Neutral cysteine protease bleomycin hydrolase is essential for the breakdown of deiminated filaggrin into amino acids

Homocysteine Thiolactone Detoxifying Enzymes and Alzheimer's Disease

Elevated levels of homocysteine (Hcy) and related metabolites are associated with Alzheimer's disease (AD). Severe hyperhomocysteinemia causes neurological deficits and worsens behavioral and biochemical traits associated with AD. Although Hcy is precluded from entering the Genetic Code by proofreading mechanisms of aminoacyl-tRNA synthetases, and thus is a non-protein amino acid, it can be attached to proteins via an N-homocysteinylation reaction mediated by Hcy-thiolactone. Because N-homocysteinylation is detrimental to a protein's function and biological integrity, Hcy-thiolactone-detoxifying enzymes-PON1, BLMH, BPHL-have evolved. This narrative review provides an account of the biological function of these enzymes and of the consequences of their impairments, leading to the phenotype characteristic of AD. Overall, accumulating evidence discussed in this review supports a hypothesis that Hcy-thiolactone contributes to neurodegeneration associated with a dysregulated Hcy metabolism.

Prolyl Endopeptidase Is Involved in Filaggrinolysis and Cornification

FLG is a well-known biomarker of atopic dermatitis and skin dryness. Its full proteolysis (or filaggrinolysis) produces the major constituents of the natural moisturizing factor. Some proteases/peptidases remain to be identified in this multistep process. Mining 16 omics analyses, we identified prolyl endopeptidase (PREP) as a candidate peptidase. Indirect immunofluorescence and confocal analysis demonstrated its localization in the granular and deep cornified layers, where it colocalized with FLG. Tandem mass spectroscopy and fluorescent quenching activity assays showed that PREP cleaved several synthetic peptides derived from the FLG sequence, at the carboxyl side of an internal proline. Deimination of these peptides increased PREP enzymatic efficiency. Specific inhibition of PREP in reconstructed human epidermis using benzyloxycarbonyl-pro-prolinal induced the accumulation of FLG monomers. Downregulation of PREP expression in reconstructed human epidermis using RNA interference confirmed the impact of PREP on FLG metabolism and highlighted a more general role of PREP in keratinocyte differentiation. Indeed, quantitative global proteomic, western blotting, and RT-qPCR analyses showed a strong reduction in the expression of bleomycin hydrolase, known to be involved in filaggrinolysis, and of several other actors of cornification such as loricrin. Consequently, at the functional level, the transepidermal electric resistance was drastically reduced.

The stratum corneum barrier: impaired function in relation to associated lipids and proteins

The skin is the largest organ of the human body and is widely considered to be the first-line defense of the body, providing essential protection against mechanical, physical, and chemical damage. Keratinocytes are the primary cells of the outer layer of the epidermis, which acts as a mechanical and permeability barrier. The epidermis is a permanently renewed tissue where undifferentiated keratinocytes located at the basal layer proliferate and migrate to the overlying layers. Here we report that some components of keratinocytes affect the formation and differentiation of the stratum corneum, which is the most specialized layer of the epidermis.

Investigation of the Alternations in the Muscle Quality of Swimming Crab (Ovalipes punctatus) during Cold-Chain Transportation Using Physicochemical and TMT-Based Quantitative Proteomic Analysis

Physicochemical properties and protein alterations in Ovalipes punctatus during cold-chain transportation were examined via sensory scores, water-holding capacity (WHC), glucose (GLU) content, catalase (CAT) activity, urea nitrogen (UN) content, and tandem mass tag (TMT)-based proteomic analysis. The results revealed that sensory characteristics and texture of crab muscle deteriorated during transportation. Proteomic analysis revealed 442 and 470 different expressed proteins (DEPs) in crabs after 18 h (FC) and 36 h (DC) of transportation compared with live crabs (LC). Proteins related to muscle structure and amino acid metabolism significantly changed, as evidenced by the decreased WHC and sensory scores of crab muscle. Glycolysis, calcium signaling, and peroxisome pathways were upregulated in the FC/LC comparison, aligning with the changes in GLU content and CAT activity, revealing the stress response of energy metabolism and immune response in crabs during 0-18 h of transportation. The downregulated tricarboxylic acid (TCA) cycle and carcinogenesis-reactive oxygen species pathways were correlated with the decreasing trend in CAT activity, suggesting a gradual retardation in both energy and antioxidant metabolism in crabs during 18-36 h of transportation. Furthermore, the regulated purine nucleoside metabolic and nucleoside diphosphate-related processes, with the increasing changes in UN content, revealed the accumulation of metabolites in crabs.

Jianpi-Yangxue-Jiedu decoction improves the energy metabolism of psoriasis mice by regulating the electron transfer of oxidative phosphorylation

ETHNOPHARMACOLOGICAL RELEVANCE

The inflammatory skin condition psoriasis is immune-related. The decoction of Jianpi-Yangxue-Jiiedu (JPYX) is a useful medication for psoriasis. However, the underlying mechanics of JPYX have not yet been clarified.

AIM OF THE STUDY

The objective of this study was to investigate the mechanism underlying the efficacy of JPYX in the treatment of psoriasis in the context of a high-fat diet.

MATERIALS AND METHODS

This work generated a high-fat feeding model of imiquimod (IMQ)-induced psoriasis-like lesion mice. The blood composition of JPYX was examined using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The mechanism of JPYX decoction for treating psoriasis was predicted using methods of network pharmacology, metabolomics, and transcriptomics.

RESULTS

JPYX prevented the release of inflammatory cytokines, decreased keratinocyte proliferation, enhanced the percentage of Treg cells in the skin, lymph nodes, and thymus, and greatly alleviated psoriatic lesions. Network pharmacology predicted that IL-1β, TNF, STAT3, and EGFR may be potential targets, and KEGG results showed that PI3K-AKT-mTOR may be a potential mechanism of action. Verification of experimental data demonstrated that the JPYX decoction dramatically decreased mTOR and AKT phosphorylation. According to metabolomics analysis, amino acids and their metabolites, benzene and its substitutes, aldehyde ketone esters, heterocyclic compounds, etc. were the primary metabolites regulated by JPYX. KEGG enrichment analysis of differential metabolites was performed. Fatty acid biosynthesis, Type I polyketide structures, Steroid hormone biosynthesis, Biosynthesis of unsaturated fatty acid, etc. Transcriptomic results showed that JPYX significantly regulated skin development, keratinocyte differentiation, and oxidative phosphorylation. Further experimental data verification showed that JPYX decoction significantly reduced the mRNA levels of mt-Nd4, mt-Nd5, mt-Nd1, Ifi205, Ifi211, and mt-Atp8.

CONCLUSIONS

JPYX may improve psoriasis by regulating the metabolic pathways of fatty acids and electron transport of oxidative phosphorylation.

Functional properties and skin care effects of sodium trehalose sulfate

BACKGROUND

It is known that heparinoid, a mucopolysaccharide polysulfate, is effective in improving rough skin and promoting blood circulation as medicines for diseased areas. However, heparinoid has a molecular weight of more than 5000 and cannot penetrate healthy stratum corneum.

OBJECTIVE

We tested the efficacy of sulfated oligosaccharides with a molecular weight of less than 2000 on the human skin barrier function and moisturizing function.

METHODS

We measured the transepidermal water loss (TEWL) of a three-dimensional human epidermis model cultured for 3 days after topical application of sulfated oligosaccharides, then observed the effects on TEWL suppression. The mRNA levels of proteins involved in intercellular lipid transport and storage in the stratum corneum, and moisture retention were measured using RT-qPCR.

RESULTS

An increase in the mRNA levels of the ATP-binding cassette subfamily A member 12 (ABCA12), which transports lipids into stratum granulosum, was confirmed. Increases were also observed in the mRNA levels of filaggrin (FLG), which is involved in the generation of natural moisturizing factors, and of caspase-14, calpain-1 and bleomycin hydrolase, which are involved in the degradation of FLG. Antibody staining confirmed that the application of sodium trehalose sulfate to 3D model skin resulted in more ABCA12, ceramide, transglutaminase1, and FLG than those in controls. In a randomized, placebo-controlled, double-blind study, participants with low stratum corneum water content applied a lotion and emulsion containing sodium trehalose sulfate to their faces for 4 weeks. Sodium trehalose sulfate decreased the TEWL and increased the stratum corneum water content.

CONCLUSION

These results suggest that cosmetics containing sodium trehalose sulfate act on the epidermis by increasing barrier factors and moisturizing factors, thereby ameliorating dry skin.

Oat (Avena sativa L.) Sprouts Restore Skin Barrier Function by Modulating the Expression of the Epidermal Differentiation Complex in Models of Skin Irritation

Oats (Avena sativa L.) are used as therapeutic plants, particularly in dermatology. Despite numerous studies on their skin moisturization, anti-inflammation, and antioxidation effects, the precise molecular mechanisms of these effects are only partially understood. In this study, the efficacy of oat sprouts in the treatment of allergic contact dermatitis (ACD) was investigated, and their specific phytoconstituents and exact mechanisms of action were identified. In the in vivo ACD model, by stimulating the mitogen-activated protein kinase signaling pathway, oat sprouts increased the expression levels of proteins associated with skin barrier formation, which are produced during the differentiation of keratinocytes. In addition, in a lipopolysaccharide-induced skin irritation model using HaCaT, steroidal saponins (avenacoside B and 26-deglucoavenacoside B) and a flavonoid (isovitexin-2-o-arabinoside) of oat sprouts regulated the genetic expression of the same proteins located on the adjacent locus of human chromosomes known as the epidermal differentiation complex (EDC). Furthermore, oat sprouts showed immunomodulatory functions. These findings suggest the potential for expanding the use of oat sprouts as a treatment option for various diseases characterized by skin barrier disruption.

Skin Barrier Function: The Interplay of Physical, Chemical, and Immunologic Properties

An intact barrier function of the skin is important in maintaining skin health. The regulation of the skin barrier depends on a multitude of molecular and immunological signaling pathways. By examining the regulation of a healthy skin barrier, including maintenance of the acid mantle and appropriate levels of ceramides, dermatologists can better formulate solutions to address issues that are related to a disrupted skin barrier. Conversely, by understanding specific skin barrier disruptions that are associated with specific conditions, such as atopic dermatitis or psoriasis, the development of new compounds could target signaling pathways to provide more effective relief for patients. We aim to review key factors mediating skin barrier regulation and inflammation, including skin acidity, interleukins, nuclear factor kappa B, and sirtuin 3. Furthermore, we will discuss current and emerging treatment options for skin barrier conditions.

Deimination in epidermal barrier and hair formation

Peptidylarginine deiminases (PADs) transform a protein arginine residue into the non-standard amino acid citrulline. This calcium-dependent post-translational modification of proteins is called citrullination or deimination. As described in this special issue, PADs play a role in various physiological processes, and PAD deregulations are involved in many human diseases. Three PADs are expressed in the epidermis, where their roles begin to be deciphered. PAD1 and PAD3 are involved in keratinocyte differentiation, particularly in the epidermal barrier function, keratins, filaggrin and filaggrin-related proteins being the most abundant deiminated epidermal proteins. Reduced amounts of deiminated proteins and PAD1 expression may be involved in the pathogenesis of psoriasis and atopic dermatitis, two very frequent and chronic skin inflammatory diseases. The trichohyalin/PAD3/transglutaminase three pathway is important for hair shaft formation. Mutations of the PADI3 gene, leading to a decreased activity or abnormal localization of the corresponding isotype, are the cause of a rare hair disorder called uncombable hair syndrome, and are associated with the central centrifugal cicatricial alopecia, a frequent alopecia mainly affecting women of African ancestry. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

In silico analysis of the profilaggrin sequence indicates alterations in the stability, degradation route, and intracellular protein fate in filaggrin null mutation carriers

Background: Loss of function mutation in FLG is the major genetic risk factor for atopic dermatitis (AD) and other allergic manifestations. Presently, little is known about the cellular turnover and stability of profilaggrin, the protein encoded by FLG. Since ubiquitination directly regulates the cellular fate of numerous proteins, their degradation and trafficking, this process could influence the concentration of filaggrin in the skin. Objective: To determine the elements mediating the interaction of profilaggrin with the ubiquitin-proteasome system (i.e., degron motifs and ubiquitination sites), the features responsible for its stability, and the effect of nonsense and frameshift mutations on profilaggrin turnover. Methods: The effect of inhibition of proteasome and deubiquitinases on the level and modifications of profilaggrin and processed products was assessed by immunoblotting. Wild-type profilaggrin sequence and its mutated variants were analysed in silico using the DEGRONOPEDIA and Clustal Omega tool. Results: Inhibition of proteasome and deubiquitinases stabilizes profilaggrin and its high molecular weight of presumably ubiquitinated derivatives. In silico analysis of the sequence determined that profilaggrin contains 18 known degron motifs as well as multiple canonical and non-canonical ubiquitination-prone residues. FLG mutations generate products with increased stability scores, altered usage of the ubiquitination marks, and the frequent appearance of novel degrons, including those promoting C-terminus-mediated degradation routes. Conclusion: The proteasome is involved in the turnover of profilaggrin, which contains multiple degrons and ubiquitination-prone residues. FLG mutations alter those key elements, affecting the degradation routes and the mutated products' stability.

Investigations into the filaggrin null phenotype: showcasing the methodology for CRISPR/Cas9 editing of human keratinocytes

Ever since the association between filaggrin (FLG) loss-of-function mutations and ichthyosis vulgaris and atopic dermatitis disease onset was identified, filaggrins function has been under investigation. Intra-individual genomic predisposition, immunological confounders, and environmental interactions complicate the comparison between FLG genotypes and related causal effects. Using CRISPR/Cas9, we generated human FLG knockout (ΔFLG) N/TERT-2G keratinocytes. Filaggrin deficiency was demonstrated by immunohistochemistry of human epidermal equivalent (HEE) cultures. Next to (partial) loss of structural proteins (IVL, HRNR, KRT2, and TGM1), the stratum corneum was more dense and lacked the typical basket weave appearance. In addition, electrical impedance spectroscopy and transepidermal water loss analyses highlighted a compromised epidermal barrier in ΔFLG-HEEs. Correction of FLG reinstated the presence of keratohyalin granules in the stratum granulosum, filaggrin protein expression, and expression of aforementioned proteins. The beneficial effects on stratum corneum formation were reflected by normalization of EIS and TEWL. This study demonstrates the causal phenotypical and functional consequences of filaggrin deficiency, indicating filaggrin is not only central in epidermal barrier function but also vital for epidermal differentiation by orchestrating the expression of other important epidermal proteins. These observations pave the way to fundamental investigations into the exact role of filaggrin in skin biology and disease.

Increased production of natural moisturizing factors and bleomycin hydrolase activity in elderly human skin

BACKGROUND

Bleomycin hydrolase (BH), which is expressed in the stratum granulosum and lower stratum corneum (SC), is involved in final filaggrin degradation. Furthermore, BH plays an essential role in producing free amino acids, which constitute the majority of natural moisturizing factors (NMF). However, the effects of BH expression and protease activity on human skin aging remain unclear.

OBJECTIVE

This study was designed to evaluate the activity and expression patterns of BH in SC extracts from healthy young and elderly individuals.

METHODS

SC samples were collected by tape stripping. BH activity was assessed by measuring the citrulline aminopeptidase activity. BH expression was determined by Western blotting, and NMF was quantified by liquid chromatography/mass spectrometry. Skin barrier function was determined by measuring SC hydration, transepidermal water loss (TEWL), and skin pH.

RESULTS

The activity and expression of BH were higher in the elderly skin than in young skin, and BH activity was correlated with BH expression levels. Evaluation of the NMF showed that the levels of total amino acids, such as glycine, serine, aspartic acid, citrulline, pyrrolidone carboxylic acid (a metabolite of glutamic acid), and trans-urocanic acid (a metabolite of histidine), were significantly higher in elderly skin than in young skin. Moreover, SC hydration and TEWL were significantly lower in elderly, indicating dry skin, and pH was significantly higher in elderly, indicating greater skin alkalinization.

CONCLUSION

These results suggest that BH activity and expression, as well as NMF amino acids, increase in elderly people as compensatory mechanisms against dry skin.

The moisturizing effect of Capparis spinosa fruit extract targeting filaggrin synthesis and degradation

BACKGROUND

Small molecular natural products, such as betaine, have unique moisturizing advantages. Capparis spinosa L. fruit is rich in quaternary ammonium alkaloids such as betaine and stachydrine. However, few studies investigated its efficacy and mechanism on human skin.

OBJECTIVE

Polysaccharides-free C. spinosa fruit extract (CS) was obtained to study its moisturizing effect and mechanisms focusing on filaggrin (FLG) synthesis and degradation.

METHODS

The clinical moisturizing test was carried out on human arms, calves, and faces after CS treatment for 0.5-6 h. The change in the level of FLG, caspase 14, loricrin, and transglutaminase 5 (TGM 5) was measured by immunofluorescence after CS treatment for 4 and 24 h in a reconstructed epidermis model. Also, the content of pyrrolidone carboxylic acid (PCA) in the stratum corneum was tested by high-performance liquid chromatography (HPLC) both in the epidermis model and human calves.

RESULTS

Compared with glycerin (positive control), 5% CS showed a strong skin hydration effect on arms and calves when applied for 0.5-6 h. Also, the face hydration increased at 0.5 and 4 h. In addition, 3% CS applied to the recombinant epidermis model under low humidity promoted the immunodetected levels of caspase 14 and PCA content but reduced the levels of FLG at 4 h, however, the levels of FLG, loricrin, and TGM 5 were promoted at 24 h. Meanwhile, CS treatment for 4 h in human calves increased the PCA content in the stratum corneum by 29.9%.

CONCLUSIONS

Topical application of CS on human skin showed an instant and long-lasting increase in skin hydration by regulating the FLG network. It promoted FLG degradation to form PCA at 4 h both in vivo and in vitro, increasing FLG synthesis after 24 h, potentially reforming the FLG monomer reservoir to alleviate the skin's dry condition.

The ion balance of Shotokuseki extract promotes filaggrin fragmentation and increases amino acid production and pyrrolidone carboxylic acid content in three-dimensional cultured human epidermis

Natural moisturizing factor (NMF) in the stratum corneum contributes to the retention of moisture there. The purpose of this study was to determine the penetration of ions in Shotokuseki extract (SE) into the three-dimensional cultured epidermis and the effect of NMF on the biosynthesis of amino acids and pyrrolidone carboxylic acid formation. Various ions, amino acids and pyrrolidone carboxylic acid were quantified by inductively coupled plasma mass spectrometry, fully automatic amino acid analyzer or high-performance liquid chromatography (HPLC) in three-dimensional cultured epidermis after application of SE. Gene expression levels of profilaggrin, calpain1, caspase14, and bleomycin hydrolase, which are involved in NMF production, were determined by reverse-transcription qPCR and bleomycin hydrolase activity was determined by aminopeptidase assay. The application of SE increased Na, K, Mg, Ca, Al, and Fe levels in three-dimensional cultured epidermis. The mRNA levels of the starting material of amino acid synthesis profilaggrin, and calpain1 and bleomycin hydrolase, which are involved in its fragmentation, increased. The activity of bleomycin hydrolase also increased. Furthermore, the levels of amino acids and pyrrolidone carboxylic acid increased in the three-dimensional cultured epidermis. This suggests that the ionic composition of SE may be involved in its moisturizing effect on the stratum corneum.

Revisiting the Roles of Filaggrin in Atopic Dermatitis

The discovery in 2006 that loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and can predispose to atopic dermatitis (AD) galvanized the dermatology research community and shed new light on a skin protein that was first identified in 1981. However, although outstanding work has uncovered several key functions of filaggrin in epidermal homeostasis, a comprehensive understanding of how filaggrin deficiency contributes to AD is still incomplete, including details of the upstream factors that lead to the reduced amounts of filaggrin, regardless of genotype. In this review, we re-evaluate data focusing on the roles of filaggrin in the epidermis, as well as in AD. Filaggrin is important for alignment of keratin intermediate filaments, control of keratinocyte shape, and maintenance of epidermal texture via production of water-retaining molecules. Moreover, filaggrin deficiency leads to cellular abnormalities in keratinocytes and induces subtle epidermal barrier impairment that is sufficient enough to facilitate the ingress of certain exogenous molecules into the epidermis. However, although FLG null mutations regulate skin moisture in non-lesional AD skin, filaggrin deficiency per se does not lead to the neutralization of skin surface pH or to excessive transepidermal water loss in atopic skin. Separating facts from chaff regarding the functions of filaggrin in the epidermis is necessary for the design efficacious therapies to treat dry and atopic skin.

Oral supplementation of sea cucumber and its hydrolysate mitigates ultraviolet A-induced photoaging in hairless mice

BACKGROUND

Chronic exposure to ultraviolet (UV) radiation promotes skin photoaging, which is clinically characterized by dryness, laxity, and wrinkling. Sea cucumber (Stichopus japonicus) (SC) is a marine organism with culinary and medicinal applications, especially in Asian countries. It is also a potential nutraceutical as it exhibits bioactive effects, such as antioxidant, antitumor, and anticancer activity. This study examined the effects of SC and its hydrolysate (SCH) on ultraviolet A (UVA) induced skin barrier function and wrinkle formation using hairless mice.

RESULTS

Ultraviolet A significantly induced transepidermal water loss and wrinkle formation, which were significantly mitigated upon oral administration of SC and SCH. Sea cucumber also mitigated the UVA-induced downregulation of epidermal natural moisturizing factors and the upregulation of Aqp3, Mmp13, Tnfa, and Il6 mRNA levels in the mouse skin.

CONCLUSION

Taken together, these results suggest that dietary SC and SCH exert anti-photoaging effects by modulating filaggrin synthesis and desquamation in the epidermis and regulating the NF-κB pathway in the skin. Our research indicates that SC and SCH have potential applications in nutricosmetics for photoaging. © 2021 Society of Chemical Industry.

Stratum corneum as polymer sheet: concept and cornification processes

The skin barrier protects our body from external insults and water loss through a specialized layer, the stratum corneum. The stratum corneum, an accumulation of dead keratinocytes (corneocytes), comprises lipids and supporting cell bodies. We propose a framework of lipid-filled polymer sheet of corneocytes, a unique structure that achieves flexibility and robustness, updating the rigid image of the historical bricks-and-mortar model. The polymerization of polymer sheet (cornification) by cell death of keratinocytes (corneoptosis) is delicately and dynamically controlled by cytoplasmic calcium ion and pH. Understanding the structure and formation of the stratum corneum can lead to better treatments for skin diseases and a better understanding of the evolution of the stratum corneum.

The Discovery and Function of Filaggrin

Keratohyalin granules were discovered in the mid-19th century in cells that terminally differentiate to form the outer, cornified layer of the epidermis. The first indications of the composition of these structures emerged in the 1960s from a histochemical stain for histidine, followed by radioautographic evidence of a high incidence of histidine incorporation into newly synthesized proteins in cells containing the granules. Research during the next three decades revealed the structure and function of a major protein in these granules, which was initially called the ‘histidine-rich protein’. Steinert and Dale named the protein ‘filaggrin’ in 1981 because of its ability to aggregate keratin intermediate filaments. The human gene for the precursor, ‘profilaggrin,’ was reported in 1991 to encode 10, 11 or 12 nearly identical repeats. Remarkably, the mouse and rat genes encode up to 20 repeats. The lifetime of filaggrin is the time required for keratinocytes in the granular layer to move into the inner cornified layer. During this transition, filaggrin facilitates the collapse of corneocytes into ‘building blocks’ that become an impermeable surface barrier. The subsequent degradation of filaggrin is as remarkable as its synthesis, and the end-products aid in maintaining moisture in the cornified layer. It was apparent that ichthyosis vulgaris and atopic dermatitis were associated with the absence of this protein. McLean’s team in 2006 identified the cause of these diseases by discovering loss-of-function mutations in the profilaggrin gene, which led to dysfunction of the surface barrier. This story illustrates the complexity in maintaining a healthy, functional epidermis.

New Functions of Low-Molecular-Weight Hyaluronic Acid on Epidermis Filaggrin Production and Degradation

Hyaluronic acid (HA) is a high-molecular-weight polysaccharide with high moisturizing power. It is composed of repeating disaccharides of N-acetyl-D-glucosamine and D-glucuronic acid. Low-molecular-weight hyaluronan (LMHA) is obtained by changing the molecular weight or modifying the functional groups of HA and is commonly used together with HA in cosmetics. The objective of this study was to determine whether LMHA promotes the synthesis of filaggrin (FLG). We also investigated whether LMHA activates FLG-degrading enzymes. Three-dimensional (3D) models of the human epidermis were cultured with LMHA. Real-time PCR was used to quantify the mRNA levels of profilaggrin (proFLG), involucrin (IVL), and FLG-degrading enzymes. FLG protein levels were measured by fluorescent antibody staining and Western blotting. The mRNA was quantified using a 3D epidermis model, and it was observed that the mRNA levels of proFLG, IVL, caspase-14 (CASP14), and bleomycin hydrolase were increased by the application of LMHA. Immunofluorescence results showed an increase in FLG proteins, and results from experiments using 3D epidermis models showed that LMHA increased the activity of CASP14. This suggests that the topical application of LMHA would result in an increase in natural moisturizing factor and promote moisturization of the stratum corneum.

Cracking the Skin Barrier: Liquid-Liquid Phase Separation Shines under the Skin

Central to forming and sustaining the skin’s barrier, epidermal keratinocytes (KCs) fluxing to the skin surface undergo a rapid and enigmatic transformation into flat, enucleated squames. At the crux of this transformation are intracellular keratohyalin granules (KGs) that suddenly disappear as terminally differentiating KCs transition to the cornified skin surface. Defects in KGs have long been linked to skin barrier disorders. Through the biophysical lens of liquid-liquid phase separation (LLPS), these enigmatic KGs recently emerged as liquid-like membraneless organelles whose assembly and subsequent pH-triggered disassembly drive squame formation. To stimulate future efforts toward cracking the complex process of skin barrier formation, in this review, we integrate the key concepts and foundational work spanning the fields of LLPS and epidermal biology. We review the current progress in the skin and discuss implications in the broader context of membraneless organelles across stratifying epithelia. The discovery of environmentally sensitive LLPS dynamics in the skin points to new avenues for dissecting the skin barrier and for addressing skin barrier disorders. We argue that skin and its appendages offer outstanding models to uncover LLPS-driven mechanisms in tissue biology.

Enhanced phenotype of calcipotriol-induced atopic dermatitis in filaggrin-deficient mice

Impaired function of filaggrin (FLG) is a major predisposing factor for atopic dermatitis (AD). Several studies on FLG-deficient (Flg^-/- ) mice have indicated an essential role for FLG in the skin barrier and the development of AD, but none of the studies have described the characteristics on Flg^-/- mice with calcipotriol (CPT)-induced atopic dermatitis, which restricts the comprehensive understanding of functions of FLG. The present study sought to generate Flg^-/- mice and applied CPT to produce AD-like dermatitis for in vivo analysis of the FLG functions. CPT was applied on the skin of Flg^-/- mice to establish the AD-like dermatitis mouse model. The lesion inflammation was evaluated by gross ear thickness, histopathology, immunofluorescence, and cytokine production. Also, mucopolysaccharide polysulfate (MPS) and ceramide were used to observe the therapeutic function in this model. The results showed that the inflammation of CPT-induced dermatitis in Flg^-/- mice was more severer than that of wild-type (WT) mice, as evident by the increased level of gross appearance, ear thickness, inflammatory cell infiltration (mast cells and CD3⁺ T cells), and inflammatory cytokine expression (interleukin (IL)-4, IL-6, IL-13, and thymic stromal lymphopoietin (TSLP)). The emollients MPS and ceramide partially restored the epidermal function and alleviated the skin inflammation in Flg^-/- mice with CPT-induced AD-like dermatitis. The current study demonstrated that skin barrier protein FLG is critical in the pathogenesis of AD. Also, the AD mouse model induced by CPT in Flg^-/- mice could be utilized to search for drug targets in AD.

PAD2-mediated citrullination of Fibulin-5 promotes elastogenesis

The formation of elastic fibers is active only in the perinatal period. How elastogenesis is developmentally regulated is not fully understood. Citrullination is a unique form of post-translational modification catalyzed by peptidylarginine deiminases (PADs), including PAD1-4. Its physiological role is largely unknown. By using an unbiased proteomic approach of lung tissues, we discovered that FBLN5 and LTBP4, two key elastogenic proteins, were temporally modified in mouse and human lungs. We further demonstrated that PAD2 citrullinated FBLN5 preferentially in young lungs compared to adult lungs. Genetic ablation of PAD2 resulted in attenuated elastogenesis in vitro and age-dependent emphysema in vivo. Mechanistically, citrullination protected FBLN5 from proteolysis and subsequent inactivation of its elastogenic activity. Furthermore, citrullinated but not native FBLN5 partially rescued in vitro elastogenesis in the absence of PAD activity. Our data uncover a novel function of citrullination, namely promoting elastogenesis, and provide additional insights to how elastogenesis is regulated.

Relationship between lip skin biophysical and biochemical characteristics with corneocyte unevenness ratio as a new parameter to assess the severity of lip scaling

Objective

Lip skin dryness and chapping are major concerns related to lip skin care in many populations. The distinctive features of lip skin, such as the low water‐holding capacity and weak skin barrier, are strongly associated with these problems; however, few studies have examined lip skin characteristics and the mechanisms underlying these issues. This study was conducted to identify the biophysical properties of dry lip skin and molecular targets affecting lip skin physiology.

Methods

Skin hydration, transepidermal water loss and lip skin scaling were evaluated in 40 female subjects. Skin scaling was assessed as a percentage area divided into five categories (G0, G1, G2, G3 and G4) according to the thickness level of tape‐stripped corneocytes. The activities and amounts of proteases, cathepsin D and bleomycin hydrolase were measured as markers for the desquamation process and skin hydration, respectively.

Results

Skin hydration showed a significantly positive correlation with the percentage area of evenly thin corneocytes (G0) and negative correlations with the percentage areas of slightly thick to severely thick corneocytes (G1‐G4). The corneocyte unevenness ratio (CUR) was calculated by dividing the sum of the G1, G2, G3 and G4 values with the G0 value. The CUR was significantly negatively correlated with skin hydration, suggesting that CUR is a new parameter representing the severity of lip scaling. Subjects with lower hydration and higher CUR had higher bleomycin hydrolase activity and lower cathepsin D activity, respectively, than subjects with higher hydration and lower CUR.

Conclusion

Our study revealed a correlation between lip skin hydration and severity of lip scaling and verified the association of protease activity with the hydration and chapping state of lip skin. These observations provide a basis for further studies of the persistent problem of lip skin dryness and chapping.

Effect of Lactic Fermentation Products on Human Epidermal Cell Differentiation, Ceramide Content, and Amino Acid Production

INTRODUCTION

Lactic fermentation products (LFPs) are thought to affect "good" bacteria in the gut. We previously reported that oral administration of LFPs has beneficial therapeutic effects in a mouse model of atopic dermatitis. However, it is unclear how LFPs affect human epidermal cell differentiation, ceramide (Cer), and amino acid production.

OBJECTIVE

The aim of this study was to determine the effects of LFPs on epidermal cell differentiation, by assessing amino acid and Cer production.

METHODS

A 3-dimensional cultured human epidermis model and normal human epidermal keratinocytes were used. Cytotoxicity tests were performed using alamar Blue. Transepidermal water loss (TEWL) was used as an index to assess barrier function. Keratin 1 (K1), keratin 5 (K5), keratin 10 (K10), involucrin (INV), calpain 1, and transglutaminase (TGase) (markers of differentiation) and profilaggrin (proFLG) and bleomycin hydrolase (amino acid synthesis-related genes) expression levels were quantified by RT-PCR. In addition, TGase protein levels were measured by Western blotting. The intercellular lipid content of the stratum corneum was measured by high-performance thin-layer chromatography. Amino acids were quantified using an amino acid analyzer. Finally, bound water content in the stratum corneum was measured by differential scanning calorimetry.

RESULTS

Cell viability did not change, but TEWL was significantly decreased in the cells treated with LFPs compared with the control cells. Treatment with LFPs significantly increased expression of the late-differentiation markers INV and TGase at the RNA level. Furthermore, TGase protein expression was significantly increased by treatment with LFPs. Treating a 3-dimensional cultured epidermis model with LFPs significantly increased the intercellular lipid content of the stratum corneum and production of the amino acid arginine (Arg). The amount of bound water in the stratum corneum was increased significantly in the LFP application group.

CONCLUSION

Treatment with LFPs promotes human epidermal cell differentiation and increases the intercellular content of the free fatty acid, Chol, Cer [NS], Cer [AS], and Cer [AP]. This may result in improved skin barrier function. The increased amount of Arg observed in keratinocytes may help improve water retention.

The stratum corneum water content and natural moisturization factor composition evolve with age and depend on body site

BACKGROUND

The study objective was to examine if age and chronic environmental exposure affect the water content and the composition of the natural moisturizing factors (NMFs) of the stratum corneum (SC).

METHODS

Forty healthy Caucasian women 18-70 years of age were recruited. Measurements were done on the cheek and on two skin sites on the arm (one relatively protected and one exposed to environmental factors). SC water content and NMF composition were measured by Raman confocal microspectroscopy.

RESULTS

The SC water content was gradually reduced with age, reaching statistically significant levels only on the exposed arm site. The SC water content remained higher on the face than on the two arm sites throughout the ages tested. The age-dependent concentration changes of various amino acids were species-specific, potentially indicating different protein sources. Interestingly, on the arm sites, the sum of decreasing amino acid concentrations is compensated by the sum of those increasing, resulting in constant total amino acid content. However, on the face, the total amino acid content statistically increased with age potentially relating to the declining cell turnover rates. The lactate content was higher on the face for all ages and statistically decreased on both arm sites.

CONCLUSION

Both chronological aging and chronic exposure to environmental factors mildly affect SC hydration, while they have variable effects in the concentrations of NMF components. The dynamics of NMF composition may at least partially explain the age-related changes in SC hydration.

PPAD Activity Promotes Outer Membrane Vesicle Biogenesis and Surface Translocation by Porphyromonas gingivalis

Gram-negative bacteria produce nanosized OMVs that are actively released into their surroundings. The oral anaerobe P. gingivalis is prolific in OMV production, and many of the proteins packaged in these vesicles are proteolytic or protein-modifying enzymes.

Many bacteria switch between a sessile and a motile mode in response to environmental and host-related signals. Porphyromonas gingivalis, an oral anaerobe implicated in the etiology of chronic periodontal disease, has long been described as a nonmotile bacterium. And yet, recent studies have shown that under certain conditions, P. gingivalis is capable of surface translocation. Considering these findings, this work aimed to increase our understanding of how P. gingivalis transitions between sessile growth and surface migration. Here, we show that the peptidylarginine deiminase secreted by P. gingivalis (PPAD), an enzyme previously shown to be upregulated during surface translocation and to constrain biofilm formation, promotes surface translocation. In the absence of PPAD, the production of outer membrane vesicles (OMVs) was drastically reduced. In turn, there was a reduction in gingipain-mediated proteolysis and a reduced zone of hydration around the site of inoculation. Transcriptome sequencing (RNA-Seq) and metabolomics analyses also showed that these changes corresponded to a shift in arginine metabolism. Overall, this report provides new evidence for the functional relevance of PPAD and proteases, as well as the importance of PPAD activity in OMV biogenesis and release. Our findings support the model that citrullination is a critical mechanism during lifestyle transition between surface-attached growth and surface translocation by modulating OMV-mediated proteolysis and arginine metabolism.

IMPORTANCE Gram-negative bacteria produce nanosized OMVs that are actively released into their surroundings. The oral anaerobe P. gingivalis is prolific in OMV production, and many of the proteins packaged in these vesicles are proteolytic or protein-modifying enzymes. This includes key virulence determinants, such as the gingipains and PPAD (a unique peptidylarginine deiminase). Here, we show that PPAD activity (citrullination) is involved in OMV biogenesis. The study revealed an unusual mechanism that allows this bacterium to transform its surroundings. Since OMVs are detected in circulation and in systemic tissues, our study results also support the notion that PPAD activity may be a key factor in the correlation between periodontitis and systemic diseases, further supporting the idea of PPAD as an important therapeutic target.

Skin barrier dysfunction and filaggrin

Skin barrier dysfunction caused by endogenous or exogenous factors can lead to various disorders such as xerosis cutis, ichthyoses, and atopic dermatitis. Filaggrin is a pivotal structural protein of the stratum corneum (SC) and provides natural moisturizing factors that play a role in skin barrier functions. Filaggrin aggregates keratin filaments, resulting in the formation of a keratin network, which binds cornified envelopes and collapse keratinocytes to flattened corneocytes. This complex network contributes to the physical strength of the skin. Filaggrin is degraded by caspase-14, calpain 1, and bleomycin hydrolases into amino acids and amino acid metabolites such as trans-urocanic acid and pyrrolidone carboxylic acid, which are pivotal natural moisturizing factors in the SC. Accordingly, filaggrin is important for the pathophysiology of skin barrier disorders, and its deficiency or dysfunction leads to a variety of skin disorders. Here, the roles and biology of filaggrin, related skin diseases, and a therapeutic strategy targeting filaggrin are reviewed. In addition, several drug candidates of different mode of actions targeting filaggrin, along with their clinical efficacy, are discussed.

Deimination, Intermediate Filaments and Associated Proteins

Deimination (or citrullination) is a post-translational modification catalyzed by a calcium-dependent enzyme family of five peptidylarginine deiminases (PADs). Deimination is involved in physiological processes (cell differentiation, embryogenesis, innate and adaptive immunity, etc.) and in autoimmune diseases (rheumatoid arthritis, multiple sclerosis and lupus), cancers and neurodegenerative diseases. Intermediate filaments (IF) and associated proteins (IFAP) are major substrates of PADs. Here, we focus on the effects of deimination on the polymerization and solubility properties of IF proteins and on the proteolysis and cross-linking of IFAP, to finally expose some features of interest and some limitations of citrullinomes.

The matriptase-prostasin proteolytic cascade in dermatologic diseases

The proper development and function of skin and hair are dependent on proteolytic activities. Specifically, the matriptase-prostasin cascade is a series of proteolytic reactions in the epidermis integral to normal regulation of desquamation. An increasing amount of research describing this pathway has recently become available, and the importance of this pathway is exhibited by the association of genetic defects in this pathway with human diseases of the skin and hair. Given the relevance of this pathway to dermatology, we provide a review of the current understanding of its relevance to distinct clinical entities, including ichthyosis-hypotrichosis and Netherton syndromes.

Extracellular Vesicles Derived from Senescent Fibroblasts Attenuate the Dermal Effect on Keratinocyte Differentiation

The skin is a multilayered and primary defensive organ. Intimate intercellular communication in the skin is necessary to ensure effective surveillance. Extracellular vesicles (EVs) are being explored for their involvement in intercellular skin communication. The aim of this study was to evaluate how human dermal fibroblasts (HDFs) accelerate EV production during senescence and the effects of senescence-associated EVs on epidermal homeostasis. Replicative senescent HDFs were assessed with senescence-associated β-galactosidase staining and the expression of senescence-related markers. Isolated EVs were characterized by dynamic light scattering and EV marker expression. EVs secreted from untreated young or senescent HDFs, or from those treated with a nSMase inhibitor, antioxidant, and lysosomal activity regulators, were determined by sandwich ELISA for CD81. Human epidermal keratinocytes were treated with young- and senescent HDF-derived EVs. Compared to young HDFs, senescent HDFs produced relatively high levels of EVs due to the increased nSMase activity, oxidative stress, and altered lysosomal activity. The nSMase inhibitor, antioxidant, and agents that recovered lysosomal activity reduced EV secretion in senescent HDFs. Relative to young HDF-derived EVs, senescent HDF-derived EVs were less supportive in keratinocyte differentiation and barrier function but increased proinflammatory cytokine IL-6 levels. Our study suggests that dermis-derived EVs may regulate epidermal homeostasis by reflecting cellular status, which provides insight as to how the dermis communicates with the epidermis and influences skin senescence.

Novel petrolatum-based ointment that is highly moisturizing and has superior usability with increased adherence in patients with facial dry skin

BACKGROUND

Petrolatum is often used to suppress water evaporation from the skin surface. However, its stickiness, shininess, and other factors make it inconvenient for continuous use.

OBJECTIVE

To compare the effectiveness and usability between a newly developed petrolatum-based ointment (NOV^® II Moisture Balm) and white petrolatum.

METHODS

Twenty-nine subjects with atopic dermatitis or xeroderma with symptoms of dry skin applied NOV^® II Moisture Balm on the right sides of the face and white petrolatum on the left side, respectively, for 8-12 weeks. The skin conditions (erythema, exudate/crusting, dryness, and itch) were scored, stratum corneum water content and transepidermal water loss (TEWL) were measured, and the free amino acid and thymic stromal lymphopoietin (TSLP) levels in the stratum corneum were analyzed before and end of the trial.

RESULTS

Dryness, exudate/crusting, and TEWL decreased significantly on both the white petrolatum and the NOV^® II Moisture Balm sides, while stratum corneum water content and the free amino acid levels in the stratum corneum increased significantly. On the NOV^® II Moisture Balm side, erythema and the TSLP levels decreased significantly. In a questionnaire on usability, the subjects felt NOV^® II Moisture Balm spread better and were less sticky and shiny than white petrolatum, and more subjects wanted to continue using NOV^® II Moisture Balm.

CONCLUSIONS

NOV^® II Moisture Balm was equivalent to white petrolatum in moisturizing and improving the physiologic functions of the skin, but had superior usability.

Deimination and Peptidylarginine Deiminases in Skin Physiology and Diseases

Deimination, also known as citrullination, corresponds to the conversion of the amino acid arginine, within a peptide sequence, into the non-standard amino acid citrulline. This post-translational modification is catalyzed by a family of calcium-dependent enzymes called peptidylarginine deiminases (PADs). Deimination is implicated in a growing number of physiological processes (innate and adaptive immunity, gene regulation, embryonic development, etc.) and concerns several human diseases (rheumatoid arthritis, neurodegenerative diseases, female infertility, cancer, etc.). Here, we update the involvement of PADs in both the homeostasis of skin and skin diseases. We particularly focus on keratinocyte differentiation and the epidermal barrier function, and on hair follicles. Indeed, alteration of PAD activity in the hair shaft is responsible for two hair disorders, the uncombable hair syndrome and a particular form of inflammatory scarring alopecia, mainly affecting women of African ancestry.

Bleomycin hydrolase regulates the release of chemokines important for inflammation and wound healing by keratinocytes

Bleomycin hydrolase (BLMH) is a well-conserved cysteine protease widely expressed in several mammalian tissues. In skin, which contains high levels of BLMH, this protease is involved in the degradation of citrullinated filaggrin monomers into free amino acids important for skin hydration. Interestingly, the expression and activity of BLMH is reduced in patients with atopic dermatitis (AD) and psoriasis, and BLMH knockout mice acquire tail dermatitis. Apart from its already known function, we have discovered a novel role of BLMH in the regulation of inflammatory chemokines and wound healing. We show that lowered BLMH levels in keratinocytes result in increased release of the pro-inflammatory chemokines CXCL8 and GROα, which are upregulated in skin from AD patients compared to healthy individuals. Conditioned media from keratinocytes expressing low levels of BLMH increased chemotaxis by neutrophils and caused a delayed wound healing in the presence of low-level TNFα. This defective wound healing was improved by blocking the shared receptor of CXCL8 and GROα, namely CXCR2, using a specific receptor antagonist. Collectively, our results present a novel function of BLMH in regulating the secretion of chemokines involved in inflammation and wound healing in human keratinocytes.

Direct Quantification of Natural Moisturizing Factors in Stratum Corneum using Direct Analysis in Real Time Mass Spectrometry with Inkjet-Printing Technique

Proper hydration of the stratum corneum, the skin's outermost layer, is essential for healthy skin. Water-soluble substances called natural moisturizing factors (NMF) are responsible for maintaining adequate moisture in the skin and are closely associated with a variety of the skin's functions. Therefore, quantitative analysis methods for NMF are indispensable when attempting to clarify one of the mechanisms of hydration and its effect on the skin. This study sought to develop a quick and simple analytical technique, which can quantify NMF from the skin without the need for extraction or separation, using direct analysis in real time-mass spectrometry (DART-MS). The goal was to deliver a high quantitative capability, so a unique inkjet printing technique was employed to evenly coat a stable isotope-labeled internal standard (SIL-IS) on tape-stripped skin. This technique allowed for the quantification of 26 NMF with established calibration curves and comparatively high linear correlations. The speed of measurement was found to be advantageous as 100 strips of tape can be measured in roughly 2 hours. The effectiveness of the inkjet coating was also verified by comparing its precision with that of conventional pipetting. This new technique can be an alternative method to quantify NMF rapidly and perhaps allow for a clearer elucidation of their function in skin.

The role of filaggrin in atopic dermatitis and allergic disease

OBJECTIVE

To provide an overview of filaggrin biology and the role of filaggrin variants in atopic dermatitis (AD) and allergic disease.

DATA SOURCES

We performed a PubMed literature review consisting mainly of studies relating to filaggrin in the last 5 years.

STUDY SELECTIONS

We selected articles that were found in PubMed using the search terms filaggrin, atopic dermatitis, skin barrier, and atopy.

RESULTS

Filaggrin plays an important role in the development of AD and allergic disease. Novel methods in measuring filaggrin expression and identifying filaggrin mutations aid in stratifying this patient cohort. We review new insights into understanding the role of filaggrin in AD and allergic disease.

CONCLUSION

Filaggrin remains a very important player in the pathogenesis of atopic dermatitis and allergic disease. This review looks at recent studies that aid our understanding of this crucial epidermal protein.

The role of atopy in the pathogenesis of bleomycin pulmonary toxicity

INTRODUCTION

Bleomycin pulmonary toxicity (BPT) is a potentially life-threatening consequence of bleomycin usage in patients. An overproduction of epithelium-derived cytokines, habitually linked to allergic inflammation, has been recently revealed in experimental models of BPT.

METHODS

We assessed retrospectively our cohort of patients with Hodgkin Lymphoma treated with bleomycin between 2014 and 2016 for their demographic, clinical features, including BPT development, atopy status and risk factors for BPT. Then they were invited for allergy testing and blood sample collection. The samples were stimulated with different stimuli (Bleomycin, IL-33, TSLP) for 24 h on cell culture. The culture supernatants were analysed for TGF-β, Galectin3, Arginin, Amphiregulin, Eotaxin, IFNγ, TNFα, IL1β, 4, 5, 6, 10, 13, 17, MIP-1α, and bleomycin hydrolase (BLH) levels.

RESULTS

The cohort consisted of 51 patients showed that atopy was the only significant risk factor for BPT occurrence (OR: 7.2, p = 0.007). Fourteen subjects were included for blood analysis. The analysis of supernatants at the unstimulated condition revealed that BLH and Amphiregulin were significantly lower in patients who had BPT than controls. The BLH cut-off that best identified a history of BPT was 175.31 (Sensitivity: 62.5%, specificity: 100%). Following the stimulation, BLH reduced compared to the unstimulated condition and the difference between groups remained significant (p < 0.05).

CONCLUSION

Our study is the first to report that low levels of bleomycin hydrolase in allergic individuals may be predisposing to a possible pathway of fibrosis.

Amino acids as wetting agents: surface translocation by Porphyromonas gingivalis

Our understanding of how oral microbiota adapt in response to changes in their surroundings remains limited. This is particularly true of the slow-growing anaerobes that persist below the gum line. Here, we report that the oral anaerobe Porphyromonas gingivalis strain 381 can surface translocate when sandwiched between two surfaces. We show that during movement, this bacterium alters its metabolism, specifically side products of arginine utilization including citrulline and ornithine accumulated in the translocating cells; while arginine, N-acetyl-arginine, and the polyamine putrescine, which is produced from arginine were consumed. In addition, our results indicate that movement requires modification of the surrounding environment via proteolysis, cell dispersion, cell-on-cell rolling, and sub-diffusive cell-driven motility. We also show that production of fimbriae and fimbriae-associated proteins; as well as the regulation of contact-dependent growth inhibition genes, which are known to be involved in self-nonself discrimination, and the type IX secretion system are central to surface translocation. These studies provide a first glimpse into P. gingivalis motility and its relationship to ecological variables.

Reconstructed Skin Models Revealed Unexpected Differences in Epidermal African and Caucasian Skin

Clinical observations of both normal and pathological skin have shown that there is a heterogeneity based on the skin origin type. Beside external factors, intrinsic differences in skin cells could be a central element to determine skin types. This study aimed to understand the in vitro behaviour of epidermal cells of African and Caucasian skin types in the context of 3D reconstructed skin. Full-thickness skin models were constructed with site matched human keratinocytes and papillary fibroblasts to investigate potential skin type related differences. We report that reconstructed skin epidermis exhibited remarkable differences regarding stratification and differentiation according to skin types, as demonstrated by histological appearance, gene expression analysed by DNA microarray and quantitative proteomic analysis. Signalling pathways and processes related to terminal differentiation and lipid/ceramide metabolism were up-regulated in epidermis constructed with keratinocytes from Caucasian skin type when compared to that of keratinocytes from African skin type. Specifically, the expression of proteins involved in the processing of filaggrins was found different between skin models. Overall, we show unexpected differences in epidermal morphogenesis and differentiation between keratinocytes of Caucasian and African skin types in in vitro reconstructed skin containing papillary fibroblasts that could explain the differences in ethnic related skin behaviour.

Peptidylarginine Deiminase Inhibitor Cl-Amidine Attenuates Cornification and Interferes with the Regulation of Autophagy in Reconstructed Human Epidermis

Deimination, a post-translational modification catalyzed by a family of enzymes called peptidylarginine deiminases (PADs), is the conversion of arginine into citrulline residues in a protein. Deimination has been associated with numerous physiological and pathological processes. Our aim was to study its implication in the homeostasis of human epidermis, where three PADs are expressed, namely PAD1, 2, and 3. Three-dimensional reconstructed human epidermis (RHEs) were treated for 2 days with increased concentrations (0-800 μM) of Cl-amidine, a specific PAD inhibitor. Cl-amidine treatments inhibited deimination in a dose-dependent manner and were not cytotoxic for keratinocytes. At 800 μM , Cl-amidine was shown to reduce deimination by half, alter keratinocyte differentiation, decrease the number of corneocyte layers, significantly increase the number of transitional cells, induce clustering of mitochondria and of heterogeneous vesicles in the cytoplasm of granular keratinocytes, and upregulate the expression of autophagy proteins, including LC3-II, sestrin-2, and p62/SQSTM1. LC3 and PADs were further shown to partially co-localize in the upper epidermis. These results demonstrated that Cl-amidine treatments slow down cornification and alter autophagy in the granular layer. They suggest that PAD1 and/or PAD3 play a role in the constitutive epidermal autophagy process that appears as an important step in cornification.

Homocysteine Modification in Protein Structure/Function and Human Disease

Epidemiological studies established that elevated homocysteine, an important intermediate in folate, vitamin B₁₂, and one carbon metabolism, is associated with poor health, including heart and brain diseases. Earlier studies show that patients with severe hyperhomocysteinemia, first identified in the 1960s, exhibit neurological and cardiovascular abnormalities and premature death due to vascular complications. Although homocysteine is considered to be a nonprotein amino acid, studies over the past 2 decades have led to discoveries of protein-related homocysteine metabolism and mechanisms by which homocysteine can become a component of proteins. Homocysteine-containing proteins lose their biological function and acquire cytotoxic, proinflammatory, proatherothrombotic, and proneuropathic properties, which can account for the various disease phenotypes associated with hyperhomocysteinemia. This review describes mechanisms by which hyperhomocysteinemia affects cellular proteostasis, provides a comprehensive account of the biological chemistry of homocysteine-containing proteins, and discusses pathophysiological consequences and clinical implications of their formation.

A Commensal Dipeptidyl Aminopeptidase with Specificity for N-Terminal Glycine Degrades Human-Produced Antimicrobial Peptides in Vitro

Proteases within the C1B hydrolase family are encoded by many organisms. We subjected a putative C1B-like cysteine protease secreted by the human gut commensal Parabacteroides distasonis to mass spectrometry-based substrate profiling to find preferred peptide substrates. The P. distasonis protease, which we termed Pd_dinase, has a sequential diaminopeptidase activity with strong specificity for N-terminal glycine residues. Using the substrate sequence information, we verified the importance of the P2 glycine residue with a panel of fluorogenic substrates and calculated k_cat and K_M for the dipeptide glycine-arginine-AMC. A potent and irreversible dipeptide inhibitor with a C-terminal acyloxymethyl ketone warhead, glycine-arginine- AOMK, was then synthesized and demonstrated that the Pd_dinase active site requires a free N-terminal amine for potent and rapid inhibition. We next determined the homohexameric Pd_dinase structure in complex with glycine-arginine- AOMK and uncovered unexpected active site features that govern the strict substrate preferences and differentiate this protease from members of the C1B and broader papain-like C1 protease families. We finally showed that Pd_dinase hydrolyzes several human antimicrobial peptides and therefore posit that this P. distasonis enzyme may be secreted into the extracellular milieu to assist in gut colonization by inactivation of host antimicrobial peptides.

Early-life regional and temporal variation in filaggrin-derived natural moisturizing factor, filaggrin-processing enzyme activity, corneocyte phenotypes and plasmin activity: implications for atopic dermatitis

Background

Filaggrin is central to the pathogenesis of atopic dermatitis (AD). The cheeks are a common initiation site of infantile AD. Regional and temporal expression of levels of filaggrin degradation products [natural moisturizing factors (NMFs)], activities of filaggrin‐processing enzymes [bleomycin hydrolase (BH) and calpain‐1 (C‐1)] and plasmin, and corneocyte envelope (CE) maturity in early life are largely unknown.

Objectives

We conducted a cross‐sectional, observational study investigating regional and age‐dependent variations in NMF levels, activity of proteases and CE maturity in stratum corneum (SC) from infants to determine whether these factors could explain the observed predilection sites for AD in early life.

Methods

We measured NMF using a tape‐stripping method at seven sites in the SC of 129 children (aged < 12 months to 72 months) and in three sites in 56 neonates and infants (< 48 h to 3 months). In 37 of these neonates and infants, corneocyte size, maturity, BH, C‐1 and plasmin activities were determined.

Results

NMF levels are low at birth and increase with age. Cheek SC, compared with elbow flexure and nasal tip, has the lowest NMF in the first year of life and is the slowest to reach stable levels. Cheek corneocytes remain immature. Plasmin, BH and C‐1 activities are all elevated by 1 month of age in exposed cheek skin, but not in elbow skin.

Conclusions

Regional and temporal differences in NMF levels, CE maturity and protease activities may explain the predilection for AD to affect the cheeks initially and are supportive of this site as key for allergen priming in early childhood. These observations will help design early intervention and treatment strategies for AD.

What's already known about this topic?

Atopic dermatitis (AD) frequently starts in early infancy, and the first eczematous lesions emerge on the cheeks.

Filaggrin is a major structural protein in the stratum corneum (SC).

Filaggrin deficiency is associated with the development of AD and, in the context of AD, food allergies and asthma.

Filaggrin is metabolized into natural moisturizing factors (NMFs), which can be measured in the SC.

What does this study add?

Regional differences in NMF levels, corneocyte envelope immaturity and protease activities may help explain why infantile AD most often initially affects the cheeks.

Filaggrin processing, corneocyte maturity, and protease activities show regional and temporal differences in infant skin.

These findings may explain disease patterns in early‐life AD.

What is the translational message?

Cheek skin may be highly relevant for allergen priming.

Emollient therapy at the vulnerable cheek site might help to prevent AD and/or food sensitization.

Linked Editorial: https://doi.org/10.1111/bjd.16806.

https://doi.org/10.1111/bjd.16959 available online

https://goo.gl/Uqv3dl

Orchestrated control of filaggrin-actin scaffolds underpins cornification

Epidermal stratification critically depends on keratinocyte differentiation and programmed death by cornification, leading to formation of a protective skin barrier. Cornification is dynamically controlled by the protein filaggrin, rapidly released from keratohyalin granules (KHGs). However, the mechanisms of cornification largely remain elusive, partly due to limitations of the observation techniques employed to study filaggrin organization in keratinocytes. Moreover, while the abundance of keratins within KHGs has been well described, it is not clear whether actin also contributes to their formation or fate. We employed advanced (super-resolution) microscopy to examine filaggrin organization and dynamics in skin and human keratinocytes during differentiation. We found that filaggrin organization depends on the cytoplasmic actin cytoskeleton, including the role for α- and β-actin scaffolds. Filaggrin-containing KHGs displayed high mobility and migrated toward the nucleus during differentiation. Pharmacological disruption targeting actin networks resulted in granule disintegration and accelerated cornification. We identified the role of AKT serine/threonine kinase 1 (AKT1), which controls binding preference and function of heat shock protein B1 (HspB1), facilitating the switch from actin stabilization to filaggrin processing. Our results suggest an extended model of cornification in which filaggrin utilizes actins to effectively control keratinocyte differentiation and death, promoting epidermal stratification and formation of a fully functional skin barrier.

Barrier dysfunction in the skin allergy

The skin is continuously exposed to external pathogens, and its barrier function is critical for skin homeostasis. Previous studies have shown that the barrier dysfunction is one of the most predisposing factors for the development of skin allergic diseases such as atopic dermatitis. In this article, we summarize how the physical barrier of the skin is organized and review its link to the pathomechanism of skin allergic diseases. We describe the formation of the SC barrier in terms of the following five categories: 1) filaggrin metabolism; 2) cornified envelope; 3) intercellular lipids; 4) corneodesmosome; and 5) corneocyte desquamation. New approaches to restoring the skin barrier function are also discussed.

Feeding filaggrin: effects of l-histidine supplementation in atopic dermatitis

Atopic dermatitis (AD), also known as eczema, is one of the most common chronic skin conditions worldwide, affecting up to 16% of children and 10% of adults. It is incurable and has significant psychosocial and economic impacts on the affected individuals. AD etiology has been linked to deficiencies in the skin barrier protein, filaggrin. In mammalian skin, l-histidine is rapidly incorporated into filaggrin. Subsequent filaggrin proteolysis releases l-histidine as an important natural moisturizing factor (NMF). In vitro studies were conducted to investigate the influence of l-histidine on filaggrin processing and barrier function in human skin-equivalent models. Our further aim was to examine the effects of daily oral l-histidine supplementation on disease severity in adult AD patients. We conducted a randomized, double-blind, placebo-controlled, crossover, nutritional supplementation pilot study to explore the effects of oral l-histidine in adult AD patients (n=24). In vitro studies demonstrated that l-histidine significantly increased both filaggrin formation and skin barrier function (P<0.01, respectively). Data from the clinical study indicated that once daily oral l-histidine significantly reduced (P<0.003) AD disease severity by 34% (physician assessment using the SCORingAD tool) and 39% (patient self-assessment using the Patient Oriented Eczema Measure tool) after 4 weeks of treatment. No improvement was noted with the placebo (P>0.32). The clinical effect of oral l-histidine in AD was similar to that of mid-potency topical corticosteroids and combined with its safety profile suggests that it may be a safe, nonsteroidal approach suitable for long-term use in skin conditions that are associated with filaggrin deficits such as AD.