Real-time PCR quantification of the canine filaggrin orthologue in the skin of atopic and non-atopic dogs: a pilot study

Abstract

BackgroundCanine atopic dermatitis (AD) is a common inflammatory skin disease associated with defects in the epidermal barrier, particularly in West Highland white terriers (WHWTs). It shares many similarities with human AD, and so may be a useful animal model for this disease. Epidermal dysfunction in human AD can be caused by mutations in the gene encoding the epidermal protein filaggrin (FLG) and, in some atopic patients, be associated with altered FLG mRNA and protein expression in lesional and/or non-lesional skin. In experimental models of canine AD, mRNA expression of the orthologous canine filaggrin gene may be reduced in non-lesional skin compared with healthy controls. However, there is no published data on canine filaggrin mRNA expression in the skin of dogs with naturally-occurring AD. Hence, the aim of this pilot study was to develop a reverse transcriptase real-time PCR assay to compare filaggrin mRNA expression in the skin of atopic (n = 7) and non-atopic dogs (n = 5) from five breeds, including eight WHWTs.FindingsOverall, filaggrin mRNA expression in non-lesional atopic skin was decreased compared to non-lesional non-atopic skin (two fold change); however this difference was only statistically significant in the subgroup of WHWTs (P = 0.03).ConclusionsAlthough limited by the small sample size, these results indicate that, comparable to some cases of human AD, altered filaggrin mRNA expression may exist in the skin of some atopic dogs with naturally-occurring disease. Additional studies, including larger sample numbers, will be necessary to confirm this finding and to investigate whether mutations in the filaggrin gene exist and contribute to epidermal lesions of AD in dogs.

Altered mRNA and protein expression of filaggrin in the skin of a canine animal model for atopic dermatitis

“…It has been reported that canine atopic skin has increased degradation of ceramides due to increased enzymatic activity. The same may be true for increased degradation of proteins, such as filaggrin, explaining why most studies in atopic dogs have failed to identify a genetic mutation in the filaggrin gene . It is also known that an increased cutaneous pH in atopic skin induces an increase in the activity of proteases, which may result in excessive degradation of proteins, including filaggrin.…”

“…The same may be true for increased degradation of proteins, such as filaggrin, explaining why most studies in atopic dogs have failed to identify a genetic mutation in the filaggrin gene. 24,25 It is also known that an increased cutaneous pH in atopic skin induces an increase in the activity of proteases, 7 which may result in excessive degradation of proteins, including filaggrin. Another explanation could be the increased activity of anti-proteases, which does not allow the degradation of profilaggrin into filaggrin monomers, as recently reported in people with AD.…”

“…Two studies 25,26 have identified SNPs not confirmed by others. 24,41,42 In the former studies, 25,26 an association between SNPs, breed and geographical location has been suggested; three SNPs associated with canine AD have been identified in Labrador retrievers in the UK and small-breed dogs (toy poodles, shih tzus and pugs) in Thailand. 25,26 The experimental model for canine AD has many advantages.…”

“…20,21 In dogs, the disruption of the skin barrier, as a predisposing factor of AD, has only been hypothesized recently. Three studies showed a decreased immunohistochemical staining 22,23 and mRNA expression 24 along with a nonhomogeneous distribution of filaggrin protein in canine skin, suggesting a potential involvement of filaggrin in the pathogenesis of canine AD. Chervet et al 22 specifically demonstrated that approximately 20% of dogs with naturally occurring AD showed a decreased expression of filaggrin when an antibody directed against the C-terminal portion of the molecule was used, supporting the usefulness of dogs as a model for the human disease.…”

“…In dogs, the disruption of the skin barrier, as a predisposing factor of AD, has only been hypothesized recently. Three studies showed a decreased immunohistochemical staining and mRNA expression along with a nonhomogeneous distribution of filaggrin protein in canine skin, suggesting a potential involvement of filaggrin in the pathogenesis of canine AD. Chervet et al .…”