Plasticity of the urothelial phenotype: effects of gastro-intestinal mesenchyme/stroma and implications for urinary tract reconstruction

The present study tests the hypothesis that heterotypic stromal-epithelial interactions cause phenotypic changes in urothelium. The rational for the experimental design is to simulate heterotypic stromal-epithelial interactions that are created at the anastomotic site of intestinal-bladder augmentations and internal urinary diversions where the urothelium is in direct contact with the gastro-intestinal tract tissues. Tissue recombination experiments were performed by combining 14-day embryonic rat and mouse rectal mesenchyme with urothelium from embryonic, newborn, and adult mice or rats. All tissue recombinants were grown beneath the renal capsule of athymic mouse hosts for 6-16 weeks. Analyses were performed to detect expression of uroplakins, cytokeratin 7, 14, 19 and mucin secreting epithelial cells via Periodic Acid-Schiff (PAS). The phenotype of both mouse and rat urothelium was changed to a glandular morphology under the influence of rectal mesenchyme. Immunohistochemical staining revealed a loss of the urothelial specific uroplakins and cytokeratins 7, 14, and 19 (characteristic of urothelium). Histologic analysis revealed the presence of mucin secreting glandular structures which stained positive for PAS. The urothelial transdifferentiation into glandular epithelium was not a function of epithelial age and occurred in the embryonic, newborn and adult urothelium. Likewise, rectal mesenchyme from embryonic, neonatal, and adult animals was able to induce glandular differentiation in bladder epithelium. Urothelium exhibits the plasticity to change into an intestinal like epithelium as a result of mesenchymal/stromal stimulation from the gastro-intestinal tract. This experimental result is germane to heterotypic stromal-epithelial interactions that are created in patients with urinary tract reconstructions (intestinal augmentations, de-mucosalized urothelial lined bladder patches, and internal urinary diversion such as ureterosigmoidostomies). We propose that heterotypic stromal-epithelial interactions may play a role in determining histodifferentiation of urothelial cells at the anastomotic site between bowel and bladder tissue in patients with gastro-intestinal urothelial reconstructions.