Effects of nitric oxide on HIF‐1α and FIH‐1 following Clostridium difficile toxin exposure

Abstract

Clostridium difficile (C.diff) is a leading cause of infectious colitis in humans. C.diff toxins disrupt the intestinal epithelial barrier and induce the release of proinflammatory mediators. The hypoxia‐inducible factor‐1 (HIF‐1α) is a stress‐induced transcription factor that mediates mucosal and barrier protective genes. Nitric oxide (NO) and the factor‐inhibiting HIF‐1α (FIH‐1) modulate HIF‐1α expression and signaling, respectively. We hypothesize that NO produced during C.diff toxin‐induced intestinal injury is an important signal to activate HIF‐1α‐mediated protection against C.diff toxin‐induced damage.The in vitro studies analyzed HIF‐1α and FIH‐1 levels during toxin exposure of Caco2 cells. Cells were challenged with both toxin and nitric oxide synthase (NOS) inhibitors to study NO effects on HIF‐1α/FIH‐1 expression. In vivo studies assessed ileal loop tissue from toxin‐treated wild‐type (WT) and inducible NOS knockout (iNOS KO) mice.We have identified that HIF‐1α levels increase at least two‐fold in toxin‐treated cells. FIH‐1 levels also show a 35% decrease in response to toxin. This increase in HIF‐1α protein was suppressed with NOS inhibition. In vivo, serum NO levels increased with toxin exposure; a response which was abrogated in iNOS KO mice.Further study is needed to demonstrate a direct effect of NO on HIF‐1α levels in response to C.diff toxin in vivo. Funding provided by CAG and CIHR.