Bacterial Periplasmic Oxidoreductases Control the Activity of Oxidized Human Antimicrobial ß-Defensin 1.

The antimicrobial peptide human ß-defensin 1 (hBD1) is continuously produced by epithelial cells in many tissues. Compared to other defensins, hBD1 has only minor antibiotic activity in its native state. After reduction of its disulfide bridges, however, it becomes a potent antimicrobial agent against bacteria, while the oxidized native form (hBD1ox) shows specific activity against Gram-negative bacteria. We show that the killing mechanism of hBD1ox depends on aerobic growth conditions and bacterial enzymes. We analyzed the different activities of hBD1 using mutants of Escherichia coli lacking one or more specific proteins of their outer membrane, cytosol, or redox systems. We discovered that DsbA and DsbB are essential for the antimicrobial activity of hBD1ox but not for that of reduced hBD1 (hBD1red). Furthermore, our results strongly suggest that hBD1ox uses outer membrane protein FepA to penetrate the bacterial periplasm space. In contrast, other bacterial proteins in the outer membrane and cytosol did not modify the antimicrobial activity. Using immunogold labeling, we identified the localization of hBD1ox in the periplasmic space and partly in the outer membrane of E. coli However, in resistant mutants lacking DsbA and DsbB, hBD1ox was detected mainly in the bacterial cytosol. In summary, we discovered that hBD1ox could use FepA to enter the periplasmic space, where its activity depends on presence of DsbA and DsbB. HBD1ox concentrates in the periplasm in Gram-negative bacteria, which finally leads to bleb formation and death of the bacteria. Thus, the bacterial redox system plays an essential role in mechanisms of resistance against host-derived peptides such as hBD1.

Chronic Heavy Alcohol Use is Associated with Upregulated Paneth Cell Antimicrobials in Gastric Mucosa.

OBJECTIVES: How alcohol consumption affects the integrity and the defense mechanisms of the mucosa in the upper gastrointestinal tract is largely unknown. We examined the effect of heavy alcohol use on gastric and duodenal Paneth-cell-derived and epithelial antimicrobial peptides (AMPs), cytokines, and the Wnt pathway, an important regulator of epithelial regeneration. METHODS: In 22 patients with heavy alcohol use and 17 control subjects, biopsies from gastric corpus, antrum, and duodenum were examined for messenger RNA (mRNA) of AMPs, cytokines, and Wnt pathway factors using real-time PCR. The expression of the α-defensin HD5 was analyzed immunohistochemically. The effect of alcohol exposure on Wnt signaling and AMP production was also studied in a gastric cell line using mRNA and reporter gene assays. RESULTS: Heavy alcohol use was associated with increased expression of Paneth cell HD5 and HD6 mRNA in the antrum, where these products are normally absent (HD5 mRNA in controls vs. PATIENTS: 2100±900 and 365 500±161 600, HD6 mRNA: 320±130 and 58 300±32 600 copies per 10 ng total RNA, means±s.e.m., P value: 0.022 and 0.011). Upregulated HD5 was independent of intestinal metaplasia that was observed in a minority of patients. No significant differences were found for ß-defensins and cytokines (interleukins IL1ß, IL6, IL8, IL10). In patients, Wnt pathway factors showed a trend toward higher levels. In vitro, ethanol exposure induced the production of HD5 and HD6 and activation of the Wnt pathway. CONCLUSIONS: Alcohol exposure can induce gastric Paneth cell AMP expression. This may be linked to Wnt pathway activation, which has an important role in the epithelial regenerative homeostasis.

Cell-mediated reduction of human ß-defensin 1: a major role for mucosal thioredoxin.

Human ß-defensin 1 (hBD-1) is an antimicrobial peptide expressed by epithelia and hematopoietic cells. We demonstrated recently that hBD-1 shows activity against enteric commensals and Candida species only after its disulfide bonds have been reduced by thioredoxin (TRX) or a reducing environment. Here we show that besides TRX, glutaredoxin (GRX) is also able to reduce hBD-1, although with far less efficacy. Moreover, living intestinal and lymphoid cells can effectively catalyze reduction of extracellular hBD-1. By chemical inhibition of the TRX system or specific knockdown of TRX, we demonstrate that cell-mediated reduction is largely dependent on TRX. Quantitative PCR in intestinal tissues of healthy controls and inflammatory bowel disease patients revealed altered expression of some, although not all, redox enzymes, especially in ulcerative colitis. Reduced hBD-1 and TRX localize to extracellular colonic mucus, suggesting that secreted or membrane-bound TRX converts hBD-1 to a potent antimicrobial peptide in vivo.