Cassimeris, L. | Search bioRxiv

bioRxiv2020

Interleukin-17 pathway activation in Equus caballus supporting limb laminitis

Supporting Limb Laminitis (SLL) is a painful and crippling secondary complication of orthopedic injuries and infections in horses, often resulting in euthanasia. Due to altered weight bearing, SLL causes structural alternations and inflammation of the interdigitating layers of specialized epidermal and dermal tissues, the lamellae, which suspend the equine distal phalanx from the hoof capsule. Activation of the interleukin-17 (IL-17)-dependent inflammatory pathway is an epidermal stress response that contributes to physiologic cutaneous wound healing as well as pathological skin conditions. To test the hypothesis that IL-17 pathway activation is involved in equine epidermal lamellae in SLL, we analyzed the expression of the IL-17 receptor subunit A and 11 genes upregulated by IL-17 in lamellar tissue isolated from Thoroughbreds euthanized due to naturally occurring SLL and in age and breed matched non-laminitic controls. The IL-17 Receptor A subunit was expressed in both non-laminitic and laminitic tissues. In severe acute SLL (n=7) compared to non-laminitic controls (n=8), quantitative PCR demonstrated [~]20-100 fold upregulation of {beta} defensin 4 (E. caballus gene DEFB4B) and S100A9 genes. DEFB4B was also upregulated in developmental (n=8), moderate acute (n=7), and severe chronic (n=5) samples. By RT-PCR, S100A8, MMP9, and PTSG2 (COX2) expression was upregulated in most or all severe acute SLL samples, whereas several other genes, CCL2, CxCL8, TNF, IL6 and MMP1 were detected in some, but not all, severe acute samples. PTGS2, CCL2, TNF and IL6 were also expressed in some, but not all, developmental and moderate acute disease stages. Moreover, expression of DEFB4 by in situ hybridization and calprotectin (S100A9/S100A8) protein by immunofluorescence was detected in keratinocytes, primarily in suprabasal cell layers, from SLL samples. These data support the hypothesis that the IL-17 inflammatory pathway is active in equine SLL, and that similarities exist between equine and human epidermal tissue responses to stresses and/or damage.

immunology↗

bioRxiv2019

The expression of equine keratins K42 and K124 is restricted to the hoof epidermal lamellae of Equus caballus

The equine hoof inner epithelium is folded into primary and secondary epidermal lamellae which increase the dermo-epidermal junction surface area of the hoof and can be affected by laminitis, a common disease of equids. Two keratin proteins (K), K42 and K124, are the most abundant keratins in the hoof lamellar tissue of Equus caballus. We hypothesize that these keratins are lamellar tissue-specific and could serve as differentiation- and disease-specific markers. Our objective was to characterize the expression of K42 and K124 in equine stratified epithelia and to generate monoclonal antibodies against K42 and K124. By RT-PCR analysis, keratin gene (KRT) KRT42 and KRT124 expression was present in lamellar tissue, but not cornea, haired skin, or hoof coronet. In situ hybridization studies showed that KRT124 localized to the suprabasal and, to a lesser extent, basal cells of the lamellae, was absent from haired skin and hoof coronet, and abruptly transitions from KRT124-negative coronet to KRT124-positive proximal lamellae. A monoclonal antibody generated against full-length recombinant equine K42 detected a lamellar keratin of the appropriate size, but also cross-reacted with other epidermal keratins. Three monoclonal antibodies generated against N- and C-terminal K124 peptides detected a band of the appropriate size in lamellar tissue and did not cross-react with proteins from haired skin, corneal limbus, hoof coronet, tongue, glabrous skin, oral mucosa, or chestnut on immunoblots. K124 localized to lamellar cells by indirect immunofluorescence. This is the first study to demonstrate the localization and expression of a hoof lamellar-specific keratin, K124, and to validate anti-K124 monoclonal antibodies.

cell biology↗