Persistent urothelial differentiation changes in the reconstructed exstrophic bladder: Congenital or acquired dysfunction of the epithelial barrier?

Background: We have previously characterised the urothelium from infants with classic bladder exstrophy (CBE) for the expression of urothelial differentiation-associated markers. We found abnormal expression patterns of uroplakin 3a, cytokeratin 13, cytokeratin 20 and claudin 4 in the majority of bladder biopsies taken at the time of primary bladder closure. Abnormal urothelial differentiation results in a compromised urothelial barrier with potential implications on bladder development and the success of reconstructive surgery.

Objective: To investigate whether the urothelial differentiation changes observed in the unclosed exstrophic bladder persist after successful primary exstrophy repair.

Design, setting and participants: From 2005 to 2018 bladder biopsies from 115 children with CBE obtained at the time of primary bladder closure (n = 67, median age: 8.1 weeks) and during secondary procedures aimed at achieving continence (n = 48, median age: 6.8 years) were prospectively collected. Following histological assessment immunohistochemistry was used to investigate the expression of uroplakin 3a, cytokeratin 13 and 20 and claudin 4, well-characterized markers associated with the terminally-differentiated, fully functional urothelial phenotype. The urothelium from 16 children with VUR and with non-refluxing disorders of the urinary tract served as controls.

Results: Tissue specimen from 100 children were included in the analysis. Only 32% of bladder specimens from children having undergone successful primary bladder closure in early infancy displayed a fully differentiated urothelial phenotype with regular expression of all 4 markers. The remaining bladders revealed irregular or absent marker expression suggesting abnormal urothelial differentiation. 86% of the samples had inflammatory, proliferative or metaplastic histological changes.

Conclusion: Our results suggest persisting urothelial differentiation changes in two-thirds of exstrophic bladders following successful bladder closure in early infancy. Despite some limitations, the findings provide a platform for translational studies into the role of the urothelium for the developmental potential of the exstrophic bladder and the success of reconstructive surgery.