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Objectives: Similar to other epithelia, urothelium in vivo has a hierarchal organization of cells each with specific gradients of differentiation. While distinct cell types have been described as important in bladder cancer in vitro, clonal and proliferative capacities of normal urothelial cells have not been characterized., Materials and Methods: Three cell types and colony types were identified from primary porcine urothelial culture. Proliferative activity, patterns of apoptosis and differentiation, colony forming efficiency and ability to change phenotype with passage were determined and compared., Results: Small, T-I colonies with large flattened (type-1) cells had low levels of proliferation and high levels of apoptosis. Large T-III colonies had a central area of small (type-3) cells surrounded by type-1 and type-2 cells. Proliferation and apoptosis were asymmetrically distributed in the periphery of T-II and T-III colonies. T-III colonies proved to be significantly more clonogenic and proliferative. With appropriate induction, type-1 cells were able to proliferate upon passage and form type-3 cells, yet long-term culture demonstrated that progeny of type-1 cells appeared to have inherited a clonogenic handicap., Conclusions: Type-3 cells in the centre of T-III colonies appear to harbour stem-like qualities with a relatively low proliferative and apoptotic index at homeostasis and the ability to become highly proliferative upon passage. This study demonstrates that distinct urothelial cell types with differing clonal capacities can be isolated from the bladder and these cells may have implications for tissue engineering and carcinogenesis.

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.