Increased retinoic acid levels through ablation of Cyp26b1 determine the processes of embryonic skin barrier formation and peridermal development
ABSTRACT The process by which the periderm transitions to stratified epidermis with the establishment of the skin barrier is unknown. Understanding the cellular and molecular processes involved is crucial for the treatment of human pathologies, where abnormal skin development and barrier dysfunction are associated with hypothermia and perinatal dehydration. For the first time, we demonstrate that retinoic acid (RA) levels are important for periderm desquamation, embryonic skin differentiation and barrier formation. Although excess exogenous RA has been known to have teratogenic effects, little is known about the consequences of elevated endogenous retinoids in skin during embryogenesis. Absence of cytochrome P450, family 26, subfamily b, polypeptide 1 (Cyp26b1), a retinoic-acid-degrading enzyme, results in aberrant epidermal differentiation and filaggrin expression, defective cornified envelopes and skin barrier formation, in conjunction with peridermal retention. We show that these alterations are RA dependent because administration of exogenous RA in vivo and to organotypic skin cultures phenocopy Cyp26b1(-/-) skin abnormalities. Furthermore, utilizing the Flaky tail (Ft/Ft) mice, a mouse model for human ichthyosis, characterized by mutations in the filaggrin gene, we establish that proper differentiation and barrier formation is a prerequisite for periderm sloughing. These results are important in understanding pathologies associated with abnormal embryonic skin development and barrier dysfunction.
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- "The 11Enh-Cre; Cyp26b1 flox/+ mice were used as controls. For genotyping, genomic DNA was isolated from the tail tips or embryonic skin and subjected to PCR analysis, according to a previously described method for the Cre transgene  and Cyp26b1 allele  "
ABSTRACT: Retinoic acid (RA) is an active metabolite of vitamin A and plays important roles in embryonic development. CYP26 enzymes degrade RA and have specific expression patterns that produce a RA gradient, which regulates the patterning of various structures in the embryo. However, it has not been addressed whether a RA gradient also exists and functions in organs after birth. We found localized RA activities in the diaphyseal portion of the growth plate cartilage were associated with the specific expression of Cyp26b1 in the epiphyseal portion in juvenile mice. To disturb the distribution of RA, we generated mice lacking Cyp26b1 specifically in chondrocytes (Cyp26b1(Δchon) cKO). These mice showed reduced skeletal growth in the juvenile stage. Additionally, their growth plate cartilage showed decreased proliferation rates of proliferative chondrocytes, which was associated with a reduced height in the zone of proliferative chondrocytes, and closed focally by four weeks of age, while wild-type mouse growth plates never closed. Feeding the Cyp26b1 cKO mice a vitamin A-deficient diet partially reversed these abnormalities of the growth plate cartilage. These results collectively suggest that Cyp26b1 in the growth plate regulates the proliferation rates of chondrocytes and is responsible for the normal function of the growth plate and growing bones in juvenile mice, probably by limiting the RA distribution in the growth plate proliferating zone.Biochemical and Biophysical Research Communications 10/2014; 454(1). DOI:10.1016/j.bbrc.2014.10.001 · 2.30 Impact Factor
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- "These observations suggest that filaggrin deficiency alone is able to induce mild inflammation  and predispose to allergic response , . On the other hand, the matted coat mutation is likely to amplify the dysfunction of the barrier, and to accelerate/enhance the inflammatory reaction, eventually after changes in upper epidermis biophysical properties , , , (Table S6 in File S1). Beyond filaggrin deficiency, mechanical or genetic barrier disruption over time can lead to increased expression of proinflammatory cytokines and recruitment of LCs on the site of lesion , , , , , according to environmental and experimental conditions , . "
ABSTRACT: Loss-of-function mutations in human profilaggrin gene have been identified as the cause of ichthyosis vulgaris (IV), and as a major predisposition factor for atopic dermatitis (AD). Similarly, flaky tail (a/a ma ft/ma ft/J) mice were described as a model for IV, and shown to be predisposed to eczema. The aim of this study was to correlate the flaky tail mouse phenotype with human IV and AD, in order to dissect early molecular events leading to atopic dermatitis in mice and men, suffering from filaggrin deficiency. Thus, 5-days old flaky tail pups were analyzed histologically, expression of cytokines was measured in skin and signaling pathways were investigated by protein analysis. Human biopsies of IV and AD patients were analyzed histologically and by real time PCR assays. Our data show acanthosis and hyperproliferation in flaky tail epidermis, associated with increased IL1β and thymic stromal lymphopoietin (TSLP) expression, and Th2-polarization. Consequently, NFκB and Stat pathways were activated, and IL6 mRNA levels were increased. Further, quantitative analysis of late epidermal differentiation markers revealed increased Small proline-rich protein 2A (Sprr2a) synthesis. Th2-polarization and Sprr2a increase may result from high TSLP expression, as shown after analysis of 5-days old K14-TSLP tg mouse skin biopsies. Our findings in the flaky tail mouse correlate with data obtained from patient biopsies of AD, but not IV. We propose that proinflammatory cytokines are responsible for acanthosis in flaky tail epidermis, and together with the Th2-derived cytokines lead to morphological changes. Accordingly, the a/a ma ft/ma ft/J mouse model can be used as an appropriate model to study early AD onset associated with profilaggrin deficiency.PLoS ONE 07/2013; 8(7):e67869. DOI:10.1371/journal.pone.0067869 · 3.23 Impact Factor
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- "If aberrant exposure to late-stage amniotic fluid is the driving force behind the compensatory response seen in the LKO, then other mouse models with in utero barrier defects should also exhibit activation of Nrf2. Therefore, we analyzed the flaky tail mouse (ft/ft), which lacks the major barrier component, filaggrin (Fallon et al., 2009), and was also shown to have a barrier defect in utero (Okano et al., 2012). Consistent with our hypothesis , a pronounced nuclear accumulation of Nrf2 was also observed in the suprabasal layers of E17.5 ft/ft epidermis (Figure 1E). "
ABSTRACT: The loss of loricrin, a major component of the cornified envelope, results in a delay of epidermal barrier formation. Therefore, the living layers of the epidermis are aberrantly exposed to late-stage amniotic fluid, which may serve as the signal to upregulate genes that functionally compensate for the loss of loricrin. Consistent with this hypothesis, metabolomic studies revealed marked changes in amniotic fluid between E14.5 and E16.5 days postcoitum. In addition, we discovered that the Nrf2/Keap1 pathway detects these compositional changes and directly upregulates the expression of genes involved in the compensatory response, thus ensuring postnatal survival. In support of this finding, we demonstrate that genetically blocking the Nrf2 pathway abolishes the compensatory response and that preemptively activating Nrf2 pharmacologically rescues the delay in barrier formation in utero. Our findings reveal that the functions of Nrf2 and the composition of amniotic fluid have coevolved to ensure the formation of a functional barrier.Developmental Cell 12/2012; 23(6):1238-46. DOI:10.1016/j.devcel.2012.11.002 · 9.71 Impact Factor