Rapamycin selectively inhibits expression of an inducible keratin (K6a) in human keratinocytes and improves symptoms in pachyonychia congenita patients

Pachyonychia Congenita: Clinical Features and Future Treatments

Pachyonychia congenita (PC) is a rare, autosomal dominant inherited disorder of keratinization that is characterized by a triad of focal palmoplantar keratoderma, plantar pain, and hypertrophic nail dystrophy. It can be debilitating, causing significantly impaired mobility. PC is diagnosed clinically alongside identification of a heterozygous pathogenic mutation in one of five keratin genes: KRT6A, KRT6B, KRT6C, KRT16, or KRT17. Each keratin gene mutation is associated with a distinct clinical phenotype, with variable age of onset and additional features, which has allowed classification by genotype. Additional features include pilosebaceous cysts, follicular hyperkeratosis, natal teeth, oral leukokeratosis, hidradenitis suppurativa, itching, and neurovascular structures. Although classed as rare, the prevalence of PC is likely to be underestimated. There is no cure or specific treatment for PC at present. Current treatments are limited to conservative measures to reduce plantar friction and trauma, mechanical debridement, topical treatments, and treatments for associated features or complications, most commonly infection. However, through active research in collaboration with PC Project, a patient-advocacy group, and the International PC Research Registry, a global registry of PC patients, there are now many new potential therapeutic options on the horizon. This review summarizes the clinical features associated with PC and highlights the current and future treatment of its manifestations.

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.

Keratins 6, 16, and 17 in Health and Disease: A Summary of Recent Findings

Keratins 6, 16, and 17 occupy unique positions within the keratin family. These proteins are not commonly found in the healthy, intact epidermis, but their expression increases in response to damage, inflammation, and hereditary skin conditions, as well as cancerous cell transformations and tumor growth. As a result, there is an active investigation into the potential use of these proteins as biomarkers for different pathologies. Recent studies have revealed the role of these keratins in regulating keratinocyte migration, proliferation, and growth, and more recently, their nuclear functions, including their role in maintaining nuclear structure and responding to DNA damage, have also been identified. This review aims to summarize the latest research on keratins 6, 16, and 17, their regulation in the epidermis, and their potential use as biomarkers in various skin conditions.

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.

A novel heterozygous frameshift mutation in the KRT6A gene responsible for an uncommon phenotype of pachyonychia congenita: One case report and review of literature

Pachyonychia congenita is an uncommon autosomal dominant skin disorder characterized by hypertrophic nail dystrophy, palmoplantar keratoderma, oral leukokeratosis, and cutaneous cysts. And fissured tongue is rarely reported in patients with pachyonychia congenita. The disease is primarily associated with mutations in five keratin genes, namely KRT6A, KRT6B, KRT6C, KRT16 or KRT17. Herein we report a 9-year-old Chinese girl who has thickened nails, keratinized plaques, and fissured tongue since birth. To investigate the underlying genetic cause, whole-exome sequencing and Sanger sequencing were performed in this patient and her family members. We identified a candidate variant c.1460-2_1460del (p.S487Lfs*21) in the KRT6A gene (NM_005554.4) by whole-exome sequencing. Sanger sequencing revealed the absence of the mutation in both parents, indicating that it is a de novo variant. Thus, the novel heterozygous frameshift mutation c.1460-2_1460del (p.S487Lfs*21) within exon 9 of KRT6A was identified as the genetic cause of the patient. Our study identified a rare de novo heterozygous frameshift mutation in the KRT6A gene in a patient with pachyonychia congenita presenting fissured tongue. Our findings expand the KRT6A gene mutation spectrum of Pachyonychia congenita, and will contribute to the future genetic counseling and gene therapy for this disease.

Posttranslational modifications of keratins and their associated proteins as therapeutic targets in keratin diseases

The keratin cytoskeleton protects epithelia against mechanical, nonmechanical, and physical stresses, and participates in multiple signaling pathways that regulate cell integrity and resilience. Keratin gene mutations cause multiple rare monoallelic epithelial diseases termed keratinopathies, including the skin diseases Epidermolysis Bullosa Simplex (EBS) and Pachyonychia Congenita (PC), with limited available therapies. The disease-related keratin mutations trigger posttranslational modifications (PTMs) in keratins and their associated proteins that can aggravate the disease. Recent findings of drug high-throughput screening have led to the identification of compounds that may be repurposed, since they are used for other human diseases, to treat keratinopathies. These drugs target unique PTM pathways and sites, including phosphorylation and acetylation of keratins and their associated proteins, and have shed insights into keratin regulation and interactions. They also offer the prospect of testing the use of drug mixtures, with the long view of possible beneficial human use coupled with increased efficacy and lower side effects.

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.

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

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

Treatment of Painful Palmoplantar Keratoderma Related to Pachyonychia Congenita Using EGFR Inhibitors

Pachyonychia congenita (PC) is a genodermatosis associated with severe painful palmoplantar keratoderma (PPK) and thickened dystrophic nails caused by autosomal dominant-negative mutations in five genes encoding keratins 6A-B-C, 16, and 17. The mechanical, surgical, or medical options for painful PC are inefficient. Given ErbB/Her family members’ role in epidermal homeostasis, this study sought to investigate the possibility of treating PC patients with PPK by blocking signaling either with EGFR (Her1) inhibitor erlotinib or lapatinib, a dual EGFR(Her1)/Her2. After 1 month of therapy with oral erlotinib treatment at 75 mg/day, the pain disappeared for patient #1, with partially reduced hyperkeratosis, while increasing the dose to 100 mg/day resulted in painful skin fissures. Therapy replacement with erlotinib cream at 0.2% was inconclusive, and substitution with oral lapatinib at alternating doses of 500 and 750 mg/day achieved a good compromise between pain reduction, symptom improvements, and side effects. Patient #2′s treatment with erlotinib cream failed to display significant improvements. Oral erlotinib started at 75 mg/day then reduced to 25 mg/day because of the formation of an acneiform rash. Treatment considerably improved the patient’s condition, with an almost complete disappearance of pain. Oral Her1 or 1/2 inhibitors reduced pain, improved two PC patients’ quality of life, and offered promising therapeutic perspectives.

Drug Repurposing Reveals mTOR Inhibition as a Promising Strategy for Epidermolysis Bullosa Simplex

Drug repurposing has the potential to discover new treatments for diseases with high unmet medical needs. Lee et al. (2021) combined transcriptomics and computational analysis of drug-target databases to identify novel therapies for epidermolysis bullosa simplex. Differential gene expression analysis of blister epidermis identified the phosphoinositide 3-kinase/protein kinase B/mTOR signaling pathway as central. A pilot study using a topical mTOR inhibitor showed marked improvement.

Transcriptomic Repositioning Analysis Identifies mTOR Inhibitor as Potential Therapy for Epidermolysis Bullosa Simplex

Expression-based systematic drug repositioning has been explored to predict novel treatments for a number of skin disorders. In this study, we utilize this approach to identify, to our knowledge, previously unreported therapies for epidermolysis bullosa simplex (EBS). RNA sequencing analysis was performed on skin biopsies of acute blisters (<1 week old) (n = 9) and nonblistered epidermis (n = 11) obtained from 11 patients with EBS. Transcriptomic analysis of blistered epidermis in patients with EBS revealed a set of 1,276 genes dysregulated in EBS blisters. The IL-6, IL-8, and IL-10 pathways were upregulated in the epidermis from EBS. Consistent with this, predicted upstream regulators included TNF-α, IL-1β, IL-2, IL-6, phosphatidylinositol 3-kinase, and mTOR. The 1,276 gene EBS blister signature was integrated with molecular signatures from cell lines treated with 2,423 drugs using the Connectivity Map CLUE platform. The mTOR inhibitors and phosphatidylinositol 3-kinase inhibitors most opposed the EBS signature. To determine whether mTOR inhibitors could be used clinically in EBS, we conducted an independent pilot study of two patients with EBS treated with topical sirolimus for painful plantar keratoderma due to chronic blistering. Both individuals experienced marked clinical improvement and a notable reduction of keratoderma. In summary, a computational drug repositioning analysis successfully identified, to our knowledge, previously unreported targets in the treatment of EBS.

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.

Targeted Inhibition of the Epidermal Growth Factor Receptor and Mammalian Target of Rapamycin Signaling Pathways in Olmsted Syndrome

Importance

Olmsted syndrome is a rare and disabling genodermatosis for which no successful treatment is currently available.

Objective

To evaluate the clinical response to the mammalian target of rapamycin (mTOR) inhibitor sirolimus and/or the epidermal growth factor receptor (EGFR) inhibitor erlotinib among patients with Olmsted syndrome.

Design, Setting, and Participants

This case series focused on 4 children with treatment-refractory Olmsted syndrome. These children received treatments (initiated in 2017 and 2018) at the outpatient dermatology clinic at the Children's Hospital of Wisconsin in Milwaukee, Wisconsin; Children's National Hospital in Washington, DC; and Hospital Infantil Pequeno Príncipe, Curitiba in Paraná, Brazil.

Exposures

Immunohistochemical analyses for mTOR and EGFR activation were performed on skin biopsy specimens from 2 patients. Oral sirolimus was administered to these 2 patients at a dosage of 0.8 mg/m2 twice daily, titrated to a goal trough whole-blood concentration of 10 to 15 ng/mL. Erlotinib was administered to all 4 patients at a dosage of 2 mg/kg/d.

Main Outcomes and Measures

Clinical responses were assessed with visual analog scales for pruritus and pain and/or the Children's Dermatology Life Quality Index. Adverse effects were monitored throughout treatment.

Results

Four patients (mean [SD] age, 7 [6] years; 2 boys and 2 girls) were analyzed. Lesional skin immunostaining showed increased phosphorylated ribosomal protein S6 (RPS6) and phosphorylated EGFR staining in the epidermis, indicating enhanced mTOR and EGFR signaling activation. Patients 1 and 2 were initially treated with sirolimus, displaying substantial clinical improvement in erythema and periorificial hyperkeratosis afterward. When switched to erlotinib, these patients showed substantial palmoplantar keratoderma (PPK) improvement. Patients 3 and 4 were treated with erlotinib only and later showed rapid and near complete resolution of PPK and substantial improvement in Children's Dermatology Life Quality Index scores. All 4 patients had sustained improvements in pruritus and pain. No severe adverse effects were reported.

Conclusions and Relevance

This study's findings suggest that the EGFR-mTOR cascade may play a substantial role in the pathophysiological process of Olmsted syndrome and may serve as a major therapeutic target. Oral sirolimus and erlotinib may be a promising, life-altering treatment for pediatric patients with Olmsted syndrome.

Treatment of hereditary palmoplantar keratoderma: a review by analysis of the literature

BACKGROUND

No specific or curative therapy exists for hereditary palmoplantar keratoderma (hPPK), which can profoundly alter patient quality of life, leading sometimes to severe functional impairment and pain. The rarity and the aetiological diversity of this group of disorders can explain the difficulty in comparing the efficacy of available treatments.

OBJECTIVES

To review the different treatments tried in patients with hPPK since 2008, their efficacy and safety, with an evaluation of the various therapeutic modalities that can be used to treat hPPK.

METHODS

We undertook a comprehensive review of the literature data published since 2008.

RESULTS

Only a few case series and individual case reports were identified. Topical (emollients, keratolytics, retinoids, steroids) and systemic treatments (mostly different retinoids), often combined, are used to relieve symptoms. Oral retinoids appear to be the most efficient treatment, but not in all PPK forms, and with variable tolerance. New targeted treatments, according to the specific mechanisms of hPPK, appear promising for the future.

CONCLUSIONS

More studies using robust methodology and involving larger cohorts of well-characterized patients (phenotype-genotype) are necessary and should be prioritized by structured networks, such as the European Network for Rare Skin Diseases (ERN-Skin), with the aim of better management of patients with rare skin diseases.

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.

Pachyonychia congenita responding favorably to a combination of surgical and medical therapies

Pachyonychia congenital (PC) is a rare genetic disorder of cornification and is classified into five types on the basis of keratin gene involved. There are no established treatment options available for PC. Sirolimus in both topical and oral form has been studied in management of PC. We report a young female with a novel genetic mutation in KRT6A gene who presented with painful palmoplantar hyperkeratosis and onychogryphosis, which was cosmetically disfiguring. She was prescribed oral sirolimus after all investigations. There was significant improvement in pain within a week. Pain relief was sustained at 1 year follow-up with topical treatment only. Serial nail avulsion surgeries were also done with showed significant cosmetic improvement in the nails. Medical therapies can be combined with surgery for a better cosmetic outcome and improvement in patient quality of life.

Keratin 6a mutations lead to impaired mitochondrial quality control

BACKGROUND

Epidermal differentiation is a multilevel process in which keratinocytes need to lose their organelles, including their mitochondria, by autophagy. Disturbed autophagy leads to thickening of the epidermis as seen in pachyonychia congenita (PC), a rare skin disease caused by mutations in keratins 6, 16 and 17.

OBJECTIVES

To ask if mitophagy, the selective degradation of mitochondria by autophagy, is disturbed in PC and, if so, at which stage.

METHODS

Immortalized keratinocytes derived from patients with PC were used in fluorescence-based and biochemical assays to dissect the different steps of mitophagy.

RESULTS

PC keratinocytes accumulated old mitochondria and displayed disturbed clearance of mitochondria after mitochondrial uncoupling. However, early mitophagy steps and autophagosome formation were not affected. We observed that autolysosomes accumulate in PC and are not sufficiently recycled.

CONCLUSIONS

We propose an influence of keratins on autolysosomal degradation and recycling. What's already known about this topic? Terminal epidermal differentiation is a multistep process that includes the elimination of cellular components by autophagy. Autophagy-impaired keratinocytes have been shown to result in thickening of epidermal layers. Hyperkeratosis also occurs in pachyonychia congenita (PC), a rare skin disease caused by mutations in keratins 6, 16 and 17. What does this study add? Keratins contribute to mitochondrial quality control as well as maintenance of mitochondria-endoplasmic reticulum contact sites. Keratins influence autolysosomal maturation or reformation. What is the translational message? Overaged mitochondria and autolysosomes accumulate in PC. Mutations in keratin 6a lead to severely impaired mitophagy, which might contribute to PC pathogenesis.

Peripheral neuropathic changes in pachyonychia congenita

We compared patterns of intraepidermal nerve fibers and mechanoreceptors from affected and unaffected plantar skin from patients with pachyonychia congenita (PC) and control subjects. Plantar biopsies from 10 genetically confirmed patients with PC (with a mutation in KRT6A) were performed at the ball of the foot (affected skin) and the arch (unaffected) and were compared to biopsies from corresponding locations in 10 control subjects. Tissue was processed to visualize intraepidermal nerve fibers (IENF) (PGP9.5), subsets of IENF (CGRP, substance P, tyrosine hydroxylase), myelinated nerve fiber (neurofilament H, NFH), blood vessels (CD31), Meissner corpuscles, and Merkel cells (MCs). Structures were quantified using stereology or validated quantification methods. We observed that PC-affected plantar skin had significantly lower sweat gland innervation (sweat gland nerve fiber density) and reduced numbers of Meissner corpuscles compared to PC-unaffected or anatomically matched control skin. In contrast, Merkel cell densities and blood vessel counts were higher in PC-affected skin compared to either control or PC-unaffected skin. There were no differences in myelinated nerve fiber densities, SP, or CGRP between the groups. Pressure pain thresholds in PC-affected skin were lower compared to PC-unaffected and anatomically matched control skin. Additionally, MC densities in callused plantar skin from healthy runners with callus and one subject with a nonpainful palmoplantar keratoderma (AQP5 mutation) were similar to PC-unaffected and control skin consistent with callus alone not being sufficient to increase MC number. These findings suggest that alterations in PC extend beyond keratinocytes and may provide strategies to study neuropathic pain in PC.

Management of Plantar KeratodermasLessons from Pachyonychia Congenita

Plantar keratodermas can arise due to a variety of genetically inherited mutations. The need to distinguish between different plantar keratoderma disorders is becoming increasingly apparent because there is evidence that they do not respond identically to treatment. Diagnosis can be aided by observation of other clinical manifestations, such as palmar keratoderma, more widespread hyperkeratosis of the epidermis, hair and nail dystrophies, or erythroderma. However, there are frequent cases of plantar keratoderma that occur in isolation. This review focuses on the rare autosomal dominant keratin disorder pachyonychia congenita, which presents with particularly painful plantar keratoderma for which there is no specific treatment. Typically, patients regularly trim/pare/file/grind their calluses and file/grind/clip their nails. Topical agents, including keratolytics (eg, salicylic acid, urea) and moisturizers, can provide limited benefit by softening the skin. For some patients, retinoids help to thin calluses but may lead to increased pain. This finding has stimulated a drive for alternative treatment options, from gene therapy to alternative nongenetic methods that focus on novel findings regarding the pathogenesis of pachyonychia congenita and the function of the underlying genes.

Inflammation dependent mTORC1 signaling interferes with the switch from keratinocyte proliferation to differentiation

Psoriasis is a frequent and often severe inflammatory skin disease, characterized by altered epidermal homeostasis. Since we found previously that Akt/mTOR signaling is hyperactivated in psoriatic skin, we aimed at elucidating the role of aberrant mTORC1 signaling in this disease. We found that under healthy conditions mTOR signaling was shut off when keratinocytes switch from proliferation to terminal differentiation. Inflammatory cytokines (IL-1β, IL-17A, TNF-α) induced aberrant mTOR activity which led to enhanced proliferation and reduced expression of differentiation markers. Conversely, regular differentiation could be restored if mTORC1 signaling was blocked. In mice, activation of mTOR through the agonist MHY1485 also led to aberrant epidermal organization and involucrin distribution. In summary, these results not only identify mTORC1 as an important signal integrator pivotal for the cells fate to either proliferate or differentiate, but emphasize the role of inflammation-dependent mTOR activation as a psoriatic pathomechanism.

Successful Treatment of a Complex Vascular Malformation With Sirolimus and Surgical Resection

Management of complex vascular malformation represents a challenge as it may include a wide variety of options such as embolization, laser therapy, sclerotherapy, and surgical resection but may lead to significant morbidity and is associated with high recurrence rates. In extreme and/or recurrent cases, successful use of sirolimus has been described. We report a case of large unresectable complex venous malformation treated with oral sirolimus for 24 months. Therapy was well tolerated. Patient had substantial improvement in symptoms and shrinkage of the lesion. The Medical Therapy made excision of the malformation possible and patient had a successful surgical procedure. This report provides further evidence that sirolimus should be considered as part of the armamentarium in the management of these rare conditions.

Elucidation of the mTOR Pathway and Therapeutic Applications in Dermatology

The member of the phosphatidylinositol 3-kinase family, mammalian target of rapamycin, is involved in modulating inflammatory response and regulating cellular processes associated with growth, differentiation, and angiogenesis. Recent years have seen major advances in our understanding of the mammalian target of rapamycin signaling pathway and the implication of this pathway in multiple genetic and inflammatory diseases and tumors. The development of the mammalian target of rapamycin inhibitors has given rise to new treatment approaches that have led to substantially improved outcomes in many diseases. In this article, we review the role of the mammalian target of rapamycin signaling pathway in the different skin diseases with which it has been associated, examine the therapeutic applications of drugs targeting this pathway, and provide an overview of current trends and future directions in research.

Efficacy of botulinum toxin in pachyonychia congenita type 1: report of two new cases

Pachyonychia congenita (PC) is a rare genodermatosis caused by a mutation in keratin genes, which can lead to hypertrophic nail dystrophy and focal palmoplantar keratoderma (predominantly plantar), amongst other manifestations. Painful blisters and callosities, sometimes exacerbated by hyperhidrosis, are major issues that can have a significant impact on patient quality of life. Many alternative treatments for this condition have been applied with variable and partial clinical response, but a definitive cure for this disease has yet to be discovered. After obtaining informed consent, two patients with genetically confirmed PC type 1 were treated with plantar injections of botulinum toxin type A. Both patients showed a marked improvement in pain and blistering with an average response time of one week, a six-month mean duration of effectiveness, and a lack of any side effects or tachyphylaxis.

Advances in the therapeutic use of mammalian target of rapamycin (mTOR) inhibitors in dermatology

Significant developments in the use of mammalian target of rapamycin (mTOR) inhibitors (mTORIs) as immunosuppressant and antiproliferative agents have been made. Recent advances in the understanding of the mTOR signaling pathway and its downstream effects on tumorigenesis and vascular proliferation have broadened the clinical applications of mTORIs in many challenging disorders such as tuberous sclerosis complex, pachyonychia congenita, complex vascular anomalies, and inflammatory dermatoses. Systemic mTORI therapy has shown benefits in these areas, but is associated with significant side effects that sometimes necessitate drug holidays. To mitigate the side effects of systemic mTORIs for dermatologic applications, preliminary work to assess the potential of percutaneous therapy has been performed, and the evidence suggests that percutaneous delivery of mTORIs may allow for effective long-term therapy while avoiding systemic toxicities. Additional large placebo-controlled, double-blinded, randomized studies are needed to assess the efficacy, safety, duration, and tolerability of topical treatments. The objective of this review is to provide updated information on the novel use of mTORIs in the management of many cutaneous disorders.

Gene expression profiling in pachyonychia congenita skin

BACKGROUND

Pachyonychia congenita (PC) is a skin disorder resulting from mutations in keratin (K) proteins including K6a, K6b, K16, and K17. One of the major symptoms is painful plantar keratoderma. The pathogenic sequelae resulting from the keratin mutations remain unclear.

OBJECTIVE

To better understand PC pathogenesis.

METHODS

RNA profiling was performed on biopsies taken from PC-involved and uninvolved plantar skin of seven genotyped PC patients (two K6a, one K6b, three K16, and one K17) as well as from control volunteers. Protein profiling was generated from tape-stripping samples.

RESULTS

A comparison of PC-involved skin biopsies to adjacent uninvolved plantar skin identified 112 differentially-expressed mRNAs common to patient groups harboring K6 (i.e., both K6a and K6b) and K16 mutations. Among these mRNAs, 25 encode structural proteins including keratins, small proline-rich and late cornified envelope proteins, 20 are related to metabolism and 16 encode proteases, peptidases, and their inhibitors including kallikrein-related peptidases (KLKs), and serine protease inhibitors (SERPINs). mRNAs were also identified to be differentially expressed only in K6 (81) or K16 (141) patient samples. Furthermore, 13 mRNAs were identified that may be involved in pain including nociception and neuropathy. Protein profiling, comparing three K6a plantar tape-stripping samples to non-PC controls, showed changes in the PC corneocytes similar, but not identical, to the mRNA analysis.

CONCLUSION

Many differentially-expressed genes identified in PC-involved skin encode components critical for skin barrier homeostasis including keratinocyte proliferation, differentiation, cornification, and desquamation. The profiling data provide a foundation for unraveling the pathogenesis of PC and identifying targets for developing effective PC therapeutics.

Pachyonychia congenita cornered: report on the 11th Annual International Pachyonychia Congenita Consortium Meeting

This is a report of the research presented at the 11th Annual Meeting of the International Pachyonychia Congenita Consortium, held on 6 May 2014 in Albuquerque, NM, U.S.A. This year's meeting was divided into five corners concerning pachyonychia congenita (PC) research: (i) 'PC Pathogenesis Cornered', an overview of recent keratin research, for PC and other skin disorders; (ii) 'From All Corners of …', an outline of other genetic disorders that we can learn from; (iii) 'Fighting For Our Corner', an outline of National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases programmes and U.S. funding opportunities applicable to rare skin disorders; (iv) 'The PC Corner', focusing on recent clinical studies related to PC; and (v) 'Clinical Corners: Turning the Corner?', an update on ongoing PC clinical trials.

Report of the 10th Annual International Pachyonychia Congenita Consortium Meeting

The International Pachyonychia Congenita Consortium (IPCC) was founded in 2004 in Park City, Utah, USA. Its goal is to find a cure for pachyonychia congenita, a rare keratinizing disorder. From February 14th–17th, 2013, the group convened in Park City for their tenth annual meeting. The 2013 meeting focused on how to best move forward with clinical trials and on learning from work in other scientific areas, with an emphasis on understanding mechanisms of pain and hyperkeratosis. Considerable time was spent on discussing the best way to move forward with development of new treatments and how to obtain or develop tools that can measure treatment outcomes in PC.

Management of ichthyosis and related conditions gene-based diagnosis and emerging gene-based therapy

Knowledge of the molecular basis of many inherited diseases has grown exponentially during the past decade. Inherited skin diseases, including the ichthyoses and related conditions, benefited from that explosion of information, much of which has relevance for the clinical setting. In this section, the authors review the genes now known to be involved in ichthyosis, the methods for detecting mutations in those genes in the clinical diagnostic laboratory, options for using that information for diagnosis and pregnancy/family planning decisions, and current and future therapies based on the knowledge of the molecular basis of the ichthyosis.

Best treatment practices for pachyonychia congenita

BACKGROUND

Numerous therapeutic modalities have been proposed to treat the manifestations of pachyonychia congenita (PC). While research hopes lie with molecular therapies, patients are in need of answers regarding the efficacy of conventional treatments.

AIM OF THE STUDY

To determine patients' experience and preferences regarding conventional treatments for PC.

METHODS

The study population included 120 PC patients from 20 countries. The study was based on a patient survey developed by physicians and researchers from the International Pachyonychia Congenita Consortium and conducted via the internet. Using an effectiveness scale of 1 to 5, the patients were asked to grade treatments for different manifestations, including keratoderma, cysts, follicular hyperkeratosis, fingernail and toenail involvement.

RESULTS

Patients reported surgical treatments being most effective for cysts and mechanical treatments the most effective conventional therapeutic approach for all other investigated manifestations. The other conventional medical treatments were found to be non-effective to only slightly effective. Among patients with keratoderma, older people were more likely to report beneficial effect from mechanical treatments (P = 0.04), topical retinoids (P = 0.04) and topical steroids (P = 0.02). Likewise, females were more inclined to report filing and grinding beneficial than males (P = 0.02). Finally, carriers of KRT16 and KRT6a were more likely to benefit from keratolytics than carriers of mutations in KRT17 (P = 0.04).

CONCLUSIONS

None of the currently available therapeutic options for PC are ideal, although they provide some relief, with mechanical/surgical options being preferred over medical therapies. These results emphasize the need for more efficient and targeted therapies.

Progress towards genetic and pharmacological therapies for keratin genodermatoses: current perspective and future promise

Hereditary keratin disorders of the skin and its appendages comprise a large group of clinically heterogeneous disfiguring blistering and ichthyotic diseases, primarily characterized by the loss of tissue integrity, blistering and hyperkeratosis in severely affected tissues. Pathogenic mutations in keratins cause these afflictions. Typically, these mutations in concert with characteristic features have formed the basis for improved disease diagnosis, prognosis and most recently therapy development. Examples include epidermolysis bullosa simplex, keratinopathic ichthyosis, pachyonychia congenita and several other tissue-specific hereditary keratinopathies. Understanding the molecular and genetic events underlying skin dysfunction has initiated alternative treatment approaches that may provide novel therapeutic opportunities for affected patients. Animal and in vitro disease modelling studies have shed more light on molecular pathogenesis, further defining the role of keratins in disease processes and promoting the translational development of new gene and pharmacological therapeutic strategies. Given that the molecular basis for these monogenic disorders is well established, gene therapy and drug discovery targeting pharmacological compounds with the ability to reinforce the compromised cytoskeleton may lead to promising new therapeutic strategies for treating hereditary keratinopathies. In this review, we will summarize and discuss recent advances in the preclinical and clinical modelling and development of gene, natural product, pharmacological and protein-based therapies for these disorders, highlighting the feasibility of new approaches for translational clinical therapy.

Keratin gene mutations in disorders of human skin and its appendages

Keratins, the major structural protein of all epithelia are a diverse group of cytoskeletal scaffolding proteins that form intermediate filament networks, providing structural support to keratinocytes that maintain the integrity of the skin. Expression of keratin genes is usually regulated by differentiation of the epidermal cells within the stratifying squamous epithelium. Amongst the 54 known functional keratin genes in humans, about 22 different genes including, the cornea, hair and hair follicle-specific keratins have been implicated in a wide range of hereditary diseases. The exact phenotype of each disease usually reflects the spatial expression level and the types of mutated keratin genes, the location of the mutations and their consequences at sub-cellular levels as well as other epigenetic and/or environmental factors. The identification of specific pathogenic mutations in keratin disorders formed the basis of our understanding that led to re-classification, improved diagnosis with prognostic implications, prenatal testing and genetic counseling in severe keratin genodermatoses. Molecular defects in cutaneous keratin genes encoding for keratin intermediate filaments (KIFs) causes keratinocytes and tissue-specific fragility, accounting for a large number of genetic disorders in human skin and its appendages. These diseases are characterized by keratinocytes fragility (cytolysis), intra-epidermal blistering, hyperkeratosis, and keratin filament aggregation in severely affected tissues. Examples include epidermolysis bullosa simplex (EBS; K5, K14), keratinopathic ichthyosis (KPI; K1, K2, K10) i.e. epidermolytic ichthyosis (EI; K1, K10) and ichthyosis bullosa of Siemens (IBS; K2), pachyonychia congenita (PC; K6a, K6b, K16, K17), epidermolytic palmo-plantar keratoderma (EPPK; K9, (K1)), monilethrix (K81, K83, K86), ectodermal dysplasia (ED; K85) and steatocystoma multiplex. These keratins also have been identified to have roles in apoptosis, cell proliferation, wound healing, tissue polarity and remodeling. This review summarizes and discusses the clinical, ultrastructural, molecular genetics and biochemical characteristics of a broad spectrum of keratin-related genodermatoses, with special clinical emphasis on EBS, EI and PC. We also highlight current and emerging model tools for prognostic future therapies. Hopefully, disease modeling and in-depth understanding of the molecular pathogenesis of the diseases may lead to the development of novel therapies for several hereditary cutaneous diseases.

Toll-like receptors: role in dermatological disease

Toll-like receptors (TLRs) are a class of conserved receptors that recognize pathogen-associated molecular patterns (PAMPs) present in microbes. In humans, at least ten TLRs have been identified, and their recognition targets range from bacterial endotoxins to lipopeptides, DNA, dsRNA, ssRNA, fungal products, and several host factors. Of dermatological interest, these receptors are expressed on several skin cells including keratinocytes, melanocytes, and Langerhans cells. TLRs are essential in identifying microbial products and are known to link the innate and adaptive immune systems. Over the years, there have been significant advances in our understanding of TLRs in skin inflammation, cutaneous malignancies, and defence mechanisms. In this paper, we will describe the association between TLRs and various skin pathologies and discuss proposed TLR therapeutics.