Epidemiological studies have shown that lower urinary tract symptoms (LUTS), such as nocturia, urinary incontinence and urgency, are common among both men and women, with age-related increases seen in both sexes. The pathophysiology of LUTS, particularly in the elderly, is multifactorial. Pelvic arterial occlusive disease, including atherosclerosis, has recently been suggested to cause chronic bladder ischemia, which may play an key role in the development of LUTS in men and women. However, the mechanisms underlying the changes in bladder function caused by chronic ischemia have not been completely elucidated. On the other hand, Uroplakin (UP) Ia, UP Ib, UP II, and UP III are well known to be critical to normal urothelial barrier function1). Recent studies have suggested that UPs play a role in the homeostasis of urinary bladder mucosa and UP defects lead to abnormal voiding patterns2). Whether arterial occlusive disease-related chronic ischemia affects UPs in the bladder has not been established. This study aimed to investigate the effects of arterial occlusive disease-related chronic ischemia on UPs in the bladder using a rat model of chronic bladder ischemia (CBI).

Adult male Sprague-Dawley rats (16 weeks old) were divided into two groups (control and CBI; n=10 each). The CBI group underwent balloon endothelial injury of bilateral iliac arteries and received a 2% cholesterol diet for 8 weeks to induce arterial occlusive disease-related chronic ischemia. The control group received regular diet for 8 weeks. After monitoring urine output for 24 h, bladders and common iliac arteries were harvested for pharmacological and histological examinations. We used western blotting to measure expressions of UP Ia, UP Ib, UP II UP III and HIF1α, an oxidative stress marker, in the bladder of this rat model. Bladder was processed for immunohistochemical staining of UPs. All values are expressed as mean ± standard deviation. Values of P<0.05 were considered statistically significant.

Wet weights of the body and bladder did not differ significantly between groups (body weight: control, 526 ± 18 g; CBI, 536 ± 34 g). Mean arterial wall thickness was significantly greater in the CBI group (116.3 ± 23.8 μm) than in the control group (82.0 ± 26.3 μm; P<0.001). Metabolic cage studies showed that mean and maximum voided volumes were significantly smaller in the CBI group than in the control group (control vs CBI, mean voided volume: 1.46 ± 0.33 ml vs 1.01 ±0.21 ml, P=0.001; maximum voided volume: 2.62 ± 0.60 ml vs 2.01 ± 0.41 ml, P=0.023). Western blot analysis showed expression of HIF1α was significantly increased, and UP II expression was significantly decreased (P=0.011) in the CBI group as compared with the control group. However, no significant differences were found in UP Ia, UP Ib or UP III expression between groups (Figure.1). With immunohistochemical staining, UP II-positive cells are located mostly on urothelium. The percentage of UP II-positive cells was significantly lower in the CBI group (63.0 ± 0.11%) than in the control group (92.1 ± 0.1%, P<0.001) (Figure.2).

In this study, increased levels of the oxidative stress marker and decreased voided volume in the CBI group indicated that pelvic arterial occlusive disease caused ischemia/reperfusion injury and lower urinary tract dysfunction (LUTD) in a rat model of chronic bladder ischemia. Our results also demonstrated that expression of UP II in urothelium was reduced in chronically ischemic bladder in rats. One possibility is that chronic ischemia contributed to LUTD by impairing normal urothelial barrier function through reduced expression of UP II in rat.

Our results suggest that chronic ischemia induced by pelvic arterial occlusive disease may cause UP II defects in the urinary bladder mucosa of rat. UP II deficiency may be one cause of chronic ischemia-related LUTD.

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