Alterations in expression of HIF-1α, HIF-2α, and VEGF by idiopathic overactive bladder urothelial cells during stretch suggest role for hypoxia

Objectives: To test the hypothesis that hypoxia plays a role in overactive bladder (OAB) symptoms by studying how the in vitro stretch of primary cultured bladder urothelial cells (BUCs) from those with OAB and asymptomatic subjects altered the expression of angiogenic factors. The angiogenic factors included hypoxia-inducible factor-1 alpha subunit (HIF-1α), HIF-2 alpha subunit (HIF-2α), and vascular endothelial growth factor (VEGF). Methods: HIF-1α, HIF-2α, and VEGF mRNA expression were analyzed using real-time quantitative polymerase chain reaction. Fluorescence-activated cell sorting was used to measure the protein expression. The release of VEGF in the supernatant of stretched OAB and normal BUCs was measured using enzyme-linked immunosorbent assay. Results: Stretching of OAB BUCs increased the expression of mRNA for HIF-1α, HIF-2α, and VEGF by 1.5-fold (P < .01), 1.5-fold (P < .01), and 3.5-fold (P < .001) compared with unstretched OAB BUCs. This augmentation was not detected when comparing stretched normal BUCs with unstretched normal BUCs. Using fluorescence-activated cell sorting quantitation, only HIF-2α was significantly increased (P < .01). Measuring VEGF in the supernatant revealed that stretched OAB BUCs released significantly more VEGF than nonstretched OAB BUCs at multiple points. In contrast, stretched normal BUCs did not release VEGF. Conclusions: OAB BUCs responded to stretch by expressing increased angiogenic markers, HIF-1α, HIF-2α, and/or VEGF, measured at the transcript and protein levels. This suggests that OAB BUCs respond as if they were primed by hypoxia. This knowledge adds to the pathophysiologic understanding of OAB.

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