Laminin α5 in the keratinocyte basement membrane is required for epidermal– dermal intercommunication Jeannine Wegner a,b , Karin Loser b,c , Gunita Apsite a,b , Roswitha Nischt d , Beate Eckes d , Thomas Krieg d , Sabine Werner e and Lydia Sorokin a,b a - Institute of Physiological Chemistry and Pathobiochemistry, University of Muenster, Germany b - Cells-in-Motion Cluster of Excellence, University of Muenster, Germany c - Department of Dermatology, University of Muenster, Germany d - Department of Dermatology, University of Cologne, Germany e - Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, Switzerland Correspondence to Lydia Sorokin: Institute of Physiological Chemistry and Pathobiochemistry, University of Muenster, Waldeyerstrasse 15, 48149 Muenster, Germany. sorokin@uni-muenster.de http://dx.doi.org/10.1016/j.matbio.2016.05.001 Edited by R. Iozzo Abstract Laminin α5 is broadly expressed in the epidermal basement membrane (BM) of mature mice and its elimination at this site (Lama5 Ker5 mouse) results in hyperproliferation of basal keratinocytes and a delay in hair follicle development, which correlated with upregulation of the dermally-derived laminin α2 and laminin α4 chains in the epidermal BM and of tenascin-C subjacent to the BM. In vitro studies revealed laminin 511 to be strongly adhesive for primary keratinocytes and that loss of laminin α5 does not result in cell autonomous defects in proliferation. Flow cytometry reveals that the loss of laminin α5 resulted in increased numbers of CD45 + , CD4 + and CD11b + immune cells in the skin, which temporo-spatial analyses revealed were detectable only subsequent to the loss of laminin α5 and the appearance of the hyperproliferative keratinocyte phenotype. These findings indicate that immune cell changes are the consequence and not the cause of keratinocyte hyperproliferation. Loss of laminin α5 in the epidermal BM was also associated with changes in the expression of several dermally-derived growth factors involved in keratinocyte proliferation and hair follicle development in adult but not new born Lama5 Ker5 skin, including KGF, EGF and KGF-2. In situ binding of FGF-receptor-2α (IIIb)-Fc chimera (FGFR2IIIb) to mouse skin sections revealed decoration of several BMs, including the epidermal BM, which was absent in Lama5 Ker5 skin. This indicates reduced levels of FGFR2IIIb ligands, which include KGF and KGF-2, in the epidermal BM of adult Lama5 Ker5 skin. Our data suggest an initial inhibitory effect of laminin α5 on basal keratinocyte proliferation and migration, which is exacerbated by subsequent changes in growth factor expression by epidermal and dermal cells, implicating laminin α5 in epidermal–dermal intercommunication. © 2016 Published by Elsevier B.V. Introduction The epidermis of the skin, a stratified layer of epithelial keratinocytes, is anchored to a highly specialized basement membrane (BM) that separates the epidermis from the mesenchymal cells of the dermis. Reciprocal epithelial–mesenchymal interac- tions between the epidermis and the underlying dermis are considered major driving forces in skin development and homeostasis [1]. The BM provides specific spatial information that is important for skin homeostasis, and mediates molecular signals from both the epidermis and the dermis that is directly conveyed via cellular receptor complexes or, indirectly, via the presentation of growth factors by the BM. Analysis of human genetic diseases and of mutant mice has revealed that cell–cell junctional components and hemidesmosome components and their binding partners in the BM are essential for integrity of the skin. In addition, there is a growing body of information on cytokines, which regulate development and regener- ation of the skin and its appendages. MATBIO-1255; No. of pages: 18; 4C: 0022-2836/© 2016 Published by Elsevier B.V. Matrix Biol. (2016) xx, xxx–xxx Article Please cite this article as: J. Wegner, et al., Laminin α5 in the keratinocyte basement membrane is required for epidermal– dermal intercommunication, Matrix Biol (2016), http://dx.doi.org/10.1016/j.matbio.2016.05.001