Epidermal stratification requires retromer-mediated desmoglein-1 recycling

The desmosome as a dynamic membrane domain

Cell junctions integrate extracellular signals with intracellular responses to polarize tissues, pattern organs, and maintain tissue architecture by promoting cell-cell adhesion and communication. In this review, we explore the mechanisms whereby the adhesive junctions, adherens junctions and desmosomes, co-assemble and then segregate into unique plasma membrane domains. In addition, we highlight emerging evidence that these junctions are spatially and functionally integrated with the endoplasmic reticulum to mediate stress sensing and calcium homeostasis. We conclude with a discussion of the role of the endoplasmic reticulum in the mechanical stress response and how disruption of these connections may cause disease.

Unbiased screening identifies regulators of cell-cell adhesion and treatment options in pemphigus

Cell-cell junctions, and specifically desmosomes, are crucial for robust intercellular adhesion. Desmosomal function is compromised in the autoimmune blistering skin disease pemphigus vulgaris. We combine whole-genome knockout screening and a promotor screen of the desmosomal gene desmoglein 3 in human keratinocytes to identify novel regulators of intercellular adhesion. Kruppel-like-factor 5 (KLF5) directly binds to the desmoglein 3 regulatory region and promotes adhesion. Reduced levels of KLF5 in patient tissue indicate a role in pemphigus vulgaris. Autoantibody fractions from patients impair intercellular adhesion and reduce KLF5 levels in in vitro and in vivo disease models. These effects were dependent on increased activity of histone deacetylase 3, leading to transcriptional repression of KLF5. Inhibiting histone deacetylase 3 increases KLF5 levels and protects against the deleterious effects of autoantibodies in murine and human pemphigus vulgaris models. Together, KLF5 and histone deacetylase 3 are regulators of desmoglein 3 gene expression and intercellular adhesion and represent potential therapeutic targets in pemphigus vulgaris.

The desmosome comes into focus

The desmosome is a cell-cell adhesive junction that provides integrity and mechanical resistance to tissues through its attachment to the intermediate filament cytoskeleton. Defects in desmosomes cause diseases impacting the heart, epidermis, and other epithelia. In this review, we provide a historical perspective on the discovery of the desmosome and how the evolution of cellular imaging technologies revealed insights into desmosome structure and function. We also discuss recent findings using contemporary imaging approaches that have informed the molecular order, three-dimensional architecture, and associations of desmosomes with organelles such as the endoplasmic reticulum. Finally, we provide an updated model of desmosome molecular organization and speculate upon novel functions of this cell junction as a signaling center for sensing mechanical and other forms of cell stress.

Desmosomes at a glance

Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the intermediate filament cytoskeleton to cell-cell junctions. Their ability to dynamically counter the contractile forces generated by actin-associated adherens junctions is particularly important in tissues under high mechanical stress, such as the skin and heart. Much more than the simple cellular 'spot welds' depicted in textbooks, desmosomes are in fact dynamic structures that can sense and respond to changes in their mechanical environment and external stressors like ultraviolet light and pathogens. These environmental signals are transmitted intracellularly via desmosome-dependent mechanochemical pathways that drive the physiological processes of morphogenesis and differentiation. This Cell Science at a Glance article and the accompanying poster review desmosome structure and assembly, highlight recent insights into how desmosomes integrate chemical and mechanical signaling in the epidermis, and discuss desmosomes as targets in human disease.

ZNPs reduce epidermal mechanical strain resistance by promoting desmosomal cadherin endocytosis via mTORC1-TFEB-BLOC1S3 axis

Zinc oxide nanoparticles (ZNPs) are widely used in sunscreens and nanomedicines, and it was recently confirmed that ZNPs can penetrate stratum corneum into deep epidermis. Therefore, it is necessary to determine the impact of ZNPs on epidermis. In this study, ZNPs were applied to mouse skin at a relatively low concentration for one week. As a result, desmosomes in epidermal tissues were depolymerized, epidermal mechanical strain resistance was reduced, and the levels of desmosomal cadherins were decreased in cell membrane lysates and increased in cytoplasmic lysates. This finding suggested that ZNPs promote desmosomal cadherin endocytosis, which causes desmosome depolymerization. In further studies, ZNPs were proved to decrease mammalian target of rapamycin complex 1 (mTORC1) activity, activate transcription factor EB (TFEB), upregulate biogenesis of lysosome-related organelle complex 1 subunit 3 (BLOC1S3) and consequently promote desmosomal cadherin endocytosis. In addition, the key role of mTORC1 in ZNP-induced decrease in mechanical strain resistance was determined both in vitro and in vivo. It can be concluded that ZNPs reduce epidermal mechanical strain resistance by promoting desmosomal cadherin endocytosis via the mTORC1-TFEB-BLOC1S3 axis. This study helps elucidate the biological effects of ZNPs and suggests that ZNPs increase the risk of epidermal fragmentation.

A desmosomal cadherin controls multipotent hair follicle stem cell quiescence and orchestrates regeneration through adhesion signaling

Stem cells (SCs) are critical to maintain tissue homeostasis. However, it is currently not known whether signaling through cell junctions protects quiescent epithelial SC reservoirs from depletion during disease-inflicted damage. Using the autoimmune model disease pemphigus vulgaris (PV), this study reveals an unprecedented role for a desmosomal cadherin in governing SC quiescence and regeneration through adhesion signaling in the multipotent mouse hair follicle compartment known as the bulge. Autoantibody-mediated, mechanical uncoupling of desmoglein (Dsg) 3 transadhesion activates quiescent bulge SC which lose their multipotency and stemness, become actively cycling, and finally delaminate from their epithelial niche. This then initiates a self-organized regenerative program which restores Dsg3 function and bulge morphology including SC quiescence and multipotency. These profound changes are triggered by the sole loss of functional Dsg3, resemble major signaling events in Dsg3-/- mice, and are driven by SC-relevant EGFR activation and Wnt modulation requiring longitudinal repression of Hedgehog signaling.

A keratin code defines the textile nature of epithelial tissue architecture

We suggest that the human body can be viewed as of textile nature whose fabric consists of interconnected fiber systems. These fiber systems form highly dynamic scaffolds, which respond to environmental changes at different temporal and spatial scales. This is especially relevant at sites where epithelia border on connective tissue regions that are exposed to dynamic microenvironments. We propose that the enormous heterogeneity and adaptability of epithelia are based on a "keratin code", which results from the cell-specific expression and posttranslational modification of keratin isotypes. It thereby defines unique cytoskeletal intermediate filament networks that are coupled across cells and to the correspondingly heterogeneous fibers of the underlying extracellular matrix. The resulting fabric confers unique local properties.

Exosome Liberation by Human Neutrophils under L-Amino Acid Oxidase of Calloselasma rhodostoma Venom Action

L-Amino acid oxidase (LAAO) is an enzyme found in snake venom that has multifaceted effects, including the generation of hydrogen peroxide (H2O2) during oxidative reactions, leading to various biological and pharmacological outcomes such as apoptosis, cytotoxicity, modulation of platelet aggregation, hemorrhage, and neutrophil activation. Human neutrophils respond to LAAO by enhancing chemotaxis, and phagocytosis, and releasing reactive oxygen species (ROS) and pro-inflammatory mediators. Exosomes cellular nanovesicles play vital roles in intercellular communication, including immune responses. This study investigates the impact of Calloselasma rhodostoma snake venom-derived LAAO (Cr-LAAO) on human neutrophil exosome release, including activation patterns, exosome formation, and content. Neutrophils isolated from healthy donors were stimulated with Cr-LAAO (100 μg/mL) for 3 h, followed by exosome isolation and analysis. Results show that Cr-LAAO induces the release of exosomes with distinct protein content compared to the negative control. Proteomic analysis reveals proteins related to the regulation of immune responses and blood coagulation. This study uncovers Cr-LAAO's ability to activate human neutrophils, leading to exosome release and facilitating intercellular communication, offering insights into potential therapeutic approaches for inflammatory and immunological disorders.

Dsg3 epitope-specific signalling in pemphigus

Introduction

Pemphigus is an autoantibody driven disease that impairs the barrier function of the skin and mucosa by disrupting desmosomes and thereby impeding cellular cohesion. It is known that the different clinical phenotypes of pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are dependent on the autoantibody profile and target antigens that, amongst others, are primarily desmoglein (Dsg)1 and/or Dsg3 for PV and Dsg1 for PF. However, it was reported that autoantibodiesagainst different epitopes of Dsg1 and Dsg3 can be pathogenic or not. The underlying mechanisms are very complex and involve both direct inhibition of Dsg interactions and downstream signalling. The aim of this study was to find out whether there is target-epitope-specific Dsg3 signalling by comparing the effects of the two pathogenic murine IgGs, 2G4 and AK23.

Methods

Dispase-based dissociation assay, Western Blot analysis, Stimulated emission depletion microscopy, Fura-based Ca2+ flux measurements, Rho/Rac G-Protein-linked immunosorbent assay, Enzyme-linked immunosorbent assay.

Results

The IgGs are directed against the EC5 and EC1 domain of Dsg3, respectively. The data show that 2G4 was less effective in causing loss of cell adhesion, compared to AK23. STED imaging revealed that both autoantibodies had similar effects on keratin retraction and reduction of desmosome number whereas only AK23 induced Dsg3 depletion. Moreover, both antibodies induced phosphorylation of p38MAPK and Akt whereas Src was phosphorylated upon treatment with AK23 only. Interestingly, Src and Akt activation were p38MAPK-dependent. All pathogenic effects were rescued by p38MAPK inhibition and AK23-mediated effects were also ameliorated by Src inhibition.

Discussion

The results give first insights into pemphigus autoantibody-induced Dsg3 epitope-specific signalling which is involved in pathogenic events such as Dsg3 depletion.