Hypoxia-independent activation of HIF-1 by Enterobacteriaceae and their siderophores

Background & Aims: Hypoxia inducible factor-1 (HIF-1) is the key transcriptional regulator during adaptation to hypoxia. Recent studies provide evidence for HIF-1 activation during bacterial infections. However, molecular details of how bacteria activate HIF-1 remain unclear. Here, we pursued the role of bacterial siderophores in HIF-1 activation during infection with Enterobacteriaceae. Methods: In vivo, HIF-1 activation and HIF-1-dependent gene induction in Peyer's patches were analyzed after orogastric infection with Yersinia enterocolitica. The course of an orogastric Y enterocolitica infection was determined using mice with a deletion of HIF-1 a in the intestine. In vitro, the mechanism of HIF-1 activation was analyzed in infections with Y enterocolitica, Salmonella enterica subsp enterica, and Enterobacter aerogenes. Results: Infection of mice with Y enterocolitica led to functional activation of HIF-1 in Peyer's patches. Because mice with deletion of RIF-1 alpha in the intestinal epithelium showed a significantly higher susceptibility to orogastric Y enterocolitica infections, bacterial HIF-1 activation appears to represent a host defense mechanism. Additional studies with Y enterocolitica, S enterica subsp enterica, or E aerogenes, and, moreover, application of their siderophores (yersiniabactin, salmochelin, aerobactin) caused a robust, dose-dependent HIF-1 response in human epithelia and endothelia, independent of cellular hypoxia. HIF-1 activation occurs most likely because of inhibition of prolythydroxylase activity and is abolished upon infection with siderophore uptake deficient bacteria. Conclusions: Taken together, this study reveals what we believe to be a previously unrecognized role of bacterial siderophores for hypoxia-independent activation of HIF-1 during infection with human pathogenic bacteria.