title: HIF-mediated metabolic switching in bladder outlet obstruction mitigates the relaxing effect of mitochondrial inhibition.
abstract: Prior work demonstrated increased levels of hypoxia-inducible factor-1α (HIF-1α) in the bladder following outlet obstruction, associated with bladder growth and fibrosis. Here we hypothesized that HIF induction in outlet obstruction also switches energetic support of contraction from mitochondrial respiration to glycolysis. To address this hypothesis, we created infravesical outlet obstruction in female Sprague-Dawley rats and examined HIF induction and transcriptional activation. HIF-1α increased after 6 weeks of outlet obstruction as assessed by western blotting and yet transcription factor-binding site analysis indicated HIF activation already at 10 days of obstruction. Accumulation HIF-2α and of Arnt2 proteins were found at 10 days, providing an explanation for the lack of correlation between HIF-1α protein and transcriptional activation. HIF signature targets, including Slc2a1, Tpi1, Eno1 and Ldha increased in obstructed compared with sham-operated bladders. The autophagy markers Bnip3 and LC3B-II were also increased at 6 week of obstruction, but electron microscopy did not support mitophagy. Mitochondria were, however, remodeled with increased expression of Cox4 compared with other markers. In keeping with a switch toward glycolytic support of contraction, we found that relaxation by the mitochondrial inhibitor cyanide was reduced in obstructed bladders. This was mimicked by organ culture with the HIF-inducer dimethyloxalylglycine, which also upregulated expression of Ldha. On the basis of these findings, we conclude that HIF activation in outlet obstruction involves mechanisms beyond the accumulation of HIF-1α protein and that it results in a switch of the energetic support of contraction to anaerobic glycolysis. This metabolic adaptation encompasses increased expression of glucose transporters and glycolytic enzymes combined with mitochondrial remodeling. Together, these changes uphold contractility when mitochondrial respiration is limited.
authors.affiliation: 1] Department of Experimental Medical Science, Lund University, Biomedical Centre, BMC D12, Lund, Sweden [2] Department of Biology, Faculty of Science, Sölvegatan 35, Lund, Sweden.
authors.forename: Mari
authors.initials: M
authors.lastname: Ekman
authors.affiliation: Department of Urology, Clinical Sciences, Lund University, Lund, Sweden.
authors.forename: Bengt
authors.initials: B
authors.lastname: Uvelius
authors.affiliation: Department of Experimental Medical Science, Lund University, Biomedical Centre, BMC D12, Lund, Sweden.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Albinsson
authors.affiliation: Department of Experimental Medical Science, Lund University, Biomedical Centre, BMC D12, Lund, Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Swärd
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism / Q000502:physiology*; D005260:Female; D051246:Glucose Transport Proteins, Facilitative / Q000378:metabolism; D006019:Glycolysis; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology*; D007527:Isoenzymes / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D000080864:Lactate Dehydrogenase 5; D008928:Mitochondria / Q000378:metabolism; D063306:Mitophagy; D009130:Muscle, Smooth / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D001748:Urinary Bladder Neck Obstruction / Q000378:metabolism*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D051246:Glucose Transport Proteins, Facilitative; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase; D000080864:Lactate Dehydrogenase 5; D000099162:Endothelial PAS Domain-Containing Protein 1; C490991:Arnt2 protein, rat; C497444:Hif1a protein, rat