Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA121

Poster Communications

Importance of hypoxia-inducible factors (HIF-1 and HIF-2) for the pathophysiology of inflammatory bowel disease

E. Hammel1, J. Fandrey1, S. Winning1

1. Instiute of Physiology, University of Duisburg-Essen, Essen, Germany.

About 400,000 people in Germany suffer from inflammatory bowel diseases (IBD). The most common IBD types are Crohn's disease and ulcerative colitis. At present, these types of disease are not curable and their causes are not completely known. Inflammation is characterized by lack of oxygen (inflammatory hypoxia). The cellular adaptation to hypoxia is regulated by the transcription factors hypoxia-inducible factors (HIF-1 and HIF-2). In IBD the current state of knowledge is mainly limited to the function of HIF-1. Previous work of our group has shown that HIF-1 in myeloid cells plays a disease-promoting role in the animal model of dextran sodium sulfate (DSS) -induced colitis 1. Based on this work, first experiments were done with HIF1+f/+f x HIF2+f/+f mice (WT) and Lyz2-Cre/HIF1+f/+f x HIF2+f/+f mice (KO). For acute inflammation, mice received 2.5% (w/v) DSS (MP Biomedicals, MW 36-50 kDa) in drinking water for six days while control mice (C: n=8) received normal drinking water. The course of disease was recorded by body weight, stool consistency and occult blood in the feces being important for the Disease Activity Index (DAI) as clinical classification 2. Afterwards, severity of disease was analyzed macroscopically (changes in weight and length of colon) and microscopically (antigen specific immunohistochemistry and histology score 2. Also HIF-regulated gene expression in colon tissue was analyzed by quantitative PCR as well as by immuno blot. The DAI during DSS-treatment increased on day 4 and indicated colitis while control mice remained unaffected. Also DSS-treated animals showed a 1.5 fold higher colon weight to length ratio and a 4-fold higher Histology Score for destroyed tissue than control mice, which are hallmarks for intestinal inflammation. Furthermore, treated animals showed a significantly lower mRNA expression of epithelial mucin muc3 and a significant higher expression of cytokines like tumor necrosis factor α (tnfα) and lipocalin-2 (lcn-2) than control mice being an indication for inflammation. In KO mice, epithelial mucin muc2 expression was significantly lower than in WT mice under treated and untreated conditions. In further experiments, the influence of myeloid HIF-2 in the course of disease of DSS-induced colitis is to be studied in vivo. In addition, in vitro studies with murine myeloid cells carrying a hif-2a knockout or hif-1a / hif-2a double knockout should be performed. HIF-regulated gene expression will be studied in bone marrow-derived macrophages under normoxic (21% O2) and hypoxic (1% O2) conditions. Our data suggest that additional knockout of HIF-2α might be able to reverse the disease ameliorating effect of myeloid hif-1a knockout in experimental colitis. HIF-2 could therefore play an antagonist role to HIF-1 but further experiments with animals carrying a hif-2a knockout in myeloid cells need to be done.

Where applicable, experiments conform with Society ethical requirements