Increased filaggrin-metabolizing enzyme activity in atopic skin: a pilot study using a canine model of atopic dermatitis

Background - Filaggrin (FLG) and its metabolites are essential for skin barrier function and hydration of the stratum corneum. Alteration of the FLG metabolism could be the basis for an abnormal skin barrier in allergic dogs. Objectives - To investigate the expression and distribution of calpain-1, caspase-14, furin and matriptase, four enzymes involved in FLG metabolism, in the skin of atopic and healthy beagles. Methods - Skin biopsies were collected from four healthy and four atopic beagles before and after allergen exposure. The dogs were challenged for three consecutive days to mimic an acute exposure, or once weekly to mimic a chronic exposure to allergens. Skin biopsies were taken on days 0 (nonlesional), 3 and 10 in the acute model and on days 0 (nonlesional), 14 and 28 in the chronic model. Four healthy dogs were used as controls. Indirect immunofluorescence was used to analyse the distribution and the expression of FLG enzymes in a semi-quantitative manner. Five consecutive pictures/section were taken and the intensity analysed tracing the epidermis and using ImageJ on the traced areas. The enzymes' expression was compared between healthy and atopic nonlesional skin (Day 0) and over time in each group. Results - All enzymes were expressed in all layers of the epidermis. A significantly higher expression of calpain1 (P = 0.028), caspase 14 (P = 0.028) and matriptase (P = 0.028) was evident in atopic compared to control dogs on Day 0. No differences over time were seen for any enzyme analysed. Conclusions and clinical importance -This preliminary study suggests an abnormal catabolism of FLG in canine atopic skin.