Elsevier

European Journal of Cell Biology

Volume 90, Issues 2–3, February–March 2011, Pages 270-277
European Journal of Cell Biology

Conditional ablation of integrin alpha-6 in mouse epidermis leads to skin fragility and inflammation

https://doi.org/10.1016/j.ejcb.2010.09.003Get rights and content

Abstract

Hemidesmosomes (HDs) are essential anchorage junctions which mediate the firm attachment of epithelia to the underlying basement membranes, of which one main component is the integrin α6β4. These specific junctions are also able to trigger signalling pathways, via the recruitment and interactions of signalling molecules with HD components such as the cytoplasmic tail of the β4 integrin or the plakin plectin. HDs must also assemble and disassemble depending on the tissue context for example during tissue remodelling. Alterations of HD components or their loss result in skin blistering disorders known as epidermolysis bullosa. Since mice lacking integrin α6 die at birth with severe skin blistering, we have produced a mouse line in which epidermal deletion of integrin α6 can be controlled by tamoxifen injection. We observed that the deletion was mosaic, but that hairless skin such as ears, tails and paws were affected and showed chronic inflammation associated with hyperproliferation, and expression of laminin-111. Interestingly, two cytokines, amphiregulin and epiregulin, previously found increased in integrin α6 deficient cultured keratinocytes, were also increased here in the affected skin. In detached areas, we validate clearly that the absence of integrin α6 leads to a delocalisation of plectin, and the complete disappearance of HD structures.

Introduction

Hemidesmosomes (HDs) represent the main cellular junctions that ensure the anchorage of epithelial cells to the underlying basement membrane (BM), in stratified epithelia such as the skin and certain complex or simple epithelia. These multi-protein complexes form strong and stable adherent junctions, essential to maintain tissue integrity. HDs are formed by the association of the transmembrane receptor α6β4 integrin, the Bullous Pemphigoid (BP) antigens 180 and 230 (BP180/Collagen XVII and BP230, respectively), plectin, and CD151. The α6β4 integrin receptor, the core component of these multi-protein complexes, binds mainly to the BM laminin-332. The cytoplasmic tail of integrin β4 then establishes interactions with plaque components as plectin, which in turn interacts with the keratin intermediate filaments network. Recent reviews provide extensive descriptions of the architecture and process of assembly of HDs (Litjens et al., 2006, Zhang and Labouesse, 2010).

HDs are considered stable anchorage junctions that confer skin resistance to mechanical stress. Indeed, mutations in each hemidesmosomal component result in loss of skin integrity, characterised by severe skin blistering, observed in the human disease, epidermolysis bullosa (EB). Several types of EB have been described which differ by the level of splitting, in tight correlation with the subcellular localisation of the altered molecule (Pulkkinen and Uitto, 1999). In particular, loss of function of either the α6 or β4 integrin subunit or of each of the three chains of laminin-332 are the cause of junctional epidermolysis bullosa (JEB), where an epidermis–dermis detachment occurs precisely at the level of the BM (Pulkkinen and Uitto, 1999, Schneider et al., 2007). Similar phenotypes are observed after genetic ablation in mice.

Due to neonatal death associated with complete detachment of the epidermis, further studies, in particular in adult epidermis were not possible in integrin α6 total knock-out mice. To overcome this limitation, we have produced a skin-specific deletion of the integrin α6 gene using the Cre-loxP technology. While constitutive deletion leads to a severe phenotype and neonatal death, tamoxifen-controlled deletion leads to much milder defects associated with inflammation.

Section snippets

Animals

Mice carrying a conditional allele of the ITGA6 gene, α6fl/fl, will be described elsewhere. α6fl/fl mice were crossed with α6+/− animals (Georges-Labouesse et al., 1996), in order to generate α6fl/− mice. The resulting animals were then crossed with 2 different transgenic lines expressing a constitutively active version (K14-Cre) or a tamoxifen-dependent version (K14-Cre-ERT2) of the Cre recombinase under the control of the keratin 14 (K14) promoter (Indra et al., 1999), giving rise to α6fl/−

Generation of transgenic mice carrying targeted inactivation of α6 integrin in the epidermis

The germline inactivation of the α6 gene (ITGA6) in mouse resulted in lethality at the time of birth with severe skin detachment, which precluded further analyses of α6β4 integrin functions in postnatal and adult mice (Georges-Labouesse et al., 1996). To circumvent the neonatal lethality, we generated a mutant mouse line carrying α6 floxed alleles, α6fl/fl, allowing the conditional deletion of the gene in the presence of the Cre recombinase. To investigate the role of α6β4 integrin in adult

Discussion

Junctional epidermolysis bullosa (JEB) in humans, characterised by skin fragility with presence of blisters and erosions at birth or shortly thereafter, is associated with genetic alterations in particular in the α6 and β4 integrin genes (Pulkkinen and Uitto, 1999). In mouse, the total knock-out of the gene resulted in severe skin detachment and lethality at birth (Georges-Labouesse et al., 1996). To analyse the function of α6 integrin specifically in the adult mouse epidermis, we generated a

Acknowledgements

We thank the IGBMC animal facility staff for their help and S. Muller for histopathological analysis, L. Sorokin, and T. Sasaki for the kind gift of antibodies and M. Li for helpful discussions. We are grateful to D. Metzger and P. Chambon who made available to us the K14-Cre and K14-Cre-ERT2 mice. This work was supported by funds from Inserm (Programme National de Recherche en Dermatologie, PNRD), CNRS, and Université de Strasbourg (UdS) as well as by grants from the Société de recherche

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    1

    Present address: Transgene SA, Boulevard Gonthier d’Andernach, Parc d’Innovation – CS80166, F-67405 Illkirch-Graffenstaden, France.

    2

    Present address: Department of Pharmaceutical Sciences, College of Pharmacy, Oregon State University, Corvallis, OR 97331, USA.

    3

    Present address: Institut de Génétique et Développement, Université de Rennes 1, Faculté de Médecine, Rennes Cedex, France.

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