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

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.

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.

Challenges in Treating Genodermatoses: New Therapies at the Horizon

Genodermatoses are rare inherited skin diseases that frequently affect other organs. They often have marked effects on wellbeing and may cause early death. Progress in molecular genetics and translational research has unravelled many underlying pathological mechanisms, and in several disorders with high unmet need, has opened the way for the introduction of innovative treatments. One approach is to intervene where cell-signaling pathways are dysregulated, in the case of overactive pathways by the use of selective inhibitors, or when the activity of an essential factor is decreased by augmenting a molecular component to correct disequilibrium in the pathway. Where inflammatory reactions have been induced by a genetically altered protein, another possible approach is to suppress the inflammation directly. Depending on the nature of the genodermatosis, the implicated protein or even on the particular mutation, to correct the consequences or the genetic defect, may require a highly personalised stratagem. Repurposed drugs, can be used to bring about a "read through" strategy especially where the genetic defect induces premature termination codons. Sometimes the defective protein can be replaced by a normal functioning one. Cell therapies with allogeneic normal keratinocytes or fibroblasts may restore the integrity of diseased skin and allogeneic bone marrow or mesenchymal cells may additionally rescue other affected organs. Genetic engineering is expanding rapidly. The insertion of a normal functioning gene into cells of the recipient is since long explored. More recently, genome editing, allows reframing, insertion or deletion of exons or disruption of aberrantly functioning genes. There are now several examples where these stratagems are being explored in the (pre)clinical phase of therapeutic trial programmes. Another stratagem, designed to reduce the severity of a given disease involves the use of RNAi to attenuate expression of a harmful protein by decreasing abundance of the cognate transcript. Most of these strategies are short-lasting and will thus require intermittent life-long administration. In contrast, insertion of healthy copies of the relevant gene or editing the disease locus in the genome to correct harmful mutations in stem cells is more likely to induce a permanent cure. Here we discuss the potential advantages and drawbacks of applying these technologies in patients with these genetic conditions. Given the severity of many genodermatoses, prevention of transmission to future generations remains an important goal including offering reproductive choices, such as preimplantation genetic testing, which can allow selection of an unaffected embryo for transfer to the uterus.

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.

Distinctions in the Management, Patient Impact, and Clinical Profiles of Pachyonychia Congenita Subtypes

Introduction

Pachyonychia congenita (PC) is a rare dermatosis that confers lifelong physical and emotional morbidities in affected patients. However, the clinical findings, treatments, and psychosocial impact of this disease have not been adequately described. The International PC Research Registry (IPCRR), a multinational initiative to collect data on PC patients, has allowed an opportunity to distinguish the salient features of this disease. We aimed to characterize the breadth and extent of nail disease, treatments, and quality of life in PC patients, and to describe any significant differences in clinical presentation or treatment of PC subtypes.

Methods

The most recent IPCRR patient survey data consisting of an 857-response questionnaire and a 102-response addendum were analyzed in a retrospective analysis. The survey data were collected as part of a multinational, multicenter initiative and comprise the largest representative population of PC to date. Participants (survey respondents) were included in the study based on questionnaire responses and a genetic confirmation of having a PC subtype.

Results

A total of 857 survey responses were collected. Genetic variations among PC subtypes influence nail disease onset and severity of symptoms. Nail disease negatively impacts patients' emotional health, especially during the adolescent and young adult years. Nail treatment tools vary little in terms of effectiveness and acquired infection rates.

Conclusion and Discussion

Patients with different PC subtypes have distinct clinical nail presentations and psychosocial impact. Genetic testing should be used to confirm PC diagnoses. Further characterization of PC, especially the rarer subtypes, may allow for more individualized patient education.

Berry-Derived Polyphenols in Cardiovascular Pathologies: Mechanisms of Disease and the Role of Diet and Sex

Cardiovascular disease (CVD) prevalence, pathogenesis, and manifestation is differentially influenced by biological sex. Berry polyphenols target several signaling pathways pertinent to CVD development, including inflammation, oxidative stress, and cardiac and vascular remodeling, and there are innate differences in these pathways that also vary by sex. There is limited research systematically investigating sex differences in berry polyphenol effects on these pathways, but there are fundamental findings at this time that suggest a sex-specific effect. This review will detail mechanisms within these pathological pathways, how they differ by sex, and how they may be individually targeted by berry polyphenols in a sex-specific manner. Because of the substantial polyphenolic profile of berries, berry consumption represents a promising interventional tool in the treatment and prevention of CVD in both sexes, but the mechanisms in which they function within each sex may vary.

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.

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.

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.