Comparison of cellular location and expression of Plakophilin‐2 in epidermal cells from nonlesional atopic skin and healthy skin in German shepherd dogs

Abstract

BackgroundCanine atopic dermatitis (CAD) is an inflammatory and pruritic allergic skin disease caused by interactions between genetic and environmental factors. Previously, a genome‐wide significant risk locus on canine chromosome 27 for CAD was identified in German shepherd dogs (GSDs) and Plakophilin‐2 (PKP2) was defined as the top candidate gene. PKP2 constitutes a crucial component of desmosomes and also is important in signalling, metabolic and transcriptional activities.ObjectivesThe main objective was to evaluate the role of PKP2 in CAD by investigating PKP2 expression and desmosome structure in nonlesional skin from CAD‐affected (carrying the top GWAS SNP risk allele) and healthy GSDs. We also aimed at defining the cell types in the skin that express PKP2 and its intracellular location.Animals/MethodsSkin biopsies were collected from nine CAD‐affected and five control GSDs. The biopsies were frozen for immunofluorescence and fixed for electron microscopy immunolabelling and morphology.ResultsWe observed the novel finding of PKP2 expression in dendritic cells and T cells in dog skin. Moreover, we detected that PKP2 was more evenly expressed within keratinocytes compared to its desmosomal binding‐partner plakoglobin. PKP2 protein was located in the nucleus and on keratin filaments attached to desmosomes. No difference in PKP2 abundance between CAD cases and controls was observed.ConclusionPlakophilin‐2 protein in dog skin is expressed in both epithelial and immune cells; based on its subcellular location its functional role is implicated in both nuclear and structural processes.

Transcriptomes from German shepherd dogs reveal differences in immune activity between atopic dermatitis affected and control skin

“…Since a skin biopsy consists of many cell types, a difference in PKP2 gene expression in specific cell types such as T-cells or dendritic cells may be undetectable. However, no difference in PKP2 protein expression intensity in dendritic cells was detected between CAD cases and controls (Ardesjo-Lundgren et al 2017). Nevertheless, we cannot rule out that there is an altered PKP2 expression in CAD but the right target tissue, cell type, and/or disease state need to be defined.…”

“…However, we detected no difference in PKP2 gene expression in the skin between the CAD cases carrying risk alleles compared to the controls with the control genotype. Two additional biopsies from axillary skin and three biopsies from the back region of each dog were included at sampling and were fixed for protein expression studies (Ardesjo-Lundgren et al 2017), which included a few more dogs compared to the present study. In that study, T-cells and dendritic cell infiltration were identified in canine axillary skin and high PKP2 protein expression was reported in keratinocytes, Tcells, and dendritic cells, but with no differences between CAD cases and controls.…”

“…In that study, T-cells and dendritic cell infiltration were identified in canine axillary skin and high PKP2 protein expression was reported in keratinocytes, Tcells, and dendritic cells, but with no differences between CAD cases and controls. The majority of the CAD cases had been under long-term systemic corticosteroid treatment (> 1 year) at the time of sampling (Ardesjo-Lundgren et al 2017), and corticosteroids are known to inhibit activation of especially lymphocytes but also dendritic cells (Ashwell et al 2000;Ashworth et al 1988;Gillis et al 1979;Leung and Bloom 2003). Since a skin biopsy consists of many cell types, a difference in PKP2 gene expression in specific cell types such as T-cells or dendritic cells may be undetectable.…”

Atopic dermatitis in cats and dogs: a difficult disease for animals and owners

“…In atopic German shepherds a significant association with chromosome 27 was determined, especially with genes that had a connection to plakophilin 2 production [ 11 ]. Plakophilin 2 is an important structural protein, which is expressed in epithelial and immune cells [ 11 , 12 ]. The predisposition of German shepherds for AD is likely due to a risk haplotype in combination with multiple variants resulting in a changed expression of the plakophilin 2 gene and nearby genes [ 11 ].…”

Bayesian model and selection signature analyses reveal risk factors for canine atopic dermatitis

“…In concordance with human AD genes, the associated regions in dog harbor genes implicated in both innate and adaptive immunity, inflammation, and skin barrier formation. However, replication and functional validation of these loci have been limited [16][17][18] and the genetic background in canine AD appears more complex than initially suggested, even within breeds 19 .…”