Gastroenterology

Gastroenterology

Volume 138, Issue 2, February 2010, Pages 649-658
Gastroenterology

Basic—Alimentary Tract
Lysophosphatidic Acid Stimulates the Intestinal Brush Border Na+/H+ Exchanger 3 and Fluid Absorption via LPA5 and NHERF2

https://doi.org/10.1053/j.gastro.2009.09.055Get rights and content

Background & Aims

Diarrhea results from reduced net fluid and salt absorption caused by an imbalance in intestinal absorption and secretion. The bulk of sodium and water absorption in the intestine is mediated by Na+/H+ exchanger 3 (NHE3), located in the luminal membrane of enterocytes. We investigated the effect of lysophosphatidic acid (LPA) on Na+/H+ exchanger activity and Na+-dependent fluid absorption in the intestine.

Methods

We analyzed the effects of LPA on fluid absorption in intestines of wild-type mice and mice deficient in Na+/H+ exchanger regulatory factor 2 (NHERF2; Nherf2−/−) or LPA2 (Lpa2−/−). Roles of LPA5 and NHERF2 were determined by analysis of heterologous expression.

Results

Under basal conditions, LPA increased fluid absorption in an NHE3-dependent manner and restored the net fluid loss in a mouse model of acute diarrhea. Expression of the LPA receptor LPA5 was necessary for LPA-induced stimulation of NHE3 activity in colonic epithelial cells. Stimulation of NHE3 by the LPA-LPA5 signaling required coexpression of NHERF2, which interacted with LPA5. LPA-mediated intestinal fluid absorption was impaired in Nherf2−/− mice, demonstrating the requirement for NHERF2 in LPA5 activity. However, fluid absorption was unaltered in Lpa2−/− mice. LPA stimulated NHE3 and fluid absorption in part by increasing NHE3 protein abundance at the brush border membrane of intestinal epithelial cells.

Conclusions

LPA is a potent stimulant of NHE3 and fluid absorption in the intestine, signaling through LPA5. Regulation by LPA5 depends on its interaction with NHERF2. LPA might be useful in the treatment of certain diarrheal diseases.

Section snippets

Animals

Lpa2/ mice in C57BL/6 background were reported recently.13Nherf2/ mice10 were bred in C57BL/6 or FVB/N background for at least 15 generations. Nherf2/ mice on C57BL/6 background were compared with Lpa2/ mice, and Nherf2/ mice on the FVB/N background were compared with mice deficient for other NHERF proteins.10 Age- and sex-matched littermates of the same respective genetic background were used as controls. It was made certain that both genetic backgrounds responded similarly to LPA (

LPA Induces NHE3-Dependent Water Absorption In Vivo

We sought to test whether LPA can regulate NHE3-dependent intestinal fluid absorption, which is the hallmark of diarrhea. We adapted the in vivo perfusion system in which a small loop of intestine of an anesthetized mouse is perfused in a recirculating manner.15Figure 1A depicts typical changes in fluid absorption over 3 hours. There was a net absorption of fluid in the ileum at the rate of 50.6 ± 3.7 μL/cm/h at basal conditions (Figure 1B). To determine the effect of LPA, 20 μM LPA was

Discussion

In the present study, we investigated the effect of LPA on NHE3 activity and NHE3-mediated fluid absorption in the intestine. We found that LPA is a potent stimulator of Na+ and fluid absorption. The presence of LPA is able to overcome diarrhea induced by CT or TNF-α, suggesting its potential therapeutic usage. LPA specifically acted on NHE3, but not on NHE1 or NHE2. Moreover, this regulation was dependent on the presence of NHERF2 as demonstrated both in vitro and in vivo. Our study identifies

Acknowledgments

Drs Lin and Yeruva contributed equally to this work.

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    Conflicts of interest The authors disclose no conflicts.

    Funding This work was funded by National Institutes of Health grants DK061416 (CCY), MH51699 and HD50685 (JC) and by DFGSFB621-C9 (US). SL was supported by the Crohn's and Colitis Foundation of America. PH was supported by the American Heart Association. AS and MC were supported by postdoctoral stipends of the Hannover biomedical Research School that were funded by the DAAD and Abbot GmbH via the “matching fund” program. We thank the Emory Digestive Disease Research Development Center (supported by DK064399) for the use of light microscope and the Zeiss 510 confocal microscope and the Volkswagen Stiftung for funding of the Leica LSM.

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