Korean J Physiol Pharmacol.  2018 May;22(3):269-275. 10.4196/kjpp.2018.22.3.269.

Up-regulation of NHE8 by somatostatin ameliorates the diarrhea symptom in infectious colitis mice model

• Lei X
• Cai L
• Li X
• Xu H
• Geng C
• Wang C

• KMID: 2410091
• DOI: http://doi.org/10.4196/kjpp.2018.22.3.269

Abstract

Na⁺/H⁺ exchangers (NHEs) have been shown to be involved in regulating cell volume and maintaining fluid and electrolyte homeostasis. Pooled evidences have suggested that loss of Na⁺/H⁺ exchanger isoform 8 (NHE8) impairs intestinal mucosa. Whether NHE8 participates in the pathology of infectious colitis is still unknown. Our previous study demonstrated that somatostatin (SST) could stimulate the expression of intestinal NHE8 so as to facilitate Na⁺ absorption under normal condition. This study further explored whether NHE8 participates in the pathological processes of infectious colitis and the effects of SST on intestinal NHE8 expression in the setting of infectious colitis. Our data showed that NHE8 expression was reduced in Citrobacter rodentium (CR) infected mice. Up-regulation of NHE8 improved diarrhea symptom and mucosal damage induced by CR. In vitro, a similar observation was also seen in Enteropathogenic E. coli (EPEC) infected Caco-2 cells. Seglitide, a SST receptor (SSTR) 2 agonist, partly reversed the inhibiting action of EPEC on NHE8 expression, but SSTR5 agonist (L-817,818) had no effect on the expression of NHE8. Moreover, SST blocked the phosphorylation of p38 in EPEC-infected Caco-2 cells. Taken together, these results suggest that enhancement of intestinal NHE8 expression by SST could ameliorate the symptoms of mice with infectious colitis.

Keyword

Anti-inflammatory agents; Colitis; Diarrhea; NHE8 protein; Somatostatin

MeSH Terms

Absorption
Animals
Anti-Inflammatory Agents
Caco-2 Cells
Cell Size
Citrobacter rodentium
Colitis*
Diarrhea*
Enteropathogenic Escherichia coli
Homeostasis
Humans
In Vitro Techniques
Intestinal Mucosa
Mice*
Pathologic Processes
Pathology
Phosphorylation
Somatostatin*
Up-Regulation*
Anti-Inflammatory Agents
Somatostatin

Figure

• 

  Fig. 1 Establishment of infectious colitis mice models by C. rodentium(CR) gavage.Various parameters were observed. (A) Diarrhea scores; (B) Concentration of somatostatin (SST) in CR-infected mice. (p<0.05 for CR group vs. CT (control group); unpaired Student's t-test). (C) colonic histology observation (×400 magnification). Results were reported as the mean±SD from 18 mice (p<0.05 for CR [n=9] vs. CT [n=9]; unpaired Student's t-test).

• 

  Fig. 2 Expression of Na+/H+ exchanger 8 (NHE8) protein in C. rodentium-infected mice and EPEC-infected Caco-2 cells.NHE8 expression was calculated by the band density of the NHE8 normalized to the GAPDH band. Results are presented as the mean±SD from 3 independent experiments. (A) Expression of NHE8 protein in the proximal colon. (B) Expression of the NHE8 protein in the distal colon (p<0.05 for C. rodentium-infected mice (CR) vs. control mice (CT) or octreotide-treated CR-infected mice (CR+Oct); one-way ANOVA). (C) Expression of NHE8 protein in EPEC-infected (EPEC) Caco-2 cells (p<0.05 for EPEC group vs. CT or SST-treated group [EPEC+SST]; one-way ANOVA).

• 

  Fig. 3 (A) Effect of octreotide on diarrhea score in C. rodentium-infected mice (p<0.05 for CR vs. CR+Oct; unpaired Student's t-test). (B) Colonic histology observation in both two groups (×400 magnification).

• 

  Fig. 4 Effect of SSTR agonists on the expression of NHE8 protein in Caco-2 cells exposed to EPEC (p<0.05 for EPEC vs. EPEC+ seglitidetreated group; unpaired Student's t-test).Results are presented as the mean±SD from 3 independent experiments.

• 

  Fig. 5 (A) Effect of SST on the phosphorylation of p38 in Caco-2 cells exposed to EPEC. (B) Effect of SST on the phosphorylation of ERK in Caco-2 cells exposed to EPEC (p<0.05 for EPEC vs. CT or EPEC+SST; one-way ANOVA). Results are presented as the mean±SD from 3 independent experiments.

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