MESENCHYMAL-EPITHELIAL INTERACTIONS IN BLADDER SMOOTH-MUSCLE DEVELOPMENT - EPITHELIAL SPECIFICITY

Purpose: We previously showed that mesenchymal-epithelial interactions are necessary for the development of bladder smooth muscle. Specifica lly without bladder epithelium embryonic bladder mesenchyme does not d ifferentiate into smooth muscle. We determine whether this process is specific to bladder epithelium or whether epithelial cells from other organ systems induce bladder mesenchyme to differentiate into smooth m uscle, as well as whether epithelial age is an important variable. Mat erials and Methods: We recombined 14-day bladder mesenchyme before smo oth muscle differentiation with rat epithelium from 14-day, 19-day, ne wborn and adult bladder, ureter, colon, ileum, stomach, cornea and epi dermis. In addition, bladder epithelium was recombined with 14-day emb ryonic small intestinal, 14-day embryonic gastric and newborn seminal vesicle mesenchyme. All tissue recombinants were grafted under the ren al capsule of an adult rat syngeneic host for 3 weeks. Results: Immuno histochemical analysis with antibodies directed against smooth muscle alpha-actin revealed that all epithelial types studied induced bladder mesenchyme to differentiate into smooth muscle, although to different degrees. Induction of smooth muscle was independent of urothelial age . In addition, bladder epithelium induced intestinal, gastric and semi nal vesicle mesenchyme to differentiate into smooth muscle and express an overall morphological pattern indicative of the bladder fibromuscu lar wall. Conclusions: The mechanism whereby urothelium induces bladde r mesenchyme to differentiate into smooth muscle is not specific to em bryonic urothelium. Older urothelium and heterotypic epithelium also i nduce smooth muscle differentiation. With the common use of bowel, sto mach and ureteral segments for bladder augmentation it is important to understand the interaction of different types of epithelium with the native bladder.