Frontiers in epidermal barrier homeostasis--an approach to mathematical modelling of epidermal calcium dynamics

Intact epidermal barrier function is crucial for survival and is associated with the presence of gradients of both calcium ion concentration and electric potential. Although many molecules, including ion channels and pumps, are known to contribute to maintenance of these gradients, the mechanisms involved in epidermal calcium ion dynamics have not been clarified. We have established that a variety of neurotransmitters and their receptors, originally found in the brain, are expressed in keratinocytes and are also associated with barrier homeostasis. Moreover, keratinocytes and neurons show some similarities of electrochemical behaviour. As mathematical modelling and computer simulation have been employed to understand electrochemical phenomena in brain science, we considered that a similar approach might be applicable to describe the dynamics of epidermal electrochemical phenomena associated with barrier homeostasis. Such methodology would also be potentially useful to address a number of difficult problems in clinical dermatology, such as ageing and itching. Although this work is at a very early stage, in this essay, we discuss the background to our approach and we present some preliminary results of simulation of barrier recovery.

Nuclear envelope localization of Ran-binding protein 2 and Ran-GTPase-activating protein 1 in psoriatic epidermal keratinocytes

The nuclear localization signal (NLS)-containing proteins LEDGF and STAT3 localize to the nucleus in both the spinous and basal layers of the epidermis in psoriatic skin, where they function as transcription factors or co-factors to activate epidermal keratinocytes (KCs). However, the mechanism underlying the localization of these proteins remains to be elucidated. We investigated the differential nucleocytoplasmic transport of NLS-containing proteins as a potential pathogenic mechanism for psoriasis vulgaris. Nucleoporins play an important role in the Ran-GTP-dependent nucleocytoplasmic transport of NLS-containing proteins. We showed, using immunohistochemical staining, that the nucleoporins Ran-binding protein 2 (RanBP2) and Ran-GTPase-activating protein 1 (RanGAP1) have greater expression on the nuclear envelope in psoriatic epidermal KCs than in KCs from healthy controls. We then studied the signalling pathways involved in the regulation of these proteins in HaCaT cells. The two major downstream pathways of epidermal growth factor receptor (EGFR) signalling activated in psoriatic KCs are the MAPK/Erk/1/2 and the phosphatidylinositol-3-kinase/Akt pathways. Therefore, we treated HaCaT cells with inhibitors to disrupt the MAP kinase kinase 1 (MEK1), PI3-kinase, or mTOR pathways. RanBP2 and RanGAP1 protein expression levels were significantly greater in the nuclear envelope of HaCaT cells that were not treated with inhibitors than in cells treated with a combination of PI3-kinase and MEK1 inhibitors or mTOR and MEK1 inhibitors. These results suggest that adequate nuclear envelope expression of RanBP2 and RanGAP1 could be a prerequisite for nucleocytoplasmic transport in KCs in psoriatic epidermis.

Differential expression of transglutaminase genes in patients with chronic periodontitis

OBJECTIVE

Gingival epithelium plays a key role in the protection of oral tissues from microbial challenge, especially during the periodontal disease. This study was aimed to evaluate levels of mRNA transcripts of different forms of transglutaminase in the human gingival tissues from patients with chronic periodontitis and relative controls.

SUBJECTS AND METHODS

This study included 22 patients with chronic periodontitis (CP) and 22 healthy controls. For each patient, the values of probing depth (PD), clinical attachment level (CAL), and bleeding on probing (BOP) were recorded. Gene expression of transglutaminase 1, transglutaminase 2, transglutaminase 3, and metalloprotease 2 was evaluated by real-time PCR, while that of Factor XIIIA and metalloprotease 9 by RT-PCR.

RESULTS

The values of all the clinical parameters were significantly higher in the CP group than in the healthy control group (P < 0.05). In the CP group, the mRNA expression of transglutaminase 1 and transglutaminase 3 was significantly decreased in comparison with healthy control group. A slight nonsignificant changes of transglutaminase 2 gene expression were observed in samples from CP patients in comparison with controls.

CONCLUSIONS

These observations suggest that transglutaminase gene expression may be modified in response to chronic injury in the damaged gingival and emphasizes the key role of these enzymes in gingival remodelling/healing and adaptive processes.

Human pigmentation: A side effect adapted from a primitive organism's survival. Part 2: The melanocyte as mentor of the keratinocye

Pigmentation featured millions of years ago and perhaps began with an amoeba frightening off a predator with some agent such as dopamine to prevent its attachment for phagocytosis by an enemy. This paper suggests that the environmental forces of grip and stick, rather than pure chemical influences, deserve greater emphasis, and that the influence of the mechanical forces involved in grip and stick or release from attachment, all point to control of proteases as a function underlying pigmentation. How and why pigmentation varies with temperature and sunlight is discussed. The toxicity of melanin, pH, transepidermal water loss, and the influence of endocrine factors are also addressed.

Chrysanthemum boreale Makino essential oil induces keratinocyte proliferation and skin regeneration

We investigated the effect of essential oil from the flower of Chrysanthemum boreale Makino (CBMEO) on growth of human keratinocytes (HaCaTs) and explored a possible mechanism for this response. CBMEO was extracted using the steam distillation method. CBMEO contained a total of 33 compounds. CBMEO stimulated HaCaT proliferation (EC50, 0.028 μg/mL) and also induced phosphorylation of Akt and ERK1/2 in HaCaTs (EC50, 0.007 and 0.005 μg/mL, for phosphorylated Akt and ERK1/2, respectively). Moreover, CBMEO promoted wound closure in the dorsal side skin of rat tail. This study demonstrated that CBMEO can stimulate growth of human skin keratinocytes, probably through the Akt and ERK1/2 pathways. Therefore, CBMEO may be helpful in skin regeneration and wound healing in human skin, and may also be a possible cosmetic material for skin beauty.

Immature truncated O-glycophenotype of cancer directly induces oncogenic features

Aberrant expression of immature truncated O-glycans is a characteristic feature observed on virtually all epithelial cancer cells, and a very high frequency is observed in early epithelial premalignant lesions that precede the development of adenocarcinomas. Expression of the truncated O-glycan structures Tn and sialyl-Tn is strongly associated with poor prognosis and overall low survival. The genetic and biosynthetic mechanisms leading to accumulation of truncated O-glycans are not fully understood and include mutation or dysregulation of glycosyltransferases involved in elongation of O-glycans, as well as relocation of glycosyltransferases controlling initiation of O-glycosylation from Golgi to endoplasmic reticulum. Truncated O-glycans have been proposed to play functional roles for cancer-cell invasiveness, but our understanding of the biological functions of aberrant glycosylation in cancer is still highly limited. Here, we used exome sequencing of most glycosyltransferases in a large series of primary and metastatic pancreatic cancers to rule out somatic mutations as a cause of expression of truncated O-glycans. Instead, we found hypermethylation of core 1 β3-Gal-T-specific molecular chaperone, a key chaperone for O-glycan elongation, as the most prevalent cause. We next used gene editing to produce isogenic cell systems with and without homogenous truncated O-glycans that enabled, to our knowledge, the first polyomic and side-by-side evaluation of the cancer O-glycophenotype in an organotypic tissue model and in xenografts. The results strongly suggest that truncation of O-glycans directly induces oncogenic features of cell growth and invasion. The study provides support for targeting cancer-specific truncated O-glycans with immunotherapeutic measures.

Using organotypic (raft) epithelial tissue cultures for the biosynthesis and isolation of infectious human papillomaviruses

Papillomaviruses have a strict tropism for epithelial cells, and they are fully reliant on cellular differentiation for completion of their life cycles, resulting in the production of progeny virions. Thus, a permissive environment for full viral replication in vitro-wherein virion morphogenesis occurs under cooperative viral and cellular cues-requires the cultivation of epithelium. Presented in the first section of this unit is a protocol to grow differentiating epithelial tissues that mimic many important morphological and biochemical aspects of normal skin. The technique involves growing epidermal cells atop a dermal equivalent consisting of live fibroblasts and a collagen lattice. Epithelial stratification and differentiation ensues when the keratinocyte-dermal equivalent is placed at the air-liquid interface. The apparent floating nature of the cell-matrix in this method led to the nickname "raft" cultures. The general technique can be applied to normal low passage keratinocytes, to cells stably transfected with papillomavirus genes or genomes, or keratinocytes established from neoplastic lesions. However, infectious papillomavirus particles have only been isolated from organotypic epithelial cultures initiated with cells that maintain oncogenic human papillomavirus genomes in an extrachomosomal replicative form. The second section of this unit is dedicated to a virion isolation method that minimizes aerosol and skin exposure to these human carcinogens. Although the focus of the protocols is on the growth of tissues that yields infectious papillomavirus progeny, this culture system facilitates the investigation of these fastidious viruses during their complex replicative cycles, and raft tissues can be manipulated and harvested at any point during the process. Importantly, a single-step virus growth cycle is achieved in this process, as it is unlikely that progeny virions are released to initiate subsequent rounds of infection.

Effects of low molecular weight soybean peptide on mRNA and protein expression levels of differentiation markers in normal human epidermal keratinocytes

Low molecular weight soybean peptide (LSP) was applied to normal human epidermal keratinocytes, and the results showed a significant increase in the gene expression levels of involucrin, transglutaminase, and profilaggrin. Filaggrin protein levels were also significantly higher. It is possible that LSP has an epidermal cell differentiation-promoting effect and may be able to regulate metabolism of the epidermis.

Effect of gamma-hydroxybutyrate on keratinocytes proliferation: A preliminary prospective controlled study in severe burn patients

BACKGROUND

Hypermetabolism and hyposomatotropism related to severe burns lead to impaired wound healing. Growth hormone (GH) boosts wound healing notably following stimulation of the production of insulin-like growth factor-1 (IGF1), a mitogen factor for keratinocytes. Gamma-hydroxybutyrate (GHB) stimulates endogenous GH secretion.

AIM

To assess effects of GHB sedation on keratinocytes proliferation (based on immunohistochemical techniques).

DESIGN

Monocentric, prospective, controlled trial.

MATERIALS AND METHODS

Patients (aging 18-65 years, burn surface area >30%, expected to be sedated for at least one month) were alternately allocated, at the 5(th) day following injury, in three groups according to the intravenous GHB dose administered for 21 days: Evening bolus of 50 mg/kg (Group B), continuous infusion at the rate of 10 mg/kg/h (Group C), or absence of GHB (Group P). They all received local standard cares. Immunohistochemistry (Ki67/MIB-1, Ulex europaeus agglutinin-1 and Mac 387 antibodies) was performed at D21 on adjacent unburned skin sample for assessing any keratinocyte activation. Serum IGF1 levels were measured at initiation and completion of the protocol.

STATISTICAL ANALYSIS

Categorical variables were compared with Chi-square test. Comparisons of medians were made using Kruskal-Wallis test. Post hoc analyses were performed using Mann-Whitney test with Bonferroni correction for multiple comparisons. A P < 0.05 was considered to be statistically significant.

RESULTS

A total of 14 patients completed the study (Group B: n = 5, Group C: n = 5, Group P: n = 4). Continuous administration of GHB was associated with a significant higher Ki67 immunolabeling at D21 (P = 0.049) and with a significant higher increase in the IGF1 concentrations at D21 (P = 0.024). No adverse effects were disclosed.

CONCLUSIONS

Our preliminary data support a positive effect of GHB on keratinocyte proliferation and are encouraging enough to warrant large prospective studies.

Human pigmentation: A side effect adapted from a primitive organism's survival, acting through cell attachment with an affinity for the keratinocyte and for elastin: Part I

Pigmentation featured millions of years ago and perhaps began with an amoeba frightening off a predator with some agent such as dopamine to prevent its attachment for phagocytosis by an enemy. This paper suggests that the environmental forces of grip and stick deserve greater emphasis and that mechanical forces involved in grip and stick or release from attachment, all point to control of proteases underlying pigmentation. There is an affinity for elastin as a pathway for melanin to exit its peripheral location in the epidermis into lymphatics and play a humeral role in defense mechanisms. The hair follicle follows the epidermal-dermal pattern of behavior with an affinity for elastin, a controlling function of melanin and through the bulge, an influence of mechanical forces and control by protease inhibitors.

Modulation of keratin 1, 10 and involucrin expression as part of the complex response of the human keratinocyte cell line HaCaT to ultraviolet radiation

Skin exposure to ultraviolet (UV) light evokes a complex stress response in keratinocytes. Keratin filament organization provides structural stability and mechanical integrity of keratinocytes. Involucrin is a transglutaminase substrate protein contributing to the formation of insoluble cornified envelopes. However, a more complex role for keratins and involucrin has been proposed, including the regulation of cell stress response. The aim was to evaluate modulations of keratin 1, 10 and involucrin expression in HaCaT in the light of the complex response of these cells to UV-B radiation, including effects on c-Jun and matrix metalloproteinase 1 (MMP-1) gene expression and production of interleukin (IL) 6 and 8. A UV-B (300±5 nm) dose of 10 mJ/cm² was selected since this dose resulted in a partial decrease in cell viability in contrast to higher UV-B doses, which induced complete cell death 48 h after treatment. The UV-B radiation induced significant expression of keratin 1 and 10 and decreased expression of involucrin. This was accompanied by increased expression of c-Jun and MMP-1 and IL-6 and IL-8 production. The data suggest that the expression of keratin 1, 10 and involucrin is modulated in HaCaT keratinocytes as a part of the complex stress response to UV radiation.

Nanostructured anti-bacterial poly-lactic-co-glycolic acid films for skin tissue engineering applications

Major issues faced with the use of today's skin grafts are infection, scar tissue formation, insufficient keratinocyte (or skin producing cells) proliferation and high production costs. To overcome these limitations, we propose here for the first time, a nanofeatured poly(lactide-co-glycolide) (PLGA) membrane as a next generation antibacterial skin graft material. An alkaline surface treatment method was used to create random nanofeatures on PLGA membranes where sodium hydroxide (NaOH) concentration and exposure times were altered to control surface morphology. Most significantly, and without the use of antibiotics, results showed a decrease in Staphylococcus aureus (a dangerous pathogen infecting skin grafts) growth for up to ∼40% after 2 days of culture on nanofeatured PLGA membranes compared to untreated controls. Results also showed that while bacteria growth was stunted, mammalian cell growth was not. Specifically, cell culture results showed an increase in human epidermal keratinocyte density, while the density of scar tissue forming human dermal fibroblasts, did not change on nanofeatured PLGA surfaces compared to the untreated controls after 3 days of culture. These findings indicate that the alkaline treatment of PLGA membranes is a promising quick and effective manner to limit scar tissue formation and bacterial invasion while increasing skin cell proliferation for improving numerous wound-healing applications.

Novel method for isolating human melanoblasts from keratinocyte culture

The characterization of melanoblasts is important for understanding their in vivo development, melanoma formation, and pigment-related disorders. However, no methods have been reported for the isolation of melanoblasts from human skin. Using a 'calcium-pulse' technique, involving the differentiation of human keratinocytes with high calcium and the subsequent spontaneous separation of the epidermal sheets, we effectively isolated human melanoblasts (keratinocyte-adapted melanoblasts, KaMBs) from keratinocyte culture. The KaMBs expressed early melanogenesis-related genes, including BRN2, which is a known melanoblast marker. Moreover, the KaMBs displayed much higher proliferative and growth capacities than the primary melanocytes. Considering that keratinocytes might provide an in vivo-like environment for KaMBs during isolation and in vitro culture, the 'calcium-pulse' technique offers an unprecedented, easy, and efficient method for the isolation of human melanoblasts, retaining the original characteristics of these cells.

Human keratinocyte cultures in the investigation of early steps of human papillomavirus infection

Human papillomaviruses (HPVs) are non-enveloped DNA viruses that are highly tropic for mucosal and cutaneous epithelia. The HPV life cycle is tightly linked to epithelial cell differentiation, where HPVs only infect the basal proliferating keratinocytes, and progeny virus assembly and release only occurs in differentiated upper-layer keratinocytes. Therefore, human keratinocyte monolayer cultures provide a useful model to study the early stages of HPV infection. However, previous reports have shown some conflicting results of virus-host interactions during HPV entry, which may be partly attributable to the different cell culture models used to examine these steps of HPV infection. Thus, there is a need to have a standardized in vitro model system to study virus-host interactions during HPV entry. Here, we describe the three most widely accepted keratinocyte models for studying HPV infection: primary human foreskin keratinocytes, normal immortalized keratinocytes, and transformed HaCaT keratinocytes. We also describe methods to genetically manipulate these cells, enabling the study of candidate host genes that may be important during HPV infection. Lastly, we outline simple and robust methods to assay HPV infectivity, which can be used to determine whether knockdown or overexpression of a particular gene affects HPV entry.

Immunology of psoriasis

The skin is the front line of defense against insult and injury and contains many epidermal and immune elements that comprise the skin-associated lymphoid tissue (SALT). The reaction of these components to injury allows an effective cutaneous response to restore homeostasis. Psoriasis vulgaris is the best-understood and most accessible human disease that is mediated by T cells and dendritic cells. Inflammatory myeloid dendritic cells release IL-23 and IL-12 to activate IL-17-producing T cells, Th1 cells, and Th22 cells to produce abundant psoriatic cytokines IL-17, IFN-γ, TNF, and IL-22. These cytokines mediate effects on keratinocytes to amplify psoriatic inflammation. Therapeutic studies with anticytokine antibodies have shown the importance of the key cytokines IL-23, TNF, and IL-17 in this process. We discuss the genetic background of psoriasis and its relationship to immune function, specifically genetic mutations, key PSORS loci, single nucleotide polymorphisms, and the skin transcriptome. The association between comorbidities and psoriasis is reviewed by correlating the skin transcriptome and serum proteins. Psoriasis-related cytokine-response pathways are considered in the context of the transcriptome of different mouse models. This approach offers a model for other inflammatory skin and autoimmune diseases.

The functional relevance of polyploidization in the skin

Cell proliferation and differentiation are tightly coupled through the regulation of the cell division cycle. To preserve specific functional properties in differentiated cells, distinct variants of the basic mitotic cell cycle are used in various mammalian tissues, leading to the formation of polyploid cells. In this issue of Experimental Dermatology, Gandarillas and Freije discuss the evidences for polyploidization in keratinocytes, a process whose physiological relevance is now becoming evident. A better evaluation of these unconventional cell cycles is required not only to improve our understanding of the development and structure of the epidermis but also for future therapies against skin diseases.

Expression of midkine in normal human skin, dermatitis and neoplasms: association with differentiation of keratinocytes

Midkine is a 13-kDa heparin-binding growth factor. It promotes growth, survival, migration and gene expression of various target cells and play roles in many diseases. In normal adult tissues, midkine expression is highly restricted; however, midkine expression levels are high in various malignant tumors. The major biological roles of midkine can be categorized into three areas, namely, the nervous system, cancer and inflammation. Thus far, midkine has not been studied extensively in diseased human skin. We performed immunohistochemistry tests by using anti-midkine antibodies to study the expression of midkine in normal skin and skin samples of 26 different cutaneous diseases. In addition, we investigated the expression pattern of the midkine gene in cultured keratinocytes. In normal skin, midkine expression was observed in the secretory coils of the eccrine sweat glands, outer root sheath and inner root sheath. Among the cutaneous tumors, the majority of keratinocyte-derived neoplasms were positive for midkine. Tumors that were not derived from keratinocytes were negative for midkine. In cultured keratinocytes, the midkine gene was expressed earlier than the genes required for keratinization, for example, cytokeratin 10 and transglutaminase 1. Because midkine is expressed in the keratinized areas of normal skin, neoplasms and inflammation, it may play a role as a modulator of keratinization in the skin.

Upregulation of miR-18a-5p contributes to epidermal necrolysis in severe drug eruptions

BACKGROUND

Toxic epidermal necrolysis (TEN) is a severe drug-induced cutaneous reaction. Although one of the primary histologic features of TEN is keratinocyte apoptosis, its exact mechanism remains unknown.

OBJECTIVES

We investigated the role of microRNAs (miRNAs) in the pathogenesis of severe drug eruptions and evaluated the possibility that miRNA can be a disease marker.

METHODS

miRNAs were extracted from tissues and sera of patients. PCR array analyses were performed to identify pathogenic miRNAs. The results were confirmed with quantitative real-time PCR, in situ hybridization, transient transfection of small interfering RNAs or miRNA mimics into cultured keratinocytes, flow cytometry, immunoblotting, luciferase assay, and immunohistochemistry.

RESULTS

PCR array analysis and real-time PCR using tissue miRNAs demonstrated that the miR-18a-5p level was increased in the skin of patients with TEN in vivo. Transfection of the miR-18a-5p mimic into keratinocytes in vitro resulted in increased apoptotic cell numbers and caspase-9 activity, which were also increased in the skin of patients with TEN. The miR-18a-5p mimic also downregulated the expression of B-cell lymphoma/leukemia-2-like protein 10 (BCL2L10), an anti-intrinsic apoptotic molecule. A luciferase assay with the BCL2L10 3' untranslated region showed BCL2L10 is directly targeted by miR-18a-5p. The protein and mRNA expressions of BCL2L10 were decreased in the skin of patients with TEN. Transfection with BCL2L10 small interfering RNA induced keratinocyte apoptosis and caspase activity. Furthermore, serum miR-18a-5p levels tended to be increased in patients with TEN and were correlated with areas of skin erythema or erosion in patients with drug eruptions.

CONCLUSIONS

Our results indicated that downregulated BCL2L10 caused by miR-18a-5p overexpression mediates intrinsic keratinocyte apoptosis in patients with TEN. Serum miR-18a-5p levels can be a useful disease marker for drug eruptions.

Activation of transient receptor potential melastatin 8 reduces ultraviolet B-induced prostaglandin E2 production in keratinocytes

Transient receptor potential melastatin 8 (TRPM8) is a member of the TRP family, and is activated at temperatures below 22°C, or by cooling compounds such as menthol. In this study, it was found that a new role of TRPM8 activation on prostaglandin E2 (PGE2), an inflammatory cytokine and dendritogenesis stimulator of normal human melanocytes. Normal human keratinocytes were pretreated with menthol or incubated at 22°C for TRPM8 activation before ultraviolet (UV)-B irradiation. To examine the specificity between TRPM8 activation and PGE2 release, we inhibited TRPM8 with the antagonist (capsazepine), or introduced TRPM8 siRNA for a gene silencing experiment. UV-B irradiation significantly induced PGE2 release in normal human keratinocytes. Interestingly, activation of TRPM8 at 22°C or with menthol inhibited UV-B-induced PGE2 release. The effect of the TRPM8 agonist was completely blocked by pretreatment with the TRPM8 antagonist, capsazepine. When TRPM8 expression was suppressed by siRNA, UV-B irradiation still upregulated PGE2 in keratinocytes, but pretreatment of menthol or low temperature did not inhibit UV-B-induced PGE2. In conclusion, the activation of TRPM8 inhibits UV-B-induced PGE2 production in keratinocytes, and the activation of TRPM8 may reduce inflammatory responses in skin.

Histamine induces proliferation in keratinocytes from patients with atopic dermatitis through the histamine 4 receptor

BACKGROUND

Epidermal hyperproliferation resulting in acanthosis is an important clinical observation in patients with atopic dermatitis, and its underlying mechanisms are not completely understood.

OBJECTIVE

Because increased levels of histamine are present in lesional skin, we investigated the effect of histamine, especially with regard to histamine 4 receptor (H4R) activation, on the proliferation of human and murine keratinocytes.

METHODS

The expression of H4R on human and murine keratinocytes was detected by using real-time PCR. Keratinocyte proliferation was evaluated by using different in vitro cell proliferation assays, scratch assays, and measurement of the epidermal thickness of murine skin.

RESULTS

We detected H4R mRNA on foreskin keratinocytes and on outer root sheath keratinocytes; H4R mRNA was more abundant in keratinocytes from patients with atopic dermatitis compared with those from nonatopic donors. Stimulation of foreskin keratinocytes, atopic dermatitis outer root sheath keratinocytes, and H4R-transfected HaCaT cells with histamine and H4R agonist resulted in an increase in proliferation, which was blocked with the H4R-specific antagonist JNJ7777120. Abdominal epidermis of H4R-deficient mice was significantly thinner, and the in vitro proliferation of keratinocytes derived from H4R-deficient mice was lower compared with that seen in control mice. Interestingly, we only detected H4R expression on murine keratinocytes after stimulation with LPS and peptidoglycan.

CONCLUSION

H4R is highly expressed on keratinocytes from patients with atopic dermatitis, and its stimulation induces keratinocyte proliferation. This might represent a mechanism that contributes to the epidermal hyperplasia observed in patients with atopic dermatitis.

Dissecting the psoriasis transcriptome: inflammatory- and cytokine-driven gene expression in lesions from 163 patients

BACKGROUND

Psoriasis lesions are characterized by large-scale shifts in gene expression. Mechanisms that underlie differentially expressed genes (DEGs), however, are not completely understood. We analyzed existing datasets to evaluate genome-wide expression in lesions from 163 psoriasis patients. Our aims were to identify mechanisms that drive differential expression and to characterize heterogeneity among lesions in this large sample.

RESULTS

We identified 1233 psoriasis-increased DEGs and 977 psoriasis-decreased DEGs. Increased DEGs were attributed to keratinocyte activity (56%) and infiltration of lesions by T-cells (14%) and macrophages (11%). Decreased DEGs, in contrast, were associated with adipose tissue (63%), epidermis (14%) and dermis (4%). KC/epidermis DEGs were enriched for genes induced by IL-1, IL-17A and IL-20 family cytokines, and were also disproportionately associated with AP-1 binding sites. Among all patients, 50% exhibited a heightened inflammatory signature, with increased expression of genes expressed by T-cells, monocytes and dendritic cells. 66% of patients displayed an IFN-γ-strong signature, with increased expression of genes induced by IFN-γ in addition to several other cytokines (e.g., IL-1, IL-17A and TNF). We show that such differences in gene expression can be used to differentiate between etanercept responders and non-responders.

CONCLUSIONS

Psoriasis DEGs are partly explained by shifts in the cellular composition of psoriasis lesions. Epidermal DEGs, however, may be driven by the activity of AP-1 and cellular responses to IL-1, IL-17A and IL-20 family cytokines. Among patients, we uncovered a range of inflammatory- and cytokine-associated gene expression patterns. Such patterns may provide biomarkers for predicting individual responses to biologic therapy.

Enhancement of lysine acetylation accelerates wound repair

In physiopathological conditions, such as diabetes, wound healing is significantly compromised and chronic complications, including ulcers, may occur. In a mouse model of skin repair, we recently reported that wound treatment with Sirtuin activators and class I HDAC inhibitors induced keratinocyte proliferation and enhanced healing via a nitric oxide (NO) dependent mechanism. We observed an increase in total protein acetylation in the wound area, as determined by acetylation of α-tubulin and histone H3 Lysine 9. We reasoned that this process activated cell function as well as regulated gene expression to foster tissue repair. We report here that the direct activation of P300/CBP-associated factor (PCAF) by the histone acetylase activator pentadecylidenemalonate 1b (SPV-106) induced Lysine acetylation in the wound area. This intervention was sufficient to enhance repair process by a NO-independent mechanism. Hence, an impairment of PCAF and/or other GCN5 family acetylases may delay skin repair in physiopathological conditions.

Protective role of vitamin D signaling in skin cancer formation

Vitamin D sufficiency is associated with protection against malignancy in a number of tissues clinically, and a strong body of evidence from animal and cell culture studies supports this protective role. Cancers in the skin differ, however, in that higher serum levels of 25OHD are associated with increased basal cell carcinomas (BCC), the most common form of epidermal malignancy. This result may be interpreted as indicating the role of UVR (spectrum 280-320) in producing vitamin D in the skin as well as causing those DNA mutations and proliferative changes that lead to epidermal malignancies. Recent animal studies have shown that mice lacking the vitamin D receptor (VDR) are predisposed to developing skin tumors either from chemical carcinogens such as 7,12-dimethylbenzanthracene (DMBA) or chronic UVR exposure. Such studies suggest that vitamin D production and subsequent signaling through the VDR in the skin may have evolved in part as a protective mechanism against UVR induced epidermal cancer formation. In this manuscript we provide evidence indicating that vitamin D signaling protects the skin from cancer formation by controlling keratinocyte proliferation and differentiation, facilitating DNA repair, and suppressing activation of the hedgehog (Hh) pathway following UVR exposure. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Impaired nuclear translocation of glucocorticoid receptors: novel findings from psoriatic epidermal keratinocytes

Psoriasis is a chronic proliferative skin disease and is usually treated with topical glucocorticoids, which act through the glucocorticoid receptor (GR), a component of the physiological systems essential for immune responses, differentiation, and homeostasis. To investigate the possible role of GR in the pathogenesis of psoriasis, normal and psoriatic lesional skin were recruited. Firstly, the immunolocalization of GR in the skin and cultured epidermal keratinocytes were determined by immunofluorescence. In normal skin and cultured human epidermal keratinocytes, intracellular GR is localized in the nuclei, while in psoriatic skin and cultured keratinocytes, GR is in the cytoplasm. Next, we investigated possible factors associated with the cytoplasmic distribution. We found that VEGF and IFN-γ led to impaired nuclear translocation of GR through p53 and microtubule-inhibitor, vincristine, and inhibited nuclear uptake of GR in normal keratinocytes. In addition to dexamethasone, interleukin (IL)-13 was also able to transfer GR into nuclei of psoriatic keratinocytes. Furthermore, discontinuation of dexamethasone induced cytoplasmic retention of GR in normal keratinocytes. In contrast, energy depletion of normal epidermal keratinocytes did not change the nuclear distribution of GR. To confirm our findings in vivo, an imiquimod-induced psoriasis-like skin mouse model was included. IL-13 ameliorated (but vincristine exacerbated) the skin lesions on the mouse. Taken together, our findings define that impaired nuclear translocation of GR is associated with VEGF, IFN-γ, p53, and microtubule. Therapeutic strategies designed to accumulate GR in the nucleus, such as IL-13, may be beneficial for the therapy of psoriasis.

Rhcg1 and Rhbg mediate ammonia excretion by ionocytes and keratinocytes in the skin of zebrafish larvae: H+-ATPase-linked active ammonia excretion by ionocytes

In zebrafish, Rhcg1 was found in apical membranes of skin ionocytes [H⁺-ATPase-rich (HR) cells], which are similar to α-type intercalated cells in mammalian collecting ducts. However, the cellular distribution and role of Rhbg in zebrafish larvae have not been well investigated. In addition, HR cells were hypothesized to excrete ammonia against concentration gradients. In this study, we attempted to compare the roles of Rhbg and Rhcg1 in ammonia excretion by larval skin and compare the capability of skin cells to excrete ammonia against concentration gradients. Using in situ hybridization and immunohistochemistry, Rhbg was localized to both apical and basolateral membranes of skin keratinocytes. A scanning ion-selective electrode technique (SIET) was applied to measure the NH₄⁺ flux at the apical surface of keratinocytes and HR cells. Knockdown of Rhbg with morpholino oligonucleotides suppressed ammonia excretion by keratinocytes and induced compensatory ammonia excretion by HR cells. To compare the capability of cells to excrete ammonia against gradients, NH₄⁺ flux of cells was determined in larvae exposed to serial concentrations of external NH₄⁺. Results showed that HR cells excreted NH₄⁺ against higher NH₄⁺ concentration than did keratinocytes. Knockdown of the expression of either Rhcg1 or H⁺ -ATPase in HR cells suppressed the capability of HR cells.