Constitutive Autophagy and Nucleophagy during Epidermal Differentiation

Biogenesis of specialized lysosomes in differentiated keratinocytes relies on close apposition with the Golgi apparatus

Intracellular organelles support cellular physiology in diverse conditions. In the skin, epidermal keratinocytes undergo differentiation with gradual changes in cellular physiology, accompanying remodeling of lysosomes and the Golgi apparatus. However, it was not known whether changes in Golgi and lysosome morphology and their redistribution were linked. Here, we show that disassembled Golgi is distributed in close physical apposition to lysosomes in differentiated keratinocytes. This atypical localization requires the Golgi tethering protein GRASP65, which is associated with both the Golgi and lysosome membranes. Depletion of GRASP65 results in the loss of Golgi-lysosome apposition and the malformation of lysosomes, defined by their aberrant morphology, size, and function. Surprisingly, a trans-Golgi enzyme and secretory Golgi cargoes are extensively localized to the lysosome lumen and secreted to the cell surface, contributing to total protein secretion of differentiated keratinocytes but not in proliferative precursors, indicating that lysosomes acquire specialization during differentiation. We further demonstrate that the secretory function of the Golgi apparatus is critical to maintain keratinocyte lysosomes. Our study uncovers a novel form of Golgi-lysosome cross-talk and its role in maintaining specialized secretory lysosomes in differentiated keratinocytes.

The WD Domain of Atg16l1 Crucial for LC3-Associated Phagocytosis Is Not Required for Preserving Skin Barrier Function in Mice

The skin is a multifunctional organ, forming a barrier between the external and internal environment, thereby functioning as a safeguard against extrinsic factors. Autophagy has been implicated in epidermal differentiation and in preserving skin homeostasis. LC3-associated phagocytosis (LAP) uses some but not all components of autophagy. The Atg16l1 (Δ WD) mouse model lacks the WD40 domain required for LAP and has been widely used to study the effects of LAP deficiency and autophagy on tissue homeostasis and response to infection. In this study, the Δ WD model was used to study the relationship between LAP and skin homeostasis by determining whether LAP-deficient mice display a cutaneous phenotype. Skin histology of wild-type and Δ WD mice aged 1 year revealed minor morphological differences in the tail skin dermal layer. RT-qPCR and western blot analysis showed no differences in key keratin expression between genotypes. Skin barrier formation, assessed by dye permeation assays, demonstrated full and proper formation of the skin barrier at embryonic day 18.5 in both genotypes. Biomechanical analysis of the skin showed decreased skin elasticity in aged Δ WD but not wild-type mice. In summary, the LAP-deficient Δ WD mice displayed subtle alterations in dermal histology and age-related biomechanical changes.

Exploring the role of autophagy in psoriasis pathogenesis: Insights into sustained inflammation and dysfunctional keratinocyte differentiation

Psoriasis is a common and prevalent chronic papulosquamous cutaneous disorder characterized by sustained inflammation, uncontrolled keratinocyte proliferation, dysfunctional differentiation, and angiogenesis. Autophagy, an intracellular catabolic process, can be induced in response to nutrient stress. It entails the degradation of cellular constituents through the lysosomal machinery, and its association with psoriasis has been well-documented. Nevertheless, there remains a notable dearth of research concerning the involvement of autophagy in the pathogenesis of psoriasis within human skin. This review provides a comprehensive overview of autophagy in psoriasis pathogenesis, focusing on its involvement in two key pathological manifestations: sustained inflammation and uncontrolled keratinocyte proliferation and differentiation. Additionally, it discusses potential avenues for disease management.

VAMP2 controls murine epidermal differentiation and carcinogenesis by regulation of nucleophagy

Differentiation of murine epidermal stem/progenitor cells involves the permanent withdrawal from the cell cycle, the synthesis of various protein and lipid components for the cornified envelope, and the controlled dissolution of cellular organelles and nuclei. Deregulated epidermal differentiation contributes to the development of various skin diseases, including skin cancers. With a genome-wide shRNA screen, we identified vesicle-associated membrane protein 2 (VAMP2) as a critical factor involved in skin differentiation. Deletion of VAMP2 leads to aberrant skin stratification and enucleation in vivo. With quantitative proteomics, we further identified an autophagy protein, focal adhesion kinase family interacting protein of 200 kDa (FIP200), as a binding partner of VAMP2. Additionally, we showed that both VAMP2 and FIP200 are critical for murine keratinocyte enucleation and epidermal differentiation. Loss of VAMP2 or FIP200 enhances cutaneous carcinogenesis in vivo. Together, our findings identify important molecular mechanisms underlying epidermal differentiation and skin tumorigenesis.

The link between autophagy and psoriasis

Autophagy is a lysosome-dependent, self-renewal mechanism that degrades and recycles cellular components in eukaryotic cells to maintain the homeostasis of the intracellular environment. Psoriasis is featured by increased inflammatory response, epidermal hyperproliferation and abnormal differentiation, infiltration of immune cells and increased expression levels of both endothelial adhesion molecules and angiogenic mediators. Evidence indicates that autophagy has important roles in many different types of cells, such as lymphocytes, keratinocytes, monocytes and mesenchymal stem cells (MSCs). This paper will review the role of autophagy in the pathogenesis of psoriasis and strategies for therapeutic modulation. Key Message Autophagy regulates the functions of cutaneous cells (MSCs, KCs, T cells and endothelial cells). Since reduced autophagy contributes in part to the pathogenesis of psoriasis, enhancement of autophagy can be an alternative approach to mitigate psoriasis.

The multifaceted role of autophagy in skin autoimmune disorders: a guardian or culprit?

Autophagy is a cellular process that functions to maintain intracellular homeostasis via the degradation and recycling of defective organelles or damaged proteins. This dynamic mechanism participates in various biological processes, such as the regulation of cellular differentiation, proliferation, survival, and the modulation of inflammation and immune responses. Recent evidence has demonstrated the involvement of polymorphisms in autophagy-related genes in various skin autoimmune diseases. In addition, autophagy, along with autophagy-related proteins, also contributes to homeostasis maintenance and immune regulation in the skin, which is associated with skin autoimmune disorders. This review aims to provide an overview of the multifaceted role of autophagy in skin autoimmune diseases and shed light on the potential of autophagy-targeting therapeutic strategies in dermatology.

Skin barrier-inflammatory pathway is a driver of the psoriasis-atopic dermatitis transition

As chronic inflammatory conditions driven by immune dysregulation are influenced by genetics and environment factors, psoriasis and atopic dermatitis (AD) have traditionally been considered to be distinct diseases characterized by different T cell responses. Psoriasis, associated with type 17 helper T (Th17)-mediated inflammation, presents as well-defined scaly plaques with minimal pruritus. AD, primarily linked to Th2-mediated inflammation, presents with poorly defined erythema, dry skin, and intense itching. However, psoriasis and AD may overlap or transition into one another spontaneously, independent of biological agent usage. Emerging evidence suggests that defects in skin barrier-related molecules interact with the polarization of T cells, which forms a skin barrier-inflammatory loop with them. This loop contributes to the chronicity of the primary disease or the transition between psoriasis and AD. This review aimed to elucidate the mechanisms underlying skin barrier defects in driving the overlap between psoriasis and AD. In this review, the importance of repairing the skin barrier was underscored, and the significance of tailoring biologic treatments based on individual immune status instead of solely adhering to the treatment guidelines for AD or psoriasis was emphasized.

Dictamnine Ameliorates DNFB-Induced Atopic Dermatitis Like Skin Lesions in Mice by Inhibiting M1 Macrophage Polarization and Promoting Autophagy

Autophagy and M1 macrophage polarization play important roles in the regulation of inflammation in atopic dermatitis (AD). Dictamnine is one of the main ingredients in Cortex Dictamni, a widely used traditional Chinese medicine for the treatment of dermatitis. In the present study, we investigated the anti-inflammatory effects of dictamnine on AD like skin lesions and M1 macrophage polarization. A 2,4-dinitrofluorobenzene (DNFB) triggered AD like skin lesions models in mice was established to identify the ameliorative effects of dictamnine on AD in vivo. In addition, an M1 macrophage polarization model was co-stimulated by lipopolysaccharide (LPS) and interferon-γ (IFN-γ) using phorbol myristate acetate (PMA) differentiated THP-1 cells, to investigate the effect of dictamnine on promoting autophagy and inhibiting inflammatory factor release. Dictamnine suppressed DNFB-induced skin inflammation by inhibiting M1 macrophage polarization, up-regulating the expression of microtubule-associated protein 1A/1B-light chain 3 (LC3) expression, and promoting macrophage autophagy at inflammatory sites. Dictamnine also could reduce the release of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1), and interleukin-8 (IL-8), and down-regulate the mRNA expression of these genes in LPS-IFN-γ triggered M1 polarized macrophages. Dictamnine ameliorates AD like skin lesions by inhibiting M1 macrophage polarization and promoting autophagy. Hence, dictamnine is expected to be a potential therapeutic candidate for AD.

Insights into Autophagic Machinery and Lysosomal Function in Cells Involved in the Psoriatic Immune-Mediated Inflammatory Cascade

Impaired autophagy, due to the dysfunction of lysosomal organelles, contributes to maladaptive responses by pathways central to the immune system. Deciphering the immune-inflammatory ecosystem is essential, but remains a major challenge in terms of understanding the mechanisms responsible for autoimmune diseases. Accumulating evidence implicates a role that is played by a dysfunctional autophagy-lysosomal pathway (ALP) and an immune niche in psoriasis (Ps), one of the most common chronic skin diseases, characterized by the co-existence of autoimmune and autoinflammatory responses. The dysregulated autophagy associated with the defective lysosomal system is only one aspect of Ps pathogenesis. It probably cannot fully explain the pathomechanism involved in Ps, but it is likely important and should be seriously considered in Ps research. This review provides a recent update on discoveries in the field. Also, it sheds light on how the dysregulation of intracellular pathways, coming from modulated autophagy and endolysosomal trafficking, characteristic of key players of the disease, i.e., skin-resident cells, as well as circulating immune cells, may be responsible for immune impairment and the development of Ps.

HMGB1 promotes chemoresistance in small cell lung cancer by inducing PARP1-related nucleophagy

INTRODUCTION

Small cell lung cancer (SCLC) is prone to chemoresistance, which is closely related to genome homeostasis-related processes, such as DNA damage and repair. Nucleophagy is the elimination of specific nuclear substances by cells themselves and is responsible for maintaining genome and chromosome stability. However, the roles of nucleophagy in tumour chemoresistance have not been investigated.

OBJECTIVES

The aim of this work was to elucidate the mechanism of chemoresistance in SCLC and reverse this chemoresistance.

METHODS

RNA-seq data from SCLC cohorts, chemosensitive SCLC cells and the corresponding chemoresistant cells were used to discover genes associated with chemoresistance and patient prognosis. In vitro and in vivo experiments were performed to verify the effect of high-mobility group box 1 (HMGB1) knockdown or overexpression on the chemotherapeutic response in SCLC. The regulatory effect of HMGB1 on nucleophagy was then investigated by coimmunoprecipitation (co-IP) and mass spectrometry (MS), and the underlying mechanism was explored using pharmacological inhibitors and mutant proteins.

RESULTS

HMGB1 is a factor indicating poor prognosis and promotes chemoresistance in SCLC. Mechanistically, HMGB1 significantly increases PARP1-LC3 binding to promote nucleophagy via PARP1 PARylation, which leads to PARP1 turnover from DNA lesions and chemoresistance. Furthermore, chemoresistance in SCLC can be attenuated by blockade of the PARP1-LC3 interaction or PARP1 inhibitor (PARPi) treatment.

CONCLUSIONS

HMGB1 can induce PARP1 self-modification, which promotes the interaction of PARP1 with LC3 to promote nucleophagy and thus chemoresistance in SCLC. HMGB1 could be a predictive biomarker for the PARPi response in patients with SCLC. Combining chemotherapy with PARPi treatment is an effective therapeutic strategy for overcoming SCLC chemoresistance.

Signaling pathways and targeted therapies for psoriasis

Psoriasis is a common, chronic, and inflammatory skin disease with a high burden on individuals, health systems, and society worldwide. With the immunological pathologies and pathogenesis of psoriasis becoming gradually revealed, the therapeutic approaches for this disease have gained revolutionary progress. Nevertheless, the mechanisms of less common forms of psoriasis remain elusive. Furthermore, severe adverse effects and the recurrence of disease upon treatment cessation should be noted and addressed during the treatment, which, however, has been rarely explored with the integration of preliminary findings. Therefore, it is crucial to have a comprehensive understanding of the mechanisms behind psoriasis pathogenesis, which might offer new insights for research and lead to more substantive progress in therapeutic approaches and expand clinical options for psoriasis treatment. In this review, we looked to briefly introduce the epidemiology, clinical subtypes, pathophysiology, and comorbidities of psoriasis and systematically discuss the signaling pathways involving extracellular cytokines and intracellular transmission, as well as the cross-talk between them. In the discussion, we also paid more attention to the potential metabolic and epigenetic mechanisms of psoriasis and the molecular mechanistic cascades related to its comorbidities. This review also outlined current treatment for psoriasis, especially targeted therapies and novel therapeutic strategies, as well as the potential mechanism of disease recurrence.

Phenol-Soluble Modulin α3 Stimulates Autophagy in HaCaT Keratinocytes

BACKGROUND

Phenol-soluble modulins (PSMs) are pore-forming toxins (PFTs) produced by staphylococci. PSMs exert diverse cellular effects, including lytic, pro-apoptotic, pro-inflammatory and antimicrobial actions. Since the effects of PSMs on autophagy have not yet been reported, we evaluated the autophagic activity in HaCaT keratinocytes treated with recombinant PSMα3.

METHODS

The autophagic flux and levels of autophagic marker proteins were determined using Western blot analysis. Subcellular localization of LC3B and Beclin-1 was investigated using an indirect immunofluorescence assay. The ultrastructural features of control and PSMα3-treated cells were evaluated via transmission electron microscopy. Cytoplasmic acidification was measured via acridine orange staining. Phosphorylation levels of protein kinases, implicated in autophagy regulation, were studied using a phospho-kinase array and Western blot analysis.

RESULTS

PSMα3 facilitated the intracellular redistribution of LC3B, increased the average number of autophagosomes per cell, promoted the development of acidic vesicular organelles, elevated the levels of LC3B-II, stimulated autophagic flux and triggered a significant decrease in the net autophagic turnover rate. PSMα3 induced the accumulation of autophagosomes/autolysosomes, amphisomes and multilamellar bodies at the 0.5, 6 and 24 h time points, respectively. The phospho-Akt1/2/3 (T308 and S473), and phospho-mTOR (S2448) levels were decreased, whereas the phospho-Erk1/2 (T202/Y204 and T185/Y187) level was increased in PSMα3-treated cells.

CONCLUSIONS

In HaCaT keratinocytes, PSMα3 stimulates autophagy. The increased autophagic activity elicited by sub-lytic PSM concentrations might be an integral part of the cellular defense mechanisms protecting skin homeostasis.

Phytochemicals: Targeting autophagy to treat psoriasis

BACKGROUND

Psoriasis is an immune-mediated chronic inflammatory skin disease characterized by well-defined erythema and white scales, which affects approximately 2% of the worldwide population and causes long-term distress to patients. Therefore, development of safe and effective therapeutic drugs is imminent. Autophagy, an evolutionarily conserved catabolic process, degrades intracellular constituents to maintain cellular energy homeostasis. Numerous studies have revealed that autophagy is closely related to immune function, such as removal of intracellular bacteria, inflammatory cytokine secretion, antigen presentation, and lymphocyte development. Phytochemicals derived from natural plants are often used to treat psoriasis due to their unique therapeutic properties and favorable safety. So far, a mass of phytochemicals have been proven to be able to activate autophagy and thus alleviate psoriasis. This review aimed to provide directions for finding phytochemicals that target autophagy to treat psoriasis.

METHODS

The relevant literatures were collected from classical TCM books and a variety of databases (PubMed, Google Scholar, ScienceDirect, Springer Link, Web of Science and China National Knowledge Infrastructure) till December 2022. Search terms were "Phytochemical", "Psoriasis" and "Autophagy". The retrieved data followed PRISMA criteria (preferred reporting items for systematic review).

RESULTS

Phytochemicals treat psoriasis mainly through regulating immune cell function, inhibiting excessive inflammatory response, and reducing oxidative stress. While the role and mechanism of autophagy in the pathogenesis of psoriasis have been confirmed in human trials, most of the evidence for phytochemicals that target autophagy to treat psoriasis comes from animal studies. The research focusing on the role of phytochemical-mediated autophagy in the prevention and treatment of psoriasis is limited, and the definite relationship between phytochemical-regulated autophagy and treatment of psoriasis still deserves further experimental confirmation.

CONCLUSIONS

Phytochemicals with autophagic activities will provide new insights into the therapeutic intervention for psoriasis.

Autophagy as a caretaker of nuclear integrity

Due to their essential functions, dysregulation of nuclear pore complexes (NPCs) is strongly associated with numerous human diseases, including neurodegeneration and cancer. On a cellular level, longevity of scaffold nucleoporins in postmitotic cells of both C. elegans and mammals renders them vulnerable to age-related damage, which is associated with an increase in pore leakiness and accumulation of intranuclear aggregates in rat brain cells. Thus, understanding the mechanisms which underpin the homeostasis of this complex, as well as other nuclear proteins, is essential. In this review, autophagy-mediated degradation pathways governing nuclear components in yeast will be discussed, with a particular focus on NPCs. Furthermore, the various nuclear degradation mechanisms identified thus far in diverse eukaryotes will also be highlighted.

Increased apoptosis of gingival epithelium is associated with impaired autophagic flux in medication-related osteonecrosis of the jaw

Macroautophagy/autophagy has both negative and positive aspects in the development of many diseases. Yet, its exact role and specific mechanism in the onset of medication-related osteonecrosis of the jaw (MRONJ) is still not fully understood. Retarded gingiva healing is the primary clinical manifestation in patients with MRONJ. In this study, we aimed to explore the relationship between autophagy and apoptosis in MRONJ gingival epithelium and search for a method to prevent this disease. First, we examined clinical samples from patients diagnosed with MRONJ and healthy controls, finding that autophagy-related markers MAP1LC3/LC3 and SQSTM1/p62 synchronously increased, thus suggesting that autophagic flux was suppressed in MRONJ. Moreover, mRNA sequencing analysis and TUNEL assay showed that the process of apoptosis was upregulated in patients and animals with MRONJ, indicating autophagy and apoptosis participate in the development of MRONJ. Furthermore, the level of autophagy and apoptosis in zoledronic acid (ZA)-treated human keratinocytes cell lines (HaCaT cells) was concentration dependent in vitro. In addition, we also found that RAB7 (RAB7, member RAS oncogene family) activator ML098 could rescue MRONJ gingival lesions in mice by activating the autophagic flux and downregulating apoptosis. To sum up, this study demonstrated that autophagic flux is impaired in the gingival epithelium during MRONJ, and the rescued autophagic flux could prevent the occurrence of MRONJ.Abbreviations: ACTB: actin beta; Baf-A1: bafilomycin A1; CASP3: caspase 3; CASP8: caspase 8; CT: computed tomography; DMSO: dimethyl sulfoxide; GFP: green fluorescent protein; HaCaT cells: human keratinocytes cell lines; H&E: hematoxylin and eosin; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MRONJ: medication-related osteonecrosis of the jaw; PARP: poly(ADP-ribose) polymerase; RAB7: RAB7, member RAS oncogene family; RFP: red fluorescent protein; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; ZA: zoledronic acid.

Multi-modal skin atlas identifies a multicellular immune-stromal community associated with altered cornification and specific T cell expansion in atopic dermatitis

In healthy skin, a cutaneous immune system maintains the balance between tolerance towards innocuous environmental antigens and immune responses against pathological agents. In atopic dermatitis (AD), barrier and immune dysfunction result in chronic tissue inflammation. Our understanding of the skin tissue ecosystem in AD remains incomplete with regard to the hallmarks of pathological barrier formation, and cellular state and clonal composition of disease-promoting cells. Here, we generated a multi-modal cell census of 310,691 cells spanning 86 cell subsets from whole skin tissue of 19 adult individuals, including non-lesional and lesional skin from 11 AD patients, and integrated it with 396,321 cells from four studies into a comprehensive human skin cell atlas in health and disease. Reconstruction of human keratinocyte differentiation from basal to cornified layers revealed a disrupted cornification trajectory in AD. This disrupted epithelial differentiation was associated with signals from a unique immune and stromal multicellular community comprised of MMP12 + dendritic cells (DCs), mature migratory DCs, cycling ILCs, NK cells, inflammatory CCL19 + IL4I1 + fibroblasts, and clonally expanded IL13 + IL22 + IL26 + T cells with overlapping type 2 and type 17 characteristics. Cell subsets within this immune and stromal multicellular community were connected by multiple inter-cellular positive feedback loops predicted to impact community assembly and maintenance. AD GWAS gene expression was enriched both in disrupted cornified keratinocytes and in cell subsets from the lesional immune and stromal multicellular community including IL13 + IL22 + IL26 + T cells and ILCs, suggesting that epithelial or immune dysfunction in the context of the observed cellular communication network can initiate and then converge towards AD. Our work highlights specific, disease-associated cell subsets and interactions as potential targets in progression and resolution of chronic inflammation.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Gasdermin A Is Required for Epidermal Cornification during Skin Barrier Regeneration and in an Atopic Dermatitis-Like Model

Atopic dermatitis is featured with impaired skin barrier. The stratum corneum and the intercellular tight junctions constitute the permeability barrier, which is essential to protect water loss in the host and prevent pathogen entry. The epidermal barrier is constantly renewed by differentiating keratinocytes through cornification, during which autophagy contributes to elimination of organelles and nucleus. The human GSDMA and its mouse homologs Gsdma1-3 are expressed in the suprabasal epidermis. Although a pyroptotic role of GSDMA/Gsdma1 in host defense against Streptococcus pyogenes has been reported, the physiological function of Gsdma1/a2/a3 in epidermal homeostasis remains elusive. Here, through repeated epidermal barrier disruption, we found that tight junction formation and stratum corneum maturation were defective in the Gsdma1/a3-deficient epidermis. Using comparative gene profiling analysis, mitochondrial respiration measurement, and in vivo tracing of mitophagy, our data indicate that Gsdma1/a3 activation leads to mitochondrial dysfunction and subsequently facilitates mitochondrial turnover and epidermal cornification. In calcipotriol (MC903)-induced atopic dermatitis-like animal model, we showed that Gsdma1/a3-deficiency selectively enhanced the T helper type 2 response. Remarkably, the GSDMA expression is reduced in the epidermis of patients with atopic dermatitis compared with that of normal individuals. Gsdma1/a3-deficiency might be involved in atopic dermatitis pathogenesis, likely through GSDMA-mediated epidermal differentiation and cornification.

Down-regulation of peptidylarginine deiminase type 1 in reconstructed human epidermis disturbs nucleophagy in the granular layer and affects barrier function

Deimination is a post-translational modification catalyzed by a family of enzymes named peptidylarginine deiminases (PADs). PADs transform arginine residues of protein substrates into citrulline. Deimination has been associated with numerous physiological and pathological processes. In human skin, three PADs are expressed (PAD1-3). While PAD3 is important for hair shape formation, the role of PAD1 is less clear. To decipher the main role(s) of PAD1 in epidermal differentiation, its expression was down-regulated using lentivirus-mediated shRNA interference in primary keratinocytes and in three-dimensional reconstructed human epidermis (RHE). Compared to normal RHEs, down-regulation of PAD1 caused a drastic reduction in deiminated proteins. Whereas proliferation of keratinocytes was not affected, their differentiation was disturbed at molecular, cellular and functional levels. The number of corneocyte layers was significantly reduced, expression of filaggrin and cornified cell envelope components, such as loricrin and transglutaminases, was down-regulated, epidermal permeability increased and trans-epidermal-electric resistance diminished drastically. Keratohyalin granule density decreased and nucleophagy in the granular layer was disturbed. These results demonstrate that PAD1 is the main regulator of protein deimination in RHE. Its deficiency alters epidermal homeostasis, affecting the differentiation of keratinocytes, especially the cornification process, a special kind of programmed cell death.

Alterations of Autophagy Modify Lipids in Epidermal Keratinocytes

Background

The skin barrier is the first line of defense of the body, while skin lipids play an important role in the skin permeability barrier. Lamellar bodies are also involved in maintaining the stability of the skin permeability barrier. However, the exact origin of lamellar bodies remains unclear. Recent studies have suggested that autophagy may participate in the formation of lamellar bodies.

Aim

This study aimed to investigate the role of autophagy in the formation of lamellar bodies in keratinocytes and the regulation of keratinocyte lipids.

Methods

Keratinocytes were incubated with autophagy inducer Rapamycin and autophagy inhibitor Bafilomycin A1. The changes in autophagy flux were detected by Western blot, and the formation of lamellar bodies was observed by transmission electron microscopy. Furthermore, the changes in keratinocytes lipidomics were detected by liquid chromatography-mass spectrometry.

Results

Our research showed that the autophagy inducer promoted autophagy activation and formation of lamellar bodies in keratinocytes, while the inhibitor inhibited autophagy signals and the formation of lamellar bodies in keratinocytes. In addition, the lipidomics results revealed a significant change in glycerophospholipids after autophagy induction and autophagy inhibition.

Conclusion

These results demonstrate that autophagy may play an essential role in skin lipids via glycerophospholipids pathway.

IL-17A-targeting fenofibrate attenuates inflammation in psoriasis by inducing autophagy

IL-17A is a critical pro-inflammatory cytokine in autoimmune diseases such as psoriasis. Targeting of IL-17A is an effective strategy to treat patients with autoimmune diseases; however, relevant small molecule therapeutics have not yet been developed. Here, the small molecule drug fenofibrate was validated as an inhibitor of IL-17A through ELISA and surface plasmon resonance (SPR) assays. We further confirmed that fenofibrate blocked IL-17A signalings including the mitogen-activated protein kinase (MAPK) and NF-κB signaling pathways, in IL-17A-treated HaCaT cells, HEKa (human primary epidermal keratinocytes) and imiquimod (IMQ)-induced psoriasis mouse model. Fenofibrate attenuated systemic inflammation by suppressing Th17 populations and inflammatory cytokines, such as IL-1β, IL-6, IL-17A, and tumor necrosis factor (TNF). Surprisingly, fenofibrate upregulated LC3 and p62 in the psoriatic mouse group. The autophagy changes were caused by ULK1 pathway in hIL-17A-treated HaCaT and HEKa. In addition, the enhancement of autophagy by fenofibrate exerted anti-inflammatory effects, as demonstrated by the suppression of IL-6 and IL-8 in the IL-17A-treated keratinocytes. Thus, IL-17A-targeting fenofibrate can be a potential therapeutic for psoriasis and other autoimmune diseases via regulating autophagy.

Current and emerging prospects in the psoriatic treatment

Psoriasis is an autoimmune chronic disorder that causes inflammation and a scaly epidermis. The exact pathogenesis of the disease is not known yet. According to the studies, psoriasis is considered an immune-mediated disease. Until now it is believed that genetic and environmental factors are responsible for the disease. There are many comorbidities associated with psoriasis which increases difficulties as patients in some cases get addicted to drugs, alcohol, and smoking which reduces their quality of life. The patient may face social ignorance or suicidal thoughts which may arise in the patient's mind. Due to the undefined trigger of the disease, the treatment is not fully established but by considering the severe impact of the disease researchers are focusing on novel approaches for successful treatment. which has succeeded to a large extent. Here we review pathogenesis, problems faced by psoriatic patients, the need for the development of new treatments over conventional therapies, and the history of psoriatic treatments. We thoroughly focus on emerging treatments like biologics, biosimilars, and small molecules which are now showing more efficacy and safety than conventional treatments. Also, this review article discusses novel approaches which are now in research such as drug repurposing, treatment by stimulation of the vagus nerve, regulation of microbiota, and autophagy for improving disease conditions.

Micromotor-Assisted Keratinocytes Migration in a Floating Paper Chip

In vitro epidermis models are important to evaluate and study disease progression and possible dermal drug delivery. An in vitro epidermis model using floating paper chips as a scaffold for proliferation and differentiation of primary human keratinocytes is reported. The formation of the four main layers of the epidermis (i.e., basal, spinosum, granulose, and cornified layers) is confirmed. The development of a cornified layer and the tight junction formation are evaluated as well as the alterations of organelles during the differentiation process. Further, this in vitro model is used to assess keratinocyte migration. Finally, magnetic micromotors are assembled, and their ability to aid cell migration on paper chips is confirmed when a static magnetic field is present. Taken together, this attempt to combine bottom-up synthetic biology with dermatology offers interesting opportunities for studying skin disease pathologies and evaluate possible treatments.

The Epidermal Keratinocyte as a Therapeutic Target for Management of Diabetic Wounds

Diabetes mellitus (DM) is an important cause of chronic wounds and non-traumatic amputation. The prevalence and number of cases of diabetic mellitus are increasing worldwide. Keratinocytes, the outermost layer of the epidermis, play an important role in wound healing. A high glucose environment may disrupt the physiologic functions of keratinocytes, resulting in prolonged inflammation, impaired proliferation, and the migration of keratinocytes and impaired angiogenesis. This review provides an overview of keratinocyte dysfunctions in a high glucose environment. Effective and safe therapeutic approaches for promoting diabetic wound healing can be developed if molecular mechanisms responsible for keratinocyte dysfunction in high glucose environments are elucidated.

Snapshots from within the cell: Novel trafficking and non trafficking functions of Snap29 during tissue morphogenesis

Membrane trafficking is a core cellular process that supports diversification of cell shapes and behaviors relevant to morphogenesis during development and in adult organisms. However, how precisely trafficking components regulate specific differentiation programs is incompletely understood. Snap29 is a multifaceted Soluble N-ethylmaleimide-sensitive factor Attachment protein Receptor, involved in a wide range of trafficking and non-trafficking processes in most cells. A body of knowledge, accrued over more than two decades since its discovery, reveals that Snap29 is essential for establishing and maintaining the operation of a number of cellular events that support cell polarity and signaling. In this review, we first summarize established functions of Snap29 and then we focus on novel ones in the context of autophagy, Golgi trafficking and vesicle fusion at the plasma membrane, as well as on non-trafficking activities of Snap29. We further describe emerging evidence regarding the compartmentalisation and regulation of Snap29. Finally, we explore how the loss of distinct functions of human Snap29 may lead to the clinical manifestations of congenital disorders such as CEDNIK syndrome and how altered SNAP29 activity may contribute to the pathogenesis of cancer, viral infection and neurodegenerative diseases.

Glutamine Produces Ammonium to Tune Lysosomal pH and Regulate Lysosomal Function

Glutamine is one of the most abundant amino acids in the cell. In mitochondria, glutaminases 1 and 2 (GLS1/2) hydrolyze glutamine to glutamate, which serves as the precursor of multiple metabolites. Here, we show that ammonium generated during GLS1/2-mediated glutaminolysis regulates lysosomal pH and in turn lysosomal degradation. In primary human skin fibroblasts BJ cells and mouse embryonic fibroblasts, deprivation of total amino acids for 1 h increased lysosomal degradation capacity as shown by the increased turnover of lipidated microtubule-associated proteins 1A/1B light chain 3B (LC3-II), several autophagic receptors, and endocytosed DQ-BSA. Removal of glutamine but not any other amino acids from the culture medium enhanced lysosomal degradation similarly as total amino acid starvation. The presence of glutamine in regular culture media increased lysosomal pH by >0.5 pH unit and the removal of glutamine caused lysosomal acidification. GLS1/2 knockdown, GLS1 antagonist, or ammonium scavengers reduced lysosomal pH in the presence of glutamine. The addition of glutamine or NH₄Cl prevented the increase in lysosomal degradation and curtailed the extension of mTORC1 function during the early time period of amino acid starvation. Our findings suggest that glutamine tunes lysosomal pH by producing ammonium, which regulates lysosomal degradation to meet the demands of cellular activities. During the early stage of amino acid starvation, the glutamine-dependent mechanism allows more efficient use of internal reserves and endocytosed proteins to extend mTORC1 activation such that the normal anabolism is not easily interrupted by a brief disruption of the amino acid supply.

Cathelicidin LL-37 Activates Human Keratinocyte Autophagy through the P2X₇, Mechanistic Target of Rapamycin, and MAPK Pathways

Human cathelicidin LL-37 is a multifunctional antimicrobial peptide that exhibits antimicrobial and immunomodulatory activities. LL-37 regulates skin barrier function and was recently reported to activate autophagy in macrophages. Because autophagy deficiency is associated with skin diseases characterized by a dysfunctional epidermal barrier, we hypothesized that LL-37 might regulate the skin barrier through autophagy modulation. We showed that LL-37 activated autophagy in human keratinocytes and three-dimensional skin equivalent models as indicated by increases in LC3 puncta formation, decreases in p62, and autophagosome and autolysosome formation. LL-37‒induced autophagy was suppressed by P2X₇ receptor, adenosine monophosphate‒activated protein kinase, and unc-51-like kinase 1 inhibitors, suggesting that the P2X₇, adenosine monophosphate‒activated protein kinase, and unc-51-like kinase 1 pathways are involved. Moreover, LL-37 enhanced the phosphorylation of adenosine monophosphate‒activated protein kinase and unc-51-like kinase 1. In addition, LL-37‒mediated autophagy involves the mechanistic target of rapamycin and MAPK pathways. Interestingly, the LL-37‒induced distribution of tight junction proteins and improvement in the tight junction barrier were inhibited in autophagy-deficient keratinocytes and keratinocytes and skin models treated with autophagy inhibitors, indicating that the LL-37‒mediated tight junction barrier is associated with autophagy activation. Collectively, these findings suggest that LL-37 is a potential therapeutic target for skin diseases characterized by dysfunctional autophagy and skin barriers.

Inactivation of Autophagy in Keratinocytes Reduces Tumor Growth in Mouse Models of Epithelial Skin Cancer

Autophagy is a ubiquitous degradation mechanism, which plays a critical role in cellular homeostasis. To test whether autophagy suppresses or supports the growth of tumors in the epidermis of the skin, we inactivated the essential autophagy gene Atg7 specifically in the epidermal keratinocytes of mice (Atg7^∆ep) and subjected such mutant mice and fully autophagy-competent mice to tumorigenesis. The lack of epithelial Atg7 did not prevent tumor formation in response to 7, 12-dimethylbenz(a)anthracene (DMBA) as the initiator and 12-O tetradecanoylphorbol-13-acetate (TPA) as the promoter of tumor growth. However, the number of tumors per mouse was reduced in mice with epithelial Atg7 deficiency. In the K5-SOS EGFR^wa2/wa2 mouse model, epithelial tumors were initiated by Son of sevenless (SOS) in response to wounding. Within 12 weeks after tumor initiation, 60% of the autophagy-competent K5-SOS EGFR^wa2/wa2 mice had tumors of 1 cm diameter and had to be sacrificed, whereas none of the Atg7^∆ep K5-SOS EGFR^wa2/wa2 mice formed tumors of this size. In summary, the deletion of Atg7 reduced the growth of epithelial tumors in these two mouse models of skin cancer. Thus, our data show that the inhibition of autophagy limits the growth of epithelial skin tumors.

Autophagy plays an essential role in ultraviolet radiation-driven skin photoaging

Photoaging is characterized by a chronic inflammatory response to UV light. One of the most prominent features of cutaneous photoaging is wrinkling, which is due primarily to a loss of collagen fibers and deposits of abnormal degenerative elastotic material within the dermis (actinic elastosis). These changes are thought to be mediated by inflammation, with subsequent upregulation of extracellular matrix-degrading proteases and down-regulation of collagen synthesis. Autophagy is a vital homeostatic cellular process of either clearing surplus or damaged cell components notably lipids and proteins or recycling the content of the cells’ cytoplasm to promote cell survival and adaptive responses during starvation and other oxidative and/or genotoxic stress conditions. Autophagy may also become a means of supplying nutrients to maintain a high cellular proliferation rate when needed. It has been suggested that loss of autophagy leads to both photodamage and the initiation of photoaging in UV exposed skin. Moreover, UV radiation of sunlight is capable of regulating a number of autophagy-linked genes. This review will focus on the protective effect of autophagy in the skin cells damaged by UV radiation. We hope to draw attention to the significance of autophagy regulation in the prevention and treatment of skin photoaging.

Consequences of Autophagy Deletion on the Age-Related Changes in the Epidermal Lipidome of Mice

Autophagy is a controlled mechanism of intracellular self-digestion with functions in metabolic adaptation to stress, in development, in proteostasis and in maintaining cellular homeostasis in ageing. Deletion of autophagy in epidermal keratinocytes does not prevent the formation of a functional epidermis and the permeability barrier but causes increased susceptibility to damage stress and metabolic alterations and accelerated ageing phenotypes. We here investigated how epidermal autophagy deficiency using Keratin 14 driven Atg7 deletion would affect the lipid composition of the epidermis of young and old mice. Using mass spectrometric lipidomics we found a reduction of age-related accumulation of storage lipids in the epidermis of autophagy-deficient mice, and specific changes in chain length and saturation of fatty acids in several lipid classes. Transcriptomics and immunostaining suggest that these changes are accompanied by changes in expression and localisation of lipid and fatty acid transporter proteins, most notably fatty acid binding protein 5 (FABP5) in autophagy knockouts. Thus, maintaining autophagic activity at an advanced age may be necessary to maintain epidermal lipid homeostasis in mammals.

mTORC1 Activity in Psoriatic Lesions Is Mediated by Aberrant Regulation through the Tuberous Sclerosis Complex

In the basal, proliferative layer of healthy skin, the mTOR complex 1 (mTORC1) is activated, thus regulating proliferation while preventing differentiation. When cells leave the proliferative, basal compartment, mTORC1 signaling is turned off, which allows differentiation. Under inflammatory conditions, this switch is hijacked by cytokines and prevents proper differentiation. It is currently unknown how mTORC1 is regulated to mediate these effects on keratinocyte differentiation. In other tissues, mTORC1 activity is controlled through various pathways via the tuberous sclerosis complex (TSC). Thus, we investigated whether the TS complex is regulated by proinflammatory cytokines and contributes to the pathogenesis of psoriasis. TNF-α as well as IL-1β induced the phosphorylation of TSC2, especially on S939 via the PI3-K/AKT and MAPK pathway. Surprisingly, increased TSC2 phosphorylation could not be detected in psoriasis patients. Instead, TSC2 was strongly downregulated in lesional psoriatic skin compared to non-lesional skin of the same patients or healthy skin. In vitro inflammatory cytokines induced dissociation of TSC2 from the lysosome, followed by destabilization of the TS complex and degradation. Thus, we assume that in psoriasis, inflammatory cytokines induce strong TSC2 phosphorylation, which in turn leads to its degradation. Consequently, chronic mTORC1 activity impairs ordered keratinocyte differentiation and contributes to the phenotypical changes seen in the psoriatic epidermis.

Transcriptomic Analysis of Circulating Leukocytes Obtained during the Recovery from Clinical Mastitis Caused by Escherichia coli in Holstein Dairy Cows

Simple Summary

Escherichia coli is a bacterium which infects cow udders causing clinical mastitis, a potentially severe disease with welfare and economic consequences. During an infection, white blood cells (leukocytes) enter the udder to provide immune defence and assist tissue repair. We sequenced RNA derived from circulating leukocytes to investigate which genes are up- or down-regulated in dairy cows with naturally occurring cases of clinical mastitis in comparison with healthy control cows from the same farm. We also looked for genetic variations between infected and healthy cows. Blood samples were taken either EARLY (around 10 days) or LATE (after 4 weeks) during the recovery phase after diagnosis. Many genes (1090) with immune and inflammatory functions were up-regulated during the EARLY phase. By the LATE phase only 29 genes were up-regulated including six haemoglobin subunits, possibly important for the production of new red blood corpuscles. Twelve genetic variations which were associated with an increased or decreased expression of some important immune genes were identified between the infected and control cows. These results show that the initial inflammatory response to E. coli continued for at least 10 days despite the cows having received prompt veterinary treatment, but they had largely recovered within 4 weeks. Genetic differences between cows may predispose some animals to infection.

Abstract

The risk and severity of clinical infection with Escherichia coli as a causative pathogen for bovine mastitis is influenced by the hosts’ phenotypic and genotypic variables. We used RNA-Seq analysis of circulating leukocytes to investigate global transcriptomic profiles and genetic variants from Holstein cows with naturally occurring cases of clinical mastitis, diagnosed using clinical symptoms and milk microbiology. Healthy lactation-matched cows served as controls (CONT, n = 6). Blood samples were collected at two time periods during the recovery phase post diagnosis: EARLY (10.3 ± 1.8 days, n = 6) and LATE (46.7 ± 11 days, n = 3). Differentially expressed genes (DEGs) between the groups were identified using CLC Genomics Workbench V21 and subjected to enrichment analysis. Variant calling was performed following GATKv3.8 best practice. The comparison of E. coli(+) EARLY and CONT cows found the up-regulation of 1090 DEGs, mainly with immune and inflammatory functions. The key signalling pathways involved NOD-like and interleukin-1 receptors and chemokines. Many up-regulated DEGs encoded antimicrobial peptides including cathelicidins, beta-defensins, S100 calcium binding proteins, haptoglobin and lactoferrin. Inflammation had largely resolved in the E. coli(+) LATE group, with only 29 up-regulated DEGs. Both EARLY and LATE cows had up-regulated DEGs encoding ATP binding cassette (ABC) transporters and haemoglobin subunits were also up-regulated in LATE cows. Twelve candidate genetic variants were identified in DEGs between the infected and CONT cows. Three were in contiguous genes WIPI1, ARSG and SLC16A6 on BTA19. Two others (RAC2 and ARHGAP26) encode a Rho-family GTPase and Rho GTPase-activating protein 26. These results show that the initial inflammatory response to E. coli continued for at least 10 days despite prompt treatment and provide preliminary evidence for genetic differences between cows that may predispose them to infection.

Autophagy: Guardian of Skin Barrier

Autophagy is a major degradation pathway that removes harmful intracellular substances to maintain homeostasis. Various stressors, such as starvation and oxidative stress, upregulate autophagy, and the dysregulation of autophagy is associated with various human diseases, including cancer and skin diseases. The skin is the first defense barrier against external environmental hazards such as invading pathogens, ultraviolet rays, chemical toxins, and heat. Although the skin is exposed to various stressors that can activate autophagy, the roles of autophagy in the skin have not yet been fully elucidated. Accumulating evidence suggests that autophagy is closely associated with pathogenesis and the treatment of immune-related skin diseases. In this study, we review how autophagy interacts with skin cells, including keratinocytes and immune cells, enabling them to successfully perform their protective functions by eliminating pathogens and maintaining skin homeostasis. Furthermore, we discuss the implications of autophagy in immune-related skin diseases, such as alopecia areata, psoriasis, and atopic dermatitis, and suggest that a combination of autophagy modulators with conventional therapies may be a better strategy for the treatment of these diseases.

The regulation of skin homeostasis, repair and the pathogenesis of skin diseases by spatiotemporal activation of epidermal mTOR signaling

The epidermis, the outmost layer of the skin, is a stratified squamous epithelium that protects the body from the external world. The epidermis and its appendages need constantly renew themselves and replace the damaged tissues caused by environmental assaults. The mechanistic target of rapamycin (mTOR) signaling is a central controller of cell growth and metabolism that plays a critical role in development, homeostasis and diseases. Recent findings suggest that mTOR signaling is activated in a spatiotemporal and context-dependent manner in the epidermis, coordinating diverse skin homeostatic processes. Dysregulation of mTOR signaling underlies the pathogenesis of skin diseases, including psoriasis and skin cancer. In this review, we discuss the role of epidermal mTOR signaling activity and function in skin, with a focus on skin barrier formation, hair regeneration, wound repair, as well as skin pathological disorders. We propose that fine-tuned control of mTOR signaling is essential for epidermal structural and functional integrity.

Human-β-defensin-3 attenuates atopic dermatitis-like inflammation through autophagy activation and the aryl hydrocarbon receptor signaling pathway

Human β-defensin-3 (hBD-3) exhibits antimicrobial and immunomodulatory activities; however, its contribution to autophagy regulation remains unclear, and the role of autophagy in the regulation of the epidermal barrier in atopic dermatitis (AD) is poorly understood. Here, keratinocyte autophagy was restrained in the skin lesions of patients with AD and murine models of AD. Interestingly, hBD-3 alleviated the IL-4– and IL-13–mediated impairment of the tight junction (TJ) barrier through keratinocyte autophagy activation, which involved aryl hydrocarbon receptor (AhR) signaling. While autophagy deficiency impaired the epidermal barrier and exacerbated inflammation, hBD-3 attenuated skin inflammation and enhanced the TJ barrier in AD. Importantly, hBD-3–mediated improvement of the TJ barrier was abolished in autophagy-deficient AD mice and in AhR-suppressed AD mice, suggesting a role for hBD-3–mediated autophagy in the regulation of the epidermal barrier and inflammation in AD. Thus, autophagy contributes to the pathogenesis of AD, and hBD-3 could be used for therapeutic purposes.

Effects of Autophagy Modulators and Dioxin on the Expression of Epidermal Differentiation Proteins on Psoriasis-Like Keratinocytes in vitro and ex vivo

Objective

Psoriasis is a chronic inflammatory skin disorder associated with impairment of epidermal differentiation. Many signaling pathways, including those involved in aryl hydrocarbon receptor (AHR) and autophagy dysfunction, are reportedly associated with the pathogenesis of psoriasis. However, the discrete effects of dioxin via AHR activation or autophagy on the epidermal barrier remain unclear. In the current study, we evaluated the effects of autophagy modulators (chloroquine [CQ] and rapamycin) and the AHR agonist TCDD on the expression of epidermal barrier proteins in psoriasis-like keratinocytes and psoriasis lesional skin tissue culture.

Methods

Polycytokine-stimulated human keratinocytes and psoriasis skin biopsies were treated with TCDD, CQ, or rapamycin, and the expression of keratinocyte differentiation-related factors, such as S100A7, S100A8, HRNR, IVL, FLG, and KRT10, was examined by Western blotting or quantitative-polymerase chain reaction.

Results

TCDD upregulated S100A7 and S100A8 expression in polycytokine-stimulated HaCaT cells compared to that in unstimulated cells. CQ decreased HRNR, IVL, and KRT10 mRNA levels, while rapamycin increased HRNR, IVL, and KRT10 mRNA levels in HaCaT cells relative to that in unstimulated cells. Co-treatment with CQ reversed TCDD-induced elevation in FLG, HRNR, and IVL mRNA expression. In psoriasis skin tissue, TCDD induced the upregulation of HRNR, IVL, S100A7, and S100A8 compared with that in normal skin. In ex vivo cultures treated with CQ, IVL expression in psoriasis skin tissue was repressed compared to that in normal skin tissue.

Conclusion

Our data suggest that autophagy modulation or AHR activation affects processes involved in epidermal differentiation and relates to the pathogenesis of chronic inflammatory skin diseases with skin barrier abnormalities such as psoriasis.

Role of mTOR Signaling Cascade in Epidermal Morphogenesis and Skin Barrier Formation

Simple Summary

The skin epidermis is a stratified multilayered epithelium that provides a life-sustaining protective and defensive barrier for our body. The barrier machinery is established and maintained through a tightly regulated keratinocyte differentiation program. Under normal conditions, the basal layer keratinocytes undergo active proliferation and migration upward, differentiating into the suprabasal layer cells. Perturbation of the epidermal differentiation program often results in skin barrier defects and inflammatory skin disorders. The protein kinase mechanistic target of rapamycin (mTOR) is the central hub of cell growth, metabolism and nutrient signaling. Over the past several years, we and others using transgenic mouse models have unraveled that mTOR signaling is critical for epidermal differentiation and barrier formation. On the other hand, there is increasing evidence that disturbed activation of mTOR signaling is significantly implicated in the development of various skin diseases. In this review, we focus on the formation of skin barrier and discuss the current understanding on how mTOR signaling networks, including upstream inputs, kinases and downstream effectors, regulate epidermal differentiation and skin barrier formation. We hope this review will help us better understand the metabolic signaling in the epidermis, which may open new vistas for epidermal barrier defect-associated disease therapy.

Abstract

The skin epidermis, with its capacity for lifelong self-renewal and rapid repairing response upon injury, must maintain an active status in metabolism. Mechanistic target of rapamycin (mTOR) signaling is a central controller of cellular growth and metabolism that coordinates diverse physiological and pathological processes in a variety of tissues and organs. Recent evidence with genetic mouse models highlights an essential role of the mTOR signaling network in epidermal morphogenesis and barrier formation. In this review, we focus on the recent advances in understanding how mTOR signaling networks, including upstream inputs, kinases and downstream effectors, regulate epidermal morphogenesis and skin barrier formation. Understanding the details of the metabolic signaling will be critical for the development of novel pharmacological approaches to promote skin barrier regeneration and to treat epidermal barrier defect-associated diseases.

Loricrin at the Boundary between Inside and Outside

Cornification is a specialized mode of the cell-death program exclusively allowed for terrestrial amniotes. Recent investigations suggest that loricrin (LOR) is an important cornification effector. As the connotation of its name (“lorica” meaning an armor in Latin) suggests, the keratin-associated protein LOR promotes the maturation of the epidermal structure through organizing covalent cross-linkages, endowing the epidermis with the protection against oxidative injuries. By reviewing cornification mechanisms, we seek to classify ichthyosiform dermatoses based on their function, rather than clinical manifestations. We also reviewed recent mechanistic insights into the Kelch-like erythroid cell-derived protein with the cap “n” collar homology-associated protein 1/nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway in skin health and diseases, as LOR and NRF2 coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of cross-talking between keratinocytes and epidermal resident leukocytes, dissecting an LOR immunomodulatory function.

The Biology of Varicella-Zoster Virus Replication in the Skin

The replication of varicella-zoster virus (VZV) in skin is critical to its pathogenesis and spread. Primary infection causes chickenpox, which is characterised by centrally distributed skin blistering lesions that are rich in infectious virus. Cell-free virus in the cutaneous blistering lesions not only spreads to cause further cases, but infects sensory nerve endings, leading to the establishment of lifelong latency in sensory and autonomic ganglia. The reactivation of virus to cause herpes zoster is again characterised by localised painful skin blistering rash containing infectious virus. The development of in vitro and in vivo models of VZV skin replication has revealed aspects of VZV replication and pathogenesis in this important target organ and improved our understanding of the vaccine strain vOKa attenuation. In this review, we outline the current knowledge on VZV interaction with host signalling pathways, the viral association with proteins associated with epidermal terminal differentiation, and how these interconnect with the VZV life cycle to facilitate viral replication and shedding.

Autophagy and Skin Diseases

Autophagy is a highly conserved lysosomal degradation system that involves the creation of autophagosomes, which eventually fuse with lysosomes and breakdown misfolded proteins and damaged organelles with their enzymes. Autophagy is widely known for its function in cellular homeostasis under physiological and pathological settings. Defects in autophagy have been implicated in the pathophysiology of a variety of human diseases. The new line of evidence suggests that autophagy is inextricably linked to skin disorders. This review summarizes the principles behind autophagy and highlights current findings of autophagy's role in skin disorders and strategies for therapeutic modulation.

Melanoma secretion of transforming growth factor-β2 leads to loss of epidermal AMBRA1 threatening epidermal integrity and facilitating tumour ulceration

BACKGROUND

For patients with early American Joint Committee on Cancer (AJCC)-stage melanoma the combined loss of the autophagy regulatory protein AMBRA1 and the terminal differentiation marker loricrin in the peritumoral epidermis is associated with a significantly increased risk of metastasis.

OBJECTIVES

The aim of the present study was to evaluate the potential contribution of melanoma paracrine transforming growth factor (TGF)-β signalling to the loss of AMBRA1 in the epidermis overlying the primary tumour and disruption of epidermal integrity.

METHODS

Immunohistochemistry was used to analyse AMBRA1 and TGF-β2 in a cohort of 109 AJCC all-stage melanomas, and TGF-β2 and claudin-1 in a cohort of 30 or 42 AJCC stage I melanomas, respectively, with known AMBRA1 and loricrin (AMLo) expression. Evidence of pre-ulceration was analysed in a cohort of 42 melanomas, with TGF-β2 signalling evaluated in primary keratinocytes.

RESULTS

Increased tumoral TGF-β2 was significantly associated with loss of peritumoral AMBRA1 (P < 0·05), ulceration (P < 0·001), AMLo high-risk status (P < 0·05) and metastasis (P < 0·01). TGF-β2 treatment of keratinocytes resulted in downregulation of AMBRA1, loricrin and claudin-1, while knockdown of AMBRA1 was associated with decreased expression of claudin-1 and increased proliferation of keratinocytes (P < 0·05). Importantly, we show loss of AMBRA1 in the peritumoral epidermis was associated with decreased claudin-1 expression (P < 0·05), parakeratosis (P < 0·01) and cleft formation in the dermoepidermal junction (P < 0·05).

CONCLUSIONS

Collectively, these data suggest a paracrine mechanism whereby TGF-β2 causes loss of AMBRA1 overlying high-risk AJCC early-stage melanomas and reduced epidermal integrity, thereby facilitating erosion of the epidermis and tumour ulceration.

Phenotypical Conversions of Dermal Adipocytes as Pathophysiological Steps in Inflammatory Cutaneous Disorders

Adipocytes from the superficial layer of subcutaneous adipose tissue undergo cyclic de- and re-differentiation, which can significantly influence the development of skin inflammation under different cutaneous conditions. This inflammation can be connected with local loading of the reticular dermis with lipids released due to de-differentiation of adipocytes during the catagen phase of the hair follicle cycle. Alternatively, the inflammation parallels a widespread release of cathelicidin, which typically takes place in the anagen phase (especially in the presence of pathogens). Additionally, trans-differentiation of dermal adipocytes into myofibroblasts, which can occur under some pathological conditions, can be responsible for the development of collateral scarring in acne. Here, we provide an overview of such cellular conversions in the skin and discuss their possible involvement in the pathophysiology of inflammatory skin conditions, such as acne and psoriasis.

Stratum corneum as polymer sheet: concept and cornification processes

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

MiR-30a-5p Alters Epidermal Terminal Differentiation during Aging by Regulating BNIP3L/NIX-Dependent Mitophagy

Chronological aging is characterized by an alteration in the genes' regulatory network. In human skin, epidermal keratinocytes fail to differentiate properly with aging, leading to the weakening of the epidermal function. MiR-30a is particularly overexpressed with epidermal aging, but the downstream molecular mechanisms are still uncovered. The aim of this study was to decipher the effects of miR-30a overexpression in the human epidermis, with a focus on keratinocyte differentiation. We formally identified the mitophagy receptor BNIP3L as a direct target of miR-30a. Using a 3D organotypic model of reconstructed human epidermis overexpressing miR-30a, we observed a strong reduction in BNIP3L expression in the granular layer. In human epidermal sections of skin biopsies from donors of different ages, we observed a similar pattern of BNIP3L decreasing with aging. Moreover, human primary keratinocytes undergoing differentiation in vitro also showed a decreased expression of BNIP3L with age, together with a retention of mitochondria. Moreover, aging is associated with altered mitochondrial metabolism in primary keratinocytes, including decreased ATP-linked respiration. Thus, miR-30a is a negative regulator of programmed mitophagy during keratinocytes terminal differentiation, impairing epidermal homeostasis with aging.

Variant Enrichment Analysis to Explore Pathways Functionality in Complex Autoinflammatory Skin Disorders through Whole Exome Sequencing Analysis

The challenge of unravelling the molecular basis of multifactorial disorders nowadays cannot rely just on association studies searching for potential causative variants shared by groups of patients and not present in healthy individuals; indeed, association studies have as a main limitation the lack of information on the interactions between the disease-causing variants. Thus, new genomic analysis tools focusing on disrupted pathways rather than associated gene variants are required to better understand the complexity of a disease. Therefore, we developed the Variant Enrichment Analysis (VEA) workflow, a tool applicable for whole exome sequencing data, able to find differences between the numbers of genetic variants in a given pathway in comparison with a reference dataset. In this study, we applied VEA to discover novel pathways altered in patients with complex autoinflammatory skin disorders, namely PASH (n = 9), 3 of whom are overlapping with SAPHO) and PAPASH (n = 3). With this approach we have been able to identify pathways related to neutrophil and endothelial cells homeostasis/activations, as disrupted in our patients. We hypothesized that unregulated neutrophil transendothelial migration could elicit increased neutrophil infiltration and tissue damage. Based on our findings, VEA, in our experimental dataset, allowed us to predict novel pathways impaired in subjects with autoinflammatory skin disorders.

Predominant Role of mTOR Signaling in Skin Diseases with Therapeutic Potential

The serine/threonine kinase mechanistic target of rapamycin (mTOR) plays a pivotal role in the regulation of cell proliferation, survival, and motility in response to availability of energy and nutrients as well as mitogens. The mTOR signaling axis regulates important biological processes, including cellular growth, metabolism, and survival in many tissues. In the skin, dysregulation of PI3K/AKT/mTOR pathway may lead to severe pathological conditions characterized by uncontrolled proliferation and inflammation, including skin hyperproliferative as well as malignant diseases. Herein, we provide an update on the current knowledge regarding the pathogenic implication of the mTOR pathway in skin diseases with inflammatory features (such as psoriasis, atopic dermatitis, pemphigus, and acne) and malignant characteristics (such as cutaneous T cell lymphoma and melanoma) while we critically discuss current and future perspectives for therapeutic targeting of mTOR axis in clinical practice.

Autophagy of the Nucleus in Health and Disease

Nucleophagy is an organelle-selective subtype of autophagy that targets nuclear material for degradation. The macroautophagic delivery of micronuclei to the vacuole, together with the nucleus-vacuole junction-dependent microautophagic degradation of nuclear material, were first observed in yeast. Nuclear pore complexes and ribosomal DNA are typically excluded during conventional macronucleophagy and micronucleophagy, indicating that degradation of nuclear cargo is tightly regulated. In mammals, similarly to other autophagy subtypes, nucleophagy is crucial for cellular differentiation and development, in addition to enabling cells to respond to various nuclear insults and cell cycle perturbations. A common denominator of all nucleophagic processes characterized in diverse organisms is the dependence on the core autophagic machinery. Here, we survey recent studies investigating the autophagic processing of nuclear components. We discuss nucleophagic events in the context of pathology, such as neurodegeneration, cancer, DNA damage, and ageing.

Light chain 3 immunoexpression in psoriasis

Autophagy dysregulation is involved in many diseases. The implication of autophagy in psoriasis pathogenesis is still uncertain. To investigate the role of Light Chain 3 (LC3), a good marker for autophagy, in psoriatic skin based on immunohistochemical study and correlate its expression - for the first time to the best of our knowledge - to clinicopathological data Prospective case-control study was conducted on 60 subjects (30 control, 30 psoriasis patients). Skin biopsies from control, lesional, and perilesional skin were processed for routine histopathological examination and LC3 immunoreaction assessment. There was a significant upregulation of the epidermal and dermal LC3 immunoreaction in the lesional skin compared with the control and perilesional skin specimens (P < .001). A significant positive correlation between the epidermal and dermal LC3 H scores in the lesional and perilesional skin was recorded. There was a non-significant relationship between the H score in the lesional skin and disease severity. LC3 could be considered in psoriasis pathogenesis; however, LC3 was not related to the severity of the disease. The findings might offer a novel target therapy for psoriasis patients.

Beclin 1, LC3 and P62 Expression in Equine Sarcoids

Simple Summary

Equine sarcoids, caused by bovine papillomaviruses, are equine skin tumors of fibroblastic origin. It is well known that bovine papillomaviruses are able to interfere with the survival and proliferation of cells by regulating autophagy, a mechanism implicated in the breakdown and reuse of old and damaged cellular material. The present study focused on the evaluation in equine sarcoids and normal skins of the expression level of some of the main proteins involved in the autophagic pathway, such as Beclin 1, LC3 and P62, by immunohistochemical and biochemical techniques. Results obtained in equine sarcoids suggested an alteration of the autophagic process which could lead to a predominance of a particular population of fibroblast. Those fibroblasts could survive longer in a hypoxic microenvironment and produce more and/or altered collagen, giving an origin to the equine sarcoid.

Abstract

Background: It is well known that δ-bovine papillomaviruses (BPV-1, BPV-2 and BPV-13) are one of the major causative agents of equine sarcoids, the most common equine skin tumors. Different viruses, including papillomaviruses, evolved ingenious strategies to modulate autophagy, a complex process involved in degradation and recycling of old and damaged material. Methods: The aim of this study was to evaluate, by immunohistochemistry (IHC) and Western blot (WB) analysis, the expression of the main related autophagy proteins (Beclin 1, protein light chain 3 (LC3) and P62), in 35 BPV1/2 positive equine sarcoids and 5 BPV negative normal skin samples. Results: Sarcoid samples showed from strong-to-moderate cytoplasmic immunostaining, respectively, for Beclin 1 and P62 in >60% of neoplastic fibroblasts, while LC3 immunostaining was weak to moderate in ≤60% of neoplastic fibroblasts. Western blot analysis confirmed the specificity of the antibodies and revealed no activation of autophagic flux despite Beclin 1 overexpression in sarcoid samples. Conclusion: Results could suggest the activation of the initial phase of autophagy in equine sarcoids, and its impairment during the following steps. The impairment of autophagy could lead to a selection of a quiescent population of fibroblasts, which survive longer in a hypoxic microenvironment and produced more and/or altered collagen.

Atg5 Regulates Selective Autophagy of the Parental Macronucleus during Tetrahymena Sexual Reproduction

Nuclear autophagy is an important selective autophagy process. The selective autophagy of sexual development micronuclei (MICs) and the programmed nuclear degradation of parental macronucleus (paMAC) occur during sexual reproduction in Tetrahymena thermophila. The molecular regulatory mechanism of nuclear selective autophagy is unclear. In this study, the autophagy-related protein Atg5 was identified from T. thermophila. Atg5 was localized in the cytoplasm in the early sexual-development stage and was localized in the paMAC in the late sexual-development stage. During this stage, the degradation of meiotic products of MIC was delayed in atg5i mutants. Furthermore, paMAC was abnormally enlarged and delayed or failed to degrade. The expression level and lipidation of Atg8.2 significantly decreased in the mutants. All these results indicated that Atg5 was involved in the regulation of the selective autophagy of paMAC by regulating Atg8.2 in Tetrahymena.