Mechanism of down regulation of Na-H exchanger-2 in experimental colitis

Abstract

BackgroundThe Na-H exchanger [NHE] performs an electroneutral uptake of NaCl and water from the lumen of the gastrointestinal tract. There are several distinct NHE isoforms, some of which show an altered expression in the inflammatory bowel diseases (IBD). In this study, we examined a role of NHE-2 in experimental colitis.MethodsColitis was induced in male Sprague-Dawley rats by intra-rectal administration of trinitrobenzenesulphonic acid (TNBS). On day 6 post-TNBS, the animals were sacrificed, colonic and ileal segments were taken out, cleaned with phosphate buffered saline and used in this study.ResultsThere was a significant decrease in the level of NHE-2 protein as measured by ECL western blot analysis and confocal immunofluorescence microscopy. The levels of NHE-2 mRNA and heteronuclear RNA measured by an end-point RT-PCR and a real time PCR were also decreased significantly in the inflamed colon. However, there was no change in the level of NHE-2 protein in response to in vitro TNF-α treatment of uninflamed rat colonic segment. These changes were selective and localized to the colon as actin, an internal control, remained unchanged. Confocal immunofluorescence microscopy revealed co-localization of NHE-2 and NHE-3 in the brush borders of colonic epithelial cells. Inflamed colon showed a significant increase in myeloperoxidase activity and colon hypertrophy. In addition, there was a significant decrease in body weight and goblet cells’ mucin staining in the TNBS treated colon. These changes were not conspicuous in the non-inflamed ileum.ConclusionsThese findings demonstrate suppression of NHE-2 expression on the brush borders in the colonic epithelial cells which is regulated transcriptionally. However a role of TNF-α in the regulation of NHE-2 is discounted in the present model of colitis. This decrease in the NHE-2 expression will lead to a loss of electrolyte and water uptake thus contributing to the symptoms associated with IBD.

Pathophysiology of IBD associated diarrhea

“… 37 A significant decrease in colonic NHE2 mRNA and protein expression is also reported in rat model of TNBS induced colitis. 38 Surprisingly, no change in the expression of NHE2 is reported in biopsies from UC patients and in mouse model of DSS induced colitis. 35 Also, NHE2 KO mice neither show alterations in intestinal Na + absorption nor a diarrheal phenotype.…”

NHA2 promotes cyst development in an in vitro model of polycystic kidney disease

“…Of note, down‐regulation of related NHE2 isoform observed in our analysis of patient cysts could indicate renal inflammation driven by proinflammatory cytokines (Soleiman et al . ).…”

Uncoupling of Carbonic Anhydrase from Na-H exchanger-1 in Experimental Colitis: A Possible Mechanistic Link with Na-H Exchanger

“…Body weight recorded just before the induction of colitis was considered as the day 0 weight, and the weight recorded just before sacrifice was designated as the day 6 post-TNBS weight. Changes in the body weight were calculated and compared to their respective weights on day 0 [17,29]. Colon lengths and weights were also recorded on day 6, and changes were calculated with respect to the uninflamed colons in the controls.…”

“…IBD conditions are frequently associated with diarrhea, pain, and altered muscle contractility. With regard to the role of other transporters in relation to Na–H exchanger-1 (NHE-1), our laboratory and others have reported impairment of Na + transporting mechanisms including Na/K-ATPase (sodium pump) and Na–H exchanger (NHE) in the inflamed GI tract [14,15,16,17]. These changes may lead to increased amounts of Na + , Cl − , and water in the luminal contents.…”