Keratinocytes display normal proliferation, survival and differentiation in conditional β4-integrin knockout mice

Strategy for the Optimization of Read-Through Therapy for Junctional Epidermolysis Bullosa with COL17A1 Nonsense Mutation

Read-through therapy suppresses premature termination codons and induces read-through activity, consequently restoring missing proteins. Aminoglycosides are widely studied as read-through drugs in different human genetic disorders, including hereditary skin diseases. Our previous work revealed that aminoglycosides affect COL17A1 nonsense mutations and represent a therapeutic option to alleviate disease severity. However, the amount of restored type XVII collagen (C17) in C17-deficient junctional epidermolysis bullosa keratinocytes was <1% relative to that in normal keratinocytes and was achieved only after high-dose gentamicin treatment, which induced deep transcriptional changes. Therefore, in this study, we designed a strategy combining aminoglycosides with compounds known to reduce their side effects. We developed translational read-through-inducing drug cocktail, version 5 containing low dosage of aminoglycosides, CC-90009, NMDI-14, melatonin, and apocynin that was able to induce about 20% of missing C17 without cell toxicity or an effect on in vitro wound closure. Translational read-through-inducing drugs cocktail, version 5 significantly induced COL17A1 expression and reverted the proinflammatory phenotype of C17-deficient junctional epidermolysis bullosa keratinocytes. Evaluation of this drug cocktail regarding its stability, penetration, and efficacy as a topical treatment remains to be determined. Translational read-through-inducing drug cocktail, version 5 might represent an improved therapeutic strategy for junctional epidermolysis bullosa and for other genetic skin disorders.

METTL14-mediated N6-methyladenosine modification of Col17a1/Itgα6/Itgβ4 governs epidermal homeostasis

BACKGROUND

N6-methyladenosine (m6A) is the most abundant and reversible modification occurring in eukaryotic mRNAs, however, its functions in mammalian epidermal development are still not fully elucidated.

OBJECTIVE

To explore the role of METTL14 (Methyltransferase like 14), one of the m6A methyltransferases, in maintaining epidermal homeostasis.

METHODS

We constructed mice with Mettl14-inactivation in the epidermal basal cells. The phenotype was explored by H&E staining and immunofluorescence staining. To explore the underlying mechanisms, we performed RNA-seq, Ribosome profiling and MeRIP-seq on wild-type and Mettl14-inactivation epidermal keratinocytes. Moreover, HaCaT cells were used for in vitro validation.

RESULTS

Inactivation of Mettl14 in murine epidermis led to transient thicker epidermis and exhaustion of the epidermal stem cell pool. Interestingly, we found that the mRNA of type XVII collagen (Col17a1), integrin β4 (Itgβ4) and α6 (Itgα6) had m6A modifications, and the proteins expression were decreased in Mettl14-inactivated epidermis. Furthermore, in epidermis-specific Mettl4-inactivated mice, the epidermis was detached from the dermis and presented a phenotype similar to junctional epidermolysis bullosa (JEB), which may result from hemidesmosomes damage (decrease of COL17A1, ITGB4 and ITGA6). Knockdown of Mettl14 in HaCaT cells impaired the self-renewal and decreased the protein level of COL17A1, ITGB4 and ITGA6 and Itgβ4 knockdown inhibited colony formation.

CONCLUSION

Our study highlighted the role of METTL14 in the maintenance of epidermal homeostasis and identified its critical role through m6A-mediated translational inhibition of Col17a1, Itgβ4 and Itgα6. Our study suggested that METTL14 may be a potential therapeutic target for the treatment of hemidesmosomes-deficient diseases, such as JEB.

Amino Acid Substitution in the Cysteine-Rich Region of the Integrin β4 Subunit Causes Late-Onset Mild Junctional Epidermolysis Bullosa without Extracutaneous Involvement

Integrin α6β4, encoded by ITGA6 and ITGB4, is a transmembrane component of hemidesmosomes and plays an important role in connecting keratinocytes with extracellular matrix proteins. ITGB4 or ITGA6 biallelic pathogenic variants cause junctional epidermolysis bullosa (JEB) with pyloric atresia, which is associated with high lethality. Patients who survive usually develop JEB of intermediate severity and urorenal manifestations. In this study, we report a very rare subtype of late-onset, nonsyndromic JEB associated with a recurrent amino acid substitution in the highly conserved cysteine-rich tandem repeats of the integrin β4 subunit. Literature review shows that among the patients diagnosed with ITGB4 mutations, only two had no extracutaneous manifestations, and only two patients with JEB with pyloric atresia carried missense mutations located in cysteine-rich tandem repeats. We analyzed the consequences of the novel ITGB4 variant c.1642G>A, p.Gly548Arg, on the clinical phenotype, the predicted protein structure, cellular phenotype, and gene expression pattern to show its pathogenicity. The results indicated that the p.Gly548Arg amino acid substitution affected the protein structure of integrin β4 subunits and disrupted the stability of hemidesmosomes and in turn impaired the adhesion of keratinocytes. RNA-sequencing results indicated similar changes in extracellular matrix structure organization and differentiation in keratinocytes completely devoid of integrin β4 and with the amino acid substitution p.Gly548Arg, which further supports the dysregulation of the function of the integrin β4 subunit caused by p.Gly548Arg. Our results provided evidence for a late-onset, mild JEB subtype without extracutaneous manifestations and extend the ITGB4-related genotype-phenotype correlations.

Effects of an Adipose Mesenchymal Stem Cell-Derived Conditioned medium and TGF-β1 on Human Keratinocytes In Vitro

Human keratinocytes play a crucial role during skin wound healing and in skin replacement therapies. The secretome of adipose-derived stem cells (ASCs) has been shown to secrete pro-healing factors, among which include TGF-β1, which is essential for keratinocyte migration and the re-epithelialization of cutaneous wounds during skin wound healing. The benefits of an ASC conditioned medium (ASC-CM) are primarily orchestrated by trophic factors that mediate autocrine and paracrine effects in keratinocytes. Here, we evaluated the composition and the innate characteristics of the ASC secretome and its biological effects on keratinocyte maturation and wound healing in vitro. In particular, we detected high levels of different growth factors, such as HGF, FGFb, and VEGF, and other factors, such as TIMP1 and 4, IL8, PAI-1, uPA, and IGFBP-3, in the ASC-CM. Further, we investigated, using immunofluorescence and flow cytometry, the distinct effects of a human ASC-CM and/or synthetic TGF-β1 on human keratinocyte proliferation, migration, and cell apoptosis suppression. We demonstrated that the ASC-CM increased keratinocyte proliferation as compared to TGF-β1 treatment. Further, we found that the ASC-CM exerted cell cycle progression in keratinocytes via regulating the phases G1, S, and G2/M. In particular, cells subjected to the ASC-CM demonstrated increased DNA synthesis (S phase) compared to the TGF-β1-treated KCs, which showed a pronounced G0/G1 phase. Furthermore, both the ASC-CM and TGF-β1 conditions resulted in a decreased expression of the late differentiation marker CK10 in human keratinocytes in vitro, whereas both treatments enhanced transglutaminase 3 and loricrin expression. Interestingly, the ASC-CM promoted significantly increased numbers of keratinocytes expressing epidermal basal keratinocyte markers, such DLL1 and Jagged2 Notch ligands, whereas those ligands were significantly decreased in TGF-β1-treated keratinocytes. In conclusion, our findings suggest that the ASC-CM is a potent stimulator of human keratinocyte proliferation in vitro, particularly supporting basal keratinocytes, which are crucial for a successful skin coverage after transplantation. In contrast, TGF-β1 treatment decreased keratinocyte proliferation and specifically increased the expression of differentiation markers in vitro.

Mechanotransduction through hemidesmosomes during aging and longevity

Hemidesmosomes are structural protein complexes localized at the interface of tissues with high mechanical demand and shear forces. Beyond tissue anchoring, hemidesmosomes have emerged as force-modulating structures important for translating mechanical cues into biochemical and transcriptional adaptation (i.e. mechanotransduction) across tissues. Here, we discuss the recent insights into the roles of hemidesmosomes in age-related tissue regeneration and aging in C. elegans, mice and humans. We highlight the emerging concept of preserved dynamic mechanoregulation of hemidesmosomes in tissue maintenance and healthy aging.

Wnt/β-Catenin Signaling Stabilizes Hemidesmosomes in Keratinocytes

Hemidesmosomes (HDs) are adhesion complexes that promote epithelial-stromal attachment in stratified and complex epithelia, including the epidermis. In various biological processes, such as differentiation and migration of epidermal keratinocytes during wound healing or carcinoma invasion, quick assembly and disassembly of HDs are prerequisites. In this study, we show that inhibition of Wnt/β-catenin signaling disturbs HD organization in keratinocytes. Screening with inhibitors identified the depletion of HD components and HD-like structures through Wnt inhibition, but keratinocyte differentiation was not affected. Wnt inhibition significantly diminished plectin and type XVII collagen expression in the basal side of Wnt-inhibited cells and the dermo-epidermal junction of the Wnt-inactive murine basal epidermis. Similar to Wnt inhibition, PLEC-knockout cells or cells with plectin-type XVII collagen binding defects showed type XVII collagen reduction in the basal side of the cells, implying the possible involvement of Wnt/β-catenin signaling in HD assembly. Atypical protein kinase C inhibition ameliorated the phenotypes of Wnt-inhibited cells. These findings show that Wnt/β-catenin signaling regulates the localization of HD components in keratinocytes and that the atypical protein kinase C pathway is involved in Wnt inhibition‒induced HD disarrangement. Our study suggests that the Wnt signaling pathway could be a potential therapeutic target for treating HD-defective diseases, such as epidermolysis bullosa.

Laminin 332 Is Indispensable for Homeostatic Epidermal Differentiation Programs

The skin epidermis is attached to the underlying dermis by a laminin 332 (Lm332)-rich basement membrane. Consequently, loss of Lm332 leads to the severe blistering disorder epidermolysis bullosa junctionalis in humans and animals. Owing to the indispensable role of Lm332 in keratinocyte adhesion in vivo, the severity of the disease has limited research into other functions of the protein. We have conditionally disrupted Lm332 expression in basal keratinocytes of adult mice. Although blisters develop along the interfollicular epidermis, hair follicle basal cells provide sufficient anchorage of the epidermis to the dermis, making inducible deletion of the Lama3 gene compatible with life. Loss of Lm332 promoted the thickening of the epidermis and exaggerated desquamation. Global RNA expression analysis revealed major changes in the expression of keratins, cornified envelope proteins, and cellular stress markers. These modifications of the keratinocyte genetic program are accompanied by changes in cell shape and disorganization of the actin cytoskeleton. These data indicate that loss of Lm332-mediated progenitor cell adhesion alters cell fate and disturbs epidermal homeostasis.

The adhesive heterogeneity of different compartments of oral mucosal rete ridges

Rete ridges play a critical role in maintaining epidermal structure and mechanical properties. Notably, rete ridges can be divided into three compartments: the base, slope and tip. The present study aims to explore whether these three compartments have distinct adhesive functions. We collected 28 normal masticatory mucosae to prepare paraffin-embedded sections. Immunohistochemistry and immunofluorescent staining were used to analyse the expression pattern of integrin α6 and β4 in different compartments of the rete ridges. To observe whether the different compartments had distinct adhesive forces, dermal-epidermal junction separation experiments were performed by peeling the oral epithelium from the lamina propria after treatment with cold saline for 72 h. The results showed that integrin α6 and β4 prefer the basal layer keratinocytes closely adjacent to the base compartment of the rete ridges. The oral mucosal epithelium separated from the underlying lamina propria at the tip of rete ridges when they were peeled after the cold saline treatment. In conclusion, the adhesive force of the basal layer keratinocytes at the base of the rete ridges is stronger than at the tip.

Expression of keratins 8, 18, and 19 in epithelia of atrophic oral lichen planus

Keratins form intermediate filaments of the cytoskeleton in keratinocytes and have roles in cell structure, signaling, intracellular transport, and cell death. Oral lichen planus (OLP) is an oral inflammatory disease with derangements in basal keratinocytes and disruption of the basal membrane. Here, we focused on epithelial expression of keratins 8, 18, and 19 because these proteins are known to modulate cell death. Biopsies were taken from buccal oral mucosa of persons with normal oral mucosa (n = 10) or atrophic OLP (n = 10). Cultured normal oral keratinocytes (n = 4) showed expression of mRNA and protein for keratins 8, 18, and 19. Immunohistochemistry showed consistent staining for keratins 8 and 18 in basal keratinocytes of normal oral mucosa. In OLP, staining for keratin (K)8 was mostly negative and staining for K18 was weak. Keratin 19 was expressed irregularly in most biopsies of normal oral mucosa and not at all in OLP. Several mononuclear leukocytes in the cellular infiltrate showed membrane staining for K8 and K18. Positive staining for K16 confirmed partial collapse of the basal cell layer in OLP. The basal cell niche in OLP therefore appeared to be partly populated with keratinocytes demonstrating a higher degree of differentiation (K8^-  K18^-  K19^-  K16⁺ ); consequently, such areas may be more susceptible to the action of cell death factors released from the cell infiltrate as a result of lacking the protective, normal keratin present in the basal epithelial cell layer of normal oral mucosa.

Role of Integrins in Resistance to Therapies Targeting Growth Factor Receptors in Cancer

Integrins contribute to cancer progression and aggressiveness by activating intracellular signal transduction pathways and transducing mechanical tension forces. Remarkably, these adhesion receptors share common signaling networks with receptor tyrosine kinases (RTKs) and support their oncogenic activity, thereby promoting cancer cell proliferation, survival and invasion. During the last decade, preclinical studies have revealed that integrins play an important role in resistance to therapies targeting RTKs and their downstream pathways. A remarkable feature of integrins is their wide-ranging interconnection with RTKs, which helps cancer cells to adapt and better survive therapeutic treatments. In this context, we should consider not only the integrins expressed in cancer cells but also those expressed in stromal cells, since these can mechanically increase the rigidity of the tumor microenvironment and confer resistance to treatment. This review presents some of these mechanisms and outlines new treatment options for improving the efficacy of therapies targeting RTK signaling.

ITGB4 deficiency in bronchial epithelial cells directs airway inflammation and bipolar disorder-related behavior

BACKGROUND

Chronic persistent airway inflammation has been associated with the comorbidity of asthma and bipolar disorder (BD). However, the direct relevance between airway inflammation and BD-like psychiatric comorbidity is almost unknown. Integrin β4 (ITGB4) is downregulated on the airway epithelial of asthma patients, which might play a critical role in the parthenogenesis of airway inflammation. So this study aimed to examine the role of ITGB4 deficiency in mediating airway inflammation and further leading to the BD-like behaviors.

METHODS

ITGB4^-/- mice were generated by mating ITGB4^fl/fl mice with CCSP-rtTA^tg/-/TetO-Cretg/tg mice. Mania-like behavior tests were performed, including hyperlocomotion, D-amphetamine-induced hyperactivity, open-field test, and elevated plus-maze test. Depressive-like behavior tests were carried out, including sucrose preference, forced swimming, and learned helplessness. Inflammatory cells (Th17, Th1, Th2) in the lung were examined by flow cytometry. Futhermore, inflammatory cytokines (IL-4, IL-13) in bronchoalveolar lavage fluid and sera were detected by ELISA. Protein expression of the IL-4Rα on choroid plexus, microglial marker (IBA1), and synapse-associated proteins (synaptophysin, SYP) in the hippocampus and prefrontal cortex were examined by western blotting. Additionally, proinflammatory cytokines (IL-1β, IL-6, and TNF-α) in the hippocampus and prefrontal cortex were detected by immunohistochemistry. Inflammatory disorder in the lung, hippocampus, and prefrontal cortex was tested by hematoxylin and eosin (H&E) staining. And cell apoptosis in the hippocampus and prefrontal cortex was measured by TUNEL test.

RESULTS

ITGB4^-/- mice exhibited mania-like behavior, including hyperlocomotion, D-amphetamine-induced hyperactivity, and reduced anxiety-like behavior. While under stressful conditions, ITGB4^-/- mice manifested depressive-like behavior, including anhedonia, behavioral despair, and enhanced learned helplessness. At the same time, ITGB4^-/- mice mainly exerted Th2-type inflammation in periphery, like the number and major cytokines IL-4 and IL-13 of Th2-type inflammation. ITGB4^-/- mice also showed a significant increase of microglia and pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α in the hippocampus and prefrontal cortex. Additionally, neuron damage, increased neuron apoptosis, and the decrease of SYP were found in ITGB4^-/- mice.

CONCLUSIONS

These findings confirmed that airway inflammatory induced by ITGB4 deficiency is the important incentive for the BD-like behavior during asthma pathogenesis. The ITGB4-deficient mice provide a validated animal model for us to study the possible mechanism of BD-like psychiatric comorbidity of asthma patients.

Complexes of α6β4 integrin and vimentin act as signaling hubs to regulate epithelial cell migration

We find that clusters of β4 integrin, organized into distinct puncta, localize along vimentin filaments within lamellipodia at the cell edge of A549 cells, as assessed by interferometric photoactivated localization microscopy. Moreover, puncta and vimentin filaments exhibit a dynamic interplay in live cells, as viewed by structured-illumination microscopy, with β4 integrin puncta that associate with vimentin persisting for longer than those that do not. Interestingly, in A549 cells β4 integrin regulates vimentin cytoskeleton organization. When β4 integrin is knocked down there is a loss of vimentin filaments from lamellipodia. However, in these conditions, vimentin filaments instead concentrate around the nucleus. Although β4 integrin organization is unaffected in vimentin-deficient A549 cells, such cells move in a less-directed fashion and exhibit reduced Rac1 activity, mimicking the phenotype of β4 integrin-deficient A549 cells. Moreover, in vimentin-deficient cells, Rac1 fails to cluster at sites enriched in α6β4 integrin heterodimers. The aberrant motility of both β4 integrin and vimentin-deficient cells is rescued by expression of active Rac1, leading us to propose that complexes of β4 integrin and vimentin act as signaling hubs, regulating cell motility behavior.

ITGB4 is essential for containing HDM-induced airway inflammation and airway hyperresponsiveness

Airway epithelial cells play a significant role in the pathogenesis of asthma. Although the structural and functional defects of airway epithelial cells have been postulated to increase asthma susceptibility and exacerbate asthma severity, the mechanism and implication of these defects remain uncertain. Integrin β4 (ITGB4) is a structural adhesion molecule that is downregulated in the airway epithelium of asthma patients. In this study, we demonstrated that ITGB4 deficiency leads to severe allergy-induced airway inflammation and airway hyper-responsiveness (AHR) in mice. After house dust mite (HDM) challenge, epithelial cell-specific ITGB4-deleted mice showed increased lymphocyte, eosinophil, and neutrophil infiltration into lung compared with that of the wild-type mice. ITGB4 deficiency also resulted in increased expression of the Th2 cytokine IL-4, IL-13, and the Th17 cytokine IL-17A in the lung tissue and in the T cells after HDM challenge. The aggravated inflammation in ITGB4 defect mice was partly caused by enhanced disrupted epithelial barrier integrity after HDM stress, which induced the increased thymic stromal lymphopoietin secretion from airway epithelial cells. This study therefore demonstrates that ITGB4 plays a pivotal role in containing allergen-mediated lung inflammation and airway hyper-responsiveness in allergic asthma.

Knockout of the Arp2/3 complex in epidermis causes a psoriasis-like disease hallmarked by hyperactivation of transcription factor Nrf2

The Arp2/3 complex assembles branched actin filaments, which are key to many cellular processes, but its organismal roles remain poorly understood. Here, we employed conditional Arpc4 knockout mice to study the function of the Arp2/3 complex in the epidermis. We found that depletion of the Arp2/3 complex by knockout of Arpc4 results in skin abnormalities at birth that evolve into a severe psoriasis-like disease hallmarked by hyperactivation of transcription factor Nrf2. Knockout of Arpc4 in cultured keratinocytes was sufficient to induce nuclear accumulation of Nrf2, upregulation of Nrf2 target genes and decreased filamentous actin levels. Furthermore, pharmacological inhibition of the Arp2/3 complex unmasked the role of branched actin filaments in Nrf2 regulation. Consistent with this, we revealed that Nrf2 associates with the actin cytoskeleton in cells and binds to filamentous actin in vitro Finally, we discovered that Arpc4 is downregulated in both human and mouse psoriatic epidermis. Thus, the Arp2/3 complex affects keratinocyte shape and transcriptome through an actin-based cell-autonomous mechanism that influences epidermal morphogenesis and homeostasis.

α6β4 Integrin Regulates the Collective Migration of Epithelial Cells

α₆β₄ integrin is localized in a unique punctate distribution at the cell-substratum interface along the leading front of single, front-rear-polarized A549 cells. These puncta are interspersed between focal adhesions and lack association with the actin cytoskeleton. Knockdown of β₄ integrin in A549 cells inhibits their directed migration, with knockdown cells exhibiting large focal adhesions and reduced actin dynamics. Despite these changes, the speed of knockdown cells is equivalent to control cells. Interestingly, in such cells, α₆ integrin retains its punctate distribution. Moreover, in β₄ integrin knockdown cells, we observe a loss of β₁ integrin from focal adhesions and an enhanced association with α₆ integrin. We confirmed the switch in the β integrin binding partner of α₆ integrin in the knockdown cells by immunoprecipitation. We next investigated the role of β₄ integrin in collective cell migration. Wounded monolayers of β₄ integrin knockdown cells exhibit reduced collective migration compared with controls. When we forced expression of β₄ integrin in the leader cells of wounded monolayers, collective migration was restored. Similarly, forced expression of β₄ integrin in primary rat alveolar epithelial cells also promotes collective cell migration. In addition, we interrogated the pathway by which β₄ integrin regulates A549 cell-directed migration. Constitutively active Ras-related C3 botulinum toxin substrate 1 rescues motility defects resulting from β₄ integrin deficiency. Together, our results support the hypothesis that α₆β₄ integrin is a positive regulator of collective cell migration of A549 cells through influence on signal pathways in leader cells.

Contractility Assay for Established Myoepithelial Cell Lines

The capacity of mammary myoepithelial cells to contract in response to suckling stimuli is essential for lactation. We describe here a protocol for studying the contractile activity of myoepithelial cells in vitro. This protocol includes the establishment of stable myoepithelial cell lines from mouse mammary glands and quantitative evaluation of the contraction and subsequent relaxation of cultured myoepithelial cells in response to oxytocin. It can be used for analyses of mouse mutants with gene deletions or overexpression altering myoepithelial cell function.

Tension in Cancer

Integrins represent a large family of cell receptors that mediate adhesion to the extracellular matrix (ECM), thereby modulating a variety of cellular functions that are required for proliferation, migration, malignant conversion and invasiveness. During tumorigenesis the conversion of a tumor cell from sessile, stationary phenotype to an invasive phenotype requires the ability of tumor cells to interact with their environment in order to transduce signals from the ECM into the cells. Hence, there is increasing evidence that changes in the composition, topography and tension of tumor matrix can be sensed by integrin receptors, leading to the regulation of intracellular signalling events which subsequently help to fuel cancer progression. The fact that intracellular signals perceived from integrin ligand binding impact on almost all steps of tumor progression, including tumor cell proliferation, survival, metastatic dissemination and colonization of a metastatic niche, renders integrins as ideal candidates for the development of therapeutic agents. In this review we summarize the role of integrins in cancer with the special focus on cancer therapies and the recent progress that has been made in the understanding of “integrin-induced tension in cancer”. Finally, we conclude with clinical evidence for the role of integrin-mediated mechanotransduction in the development of therapy-resistant tumors.

Epigenetic Regulation of Epidermal Stem Cell Biomarkers and Their Role in Wound Healing

As an actively renewable tissue, changes in skin architecture are subjected to the regulation of stem cells that maintain the population of cells responsible for the formation of epidermal layers. Stems cells retain their self-renewal property and express biomarkers that are unique to this population. However, differential regulation of the biomarkers can initiate the pathway of terminal cell differentiation. Although, pockets of non-clarity in stem cell maintenance and differentiation in skin still exist, the influence of epigenetics in epidermal stem cell functions and differentiation in skin homeostasis and wound healing is clearly evident. The focus of this review is to discuss the epigenetic regulation of confirmed and probable epidermal stem cell biomarkers in epidermal stratification of normal skin and in diseased states. The role of epigenetics in wound healing, especially in diseased states of diabetes and cancer, will also be conveyed.

Focal-adhesion-independent integrin-αv regulation of FAK and c-Myc is necessary for 3D skin formation and tumor invasion

Integrins play crucial roles in epithelial adhesion, proliferation, wound healing and cancer. In the epidermis, the roles of many integrin subunits are incompletely defined and mechanistic details regarding their functions are lacking. We performed a multiplexed small hairpin (sh)RNA screen to define roles for each subunit in human organotypic skin. We show that integrin-αv (also known as ITGAV) heterodimers are essential for epidermal generation, with integrin-αv loss driving a keratinocyte G1-S cell cycle block. Surprisingly, integrin αv is not localized within keratinocyte focal adhesions, and instead maintains proliferation by controlling cellular (c)-Myc translation through FAK, p38β and p90RSK1. These phenotypes depend only on the binding partners of integrin-αv--integrin β5 and integrin β6 (also known as ITGB5 and ITGB6, respectively). Through inducible depletion of integrin αv in both normal organotypic epidermis and Ras-driven invasive neoplasia, we show that integrin αv is required for de novo tissue generation and neoplastic invasion but that it is dispensable for epidermal maintenance. Heterodimers of integrin αv with integrin β5 (integrin αvβ5) or integrin β6 (integrin αvβ6) are required to similar extents for neoplastic invasion, thus identifying integrin αvβ5 and integrin αvβ6 heterodimers as potential therapeutic targets for epidermal squamous cell carcinoma.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Keratins Stabilize Hemidesmosomes through Regulation of β4-Integrin Turnover

Epidermal integrity and wound healing depend on remodeling of cell-matrix contacts including hemidesmosomes. Mutations in β4-integrin and plectin lead to severe epidermolysis bullosa (EB). Whether mutations in keratins K5 or K14, which cause EB simplex, also compromise cell-matrix adhesion through altering hemidesmosomal components is not well investigated. In particular, the dependence of β4-integrin endocytosis and turnover on keratins remains incompletely understood. Here, we show that the absence of keratins causes loss of plectin-β4-integrin interaction and elevated β4-integrin phosphorylation at Ser1354 and Ser1362. This triggered a caveolin-dependent endocytosis of β4-integrin but not of other integrins through Rab5 and Rab11 compartments in keratinocytes. Expressing a phospho-deficient β4-integrin mutant reduces β4-integrin endocytosis and rescues plectin localization in keratin-free cells. β4-integrin phosphorylation in the absence of keratins resulted from elevated Erk1/2 activity downstream of increased EGFR and PKCα signaling. Further, increased Erk1/2 phosphorylation and altered plectin localization occur in keratin-deficient mouse epidermis in vivo. Strikingly, expression of the K14-R125P EBS mutant also resulted in plectin mislocalization and elevated β4-integrin turnover, suggesting disease relevance. Our data underscore a major role of keratins in controlling β4-integrin endocytosis involving a plectin-Erk1/2-dependent mechanism relevant for epidermal differentiation and pathogenesis.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Remodeling of keratin-coupled cell adhesion complexes

Epithelial cells constitute the main barrier between the inside and outside of organs, acting as gatekeepers of their structure and integrity. Hemidesmosomes and desmosomes are respectively cell-matrix and cell-cell adhesions coupled to the intermediate filament cytoskeleton. These adhesions ensure mechanical integrity of the epithelial barrier. Although desmosomes and hemidesmosomes are essential in maintaining strong cell-cell and cell-matrix adhesions, there is an emerging view that they should be remodeled in order to maintain epithelial homeostasis. Here we review the adhesion properties of desmosomes and hemidesmosomes, as well as the mechanisms driving their remodeling. We also discuss recent data suggesting that keratin-coupled adhesion complexes can sense the biomechanical cellular environment and participate in the cellular response to such external cues.

The integrin adhesome: from genes and proteins to human disease

The adhesive interactions of cells with their environment through the integrin family of transmembrane receptors have key roles in regulating multiple aspects of cellular physiology, including cell proliferation, viability, differentiation and migration. Consequently, failure to establish functional cell adhesions, and thus the assembly of associated cytoplasmic scaffolding and signalling networks, can have severe pathological effects. The roles of specific constituents of integrin-mediated adhesions, which are collectively known as the 'integrin adhesome', in diverse pathological states are becoming clear. Indeed, the prominence of mutations in specific adhesome molecules in various human diseases is now appreciated, and experimental as well as in silico approaches provide insights into the molecular mechanisms underlying these pathological conditions.

Signaling events mediated by α3β1 integrin are essential for mammary tumorigenesis

The constitutive activation of β-catenin signaling in the mammary basal epithelial cell layer in transgenic K5ΔNβcat mice leads to basal-type tumor development. Integrins of the β1 family and integrin-mediated signaling events have an important role in breast tumor growth and progression. We show here that the deletion of α3β1 integrin, a major laminin receptor, from the basal layer of the mammary epithelium of K5ΔNβcat mice completely prevented the tumorigenesis induced by β-catenin signaling. Moreover, the depletion of α3β1 integrin from a spontaneously transformed mouse mammary basal epithelial cell line (MEC) prevented the cells from forming colonies in soft agar and greatly reduced tumor development in orthotopic grafts. Inhibition of the integrin signaling intermediates Rac1 or PAK1 (P21-activated Kinase 1) in MEC affected tumor cell growth in soft agar, whereas the expression of activated forms of these effectors in α3-depleted cells rescued the capacity of these cells to grow in non-adherent conditions. Similarly, the tumorigenic potential of α3-depleted cells was restored by the expression of activated PAK1, as assessed by orthotopic transplantation assay. In three-dimensional Matrigel culture, MEC survival and proliferation were affected by the depletion of α3β1 integrin, which also significantly decreased the activation of focal adhesion kinase (FAK), mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK). Our data suggest that the activation of signaling cascades downstream from α3β1 and involving the Rac1/PAK1 pathway, MAPK and JNK, promotes prosurvival and proproliferative signals required for the malignant growth of basal mammary epithelial cells, providing further insight into the molecular mechanisms underlying breast cancer initiation and progression.

Focal adhesion complex proteins in epidermis and squamous cell carcinoma

Focal adhesions (FAs) are large, integrin-containing, multi-protein assemblies spanning the plasma membrane that link the cellular cytoskeleton to surrounding extracellular matrix. They play critical roles in adhesion and cell signaling and are major regulators of epithelial homeostasis, tissue response to injury, and tumorigenesis. Most integrin subunits and their associated FA proteins are expressed in skin, and murine genetic models have provided insight into the functional roles of FAs in normal and neoplastic epidermis. Here, we discuss the roles of these proteins in normal epidermal proliferation, adhesion, wound healing, and cancer. While many downstream signaling mechanisms remain unclear, the critically important roles of FAs are highlighted by the development of therapeutics targeting FAs for human cancer.

Collagen VII plays a dual role in wound healing

Although a host of intracellular signals is known to contribute to wound healing, the role of the cell microenvironment in tissue repair remains elusive. Here we employed 2 different mouse models of genetic skin fragility to assess the role of the basement membrane protein collagen VII (COL7A1) in wound healing. COL7A1 secures the attachment of the epidermis to the dermis, and its mutations cause a human skin fragility disorder coined recessive dystrophic epidermolysis bullosa (RDEB) that is associated with a constant wound burden. We show that COL7A1 is instrumental for skin wound closure by 2 interconnected mechanisms. First, COL7A1 was required for re-epithelialization through organization of laminin-332 at the dermal-epidermal junction. Its loss perturbs laminin-332 organization during wound healing, which in turn abrogates strictly polarized expression of integrin α6β4 in basal keratinocytes and negatively impacts the laminin-332/integrin α6β4 signaling axis guiding keratinocyte migration. Second, COL7A1 supported dermal fibroblast migration and regulates their cytokine production in the granulation tissue. These findings, which were validated in human wounds, identify COL7A1 as a critical player in physiological wound healing in humans and mice and may facilitate development of therapeutic strategies not only for RDEB, but also for other chronic wounds.

Use of an in vivo animal model for assessing the role of integrin α(6)β(4) and syndecan-1 in early steps in papillomavirus infection

Human papillomaviruses (HPV) are small DNA tumor viruses. HPV infection requires entry of virions into epithelial host cells that support the viral life cycle. Here, we used an in vivo mouse model, in which HPV pseudoviruses (PVs) are scored for their ability to transduce reporter genes, to test the role of various cellular proteins in entry. We initially investigated the role of integrin α(6)β(4) in mediating early steps of HPV infection. Deficiency of integrin α(6)β(4) is modestly but significantly suppressed reporter-gene transduction by PVs in conditional integrin β(4) knockout mice. We also investigated the role of syndecan 1, a heparin sulfate proteoglycan (HSPG) for its role in HPV infection. We did not see a significant reduction in reporter-gene transduction by PVs in syndecan-1 null mice. This indicates that this HSPG is not essential for early steps in HPV infection, but does not discount a need of other HSPGs in mediating HPV infection.

Keratins mediate localization of hemidesmosomes and repress cell motility

The keratin (K)-hemidesmosome (HD) interaction is crucial for cell-matrix adhesion and migration in several epithelia, including the epidermis. Mutations in constituent proteins cause severe blistering skin disorders by disrupting the adhesion complex. Despite extensive studies, the role of keratins in HD assembly and maintenance is only partially understood. Here we address this issue in keratinocytes in which all keratins are depleted by genome engineering. Unexpectedly, such keratinocytes maintain many characteristics of their normal counterparts. However, the absence of the entire keratin cytoskeleton leads to loss of plectin from the hemidesmosomal plaque and scattering of the HD transmembrane core along the basement membrane zone. To investigate the functional consequences, we performed migration and adhesion assays. These revealed that, in the absence of keratins, keratinocytes adhere much faster to extracellular matrix substrates and migrate approximately two times faster compared with wild-type cells. Reexpression of the single keratin pair K5 and K14 fully reversed the above phenotype. Our data uncover a role of keratins, which to our knowledge is previously unreported, in the maintenance of HDs upstream of plectin, with implications for epidermal homeostasis and pathogenesis. They support the view that the downregulation of keratins observed during epithelial-mesenchymal transition supports the migratory and invasive behavior of tumor cells.

Collagen XVII (BP180) modulates keratinocyte expression of the proinflammatory chemokine, IL-8

Collagen XVII (COL17), a transmembrane protein expressed in epidermal keratinocytes (EK), is targeted by pathogenic autoantibodies in bullous pemphigoid. Treatment of EK with anti-COL17 autoantibodies triggers the production of proinflammatory cytokines. In this study, we test the hypothesis that COL17 is involved in the regulation of the EK proinflammatory response, using IL-8 expression as the primary readout. The absence of COL17 in EK derived from a junctional epidermolysis bullosa patient or shRNA-mediated knockdown of COL17 in normal EK resulted in a dysregulation of IL-8 responses under various conditions. The COL17-deficient cells showed an abnormally high IL-8 response after treatment with lipopolysaccharide (LPS), ultraviolet-B radiation or tumor necrosis factor, but exhibited a blunted IL-8 response to phorbol 12-myristate 13-acetate exposure. Induction of COL17 expression in COL17-negative EK led to a normalization of the LPS-induced proinflammatory response. Although α6β4 integrin was found to be up-regulated in COL17-deficient EK, siRNA-mediated knockdown of the α6 and β4 subunits revealed that COL17's effects on the LPS IL-8 response are not dependent on this integrin. In LPS-treated cells, inhibition of NF-kappa B activity in COL17-negative EK resulted in a normalization of their IL-8 response, and expression of an NF-kappa B-driven reporter was shown to be higher in COL17-deficient, compared with normal EK. These findings support the hypothesis that COL17 plays an important regulatory role in the EK proinflammatory response, acting largely via NF-kappa B. Future investigations will focus on further defining the molecular basis of this novel control network.

α6β4 integrin, a master regulator of expression of integrins in human keratinocytes

Three major laminin and collagen-binding integrins in skin (α6β4, α3β1, and α2β1) are involved in keratinocyte adhesion to the dermis and dissemination of skin cells during wound healing and/or tumorigenesis. Knockdown of α6 integrin in keratinocytes not only results in motility defects but also leads to decreased surface expression of the α2, α3, and β4 integrin subunits. Whereas α2 integrin mRNA levels are decreased in α6 integrin knockdown cells, α3 and β4 integrin mRNAs levels are unaffected. Expression of either α6 or α3 integrin in α6 integrin knockdown cells restores α2 integrin mRNA levels. Moreover, re-expression of α6 integrin increases β4 integrin protein at the cell surface, which results in an increase in α3 integrin expression via activation of initiation factor 4E-binding protein 1. Our data indicate that the α6β4 integrin is a master regulator of transcription and translation of other integrin subunits and underscore its pivotal role in wound healing and cancer.

Blood pressure influences end-stage renal disease of Cd151 knockout mice

Podocytes of the kidney adhere tightly to the underlying glomerular basement membrane (GBM) in order to maintain a functional filtration barrier. The clinical importance of podocyte binding to the GBM via an integrin-laminin-actin axis has been illustrated in models with altered function of α3β1 integrin, integrin-linked kinase, laminin-521, and α-actinin 4. Here we expanded on the podocyte-GBM binding model by showing that the main podocyte adhesion receptor, integrin α3β1, interacts with the tetraspanin CD151 in situ in humans. Deletion of Cd151 in mouse glomerular epithelial cells led to reduced adhesive strength to laminin by redistributing α3β1 at the cell-matrix interface. Moreover, in vivo podocyte-specific deletion of Cd151 led to glomerular nephropathy. Although global Cd151-null B6 mice were not susceptible to renal disease, as has been shown previously, increasing blood and transcapillary filtration pressure induced nephropathy in these mice. Importantly, blocking the angiotensin-converting enzyme in renal disease-susceptible global Cd151-null FVB mice prolonged their median life span. Together, these results establish CD151 as a crucial modifier of integrin-mediated adhesion of podocytes to the GBM and show that blood pressure is an important factor in the initiation and progression of Cd151 knockout-induced nephropathy.

Deconstructing the skin: cytoarchitectural determinants of epidermal morphogenesis

To provide a stable environmental barrier, the epidermis requires an integrated network of cytoskeletal elements and cellular junctions. Nevertheless, the epidermis ranks among the body's most dynamic tissues, continually regenerating itself and responding to cutaneous insults. As keratinocytes journey from the basal compartment towards the cornified layers, they completely reorganize their adhesive junctions and cytoskeleton. These architectural components are more than just rivets and scaffolds - they are active participants in epidermal morphogenesis that regulate epidermal polarization, signalling and barrier formation.

Integrin α6β4 identifies an adult distal lung epithelial population with regenerative potential in mice

Laminins and their integrin receptors are implicated in epithelial cell differentiation and progenitor cell maintenance. We report here that a previously unrecognized subpopulation of mouse alveolar epithelial cells (AECs) expressing the laminin receptor α6β4, but little or no pro-surfactant C (pro-SPC), is endowed with regenerative potential. Ex vivo, this subpopulation expanded clonally as progenitors but also differentiated toward mature cell types. Integrin β4 itself was not required for AEC proliferation or differentiation. An in vivo embryonic lung organoid assay, which we believe to be novel, was used to show that purified β4+ adult AECs admixed with E14.5 lung single-cell suspensions and implanted under kidney capsules self-organized into distinct Clara cell 10-kDa secretory protein (CC10+) airway-like and SPC+ saccular structures within 6 days. Using a bleomycin model of lung injury and an SPC-driven inducible cre to fate-map AECs, we found the majority of type II AECs in fibrotic areas were not derived from preexisting type II AECs, demonstrating that SPC- progenitor cells replenished type II AECs during repair. Our findings support the idea that there is a stable AEC progenitor population in the adult lung, provide in vivo evidence of AEC progenitor cell differentiation after parenchymal injury, and identify a strong candidate progenitor cell for maintenance of type II AECs during lung repair.

Control of mammary myoepithelial cell contractile function by α3β1 integrin signalling

In the functionally differentiated mammary gland, basal myoepithelial cells contract to eject the milk produced by luminal epithelial cells from the body. We report that conditional deletion of a laminin receptor, α3β1 integrin, from myoepithelial cells leads to low rates of milk ejection due to a contractility defect but does not interfere with the integrity or functional differentiation of the mammary epithelium. In lactating mammary gland, in the absence of α3β1, focal adhesion kinase phosphorylation is impaired, the Rho/Rac balance is altered and myosin light-chain (MLC) phosphorylation is sustained. Cultured mammary myoepithelial cells depleted of α3β1 contract in response to oxytocin, but are unable to maintain the state of post-contractile relaxation. The expression of constitutively active Rac or its effector p21-activated kinase (PAK), or treatment with MLC kinase (MLCK) inhibitor, rescues the relaxation capacity of mutant cells, strongly suggesting that α3β1-mediated stimulation of the Rac/PAK pathway is required for the inhibition of MLCK activity, permitting completion of the myoepithelial cell contraction/relaxation cycle and successful lactation. This is the first study highlighting the impact of α3β1 integrin signalling on mammary gland function.

Structure-function analysis of tetraspanin CD151 reveals distinct requirements for tumor cell behaviors mediated by α3β1 versus α6β4 integrin

The basement membrane protein laminin-332 (laminin-5) mediates both stable cell adhesion and rapid cell migration and thus has the potential to either restrain or promote tumor cell metastasis. The major cellular receptors for laminin-332 are integrin α3β1, which mediates rapid tumor cell migration, and integrin α6β4, which often mediates stable cell attachment. Tetraspanin protein CD151 interacts directly with both α3β1 and α6β4 integrins and with other tetraspanins, thereby promoting α3β1 and α6β4 association with tetraspanin-enriched microdomains on the cell surface. To explore the possibility of selectively modulating tumor cell responses to laminin-332, we re-expressed a series of CD151 mutants in epidermoid carcinoma cells with near total, RNAi-mediated silencing of endogenous CD151. The interactions of CD151 with its integrin partners or its interactions with other tetraspanins were selectively disrupted by specific mutations in the CD151 large extracellular loop (EC2 domain) or in intracellular CD151 palmitoylation sites, respectively. CD151-integrin association and CD151-tetraspanin association were both important for α3β1 integrin-dependent initial adhesion and rapid migration on laminin-332. Remarkably, however, only CD151-integrin association was required for stable, α6β4 integrin-dependent cell attachment on laminin-332. In addition, we found that a QRD amino acid motif in the CD151 EC2 domain, which had been thought to be crucial for CD151-integrin interaction, is not essential for CD151-integrin association or for the ability of CD151 to promote several different integrin functions. These new data suggest potential strategies for selectively modulating migratory cell responses to laminin-332, while leaving stable cell attachment on laminin-332 intact.

Genetic analyses of integrin signaling

The development of multicellular organisms, as well as maintenance of organ architecture and function, requires robust regulation of cell fates. This is in part achieved by conserved signaling pathways through which cells process extracellular information and translate this information into changes in proliferation, differentiation, migration, and cell shape. Gene deletion studies in higher eukaryotes have assigned critical roles for components of the extracellular matrix (ECM) and their cellular receptors in a vast number of developmental processes, indicating that a large proportion of this signaling is regulated by cell-ECM interactions. In addition, genetic alterations in components of this signaling axis play causative roles in several human diseases. This review will discuss what genetic analyses in mice and lower organisms have taught us about adhesion signaling in development and disease.

Modulation of vascular endothelial cell senescence by integrin β4

Increasing evidence has demonstrated that the senescence of vascular endothelial cells (VECs) has critical roles in the pathogenesis of vascular dysfunction. Finding important factors that regulate VEC senescence will help provide novel therapeutic strategies for vascular disorders. Previously, we found that integrin β4 was involved in VEC senescence. However, the mechanism underlying VEC senescence mediated by integrin β4 remains poorly understand. In this study, we used a mouse in vivo model and showed that the level of integrin β4 in the endothelium of mouse thoracic aorta was increased during natural aging and atherosclerosis. Furthermore, we found that H-ras, caveolin-1, and AP-1 were implicated in the senescent signal pathway mediated by integrin β4 in human umbilical vein ECs (HUVECs). Knockdown of integrin β4 could attenuate HUVEC senescent features, including increased interleukin-8 (IL-8) release and decreased endothelial nitric oxide synthase (eNOS) and NO levels and mitochondrial membrane potential in vitro. Our findings provide new clues illustrating the mechanism of VEC senescence. Integrin β4 might be a potential target for therapy in cardiovascular diseases.

The making of hemidesmosome structures in vivo

Hemidesmosomes are evolutionarily conserved attachment complexes linked to intermediate filaments that connect epithelial cells to the extracellular matrix. They provide tissue integrity and resistance to mechanical forces. Alterations in hemidesmosome structures are responsible for skin blistering, carcinoma invasion, and wound-healing defects. Valuable information about hemidesmosome assembly and disassembly has been obtained from in vitro cell culture studies. However, how these processes take place in vivo still remains elusive. Here, we discuss recent data about the formation and reorganization of hemidesmosomes in several in vivo model systems, particularly zebrafish and Caenorhabditis elegans, focusing on various factors affecting their dynamics. Mechanisms found in different organisms reveal that hemidesmosome formation and maintenance in vivo are carefully controlled by ECM protein folding, ECM-receptor expression and trafficking, and by post-translational modification of hemidesmosome components. These findings validate and extend the in vitro studies, and shed light on our understanding about hemidesmosomes across species.

Gammadelta T cells are reduced and rendered unresponsive by hyperglycemia and chronic TNFalpha in mouse models of obesity and metabolic disease

Epithelial cells provide an initial line of defense against damage and pathogens in barrier tissues such as the skin; however this balance is disrupted in obesity and metabolic disease. Skin γδ T cells recognize epithelial damage, and release cytokines and growth factors that facilitate wound repair. We report here that hyperglycemia results in impaired skin γδ T cell proliferation due to altered STAT5 signaling, ultimately resulting in half the number of γδ T cells populating the epidermis. Skin γδ T cells that overcome this hyperglycemic state are unresponsive to epithelial cell damage due to chronic inflammatory mediators, including TNFα. Cytokine and growth factor production at the site of tissue damage was partially restored by administering neutralizing TNFα antibodies in vivo. Thus, metabolic disease negatively impacts homeostasis and functionality of skin γδ T cells, rendering host defense mechanisms vulnerable to injury and infection.

Integrin-blocking antibodies delay keratinocyte re-epithelialization in a human three-dimensional wound healing model

The alpha6beta4 integrin plays a significant role in tumor growth, angiogenesis and metastasis through modulation of growth factor signaling, and is a potentially important therapeutic target. However, alpha6beta4-mediated cell-matrix adhesion is critical in normal keratinocyte attachment, signaling and anchorage to the basement membrane through its interaction with laminin-5, raising potential risks for targeted therapy. Bioengineered Human Skin Equivalent (HSE), which have been shown to mimic their normal and wounded counterparts, have been used here to investigate the consequences of targeting beta4 to establish toxic effects on normal tissue homeostasis and epithelial wound repair. We tested two antibodies directed to different beta4 epitopes, one adhesion-blocking (ASC-8) and one non-adhesion blocking (ASC-3), and determined that these antibodies were appropriately localized to the basal surface of keratinocytes at the basement membrane interface where beta4 is expressed. While normal tissue architecture was not altered, ASC-8 induced a sub-basal split at the basement membrane in non-wounded tissue. In addition, wound closure was significantly inhibited by ASC-8, but not by ASC-3, as the epithelial tongue only covered 40 percent of the wound area at 120 hours post-wounding. These results demonstrate beta4 adhesion-blocking antibodies may have adverse effects on normal tissue, whereas antibodies directed to other epitopes may provide safer alternatives for therapy. Taken together, we conclude that these three-dimensional tissue models provide a biologically relevant platform to identify toxic effects induced by candidate therapeutics, which will allow generation of findings that are more predictive of in vivo responses early in the drug development process.

Animal models of epidermolysis bullosa

For more than 2 decades, animal models have been used to clarify the pathogenic mechanisms of human diseases and develop new therapeutics for these diseases. Several therapies for human diseases have become available through trials using animal models. Epidermolysis bullosa (EB) is one of the most severe inherited skin disorders, whose effective treatments have not been fully available. EB is characterized by abnormalities of the proteins that consist of the dermoepidermal junction. EB has been classified into three major subtypes according to the level of skin cleavage: EB simplex, junctional EB, and dystrophic EB. To date, 13 genes have been shown to cause EB phenotype. After the discovery of the causative genes responsible for each EB subtype, many researchers have tried to develop EB animal models by genetically manipulating the corresponding genes.