Background Global consensus on the standardization of terminology for interstitial cystitis/bladder pain syndrome is lacking and is in the formative stages. The Workshop on Hunner lesion versus non‐Hunner lesion at the 2018 International Consultation on Interstitial Cystitis Japan discussed prevalence, performance and outcome of endoscopy, the role of histopathology, and markers. Methods A panel of experts reviewed the literature regarding Hunner lesion vs. non‐Hunner lesion interstitial cystitis/bladder pain syndrome. Results The prevalence of Hunner lesion has been reported to be 5–57%. Older age and smaller anatomic bladder capacity were associated with Hunner lesions. Cystoscopy using local anesthesia is not adequate in diagnosing interstitial cystitis but is needed to rule out confusable diseases. Cystoscopy with hydrodistention and redistention of the bladder is considered standard. A Hunner lesion is visualized as a quite typical inflammatory reaction: a reddened mucosal area with small vessels radiating towards a central scar, splitting at distension, usually associated with a waterfall bleeding pattern. Biopsies from the inflamed area show inflammatory infiltrates, granulation tissue, detrusor mastocytosis, and fibrin deposits. Ablation of Hunner lesions includes transurethral resection of lesions, fulguration, laser ablation, and cortical steroid injections. Mast cell density is a somewhat controversial matter, described differently in different studies: marked increase in Hunner lesion vs. non‐Hunner lesion in the majority of studies, no difference in a few. Nitric oxide appears to be a definitive marker in distinguishing Hunner lesion vs. non‐Hunner lesion disease. Macrophage migration inhibitory factor is elevated in Hunner lesion patients. Increased level of urinary proinflammatory genes expression has also been found in Hunner lesion subjects. Conclusions Hunner lesion patients are clinically and pathologically distinct from non‐Hunner lesion bladder pain syndrome patients.

Results suggest no significant differences between the Tokyo and Connaught strains in the complete response, recurrence-free survival or adverse event rate.

Day-night changes in the storage capacity of the urinary bladder are indispensable for sound sleep. Connexin 43 (Cx43), a major gap junction protein, forms hemichannels as a pathway of ATP in other cell types, and the urinary bladder utilizes ATP as a mechanotransduction signals to modulate its capacity. Here, we demonstrate that the circadian clock of the urothelium regulates diurnal ATP release through Cx43 hemichannels. Cx43 was expressed in human and mouse urothelium, and clock genes oscillated in the mouse urothelium accompanied by daily cycles in the expression of Cx43 and extracellular ATP release into the bladder lumen. Equivalent chronological changes in Cx43 and ATP were observed in immortalized human urothelial cells, but these diurnal changes were lost in both arrhythmic Bmal1-knockout mice and in BMAL1-knockdown urothelial cells. ATP release was increased by Cx43 overexpression and was decreased in Cx43 knockdown or in the presence of a selective Cx43 hemichannel blocker, which indicated that Cx43 hemichannels are considered part of the components regulating ATP release in the urothelium. Thus, a functional circadian rhythm exists in the urothelium, and coordinates Cx43 expression and function as hemichannels that provide a direct pathway of ATP release for mechanotransduction and signalling in the urothelium.

To better understand the roles played by signaling molecules in the bladder, we established a protocol of intravital imaging of the bladder of mice expressing a Förster/fluorescence resonance energy transfer (FRET) biosensor for extracellular signal‐regulated kinase (ERK), which plays critical roles not only in cell growth but also stress responses. With an upright two‐photon excitation microscope and a vacuum‐stabilized imaging window, cellular ERK activity was visualized in the whole bladder wall, from adventitia to urothelium. We found that bladder distention caused by elevated intravesical pressure (IVP) activated ERK in the urothelium, but not in the detrusor smooth muscle. When bladder distension was prevented, high IVP failed to activate ERK, suggesting that mechanical stretch, but not the high IVP, caused ERK activation. To delineate its molecular mechanism, the stretch‐induced ERK activation was reproduced in an hTERT‐immortalized human urothelial cell line (TRT‐HU1) in vitro. We found that uniaxial stretch raised the ATP concentration in the culture medium and that inhibition of ATP signaling by apyrase or suramin suppressed the stretch‐induced ERK activation in TRT‐HU1 cells. In agreement with this in vitro observation, pretreatment with apyrase or suramin suppressed the high IVP‐induced urothelial ERK activation in vivo. Thus, we propose that mechanical stretch induces intravesical secretion of ATP and thereby activates ERK in the urothelium. Our method of intravital imaging of the bladder of FRET biosensor‐expressing mice should open a pathway for the future association of physiological stimuli with the activities of intracellular signaling networks.

Connexin43 (Cx43), the main gap junction and hemichannel forming protein in the urinary bladder, participates in the regulation of bladder motor and sensory functions and has been reported as an important modulator of day–night variations in functional bladder capacity. However, because Cx43 is expressed throughout the bladder, the actual role played by the detrusor and the urothelial Cx43 is still unknown. For this purpose, we generated urothelium-specific Cx43 knockout (uCx43KO) mice using Cre-LoxP system. We evaluated the day–night micturition pattern and the urothelial Cx43 hemichannel function of the uCx43KO mice by measuring luminal ATP release after bladder distention. In wild-type (WT) mice, distention-induced ATP release was elevated, and functional bladder capacity was decreased in the animals’ active phase (nighttime) when Cx43 expression was also high compared to levels measured in the sleep phase (daytime). These day–night differences in urothelial ATP release and functional bladder capacity were attenuated in uCx43KO mice that, in the active phase, displayed lower ATP release and higher functional bladder capacity than WT mice. These findings indicate that urothelial Cx43 mediated ATP signaling and coordination of urothelial activity are essential for proper perception and regulation of responses to bladder distension in the animals’ awake, active phase.