Mitogen-activated kinase pathway activation in epidermal lamellae in the acute stages of carbohydrate overload laminitis models and the effect of regional deep hypothermia on signalling pathways

Reasons for performing study: In sepsis models, mitogen-activated protein kinases (MAPKs) are reported to incite inflammatory injury to tissues and are purported to be a therapeutic target.

Objectives: To assess MAPK signalling in lamellae in sepsis-related laminitis (SRL) at different time points after induction of laminitis via carbohydrate overload, and to determine the effect of regional deep hypothermia (RDH) on MAPK signalling.

Study design: In vitro study using archived tissue samples.

Methods: Lamellar concentrations of MAPKs were assessed in archived lamellar samples from 2 studies: 1) the starch gruel model of SRL with 3 groups (n = 6/group) of horses (control, onset of fever [DEV] Obel Grade 1 lameness [OG1]); and 2) from limbs maintained at ambient (AMB) and hypothermic (ICE) temperatures (n = 6/group) in animals given a bolus of oligofructose. Immunoblotting and immunolocalisation were used to assess lamellar concentrations and cellular localisation of total and activated (phosphorylated) forms of p38 MAPK, extracellular-regulated kinase (ERK) 1/2, and stress-activated protein kinase/c-jun N terminal kinase (SAPK/JNK) 1/2.

Results: Lamellar samples had statistically significant increased concentrations of activated ERK 1/2 at the onset of OG1 laminitis (vs. control) in the starch gruel model, but showed no significant change between ICE and AMB limbs in the RDH model. Phospho-SAPK/JNK 1/2 exhibited a similar significant increase in the OG1 samples, but was also increased in ICE (vs. AMB) limbs. No statistically significant changes in lamellar p38 MAPK concentrations were noted.

Conclusions: Increased concentrations of activated ERK 1/2 and SAPK/JNK in the acute stages of SRL indicate a possible role of these signalling proteins in lamellar injury. Signalling related to ERK 1/2 and SAPK/JNK 1/2 pathways should be further investigated to determine if these play a detrimental role in laminitis and may be therapeutic targets to be manipulated independently of RDH.