Lethal, neonatal ichthyosis with increased proteolytic processing of filaggrin in a mouse model of Netherton syndrome

Kallikrein 5 induces atopic dermatitis-like lesions through PAR2-mediated thymic stromal lymphopoietin expression in Netherton syndrome

Netherton syndrome (NS) is a severe genetic skin disease with constant atopic manifestations that is caused by mutations in the serine protease inhibitor Kazal-type 5 (SPINK5) gene, which encodes the protease inhibitor lymphoepithelial Kazal-type–related inhibitor (LEKTI). Lack of LEKTI causes stratum corneum detachment secondary to epidermal proteases hyperactivity. This skin barrier defect favors allergen absorption and is generally regarded as the underlying cause for atopy in NS. We show for the first time that the pro-Th2 cytokine thymic stromal lymphopoietin (TSLP), the thymus and activation-regulated chemokine, and the macrophage-derived chemokine are overexpressed in LEKTI-deficient epidermis. This is part of an original biological cascade in which unregulated kallikrein (KLK) 5 directly activates proteinase-activated receptor 2 and induces nuclear factor κB–mediated overexpression of TSLP, intercellular adhesion molecule 1, tumor necrosis factor α, and IL8. This proinflammatory and proallergic pathway is independent of the primary epithelial failure and is activated under basal conditions in NS keratinocytes. This cell-autonomous process is already established in the epidermis of Spink5^−/− embryos, and the resulting proinflammatory microenvironment leads to eosinophilic and mast cell infiltration in a skin graft model in nude mice. Collectively, these data establish that uncontrolled KLK5 activity in NS epidermis can trigger atopic dermatitis (AD)–like lesions, independently of the environment and the adaptive immune system. They illustrate the crucial role of protease signaling in skin inflammation and point to new therapeutic targets for NS as well as candidate genes for AD and atopy.

Interpreting neonatal lethal phenotypes in mouse mutants: insights into gene function and human diseases

The mouse represents the model of choice to study the biological function of mammalian genes through mutation of its genome. However, the biggest challenge of mouse geneticists remains the phenotypic analysis of mouse mutants. A survey of mouse mutant databases reveals a surprisingly high number of gene mutations leading to neonatal death. These genetically modified mouse mutants have been instrumental in elucidating gene function and have become important models of congenital human diseases. The main complication when phenotyping mutant mice dying during the neonatal period is the large spectrum of physiological systems whose defects can challenge neonatal survival. Here, we present a comprehensive review of gene mutations leading to neonatal lethality and discuss the impact of these mutations on the major physiological processes critical to mouse newborn survival: parturition, breathing, suckling, and homeostasis. Selected examples of mouse mutants are highlighted to illustrate how the precise identification of the timing and cause of death associated with these physiological processes allows for a more profound understanding of the underlying cellular and molecular defects. This review provides a guide for the analysis of neonatal lethal phenotypes in mutant mice that will be helpful for dissecting out the function of specific genes during mouse development.

Ichthyosis, follicular atrophoderma, and hypotrichosis caused by mutations in ST14 is associated with impaired profilaggrin processing

Congenital ichthyosis encompasses a heterogeneous group of disorders of cornification. Isolated forms and syndromic ichthyosis can be differentiated. We have analyzed two consanguineous families from the United Arab Emirates and Turkey with an autosomal recessive syndrome of diffuse congenital ichthyosis, patchy follicular atrophoderma, generalized and diffuse nonscarring hypotrichosis, marked hypohidrosis, and woolly hair (OMIM 602400). By genome-wide analysis, we found a homozygous interval on chromosome 11q24-q25 and obtained a LOD score of 4.0 at D11S910. We identified a homozygous splice-site mutation in the Arab patients and a frame-shift deletion in the Turkish patient in the gene suppression of tumorigenicity-14 (ST14). The product of ST14, matriptase, is a type II transmembrane serine protease synthesized in most human epithelia. Two missense mutations in ST14 were recently described in patients with a phenotype of ichthyosis and hypotrichosis, indicating diverse activities of matriptase in the epidermis and hair follicles. Here we have further demonstrated the loss of matriptase in differentiated patient keratinocytes, reduced proteolytic activation of prostasin, and disturbed processing of profilaggrin. As filaggrin monomers play a pivotal role in epidermal barrier formation, these findings reveal the link between congenital disorders of keratinization and filaggrin processing in the human skin.

Targeted deletion of the murine corneodesmosin gene delineates its essential role in skin and hair physiology

Controlled proteolytic degradation of specialized junctional structures, corneodesmosomes, by epidermal proteases is an essential process for physiological desquamation of the skin. Corneodesmosin (CDSN) is an extracellular component of corneodesmosomes and, although considerable debate still exists, genetic studies have suggested that the CDSN gene in the major psoriasis-susceptibility locus (PSORS1) may be responsible for susceptibility to psoriasis, a human skin disorder characterized by excessive growth and aberrant differentiation of keratinocytes. CDSN is also expressed in the inner root sheath of hair follicles, and a heterozygous nonsense mutation of the CDSN gene in humans is associated with scalp-specific hair loss of poorly defined etiology. Here, we have investigated the pathogenetic roles of CDSN loss of function in the development of skin diseases by generating a mouse strain with targeted deletion of the Cdsn gene. Cdsn-deficient mouse skin showed detachment of the stratum corneum from the underlying granular layer and/or detachment within the upper granular layers due to the disrupted integrity of the corneodesmosomes. When grafted onto immunodeficient mice, Cdsn-deficient skin showed rapid hair loss together with epidermal abnormalities resembling psoriasis. These results underscore the essential roles of CDSN in hair physiology and suggest functional relevance of CDSN gene polymorphisms to psoriasis susceptibility.

Disruption of epidermal specific gene expression and delayed skin development in AP-2 gamma mutant mice

Summary Sentence: Conditional ablation of AP-2 gamma results in a delay in skin development and abnormal expression of p63, K14, K1, filaggrin, repetin and secreted Ly6/Plaur domain containing 1, key genes required for epidermal development and differentiation. The development of the epidermis, a stratified squamous epithelium, is dependent on the regulated differentiation of keratinocytes. Differentiation begins with the initiation of stratification, a process tightly controlled through proper gene expression. AP-2 gamma is expressed in skin and previous research suggested a pathway where p63 gene induction results in increased expression of AP-2 gamma, which in turn is responsible for induction of K14. This study uses a conditional gene ablation model to further explore the role of AP-2 gamma in skin development. Mice deficient for AP-2 gamma exhibited delayed expression of p63, K14, and K1, key genes required for development and differentiation of the epidermis. In addition, microarray analysis of E16.5 skin revealed delayed expression of additional late epidermal differentiation genes: filaggrin, repetin and secreted Ly6/Plaur domain containing 1, in mutant mice. The genetic delay in skin development was further confirmed by a functional delay in the formation of an epidermal barrier. These results document an important role for AP-2 gamma in skin development, and reveal the existence of regulatory factors that can compensate for AP-2 gamma in its absence.

Cervical remodeling during pregnancy and parturition: molecular characterization of the softening phase in mice

Cervical remodeling during pregnancy and parturition is a single progressive process that can be loosely divided into four overlapping phases termed softening, ripening, dilation/labor, and post partum repair. Elucidating the molecular mechanisms that facilitate all phases of cervical remodeling is critical for an understanding of parturition and for identifying processes that are misregulated in preterm labor, a significant cause of perinatal morbidity. In the present study, biomechanical measurements indicate that softening was initiated between gestation days 10 and 12 of mouse pregnancy, and in contrast to cervical ripening on day 18, the softened cervix maintains tissue strength. Although preceded by increased collagen solubility, cervical softening is not characterized by significant increases in cell proliferation, tissue hydration or changes in the distribution of inflammatory cells. Gene expression studies reveal a potentially important role of cervical epithelia during softening and ripening in maintenance of an immunomucosal barrier that protects the stromal compartment during matrix remodeling. Expression of two genes involved in repair and protection of the epithelial permeability barrier in the gut (trefoil factor 1) and skin (serine protease inhibitor Kazal type 5) were increased during softening and/or ripening. Another gene whose function remains to be elucidated, purkinje cell protein 4, declines in expression as remodeling progressed. Collectively, these results indicate that cervical softening during pregnancy is a unique phase of the tissue remodeling process characterized by increased collagen solubility, maintenance of tissue strength, and upregulation of genes involved in mucosal protection.

Cutaneous human papillomaviruses down-regulate AKT1, whereas AKT2 up-regulation and activation associates with tumors

Epithelial tumorigenesis has been linked to AKT up-regulation. Human papillomaviruses (HPV) cause anogenital cancers and anogenital HPV infection up-regulates AKT activity. Mounting evidence points to a role for cutaneous HPVs as etiologic factors in skin tumorigenesis. High-risk cutaneous beta HPVs have been linked to carcinogenesis in immunosuppressed patients, and high-risk cutaneous HPV8 genes enhance tumorigenesis in transgenic mice. We find that, in contrast to anogenital HPVs, cutaneous HPV8 early genes down-regulate epidermal AKT activity by down-regulating AKT1 isoform levels. This down-regulation occurs before papilloma formation or tumorigenesis and leads to cutaneous differentiation changes that may weaken the epidermal squame for viral release. We find that, in viral warts (papillomas) and HPV gene-induced epidermal tumors, AKT activity can be activated focally by up-regulation and phosphorylation of the AKT2 isoform. In squamous cell carcinomas (SCC), AKT1 down-regulation is also common, consistent with a viral influence, whereas AKT2 up-regulation is widespread. Activation of up-regulated AKT2 by serine phosphorylation associates with high-grade tumors. Our data suggest that AKT2 up-regulation is characteristic of SCC and that coincident AKT2 activation through serine phosphorylation correlates with malignancy. These findings highlight differences between the effects of anogenital and cutaneous HPV on epithelial AKT activity and furthermore show that AKT isoforms can behave differently during epidermal tumorigenesis. These findings also suggest AKT2 as a possible therapeutic tumor target in SCC.

Autosomal ichthyosis with hypotrichosis syndrome displays low matriptase proteolytic activity and is phenocopied in ST14 hypomorphic mice

Human autosomal recessive ichthyosis with hypotrichosis (ARIH) is an inherited disorder recently linked to homozygosity for a point mutation in the ST14 gene that causes a G827R mutation in the matriptase serine protease domain (G216 in chymotrypsin numbering). Here we show that human G827R matriptase has strongly reduced proteolytic activity toward small molecule substrates, as well as toward its candidate epidermal target, prostasin. To further investigate the possible contribution of low matriptase activity to ARIH, we generated an ST14 hypomorphic mouse strain that displays a 100-fold reduction in epidermal matriptase mRNA levels. Interestingly, unlike ST14 null mice, ST14 hypomorphic mice were viable and fertile but displayed a spectrum of abnormalities that strikingly resembled ARIH. Thus, ST14 hypomorphic mice developed hyperproliferative and retention ichthyosis with impaired desquamation, hypotrichosis with brittle, thin, uneven, and sparse hair, and tooth defects. Biochemical analysis of ST14 hypomorphic epidermis revealed reduced prostasin proteolytic activation and profilaggrin proteolytic processing, compatible with a primary role of matriptase in this process. This work strongly indicates that reduced activity of a matriptase-prostasin proteolytic cascade is the etiological origin of human ARIH and provides an important mouse model for the exploration of matriptase function in ARIH, as well as multiple other physiological and pathological processes.

LEKTI fragments specifically inhibit KLK5, KLK7, and KLK14 and control desquamation through a pH-dependent interaction

LEKTI is a 15-domain serine proteinase inhibitor whose defective expression underlies the severe autosomal recessive ichthyosiform skin disease, Netherton syndrome. Here, we show that LEKTI is produced as a precursor rapidly cleaved by furin, generating a variety of single or multidomain LEKTI fragments secreted in cultured keratinocytes and in the epidermis. The identity of these biological fragments (D1, D5, D6, D8-D11, and D9-D15) was inferred from biochemical analysis, using a panel of LEKTI antibodies. The functional inhibitory capacity of each fragment was tested on a panel of serine proteases. All LEKTI fragments, except D1, showed specific and differential inhibition of human kallikreins 5, 7, and 14. The strongest inhibition was observed with D8-D11, toward KLK5. Kinetics analysis revealed that this interaction is rapid and irreversible, reflecting an extremely tight binding complex. We demonstrated that pH variations govern this interaction, leading to the release of active KLK5 from the complex at acidic pH. These results identify KLK5, a key actor of the desquamation process, as the major target of LEKTI. They disclose a new mechanism of skin homeostasis by which the epidermal pH gradient allows precisely regulated KLK5 activity and corneodesmosomal cleavage in the most superficial layers of the stratum corneum.

Tissue kallikrein proteolytic cascade pathways in normal physiology and cancer

Human tissue kallikreins (KLKs or kallikrein-related peptidases) are a subgroup of extracellular serine proteases that act on a wide variety of physiological substrates, while they display aberrant expression patterns in certain types of cancer. Differential expression patterns lead to the exploitation of these proteins as new cancer biomarkers for hormone-dependent malignancies, in particular. The prostate-specific antigen or kallikrein-related peptidase 3 (PSA/KLK3) is an established tumor marker for the diagnosis and monitoring of prostate cancer. It is well documented that specific KLK genes are co-expressed in tissues and in various pathologies suggesting their participation in complex proteolytic cascades. Here, we review the currently established knowledge on the involvement of KLK proteolytic cascades in the regulation of physiological and pathological processes in prostate tissue and in skin. It is well established that the activity of KLKs is often regulated by auto-activation and subsequent autolytic internal cleavage leading to enzymatic inactivation, as well as by inhibitory serpins or by allosteric inhibition by zinc ions. Redistribution of zinc ions and alterations in their concentration due to physiological or pathological reasons activates specific KLKs initiating the kallikrein cascade(s). Recent studies on kallikrein substrate specificity allowed for the construction of a kallikrein interaction network involved in semen liquefaction and prostate cancer, as well as in skin pathologies, such as skin desquamation, psoriasis and cancer. Furthermore, we discuss the crosstalks between known proteolytic pathways and the kallikrein cascades, with emphasis on the activation of plasmin and its implications in prostate cancer. These findings may have clinical implications for the underlying molecular mechanism and management of cancer and other disorders in which KLK activity is elevated.

The SPINK gene family and celiac disease susceptibility

The gene family of serine protease inhibitors of the Kazal type (SPINK) are functional and positional candidate genes for celiac disease (CD). Our aim was to assess the gut mucosal gene expression and genetic association of SPINK1, -2, -4, and -5 in the Dutch CD population. Gene expression was determined for all four SPINK genes by quantitative reverse-transcription polymerase chain reaction in duodenal biopsy samples from untreated (n=15) and diet-treated patients (n=31) and controls (n=16). Genetic association of the four SPINK genes was tested within a total of 18 haplotype tagging SNPs, one coding SNP, 310 patients, and 180 controls. The SPINK4 study cohort was further expanded to include 479 CD cases and 540 controls. SPINK4 DNA sequence analysis was performed on six members of a multigeneration CD family to detect possible point mutations or deletions. SPINK4 showed differential gene expression, which was at its highest in untreated patients and dropped sharply upon commencement of a gluten-free diet. Genetic association tests for all four SPINK genes were negative, including SPINK4 in the extended case/control cohort. No SPINK4 mutations or deletions were observed in the multigeneration CD family with linkage to chromosome 9p21-13 nor was the coding SNP disease-specific. SPINK4 exhibits CD pathology-related differential gene expression, likely derived from altered goblet cell activity. All of the four SPINK genes tested do not contribute to the genetic risk for CD in the Dutch population.

AKT-dependent HspB1 (Hsp27) activity in epidermal differentiation

AKT activity has been reported in the epidermis associated with keratinocyte survival and differentiation. We show in developing skin that Akt activity associates first with post-proliferative, para-basal keratinocytes and later with terminally differentiated keratinocytes that are forming the fetal stratum corneum. In adult epidermis the dominant Akt activity is in these highly differentiated granular keratinocytes, involved in stratum corneum assembly. Stratum corneum is crucial for protective barrier activity, and its formation involves complex and poorly understood processes such as nuclear dissolution, keratin filament aggregation, and assembly of a multiprotein cell cornified envelope. A key protein in these processes is filaggrin. We show that one target of Akt in granular keratinocytes is HspB1 (heat shock protein 27). Loss of epidermal HspB1 caused hyperkeratinization and misprocessing of filaggrin. Akt-mediated HspB1 phosphorylation promotes a transient interaction with filaggrin and intracellular redistribution of HspB1. This is the first demonstration of a specific interaction between HspB1 and a stratum corneum protein and indicates that HspB1 has chaperone activity during stratum corneum formation. This work demonstrates a new role for Akt in epidermis.

Netherton syndrome: mutation analysis of two Taiwanese families

Netherton syndrome (NS) is a severe autosomal recessive skin disorder characterized by congenital ichthyosiform erythroderma, hair shaft abnormalities, and atopic diathesis. Recently, pathogenic mutations were identified in serine protease inhibitor Kazal-type 5 (SPINK5), the gene that encodes lympho-epithelial Kazal-type related inhibitor (LEKTI), a type of serine protease inhibitor involved in the regulation of skin barrier formation and immunity. In the present report, we describe the mutation analysis of two Taiwanese patients with NS. Patient 1 has heterozygous mutations; the maternal allele has novel T808I (C-T transition in codon 808) and the paternal allele has recurrent R790X (C-T transition in codon 790). Patient 2 is homozygous for a novel polymorphism R267Q (G-A transition in codon 267). The change was not detected in the patient's father. Haplotype analysis revealed that the patient was homozygous for the 5 single nucleotide polymorphisms in the genomic sequence of SPINK5 as well as the flanking (GT)(17) and D5S413, in addition to the discrepancy of R267Q. Nevertheless real-time quantitative PCR analysis revealed no microdeletion in the genomic sequence of SPINK5. Thus uniparental disomy of maternal SPINK5 allele was indicated.

Depletion of ceramides with very long chain fatty acids causes defective skin permeability barrier function, and neonatal lethality in ELOVL4 deficient mice

Very long chain fatty acids (VLCFA), either free or as components of glycerolipids and sphingolipids, are present in many organs. Elongation of very long chain fatty acids-4 (ELOVL4) belongs to a family of 6 members of putative fatty acid elongases that are involved in the formation of VLCFA. Mutations in ELOVL4 were found to be responsible for an autosomal dominant form of Stargardt's-like macular dystrophy (STGD3) in human. We have previously disrupted the mouse Elovl4 gene, and found that Elovl4^+/- mice were developmentally normal, suggesting that haploinsufficiency of ELOVL4 is not a cause for the juvenile retinal degeneration in STGD3 patients. However, Elovl4^-/- mice died within several hours of birth for unknown reason(s). To study functions of ELOVL4 further, we have explored the causes for the postnatal lethality in Elovl4^-/- mice. Our data indicated that the mutant mice exhibited reduced thickness of the dermis, delayed differentiation of keratinocytes, and abnormal structure of the stratum corneum. We showed that all Elovl4^-/- mice exhibited defective skin water permeability barrier function, leading to the early postnatal death. We further showed that the absence of ELOVL4 results in depletion in the epidermis of ceramides with ω-hydroxy very long chain fatty acids (≥C28) and accumulation of ceramides with non ω-hydroxy fatty acids of C26, implicating C26 fatty acids as possible substrates of ELOVL4. These data demonstrate that ELOVL4 is required for VLCFA synthesis that is essential for water permeability barrier function of skin.

Advances in understanding the genetic basis of inherited single gene skin barrier disorders: new clues to key genes that may be involved in the pathogenesis of atopic dermatitis

Increasing knowledge of genomic DNA sequences and genetic databases has led to the characterization of the molecular basis of several inherited skin disorders. In this review we summarize some of the major recent discoveries that have been made in defining the pathogenic mutations that cause inherited disorders of the skin barrier leading to skin scaling or increased transepidermal water loss in either rare disorders (Netherton’s syndrome or harlequin ichthyosis) or more common genodermatoses (ichthyosis vulgaris). These molecular breakthroughs have led to more accurate diagnoses, better genetic counselling and, where appropriate, the feasibility of DNA-based prenatal diagnosis, as well as the possibility of developing newer forms of treatment, including gene or protein therapy. Identifying the molecular basis of these conditions, especially ichthyosis vulgaris, has also provided dramatic new insight into the genetic abnormalities in the common disorder, atopic dermatitis. Thus research on the relatively rare single gene inherited skin disorders not only has benefits for patients and their families with these uncommon conditions but also has the potential to yield fresh and significant new information about very common skin diseases.

Evidence for a matriptase-prostasin proteolytic cascade regulating terminal epidermal differentiation

Recent gene ablation studies in mice have shown that matriptase, a type II transmembrane serine protease, and prostasin, a glycosylphosphatidylinositol-anchored membrane serine protease, are both required for processing of the epidermis-specific polyprotein, profilaggrin, stratum corneum formation, and acquisition of epidermal barrier function. Here we present evidence that matriptase acts upstream of prostasin in a zymogen activation cascade that regulates terminal epidermal differentiation and is required for prostasin zymogen activation. Enzymatic gene trapping of matriptase combined with prostasin immunohistochemistry revealed that matriptase was co-localized with prostasin in transitional layer cells of the epidermis and that the developmental onset of expression of the two membrane proteases was coordinated and correlated with acquisition of epidermal barrier function. Purified soluble matriptase efficiently converted soluble prostasin zymogen to an active two-chain form that formed SDS-stable complexes with the serpin protease nexin-1. Whereas two forms of prostasin with molecular weights corresponding to the prostasin zymogen and active prostasin were present in wild type epidermis, prostasin was exclusively found in the zymogen form in matriptase-deficient epidermis. These data suggest that matriptase, an autoactivating protease, acts upstream from prostasin to initiate a zymogen cascade that is essential for epidermal differentiation.

Delineation of matriptase protein expression by enzymatic gene trapping suggests diverging roles in barrier function, hair formation, and squamous cell carcinogenesis

The membrane serine protease matriptase is required for epidermal barrier function, hair formation, and thymocyte development in mice, and dysregulated matriptase expression causes epidermal squamous cell carcinoma. To elucidate the specific functions of matriptase in normal and aberrant epidermal differentiation, we used enzymatic gene trapping combined with immunohistochemical, ultrastructural, and barrier function assays to delineate the spatio-temporal expression and function of matriptase in mouse keratinized tissue development, homeostasis, and malignant transformation. In the interfollicular epidermis, matriptase expression was restricted to postmitotic transitional layer keratinocytes undergoing terminal differentiation. Matriptase was also expressed in keratinizing oral epithelium, where it was required for oral barrier function, and in thymic epithelium. In all three tissues, matriptase colocalized with profilaggrin. In staged embryos, the onset of epidermal matriptase expression coincided with that of profilaggrin expression and acquisition of the epidermal barrier. In marked contrast to stratifying keritinized epithelium, matripase expression commenced already in undifferentiated and rapidly proliferating profilaggrin-negative matrix cells and displayed hair growth cycle-dependent expression. Exposure of the epidermis to carcinogens led to the gradual appearance of matriptase in a keratin-5-positive proliferative cell compartment during malignant progression. Combined with previous studies, these data suggest that matriptase has diverging functions in the genesis of stratified keratinized epithelium, hair follicles, and squamous cell carcinoma.

Corneodesmosomal cadherins are preferential targets of stratum corneum trypsin- and chymotrypsin-like hyperactivity in Netherton syndrome

SPINK5 (serine protease inhibitor Kazal-type 5), encoding the protease inhibitor LEKTI (lympho-epithelial Kazal-type related inhibitor), is the defective gene in Netherton syndrome (NS), a severe inherited keratinizing disorder. We have recently demonstrated epidermal protease hyperactivity in Spink5(-/-) mice resulting in desmosomal protein degradation. Herein, we investigated the molecular mechanism underlying the epidermal defect in 15 patients with NS. We demonstrated that, in a majority of patients, desmoglein 1 (Dsg1) and desmocollin 1 (Dsc1) were dramatically reduced in the upper most living layers of the epidermis. These defects were associated with premature degradation of corneodesmosomes. Stratum corneum tryptic enzyme (SCTE)-like and stratum corneum chymotryptic enzyme (SCCE)-like activities were increased, suggesting that these proteases participate in the premature degradation of corneodesmosomal cadherins. SCTE and SCCE expression was extended to the cell layers where Dsg1 and Dsc1 immunostaining was reduced. In contrast, a subset of six patients with normal epidermal protease activity or residual LEKTI expression displayed apparently normal cadherin expression and less severe disease manifestations. This suggests a degree of correlation between cadherin degradation and clinical severity. This work further supports the implication of premature corneodesmosomal cadherin degradation in the pathogenesis of NS and provides evidence for additional factors playing a role in disease expression.

Restoration of fatty aldehyde dehydrogenase deficiency in Sjögren-Larsson syndrome

Sjögren-Larsson syndrome (SLS) is an autosomal recessive neurocutaneous disorder caused by mutation in the ALDH3A2 gene that codes for human fatty aldehyde dehydrogenase (FALDH). Sjögren-Larsson syndrome patients lack FALDH, which catalyzes the oxidation of long-chain aliphatic aldehydes to fatty acids. The impaired FALDH activity leads to congenital ichthyosis, mental retardation and spasticity. The current lack of treatment is an impetus to develop gene therapy strategies by introducing functional FALDH into defective cells. We delivered human FALDH into keratinocytes of SLS patients using recombinant adeno-associated virus-2 vectors. Transduction of SLS keratinocytes resulted in an augmentation of FALDH activity comparable to phenotypically normal heterozygous carriers. Toxicity of long-chain aldehydes for FALDH-deficient cells decreased almost to the level of unaffected keratinocytes. Three-dimensional culture of corrected SLS keratinocytes revealed an ameliorated FALDH expression. These studies demonstrate the restoration of FALDH in human SLS cells supporting the concept of gene therapy as a potential future treatment option for SLS.

SPINK5, the defective gene in netherton syndrome, encodes multiple LEKTI isoforms derived from alternative pre-mRNA processing

The multidomain serine protease inhibitor lymphoepithelial Kazal-type related inhibitor (LEKTI) represents a key regulator of the proteolytic events occurring during epidermal barrier formation and hair development, as attested by the severe autosomal recessive ichthyosiform skin condition Netherton syndrome (NS) caused by mutations in its encoding gene, serine protease inhibitor Kazal-type 5 (SPINK5). Synthesized as a proprotein, LEKTI is rapidly cleaved intracellularly, thus generating a number of potentially bioactive fragments that are secreted. Here, we show that SPINK5 generates three classes of transcripts encoding three different LEKTI isoforms, which differ in their C-terminal portion. In addition to the previously described 15 domain isoform, SPINK5 encodes a shorter LEKTI isoform composed of only the first 13 domains, as well as a longer isoform carrying a 30-amino-acid residue insertion between the 13th and 14th inhibitory domains. We demonstrate that variable amounts of SPINK5 alternative transcripts are detected in all SPINK5 transcriptionally active tissues. Finally, we show that in differentiated cultured human keratinocytes all SPINK5 alternative transcripts are translated into protein and that the LEKTI precursors generate distinct secreted C-terminal proteolytic fragments from a similar cleavage site. Since several data indicate a biological role for the pro-LEKTI-cleaved polypeptides, we hypothesize that the alternative processing of the SPINK5 pre-messenger RNA represents an additional mechanism to further increase the structural and functional diversity of the LEKTI bioactive fragments.

Netherton syndrome in two Japanese siblings with a novel mutation in the SPINK5 gene: immunohistochemical studies of LEKTI and other epidermal molecules

BACKGROUND

Netherton syndrome (NS) is a severe autosomal recessive disorder characterized by ichthyosiform erythroderma, bamboo hair and atopy. The disease is caused by mutations in the SPINK5 gene, which encodes a putative serine protease inhibitor, LEKTI (lymphoepithelial Kazal-type-related inhibitor). Previous studies have clearly shown a crucial role for LEKTI in skin barrier formation.

OBJECTIVES

To identify pathogenic mutations in two Japanese siblings with NS, and further to investigate the consequences of the mutations at the protein level.

METHODS

To screen for mutations in the SPINK5 gene, all of its exons and splice junctions were amplified by polymerase chain reaction and directly sequenced. In addition, immunohistochemical staining of LEKTI, desmoglein (Dsg) 1 and elafin was performed with their specific antibodies.

RESULTS

Mutation analysis resulted in the identification of compound heterozygous mutations, Q713X and R790X, in the SPINK5 gene of both patients. The former one is a novel mutation. Immunohistochemical studies in one patient demonstrated a complete absence of LEKTI and a strong expression of elafin in the patient's skin. Dsg1 was normally expressed in our patient.

CONCLUSIONS

In this report, we describe compound heterozygous mutations in the SPINK5 gene in two Japanese siblings with NS. The result of immunohistochemistry shows LEKTI deficiency and upregulation of elafin in the skin of one patient. Furthermore, our data indicate that degradation of Dsg1 does not always occur in NS.