The mechanoreceptor TRPV4 is localized in adherence junctions of the human bladder urothelium: a morphological study.

PURPOSE

TRPV4 (transient receptor potential vanilloid 4 channel) is a nonselective cation channel involved in different sensory functions that was recently implicated in bladder mechanosensation. We investigated the cellular site of TRPV4 in bladder urothelium and explored a molecular connection between TRPV4 and urothelial adherence junctions.

MATERIALS AND METHODS

We obtained healthy tissues sections from cystectomy in humans due to cancer in 3 and noncancerous conditions in 2. Besides human biopsies tissues from 7 normal and 7 TRPV4-/-mice, and the urothelial cell line RT4 were also used. Experiments were done with polyclonal antibody against TRPV4 (against the N-terminus of rat TRPV4). A molecular connection between TRPV4 and different adherence junction components was investigated using immunofluorescence, Western blot and immunoprecipitation.

RESULTS

Results revealed TRPV4 on urothelial cell membranes near adherence junctions. Results were comparable in the urothelial cell line, human bladders and mouse bladders. Subsequent immunoprecipitation experiments established a molecular connection of TRPV4 to α-catenin, an integral part of the adherence junction that catenates E-cadherin to the actin-microfilament network.

CONCLUSIONS

Results provide evidence for the location of TRPV4 in human bladder urothelium. TRPV4 is molecularly connected to adherence junctions on the urothelial cell membrane. TRPV4 coupling to a rigid intracellular and intercellular structural network would agree with the hypothesis that TRPV4 can be activated by bladder stretch.