Shwachman-Diamond syndrome presenting with early ichthyosis, associated dermal and epidermal intracellular lipid droplets, hypoglycemia, and later distinctive clinical SDS phenotype.

Shwachman-Diamond syndrome (SDS) is a recessive ribosomopathy, characterized by bone marrow failure and exocrine pancreatic insufficiency (ePI) often associated with neurodevelopmental and skeletal abnormalities. The aim of this report is to describe a SDS patient with early ichthyosis associated with dermal and epidermal intracellular lipid droplets (iLDs), hypoglycemia and later a distinctive clinical SDS phenotype. At 3 months of age, she had ichthyosis, growth retardation, and failure to thrive. She had not cytopenia. Ultrasonography (US) showed pancreatic diffuse high echogenicity. Subsequently fasting hypoketotic hypoglycemia occurred without permanent hepatomegaly or hyperlipidemia. Continuous gavage feeding was followed by clinical improvement including ichthyosis and hypoglycemia. After 14 months of age, she developed persistent neutropenia and ePI consistent with SDS. The ichthyotic skin biopsy, performed at 5 months of age, disclosed iLDs in all epidermal layers, in melanocytes, eccrine sweat glands, Schwann cells and dermal fibroblasts. These iLDs were reminiscent of those described in Dorfman-Chanarin syndrome (DCS) or Wolman's disease. Both LIPA and CGI-58 analysis did not revealed pathogenic mutation. By sequencing SBDS, a compound heterozygous for a previously reported gene mutation (c.258 + 2T>C) and a novel mutation (c.284T>G) were found. Defective SBDS may hypothetically interfere as in DCS, with neutral lipid metabolism and play a role in the SDS phenotype such as ichthyosis with dermal and epidermal iLDs and hypoglycemia. This interference with neutral lipid metabolism must most likely occur in the cytoplasm compartment as in DCS and not in the lysosomal compartment as in Wolman's disease. © 2016 Wiley Periodicals, Inc.

Caspase-14 protects against epidermal UVB photodamage and water loss.

Caspase-14 belongs to a conserved family of aspartate-specific proteinases. Its expression is restricted almost exclusively to the suprabasal layers of the epidermis and the hair follicles. Moreover, the proteolytic activation of caspase-14 is associated with stratum corneum formation, implicating caspase-14 in terminal keratinocyte differentiation and cornification. Here, we show that the skin of caspase-14-deficient mice was shiny and lichenified, indicating an altered stratum-corneum composition. Caspase-14-deficient epidermis contained significantly more alveolar keratohyalin F-granules, the profilaggrin stores. Accordingly, caspase-14-deficient epidermis is characterized by an altered profilaggrin processing pattern and we show that recombinant caspase-14 can directly cleave profilaggrin in vitro. Caspase-14-deficient epidermis is characterized by reduced skin-hydration levels and increased water loss. In view of the important role of filaggrin in the structure and moisturization of the skin, the knockout phenotype could be explained by an aberrant processing of filaggrin. Importantly, the skin of caspase-14-deficient mice was highly sensitive to the formation of cyclobutane pyrimidine dimers after UVB irradiation, leading to increased levels of UVB-induced apoptosis. Removal of the stratum corneum indicate that caspase-14 controls the UVB scavenging capacity of the stratum corneum.

Filaggrin genotype in ichthyosis vulgaris predicts abnormalities in epidermal structure and function.

Although it is widely accepted that filaggrin (FLG) deficiency contributes to an abnormal barrier function in ichthyosis vulgaris and atopic dermatitis, the pathomechanism of how FLG deficiency provokes a barrier abnormality in humans is unknown. We report here that the presence of FLG mutations in Caucasians predicts dose-dependent alterations in epidermal permeability barrier function. Although FLG is an intracellular protein, the barrier abnormality occurred solely via a paracellular route in affected stratum corneum. Abnormal barrier function correlated with alterations in keratin filament organization (perinuclear retraction), impaired loading of lamellar body contents, followed by nonuniform extracellular distribution of secreted organelle contents, and abnormalities in lamellar bilayer architecture. In addition, we observed reductions in corneodesmosome density and tight junction protein expression. Thus, FLG deficiency provokes alterations in keratinocyte architecture that influence epidermal functions localizing to the extracellular matrix. These results clarify how FLG mutations impair epidermal permeability barrier function.

Cannabinoid receptors 1 and 2 oppositely regulate epidermal permeability barrier status and differentiation.

Cannabinoid receptors (CBR) 1 and 2 have been implicated in keratinocyte differentiation/proliferation. How CB receptors affect epidermal permeability barrier and stratum corneum structure and function remains unclear. Permeability barrier abrogation was induced by sequential tape-stripping of the SC and assessed in both CB1R and CB2R knockout (-/-) mice in comparison with wild-type (+/+) littermates. Absence of CB1R delays permeability barrier recovery, while the latter was found to be accelerated in CB2R -/- mice. While increased lamellar body (LB) secretion is observed in CB2R -/- mice accounting for the enhanced recovery, CB1R -/- animals display strong alterations in lipid bilayer structures. Markers for epidermal differentiation (i.e. filaggrin, loricrin and involucrin) and terminal differentiation (i.e. TUNEL assay and caspase-14 activation) were respectively decreased and increased in CB1R and CB2R -/- mice. Surprisingly, CB1R agonist treatment of human cultured keratinocytes increases mRNA of p21 and cytokeratin 1 and 10 and decreases cyclin D1 but protein levels remained unchanged. Such paradox could partially be explained by the increase in non-phosphorylated-4E-BP1, an inhibitor of mRNA translation, following CB1R agonist treatment. Altogether, these observations put forward the importance and the complexity of cannabinoid signalling for the regulation of permeability barrier and epidermal differentiation.

Functional skin adaptation in infancy - almost complete but not fully competent.

Early postnatal life is a period of active functional reorganization and cutaneous physiological adaptation to the extrauterine environment. Skin as the outermost organ of mammalians is endowed of multiple functions such as protection, secretion, absorption and thermoregulation. Birth stimulates the epidermal barrier maturation and the skin surface acidification especially in premature infants. In full-term infants the developed stratum corneum accomplishes competent barrier function, in contrast to prematures. Complete barrier maturation in preterm infants is fulfilled by 2-4 weeks of the postnatal life. However, in preterms with 23-25 weeks gestational age this process takes longer. Versatile regulatory mechanisms, namely skin surface acidity, calcium ion gradient and nuclear hormone receptors/ligands are interrelated in the complex postnatal newborn adaptation. The skin of newborns is adjusting quickly to the challenging environmental conditions of the postpartum. However, certain functions, for example, microcirculation, continue to develop even beyond the neonatal period, that is, up to the age of 14-17 weeks. Different environmental factors (for instance, dry and cold climate, diapers and cosmetic care procedures) influence the postnatal development of skin functional parameters such as stratum corneum hydration and the permeability barrier especially in premature infants. The aim of this article is to summarize the current knowledge on skin physiology in newborn and infants with a practical approach and to discuss the possible clinical consequences. This review offers the readership a critical and practical overview of skin physiology in newborns and infants. It emphasizes possible new research fields in neonatal and infantile skin physiology.

LEKTI fragments specifically inhibit KLK5, KLK7, and KLK14 and control desquamation through a pH-dependent interaction.

LEKTI is a 15-domain serine proteinase inhibitor whose defective expression underlies the severe autosomal recessive ichthyosiform skin disease, Netherton syndrome. Here, we show that LEKTI is produced as a precursor rapidly cleaved by furin, generating a variety of single or multidomain LEKTI fragments secreted in cultured keratinocytes and in the epidermis. The identity of these biological fragments (D1, D5, D6, D8-D11, and D9-D15) was inferred from biochemical analysis, using a panel of LEKTI antibodies. The functional inhibitory capacity of each fragment was tested on a panel of serine proteases. All LEKTI fragments, except D1, showed specific and differential inhibition of human kallikreins 5, 7, and 14. The strongest inhibition was observed with D8-D11, toward KLK5. Kinetics analysis revealed that this interaction is rapid and irreversible, reflecting an extremely tight binding complex. We demonstrated that pH variations govern this interaction, leading to the release of active KLK5 from the complex at acidic pH. These results identify KLK5, a key actor of the desquamation process, as the major target of LEKTI. They disclose a new mechanism of skin homeostasis by which the epidermal pH gradient allows precisely regulated KLK5 activity and corneodesmosomal cleavage in the most superficial layers of the stratum corneum.

Clinical scoring and biophysical evaluation of nasolabial skin barrier damage caused by rhinorrhea.

BACKGROUND: An acute viral cold is a very common illness and is characterized by sneezing and a runny nose. Because of rhinorrhea and frequent use of handkerchiefs, the skin around the nose feels uncomfortably dry and flaky. OBJECTIVES/METHODS: To evaluate the nasolabial skin barrier impairment, 14 female volunteers with a common cold were recruited. Visually assessed clinical scoring and/or biophysical measurements--including transepidermal water loss, stratum corneum hydration, skin colour, squamometry, skin pH, and a skin surface lipid profile analysis--were carried out at the start of the cold, a second time when the severity of the cold symptoms was maximal, and finally when the volunteers felt healthy again and stopped using handkerchiefs. RESULTS AND CONCLUSIONS: Transepidermal water loss assessments showed significantly higher measurements on the maximum outcome of the nasal cold compared with the time-point when the symptoms of the cold had disappeared. This was in accordance with skin colour chroma a* measurements and the visually assessed skin erythema and scaliness scores, indicating that the superficial nasolabial skin barrier was inferior at the maximum of a nasal cold in comparison with the skin condition when volunteers were fully recovered.

Daily treatment with adapalene gel 0.1% maintains initial improvement of acne vulgaris previously treated with oral lymecycline.

Topical retinoids are often recommended for preventing acne recurrence, but there are relatively few well-controlled maintenance studies published. The objective of the present study was to assess the maintenance effect of adapalene gel 0.1% relative to gel vehicle in subjects successfully treated in a previous 12-week adapalene-lymecycline 300 mg combination therapy study. This was a multicentre, investigator-blind, randomised, controlled study in 19 European centres. A total of 136 subjects with moderate to moderately-severe acne vulgaris who showed at least moderate improvement from baseline when treated with either adapalene plus lymecycline or lymecycline plus gel vehicle in a previous 12 week study were included. Subjects were randomised to receive adapalene gel 0.1% or vehicle once-daily for 12 weeks. Efficacy and safety criteria included maintenance rate, percent reduction in lesion counts (total, inflammatory, non inflammatory), global severity assessment, cutaneous tolerability, and adverse events. Adapalene provided better results relative to gel vehicle for all efficacy assessments. The maintenance rate for total lesions was 84.7% vs. 63.5% (P = 0.0049) with adapalene and the vehicle, respectively. Adapalene was safe and well tolerated in this study. This study demonstrates a clinical benefit of continued treatment with adapalene gel 0.1% as a maintenance therapy for acne.

Serine protease signaling of epidermal permeability barrier homeostasis.

Evidence is growing that protease-activated receptor-2 (PAR-2) plays a key role in epithelial inflammation. We hypothesized here that PAR-2 plays a central role in epidermal permeability barrier homeostasis by mediating signaling from serine proteases (SP) in the stratum corneum (SC). Since the SC contains tryptic- and chymotryptic-like activity, we assessed the influence of SP activation/inhibition on barrier function. Acute barrier disruption increases SP activity and blockade by topical SP inhibitors (SPI) accelerates barrier recovery after acute abrogation. This improvement in barrier function is due to accelerated lamellar body (LB) secretion. Since tryptic SP signal certain downstream responses through PAR-2, we assessed its potential role in mediating the negative effects of SP on permeability barrier. Firstly, PAR-2 is expressed in the outer nucleated layers of the epidermis and most specifically under basal condition to the lipid raft (LR) domains. Secondly, tape stripping-induced barrier abrogation provokes PAR-2 activation, as shown by receptor internalization (i.e. receptor movement from LR to cytolpasmic domains). Thirdly, topical applications of PAR-2 agonist peptide, SLIGRL, delay permeability barrier recovery and inhibit LB secretion, while, conversely, PAR-2 knockout mice display accelerated barrier recovery kinetics and enhanced LB secretion, paralleled by increased LR formation and caveolin-1 expression. These results demonstrate first, the importance of SP/SPI balance for normal permeability barrier homeostasis, and second, they identify PAR-2 as a novel signaling mechanism of permeability barrier, that is, of response linked to LB secretion.

Serine protease activity and residual LEKTI expression determine phenotype in Netherton syndrome.

Mutations in the SPINK5 gene encoding the serine protease (SP) inhibitor, lymphoepithelial-Kazal-type 5 inhibitor (LEKTI), cause Netherton syndrome (NS), a life-threatening disease, owing to proteolysis of the stratum corneum (SC). We assessed here the basis for phenotypic variations in nine patients with "mild", "moderate", and "severe" NS. The magnitude of SP activation correlated with both the barrier defect and clinical severity, and inversely with residual LEKTI expression. LEKTI co-localizes within the SC with kallikreins 5 and 7 and inhibits both SP. The permeability barrier abnormality in NS was further linked to SC thinning and proteolysis of two lipid hydrolases (beta-glucocerebrosidase and acidic sphingomyelinase), with resultant disorganization of extracellular lamellar membranes. SC attenuation correlated with phenotype-dependent, SP activation, and loss of corneodesmosomes, owing to desmoglein (DSG)1 and desmocollin (DSC)1 degradation. Although excess SP activity extended into the nucleated layers in NS, degrading desmosomal mid-line structures with loss of DSG1/DSC1, the integrity of the nucleated epidermis appears to be maintained by compensatory upregulation of DSG3/DSC3. Maintenance of sufficient permeability barrier function for survival correlated with a compensatory acceleration of lamellar body secretion, providing a partial permeability barrier in NS. These studies provide a mechanistic basis for phenotypic variations in NS, and describe compensatory mechanisms that permit survival of NS patients in the face of unrelenting SP attack.

Sustained serine proteases activity by prolonged increase in pH leads to degradation of lipid processing enzymes and profound alterations of barrier function and stratum corneum integrity.

We showed recently that short-term increases in stratum corneum (SC) pH are accompanied by minor alterations in permeability barrier homeostasis and SC integrity/cohesion. Since prolonged SC neutralization more closely mirrors clinical situations (i.e., neonatal skin, occupational dermatitis conditions), we assessed here whether sustained elevations of SC pH by long-term application of 1,1,3,3-tetramethylguanidine superbase provoke profound alterations in SC function. Sustained SC neutralization altered not only barrier recovery kinetics but also basal permeability barrier function. These abnormalities were attributable to a decrease in beta-glucocerebrosidase (beta-GlcCer'ase) and acidic sphingomyelinase (aSMase) catalytic activity and enzyme degradation consequent to a pH-induced sustained serine protease (SP) activity. The role of SP in this process was shown by the normalization of enzyme activities/content by co-applied SP inhibitors (SPI). To address whether lipid-processing enzymes are potential substrates for the stratum corneum chymotryptic enzyme (SCCE), protein extracts from human SC were treated for 2 h at 37 degrees C with recombinant active SCCE at pH 7.2. Recombinant SCCE induced a significant decrease in the immunoblotting of both beta-GlcCer'ase or aSMase compared with control experiments performed in the absence of the active SCCE. Finally, with sustained SC neutralization, SC integrity/cohesion deteriorated, attributable to SP-mediated degradation of corneodesmosomes (CD) as well as CD constituent proteins, desmoglein 1. These abnormalities were again reversed by co-applied SPI. In conclusion, prolonged SC neutralization provokes profound abnormalities in SC function, due to pH-induced high SP activity that, in turn, degrades lipid processing enzymes and CD proteins.

pH directly regulates epidermal permeability barrier homeostasis, and stratum corneum integrity/cohesion.

Both exposure of stratum corneum to neutral pH buffers and blockade of acidification mechanisms disturb cutaneous permeability barrier homeostasis and stratum corneum integrity/cohesion, but these approaches all introduce potentially confounding variables. To study the consequences of stratum corneum neutralization, independent of hydration, we applied two chemically unrelated superbases, 1,1,3,3-tetramethylguanidine or 1,8-diazabicyclo [5,4,0] undec-7-ene, in propylene glycol:ethanol (7:3) to hairless mouse skin and assessed whether discrete pH changes alone regulate cutaneous permeability barrier function and stratum corneum integrity/cohesion, as well as the responsible mechanisms. Both 1,1,3,3-tetramethylguanidine and 1,8-diazabicyclo [5,4,0] undec-7-ene applications increased skin surface pH in parallel with abnormalities in both barrier homeostasis and stratum corneum integrity/cohesion. The latter was attributable to rapid activation (<20 min) of serine proteases, assessed by in situ zymography, followed by serine-protease-mediated degradation of corneodesmosomes. Western blotting revealed degradation of desmoglein 1, a key corneodesmosome structural protein, in parallel with loss of corneodesmosomes. Coapplication of serine protease inhibitors with the superbase normalized stratum corneum integrity/cohesion. The superbases also delayed permeability barrier recovery, attributable to decreased beta-glucocerebrosidase activity, assessed zymographically, resulting in a lipid-processing defect on electron microscopy. These studies demonstrate unequivocally that stratum corneum neutralization alone provokes stratum corneum functional abnormalities, including aberrant permeability barrier homeostasis and decreased stratum corneum integrity/cohesion, as well as the mechanisms responsible for these abnormalities.

Role of peroxisome proliferator-activated receptor alpha in epidermal development in utero.

The protective function of the skin is mediated by the stratum corneum, the outermost layer of the skin, which is the end-product of epidermal differentiation. Previously, we showed that fetal rat skin explants complete the late-stage milestones of epidermal development when grown in a serum- and growth-factor-free medium, suggesting that endogenous metabolites could regulate the late program that leads to barrier formation. Because a variety of endogenous free fatty acids are known activators, peroxisome proliferator-activated receptor alpha (PPAR-alpha) is a potential candidate for this key regulatory role. Indeed, whereas PPAR-alpha expression is first noted at gestational day 13.5 and peaks between days 14.5 and 15.5, fatty acid synthesis is very active in fetal rodent epidermis peaking at gestational day 17. Furthermore, we have reported that both epidermal differentiation and stratum corneum formation in utero are stimulated by pharmacologic activation of PPAR-alpha. This study was designed to test whether PPAR-alpha plays a physiologic role in epidermal differentiation and stratum corneum formation in utero. In PPAR-alpha-/- mice we observed delayed stratum corneum formation between day 18.5 of gestation and birth. Concurrently, there was diminished beta-glucocerebrosidase activity at the stratum granulosum-stratum corneum junction and a modest decrease in both involucrin and loricrin protein expression, markers of keratinocyte differentiation. Both the number of stratum corneum cell layers was reduced and the processing of the lamellar bilayers was delayed in animals lacking PPAR-alpha, indicating a transient functional defect. In contrast, the lamellar body secretory system as well as rates of epidermal proliferation and cell death appeared normal in PPAR-alpha-/- mice. These results indicate that PPAR-alpha plays a physiologic role during fetal stratum corneum development. The transient and incomplete nature of the developmental delay, however, is consistent with regulation of the late stages of epidermal development by multiple factors.

Short-term glucocorticoid treatment compromises both permeability barrier homeostasis and stratum corneum integrity: inhibition of epidermal lipid synthesis accounts for functional abnormalities.

Prolonged exposure of human epidermis to excess endogenous or exogenous glucocorticoids can result in well-recognized cutaneous abnormalities. Here, we determined whether short-term glucocorticoid treatment would also display adverse effects, specifically on two key epidermal functions, permeability barrier homeostasis and stratum corneum integrity and cohesion, and the basis for such changes. In humans 3 d of treatment with a potent, commonly employed topical glucocorticoid (clobetasol), applied topically, produced a deterioration in barrier homeostasis, characterized by delayed barrier recovery and abnormal stratum corneum integrity (rate of barrier disruption with tape strippings) and stratum corneum cohesion (microg protein removed per stripping). Short-term systemic and topical glucocorticoid produced similar functional defects in mice, where the basis for these abnormalities was explored further. Both the production and secretion of lamellar bodies were profoundly decreased in topical glucocorticoid-treated mice resulting in decreased extracellular lamellar bilayers. These structural changes, in turn, were attributable to a profound global inhibition of lipid synthesis, demonstrated both in epidermis and in cultured human keratinocytes. The basis for the abnormality in stratum corneum integrity and cohesion was a diminution in the density of corneodesmosomes in the lower stratum corneum. We next performed topical replacement studies to determine whether lipid deficiency accounts for the glucocorticoid-induced functional abnormalities. The abnormalities in both permeability barrier homeostasis and stratum corneum integrity were corrected by topical applications of an equimolar distribution of free fatty acids, cholesterol, and ceramides, indicating that glucocorticoid-induced inhibition of epidermal lipid synthesis accounts for the derangements in both cutaneous barrier function and stratum corneum integrity/cohesion. These studies indicate that even short-term exposure to potent glucocorticosteroids can exert profound negative effects on cutaneous structure and function. Finally, topical replenishment with epidermal physiologic lipids could represent a potential method to reduce the adverse cutaneous effects of both topical glucocorticoid treatment and Cushing's syndrome.

Basis for abnormal desquamation and permeability barrier dysfunction in RXLI.

Mutations in the gene for steroid sulfatase (SSase), are responsible for recessive x-linked ichthyosis (RXLI). As a consequence of SSase deficiency, its substrate, cholesterol sulfate (CSO4), accumulates in the epidermis. Accumulation of this amphipathic lipid in the outer epidermis provokes both a typical scaling phenotype and permeability barrier dysfunction. Research on RXLI has illuminated several, potentially overlapping pathogenic mechanisms and provided insights about the role of SSase and CSO4 in normal differentiation, barrier maintenance, and desquamation. We now show here that SSase is concentrated in lamellar bodies (LB), and secreted into the SC interstices, along with other LB-derived lipid hydrolases. There, it degrades CSO4, generating some cholesterol for the barrier, while the progressive decline in CSO4 (a serine protease (SP) inhibitor) permits corneodesmosome (CD) degradation leading to normal desquamation. Two molecular pathways contribute to disease pathogenesis in RXLI: 1) excess CSO4 produces nonlamellar phase separation in the stratum corneum (SC) interstices, explaining the barrier abnormality. 2) The increased CSO4 in the SC interstices inhibit activity sufficiently to delay CD degradation, leading to corneocyte retention. We also show here that increased Ca++ in the SC interstices in RXLI could contribute to corneocyte retention, by increasing CD and interlamellar cohesion. RXLI represents one of the best understood diseases in dermatology--from the gene to the SC interstices, its etiology and pathogenesis are becoming clear, and assessment of disease mechanisms in RXLI led to new insights about the role of SSase and CSO4 in epidermis terminal differentiation.

Structural and functional consequences of loricrin mutations in human loricrin keratoderma (Vohwinkel syndrome with ichthyosis).

Although loricrin is the predominant protein of the cornified envelope (CE) in keratinocytes, loss or gain of loricrin function in mouse models produces only modest skin phenotypes. In contrast, insertional mutations resulting in a frameshift in the C-terminal domain of loricrin produce the characteristic ichthyosis of loricrin keratoderma in mouse and man. To ascertain the basis for the loricrin keratoderma phenotype, we assessed epidermal structure and stratum corneum (SC) function in a previously genotyped human loricrin keratoderma kindred. Our studies revealed abnormal corneocyte fragility and basal permeability barrier function, but accelerated repair kinetics. Despite fragility, increased water loss occurred predominantly via extracellular domains, which correlated with disorganized lamellar bilayers that were linked spatially to discontinuities of the CE. Accelerated barrier recovery was explicable by amplified lamellar body secretion, while partial normalization of the CE in the outer SC correlated with persistence of abundant calcium in the extracellular spaces (positioned to activate transglutaminase-1). These results show that the barrier abnormality in loricrin keratoderma is linked to a defective CE scaffold, resulting in increased extracellular permeability, as shown previously for another "scaffold disorder", lamellar ichthyosis. But in contrast to lamellar ichthyosis, the CE scaffold partially normalizes in the outer SC in loricrin keratoderma.

Functional consequences of a neutral pH in neonatal rat stratum corneum.

At birth, neonatal stratum corneum (SC) pH is close to neutral but acidifies with maturation, which can be ascribed, in part, to secretory phospholipase A(2) and sodium/hydrogen antiporter 1 (NHE1) activities. Here we assessed the functional consequences of a neutral SC pH in a newborn rat model. While basal transepidermal water loss rates are near normal, barrier recovery (BR) rates after acute barrier disruption were delayed in newborn animals. The abnormality in barrier homeostasis could be improved by topical applications of an acidic buffer, indicating that barrier abnormality is primarily due to high SC pH. The delay in BR correlated with incompletely processed lamellar membranes and decreased activity of beta-glucocerebrosidase. Inhibition of NHE1 delayed BR after acute barrier perturbation. SC integrity was abnormal in newborn animals. Electron microscopy demonstrated decreased corneodesmosomes (CD) in newborn animals with decreased expression of desmoglein 1 and corneodesmosin. Serine protease activation appears to be responsible for CD degradation in newborn animals, because serine protease activity is increased in the SC and it can be reduced by acidification of the SC. The delay in acidification of neonatal SC results in abnormalities in permeability barrier homeostasis and SC integrity and are likely due to pH-induced modulations in enzyme activity.

The effect of two moisturisers on skin barrier damage in allergic contact dermatitis.

Nickel (Ni)-induced allergic contact dermatitis (ACD) was performed in human volunteers to study the role of moisturisers in preventing ACD-related skin barrier damage. 15 Ni-sensitive females (mean age: 29.5 years; range: 23-38) were included. On days 1, 21, 24 and 26, TEWL, stratum corneum (SC)-capacitance and clinical score were evaluated on four test sites on the right and left forearms. Both a highly and a poorly hydrating moisturising formulation were applied on two sites from days 1 to 21, after which Ni-ACD was induced on the 2 pre-treated sites and one non-treated area. On day 24, TEWL values were significantly increased on the site pre-treated with poorly hydrating product compared to the rich formulation pre-treated site. SC-hydration was significantly improved on the latter site on days 21, 23 and 26. Long-term use of inadequate moisturiser increases skin barrier damage due to Ni-ACD.

Caspase-14-deficient mice are more prone to the development of parakeratosis.

Caspase-14 is an important protease in the proper formation of a fully functional skin barrier. Newborn mice that are deficient in caspase-14 exhibit increased transepidermal water loss and are highly sensitive to UVB-induced photodamage. Decreased caspase-14 expression and incomplete caspase-14 processing in lesional psoriatic parakeratotic stratum corneum has been reported previously. In this study, we show that caspase-14-deficient skin frequently displays incompletely cornified cells in the transitional zone between the granular and the cornified layers, pointing to a delay in cornification. We also demonstrate that after challenge of epidermal permeability barrier function by repetitive acetone treatment, a higher incidence of large parakeratotic plaques was observed in caspase-14-deficient skin. Furthermore, caspase-14-deficient mice are more prone than control mice to the development of parakeratosis upon induction of psoriasis-like dermatitis by imiquimod treatment. These results show that lack of caspase-14 expression predisposes to the development of parakeratosis and that caspase-14 has an important role in keratinocyte terminal differentiation and the maintenance of normal stratum corneum, especially in conditions causing epidermal hyperproliferation.