Comparative immunohistochemical characterization of interstitial cells in the urinary bladder of human, guinea pig and pig.

Interstitial cells (ICs) are thought to play a functional role in urinary bladder. Animal models are commonly used to elucidate bladder physiology and pathophysiology. However, inter-species comparative studies on ICs are rare. We therefore analyzed ICs and their distribution in the upper lamina propria (ULP), the deeper lamina propria (DLP) and the detrusor muscular layer (DET) of human, guinea pig (GP) and pig. Paraffin slices were examined by immunohistochemistry and 3D confocal immunofluorescence of the mesenchymal intermediate filament vimentin (VIM), alpha-smooth muscle actin (αSMA), platelet-derived growth factor receptor alpha (PDGFRα) and transient receptor potential cation channel A1 (TRPA1). Image stacks were processed for analysis using Huygens software; quantitative analysis was performed with Fiji macros. ICs were identified by immunoreactivity for VIM (excluding blood vessels). In all species ≥ 75% of ULP ICs were VIM+/PDGFRα+ and ≥ 90% were VIM+/TRPA1+. In human and pig ≥ 74% of ULP ICs were VIM+/αSMA+, while in GP the percentage differed significantly with only 37% VIM+/αSMA+ ICs. Additionally, over 90% of αSMA+ ICs were also TRPA1+ and PDGFRα+ in human, GP and pig. In all three species, TRPA1+ and PDGFRα+ ICs point to an active role for these cells in bladder physiology, regarding afferent signaling processes and signal modification. We hypothesize that decline in αSMA-positivity in GP reflects adaptation of bladder histology to smaller bladder size. In our experiments, pig bladder proved to be highly comparable to human urinary bladder and seems to provide safer interpretation of experimental findings than GP.

The stem cell growth factor receptor KIT is not expressed on interstitial cells in bladder.

The mast/stem cell growth factor receptor KIT has long been assumed to be a specific marker for interstitial cells of Cajal (ICC) in the bladder, with possible druggable perspectives. However, several authors have challenged the presence of KIT+ ICC in recent years. The aim of this study was therefore to attempt to clarify the conflicting reports on KIT expression in the bladder of human beings, rat, mouse and guinea pig and to elucidate the possible role of antibody-related issues and interspecies differences in this matter. Fresh samples were obtained from human, rat, mouse and guinea pig cystectomies and processed for single/double immunohistochemistry/immunofluorescence. Specific antibodies against KIT, mast cell tryptase (MCT), anoctamin-1 (ANO1) and vimentin were used to characterize the cell types expressing KIT. Gut (jejunum) tissue was used as an external antibody control. Our results revealed KIT expression on mast cells but not on ICC in human, rat, mouse and guinea pig bladder. Parallel immunohistochemistry showed KIT expression on ICC in human, rat, mouse and guinea pig gut, which confirmed the selectivity of the KIT antibody clones. In conclusion, we have shown that KIT+ cells in human, rat, mouse and guinea pig bladder are mast cells and not ICC. The present report is important as it opposes the idea that KIT+ ICC are present in bladder. In this perspective, functional concepts of KIT+ ICC being involved in sensory and/or motor aspects of bladder physiology should be revised.

Comparative study of the organisation and phenotypes of bladder interstitial cells in human, mouse and rat.

With most research on interstitial cells (IC) in the bladder being conducted on animal models, it remains unclear whether all structural and functional data on IC from animal models can be translated to the human context. This prompted us to compare the structural and immunohistochemical properties of IC in bladders from mouse, rat and human. Tissue samples were obtained from the bladder dome and subsequently processed for immunohistochemistry and electron microscopy. The ultrastructural properties of IC were compared by means of electron microscopy and IC were additionally characterized with single/double immunohistochemistry/immunofluorescence. Our results reveal a similar organization of the IC network in the upper lamina propria (ULP), the deep lamina propria (DLP) and the detrusor muscle in human, rat and mouse bladders. Furthermore, despite several similarities in IC phenotypes, we also found several obvious inter-species differences in IC, especially in the ULP. Most remarkably in this respect, ULP IC in human bladder predominantly displayed a myoid phenotype with abundant presence of contractile micro-filaments, while those in rat and mouse bladders showed a fibroblast phenotype. In conclusion, the organization of ULP IC, DLP IC and detrusor IC is comparable in human, rat and mouse bladders, although several obvious inter-species differences in IC phenotypes were found. The present data show that translating research data on IC in laboratory animals to the human setting should be carried out with caution.