Using transgenic models to study the pathogenesis of keratin-based inherited skin diseases

Vitamin C compounds mixture prevents skin barrier alterations and inflammatory responses upon real life multi pollutant exposure

Cutaneous tissues is among the main target of outdoor stressors such as ozone (O3 ), particulate matter (PM), and ultraviolet radiation (UV) all involved in inducing extrinsic skin aging. Only a few reports have studied the multipollutant interaction and its effect on skin damage. In the present work, we intended to evaluate the ability of pollutants such as O3 and PM to further aggravate cutaneous UV damage. In addition, the preventive properties of a cosmeceutical formulation mixture (AOX mix) containing 15% vitamin C (L-ascorbic acid), 1% vitamin E (α-tocopherol) and 0.5% ferulic acid was also investigated. Skin explants obtained from three different subjects were exposed to 200 mJ UV light, 0.25 ppm O3 for 2 h, and 30 min of diesel engine exhaust (DEE), alone or in combination for 4 days (time point D1 and D4). The results showed a clear additive effect of O3 and DEE in combination with UV in terms of keratin 10, Desmocollin and Claudin loss. In addition, the multipollutant exposure significantly induced the inflammatory response measured as NLRP1/ASC co-localization suggesting the activation of the inflammasome machinery. Finally, the loss of Aquaporin3 was also affected by the combined outdoor stressors. Furthermore, daily topical pre-treatment with the AOX Mix significantly prevented the cutaneous changes induced by the multipollutants. In conclusion, this study is among the first to investigate the combined effects of three of the most harmful outdoor stressors on human skin and confirms that daily topical of an antioxidant application may prevent pollution-induced skin damage.

Alteration of Oral and Perioral Soft Tissue in Mice following Incisor Tooth Extraction

Oral and perioral soft tissues cooperate with other oral and pharyngeal organs to facilitate mastication and swallowing. It is essential for these tissues to maintain their morphology for efficient function. Recently, it was reported that the morphology of oral and perioral soft tissue can be altered by aging or orthodontic treatment. However, it remains unclear whether tooth loss can alter these tissues’ morphology. This study examined whether tooth loss could alter lip morphology. First, an analysis of human anatomy suggested that tooth loss altered lip morphology. Next, a murine model of tooth loss was established by extracting an incisor; micro-computed tomography revealed that a new bone replaced the extraction socket. Body weight was significantly lower in the tooth loss (UH) group than in the non-extraction control (NH) group. The upper lip showed a greater degree of morphological variation in the UH group. Proteomic analysis and immunohistochemical staining of the upper lip illustrated that S100A8/9 expression was higher in the UH group, suggesting that tooth loss induced lip inflammation. Finally, soft-diet feeding improved lip deformity associated with tooth loss, but not inflammation. Therefore, soft-diet feeding is essential for preventing lip morphological changes after tooth loss.

Gene expression analysis of skin grafts and cultured keratinocytes using synthetic RNA normalization reveals insights into differentiation and growth control

Background

Keratinocytes (KCs) are the most frequent cells in the epidermis, and they are often isolated and cultured in vitro to study the molecular biology of the skin. Cultured primary cells and various immortalized cells have been frequently used as skin models but their comparability to intact skin has been questioned. Moreover, when analyzing KC transcriptomes, fluctuation of polyA+ RNA content during the KCs’ lifecycle has been omitted.

Results

We performed STRT RNA sequencing on 10 ng samples of total RNA from three different sample types: i) epidermal tissue (split-thickness skin grafts), ii) cultured primary KCs, and iii) HaCaT cell line. We observed significant variation in cellular polyA+ RNA content between tissue and cell culture samples of KCs. The use of synthetic RNAs and SAMstrt in normalization enabled comparison of gene expression levels in the highly heterogenous samples and facilitated discovery of differences between the tissue samples and cultured cells. The transcriptome analysis sensitively revealed genes involved in KC differentiation in skin grafts and cell cycle regulation related genes in cultured KCs and emphasized the fluctuation of transcription factors and non-coding RNAs associated to sample types.

Conclusions

The epidermal keratinocytes derived from tissue and cell culture samples showed highly different polyA+ RNA contents. The use of SAMstrt and synthetic RNA based normalization allowed the comparison between tissue and cell culture samples and thus proved to be valuable tools for RNA-seq analysis with translational approach. Transciptomics revealed clear difference both between tissue and cell culture samples and between primary KCs and immortalized HaCaT cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1671-5) contains supplementary material, which is available to authorized users.

A case of bullous congenital ichthyosiform erythroderma (BCIE) caused by a mutation in the 1A helix initiation motif of keratin 1

Bullous congenital ichthyosiform erythroderma (BCIE) is an autosomally dominant inherited disorder characterized by erythematous, erosive, and bullous skin lesions over the entire body at birth and abnormal hyperkeratosis on the palmoplantar sufaces as the patient grows older. BCIE is caused by a mutation in the keratin 1 (K1) and/or keratin 10 (K10) genes, and most pathogenic mutations are found within the helix initiation and termination motifs of the central helical rod domain (K1 and K10) or the upstream H1 homology domain (K10). In addition to inherited cases, sporadic cases due to a new mutation account for approximately half the total cases of BCIE. We report herein a typical sporadic case of BCIE with erythroderma, erosion, and blisters on the entire body surface at birth and palmoplantar and flexuaral areas of hyperkeratosis in the later stage. We found in this case a novel mutation, 559C to T, at amino acid position 187, which resulted in a leucine to phenylalanine substitution within the helix initiation motif of K1.

Altered T cell differentiation and Notch signaling induced by the ectopic expression of keratin K10 in the epithelial cells of the thymus

Transgenic mice expressing hK10 under the keratin K5 promoter display several alterations in the epidermis including decreased cell proliferation, and reduced susceptibility to tumor development. Given that K5 promoter is also active in the epithelial cells of the thymus, we explored the possible alterations of the thymus because of K10 transgene expression. We found severe thymic alterations, which affect not only the thymic epithelial cells (TEC), but also thymocytes. We observed altered architecture and premature thymus involution in the transgenic mice associated with increased apoptosis and reduced proliferation of the thymocytes. Interestingly, prior to the development of this detrimental phenotype, thymocytes of the transgenic mice also displayed altered differentiation, which is aggravated later on. Molecular characterization of this phenotype indicated that Akt activity is reduced in TEC, but not in thymocytes. In addition, we also observed altered expression of Notch family members and some of their ligands both in TEC and T cells. This produces reduced Notch activity in TEC but increased Notch activity in thymocytes, which is detectable prior to the disruption of the thymic architecture. In addition, we also detect altered Notch expression in the epidermis of bK5hK10 transgenic mice. Collectively the present data indicate that keratin K10 may induce severe alterations not only in a cell autonomous manner, but also in neighboring cells by the modulation of signals involved in cell-cell interactions.

Overcoming functional redundancy to elicit pachyonychia congenita-like nail lesions in transgenic mice

Mutations affecting the coding sequence of intermediate filament (IF) proteins account for >30 disorders, including numerous skin bullous diseases, myopathies, neuropathies, and even progeria. The manipulation of IF genes in mice has been widely successful for modeling key features of such clinically distinct disorders. A notable exception is pachyonychia congenita (PC), a disorder in which the nail and other epithelial appendages are profoundly aberrant. Most cases of PC are due to mutations in one of the following keratin-encoding genes: K6, K16, and K17. Yet null alleles obliterating the function of both K6 genes (K6alpha and K6beta) or the K17 gene, as well as the targeted expression of a dominant-negative K6alpha mutant, elicit only a subset of PC-specific epithelial lesions (excluding that of the nail in mice). We show that newborn mice null for K6alpha, K6beta, and K17 exhibit severe lysis restricted to the nail bed epithelium, where all three genes are robustly expressed, providing strong evidence that this region of the nail unit is initially targeted in PC. Our findings point to significant redundancy among the multiple keratins expressed in hair and nail, which can be related to the common ancestry, clustered organization, and sequence relatedness of specific keratin genes.

Derivation of human embryonic germ cells: an alternative source of pluripotent stem cells

Based on evidence suggesting similarities to human embryonic stem cells, human embryonic germ (hEG) cells have been advocated as an alternative pluripotent stem cell resource but have so far received limited attention. To redress this imbalance, human fetal gonads were collected for the isolation and culture of primordial germ cells at 7-9 weeks postconception. We provide evidence for the derivation, culture, and differentiation of hEG cells in vitro. This evidence includes the expression of markers characteristic of pluripotent cells, the retention of normal XX or XY karyotypes, and the demonstration of pluripotency, as suggested by the expression of markers indicative of differentiation along the three germ lineages (ectoderm, mesoderm, and endoderm) and an associated loss of pluripotent markers. In assessing this differentiation, however, we also demonstrate a hitherto unacknowledged overlap in gene expression profiles between undifferentiated and differentiated cell types, highlighting the difficulty in ascribing cell lineage by gene expression analyses. Furthermore, we draw attention to the problems inherent in the management of these cells in prolonged culture, chiefly the difficulty in preventing spontaneous differentiation, which hinders the isolation of pure, undifferentiated clonal lines. While these data advocate the pursuit of pluripotent hEG cell studies with relevance to early human embryonic development, culture limitations carry implications for their potential applicability to ambitious cell replacement therapies.

Severe abnormalities in the oral mucosa induced by suprabasal expression of epidermal keratin K10 in transgenic mice

Previous studies have demonstrated that keratin K10 plays an important role in mediating cell signaling processes, since the ectopic expression of this keratin induces cell cycle arrest in proliferating cells in vitro and in vivo. However, apart from its well known function of providing epithelial cells with resilience to mechanical trauma, little is known about its possible roles in nondividing cells. To investigate what these might be, transgenic mice were generated in which the expression of K10 was driven by bovine K6beta gene control elements (bK6(beta)hK10). The transgenic mice displayed severe abnormalities in the tongue and palate but not in other K6-expressing cells such as those of the esophagus, nails, and hair follicles. The lesions in the tongue and palate included the cytolysis of epithelial suprabasal cells associated with an acute inflammatory response and lymphocyte infiltration. The alterations in the oral mucosa caused the death of transgenic pups soon after birth, probably because suckling was impaired. These anomalies, together with others found in the teeth, are reminiscent of the lesions observed in some patients with pachyonychia congenita, an inherited epithelial fragility associated with mutations in keratins K6 and K16. Although no epithelial fragility was observed in the bK6(beta)hK10 oral epithelia of the experimental mice, necrotic processes were seen. Collectively, these data show that the carefully regulated tissue- and differentiation-specific patterns displayed by the keratin genes have dramatic consequences on the biological behavior of epithelial cells and that changes in the specific composition of the keratin intermediate filament cytoskeleton can affect their physiology, in particular those of the oral mucosa.

Beyond structure: do intermediate filaments modulate cell signalling?

Intermediate filament (IF) proteins form the largest family of cytoskeletal proteins in mammalian cells. The function of these proteins has long been thought to be only structural. However, this single function does not explain their diverse tissue- and differentiation-specific expression patterns. Evidence is now emerging that IF also act as an important framework for the modulation and control of essential cell processes, in particular, signal transduction events. Here, we review the most recent developments in this growing and exciting new field.

Pairwise assembly determines the intrinsic potential for self-organization and mechanical properties of keratin filaments

Most type I and II keratin genes are spatially and temporally regulated in a pairwise manner in epithelial tissues, where they represent the major structural proteins. Epithelia can be partitioned into simple (single-layered) and complex (multilayered) types. We compared the structural and mechanical properties of natural keratin polymers occurring in complex (K5-K14) and simple (K8-K18) epithelia. The intrinsic properties of these distantly related keratin filaments, whether dispersed or bundled in vitro, were surprisingly similar in all respects when at high polymer concentration. When type I and II assembly partners were switched to give rise to mismatched polymers (K5-K18; K8-K14), the interfilament interactions, which determine the structural and mechanical properties of keratin polymers, were significantly altered. We also show that a K5-K16 polymer exhibits lesser elasticity than K5- K14, which may help explain the inability of K16 to fully rescue the skin blistering characteristic of K14 null mice. The property of self-interaction exhibited by keratin filaments is likely to assist their function in vivo and may account for the relative paucity of cytoplasmic and keratin-specific cross-linkers. Our findings underscore the fundamental importance of pairwise polymerization and have implications for the functional significance of keratin sequence diversity.

Epithelial-stromal tissue interaction in paramesonephric (Müllerian) epithelial differentiation

During organogenesis, the middle to caudal portion of Müllerian epithelium differentiates into uterine and vaginal epithelia in females. Functional differentiation of uterine and vaginal epithelia occurs in adulthood, and is regulated by 17beta-estradiol (E(2)) and progesterone. In this report, the roles of mesenchyme/stroma in differentiation of uterine and vaginal epithelia were studied in tissue recombination experiments. At birth, Müllerian epithelium was negative for uterine and vaginal epithelial markers. Tissue recombinant experiments showed that uterine and vaginal gene expression patterns were induced in neonatal Müllerian epithelium by the respective mesenchymes. Differentiated adult uterine and vaginal epithelia did not change their original gene expression in response to heterotypic mesenchymal induction. In the adult vagina, E(2) induced expression of involucrin, a CCAAT/enhancer-binding protein beta and cytokeratin 1 via estrogen receptor alpha (ERalpha). Tissue recombination experiments with wild-type and ERalpha knockout mice demonstrated that epithelial gene expression is regulated by E(2) via epithelial-stromal tissue interactions. Uterine/vaginal heterotypic tissue recombinations demonstrated that functional differentiation of uterine and vaginal epithelia required organ-specific stromal factors. In contrast, stromal signals regulating epithelial proliferation appeared to be nonspecific in the uterus and vagina.

Increased levels of keratin 16 alter epithelialization potential of mouse skin keratinocytes in vivo and ex vivo

The process of wound repair in adult skin is complex, involving dermal contraction and epithelial migration to repair the lesion and restore the skin's barrier properties. At the wound edge, keratinocytes undergo many changes that engender an epithelialization behavior. The type II keratin 6 and type I keratins 16 and 17 are induced well before cell migration begins, but the role of these proteins is not understood. Forced expression of human K16 in skin epithelia of transgenic mice has been shown to cause dose-dependent skin lesions concomitant with alterations in keratin filament organization and in cell adhesion. Here we show, with the use of a quantitative assay, that these transgenic mice show a delay in the closure of full-thickness skin wounds in situ compared with wild-type and low-expressing K16 transgenic mice. We adapted and validated an ex vivo skin explant culture system to better assess epithelialization in a wound-like environment. Transgenic K16 explants exhibit a significant reduction of keratinocyte outgrowth in this setting. This delay is transgene dose-dependent, and is more severe when K16 is expressed in mitotic compared with post-mitotic keratinocytes. Various lines of evidence suggest that the mechanism(s) involved is complex and not strictly cell autonomous. These findings have important implications for the function of K16 in vivo.

The 'ins' and 'outs' of intermediate filament organization

A major function shared by several types of cytoplasmic intermediate filaments (IFs) is to stabilize cellular architecture against the mechanical forces it is subjected to. As for other fibrous cytoskeletal arrays, a crucial determinant of this function is the spatial organization of IFs in the cytoplasm. However, very few crossbridging proteins are specific for IFs - most IF-associated proteins known to exert a structural role act to tether IFs to other major cytoskeletal elements, such as F-actin, microtubules or adhesion complexes. In addition, IFs are endowed with the ability to participate in their own organization. This intriguing property is probably connected to the unusual degree of sequence diversity and sequence-specific regulation that characterize IF genes and their proteins. This dependence upon a combination of extrinsic and intrinsic determinants contributes to distinguish IFs from other fibrous cytoskeletal polymers and is key to their function.

Forced expression of keratin 16 alters the adhesion, differentiation, and migration of mouse skin keratinocytes

Injury to the skin results in an induction of keratins K6, K16, and K17 concomitant with activation of keratinocytes for reepithelialization. Forced expression of human K16 in skin epithelia of transgenic mice causes a phenotype that mimics several aspects of keratinocyte activation. Two types of transgenic keratinocytes, with forced expression of either human K16 or a K16-C14 chimeric cDNA, were analyzed in primary culture to assess the impact of K16 expression at a cellular level. High K16-C14-expressing and low K16-expressing transgenic keratinocytes behave similar to wild type in all aspects tested. In contrast, high K16-expressing transgenic keratinocytes show alterations in plating efficiency and calcium-induced differentiation, but proliferate normally. Migration of keratinocytes is reduced in K16 transgenic skin explants compared with controls. Finally, a subset of high K16-expressing transgenic keratinocytes develops major changes in the organization of keratin filaments in a time- and calcium concentration-dependent manner. These changes coincide with alterations in keratin content while the steady-state levels of K16 protein remain stable. We conclude that forced expression of K16 in progenitor skin keratinocytes directly impacts properties such as adhesion, differentiation, and migration, and that these effects depend upon determinants contained within its carboxy terminus.

Introducing a null mutation in the mouse K6alpha and K6beta genes reveals their essential structural role in the oral mucosa

Mammalian genomes feature multiple genes encoding highly related keratin 6 (K6) isoforms. These type II keratins show a complex regulation with constitutive and inducible components in several stratified epithelia, including the oral mucosa and skin. Two functional genes, K6alpha and K6beta, exist in a head-to-tail tandem array in mouse genomes. We inactivated these two genes simultaneously via targeting and homologous recombination. K6 null mice are viable and initially indistinguishable from their littermates. Starting at two to three days after birth, they show a growth delay associated with reduced milk intake and the presence of white plaques in the posterior region of dorsal tongue and upper palate. These regions are subjected to greater mechanical stress during suckling. Morphological analyses implicate the filiform papillae as being particularly sensitive to trauma in K6alpha/K6beta null mice, and establish the complete absence of keratin filaments in their anterior compartment. All null mice die about a week after birth. These studies demonstrate an essential structural role for K6 isoforms in the oral mucosa, and implicate filiform papillae as being the major stress bearing structures in dorsal tongue epithelium.