Pathogenic Escherichia coli increase Cl- secretion from intestinal epithelia by upregulating galanin-1 receptor expression

Galanin is widely distributed in enteric nerve terminals lining the human g astrointestinal (GI) tract. We have shown previously that galanin-l recepto rs (Gal1-R) are expressed by epithelial cells lining the human GI tract, an d upon activation cause Cl- secretion. Because expression of this receptor is transcriptionally regulated by nuclear factor-kappa B (NF-kappa B), whic h is activated by enteric pathogens as a part of the host epithelial respon se to infection, we investigated whether such bacterial pathogens could dir ectly increase Gal1-R expression in the T84-cell model system. Pathogenic E scherichia coli, but not nonpathogenic E. coli, activate a p50/p65 NF-kappa B complex that binds to oligonucleotides corresponding to a recognition si te located within the 5' flanking region of the human GAL1R gene. Pathogeni c E. coli, but not normal commensal organisms, increase Gal1-R mRNA synthes is and [I-125]galanin binding sites. Whereas galanin increases short-circui t current (Isc) approximately 5-fold in uninfected T84 cells, exposure to p athogenic, but not nonpathogenic, E. coli results in galanin increasing Isc approximately 20-fold. To confirm the validity of these in vitro observati ons, we also studied C57BL/GJ mice infected with enterohemorrhagic E. coli (EHEC) by gavage. Infection caused a progressive increase in both NF-KB act ivation and Gal1-R expression, with maximal levels of both observed 3 days after gavage. Ussing chamber studies revealed that colons infected with EHE C, but not those exposed to normal colonic flora, markedly increased Isc in response to galanin. These data indicate that pathogen-induced increases i n Gal1-R expression by epithelial cells lining the colon may represent a no vel unifying pathway responsible for at least a portion of the excessive fl uid secretion observed during infectious diarrhea.