D-glucose acts via sodium/glucose cotransporter 1 to increase NHE3 in mouse jejunal brush border by a Na+/H+ exchange regulatory factor 2-dependent process.
OBJECTIVE
Oral rehydration solutions reduce diarrhea-associated mortality. Stimulated sodium absorption by these solutions is mediated by the Na(+)/H(+) hydrogen exchanger NHE3 and is increased by Na(+)-glucose co-transport in vitro, but the mechanisms of this up-regulated process are only partially understood.


METHODS
Intracellular pH was measured in jejunal enterocytes of wild-type mice and mice with disrupted Na+/H+ exchange regulatory co-factor 2 (NHERF2-/- mice) by multiphoton microscopy. Diarrhea was induced by cholera toxin. Caco-2BBe cells that express NHE3 and the sodium/glucose cotransporter 1 (SGLT1) were studied by fluorometry, before and after siRNA-mediated knockdown of NHERF1 or NHERF2. NHE3 distribution was assessed by cell-surface biotinylation and confocal microscopy. Brush-border mobility was determined by fluorescence recovery after photobleaching and confocal microscopy.


RESULTS
The nonmetabolized SGLT1 substrate α-methyl-D-Glu (α-MD-G) activated jejunal NHE3; this process required Akt and NHERF2. α-MD-G normalized NHE3 activity after cholera toxin-induced diarrhea. α-MD-G-stimulated jejunal NHE3 activity was defective in NHERF2-/- mice and cells with NHERF2 knockdown, but occurred normally with NHERF1 knockdown; was associated with increased NHE3 surface expression in Caco-2 cells, which also was NHERF2-dependent; was associated with dissociation of NHE3 from NHERF2 and an increase in the NHE3 mobile fraction from the brush border; and was accompanied by a NHERF2 ezrin-radixin-moesin-binding domain-dependent increase in co-precipitation of ezrin with NHE3.


CONCLUSIONS
SGLT1-mediated Na-glucose co-transport stimulates NHE3 activity in vivo by an Akt- and NHERF2-dependent signaling pathway. It is associated with increased brush-border NHE3 and association between ezrin and NHE3. Activation of NHE3 corrects cholera toxin-induced defects in Na absorption and might contribute to the efficacy of oral rehydration solutions.
Lin
Rong
R
Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Murtazina
Rakhilya
R
Cha
Boyoung
B
Chakraborty
Molee
M
Sarker
Rafiquel
R
Chen
Tian-E
TE
Lin
Zhihong
Z
Hogema
Boris M
BM
de Jonge
Hugo R
HR
Seidler
Ursula
U
Turner
Jerrold R
JR
Li
Xuhang
X
Kovbasnjuk
Olga
O
Donowitz
Mark
M
D000818:Animals; D018938:Caco-2 Cells; D002772:Cholera Toxin / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003967:Diarrhea / Q000139:chemically induced / Q000628:therapy*; D005440:Fluid Therapy; D005947:Glucose / Q000008:administration & dosage* / Q000378:metabolism; D006801:Humans; D007408:Intestinal Absorption; D007583:Jejunum / Q000378:metabolism; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008871:Microvilli / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D051269:Sodium-Glucose Transporter 1 / Q000235:genetics / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D000099149:Ezrin
D002772:Cholera Toxin; D003598:Cytoskeletal Proteins; D005947:Glucose; D008757:Methylglucosides; D010750:Phosphoproteins; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D012964:Sodium; D051269:Sodium-Glucose Transporter 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000099149:Ezrin; C000613385:SLC9A3 protein, human; C000613386:Slc9a3 protein, mouse; C093376:sodium-hydrogen exchanger regulatory factor; C027020:methylglucoside