The possible association between AQP9 in the intestinal epithelium and acute liver injury‑induced intestinal epithelium damage

Abstract

The present study aimed to investigate the expression and function of aquaporin (AQP)9 in the intestinal tract of acute liver injury rat models. A total of 20 Sprague Dawley rats were randomly divided into four groups: Normal control (NC) group and acute liver injury groups (24, 48 and 72 h). Acute liver injury rat models were established using D‑amino galactose, and the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (Tbil) and albumin were determined using an automatic biochemical analyzer. Proteins levels of myosin light chain kinase (MLCK) in rat intestinal mucosa were investigated via immunohistochemistry. Pathological features were observed using hematoxylin and eosin (H&E) staining. MLCK, AQP9 and claudin‑1 protein expression levels were detected via western blotting. Levels of ALT and AST in acute liver injury rats were revealed to steadily increase between 24 and 48 h time intervals, reaching a peak level at 48 h. Furthermore, TBil levels increased significantly until 72 h. Levels of ALT were revealed to significantly increase until the 48 h time interval, and then steadily decreased until the 72 h time interval. The acute liver injury 72 h group exhibited the greatest levels of MLCK expression among the three acute liver injury groups; however, all three acute liver injury groups exhibited enhanced levels of MLCK expression compared with the NC group. Protein levels of AQP9 and claudin‑1 were enhanced in the NC group compared with the three acute liver injury groups. H&E staining demonstrated that terminal ileum mucosal layer tissues obtained from the acute liver injury rats exhibited visible neutrophil infiltration. Furthermore, the results revealed that levels of tumor necrosis factor‑α, interleukin (IL)‑6 and IL‑10 serum cytokines were significantly increased in the acute liver injury groups. In addition, AQP9 protein expression was suppressed in acute liver injury rats, which induced pathological alterations in terminal ileum tissues may be associated with changes of claudin‑1 and MLCK protein levels.

Keywords: aquaporin 9; light junction; intestinal epithelium damage; acute liver injury; myosin light chain kinase; claudin-1.

Figure 1.

Liver tissues were pathologically examined using hematoxylin and eosin staining (magnification, ×200). Acute liver injury models were established by intraperitoneal injection of D-galactosamine (200 mg/kg), and acute liver injury model rats were then separated into three groups and sacrificed at 24, 48 and 72 h time intervals. Arrows indicate areas of necrosis. M, model.

Figure 2.

Terminal ileum tissues were investigated via histopathology using H&E staining (magnification, ×200). The complete mucosal structure was visualized in terminal ileum tissue obtained from the normal control group, in the absence of inflammation, necrosis and shedding. However, terminal ileum tissue obtained from rats in acute liver injury model groups exhibited increasing levels of neutrophil infiltration (star) in a time-dependent manner, interstitial edema in the villus mucosa and submucosa. Damage to villi (arrow) was observed in terminal ileum tissue obtained from rats in the 72 h acute liver injury model group. M, model; H&E, hematoxylin and eosin.

Figure 3.

MLCK protein expression was detected by immunohistochemistry (magnification, ×400). Terminal ileum tissues obtained from the four experimental groups were used for immunohistochemistry analysis. Quantification data of MLCK expression is presented. *P<0.05 vs. the normal control group. M, model; MLCK, myosin light chain kinase.

Figure 4.

MLCK, AQP9 and claudin-1 protein expression levels were detected via western blotting. Representative blots are presented in the upper panel; Bottom panel: Quantification data are presented. *P<0.05 vs. the normal control group. AQP9, aquaporin 9; MLCK, myosin light chain kinase.