Adaptation processes to hypoxia in equine and lagomorph jejunum epithelium

• Applicant: Professorin Dr. Franziska Dengler
• Subject Area: Veterinary Medical Science
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316183467

In spite of the gastrointestinal epithelium's ability to adapt to different oxygenation conditions, hypoxia can induce severe damage in the enterocytes. In horses, strangulation of jejunal loops often causes hypoxia in the affected part of the gut, leading to the animal's death even after surgical intervention. Thus, a more detailed knowledge of possible adaptation mechanisms would not only help understand epithelial reactions to hypoxia but also improve the therapeutic management. We assume that a successful adaptation of the gastrointestinal epithelium to hypoxia includes short-term as well as long-term alterations. In the project, the involvement of AMP-activated proteinkinase (AMPK) and hypoxia-inducible factor (HIF) 1 in the adaptation of equine (and lagomorph) jejunum epithelium to hypoxia will be investigated. Both regulatory mechanisms play a crucial role in the modulation of glucose uptake into the cells and may possibly also secure the energy supply of enterocytes under hypoxic conditions. Thus, we hypothesize that the apical uptake of glucose on the classical and energy-consuming route via sodium-glucose-cotransporter (SGLT1) is diminished under hypoxia. In contrast, glucose uptake is extended by an increased integration of the energetically more efficient glucose transporter (GLUT) 1 and/or 2 into the apical and/or basolateral cell membrane mediated by AMPK and/or HIF1. Thereby more glucose would be available for the enhanced anaerobic glycolysis without additional expense of energy. Additionally, we want to elucidate if the export of the metabolites of this anaerobic glycolysis (mainly lactate) is also regulated by AMPK and/or HIF1, focussing on monocarboxylate transporters (MCT) 1 and 4. Due to the anatomical and physiological commonalities we use rabbits as model animals to establish experimental setups and test the hypotheses. Subsequently, these results will be verified in horses. The Ussing chamber technique will be used to simulate hypoxia in isolated jejunal epithelia and radioactively labelled glucose will be traced in transepithelial transport as well as its uptake across the apical and basolateral membrane of the epithelium and the export of its metabolites. By addition of specific inhibitors for SGLT1, GLUT1 and 2 as well as MCT1 and 4 their involvement in the transport will be characterized under hypoxic and control conditions. Besides functional studies, these transport proteins will be quantified on mRNA expression level by RT-qPCR as well. The involvement of AMPK and HIF1 will be investigated by use of specific agonists and antagonists and their activation will be verified in western blot studies.

• DFG Programme: Research Grants