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

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.

Abbreviations used in this paper: Apc, adenomatous polypopsis coli, BSA, bovine serum albumin, CT, cholera toxin, CFTR, cystic fibrosis transmembrane conductance regulator, LPA, lysophosphatidic acid, mRNA, messenger RNA, NHE3, Na⁺/H⁺ exchanger type 3, NHERF, Na⁺/H⁺ exchanger regulatory factor, OK, opossum kidney, PBS, phosphate-buffered saline, PCR, polymerase chain reaction, PDZ, postsynaptic density 95, discs large, and zonula occludens–1, PDZK1, PDZ domain containing protein in kidney 1, RT, reverse transcription, TNF-α, tumor necrosis factor−α, WT, wild-type