BOO induces fibrosis and EMT in urothelial cells which can be recapitulated in vitro through elevated storage and voiding pressure cycles

Purpose To determine the unique contributions from elevated voiding and storage pressures in the development of fibrosis and the epithelial-to-mesenchymal transition (EMT) in urothelial cells, and how progressive BOO pressure cycling is an important mechanical cue leading to these pathological changes. Materials and methods Urothelial cells isolated from control, SHAM, 2 (acute)- or 6 (chronic)-week BOO rats treated with an inflammasome inhibitor or no drug. Total RNA was isolated and RT-PCR was conducted with custom primers for pro-fibrotic and EMT genes. In separate experiments, a rat urothelial cell line was exposed to cyclic pressure regimes characteristic of acute and chronic BOO in the presence or absence of an inflammasome inhibitor. Following exposure, RT-PCR was conducted, collagen content was determined and intracellular caspase-1 activity was measured. Results Urothelial cells isolated from acute and chronic BOO rat models demonstrated expression of pro-fibrotic and EMT genes. Similarly, MYP3 rat urothelial cells subjected to pressure cycling regimes that reflect intravesical pressures in the acute or chronic BOO bladder also demonstrated increased expression of pro-fibrotic and EMT genes, along with elevated soluble collagen. Treatment with inflammasome inhibitors reduced expression of pro-fibrotic genes in the rat model and pressure cycling model but had a limited effect on EMT. Conclusion These results indicate that acute and chronic BOO pressure cycling are essential in the initiation and progression of fibrosis in the bladder via the NLRP3 inflammasome, but also provide new evidence that there is also an alternative NLRP3-independent pathway leading to EMT and fibrosis.