Structural differences between the bladder dome and trigone revealed by mRNA expression analysis of cold‐cut biopsies

What’s known on the subject? and What does the study add? In this paper we established the mRNA expression profiles of selected genes involved in bladder contractility and epithelial permeability in the bladder dome and trigone in order to evaluate the use of cold cut biopsies for comparative quantitative studies reflecting the anatomical differences between the bladder regions. Using QPCR and immunofluorescence we demonstrated differences in the amount of smooth muscle and the structure of urothelium of the dome and trigon. Our mRNA and immunofluorescence data show that cold cut biopsies from the bladder dome have a higher relative SM content compared to the trigone, reflecting a well-developed network of sub-urothelial myofibroblasts and muscularis mucosae present in the bladder dome. An up-regulation of the genes encoding the tight junction proteins in the bladder trigone is independent of the urothelium content, and might imply further discrepancy between these regions. OBJECTIVE • To establish the mRNA expression profiles of selected genes involved in bladder contractility and epithelial permeability in the bladder dome and trigone in order to evaluate the use of cold-cut biopsies for comparative quantitative studies into the anatomical differences between these two bladder regions. PATIENTS AND METHODS • After informed consent, cold-cut biopsies from the bladder dome and trigone were obtained from eight asymptomatic subjects. • RNA was extracted from muscle biopsies, and the expression levels of selected genes were analysed using TaqMan real-time PCR-based gene expression assays. • Protein levels and localization were investigated by immunofluorescence. RESULTS • mRNA levels of NK2 receptor, P2X1, ASIC1a and muscarinic cholinergic receptors M2, and M3 were significantly higher in the dome than in the trigone (P < 0.05). In contrast, the mRNA levels of cellular adhesion and tight junction proteins were up-regulated in the trigone. • There were no significant differences in expression levels of NK1R, and TRPV1 between the dome and trigone. • Although the mRNA levels of uroplakin UP2 were similar in both sample groups, the smooth muscle (SM) markers were up-regulated in the dome biopsies, indicating the higher SM content of these biopsies. • Consistent with these observations, when normalizing for the SM content, there were no significant differences in the levels of SM-specific markers between the two sample groups. In contrast, occludin, junctional adhesion molecule 1, claudins 1 and 4, γ-catenin and E-cadherin were up-regulated in the trigone. • These observations were confirmed by immunofluorescence labelling, showing differences in the amount of SM and in the structure of urothelium of the dome and trigone. CONCLUSIONS • Our mRNA and immunofluorescence data show that cold-cut biopsies from the bladder dome have a higher relative SM content compared with the trigone, reflecting a well-developed network of suburothelial myofibroblasts and muscularis mucosae present in the bladder dome. • An up-regulation of the genes encoding the tight junction proteins in the bladder trigone is independent of the urothelium content, and might imply further discrepancy between these regions.