In Vivo and In Vitro Evidence of the Involvement of CXCL1, a Keratinocyte‐Derived Chemokine, in Equine Laminitis

Abstract

C-X-C motif ligand 1 (CXCL1) is an important chemokine of epithelial origin in rodents and humans. To assess in vivo and in vitro the regulation of CXCL1 in equine laminitis. Twenty adult horses. Real-time quantitative polymerase chain reaction (PCR) was used to assess expression of CXCL1 in samples of laminae, liver, skin, and lung from the black walnut extract (BWE) model of laminitis, and in cultured equine epithelial cells (EpCs). Tissue was obtained from control animals (CON, n = 5), and at 1.5 hours (early time point [ETP] group, n = 5), at the onset of leukopenia (developmental time point [DTP] group, n = 5), and at the onset of lameness (LAM group, n = 5) after BWE administration. EpCs were exposed to Toll-like/Nod receptor ligands, oxidative stress agents, and reduced atmospheric oxygen (3%). In situ PCR was used to localize the laminar cell types undergoing CXCL1 mRNA expression. Increases in laminar CXCL1 mRNA concentrations occurred in the ETP (163-fold [P= .0001]) and DTP groups (21-fold [P= .005]). Smaller increases in CXCL1 expression occurred in other tissues and organs. In cultured EpCs, increases (P < .05) in CXCL1 mRNA concentration occurred after exposure to lipopolysaccharide (LPS [28-fold]), xanthine/xanthine oxidase (3.5-fold), and H(2)O(2) (2-fold). Hypoxia enhanced the LPS-induced increase in CXCL1 mRNA (P= .007). CXCL1 gene expression was localized to laminar EpCs, endothelial cells, and emigrating leukocytes. These findings indicate that CXCL1 plays an early and possibly initiating role in neutrophil accumulation in the BWE laminitis model, and that laminar keratinocytes are an important source of this chemokine. New therapies using chemokine receptor antagonists may be indicated.