Atopic dermatitis (AD) is a chronic inflammatory skin disease in which the skin barrier function is disrupted. In this inflammatory AD environment, cytokines are upregulated, but the cytokine effect on the AD skin barrier is not fully understood. We aimed to investigate the influence of Th2 (IL-4, IL-13, IL-31) and pro-inflammatory (tumor necrosis factor alpha (TNF-α)) cytokines on epidermal morphogenesis, proliferation, differentiation, and stratum corneum lipid properties. For this purpose, we used the Leiden epidermal model (LEM) in which the medium was supplemented with these cytokines. Our results show that IL-4, IL-13, IL-31, and TNF-α induce spongiosis, augment TSLP secretion by keratinocytes, and alter early and terminal differentiation-protein expression in LEMs. TNF-α alone or in combination with Th2 cytokines decreases the level of long chain free fatty acids (FFAs) and ester linked ω-hydroxy (EO) ceramides, consequently affecting the lipid organization. IL-31 increases long chain FFAs in LEMs but decreases relative abundance of EO ceramides. These findings clearly show that supplementation with TNF-α and Th2 cytokines influence epidermal morphogenesis and barrier function. As a result, these LEMs show similar characteristics as found in AD skin and can be used as an excellent tool for screening formulations and drugs for the treatment of AD.

This study shows that alterations in the expression of key enzymes involved in SC lipid synthesis contribute to changes in the lipid composition in AD skin and inflammation may influence expression of these enzymes.

This study shows that NEMs, with FLG-KD and/or cultured in the presence of IL-31, mimic the skin of patients with atopic dermatitis in several aspects, including enhanced bacterial colonization, increased inflammatory and reduced protective responses.

Netherton syndrome (NTS) is a rare genetic skin disease caused by mutations in the serine protease inhibitor Kazal-type 5 gene, which encodes the lympho-epithelial Kazal-type-related inhibitor. NTS patients have profoundly impaired skin barrier function. As stratum corneum (SC) lipids have a crucial role in the skin barrier function, we investigated the SC lipid composition and organization in NTS patients. We studied the SC lipid composition by means of mass spectrometry, and the lipid organization was examined by infrared spectroscopy and X-ray diffraction. Decreased free fatty acid (FFA) chain length and increased levels of monounsaturated FFAs were observed in the SC of NTS patients compared with controls. Furthermore, the level of short-chain ceramides (CERs) was enhanced in NTS patients and a strong reduction in long-chain CER levels was seen in several patients. The changes in lipid composition modified the lipid organization leading to an increased disordering of the lipids compared with the controls. In addition, in a subgroup of patients the organization of the lipid layers changed dramatically. The altered FFA and CER profiles in NTS patients corresponded to changes in the expression of enzymes involved in SC lipid processing. The observed changes in lipid composition, lipid organization, and enzyme expression are likely to contribute to the barrier dysfunction in NTS.

The etiology and pathogenesis of rheumatoid arthritis (RA) are influenced by environmental and genetic risk factors. Shared epitope-coding HLA-DRB1 alleles increase RA risk and severity; however, the underlying mechanisms of action remain unclear. In contrast, several other DRB1 alleles protect against RA. Additionally, genome-wide association studies suggest that RA associates with other, HLA and non-HLA, genes but the relative contributions of such risk loci to RA are incompletely understood. Future research challenges include integrating the epidemiological and genomic data into validated arthritogenic pathways, and determining the mechanisms of interaction between RA risk genes and environmental influences.

Human skin equivalents (HSEs) can be considered a valuable tool to study aspects of human skin, including the skin barrier, or to perform chemical or toxicological screenings. HSEs are three-dimensional skin models that are usually established using primary keratinocytes and closely mimic human skin. The use of primary keratinocytes has several drawbacks, including a limited in vitro life span and large donor-donor variation. This makes them less favorable for in vitro toxicity screenings. Usage of an established keratinocyte cell line circumvents these drawbacks and enables the generation of easy-to-generate and reproducible HSEs, which can be used for pharmacological and/or toxicological screenings. For such screenings, a proper barrier function is required. In this study, we investigated the barrier properties of HSEs established with the keratinocyte cell line N/TERT (N-HSEs). N-HSEs showed comparable tissue morphology and expression of several epidermal proteins compared with HSEs established with primary keratinocytes. Our results clearly demonstrate that N-HSEs not only contain several stratum corneum (SC) barrier properties similar to HSEs, including the presence of the long periodicity phase and a comparable SC permeability, but also show some differences in lipid composition. Nonetheless, the similarities in barrier properties makes N/TERT cells a promising alternative for primary keratinocytes to generate HSEs.

SignificanceThis study identifies a mechanistic basis for the enigmatic, long-observed interaction between the rheumatoid arthritis shared epitope (SE)—the most significant genetic risk factor in this disease—and exposure to environmental pollutants, such as cigarette smoke. Specifically, we show that the SE, acting as a signal transduction ligand, cooperates with the aryl hydrocarbon receptor-activated pathway, and together facilitate cellular events that culminate in inflammation and bone destruction in experimental autoimmune arthritis. The cross-talk between the two pathways is mediated by nuclear factor kappa B.

Human skin mainly functions as an effective barrier against unwanted environmental influences. The barrier function strongly relies on the outermost layer of the skin, the stratum corneum (SC), which is composed of corneocytes embedded in an extracellular lipid matrix. The importance of a proper barrier function is shown in various skin disorders such as atopic dermatitis (AD), a complex human skin disorder strongly associated with filaggrin (FLG) null mutations, but their role in barrier function is yet unclear. To study the role of FLG in SC barrier properties in terms of SC lipid organization and lipid composition, we generated an N/TERT-based 3D-skin equivalent (NSE) after knock-down of FLG with shRNA. In these NSEs, we examined epidermal morphogenesis by evaluating the expression of differentiation markers keratin 10, FLG, loricrin and the proliferation marker ki67. Furthermore, the SC was extensively analysed for lipid organization, lipid composition and SC permeability. Our results demonstrate that FLG knock-down (FLG-KD) did not affect epidermal morphogenesis, SC lipid organization, lipid composition and SC permeability for a lipophilic compound in NSEs. Therefore, our findings indicate that FLG-KD alone does not necessarily affect the functionality of a proper barrier function.