Ectopic expression of desmin in the epidermis of transgenic mice permits development of a normal epidermis

High-Throughput Screening for Drugs that Modulate Intermediate Filament Proteins

Intermediate filament (IF) proteins have unique and complex cell and tissue distribution. Importantly, IF gene mutations cause or predispose to more than 80 human tissue-specific diseases (IF-pathies), with the most severe disease phenotypes being due to mutations at conserved residues that result in a disrupted IF network. A critical need for the entire IF-pathy field is the identification of drugs that can ameliorate or cure these diseases, particularly since all current therapies target the IF-pathy complication, such as diabetes or cardiovascular disease, rather than the mutant IF protein or gene. We describe a high-throughput approach to identify drugs that can normalize disrupted IF proteins. This approach utilizes transduction of lentivirus that expresses green fluorescent protein-tagged keratin 18 (K18) R90C in A549 cells. The readout is drug "hits" that convert the dot-like keratin filament distribution, due to the R90C mutation, to a wild-type-like filamentous array. A similar strategy can be used to screen thousands of compounds and can be utilized for practically any IF protein with a filament-disrupting mutation, and could therefore potentially target many IF-pathies. "Hits" of interest require validation in cell culture then using in vivo experimental models. Approaches to study the mechanism of mutant IF normalization by potential drugs of interest are also described. The ultimate goal of this drug screening approach is to identify effective and safe compounds that can potentially be tested for clinical efficacy in patients.

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.

Beyond expectations: novel insights into epidermal keratin function and regulation

The epidermis is a stratified epithelium that relies on its cytoskeleton and cell junctions to protect the body against mechanical injury, dehydration, and infections. Keratin intermediate filament proteins are involved in many of these functions by forming cell-specific cytoskeletal scaffolds crucial for the maintenance of cell and tissue integrity. In response to various stresses, the expression and organization of keratins are altered at transcriptional and posttranslational levels to restore tissue homeostasis. Failure to restore tissue homeostasis in the presence of keratin gene mutations results in acute and chronic skin disorders for which currently no rational therapies are available. Here, we review the recent progress on the role of keratins in cytoarchitecture, adhesion, signaling, and inflammation. By focusing on epidermal keratins, we illustrate the contribution of keratin isotypes to differentiated epithelial functions.

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.

Proteomic modification in gills and brains of medaka fish (Oryzias melastigma) after exposure to a sodium channel activator neurotoxin, brevetoxin-1

Although brevetoxins (PbTxs) produced by the marine dinoflagellate Karenia brevis are known to be absorbed across gill membranes and exert their acute toxic effects through an ion-channel mediated pathway in neural tissue, the exact biochemical mechanism concerning PbTxs neurotoxicity in neural tissue and gas-exchange organs has not been well elucidated. In this study, we calculated the LC(50) value of PbTx-1 using the medaka fish model, and presented the molecular responses of sub-acute exposure to PbTx-1 with proteomic method. By adopting two-dimensional electrophoresis, the abundances of 14 and 24 proteins were found to be remarkably altered in the gills and brains, respectively, in response to toxin exposure. Thirteen gill and twenty brain proteins were identified using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry analysis. These proteins could be categorized into diverse functional classes such as cell structure, macromolecule metabolism, signal transduction and neurotransmitter release. These findings can help to elucidate the possible pathways by which aquatic toxins affect marine organisms within target organs.

Biomarker candidate discovery in Atlantic cod (Gadus morhua) continuously exposed to North Sea produced water from egg to fry

In this study Atlantic cod (Gadus morhua) were exposed to different levels of North Sea produced water (PW) and 17beta-oestradiol (E(2)), a natural oestrogen, from egg to fry stage (90 days). By comparing changes in protein expression following E(2) exposure to changes induced by PW treatment, we were able to compare the induced changes by PW to the mode of action of oestrogens. Changes in the proteome in response to exposure in whole cod fry (approximately 80 days post-hatching, dph) were detected by two-dimensional gel electrophoresis and image analysis and identified by MALDI-ToF-ToF mass spectrometry, using a newly developed cod EST database and the NCBI database. Many of the protein changes occurred at low levels (0.01% and 0.1% PW) of exposure, indicating putative biological responses at lower levels than previously detected. Using discriminant analysis, we identified a set of protein changes that may be useful as biomarker candidates of produced water (PW) and oestradiol exposure in Atlantic cod fry. The biomarker candidates discovered in this study may, following validation, prove effective as diagnostic tools in monitoring exposure and effects of discharges from the petroleum industry offshore, aiding future environmental risk analysis and risk management.

Epidermolysis bullosa simplex: a paradigm for disorders of tissue fragility

Epidermolysis bullosa (EB) simplex is a rare genetic condition typified by superficial bullous lesions that result from frictional trauma to the skin. Most cases are due to dominantly acting mutations in either keratin 14 (K14) or K5, the type I and II intermediate filament (IF) proteins tasked with forming a pancytoplasmic network of 10-nm filaments in basal keratinocytes of the epidermis and in other stratified epithelia. Defects in K5/K14 filament network architecture cause basal keratinocytes to become fragile and account for their trauma-induced rupture. Here we review how laboratory investigations centered on keratin biology have deepened our understanding of the etiology and pathophysiology of EB simplex and revealed novel avenues for its therapy.

Induction of inflammatory cytokines by a keratin mutation and their repression by a small molecule in a mouse model for EBS

Epidermolysis bullosa simplex (EBS) is a skin disorder caused by mutations in keratin (K) 5 or K14 genes. It is widely regarded as a mechanobullous disease, resulting from a weakened cytoskeleton, causing extensive cytolysis. It was postulated by others that certain K14 mutations induce tumor necrosis factor-alpha (TNF-alpha) and increase apoptosis. Here, we report that in K5-/- mice and in a cell culture model of EBS, the mRNA and protein levels of TNF-alpha remain unaltered. Transcriptome analysis of K5-/- mice revealed, however, that the proinflammatory cytokines IL-6 and IL-1beta were significantly upregulated at the mRNA level in K5-/- mouse skin. These results were confirmed by TaqMan real-time PCR and ELISA assays. We hypothesize that keratin mutations contribute to EBS in a mouse model by inducing local inflammation that mediates a stress response. Following clinical reports, we applied the small molecule doxycycline to K5-/- mice. We demonstrate that doxycycline extended the survival of neonatal K5-/- mice from less than 1 to up to 8 hours. Microarray and TaqMan real-time PCR showed a downregulation of matrix metalloproteinase 13 and IL-1beta, indicating an effect of doxycycline on transcription. Our data offer a novel small molecule-based therapy approach for EBS.

Intermediate filaments: a historical perspective

Intracellular protein filaments intermediate in size between actin microfilaments and microtubules are composed of a surprising variety of tissue specific proteins commonly interconnected with other filamentous systems for mechanical stability and decorated by a variety of proteins that provide specialized functions. The sequence conservation of the coiled-coil, alpha-helical structure responsible for polymerization into individual 10 nm filaments defines the classification of intermediate filament proteins into a large gene family. Individual filaments further assemble into bundles and branched cytoskeletons visible in the light microscope. However, it is the diversity of the variable terminal domains that likely contributes most to different functions. The search for the functions of intermediate filament proteins has led to discoveries of roles in diseases of the skin, heart, muscle, liver, brain, adipose tissues and even premature aging. The diversity of uses of intermediate filaments as structural elements and scaffolds for organizing the distribution of decorating molecules contrasts with other cytoskeletal elements. This review is an attempt to provide some recollection of how such a diverse field emerged and changed over about 30 years.

Gene therapy in combination with tissue engineering to treat epidermolysis bullosa

In the last 20 years epidermal stem cells have been extensively used for tissue regeneration of epidermis and other epithelial surfaces. The tremendous progress achieved has led to the development of protocols aimed at the correction of rare genetic disorders such as epidermolysis bullosa (EB), a severe, often lethal, blistering disorder of the skin. Approximately 400,000-500,000 people are affected worldwide and no definitive treatments have yet been developed. Gene therapy might represent an alternative therapeutic approach. This paper reviews the different strategies used to genetically modify keratinocytes from EB patients and addresses issues such as the use of in vivo or ex vivo approaches, how to target keratinocytes with stem cell properties in order to have long-term therapeutic gene expression, and which gene transfer agents should be used. The progress made has led the authors' group to submit a request for a Phase I/II ex vivo therapy clinical trial for patients with junctional EB.

Gene therapy of epidermolysis bullosa

Easy access to the organ and identification of underlying mutations in epidermolysis bullosa (EB) facilitated the first cutaneous gene therapy experiments in vitro in the mid-1990s. The leading technology was transduction of the respective cDNA carried by a retroviral vector. Using this approach, the genotypic and phenotypic hallmark features of the recessive forms of junctional EB, which are caused by loss of function of the structural proteins laminin-5 or bullous pemphigoid antigen 2/type XVII collagen of the dermo-epidermal basement membrane zone, have been corrected in vitro and in vivo using xenograft mouse models. Recently, this approach has also been shown to be feasible for the large COL7A1 gene (mutated in dystrophic EB), applying PhiC31 integrase or lentiviral vectors. Neither of these approaches has made it into a successful Phase I study on EB patients. Therefore, alternative approaches to gene correction, including modulation of splicing, are being investigated for gene therapy in EB.

Functional improvement of mutant keratin cells on addition of desmin: an alternative approach to gene therapy for dominant diseases

A major challenge to the concept of gene therapy for dominant disorders is the silencing or repairing of the mutant allele. Supplementation therapy is an alternative approach that aims to bypass the defective gene by inducing the expression of another gene, with similar function but not susceptible to the disrupting effect of the mutant one. Epidermolysis bullosa simplex (EBS) is a genetic skin fragility disorder caused by mutations in the genes for keratins K5 or K14, the intermediate filaments present in the basal cells of the epidermis. Keratin diseases are nearly all dominant in their inheritance. In cultured keratinocytes, mutant keratin renders cells more sensitive to a variety of stress stimuli such as osmotic shock, heat shock or scratch wounding. Using a 'severe' disease cell culture model system, we demonstrate reversion towards wild-type responses to stress after transfection with human desmin, an intermediate filament protein normally expressed in muscle cells. Such a supplementation therapy approach could be widely applicable to patients with related individual mutations and would avoid some of the financial obstacles to gene therapy for rare diseases.

Bfsp2 mutation found in mouse 129 strains causes the loss of CP49' and induces vimentin-dependent changes in the lens fibre cell cytoskeleton

Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.

Bfsp2 mutation found in mouse 129 strains causes the loss of CP49 and induces vimentin-dependent changes in the lens fibre cell cytoskeleton

Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.

Functional complexity of intermediate filament cytoskeletons: from structure to assembly to gene ablation

The cell biology of intermediate filament (IF) proteins and their filaments is complicated by the fact that the members of the gene family, which in humans amount to at least 65, are differentially expressed in very complex patterns during embryonic development. Thus, different tissues and cells express entirely different sets and amounts of IF proteins, the only exception being the nuclear B-type lamins, which are found in every cell. Moreover, in the course of evolution the individual members of this family have, within one species, diverged so much from each other with regard to sequence and thus molecular properties that it is hard to envision a unifying kind of function for them. The known epidermolytic diseases, caused by single point mutations in keratins, have been used as an argument for a role of IFs in mechanical "stress resistance," something one would not have easily ascribed to the beaded chain filaments, a special type of IF in the eye lens, or to nuclear lamins. Therefore, the power of plastic dish cell biology may be limited in revealing functional clues for these structural elements, and it may therefore be of interest to go to the extreme ends of the life sciences, i.e., from the molecular properties of individual molecules including their structure at the atomic level to targeted inactivation of their genes in living animals, mouse, and worm to define their role more precisely in metazoan cell physiology.

Phenotypes, genotypes and their contribution to understanding keratin function

A large number of mutations in keratin genes underlie inherited tissue fragility disorders of epithelia. The genotype-phenotype correlations emerging from these studies provide a rich source of information about the function of keratins that would have taken decades to achieve by a purely transgenic approach. Human disease studies are being supplemented by engineered mouse mutant studies, which give access to the effects of genetic alterations unlikely to occur naturally. Evidence is emerging that the great diversity of keratins might be required to enable cells to adapt their structure in response to different signalling pathways.