Hypoxia-Inducible Factor Signaling Provides Protection in Clostridium difficile-Induced Intestinal Injury

Abstract

Background & Aims Clostridium difficile (C.difficile) is the leading cause of nosocomial infectious diarrhea. Increasing incidence, antibiotic resistance and more virulent strains have dramatically increased the number of C.difficile-related deaths worldwide. The innate host response mechanisms to C.difficile are not resolved; however, we hypothesize that hypoxia-inducible factor (HIF-1) plays an innate protective role in C.difficile colitis. Thus, we assessed the impact of C.difficile toxins on the regulation of HIF-1 and evaluated the role of HIF-1α in C.difficile-mediated injury/inflammation. Methods In vitro studies assessed HIF-1α mRNA, protein levels and DNA binding events in human mucosal biopsies and Caco-2 cells exposed to C.difficile toxins. In vivo studies employed the murine ileal loop model of C.difficile toxin-induced intestinal injury. Mice with targeted deletion of HIF-1α in the intestinal epithelium were used to assess the impact of HIF-1α signaling in response to C.difficile toxin. Results Mucosal biopsies and Caco-2 cells exposed to C.difficile toxin displayed a significant increase in HIF-1α transcription and protein levels. Toxin-induced DNA binding was also observed in Caco-2 cells. Toxin-induced HIF-1α accumulation was attenuated by nitric oxide synthase inhibitors. In vivo, deletion of intestinal epithelial HIF-1α resulted in more severe toxin-induced intestinal injury and inflammation. In contrast, stabilization of HIF-1α, with dimethyloxallyl glycine, attenuated toxin-induced injury and inflammation. This was associated with an induction of HIF-1-regulated protective factors including VEGFa, CD73 and intestinal trefoil factor and down-regulation of proinflammatory molecules TNF and KC. Conclusions Our study is the first to describe the innate protective role for HIF-1α in response to C.difficile toxins. Harnessing the innate protective actions of HIF-1α in response to C.difficile toxins may represent a novel form of therapy for C.difficile-associated disease.

Hypoxia-dependent regulation of inflammatory pathways in immune cells

“…Consistent with these findings, loss of HIF-1α in mice increases susceptibility to P. aeruginosa-mediated keratitis (110). In other models of infection including Clostridium, Streptococcus, Staphylococcus, and Acinetobacter species, HIF has also been largely found to be protective against pathogens (111)(112)(113)(114)(115). Given the evolving issue of antimicrobial resistance in multiple pathogens, future studies will undoubtedly expand on the fascinating potential of targeting host oxygen-sensing pathways for the purpose of regulating host immunity in infectious disease.…”

Oxygen metabolism and barrier regulation in the intestinal mucosa

“…Mucosa-associated microbiota are likely also prominent modulators of potential hypoxia-elicited autophagic responses (see Figure 2). Both commensal and pathogenic species have been shown to influence mucosal pO 2 and/or enterocyte HIF signaling (95,121,122), and ablation of epithelial HIF-1 increases susceptibility to pathogen infection in a number of studies (95,121). Reciprocally, intestinal oxygenation directly shapes the composition of gut microbial communities, and oxidative changes in intestinal inflammation may underlie the dysbiosis characteristic of IBD (5).…”

Hydroxylases as therapeutic targets in inflammatory bowel disease

“…[38][39][40][41][42] The expression of hypoxia-inducible transcription factors such as HIF in mucosal tissue has been demonstrated to be increased in diseases of the GI tract including celiac disease 43 and IBD. 31 Although most studies support a protective role for HIF activation in inflammatory conditions of the gut, 27,44,45 its activation has also been proposed to be detrimental. 46 The cellular transcriptional response to hypoxia is not restricted to regulation by HIF and multiple other transcriptional pathways demonstrate hypoxic sensitivity.…”

“…60,61 While these initial studies utilized chemical models of acute colitis, subsequent studies using genetic-, ischemic-and toxin-based acute and chronic models support a protective role for hydroxylase inhibition in colitis. 44,45,62,63 More recently, the mechanisms underpinning the protective effects of hydroxylase inhibitors have become clearer (Figure 1). These mechanisms will be described below.…”