Urothelial progenitor cells: regional differences in the rat bladder

Objectives: Because the trigone is a unique region in the caudal bladder with a higher risk of neoplasia, we hypothesized that this area would have a high proportion of progenitor cells. As yet there is no marker nor methodology to specifically isolate urothelial stem cells, and thus demonstrate multi-potential differentiation and self-renewal. Here, our goal was to evaluate the distribution of progenitor cells that carry two general major attributes of stem cells: clonogenicity and proliferative capacity. Materials and methods: The bladders of Fisher rats were divided into caudal and cephalic segments and primary cultures were established from the harvested urothelial cells. Results: We found that colony-forming efficiency was almost 2-fold higher for cells from the caudal bladder compared to the cephalic bladder. Doubling time was significantly faster for cells harvested from the caudal bladder at initial plating. This suggested that the caudal bladder harbours a higher density of urothelial progenitor cells. With passage to p4, the differences between the upper and lower bladder were lost, suggesting selection of proliferative cells with serial passage. Based on Ki-67 staining, there was no geographical difference in cell proliferation under normal homeostatic in vivo conditions. Conclusions: These results demonstrate geographical sequestration of urothelial progenitor cells to the area of the bladder that encompasses the bladder neck and trigone, which may be a factor in pathological disparities between the trigone and remaining bladder.