The keratins and their disorders

Decreased Skin Barrier Lipid Acylceramide and Differentiation-Dependent Gene Expression in Ichthyosis Gene Nipal4-Knockout Mice

NIPAL4 is one of the causative genes for autosomal recessive congenital ichthyosis. However, the role of NIPAL4 in skin barrier formation and the molecular mechanism of ichthyosis pathology caused by NIPAL4 mutations, have not yet been determined. Here, we found that Nipal4-knockout (KO) mice exhibited neonatal lethality due to skin barrier defects. Histological analyses showed several morphological abnormalities in the Nipal4-KO epidermis, including impairment of lipid multilayer structure formation, hyperkeratosis, immature keratohyalin granules, and developed heterochromatin structures. The levels of the skin barrier lipid acylceramide were decreased in Nipal4-KO mice. Expression of genes involved in skin barrier formation normally increases during keratinocyte differentiation, in which chromatin remodeling is involved. However, the induction of Krt1, Lor, Flg, Elovl1, and Dgat2 was impaired in Nipal4-KO mice. NIPAL4 is a putative Mg²⁺ transporter, and Mg²⁺ concentration in differentiated keratinocytes of Nipal4-KO mice was indeed lower than that of wild-type mice. Our results suggest that low Mg²⁺ concentration causes aberration in the proper chromatin remodeling process, which in turn leads to failure of differentiation-dependent gene induction in keratinocytes. Our findings provide insights into Mg²⁺-dependent regulation of gene expression and skin barrier formation during keratinocyte differentiation.

Current approaches to the diagnosis and treatment of white sponge nevus

White sponge nevus (WSN) in the oral mucosa is a rare autosomal dominant genetic disease. The involved mucosa is white or greyish, thickened, folded and spongy. The genes associated with WSN include mutant cytokeratin keratin 4 (KRT4) and keratin 13 (KRT13). In recent years, new cases of WSN and associated mutations have been reported. Here, we summarise the recent progress in our understanding of WSN, including clinical reports, genetics, animal models, treatment, pathogenic mechanisms and future directions. Gene-based diagnosis and gene therapy for WSN may become available in the near future and could provide a reference and instruction for treating other KRT-associated diseases.

Coumarin derivatives, but not coumarin itself, cause skin irritation via topical delivery

Coumarin and its derivatives are widely employed as a fragrance in cosmetics and skin care products. The skin absorption level and possible disruption to the skin by topical application of coumarins were evaluated in this study. Percutaneous absorption of osthole, daphnoretin, coumarin, byakangelicin, and 7-hydroxycoumarin was assessed in vitro and in vivo. Skin physiology measurements and immunoblotting were utilized as methodologies for validating toxicity. The relationship between structures and permeation/toxicity of coumarins was elucidated. Both equimolar concentration and saturated solubility in 30% ethanol were used as the applied dose. Osthole with the most lipophilic characteristic demonstrated the greatest skin accumulation, followed by coumarin and 7-hydroxycoumarin. Coumarin was the permeant with the highest flux across the skin. The trend of in vivo deposition was consistent with that of the in vitro profiles. Skin uptake of osthole was 8-fold higher than that of coumarin. Hair follicles played a significant role as a pathway for transport of coumarin according to the examination of follicular accumulation. Osthole and 7-hydroxycoumarin slightly, but significantly, enhanced transepidermal water loss after a consecutive 5-day administration. The immunoblotting profiling verified the role of proliferation in skin damage induced by osthole, byakangelicin, and 7-hydroxycoumarin. The proliferation-related proteins examined in this work included glucose-regulated proteins, cytokeratin, and C-myc. Daphnoretin and coumarin showed a negligible alteration on protein biomarkers. The experimental results suggested that skin irritation caused by coumarins was mainly derived from the analogs but not from coumarin itself.

Keloid-derived keratinocytes exhibit an abnormal gene expression profile consistent with a distinct causal role in keloid pathology

Keloids are disfiguring scars that extend beyond the original wound borders and resist treatment. Keloids exhibit excessive extracellular matrix deposition, although the underlying mechanisms remain unclear. To better understand the molecular basis of keloid scarring, here we define the genomic profiles of keloid fibroblasts and keratinocytes. In both cell types, keloid-derived cells exhibit differential expression of genes encompassing a diverse set of functional categories. Strikingly, keloid keratinocytes exhibited decreased expression of a set of transcription factor, cell adhesion, and intermediate filament genes essential for normal epidermal morphology. Conversely, they exhibit elevated expression of genes associated with wound healing, cellular motility, and vascular development. A substantial number of genes involved in epithelial-mesenchymal transition were also up-regulated in keloid keratinocytes, implicating this process in keloid pathology. Furthermore, keloid keratinocytes displayed significantly higher migration rates than normal keratinocytes in vitro and reduced expression of desmosomal proteins in vivo. Previous studies suggested that keratinocytes contribute to keloid scarring by regulating extracellular matrix production in fibroblasts. Our current results show fundamental abnormalities in keloid keratinocytes, suggesting they have a profoundly more direct role in keloid scarring than previously appreciated. Therefore, development of novel therapies should target both fibroblast and keratinocyte populations for increased efficacy.

Dermal toxicity elicited by phthalates: evaluation of skin absorption, immunohistology, and functional proteomics

The toxicity of phthalates is an important concern in the fields of environmental health and toxicology. Dermal exposure via skin care products, soil, and dust is a main route for phthalate delivery. We had explored the effect of topically-applied phthalates on skin absorption and toxicity. Immunohistology, functional proteomics, and Western blotting were employed as methodologies for validating phthalate toxicity. Among 5 phthalates tested, di(2-ethylhexyl)phthalate (DEHP) showed the highest skin reservoir. Only diethyl phthalate (DEP) and dibutyl phthalate (DBP) could penetrate across skin. Strat-M(®) membrane could be used as permeation barrier for predicting phthalate penetration through skin. The accumulation of DEHP in hair follicles was ∼15nmol/cm(2), which was significantly greater than DBP and DEP. DBP induced apoptosis of keratinocytes and fibroblasts via caspase-3 activation. This result was confirmed by downregulation of 14-3-3 and immunohistology of TUNEL. On the other hand, the HSP60 overexpression and immunostaining of COX-2 suggested inflammatory response induced by DEP and DEHP. The proteomic profiling verified the role of calcium homeostasis on skin inflammation. Some proteins investigated in this study can be sensitive biomarkers for dermal toxicity of phthalates. These included HSPs, 14-3-3, and cytokeratin. This work provided novel platforms for examining phthalate toxicity on skin.

Keratin k15 as a biomarker of epidermal stem cells

Keratin 15 (K15) is type I keratin protein co-expressed with the K5/K14 pair present in the basal keratinocytes of all stratified epithelia. Although it is a minor component of the cytoskeleton with a variable expression pattern, nonetheless its expression has been reported as a stem cell marker in the bulge of hair follicles. Conversely, suprabasal expression of K15 has also been reported in both normal and diseased tissues, which is inconsistent with its role as a stem cell marker. Our recently published work has given evidence of the molecular pathways that seem to control the expression of K15 in undifferentiated and differentiated cells. In this article, we have critically reviewed the published work to establish the reliability of K15 as an epidermal stem cell marker.

Analysis of the KRT9 gene in a Mexican family with epidermolytic palmoplantar keratoderma

Epidermolytic palmoplantar keratoderma (EPPK), an autosomal-dominant genodermatosis, is the most frequently occurring hereditary palmoplantar keratoderma. EPPK is characterized by hyperkeratosis of the palms and soles. Approximately 90% of patients present with mutations in the KRT9 gene, which encodes for keratin 9. Many of these mutations are located within the highly conserved coil 1A region of the alpha-helical rod domain of keratin 9, an important domain for keratin heterodimerization. The objective was to assess the clinical and molecular characteristics of a Mexican family with EPPK. The clinical characteristics of members of this family were analyzed. The KRT9 gene of affected members was polymerase chain reaction amplified from genomic DNA and sequenced. All affected members of the family had hyperkeratosis of the palms and soles with knuckle pads. The R163W mutation in the KRT9 gene was present in all affected individuals who were tested. Although R163W is the most frequent KRT9 mutation in patients with EPPK, only two families have been reported with knuckle pads associated with this mutation. Our findings indicate that knuckle pads can be associated with EPPK and the R163W mutation in a family with a genetic background different from that described here.

Ichthyosis bullosa of Siemens

BACKGROUND

Ichthyosis bullosa of Siemens (IBS) is a rare hyperkeratotic blistering condition caused by mutations in keratin 2e gene.

MAIN OBSERVATIONS

This is a case of a 18-year-old female with generalized blisters, erosions and thickened skin since she was 3 months old. As she aged, there was decrease in development of blisters and erosions, with accompanying increase in severity of hyperkeratosis. Skin punch biopsy showed overlying basket weave hyperkeratosis and acanthosis, prominent vacuolization of the granular cell layer, and intraepidermal blisters with the split at the granular layer. The patient was treated with emollients, with marked improvement.

CONCLUSIONS

Mutations in the different keratin genes have been shown to underlie a wide range of disorders of keratinization. Epidermolytic hyperkeratosis and ichthyosis bullosa of Siemens are distinct disorders with mutations in different genes. Although molecular genetic testing should ideally be done for confirmation of diagnosis, ichthyosis bullosa of Siemens could be diagnosed in this patients based on key clinical characteristics.

Two novel recessive mutations in KRT14 identified in a cohort of 21 Spanish families with epidermolysis bullosa simplex

BACKGROUND

Basal epidermolysis bullosa simplex (EBS) is a group of blistering genodermatoses mostly caused by mutations in the keratin genes, KRT5 and KRT14. Recessive mutations represent about 5% of all EBS mutations, being common and specific in populations with high consanguinity, where affected patients show severe phenotypes.

OBJECTIVES

To accomplish the first mutational analysis in patients of Spanish origin with EBS and to delineate a comprehensive genotype-phenotype correlation.

METHODS

Twenty-one EBS families were analysed. Immunofluorescence mapping at the dermoepidermal junction level was performed on skin biopsies from patients. Mutation screening of the entire coding sequences of KRT5 and KRT14 in genomic DNA was assessed by polymerase chain reaction and direct sequencing.

RESULTS

KRT5 or KRT14 causative mutations were identified in 18 of the 21 EBS families. A total of 14 different mutations were disclosed, of which 12 were dominant missense mutations and two truncating recessive mutations. Five of the 14 mutations were novel including three dominant in KRT5 (p.V186E, p.T321P and p.A428T) and two recessive in KRT14 (p.K116X and p.K250RfsX8). The two patients with EBS carrying homozygous recessive mutations were affected by severe phenotypes and belonged to consanguineous families. All five families with the EBS Dowling-Meara subtype carried recurrent mutations affecting the highly conserved ends of the α-helical rod domain of K5 and K14. The seven mutations associated with the localized EBS subtype were widely distributed along the KRT5 and KRT14 genes. Two families with mottled pigmentation carried the P25L mutation in KRT5, commonly associated with this subtype.

CONCLUSIONS

This study further confirms the genotype-phenotype correlation established for EBS in other ethnic groups, and is the first in a Mediterranean country (excluding Israel). This study adds two novel recessive mutations to the worldwide record to date, which includes a total of 14 mutations. As in previous reports, the recessive mutations resulted in a lack of keratin K14, giving rise to a generalized and severe presentation.

Regulation of keratin expression by retinoids

Vitamin A and its natural and synthetic metabolites (retinoids) affect growth and differentiation of human skin and among the genes affected by retinoids in epidermis are keratin genes. Keratins are intermediate filament proteins that have essential functions in maintaining the structural integrity of epidermis and its appendages. Their expressions are under strict control to produce keratins that are optimally adapted to their environment. In this article, retinoid regulation of keratin expression in cultured human epidermal keratinocytes and in human skin in vivo will be reviewed. The direct and indirect mechanisms involved will be discussed and novel therapeutic strategies will be proposed for utilizing retinoids in skin disorders due to keratin mutations (e.g., epidermolysis bullosa simplex and epidermolytic ichthyosis).

E1--E4-mediated keratin phosphorylation and ubiquitylation: a mechanism for keratin depletion in HPV16-infected epithelium

The keratin IF network of epidermal keratinocytes provides a protective barrier against mechanical insult, it is also a major player in absorbing stress in these cells. The human papilloma virus (HPV) type 16 E1--E4 protein accumulates in the upper layers of HPV16-infected epithelium and is known to associate with and reorganise the keratin IF network in cells in culture. Here, we show that this function is conserved amongst a number of HPV alpha-group E1--E4 proteins and that the differentiation-dependent keratins are also targeted. Using time-lapse microscopy, HPV16 E1--E4 was found to effect a dramatic cessation of keratin IF network dynamics by associating with both soluble and insoluble keratin. Network disruption was accompanied by keratin hyperphosphorylation at several sites, including K8 S73, which is typically phosphorylated in response to stress stimuli. Keratin immunoprecipitated from E1--E4-expressing cells was also found to be ubiquitylated, indicating that it is targeted for proteasomal degradation. Interestingly, the accumulation of hyperphosphorylated, ubiquitylated E1--E4-keratin structures was found to result in an impairment of proteasomal function. These observations shed new light on the mechanism of keratin IF network reorganisation mediated by HPV16 E1--E4 and provide an insight into the depletion of keratin co-incident with E1--E4 accumulation observed in HPV-infected epithelium.

Differential Proteomics Identifies Protein Biomarkers That Predict Local Relapse of Head and Neck Squamous Cell Carcinomas

PURPOSE: The 5-year survival rates of head and neck squamous cell carcinomas (HNSCC) remain disappointing. HNSCCs develop in precursor fields of genetically altered cells that are often not completely resected when the tumor is excised, causing local relapse. These precursor fields are mostly recognized as dysplasia, but histologic grading cannot reliably predict malignant transformation. Our aim was to discover and validate protein biomarkers that can detect precursor fields and predict local relapse in HNSCC using immunostaining of surgical margins. EXPERIMENTAL DESIGN: We compared paired and genetically characterized normal, precursor, and tumor tissues of eight patients by proteome analysis to identify differentially expressed proteins. The prognostic value of candidate protein biomarkers was evaluated by immunohistochemical analysis of 222 surgical margins of 46 HNSCC patients who developed local relapse or remained disease free. Significant associations were determined by Kaplan-Meier survival analysis and Cox-proportional hazards models. RESULTS: Forty proteins showed significant differential expression (false discovery rate-corrected P < 0.05). Most discriminative markers suited for immunostaining were keratin 4 and cornulin. Low expression in the surgical margins of keratin 4 (hazard ratio, 3.8; P = 0.002), cornulin (hazard ratio, 2.7; P = 0.025), and their combination (hazard ratio, 8.8; P = 0.0005) showed a highly significant association with the development of local relapse. Dysplasia grading had no prognostic relevance. CONCLUSIONS: Immunohistochemical assessment of keratin 4 and cornulin expression in surgical margins of HNSCC patients outperforms histopathologic grading in predicting the risk for local relapse. These markers can be used to initiate more frequent and lifelong surveillance of patients at high risk of local relapse, and enable selection for adjuvant treatment or tertiary prevention trials. (Clin Cancer Res 2009;15(24):7666-75).

Aberrant cytokeratin expression during arsenic-induced acquired malignant phenotype in human HaCaT keratinocytes consistent with epidermal carcinogenesis

Inorganic arsenic is a known human skin carcinogen. Chronic arsenic exposure results in various human skin lesions, including hyperkeratosis and squamous cell carcinoma (SCC), both characterized by distorted cytokeratin (CK) production. Prior work shows the human skin keratinocyte HaCaT cell line, when exposed chronically for >25 weeks to a low level of inorganic arsenite (100nM) results in cells able to produce aggressive SCC upon inoculation into nude mice. In the present study, CK expression analysis was performed in arsenic-exposed HaCaT cells during the progressive acquisition of this malignant phenotype (0-20 weeks) to further validate this model as relevant to epidermal carcinogenesis induced by arsenic in humans. Indeed, we observed clear evidence of acquired cancer phenotype by 20 weeks of arsenite exposure including the formation of giant cells, a >4-fold increase in colony formation in soft agar and a approximately 2.5-fold increase in matrix metalloproteinase-9 secretion, an enzyme often secreted by cancer cells to help invade through the local extra-cellular matrix. During this acquired malignant phenotype, various CK genes showed markedly altered expression at the transcript and protein levels in a time-dependent manner. For example, CK1, a marker of hyperkeratosis, increased up to 34-fold during arsenic-induced transformation, while CK13, a marker for dermal cancer progression, increased up to 45-fold. The stem cell marker, CK15, increased up to 7-fold, particularly during the later stages of arsenic exposure, indicating a potential emergence of cancer stem-like cells with arsenic-induced acquired malignant phenotype. The expression of involucrin and loricrin, markers for keratinocyte differentiation, increased up to 9-fold. Thus, during arsenic-induced acquired cancer phenotype in human keratinocytes, dramatic and dynamic alterations in CK expression occur which are consistent with the process of epidermal carcinogenesis helping validate this as an appropriate model for the study of arsenic-induced skin cancer.

Keratinocyte-specific Smad2 ablation results in increased epithelial-mesenchymal transition during skin cancer formation and progression

TGF-beta and its signaling mediators, Smad2, -3, and -4, are involved with tumor suppression and promotion functions. Smad4-/- mouse epidermis develops spontaneous skin squamous cell carcinomas (SCCs), and Smad3-/- mice are resistant to carcinogen-induced skin cancer; however, the role of Smad2 in skin carcinogenesis has not been explored. In the present study, we found that Smad2 and Smad4, but not Smad3, were frequently lost in human SCCs. Mice with keratinocyte-specific Smad2 deletion exhibited accelerated formation and malignant progression of chemically induced skin tumors compared with WT mice. Consistent with the loss of Smad2 in poorly differentiated human SCCs, Smad2-/- tumors were poorly differentiated and underwent epithelial-mesenchymal transition (EMT) prior to spontaneous Smad4 loss. Reduced E-cadherin and activation of its transcriptional repressor Snail were also found in Smad2-/- mouse epidermis and occurred more frequently in Smad2-negative human SCCs than in Smad2-positive SCCs. Knocking down Snail abrogated Smad2 loss-associated EMT, suggesting that Snail upregulation is a major mediator of Smad2 loss-associated EMT. Furthermore, Smad2 loss led to a significant increase in Smad4 binding to the Snail promoter, and knocking down either Smad3 or Smad4 in keratinocytes abrogated Smad2 loss-associated Snail overexpression. Our data suggest that enhanced Smad3/Smad4-mediated Snail transcription contributed to Smad2 loss-associated EMT during skin carcinogenesis.

NG2 proteoglycan expression in mouse skin: altered postnatal skin development in the NG2 null mouse

In early postnatal mouse skin, the NG2 proteoglycan is expressed in the subcutis, the dermis, the outer root sheath of hair follicles, and the basal keratinocyte layer of the epidermis. With further development, NG2 is most prominently expressed by stem cells in the hair follicle bulge region, as also observed in adult human skin. During telogen and anagen phases of the adult hair cycle, NG2 is also found in stem cell populations that reside in dermal papillae and the outer root sheaths of hair follicles. Ablation of NG2 produces alterations in both the epidermis and subcutis layers of neonatal skin. Compared with wild type, the NG2 null epidermis does not achieve its full thickness due to reduced proliferation of basal keratinocytes that serve as the stem cell population in this layer. Thickening of the subcutis is also delayed in NG2 null skin due to deficiencies in the adipocyte population.

Identification of a Keratin 4 Mutation in a Chemically Induced Mouse Mutant that Models White Sponge Nevus

With the goal of increasing the number of genetic entry points for studying physiologic processes and human disease, large-scale, systematic, chemical mutagenesis projects in mice have been initiated in several different centers. We have been studying mouse mutants that exhibit dominantly inherited defects in either skin and/or hair color. Here, we describe a bright coat color mutant, Bright coat color 1 (Bcc1), which develops light-colored hair at 4 weeks of age, and when homozygous exhibits oral leukoplakia and blistering, and growth retardation. We identified a missense mutation in mutant animals that predicts an N154S amino-acid substitution in the 1A domain of Keratin 4 (encoded by the Krt2-4 gene), a region known to be mutated in human patients with white sponge nevus (WSN). Bcc1 recapitulates the gross pathologic, histologic, and genetic aspects of the human disorder, WSN.

Naegeli-Franceschetti-Jadassohn syndrome and dermatopathia pigmentosa reticularis: two allelic ectodermal dysplasias caused by dominant mutations in KRT14

Naegeli-Franceschetti-Jadassohn syndrome (NFJS) and dermatopathia pigmentosa reticularis (DPR) are two closely related autosomal dominant ectodermal dysplasia syndromes that clinically share complete absence of dermatoglyphics (fingerprint lines), a reticulate pattern of skin hyperpigmentation, thickening of the palms and soles (palmoplantar keratoderma), abnormal sweating, and other subtle developmental anomalies of the teeth, hair, and skin. To decipher the molecular basis of these disorders, we studied one family with DPR and four families with NFJS. We initially reassessed linkage of NFJS/DPR to a previously established locus on 17q11.2-q21. Combined multipoint analysis generated a maximal LOD score of 8.3 at marker D17S800 at a recombination fraction of 0. The disease interval was found to harbor 230 genes, including a large cluster of keratin genes. Heterozygous nonsense or frameshift mutations in KRT14 were found to segregate with the disease trait in all five families. In contrast with KRT14 mutations affecting the central alpha -helical rod domain of keratin 14, which are known to cause epidermolysis bullosa simplex, NFJS/DPR-associated mutations were found in a region of the gene encoding the nonhelical head (E1/V1) domain and are predicted to result in very early termination of translation. These data suggest that KRT14 plays an important role during ontogenesis of dermatoglyphics and sweat glands. Among other functions, the N-terminal part of keratin molecules has been shown to confer protection against proapoptotic signals. Ultrastructural examination of patient skin biopsy specimens provided evidence for increased apoptotic activity in the basal cell layer where KRT14 is expressed, suggesting that apoptosis is an important mechanism in the pathogenesis of NFJS/DPR.

A mutation in the hair matrix and cuticle keratin KRTHB5 gene causes ectodermal dysplasia of hair and nail type

BACKGROUND

Ectodermal dysplasias are developmental disorders affecting tissues of ectodermal origin. To date, four different types of ectodermal dysplasia involving only hair and nails have been described. In an effort to understand the molecular bases of this form of ectodermal dysplasia, large Pakistani consanguineous kindred with multiple affected individuals has been ascertained from a remote region in Pakistan.

OBJECTIVE

To identify the gene underlying the phenotype.

METHODS

Microsatellite markers were genotyped in candidate regions and two point and multipoint parametric linkage analysis carried out.

RESULTS

The disease locus was mapped to a 16.6 centimorgan region on chromosome 12q12-q14.1 (Zmax = 8.2), which harbours six type II hair keratin genes. DNA sequence analysis revealed a homozygous missense mutation in the hair matrix and cuticle keratin KRTHB5, leading to histidine substitution of a conserved arginine residue (R78H) located in the head domain.

CONCLUSIONS

This report provides the first direct evidence relating to the molecular pathogenesis of pure hair-nail ectodermal dysplasias.

What is the biological basis of pattern formation of skin lesions?

Pattern recognition is at the heart of clinical dermatology and dermatopathology. Yet, while every practitioner of the art of dermatological diagnosis recognizes the supreme value of diagnostic cues provided by defined patterns of 'efflorescences', few contemplate on the biological basis of pattern formation in and of skin lesions. Vice versa, developmental and theoretical biologists, who would be best prepared to study skin lesion patterns, are lamentably slow to discover this field as a uniquely instructive testing ground for probing theoretical concepts on pattern generation in the human system. As a result, we have at best scraped the surface of understanding the biological basis of pattern formation of skin lesions, and widely open questions dominate over definitive answer. As a symmetry-breaking force, pattern formation represents one of the most fundamental principles that nature enlists for system organization. Thus, the peculiar and often characteristic arrangements that skin lesions display provide a unique opportunity to reflect upon--and to experimentally dissect--the powerful organizing principles at the crossroads of developmental, skin and theoretical biology, genetics, and clinical dermatology that underlie these--increasingly less enigmatic--phenomena. The current 'Controversies' feature offers a range of different perspectives on how pattern formation of skin lesions can be approached. With this, we hope to encourage more systematic interdisciplinary research efforts geared at unraveling the many unsolved, yet utterly fascinating mysteries of dermatological pattern formation. In short: never a dull pattern!

Heavy water labeling of keratin as a non-invasive biomarker of skin turnover in vivo in rodents and humans

Measurement of skin turnover has been problematic in humans. Heavy water (2H2O) labeling has recently been developed as a safe, simple method to study in vivo kinetics of many biosynthetic processes, including DNA and protein synthesis. Here, we apply this approach to the measurement of 2H incorporation into skin keratin and show close agreement between keratin and keratinocyte turnover data in the epidermis of rodents. Elevated turnover rates of both keratin and keratinocytes were observed in the epidermis of the flaky skin mouse, although topical treatments effective in human psoriasis had no effect on either turnover rate in these mice. In humans, keratin turnover was monitored non-invasively by serial tape stripping during and after 2H2O labeling. Kinetic data were consistent with previous estimates of epidermal turnover, with a lag time of 18 days before label appeared at the skin surface and a transit time of 4-5 weeks. Variability in skin keratin turnover rates was present among healthy individuals. In summary, 2H2O labeling of skin keratin represents a non-invasive approach for assessing skin turnover dynamics in pre-clinical models and in human subjects.

Epidermolysis bullosa simplex: recurrent and de novo mutations in the KRT5 and KRT14 genes, phenotype/genotype correlations, and implications for genetic counseling and prenatal diagnosis

Epidermolysis bullosa simplex (EBS) is a mechano-bullous disorder characterized by intraepidermal blistering within the basal keratinocytes as a result of trauma to the skin. As part of the DNA diagnostics program, our laboratory has analyzed a cohort of 57 patients with the initial referral diagnosis of EBS. Among these patients, 18 were found to harbor heterozygous mutations in the keratin 5 or keratin 14 genes, KRT5 and KRT14, respectively, whereas in 14 cases, the disease was associated with mutations in both alleles of the plectin gene. Among the keratin mutations, 12 were distinct and six were novel, and in most cases there was no family history of a blistering disease. Prenatal diagnosis of eight pregnancies with keratin gene mutations, at risk for EBS either because one of the parents was affected (three cases) or history of a previously affected child as a result of a de novo mutation (five cases), predicted two fetuses being affected and six being normal. No recurrence of the de novo mutations in these pregnancies was disclosed. Collectively, the data suggest that a significant number of cases diagnosed as EBS are due to plectin mutations, and many cases result from de novo mutations in KRT5 and KRT14 genes. These findings have implications for genetic counseling and prenatal diagnosis for EBS.