Dose-dependent role of claudin-1 in vivo in orchestrating features of atopic dermatitis

Neutrophils in Atopic Dermatitis

Neutrophils have a critical role in inflammation. Recent studies have identified their distinctive presence in certain types of atopic dermatitis (AD), yet their exact function remains unclear. This review aims to compile studies elucidating the role of neutrophils in AD pathophysiology. Proteins released by neutrophils, including myeloperoxidase, elastase, and lipocalin, contribute to pruritus progression in AD. Neutrophilic oxidative stress and the formation of neutrophil extracellular traps may further worsen AD. Elevated neutrophil elastase and high-mobility group box 1 protein expression in AD patients' skin exacerbates epidermal barrier defects. Neutrophil-mast cell interactions in allergic inflammation steer the immunological response toward Th2 imbalance and activate the Th17 pathway, particularly in response to allergens or infections linked to AD. Notably, drugs alleviating pruritic symptoms in AD inhibit neutrophilic inflammation. In conclusion, these findings underscore that neutrophils may be therapeutic targets for AD symptoms, emphasizing their inclusion in AD treatment strategies.

Bilateral deficiency of Meissner corpuscles and papillary microvessels in patients with acute complex regional pain syndrome

ABSTRACT

Complex regional pain syndrome (CRPS) presents postinjury with disproportionate pain and neuropathic, autonomic, motor symptoms, and skin texture affection. However, the origin of these multiplex changes is unclear. Skin biopsies offer a window to analyze the somatosensory and vascular system as well as skin trophicity with their protecting barriers. In previous studies, barrier-protective exosomal microRNAs were altered in CRPS. We here postulated that tissue architecture and barrier proteins are already altered at the beginning of CRPS. We analyzed ipsilateral and contralateral skin biopsies of 20 fully phenotyped early CRPS patients compared with 20 age- and sex-matched healthy controls. We established several automated unbiased methods to comprehensively analyze microvessels and somatosensory receptors as well as barrier proteins, including claudin-1, claudin-5, and claudin-19. Meissner corpuscles in the skin were bilaterally reduced in acute CRPS patients with some of them lacking these completely. The number of Merkel cells and the intraepidermal nerve fiber density were not different between the groups. Dermal papillary microvessels were bilaterally less abundant in CRPS, especially in patients with allodynia. Barrier proteins in keratinocytes, perineurium of dermal nerves, Schwann cells, and papillary microvessels were not affected in early CRPS. Bilateral changes in the tissue architecture in early CRPS might indicate a predisposition for CRPS that manifests after injury. Further studies should evaluate whether these changes might be used to identify risk patients for CRPS after trauma and as biomarkers for outcome.

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

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

CLDN1 knock out keratinocytes as a model to investigate multiple skin disorders

The transmembrane protein claudin-1 is critical for formation of the epidermal barrier structure called tight junctions (TJ) and has been shown to be important in multiple disease states. These include neonatal ichthyosis and sclerosing cholangitis syndrome, atopic dermatitis and various viral infections. To develop a model to investigate the role of claudin-1 in different disease settings, we used CRISPR/Cas9 to generate human immortalized keratinocyte (KC) lines lacking claudin-1 (CLDN1 KO). We then determined whether loss of claudin-1 expression affects epidermal barrier formation/function and KC differentiation/stratification. The absence of claudin-1 resulted in significantly reduced barrier function in both monolayer and organotypic cultures. CLDN1 KO cells demonstrated decreases in gene transcripts encoding the barrier protein filaggrin and the differentiation marker cytokeratin-10. Marked morphological differences were also observed in CLDN1 KO organotypic cultures including diminished stratification and reduced formation of the stratum granulosum. We also detected increased proliferative KC in the basale layer of CLDN1 KO organotypic cultures. These results further support the role of claudin-1 in epidermal barrier and suggest an additional role of this protein in appropriate stratification of the epidermis.

Unraveling the skin; a comprehensive review of atopic dermatitis, current understanding, and approaches

Atopic dermatitis, also known as atopic eczema, is a chronic inflammatory skin disease characterized by red pruritic skin lesions, xerosis, ichthyosis, and skin pain. Among the social impacts of atopic dermatitis are difficulties and detachment in relationships and social stigmatization. Additionally, atopic dermatitis is known to cause sleep disturbance, anxiety, hyperactivity, and depression. Although the pathological process behind atopic dermatitis is not fully known, it appears to be a combination of epidermal barrier dysfunction and immune dysregulation. Skin is the largest organ of the human body which acts as a mechanical barrier to toxins and UV light and a natural barrier against water loss. Both functions face significant challenges due to atopic dermatitis. The list of factors that can potentially trigger or contribute to atopic dermatitis is extensive, ranging from genetic factors, family history, dietary choices, immune triggers, and environmental factors. Consequently, prevention, early clinical diagnosis, and effective treatment may be the only resolutions to combat this burdensome disease. Ensuring safe and targeted drug delivery to the skin layers, without reaching the systemic circulation is a promising option raised by nano-delivery systems in dermatology. In this review, we explored the current understanding and approaches of atopic dermatitis and outlined a range of the most recent therapeutics and dosage forms brought by nanotechnology. This review was conducted using PubMed, Google Scholar, and ScienceDirect databases.

High-intensity exercise impairs intestinal barrier function by generating oxidative stress

The intestine functions as a barrier preventing the entry of extrinsic factors into the body. This barrier function is disrupted by oxidative damage along with an impaired mucosal layer. Excessive exercise can generate oxidative stress in the intestinal tissue; however, the effect of exercise-induced oxidative stress on intestinal permeability is unclear. In this study, we examined the involvement of oxidative stress in barrier function of the ileum of mice following high-intensity exercise. Male ICR mice (12-week-old) were divided into sedentary and exercise groups. Mice in the exercise group underwent a single bout of treadmill running, and the ileum was collected for histological and biochemical analyses. Plasma fluorescence intensity level after oral administration of fluorescein isothiocyanate-dextran gradually increased until 30 min after exercise in response to intensity of exercise. Relatively high levels of oxidative proteins and low level of claudin-1, a tight-junction protein, were observed in the exercise group. Treatment with a xanthine oxidase inhibitor suppressed exercise-induced increases in intestinal permeability. Moreover, excessive exercise training for two weeks led to relatively high intestinal permeability at rest. These results suggest that high-intensity exercise increases intestinal permeability and tight junction damage, which may be mediated by oxidative stress.

Decreased TET2/5-hmC reduces the integrity of the epidermal barrier via epigenetic dysregulation of filaggrin in psoriatic lesions

BACKGROUND

TET2 participates in tumor progression and intrinsic immune homeostasis via epigenetic regulation. TET2 has been reported to be involved in maintaining epithelial barrier homeostasis and inflammation. Abnormal epidermal barrier function and TET2 expression have been detected in psoriatic lesions. However, the mechanisms underlying the role of TET2 in psoriasis have not yet been elucidated.

OBJECTIVE

To define the role of TET2 in maintaining epithelial barrier homeostasis and the exact epigenetic mechanism in the dysfunction of the epidermal barrier in psoriasis.

METHODS

We analyzed human psoriatic skin lesions and datasets from the GEO database, and detected the expression of TET2/5-hmC together with barrier molecules by immunohistochemistry. We constructed epidermal-specific TET2 knockout mice to observe the effect of TET2 deficiency on epidermal barrier function via toluidine blue penetration assay. Further, we analyzed changes in the expression of epidermal barrier molecules by immunofluorescence in TET2-specific knockout mice and psoriatic model mice.

RESULTS

We found that decreased expression of TET2/5-hmC correlated with dysregulated barrier molecules in human psoriatic lesions. Epidermal-specific TET2 knockout mice showed elevated transdermal water loss associated with abnormal epidermal barrier molecules. Furthermore, we observed that TET2 knockdown in keratinocytes reduced filaggrin expression via filaggrin promoter methylation.

CONCLUSION

Aberrant epidermal TET2 affects the integrity of the epidermal barrier through the epigenetic dysregulation of epidermal barrier molecules, particularly filaggrin. Reduced TET2 expression is a critical factor contributing to an abnormal epidermal barrier in psoriasis.

CLDN1 Arg81His founder variant causes ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC) syndrome in Moroccan Jews

Neonatal ichthyosis and sclerosing cholangitis syndrome (NISCH), also known as ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC), is an extremely rare disease of autosomal recessive inheritance, resulting from loss of function of the tight junction protein claudin-1. Its clinical presentation is highly variable, and is characterized by liver and ectodermal involvement. Although most ILVASC cases described to date were attributed to homozygous truncating variants in CLDN1, a single missense variant CLDN1 p.Arg81His, associated with isolated skin ichthyosis phenotype, has been recently reported in a family of Moroccan Jewish descent. We now describe seven patients with ILVASC, originating from four non consanguineous families of North African Jewish ancestry (including one previously reported family), harboring CLDN1 p.Arg81His variant, and broaden the phenotypic spectrum attributed to this variant to include teeth, hair, and liver/bile duct involvement, characteristic of ILVASC. Furthermore, we provide additional evidence for pathogenicity of the CLDN1 p.Arg81His variant by transmission electron microscopy of the affected skin, revealing distorted tight junction architecture, and show through haplotype analysis in the vicinity of the CLDN1 gene, that this variant represents a founder variant in Jews of Moroccan descent with an estimated carrier frequency of 1:220.

Are the Cutaneous Microbiota a Guardian of the Skin's Physical Barrier? The Intricate Relationship between Skin Microbes and Barrier Integrity

The skin is a tightly regulated, balanced interface that maintains our integrity through a complex barrier comprising physical or mechanical, chemical, microbiological, and immunological components. The skin's microbiota affect various properties, one of which is the establishment and maintenance of the physical barrier. This is achieved by influencing multiple processes, including keratinocyte differentiation, stratum corneum formation, and regulation of intercellular contacts. In this review, we summarize the potential contribution of Cutibacterium acnes to these events and outline the contribution of bacterially induced barrier defects to the pathogenesis of acne vulgaris. With the combined effects of a Westernized lifestyle, microbial dysbiosis, epithelial barrier defects, and inflammation, the development of acne is very similar to that of several other multifactorial diseases of barrier organs (e.g., inflammatory bowel disease, celiac disease, asthma, atopic dermatitis, and chronic rhinosinusitis). Therefore, the management of acne requires a complex approach, which should be taken into account when designing novel treatments that address not only the inflammatory and microbial components but also the maintenance and strengthening of the cutaneous physical barrier.

Research progress of Claudin-low breast cancer

Claudin-low breast cancer (CLBC) is a subgroup of breast cancer discovered at the molecular level in 2007. Claudin is one of the primary proteins that make up tight junctions, and it plays crucial roles in anti-inflammatory and antitumor responses as well as the maintenance of water and electrolyte balance. Decreased expression of claudin results in the disruption of tight junction structures and the activation of downstream signaling pathways, which can lead to tumor formation. The origin of Claudin-low breast cancer is still in dispute. Claudin-low breast cancer is characterized by low expression of Claudin3, 4, 7, E-cadherin, and HER2 and high expression of Vimentin, Snai 1/2, Twist 1/2, Zeb 1/2, and ALDH1, as well as stem cell characteristics. The clinical onset of claudin-low breast cancer is at menopause age, and its histological grade is higher. This subtype of breast cancer is more likely to spread to lymph nodes than other subtypes. Claudin-low breast cancer is frequently accompanied by increased invasiveness and a poor prognosis. According to a clinical retrospective analysis, claudin-low breast cancer can achieve low pathological complete remission. At present, although several therapeutic targets of claudin-low breast cancer have been identified, the effective treatment remains in basic research stages, and no animal studies or clinical trials have been designed. The origin, molecular biological characteristics, pathological characteristics, treatment, and prognosis of CLBC are extensively discussed in this article. This will contribute to a comprehensive understanding of CLBC and serve as the foundation for the individualization of breast cancer treatment.

Coffea arabica Extract Attenuates Atopic Dermatitis-like Skin Lesions by Regulating NLRP3 Inflammasome Expression and Skin Barrier Functions

Atopic dermatitis (AD) is a common skin disease worldwide. The major causes of AD are skin barrier defects, immune dysfunction, and oxidative stress. In this study, we investigated the anti-oxidation and anti-inflammation effects of Coffea arabica extract (CAE) and its regulation of the skin barrier and immune functions in AD. In vitro experiments revealed that CAE decreased the reactive oxygen species levels and inhibited the translocation of nuclear factor-κB (NF-κB), further reducing the secretion of interleukin (IL)-1β and IL-6 induced by interferon-γ (IFN-γ)/tumor necrosis factor-α (TNF-α). Moreover, CAE decreased IFN-γ/TNF-α-induced NLR family pyrin domain-containing 3 (NLRP3), caspase-1, high-mobility group box 1 (HMGB1), and receptor for advanced glycation end products (RAGE) expression levels. It also restored the protein levels of skin barrier function-related markers including filaggrin and claudin-1. In vivo experiments revealed that CAE not only reduced the redness of the backs of mice caused by 2,4-dinitrochlorobenzene (DNCB) but also reduced the levels of pro-inflammatory factors in their skin. CAE also reduced transepidermal water loss (TEWL) and immune cell infiltration in DNCB-treated mice. Overall, CAE exerted anti-oxidation and anti-inflammation effects and ameliorated skin barrier dysfunction, suggesting its potential as an active ingredient for AD treatment.

Calcitriol, an Active Form of Vitamin D3, Mitigates Skin Barrier Dysfunction in Atopic Dermatitis NC/Nga Mice

Atopic dermatitis and psoriasis are prevalent chronic inflammatory skin diseases that are characterized by dysfunctional skin barriers and substantially impact patients' quality of life. Vitamin D3 regulates immune responses and keratinocyte differentiation and improves psoriasis symptoms; however, its effects on atopic dermatitis remain unclear. Here, we investigated the effects of calcitriol, an active form of vitamin D3, on an NC/Nga mouse model of atopic dermatitis. We observed that the topical application of calcitriol decreased the dermatitis scores and epidermal thickness of NC/Nga mice with atopic dermatitis compared to untreated mice. In addition, both stratum corneum barrier function as assessed by the measurement of transepidermal water loss and tight junction barrier function as evaluated by biotin tracer permeability assay were improved following calcitriol treatment. Moreover, calcitriol treatment reversed the decrease in the expression of skin barrier-related proteins and decreased the expression of inflammatory cytokines such as interleukin (IL)-13 and IL-33 in mice with atopic dermatitis. These findings suggest that the topical application of calcitriol might improve the symptoms of atopic dermatitis by repairing the dysfunctional epidermal and tight junction barriers. Our results suggest that calcitriol might be a viable therapeutic agent for the treatment of atopic dermatitis in addition to psoriasis.

The diet-microbiota axis: a key regulator of intestinal permeability in human health and disease

The intestinal barrier orchestrates selective permeability to nutrients and metabolites while excluding noxious stimuli. Recent scientific advances establishing a causal role for the gut microbiota in human health outcomes have generated a resurgent interest toward intestinal permeability. Considering the well-established role of the gut barrier in protection against foreign antigens, there is mounting evidence for a causal link between gut permeability and the microbiome in regulating human health. However, an understanding of the dynamic host-microbiota interactions that govern intestinal barrier functions remains poorly defined. Furthermore, the system-level mechanisms by which microbiome-targeted therapies, such as probiotics and prebiotics, simultaneously promote intestinal barrier function and host health remain an area of active investigation. This review summarizes the recent advances in understanding the dynamics of intestinal permeability in human health and its integration with gut microbiota. We further summarize mechanisms by which probiotics/prebiotics influence the gut microbiota and intestinal barrier functions.

The Effects of Mucopolysaccharide Polysulfate on Steroid-Induced Tight Junction Barrier Dysfunction in Human Epidermal Keratinocytes and a 3D Skin Model

INTRODUCTION

The long-term use of topical corticosteroids (TCS) is associated with side effects such as skin atrophy and barrier deterioration. Moisturizers, such as mucopolysaccharide polysulfate (MPS), have been reported to prevent relapses in atopic dermatitis (AD) when used in combination with TCS. However, the mechanisms underlying the positive effects of MPS in combination with TCS in AD are poorly understood. In the present study, we investigated the effects of MPS in combination with clobetasol 17-propionate (CP) on tight junction (TJ) barrier function in human epidermal keratinocytes (HEKa) and 3D skin models.

METHODS

The expression of claudin-1, which is crucial for TJ barrier function in keratinocytes, and transepithelial electrical resistance (TEER) was measured in CP-treated human keratinocytes incubated with and without MPS. A TJ permeability assay, using Sulfo-NHS-Biotin as a tracer, was also conducted in a 3D skin model.

RESULTS

CP reduced claudin-1 expression and TEER in human keratinocytes, whereas MPS inhibited these CP-induced effects. Moreover, MPS inhibited the increase in CP-induced TJ permeability in a 3D skin model.

CONCLUSION

The present study demonstrated that MPS improved TJ barrier impairment induced by CP. The improvement of TJ barrier function may partially be responsible for the delayed relapse of AD induced by the combination of MPS and TCS.

Osthole relieves skin damage and inhibits chronic itch through modulation of Akt/ZO-3 pathway in atopic dermatitis

Atopic dermatitis (AD) is the most prevalent chronic inflammatory skin condition and significantly reduces quality of life. Tight junction (TJ), which is located directly beneath the stratum corneum, maintains skin barrier function and aids in the identification of the cell's "territory". We evaluated seventeen TJ related genes to explore AD related alterations of TJ. Remarkably, we found that the expression of ZO-3, a gene that had not been linked to the development of TJ in AD, was significantly down-regulated in the skin of AD mice and patients. siRNA mediated knock-down of ZO-3 significantly decreased transepithelial electrical resistance in HaCaT cells, demonstrating that ZO-3 is essential to epidermal barrier function. In addition to ZO-3 downregulation, protein kinase B (Akt) phosphorylation was increased in the skin of AD mice. We further confirmed an inverse relationship between Akt phosphorylation and ZO-3 expression in AD using HaCaT cells and mouse model. Finally, we tested the efficacy of osthole as a treatment for AD in mice and HaCaT cells. Osthole inhibits Akt phosphorylation, and thereby enhances ZO-3 expression in mouse models of AD, resulting in greatly lessened AD associated skin damage and chronic itch, and osthole also increased the expression of ZO-3 in HaCaT cells by inhibiting the phosphorylation of Akt. Together, we established that ZO-3 is essential for the development of TJ in AD skin and HaCaT cells, and our findings provide fresh support for osthole's ability to protect ZO-3 expression and the epidermal barrier in AD.

The Antimicrobial Peptide AMP-IBP5 Suppresses Dermatitis-like Lesions in a Mouse Model of Atopic Dermatitis through the Low-Density Lipoprotein Receptor-Related Protein-1 Receptor

The antimicrobial peptide derived from insulin-like growth factor-binding protein 5 (AMP-IBP5) exhibits antimicrobial activities and immunomodulatory functions in keratinocytes and fibroblasts. However, its role in regulating skin barrier function remains unclear. Here, we investigated the effects of AMP-IBP5 on the skin barrier and its role in the pathogenesis of atopic dermatitis (AD). 2,4-Dinitrochlorobenzene was used to induce AD-like skin inflammation. Transepithelial electrical resistance and permeability assays were used to investigate tight junction (TJ) barrier function in normal human epidermal keratinocytes and mice. AMP-IBP5 increased the expression of TJ-related proteins and their distribution along the intercellular borders. AMP-IBP5 also improved TJ barrier function through activation of the atypical protein kinase C and Rac1 pathways. In AD mice, AMP-IBP5 ameliorated dermatitis-like symptoms restored the expression of TJ-related proteins, suppressed the expression of inflammatory and pruritic cytokines, and improved skin barrier function. Interestingly, the ability of AMP-IBP5 to alleviate inflammation and improve skin barrier function in AD mice was abolished in mice treated with an antagonist of the low-density lipoprotein receptor-related protein-1 (LRP1) receptor. Collectively, these findings indicate that AMP-IBP5 may ameliorate AD-like inflammation and enhance skin barrier function through LRP1, suggesting a possible role for AMP-IBP5 in the treatment of AD.

Mechanisms of paracellular transport of magnesium in intestinal and renal epithelia

Magnesium is the fourth most abundant cation in the body. It plays a critical role in many biological processes, including the process of energy release. Paracellular transport of magnesium is mandatory for magnesium homeostasis. In addition to intestinal absorption that occurs in part across the paracellular pathway, magnesium is reabsorbed by the kidney tubule. The bulk of magnesium is reabsorbed through the paracellular pathway in the proximal tubule and the thick ascending limb of the loop of Henle. The finding that rare genetic diseases due to pathogenic variants in genes encoding specific claudins (CLDNs), proteins located at the tight junction that determine the selectivity and the permeability of the paracellular pathway, led to an awareness of their importance in magnesium homeostasis. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is caused by a loss of function of CLDN16 or CLDN19. Pathogenic CLDN10 variants cause HELIX syndrome, which is associated with a severe renal loss of sodium chloride and hypermagnesemia. The present review summarizes the current knowledge of the mechanisms and factors involved in paracellular magnesium permeability. The review also highlights some of the unresolved questions that need to be addressed.

The Role of Tight Junctions in Atopic Dermatitis: A Systematic Review

BACKGROUND

Tight junctions are transmembrane proteins that regulate the permeability of water, solutes including ions, and water-soluble molecules. The objective of this systematic review is to focus on the current knowledge regarding the role of tight junctions in atopic dermatitis and the possible impact on their therapeutic potential.

METHODS

A literature search was performed in PubMed, Google Scholar, and Cochrane library between 2009 and 2022. After evaluation of the literature and taking into consideration their content, 55 articles were finally included.

RESULTS

TJs' role in atopic dermatitis extends from a microscopic scale to having macroscopic effects, such as increased susceptibility to pathogens and infections and worsening of atopic dermatitis features. Impaired TJ barrier function and skin permeability in AD lesions is correlated with cldn-1 levels. Th2 inflammation inhibits the expression of cldn-1 and cldn-23. Scratching has also been reported to decrease cldn-1 expression. Dysfunctional TJs' interaction with Langerhans cells could increase allergen penetration. Susceptibility to cutaneous infections in AD patients could also be affected by TJ cohesion.

CONCLUSIONS

Dysfunction of TJs and their components, especially claudins, have a significant role in the pathogenesis and vicious circle of inflammation in AD. Discovering more basic science data regarding TJ functionality may be the key for the use of specific/targeted therapies in order to improve epidermal barrier function in AD.

Short- and long-term polystyrene nano- and microplastic exposure promotes oxidative stress and divergently affects skin cell architecture and Wnt/beta-catenin signaling

Nano- and microplastic particles (NMP) are strong environmental contaminants affecting marine ecosystems and human health. The negligible use of biodegradable plastics and the lack of knowledge about plastic uptake, accumulation, and functional consequences led us to investigate the short- and long-term effects in freshly isolated skin cells from mice. Using fluorescent NMP of several sizes (200 nm to 6 µm), efficient cellular uptake was observed, causing, however, only minor acute toxicity as metabolic activity and apoptosis data suggested, albeit changes in intracellular reactive species and thiol levels were observed. The internalized NMP induced an altered expression of various targets of the nuclear factor-2-related transcription factor 2 pathway and were accompanied by changed antioxidant and oxidative stress signaling responses, as suggested by altered heme oxygenase 1 and glutathione peroxide 2 levels. A highly increased beta-catenin expression under acute but not chronic NMP exposure was concomitant with a strong translocation from membrane to the nucleus and subsequent transcription activation of Wnt signaling target genes after both single-dose and chronic long-term NMP exposure. Moreover, fibroblast-to-myofibroblast transdifferentiation accompanied by an increase of α smooth muscle actin and collagen expression was observed. Together with several NMP-induced changes in junctional and adherence protein expression, our study for the first time elucidates the acute and chronic effects of NMP of different sizes in primary skin cells' signaling and functional biology, contributing to a better understanding of nano- and microplastic to health risks in higher vertebrates.

Tight Junctions, the Epithelial Barrier, and Toll-like Receptor-4 During Lung Injury

Lung epithelium is constantly exposed to the environment and is critically important for the orchestration of initial responses to infectious organisms, toxins, and allergic stimuli, and maintenance of normal gaseous exchange and pulmonary function. The integrity of lung epithelium, fluid balance, and transport of molecules is dictated by the tight junctions (TJs). The TJs are formed between adjacent cells. We have focused on the topic of the TJ structure and function in lung epithelial cells. This review includes a summary of the last twenty years of literature reports published on the disrupted TJs and epithelial barrier in various lung conditions and expression and regulation of specific TJ proteins against pathogenic stimuli. We discuss the molecular signaling and crosstalk among signaling pathways that control the TJ structure and function. The Toll-like receptor-4 (TLR4) recognizes the pathogen- and damage-associated molecular patterns released during lung injury and inflammation and coordinates cellular responses. The molecular aspects of TLR4 signaling in the context of TJs or the epithelial barrier are not fully known. We describe the current knowledge and possible networking of the TLR4-signaling with cellular and molecular mechanisms of TJs, lung epithelial barrier function, and resistance to treatment strategies.

Effects of Dietary Fiber on Growth Performance, Nutrient Digestibility and Intestinal Health in Different Pig Breeds

To explore the effect of dietary fiber on growth performance and intestinal health in different pig breeds, forty Taoyuan and Duroc pigs (pure breeds) of 60 days of age were randomly divided into a 2 (diet) × 2 (breed) factorial experiment (n = 10), and fed with a basal diet (BD) or high-fiber diet (HFD). The trial lasted for 28 d, and results showed that the Taoyuan pigs had a higher average daily feed intake (ADFI) than the Duroc pigs (p < 0.05). The average daily gain (ADG) and digestibilities of gross energy (GE) and crude protein (CP) were higher in Taoyuan pigs than in the Duroc pigs under HFD feeding (p < 0.05). The HFD increased the superoxide dismutase (SOD) and catalase (CAT) activity in Taoyuan pigs (p < 0.05). Interestingly, Taoyuan pigs had a higher jejunal villus height and ratio of villus height to crypt depth (V/C) than the Duroc pigs. The HFD significantly improved the villus height and V/C ratio in duodenum and jejunum (p < 0.05). The HFD also increased the jejunal maltase and ileal sucrase activities in Duroc and Taoyuan pigs, respectively (p < 0.05). Taoyuan pigs had a higher expression level of duodenal fatty acid transport protein-1 (FATP-1) than the Duroc pigs (p < 0.05). Furthermore, the HFD acutely improved the expression levels of ileal SGLT-1 and GLUT-2, and the expression levels of jejunal occludin and claudin-1 in Taoyuan pigs (p < 0.05). Importantly, Taoyuan pigs had a higher colonic Bifidobacterium abundance than the Duroc pigs (p < 0.05). The HFD not only elevated the colonic Lactobacillus abundance and butyrate acid content in Taoyuan pigs, but also increased the acetic and propionic acid contents in both the pig breeds (p < 0.05). These results indicated a difference in dietary fiber (DF) utilization by the two pig breeds, and results may also suggest a beneficial character of DF in regulating intestinal health.

Cutaneous dysbiosis may amplify barrier dysfunction in patients with atopic dermatitis

Atopic dermatitis (AD) is associated with cutaneous dysbiosis, barrier defects, and immune dysregulation, but the interplay between these factors needs further study. Early-onset barrier dysfunction may facilitate an innate immune response to commensal organisms and, consequently, the development of allergic sensitization. We aimed to compare the cutaneous microbiome in patients with active dermatitis with and without a history of childhood flexural dermatitis (atopic dermatitis). Next-gen Ion-Torrent deep-sequencing identified AD-associated changes in the skin bacterial microbiome ("bacteriome") and fungal microbiome ("mycobiome") of affected skin in swabs from areas of skin affected by dermatitis. Data were analyzed for diversity, abundance, and inter-kingdom correlations. Microbial interactions were assessed in biofilms using metabolic activity (XTT) assay and scanning electron microscopy (SEM), while host-pathogen interactions were determined in cultured primary keratinocytes exposed to biofilms. Increased richness and abundance of Staphylococcus, Lactococcus, and Alternaria were found in atopics. Staphylococcus and Alternaria formed robust mixed-species biofilms (based on XTT and SEM) that were resistant to antifungals/antimicrobials. Furthermore, their biofilm supernatant was capable of influencing keratinocytes biology (pro-inflammatory cytokines and structural proteins), suggesting an additive effect on AD-associated host response. In conclusion, microbial inter-kingdom and host-microbiome interactions may play a critical role in the modulation of atopic dermatitis to a greater extent than in non-atopic adults with allergic contact dermatitis.

English Version of Clinical Practice Guidelines for the Management of Atopic Dermatitis 2021

This is the English version of the Clinical Practice Guidelines for the Management of Atopic Dermatitis 2021. Atopic dermatitis (AD) is a disease characterized by relapsing eczema with pruritus as a primary lesion. In Japan, from the perspective of evidence-based medicine, the current strategies for the treatment of AD consist of three primary measures: (i) use of topical corticosteroids, tacrolimus ointment, and delgocitinib ointment as the main treatment of the inflammation; (ii) topical application of emollients to treat the cutaneous barrier dysfunction; and (iii) avoidance of apparent exacerbating factors, psychological counseling, and advice about daily life. In the present revised guidelines, descriptions of three new drugs, namely, dupilumab, delgocitinib, and baricitinib, have been added. The guidelines present recommendations to review clinical research articles, evaluate the balance between the advantages and disadvantages of medical activities, and optimize medical activity-related patient outcomes with respect to several important points requiring decision-making in clinical practice.

Herpes Simplex Virus 1 Can Bypass Impaired Epidermal Barriers upon Ex Vivo Infection of Skin from Atopic Dermatitis Patients

To infect its human host, herpes simplex virus 1 (HSV-1) must overcome the protective barriers of skin and mucosa. Here, we addressed whether pathological skin conditions can facilitate viral entry via the skin surface and used ex vivo infection studies to explore viral invasion in atopic dermatitis (AD) skin characterized by disturbed barrier functions. Our focus was on the visualization of the onset of infection in single cells to determine the primary entry portals in the epidermis. After ex vivo infection of lesional AD skin, we observed infected cells in suprabasal layers indicating successful invasion in the epidermis via the skin surface which was never detected in control skin where only sample edges allowed viral access. The redistribution of filaggrin, loricrin, and tight-junction components in the lesional skin samples suggested multiple defective mechanical barriers. To dissect the parameters that contribute to HSV-1 invasion, we induced an AD-like phenotype by adding the Th2 cytokines interleukin 4 (IL-4) and IL-13 to healthy human skin samples. Strikingly, we detected infected cells in the epidermis, implying that the IL-4/IL-13-driven inflammation is sufficient to induce modifications allowing HSV-1 to penetrate the skin surface. In summary, not only did lesional AD skin facilitate HSV-1 penetration but IL-4/IL-13 responses alone allowed virus invasion. Our results suggest that the defective epidermal barriers of AD skin and the inflammation-induced altered barriers in healthy skin can make receptors accessible for HSV-1.

IMPORTANCE Herpes simplex virus 1 (HSV-1) can target skin to establish primary infection in the epithelium. While the human skin provides effective barriers against viral invasion under healthy conditions, a prominent example of successful invasion is the disseminated HSV-1 infection in the skin of atopic dermatitis (AD) patients. AD is characterized by impaired epidermal barrier functions, chronic inflammation, and dysbiosis of skin microbiota. We addressed the initial invasion process of HSV-1 in atopic dermatitis skin to understand whether the physical barrier functions are sufficiently disturbed to allow the virus to invade skin and reach its receptors on skin cells. Our results demonstrate that HSV-1 can indeed penetrate and initiate infection in atopic dermatitis skin. Since treatment of skin with IL-4 and IL-13 already resulted in successful invasion, we assume that inflammation-induced barrier defects play an important role for the facilitated access of HSV-1 to its target cells.

Claudin-1 Mediated Tight Junction Dysfunction as a Contributor to Atopic March

Atopic march refers to the phenomenon wherein the occurrence of asthma and food allergy tends to increase after atopic dermatitis. The mechanism underlying the progression of allergic inflammation from the skin to gastrointestinal (GI) tract and airways has still remained elusive. Impaired skin barrier was proposed as a risk factor for allergic sensitization. Claudin-1 protein forms tight junctions and is highly expressed in the epithelium of the skin, airways, and GI tract, thus, the downregulation of claudin-1 expression level caused by CLDN-1 gene polymorphism can mediate common dysregulation of epithelial barrier function in these organs, potentially leading to allergic sensitization at various sites. Importantly, in patients with atopic dermatitis, asthma, and food allergy, claudin-1 expression level was significantly downregulated in the skin, bronchial and intestinal epithelium, respectively. Knockdown of claudin-1 expression level in mouse models of atopic dermatitis and allergic asthma exacerbated allergic inflammation, proving that downregulation of claudin-1 expression level contributes to the pathogenesis of allergic diseases. Therefore, we hypothesized that the tight junction dysfunction mediated by downregulation of claudin-1 expression level contributes to atopic march. Further validation with clinical data from patients with atopic march or mouse models of atopic march is needed. If this hypothesis can be fully confirmed, impaired claudin-1 expression level may be a risk factor and likely a diagnostic marker for atopic march. Claudin-1 may serve as a valuable target to slowdown or block the progression of atopic march.

Mechanotransduction in Skin Inflammation

In the process of mechanotransduction, the cells in the body perceive and interpret mechanical stimuli to maintain tissue homeostasis and respond to the environmental changes. Increasing evidence points towards dysregulated mechanotransduction as a pathologically relevant factor in human diseases, including inflammatory conditions. Skin is the organ that constantly undergoes considerable mechanical stresses, and the ability of mechanical factors to provoke inflammatory processes in the skin has long been known, with the Koebner phenomenon being an example. However, the molecular mechanisms and key factors linking mechanotransduction and cutaneous inflammation remain understudied. In this review, we outline the key players in the tissue's mechanical homeostasis, the available data, and the gaps in our current understanding of their aberrant regulation in chronic cutaneous inflammation. We mainly focus on psoriasis as one of the most studied skin inflammatory diseases; we also discuss mechanotransduction in the context of skin fibrosis as a result of chronic inflammation. Even though the role of mechanotransduction in inflammation of the simple epithelia of internal organs is being actively studied, we conclude that the mechanoregulation in the stratified epidermis of the skin requires more attention in future translational research.

Atopic dermatitis: molecular, cellular, and clinical aspects

Atopic dermatitis (AD) is a complicated, inflammatory skin disease, which numerous genetic and environmental factors play roles in its development. AD is categorized into different phenotypes and stages, although they are mostly similar in their pathophysiological aspects. Immune response alterations and structural distortions of the skin-barrier layer are evident in AD patients. Genetic makeup, lifestyle, and environment are also significantly involved in contextual factors. Genes involved in AD-susceptibility, including filaggrin and natural moisturizing, cause considerable structural modifications in the skin's lipid bilayer and cornified envelope. Additionally, the skin's decreased integrity and altered structure are accompanied by biochemical changes in the normal skin microflora's dysbiosis. The dynamic immunological responses, genetic susceptibilities, and structural modifications associated with AD's pathophysiology will be extensively discussed in this review, each according to the latest achievements and findings.

TNF-α induces Claudin-1 expression in renal tubules in Alport mice

Claudin-1 (CL-1) is responsible for the paracellular barrier function of glomerular parietal epithelial cells (PEC) in kidneys, but the role of CL-1 in proximal tubules remains to be elucidated. In this study, to evaluate CL-1 as a potential therapeutic drug target for chronic kidney disease, we investigated change of CL-1 expression in the proximal tubules of diseased kidney and elucidated the factors that induced this change. We established Alport mice as a kidney disease model and investigated the expression of CL-1 in diseased kidney using quantitative PCR and immunohistochemistry (IHC). Compared to wild type mice, Alport mice showed significant increases in plasma creatinine, urea nitrogen and urinary albumin excretion. CL-1 mRNA was increased significantly in the kidney cortex and CL-1 was localized on the adjacent cell surfaces of PECs and proximal tubular epithelial cells. The infiltration of inflammatory cells around proximal tubules and a significant increase in TNF-α mRNA were observed in diseased kidneys. To reveal factors that induce CL-1, we analyzed the induction of CL-1 by albumin or tumor necrosis factor (TNF)-α in human proximal tubular cells (RPTEC/TERT1) using quantitative PCR and Western blotting. TNF-α increased CL-1 expression dose-dependently, though albumin did not affect CL-1 expression in RPTEC/TERT1. In addition, both CL-1 and TNF-α expression were significantly increased in UUO mice, which are commonly used as a model of tubulointerstitial inflammation without albuminuria. These results indicate that CL-1 expression is induced by inflammation, not by albuminuria in diseased proximal tubules. Moreover, we examined the localization of CL-1 in the kidney of IgA nephropathy patients by IHC and found CL-1 expression was also elevated in the proximal tubular cells. Taken together, CL-1 expression is increased in the proximal tubular epithelial cells of diseased kidney. Inflammatory cells around the tubular epithelium may produce TNF-α which in turn induces CL-1 expression.

Exacerbating factors and disease burden in patients with atopic dermatitis

The number of patients with atopic dermatitis is on the rise worldwide, and Japan is no exception. According to recent estimates of the percentage of patients with atopic dermatitis in Japan by age, the majority of patients are between 20 and 44 years old. Because the peak age of onset of atopic dermatitis is during infancy, many patients may experience prolonged symptoms from infancy to adulthood. A prolonged clinical course also increases the burden of atopic dermatitis on affected patients. Decreased productivity due to work disruptions, reduced daily activity, higher direct medical costs, fatigue, and daytime sleepiness due to sleep disturbances are typical burdens on patients with atopic dermatitis. In order to reduce these burdens, it is necessary to shorten its clinical course and achieve long-term control without relying on medications, possibly by using avoidance or coping measures of aggravating factors. Typical aggravating factors of atopic dermatitis include irritant dermatitis, food allergy in children, sweating, and psychological stress in adults. Food allergy places a heavy burden on the quality of life of affected patients and their families. The effectiveness of educational interventions for sweating and psychological stress is unclear. We must also evaluate the economic burden and cost-effectiveness of interventions on the patient as aggravating factors to be addressed.

The Epidermis: Redox Governor of Health and Diseases

A functional epithelial barrier necessitates protection against dehydration, and ichthyoses are caused by defects in maintaining the permeability barrier in the stratum corneum (SC), the uppermost protective layer composed of dead cells and secretory materials from the living layer stratum granulosum (SG). We have found that loricrin (LOR) is an essential effector of cornification that occurs in the uppermost layer of SG (SG1). LOR promotes the maturation of corneocytes and extracellular adhesion structure through organizing disulfide cross-linkages, albeit being dispensable for the SC permeability barrier. This review takes psoriasis and AD as the prototype of impaired cornification. Despite exhibiting immunological traits that oppose each other, both conditions share the epidermal differentiation complex as a susceptible locus. We also review recent mechanistic insights on skin diseases, focusing on the Kelch-like erythroid cell-derived protein with the cap "n" collar homology-associated protein 1/NFE2-related factor 2 signaling pathway, as they coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of thiol-mediated crosstalk between keratinocytes and leukocytes in the epidermis that was put forward earlier.

14-3-3 proteins stabilize LGI1-ADAM22 levels to regulate seizure thresholds in mice

What percentage of the protein function is required to prevent disease symptoms is a fundamental question in genetic disorders. Decreased transsynaptic LGI1-ADAM22 protein complexes, because of their mutations or autoantibodies, cause epilepsy and amnesia. However, it remains unclear how LGI1-ADAM22 levels are regulated and how much LGI1-ADAM22 function is required. Here, by genetic and structural analysis, we demonstrate that quantitative dual phosphorylation of ADAM22 by protein kinase A (PKA) mediates high-affinity binding of ADAM22 to dimerized 14-3-3. This interaction protects LGI1-ADAM22 from endocytosis-dependent degradation. Accordingly, forskolin-induced PKA activation increases ADAM22 levels. Leveraging a series of ADAM22 and LGI1 hypomorphic mice, we find that ∼50% of LGI1 and ∼10% of ADAM22 levels are sufficient to prevent lethal epilepsy. Furthermore, ADAM22 function is required in excitatory and inhibitory neurons. These results suggest strategies to increase LGI1-ADAM22 complexes over the required levels by targeting PKA or 14-3-3 for epilepsy treatment.

MiRNA-132/212 regulates tight junction stabilization in blood-brain barrier after stroke

MicroRNA-132/212 has been supposed as a critical gene related to the blood–brain barrier (BBB) protection after stroke, but its regulation pathway including the upstream regulator and downstream targets is still unclear. Herein, we demonstrated the cAMP response element-binding protein (CREB)-regulated transcription coactivator-1 (CRTC1) to be the upstream regulator of miRNA-132/212 using CRTC1 knockout and wild-type mice. CRTC1 deletion led to the reduction of miRNA-132/212 expression in mice brain after ischemic stroke, significantly increased infarct volume, and aggravated BBB permeability with worsening neurological deficits. Furthermore, we identified that miRNA-132 repressed Claudin-1, tight junction-associated protein-1 (TJAP-1), and RNA-binding Fox-1 (RBFox-1) by directly binding to their respective 3′-untranslated regions, which alleviated the ischemic damage by enhancing neuronal survival and BBB integrity. Moreover, the co-culture of endothelial cells with CRTC1-deficient neurons aggravated the cell vulnerability to hypoxia, also supporting the idea that miRNA-132/212 cluster is regulated by CRTC1 and acts as a crucial role in the mitigation of ischemic damage. This work is a step forward for understanding the role of miRNA-132/212 in neurovascular interaction and may be helpful for potential gene therapy of ischemic stroke.

Docosahexaenoic Acid Modulates Paracellular Absorption of Testosterone and Claudin-1 Expression in a Tissue-Engineered Skin Model

Healthy skin moLEdels produced by tissue-engineering often present a suboptimal skin barrier function as compared with normal human skin. Moreover, skin substitutes reconstructed according to the self-assembly method were found to be deficient in polyunsaturated fatty acids (PUFAs). Therefore, in this study, we investigated the effects of a supplementation of the culture media with docosahexaenoic acid (DHA) on the barrier function of skin substitutes. To this end, 10 μM DHA-supplemented skin substitutes were produced (n = 3), analyzed, and compared with controls (substitutes without supplementation). A Franz cell diffusion system, followed by ultra-performance liquid chromatography, was used to perform a skin permeability to testosterone assay. We then used gas chromatography to quantify the PUFAs found in the epidermal phospholipid fraction of the skin substitutes, which showed successful DHA incorporation. The permeability to testosterone was decreased following DHA supplementation and the lipid profile was improved. Differences in the expression of the tight junction (TJ) proteins claudin-1, claudin-4, occludin, and TJ protein-1 were observed, principally a significant increase in claudin-1 expression, which was furthermore confirmed by Western blot analyses. In conclusion, these results confirm that the DHA supplementation of cell culture media modulates different aspects of skin barrier function in vitro and reflects the importance of n-3 PUFAs regarding the lipid metabolism in keratinocytes.

Claudin-7 in keratinocytes is downregulated by the inhibition of HMG-CoA reductase and is highly expressed in the stratum granulosum of the psoriatic epidermis

BACKGROUND

Cholesterol is de novo synthesized in the upper epidermis and plays an important role in maintaining the normality of skin. Studying the impact of the inhibition of cholesterol de novo synthesis in the epidermis may help understand how skin homeostasis is regulated.

OBJECTIVE

In this study, we created a gene expression profile to investigate the effect of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors on epidermal homeostasis.

METHODS

A microarray analysis was performed using normal keratinocytes with or without HMG-CoA reductase inhibitor (pitavastatin) treatment. Real-time PCR confirmed the reproducibility of genes with altered expression in keratinocytes treated with HMG-CoA reductase inhibitors. Among these genes, we focused on reduced expression of claudin 7 histologically confirmed by immunohistochemical staining, in situ hybridization, and immunoelectron microscopy.

RESULTS

Claudin-7 was highly expressed in the stratum granulosum of psoriatic lesions but was not expressed in the normal epidermis. Immunoelectron microscopy revealed that claudin-7 was localized in the keratohyalin granules of psoriatic lesions.

CONCLUSION

These results indicate that claudin-7 expression was regulated by HMG-CoA reductase in the epidermis and might play a pathogenic role in the keratohyalin granules found in the epidermal granular layer of psoriasis.

Direct assessment of individual skin barrier components by electrical impedance spectroscopy

BACKGROUND

Expression of the tight junction proteins Cldn1 and 4 is altered in skin diseases such as atopic dermatitis, and Cldn1 deficiency affects skin barrier formation. Impedance spectroscopy (IS) has been proven to allow detection of alterations in the skin barrier but is currently unable to separate effects on viable epidermis (VE) and stratum corneum (SC).

METHODS

Effects of siRNA-mediated Cldn1 and 4 knockdown in reconstructed human epidermis (RHE) on VE and SC barrier function were investigated with Ussing chamber-based IS. Barrier components were sequentially altered, employing iron oxide nanoparticles and EGTA, to identify their contribution to the impedance spectrum. Resistance changes due to apically applied hyperosmolar electrolyte were used to identify barrier defects non-invasively.

RESULTS

IS of RHE yielded two relaxation frequencies, representing the barrier properties of the SC (~1000 Hz) and VE (~100 Hz). As proof of concept, it was shown that the Cldn1 knockdown-induced resistance drop arises from the impairment of both SC and VE, indicated by a shift of both relaxation frequencies. Hyperosmolar electrolyte penetration allowed non-invasive detection of Cldn1 knockdown via time-dependent frequency shifts. The absence of Cldn4 knockdown-induced changes revealed the weaknesses of transepithelial electrical resistance analysis.

CONCLUSION

In conclusion, the present technique allows to separately measure the barrier properties of SC and VE and further evaluate the Cldn1 and 4 knockdown impact on the skin barrier. As the measurement with agarose-embedded electrolyte allowed non-invasive identification of the Cldn1 knockdown, this opens the way to detailed in vivo skin barrier assessment.

The Influence of Microbiome Dysbiosis and Bacterial Biofilms on Epidermal Barrier Function in Atopic Dermatitis-An Update

Atopic dermatitis (AD) is a common inflammatory dermatosis affecting up to 30% of children and 10% of adults worldwide. AD is primarily driven by an epidermal barrier defect which triggers immune dysregulation within the skin. According to recent research such phenomena are closely related to the microbial dysbiosis of the skin. There is growing evidence that cutaneous microbiota and bacterial biofilms negatively affect skin barrier function, contributing to the onset and exacerbation of AD. This review summarizes the latest data on the mechanisms leading to microbiome dysbiosis and biofilm formation in AD, and the influence of these phenomena on skin barrier function.

Tsc1 regulates tight junction independent of mTORC1

Tuberous sclerosis complex 1 (Tsc1) is a tumor suppressor that functions together with Tsc2 to negatively regulate the mechanistic target of rapamycin complex 1 (mTORC1) activity. Here, we show that Tsc1 has a critical role in the tight junction (TJ) formation of epithelium, independent of its role in Tsc2 and mTORC1 regulation. When an epithelial cell establishes contact with neighboring cells, Tsc1, but not Tsc2, migrates from the cytoplasm to junctional membranes, in which it binds myosin 6 to anchor the perijunctional actin cytoskeleton to β-catenin and ZO-1. In its absence, perijunctional actin cytoskeleton fails to form. In mice, intestine-specific or inducible, whole-body Tsc1 ablation disrupts adherens junction/TJ structures in intestine or skin epithelia, respectively, causing Crohn's disease-like symptoms in the intestine or psoriasis-like phenotypes on the skin. In patients with Crohn's disease or psoriasis, junctional Tsc1 levels in epithelial tissues are markedly reduced, concomitant with the TJ structure impairment, suggesting that Tsc1 deficiency may underlie TJ-related diseases. These findings establish an essential role of Tsc1 in the formation of cell junctions and underpin its association with TJ-related human diseases.

Effect of 3D-Fibroblast Dermis Constructed by Layer-by-Layer Cell Coating Technique on Tight Junction Formation and Function in Full-Thickness Skin Equivalent

Human skin equivalents (HSEs) consisting of an epidermis and dermis have been used as promising tools for drug evaluation and for clinical applications in regenerative medicine. Normal human dermal fibroblasts (NHDFs) are essential for the fabrication of HSEs because they play an important role in the maturation of the epidermis. Recently, epidermal tight junctions (TJs), which are complex cell-cell junctions, have attracted much attention as a second barrier and regulator for other barrier functions. In a previous study, we revealed the expression of TJ-related proteins and the time course of formation of TJ structure in the HSE (layer-by-layer (LbL)-three-dimensional (3D) Skin) constructed by layer-by-layer (LbL) cell coating technique that have a unique dermis consisting of NHDFs only (3D-fibroblast dermis). However, the effect of the 3D-fibroblast dermis on the formation of functional epidermal TJs is unknown. In this study, we investigated the effect of the 3D-fibroblast dermis on the expression of TJ-related proteins and TJ function in LbL-3D Skin. We demonstrated that the 3D-fibroblast dermis affects the long-term expression of TJ-related proteins and the formation of TJ with barrier function in the epidermis. These results show that the 3D-fibroblast dermis in LbL-3D Skin contributes to the formation and maintenance of functional TJs as in native human skin by direct contact with KCs.

Interferon-γ downregulates tight junction function, which is rescued by interleukin-17A

Although atopic dermatitis (AD) has been reported to be a typical type 2 immune response disease, it is also an inflammatory skin disease that involves cytokines, such as Th1, Th17 and Th22. However, little is known about the mechanism by which the candidate cytokines, alone or in combination, are involved in AD pathology. Differences in cytokine balance, which contribute to the complexity of AD pathology, may influence the stratum corneum barrier function through tight junction (TJ) functional stability and contribute to disease severity. To confirm the regulatory mechanism of TJ protein expression in AD, we investigated the Th1 and Th17 pathways, which are the initiation factors of chronic AD pathology. We examined the effects of these cytokines on TJ protein expression in normal human epidermal keratinocytes in vitro, and also examined their function in a human skin equivalent model. We observed a time‐ and dose‐dependent inhibitory effect of IFN‐γ on claudin‐1 expression via the IFN‐γ receptor/JAK/STAT signalling pathway. IFN‐γ impaired TJ function in a human skin equivalent model. Moreover, we investigated co‐stimulation with IL‐17A, which is highly expressed in AD skin lesions and found that IL‐17A restores IFN‐γ‐induced TJ dysfunction. This restoration of TJ function was mediated by atypical protein kinase C zeta activation without recovery of TJ protein expression. These results are informative for personalized AD treatment via systemic therapies using anti‐cytokine antibodies and/or JAK inhibitors.

Grainyhead-like transcription factors: guardians of the skin barrier

There has been selective pressure to maintain a skin barrier since terrestrial animals evolved 360 million years ago. These animals acquired an unique integumentary system with a keratinized, stratified, squamous epithelium surface barrier. The barrier protects against dehydration and entry of microbes and toxins. The skin barrier centres on the stratum corneum layer of the epidermis and consists of cornified envelopes cemented by the intercorneocyte lipid matrix. Multiple components of the barrier undergo cross-linking by transglutaminase (TGM) enzymes, while keratins provide additional mechanical strength. Cellular tight junctions also are crucial for barrier integrity. The grainyhead-like (GRHL) transcription factors regulate the formation and maintenance of the integument in diverse species. GRHL3 is essential for formation of the skin barrier during embryonic development, whereas GRHL1 maintains the skin barrier postnatally. This is achieved by transactivation of Tgm1 and Tgm5, respectively. In addition to its barrier function, GRHL3 plays key roles in wound repair and as an epidermal tumour suppressor. In its former role, GRHL3 activates the planar cell polarity signalling pathway to mediate wound healing by providing directional migration cues. In squamous epithelium, GRHL3 regulates the balance between proliferation and differentiation, and its loss induces squamous cell carcinoma (SCC). In the skin, this is mediated through increased expression of MIR21, which reduces the expression levels of GRHL3 and its direct target, PTEN, leading to activation of the PI3K-AKT signalling pathway. These data position the GRHL family as master regulators of epidermal homeostasis across a vast gulf of evolutionary history.

IL-13 modulates ∆Np63 levels causing altered expression of barrier- and inflammation-related molecules in human keratinocytes: A possible explanation for chronicity of atopic dermatitis

BACKGROUND

Barrier disruption and an excessive immune response in keratinocytes are now considered to have important roles in the pathophysiology of atopic dermatitis (AD). Furthermore, disturbed keratinocyte differentiation is considered to underlie AD. ΔNp63, a p53-like transcription factor, is a major regulator of keratinocyte differentiation. However, the functional significance of ΔNp63 in AD has not been clarified.

OBJECTIVE

In this study, we aimed to investigate the influence of the type 2 inflammatory environment on ΔNp63 expression and AD-associated molecules regulated by ΔNp63 in keratinocytes.

METHODS

The immunohistochemical expression profiles of ΔNp63 and AD-related molecules were evaluated in human skin tissue. The function of ΔNp63 in the regulation of AD-related molecules and the influence of the type 2 inflammatory environment on ΔNp63 expression were investigated using human primary keratinocytes. Expression of ΔNp63 was manipulated using the RNA interfering method.

RESULTS

In healthy skin tissue, we observed an inverse expression pattern between ∆Np63 and some barrier-related proteins including filaggrin, caspase-14, claudin-1, and claudin-4. ΔNp63 regulated expression of these genes and proteins. In addition, production of IL-1β and IL-33, pro-inflammatory cytokines, was modulated by ΔNp63. Furthermore, prolonged IL-13 exposure increased the thickness of the three-dimensional culture of keratinocytes. IL-13 interfered with ΔNp63 downregulation during calcium-induced keratinocyte differentiation. IL-13 modulated some barrier-related and inflammation-related molecules, which were regulated by ΔNp63.

CONCLUSIONS

We have shown that ΔNp63 modulated AD-related barrier and inflammatory molecules. In addition, ΔNp63 expression was affected by IL-4/IL-13. IL-13-ΔNp63 axis would integrate two major factors of AD pathogenesis: dysregulated barrier and inflammation.

A combination of Olea europaea leaf extract and Spirodela polyrhiza extract alleviates atopic dermatitis by modulating immune balance and skin barrier function in a 1-chloro-2,4-dinitrobenzene-induced murine model

BACKGROUND

Atopic dermatitis is a chronic inflammatory skin disease in humans. Although Olea europaea leaf extract (OLE) and Spirodela polyrhiza extract (SPE) have been used to protect against skin damage, the effects of their combined administration on atopic dermatitis have yet to studied.

PURPOSE

In this study, we evaluated the potential therapeutic effects of an OLE and SPE combination on the progression of atopic dermatitis and the possible mechanisms underlying these effects in 1-chloro-2,4-dinitrobenzene (DNCB)-treated NC/Nga mice.

METHODS

Atopic dermatitis was induced by topical application of 0.2% w/v DNCB prepared in an olive oil:acetone solution (1:3), and thereafter OLE, SPE and OLE + SPE were administered orally for 5 weeks. We determined atopic dermatitis symptoms, serum IgE levels, and levels of cytokine- and gene expression in the dorsal skin and splenocytes, and performed histological and immune cell subtype analyses. The expression of skin barrier-related proteins (filaggrin, sirtuin 1, and claudin 1) was also evaluated.

RESULTS

The OLE + SPE combination significantly ameliorated atopic dermatitis symptoms, including dermatitis scores, and reduced epidermal thickness and infiltration of different inflammatory cells in mice with DNCB-induced atopic dermatitis. It also significantly reduced the number of CD4⁺, CD8⁺, and CD4⁺/CD69⁺ T cells; immunoglobulin E-producing B cells (CD23⁺/B220⁺) in the axillary lymph nodes; CD3⁺ T-cell eosinophils (chemokine-chemokine receptor 3⁺/CD11b⁺) in the skin; and CD3⁺ T cells, immunoglobulin E-producing B cells (CD23⁺/B220⁺), and eosinophils in peripheral blood mononuclear cells. Additionally, the experimental combination lowered levels of serum immunoglobulin E and histamine, as well as Th2-mediated cytokines, and interleukin-4, -5, and -13, whereas it increased the levels of Th1-mediated cytokine interferon-γ in splenocytes. Furthermore, the preparation significantly restored expression of the skin barrier-related proteins filaggrin, sirtuin 1, and claudin 1, and also reduced the expression of the inflammatory cytokine interleukin-6 and chemokine-chemokine receptor 3, as well as the pruritus-related cytokine interleukin-31 and interleukin-31 receptor, in atopic dermatitis skin lesions.

CONCLUSION

Taken together, our findings indicate that administration of a combination of OLE and SPE can alleviate atopic dermatitis symptoms by regulating immune balance and skin barrier function and may be an effective therapeutic option for the treatment of atopic dermatitis.

Costello syndrome model mice with a HrasG12S/+ mutation are susceptible to develop house dust mite-induced atopic dermatitis

Costello syndrome is an autosomal dominant disorder that is caused by germline HRAS mutations. Patients with Costello syndrome present craniofacial abnormalities, cardiac defects, and cancer predisposition, as well as skin abnormalities, including papillomas, keratosis pilaris, and eczematous dermatitis. However, the mechanisms underlying the dermatological abnormalities remain unclear. Here, we demonstrated that knock-in mice expressing an Hras G12S mutation (Hras^G12S/+ mice) are susceptible to develop atopic dermatitis (AD)-like skin lesions, including eczema, pruritus, elevated serum IgE levels, acanthosis, and the infiltration of mast cells, basophils, and type-2 innate lymphoid cells in the dermis, after stimulation with house dust mite allergens (Dermatophagoides farinae, Dfb). Reduced skin barrier function, increased proliferation of phosphorylated ERK (p-ERK)-positive epidermal cells, and increased Th2-type cytokines as well as epithelial cell-derived cytokines, including IL-33, were observed in the skin tissue of Hras^G12S/+ mice compared with Hras^+/+ mice. Cultured Hras^G12S/+ keratinocytes exhibited increased IL-33 expression after Dfb stimulation. PD0325901, an MEK inhibitor, ameliorated AD-like symptoms in Hras^G12S/+ mice, showing decreased proliferation of p-ERK-positive epidermal cells and decreased expression of IL-33. Our findings indicate that the epidermis of Hras^G12S/+ mice stimulated by Dfb strongly induced IL-33 expression and type-2 innate lymphoid cells, resulting in AD-like skin lesions. These results suggest that the epidermis of Hras^G12S/+ mice are prone to development of eczematous dermatitis stimulated with house dust mite allergens.

Cutibacterium acnes regulates the epidermal barrier properties of HPV-KER human immortalized keratinocyte cultures

Our skin provides a physical barrier to separate the internal part of our body from the environment. Maintenance of complex barrier functions is achieved through anatomical structures in the skin, the stratified squamous epithelium specialized junctional organelles, called tight junctions (TJs). Several members of our microbial communities are known to affect the differentiation state and function of the colonized organ. Whether and how interactions between skin cells and cutaneous microbes, including Cutibacterium acnes (C. acnes), modify the structure and/or function of our skin is currently only partly understood. Thus, in our studies, we investigated whether C. acnes may affect the epidermal barrier using in vitro model systems. Real-time cellular analysis showed that depending on the keratinocyte differentiation state, the applied C. acnes strains and their dose, the measured impedance values change, together with the expression of selected TJ proteins. These may reflect barrier alterations, which can be partially restored upon antibiotic–antimycotic treatment. Our findings suggest that C. acnes can actively modify the barrier properties of cultured keratinocytes, possibly through alteration of tight cell-to-cell contacts. Similar events may play important roles in our skin, in the maintenance of cutaneous homeostasis.

Skin Barriers in Dermal Drug Delivery: Which Barriers Have to Be Overcome and How Can We Measure Them?

Although, drugs are required in the various skin compartments such as viable epidermis, dermis, or hair follicles, to efficiently treat skin diseases, drug delivery into and across the skin is still challenging. An improved understanding of skin barrier physiology is mandatory to optimize drug penetration and permeation. The various barriers of the skin have to be known in detail, which means methods are needed to measure their functionality and outside-in or inside-out passage of molecules through the various barriers. In this review, we summarize our current knowledge about mechanical barriers, i.e., stratum corneum and tight junctions, in interfollicular epidermis, hair follicles and glands. Furthermore, we discuss the barrier properties of the basement membrane and dermal blood vessels. Barrier alterations found in skin of patients with atopic dermatitis are described. Finally, we critically compare the up-to-date applicability of several physical, biochemical and microscopic methods such as transepidermal water loss, impedance spectroscopy, Raman spectroscopy, immunohistochemical stainings, optical coherence microscopy and multiphoton microscopy to distinctly address the different barriers and to measure permeation through these barriers in vitro and in vivo.

Skin Barrier Abnormalities and Immune Dysfunction in Atopic Dermatitis

Atopic dermatitis (AD) is a common and relapsing skin disease that is characterized by skin barrier dysfunction, inflammation, and chronic pruritus. While AD was previously thought to occur primarily in children, increasing evidence suggests that AD is more common in adults than previously assumed. Accumulating evidence from experimental, genetic, and clinical studies indicates that AD expression is a precondition for the later development of other atopic diseases, such as asthma, food allergies, and allergic rhinitis. Although the exact mechanisms of the disease pathogenesis remain unclear, it is evident that both cutaneous barrier dysfunction and immune dysregulation are critical etiologies of AD pathology. This review explores recent findings on AD and the possible underlying mechanisms involved in its pathogenesis, which is characterized by dysregulation of immunological and skin barrier integrity and function, supporting the idea that AD is a systemic disease. These findings provide further insights for therapeutic developments aiming to repair the skin barrier and decrease inflammation.

Tight junctions in the development of asthma, chronic rhinosinusitis, atopic dermatitis, eosinophilic esophagitis, and inflammatory bowel diseases

This review focuses on recent developments related to asthma, chronic rhinosinusitis, atopic dermatitis (AD), eosinophilic esophagitis, and inflammatory bowel diseases (IBD), with a particular focus on tight junctions (TJs) and their role in the pathogenetic mechanisms of these diseases. Lung, skin, and intestinal surfaces are lined by epithelial cells that interact with environmental factors and immune cells. Therefore, together with the cellular immune system, the epithelium performs a pivotal role as the first line physical barrier against external antigens. Paracellular space is almost exclusively sealed by TJs and is maintained by complex protein-protein interactions. Thus, TJ dysfunction increases paracellular permeability, resulting in enhanced flux across TJs. Epithelial TJ dysfunction also causes immune cell activation and contributes to the pathogenesis of chronic lung, skin, and intestinal inflammation. Characterization of TJ protein alteration is one of the key factors for enhancing our understanding of allergic diseases as well as IBDs. Furthermore, TJ-based epithelial disturbance can promote immune cell behaviors, such as those in dendritic cells, Th2 cells, Th17 cells, and innate lymphoid cells (ILCs), thereby offering new insights into TJ-based targets. The purpose of this review is to illustrate how TJ dysfunction can lead to the disruption of the immune homeostasis in barrier tissues and subsequent inflammation. This review also highlights the various TJ barrier dysfunctions across different organ sites, which would help to develop future drugs to target allergic diseases and IBD.

Characteristics of the nerve barrier and the blood dorsal root ganglion barrier in health and disease

A variety of barriers ensures the protection of the peripheral nervous system from noxious blood-borne or surrounding stimuli. In this review, anatomy and functioning of the blood nerve barrier (BNB) and the blood DRG barrier (BDB) will be presented and key tight junction proteins described: ZO-1, claudin-1, -3, -5, -11, -12, -19, occludin, and tricellulin. Different diseases can lead to or be accompanied by nerve barrier disruption; impairment of nerve barriers in turn worsens pathology. Peripheral nerve injury, diabetic neuropathy and inflammatory polyneuropathy cause an increased permeability of BNB and BDB. Knowledge and understanding of these mechanisms might ultimately lead to the invention of drugs to control barrier function and help ameliorating neurological diseases.

Claudin-1 decrease impacts epidermal barrier function in atopic dermatitis lesions dose-dependently

The transmembrane protein claudin-1 is a major component of epidermal tight junctions (TJs), which create a dynamic paracellular barrier in the epidermis. Claudin-1 downregulation has been linked to atopic dermatitis (AD) pathogenesis but variable levels of claudin-1 have also been observed in healthy skin. To elucidate the impact of different levels of claudin-1 in healthy and diseased skin we determined claudin-1 levels in AD patients and controls and correlated them to TJ and skin barrier function. We observed a strikingly broad range of claudin-1 levels with stable TJ and overall skin barrier function in healthy and non-lesional skin. However, a significant decrease in TJ barrier function was detected in lesional AD skin where claudin-1 levels were further reduced. Investigations on reconstructed human epidermis expressing different levels of claudin-1 revealed that claudin-1 levels correlated with inside-out and outside-in barrier function, with a higher coherence for smaller molecular tracers. Claudin-1 decrease induced keratinocyte-autonomous IL-1β expression and fostered inflammatory epidermal responses to non-pathogenic Staphylococci. In conclusion, claudin-1 decrease beyond a threshold level results in TJ and epidermal barrier function impairment and induces inflammation in human epidermis. Increasing claudin-1 levels might improve barrier function and decrease inflammation and therefore be a target for AD treatment.