Genome-wide analysis of gene expression in Krt1+/+ versus Krt1-/- epidermis and full-thickness skin.
ABSTRACT: Keratin 1 (KRT1) and its heterodimer partner keratin 10 (KRT10) constitute the intermediate filament cytoskeleton of suprabasal skin keratinocytes. They participate in formation of the epidermal barrier, which protects against dehydration and inflammation. Mutations in KRT1 cause keratinopathic ichthyosis with erythema, recurrent inflammation, and barrier defects. Here, we show that genetic deletion of Krt1 in mice causes a defective inside-out epidermal barrier, pre- and postnatal increases in Mrp8/Mrp14, interleukin (IL) 18, IL-33, and thymic stromal lymphopoietin (TSLP) in skin extracts, and systemic release of IL-18 into newborn serum. Perinatal lethality was partially rescued by treatment with glucocorticoids to promote barrier repair or with IL- 18-blocking antibodies in utero. In human keratinocytes, IL-18 release was cellautonomous and caspase-1-dependent, indicating KRT1-dependent inflammasome activation. Our data reveal a novl function of KRT1 in controlling inflammasome activity and stimulating barrier formation, thereby integrating the keratin cytoskeleton into the epidermal immune response. In view of their widespread expression, keratins merit investigation of their functions in inflammatory conditions, including asthma and inflammatory bowel disorders. Total RNA was obtained from epidermis or full-thickness skin of Krt1+/+ and Krt1-/- mice (C57BL/6 background) at P0 (newborn).
Project description:The epidermal barrier protects the body against mechanical injury, infection and dehydration. The respective contribution of type I and type II keratins which form the major cytoskeleton in epidermal keratinocytes in barrier formation and stress protection is incompletely understood. Here, we reveal a novel mechanism by which keratins control anti-oxidant responses through barrier-dependent and cell-autonomous mechanisms. Mice lacking the entire type I (KtyI) or type II (KtyII) keratin gene clusters suffer from distinct prenatal barrier defects. Comparative transcriptome profiling identifies essential cornified envelope components and reveals strong upregulation of the bZIP transcription factor Nrf2 in situ. Isolated keratinocytes from both strains of mice show elevated mitochondrial oxygen consumption and Nrf2 activity, decreased upon keratin re-expression. We propose a model in which keratins control mitochondria-derived oxidative stress via Nrf2 activation. Our findings reveal major contributions of keratins to chronic inflammation and autoimmune disorders. Total RNA obtained from E18.5 embryo back skin from typeI and II keratin knockout compared with respective wild type.
Project description:Keratins are the main intermediate filament proteins of epithelial cells. In keratinocytes of the mammalian epidermis they form a cytoskeleton that resists mechanical stress and thereby are essential for the function of the skin as a barrier against the environment. Here, we performed a comparative genomics study of epidermal keratin genes in terrestrial and fully aquatic mammals to determine adaptations of the epidermal keratin cytoskeleton to different environments. We show that keratins K5 and K14 of the innermost (basal), proliferation-competent layer of the epidermis are conserved in all mammals investigated. In contrast, K1 and K10, which form the main part of the cytoskeleton in the outer (suprabasal) layers of the epidermis of terrestrial mammals, have been lost in whales and dolphins (cetaceans) and in the manatee. Whereas in terrestrial mammalian epidermis K6 and K17 are expressed only upon stress-induced epidermal thickening, high levels of K6 and K17 are consistently present in dolphin skin, indicating constitutive expression and substitution of K1 and K10. K2 and K9, which are expressed in a body site-restricted manner in human and mouse suprabasal epidermis, have been lost not only in cetaceans and manatee but also in some terrestrial mammals. The evolution of alternative splicing of K10 and differentiation-dependent upregulation of K23 have increased the complexity of keratin expression in the epidermis of terrestrial mammals. Taken together, these results reveal evolutionary diversification of the epidermal cytoskeleton in mammals and suggest a complete replacement of the quantitatively predominant epidermal proteins of terrestrial mammals by originally stress-inducible keratins in cetaceans.
Project description:Inflammasomes are multimeric protein complexes that assemble upon sensing of a variety of stress factors. Their formation results in caspase-1-mediated activation and secretion of the pro-inflammatory cytokines pro-interleukin(IL)-1? and -18, which induce an inflammatory response. Inflammation is supported by a lytic form of cell death, termed pyroptosis. Innate immune cells, such as macrophages or dendritic cells, express and activate inflammasomes. However, it has also been demonstrated that human primary keratinocytes activate different types of inflammasomes in vitro, for example, upon UVB irradiation or viral infection. Keratinocytes are the main cell type of the epidermis, the outermost layer of the body, and form a protective barrier consisting of a stratified multi-layered epithelium. In human, gain-of-function mutations of the NLRP1 gene cause syndromes mediated by inflammasome activation in keratinocytes that are characterised by skin inflammation and skin cancer susceptibility. Here we demonstrate that murine keratinocytes do not activate inflammasomes in response to stimuli, which induce IL-1? and -18 secretion by human keratinocytes. Whereas murine keratinocytes produced caspase-1 and proIL-18, expression of the inflammasome proteins Nlrp1, Nlrp3, Aim2, Asc, and proIL-1? was, compared to human keratinocytes or murine dendritic cells, very low or even undetectable. Priming of murine keratinocytes with cytokines commonly used for induction of proIL-1? and inflammasome protein expression did not rescue inflammasome activation. Nevertheless, UVB-induced inflammation and neutrophil recruitment in murine skin was dependent on IL-1? and caspase-1. However, also under these conditions, we did not detect expression of proIL-1? by keratinocytes in murine skin, but by immune cells. These results demonstrate a higher immunological competence of human compared to murine keratinocytes, which is reflected by stress-induced IL-1? secretion that is mediated by inflammasomes. Therefore, keratinocytes in human skin can exert immune functions, which are carried out by professional immune cells in murine skin.
Project description:Neural-Wiskott Aldrich Syndrome Protein (N-WASP) is expressed ubiquitously and regulates actin cytoskeleton remodeling. In order to characterize the role of N-WASP in epidermal homeostasis and cutaneous biology, we generated conditional N-WASP knockout mouse using CK14-cre (cytokeratin 14) to ablate expression of N-WASP in keratinocytes. N-WASPK14KO (N-WASP fl/fl ; CK14-Cre) mice were born following Mendelian genetics suggesting that N-WASP expression in keratinocytes is not essential during embryogenesis. N-WASPK14KO mice exhibited stunted growth, alopecia, dry and wrinkled skin. The dry skin in N-WASPK14KO mice is probably due to increased transepidermal water loss (TEWL) caused by barrier function defects as revealed by dye penetration assay. N-WASPK14KO mice developed spontaneous inflammation in the neck and face 10 weeks after birth. Histological staining revealed thickening of the epidermis, abnormal cornified layer and extensive infiltration of immune cells (mast cells, eosinophils and T-lymphocytes) in N-WASPK14KO mice skin compared to control mice. N-WASPK14KO mice had higher serum levels of IL-1?, TNF-?, IL-6 and IL-17 compared to control mice. Thus our results suggest that conditional N-WASP knockout in keratinocytes leads to compromised skin barrier, higher infiltration of immune cells and hyperproliferation of keratinocytes due to increased production of cytokines highlighting the importance of N-WASP in maintaining the skin homeostasis.
Project description:Keratinocytes constitute the majority of cells in the skin's epidermis, the first line of defence against percutaneous pathogens. Schistosome larvae (cercariae) actively penetrate the epidermis to establish infection, however the response of keratinocytes to invading cercariae has not been investigated. Here we address the hypothesis that cercariae activate epidermal keratinocytes to promote the development of a pro-inflammatory immune response in the skin. C57BL/6 mice were exposed to Schistosoma mansoni cercariae via each pinna and non-haematopoietic cells isolated from epidermal tissue were characterised for the presence of different keratinocyte sub-sets at 6, 24 and 96 h p.i. We identified an expansion of epidermal keratinocyte precursors (CD45(-), CD326(-), CD34(+)) within 24 h of infection relative to naïve animals. Following infection, cells within the precursor population displayed a more differentiated phenotype (?6integrin(-)) than in uninfected skin. Parallel immunohistochemical analysis of pinnae cryosections showed that this expansion corresponded to an increase in the intensity of CD34 staining, specifically in the basal bulge region of hair follicles of infected mice, and a higher frequency of keratinocyte Ki67(+) nuclei in both the hair follicle and interfollicular epidermis. Expression of pro-inflammatory cytokine and stress-associated keratin 6b genes was also transiently upregulated in the epidermal tissue of infected mice. In vitro exposure of keratinocyte precursors isolated from neonatal mouse skin to excretory/secretory antigens released by penetrating cercariae elicited IL-1? and IL-1? production, supporting a role for keratinocyte precursors in initiating cutaneous inflammatory immune responses. Together, these observations indicate that S.mansoni cercariae and their excretory/secretory products act directly upon epidermal keratinocytes, which respond by initiating barrier repair and pro-inflammatory mechanisms similar to those observed in epidermal wound healing.
Project description:Inflammatory skin disorders result in significant epidermal changes, including keratinocyte hyperproliferation, incomplete differentiation, and impaired barrier. Here we test whether, conversely, an impaired epidermal barrier can promote an inflammatory response. Mice lacking the transcription factor Kruppel-like factor 4 (Klf4) have a severe defect in epidermal barrier acquisition. Transcription profiling of Klf4(-/-) newborn skin revealed similar changes in gene expression to involved psoriatic plaques, including a significant upregulation of the gap junction protein connexin 26 (Cx26). Ectopic expression of Cx26 from the epidermis-specific involucrin (INV) promoter (INV-Cx26) demonstrated that downregulation of Cx26 is required for barrier acquisition during development. In juvenile and adult mice, persistent Cx26 expression kept wounded epidermis in a hyperproliferative state, blocked the transition to remodeling, and led to an infiltration of immune cells. Mechanistically, ectopic expression of Cx26 in keratinocytes resulted in increased ATP release, which delayed epidermal barrier recovery and promoted an inflammatory response in resident immune cells. These results provide a molecular link between barrier acquisition in utero and epidermal remodeling after wounding. More generally, these studies suggest that the most effective treatments for inflammatory skin disorders might concomitantly suppress the immune response and enhance epidermal differentiation to restore the barrier.
Project description:In an effort to understand the role of Distal-less 3 (Dlx3) in cutaneous biology and pathophysiology, we generated and characterized a mouse model with epidermal ablation of Dlx3. K14cre;Dlx3(Kin/f) mice exhibited epidermal hyperproliferation and abnormal differentiation of keratinocytes. Results from subsequent analyses revealed cutaneous inflammation that featured accumulation of IL-17-producing CD4(+) T, CD8(+) T, and ?? T cells in the skin and lymph nodes of K14cre;Dlx3(Kin/f) mice. The gene expression signature of K14cre;Dlx3(Kin/f) skin shared features with lesional psoriatic skin, and Dlx3 expression was markedly and selectively decreased in psoriatic skin. Interestingly, cultured Dlx3 null keratinocytes triggered cytokine production that is potentially linked to inflammatory responses in K14cre;Dlx3(Kin/f) mice. Thus, Dlx3 ablation in epidermis is linked to altered epidermal differentiation, barrier development, and IL-17-associated skin inflammation. This model provides a platform that will allow the systematic exploration of the contributions of keratinocytes to cutaneous inflammation.
Project description:Rationale: Cdc42 is a Rho GTPase that regulates diverse cellular functions. Here, we used genetic techniques to investigate the role of Cdc42 in epidermal development and epidermal barrier formation. Methods: Keratinocyte-restricted Cdc42 knockout mice were generated with the Cre-LoxP system under the keratin 14 (K14) promoter. The skin and other tissues were collected from mutant and wild-type mice, and their cellular, molecular, morphological, and physiological features were analyzed. Results: Loss of Cdc42 in the epidermis in vivo resulted in neonatal lethality and impairment of epidermal barrier formation. Cdc42 deficiency led to the loss of epidermal stem cells. The absence of Cdc42 led to increased thickening of the epidermis, which was associated with increased proliferation and reduced apoptosis of keratinocytes. In addition, Cdc42 deficiency damaged tight junctions, adherens junctions and desmosomes. RNA sequencing results showed that the most significantly altered genes were enriched by the terms of "keratinization" and "cornified envelope" (CE). Among the differentially expressed genes in the CE term, several members of the small proline-rich protein (SPRR) family were upregulated. Further study revealed that there may be a Cdc42-SPRR pathway, which may correlate with epidermal barrier function. Conclusions: Our study indicates that Cdc42 is essential for epidermal development and epidermal barrier formation. Defects in Cdc42-SPRR signaling may be associated with skin barrier dysfunction and a variety of skin diseases.
Project description:Diabetes causes skin complications, including xerosis and foot ulcers. Ulcers complicated by infections exacerbate skin conditions, and in severe cases, limb/toe amputations are required to prevent the development of sepsis. Here, we hypothesize that hyperglycemia induces skin barrier dysfunction with alterations of epidermal integrity. The effects of hyperglycemia on the epidermis were examined in streptozotocin-induced diabetic mice with/without insulin therapy. The results showed that dye leakages were prominent, and transepidermal water loss after tape stripping was exacerbated in diabetic mice. These data indicate that hyperglycemia impaired skin barrier functions. Additionally, the distribution of the protein associated with the tight junction structure, tight junction protein-1 (ZO-1), was characterized by diffuse and significantly wider expression in the diabetic mice compared to that in the control mice. In turn, epidermal cell number was significantly reduced and basal cells were irregularly aligned with ultrastructural alterations in diabetic mice. In contrast, the number of corneocytes, namely, denucleated and terminally differentiated keratinocytes significantly increased, while their sensitivity to mechanical stress was enhanced in the diabetic mice. We found that cell proliferation was significantly decreased, while apoptotic cells were comparable in the skin of diabetic mice, compared to those in the control mice. In the epidermis, Keratin 5 and keratin 14 expressions were reduced, while keratin 10 and loricrin were ectopically induced in diabetic mice. These data suggest that hyperglycemia altered keratinocyte proliferation/differentiation. Finally, these phenotypes observed in diabetic mice were mitigated by insulin treatment. Reduction in basal cell number and perturbation of the proliferation/differentiation process could be the underlying mechanisms for impaired skin barrier functions in diabetic mice.
Project description:To understand the role of epidermal keratinocytes in immunopathology of skin diseases with predominant T helper (Th) cell responses, we measured the genome-wide transcriptional profile of human keratinocytes in response to IFNgamma, IL-4, IL-17A or IL-22, major cytokines produced by Th1, Th2, Th17 or Th22 cells, respectively. IL-6 was also included in the transcriptional profile analysis because a variety of pro-inflammatory stimuli stimulate human keratinocytes to produce IL-6 that has an autocrine or paracrine role in epidermal immunity. We aimed to discover commonly expressed genes in human keratinocytes in response to pro-inflammatory cytokines, which would be associated with common pathophysiological responses in various skin diseases such as skin permeability barrier disruption or epidermal hyperplasia. Normal human keratinocytes (NHKs) were stimulated with IFNγ, IL-4, IL-6, IL-17A and IL-22 for 24 hours and harvested for total RNA extraction and hybridization on Affymetrix microarrays.