Enteropathogenic Escherichia coli infection inhibits intestinal serotonin transporter function and expression.
OBJECTIVE
Serotonin transporter (SERT) plays a critical role in regulating serotonin (5-hydroxytryptamine [5-HT]) availability in the gut. Elevated 5-HT levels are associated with diarrheal conditions such as irritable bowel syndrome and enteric infections. Whether alteration in SERT activity contributes to the pathophysiology of diarrhea induced by the food-borne pathogen enteropathogenic Escherichia coli (EPEC) is not known. The present studies examined the effects of EPEC infection on SERT activity and expression in intestinal epithelial cells and elucidated the underlying mechanisms.


METHODS
Caco-2 cells as a model of human intestinal epithelia and EPEC-infected C57BL/6J mouse model of infection were utilized. SERT activity was measured as Na(+) and Cl(-) dependent (3)[H] 5-HT uptake. SERT expression was measured by real-time quantitative reverse-transcription polymerase chain reaction, Western blotting, and immunofluorescence studies.


RESULTS
Infection of Caco-2 cells with EPEC for 30-120 minutes decreased apical SERT activity (P < .001) in a type 3 secretion system dependent manner and via involvement of protein tyrosine phosphatases. EPEC infection decreased V(max) of the transporter; whereas cell surface biotinylation studies revealed no alteration in the cellular or plasma membrane content of SERT in Caco-2 cells. EPEC infection of mice (24 hours) reduced SERT immunostaining with a corresponding decrease in SERT messenger RNA levels, 5-HT uptake, and mucosal 5-HT content in the small intestine.


CONCLUSIONS
Our results demonstrate inhibition of SERT by EPEC and define the mechanisms underlying these effects. These data may aid in the development of a novel pharmacotherapy to modulate the serotonergic system in treatment of infectious diarrheal diseases.
Esmaili
Ali
A
Section of Digestive Diseases and Nutrition, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
Nazir
Saad F
SF
Borthakur
Alip
A
Yu
Dan
D
Turner
Jerrold R
JR
Saksena
Seema
S
Singla
Amika
A
Hecht
Gail A
GA
Alrefai
Waddah A
WA
Gill
Ravinder K
RK
D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D018938:Caco-2 Cells; D004195:Disease Models, Animal; D015536:Down-Regulation; D054308:Enteropathogenic Escherichia coli / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000378:metabolism* / Q000382:microbiology; D005455:Fluorescent Antibody Technique; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000382:microbiology; D007421:Intestine, Small / Q000378:metabolism* / Q000382:microbiology; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C493231:Slc6a4 protein, mouse; D012701:Serotonin; D017027:Protein Tyrosine Phosphatases