Activation of c-Jun N-terminal kinase (JNK) signalling in experimentally induced gastric lesions in rats

Abstract

The c-Jun N-terminal kinase (JNK) participates in intracellular signalling cascades that mediate inflammatory responses. Therefore, the JNK signalling may be involved in gastric injury and inhibition of this pathway may form the basis of a new strategy for the treatment of gastric injury. The aim of this study was to determine whether JNK participates in the formation of gastric lesions in an experimental model. Acute gastric injury was induced in Sprague-Dawley rats by intragastric administration of 100% ethanol. The amount of phospho-JNK in the rat stomach was determined using immunohistochemistry and Western analysis. Animals received subcutaneous injections of a specific JNK inhibitor SP600125 or vehicle and the extent of mucosal damage in the stomach was determined. Western analysis revealed early phosphorylation of JNK and, to a lesser extent, p38 as well as late phosphorylation of the p42/44 extracellular signal-related kinases during the development of gastric lesions. JNK was phosphorylated in epithelial cells and in occasional mononuclear cells present at lesion sites. These cells were rarely found in samples from control specimens. Treatment with SP600125 significantly reduced the extent of gastric lesions. These findings indicate that experimental gastric injury is associated with activation of the JNK signalling pathway, and also suggest that JNK inhibitors may play a role in the treatment of gastric injury in humans.

Fig. 1

Time course for changes in gastric tissue damage. Gastric injury was induced by intragastric administration of 100% ethanol and tissue damage was assessed by stomach weight and lesion morphology (range from 0, normal to 3, maximal activity) at the indicated time-points. Each point represents the mean ± SEM for 4–8 animals. P < 0·05 versus control.

Fig. 2

0. Histological manifestations of gastric lesions (a) before and (b) 1 h, (c) 24 h and (d) 4 days after exposure to 100% ethanol (haematoxylin and eosin).

Fig. 3

Time course-changes in the extent of MAPKs phosphorylation during ethanol-induced gastric injury in rats. Gastric injury was induced by intragastric administration of 100% ethanol. Expression of phospho-ERK, ERK, phospho-p38, p38, phospho-JNK, and JNK in tissue homogenates was determined by Western blotting. A representative Western blot of three separate experiments is shown.

Fig. 4

Localization of phospho-JNK immunoreactivity in stomach sections of rats (a) before and (b) 24 h after intragastric administration of 100% ethanol. Staining of epithelial cells and occasional mononuclear cells for phospho-JNK is demonstrated. Control slides incubated with control IgG or saline showed no immunoreactivity, and staining was greatly reduced after preincubation of the primary antibody with recombinant phospho-JNK (not shown).

Fig. 5

Effects of SP600125 on tissue damage in ethanol-induced gastric injury in rats. Rats received SP600125 (30 mg/kg) or vehicle by subcutaneous injection 2 h before and 12 h after exposure to ethanol, and the severity of injury was evaluated by stomach weight and lesion morphology (range from 0, normal to 3, maximal activity) 24 h following the induction of injury. Bars represent mean values ± SEM for 9 rats per group.

Fig. 6

Photographs showing the macroscopic (a,b) and microscopic (c,d) appearance of ethanol-induced gastric injury after treatment with vehicle (a,c) or SP600125 (b,d). Rats received SP600125 (30 mg/kg) or vehicle by subcutaneous injection 2 h before and 12 h after induction of gastric injury. The stomach was opened along the greater curvature 24 h after the induction of injury. Note that severe mucosal and submucosal inflammation with erosive injury was less severe in the SP600125-treated rat (haematoxylin and eosin). Original magnification ×100.