Immunohistochemical evaluation of filaggrin polyclonal antibody in atopic and normal beagles

Studies Using Antibodies against Filaggrin and Filaggrin 2 in Canine Normal and Atopic Skin Biopsies

Filaggrin is important for the skin barrier and atopic dermatitis. Another filaggrin-like protein, filaggrin 2, has been described. We evaluated antibodies against both filaggrins in normal and atopic skin biopsies from dogs before and after allergen challenges (D0, D1, D3 and D10). Filaggrins expression was evaluated by immunohistochemistry and Western blot. We used PCR to investigate changes in filaggrin gene expression. Effects of group (p = 0.0134) and time (p = 0.0422) were shown for the intensity of filaggrin staining. Only an effect of group was found for filaggrin 2 (p = 0.0129). Atopic samples had higher intensity of staining than normal dogs [filaggrin on D3 (p = 0.0155) and filaggrin 2 on D3 (p = 0.0038) and D10 (p < 0.0001)]. Atopic samples showed increased epidermal thickness after allergen exposure (D3 vs. D0, p = 0.005), while normal dogs did not. In atopic samples, significant increased gene expression was found for filaggrin overtime but not for filaggrin 2. Western blot showed an increase in filaggrin 2 on D3. A small size band (15 kD) containing a filaggrin sequence was found in Western blots of atopic samples only. We conclude that atopic skin reacts to allergen exposure by proliferating and increasing filaggrin production but that it also has more extensive filaggrin degradation compared to normal skin.

A review of cutaneous hypersensitivity reactions in dogs: A diagnostician's guide to allergy

Allergic dermatoses are common in people and domestic animals. Resultant lesions are routinely biopsied and submitted for histological examination to confirm a diagnosis or rule out diseases with overlapping or atypical clinical features. Diagnostic pathologists and clinicians are often faced with the difficult task of determining whether an allergic reaction pattern is present on both the microscopic and macroscopic levels and correlating histopathologic findings with clinical and historical data to achieve a precise clinical diagnosis. The bulk of the current veterinary literature on allergic dermatoses focuses on atopic dermatitis in dogs, distantly followed by cats, horses, and other animals. The objectives of this review are to demonstrate the key histopathologic and clinical diagnostic features of the various allergy-mediated reaction patterns, and to provide diagnosticians with a practical guide for clinicopathological correlations. Current concepts in the pathophysiology of immediate hypersensitivity reactions, with a focus on atopic dermatitis, are discussed. Points of potential histopathologic overlap between the "classic" allergic reaction pattern and less common inflammatory, predominately eosinophilic, conditions that may mimic this pattern will be discussed with the goal of highlighting the critical need for collaboration between pathologists and clinicians in furthering patient care.

Immunolocalization and Expression of JAK1 and JAK3 in the Skin of Dust Mite-Sensitive Beagle Dogs before and after Allergen Exposure

Janus kinase (JAK) pathways have emerged as targets of treatment, yet localization and expression of JAK1 and JAK3 in canine atopic skin have not been studied. This study aimed to compare the localization and expression of JAK1 and JAK3 in the skin of atopic dogs before and after allergen exposure. Skin biopsies taken from atopic beagles sensitized to house dust mites (HDM) before (D0) and after four weeks (D28) of allergen exposure were stained. Staining was subjectively scored by examiners unaware of the source of the slides. Image J was used for the semiquantitative assessment of staining intensity. JAK1 and JAK3 staining was epidermal and dermal. JAK1 staining was cytoplasmic, primarily found in basal keratinocytes and dermal cells, while JAK 3 was nuclear (all epidermal levels and on dermal inflammatory cells). Epidermal thickness was significantly higher on D28 than on D0 (p < 0.0001). For JAK1, epidermal staining divided by epithelial thickness was significantly lower on D28 (p = 0.0002) compared to D0. For JAK3 staining, intensity in the dermis was significantly higher on D28 (p = 0.0405) compared to D0. We conclude that decreased expression of JAK1 in the epidermis and increased expression of JAK3 in the dermis of atopic dogs occur after allergen exposure.

Differences in Behavior between Normal and Atopic Keratinocytes in Culture: Pilot Studies

Skin barrier dysfunction is important in atopic dermatitis and can be secondary to inflammation. Observation of keratinocytes in culture may show intrinsic differences. TransEpithelial Electrical Resistance (TEER) measures epithelial permeability. We cultured normal and atopic keratinocytes and found that TEER of atopic keratinocytes was significantly lower (p < 0.0001) than that of normals. Atopic keratinocytes grew upwards, first creating isolated dome-like structures and later horizontally into a monolayer. At time of confluence (D0), atopic keratinocytes were more differentiated, with higher filaggrin gene expression than normals. No differences existed between groups for TJ proteins (claudin, occludin, and Zonula Occludens-1) on D0 and D6. On D6, claudin and occludin were higher than D0, in normal (p = 0.0296 and p = 0.0011) and atopic keratinocytes (p = 0.0348 and 0.0491). Immunofluorescent staining showed nuclear location of filaggrin on D0 and cytoplasmic on D6. ANOVA showed increased cell size from D0 to D6 in both groups (effect of time, p = 0.0076) but no differences between groups. Significant subject effect (p = 0.0022) was found, indicating that cell size was subject-dependent but not disease-dependent. No difference for continuity for TJ protein existed between groups. These observations suggest that decreased TEER in atopics is not linked to TJ differences but is possibly linked to different growth behavior.

Update on canine filaggrin: a review

Human filaggrin (FLG) plays a key role in epidermal barrier function, and loss-of-function mutations of its gene are primarily responsible for the development of human atopic dermatitis (AD). FLG expression is also reduced in the epidermis of atopic patients, due to the transcriptional effect of Th2 type cytokines. Canine atopic dermatitis (CAD) is a prevalent skin disease that shares many clinical and pathogenic features with its human homologue. The aim of this review is discuss current knowledge on canine filaggrin (Flg) in both healthy and atopic dogs, as compared to the human protein. Although the molecular structures of the two proteins, as deduced from the sequences of their gene, are different, their sites of expression and their proteolytic processing in the normal epidermis are similar. Concerning the expression of Flg in CAD, conflicting results have been published at the mRNA level and little accurate information is available at the protein level. It derives from a large precursor, named profilaggrin (proFLG), formed by several FLG units and stored in keratohyalin granules of the stratum granulosum. Canine and human proFLG sequences display little amino acid similarity (33% as shown using the Basic Local Alignment Search Tool (BLAST)) except at the level of the S100 homologous part of the N-terminus (75%). Genetic studies in the dog are at an early stage and are limited by the variety of breeds and the small number of cases included. Many questions remain unanswered about the involvement of Flg in CAD pathogenesis.

Decreased expression of caspase-14 in an experimental model of canine atopic dermatitis

Alterations in skin barrier function and filaggrin expression have been reported in atopic dermatitis (AD). Caspase-14, a protease important for filaggrin processing, is decreased in human AD. Atopic Beagle dogs with skin barrier alterations have been validated as model for AD. This study aimed to investigate caspase-14 in normal and atopic Beagle dogs. Skin biopsies from non-lesional and control skin were analyzed for caspase-14 by immunofluorescence. Six images/sections were blindly scored for intensity. Data were tested with unpaired Student's t test. A P value of <0.05 was considered significant. Caspase-14 was decreased in atopic compared to normal skin both quantitatively (P <0.001) and qualitatively (P = 0.006; agreement = 0.93; consistency = 0.94). In conclusion, caspase-14 is decreased in this model similarly to reports in humans, highlighting the relevance of filaggrin metabolic defects in AD.

The genomics revolution: will canine atopic dermatitis be predictable and preventable?

BACKGROUND

Heritability studies suggest that atopic dermatitis (AD) involves multiple genes and interactions with environmental factors. Advances in genomics have given us powerful techniques to study the genetics of AD.

OBJECTIVE

To review the application of these techniques to canine AD.

RESULTS

Candidate genes can be studied using quantitative PCR and genomic techniques, but these are hypothesis-dependent techniques and may miss novel genes. Hypothesis-free techniques avoid this limitation. Microarrays quantify expression of large numbers of genes, although false-positive associations are common. In the future, expression profiling could be used to produce a complete tissue transcriptome. Genome-wide linkage studies can detect AD-associated loci if enough affected dogs and unaffected relatives are recruited. Genome-wide association studies can be used to discover AD-associated single nucleotide polymorphisms without relying on related dogs. Genomic studies in dogs have implicated numerous genes in the pathogenesis of AD, including those involved in innate and adaptive immunity, inflammation, cell cycle, apoptosis, skin barrier formation and transcription regulation. These findings, however, have been inconsistent, and problems include low case numbers, inappropriate controls, inconsistent diagnosis, incomplete genome coverage, low-penetrance mutations and environmental factors.

CONCLUSIONS

Canine AD has a complex genotype that varies between breeds and gene pools. Breeding programmes to eliminate AD are therefore unlikely to succeed, but this complexity could explain variations in clinical phenotype and response to treatment. Genotyping of affected dogs will identify novel target molecules and enable better targeting of treatment and management options. However, we must avoid misuse of genomic data.

The stratum corneum: the rampart of the mammalian body

BACKGROUND

The stratum corneum (SC) is the outermost region of the epidermis and plays key roles in cutaneous barrier function in mammals. The SC is composed of 'bricks', represented by flattened, protein-enriched corneocytes, and 'mortar', represented by intercellular lipid-enriched layers. As a result of this 'bricks and mortar' structure, the SC can be considered as a 'rampart' that encloses water and solutes essential for physiological homeostasis and that protects mammals from physical, chemical and biological assaults.

STRUCTURES AND FUNCTIONS

The corneocyte cytoskeleton contains tight bundles of keratin intermediate filaments aggregated with filaggrin monomers, which are subsequently degraded into natural moisturizing compounds by various proteases, including caspase 14. A cornified cell envelope is formed on the inner surface of the corneocyte plasma membrane by transglutaminase-catalysed cross-linking of involucrin and loricrin. Ceramides form a lipid envelope by covalently binding to the cornified cell envelope, and extracellular lamellar lipids play an important role in permeability barrier function. Corneodesmosomes are the main adhesive structures in the SC and are degraded by certain serine proteases, such as kallikreins, during desquamation.

CLINICAL RELEVANCE

The roles of the different SC components, including the structural proteins in corneocytes, extracellular lipids and some proteins associated with lipid metabolism, have been investigated in genetically engineered mice and in naturally occurring hereditary skin diseases, such as ichthyosis, ichthyosis syndrome and atopic dermatitis in humans, cattle and dogs.

Canine atopic dermatitis - what have we learned?

Canine atopic dermatitis is a complex multifactorial disease. Here, Tim Nuttall, Maarja Uri and Richard Halliwell, representing three generations of veterinary dermatologists, describe the research underpinning our understanding of the condition and highlight its relevance to clinical practice.

Investigation of the effect of probiotic exposure on filaggrin expression in an experimental model of canine atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) results from complex interactions between an impaired skin barrier and immunological stimulation. Filaggrin is a key protein for the skin barrier, and its expression is decreased in subsets of atopic dogs and can be modified by inflammation; thus, immunomodulatory approaches may alter its expression. Probiotics have been explored for the prevention and treatment of allergies, owing to their immunomodulatory properties; however, it is currently unknown whether they can modulate filaggrin expression.

OBJECTIVE

The purpose of this study was to evaluate whether probiotics can modulate filaggrin expression in an experimental model of canine AD.

ANIMALS AND METHODS

Eighteen atopic (11 probiotic exposed and seven control) and five normal beagles were challenged for three consecutive days with Dermatophagoides farinae. Skin biopsies were taken before (day 0), at the peak (day 3) and after the end of the allergen challenge (day 10). Immunohistochemistry for filaggrin was done using a polyclonal antibody specific for canine filaggrin, and staining was scored both subjectively (for intensity, granularity and continuity) and objectively, by tracing the stratum granulosum and calculating the percentage of filaggrin per unit traced area.

RESULTS

Analysis of variance of the percentage of filaggrin in the stratum granulosum showed a significant effect of group (P = 0.0414, AD < normal), time (P = 0.0066, days 3 and 10 > day 0) and marginal group × time interaction (P = 0.0606). Within the atopic group, exposure to probiotics did not change filaggrin expression. No significant differences were found in the subjective scores among groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

It is concluded that probiotic exposure early in life does not alter filaggrin expression in this AD model.

Histologic morphology and involucrin, filaggrin, and keratin expression in normal canine skin from dogs of different breeds and coat types

The purpose of this study was to measure the thickness of canine epidermis at various anatomical sites according to localization of cornified envelopes (involucrin and filaggrin), keratins (keratin 10, 5), and their mRNA expression. This was done in the skin of five breeds of dogs including seven poodles, six golden retrievers, six Shih Tzus, four pugs, and four Labrador retrievers. Epidermal thickness of the stratum corneum and nucleated epidermal layer was significantly different. The greatest thickness was observed in the digital web area and the thinnest epidermis was in the axilla. Epidermal thickness was also significantly different between the breeds (p < 0.05). Immunohistochemical staining scores revealed significant decreases of involucrin, filaggrin, and keratin 10 in the ventral and weight-bearing sites, and a relative increase of keratin 5 (p < 0.05). q-PCR analysis showed that their the levels of mRNA were positively correlated with expression of the corresponding proteins in skin samples (p < 0.05). The present study is the first to report the relationship between epidermal gene expression and histologic morphology of the skin in normal dogs. Further studies will be essential to fully understand the pathogenesis of skin barrier dysfunctions in canines.

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

BACKGROUND

Canine 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.

FINDINGS

Overall, 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).

CONCLUSIONS

Although 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.