Aquaporin-4 Is Downregulated in the Basolateral Membrane of Ileum Epithelial Cells during Enterotoxigenic Escherichia coli-Induced Diarrhea in Mice.

Di Zhang,Haizhu Zhou,Kaiqi Zhang,Bo Xu,Longfei Yang,Hongxia Ma,Xin Ma,Weiheng Su,Yuan Zhao

doi:10.3389/fmicb.2017.02655

Abstract

Enterotoxigenic Escherichia coli (ETEC) are opportunistic pathogens that colonize the small intestine, produce enterotoxins and induce diarrhea. Some aquaporins (AQPs), such as AQP3 and AQP8, have been reported to participate in diarrhea by decreasing cellular influx in the gastrointestinal (GI) tract. AQP4 is another important water channel in the GI tract, but its role in ETEC-induced diarrhea has not been reported. Here, we demonstrated the potential roles of AQP4 in ETEC-induced diarrhea. Reverse transcription-polymerase chain reaction (RT-PCR) and western blotting showed that AQP4 was expressed in the mouse ileum, but not in the duodenum or jejunum while immunohistochemical staining showed that AQP4 localized to the basolateral membrane of ileum epithelial cells. Using an ETEC-induced mice diarrhea model, we demonstrated that both AQP4 mRNA level and the AQP4 protein level in the ileum decreased gradually over a time course of 7 days. These results suggest that AQP4 plays a role in the pathogenesis of ETEC-induced diarrhea by mediating water transport.

Highlights

The gastrointestinal (GI) tract transports more than 9 L of fluids on a daily basis by both absorptive and secretory processes including liquid in the diet (2 L) and intestinal secretions (7 L) (Masyuk et al, 2002)
Using Reverse transcription-polymerase chain reaction (RT-PCR), AQP4 mRNA was detected in the ileum in a significant amount and in the jejunum at a barely detectable level, but not in the duodenum of wild-type mice (Figure 1A)
To further localize AQP4, we performed an immunohistochemical analysis of the small intestine using polyclonal AQP4 antibodies, which showed that the AQP4 protein resided in the basolateral membrane of ileum epithelial cells, but not in the jejunum (Figure 1C)

Summary

Introduction

The gastrointestinal (GI) tract transports more than 9 L of fluids on a daily basis by both absorptive and secretory processes including liquid in the diet (2 L) and intestinal secretions (7 L) (Masyuk et al, 2002). A disturbance in the absorptive mechanism can lead to excessive fluid loss from the GI tract and result in diarrhea. Aquaporins (AQPs) play important roles in transcellular water transport, and they are involved in diseases that are characterized by alterations in water transport, such as diarrhea (Zhu et al, 2016). AQP1, 3, 7, 9, 10, and 11 have been identified in the intestine of humans and rats, but their roles in diarrhea have not been fully explored (Hamabata et al, 2002; Laforenza et al, 2010). AQP4 is another important water channel in the GI tract, and it has been shown to be expressed and localized in the small intestine. Sakai et al reported that the gene expression levels of AQP4 and AQP8 in the colon decreased significantly in AQP4 Is Downregulated in ETEC-Induced Diarrhea Mice

Methods

Results

Conclusion