Butyrate induces intestinal sodium absorption via Sp3-mediated transcriptional up-regulation of epithelial sodium channels.
OBJECTIVE
The epithelial sodium channel (ENaC) is the rate-limiting factor for colonic electrogenic sodium absorption. This study aimed to investigate ENaC regulation by butyrate, a short-chain fatty acid (SCFA) produced by intestinal bacteria.


METHODS
ENaC was examined in HT-29/B6 cells and glucocorticoid receptor(GR)-transfected HT-29/B6 cells (HT-29/B6-GR) by reverse-transcription polymerase chain reaction, real-time polymerase chain reaction, and confocal microscopy. ENaC promoters were investigated by deletion/mutation analysis, electrophoretic mobility shift assays, and quantitative chromatin immunoprecipitation. Sodium transport of HT-29/B6-GR cells and rat distal colon was quantified in Ussing chambers.


RESULTS
Butyrate up-regulated beta- and gamma-ENaC mRNA expression in HT-29/B6 cells and induced transcription from beta- and gamma-ENaC promoter constructs. The gamma-ENaC promoter could also be induced by the SCFA propionate but not by acetate. Deletion/mutation assays revealed that activation of the gamma-ENaC promoter depended on 2 GC boxes, which were shown to bind Sp1 and Sp3 in vitro. Although both transcription factors increased butyrate-mediated gamma-ENaC transcription upon overexpression, chromatin immunoprecipitation revealed that only Sp3 binds to the gamma-ENaC promoter in vivo and that Sp3 binding is enhanced by butyrate. Transcriptional ENaC induction by butyrate led to synthesis of gamma-ENaC subunits, but correct targeting of ENaC channels to the apical cell membrane was dependent on corticosteroid hormones. Finally, butyrate substantially increased electrogenic sodium absorption via ENaC in the presence of corticosteroid hormones in HT-29/B6-GR cells and in rat distal colon.


CONCLUSIONS
Concerted action of SCFA and corticosteroid hormones is required for induction of ENaC and maintenance of intestinal electrogenic sodium absorption.
Zeissig
Sebastian
S
Department of Gastroenterology, Infectious Diseases, and Rheumatology, Charité, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany.
Fromm
Anja
A
Mankertz
Joachim
J
Weiske
Jörg
J
Zeitz
Martin
M
Fromm
Michael
M
Schulzke
Jörg-Dieter
JD
D000305:Adrenal Cortex Hormones / Q000494:pharmacology; D000818:Animals; D002087:Butyrates / Q000378:metabolism* / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D053503:Epithelial Sodium Channels / Q000235:genetics* / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D019073:HT29 Cells; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D008297:Male; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000378:metabolism; D051705:Sp3 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D000305:Adrenal Cortex Hormones; D002087:Butyrates; D053503:Epithelial Sodium Channels; C507048:SCNN1B protein, human; C507052:SCNN1G protein, human; C497121:SP3 protein, human; D016329:Sp1 Transcription Factor; D051705:Sp3 Transcription Factor; D012964:Sodium