Abstract
Supporting Limb Laminitis (SLL) is a painful and crippling secondary complication of orthopedic injuries and infections in horses, often resulting in euthanasia. SLL causes structural alterations 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-17A (IL-17A)-dependent inflammatory pathway is an epidermal stress response that contributes to physiologic cutaneous wound healing as well as pathological skin conditions. As a first test of the hypothesis that hoof lamellae of horses diagnosed with SLL also respond to stress by activating the IL-17A pathway, the expression of IL-17A, IL-17 receptor subunit A and 11 IL-17A effector genes was measured by RT-PCR or qPCR. Lamellar tissue was isolated from Thoroughbreds euthanized due to naturally occurring SLL and in age and breed matched non-laminitic controls. By RT-PCR, the IL-17 Receptor A subunit was expressed in both non-laminitic and laminitic tissues, while IL-17A was primarily detectable in laminitic tissues. IL-17A target gene expression was undetectable in non-laminitic samples with the exception of weak detection of DEFB4B, S100A9 and PTSG2. In contrast, all target genes examined, except CCL20, were expressed by some or all laminitic samples. By qPCR, severe acute (n = 7) SLL expressed ~15–100 fold higher levels of DEFB4B and S100A9 genes compared to non-laminitic controls (n = 8). DEFB4B was also upregulated in developmental/subclinical (n = 8) and moderate acute (n = 7) by ~ 5-fold, and in severe chronic (n = 5) by ~15–200 fold. In situ hybridization (DEFB4) and immunofluorescence (calprotectin, a dimer of S100A9/S100A8 proteins) demonstrated expression in keratinocytes, primarily in suprabasal cell layers, from SLL samples. These data demonstrate upregulation of a cohort of IL-17A target genes in SLL and support the hypothesis that similarities in the response to stresses and damage exist between equine and human epidermal tissues.
Highlights
Equine laminitis is a common, progressive, crippling and currently incurable disease often necessitating euthanasia to end suffering
To examine whether lamellar tissue responds to IL-17A, we examined target gene expression
Given the high expression of ß defensin 4 in IL-17A-treated human keratinocytes [30], we used qPCR to examine relative expression levels of DEFB4B mRNA in Supporting Limb Laminitis (SLL) samples compared to non-laminitic controls (Fig 4)
Summary
Equine laminitis is a common, progressive, crippling and currently incurable disease often necessitating euthanasia to end suffering. Keratin 14 is expressed within lamellar epidermal basal cells [5,6,7]; equine epidermal lamellae have several architectural and molecular modifications that differ from skin, including limited stratification into basal, suprabasal and cornified layers, and expression of unique keratins not found in equine or human skin [5,6,7] These modifications are thought to impart critical functional differences that allow equine lamellar tissue to bear significantly greater mechanical tensile and compressive forces compared to skin, consistent with the functional integration of the hoof capsule and lamellae into the musculoskeletal system [8]. While differences in etiopathogenesis are reported for the different types of laminitis, several shared morphologic and molecular similarities exist, including keratinocyte apoptosis/necrosis; epidermal hyperplasia, acanthosis, dyskeratosis and hyperkeratosis; basement membrane separation; dermal inflammation; and progressive, deforming distal phalangeal osteolysis with medullary stromal activation and inflammation [9, 11, 14,15,16,17,18,19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
