Influence of digital hypothermia on lamellar events related to IL-6/gp130 signalling in equine sepsis-related laminitis.

Abstract

BACKGROUND\nInterleukin-6 (IL-6) is consistently increased in the digital lamellae in different studies of sepsis-related laminitis (SRL). IL-6 signalling through the gp130 receptor activates similar signalling (i.e. mTORC1-related signalling) previously reported to be activated in models of endocrinopathic laminitis.\n\n\nOBJECTIVES\nTo assess activation state of signalling proteins downstream of IL-6/gp130 receptor complex activation in an experimental model of SRL.\n\n\nSTUDY DESIGN\nRandomised experimental study.\n\n\nMETHODS\nLamellar phospho-(P) protein concentrations downstream of the IL-6/gp130 receptors were assessed in the oligofructose (OF) model of SRL. Fifteen Standardbred horses were administered water (CON, n = 8) or oligofructose (OF, n = 7) via nasogastric tube. At 12 hours post-OF/water administration, one randomly assigned forelimb was exposed to continuous digital hypothermia (CDH) by placement in ice water (ICE, maintained at <7 degrees Celsius); the other forelimb was maintained at ambient temperature (AMB). Lamellar tissue samples were collected after 24 h of CDH from both ICE and AMB forelimbs and immediately snap-frozen. Lamellar proteins of interest were assessed by immunoblotting and immunofluorescence.\n\n\nRESULTS\nImmunoblotting revealed increases (p<0.05) in the phosphorylation states of Akt (Ser 473), RPS6 (Ser235/236), RPS6 (Ser240/244), STAT3 (Ser727), and STAT3 (Tyr705) in lamellar tissue from OF-treated animals (AMB OF vs. AMB CON limbs); CDH resulted in decreased (p<0.05) lamellar concentrations of phosphorylated Akt, p70S6K, RPS6 (235/236), RPS6 (240/244), and STAT3 (S727) in OF-treated animals (AMB OF vs. ICE OF). Immunofluorescence showed that activated/phosphorylated forms of RPS6 and STAT3 were primarily localised to lamellar epithelial cells.\n\n\nMAIN LIMITATIONS\nThe nature, sequence, and timing of sub-cellular events in this experimental model may differ from those that accompany naturally occurring sepsis.\n\n\nCONCLUSIONS\nThere were increased lamellar concentrations of activated signalling proteins downstream of the IL-6/Gp130 receptor complex in OF-treated horses; CDH inhibited this activation for the majority of the proteins assessed. These results demonstrate similar lamellar signalling (e.g. mTORC1-related signalling) and, therefore, possible therapeutic targets occurring in sepsis-related laminitis as previously reported in models of endocrinopathic laminitis. This article is protected by copyright. All rights reserved.