The Cornified Envelope: A Versatile Contributor to the Epidermal Barrier

Ectoin attenuates cortisone-induced skin issues by suppression GR signaling and the UVB-induced overexpression of 11β-HSD1

BACKGROUND

Accelerated pace of modern work and lifestyles subject individuals to various external and psychological stressors, which, in turn, can trigger additional stress through visible signs of fatigue, hair loss, and obesity. As the primary stress hormone affecting skin health, cortisol connects to the glucocorticoid receptor (GR) to aggravate skin issues induced by stress. This activation depends on the expression of 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in skin cells, which locally converts cortisone-produced by the central and peripheral hypothalamic-pituitary-adrenal axis-into its active form.

METHODS

Our study delves deeper into stress's adverse effects on the skin, including the disruption of keratinocyte structural proteins, the loss of basement membrane proteins, and the degradation of collagen.

RESULTS

Remarkably, we discovered that Ectoin, an amino acid derivative obtained from halophilic bacteria, is capable of mitigating the inhibitory impacts of cortisone on the expression of cutaneous functional proteins, including involucrin, loricrin, laminin-5, and claudin-1. Moreover, Ectoin reduces the suppressive effect of stress on collagen and hyaluronic acid synthesis by impeding GR signal transduction. Additionally, Ectoin counterbalances the UVB-induced overexpression of 11β-HSD1, thereby diminishing the concentration of endogenous glucocorticoids.

CONCLUSION

Our findings illuminate the significant potential of Ectoin as a preventative agent against stress-induced skin maladies.

Skin barrier, phenotypic and genotypic characterisation of autosomal recessive ichthyosis in TGM1-deficient Jack Russell Terriers and response to topical ceramide

BACKGROUND

Autosomal recessive ichthyosis leads to structural or biochemical changes that impair skin barrier function.

HYPOTHESIS/OBJECTIVES

To assess (1) the phenotype and genotype in a litter of Jack Russell Terriers with autosomal recessive congenital ichthyosis (ARCI), and (2) the defective skin barrier and determine if a topical ceramide can modulate the barrier.

ANIMALS

A healthy dam and litter of Jack Russell Terrier puppies (healthy male, affected male and female), one affected adult Jack Russell Terrier and one unrelated healthy Jack Russell Terrier.

MATERIALS AND METHODS

A severe cornification defect was identified via examination of affected puppies. As the phenotype worsened, the affected puppies received a topical application of ω-0-acylceramide for 10 days. Before humane euthanasia, the skin barrier was evaluated via transepidermal water loss (TEWL), corneometry and pH in affected dogs. Genomic testing was performed, and skin samples were analysed by light and electron microscopy.

RESULTS

Affected puppies were homozygous for the 1980 bp LINE-1 insertion in the TGM1 (transglutaminase 1) gene; the unaffected littermate and the dam were heterozygous carriers. ARCI puppies were underweight and had a severe hyperkeratotic phenotype that impaired mobility. TEWL was markedly higher in affected dogs. The cutaneous pH of affected puppies was higher than the normal littermate. Treatment of the skin with ω-0-acylceramide normalised the pH to match the littermate and decreased TEWL. Electron microscopy revealed marked attenuation of the cornified envelope.

CONCLUSIONS AND CLINICAL RELEVANCE

Dogs with TGM1-deficient ARCI have an impaired skin barrier. Topical therapy can partially repair the barrier defect.

C. elegans epicuticlins define specific compartments in the apical extracellular matrix and function in wound repair

The apical extracellular matrix (aECM) of external epithelia often contains lipid-rich outer layers that contribute to permeability barrier function. The external aECM of nematodes is known as the cuticle and contains an external lipid-rich layer - the epicuticle. Epicuticlins are a family of tandem repeat cuticle proteins of unknown function. Here, we analyze the localization and function of the three C. elegans epicuticlins (EPIC proteins). EPIC-1 and EPIC-2 localize to the surface of the cuticle near the outer lipid layer, as well as to interfacial cuticles and adult-specific struts. EPIC-3 is expressed in dauer larvae and localizes to interfacial aECM in the buccal cavity. Skin wounding in the adult induces epic-3 expression, and EPIC proteins localize to wound sites. Null mutants lacking EPIC proteins are viable with reduced permeability barrier function and normal epicuticle lipid mobility. Loss of function in EPIC genes modifies the skin blistering phenotypes of Bli mutants and reduces survival after skin wounding. Our results suggest EPIC proteins define specific cortical compartments of the aECM and promote wound repair.

Strengthening the Skin Barrier by Using a Late Cornified Envelope 6A-Derived Biomimetic Peptide

Changes in the expression of cornified envelope (CE) components are a hallmark of numerous pathological skin conditions and aging, underlying the importance of this stratum corneum structure in the homeostasis of the epidermal barrier. We performed a detailed characterisation of LCE6A, a member of the Late Cornified Envelope protein family. Immunohistochemical and immunoblot experiments confirmed that LCE6A is expressed late during epidermal differentiation. Crosslinking assays of recombinant LCE6A performed either in situ on human skin sections or in vitro demonstrated that LCE6A is indeed a substrate of transglutaminases and crosslinked to CEs. LCE6A-derived peptides containing a glutamine-lysine sequence retained these properties of the full-length protein and reinforced the mechanical resistance of CE submitted to sonication. We designed P26, a LCE6A-derived biomimetic peptide that similarly reinforced CE in vitro, and evaluated its protective properties ex vivo, on human skin explants, and in two double blind and vehicle-controlled clinical trials. P26 was able to protect the skin from barrier disruption, to limit the damage resulting from a defective barrier, and could improve the signs of aging such as loss of skin firmness and increased skin roughness. Hence, our detailed characterisation of LCE6A as a component of the CE enabled us to develop a LCE6A-derived peptide, biologically active with a new and original mode of action that could be of great interest as a cosmetic ingredient and a pharmacologic agent.

Comparative genomics of sirenians reveals evolution of filaggrin and caspase-14 upon adaptation of the epidermis to aquatic life

The mammalian epidermis has evolved to protect the body in a dry environment. Genes of the epidermal differentiation complex (EDC), such as FLG (filaggrin), are implicated in the barrier function of the epidermis. Here, we investigated the molecular evolution of the EDC in sirenians (manatees and dugong), which have adapted to fully aquatic life, in comparison to the EDC of terrestrial mammals and aquatic mammals of the clade Cetacea (whales and dolphins). We show that the main subtypes of EDC genes are conserved or even duplicated, like late cornified envelope (LCE) genes of the dugong, whereas specific EDC genes have undergone inactivating mutations in sirenians. FLG contains premature stop codons in the dugong, and the ortholog of human CASP14 (caspase-14), which proteolytically processes filaggrin, is pseudogenized in the same species. As FLG and CASP14 have also been lost in whales, these mutations represent convergent evolution of skin barrier genes in different lineages of aquatic mammals. In contrast to the dugong, the manatee has retained functional FLG and CASP14 genes. FLG2 (filaggrin 2) is truncated in both species of sirenians investigated. We conclude that the land-to-water transition of sirenians was associated with modifications of the epidermal barrier at the molecular level.

ZNF750 Regulates Skin Barrier Function by Driving Cornified Envelope and Lipid Processing Pathways

The epidermis is a constantly renewing stratified epithelial tissue that provides essential protective barrier functions. The major barrier is located at the outermost layers of the epidermis, formed by terminally differentiated keratinocytes reinforced by proteins of their cornified envelope and sequestered intercellular lipids. Disruptions to epidermal differentiation characterize various skin disorders. ZNF750 is an epithelial transcription factor essential for in vitro keratinocyte differentiation, whose truncating mutation in humans causes autosomal dominant psoriasis-like skin disease. In this study, we utilized an epidermal-specific Znf750 conditional knockout mouse model to uncover the role ZNF750 plays in epidermal development. We show that deletion of Znf750 in the developing skin does not block epidermal differentiation completely, suggesting in vivo compensatory feedback mechanisms, although it does result in impaired barrier function and perinatal lethality. Molecular dissection revealed ultrastructural defects in the differentiated layers of the epidermis, accompanied by alterations in the expression of ZNF750-dependent genes encoding key cornified envelope precursor proteins and lipid-processing enzymes, including gene subsets known to be mutated in human skin diseases involving impaired barrier function. Together, our findings provide molecular insights into the pathogenesis of human skin disease by linking ZNF750 to a subset of epidermal differentiation genes involved in barrier formation pathways.

C. elegans epicuticlins define specific compartments in the apical extracellular matrix and function in wound repair

The apical extracellular matrix (aECM) of external epithelia often contains lipid-rich outer layers that contribute to permeability barrier function. The external aECM of nematode is known as the cuticle and contains an external lipid-rich layer, the epicuticle. Epicuticlins are a family of tandem repeat proteins originally identified as components of the insoluble fraction of the cuticular aECM and thought to localize in or near epicuticle. However, there has been little in vivo analysis of epicuticlins. Here, we report the localization analysis of the three C. elegans epicuticlins (EPIC proteins) using fluorescent protein knock-ins to visualize endogenously expressed proteins, and further examine their in vivo function using genetic null mutants. By TIRF microscopy, we find that EPIC-1 and EPIC-2 localize to the surface of the cuticle in larval and adult stages in close proximity to the outer lipid layer. EPIC-1 and EPIC-2 also localize to interfacial cuticles and adult-specific cuticle struts. EPIC-3 expression is restricted to the stress-induced dauer stage, where it localizes to interfacial aECM in the buccal cavity. Strikingly, skin wounding in the adult induces epic-3 expression, and EPIC-3::mNG localizes to wound scars. Null mutants lacking one, two, or all three EPIC proteins display reduced survival after skin wounding yet are viable with low penetrance defects in epidermal morphogenesis. Our results suggest EPIC proteins define specific aECM compartments and have roles in wound repair.