Sulfur mustard induces differentiation in human primary keratinocytes: opposite roles of p38 and ERK1/2 MAPK

B-Raf inhibitor vemurafenib counteracts sulfur mustard-induced epidermal impairment through MAPK/ERK signaling

The chemical warfare agent sulfur mustard (SM) causes severe cutaneous lesions characterized by epidermal cell death, apoptosis, and inflammation. At present, the molecular mechanisms underlying SM-induced injury are not well understood, and there is no standard treatment protocol for SM-exposed patients. Here, we conducted a high-content screening of the Food and Drug Administration (FDA)-approved drug library of 1018 compounds against SM injury on an immortal human keratinocyte HaCaT cell line, focusing on cell survival. We found that the B-Raf inhibitor vemurafenib had an apparent therapeutic effect on HaCaT cells and resisted SM toxicity. Other tested B-Raf inhibitors, both type-I (dabrafenib and encorafenib) and type-II (RAF265 and AZ628), also exhibited potent therapeutic effects on SM-exposed HaCaT cells. Both SM and vemurafenib triggered extracellular signal-related kinase (ERK) activation. The therapeutic effect of vemurafenib in HaCaT cells during SM injury was ERK-dependent, indicating a specific role of ERK in keratinocyte regulatory mechanisms. Furthermore, vemurafenib partially improved cutaneous damage in a mouse ear vesicant model. Collectively, our results provide evidence that the B-Raf inhibitor vemurafenib is a potential therapeutic agent against SM injury, and oncogenic B-Raf might be an exciting new therapeutic target following exposure to mustard vesicating agents.

Impairment of endothelial progenitor cells function in patient with mustard gas intoxication

Background: Sulfur mustard (SM), also known as mustard gas, was first widely used in the Iraq-Iran. After SM exposure, the most prominent clinical signs are the development of extensive non-healing skin wounds and pulmonary signs, persisting over long time. Since the most frequent complications in SM-intoxicated patients are respiratory and dermatologic lesions, and with respect to the important role of endothelial progenitor cells (EPCs) in the pathophysiology of these lesion, we conducted this study to recognize the potential effects of SM on biological features of EPCs in patients exposed with this gas.Methods: In this study, 30 patients with the history of SM exposure during the Iran-Iraq war (1984-1988), 27 patients with pulmonary signs with no history of SM exposure and 20 healthy participants were included. Cell population and function of EPCs were assessed 4 years post-exposure. For this purpose, circulating EPCs (cEPCs) were harvested and cultivated, then the biological features of these cells, including migratory, proliferative, and tubulogenic activities were analyzed. We also measured serum antioxidants levels and mRNA levels of some proangiogenic factors in EPCs from SM-intoxicated patients.Results: Our results showed lesser number of cEPCs in patients exposed with SM, which was associated with decreased proliferative, migratory, and tubulogenic activity of these cells. Also, we found the lesser serum activity of SOD, GPX and MDA in the SM group than in the healthy control group.Conclusions: SM exposure resulted in decreased proliferation and migration of EPCs, which was associated with decreased tubule formation and angiogenic factors.

Skin sensitizing effects of sulfur mustard and other alkylating agents in accordance to OECD guidelines

Vesicants cause a multitude of cutaneous reactions like erythema, blisters and ulcerations. After exposure to sulfur mustard (SM) and related compounds, patients present dermal symptoms typically known for chemicals categorized as skin sensitizer (e.g. hypersensitivity and flare-up phenomena). However, although some case reports led to the assumption that SM and other alkylating compounds represent sensitizers, a comprehensive investigation of SM-triggered immunological responses has not been conducted so far. Based on a well-structured system of in chemico and in vitro test methods, the Organization for Economic Co-operation and Development (OECD) established procedures to categorize agents on their skin sensitizing abilities. In this study, the skin sensitizing potential of SM and three related alkylating agents (AAs) was assessed following the OECD test guidelines. Besides SM, investigated AAs were chlorambucil (CHL), nitrogen mustard (HN3) and 2-chloroethyl ethyl sulfide (CEES). The methods are described in detail in the EURL ECVAM DataBase service on ALternative Methods to animal experimentation (DB-ALM). In accordance to OECD recommendations, skin sensitization is a pathophysiological process starting with a molecular initiating step and ending with the in vivo outcome of an allergic contact dermatitis. This concept is called adverse outcome pathway (AOP). An AOP links an adverse outcome to various key events which can be assayed by established in chemico and in vitro test methods. Positive outcome in two out of three key events indicates that the chemical can be categorized as a skin sensitizer. In this study, key event 1 "haptenation" (covalent modification of epidermal proteins), key event 2 "activation of epidermal keratinocytes" and key event 3 "activation of dendritic cells" were investigated. Covalent modification of epidermal proteins measured by using the DPRA-assay provided distinct positive results for all tested substances. Same outcome was seen in the KeratinoSens assay, investigating the activation of epidermal keratinocytes. The h-CLAT assay performed to determine the activation of dendritic cells provided positive results for SM and CEES but not for CHL and HN3. Altogether, following OECD requirements, our results suggest the classification of all investigated substances as skin sensitizers. Finally, a tentative AOP for SM-induced skin sensitization is suggested.

Knock-down of filaggrin influences the mitogen-activated protein kinases signaling pathway in normal human epidermal keratinocytes

BACKGROUND

Filaggrin is an essential structural protein of the stratum corneum binding to the keratin intermediate filaments to form a dense protein-lipid matrix. However, the function of filaggrin in epidermal terminal differentiation is not completely understood.

AIM

To evaluate the effects of filaggrin on normal human epidermal keratinocytes (NHEKs) and to investigate the relevant mechanisms.

METHODS

Short hairpin RNA (shRNA) technology was used to knock-down filaggrin in normal human epidermal keratinocytes (NHEKs). Western blot and real-time quantitative PCR (qRT-PCR) were performed to detect expression of filaggrin, differentiation-related proteins and MAPK-related proteins.

RESULTS

Filaggrin was successfully knocked down in NHEKs (99% efficiency). We found that the lack of filaggrin significantly decreased the expression of some differentiation-related proteins, including Cytokeratin 5 protein, Cytokeratin 14 protein, ST14 protein and SPRR3 protein (P<0.05). In addition, filaggrin knock-down significantly decreased expression of p-p38, p-ERK1/2, p-JNK, p-Akt, and p-NF-κB in NHEKs.

CONCLUSION

Our study shows that filaggrin regulates epidermal terminal differentiation and impairs MAPK signaling pathway in normal human epidermal keratinocytes.

MAPK Pathway Involved in Epidermal Terminal Differentiation of Normal Human Epidermal Keratinocytes

Objective

To investigate the effect of mitogen-activated protein kinase (MAPK) signaling pathway in epidermal terminal differentiation.

Methods

The MAPK pathways (p38, ERK1/2, JNK) were inhibited by SB203580, PD98059, and SP600125 in normal human epidermal keratinocytes (NHEKs), respectively. Western blotting assays were performed to detect expression of filaggrin and differentiation-related proteins. The mRNA expressions of differentiation-related proteins were detected by real-time quantitative PCR (qRT-PCR).

Results

Inhibition of MAPK pathway by SB203580, PD98059, and SP600125 resulted in significant reduction of filaggrin expression in NHEKs. Inhibition of the p38 MAPK pathway decreased the expression of differentiation-related proteins (cytokeratin 5, cytokeratin 14, ST14, and SPRR3), Akt, and NF-κB. Inhibition of JNK also suppressed expression of cytokeratin 14, SPRR3, Akt, and NF-κB. However, inhibition of ERK1/2 merely decreased expression of SPRR3 and Akt.

Conclusion

MAPK pathways regulates epidermal terminal differentiation in NHEKs. The p38 signaling pathway plays an especially important role.

Sulfur mustard skin lesions: A systematic review on pathomechanisms, treatment options and future research directions

Sulfur mustard (SM) is a chemical warfare, which has been used for one hundred years. However, its exact pathomechanisms are still incompletely understood and there is no specific therapy available so far. In this systematic review, studies published between January 2000 and July 2017 involving pathomechanisms and experimental treatments of SM-induced skin lesions were analyzed to summarize current knowledge on SM pathology, to provide an overview on novel treatment options, and to identify promising targets for future research to more effectively counter SM effects. We suggest that future studies should focus on (I) systemic effects of SM intoxication due to its distribution throughout the body, (II) removal of SM depots that continuously release active compound contributing to chronic skin damage, and (III) therapeutic options that counteract the pleiotropic effects of SM.

Chemical warfare agents. Classes and targets

Synthetic toxic chemicals (toxicants) and biological poisons (toxins) have been developed as chemical warfare agents in the last century. At the time of their initial consideration as chemical weapon, only restricted knowledge existed about their mechanisms of action. There exist two different types of acute toxic action: nonspecific cytotoxic mechanisms with multiple chemo-biological interactions versus specific mechanisms that tend to have just a single or a few target biomolecules. TRPV1- and TRPA-receptors are often involved as chemosensors that induce neurogenic inflammation. The present work briefly surveys classes and toxicologically relevant features of chemical warfare agents and describes mechanisms of toxic action.

Neglected role of hydrogen sulfide in sulfur mustard poisoning: Keap1 S-sulfhydration and subsequent Nrf2 pathway activation

Sulfur mustard (SM) is a chemical warfare agent and a terrorism choice that targets various organs and tissues, especially lung tissues. Its toxic effects are tightly associated with oxidative stress. The signaling molecule hydrogen sulfide (H₂S) protects the lungs against oxidative stress and activates the NF-E2 p45-related factor 2 (Nrf2) pathway. Here, we sought to establish whether endogenous H₂S plays a role in SM induced lesion in mouse lungs and lung cells and whether endogenous H₂S plays the role through Nrf2 pathway to protect against SM-induced oxidative damage. Furthermore, we also explored whether activation of Nrf2 by H₂S involves sulfhydration of Kelch-like ECH-associated protein-1 (Keap1). Using a mouse model of SM-induced lung injury, we demonstrated that SM-induced attenuation of the sulfide concentration was prevented by NaHS. Concomitantly, NaHS attenuates SM-induced oxidative stress. We also found that H₂S enhanced Nrf2 nuclear translocation, and stimulated expression of Nrf2-targeted downstream protein and mRNA levels. Incubation of the lung cells with NaHS decreased SM-induced ROS production. Furthermore, we also found that H₂S S-sulfhydrated Keap1, which induced Nrf2 dissociation from Keap1, and enhanced Nrf2 nuclear translocation. Our data indicate that H₂S is a critical, however, being long neglected signal molecule in SM-induced lung injury.

Dysregulated function of normal human epidermal keratinocytes in the absence of filaggrin

The aim of the present study was to investigate the impact of filaggrin knockdown on the function of normal human epidermal keratinocytes (NHEKs). Filaggrin expression levels in NHEKs were knocked down by lentivirus (LV) encoding small hairpin RNA (shRNA), with control cells infected with nonsense shRNA or not infected. Cell migration and invasion were assayed using Transwell inserts, cell adhesion and proliferation by the Cell Counting kit-8 assay, and apoptosis and cell cycle progression by flow cytometry. shRNA efficiently suppressed expression of filaggrin protein. The LV group had significantly decreased cell migration, adhesion and proliferation, and increased apoptosis compared with the control groups (P=0.027). In addition, the proportion of cells in G₁ and G₂ phases were significantly increased in the LV group compared with control groups (P=0.018). The results of the present study demonstrate that filaggrin knockdown inhibits NHEK migration, adhesion and proliferation, promotes apoptosis and disturbs cell cycle progression.

The Mixture of Salvianolic Acids from Salvia miltiorrhiza and Total Flavonoids from Anemarrhena asphodeloides Attenuate Sulfur Mustard-Induced Injury

Sulfur mustard (SM) is a vesicating chemical warfare agent used in numerous military conflicts and remains a potential chemical threat to the present day. Exposure to SM causes the depletion of cellular antioxidant thiols, mainly glutathione (GSH), which may lead to a series of SM-associated toxic responses. MSTF is the mixture of salvianolic acids (SA) of Salvia miltiorrhiza and total flavonoids (TFA) of Anemarrhena asphodeloides. SA is the main water-soluble phenolic compound in Salvia miltiorrhiza. TFA mainly includes mangiferin, isomangiferin and neomangiferin. SA and TFA possess diverse activities, including antioxidant and anti-inflammation activities. In this study, we mainly investigated the therapeutic effects of MSTF on SM toxicity in Sprague Dawley rats. Treatment with MSTF 1 h after subcutaneous injection with 3.5 mg/kg (equivalent to 0.7 LD50) SM significantly increased the survival levels of rats and attenuated the SM-induced morphological changes in the testis, small intestine and liver tissues. Treatment with MSTF at doses of 60 and 120 mg/kg caused a significant (p<0.05) reversal in SM-induced GSH depletion. Gene expression profiles revealed that treatment with MSTF had a dramatic effect on gene expression changes caused by SM. Treatment with MSTF prevented SM-induced differential expression of 93.8% (973 genes) of 1037 genes. Pathway enrichment analysis indicated that these genes were mainly involved in a total of 36 pathways, such as the MAPK signaling pathway, pathways in cancer, antigen processing and presentation. These data suggest that MSTF attenuates SM-induced injury by increasing GSH and targeting multiple pathways, including the MAPK signaling pathway, as well as antigen processing and presentation. These results suggest that MSTF has the potential to be used as a potential therapeutic agent against SM injuries.

Upregulation of miR-203 and miR-210 affect growth and differentiation of keratinocytes after exposure to sulfur mustard in normoxia and hypoxia

Exposure of the skin to sulfur mustard (SM) results in long-term complications such as impaired tissue regeneration. Previous own studies in normal human epidermal keratinocytes (NHEK) treated with SM demonstrated reduced proliferation, premature differentiation and a restricted functionality of hypoxia-mediated signaling in the cells. Here, we investigated the involvement of microRNAs, miR-203 and miR-210, in these mechanisms. SM significantly upregulated the expression of miR-203 in NHEK when cultivated under normoxic and hypoxic conditions. SM had no effect on miR-210 under normoxia. However, miR-210 levels were greatly increased in NHEK when grown in hypoxia and further elevated upon exposure of the cells to SM. In normoxia and hypoxia, inhibition of miR-203 by transfection of NHEK with complementary oligonucleotides, anti-miR-203, attenuated the SM-induced impairment of metabolic activity and proliferation, and counteracted SM-promoted keratin-1 expression in these cells. Consistent ameliorating effects on dysregulated metabolic activity, proliferation and keratin-1 expression in SM-treated NHEK were obtained upon inhibition of miR-210 in these cells grown in hypoxia. Our findings provide evidence that miR-203 and miR-210 are key regulators in normal and SM-impaired keratinocyte functionality, and suggest potential usefulness of inhibitors against miR-203 and miR-210 for target-directed therapeutical intervention to improve re-epithelialization of SM-injured skin.

Impairment of hypoxia-induced HIF-1α signaling in keratinocytes and fibroblasts by sulfur mustard is counteracted by a selective PHD-2 inhibitor

Skin exposure to sulfur mustard (SM) provokes long-term complications in wound healing. Similar to chronic wounds, SM-induced skin lesions are associated with low levels of oxygen in the wound tissue. Normally, skin cells respond to hypoxia by stabilization of the transcription factor hypoxia-inducible factor 1 alpha (HIF-1α). HIF-1α modulates expression of genes including VEGFA, BNIP3, and MMP2 that control processes such as angiogenesis, growth, and extracellular proteolysis essential for proper wound healing. The results of our studies revealed that exposure of primary normal human epidermal keratinocytes (NHEK) and primary normal human dermal fibroblasts (NHDF) to SM significantly impaired hypoxia-induced HIF-1α stabilization and target gene expression in these cells. Addition of a selective inhibitor of the oxygen-sensitive prolyl hydroxylase domain-containing protein 2 (PHD-2), IOX2, fully recovered HIF-1α stability, nuclear translocation, and target gene expression in NHEK and NHDF. Moreover, functional studies using a scratch wound assay demonstrated that the application of IOX2 efficiently counteracted SM-mediated deficiencies in monolayer regeneration under hypoxic conditions in NHEK and NHDF. Our findings describe a pathomechanism by which SM negatively affects hypoxia-stimulated HIF-1α signaling in keratinocytes and fibroblasts and thus possibly contributes to delayed wound healing in SM-injured patients that could be treated with PHD-2 inhibitors.

Identification and validation of vesicant therapeutic targets using a high-throughput siRNA screening approach

Sulfur mustard [SM, bis-(2-chloroethyl) sulfide] is a highly reactive bifunctional alkylating agent that has been used as a vesicating agent in warfare scenarios to induce severe lung, skin, and eye injury. SM cutaneous lesions are characterized by both vesication and severe inflammation, but the molecular mechanisms that lead to these signs and symptoms are not well understood. There is a pressing need for effective therapeutics to treat this injury. An understanding of the molecular mechanisms of injury and identification of potential therapeutic targets is necessary for rational therapeutic development. We have applied a high-throughput small interfering RNA (siRNA) screening approach to the problem of SM cutaneous injury in an effort to meet these needs. Our siRNA screening efforts have initially focused on SM-induced inflammation in cutaneous injury since chronic inflammation after exposure appears to play a role in progressive clinical pathology, and intervention may improve clinical outcome. Also, targets that mitigate cellular injury should reduce the inflammatory response. Historical microarray data on this injury were mined for targets and pathways implicated in inflammation, and a siRNA library of 2,017 targets was assembled for screening. Primary screening and library deconvolution were performed using human HaCaT keratinocytes and focused on cell death and inflammatory markers as end points. Using this in vitro approach, we have identified and validated novel targets for the potential treatment of SM-induced cutaneous injury.

Knockdown of filaggrin influences the epidermal terminal differentiation via MAPK pathway in normal human epidermal keratinocytes

We aimed to gain further insight into the role of the MAPK signaling pathway in terminal differentiation of normal human epidermal keratinocytes (NHEKs) with filaggrin knockdown. Filaggrin expression was knocked down by shRNA technology and the MAPK pathways were inhibited by three different inhibitors in NHEKs. The associated mRNAs and proteins were investigated by RT-PCR and western blot. Filaggrin absence inhibited the expression of differentiation-associated proteins, and blocked the protein expression of p38 MAPK, ERK1/2, JNK, Akt and NF-κB. Moreover, inhibited p38 MAPK, instead of ERK1/2 or JNK, lead to decreases in the expressions of Akt, NF-κB, and differentiation- associated proteins. In conclusion, Filaggrin might affect the epidermal terminal differentiation mainly through the p38-MAPK, NF-κB and Akt pathways. ERK1/2 and JNK might also be involved in the process.

The antimicrobial protein S100A7/psoriasin enhances the expression of keratinocyte differentiation markers and strengthens the skin's tight junction barrier

BACKGROUND

S100A7/psoriasin is a member of the S100 protein family and is encoded in the epidermal differentiation complex, which contains genes for markers of epidermal differentiation. S100A7/psoriasin is overexpressed in hyperproliferative skin diseases, where it is believed not only to exhibit antimicrobial functions, but also to induce immunomodulatory activities, including chemotaxis and cytokine/chemokine production.

OBJECTIVES

To evaluate the effect of S100A7/psoriasin on keratinocyte differentiation and regulation of the tight junction (TJ) barrier.

METHODS

Expression of differentiation markers and TJ proteins in human keratinocytes was determined by real-time polymerase chain reaction and Western blot. The changes in TJ barrier function were assessed by transepithelial electrical resistance and paracellular permeability assays. Glycogen synthase kinase-3 (GSK-3) and mitogen-activated protein kinase (MAPK) activation was analysed by Western blot, whereas β-catenin and E-cadherin activation was evaluated by Western blot and immunofluorescence.

RESULTS

S100A7/psoriasin enhanced the expression of several differentiation markers and selectively increased the expression of TJ proteins (e.g. claudins and occludin), which are known to strengthen the TJ barrier. Furthermore, S100A7/psoriasin increased β-catenin and E-cadherin accumulation at cell-cell contact, and enhanced transepithelial electrical resistance while reducing the paracellular permeability of keratinocyte layers. The data suggest that S100A7/psoriasin-mediated regulation of the TJ barrier was via both the GSK-3 and MAPK pathways, as evidenced by the inhibitory effects of inhibitors for GSK-3 and MAPKs.

CONCLUSIONS

Our finding that S100A7/psoriasin regulates differentiation and strengthens TJ barrier function provides novel evidence that, in addition to antimicrobial and immunoregulatory activities, S100A7/psoriasin is involved in skin innate immunity.

Wnt5a/β-catenin signaling drives calcium-induced differentiation of human primary keratinocytes

It is well established that a gradient of extracellular calcium within the epidermis regulates the differentiation of keratinocytes. However, the molecular mechanisms implicated in this process are not fully understood. RNA interference of the calcium-sensing receptor (CaSR) showed that CaSR is essential in calcium-induced differentiation of normal human epidermal keratinocytes (NHEKs) by increasing the levels of free intracellular calcium, which upregulates the expression of Wnt5a but not Wnt3a, Wnt4, and Dkk-1 in the cells. Subsequently, autocrine Wnt5a promotes the differentiation of NHEKs, determined by increased biosynthesis of keratin-1 and loricrin, whereas proliferation is suppressed. Addition of both Wnt5a and calcium to NHEKs activated the Wnt/β-catenin signaling pathway as indicated by (i) increased stability of β-catenin in the cells, (ii) enhanced β-catenin transcriptional activity, demonstrated by a luciferase-based β-catenin-activated reporter assay, and (iii) augmented Wnt/β-catenin target gene expression. NHEKs depleted for β-catenin had a significantly reduced susceptibility to calcium-induced differentiation. Knockdown of axin 2, an antagonist of β-catenin stability, enhanced the biosynthesis of keratin-1 and loricrin in the cells. Our findings establish a directional crosstalk between CaSR and Wnt/β-catenin signaling in keratinocyte differentiation via Wnt5a that acts as an autocrine stimulus in this process.

Nitric oxide synthase gene transfer overcomes the inhibition of wound healing by sulfur mustard in a human keratinocyte in vitro model

Sulfur mustard (SM) is a chemical warfare agent that causes extensive skin injury. Previously we reported that SM exposure resulted in suppression of inducible nitric oxide synthase (iNOS) expression to inhibit the healing of scratch wounds in a cultured normal human epidermal keratinocyte (NHEK) model. Based on this finding, the present study was to use adenovirus-mediated gene transfer of iNOS to restore the nitric oxide (NO) supply depleted by exposure to SM and to evaluate the effect of NO on wound healing inhibited by SM in NHEKs. The effect of the iNOS gene transfer on iNOS protein expression and NO generation were monitored by Western blot and flow cytometry, respectively. Wound healing with or without the iNOS gene transfer after SM exposure was assessed by light and confocal microscopy. The iNOS gene transfer via adenovirus resulted in overexpression of the iNOS and an increase in NO production regardless of SM exposure in the NHEK model. The gene transfer was also effective in overcoming the inhibition of wound healing due to SM exposure leading to the promotion of wound closure. The findings in this study suggest that the iNOS gene transfer is a promising therapeutic strategy for SM-induced skin injury.