Development-Associated Genes of the Epidermal Differentiation Complex (EDC)

The epidermal differentiation complex (EDC) is a cluster of genes that encode protein components of the outermost layers of the epidermis in mammals, reptiles and birds. The development of the stratified epidermis from a single-layered ectoderm involves an embryo-specific superficial cell layer, the periderm. An additional layer, the subperiderm, develops in crocodilians and over scutate scales of birds. Here, we review the expression of EDC genes during embryonic development. Several EDC genes are expressed predominantly or exclusively in embryo-specific cell layers, whereas others are confined to the epidermal layers that are maintained in postnatal skin. The S100 fused-type proteins scaffoldin and trichohyalin are expressed in the avian and mammalian periderm, respectively. Scaffoldin forms the so-called periderm granules, which are histological markers of the periderm in birds. Epidermal differentiation cysteine-rich protein (EDCRP) and epidermal differentiation protein containing DPCC motifs (EDDM) are expressed in the avian subperiderm where they are supposed to undergo cross-linking via disulfide bonds. Furthermore, a histidine-rich epidermal differentiation protein and feather-type corneous beta-proteins, also known as beta-keratins, are expressed in the subperiderm. The accumulating evidence for roles of EDC genes in the development of the epidermis has implications on the evolutionary diversification of the skin in amniotes.

Expression analysis of genes important for maintaining skin function in a senescence-accelerated mouse prone model

AIM

Senescence-accelerated mouse prone (SAMP) mice can reproduce the same conditions as normal aging mice in a short period. Although SAMP mice have been widely used in aging research, research on skin function in SAMP mice is lacking. In this study, to investigate the skin function of SAMP mice, we analyzed the expression of genes important for maintaining skin function.

METHODS

Eight-month-old SAMP mice and senescence-accelerated mouse resistant (SAMR) mice with normal aging were used. The expression levels of various functional genes in the skin were analyzed.

RESULTS

The dermal water content of SAMP mice was significantly lower than that of SAMR mice, indicating dry skin. The mRNA expression levels of elastin (Ela), filaggrin (Flg), loricrin (Lor), collagen type I alpha 1 chain (Col1a1) and Col1a2 in the skin of SAMP mice were all significantly decreased compared with those of SAMR mice. Hyaluronan-degrading enzyme (Hyal1) expression levels in SAMP mice were similar to those in SAMR mice, but hyaluronan synthase (Has2) levels were significantly decreased. In addition, the expression level of aquaporin-3 in the skin of SAMP mice was significantly decreased at both the mRNA and protein levels.

CONCLUSIONS

In the skin of SAMP mice, the expression levels of various skin function-regulating genes were decreased, and this phenomenon might cause skin dryness. The SAMP mouse could be a tool for analyzing skin aging. Geriatr Gerontol Int 2023; 23: 951-957.

The Epidermal Transcriptome Analysis of a Novel c.639_642dup LORICRIN Variant-Delineation of the Loricrin Keratoderma Pathology

Loricrin keratoderma (LK) is a rare autosomal dominant genodermatosis caused by LORICRIN gene mutations. The pathogenesis of the disease is not yet fully understood. So far, only 10 pathogenic variants in LORICRIN have been described, with all of them but one being deletions or insertions. The significance of rare nonsense variants remains unclear. Furthermore, no data regarding the RNA expression in affected patients are available. The aim of this study is to describe the two variants in the LORICRIN gene found in two distinct families: the novel pathogenic variant c.639_642dup and a rare c.10C > T (p.Gln4Ter) of unknown significance. We also present the results of the transcriptome analysis of the lesional loricrin keratoderma epidermis of a patient with c.639_642dup. We show that in the LK lesion, the genes associated with epidermis development and keratocyte differentiation are upregulated, while genes engaged in cell adhesion, differentiation developmental processes, ion homeostasis and transport, signaling and cell communication are downregulated. In the context of the p.Gln4Ter clinical significance evaluation, we provide data indicating that LORICRIN haploinsufficiency has no skin consequences. Our results give further insight into the pathogenesis of LK, which may have therapeutic implications in the future and important significance in the context of genetic counseling.

Potential Role of the Epidermal Differentiation Complex in the Pathogenesis of Psoriasis

The skin is the largest barrier organ of the human body and serves to protect the internal structure of the body from the harmful environment. The epidermis forms the outermost layer and is exposed to the environment. Keratinocytes are important constituent cells of the epidermis and alter their morphology and structural integrity through a highly complex differentiation process referred to as cornification. Abnormalities in the process of epidermal cornification can lead to skin barrier dysfunction. The epidermal differentiation complex (EDC) is a gene cluster located within a 2 Mb region of human chromosome 1q21. EDC is responsible for epithelial tissue development and for properties of the stratum corneum. One of the most important features of psoriasis is the abnormal terminal differentiation of keratinocytes. However, the relationship between EDC and the occurrence of psoriasis is still unclear. In this review, we summarize current knowledge regarding the physiological functions of EDC and discuss its possible contributions to the pathogenesis of psoriasis.

Allantodapsone is a Pan-Inhibitor of Staphylococcus aureus Adhesion to Fibrinogen, Loricrin, and Cytokeratin 10

Staphylococcus aureus infections have become a major challenge in health care due to increasing antibiotic resistance. We aimed to design small molecule inhibitors of S. aureus surface proteins to be developed as colonization inhibitors. We identified allantodapsone in an initial screen searching for inhibitors of clumping factors A and B (ClfA and ClfB). We used microbial adhesion assays to investigate the effect of allantodapsone on extracellular matrix protein interactions. Allantodapsone inhibited S. aureus Newman adhesion to fibrinogen with an IC50 of 21.3 μM (95% CI 4.5-102 μM), minimum adhesion inhibitory concentration (MAIC) of 100 μM (40.2 μg/mL). Additionally, allantodapsone inhibited adhesion of Lactococcus lactis strains exogenously expressing the clumping factors to fibrinogen (L. lactis ClfA, IC50 of 3.8 μM [95% CI 1.0-14.3 μM], MAIC 10 μM, 4.0 μg/mL; and L. lactis ClfB, IC50 of 11.0 μM [95% CI 0.9-13.6 μM], MAIC 33 μM, 13.3 μg/mL), indicating specific inhibition. Furthermore, the dapsone and alloxan fragments of allantodapsone did not have any inhibitory effect. Adhesion of S. aureus Newman to L2v loricrin is dependent on the expression of ClfB. Allantodapsone caused a dose dependent inhibition of S. aureus adhesion to the L2v loricrin fragment, with full inhibition at 40 μM (OD600 0.11 ± 0.01). Furthermore, recombinant ClfB protein binding to L2v loricrin was inhibited by allantodapsone (P < 0.0001). Allantodapsone also demonstrated dose dependent inhibition of S. aureus Newman adhesion to cytokeratin 10 (CK10). Allantodapsone is the first small molecule inhibitor of the S. aureus clumping factors with potential for development as a colonization inhibitor. IMPORTANCE S. aureus colonization of the nares and the skin provide a reservoir of bacteria that can be transferred to wounds that can ultimately result in systemic infections. Antibiotic resistance can make these infections difficult to treat with significant associated morbidity and mortality. We have identified and characterized a first-in-class small molecule inhibitor of the S. aureus clumping factors A and B, which has the potential to be developed further as a colonization inhibitor.

Three-Dimensional Skin Tissue Printing with Human Skin Cell Lines and Mouse Skin-Derived Epidermal and Dermal Cells

Since the skin covers most surfaces of the body, it is susceptible to damage, which can be fatal depending on the degree of injury to the skin because it defends against external attack and protects internal structures. Various types of artificial skin are being studied for transplantation to repair damaged skin, and recently, the production of replaceable skin using three-dimensional (3D) bioprinting technology has also been investigated. In this study, skin tissue was produced using a 3D bioprinter with human skin cell lines and cells extracted from mouse skin, and the printing conditions were optimized. Gelatin was used as a bioink, and fibrinogen and alginate were used for tissue hardening after printing. Printed skin tissue maintained a survival rate of 90% or more when cultured for 14 days. Culture conditions were established using 8 mM calcium chloride treatment and the skin tissue was exposed to air to optimize epidermal cell differentiation. The skin tissue was cultured for 14 days after differentiation induction by this optimized culture method, and immunofluorescent staining was performed using epidermal cell differentiation markers to investigate whether the epidermal cells had differentiated. After differentiation, loricrin, which is normally found in terminally differentiated epidermal cells, was observed in the cells at the tip of the epidermal layer, and cytokeratin 14 was expressed in the lower cells of the epidermis layer. Collectively, this study may provide optimized conditions for bioprinting and keratinization for three-dimensional skin production.

The Epidermis: Redox Governor of Health and Diseases

A functional epithelial barrier necessitates protection against dehydration, and ichthyoses are caused by defects in maintaining the permeability barrier in the stratum corneum (SC), the uppermost protective layer composed of dead cells and secretory materials from the living layer stratum granulosum (SG). We have found that loricrin (LOR) is an essential effector of cornification that occurs in the uppermost layer of SG (SG1). LOR promotes the maturation of corneocytes and extracellular adhesion structure through organizing disulfide cross-linkages, albeit being dispensable for the SC permeability barrier. This review takes psoriasis and AD as the prototype of impaired cornification. Despite exhibiting immunological traits that oppose each other, both conditions share the epidermal differentiation complex as a susceptible locus. We also review recent mechanistic insights on skin diseases, focusing on the Kelch-like erythroid cell-derived protein with the cap "n" collar homology-associated protein 1/NFE2-related factor 2 signaling pathway, as they coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of thiol-mediated crosstalk between keratinocytes and leukocytes in the epidermis that was put forward earlier.

Seeing Keratinocyte Proteins through the Looking Glass of Intrinsic Disorder

Epidermal keratinocyte proteins include many with an eccentric amino acid content (compositional bias), atypical ultrastructural fate (built-in protease sensitivity), or assembly visible at the light microscope level (cytoplasmic granules). However, when considered through the looking glass of intrinsic disorder (ID), these apparent oddities seem quite expected. Keratinocyte proteins with highly repetitive motifs are of low complexity but high adaptation, providing polymers (e.g., profilaggrin) for proteolysis into bioactive derivatives, or monomers (e.g., loricrin) repeatedly cross-linked to self and other proteins to shield underlying tissue. Keratohyalin granules developing from liquid–liquid phase separation (LLPS) show that unique biomolecular condensates (BMC) and proteinaceous membraneless organelles (PMLO) occur in these highly customized cells. We conducted bioinformatic and in silico assessments of representative keratinocyte differentiation-dependent proteins. This was conducted in the context of them having demonstrated potential ID with the prospect of that characteristic driving formation of distinctive keratinocyte structures. Intriguingly, while ID is characteristic of many of these proteins, it does not appear to guarantee LLPS, nor is it required for incorporation into certain keratinocyte protein condensates. Further examination of keratinocyte-specific proteins will provide variations in the theme of PMLO, possibly recognizing new BMC for advancements in understanding intrinsically disordered proteins as reflected by keratinocyte biology.

Protective Effect of Spirulina-Derived C-Phycocyanin against Ultraviolet B-Induced Damage in HaCaT Cells

Background and objectives: Reactive oxygen species (ROS) overwhelm the antioxidant defense system, induce oxidative stress, and increase matrix metalloproteinase (MMP) expression, resulting in skin aging. Thus, preventing ultraviolet B (UVB)-induced skin damage can attenuate skin aging. Spirulina (a biomass of cyanobacteria, also called blue-green algae) is comprised of prokaryotes, whereas microalgae are eukaryotes and are rich in phycocyanin, a powerful antioxidant. Materials and Methods: Here, we investigated the photoprotective effects of spirulina-derived C-phycocyanin (C-PC) against UVB radiation using keratinocytes (HaCaT cells). Results: UVB radiation increased MMP-1 and MMP-9 expression but decreased involucrin, filaggrin, and loricrin expression. C-PC showed no toxicity at concentrations of 5–80 μg/mL in terms of HaCaT cell viability. UVB-irradiated HaCaT cells had a 50.8% survival rate, which increased to 80.3% with C-PC treatment. MMP expression increased with UVB treatment, whereas MMP-1 and MMP-9 concentrations decreased with C-PC treatment. UVB reduced involucrin, filaggrin, and loricrin expression in HaCaT cells, but 80 μg/mL C-PC increased their expression by >25%. In the UVB radiation group, dichlorofluorescin diacetate fluorescence intensity in HaCaT cells increased by 81.6% compared with that in the control group, whereas ROS production was reduced by 51.2% and 55.1% upon treatment with 40 and 80 μg/mL C-PC, respectively. Conclusions: C-PC might reduce or prevent skin aging by reducing UVB irradiation-induced skin wrinkles and free radicals.

"Structural imprinting" of the cutaneous immune effector function

Keratinization provides tolerance to desiccation and mechanical durability. Loricrin, which is an epidermal thiol-rich protein, efficiently stabilizes terminally differentiated keratinocytes and maintains redox homeostasis. The discovery of the largely asymptomatic loricrin knockout (LKO) phenotype decades ago was rather unpredicted. Nevertheless, when including redox-driven, NF-E2-related factor 2-mediated backup responses, LKO mice provide opportunities for the observation of altered or "quasi-normal" homeostasis. Specifically, given that the tissue structure, as well as the local metabolism, transmits immunological signals, we sought to dissect the consequence of truncated epidermal differentiation program from immunological perspectives. Through a review of the aggregated evidence, we have attempted to generate an integrated view of the regulation of the peripheral immune system, which possibly occurs within the squamous epithelial tissue with truncated differentiation. This synthesis might not only provide insights into keratinization but also lead to the identification of factors intrinsic to the epidermis that imprint the immune effector function.

IL-24 Negatively Regulates Keratinocyte Differentiation Induced by Tapinarof, an Aryl Hydrocarbon Receptor Modulator: Implication in the Treatment of Atopic Dermatitis

Skin barrier dysfunction, including reduced filaggrin (FLG) and loricrin (LOR) expression, plays a critical role in atopic dermatitis (AD) development. Since aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, mediates keratinocyte differentiation, it is a potential target for AD treatment. Recently, clinical studies have shown that tapinarof, an AHR modulator, attenuated the development of AD. To examine the molecular mechanism involved in this, we analyzed tapinarof-treated normal human epidermal keratinocytes (NHEKs). Tapinarof upregulated FLG and LOR mRNA and protein expression in an AHR-dependent manner. Tapinarof also induced the secretion of IL-24, a cytokine that activates Janus kinase (JAK)-signal transducer and activator of transcription (STAT), leading to the downregulation of FLG and LOR expression. Knockdown of either IL-24 or STAT3 expression by small interfering RNA (siRNA) transfection augmented the upregulation of FLG and LOR expression induced by tapinarof, suggesting that inhibition of the IL-24/STAT3 axis during AHR activation supports the improvement of skin barrier dysfunction. Furthermore, tapinarof alone could restore the downregulation of FLG and LOR expression induced by IL-4, a key cytokine of AD, and its combination with JAK inhibitors enhanced this effect. These findings provide a new strategy for treating AD using AHR modulators and JAK inhibitors.

Human stratum corneum proteomics reveals cross-linking of a broad spectrum of proteins in cornified envelopes

Defects in keratinocyte transglutaminase (TGM1), resulting in an improper protein scaffold for deposition of the lipid barrier, comprise a major source of autosomal recessive congenital ichthyosis. For that reason, the composition and formation of the cornified (cross-linked) protein envelope of the epidermis have been of considerable interest. Since the isopeptide cross-linked protein components are not individually isolable once incorporated, purified envelopes were analysed by mass spectrometry after trypsin digestion. Quantitative estimates of the identified components revealed some 170 proteins, each comprising at least 0.001% of the total, of which keratins were major constituents accounting for ≈74% of the total. Some prevalent non-keratin constituents such as keratinocyte proline-rich protein, loricrin and late envelope protein-7 were preferentially incorporated into envelopes. The results suggest a model where, as previously observed in hair shaft and nail plate, a diversity of cellular proteins are incorporated. They also help rationalize the minimal effect on epidermis of ablating genes for specific single envelope structural components. The quantitative profile of constituent proteins provides a foundation for future exploration of envelope perturbations that may occur in pathological conditions.

Evaluation of the Efficacy of Loricrin as a Diagnostic Marker in Patients with Oral Submucous Fibrosis

Introduction:

Loricrin is usually observed in abundance in keratinizing epithelium in response to mechanical stress, which may be associated with development and malignant transformations in conditions such as oral submucous fibrosis (OSMF). Therefore, understanding of various molecular mechanisms associated with difference in gene expressions between OSMF and that of normal oral tissue is important.

Aim:

The aim of this study was to evaluate of the efficacy of loricrin as a diagnostic marker in patients with OSMF.

Materials and Methods:

Fifty formalin-fixed paraffin-embedded tissue blocks were obtained from the archives of the department. The study sample was grouped into two groups of normal mucosa (group I; n = 20) and OSMF (group II; n = 30) specimens. The study tissues were immunohistochemically stained with loricrin antibody and were further graded on basis of staining intensity.

Results:

Loricrin immunostaining was observed significantly more in OSMF cases and even in stratum granulosum in comparison to normal mucosa.

Conclusion:

Loricrin can act as an early indicator and a prognostic marker for detection of deleterious changes within epithelium in OSMF.

The KEAP1/NRF2 Signaling Pathway in Keratinization

Keratinization is a tissue adaptation, but aberrant keratinization is associated with skin disorders such as ichthyoses, atopic dermatitis, psoriasis, and acne. The disease phenotype stems from the interaction between genes and the environment; therefore, an understanding of the adaptation machinery may lead to a new appreciation of pathomechanisms. The KEAP1/NRF2 signaling pathway mediates the environmental responses of squamous epithelial tissue. The unpredicted outcome of the Keap1-null mutation in mice allowed us to revisit the basic principle of the biological process of keratinization: sulfur metabolism establishes unparalleled cytoprotection in the body wall of terrestrial mammals. We summarize the recent understanding of the KEAP1/NRF2 signaling pathway, which is a thiol-based sensor-effector apparatus, with particular focuses on epidermal differentiation in the context of the gene-environment interaction, the structure/function principles involved in KEAP1/NRF2 signaling, lessons from mouse models, and their pathological implications. This synthesis may provide insights into keratinization, which provides physical insulation and constitutes an essential innate integumentary defense system.

Regulation of Filaggrin, Loricrin, and Involucrin by IL-4, IL-13, IL-17A, IL-22, AHR, and NRF2: Pathogenic Implications in Atopic Dermatitis

Atopic dermatitis (AD) is an eczematous, pruritic skin disorder with extensive barrier dysfunction and elevated interleukin (IL)-4 and IL-13 signatures. The barrier dysfunction correlates with the downregulation of barrier-related molecules such as filaggrin (FLG), loricrin (LOR), and involucrin (IVL). IL-4 and IL-13 potently inhibit the expression of these molecules by activating signal transducer and activator of transcription (STAT)6 and STAT3. In addition to IL-4 and IL-13, IL-22 and IL-17A are probably involved in the barrier dysfunction by inhibiting the expression of these barrier-related molecules. In contrast, natural or medicinal ligands for aryl hydrocarbon receptor (AHR) are potent upregulators of FLG, LOR, and IVL expression. As IL-4, IL-13, IL-22, and IL-17A are all capable of inducing oxidative stress, antioxidative AHR agonists such as coal tar, glyteer, and tapinarof exert particular therapeutic efficacy for AD. These antioxidative AHR ligands are known to activate an antioxidative transcription factor, nuclear factor E2-related factor 2 (NRF2). This article focuses on the mechanisms by which FLG, LOR, and IVL expression is regulated by IL-4, IL-13, IL-22, and IL-17A. The author also summarizes how AHR and NRF2 dual activators exert their beneficial effects in the treatment of AD.

Loricrin: Past, Present, and Future

The terminal differentiation of the epidermis is a complex physiological process. During the past few decades, medical genetics has shown that defects in the stratum corneum (SC) permeability barrier cause a myriad of pathological conditions, ranging from common dry skin to lethal ichthyoses. Contrarily, molecular phylogenetics has revealed that amniotes have acquired a specialized form of cytoprotection cornification that provides mechanical resilience to the SC. This superior biochemical property, along with desiccation tolerance, is attributable to the proper formation of the macromolecular protein-lipid complex termed cornified cell envelopes (CE). Cornification largely depends on the peculiar biochemical and biophysical properties of loricrin, which is a major CE component. Despite its quantitative significance, loricrin knockout (LKO) mice have revealed it to be dispensable for the SC permeability barrier. Nevertheless, LKO mice have brought us valuable lessons. It is also becoming evident that absent loricrin affects skin homeostasis more profoundly in many more aspects than previously expected. Through an extensive review of aggregate evidence, we discuss herein the functional significance of the thiol-rich protein loricrin from a biochemical, genetic, pathological, metabolic, or immunological aspect with some theoretical and speculative perspectives.

Effect of AgNPs on the human reconstructed epidermis

Nanoparticles are utilized in a wide range of industries. The most studied silver nanoparticles (AgNPs) are used in medicine and also in several wound dressings due to their antimicrobial properties. The inflammatory response or potential morphological changes of skin cells after their application are not well known yet. In our study we used the model of human reconstructed epidermis (RHE), prepared in our laboratory, to evaluate whether the AgNPs penetrate through RHE, induce some morphological changes of keratinocytes or influence the production of pro-inflammatory cytokines (IL-6 and IL-8). After the application of three different concentrations (25 ppm, 2.5 ppm, 0.25 ppm) of AgNPs to of RHE for 24 hours we verified that AgNPs did not affect the production of pro-inflammatory cytokines (IL-6 and IL-8) and neither did they influence the expression of keratin K14 and loricrin. The morphology of the cells was likewise unchanged. Based on these results we conclude that AgNPs do not have any negative effect on the morphological changes and do not increase the production of pro-inflammatory cytokines.

Complex Gene Loss and Duplication Events Have Facilitated the Evolution of Multiple Loricrin Genes in Diverse Bird Species

The evolution of a mechanically resilient epidermis was a key adaptation in the transition of amniotes to a fully terrestrial lifestyle. Skin appendages usually form via a specialized type of programmed cell death known as cornification which is characterized by the formation of an insoluble cornified envelope (CE). Many of the substrates of cornification are encoded by linked genes located at a conserved genetic locus known as the epidermal differentiation complex (EDC). Loricrin is the main protein component of the mammalian CE and is encoded for by a gene located within the EDC. Recently, genes resembling mammalian loricrin, along with several other proteins most likely involved in CE formation, have been identified within the EDC of birds and several reptiles. To better understand the evolution and function of loricrin in birds, we screened the genomes of 50 avian species and 3 crocodilians to characterize their EDC regions. We found that loricrin is present within the EDC of all species investigated, and that three loricrin genes were present in birds. Phylogenetic and molecular evolution analyses found evidence that gene deletions and duplications as well as concerted evolution has shaped the evolution of avian loricrins. Our results suggest a complex evolutionary history of avian loricrins which has accompanied the evolution of bird species with diverse morphologies and lifestyles.

Ectopic transglutaminase 1 and 3 expression accelerating keratinization in oral lichen planus

Objective

Oral lichen planus (OLP) characterized by interface mucositis frequently shows hyper-keratinization. To clarify mechanisms of excess keratinization, we investigated key molecules for cornified cell envelope (CE).

Methods

Involucrin (IVL), loricrin (LOR), transglutaminase 1 (TGase 1) and transglutaminase 3 (TGase 3) were immunohistochemically examined in 20 specimens of OLP; five specimens of buccal mucosa served as controls. Subsequently, the data were statistically analyzed.

Results

IVL in OLP was localized in the cell membrane, in contrast to its localization in the cytoplasm in controls. No positive reaction indicative of LOR was noted in any specimens. Although the TGase 1 localization in controls was restricted to the upper three-quarters of the membrane, the localization in OLP was in both membrane and in the cytoplasm of full thickness mucosal layers. The TGase 3 localization pattern was dramatically altered from cytoplasmic to membranous in OLP.

Conclusion

Our data suggest that aberrant TGase 1 and TGase 3 localization and distribution are closely related to hyper-keratinization in OLP. This is the first report of ectopic transglutaminase localization in OLP.

Upregulation of FLG, LOR, and IVL Expression by Rhodiola crenulata Root Extract via Aryl Hydrocarbon Receptor: Differential Involvement of OVOL1

Rhodiola species are antioxidative, salubrious plants that are known to inhibit oxidative stress induced by ultraviolet and γ-radiation in epidermal keratinocytes. As certain phytochemicals activate aryl hydrocarbon receptors (AHR) or OVO-like 1 (OVOL1) to upregulate the expression of epidermal barrier proteins such as filaggrin (FLG), loricrin (LOR), and involucrin (IVL), we investigated such regulation by Rhodiola crenulata root extract (RCE). We demonstrated that RCE induced FLG and LOR upregulation in an AHR-OVOL1-dependent fashion. However, RCE-mediated IVL upregulation was AHR-dependent but OVOL1-independent. Coordinated upregulation of skin barrier proteins by RCE via AHR may be beneficial in the management of barrier-disrupted inflammatory skin diseases such as atopic dermatitis.

A molecular mechanism for IL-4 suppression of loricrin transcription in epidermal keratinocytes: implication for atopic dermatitis pathogenesis

Skin barrier defects play an important role in atopic dermatitis (AD) pathogenesis. Loricrin, an important barrier protein suppressed in human AD, is down-regulated by IL-4 in keratinocytes. However, the molecular mechanism is unknown. Since loricrin transcription requires p300/CBP, and Stat6 also recruits this common coactivator for its stimulated factors, we hypothesize that IL-4-activated Stat6 competes for the available endogenous p300/CBP, leading to loricrin transcription inhibition. First, we showed that loricrin is suppressed in the skin of IL-4 transgenic mice, an AD mouse model. In human keratinocytes, IL-4 down-regulation of loricrin is abrogated by a pan-Jak inhibitor, suggesting that the Jak-Stat pathway is involved. To further investigate the downstream molecular mechanism, we transfected HaCat cells with a loricrin promoter and then treated them with either IL-4 or vehicle. Not surprisingly, IL-4 greatly suppressed the promoter activity. Interestingly, this suppression was prevented when we knocked down Stat6, indicating that Stat6 participates in IL-4 regulation of loricrin. A Stat6-specific inhibitor confirmed the knockdown study. Finally, IL-4 suppression of loricrin was reversed with transfection of a CBP expression vector in a dose-dependent manner. Taken together, for the first time, we delineate a molecular mechanism for IL-4 down-regulation of loricin expression in human keratinocytes, which may play an important role in AD pathogenesis.

Antioxidant Artemisia princeps Extract Enhances the Expression of Filaggrin and Loricrin via the AHR/OVOL1 Pathway

The Japanese mugwort, Artemisia princeps (yomogi in Japanese), has anti-inflammatory and antioxidant effects. Skin care products containing Artemisia princeps extract (APE) are known to improve dry skin symptoms in atopic dermatitis. Atopic dry skin is associated with a marked reduction of skin barrier proteins, such as filaggrin (FLG) and loricrin (LOR). Recently, aryl hydrocarbon receptor (AHR), and its downstream transcription factor OVO-like 1 (OVOL1), have been shown to regulate the gene expression of FLG and LOR. The focus of this paper is to evaluate the effects of APE on the AHR/OVOL1/FLG or LOR pathway since they have remained unknown to this point. We first demonstrated that non-cytotoxic concentrations of APE significantly upregulated antioxidant enzymes, NAD(P)H dehydrogenase quinone 1 and heme oxygenase 1, in human keratinocytes. Even at these low concentrations, APE induced nuclear translocation of AHR and significantly upregulated CYP1A1 (a specific target gene for AHR activation), FLG, and LOR expression. AHR knockdown downregulated OVOL1 expression. The APE-induced upregulation of FLG and LOR was canceled in keratinocytes with AHR or OVOL1 knockdown. In conclusion, antioxidant APE is a potent phytoextract that upregulates FLG and LOR expression in an AHR/OVOL1-dependent manner and this may underpin the barrier-repairing effects of APE in treating atopic dry skin.

Transcriptome and ultrastructural changes in dystrophic Epidermolysis bullosa resemble skin aging

The aging process of skin has been investigated recently with respect to mitochondrial function and oxidative stress. We have here observed striking phenotypic and clinical similarity between skin aging and recessive dystrophic Epidermolysis bullosa (RDEB), which is caused by recessive mutations in the gene coding for collagen VII, COL7A1. Ultrastructural changes, defects in wound healing, and inflammation markers are in part shared with aged skin. We have here compared the skin transcriptomes of young adults suffering from RDEB with that of sex‐ and age‐matched healthy probands. In parallel we have compared the skin transcriptome of healthy young adults with that of elderly healthy donors. Quite surprisingly, there was a large overlap of the two gene lists that concerned a limited number of functional protein families. Most prominent among the proteins found are a number of proteins of the cornified envelope or proteins mechanistically involved in cornification and other skin proteins. Further, the overlap list contains a large number of genes with a known role in inflammation. We are documenting some of the most prominent ultrastructural and protein changes by immunofluorescence analysis of skin sections from patients, old individuals, and healthy controls.

Loricrin - an overview

Loricrin is a terminally differentiating structural protein comprising more than 70% of the cornified envelope. It contributes to the protective barrier function of the stratum corneum. In vivo, loricrin is expressed inall mammalian stratified epithelia with the highest levels of expression in humid tissues such as newborn epidermis, the epithelia of oral and anal mucosa, esophagus, foreskin, vagina and the epidermal parts of sweat ducts. Loricrin is not expressed in non keratinizing epithelia and its expression at these sites actually represents a defensive or protective mechanismof the body. An insight into this protein- “Loricrin” can shed light to its potential as a marker in the early stages of potentially malignant disorders like oral sub mucous fibrosis and leukoplakia. This compilation has been done by taking into account the existing literature, reviews and original studies on loricrin, a major component of the cornifiedcell envelope, its structure and the alterations that result due to its absence or presence of both the epidermis and the oral mucosa.

Progressive symmetric erythrokeratodermia with delayed intellectual milestones and convulsions

Progressive symmetric erythrokeratoderma is an uncommon genodermatosis and is thought to arise due to mutations in the connexin gene, however, genetic heterogenicity has been described. Very few cases of neurological involvement have been described in this unusual entity. We report a case of progressive symmetric erythrokeratoderma, with convulsions and delayed intellectual milestones.

Transgenic mice expressing a mutant form of loricrin reveal the molecular basis of the skin diseases, Vohwinkel syndrome and progressive symmetric erythrokeratoderma

Mutations in the cornified cell envelope protein loricrin have been reported recently in some patients with Vohwinkel syndrome (VS) and progressive symmetric erythrokeratoderma (PSEK). To establish a causative relationship between loricrin mutations and these diseases, we have generated transgenic mice expressing a COOH-terminal truncated form of loricrin that is similar to the protein expressed in VS and PSEK patients. At birth, transgenic mice (ML.VS) exhibited erythrokeratoderma with an epidermal barrier dysfunction. 4 d after birth, high-expressing transgenic animals showed a generalized scaling of the skin, as well as a constricting band encircling the tail and, by day 7, a thickening of the footpads. Histologically, ML. VS transgenic mice also showed retention of nuclei in the stratum corneum, a characteristic feature of VS and PSEK. Immunofluorescence and immunoelectron microscopy showed the mutant loricrin protein in the nucleus and cytoplasm of epidermal keratinocytes, but did not detect the protein in the cornified cell envelope. Transfection experiments indicated that the COOH-terminal domain of the mutant loricrin contains a nuclear localization signal. To determine whether the ML.VS phenotype resulted from dominant-negative interference of the transgene with endogenous loricrin, we mated the ML.VS transgenics with loricrin knockout mice. A severe phenotype was observed in mice that lacked expression of wild-type loricrin. Since loricrin knockout mice are largely asymptomatic (Koch, P.K., P. A. de Viragh, E. Scharer, D. Bundman, M.A. Longley, J. Bickenbach, Y. Kawachi, Y. Suga, Z. Zhou, M. Huber, et al., J. Cell Biol. 151:389-400, this issue), this phenotype may be attributed to expression of the mutant form of loricrin. Thus, deposition of the mutant protein in the nucleus appears to interfere with late stages of epidermal differentiation, resulting in a VS-like phenotype.

Lessons from loricrin-deficient mice: compensatory mechanisms maintaining skin barrier function in the absence of a major cornified envelope protein

The epidermal cornified cell envelope (CE) is a complex protein-lipid composite that replaces the plasma membrane of terminally differentiated keratinocytes. This lamellar structure is essential for the barrier function of the skin and has the ability to prevent the loss of water and ions and to protect from environmental hazards. The major protein of the epidermal CE is loricrin, contributing approximately 70% by mass. We have generated mice that are deficient for this protein. These mice showed a delay in the formation of the skin barrier in embryonic development. At birth, homozygous mutant mice weighed less than control littermates and showed skin abnormalities, such as congenital erythroderma with a shiny, translucent skin. Tape stripping experiments suggested that the stratum corneum stability was reduced in newborn Lor(-/-) mice compared with wild-type controls. Isolated mutant CEs were more easily fragmented by sonication in vitro, indicating a greater susceptibility to mechanical stress. Nevertheless, we did not detect impaired epidermal barrier function in these mice. Surprisingly, the skin phenotype disappeared 4-5 d after birth. At least one of the compensatory mechanisms preventing a more severe skin phenotype in newborn Lor(-/-) mice is an increase in the expression of other CE components, such as SPRRP2D and SPRRP2H, members of the family of "small proline rich proteins", and repetin, a member of the "fused gene" subgroup of the S100 gene family.