Involvement of corneodesmosome degradation and lamellar granule transportation in the desquamation process

Three stepwise pH progressions in stratum corneum for homeostatic maintenance of the skin

The stratum corneum is the outermost skin layer with a vital role in skin barrier function. It is comprised of dead keratinocytes (corneocytes) and is known to maintain its thickness by shedding cells, although, the precise mechanisms that safeguard stratum corneum maturation and homeostasis remain unclear. Previous ex vivo studies have suggested a neutral-to-acidic pH gradient in the stratum corneum. Here, we use intravital pH imaging at single-corneocyte resolution to demonstrate that corneocytes actually undergo differentiation to develop three distinct zones in the stratum corneum, each with a distinct pH value. We identified a moderately acidic lower, an acidic middle, and a pH-neutral upper layer in the stratum corneum, with tight junctions playing a key role in their development. The upper pH neutral zone can adjust its pH according to the external environment and has a neutral pH under steady-state conditions owing to the influence of skin microbiota. The middle acidic pH zone provides a defensive barrier against pathogens. With mathematical modeling, we demonstrate the controlled protease activation of kallikrein-related peptidases on the stratum corneum surface that results in proper corneocyte shedding in desquamation. This work adds crucial information to our understanding of how stratum corneum homeostasis is maintained.

Regional Differences in the Permeability Barrier of the Skin-Implications in Acantholytic Skin Diseases

The chemical milieu, microbiota composition, and immune activity show prominent differences in distinct healthy skin areas. The objective of the current study was to compare the major permeability barrier components (stratum corneum and tight junction (TJ)), investigate the distribution of (corneo)desmosomes and TJs, and measure barrier function in healthy sebaceous gland-rich (SGR), apocrine gland-rich (AGR), and gland-poor (GP) skin regions. Molecules involved in cornified envelope (CE) formation, desquamation, and (corneo)desmosome and TJ organization were investigated at the mRNA and protein levels using qRT-PCR and immunohistochemistry. The distribution of junction structures was visualized using confocal microscopy. Transepidermal water loss (TEWL) functional measurements were also performed. CE intracellular structural components were similarly expressed in gland-rich (SGR and AGR) and GP areas. In contrast, significantly lower extracellular protein levels of (corneo)desmosomes (DSG1 and CDSN) and TJs (OCLN and CLDN1) were detected in SGR/AGR areas compared to GP areas. In parallel, kallikrein proteases were significantly higher in gland-rich regions. Moreover, gland-rich areas were characterized by prominently disorganized junction structures ((corneo)desmosomes and TJs) and significantly higher TEWL levels compared to GP skin, which exhibited a regular distribution of junction structures. According to our findings, the permeability barrier of our skin is not uniform. Gland-rich areas are characterized by weaker permeability barrier features compared with GP regions. These findings have important clinical relevance and may explain the preferred localization of acantholytic skin diseases on gland-rich skin regions (e.g., Pemphigus foliaceus, Darier's disease, and Hailey-Hailey disease).

A Novel Tumor Suppressor SPINK5 Serves as an Independent Prognostic Predictor for Patients with Head and Neck Squamous Cell Carcinoma

BACKGROUND

In our previous study, serine protease inhibitor Kazal-type 5 (SPINK5), which encodes the product of serine protease inhibitor lymphoepithelial Kazal-type-related inhibitor (LEKTI) was found to be down-regulated in head and neck squamous cell carcinoma (HNSCC) using oligonucleotide microarrays. However, the function and clinical implications of SPINK5/LEKTI remain obscure in HNSCC.

METHODS

The endogenous expression level of SPINK5/LEKTI was further verified in 9 HNSCC cell lines and HNSCCs by means of reverse transcription-polymerase chain reaction, real-time PCR, Western blotting and immunohistochemistry. The biological function of SPINK5/LEKTI was investigated in vitro and in vivo experiments. Kaplan-Meier survival analysis and Cox proportional hazards regression model were used to determine the correlation between SPINK5/LEKTI expression and clinical outcome.

RESULTS

Down-regulation expression of SPINK5/LEKTI was found in six out of nine HNSCC cell lines and in 85.7% HNSCC specimens (P<0.0001). Upon silencing of SPINK5/LEKTI, the cell proliferation, plate colony formation and cell invasion of WU-HN6 cells were significantly increased, while exogenous overexpression of SPINK5/LEKTI, the proliferation, plate colony and invasion of WU-HN13 and HN30 cells were remarkably inhibited with the arrest of G1 cell cycle (P=0.0001, P=0.003, respectively). HNSCC patients with lower LEKTI levels had significantly inferior overall survival compared to those patients with higher LEKTI (P=0.0017) by Kaplan-Meier survival analysis. Univariate and multivariate Cox proportional hazards regression model analysis revealed that LEKTI expression was an independent prognostic predictor for HNSCC patients (HR=0.114, 95% CI:0.044-0.292, P<0.001).

CONCLUSION

Our results demonstrate that SPINK5/LEKTI might be a tumor suppressor in HNSCCs and serve as an independent prognostic predictor for HNSCC patients.

Characterization of multilamellar bodies and telocytes within the testicular interstitium of naked mole rat Heterocephalus glabe

Multilamellar bodies (MLBs) are produced and secreted by many cell types. In this study, we report the existence and ultrastructure of MLBs that are produced by Leydig cells and identification of telocytes in the testicular interstitium of naked mole rat. This study was performed on both breeder and non-breeder male naked mole rats using light microscopy, transmission electron microscopy, and morphometric approaches. In the testicular interstitium, the most prominent cells were Leydig cells, which contained numerous lipid droplets (LDs) in the cytoplasm. We found that MLBs were associated with the LDs of Leydig cells and were secreted into the extracellular or interstitial environment via exocytosis. After their release from Leydig cells, MLBs localized to the space between Leydig cells near blood vessels and attached to telocytes. We also identified telocytes in the testicular interstitium, and their cellular extensions were distributed throughout the interstitium. MLBs were aligned along the cellular extensions of telocytes, and membrane-to-membrane contact was observed between the cellular extensions of telocytes and MLBs, suggesting that telocytes may play a role in the transport of MLBs within the interstitial space. No ultrastructural differences were found in Leydig cells, telocytes, or MLBs between breeder and non-breeder testes. However, morphometric analysis revealed a significant difference in the number of MLBs between the breeder and non-breeder animals. Furthermore, both selective autophagy of LDs and non-selective autophagy were observed in Leydig cells. Typical features of macrolipophagy were also observed, as a few LDs were entirely enclosed by a limiting membrane. Remarkably, autophagy may be a key factor in the biogenesis of MLBs and steroid hormone production. The appearance of MLBs in the testicular interstitium of naked mole rats could thus be related to lipid storage and trafficking.

Mesenchymal stem cells differentiate into keratinocytes and express epidermal kallikreins: Towards an in vitro model of human epidermis

Epidermal differentiation is a complex process in which keratinocytes go through morphological and biochemical changes in approximately 15 to 30 days. Abnormal keratinocyte differentiation is involved in the pathophysiology of several skin diseases. In this scenario, mesenchymal stem cells (MSCs) emerge as a promising approach to study skin biology in both normal and pathological conditions. Herein, we have studied the differentiation of MSC from umbilical cord into keratinocytes. MSC were cultured in Dulbecco's modified Eagle's medium (DMEM) (proliferation medium) and, after characterization, differentiation was induced by culturing cells in a defined keratinocyte serum-free medium (KSFM) supplemented with epidermal growth factor (EGF) and calcium chloride ions. Cells cultivated in DMEM were used as control. Cultures were evaluated from day 1 to 23, based on the cell morphology, the expression of p63, involucrin and cytokeratins (KRTs) KRT5, KRT10 and KRT14, by quantitative polymerase chain reaction, Western blot analysis or immunofluorescence, and by the detection of epidermal kallikreins activity. In cells grown in keratinocyte serum-free medium with EGF and 1.8 mM calcium, KRT5 and KRT14 expression was shown at the first day, followed by the expression of p63 at the seventh day. KRT10 expression was detected from day seventh while involucrin was observed after this period. Data showed higher kallikrein (KLK) activity in KSFM-cultured cells from day 11th in comparison to control. These data indicate that MSC differentiated into keratinocytes similarly to that occurs in the human epidermis. KLK activity detection appears to be a good methodology for the monitoring the differentiation of MSC into the keratinocyte lineage, providing useful tools for the better understanding of the skin biology.

Shadow Cell Differentiation: A Comparative Analysis of Modes of Cell Death with Apoptosis and Epidermal/Trichilemmal Keratinization

Shadow cells are characterized by an eosinophilic cytoplasm and a ghost-like nuclear contour; the cell shape is preserved, in spite of nuclear disappearance. Shadow cell nests (SCNs) are frequently observed in pilomatricoma (PMX), where the transitional cells immediately adjacent to SCNs often have a crescent-shaped nucleus showing fragmentation similar to that of apoptotic bodies. They show nuclear accumulation of beta-catenin and DNA double strand breaks (as revealed by in situ 3′-tailing reaction or immunohistochemistry for single-stranded DNA [ssDNA]), while they are negative for cleaved caspase-3 or cleaved lamin A, suggesting that shadow cell differentiation (SCD) is a caspase-independent programmed cell death. SCD can be differentiated from epidermal keratinization (EK) and trichilemmal keratinization (TK) based on the expression pattern of beta-catenin, ssDNA, and caspase-14/CD138. SCD is observed not only in PMX, but also sometimes in basal cell carcinomas, gonadal teratomas, and various extra-cutaneous carcinomas. In particular, SCNs are found in 24$ of endometrial adenoacanthoma and are derived from squamoid morules. This establishes a link between basaloid cells in PMX and squamoid morules in endometrial adenoacanthomas as common precursors of shadow cells. Overall, it is suggested that SCD is different from, but partly similar to, apoptosis and that SCD and EK/TK should be differentiated from the standpoint of cell death/differentiation.

Physiological and functional changes in the stratum corneum restored by oestrogen in an ovariectomized mice model of climacterium

Significant decreases in hormonal levels at menopause induce physiological and functional discomfort in the skin. Representative changes at menopause are based on so-called dry skin. However, there is no evidence to explain the mechanism, even though hydration of the stratum corneum (SC) in women at menopause is comparable with that at premenopause but is enhanced by hormone replacement therapy. This study objective was to evaluate structural and functional changes in the SC in ovariectomized mice model of menopause. Hydration of the SC, recovery of the permeability barrier function, integrity and cohesion of the SC, and irritant dermatitis were analysed in mice that underwent ovariectomy with or without replacement of 17ß-estradiol. In ovariectomized mice, hydration of the SC was reduced, recovery of permeability barrier function after acute disruption was impaired, and integrity of the SC was weakened and was associated with increased cohesion and increased levels of irritant dermatitis. Oestrogen replacement treatment restored all changes. Immunohistochemistry revealed reduced levels of expression of desmoglein-1 and differentiation markers of epidermis in ovariectomized mice compared with control mice and mice with oestrogen replacement treatment. These changes might be directly associated with weakened integrity and impaired permeability barrier function of the SC in ovariectomized mice. This study results reveal that so-called dry skin at menopause is caused by not only lower hydration of the SC but also complicated structural and functional changes in the SC and skin.

iTRAQ-based quantitative proteomics of stratum corneum of dandruff scalp reveals new insights into its aetiology and similarities with atopic dermatitis

The study aimed at detecting differentially expressed proteins in the stratum corneum of dandruff versus non-dandruff scalps to better understand dandruff aetiology. iTRAQ-based quantitative proteomic analysis revealed a total of 68 differentially expressed biomarkers. A detailed analysis of their known physiological functions provided new insights into the affected metabolic pathways of a dandruff scalp. Dandruff scalp showed (1) profound changes in the expression and maturation of structural and epidermal differentiation related proteins, that are responsible for the integrity of the skin, (2) altered relevant factors that regulate skin hydration, and (3) an imbalanced physiological protease-protease inhibitor ratio. Stratum corneum proteins with antimicrobial activity, mainly those derived from sweat and sebaceous glands were also found modified. Comparing our data with those reported for atopic dermatitis revealed that about 50 % of the differentially expressed proteins in the superficial layers of the stratum corneum from dandruff and atopic dermatitis are identical.

Epidemiology, medical genetics, diagnosis and treatment of harlequin ichthyosis in Japan

Ichthyoses are a group of disorders marked by whitish, brown or dark-brown scales on the skin of almost the whole body. Harlequin ichthyosis (HI) is the most severe form. Neonatal death from HI was once common. Due to intensive neonatal care and, probably, to the early introduction of oral retinoids, HI outcome has improved. For definitive diagnosis and the exclusion of other disorders, such as lamellar ichthyosis, which also shows a collodion baby phenotype, it is helpful to refer to electron microscopy of abnormal or absent lamellar granules and a heavy accumulation of lipid droplets in the keratinocytes. ATP-binding cassette transporter A12 (ABCA12) is known as the causative gene of HI. Severe ABCA12 deficiency results in malformation of intercellular lipid layers in the cornified layers and leads to epidermal lipid barrier disruption. In HI patients, at least one mutation on each allele must be a truncation or deletion mutation to cause serious loss of ABCA12 function. Identification of the gene underlying HI has enabled DNA-based prenatal diagnosis for HI at the earlier stages of pregnancy with low risk. There are no curative treatments for HI. Abca12-deficient mice were created as a model of HI. Treatment of the model mice with retinoid or steroid has not been successful.

Genetic skin diseases related to desmosomes and corneodesmosomes

The integrity of the epidermis depends on the cohesion between keratinocytes, and desmosomes are the main adhesion structures. When cells become cornified, desmosomes are modified and transformed into corneodesmosomes. Mutations in the genes encoding desmosomal components underlie several skin diseases including palmoplantar keratoderma and forms of epidermolysis bullosa, indicating the importance of desmosomes as mechanical stress-bearing structures. Other types of genetic defects in a desmosome component (desmoglein 1), a corneodesmosome component (corneodesmosin), and an inhibitor for proteases involved in corneodesmosome degradation (LEKTI) result in three clinically overlapping conditions: SAM syndrome, an inflammatory type of peeling skin disease, and Netherton syndrome. All three result in allergies to multiple allergens due to severe barrier impairment. Conversely, impaired corneodesmosomal degradation due to matriptase mutations could lead to ichthyosis. By discovering the diverse clinical phenotypes of these diseases, we can enrich our understanding of the multifunctional roles of desmosomes and corneodesmosomes in skin biology.

Keratinocyte-specific mesotrypsin contributes to the desquamation process via kallikrein activation and LEKTI degradation

Kallikrein-related peptidases (KLKs) have critical roles in corneocyte desquamation and are regulated by lymphoepithelial Kazal-type inhibitor (LEKTI). However, it is unclear how these proteases are activated and how activated KLKs are released from LEKTI in the upper cornified layer. Recently, we reported cloning of a PRSS3 gene product, keratinocyte-specific mesotrypsin, from a cDNA library. We hypothesized that mesotrypsin is involved in the desquamation process, and the aim of the present study was to test this idea by examining the effects of mesotrypsin on representative desquamation-related enzymes pro-KLK5 and pro-KLK7. Incubation of mesotrypsin and these zymogens resulted in generation of the active forms. KLK activities were effectively inhibited by recombinant LEKTI domains D2, D2-5, D2-6, D2-7, D5, D6, D6-9, D7, D7-9, and D10-15, whereas mesotrypsin activity was not susceptible to these domains, and in fact degraded them. Immunoelectron microscopy demonstrated that mesotrypsin was localized in the cytoplasm of granular cells and intercellular spaces of the cornified layer. Proximity ligation assay showed close association between mesotrypsin and KLKs in the granular to cornified layers. Age-dependency analysis revealed that mesotrypsin was markedly downregulated in corneocyte extract from donors in their sixties, compared with younger donors. Collectively, our findings suggest that mesotrypsin contributes to the desquamation process by activating KLKs and degrading the intrinsic KLKs' inhibitor LEKTI.

A homozygous nonsense mutation in the gene for Tmem79, a component for the lamellar granule secretory system, produces spontaneous eczema in an experimental model of atopic dermatitis

BACKGROUND

Flaky tail (ma/ma Flg(ft/ft)) mice have a frameshift mutation in the filaggrin (Flg(ft)) gene and are widely used as a model of human atopic dermatitis associated with FLG mutations. These mice possess another recessive hair mutation, matted (ma), and develop spontaneous dermatitis under specific pathogen-free conditions, whereas genetically engineered Flg(-/-) mice do not.

OBJECTIVE

We identified and characterized the gene responsible for the matted hair and dermatitis phenotype in flaky tail mice.

METHODS

We narrowed down the responsible region by backcrossing ma/ma mice with wild-type mice and identified the mutation using next-generation DNA sequencing. We attempted to rescue the matted phenotype by introducing the wild-type matted transgene. We characterized the responsible gene product by using whole-mount immunostaining of epidermal sheets.

RESULTS

We demonstrated that ma, but not Flg(ft), was responsible for the dermatitis phenotype and corresponded to a Tmem79 gene nonsense mutation (c.840C>G, p.Y280*), which encoded a 5-transmembrane protein. Exogenous Tmem79 expression rescued the matted hair and dermatitis phenotype of Tmem79(ma/ma) mice. Tmem79 was mainly expressed in the trans-Golgi network in stratum granulosum cells in the epidermis in both mice and humans. The Tmem79(ma/ma) mutation impaired the lamellar granule secretory system, which resulted in altered stratum corneum formation and a subsequent spontaneous dermatitis phenotype.

CONCLUSIONS

The Tmem79(ma/ma) mutation is responsible for the spontaneous dermatitis phenotype in matted mice, probably as a result of impaired lamellar granule secretory system and altered stratum corneum barrier function.

The stratum corneum: the rampart of the mammalian body

BACKGROUND

The stratum corneum (SC) is the outermost region of the epidermis and plays key roles in cutaneous barrier function in mammals. The SC is composed of 'bricks', represented by flattened, protein-enriched corneocytes, and 'mortar', represented by intercellular lipid-enriched layers. As a result of this 'bricks and mortar' structure, the SC can be considered as a 'rampart' that encloses water and solutes essential for physiological homeostasis and that protects mammals from physical, chemical and biological assaults.

STRUCTURES AND FUNCTIONS

The corneocyte cytoskeleton contains tight bundles of keratin intermediate filaments aggregated with filaggrin monomers, which are subsequently degraded into natural moisturizing compounds by various proteases, including caspase 14. A cornified cell envelope is formed on the inner surface of the corneocyte plasma membrane by transglutaminase-catalysed cross-linking of involucrin and loricrin. Ceramides form a lipid envelope by covalently binding to the cornified cell envelope, and extracellular lamellar lipids play an important role in permeability barrier function. Corneodesmosomes are the main adhesive structures in the SC and are degraded by certain serine proteases, such as kallikreins, during desquamation.

CLINICAL RELEVANCE

The roles of the different SC components, including the structural proteins in corneocytes, extracellular lipids and some proteins associated with lipid metabolism, have been investigated in genetically engineered mice and in naturally occurring hereditary skin diseases, such as ichthyosis, ichthyosis syndrome and atopic dermatitis in humans, cattle and dogs.

Harlequin ichthyosis: ABCA12 mutations underlie defective lipid transport, reduced protease regulation and skin-barrier dysfunction

Harlequin ichthyosis (HI) is a devastating autosomal recessive congenital skin disease. It has been vital to elucidate the biological importance of the protein ABCA12 in skin-barrier permeability, following the discovery that ABCA12 gene mutations can result in this rare disease. ATP-binding cassette transporter A12 (ABCA12) is a member of the subfamily of ATP-binding cassette transporters and functions to transport lipid glucosylceramides (GlcCer) to the extracellular space through lamellar granules (LGs). GlcCer are hydrolysed into hydroxyceramides extracellularly and constitute a portion of the extracellular lamellar membrane, lipid envelope and lamellar granules. In HI skin, loss of function of ABCA12 due to null mutations results in impaired lipid lamellar membrane formation in the cornified layer, leading to defective permeability of the skin barrier. In addition, abnormal lamellar granule formation (distorted shape, reduced in number or absent) could further cause aberrant production of LG-associated desquamation enzymes, which are likely to contribute to the impaired skin barrier in HI. This article reviews current opinions on the patho-mechanisms of ABCA12 action in HI and potential therapeutic interventions based on targeted molecular therapy and gene therapy strategies.

Kallikrein-related peptidase-7 regulates caspase-14 maturation during keratinocyte terminal differentiation by generating an intermediate form

The maturation and activation mechanisms of caspases are generally well understood, except for those of caspase-14, which is activated at the onset of keratinocyte terminal differentiation. We investigated the possible involvement of epidermal proteases expressed in the late stage of differentiation, and found that the chymotrypsin-like serine protease kallikrein-related peptidase-7 (KLK7) cleaved procaspase-14 at Tyr(178), generating an intermediate form that consists of a large (20 kDa) and a small subunit (8 kDa). We prepared an antibody directed to this cleavage site (h14Y178 Ab), and confirmed that it recognized a 20-kDa band formed when procaspase-14 was incubated with chymotrypsin or KLK7. We then constructed a constitutively active form of the intermediate, revC14-Y178. The substrate specificity of revC14-Y178 was completely different from that of caspase-14, showing broad specificity for various caspase substrates except WEHD-7-amino-4-trifluoromethylcoumarin (AFC), the preferred substrate of active, mature caspase-14. K(m) values for VEID-AFC, DEVD-AFC, LEVD-AFC, and LEHD-AFC were 0.172, 0.261, 0.504, and 0.847 μM, respectively. We confirmed that the mature form of caspase-14 was generated when procaspase-14 was incubated with KLK7 or revC14-Y178. Expression of constitutively active KLK7 in cultured keratinocytes resulted in generation of both the intermediate form and the mature form of caspase-14. Immunohistochemical analysis demonstrated that the intermediate form was localized at the granular layer. Our results indicate that regulation of procaspase-14 maturation during terminal differentiation is a unique two-step process involving KLK7 and an activation intermediate of caspase-14.