HIF-1α-mediated BMP6 down-regulation leads to hyperproliferation and abnormal differentiation of keratinocytes in vitro

HSPA2 influences the differentiation and production of immunomodulatory mediators in human immortalized epidermal keratinocyte lines

Chaperone proteins constitute a molecular machinery that controls proteostasis. HSPA2 is a heat shock-non-inducible member of the human HSPA/HSP70 family, which includes several highly homologous chaperone proteins. HSPA2 exhibits a cell type-specific expression pattern in the testis, brain, and multilayered epithelia. It is a crucial male fertility-related factor, but its role in somatic cells is poorly understood. Previously, we found that HSPA2 deficiency can impair epidermal keratinocyte differentiation. In this study, we confirmed the crucial role of HSPA2 in keratinocyte differentiation by investigating immortalized keratinocytes cultured in a reconstructed human epidermis model. Moreover, we uncovered the influence of HSPA2 on immunomodulation. Transcriptomic analysis revealed that the total loss of HSPA2 affected the expression of genes related to keratinocyte differentiation and interleukin- and interferon-mediated signaling. The functional analysis confirmed bidirectional changes associated with the loss of HSPA2. The HSPA2 knockout in HaCaT and Ker-CT keratinocytes, but not HSPA2 overproduction, impaired granular layer development as evidenced by reduced levels of late keratinocyte differentiation markers, filaggrin and involucrin, along with structural abnormalities in the upper epidermal layer. Differentiation defects were accompanied by increased mRNA expression and extracellular secretion of keratinocyte-derived pro-inflammatory IL-6 cytokine and CCL2, CCL8, CXCL1, CXCL6, and CXCL10 chemokines. The loss of HSPA2 also led to increased expression of extracellular HSPA1 and interferon-stimulated genes and secretion of immune cell modulator SLAMF7. Knocking down HSPA1 expression in keratinocytes decreased the secretion of IL-6 and CCL5 release, suggesting extracellular HSPA1's role in the HSPA2-regulated molecular network. To summarize, we uncovered the complex homeostatic role of HSPA2 in epidermal keratinocytes. Our results suggest that dysfunction in HSPA2 activity could be an important pathogenicity factor and potential therapeutic target for inflammatory cutaneous diseases.

Andrographolide represses HIF-1α and VEGFA expression, thus inhibiting hypoxia-induced proliferation, oxidative stress, and inflammatory cytokine secretion in human keratinocytes

Epidermal hypoxia, hyperproliferation of keratinocytes, and inflammation in skin lesions are relevant to the pathogenesis of inflammatory skin diseases, including psoriasis. Andrographolide (Andro) is a natural labdane diterpene with diverse biofunctions. Andro has been reported to alleviate psoriasis in mice. However, the exact mechanisms need further study. Our results demonstrated that Andro inhibited hypoxia-induced proliferation of human keratinocytes. Andro also protected the keratinocytes from hypoxia-induced oxidative stress and inflammatory response. Furthermore, we found that Andro suppressed the expression of HIF-1α and VEGFA expression in hypoxia-exposed keratinocytes. Overexpression of either HIF-1α or VEGFA attenuated the inhibitory effects of Andro on hypoxia-induced proliferation, oxidative stress, and inflammatory cytokine secretion. In summary, our results demonstrated that Andro protected keratinocytes from hypoxia-induced proliferation, oxidative stress, and inflammatory cytokine secretion by suppressing HIF-1α and VEGFA expression. Our findings provide an unreported insight into the potential use of Andro as an effective agent for the treatment of inflammatory skin diseases such as psoriasis in the future.

Research Progress on Glycolysis Mechanism of Psoriasis

Psoriasis is a chronic inflammatory disease with a complex pathogenesis. Hyperplasia of glycolytic-dependent epidermal keratinocytes (KCs) is a new hallmark of psoriasis pathogenesis. Meanwhile, immune cells undergo metabolic reprogramming similar to KCs. Glycolysis provides energy for the proliferation of KCs, while it also releases lactic acid to facilitate the differentiation of immune cells. In turn, differentiated immune cells further promote KCs glycolysis by releasing inflammatory factors, thus forming an immunometabolism loop. The interaction between immune response and metabolic pathways jointly promotes the sustained proliferation of KCs and the secretion of various inflammatory factors by immune cells. Understanding the role of glycolysis in immunometabolism of psoriasis may provide new ideas for non-immunosuppressive treatment of psoriasis. This article aims to review the role of glycolysis in the pathogenesis of psoriasis and attempts to summarize the key enzymes and regulatory factors involved in psoriasis glycolysis, as well as their interactions. Finally, we discuss the pharmacological modulators of glycolysis in psoriasis.

Molecular mechanisms and drug therapy of metabolism disorders in psoriasis

Psoriasis is a prevalent skin disease affecting approximately 1%-3% of the population and imposes significant medical, social and economic burdens. Psoriasis involves multiple organs and is often complicated with obesity, diabetes, dyslipidemia, and hypertension. Because of the benefits of lipid-lowering agents and antidiabetic medications for psoriasis, metabolic abnormalities possibly play a pathogenic role in psoriasis.

This review focuses on the impacts of a variety of metabolic disorders on psoriasis and the underlying mechanisms.

In psoriasis, enhanced glycolysis, glutamine metabolism and altered fatty acid composition in the psoriatic lesion and plasma result in the excessive proliferation of keratinocytes and secretion of inflammatory cytokines. Altered metabolism is associated with the activation of MTORC signaling pathway and transcription factors such as HIF and S6K1. Therefore, MTORC1 can be a target for the treatment of psoriasis. Additionally, there are diabetes drugs and lipid-lowering drugs including TZDs, GLP-1 RAs, Metformin, statins and fibrates, which improve both metabolic levels and psoriasis symptoms.

Integrating network pharmacology, molecular docking, and experimental validation to reveal the mechanism of Radix Rehmanniae in psoriasis

BACKGROUND

Radix Rehmanniae (RR) plays an important role in treating psoriasis. However, the active compounds of RR and potential mechanisms are unclear. The current study was designed to investigate the potential active ingredients, targets, and mechanisms of RR in treating psoriasis through network pharmacology, molecular docking, and vitro experiments.

METHODS

Initially, the TCMSP database and literature retrieval were used to access the active ingredients of RR. The psoriasis target proteins were obtained from Therapeutic Target Database, OMIM, GeneCards, and DrugBank databases. The target proteins were then converted into target genes using Uniprot. Secondly, overlapping genes were obtained through Venn online tool. Then, protein-protein interactions network diagram is finished by STRING database. Next, Cytoscape software was used to acquire the top 10 hub proteins; gene ontology and Kyoto encyclopedia of genes and genomes enrichment analysis were then used to predict possible mechanisms. Afterwards, molecular docking validation of the active ingredients with the main targets was performed by AutoDock software. Finally, lipopolysaccharides induced RAW264.7, to assess the effects and molecular mechanisms by MTT, RT-qPCR, and Western blot assays.

RESULTS

Overall, there are 20 effective compounds and 33 targets involved in biological processes including apoptosis, intracellular signaling, vasodilation, and mitogen-activated protein kinase (MAPK) signaling cascade. The docking results showed strong binding capacity between the active ingredients and targets. We verified aucubin as the key active ingredient, tumor necrosis factor α, and IL6 as the core targets, and focused on the p38MAPK protein pathway. Cellular experiments showed that aucubin down-regulated the phosphorylated p38MAP protein and reduced the expression of tumor necrosis factor α mRNA, IL6 mRNA, and IL1βmRNA.

CONCLUSION

In summary, RR is featured with multicomponent, multi-target, and multi-pathway in treating psoriasis; the preliminary mechanism may be associated with the down-regulation of p38MAPK phosphorylation and curbing the expression of inflammatory factor by aucubin. This paper provides the scientific basis for Traditional Chinese medicine treating psoriasis.

The human testis-enriched HSPA2 interacts with HIF-1α in epidermal keratinocytes, yet HIF-1α stability and HIF-1-dependent gene expression rely on the HSPA (HSP70) activity

The Hypoxia-Inducible Factor 1 (HIF-1) is essential for cellular adaptation to reduced oxygen levels. It also facilitates the maintenance and re-establishment of skin homeostasis. Among others, it is involved in regulating keratinocyte differentiation. The stability of the oxygen-liable HIF-1α subunit is regulated by various non-canonical oxygen-independent mechanisms, which among others involve Heat Shock Proteins of the A family (HSPA/HSP70). This group of highly homologous chaperones and proteostasis-controlling factors includes HSPA2, a unique member crucial for spermatogenesis and implicated in the regulation of keratinocyte differentiation. HIF-1 can control the HSPA2 gene expression. In this study, we revealed that HIF-1α is the first confirmed client of HSPA2 in human somatic cells. It colocalises and interacts directly with HSPA2 in the epidermis in situ and immortalised keratinocytes in vitro. Using an in vitro model based on HSPA2-overexpressing and HSPA2-deficient variants of immortalised keratinocytes we showed that changes in HSPA2 levels do not affect the levels and intracellular localisation of HIF-1α or influence the ability of HIF-1 to modulate target gene expression. However, HIF-1α stability in keratinocytes appears critically reliant on HSPAs as a group of functionally overlapping chaperones. In addition to HSPA2, HIF-1α colocalises and forms complexes with HSPA8 and HSPA1, representing housekeeping and stress-inducible HSPA family paralogs, respectively. Chemical inhibition of HSPA activity, but not paralog-specific knockdown of HSPA8 or HSPA1 expression reduced HIF-1α levels and HIF-1-dependent gene expression. These observations suggest that pharmacological targeting of HSPAs could prevent excessive HIF-1 signalling in pathological skin conditions.

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.

IL-17A Orchestrates Reactive Oxygen Species/HIF1α-Mediated Metabolic Reprogramming in Psoriasis

Immune cell-derived IL-17A is one of the key pathogenic cytokines in psoriasis, an immunometabolic disorder. Although IL-17A is an established regulator of cutaneous immune cell biology, its functional and metabolic effects on nonimmune cells of the skin, particularly keratinocytes, have not been comprehensively explored. Using multiomics profiling and systems biology-based approaches, we systematically uncover significant roles for IL-17A in the metabolic reprogramming of human primary keratinocytes (HPKs). High-throughput liquid chromatography-tandem mass spectrometry and nuclear magnetic resonance spectroscopy revealed IL-17A-dependent regulation of multiple HPK proteins and metabolites of carbohydrate and lipid metabolism. Systems-level MitoCore modeling using flux-balance analysis identified IL-17A-mediated increases in HPK glycolysis, glutaminolysis, and lipid uptake, which were validated using biochemical cell-based assays and stable isotope-resolved metabolomics. IL-17A treatment triggered downstream mitochondrial reactive oxygen species and HIF1α expression and resultant HPK proliferation, consistent with the observed elevation of these downstream effectors in the epidermis of patients with psoriasis. Pharmacological inhibition of HIF1α or reactive oxygen species reversed IL-17A-mediated glycolysis, glutaminolysis, lipid uptake, and HPK hyperproliferation. These results identify keratinocytes as important target cells of IL-17A and reveal its involvement in multiple downstream metabolic reprogramming pathways in human skin.

Qingxiong Ointment and its Active Ingredient, Shikonin Treat Psoriasis through HIF-1 Signaling Pathway

BACKGROUND

Psoriasis is a common chronic inflammatory skin disorder. Qingxiong ointment (QX) is a natural medicinal combination frequently employed in clinical treatment of psoriasis. However, the active ingredients of QX and its precise mechanisms of improving psoriasis remain unclear. This study elucidated the effects of QX on an Imiquimod (IMQ)-induced mouse model of psoriasis while also exploring the regulation of the active ingredient of QX, shikonin, on the HIF-1 signaling pathway in HaCaT cells.

METHODS

A mouse model of psoriasis was established through topical application of IMQ, and the local therapeutic effect of QX was evaluated using dorsal skin tissue with mouse psoriatic lesion and Psoriasis Area Severity Index (PASI) scores, hematoxylin-eosin (HE) staining, and immunohistochemical staining. Elisa and qPCR were employed to identify changes in the expression of inflammation-related factors in the mouse dorsal skin. Immunofluorescence was used to assess changes in the expression of T cell subsets before and after treatment with various doses of QX. HPLC was used to analyze the content of shikonin, and network pharmacology was employed to analyze the main targets of shikonin. Immunofluorescence was used to identify the effects of shikonin on the HIF-1 signaling pathway in IL6-induced psoriasis HaCaT cells. Finally, qPCR was used to identify the differential expression of the HIF-1 signaling pathway in skin tissues.

RESULTS

QX significantly reduces PASI scores on the backs of IMQ-induced psoriasis mice. HE staining reveals alleviated epidermal thickness in the QX group. Immunohistochemical analysis shows a significant reduction in ICAM, KI67, and IL17 expression levels in the QX group. Immunofluorescence results indicate that QX can notably decrease the proportions of CD4+ T cells, γδ T cells, and CD8+ T cells while increasing the proportion of Treg cells. Network pharmacology analysis demonstrates that the main targets of shikonin are concentrated in the HIF-1 signaling pathway. Molecular docking results show favorable binding affinity between shikonin and key genes of the HIF-1 signaling pathway. Immunofluorescence results reveal that shikonin significantly reduces p-STAT3, SLC2A1, HIF1α, and NOS2 expression levels. qPCR results show significant downregulation of the HIF-1 signaling pathway at cellular and tissue levels.

CONCLUSION

Our study revealed that QX can significantly reduce the dorsal inflammatory response in the IMQ-induced psoriasis mouse model. Furthermore, we discovered that its main component, shikonin, exerts its therapeutic effect by diminishing the HIF-1 signaling pathway in HaCaT cells.

Increase of ISG15 in psoriasis lesions and its promotion of keratinocyte proliferation via the Hif-1α signalling pathway

Psoriasis is a frequent chronic, recurrent and immune-mediated inflammatory skin disease, whose pathogenesis remains unclear at present. The role of antiviral protein in the pathogenesis of psoriasis is the focus of current research. Interferon stimulated gene 15 (ISG15) is an important antiviral protein. In this study, the expression of ISG15 saw a significant increase through the immunohistochemical detection of imiquimod (IMQ)-induced mice. In the psoriasis cell model, a remarkable increase also occurred in the expression of ISG15. In this study, it was found that the cell cycle was blocked in G1/S conversion, and a reduction took place in the proliferation of keratinocytes and the expression of a cell cycle-related protein-cyclin D1 after the knockout of ISG15 in the psoriasis cell model. After that, messenger ribonucleic acid (mRNA) sequencing and Gene Ontology/Kyoto Encyclopedia of Genes and Genomes (GO/KEGG) analysis indicated its close association with the hypoxia inducible factor-1α (HIF-1α) signalling pathway. Western blot showed a decrease in the expression of HIF-1α and vascular endothelial growth factor C (VEGFC) after the knockout of the ISG15 gene. The rescue experiment verified that ISG15 promotes the proliferation of keratinocytes by regulating the HIF-1α signalling pathway. It was concluded that psoriasis cells and mouse models witnessed the increased expression of ISG15. In psoriasis, knocking out ISG15 inhibits the proliferation of keratinocytes and blocks the cell cycle. Besides, ISG15 promotes the proliferation of keratinocytes through the HIF-1α signalling pathway.

d-mannose blocks the interaction between keratinocytes and Th17 cells to alleviate psoriasis by inhibiting HIF-1α/CCL20 in mice

Psoriasis is an autoimmune chronic inflammatory skin disease with an unclear pathogenesis that is difficult to cure, causing serious physical and mental burdens for patients. Previous research showed that a mutually reinforcing vicious cycle caused by keratinocytes (KC) and a variety of immune cells plays an important role in psoriatic inflammation. d-Mannose, a widely distributed metabolite in the body, has been found to treat several metabolic diseases, but its impact on psoriasis remains unknown. Our study aims to investigate the effects of d-mannose on psoriasis and its specific mechanism. Here, we found that d-mannose alleviates psoriasis in mice both as oral and topical agents. Specifically, d-mannose down-regulated the expression of hypoxia-inducible factor 1A(HIF-1α) and inhibited the expression of chemokine CCL20 in keratinocytes, thereby inhibiting the local infiltration of Th17 cells and breaking the cycle of keratinocytes-Th17 cells. Overall, our study indicates that d-mannose alleviates cutaneous inflammation in psoriasis by inhibiting the HIF-1α/CCL20/Th17 cells axis, and d-mannose has the potential to be used as an oral and topical agent in the treatment of psoriasis.

Hypoxia in Skin Cancer: Molecular Basis and Clinical Implications

Skin cancer is one of the most prevalent cancers in the Caucasian population. In the United States, it is estimated that at least one in five people will develop skin cancer in their lifetime, leading to significant morbidity and a healthcare burden. Skin cancer mainly arises from cells in the epidermal layer of the skin, where oxygen is scarce. There are three main types of skin cancer: malignant melanoma, basal cell carcinoma, and squamous cell carcinoma. Accumulating evidence has revealed a critical role for hypoxia in the development and progression of these dermatologic malignancies. In this review, we discuss the role of hypoxia in treating and reconstructing skin cancers. We will summarize the molecular basis of hypoxia signaling pathways in relation to the major genetic variations of skin cancer.

Protective roles of tRNA-derived small RNA tRF-Ile-AAT-019 in pathological progression of psoriasis

Psoriasis is a chronic recurrent inflammatory skin disease that is characterized by abnormal proliferation and differentiation of keratinocytes (KCs), angiogenesis and skin inflammation. Transfer RNA fragments (tRFs) are tRNA-derived small RNAs (tsRNAs), which possess regulatory functions in many diseases. Their potential roles in the pathological development of psoriasis have not been established. We first identified differentially expressed (DE) tRFs from psoriatic skin lesions using small RNA sequencing, and collected additional clinical samples for validation. Then, we investigated the function and mechanism of target tRFs in vitro. As a result of our investigation: we identified 234 DE transcripts in psoriatic skin lesions compared with normal controls. Further functional analysis showed the downregulation of tRF-Ile-AAT-019 in psoriatic lesions plays a critical role in pathogenesis since it could target 3'UTR of the serine protease serpin protein E1 (SERPINE1) gene. We next demonstrated that tRF-Ile-AAT-019 could suppress SERPINE1, thus leading to decreased expressions of vascular endothelial growth factor but increased expressions of keratinocytes (KCs) differentiation markers including Keratin1 and Involucrin. In conclusion, tRF-Ile-AAT-019 plays a protective role in the pathological progression of psoriasis via targeting SERPINE1, resulting in regulation of KCs differentiation and vascular proliferation biomarkers and providing a potential novel targeting pathway for the disease treatment.

Novel cell culture system for monitoring cells during continuous and variable negative-pressure wound therapy

BACKGROUND

Although the clinical efficacy of negative-pressure wound therapy (NPWT) is well known, many of its molecular biological mechanisms remain unresolved, mainly due to the difficulty and paucity of relevant in vitro studies. We attempted to develop an in vitro cell culture system capable of real-time monitoring of cells during NPWT treatment.

MATERIALS AND METHODS

A novel negative-pressure cell culture system was developed by combining an inverted microscope, a stage-top incubator, a sealed metal chamber for cell culture, and an NPWT treatment device. Human keratinocytes, PSVK-1, were divided into ambient pressure (AP), continuous negative-pressure (NPc), and intermittent negative-pressure (NPi) groups and cultured for 24 h with scratch assay using our real-time monitoring system and device. Pressure inside the device, medium evaporation rate, and the residual wound area were compared across the groups.

RESULTS

Pressure in the device was maintained at almost the same value as set in all groups. Medium evaporation rate was significantly higher in the NPi group than in the other two groups; however, it had negligible effect on cell culture. Residual wound area after 9 h evaluated by the scratch assay was significantly smaller in the NPc and NPi groups than in the AP group.

CONCLUSION

We developed a negative-pressure cell culture device that enables negative-pressure cell culture under conditions similar to those used in clinical practice and is able to monitor cells under NPWT. Further experiments using this device would provide high-quality molecular biological evidence for NPWT.

In vivo evaluation and mechanism prediction of anti-diabetic foot ulcer based on component analysis of Ruyi Jinhuang powder

BACKGROUND

Diabetes is a metabolic disease with a high complication rate. Diabetic foot ulcers (DFUs) seriously affect the quality of life of patients. A total of 15%-20% of diabetic patients develop DFUs, which heal with difficulty over a long time and can result in amputation and disability. Traditional Chinese medicine has a unique effect in the treatment of skin ulcerative diseases. Ruyi Jinhuang powder (RHP) is one of the classic prescriptions in traditional Chinese medicine and is widely used in clinical practice.

AIM

To verify the ability of RHP to promote wound healing by electron microscopy analysis in animal models and hematoxylin-eosin (HE) staining. The effective components of RHP were extracted and identified by gas chromatography-mass spectrometry (GC-MS), and the obtained chemical components were analyzed by network pharmacology methods to predict its therapeutic mechanism.

METHODS

Sprague Dawley rats were injected with streptozotocin to establish the DFU model. HE staining was used to observe the wound tissue under an electron microscope. The chemical constituents of RHP were extracted first by supercritical fluid extraction and alcohol extraction, and then, GC-MS and ultra-performance liquid chromatography-MS were used to separately identify the chemical constituents. In addition, the "herb-component-target" link was established through the Traditional Chinese Medicine Systems Pharmacology database to obtain the target information, and the molecular docking of important components and key targets was performed in Discovery Studio software. Cytoscape software was used to visualize and analyze the relationship between the chemical composition, targets and Traditional Chinese Medicine network.

RESULTS

RHP promoted DFU healing in rats by affecting fibroblasts and nerve cells. A total of 89 chemical components were obtained by GC-MS. Network pharmacological analysis revealed that RHP was associated with 36 targets and 27 pathways in the treatment of DFU, of which the important components were luteolin, trans caryophyllene, ar-turmerone, palmitic acid, methyl palmitate, gallic acid, demethoxycurcumin, berberine, and rheic acid. The key targets were posttranscriptional silencing, topoisomerase II alpha, muscarinic acetylcholine receptor M2, interleukin 6, tumor necrosis factor and retinoic X receptor alpha, and the key pathways were the phosphoinositide 3-kinase-protein kinase B signaling pathway, neuroactive ligand-receptor interactions, and the forkhead box O signaling pathway.

CONCLUSION

Our results indicated that RHP may play a role in the treatment of DFU through these target pathways by affecting insulin resistance, altering the nervous system and immune system, participating in inflammatory responses and regulating cell proliferation, differentiation and apoptosis through other specific mechanisms.

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.

The Protective Role of pVHL in Imiquimod-Induced Psoriasis-like Skin Inflammation

Psoriasis is a chronic inflammatory disease distinguished by an excessive proliferation and abnormal differentiation of keratinocytes. Immune cells, such as T lymphocytes and neutrophils, and inflammatory cytokines, such as Tumor Necrosis Factor-α (TNF-α) and interleukin 17 (IL-17), are essential for maintaining psoriatic lesions. Additionally, a hypoxic milieu present in the skin promotes the expression of transcriptional factor hypoxia-inducible factor-1 alpha (HIF-1α). This protein regulates the expression of angiogenic and glycolytic factors, such as vascular endothelial grown factor and lactate dehydrogenase (LDH), both relevant in chronic inflammation. The von Hippel–Lindau protein (pVHL) is a negative regulator of HIF-1α. Previously, we found that pVHL was almost absent in the lesions of psoriasis patients; therefore, we investigated the impact of rescue pVHL expression in lesional skin. We used the imiquimod-induced psoriasis-like mouse model as an adenoviral vector that allowed us to express pVHL in the skin. Our data show that, in lesional skin, pVHL expression was reduced, whereas HIF-1α was increased. Remarkably, the retrieval of pVHL prevented psoriatic lesions, diminishing erythema, scale, and epidermal and vascular thickness. Furthermore, pVHL expression was capable of reducing HIF-1α, LDH, TNF-α and immune cell infiltration (mainly IL-17⁺ neutrophils). In conclusion, our results demonstrate that pVHL has a protective role to play in the pathophysiology of psoriasis.

Nrf2 activation does not affect adenoma development in a mouse model of colorectal cancer

Transcription factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2) and its main negative regulator, Kelch-like ECH associated protein 1 (Keap1), are at the interface between redox and intermediary metabolism. Nrf2 activation is protective in models of human disease and has benefits in clinical trials. Consequently, the Keap1/Nrf2 protein complex is a drug target. However, in cancer Nrf2 plays a dual role, raising concerns that Nrf2 activators may promote growth of early neoplasms. To address this concern, we examined the role of Nrf2 in development of colorectal adenomas by employing genetic, pharmacological, and metabolomic approaches. We found that colorectal adenomas that form in Gstp-/-: ApcMin/+ mice are characterized by altered one-carbon metabolism and that genetic activation, but not disruption of Nrf2, enhances these metabolic alterations. However, this enhancement is modest compared to the magnitude of metabolic differences between tumor and peri-tumoral tissues, suggesting that the metabolic changes conferred by Nrf2 activation may have little contribution to the early stages of carcinogenesis. Indeed, neither genetic (by Keap1 knockdown) nor pharmacological Nrf2 activation, nor its disruption, affected colorectal adenoma formation in this model. We conclude that pharmacological Nrf2 activation is unlikely to impact the early stages of development of colorectal cancer.

Epigenetic and metabolic interplay in cutaneous squamous cell carcinoma

With the ageing of the population and increased levels of recreational sun exposure and immunosuppression, cutaneous squamous cell carcinoma (cSCC), is both an enormous and expanding clinical and economic issue. Despite advances in therapy, up to 5000-8000 people are estimated to die every year from cSCC in the U.S., highlighting the need for both better prevention and treatments. Two emerging areas of scientific discovery that may offer new therapeutic approaches for cSCC are epigenetics and metabolism. Importantly, these disciplines display extensive crosstalk, with metabolic inputs contributing to the chromatin landscape, while the dynamic epigenome shapes transcriptional and cellular responses that feedback into cellular metabolism. Recent evidence suggests that indeed, epigenetic and metabolic dysregulation may be critical contributors to cSCC pathogenesis. Here, we synthesize the latest findings from these fast-moving fields, including how they may drive cSCC, yet also be harnessed for therapy.

Development of a constant pressure perfused ex vivo model of the equine larynx

Distal axonopathy is seen in a broad range of species including equine patients. In horses, this degenerative disorder of the recurrent laryngeal nerve is described as recurrent laryngeal neuropathy (RLN). The dysfunctional innervation of the cricoarytenoideus dorsalis muscle (CAD) leads to a loss of performance in affected horses. In general, ex vivo models of the larynx are rare and for equine patients, just one short report is available. To allow for testing new therapy approaches in an isolated organ model, we examined equine larynges in a constant pressure perfused setup. In order to check the vitality and functionality of the isolated larynx, the vessels´ reaction to norepinephrine (NE) and sodium nitroprusside (NP) as vasoactive agents was tested. Additionally, the contractility of the CAD was checked via electrical stimulation. To determine the extent of hypoxic alterations, lactate dehydrogenase (LDH) and lactate were measured and an immunofluorescent analysis of hypoxia-inducible factor (HIF-1α), a key transcription factor in hypoxia, was performed. For this, a hypoxia-induced cell culture for HIF-1α was developed. The application of NE led to an expected vasoconstriction while NP caused the expected vasodilation. During a perfusion period of 352 ±20.78 min, LDH values were in the reference range and lactate values slightly exceeded the reference range at the end of the perfusion. HIF-1α nuclear translocation could reliably be detected in the hypoxia-induced cell cultures, but not in sections of the perfused CAD. With the approach presented here, a solid basis for perfusing equine larynges was established and may serve as a tool for further investigations of equine larynx disorders as well as a transferrable model for other species.

Extracellular vesicles produced by primary human keratinocytes in response to TLR agonists induce stimulus-specific responses in antigen-presenting cells

Cells can communicate through the extracellular vesicles (EVs) they secrete. Pathogen associated molecular patterns (PAMPs), alter the biophysical and communicative properties of EVs released from cells, but the functional consequences of these changes are unknown. Characterization of keratinocyte-derived EVs after poly(I:C) treatment (poly(I:C)-EVs) showed slight differences in levels of EV markers TSG101 and Alix, a loss of CD63 and were positive for autophagosome marker LC3b-II and the cytokine IL36γ compared to EVs from unstimulated keratinocytes (control-EVs). Flagellin treatment (flagellin-EVs) led to an EV marker profile like control-EVs but lacked LC3b-II. Flagellin-EVs also lacked IL-36γ despite nearly identical intracellular levels. While poly(I:C) treatment led to the clear emergence of a > 200 nm diameter EV sub-population, these were not found in flagellin-EVs. EV associated IL-36γ colocalized with LC3b-II in density gradient analysis, equilibrating to 1.10 g/mL, indicating a common EV species. Poly(I:C), but not flagellin, induced intracellular vesicles positive for IL-36γ, LC3b-II, Alix and TSG101, consistent with fusion of autophagosomes and multivesicular bodies. Simultaneous rapamycin and flagellin treatment induced similar intracellular vesicles but was insufficient for the release of IL-36γ⁺/LC3b-II⁺ EVs. Finally, a qRT-PCR array screen showed eight cytokine/chemokine transcripts were altered (p < 0.05) in monocyte-derived Langerhans cells (LCs) when stimulated with poly(I:C)-EVs while three were altered when LCs were stimulated with flagellin-EVs compared to control-EVs. After independent confirmation, poly(I:C)-EVs upregulated BMP6 (p = 0.035) and flagellin-EVs upregulated CXCL8 (p = 0.005), VEGFA (p = 0.018) and PTGS2 (p = 0.020) compared to control-EVs. We conclude that exogenous signals derived from pathogens can alter keratinocyte-mediated modulation of the local immune responses by inducing changes in the types of EVs secreted and responses in antigen presenting cells.

Metabolic Pathways That Control Skin Homeostasis and Inflammation

Keratinocytes and skin immune cells are actively metabolizing nutrients present in their microenvironment. This is particularly important in common chronic inflammatory skin diseases such as psoriasis and atopic dermatitis, characterized by hyperproliferation of keratinocytes and expansion of inflammatory cells, thus suggesting increased cell nutritional requirements. Proliferating inflammatory cells and keratinocytes express high levels of glucose transporter (GLUT)1, l-type amino acid transporter (LAT)1, and cationic amino acid transporters (CATs). Main metabolic regulators such as hypoxia-inducible factor (HIF)-1α, MYC, and mechanistic target of rapamycin (mTOR) control immune cell activation, proliferation, and cytokine release. Here, we provide an updated perspective regarding the potential role of nutrient transporters and metabolic pathways that could be common to immune cells and keratinocytes, to control psoriasis and atopic dermatitis.

Regulatory expression of bone morphogenetic protein 6 by 2,2'-dipyridyl

BACKGROUND

Expression of hepcidin, a hormone produced by hepatocytes which negatively regulates the circulating iron levels, is known to be positively regulated by BMP6, a member of transforming growth factor (TGF)-β family. Previous studies have shown that iron status is sensed by sinusoidal endothelial cells of hepatic lamina, leading to the modulation of BMP6 expression.

METHODS

ISOS-1, HUVEC, F-2, and SK-HEP1 endothelial cells were treated with either iron or 2,2'-dipyridyl (2DP), a cell-permeable iron-chelator, and expression level of Bmp6 was examined. To identify factors affecting Bmp6 transcription, stimulus screening for regulator of transcription (SSRT) was developed.

RESULTS

Treatment with iron slightly increased the expression levels of Bmp6, while 2DP unexpectedly increased Bmp6 expression in a dose-dependent manner. 2DP-induced Bmp6 expression was resistant to co-treatment with iron. 2DP-induced Bmp6 expression was also detected in HUVEC, F-2 cells, and SK-HEP1 cells. Luciferase-based reporter assays indicated that forced expression of JunB increased the transcription of Bmp6. 2DP induced phosphorylation of JunB; co-treatment with SP600125 blocked the 2DP-induced Bmp6 expression partially. JunB-induced Bmp6 transcription was not affected by mutations of putative JunB-responsive elements. Some endoplasmic reticulum stress inducers increased the expression of Bmp6. SSRT revealed pathways regulating Bmp6 transcription positively and negatively. Hepa1-6 liver cells and C2C12 myogenic cells were prone to 2DP induced Bmp6 expression.

CONCLUSIONS

The present study reveals non‑iron-regulated Bmp6 expression in endothelial cells.

GENERAL SIGNIFICANCE

Regulatory expression of Bmp6 may be important as a key step for fine tuning of BMP activity.