional activity to that of its RAR partner plays a crucial role in vivo, because it allows RXRs to act concomitantly, within the same cell, as heterodimerization partners for repression, as well as for activation events in which they are transcriptionally active.

Overexpression of protein kinase C-alpha in the epidermis of transgenic mice results in striking alterations in phorbol ester-induced inflammation and COX-2, MIP-2 and TNF-alpha expression but not tumor promotion.

Protein kinase Calpha (PKCalpha) is one of six PKC isoforms expressed in keratinocytes of mouse epidermis. To gain an understanding of the role of epidermal PKCalpha, we have localized its expression to specific cells of normal mouse skin and examined the effect of keratin 5 (K5) promoter directed expression of PKCalpha in transgenic mice. In normal mouse skin, PKCalpha was extensively expressed in the outer root sheath (ORS) keratinocytes of the anagen hair follicle and weakly expressed in keratinocytes of interfollicular epidermis. K5-targeted expression of PKCalpha to epidermal basal keratinocytes and follicular ORS keratinocytes resulted in a tenfold increase in epidermal PKCalpha. K5-PKCalpha mice exhibited no abnormalities in keratinocyte growth and differentiation in the epidermis. However, a single topical treatment with the PKC activator, 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a striking inflammatory response characterized by edema and extensive epidermal infiltration of neutrophils that formed intraepidermal microabscesses in the epidermis. Compared to TPA-treated wild-type mice, the epidermis of TPA-treated K5-PKCalpha mice displayed increased expression of cyclooxygenase-2 (COX-2), the neutrophil chemotactic factor macrophage inflammatory protein-2 (MIP-2) mRNA and the proinflammatory cytokine TNFalpha mRNA but not IL-6 or IL-1alpha mRNA. To determine if K5-PKCalpha mice display an altered response to TPA-promotion, 7, 12-dimethylbenz[a]anthracene-initiated K5-PKCalpha mice and wild-type mice were promoted with TPA. No differences in papilloma incidence or multiplicity were observed between K5-PKCalpha mice and wild-type littermates. These results demonstrate that the overexpression of PKCalpha in epidermis increases the expression of specific proinflammatory mediators and induces cutaneous inflammation but has little to no effect on epidermal differentiation, proliferation or TPA tumor promotion.

The heterogeneity of the germinative compartment in human epidermis and its implications in pathogenesis.

In mouse epidermis keratinocytes of the basal layer seem to belong to 3 different subpopulations: stem cells, transit cells and postmitotic cells. Each subpopulation assumes a specific role in epidermal homeostasis. Recent data tend to display a similar heterogeneity among basal keratinocytes in human epidermis. This concept opens the door to an integrated understanding of epidermal renewal but also suggests new hypotheses in pathogenesis. Psoriasis, a typical example of epidermal hyperplasia, is considered from this point of view.

Expression of Gap Junction Proteins Connexin 26 and 43 Is Modulated During Differentiation of Keratinocytes in Newborn Mouse Epidermis

We examined the expression of the gap junction proteins connexin 26 (Cx26), 32 (Cx32), and 43 (Cx43) in keratinocytes of newborn mouse epidermis to elucidate which connexins are expressed in keratinocytes in intact skin of newborn mice, and whether the expression of connexins is modulated during terminal differentiation of keratinocytes. Immunofluorescent staining using antibodies against Cx26, Cx32, and Cx43 combined with type-specific anti-keratin immunohistochemistry showed that Cx26 was expressed in keratinocytes in the granular layer and in the upper part of the squamous layer, whereas Cx43 was localized in keratinocytes in the basal layer and in the lower part of the squamous layer. No specific staining of Cx32 was found in mouse epidermis. Double staining of Cx26 and Cx43 revealed that some keratinocytes in the squamous layer expressed both connexins, but that in most cases localization of the two kinds of connexins was different, i.e., Cx26 was localized on the upper surface, whereas Cx43 was present on the lower surface of the plasma membrane of keratinocytes. Northern and Western blot analyses confirmed that Cx26 and Cx43, but not Cx32, were expressed at mRNA and protein levels in newborn mouse skin. These results suggest that the modulation of connexin expression from Cx43 to Cx26 takes place during terminal differentiation of keratinocytes in mouse epidermis.

Keratinocyte-derived IL-7 serves as a growth factor for dendritic epidermal T cells in mice.

Dendritic epidermal T cells (DETC) are CD3+, CD45+, CD4-, CD8-, TCR-V gamma 3/V delta 1+ T lymphocytes that reside in symbiosis with keratinocytes in mouse epidermis. To address mechanisms by which these cells survive and proliferate within the epidermal environment, we have tested the hypothesis that cytokines secreted by neighboring keratinocytes play relevant roles. The present study was conducted to determine whether keratinocytes produce biologically relevant amounts of IL-7, and, if so, to study its effects on DETC. The long term cultured DETC line, 7-17, and freshly isolated DETC exhibited dose- and time-dependent proliferative responses to rIL-7. These responses were blocked completely by anti-IL-7 antibodies, whereas anti-IL-2 had no effect, indicating that DETC respond to IL-7 by an IL-2-independent mechanism. Proliferative responses depended on the state of cell activation; DETC stimulated 2 to 5 days earlier with Con A proliferated optimally to added IL-7, whereas cells stimulated 10 days earlier did not proliferate. DETC that failed to proliferate responded to IL-7 by showing prolonged survival; cells maintained for 7 days with IL-7 alone retained their capacity to proliferate in response to Con A. Mouse epidermal cells and Pam 212 keratinocyte line both expressed IL-7 mRNA constitutively, as demonstrated by reverse transcription-polymerase chain reaction analyses. The production of IL-7 by mouse keratinocytes was also confirmed; Pam 212 culture supernatants supported DETC proliferation, and this activity was diminished by 50% with added anti-IL-7 antibodies. These results indicate that keratinocytes produce IL-7 in biologically relevant amounts, which, in turn, serve to promote the survival and growth of DETC. IL-7-mediated communication between epithelial cells and gamma delta T cells may represent one mechanism to sustain the indefinite residence of gamma delta T cells in epithelial tissues of mice.

Reciprocal Cytokine-Mediated Cellular Interactions in Mouse Epidermis: Promotion of γ δ T-Cell Growth by IL-7 and TNFα and Inhibition of Keratinocyte Growth by γIFN

A unique subset of gamma delta T cells, termed dendritic epidermal T cells (DETC), resides in symbiosis with keratinocytes in mouse epidermis. We have shown previously that interleukin 7 (IL-7) which is produced by keratinocytes, promotes growth and prevents apoptosis in DETC. To extend this observation, we examined 12 cytokines, each of which is expressed by epidermal cells at mRNA and/or protein levels, for their capacities to modulate the growth of DETC. Cytokines examined included IL-1 alpha, IL-2, IL-3, IL-4, IL-6, IL-7, IL-8, IL-10, tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), granulocyte/macrophage-colony stimulating factor (GM-CSF), and macrophage inflammatory protein-1 alpha (MIP-1 alpha). When tested individually, IL-2 and IL-7 promoted maximal growth of the long-term cultured DETC line 7-17. When tested in combinations, synergistic growth-promoting effects were seen with IL-2 and IL-4 or IL-7, and with IL-7 and IL-4 or TNF alpha. Dose-response experiments demonstrated that TNF alpha, which is produced by keratinocytes, enhances IL-7-induced DETC proliferation, but inhibits IL-2-induced proliferation. The mouse keratinocyte-derived cell line Pam 212 was used to test these cytokines for their capacities to regulate keratinocyte growth. Only gamma IFN, which is produced by DETC, inhibited proliferation in a dose-dependent fashion. These results illustrate three reciprocal pathways by which epidermal cytokines regulate the growth of epidermal cells: 1) a paracrine mechanism by which keratinocyte-derived cytokines (e.g., IL-7 and TNF alpha) promote the growth of DETC, 2) an autocrine mechanism by which DETC-derived cytokines (e.g., IL-2 and IL-4) support their own growth, and 3) a reciprocal pathway in which a cytokine produced by resident epidermal leukocytes (e.g., gamma IFN) modulates the growth of keratinocytes.