Organ and species specificity in the stimulation of transitional epithelial cell growth by fibroblasts

Culture of transitional epithelium for urinary tract reconstruction has been problematic due, in part, to the dependence of urothelial cells on a basal layer of bladder fibroblasts for growth. In vitro studies on the effect of bladder, ureter, and intestinal fibroblast cocultures and conditioned media upon urothelial cell growth were conducted to better characterize the dependence of urothelial cells of fibroblasts.

Primary cultures of human and porcine bladder, ureter, and intestinal fibroblasts and bladder and ureter urothelial cells were established. The urothelial cells were incubated with fibroblasts in a coculture system and growth compared to that of individual fibroblast and urothelial cultures. Urothelium-specific medium was exposed to the fibroblast cultures for 6, 12, and 24 h. Urothelial cell growth in each of the fibroblast-conditioned media was evaluated.

Coculture of human urothelial cells with human bladder and ureter fibroblasts yielded increased cell growth when compared to the cells in individual culture. This improvement was greatest for the bladder fibroblasts in coculture with bladder epithelial cells. The media exposed to bladder and ureter fibroblasts for 24 h significantly increased bladder and ureter urothelial growth compared to fresh medium. Coculture with intestinal fibroblasts and exposure to intestinal fibroblast conditioned media did not significantly stimulate urothelial cell growth. Similarly, coculture and conditioned media studies of porcine urothelial cells with porcine bladder and ureter fibroblasts (but not intestinal fibroblasts) yielded increased cell growth when compared to the cells in individual culture, particularly with bladder fibroblasts. However, human urothelial cells were not stimulated by porcine bladder and ureter fibroblast conditioned media, nor were porcine urothelial cells stimulated by human bladder and ureter fibroblast conditioned media.

The ability of urinary fibroblasts to stimulate urothelial cell proliferation resides in an unidentified soluble factor secreted into the medium, independent of the presence of the fibroblasts. This factor is relatively organ and species-specific.