Modulation of the Hypoxic Response Following Partial Bladder Outlet Obstruction

Abstract

Tissue level hypoxia has been noted in animal models of partial bladder outlet obstruction. The key mechanisms linking hypoxia and obstruction induced bladder dysfunction remain unknown. 2-Methoxyestradiol is a natural derivative of 17β-estradiol and is currently used as an oncologic agent for its ability to regulate the hypoxia pathway. We investigated the ability of 2-methoxyestradiol to modulate the hypoxia response in a mouse model of bladder obstruction. A group of 5 to 6-week-old female C57BL/6 mice underwent oophorectomy and partial bladder outlet obstruction. Obstructed animals received a subcutaneous pellet of cholesterol placebo (7) or 2-methoxyestradiol plus cholesterol (7). Age matched controls underwent oophorectomy only (8). After 4 weeks the bladders of mice with partial bladder outlet obstruction and of unobstructed animals were harvested. Bladder sections (5 μm) were immunostained for Hypoxyprobe™-1, glucose transporter 1 and hypoxia inducible factor-1α. Real-time polymerase chain reaction was performed for hypoxia inducible factor-1α and lysyl oxidase. Statistical analysis was performed using 1-way ANOVA and the Wilcoxon rank sum test. Immunostaining for glucose transporter 1 and Hypoxyprobe-1 revealed the presence of tissue hypoxia after partial bladder outlet obstruction. Immunostaining and real-time polymerase chain reaction demonstrated the up-regulation of hypoxia inducible factor-1α in mice after partial bladder outlet obstruction compared to controls (p = 0.0394). Although not statistically significant, a trend toward lower gene expression of hypoxia inducible factor-1α was seen in mice receiving 2-methoxyestradiol compared to placebo (p = 0.0625). Compared to placebo, 2-methoxyestradiol treatment increased lysyl oxidase expression (p = 0.007). Murine partial bladder outlet obstruction resulted in hypoxia and up-regulation of the hypoxia inducible factor-1 pathway. Subcutaneous 2-methoxyestradiol administration attenuated this response and may be a viable tool to study the role of hypoxia after partial bladder outlet obstruction.