Locus 1 q 21 Gene Expression Changes in Atopic Dermatitis Skin Lesions : Deregulation of Small Proline-Rich Region 1 A

Background: Discovery of the significant impact of filaggrin (FLG) mutations on the genetic predisposition to atopic dermatitis (AD) focused attention on the 1q21 locus, where not only FLG but also other epidermal genes are located. In the present study, we compared 1q21 gene expression in lesional versus nonlesional AD skin. Methods: A real-time quantitative PCR analysis of 10 1q21 genes, selected on the basis of a previous microarray study, was performed in skin biopsies from 33 individuals with AD. Three alternative pathway keratins were also evaluated. Results: In chronic AD skin lesions, we observed an increase in RNA encoding involucrin, S100 calcium-binding proteins A2 and A7–A9 and small prolinerich region (SPRR) proteins 1A and 2C, with fold changes ranging from 2.0 for S100A2 to 15.4 for S100A8 (p ! 0.001, Bonferroni corrected), in parallel to the overexpression of the alternative pathway keratins 6A, 6B and 16. The loricrin (LOR) expression level was significantly decreased in lesional Received: August 4, 2008 Accepted after revision: March 25, 2009 Published online: August 6, 2009 Correspondence to: Dr. Jerzy Jarzab Department of Internal Medicine, Dermatology and Allergology Silesian Medical University, ul. Curie-Sklodowskiej 10 PL–41-800 Zabrze (Poland) Tel. /Fax +48 32 271 31 65, E-Mail jerzy.jarzab@gmail.com © 2009 S. Karger AG, Basel 1018–2438/10/1511–0028$26.00/0 Accessible online at: www.karger. com/iaa D ow nl oa de d by : 54 . 7 0. 40 . 1 1 11 /1 6/ 20 17 7 :4 1: 52 P M Locus 1q21 Gene Expression in Atopic Dermatitis Int Arch Allergy Immunol 2010;151:28–37 29 aggrin (FLG) gene, seen in approximately half of European patients [3, 4] . This gene is located on chromosome 1q21, within the human epidermal differentiation complex (EDC). At the protein level, FLG expression is very distinctly decreased or even obliterated in FLG mutation carriers [5] , while mRNA levels may be less distinctly impaired [6] . Howell et al. [7] recently documented a decrease in FLG transcript and protein in acute AD lesions and related it to the influence of IL-4 and IL-13. The EDC comprises several gene families [8] , not only the family of fused genes encoding FLG itself and FLGlike proteins, among them FLG 2, repetin, trichohyalin, cornulin and hornerin. Short tandem peptide repeats in the central region characterize another gene family, which contains loricrin (LOR), involucrin (IVL) and a small proline-rich region (SPRR) gene cluster with not less than 11 genes [9, 10] . Another group is composed of S100 family genes, with at least 14 transcripts encoding calcium-binding proteins with EF hand domains (11 of them are expressed in human epidermis). Also, 3 clusters of late envelope protein genes should be mentioned. During the physiological formation of the CE, several genes from each family are expressed in a coordinated way and the epidermal barrier activity is acquired in a stepwise manner [11] , firstly with IVL expression, followed by the expression of S100 proteins as well as SPRR proteins and, finally, LOR and FLG as late differentiation markers. A large number of CE proteins are transglutaminase substrates, used to assemble a cross-linked scaffold beneath the keratinocyte plasma membrane [12] . In normal epidermis, the major CE protein is LOR, which constitutes up to 70–80% of the total cross-linked protein mass and is cross-linked by SPRR proteins [1] . FLG, produced by post-translational proteolysis of the precursor protein, profilaggrin, plays a unique and pivotal role in cornification by promoting the formation of disulfide bonds and, as a result, aggregation of keratin filaments. Later on, FLG amino acid residues are modified and the molecule is degraded; this is instrumental in maintaining epidermal hydration and flexibility. While the expression of FLG in AD has been studied extensively at both the RNA and protein level [5, 7] , data concerning the expression of other CE genes are far less consistent [5, 13, 14] . We decided to study RNA expression because it has been proven that EDC genes are regulated mainly at the transcriptional level [15, 16] . Importantly, a large-scale DNA microarray analysis performed in AD skin biopsies by Sugiura et al. [6] indicated that several 1q21 locus genes responsible for the protective functions of the CE exhibited profound changes in their transcript expression. The authors concluded that a key abnormality in AD might be deterioration of epidermal differentiation associated with altered expression of genes located on 1q21. However, the reported level of significance was not always sufficient and, even more essentially, no validation quantitative real-time reverse transcription PCR (QPCR) study has followed until now. In our analysis, we evaluated the expression of the 1q21 genes identified by the microarray study mentioned above and compared it to that of the alternative keratinization pathway genes by applying a well-controlled QPCR approach in lesional and nonlesional skin of AD patients.