Human Β-Defensin-2 Increases Cholinergic Response in Colon Epithelium

The human β-defensin-2 (hBD-2) is expressed in epithelial cells of skin and respiratory and gastrointestinal tracts. Defensins are arginine-rich small cationic peptides with six intramolecular disulfide bonds and are antimicrobially active against a broad spectrum of pathogens. In addition, they have cytokine-like immunomodulatory properties. We hypothesized that hBD-2 also might influence epithelial cells themselves, thereby altering fluid composition in the gastrointestinal tract. We therefore tested its impact on electrogenic ion transport properties of distal colon in Ussing chamber experiments. Application of hBD-2 did not affect transepithelial voltage or resistance in cAMP-stimulated distal colon. However, it increased cholinergic Ca2+-dependent Cl− secretion. After 20 min of incubation with hBD-2, the effect of carbachol (CCh) on the equivalent short circuit current (I′sc) was enhanced twofold compared to vehicle-treated colon. Modulation of Ca2+ signaling by hBD-2 was validated by Fura-2 measurements in human colon carcinoma HT29 cells. Twenty-minute incubation with hBD-2 increased the CCh-induced Ca2+ transient by 20–30% compared to either vehicle-treated cells or cells treated with the defensins hBD-1, hBD-3, or HD-5. This effect was concentration-dependent, with an EC50 of 0.043 µg/ml, and still present in the absence of extracellular Ca2+. Also, the ionomycin-induced Ca2+ transient was increased by hBD-2 treatment. We conclude that hBD-2 facilitates cholinergic Ca2+-regulated epithelial Cl− secretion. These findings contribute to the concept of a specific interaction of antimicrobial peptides with epithelial function.