Fukushima Medical University Department of Urology
Introduction: Recently, attention has focused on the association between urothelial barrier dysfunction and lower urinary tract dysfunction (LUTD). Uroplakin (UP) is critical to normal urothelial barrier function. Some studies reported that UPs defects lead to abnormal voiding patterns. It was also reported that impairing UP II causes mast cell infiltration in the bladder and that mast cell contributed to bladder hyperactivity. Mast cell tryptase (MCT) can regulate neuronal activity by cleaving protease-activated recepter 2 (PAR2), which is expressed on C-fiber. On the other hands, the mechanisms underlying LUTD caused by chronic ischemia are not completely known. This study aimed to investigate the effects of chronic ischemia on UPs and mast cell in the bladder using a rat model of chronic bladder ischemia (CBI).
Methods: Adult male Sprague-Dawley rats (16 weeks old) were divided into two groups (control and CBI; n=10 each). The CBI group received balloon endothelial injury of bilateral iliac arteries and a 2% cholesterol diet for 8 weeks to induce chronic ischemia. The control group received regular diet for 8 weeks. After monitoring urine output for 24 h, bladders were harvested. Bladder was processed for immunohistochemical staining and methylene blue staining. We used western blotting to measure expressions of UPs(UP Ia, UP Ib, UP II, UP III) in the bladder of this rat model to examine urothelial barrier function. The expression of MCT and PAR2 were also measured to evaluate C-fiber activation by mast cell.
Results: Metabolic cage studies showed that mean voided volumes were significantly smaller in the CBI (1.46 ± 0.33 ml) than in the control (1.01 ±0.21 ml; P=0.001). In western blot analysis, UP II expression was significantly decreased (P=0.011) in the CBI compared with the control. With immunohistochemical staining, UP II-positive cells are located mostly. The percentage of UP II-positive cells on urothelium was significantly lower in the CBI (63.0 ± 0.11%) than in the control (92.1 ± 0.1%, P<0.001). The expression of MCT (P=0.024) and PAR2 (P=0.021) were significantly increased in the CBI compared with the control in western blot analysis. The methylene blue staining showed the number of mast cell was significantly more in the CBI than in the control (P=0.034).
Conclusions: Chronic ischemia might impair urothelial barrier function through reduced expression of UP II in urothelium. Urothelial barrier dysfunction contributed to mast cell infiltration and increased PAR2 on C-fiber, resulting PAR2 activation by MCT. The PAR2 activation may induce LUTD by stimulating C fiber in rat model of chronic bladder ischemia.