Oxidative stress and dysfunctional NRF2 underlie pachyonychia congenita phenotypes

Pachyonychia congenita: pathogenesis of pain and approaches to treatment

Pachyonychia congenita (PC) is an autosomal dominant genodermatosis characterized by a triad of chronic severe plantar pain, focal palmoplantar keratoderma and hypertrophic nail dystrophy. Plantar pain can be debilitating and have a profound impact on quality of life. Current therapeutic options for pain in PC are limited to lifestyle adjustment and mechanical techniques, with a small subgroup of patients benefiting from oral retinoids. This review investigates the pathogenesis of pain in PC and provides a summary of the current and future therapeutic options.

Pachyonychia Congenita: A Research Agenda Leading to New Therapeutic Approaches

Pachyonychia congenita (PC) is a dominantly inherited genetic disorder of cornification. PC stands out among other genodermatoses because despite its rarity, it has been the focus of a very large number of pioneering translational research efforts over the past 2 decades, mostly driven by a patient support organization, the Pachyonychia Congenita Project. These efforts have laid the ground for innovative strategies that may broadly impact approaches to the management of other inherited cutaneous and noncutaneous diseases. This article outlines current avenues of research in PC, expected outcomes, and potential hurdles.

Significance of stress keratin expression in normal and diseased epithelia

A group of keratin intermediate filament genes, the type II KRT6A-C and type I KRT16 and KRT17, are deemed stress responsive as they are induced in keratinocytes of surface epithelia in response to environmental stressors, in skin disorders (e.g., psoriasis) and in carcinomas. Monitoring stress keratins is widely used to identify keratinocytes in an activated state. Here, we analyze single-cell transcriptomic data from healthy and diseased human skin to explore the properties of stress keratins. Relative to keratins occurring in healthy skin, stress-induced keratins are expressed at lower levels and show lesser type I-type II pairwise regulation. Stress keratins do not "replace" the keratins expressed during normal differentiation nor reflect cellular proliferation. Instead, stress keratins are consistently co-regulated with genes with roles in differentiation, inflammation, and/or activation of innate immunity at the single-cell level. These findings provide a roadmap toward explaining the broad diversity and contextual regulation of keratins.

Vascular Endothelial Growth Factor A VEGFA Inhibition: An Effective Treatment Strategy for Psoriasis

Psoriasis is an inflammatory skin disease mediated by the immune system and characterized by an inflammatory ring, also known as an epithelial immune microenvironment (EIME). The interaction between the epithelial tissue of the skin and the immune system has a crucial role in the immune cycle of psoriasis. Although the formation of new blood vessels in skin lesions provides energy support for the proliferation of epidermal keratinocytes, the role of angiogenesis in psoriasis has not been extensively studied. Vascular endothelial growth factor A (VEGFA) is a key regulator of angiogenesis that has an important role in the development of psoriasis. VEGFA promotes angiogenesis and directly stimulates epidermal keratinocytes and infiltrating immune cells, thus contributing to the progression of psoriasis. Measuring VEGFA levels to identify angiogenic characteristics in psoriasis patients may be a predictive biomarker for disease severity and response to anti-angiogenic therapy. Clinical data have shown that anti-angiogenic therapy can improve skin lesions in psoriasis patients. Therefore, this study aimed to uncover the underestimated role of blood vessels in psoriasis, explore the relationship between VEGFA and keratinocytes in the EIME, and inspire innovative drug therapies for the treatment of psoriasis.

EGFR Signaling Is Overactive in Pachyonychia Congenita: Effective Treatment with Oral Erlotinib

Pachyonychia congenita (PC) is a rare keratinizing disorder characterized by painful palmoplantar keratoderma for which there is no standard current treatment. PC is caused by dominant mutations in keratin (K) K6A, K6B, K6C, K16, or K17 genes involved in stress, wound healing, and epidermal barrier formation. Mechanisms leading to pain and painful palmoplantar keratoderma in PC remain elusive. In this study, we show overexpression of EGFR ligands epiregulin and TGF-α as well as HER1‒EGFR and HER2 in the upper spinous layers of PC lesions. EGFR activation was confirmed by upregulated MAPK/ERK and mTOR signaling. Abnormal late terminal keratinization was associated with elevated TGM1 activity. In addition, the calcium ion permeable channel TRPV3 was significantly increased in PC-lesional skin, suggesting a predominant role of the TRPV3/EGFR signaling complex in PC. We hypothesized that this complex contributes to promoting TGM1 activity and induces the expression and shedding of EGFR ligands. To counteract this biological cascade, we treated three patients with PC with oral erlotinib for 6‒8 months. The treatment was well-tolerated and led to an early, drastic, and sustained reduction of neuropathic pain with a major improvement of QOL. Our study provides evidence that targeted pharmacological inhibition of EGFR is an effective strategy in PC.

Redox signaling at the crossroads of human health and disease

Redox biology is at the core of life sciences, accompanied by the close correlation of redox processes with biological activities. Redox homeostasis is a prerequisite for human health, in which the physiological levels of nonradical reactive oxygen species (ROS) function as the primary second messengers to modulate physiological redox signaling by orchestrating multiple redox sensors. However, excessive ROS accumulation, termed oxidative stress (OS), leads to biomolecule damage and subsequent occurrence of various diseases such as type 2 diabetes, atherosclerosis, and cancer. Herein, starting with the evolution of redox biology, we reveal the roles of ROS as multifaceted physiological modulators to mediate redox signaling and sustain redox homeostasis. In addition, we also emphasize the detailed OS mechanisms involved in the initiation and development of several important diseases. ROS as a double-edged sword in disease progression suggest two different therapeutic strategies to treat redox-relevant diseases, in which targeting ROS sources and redox-related effectors to manipulate redox homeostasis will largely promote precision medicine. Therefore, a comprehensive understanding of the redox signaling networks under physiological and pathological conditions will facilitate the development of redox medicine and benefit patients with redox-relevant diseases.

Role of Phytochemicals in Skin Photoprotection via Regulation of Nrf2

Ethnopharmacological studies have become increasingly valuable in the development of botanical products and their bioactive phytochemicals as novel and effective preventive and therapeutic strategies for various diseases including skin photoaging and photodamage-related skin problems including abnormal pigmentation and inflammation. Exploring the roles of phytochemicals in mitigating ultraviolet radiation (UVR)-induced skin damage is thus of importance to offer insights into medicinal and ethnopharmacological potential for development of novel and effective photoprotective agents. UVR plays a role in the skin premature aging (or photoaging) or impaired skin integrity and function through triggering various biological responses of skin cells including apoptosis, oxidative stress, DNA damage and inflammation. In addition, melanin produced by epidermal melanocytes play a protective role against UVR-induced skin damage and therefore hyperpigmentation mediated by UV irradiation could reflect a sign of defensive response of the skin to stress. However, alteration in melanin synthesis may be implicated in skin damage, particularly in individuals with fair skin. Oxidative stress induced by UVR contributes to the process of skin aging and inflammation through the activation of related signaling pathways such as the mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1), the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), the nuclear factor kappa B (NF-κB) and the signal transducer and activator of transcription (STAT) in epidermal keratinocytes and dermal fibroblasts. ROS formation induced by UVR also plays a role in regulation of melanogenesis in melanocytes via modulating MAPK, PI3K/Akt and the melanocortin 1 receptor (MC1R)-microphthalmia-associated transcription factor (MITF) signaling cascades. Additionally, nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated antioxidant defenses can affect the major signaling pathways involved in regulation of photoaging, inflammation associated with skin barrier dysfunction and melanogenesis. This review thus highlights the roles of phytochemicals potentially acting as Nrf2 inducers in improving photoaging, inflammation and hyperpigmentation via regulation of cellular homeostasis involved in skin integrity and function. Taken together, understanding the role of phytochemicals targeting Nrf2 in photoprotection could provide an insight into potential development of natural products as a promising strategy to delay skin photoaging and improve skin conditions.

Genotype-structurotype-phenotype correlations in pachyonychia congenita patients

Pachyonychia congenita (PC) is a genetic disorder of keratin that presents with nail dystrophy, painful palmoplantar keratoderma, and other clinical manifestations. We investigated genotype-structurotype-phenotype correlations seen with mutations in keratin genes (KRT6A, KRT6B, KRT6C, KRT16, KRT17) and utilized protein structure modeling of high frequency mutations to examine the functional importance of keratin structural domains in PC pathogenesis. Participants of the International PC Research Registry underwent genetic testing and completed a standardized survey on their symptoms. Our results support prior reports associating oral leukokeratosis with KRT6A mutations, and cutaneous cysts, follicular hyperkeratosis, and natal teeth with KRT17 mutations. Painful keratoderma was prominent with KRT6A and KRT16 mutations. Nail involvement was most common in KRT6A and least common in KRT6C patients. Across keratin subtypes, patients with coil 2B mutations had greatest impairment in ambulation, and patients with coil 1A mutations reported more emotional issues. Molecular modeling demonstrated that hotspot missense mutations in PC largely disrupted hydrophobic interactions or surface charge. The former may destabilize keratin dimers/tetramers, while the latter likely interferes with higher-order keratin filament formation. Understanding pathologic alterations in keratin structure improves our knowledge of how PC genotype correlates with clinical phenotype, advancing insight into disease pathogenesis and therapeutic development.

Nagashima-Type Palmoplantar Keratosis: Clinical Characteristics, Genetic Characterization, and Clinical Management

Nagashima-type palmoplantar keratosis (NPPK) is the most prevalent palmoplantar keratoderma (PPK) in East Asia. Homozygous or compound heterozygous loss-of-function mutations in serpin peptidase inhibitor, clade B (ovalbumin), and member 70 (SERPINB7), which encodes members of the serine protease inhibitor superfamily, have been identified as the cause of NPPK. Clinical manifestations of NPPK include well-demarcated erythema, mild to moderate hyperkeratosis on the whole palm, and sole with transgrediens, extending to the dorsal surfaces of the hands and feet, inner wrists, ankles, and the Achilles tendon areas. In this study, we perform a review of relevant clinical cases aimed at elucidating the clinical characteristics, genetic characterization, differential diagnoses, and clinical management of NPPK. A better understanding of the clinical characteristics and pathogenic gene characterization of NPPK will enhance the diagnosis of NPPK, identify related diseases, and inform on the precise therapy and prognosis. Moreover, it will promote the awareness of NPPK in non-Asian regions.

Overview of the molecular determinants contributing to the expression of Psoriasis and Psoriatic Arthritis phenotypes

Psoriasis and psoriatic arthritis are multifactorial chronic disorders whose etiopathogenesis essentially derives from the alteration of several signalling pathways and the co-occurrence of genetic, epigenetic and non-genetic susceptibility factors that altogether affect the functional and structural property of the skin. Although shared and differential susceptibility genes and molecular pathways are known to contribute to the onset of pathological phenotypes, further research is needed to dissect the molecular causes of psoriatic disease and its progression towards Psoriatic Arthritis. This review will therefore be addressed to explore differences and similarities in the etiopathogenesis and progression of both disorders, with a particular focus on genes involved in the maintenance of the skin structure and integrity (keratins and collagens), modulation of patterns of recognition (through Toll-like receptors and dectin-1) and immuno-inflammatory response (by NLRP3-dependent inflammasome) to microbial pathogens. In addition, special emphasis will be given to the contribution of epigenetic elements (methylation pattern, non-coding RNAs, chromatin modifiers and 3D genome organization) to the etiopathogenesis and progression of psoriasis and psoriatic arthritis. The evidence discussed in this review highlights how the knowledge of patients' clinical and (epi)genomic make-up could be helpful for improving the available therapeutic strategies for psoriasis and psoriatic arthritis treatment.

Non-Esterified Fatty Acid-Induced Reactive Oxygen Species Mediated Granulosa Cells Apoptosis Is Regulated by Nrf2/p53 Signaling Pathway

Negative energy balance (NEB) during the perinatal period can affect dairy cow follicular development and reduce the fecundity. Non-esterified fatty acid (NEFA) concentration is elevated during NEB, and is known to be toxic for multiple cell types. In the ovary, NEB increased NEFA, and may influences follicular growth and development. However, the effect and mechanism of NEFA on granulosa cells (GCs) in vitro remains unknown. In this study, we found that NEFA dose-dependently induced apoptosis in primary cultured granulosa cells. Mechanistically, our data showed that NEFA significantly increased reactive oxygen species (ROS) levels, resulting in the activation of endoplasmic reticulum stress (ERS) and eventually cell apoptosis in GCs. Moreover, NEFA also increased the phosphorylation levels of ERK1/2 and p38MAPK pathways, upregulated the expression of p53 and potentially promoted its translocation to the nuclear, thus transcriptionally activated Bax, a downstream gene of this pathway. NEFA also promoted nuclear factor E2 (Nrf2) expression and its level in the nuclear. To elucidate the mechanism of NEFA action, N-acetyl-l-cysteine (NAC), a ROS scavenger was used to verify the role of ROS in NEFA induced apoptosis of GCs. NAC pretreatment reversed the NEFA-induced ERS-related protein and apoptosis-related protein levels. Meanwhile, NAC pretreatment also blocked the phosphorylation of ERK1/2 and p38 induced by NEFA, and the nucleation of Nrf2 and p53, suggesting that ROS plays a crucial role in regulating the NEFA-induced apoptosis of GCs. Together, these findings provide an improved understanding of the mechanisms underlying GCs apoptosis, which could potentially be useful for improving ovarian function.

Genetic activation of Nrf2 reduces cutaneous symptoms in a murine model of Netherton syndrome

Netherton syndrome is a monogenic autosomal recessive disorder primarily characterized by the detachment of the uppermost layer of the epidermis, the stratum corneum It results from mutations in the SPINK5 gene, which codes for a kallikrein inhibitor. Uncontrolled kallikrein activity leads to premature desquamation, resulting in a severe epidermal barrier defect and subsequent life-threatening systemic infections and chronic cutaneous inflammation. Here, we show that genetic activation of the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nfe2l2/Nrf2) in keratinocytes of Spink5 knockout mice, a model for Netherton syndrome, significantly alleviates their cutaneous phenotype. Nrf2 activation promoted attachment of the stratum corneum and concomitant epidermal barrier function, and reduced the expression of pro-inflammatory cytokines such as tumor necrosis factor α and thymic stromal lymphopoietin. Mechanistically, we show that Nrf2 activation induces overexpression of secretory leukocyte protease inhibitor (Slpi), a known inhibitor of kallikrein 7 and elastase 2, in mouse and human keratinocytes in vivo and in vitro, respectively. In the Spink5-deficient epidermis, the upregulation of Slpi is likely to promote stabilization of corneodesmosomes, thereby preventing premature desquamation. Our results suggest pharmacological NRF2 activation as a promising treatment modality for Netherton syndrome patients.This article has an associated First Person interview with the first author of the paper.

Keratin 14-dependent disulfides regulate epidermal homeostasis and barrier function via 14-3-3σ and YAP1

The intermediate filament protein keratin 14 (K14) provides vital structural support in basal keratinocytes of epidermis. Recent studies evidenced a role for K14-dependent disulfide bonding in the organization and dynamics of keratin IFs in skin keratinocytes. Here we report that knock-in mice harboring a cysteine-to-alanine substitution at Krt14's codon 373 (C373A) exhibit alterations in disulfide-bonded K14 species and a barrier defect secondary to enhanced proliferation, faster transit time and altered differentiation in epidermis. A proteomics screen identified 14-3-3 as K14 interacting proteins. Follow-up studies showed that YAP1, a transcriptional effector of Hippo signaling regulated by 14-3-3sigma in skin keratinocytes, shows aberrant subcellular partitioning and function in differentiating Krt14 C373A keratinocytes. Residue C373 in K14, which is conserved in a subset of keratins, is revealed as a novel regulator of keratin organization and YAP function in early differentiating keratinocytes, with an impact on cell mechanics, homeostasis and barrier function in epidermis.

Therapeutic effects of CO-releaser/Nrf2 activator hybrids (HYCOs) in the treatment of skin wound, psoriasis and multiple sclerosis

Carbon monoxide (CO) produced by heme oxygenase-1 (HO-1) or delivered by CO-releasing molecules (CO-RMs) exerts anti-inflammatory action, a feature also exhibited by the nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of the stress response. We have recently developed new hybrid molecules (HYCOs) consisting of CO-RMs conjugated to fumaric esters known to activate Nrf2/HO-1. Here we evaluated the biological activities of manganese (Mn) and ruthenium (Ru)-based HYCOs in human monocytes and keratinocytes in vitro as well as in vivo models of inflammation. The effects of HYCOs were compared to: a) dimethyl fumarate (DMF), a known fumaric ester used in the clinic; b) a CO-RM alone; or c) the combination of the two compounds. Mn–HYCOs donated CO and up-regulated Nrf2/HO-1 in vitro more efficiently than Ru–HYCOs. However, irrespective of the metal, a strong reduction in anti-inflammatory markers in monocytes stimulated by LPS was observed with specific HYCOs. This effect was not observed with DMF, CO-RM alone or the combination of the two, indicating the enhanced potency of HYCOs compared to the separate entities. Selected HYCOs given orally to mice accelerated skin wound closure, reduced psoriasis-mediated inflammation and disease symptoms equalling or surpassing the effect of DMF, and ameliorated motor dysfunction in a mouse model of multiple sclerosis. Thus, HYCOs have potent anti-inflammatory activities that are recapitulated in disease models in which inflammation is a prominent component. Prolonged daily administration of HYCOs (up to 40 days) is well tolerated in animals. Our results clearly confirm that HYCOs possess a dual mode of action highlighting the notion that simultaneous Nrf2 targeting and CO delivery could be a clinically relevant application to combat inflammation.

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HYCOs are dual activity molecules targeting the Nrf2/HO-1 axis and delivering carbon monoxide.

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Mn- and Ru-based HYCOs were compared in in vitro and in vivo models of inflammation.

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HYCOs reduce inflammation in monocytes and increase proliferation in keratinocytes.

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Oral administration of HYCOs accelerates skin wound healing and ameliorates psoriasis and multiple sclerosis.

Altered keratinocyte differentiation is an early driver of keratin mutation-based palmoplantar keratoderma

The type I intermediate filament keratin 16 (KRT16 gene; K16 protein) is constitutively expressed in ectoderm-derived appendages and in palmar/plantar epidermis and is robustly induced when the epidermis experiences chemical, mechanical or environmental stress. Missense mutations at the KRT16 locus can cause pachyonychia congenita (PC, OMIM:167200) or focal non-epidermolytic palmoplantar keratoderma (FNEPPK, OMIM:613000), which each entail painful calluses on palmar and plantar skin. Krt16-null mice develop footpad lesions that mimic PC-associated PPK, providing an opportunity to decipher its pathophysiology, and develop therapies. We report on insight gained from a genome-wide analysis of gene expression in PPK-like lesions of Krt16-null mice. Comparison of this data set with publicly available microarray data of PPK lesions from individuals with PC revealed significant synergies in gene expression profiles. Keratin 9 (Krt9/K9), the most robustly expressed gene in differentiating volar keratinocytes, is markedly downregulated in Krt16-null paw skin, well-ahead of lesion onset, and is paralleled by pleiotropic defects in terminal differentiation. Effective prevention of PPK-like lesions in Krt16-null paw skin (via topical delivery of the Nrf2 inducer sulforaphane) involves the stimulation of Krt9 expression. These findings highlight a role for defective terminal differentiation and loss of Krt9/K9 expression as additional drivers of PC-associated PPK and highlight restoration of KRT9 expression as a worthy target for therapy. Further, we report on the novel observation that keratin 16 can localize to the nucleus of epithelial cells, implying a potential nuclear function that may be relevant to PC and FNEPPK.

A role for keratins in supporting mitochondrial organization and function in skin keratinocytes

Mitochondria fulfill essential roles in ATP production, metabolic regulation, calcium signaling, generation of reactive oxygen species (ROS), and additional determinants of cellular health. Recent studies have highlighted a role for mitochondria during cell differentiation, including in skin epidermis. The observation of oxidative stress in keratinocytes from Krt16 null mouse skin, a model for pachyonychia congenita (PC)–associated palmoplantar keratoderma, prompted us to examine the role of Keratin (K) 16 protein and its partner K6 in regulating the structure and function of mitochondria. Electron microscopy revealed major anomalies in mitochondrial ultrastructure in late stage, E18.5, Krt6a/Krt6b null embryonic mouse skin. Follow-up studies utilizing biochemical, metabolic, and live imaging readouts showed that, relative to controls, skin keratinocytes null for Krt6a/Krt6b or Krt16 exhibit elevated ROS, reduced mitochondrial respiration, intracellular distribution differences, and altered movement of mitochondria within the cell. These findings highlight a novel role for K6 and K16 in regulating mitochondrial morphology, dynamics, and function and shed new light on the causes of oxidative stress observed in PC and related keratin-based skin disorders.

Pathophysiology of pachyonychia congenita-associated palmoplantar keratoderma: new insights into skin epithelial homeostasis and avenues for treatment

BACKGROUND

Pachyonychia congenita (PC), a rare genodermatosis, primarily affects ectoderm-derived epithelial appendages and typically includes oral leukokeratosis, nail dystrophy and very painful palmoplantar keratoderma (PPK). PC dramatically impacts quality of life although it does not affect lifespan. PC can arise from mutations in any of the wound-repair-associated keratin genes KRT6A, KRT6B, KRT6C, KRT16 or KRT17. There is no cure for this condition, and current treatment options for PC symptoms are limited and palliative in nature.

OBJECTIVES

This review focuses on recent progress made towards understanding the pathophysiology of PPK lesions, the most prevalent and debilitating of all PC symptoms.

METHODS

We reviewed the relevant literature with a particular focus on the Krt16 null mouse, which spontaneously develops footpad lesions that mimic several aspects of PC-associated PPK.

RESULTS

There are three main stages of progression of PPK-like lesions in Krt16 null mice. Ahead of lesion onset, keratinocytes in the palmoplantar (footpad) skin exhibit specific defects in terminal differentiation, including loss of Krt9 expression. At the time of PPK onset, there is elevated oxidative stress and hypoactive Keap1-Nrf2 signalling. During active PPK, there is a profound defect in the ability of the epidermis to maintain or return to normal homeostasis.

CONCLUSIONS

The progress made suggests new avenues to explore for the treatment of PC-based PPK and deepens our understanding of the mechanisms controlling skin tissue homeostasis. What's already known about this topic? Pachyonychia congenita (PC) is a rare genodermatosis caused by mutations in KRT6A, KRT6B, KRT6C, KRT16 and KRT17, which are normally expressed in skin appendages and induced following injury. Individuals with PC present with multiple clinical symptoms that usually include thickened and dystrophic nails, palmoplantar keratoderma (PPK), glandular cysts and oral leukokeratosis. The study of PC pathophysiology is made challenging because of its low incidence and high complexity. There is no cure or effective treatment for PC. What does this study add? This text reviews recent progress made when studying the pathophysiology of PPK associated with PC. This recent progress points to new possibilities for devising effective therapeutics that may complement current palliative strategies.

Epithelial keratins: Biology and implications as diagnostic markers for liquid biopsies

Keratins are essential elements of the cytoskeleton of normal and malignant epithelial cells. Because carcinomas commonly maintain their specific keratin expression pattern during malignant transformation, keratins are extensively used as tumor markers in cancer diagnosis including the detection of circulating tumor cells in blood of carcinoma patients. Interestingly, recent biological insights demonstrate that epithelial keratins should not only be considered as mere tumor markers. Emerging evidence suggests an active biological role of keratins in tumor cell dissemination and metastasis. In this review, we illustrate the family of keratin proteins, summarize the latest biological insights into keratin function related to cancer metastasis and discuss the current use of keratins for detection of CTCs and other blood biomarkers used in oncology.

Connecting the Dots in the Neuroglobin-Protein Interaction Network of an Unstressed and Ferroptotic Cell Death Neuroblastoma Model

Neuroglobin is a heme protein of which increased levels provide neuroprotection against amyloid proteinopathy and hemorrhagic damage. These cellular stressors involve the promotion of ferroptosis—an iron-dependent, lipid peroxide-accreting form of cell death. Hence, we questioned whether neuroglobin could oppose ferroptosis initiation. We detected human neuroglobin (hNgb)-EGFP-expressing SH-SY5Y cells to be significantly more resistant to ferroptosis induction, identifying 0.68-fold less cell death. To elucidate the underlying pathways, this study investigated hNgb-protein interactions with a Co-IP-MS/MS approach both under a physiological and a ferroptotic condition. hNgb binds to proteins of the cellular iron metabolism (e.g., RPL15 and PCBP3) in an unstressed condition and shows an elevated binding ratio towards cell death-linked proteins, such as HNRNPA3, FAM120A, and ABRAXAS2, under ferroptotic stress. Our data also reveal a constitutive interaction between hNgb and the longevity-associated heterodimer XRCC5/XRCC6. Disentangling the involvement of hNgb and its binding partners in cellular processes, using Ingenuity Pathway Analysis, resulted in the integration of hNgb in the ubiquitination pathway, mTOR signaling, 14-3-3-mediated signaling, and the glycolysis cascade. We also detected a previously unknown strong link with motor neuropathies. Hence, this study contributes to the elucidation of neuroglobin’s involvement in cellular mechanisms that provide neuroprotection and the upkeep of homeostasis.

Sex Matters: Interfering with the Oxidative Stress Response in Pachyonychia Congenita

Pachyonychia congenita is an incurable and often debilitating genodermatosis. Topical application of the antioxidative response inducer sulforaphane, however, alleviates disease symptoms in a murine pachyonychia congenita model, forecasting clinical benefits. The Coulombe laboratory now reports sex-dependent differences in sulforaphane responsiveness of pachyonychia congenita mice, thereby dampening treatment expectations but also unveiling novel aspects of sex-specific oxidative stress reactivity in the epidermis.

Intermediate filaments and IF-associated proteins: from cell architecture to cell proliferation

Intermediate filaments (IFs), in coordination with microfilaments and microtubules, form the structural framework of the cytoskeleton and nucleus, thereby providing mechanical support against cellular stresses and anchoring intracellular organelles in place. The assembly and disassembly of IFs are mainly regulated by the phosphorylation of IF proteins. These phosphorylation states can be tracked using antibodies raised against phosphopeptides in the target proteins. IFs exert their functions through interactions with not only structural proteins, but also non-structural proteins involved in cell signaling, such as stress responses, apoptosis, and cell proliferation. This review highlights findings related to how IFs regulate cell division through phosphorylation cascades and how trichoplein, a centriolar protein originally identified as a keratin-associated protein, regulates the cell cycle through primary cilium formation.

Keratin 6 regulates collective keratinocyte migration by altering cell-cell and cell-matrix adhesion

Keratin 6 (K6) isoforms are induced in wound-proximal keratinocytes after injury to skin. Paradoxically, absence of K6 isoforms leads to faster directional cell migration. Wang et al. report that K6 promotes collective keratinocyte migration by interacting with desmoplakin and myosin IIA and stabilizing cell adhesion.

The a and b isoforms of keratin 6 (K6), a type II intermediate filament (IF) protein, are robustly induced upon injury to interfollicular epidermis. We previously showed that complete loss of K6a/K6b stimulates keratinocyte migration, correlating with enhanced Src activity. In this study, we demonstrate that this property is cell autonomous, depends on the ECM, and results from elevated speed, enhanced directionality, and an increased rate of focal adhesion disassembly. We show that myosin IIA interacts with K6a/K6b, that its levels are markedly reduced in Krt6a/Krt6b-null keratinocytes, and that inhibiting myosin ATPase activity normalizes the enhanced migration potential of Krt6a/Krt6b-null cells. Desmoplakin, which mediates attachment of IFs to desmosomes, is also expressed at reduced levels and is mislocalized to the nucleus in Krt6a/Krt6b-null cells, correlating with defects in cell adhesion. These findings reveal that K6a/K6b modulate keratinocyte migration by regulating cell–matrix and cell–cell adhesion and highlight a role for keratins in collective cell migration.

HYCO-3, a dual CO-releaser/Nrf2 activator, reduces tissue inflammation in mice challenged with lipopolysaccharide

Oxidative stress and inflammation are predominant features of several chronic diseases. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a major arbiter in counteracting these insults via up-regulation of several defensive proteins, including heme oxygenase-1 (HO-1). HO-1-derived carbon monoxide (CO) exhibits anti-inflammatory actions and can be delivered to tissues by CO-releasing agents. In this study we assessed the pharmacological and anti-inflammatory properties of HYCO-3, a dual activity compound obtained by conjugating analogues of the CO-releasing molecule CORM-401 and dimethyl fumarate (DMF), an immunomodulatory drug known to activate Nrf2. HYCO-3 induced Nrf2-dependent genes and delivered CO to cells in vitro and tissues in vivo, confirming that the two expected pharmacological properties of this agent are achieved. In mice challenged with lipopolysaccharide, orally administered HYCO-3 reduced the mRNA levels of pro-inflammatory markers (TNF-α, IL-1β and IL-6) while increasing the expression of the anti-inflammatory genes ARG1 and IL-10 in brain, liver, lung and heart. In contrast, DMF or CORM-401 alone or their combination decreased the expression of pro-inflammatory genes but had limited influence on anti-inflammatory markers. Furthermore, HYCO-3 diminished TNF-α and IL-1β in brain and liver but not in lung and heart of Nrf2^-/- mice, indicating that the CO-releasing part of this hybrid contributes to reduction of pro-inflammation and that this effect is organ-specific. These data demonstrate that the dual activity of HYCO-3 results in enhanced efficacy compared to the parent compounds indicating the potential exploitation of hybrid compounds in the development of effective anti-inflammatory therapies.

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HYCO-3 is a novel hybrid between an Nrf2 activator and a CO-releasing molecule.

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HYCO-3 induces Nrf2 and simultaneously delivers CO in vitro and in vivo.

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Oral administration of HYCO-3 reduces inflammation in mice challenged with LPS.

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In Nrf2-/- mice, the anti-inflammatory action of HYCO-3 is organ specific.

Metformin Promotes HaCaT Cell Apoptosis through Generation of Reactive Oxygen Species via Raf-1-ERK1/2-Nrf2 Inactivation

Although metformin (MET) may be useful for the treatment of psoriasis, the mechanisms underlying its method of action have yet to be fully elucidated. Here, the relationship between MET function and reactive oxygen species (ROS) levels and the underlying mechanism were explored in human immortalized keratinocyte cell line (HaCaT). HaCaT cells were incubated with MET at 0, 10, 20, 40, and 60 mM for 24 h. The cell viability was evaluated by the CCK-8 assay. The cell apoptosis rate and intracellular ROS levels were examined using flow cytometry. The protein expression and the phosphorylation levels of nuclear factor erythroid-derived 2 related factor 2 (Nrf2), Raf-1, and ERK1/2 were assessed by Western blot. The specific ROS scavenger N-acetyl-cysteine (NAC) and the specific Nrf2 agonist Oltipraz (OPZ) were used to analyze the effect of MET. MET decreased HaCaT cell proliferation and induced HaCaT cell apoptosis in a dose-dependent manner. MET was found to elevate intracellular ROS levels in a dose-dependent manner, while pretreatment with NAC attenuated these effects. MET inhibits the protein expression and the phosphorylation levels of Nrf2. The combination of OPZ and MET can significantly increase the cell viability, decrease the rate of apoptosis, and attenuate the intracellular ROS levels relative to MET alone. MET inhibits the protein expression and the phosphorylation levels of Raf-1 and ERK1/2. MET was found to attenuate Raf-1-ERK1/2 signaling in HaCaT cells to suppress the expression and phosphorylation levels of Nrf2, which contributed to the intracellular generation of ROS and the pro-apoptotic effects of MET.

A rim-and-spoke hypothesis to explain the biomechanical roles for cytoplasmic intermediate filament networks

Textbook images of keratin intermediate filament (IF) networks in epithelial cells and the functional compromization of the epidermis by keratin mutations promulgate a mechanical role for this important cytoskeletal component. In stratified epithelia, keratin filaments form prominent radial spokes that are focused onto cell-cell contact sites, i.e. the desmosomes. In this Hypothesis, we draw attention to a subset of keratin filaments that are apposed to the plasma membrane. They form a rim of filaments interconnecting the desmosomes in a circumferential network. We hypothesize that they are part of a rim-and-spoke arrangement of IFs in epithelia. From our review of the literature, we extend this functional role for the subplasmalemmal rim of IFs to any cell, in which plasma membrane support is required, provided these filaments connect directly or indirectly to the plasma membrane. Furthermore, cytoplasmic IF networks physically link the outer nuclear and plasma membranes, but their participation in mechanotransduction processes remain largely unconsidered. Therefore, we also discuss the potential biomechanical and mechanosensory role(s) of the cytoplasmic IF network in terms of such a rim (i.e. subplasmalemmal)-and-spoke arrangement for cytoplasmic IF networks.

The keratin 16 null phenotype is modestly impacted by genetic strain background in mice

The type I intermediate filament keratin 16 (K16) is constitutively expressed in ectoderm-derived appendages and is inducibly expressed in the epidermis upon barrier-compromising challenges. Dominantly acting missense alleles in KRT16 are causative for pachyonychia congenita (PC), a genodermatosis involving debilitating palmoplantar keratoderma (PPK), nail dystrophy, oral lesions and, frequently, alterations in glands and hair. C57Bl/6;Krt16^-/- mice develop oral lesions early after birth and PC-like PPK lesions as young adults. These PPK lesions have a marked dysregulation of skin barrier-related genes and innate immunity effectors (eg danger-associated molecular patterns) and are preceded by oxidative stress secondary to hypoactive Nrf2 signalling. These molecular features are present in PPK lesions of PC patients. Here, we report that all components of the C57Bl/6;Krt16^-/- mouse phenotype occur as well in the FVB strain background, albeit less severely so, a significant observation in the light of variations in the clinical presentation of individuals harbouring disease-causing mutations in the KRT16 gene.

p63 is a key regulator of iRHOM2 signalling in the keratinocyte stress response

Hyperproliferative keratinocytes induced by trauma, hyperkeratosis and/or inflammation display molecular signatures similar to those of palmoplantar epidermis. Inherited gain-of-function mutations in RHBDF2 (encoding iRHOM2) are associated with a hyperproliferative palmoplantar keratoderma and squamous oesophageal cancer syndrome (termed TOC). In contrast, genetic ablation of rhbdf2 in mice leads to a thinning of the mammalian footpad, and reduces keratinocyte hyperproliferation and migration. Here, we report that iRHOM2 is a novel target gene of p63 and that both p63 and iRHOM2 differentially regulate cellular stress-associated signalling pathways in normal and hyperproliferative keratinocytes. We demonstrate that p63-iRHOM2 regulates cell survival and response to oxidative stress via modulation of SURVIVIN and Cytoglobin, respectively. Furthermore, the antioxidant compound Sulforaphane downregulates p63-iRHOM2 expression, leading to reduced proliferation, inflammation, survival and ROS production. These findings elucidate a novel p63-associated pathway that identifies iRHOM2 modulation as a potential therapeutic target to treat hyperproliferative skin disease and neoplasia.

Protective role of integrin-linked kinase against oxidative stress and in maintenance of genomic integrity

The balance between the production of reactive oxygen species and activation of antioxidant pathways is essential to maintain a normal redox state in all tissues. Oxidative stress caused by excessive oxidant species generation can cause damage to DNA and other macromolecules, affecting cell function and viability. Here we show that integrin-linked kinase (ILK) plays a key role in eliciting a protective response to oxidative damage in epidermal cells. Inactivation of the Ilk gene causes elevated levels of intracellular oxidant species (IOS) and DNA damage in the absence of exogenous oxidative insults. In ILK-deficient cells, excessive IOS production can be prevented through inhibition of NADPH oxidase activity, with a concomitant reduction in DNA damage. Additionally, ILK is necessary for DNA repair processes following UVB-induced damage, as ILK-deficient cells show a significantly impaired ability to remove cyclobutane pyrimidine dimers following irradiation. Thus, ILK is essential to maintain cellular redox balance and, in its absence, epidermal cells become more susceptible to oxidative damage through mechanisms that involve IOS production by NADPH oxidase activity.

Chemoprevention of oxidative stress-associated oral carcinogenesis by sulforaphane depends on NRF2 and the isothiocyanate moiety

Oxidative stress is known to play an important role in oral cancer development. In this study we aimed to examine whether a chemical activator of NRF2, sulforaphane (SFN), may have chemopreventive effects on oxidative stress-associated oral carcinogenesis. We first showed that Nrf2 activation and oxidative damage were commonly seen in human samples of oral leukoplakia. With gene microarray and immunostaining, we found 4-nitroquinoline 1-oxide (4NQO) in drink activated the Nrf2 pathway and produced oxidative damage in mouse tongue. Meanwhile whole exome sequencing of mouse tongue identified mutations consistent with 4NQO's mutagenic profile. Using cultured human oral keratinocytes and 4NQO-treated mouse tongue, we found that SFN pre-treatment activated the NRF2 pathway and inhibited oxidative damage both in vitro and in vivo. On the contrary, a structural analogue of SFN without the isothiocyanate moiety did not have such effects. In a long-term chemoprevention study using wild-type and Nrf2^-/- mice, we showed that topical application of SFN activated the NRF2 pathway, inhibited oxidative damage, and prevented 4NQO-induced oral carcinogenesis in an Nrf2-dependent manner. Our data clearly demonstrate that SFN has chemopreventive effects on oxidative stress-associated oral carcinogenesis, and such effects depend on Nrf2 and the isothiocyanate moiety.

Sexual Dimorphism in Response to an NRF2 Inducer in a Model for Pachyonychia Congenita

Sex is an influential factor regarding pathophysiology and therapeutic response in human disease. Pachyonychia congenita is caused by mutations in keratin genes and typified by dystrophic lesions affecting nails, glands, oral mucosa, and palmar-plantar epidermis. Painful palmar-plantar keratoderma (PPK) severely impairs mobility in pachyonychia congenita. Mice genetically null for keratin 16 (Krt16), one of the genes mutated in pachyonychia congenita, develop pachyonychia congenita-like PPK. In male Krt16^-/- mice, oxidative stress associated with impaired glutathione synthesis and nuclear factor erythroid-derived 2 related factor 2 (NRF2)-dependent gene expression precedes PPK onset, which can be prevented by topical sulforaphane-mediated activation of NRF2. We report here that sulforaphane treatment fails to activate NRF2 and prevent PPK in female Krt16^-/- mice despite a similar set of molecular circumstances. Follow-up studies reveal a temporal shift in PPK onset in Krt16^-/- females, coinciding with sex-specific fluctuations in footpad skin glutathione levels. Dual treatment with sulforaphane and diarylpropionitrile, an estrogen receptor beta selective agonist, results in NRF2 activation, normalization of glutathione levels, and prevention of PPK in female Krt16^-/- mice. These findings point to a sex difference in NRF2 responsiveness that needs be considered when exploring NRF2 as a therapeutic target in skin disorders.

Bidirectional Association Between Psoriasis and Obesity: Benefits and Risks

Psoriasis is a chronic, immune-mediated inflammatory skin disease that is associated with several comorbidities such as obesity. This study was designed to estimate the possibility of utilizing psoriasin, nestin, keratin-16 (Krt16), and interleukin-21 (IL-21) as biochemical markers of psoriasis, to correlate these candidate psoriatic markers with biomarkers of obesity [body mass index (BMI), leptin, and resistin], and to elucidate the bidirectional association between obesity and psoriasis. Blood samples were collected from all participants (n = 108) who were classified according to their BMI into 4 groups: healthy control, obese, psoriatic, and obese psoriatic group. Plasma psoriasin, nestin, Krt16, IL-21, leptin, and resistin were estimated for all subjects. Psoriasin, nestin, Krt16, IL-21, leptin, and resistin were significantly elevated in psoriatic and obese psoriatic groups. However, only leptin, resistin, IL-21, and Krt16 were significantly increased in the obese group compared with the control group. Leptin and resistin showed significant positive correlations with psoriasis area and severity index score, psoriasin, nestin, Krt16, and IL-21. Cutoff values for psoriasin, nestin, Krt16, and IL-21 were 187.5 ng/mL, 1825 pg/mL, 33.1 ng/mL, and 128.6 ng/L, respectively. In conclusion, psoriasin, nestin, Krt16, and IL-21 can be utilized as biochemical markers of psoriasis; these psoriatic markers are significantly positively correlated with obesity biomarkers, and obesity can be considered a risk factor and/or consequence of psoriasis.

Oxidative stress management in the hair follicle: Could targeting NRF2 counter age-related hair disorders and beyond?

Widespread expression of the transcription factor, nuclear factor (erythroid-derived 2)-like 2 (NRF2), which maintains redox homeostasis, has recently been identified in the hair follicle (HF). Small molecule activators of NRF2 may therefore be useful in the management of HF pathologies associated with redox imbalance, ranging from HF greying and HF ageing via androgenetic alopecia and alopecia areata to chemotherapy-induced hair loss. Indeed, NRF2 activation has been shown to prevent peroxide-induced hair growth inhibition. Multiple parameters can increase the levels of reactive oxygen species in the HF, for example melanogenesis, depilation-induced trauma, neurogenic and autoimmune inflammation, toxic drugs, environmental stressors such as UV irradiation, genetic defects and aging-associated mitochondrial dysfunction. In this review, the potential mechanisms whereby NRF2 activation could prove beneficial in treatment of redox-associated HF disorders are therefore discussed.

Proteomic profiling of Pachyonychia congenita plantar callus

Callus samples from the ball and the arch of the foot, collected on tape circles, were compared by shotgun proteomic profiling. Pachyonychia congenita subjects were sampled who exhibited a mutation in KRT6A, KRT6B, KRT6C, KRT16 or KRT17, and the proteins were digested and analyzed by tandem mass spectrometry. In comparison with samples from unaffected control subjects, those from subjects with KRT6A or KRT16 mutations displayed the most differences in profile from normal, while those from subjects with KRT6C or KRT17 mutations showed few differences from normal. The profiles from subjects with KRT6B mutations were intermediate in protein profile differences. Degree of departure from the normal profile could be estimated by expression of numerous proteins in callus from the ball of the foot that were consistently different. By contrast, the protein profile from the arch of the foot was hardly affected. The results provide a foundation for noninvasive monitoring of the efficacy of treatments with quantitative assessment of departure from the normal phenotype.

SIGNIFICANCE

Pachyonychia congenita is an orphan disease in which the connection between the basic defect (keratin mutation) and debilitating symptoms (severe plantar pain) is poorly understood. Present work addresses the degree to which the protein profile is altered in the epidermis where the severe pain originates. The results indicate that the mutated keratins differ greatly in the degree to which they elicit perturbations in protein profile. In those cases with markedly altered protein levels, monitoring the callus profile may provide an objective measure of treatment efficacy.

Report of the 13th Annual International Pachyonychia Congenita Consortium Symposium

The International Pachyonychia Congenita Consortium (IPCC) is a group of physicians and scientists from around the world dedicated to developing therapies for pachyonychia congenita, a rare autosomal dominant skin disorder. The research presented at the 13th Annual Research Symposium of the IPCC, held on 10-11 May 2016, in Scottsdale, AZ, U.S.A., is reported here.

Gold-quercetin nanoparticles prevent metabolic endotoxemia-induced kidney injury by regulating TLR4/NF-κB signaling and Nrf2 pathway in high fat diet fed mice

High-fat diet-induced metabolic syndrome followed by chronic kidney disease caused by intestinal endotoxemia have received extensive attention. Toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) and oxidative stress-related Nrf2/Keap1 were regarded as the key target points involved in metabolic inflammation and kidney injury. However, the molecular mechanism of interaction between TLR4/NF-κB and Nrf2 activation in high-fat diet-induced renal injury is not absolutely understood. Quercetin, a natural product, has been reported to possess antitumor and anti-inflammatory effects. In this regard, this study attempted to prepare poly(d,l-lactide-co-glycolide)-loaded gold nanoparticles precipitated with quercetin (GQ) to investigate the anti-inflammatory and anti-oxidative stress effects in high-fat diet-induced kidney failure. For this study, C57BL/6 mice fed fat-rich fodder were used as the metabolic syndrome model to evaluate the protective effects of GQ on kidney injury and to determine whether TLR4/NF-κB and Nrf2 pathways were associated with the process. Moreover, histological examinations, enzyme-linked immunosorbent assay, Western blot, and basic blood tests and systemic inflammation-related indicators were used to investigate the inhibitory effects of GQ and underlying molecular mechanism by which it may reduce renal injury. Of note, podocyte injury was found to participate in endotoxin-stimulated inflammatory response. TLR4/NF-κB and Nrf2 pathways were upregulated with high-fat diet intake in mice, resulting in reduction of superoxide dismutase activity and increase in superoxide radical, H₂O₂, malondialdehyde, XO, XDH, and XO/XDH ratio. In addition, upregulation of TLR4/NF-κB and oxidative stress by endotoxin were observed in vitro, which were suppressed by GQ administration, ultimately alleviating podocyte injury. These findings indicated that GQ could restore the metabolic disorders caused by high-fat diet, which suppresses insulin resistance, lipid metabolic imbalance, and proinflammatory cytokine production. Also, it may prevent kidney injury by inhibition of TLR4/NF-κB and oxidative stress, further increasing superoxide dismutase activity.