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-1a (HIF-1a) 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-1a 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-2a and of Arnt2 proteins were found at 10 days, providing an explanation for the lack of correlation between HIF-1a 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-1a 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. Bladder outlet obstruction, such as seen in men with benign prostatic hyperplasia, is a prevalent clinical condition that leads to growth and remodeling of the urinary bladder. Prior work demonstrated increased levels of hypoxia-inducible factor-1a (HIF-1a) following bladder outlet obstruction. 1,2 Intravesical infusion of cobalt chloride, a known HIF inducer, moreover elicited bladder growth and angiogenesis similar to obstruction. 3 These findings indicate that HIF-1 has a role in remodeling and adaptation of the urinary bladder following outlet obstruction.The HIF transcription factor complex is regulated by cellular O 2 tension such that one of the heterodimeric partners, the a-subunit, is hydroxylated and degraded in normoxia. [4][5][6] In hypoxia, the hydroxylation reaction slows down and asubunits are stabilized, allowing for complex formation with HIF-1b (Arnt). The HIF complex binds to genomic hypoxia response elements and increases synthesis of proteins that promote angiogenesis and oxygen transport in blood. 7 HIF also redirects energy metabolism to allow ...

Inhibition of HIF Reduces Bladder Hypertrophy and Improves Bladder Function in Murine Model of Partial Bladder Outlet Obstruction

“…2). 5,8,10 Decreased intensity of immunostaining signals for Hif-1α and Hif-2α were observed in bladders from the PBOO plus T group. This indicated that 17-DMAG at least partly blocks HIF pathways by preventing the accumulation of Hif proteins in obstructed bladders.…”

“…5–8 In agreement with these findings previous studies demonstrated that PBOO triggers up-regulation of HIFs, which are major mediators of the hypoxic response, in patients and in animal models. 9,10 …”

“…7,10,14 This diversity of suggestions for HIF mediated mechanisms in PBOO induced bladder pathology might have been caused by the fact that HIFs involve various cell physiological responses as well as by differences among studies, including PBOO duration and severity, and species, age and gender of the animals used. 5,7,8,10,14,15 To date it is still not clear whether and how inhibition of the HIF pathways may affect pathophysiological changes in bladders that develop due to PBOO.…”

Glycobiology Modifications in Intratumoral Hypoxia: The Breathless Side of Glycans Interaction

“…HIF-1α pathway also optimizes cancer cell respiration by regulating the switch of cytochrome oxidase (COX-4) subunits [45, 46]. This metabolic adaptation includes increased expression of glucose transporters and glycolytic enzymes, combined with mitochondrial remodeling [47]. Moreover, HIF-1α induces miR-210 transcription and decreases the expression of iron-sulfur cluster assembly proteins (ISCU) and COX-10 in breast, colon, and esophageal cancer cell lines.…”

Cavin-3 (PRKCDBP) deficiency reduces the density of caveolae in smooth muscle

“…The model of partial bladder outlet obstruction used here is relevant in this regard as it entails remarkable distension-induced growth and organ remodeling. Bladder outlet obstruction for 7 days causes a three- to eight-fold increase in bladder weight, hypertrophy of the detrusor muscle layer and wide-reaching transcriptomic and proteomic changes (Krawczyk et al 2016; Ekman et al 2013, 2014). Because the bladder grows to cope with increased mechanical distension, outlet obstruction should test whether caveolae are important for chronic mechanical adaptation.…”