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.
Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Rong
R
Lin
Rakhilya
R
Murtazina
Boyoung
B
Cha
Molee
M
Chakraborty
Rafiquel
R
Sarker
Tian-E
TE
Chen
Zhihong
Z
Lin
Boris M
BM
Hogema
Hugo R
HR
de Jonge
Ursula
U
Seidler
Jerrold R
JR
Turner
Xuhang
X
Li
Olga
O
Kovbasnjuk
Mark
M
Donowitz
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