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.