Journal Article

Impact of Laminitis on the Canonical Wnt Signaling Pathway in Basal Epithelial Cells of the Equine Digital Laminae

Eades, Susan, Belknap, James K., Johnson, Philip J., Stack, Sharon, Wang, Le, Pawlak, Erica A., Cousin, Helene, Black, Samuel J.

2013

Overview

The digital laminae is a two layer tissue that attaches the distal phalanx to the inner hoof wall, thus suspending the horse's axial skeleton in the hoof capsule. This tissue fails at the epidermal:dermal junction in laminitic horses, causing crippling disease. Basal epithelial cells line the laminar epidermal:dermal junction, undergo physiological change in laminitic horses, and lose versican gene expression. Versican gene expression is purportedly under control of the canonical Wnt signaling pathway and is a trigger for mesenchymal-to-epithelial transition; thus, its repression in laminar epithelial cells of laminitic horses may be associated with suppression of the canonical Wnt signaling pathway and loss of the epithelial cell phenotype. In support of the former contention, we show, using laminae from healthy horses and horses with carbohydrate overload-induced laminitis, quantitative real-time polymerase chain reaction, Western blotting after sodium dodecylsulfate polyacrylamide gel electrophoresis, and immunofluorescent tissue staining, that positive and negative regulatory components of the canonical Wnt signaling pathway are expressed in laminar basal epithelial cells of healthy horses. Furthermore, expression of positive regulators is suppressed and negative regulators elevated in laminae of laminitic compared to healthy horses. We also show that versican gene expression in the epithelial cells correlates positively with that of β-catenin and T-cell Factor 4, consistent with regulation by the canonical Wnt signaling pathway. In addition, gene and protein expression of β-catenin correlates positively with that of integrin β4 and both are strongly suppressed in laminar basal epithelial cells of laminitic horses, which remain E-cadherin(+)/vimentin(-), excluding mesenchymal transition as contributing to loss of the adherens junction and hemidesmosome components. We propose that suppression of the canonical Wnt signaling pathway, and accompanying reduced expression of β catenin and integrin β4 in laminar basal epithelial cells reduces cell:cell and cell:basement membrane attachment, thus, destabilizing the laminar epidermal:dermal junction.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Animal sciences / Animals / Axial skeleton / beta Catenin - metabolism / Biology / Blotting, Western / Cadherins - metabolism / Carbohydrates / Cell adhesion & migration / E-cadherin / Epithelial cells / Epithelial Cells - cytology / Epithelial Cells - metabolism / Fibroblasts / Finger / Fluorescent Antibody Technique / Gel electrophoresis / Gene expression / Genes / Heparan sulfate / Hoof / Horse Diseases - physiopathology / Horses / Inflammation / Insulin / Integrin alpha6 - metabolism / Integrin beta4 - metabolism / Integrins / Kinases / Lameness, Animal - physiopathology / Laminates / Laminitis / Low density lipoprotein receptors / Lymphocytes T / Mesenchyme / Phosphorylation / Physiological aspects / Polymerase chain reaction / Protein expression / Proteins / Regulators / Signal Transduction / Signaling / Skin / Sodium / Stem cells / T cells / Transcription factors / Versican / Veterinary colleges / Veterinary medicine / Veterinary Science / Vimentin / Vimentin - metabolism / Western blotting / Wnt protein / Wnt Signaling Pathway / β-Catenin