How does the urothelium affect bladder function in health and disease? ICI-RS 2011

A biodegradable microgrooved and tissue mechanocompatible citrate-based scaffold improves bladder tissue regeneration

Chronic bladder dysfunction due to bladder disease or trauma is detrimental to affected patients as it can lead to increased risk of upper urinary tract dysfunction. Current treatment options include surgical interventions that enlarge the bladder with autologous bowel tissue to alleviate pressure on the upper urinary tract. This highly invasive procedure, termed bladder augmentation enterocystoplasty (BAE), significantly increases the risk of patient morbidity and mortality due to the incompatibility between bowel and bladder tissue. Therefore, patients would significantly benefit from an alternative treatment strategy that can regenerate healthy tissue and restore overall bladder function. Previous research has demonstrated the potential of citrate-based scaffolds co-seeded with bone marrow-derived stem/progenitor cells as an alternative graft for bladder augmentation. Recognizing that contact guidance can potentially influence tissue regeneration, we hypothesized that microtopographically patterned scaffolds would modulate cell responses and improve overall quality of the regenerated bladder tissue. We fabricated microgrooved (MG) scaffolds using the citrate-based biomaterial poly (1,8-octamethylene-citrate-co-octanol) (POCO) and co-seeded them with human bone marrow-derived mesenchymal stromal cells (MSCs) and CD34+ hematopoietic stem/progenitor cells (HSPCs). MG POCO scaffolds supported MSC and HSPC attachment, and MSC alignment within the microgrooves. All scaffolds were characterized and assessed for bladder tissue regeneration in an established nude rat bladder augmentation model. In all cases, normal physiological function was maintained post-augmentation, even without the presence of stem/progenitor cells. Urodynamic testing at 4-weeks post-augmentation for all experimental groups demonstrated that bladder capacity increased and bladder compliance was normal. Histological evaluation of the regenerated tissue revealed that cell-seeded scaffolds restored normal bladder smooth muscle content and resulted in increased revascularization and peripheral nerve regeneration. The presence of microgrooves on the cell-seeded scaffolds increased microvasculature formation by 20 % and urothelial layer thickness by 25 % in the regenerating tissue. Thus, this work demonstrates that microtopography engineering can influence bladder tissue regeneration to improve overall anatomical structure and re-establish bladder physiology.

Beyond the urothelium: Interplay between autonomic nervous system and bladder inflammation in urinary tract infection, bladder pain syndrome with interstitial cystitis and neurogenic lower urinary tract dysfunction in spinal cord injury-ICI-RS 2023

INTRODUCTION

Inflammation and neuronal hypersensitivity are reactive protective mechanisms after urothelial injury. In lower urinary tract dysfunctions (LUTD), such as urinary tract infection (UTI), bladder pain syndrome with interstitial cystitis (BPS/IC) and neurogenic LUTD after spinal cord injury (SCI), chronic inflammation can develop. It is unclear how the protective reactionary inflammation escalates into chronic disease in some patients.

METHODS

During its 2023 meeting in Bristol, the International Consultation on Incontinence-Research Society (ICI-RS) reviewed the urothelial and inflammatory changes after UTI, BPS/IC and SCI. Potential factors contributing to the evolution into chronic disease were explored in a think-tank.

RESULTS

Five topics were discussed. (1) Visceral fat metabolism participates in the systemic pro-inflammatory effect of noradrenalin in BPS/IC and SCI. Sympathetic nervous system-adipocyte-bladder crosstalk needs further investigation. (2) Sympathetic hyperactivity also potentiates immune depression in SCI and needs to be investigated in BPS/IC. Gabapentin and tumor necrosis factor-α are promising research targets. (3) The exact peripheral neurons involved in the integrative protective unit formed by nervous and immune systems need to be further identified. (4) Neurotransmitter changes in SCI and BPS/IC: Neurotransmitter crosstalk needs to be considered in identifying new therapeutic targets. (5) The change from eubiosis to dysbiosis in SCI can contribute to UTI susceptibility and needs to be unraveled.

CONCLUSIONS

The think-tank discussed whether visceral fat metabolism, immune depression through sympathetic hyperactivity, peripheral nerves and neurotransmitter crosstalk, and the change in microbiome could provide explanations in the heterogenic development of chronic inflammation in LUTD. High-priority research questions were identified.

Transient Receptor Potential Channels in Sensory Mechanisms of the Lower Urinary Tract

BACKGROUND

Urine storage and excretion require a network of interactions in the urinary tract and the central nervous system, which is mediated by a reservoir of water in the bladder and the outlet to the bladder neck, urethra, and external urethral sphincter. Through communicating and coordinating each other, micturition system eventually showed a switch-like activity pattern.

SUMMARY

At cervicothoracic and lumbosacral spine, the spinal reflex pathway of the lower urinary tract (LUT) received mechanosensory input from the urothelium to regulate the bladder contraction activity, thereby controlled urination voluntarily. Impairment of above-mentioned any level could result in lower urinary tract dysfunction, placed a huge burden on patients and society. Specific expression of purinergic receptors and transient receptor potential (TRP) channels are thought to play an important role in urinary excretion in the LUT.

KEY MESSAGES

This article reviewed the knowledge about the voiding reflex and described the role and function of TRP channels during voiding.

Detrusor Overactivity After Partial Bladder Outlet Obstruction Is Associated With High Urinary Adenosine Triphosphate Levels in Female Wistar Rats

PURPOSE

Bladder outlet obstruction (BOO) commonly causes detrusor overactivity (DO). In this study, a post hoc analysis of previous obtained data, we investigate if DO occurring in initial phases of BOO is associated with changes in urinary adenosine triphosphate (ATP) levels.

METHODS

Adult female Wistar rats were submitted to partial BOO (pBOO) or to sham obstruction. Cystometry was performed at 3 or 15 days after pBOO and saline voided was collected for ATP determination. Normality was tested using Shapiro-Wilk test. The mean frequency of voiding contractions (VCs) of the sham-operated animals at 15 days after surgery, plus or minus 3 standard deviations, was used to represent the normal range. Statistical analyses were performed using the chi-square and Mann-Whitney tests.

RESULTS

DO was indicated by a VC frequency greater than or equal to 0.9 VCs/min. DO was observed in 63% of animals at 3 days and in 33% at 15 days following pBOO. ATP levels were significantly higher in rats with DO compared to those without DO.

CONCLUSION

The DO phenotype, occurring in the initial phases of BOO, is associated with comparatively high urinary ATP levels.

Commonalities and differences in the mutational signature and somatic driver mutation landscape across solid and hollow viscus organs

Advances in sequencing have revealed a highly variegated landscape of mutational signatures and somatic driver mutations in a range of normal tissues. Normal tissues accumulate mutations at varying rates ranging from 11 per cell per year in the liver, to 1879 per cell per year in the bladder. In addition, some normal tissues are also comprised of a large proportion of cells which possess driver mutations while appearing phenotypically normal, as in the oesophagus where a majority of cells harbour driver mutations. Individual tissue proliferation and mutation rate, unique mutagenic stimuli, and local tissue architecture contribute to this highly variegated landscape which confounds the functional characterization of driver mutations found in normal tissue. In particular, our understanding of the relationship between normal tissue somatic mutations and tumour initiation or future cancer risk remains poor. Here, we describe the mutational signatures and somatic driver mutations in solid and hollow viscus organs, highlighting unique characteristics in a tissue-specific manner, while simultaneously seeking to describe commonalities which can bring forward a basic unified theory on the role of these driver mutations in tumour initiation. We discuss novel findings which can be used to inform future research in this field.

Transcriptomics Reveals Molecular Features of the Bilateral Pelvic Nerve Injury Rat Model of Detrusor Underactivity

The pathogenesis of detrusor underactivity (DU) is unclear, and the available therapeutic effects are unsatisfactory. We propose to find key molecules and pathways related to DU based on transcriptome sequencing. A rat model of bilateral pelvic nerve injury (BPNI) was established. Bladder tissues from the sham-operated group, 3 and 28 days after BPNI mapping, were taken for urodynamics, histopathology, and RNA-seq. An enrichment analysis of the screened differential expression genes was performed. Three days after BPNI, the results showed urodynamic features of overflow incontinence, while there was a recovery at 28 days after the operation. Masson staining revealed collagen deposition accompanied by progressive thickening of the smooth muscle layer as DU progressed. RNA-seq results suggested that a total of 1808 differentially expressed genes (DEGs) differed among the groups. RNA-seq and subsequent analysis confirmed that the cell cycle and immune response were significantly activated 3 days after BPNI, while extracellular matrix remodeling occurred 28 days after BPNI. Partial DEGs and pathways were verified by qRT-PCR. Validation of key proteins involved in cell cycle, inflammation, and fibrosis was performed by immunohistochemical staining and western blot, respectively. These molecular expression patterns at different time points after BPNI injury provide valuable insights into the search for therapeutic targets for DU.

Urothelial bladder afferents selectively project to L6/S1 levels and are more peptidergic than those projecting to the T13/L1 levels in female rats

This neuroanatomical study in four, adult, Sprague-Dawley female rats quantified the number of Urothelial (labeled by intravesical DiI dye administration) and Non-Urothelial (labeled by intraparenchymal injection of Fast blue dye) bladder primary afferent neurons (bPANs) located in the T13, L1, L6 and S1 dorsal root ganglia. Additional immunohistochemical labeling using antibodies to detect either Substance P or CGRP further characterized the bPAN samples as peptidergic or non-peptidergic. Cell counts indicated that Urothelial bPANs were more common at the L6/S1 levels and more likely to be identified as peptidergic when compared with bPANs characterized at T13/L1 levels and with Non-Urothelial bPANs. These studies provide additional evidence that at least two distinct neuronal populations, with differing localization of sensory terminals, differing peptide content, and differing projections to the central nervous system, are responsible for bladder sensation.

Urinary Ascites: An Imitator of Portal Hypertension-Related Ascites

Urinary ascites is a rare and lesser-known etiology of ascites that may mimic portal hypertension (pHTN). We present an unusual case of urinary ascites in a patient with no apparent risk factors for bladder rupture. A 56-year-old woman with an uncomplicated, remote history of abdominal surgery presented with recurring episodes of ascites of unknown etiology. Of note, she has a history of functional, chronic urinary retention due to paruresis, a phobia of public urination. She had abdominal distension on the exam. Paracentesis revealed an elevated serum-ascites albumin gradient (SAAG), concerning portal hypertension. Additionally, the ascites creatinine to serum creatinine ratio was found to be extremely elevated at over 1, and a CT cystogram ultimately revealed bladder rupture, indicating a source of urinary leakage into the peritoneal space. This case report discusses the clinical recognition of urinary ascites as a mimic of apparent portal hypertension-related ascites and appropriate management.

Impairment of urinary bladder mechanical properties in rat model of type 2 diabetes

AIMS

The urinary bladder is a mechanosensitive organ that accumulates, stores, and expels considerable amounts of fluid. While the neuronal bladder control via the CNS is well defined, the data on the mechanisms of local mechanical sensitivity of the bladder wall are either insufficient or contradictory. Here we compared the mechanical properties of bladder wall of normal rats and rats with modeled type 2 diabetes (T2D).

METHODS

T2D was modeled in 3-month-old Wistar male rats by combined administration of nicotinamide (230 mg/kg) and streptozotocin (65 mg/kg). Cystometry of isolated, denervated whole bladders and stress-strain tensiometry on detrusor smooth muscle (DSM) strips were used to assess the mechanical properties of bladder wall tissues from control and diabetic animals on 10th week after induction.

RESULTS

The pressure-volume cystometrograms of both control and T2D bladders featured a quasi plateau between ascending sections. T2D cystometrograms revealed markedly elevated intravesicular pressure (~100% at 1 ml) and a shortened plateau, consistent with decreased bladder wall elasticity and reduced structural bladder capacity versus control. Experiments on urothelium-intact and urothelium-devoid DSM strips have shown that the decrease of bladder walls elasticity in T2D can be explained by the switch of stretched urothelium from inducing DSM relaxation to inducing DSM contraction due to a change in the prevalent release of contractile versus relaxing urothelial factor(s).

CONCLUSIONS

The decreased elasticity of the bladder walls in T2D results from alterations in urothelium-dependent mechanosensory mechanisms. Elevated intravesical pressure in T2D may contribute to urge incontinence and/or symptoms of upper urinary tract damage.

Potential role of oxidative stress in the pathogenesis of diabetic bladder dysfunction

Diabetes mellitus is a chronic metabolic disease, posing a considerable threat to global public health. Treating systemic comorbidities has been one of the greatest clinical challenges in the management of diabetes. Diabetic bladder dysfunction, characterized by detrusor overactivity during the early stage of the disease and detrusor underactivity during the late stage, is a common urological complication of diabetes. Oxidative stress is thought to trigger hyperglycaemia-dependent tissue damage in multiple organs; thus, a growing body of literature has suggested a possible link between functional changes in urothelium, muscle and the corresponding innervations. Improved understanding of the mechanisms of oxidative stress could lead to the development of novel therapeutics to restore the redox equilibrium and scavenge excessive free radicals to normalize bladder function in patients with diabetes.

Aging-Associated Changes in Oxidative Stress Negatively Impacts the Urinary Bladder Urothelium

PURPOSE

Lower urinary tract symptoms are known to significantly increase with age, negatively impacting quality of life and self-reliance. The urothelium fulfills crucial tasks, serving as a barrier protecting the underlying bladder tissue from the harsh chemical composition of urine, and exhibits signaling properties via the release of mediators within the bladder wall that affect bladder functioning. Aging is associated with detrimental changes in cellular health, in part by increasing oxidative stress in the bladder mucosa, and more specifically the urothelium. This, in turn, may impact urothelial mitochondrial health and bioenergetics.

METHODS

We collected mucosal tissue samples from both young (3-4 months old) and aged (25-30 months old) rats. Tissue was evaluated for p21-Arc, nitrotyrosine, and cytochrome C expression by western immunoblotting. Urothelial cells were cultured for single-cell imaging to analyze basal levels of reactive oxygen species and the mitochondrial membrane potential. Mitochondrial bioenergetics and cellular respiration were investigated by the Seahorse assay, and measurements of adenosine triphosphate release were made using the luciferin-luciferase assay.

RESULTS

Aging was associated with a significant increase in biomarkers of cellular senescence, oxidative stress, and basal levels of reactive oxygen species. The mitochondrial membrane potential was significantly lower in urothelial cell cultures from aged animals, and cultures from aged animals showed a significant decrease in mitochondrial bioenergetics.

CONCLUSION

Aging-related increases in oxidative stress and excessive reactive oxygen species may be contributing factors underlying lower urinary tract symptoms in older adults. The mechanisms outlined in this study could be utilized to identify novel pharmaceutical targets to improve aging-associated bladder dysfunction.

Development, regeneration and tumorigenesis of the urothelium

The urothelium of the bladder functions as a waterproof barrier between tissue and outflowing urine. Largely quiescent during homeostasis, this unique epithelium rapidly regenerates in response to bacterial or chemical injury. The specification of the proper cell types during development and injury repair is crucial for tissue function. This Review surveys the current understanding of urothelial progenitor populations in the contexts of organogenesis, regeneration and tumorigenesis. Furthermore, we discuss pathways and signaling mechanisms involved in urothelial differentiation, and consider the relevance of this knowledge to stem cell biology and tissue regeneration.

DU Is Induced by Low Levels of Urinary ATP in a Rat Model of Partial Bladder Outlet Obstruction: The Incidence of Both Events Decreases after Deobstruction

Objectives. To investigate, in initial phases of bladder outlet obstruction (BOO), the urinary ATP levels, the incidence of detrusor underactivity (DU), and if they change after deobstruction. Methods. Adult female Wistar rats submitted to partial BOO (pBOO) and sham-obstruction were used. Cystometry was performed 3 or 15 days after pBOO and fluid was collected from the urethra for ATP determination. Bladders were harvested for morphological evaluation of the urothelium. DU was defined as the average of voiding contractions (VC) of sham-operated animals, with 3 SD at 15 days after the sham surgery. In another group of animals in which pBOO was relieved at 15 days and bladders were let to recover for 15 days, the incidence of DU and ATP levels were also accessed. The Kruskal–Wallis test was followed by Dunn’s multiple comparisons test, and Spearman’s correlation test was used. Results. DU was present in 13% and 67% of the bladders at 3 and 15 days after pBOO, respectively, and in 20% of the bladders at 15 days after deobstruction. ATP levels were significantly lower in DU/pBOO versus sham and non-DU/pBOO rats. A strong positive correlation between ATP levels and VC/min was obtained (r = 0.63). DU bladders had extensive areas in which umbrella cells appeared stretched, the width exceeding that presented by sham animals. Conclusions. Low urothelial ATP parallels with a high incidence of DU early after pBOO.

Identification of the NADPH Oxidase (Nox) Subtype and the Source of Superoxide Production in the Micturition Centre

Oxidative inflammatory damage to specialised brain centres may lead to dysfunction of their associated peripheral organs, such as the bladder. However, the source of reactive oxygen species (ROS) in specific brain regions that regulate bladder function is poorly understood. Of all ROS-generating enzymes, the NADPH oxidase (Nox) family produces ROS as its sole function and offers an advantage over other enzymes as a drug-targetable molecule to selectively control excessive ROS. We investigated whether the Nox 2 subtype is expressed in the micturition regulatory periaqueductal gray (PAG) and Barrington's nucleus (pontine micturition centre, PMC) and examined Nox-derived ROS production in these structures. C57BL/6J mice were used; PAG, PMC, cardiac tissue, and aorta were isolated. Western blot determined Nox 2 expression. Lucigenin-enhanced chemiluminescence quantified real-time superoxide production. Western blot experiments demonstrated the presence of Nox 2 in PAG and PMC. There was significant NADPH-dependent superoxide production in both brain tissues, higher than that in cardiac tissue. Superoxide generation in these brain tissues was significantly suppressed by the Nox inhibitor diphenyleneiodonium (DPI) and also reduced by the Nox-2 specific inhibitor GSK2795039, comparable to aorta. These data provide the first evidence for the presence of Nox 2 and Nox-derived ROS production in micturition centres.

l-Theanine Protects Bladder Function by Suppressing Chronic Sympathetic Hyperactivity in Spontaneously Hypertensive Rat

Chronic sympathetic hyperactivity is known to affect metabolism and cause various organ damage including bladder dysfunction. In this study, we evaluated whether l-theanine, a major amino acid found in green tea, ameliorates bladder dysfunction induced by chronic sympathetic hyperactivity as a dietary component for daily consumption. Spontaneously hypertensive rats (SHRs), as an animal model of bladder dysfunction, were divided into SHR-water and SHR-theanine groups. After 6 weeks of oral administration, the sympathetic nervous system, bladder function, and oxidative stress of bladder tissue were evaluated. The mean blood pressure, serum noradrenaline level, and media-to-lumen ratio of small arteries in the suburothelium were significantly lower in the SHR-theanine than in the SHR-water group. Micturition interval was significantly longer, and bladder capacity was significantly higher in the SHR-theanine than in the SHR-water group. Bladder strip contractility was also higher in the SHR-theanine than in the SHR-water group. Western blotting of bladder showed that expression of malondialdehyde was significantly lower in the SHR-theanine than in the SHR-water group. These results suggested that orally administered l-theanine may contribute at least partly to the prevention of bladder dysfunctions by inhibiting chronic sympathetic hyperactivity and protecting bladder contractility.

Current pharmacotherapy of overactive bladder

Overactive bladder is a symptom complex consisting of bothersome storage urinary symptoms that is highly prevalent among both sexes and has a significant impact on quality of life. Various antimuscarinic agents and the beta-3 agonists mirabegron and vibegron are currently available for the treatment of OAB. Each drug has specific pharmacologic properties, dosing schedule and tolerability profile, making it essential to individualize the medical treatment for the patient's characteristics and expectations. In this manuscript, we review the most important factors involved in the contemporary pharmacological treatment of OAB.

Psychological stress induced bladder overactivity in female mice is associated with enhanced afferent nerve activity

Psychological stress has been linked to the development and exacerbation of overactive bladder symptoms, as well as afferent sensitisation in other organ systems. Therefore, we aimed to investigate the effects of water avoidance stress on bladder afferent nerve activity in response to bladder filling and pharmaceutical stimulation with carbachol and ATP in mice. Adult female C57BL/6J mice were exposed to either water avoidance stress (WAS) for 1 h/day for 10 days or normal housing conditions. Voiding behaviour was measured before starting and 24-h after final stress exposure and then animals were euthanised to measure afferent nerve activity in association with bladder compliance, spontaneous phasic activity, contractile responses, as well as release of urothelial mediators. WAS caused increased urinary frequency without affecting urine production. The afferent nerve activity at low bladder pressures (4-7 mmHg), relevant to normal physiological filling, was significantly increased after stress. Both low and high threshold nerves demonstrated enhanced activity at physiological bladder pressures. Urothelial ATP and acetylcholine release and bladder compliance were unaffected by stress as was the detrusor response to ATP (1 mM) and carbachol (1 µM). WAS caused enhanced activity of individual afferent nerve fibres in response bladder distension. The enhanced activity was seen in both low and high threshold nerves suggesting that stressed animals may experience enhanced bladder filling sensations at lower bladder volumes as well as increased pain sensations, both potentially contributing to the increased urinary frequency seen after stress.

Molecular pathways underlying tissue injuries in the bladder with ketamine cystitis

Ketamine cystitis (KC) is a chronic bladder inflammation leading to urinary urgency, frequency, and pain. The pathogenesis of KC is complicated and involves multiple tissue injuries in the bladder. Recent studies indicated that urothelium disruption, lamina propria fibrosis and inflammation, microvascular injury, neuropathological alterations, and bladder smooth muscle (BSM) abnormalities all contribute to the pathogenesis of KC. Ketamine has been shown to induce these tissue injuries by regulating different signaling pathways. Ketamine can stimulate antiproliferative factor, adenosine triphosphate, and oxidative stress to disrupt urothelium. Lamina propria fibrosis and inflammation are associated with the activation of cyclooxygenase-2, nitric oxide synthase, immunoglobulin E, and transforming growth factor β1. Ketamine contributes to microvascular injury via the N-methyl-D aspartic receptor (NMDAR), and multiple inflammatory and angiogenic factors such as tumor necrosis factor α and vascular endothelial growth factor. For BSM abnormalities, ketamine can depress the protein kinase B, extracellular signal-regulated kinase, Cav1.2, and muscarinic receptor signaling. Elevated purinergic signaling also plays a role in BSM abnormalities. In addition, ketamine affects neuropathological alterations in the bladder by regulating NMDAR- and brain-derived neurotrophic factor-dependent signaling. Inflammatory cells also contribute to neuropathological changes via the secretion of chemical mediators. Clarifying the role and function of these signaling underlying tissue injuries in the bladder with KC can contribute to a better understanding of the pathophysiology of this disease and to the design of effective treatments for KC.

Bladder overactivity induced by psychological stress in female mice is associated with enhanced bladder contractility

AIMS

To investigates the effects of water avoidance stress on voiding behaviour and functional bladder responses in mice.

MAIN METHODS

Mice in the Stress group were exposed to water avoidance stress (WAS) for 1 h/day for 10 days, Controls were age-matched and housed normally. Voiding behaviour was measured periodically throughout the stress protocol and bladders were isolated 24-h after final stress exposure to measure bladder compliance, spontaneous phasic activity, contractile responses, and release of urothelial mediators.

KEY FINDINGS

Repeated stress exposure induced a significant increase in plasma corticosterone levels in the WAS group compared to control. An overactive bladder phenotype was observed in WAS mice, causing a significant increase in the number of voiding events observed from as early as day-3, and a 7-fold increase following 10-days' stress. This increase in voiding frequency was associated with a significant decrease in void size, an increase in the number of small voids, but no change in total voided volume. Bladders from stressed mice showed a significant increase in the maximum responses to the muscarinic agonist carbachol (p < 0.01), in addition to enhanced pressure responses to the purinergic agonists ATP (p < 0.05) and αβ-mATP (p < 0.05), and non-receptor mediated contractions to KCl (p < 0.05) compared to controls. Nerve-mediated bladder contractions to electric field stimulation were not significantly affected by stress, nor were spontaneous phasic contractions or release of urothelial ATP and acetylcholine.

SIGNIFICANCE

Repeated exposure to water avoidance stress produced an overactive bladder phenotype, confirmed by increased voiding frequency, and associated with enhanced bladder contractile responses.

Ultrastructural changes in the underactive bladder

Underactive bladder (UAB) is a symptom complex suggestive of detrusor underactivity (DU). Although it implies a primary dysfunction of the detrusor muscle, many other conditions such as advanced age, neurogenic factors, and bladder outlet obstruction also lead to UAB. The current understanding of the pathophysiology directly leading to UAB is limited. We believe that by identifying the morphological changes associated with UAB might shed light on this. Therefore, we searched literature with keywords of electron microscopy, ultrastructure, UAB, and DU to review current ultrastructural evidence concerning UAB.

Characterizing relaxin receptor expression and exploring relaxin's effect on tissue remodeling/fibrosis in the human bladder

Background

Relaxin is an endogenous protein that has been shown to have antifibrotic properties in various organ systems. There has been no characterization of relaxin’s role in the human bladder. Our objective was to characterize relaxin receptor expression in the human bladder and assess relaxin’s effect on tissue remodeling/fibrosis pathways in bladder smooth muscle cells.

Methods

Relaxin family peptide receptor 1 (RXFP1) and RXFP2 expression was assessed using quantitative reverse transcriptase-PCR (qRT-PCR) and immunohistochemistry (IHC) on primary bladder tissue. Primary human smooth muscle bladder cells were cultured and stimulated with various concentrations of relaxin. Western blot, qRTPCR, ELISA, and zymogram assays were used to analyze fibrosis/tissue remodeling pathway proteins.

Results

There was universal mRNA transcript detection and protein expression of relaxin receptors in primary bladder specimens. Immunohistochemistry demonstrated RXFP1 and RXFP2 localizing to both urothelial and smooth muscle cell layers of the bladder. 24 h of in vitro relaxin stimulation did not affect mRNA expression of selected proteins in human bladder smooth muscle cells. However, 48 h of in vitro relaxin stimulation resulted in upregulation of active (p = 0.004) and latent (p = 0.027) MMP-2 in cell lysate, and upregulation of active MMP-2 in supernatant (p = 0.04). There was a dose dependent relationship with increasing expression of MMP-2 with increasing relaxin concentration. Relaxin stimulation resulted in decreased levels of active and total TGF-β1 in supernatant and extracellular matrix (p < 0.005 with 100 ng/mL relaxin stimulation).

Conclusions

In the human bladder, relaxin receptors are expressed at the dome and trigone and localize to the urothelium and smooth muscle cell layers. Stimulation of human bladder SMCs with relaxin in vitro affects expression of MMP-2 and TGF-β1.

Voiding Behavior and Efferent Bladder Function Altered in Mice Following Social Defeat but Not Witness Trauma

Psychological stress is associated with bladder dysfunction, however, the local bladder mechanisms affected are not well understood. This study aimed to determine how psychological stress, caused by social defeat or witness trauma, affects voiding behavior and bladder function. Pairs of male C57Bl/6J mice were placed in a custom-made plexiglass chamber with an aggressor ARC(S) mouse for 1 h/day for 10 days. The social defeat mouse was in physical contact with the aggressor, while the witness was physically separated but could observe interactions between its cage-mate and the aggressor. Age matched control pairs were used for comparison. Voiding analysis was conducted periodically over the 10 days. An ex vivo whole bladder preparation was used to assess functional changes after the period of stress. Plasma corticosterone levels were significantly increased by both social defeat and witness trauma stress when compared to unstressed controls. Voiding analysis revealed a significant decrease in voiding frequency in the social defeat group compared to control animals, indicating an altered voiding phenotype. Witness trauma did not alter voiding behavior. Bladder contractile responses to cholinergic stimulation were not significantly altered in either stress group, nor was relaxation to the beta-adrenoceptor agonist isoprenaline. However, nerve evoked contractile responses were significantly increased at all frequencies in bladders from social defeat but not witness trauma mice. Purinergic contractile responses were also significantly enhanced in this group. Social defeat also resulted in increased urothelial acetylcholine release during bladder distension, with no change in ATP release. In conclusion, functional bladder changes are dependent upon stressor type. Enhanced urothelial acetylcholine may desensitize bladder sensory nerves, which, coupled with more efficient voiding contractions due to enhanced nerve-mediated and purinergic detrusor responses, may account for the altered voiding phenotype observed. This study reports a male model of social defeat stress with reduced urinary frequency, with no voiding changes observed in the witness.

TRPV4 receptor as a functional sensory molecule in bladder urothelium: Stretch-independent, tissue-specific actions and pathological implications

The newly recognized sensory role of bladder urothelium has generated intense interest in identifying its novel sensory molecules. Sensory receptor TRPV4 may serve such function. However, specific and physiologically relevant tissue actions of TRPV4, stretch-independent responses, and underlying mechanisms are unknown and its role in human conditions has not been examined. Here we showed TRPV4 expression in guinea-pig urothelium, suburothelium, and bladder smooth muscle, with urothelial predominance. Selective TRPV4 activation without stretch evoked significant ATP release-key urothelial sensory process, from live mucosa tissue, full-thickness bladder but not smooth muscle, and sustained muscle contractions. ATP release was mediated by Ca2+-dependent, pannexin/connexin-conductive pathway involving protein tyrosine kinase, but independent from vesicular transport and chloride channels. TRPV4 activation generated greater Ca2+ rise than purinergic activation in urothelial cells. There was intrinsic TRPV4 activity without exogeneous stimulus, causing ATP release. TRPV4 contributed to 50% stretch-induced ATP release. TRPV4 activation also triggered superoxide release. TRPV4 expression was increased with aging. Human bladder mucosa presented similarities to guinea pigs. Overactive bladders exhibited greater TRPV4-induced ATP release with age dependence. These data provide the first evidence in humans for the key functional role of TRPV4 in urothelium with specific mechanisms and identify TRPV4 up-regulation in aging and overactive bladders.

Purinergic receptor mediated calcium signalling in urothelial cells

Non-neuronal ATP released from the urothelium in response to bladder stretch is a key modulator of bladder mechanosensation. Whilst non-neuronal ATP acts on the underlying bladder afferent nerves to facilitate sensation, there is also the potential for ATP to act in an autocrine manner, modulating urothelial cell function. The aim of this study was to systematically characterise the functional response of primary mouse urothelial cells (PMUCs) to ATP. PMUCs isolated from male mice (14–16 weeks) were used for live-cell fluorescent calcium imaging and qRT-PCR to determine the expression profile of P2X and P2Y receptors. The majority of PMUCs (74–92%) responded to ATP (1 μM–1 mM), as indicted by an increase in intracellular calcium (iCa²⁺). PMUCs exhibited dose-dependent responses to ATP (10 nM–1 mM) in both calcium containing (2 mM, EC₅₀ = 3.49 ± 0.77 μM) or calcium free (0 mM, EC₅₀ = 9.5 ± 1.5 μM) buffers. However, maximum iCa²⁺ responses to ATP were significantly attenuated upon repetitive applications in calcium containing but not in calcium free buffer. qRT-PCR revealed expression of P2X_1–6, and P2Y_1–2, P2Y₄, P2Y₆, P2Y_11–14, but not P2X₇ in PMUCs. These findings suggest the major component of ATP induced increases in iCa²⁺ are mediated via the liberation of calcium from intracellular stores, implicating functional P2Y receptors that are ubiquitously expressed on PMUCs.

Directed differentiation of human induced pluripotent stem cells into mature stratified bladder urothelium

For augmentation or reconstruction of urinary bladder after cystectomy, bladder urothelium derived from human induced pluripotent stem cells (hiPSCs) has recently received focus. However, previous studies have only shown the emergence of cells expressing some urothelial markers among derivatives of hiPSCs, and no report has demonstrated the stratified structure, which is a particularly important attribute of the barrier function of mature bladder urothelium. In present study, we developed a method for the directed differentiation of hiPSCs into mature stratified bladder urothelium. The caudal hindgut, from which the bladder urothelium develops, was predominantly induced via the high-dose administration of CHIR99021 during definitive endoderm induction, and this treatment subsequently increased the expressions of uroplakins. Terminal differentiation, characterized by the increased expression of uroplakins, CK13, and CK20, was induced with the combination of Troglitazone + PD153035. FGF10 enhanced the expression of uroplakins and the stratification of the epithelium, and the transwell culture system further enhanced such stratification. Furthermore, the barrier function of our urothelium was demonstrated by a permeability assay using FITC-dextran. According to an immunohistological analysis, the stratified uroplakin II-positive epithelium was observed in the transwells. This method might be useful in the field of regenerative medicine of the bladder.

A Comprehensive Review of Overactive Bladder Pathophysiology: On the Way to Tailored Treatment

CONTEXT

Current literature suggests that several pathophysiological factors and mechanisms might be responsible for the nonspecific symptom complex of overactive bladder (OAB).

OBJECTIVE

To provide a comprehensive analysis of the potential pathophysiology underlying detrusor overactivity (DO) and OAB.

EVIDENCE ACQUISITION

A PubMed-based literature search was conducted in April 2018, to identify randomised controlled trials, prospective and retrospective series, animal model studies, and reviews.

EVIDENCE SYNTHESIS

OAB is a nonspecific storage symptom complex with poorly defined pathophysiology. OAB was historically thought to be caused by DO, which was either "myogenic" (urgency initiated from autonomous contraction of the detrusor muscle) or "neurogenic" (urgency signalled from the central nervous system, which initiates a detrusor contraction). Patients with OAB are often found to not have objective evidence of DO on urodynamic studies; therefore, alternative mechanisms for the development of OAB have been postulated. Increasing evidence on the role of urothelium/suburothelium and bladder afferent signalling arose in the early 2000s, emphasising an afferent "urotheliogenic" hypothesis, namely, that urgency is initiated from the urothelium/suburothelium. The urethra has also recently been regarded as a possible afferent origin of OAB-the "urethrogenic" hypothesis. Several other pathophysiological factors have been implicated, including metabolic syndrome, affective disorders, sex hormone deficiency, urinary microbiota, gastrointestinal functional disorders, and subclinical autonomic nervous system dysfunctions. These various possible mechanisms should be considered as contributing to diagnostic and treatment algorithms.

CONCLUSIONS

There is a temptation to label OAB as "idiopathic" without obvious causation, given the poorly understood nature of its pathophysiology. OAB should be seen as a complex, multifactorial symptom syndrome, resulting from multiple potential pathophysiological mechanisms. Identification of the underlying causes on an individual basis may lead to the definition of OAB phenotypes, paving the way for personalised medical care.

PATIENT SUMMARY

Overactive bladder (OAB) is a storage symptom syndrome with multiple possible causes. Identification of the mechanisms causing a patient to experience OAB symptoms may help tailor treatment to individual patients and improve outcomes.

NLRP3/IL1β inflammasome associated with the aging bladder triggers bladder dysfunction in female rats

Bladder dysfunction is associated with fibrosis-mediated aging, but the corresponding mechanism remains to be elucidated. Activation of the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome is related to chronic diseases associated with aging, including organ fibrosis. The present study aimed to explore the role of NLRP3/interleukin 1β in aging-associated bladder dysfunction. Female Sprague-Dawley rats were divided into the following two groups (n=10 rats/group): 2-month-old group (young group) and 24-month-old group (old group). Urodynamics were performed to assess the bladder function of the rats. The histological alterations were identified using Masson's trichrome staining. The protein expression of the NLRP3 inflammasome and NAD-dependent protein deacetylase sirtuin-3, mitochondrial (SIRT3) were detected by western blot analysis, and immunohistochemistry was used to examine a senescence marker (p21) and the NLRP3 inflammasome in the bladder. The localization of the key molecule Caspase1 was determined using immunofluorescence. The voiding time was longer in the old group compared with the young group. The expression levels of SIRT3 were reduced in the bladders of the old group, while those of the NLRP3 inflammasome and the senescence marker were significantly higher in the bladders of the old group compared with the young group. Increased collagen deposition leads to chronic bladder fibrosis with increased NLRP3. In the histological examination, the bladders of the old group displayed increased collagen deposition, urothelial thinning and detrusor shrinkage compared with the young group. Tissue fibrosis and urothelial alterations are the principal causes of bladder dysfunction during aging. Downregulated SIRT3 and upregulated expression of the NLRP3 inflammasome are involved in the degradation of aging bladders. Inflamm-aging is a novel mechanism underlying bladder dysfunction.

Diabetes-induced alterations in urothelium function: Enhanced ATP release and nerve-evoked contractions in the streptozotocin rat bladder

Up to 80% of patients with diabetes mellitus develop lower urinary tract complications, most commonly diabetic bladder dysfunction (DBD). The aim of this study was to investigate the impact of diabetes on the function of the inner bladder lining (urothelium). Bladder compliance and intraluminal release of urothelial mediators, adenosine triphosphate (ATP) and acetylcholine (ACh) in response to distension were investigated in whole bladders isolated from 2- and 12-week streptozotocin (STZ)-diabetic rats. Intact and urothelium-denuded bladder strips were used to assess the influence of the urothelium on bladder contractility. Intraluminal ATP release was significantly enhanced at 2 weeks of diabetes, although not at 12 weeks. In contrast, intraluminal ACh release was unaltered by diabetes. Bladder compliance was also significantly enhanced at both 2 and 12 weeks of diabetes, with greatly reduced intravesical pressures in response to distension. Nerve-evoked contractions of bladder strips were significantly greater at 2 weeks of diabetes. When the urothelium was absent, nerve-evoked contractions were reduced, but contractions remained significantly elevated at lower frequencies of stimulation (<5 Hz) in diabetics. Interestingly, although relaxations of bladder strips to isoprenaline were unaltered by diabetes, removal of the urothelium unmasked significantly enhanced relaxations in strips from 2- and 12-week diabetic animals. In conclusion, diabetes alters urothelial function. Enhanced urothelial ATP release may be involved in the hypercontractility observed at early time points of diabetes. These alterations are time-dependent and may contribute to the mechanisms at play during the development of diabetic bladder dysfunction.

Do brain structural abnormalities differentiate separate forms of urgency urinary incontinence?

AIMS

Urgency urinary incontinence (UUI) is a major problem for seniors. The underlying mechanisms of disease and therapy are unknown. We sought structural brain abnormalities that might underlie the functional differences previously observed by functional Magnetic Resonance Imaging in UUI patients versus controls, or among UUI responders versus non-responders to therapy-and thereby reveal potential disease mechanisms and therapeutic targets.

METHODS

Secondary study of a trial of biofeedback-assisted pelvic floor muscle training (BFB) in 60 women (>60 yrs) with UUI, plus 11 age-matched continent controls. Brain structural abnormalities were investigated using: (1) white-matter hyperintensities (WMH); (2) diffusion tensor imaging (DTI) to reveal white-matter pathways with impaired integrity; and (3) voxel-based morphometry (VBM) to show regions of atrophy or hypertrophy.

RESULTS

WMH burden was greater in UUI patients than controls (globally and in superior longitudinal fasciculus and cingulum), suggesting a possible causal connection. WMH burden was unexpectedly greater in responders than non-responders to BFB, and appeared to increase in non-responders but not in responders. DTI revealed even worse integrity of the cingulum than was apparent by WMH. VBM showed parahippocampal atrophy in UUI.

CONCLUSIONS

Many women with UUI have white-matter damage that interferes with pathways critical to bladder control; they can be taught by techniques like BFB to exert stronger control over the bladder. For others, in whom abnormalities of key brain areas are less marked, UUI's cause may reside elsewhere, and therapy targeting these brain centers may be less effective than therapy targeting the bladder or other brain centers.

Tadalafil attenuates hypotonicity-induced Ca2+ influx via TRPV2 and TRPV4 in primary rat bladder urothelial cell cultures

AIMS

To investigate the localization of phosphodiesterase 5 (PDE5) and the molecular mechanism underlying the effect of the PDE5 inhibitor tadalafil in signal transduction in the bladder urothelium.

METHODS

PDE5 expression in rat bladder tissues and cultured primary rat bladder urothelial cells was evaluated using immunochemistry and western blot assays. Ca²⁺ influx in cells exposed to isotonic solution, hypotonic solution, a selective transient receptor potential vanilloid 2 (TRPV2) channel agonist (cannabidiol), a selective TRPV4 channel agonist (GSK1016790A), a TRP cation channel melastatin 7 (TRPM7) channel agonist (PIP2), or a purinergic receptor agonist (ATP) in the presence or absence of 10 µM tadalafil was evaluated using calcium imaging techniques. We also evaluated stretch-induced changes in ATP concentration in the mouse bladder in the presence or absence of 100 µM tadalafil.

RESULTS

Immunochemistry and western blot analyses demonstrated that PDE5 is abundantly expressed in the bladder urothelium and in primary rat urothelial cells. Ca²⁺ influx induced by hypotonic stimulation, GSK1016790A, or cannabidiol was significantly inhibited by tadalafil, whereas ATP-induced Ca²⁺ influx was unaffected by tadalafil. PIP2 did not induce Ca2+ influx. ATP release in tadalafil-pretreated bladders significantly decreased compared to control bladders.

CONCLUSIONS

Tadalafil attenuates Ca²⁺ influx via TRPV4 and TRPV2, and inhibits ATP release in the bladder urothelium. These findings indicate that tadalafil functions as an inhibitor of urothelial signal transduction.

Regulation of Spontaneous Contractions in Intact Rat Bladder Strips and the Effects of Hydrogen Peroxide

Enhanced spontaneous contractions are associated with overactive bladder. Elevated levels of reactive oxygen species might contribute to enhanced spontaneous contractions. We investigated the regulation of spontaneous contractions and the effects of hydrogen peroxide (H₂O₂) in intact rat bladder strips. The spontaneous contractions were measured using a tissue bath system. The vehicle or the specific activators/blockers were applied and followed by the application of 0.003 g% H₂O₂. The basal tension, amplitude, and frequency of spontaneous contractions were quantified. Nisoldipine and bisindolylmaleimide 1 had no effects on spontaneous contractions. SKF96365 and Y27632 decreased basal tension and amplitude. Ryanodine slightly increased frequency. Both iberiotoxin and NS-1619 increased amplitude. Apamin reduced frequency but increased amplitude. NS-309 inhibited both the amplitude and frequency. The basal tension and amplitude increased when H₂O₂ was applied. Pretreatment with NS-309 inhibited H₂O₂-elicited augmented amplitude and frequency, while pretreatment with Y-27632 inhibited the augmented basal tension. The combined application of NS-309 and Y27632 almost eliminated spontaneous contractions and its augmentation induced by H₂O₂. In conclusion, Ca²⁺ influx, Rho kinase activation, and SK channel inactivation play important roles in spontaneous contractions in intact bladder strips, whereas only latter two mechanisms may be involved in H₂O₂-elicited increased spontaneous contractions.

Inhibitory Effects of Urothelium-related Factors

The urothelium of the bladder has long been recognized as a protective barrier between detrusor and urine. In recent years, it has become more evident that the urothelium plays a role as an active source of mediators. The urothelium can release neurotransmitters and modulators such as acetylcholine, ATP, nitric oxide, prostaglandins and neuropeptides. They exert both excitatory and inhibitory effects in modulating urinary tract motility. In addition, several studies have reported the existence of an urothelium-derived unknown inhibitory factor in the urinary bladder. By the use of a new serial cascade superfusion bioassay on guinea pig ureter, recent studies confirm that the guinea pig bladder urothelium releases a substance with inhibitory bioactivity, which was resistant to treatment with nitric oxide synthase inhibitor and cyclooxygenase inhibitor and to adenosine A1/A2 receptor blockade. Lately, a marked and quickly inactivated novel release of PGD₂ from the bladder urothelium was discovered, together with localization of prostaglandin D synthase therein. PGD₂ was found to have an inhibitory influence on nerve-induced contractions in guinea pig urinary bladder and on spontaneous contractions in the out-flow region. An altered release of excitatory and inhibitory factors is likely to play an important part in bladder motility disturbances, of which the prostanoids are a notable group. Due to the fact that the bladder is relaxed 99% of the time, not only excitatory mechanisms in the bladder are necessary to study, but also inhibitory mechanisms need considerable attention, which will contribute to the discovery of new targets to treat bladder motility disorders.

Urinary biomarkers in patients with detrusor underactivity with and without bladder function recovery

PURPOSE

Detrusor underactivity (DU) is frequently encountered in elderly patients. Part of patients with DU might have bladder function recovery after treatment. This study investigated urinary proteins in these DU patients with and without bladder function recovery.

METHODS

A total of 37 patients with chronic urinary retention and urodynamically proven DU were enrolled. After treatment, 24 DU patients had bladder function recovery whereas 13 had not, after 1-year follow-up. Urine collection at baseline was performed, and the urinary protein including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and prostaglandin E2 (PGE2) were measured by ELISA. Twenty urodynamically normal, 34 detrusor overactivity (DO) and 15 detrusor hyperactivity and inadequate contractility (DHIC) patients served as comparative groups.

RESULTS

Urinary NGF levels were significantly higher than normal in patients with DU (9.2 ± 20.3 vs 1.85 ± 2.9 pg/ml, p = 0.037). Urinary BDNF level was only significantly higher in patients with DU than that of the control group (153 ± 199 vs 77.4 ± 47.7 pg/ml, p = 0.033) but not in patients with DHIC or DO. Compared with the control group, the urinary BDNF level was significantly higher in DU patients with bladder function recovery (190 ± 239 pg/ml, p = 0.033) but not in patients without recovery (85.8 ± 43.7 pg/ml, p = 0.612). The PGE2 level was significantly higher than the control group in DU patients with bladder function recovery (1290 ± 836 pg/ml, p < 0.0001) but not in patients without recovery (383 ± 237 pg/ml, p = 0.130).

CONCLUSION

Patients with DU and higher urinary PGE2 and BDNF levels might have a chance to recover bladder function than those with a lower protein level.

Urothelial acetylcholine involvement in ATP-induced contractile responses of the rat urinary bladder

Both acetylcholine and adenosine 5'-triphosphate (ATP) are released from the urothelium. In in vivo experiments ATP has been shown to evoke contractile responses that are significantly reduced by atropine. Currently, we aimed to examine the cholinergic part of the ATP-evoked contractile response of normal and inflamed (cyclophosphamide-treated rats) bladders. A whole bladder preparation that enabled drug administration either outside or inside the urinary bladder was used. The responses were examined in bladders from control and cyclophosphamide-treated rats that were either intact or urothelium-denuded. The expression of choline acetyltransferase and carnitine acetyltransferase were examined by Western blotting of normal and inflamed bladders. Methacholine evoked larger contractions when administered to the outside of the bladder in comparison to instillation. For ATP, an opposite trend emerged. While atropine substantially reduced the ATP-induced responses at internal administration (7.4±1.1 and 3.7±0.9 mN at 10^-3M; n=13; P<0.001), it had no effect when administered outside the bladder. The removal of the urothelium caused a similar reduction of the responses to internal administration of ATP as caused by atropine. In cyclophosphamide-treated rats, neither atropine nor urothelium-denudation had any effect on the ATP-evoked responses. No changes in the expressions of the acetylcholine synthesising enzymes were observed. The current study shows that ATP induces a release of urothelial acetylcholine that contributes to the purinergic contractile response in the rat urinary bladder. This atropine-sensitive part of the purinergic contractile response is absent in the inflamed bladder. This may be one pathological mechanism involved in bladder dysfunction.

Video-urodynamic characteristics of non-neurogenic, idiopathic underactive bladder in men - A comparison of men with normal tracing and bladder outlet obstruction

Objective

Underactive bladder is frequently encountered in elderly patients. It may result from detrusor underactivity (DU) or low detrusor contractility due to a urethral sphincter inhibitory effect. This study analyzed the video-urodynamic study (VUDS) characteristics of patients with underactive bladder in a large cohort of men with lower urinary tract symptoms (LUTS).

Methods

Male patients with LUTS who had failed the initial treatment were consecutively enrolled. All patients underwent detailed urological investigations including prostate measurement, free uroflowmetry, post-void residual volume (PVR) measurement, cystoscopy and VUDS. The VUDS characteristics of the men with underactive bladder were analyzed and compared with those of men with bladder outlet obstruction and normal tracing.

Results

A total of 1329 men who underwent VUDS were included in this retrospective analysis. After VUDS, the final diagnosis was DU in 165 patients, poor relaxation of external sphincter (PRES) in 525, bladder outlet obstruction in 501, and normal tracing in 138. VUDS findings in DU patients showed a slowly increased detrusor pressure, intermittent detrusor contractions, or early decline of detrusor contraction, resulting in a low maximum flow rate (Qmax), and large PVR. In comparison with the PRES groups, DU patients were older, had reduced bladder sensation, lower detrusor pressure (Pdet), lower Qmax, larger PVR volume, and lower voiding efficiency. Patients with urodynamic PRES also had low-pressure–low-flow tracings, but their bladder sensation was similar to that with normal tracing. DU patients with very low Pdet also had low detrusor tonicity, and more medical co-morbidities than the other groups did.

Conclusion

Idiopathic underactive bladder in elderly men could be attributed to urodynamic DU and PRES. DU is associated with old age, reduced bladder sensation, low voiding efficiency, and medical co-morbidities.

Intravital imaging of mouse urothelium reveals activation of extracellular signal-regulated kinase by stretch-induced intravesical release of ATP

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.

Mathematical modelling of stretch-induced membrane traffic in bladder umbrella cells

The bladder is a complex organ that is highly adaptive to its mechanical environment. The umbrella cells in the bladder uroepithelium are of particular interest: these cells actively change their surface area through exo- and endocytosis of cytoplasmic vesicles, and likely form a critical component in the mechanosensing process that communicates the sense of 'fullness' to the nervous system. In this paper we develop a first mechanical model for vesicle trafficking in umbrella cells in response to membrane tension during bladder filling. Recent experiments conducted on a disc of uroepithelial tissue motivate our model development. These experiments subject bladder tissue to fixed pressure differences and exhibit counterintuitive area changes. Through analysis of the mathematical model and comparison with experimental data in this setup, we gain an intuitive understanding of the biophysical processes involved and calibrate the vesicle trafficking rate parameters in our model. We then adapt the model to simulate in vivo bladder filling and investigate the potential effect of abnormalities in the vesicle trafficking machinery on bladder pathologies.

Testing a Model of Self-Management of Fluid Intake in Community-Residing Long-term Indwelling Urinary Catheter Users

BACKGROUND

Urinary tract infection and blockage are serious and recurrent challenges for people with long-term indwelling catheters, and these catheter problems cause worry and anxiety when they disrupt normal daily activities.

OBJECTIVE

The goal was to determine whether urinary catheter-related self-management behaviors focusing on fluid intake would mediate fluid intake-related self-efficacy toward decreasing catheter-associated urinary tract infection (CAUTI) and/or catheter blockage.

METHODS

The sample involved data collected from 180 adult community-living, long-term indwelling urinary catheter users. The authors tested a model of fluid intake self-management related to fluid intake self-efficacy for key outcomes of CAUTI and blockage. To account for the large number of zeros in both outcomes, a zero-inflated negative binomial (ZINB) structural equation model was tested.

RESULTS

Structurally, fluid intake self-efficacy was positively associated with fluid intake self-management, suggesting that higher fluid intake self-efficacy predicts more (higher) fluid intake self-management; however, fluid intake self-management was not associated with either the frequency of CAUTIs or the presence or absence of CAUTI. Fluid intake self-efficacy was positively related to fluid intake self-management, and fluid intake self-management predicted less frequency of catheter blockage, but neither fluid intake self-efficacy nor fluid intake self-management predicted the presence or absence of blockage.

DISCUSSION

Further research is needed to better understand determinants of CAUTI in long-term catheter users and factors which might influence or prevent its occurrence. Increased confidence (self-efficacy) and self-management behaviors to promote fluid intake could be of value to long-term urinary catheter users to decrease catheter blockage.

Human Cystathionine-β-Synthase Phosphorylation on Serine227 Modulates Hydrogen Sulfide Production in Human Urothelium

Urothelium, the epithelial lining the inner surface of human bladder, plays a key role in bladder physiology and pathology. It responds to chemical, mechanical and thermal stimuli by releasing several factors and mediators. Recently it has been shown that hydrogen sulfide contributes to human bladder homeostasis. Hydrogen sulfide is mainly produced in human bladder by the action of cystathionine-β-synthase. Here, we demonstrate that human cystathionine-β-synthase activity is regulated in a cGMP/PKG-dependent manner through phosphorylation at serine 227. Incubation of human urothelium or T24 cell line with 8-Bromo-cyclic-guanosine monophosphate (8-Br-cGMP) but not dibutyryl-cyclic-adenosine monophosphate (d-cAMP) causes an increase in hydrogen sulfide production. This result is congruous with the finding that PKG is robustly expressed but PKA only weakly present in human urothelium as well as in T24 cells. The cGMP/PKG-dependent phosphorylation elicited by 8-Br-cGMP is selectively reverted by KT5823, a specific PKG inhibitor. Moreover, the silencing of cystathionine-β-synthase in T24 cells leads to a marked decrease in hydrogen sulfide production either in basal condition or following 8-Br-cGMP challenge. In order to identify the phosphorylation site, recombinant mutant proteins of cystathionine-β-synthase in which Ser32, Ser227 or Ser525 was mutated in Ala were generated. The Ser227Ala mutant cystathionine-β-synthase shows a notable reduction in basal biosynthesis of hydrogen sulfide becoming unresponsive to the 8-Br-cGMP challenge. A specific antibody that recognizes the phosphorylated form of cystathionine-β-synthase has been produced and validated by using T24 cells and human urothelium. In conclusion, human cystathionine-β-synthase can be phosphorylated in a PKG-dependent manner at Ser227 leading to an increased catalytic activity.

Receptors involved in the modulation of guinea pig urinary bladder motility by prostaglandin D2

BACKGROUND AND PURPOSE

We have described a urothelium-dependent release of PGD2 -like activity which had inhibitory effects on the motility of guinea pig urinary bladder. Here, we have pharmacologically characterized the receptors involved and localized the sites of PGD2 formation and of its receptors.

EXPERIMENTAL APPROACH

In the presence of selective DP and TP receptor antagonists alone or combined, PGD2 was applied to urothelium-denuded diclofenac-treated urinary bladder strips mounted in organ baths. Antibodies against PGD2 synthase and DP1 receptors were used with Western blots and for histochemistry.

KEY RESULTS

PGD2 inhibited nerve stimulation -induced contractions in strips of guinea pig urinary bladder with estimated pIC50 of 7.55 ± 0.15 (n = 13), an effect blocked by the DP1 receptor antagonist BW-A868C. After blockade of DP1 receptors, PGD2 enhanced the contractions, an effect abolished by the TP receptor antagonist SQ-29548. Histochemistry revealed strong immunoreactivity for PGD synthase in the urothelium/suburothelium with strongest reaction in the suburothelium. Immunoreactive DP1 receptors were found in the smooth muscle of the bladder wall with a dominant localization to smooth muscle membranes.

CONCLUSIONS AND IMPLICATIONS

In guinea pig urinary bladder, the main effect of PGD2 is an inhibitory action via DP1 receptors localized to the smooth muscle, but an excitatory effect via TP receptors can also be evoked. The urothelium with its suburothelium might signal to the smooth muscle which is rich in PGD2 receptors of the DP1 type. The results are important for our understanding of regulation of bladder motility.

Biomatrices for bladder reconstruction

There is a demand for tissue engineering of the bladder needed by patients who experience a neurogenic bladder or idiopathic detrusor overactivity. To avoid complications from augmentation cystoplasty, the field of tissue engineering seeks optimal scaffolds for bladder reconstruction. Naturally derived biomaterials as well as synthetic and natural polymers have been explored as bladder substitutes. To improve regenerative properties, these biomaterials have been conjugated with functional molecules, combined with nanotechology, or seeded with exogenous cells. Although most studies reported complete and functional bladder regeneration in small-animal models, results from large-animal models and human clinical trials varied. For functional bladder regeneration, procedures for biomaterial fabrication, incorporation of biologically active agents, introduction of nanotechnology, and application of stem-cell technology need to be standardized. Advanced molecular and medical technologies such as next generation sequencing and magnetic resonance imaging can be introduced for mechanistic understanding and non-invasive monitoring of regeneration processes, respectively.

β-Adrenoceptor-Mediated Relaxation of Carbachol-Pre-Contracted Mouse Detrusor

Aims: To study the β-adrenoceptor subtypes involved in the relaxation responses to (-)-isoprenaline in carbachol-pre-contracted (CCh) mouse detrusor muscle with intact and denuded mucosa. Methods: Isolated muscle strips from the urinary bladder of male C57BL6 mice or β2-adrenoceptor knockout mice were pre-contracted with CCh, 1 µM and relaxed with increasing concentrations of the β-adrenoceptor (β-AR) agonist (-)-isoprenaline and forskolin. For estimating the β-AR subtypes involved, subtype-selective receptor blockers were used, that is, CGP 20712A (β1-ARs), ICI 118,551 (β2-ARs), and L748,337 (β3-ARs). Results: Unlike in KCl-pre-contracted muscle, the mucosa did not affect the sensitivity of the relaxation response to (-)-isoprenaline in CCh-pre-contracted murine detrusor strips. Increasing concentrations of (-)-isoprenaline produced a biphasic concentration-relaxation response without any difference both during the presence and absence of mucosa. The relaxation fraction produced by low (-)-isoprenaline concentrations was mediated by β2-AR as evidenced by a shift of the concentration-response curve to higher concentrations with ICI 118,551, but not with CGP 20712A and L748,337, and by the absence of this fraction in β2-AR-KO mice. The relaxation response with low sensitivity to (-)-isoprenaline was not affected by any of the β-AR subtype-selective blockers and was the only response detected in detrusor strips from β2-AR-KO mice. Conclusions: In CCh-pre-contracted mouse detrusor, β2-ARs are responsible for the relaxation component with high sensitivity to (-)-isoprenaline as indicated by the conversion of a biphasic into a monophasic CRC with ICI 118,551 or by its absence in β2-AR KO mice. The mucosa does not impair relaxation under these conditions.

Formation and regeneration of the urothelium

PURPOSE OF REVIEW

This review addresses significant changes in our understanding of urothelial development and regeneration. Understanding urothelial differentiation will be important in the push to find new methods of bladder reconstruction and augmentation, as well as identification of bladder cancer stem cells.

RECENT FINDINGS

This review will cover recent findings including the identification of novel progenitor cells in the embryo and adult urothelium, function of the urothelium, and regeneration of the urothelium. Using Cre-lox recombination with cell-type-specific Cre lines, lineage studies from our laboratory have revealed novel urothelial cell types and progenitors that are critical for formation and regeneration of the urothelium. Interestingly, our studies indicate that Keratin-5-expressing basal cells, which have previously been proposed to be urothelial stem cells, are a self-renewing unipotent population, whereas P-cells, a novel urothelial cell type, are progenitors in the embryo, and intermediate cells serve as a progenitor pool in the adult.

SUMMARY

These findings could have important implications for our understanding of cancer tumorigenesis and could move the fields of regeneration and reconstruction forward.

Induction of oxidative stress causes functional alterations in mouse urothelium via a TRPM8-mediated mechanism: implications for aging

The incidence of bladder conditions such as overactive bladder syndrome and its associated urinary incontinence is highly prevalent in the elderly. However, the mechanisms underlying these disorders are unclear. Studies suggest that the urothelium forms a ‘sensory network’ with the underlying innervation, alterations in which, could compromise bladder function. As the accumulation of reactive oxygen species can cause functional alterations with age, the aim of this study was to investigate whether oxidative stress alters urothelial sensory signalling and whether the mechanism underlying the effect of oxidative stress on the urothelium plays a role in aging. Five-month-old(young) and 24-month-old (aged) mice were used. H₂O₂, used to induce oxidative stress, resulted in an increase in bladder afferent nerve activity and urothelial intracellular calcium in preparations from young mice. These functional changes were concurrent with upregulation of TRPM8 in the urothelium. Moreover, application of a TRPM8 antagonist significantly attenuated the H₂O₂-induced calcium responses. Interestingly, an upregulation of TRPM8 was also found in the urothelium from aged mice, where high oxidative stress levels were observed, together with a greater calcium response to the TRPM8 agonist WS12. Furthermore, these calcium responses were attenuated by pretreatment with the antioxidant N-acetyl-cysteine. This study shows that oxidative stress affects urothelial function involving a TRPM8-mediated mechanism and these effects may have important implications for aging. These data provide an insight into the possible mechanisms by which oxidative stress causes physiological alterations in the bladder, which may also occur in other organs susceptible to aging.

Luminal DMSO: effects on detrusor and urothelial/lamina propria function

DMSO is used as a treatment for interstitial cystitis and this study examined the effects of luminal DMSO treatment on bladder function and histology. Porcine bladder was incubated without (controls) or with DMSO (50%) applied to the luminal surface and the release of ATP, acetylcholine, and LDH assessed during incubation and in tissues strips after DMSO incubation. Luminally applied DMSO caused ATP, Ach, and LDH release from the urothelial surface during treatment, with loss of urothelial layers also evident histologically. In strips of urothelium/lamina propria from DMSO pretreated bladders the release of both ATP and Ach was depressed, while contractile responses to carbachol were enhanced. Detrusor muscle contractile responses to carbachol were not affected by DMSO pretreatment, but neurogenic responses to electrical field stimulation were enhanced. The presence of an intact urothelium/lamina propria inhibited detrusor contraction to carbachol by 53% and this inhibition was significantly reduced in DMSO pretreated tissues. Detection of LDH in the treatment medium suggests that DMSO permeabilised urothelial membranes causing leakage of cytosolic contents including ATP and Ach rather than enhancing release of these mediators. The increase in contractile response and high levels of ATP are consistent with initial flare up in IC/PBS symptoms after DMSO treatment.