Keratin disorders: from gene to therapy

Proteome-scale prediction of molecular mechanisms underlying dominant genetic diseases

Many dominant genetic disorders result from protein-altering mutations, acting primarily through dominant-negative (DN), gain-of-function (GOF), and loss-of-function (LOF) mechanisms. Deciphering the mechanisms by which dominant diseases exert their effects is often experimentally challenging and resource intensive, but is essential for developing appropriate therapeutic approaches. Diseases that arise via a LOF mechanism are more amenable to be treated by conventional gene therapy, whereas DN and GOF mechanisms may require gene editing or targeting by small molecules. Moreover, pathogenic missense mutations that act via DN and GOF mechanisms are more difficult to identify than those that act via LOF using nearly all currently available variant effect predictors. Here, we introduce a tripartite statistical model made up of support vector machine binary classifiers trained to predict whether human protein coding genes are likely to be associated with DN, GOF, or LOF molecular disease mechanisms. We test the utility of the predictions by examining biologically and clinically meaningful properties known to be associated with the mechanisms. Our results strongly support that the models are able to generalise on unseen data and offer insight into the functional attributes of proteins associated with different mechanisms. We hope that our predictions will serve as a springboard for researchers studying novel variants and those of uncertain clinical significance, guiding variant interpretation strategies and experimental characterisation. Predictions for the human UniProt reference proteome are available at https://osf.io/z4dcp/.

A novel variant in the keratin 12 gene in a four-generation Chinese family with high myopia

BACKGROUND

High myopia is a major cause of visual impairment, and genetic factors play crucial roles in the pathogenesis. We performed this study to identify candidate genes for the development of high myopia in a four-generation Chinese family with myopia.

METHODS

All family members with myopia and 100 healthy participants were included in this study. Data were obtained on demographics, disease history, and ocular examination results. We performed whole exome sequencing of the genomic DNA and Sanger sequencing to verify the variants. Functional analyses of the variant were performed using software programmes.

RESULTS

Nine of thirteen family members were found to have high myopia, amongst which two members were also diagnosed keratoconus. A missense variant in the keratin 12 gene (KRT12, p.Val410Gly) was detected in all high myopia cases but not in other family members without high myopia or the controls. The variant was predicted to be benign by online software programmes. However, modelling of the three-dimensional structure of the protein clearly revealed conformational changes caused by the mutation.

CONCLUSIONS

A missense mutation in the KRT12 gene was identified in this Chinese family, which may be associated with the pathogenesis of high myopia.

Loss of mutant p53 in HaCaT keratinocytes promotes cadmium-induced keratin 17 expression and cell death

BACKGROUND

Cadmium exposure induces dermatotoxicity and epidermal barrier disruption and leads to the development of various pathologies. HaCaT cells are immortalized human keratinocytes that are widely used as alternatives to primary human keratinocytes, particularly for evaluating cadmium toxicity. HaCaT cells bear two gain-of-function (GOF) mutations in the TP53 gene, which strongly affect p53 function. Mutant forms of p53 are known to correlate with increased resistance to various stimuli, including exposure to cytotoxic substances. In addition, keratin 17 (KRT17) was recently shown to be highly expressed in HaCaT cells in response to genotoxic stress. Moreover, p53 is a direct transcriptional repressor of KRT17. However, the impact of TP53 mutations in HaCaT cells on the regulation of cell death and keratin 17 expression is unclear. In this study, we aimed to evaluate the impact of p53 on the response to Cd-induced cytotoxicity.

METHODS AND RESULTS

Employing the MTT assay and Annexin V/propidium iodide staining, we demonstrated that knockout of TP53 leads to a decrease in the sensitivity of HaCaT cells to the cytotoxic effects of cadmium. Specifically, HaCaT cells with TP53 knockout (TP53 KO HaCaT) exhibited cell death at a cadmium concentration of 10 μM or higher, whereas wild-type cells displayed cell death at a concentration of 30 μM. Furthermore, apoptotic cells were consistently detected in TP53 KO HaCaT cells upon exposure to low concentrations of cadmium (10 and 20 μM) but not in wild-type cells. Our findings also indicate that cadmium cytotoxicity is mediated by reactive oxygen species (ROS), which were significantly increased only in TP53 knockout cells treated with 30 μM cadmium. An examination of proteomic data revealed that TP53 knockout in HaCaT cells resulted in the upregulation of proteins involved in the regulation of apoptosis, redox systems, and DNA repair. Moreover, RT‒qPCR and immunoblotting showed that cadmium toxicity leads to dose-dependent induction of keratin 17 in p53-deficient cells but not in wild-type cells.

CONCLUSIONS

The connection between mutant p53 in HaCaT keratinocytes and increased resistance to cadmium toxicity was demonstrated for the first time. Proteomic profiling revealed that TP53 knockout in HaCaT cells led to the activation of apoptosis regulatory circuits, redox systems, and DNA repair. In addition, our data support the involvement of keratin 17 in the regulation of DNA repair and cell death. Apparently, the induction of keratin 17 is p53-independent but may be inhibited by mutant p53.

Sinapine thiocyanate exhibited anti-colorectal cancer effects by inhibiting KRT6A/S100A2 axis

Sinapine thiocyanate (ST), an alkaloid existed extensively in seeds of cruciferous plants, exhibits a number of pharmacological effects, including anti-inflammatory and anti-malignancy properties. However, it is still unknown what effects and molecular mechanisms ST has on colorectal cancer (CRC). In the current study, it was indicated that ST inhibited proliferation, colony formation, and apoptosis in vitro, as well as arrested the G1 phase of CRC cells. There was a significant repressive effects of ST on invasion and migration of CRC cells in vitro. RNA-sequencing indicated that 750 differentially expressed genes existed in CRC cells after ST treatment, and enrichment analysis demonstrated that ST obviously decreased the activation of keratinization pathways. Among DEGs enriched in keratinization, keratin 6A (KRT6A) was decreased the most significant, as well as its target gene S100 calcium-binding protein A2 (S100A2). Low expression of KRT6A and S100A2 signatures indicated a favorable prognosis in CRC patients. Moreover, we found overexpression of KRT6A relieved the inhibitory effects of ST in CRC cells. Furthermore, ST inhibited the CRC cell proliferation in vivo, and reduced KRT6A and KI67 expression in xenograft tumor. Taken together, we demonstrated that ST exhibited anti-CRC properties by inhibiting KRT6A/S100A2 axis. It is possible that ST can be used as a treatment for CRC.

Targeting the KRT16-vimentin axis for metastasis in lung cancer

Lung cancer is the most diagnosed malignant cancer and the leading cause of cancer-related deaths worldwide, with advanced stage and metastasis being a major issue. The mechanism leading to metastasis is not yet understood. Here, we found that KRT16 is upregulated in metastatic lung cancer tissues and correlated with poor overall survival. Knockdown of KRT16 inhibits metastasis of lung cancer both in vitro and in vivo. Mechanistically, KRT16 interacts with vimentin, and depletion of KRT16 leads to downregulation of vimentin. KRT16 acquired its oncogenic ability by stabilizing vimentin, and vimentin is required for KRT16-driven metastasis. FBXO21 mediates the polyubiquitination and degradation of KRT16, and vimentin inhibits KRT16 ubiquitination and degradation by impairing its interaction with FBXO21. Significantly, IL-15 inhibits metastasis of lung cancer in a mouse model through upregulation of FBXO21, and the level of IL-15 in circulating serum was significantly higher in nonmetastatic lung cancer patients than in metastatic patients. Our findings indicate that targeting the FBXO21/KRT16/vimentin axis may benefit lung cancer patients with metastasis.

The application and progression of CRISPR/Cas9 technology in ophthalmological diseases

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) system is an adaptive immune defence system that has gradually evolved in bacteria and archaea to combat invading viruses and exogenous DNA. Advances in technology have enabled researchers to enhance their understanding of the immune process in vivo and its potential for use in genome editing. Thus far, applications of CRISPR/Cas9 genome editing technology in ophthalmology have included gene therapy for corneal dystrophy, glaucoma, congenital cataract, Leber's congenital amaurosis, retinitis pigmentosa, Usher syndrome, fundus neovascular disease, proliferative vitreoretinopathy, retinoblastoma and other eye diseases. Additionally, the combination of CRISPR/Cas9 genome editing technology with adeno-associated virus vector and inducible pluripotent stem cells provides further therapeutic avenues for the treatment of eye diseases. Nonetheless, many challenges remain in the development of clinically feasible retinal genome editing therapy. This review discusses the development, as well as mechanism of CRISPR/Cas9 and its applications and challenges in gene therapy for eye diseases.

KERATIN 17-related recessive atypical pachyonychia congenita with variable hair and tooth anomalies

We present the first pachyonychia congenita (PC) to involve all ectodermal derivatives and the first recessive KRT17-related PC in total seven members of two consanguineous Pakistani families. This atypical PC is characterized by an unusual combination of pachyonychia, plantar keratoderma, folliculitis, alopecia, sparse eyebrows, dental anomalies and variable acanthosis nigricans of neck, dry skin, palmoplantar hyperhidrosis, recurrent blisters on soles and/or arms, rough sparse hair on scalp and keratosis pilaris. By exome sequencing we detected homozygous KRT17 c.281G>A (p.(Arg94His)) in affected individuals, and linkage mapping indicated a single locus. Heterozygous variants in KRT17 cause PC2 (PC-K17) with main characteristics of pachyonychia, subungual keratosis, palmoplantar keratoderma, hyperhidrosis, oral leukokeratosis and epidermal cysts, or steatocystoma multiplex, both with dominant inheritance. The causative variant has been reported in heterozygous state in a family afflicted with severe steatocystoma multiplex and in a sporadic PC2 case, and thus we also define a third phenotype related to the variant. Both exome sequencing and linkage mapping demonstrated recessive inheritance whereas Sanger sequencing indicated heterozygosity for the causal variant, reiterating caution for simple targeted sequencing for genetic testing. Testing parents for variants found in sibs could uncover recessive inheritance also in other KRT genes.

Chemically Modified Biopolymers for the Formation of Biomedical Hydrogels

Biopolymers are natural polymers sourced from plants and animals, which include a variety of polysaccharides and polypeptides. The inclusion of biopolymers into biomedical hydrogels is of great interest because of their inherent biochemical and biophysical properties, such as cellular adhesion, degradation, and viscoelasticity. The objective of this Review is to provide a detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymer chemical modifications and cross-linking methods. First, the fundamentals of biopolymers and chemical conjugation methods to introduce cross-linking groups are described. Cross-linking methods to form biopolymer networks are then discussed in detail, including (i) covalent cross-linking (e.g., free radical chain polymerization, click cross-linking, cross-linking due to oxidation of phenolic groups), (ii) dynamic covalent cross-linking (e.g., Schiff base formation, disulfide formation, reversible Diels-Alder reactions), and (iii) physical cross-linking (e.g., guest-host interactions, hydrogen bonding, metal-ligand coordination, grafted biopolymers). Finally, recent advances in the use of chemically modified biopolymer hydrogels for the biofabrication of tissue scaffolds, therapeutic delivery, tissue adhesives and sealants, as well as the formation of interpenetrating network biopolymer hydrogels, are highlighted.

A review of the tortuous path of nonviral gene delivery and recent progress

Gene therapy encompasses the transfer of exogenous genetic materials into the patient's target cells to treat or prevent diseases. Nevertheless, the transfer of genetic material into desired cells is challenging and often requires specialized tools or delivery systems. For the past 40 years, scientists are mainly pursuing various viruses as gene delivery vectors, and the overall progress has been slow and far from the expectation. As an alternative, nonviral vectors have gained substantial attention due to their several advantages, including superior safety profile, enhanced payload capacity, and stealth abilities. Since nonviral vectors encounter multiple extra- and intra-cellular barriers limiting the transfer of genetic payload into the target cell nucleus, we have discussed these barriers in detail for this review. A direct approach, utilizing physical methods like electroporation, sonoporation, gene gun, eliminate the requirement for a specific carrier for gene delivery. In contrast, chemical methods of gene transfer exploit natural or synthetic compounds as carriers to increase cellular targeting and gene therapy effectiveness. We have also emphasized the recent advancements aimed at enhancing the current nonviral approaches. Therefore, in this review, we have focused on discussing the current evolving state of nonviral gene delivery systems and their future perspectives.

Mutant collagen COL11A1 enhances cancerous invasion

Collagens are the most abundant proteins in the body and comprise the basement membranes and stroma through which cancerous invasion occurs; however, a pro-neoplastic function for mutant collagens is undefined. Here we identify COL11A1 mutations in 66 of 100 cutaneous squamous cell carcinomas (cSCCs), the second most common U.S. cancer, concentrated in a triple helical region known to produce trans-dominant collagens. Analysis of COL11A1 and other collagen genes found that they are mutated across common epithelial malignancies. Knockout of mutant COL11A1 impairs cSCC tumorigenesis in vivo. Compared to otherwise genetically identical COL11A1 wild-type tissue, gene-edited mutant COL11A1 skin is characterized by induction of β1 integrin targets and accelerated neoplastic invasion. In mosaic tissue, mutant COL11A1 cells enhanced invasion by neighboring wild-type cells. These results suggest that specific collagens are commonly mutated in cancer and that mutant collagens may accelerate this process.

Development of a Corneal Bioluminescence Mouse for Real-Time In Vivo Evaluation of Gene Therapies

Purpose

The purpose of this study was to develop and characterize a novel bioluminescence transgenic mouse model that facilitates rapid evaluation of genetic medicine delivery methods for inherited and acquired corneal diseases.

Methods

Corneal expression of the firefly luciferase transgene (luc2) was achieved via insertion into the Krt12 locus, a type I intermediate filament keratin that is exclusively expressed in the cornea, to generate the Krt12luc2 mouse. The transgene includes a multiple target cassette with human pathogenic mutations in K3 and K12.

Results

The Krt12luc2 mouse exclusively expresses luc2 in the corneal epithelium under control of the keratin K12 promoter. The luc2 protein is enzymatically active, can be readily visualized, and exhibits a symmetrically consistent readout. Moreover, structural integrity of the corneal epithelium is preserved in mice that are heterozygous for the luc2 transgene (Krt12+/luc2).

Conclusions

This novel Krt12luc2 mouse model represents a potentially ideal in vivo system for evaluating the efficacies of cornea-targeting gene therapies and for establishing and/or validating new delivery modalities. Importantly, the multiple targeting cassette that is included in the Luc2 transgene will greatly reduce mouse numbers required for in vivo therapy evaluation.

Deimination, Intermediate Filaments and Associated Proteins

Deimination (or citrullination) is a post-translational modification catalyzed by a calcium-dependent enzyme family of five peptidylarginine deiminases (PADs). Deimination is involved in physiological processes (cell differentiation, embryogenesis, innate and adaptive immunity, etc.) and in autoimmune diseases (rheumatoid arthritis, multiple sclerosis and lupus), cancers and neurodegenerative diseases. Intermediate filaments (IF) and associated proteins (IFAP) are major substrates of PADs. Here, we focus on the effects of deimination on the polymerization and solubility properties of IF proteins and on the proteolysis and cross-linking of IFAP, to finally expose some features of interest and some limitations of citrullinomes.

Microbial enzymes catalyzing keratin degradation: Classification, structure, function

Keratin is an insoluble and protein-rich epidermal material found in e.g. feather, wool, hair. It is produced in substantial amounts as co-product from poultry processing plants and pig slaughterhouses. Keratin is packed by disulfide bonds and hydrogen bonds. Based on the secondary structure, keratin can be classified into α-keratin and β-keratin. Keratinases (EC 3.4.-.- peptide hydrolases) have major potential to degrade keratin for sustainable recycling of the protein and amino acids. Currently, the known keratinolytic enzymes belong to at least 14 different protease families: S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, M55 (MEROPS database). The various keratinolytic enzymes act via endo-attack (proteases in families S1, S8, S16, M4, M16, M36), exo-attack (proteases in families S9, S10, M14, M28, M38, M55) or by action only on oligopeptides (proteases in families M3, M32), respectively. Other enzymes, particularly disulfide reductases, also play a key role in keratin degradation as they catalyze the breakage of disulfide bonds for better keratinase catalysis. This review aims to contribute an overview of keratin biomass as an enzyme substrate and a systematic analysis of currently sequenced keratinolytic enzymes and their classification and reaction mechanisms. We also summarize and discuss keratinase assays, available keratinase structures and finally examine the available data on uses of keratinases in practical biorefinery protein upcycling applications.

Corneal dystrophies

Corneal dystrophies are broadly defined as inherited disorders that affect any layer of the cornea and are usually progressive, bilateral conditions that do not have systemic effects. The 2015 International Classification of Corneal Dystrophies classifies corneal dystrophies into four classes: epithelial and subepithelial dystrophies, epithelial-stromal TGFBI dystrophies, stromal dystrophies and endothelial dystrophies. Whereas some corneal dystrophies may result in few or mild symptoms and morbidity throughout a patient's lifetime, others may progress and eventually result in substantial visual and ocular disturbances that require medical or surgical intervention. Corneal transplantation, either with full-thickness or partial-thickness donor tissue, may be indicated for patients with advanced corneal dystrophies. Although corneal transplantation techniques have improved considerably over the past two decades, these surgeries are still associated with postoperative risks of disease recurrence, graft failure and other complications that may result in blindness. In addition, a global shortage of cadaveric corneal graft tissue critically limits accessibility to corneal transplantation in some parts of the world. Ongoing advances in gene therapy, regenerative therapy and cell augmentation therapy may eventually result in the development of alternative, novel treatments for corneal dystrophies, which may substantially improve the quality of life of patients with these disorders.

Effective In Vivo Topical Delivery of siRNA and Gene Silencing in Intact Corneal Epithelium Using a Modified Cell-Penetrating Peptide

Autosomal dominantly inherited genetic disorders such as corneal dystrophies are amenable to allele-specific gene silencing with small interfering RNA (siRNA). siRNA delivered to the cornea by injection, although effective, is not suitable for a frequent long-term treatment regimen, whereas topical delivery of siRNA to the cornea is hampered by the eye surface's protective mechanisms. Herein we describe an attractive and innovative alternative for topical application using cell-penetrating peptide derivatives capable of complexing siRNA non-covalently and delivering them into the cornea. Through a rational design approach, we modified derivatives of a cell-penetrating peptide, peptide for ocular delivery (POD), already proved to diffuse into the corneal layers. These POD derivatives were able to form siRNA-peptide complexes (polyplexes) of size and ζ-potential similar to those reported able to undergo cellular internalization. Successful cytoplasmic release and gene silencing in vitro was obtained when an endosomal disruptor, chloroquine, was added. A palmitoylated-POD, displaying the best delivery properties, was covalently functionalized with trifluoromethylquinoline, an analog of chloroquine. This modified POD, named trifluoromethylquinoline-palmitoyl-POD (QN-Palm-POD), when complexed with siRNA and topically applied to the eye in vivo, resulted in up to 30% knockdown of luciferase reporter gene expression in the corneal epithelium. The methods developed within represent a valid standardized approach that is ideal for screening of a range of delivery formulations.

Identification of Keratin 23 as a Hepatitis C Virus-Induced Host Factor in the Human Liver

Keratin proteins form intermediate filaments, which provide structural support for many tissues. Multiple keratin family members are reported to be associated with the progression of liver disease of multiple etiologies. For example, keratin 23 (KRT23) was reported as a stress-inducible protein, whose expression levels correlate with the severity of liver disease. Hepatitis C virus (HCV) is a human pathogen that causes chronic liver diseases including fibrosis, cirrhosis, and hepatocellular carcinoma. However, a link between KRT23 and hepatitis C virus (HCV) infection has not been reported previously. In this study, we investigated KRT23 mRNA levels in datasets from liver biopsies of chronic hepatitis C (CHC) patients and in primary human hepatocytes experimentally infected with HCV, in addition to hepatoma cells. Interestingly, in each of these specimens, we observed an HCV-dependent increase of mRNA levels. Importantly, the KRT23 protein levels in patient plasma decreased upon viral clearance. Ectopic expression of KRT23 enhanced HCV infection; however, CRIPSPR/Cas9-mediated knockout did not show altered replication efficiency. Taken together, our study identifies KRT23 as a novel, virus-induced host-factor for hepatitis C virus.

CRISPR/Cas9-Mediated Treatment Ameliorates the Phenotype of the Epidermolytic Palmoplantar Keratoderma-like Mouse

CRISPR/Cas9 has been confirmed as a distinctly efficient, simple-to-configure, highly specific genome-editing tool that has been used to treat monogenetic disorders. Epidermolytic palmoplantar keratoderma (EPPK) is a common autosomal dominant keratin disease resulting from dominant-negative mutation of the KRT9 gene, and it has no effective therapy. We performed CRISPR/Cas9-mediated treatment on a knockin (KI) transgenic mouse model that carried a small indel heterozygous mutation of Krt9, c.434delAinsGGCT (p.Tyr144delinsTrpLeu), which caused a humanized EPPK-like phenotype. The mutation within exon 1 of Krt9 generated a novel protospacer adjacent motif site, TGG, for Cas9 recognition and cutting. By delivering lentivirus vectors (LVs) encoding single-guide RNAs (sgRNAs) and Cas9 that targeted Krt9 sequence into HeLa cells engineered to constitutively express wild-type and mutant keratin 9 (K9), we found the sgRNA was highly effective in reducing expression of the mutant K9 protein in vitro. We injected the LV into the fore-paws of adult KI-Krt9 mice three times every 8 days and found that the expression of K9 decreased ∼14.6%. The phenotypic mitigation was revealed by restoration of the abnormal differentiation and aberrant proliferation of the epidermis. Our data are the first to show that CRISPR/Cas9 is a potentially powerful therapeutic option for EPPK and other PPK subtypes.

[The epidermal barrier]

The skin acts as an interface between the body and its surrounding environment. The epidermis, the surface layer of the skin, is chiefly responsible for this interactive protective function. The epidermal barrier may be subdivided into three defensive systems: the photoprotective barrier, the immune barrier, and the physical and chemical barrier of the stratum corneum or horny layer. To protect against harmful ultraviolet radiation, the epidermis has absorption factors such as melanin, produced by melanocytes, and urocanic acid, which is a degradation product of filaggrin. The epidermal immune defence system comprises an innate component, which is rapid but non-specific, together with adaptive response, which is systemic and antigen-specific, initiated by Langerhans cells. The stratum corneum, derived from terminal differentiation of epidermal keratinocytes, plays a key role as a physical and chemical permeability barrier. This horny layer is made up of corneocytes, covered with horny envelopes and linked to one another by corneodesmosomes and by extracellular matrix sheets. The epidermal barrier, which is constantly being renewed, is characterised by its extremely great capacity of adaptation to changing conditions in the environment.

Comparative proteomic analysis of amnion membrane transplantation and cross-linking treatments in an experimental alkali injury model

PURPOSE

In this study, by using a two-dimensional (2D) electrophoresis-based experimental approach, we aimed at understanding the nature of alkali injuries and the underlying mechanisms. A secondary aim was to compare the effects of cross-linking (CXL) and amnion membrane transplantation (AMT) on corneal protein compositions at the end of the early repair phase after injured with alkali.

METHOD

The right corneas of 24 rabbits were injured with a 1 N solution of NaOH. Groups were formed based on the adjuvant therapies as (1) healthy group, (2) control group, (3) CXL group, (4) AMT group. In addition to the therapies, a conventional medical treatment was applied to all groups. Left eyes were used as within-subject healthy corneas (1). The corneas were excised at day 21, and a comparative proteomic analysis was performed using 2D gel electrophoresis coupled with MALDI-TOF/TOF.

RESULT

2D gel electrophoresis revealed the presence seven protein spots whose abundance changed among the groups. Those proteins were SH3 domain-binding protein, plant homeodomain finger protein 23, S100 calcium binding protein A-11(S100 A11), keratin type 2 cytoskeletal 1 and 2, transketolase and glyceraldehyde 3-phosphate dehydrogenase. Ingenuity pathway analysis predicted that the observed changes may be linked to a central metabolic pathway, transforming growth factor beta 1. Canonical pathway analysis focused our attention to two different pathways, namely nicotinamide adenine dinucleotide repair pathway and non-oxidative branch of pentose phosphate pathway.

CONCLUSION

Our results shed some light onto the molecular mechanisms affected by alkali injury and adjuvant treatments. Further research is needed to propose medically significant target molecules that may be used for novel drug developments for alkali injury.

Astilbin decreases proliferation and improves differentiation in HaCaT keratinocytes

Psoriasis is a common chronic dermatosis characterized by keratinocyte hyperproliferation accompanied by inflammatory reactions. Pathological changes upset the balance between keratinocyte proliferation, differentiation, and death in psoriatic lesions, suggesting that molecules with topical anti-inflammatory, anti-proliferation and anti-angiogenesis abilities may be useful for its treatment. The flavonoid astilbin is the major active component extracted from the rhizome of Smilax glabra, which has been widely used in China to treat inflammatory and autoimmune diseases. Here, we investigate the potential of astilbin as a treatment for psoriasis. We reveal that astilbin inhibits the growth of HaCaT keratinocytes. Detailed study shows that astilbin leads to S phase arrest of the cell cycle by induction of p53 and p21 and activated-AMPK. Additionally, astilbin induced keratinocyte differentiation correlated with suppression of keratin 5 (KRT5) and KRT14 proteins (the markers of epidermal basal layer) and induction KRT1 and KRT10 proteins (occurring in the upper layers). Moreover, astilbin regulates the expression of VEGF in human HaCaT keratinocytes. These results suggest that astilbin may be a promising agent for psoriasis treatment.

Laryngeal manifestations of pachyonychia congenita: a clinical case and discussion on management for the otolaryngologist

BACKGROUND

Pachyonychia congenita is a rare keratinising disorder, which typically presents during the first three years of life and usually affects the nails and palmoplantar surfaces. It can involve the larynx and potentially result in life-threatening airway obstruction.

METHODS

A case report is presented and the findings of a literature review are reported. The review involved a PubMed search using the keywords 'pachyonychia congenita' together with 'larynx', 'laryngeal involvement', 'laryngeal obstruction', 'airway obstruction', 'hoarseness' and/or 'stridor'.

RESULTS

A five-year-old boy, with confirmed pachyonychia congenita, presented with complications of laryngeal involvement over a four-year period. He required three intubations and a tracheostomy for acute airway obstruction. Treatment with potassium titanyl phosphate laser laryngoscopy stabilised the progression of laryngeal disease.

CONCLUSION

Patients with pachyonychia congenita and laryngeal involvement can have a varied presentation, ranging from hoarseness to acute airway obstruction. Management can be a challenge, requiring early evaluation, regular surveillance and aggressive treatment. This paper reports our experience in managing and treating the laryngeal complications of a child with pachyonychia congenita.

Luteolin-7-glucoside inhibits IL-22/STAT3 pathway, reducing proliferation, acanthosis, and inflammation in keratinocytes and in mouse psoriatic model

The epidermis is a dynamic tissue in which keratinocytes proliferate in the basal layer and undergo a tightly controlled differentiation while moving into the suprabasal layers. The balance between keratinocyte proliferation, differentiation, and death is essential, and its perturbation can result in pathological changes. Some common skin diseases, such as psoriasis, are characterized by hyperproliferation accompanied by inflammatory reactions, suggesting that molecules with topical anti-inflammatory and ROS scavenging abilities may be useful for their treatment. Here we investigate the potential of the flavone Luteolin-7-glucoside (LUT-7G) as a treatment for psoriasis. We show that LUT-7G leads to a modification of the cell cycle and the induction of keratinocyte differentiation, with modification of energy, fatty acid, and redox metabolism. LUT-7G treatment also neutralizes the proliferative stimulus induced by the proinflammatory cytokines IL-22 and IL-6 in HEKn. Moreover, in the Imiquimod (IMQ) mouse model of psoriasis, topical administration of LUT-7G leads to a marked reduction of acanthosis and re-expression of epidermal differentiation markers. Dissection of the IL-22 signalling pathway, activated by IMQ treatment, demonstrates that LUT-7G impairs the nuclear translocation of phosphorylated (activated) STAT3, blocking the IL-22 signalling cascade. Thus LUT-7G appears to be a promising compound for the treatment of hyperproliferative and inflammatory skin diseases, such as psoriasis.

Gene Therapy and Gene Editing for the Corneal Dystrophies

Despite ever-increasing understanding of the genetic underpinnings of many corneal dystrophies, gene therapy designed to ameliorate disease has not yet been reported in any human patient. In this review, we explore the likely reasons for this apparent failure of translation. We identify the requirements for success: the genetic defect involved must have been identified and mapped, vision in the affected patient must be significantly impaired or likely to be impaired, no better or equivalently effective treatment must be available, the treatment must be capable of modulating corneal pathology, and delivery of the construct to the appropriate cell must be practicable. We consider which of the corneal dystrophies might be amenable to treatment by genetic manipulations, summarize existing therapeutic options for treatment, and explore gene editing using clustered regularly interspaced short palindromic repeat/Cas and other similar transformative technologies as the way of the future. We then summarize recent laboratory-based advances in gene delivery and the development of in vitro and in vivo models of the corneal dystrophies. Finally, we review recent experimental work that has increased our knowledge of the pathobiology of these conditions.

Microneedles As a Delivery System for Gene Therapy

Gene delivery systems can be divided to two major types: vector-based (either viral vector or non-viral vector) and physical delivery technologies. Many physical carriers, such as electroporation, gene gun, ultrasound start to be proved to have the potential to enable gene therapy. A relatively new physical delivery technology for gene delivery consists of microneedles (MNs), which has been studied in many fields and for many molecule types and indications. Microneedles can penetrate the stratum corneum, which is the main barrier for drug delivery through the skin with ease of administration and without significant pain. Many different kinds of MNs, such as metal MNs, coated MNs, dissolving MNs have turned out to be promising in gene delivery. In this review, we discussed the potential as well as the challenges of utilizing MNs to deliver nucleic acids for gene therapy. We also proposed that a combination of MNs and other gene delivery approaches may lead to a better delivery system for gene therapy.

Correction of Hair Shaft Defects through Allele-Specific Silencing of Mutant Krt75

Dominant mutations in keratin genes can cause a number of inheritable skin disorders characterized by intraepidermal blistering, epidermal hyperkeratosis, or abnormalities in skin appendages, such as nail plate dystrophy and structural defects in hair. Allele-specific silencing of mutant keratins through RNA interference is a promising therapeutic approach for suppressing the expression of mutant keratins and related phenotypes in the epidermis. However, its effectiveness on skin appendages remains to be confirmed in vivo. In this study, we developed allele specific siRNAs capable of selectively suppressing the expression of a mutant Krt75, which causes hair shaft structural defects characterized by the development of blebs along the hair shaft in mice. Hair regenerated from epidermal keratinocyte progenitor cells isolated from mutant Krt75 mouse models reproduced the blebbing phenotype when grafted in vivo. In contrast, mutant cells manipulated with a lentiviral vector expressing mutant Krt75-specific shRNA persistently suppressed this phenotype. The phenotypic correction was associated with significant reduction of mutant Krt75 mRNA in the skin grafts. Thus, data obtained from this study demonstrated the feasibility of utilizing RNA interference to achieve durable correction of hair structural phenotypes through allele-specific silencing of the mutant keratin genes.

A Small Indel Mutant Mouse Model of Epidermolytic Palmoplantar Keratoderma and Its Application to Mutant-specific shRNA Therapy

Epidermolytic palmoplantar keratoderma (EPPK) is a relatively common autosomal-dominant skin disorder caused by mutations in the keratin 9 gene (KRT9), with few therapeutic options for the affected so far. Here, we report a knock-in transgenic mouse model that carried a small insertion–deletion (indel) mutant of Krt9, c.434delAinsGGCT (p.Tyr144delinsTrpLeu), corresponding to the human mutation KRT9/c.500delAinsGGCT (p.Tyr167delinsTrpLeu), which resulted in a human EPPK-like phenotype in the weight-stress areas of the fore- and hind-paws of both Krt9^+/mut and Krt9^mut/mut mice. The phenotype confirmed that EPPK is a dominant-negative condition, such that mice heterozygotic for the K9-mutant allele (Krt9^+/mut) showed a clear EPPK-like phenotype. Then, we developed a mutant-specific short hairpin RNA (shRNA) therapy for EPPK mice. Mutant-specific shRNAs were systematically identified in vitro using a luciferase reporter gene assay and delivered into Krt9^+/mut mice. shRNA-mediated knockdown of mutant protein resulted in almost normal morphology and functions of the skin, whereas the same shRNA had a negligible effect in wild-type K9 mice. Our results suggest that EPPK can be treated by gene therapy, and this has significant implications for future clinical application.

Keratin 12 missense mutation induces the unfolded protein response and apoptosis in Meesmann epithelial corneal dystrophy

Meesmann epithelial corneal dystrophy (MECD) is a rare autosomal dominant disorder caused by dominant-negative mutations within the KRT3 or KRT12 genes, which encode the cytoskeletal protein keratins K3 and K12, respectively. To investigate the pathomechanism of this disease, we generated and phenotypically characterized a novel knock-in humanized mouse model carrying the severe, MECD-associated, K12-Leu132Pro mutation. Although no overt changes in corneal opacity were detected by slit-lamp examination, the corneas of homozygous mutant mice exhibited histological and ultrastructural epithelial cell fragility phenotypes. An altered keratin expression profile was observed in the cornea of mutant mice, confirmed by western blot, RNA-seq and quantitative real-time polymerase chain reaction. Mass spectrometry (MS) and immunohistochemistry demonstrated a similarly altered keratin profile in corneal tissue from a K12-Leu132Pro MECD patient. The K12-Leu132Pro mutation results in cytoplasmic keratin aggregates. RNA-seq analysis revealed increased chaperone gene expression, and apoptotic unfolded protein response (UPR) markers, CHOP and Caspase 12, were also increased in the MECD mice. Corneal epithelial cell apoptosis was increased 17-fold in the mutant cornea, compared with the wild-type (P < 0.001). This elevation of UPR marker expression was also observed in the human MECD cornea. This is the first reporting of a mouse model for MECD that recapitulates the human disease and is a valuable resource in understanding the pathomechanism of the disease. Although the most severe phenotype is observed in the homozygous mice, this model will still provide a test-bed for therapies not only for corneal dystrophies but also for other keratinopathies caused by similar mutations.

Skin Keratins

Keratins comprise the type I and type II intermediate filament-forming proteins and occur primarily in epithelial cells. They are encoded by 54 evolutionarily conserved genes (28 type I, 26 type II) and regulated in a pairwise and tissue type-, differentiation-, and context-dependent manner. Keratins serve multiple homeostatic and stress-enhanced mechanical and nonmechanical functions in epithelia, including the maintenance of cellular integrity, regulation of cell growth and migration, and protection from apoptosis. These functions are tightly regulated by posttranslational modifications as well as keratin-associated proteins. Genetically determined alterations in keratin-coding sequences underlie highly penetrant and rare disorders whose pathophysiology reflects cell fragility and/or altered tissue homeostasis. Moreover, keratin mutation or misregulation represents risk factors or genetic modifiers for several acute and chronic diseases. This chapter focuses on keratins that are expressed in skin epithelia, and details a number of basic protocols and assays that have proven useful for analyses being carried out in skin.

Keratins K2 and K10 are essential for the epidermal integrity of plantar skin

BACKGROUND

K1 and K2 are the main type II keratins in the suprabasal epidermis where each of them heterodimerizes with the type I keratin K10 to form intermediate filaments. In regions of the ears, tail, and soles of the mouse, only K2 is co-expressed with K10, suggesting that these keratins suffice to form a mechanically resilient cytoskeleton.

OBJECTIVE

To determine the effects of the suppression of both main keratins, K2 and K10, in the suprabasal plantar epidermis of the mouse.

METHODS

Krt2(-/-) Krt10(-/-) mice were generated by crossing Krt2(-/-) and Krt10(-/-) mice. Epidermal morphology of soles of hind-paws was examined macroscopically and histologically. Immunofluorescence analysis and quantitative PCR analysis were performed to analyze the expression of keratins in sole skin of wildtype and Krt2(-/-) Krt10(-/-) mice. Highly abundant proteins of the sole stratum corneum were determined by electrophoretic and chromatographic separation and subsequent mass spectrometry.

RESULTS

K2 and K10 are the most prominent suprabasal keratins in normal mouse soles with the exception of the footpads where K1, K9 and K10 predominate. Mice lacking both K2 and K10 were viable and developed epidermal acanthosis and hyperkeratosis in inter-footpad epidermis of the soles. The expression of keratins K1, K9 and K16 was massively increased at the RNA and protein levels in the soles of Krt2(-/-) Krt10(-/-) mice.

CONCLUSIONS

This study demonstrates that the loss of the main cytoskeletal components of plantar epidermis, i.e. K2 and K10, can be only partly compensated by the upregulation of other keratins. The thickening of the epidermis in the soles of Krt2(-/-) Krt10(-/-) mice may serve as a model for pathomechanistic aspects of palmoplantar keratoderma.

Testosterone regulates keratin 33B expression in rat penis growth through androgen receptor signaling

Androgen therapy is the mainstay of treatment for the hypogonadotropic hypogonadal micropenis because it obviously enhances penis growth in prepubescent microphallic patients. However, the molecular mechanisms of androgen treatment leading to penis growth are still largely unknown. To clarify this well-known phenomenon, we successfully generated a castrated male Sprague Dawley rat model at puberty followed by testosterone administration. Interestingly, compared with the control group, testosterone treatment stimulated a dose-dependent increase of penis weight, length, and width in castrated rats accompanied with a dramatic recovery of the pathological changes of the penis. Mechanistically, testosterone administration substantially increased the expression of androgen receptor (AR) protein. Increased AR protein in the penis could subsequently initiate transcription of its target genes, including keratin 33B (Krt33b). Importantly, we demonstrated that KRT33B is generally expressed in the rat penis and that most KRT33B expression is cytoplasmic. Furthermore, AR could directly modulate its expression by binding to a putative androgen response element sequence of the Krt33b promoter. Overall, this study reveals a novel mechanism facilitating penis growth after testosterone treatment in precastrated prepubescent animals, in which androgen enhances the expression of AR protein as well as its target genes, such as Krt33b.

Complementary roles of specific cysteines in keratin 14 toward the assembly, organization, and dynamics of intermediate filaments in skin keratinocytes

We recently showed that inter-keratin disulfide bonding plays an important role in the assembly, organization, and dynamics of keratin intermediate filaments in skin keratinocytes. In particular, cysteine 367 located in the central α-helical rod domain of keratin 14 is necessary for the formation of a stable perinuclear network of keratin filaments (with type II partner keratin 5) in skin keratinocytes analyzed by static and live cell imaging. Here, we show that two additional cysteine residues located in the non-helical head domain of K14, Cys-4 and Cys-40, also participate in inter-keratin disulfide bonding and tandemly play a key role complementary to that of Cys-367 in the assembly, organization, and dynamics of keratin filaments in skin keratinocytes in primary culture. Analysis of K14 variants with single or multiple substitutions of cysteine residues points to a spatial and temporal hierarchy in how Cys-4/Cys-40 and Cys-367 regulate keratin assembly in vitro and filament dynamics in live keratinocytes in culture. Our findings substantiate the importance and complexity of a novel determinant, namely inter-keratin disulfide bonding, for the regulation of several aspects of keratin filaments in surface epithelia.

A homozygous missense variant in type I keratin KRT25 causes autosomal recessive woolly hair

BACKGROUND

Woolly hair (WH) is a hair abnormality that is primarily characterised by tightly curled hair with abnormal growth.

METHODS

In two unrelated consanguineous Pakistani families with non-syndromic autosomal recessive (AR) WH, homozygosity mapping and linkage analysis identified a locus within 17q21.1-q22, which contains the type I keratin gene cluster. A DNA sample from an affected individual from each family underwent exome sequencing.

RESULTS

A homozygous missense variant c.950T>C (p.(Leu317Pro)) within KRT25 segregated with ARWH in both families, and has a combined maximum two-point LOD score of 7.9 at ϴ=0. The KRT25 variant is predicted to result in disruption of the second α-helical rod domain and the entire protein structure, thus possibly interfering with heterodimerisation of K25 with type II keratins within the inner root sheath (IRS) of the hair follicle and the medulla of the hair shaft.

CONCLUSIONS

Our findings implicate a novel gene involved in human hair abnormality, and are consistent with the curled, fragile hair found in mice with Krt25 mutations, and further support the role of IRS-specific type I keratins in hair follicle development and maintenance of hair texture.

A role for disulfide bonding in keratin intermediate filament organization and dynamics in skin keratinocytes

Disulfide bonds involving cysteine 367 in K14 play a crucial role in the assembly, dynamics, and organization of K14-containing filaments in epidermal keratinocytes.

We recently reported that a trans-dimer, homotypic disulfide bond involving Cys367 in keratin 14 (K14) occurs in an atomic-resolution structure of the interacting K5/K14 2B domains and in keratinocyte cell lines. Here we show that a sizable fraction of the K14 and K5 protein pools participates in interkeratin disulfide bonding in primary cultures of mouse skin keratinocytes. By comparing the properties of wild-type K14 with a completely cysteine-free variant thereof, we found that K14-dependent disulfide bonding limited filament elongation during polymerization in vitro but was necessary for the genesis of a perinuclear-concentrated network of keratin filaments, normal keratin cycling, and the sessile behavior of the nucleus and whole cell in keratinocytes studied by live imaging. Many of these phenotypes were rescued when analyzing a K14 variant harboring a single Cys residue at position 367. These findings establish disulfide bonding as a novel and important mechanism regulating the assembly, intracellular organization, and dynamics of K14-containing intermediate filaments in skin keratinocytes.

Keratins in health and disease

The cytoprotective keratins (K) compose the intermediate filaments of epithelial cells and their inherited and spontaneous mutations give rise to keratinopathies. For example, mutations in K1/K5/K10/K14 cause epidermal skin diseases whereas simple epithelial K8/K18/K19 variants predispose to development of several liver disorders. Due to their abundance, tissue- and context-specific expression, keratins constitute excellent diagnostic markers of both neoplastic and non-neoplastic diseases. During injury and in disease, keratin expression levels, cellular localization or posttranslational modifications are altered. Accumulating evidence suggests that these changes modulate multiple processes including cell migration, tumor growth/metastasis and development of infections. Therefore, our understanding of keratins is shifting from diagnostic markers to active disease modifiers.

In vivo gene silencing following non-invasive siRNA delivery into the skin using a novel topical formulation

Therapeutics based on short interfering RNAs (siRNAs), which act by inhibiting the expression of target transcripts, represent a novel class of potent and highly specific next-generation treatments for human skin diseases. Unfortunately, the intrinsic barrier properties of the skin combined with the large size and negative charge of siRNAs make epidermal delivery of these macromolecules quite challenging. To help evaluate the in vivo activity of these therapeutics and refine delivery strategies we generated an innovative reporter mouse model that predominantly expresses firefly luciferase (luc2p) in the paw epidermis--the region of murine epidermis that most closely models the tissue architecture of human skin. Combining this animal model with state-of-the-art live animal imaging techniques, we have developed a real-time in vivo analysis work-flow that has allowed us to compare and contrast the efficacies of a wide range nucleic acid-based gene silencing reagents in the skin of live animals. While inhibition was achieved with all of the reagents tested, only the commercially available "self-delivery" modified Accell-siRNAs (Dharmacon) produced potent and sustained in vivo gene silencing. Together, these findings highlight just how informative reliable reporter mouse models can be when assessing novel therapeutics in vivo. Using this work-flow, we developed a novel clinically-relevant topical formulation that facilitates non-invasive epidermal delivery of unmodified and "self-delivery" siRNAs. Remarkably, a sustained >40% luc2p inhibition was observed after two 1-hour treatments with Accell-siRNAs in our topical formulation. Importantly, our ability to successfully deliver siRNA molecules topically brings these novel RNAi-based therapeutics one-step closer to clinical use.

Identification of genes important for cutaneous function revealed by a large scale reverse genetic screen in the mouse

The skin is a highly regenerative organ which plays critical roles in protecting the body and sensing its environment. Consequently, morbidity and mortality associated with skin defects represent a significant health issue. To identify genes important in skin development and homeostasis, we have applied a high throughput, multi-parameter phenotype screen to the conditional targeted mutant mice generated by the Wellcome Trust Sanger Institute's Mouse Genetics Project (Sanger-MGP). A total of 562 different mouse lines were subjected to a variety of tests assessing cutaneous expression, macroscopic clinical disease, histological change, hair follicle cycling, and aberrant marker expression. Cutaneous lesions were associated with mutations in 23 different genes. Many of these were not previously associated with skin disease in the organ (Mysm1, Vangl1, Trpc4ap, Nom1, Sparc, Farp2, and Prkab1), while others were ascribed new cutaneous functions on the basis of the screening approach (Krt76, Lrig1, Myo5a, Nsun2, and Nf1). The integration of these skin specific screening protocols into the Sanger-MGP primary phenotyping pipelines marks the largest reported reverse genetic screen undertaken in any organ and defines approaches to maximise the productivity of future projects of this nature, while flagging genes for further characterisation.

Defective channels lead to an impaired skin barrier

Channels are integral membrane proteins that form a pore, allowing the passive movement of ions or molecules across a membrane (along a gradient), either between compartments within a cell, between intracellular and extracellular environments or between adjacent cells. The ability of cells to communicate with one another and with their environment is a crucial part of the normal physiology of a tissue that allows it to carry out its function. Cell communication is particularly important during keratinocyte differentiation and formation of the skin barrier. Keratinocytes in the skin epidermis undergo a programme of apoptosis-driven terminal differentiation, whereby proliferating keratinocytes in the basal (deepest) layer of the epidermis stop proliferating, exit the basal layer and move up through the spinous and granular layers of the epidermis to form the stratum corneum, the external barrier. Genes encoding different families of channel proteins have been found to harbour mutations linked to a variety of rare inherited monogenic skin diseases. In this Commentary, we discuss how human genetic findings in aquaporin (AQP) and transient receptor potential (TRP) channels reveal different mechanisms by which these channel proteins function to ensure the proper formation and maintenance of the skin barrier.

Directed expression of a chimeric type II keratin partially rescues keratin 5-null mice

The crucial role of structural support fulfilled by keratin intermediate filaments (IFs) in surface epithelia likely requires that they be organized into cross-linked networks. For IFs comprised of keratins 5 and 14 (K5 and K14), which occur in basal keratinocytes of the epidermis, formation of cross-linked bundles is, in part, self-driven through cis-acting determinants. Here, we targeted the expression of a bundling-competent KRT5/KRT8 chimeric cDNA (KRT8bc) or bundling-deficient wild type KRT8 as a control to the epidermal basal layer of Krt5-null mice to assess the functional importance of keratin IF self-organization in vivo. Such targeted expression of K8bc rescued Krt5-null mice with a 47% frequency, whereas K8 completely failed to do so. This outcome correlated with lower than expected levels of K8bc and especially K8 mRNA and protein in the epidermis of E18.5 replacement embryos. Ex vivo culture of embryonic skin keratinocytes confirmed the ability of K8bc to form IFs in the absence of K5. Additionally, electron microscopy analysis of E18.5 embryonic skin revealed that the striking defects observed in keratin IF bundling, cytoarchitecture, and mitochondria are partially restored by K8bc expression. As young adults, viable KRT8bc replacement mice develop alopecia and chronic skin lesions, indicating that the skin epithelia are not completely normal. These findings are consistent with a contribution of self-mediated organization of keratin IFs to structural support and cytoarchitecture in basal layer keratinocytes of the epidermis and underscore the importance of context-dependent regulation for keratin genes and proteins in vivo.

KRT9 gene mutation as a reliable indicator in the prenatal molecular diagnosis of epidermolytic palmoplantar keratoderma

Epidermolytic palmoplantar keratoderma (EPPK) is the most frequent form of such keratodermas. It is inherited in an autosomal dominant pattern and is clinically characterized by diffuse yellowish thickening of the skin on the palms and soles with erythematous borders during the first weeks or months after birth. EPPK is generally caused by mutations of the KRT9 gene. More than 26 KRT9 gene mutations responsible for EPPK have been described (Human Intermediate Filament Database, www.interfil.org), and many of these variants are located within the highly-conserved coil 1A region of the α-helical rod domain of keratin 9. Unfortunately, there is no satisfactory treatment for EPPK. Thus, prenatal molecular diagnosis or pre-pregnancy diagnosis is crucial and benefits those affected who seek healthy descendants. In the present study, we performed amniotic fluid-DNA-based prenatal testing for three at-risk pregnant EPPK women from three unrelated southern Chinese families who carried the KRT9 missense mutations p.Arg163Trp and p.Arg163Gln, and successfully helped two families to bear normal daughters. We suggest that before the successful application of preimplantation genetic diagnosis (PGD), and noninvasive prenatal diagnosis of EPPK that analyzes fetal cells or cell-free DNA in maternal blood, prenatal genetic diagnosis by amniocentesis or chorionic villus sampling (CVS) offers a quite acceptable option for EPPK couples-at-risk to avoid the birth of affected offspring, especially in low- and middle-income countries.