Mucosal signaling in the bladder

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.

Sensory Neurons, PIEZO Channels and PAC1 Receptors Regulate the Mechanosensitive Release of Soluble Ectonucleotidases in the Murine Urinary Bladder Lamina Propria

The urinary bladder requires adequate concentrations of extracellular adenosine 5'-triphosphate (ATP) and other purines at receptor sites to function properly. Sequential dephosphorylation of ATP to ADP, AMP and adenosine (ADO) by membrane-bound and soluble ectonucleotidases (s-ENTDs) is essential for achieving suitable extracellular levels of purine mediators. S-ENTDs, in particular, are released in the bladder suburothelium/lamina propria (LP) in a mechanosensitive manner. Using 1,N⁶-etheno-ATP (eATP) as substrate and sensitive HPLC-FLD methodology, we evaluated the degradation of eATP to eADP, eAMP and eADO in solutions that were in contact with the LP of ex vivo mouse detrusor-free bladders during filling prior to substrate addition. The inhibition of neural activity with tetrodotoxin and ω-conotoxin GVIA, of PIEZO channels with GsMTx4 and D-GsMTx4 and of the pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1) with PACAP6-38 all increased the distention-induced but not spontaneous release of s-ENTDs in LP. It is conceivable, therefore, that the activation of these mechanisms in response to distention restricts the further release of s-ENTDs and prevents excessive hydrolysis of ATP. Together, these data suggest that afferent neurons, PIEZO channels, PAC1 receptors and s-ENTDs form a system that operates a highly regulated homeostatic mechanism to maintain proper extracellular purine concentrations in the LP and ensure normal bladder excitability during bladder filling.

Gene Expression-Based Functional Differences between the Bladder Body and Trigonal Urothelium in Adolescent Female Patients with Micturition Dysfunction

The aim of this study is to determine the molecular differences between the urothelial transcriptomes of the bladder body and trigone. The transcriptomes of the bladder body and trigonal epithelia were analyzed by massive sequencing of total epithelial RNA. The profiles of urothelial and urinal microbiomes were assessed by amplicon sequencing of bacterial 16S rRNA genes in 17 adolescent females with pain and micturition dysfunction and control female subjects. The RNA sequencing identified 10,261 differentially expressed genes (DEGs) in the urothelia of the bladder body and trigone, with the top 1000 DEGs at these locations annotated to 36 and 77 of the Reactome-related pathways in the bladder body and trigone, respectively. These pathways represented 11 categories enriched in the bladder body urothelium, including extracellular matrix organization, the neuronal system, and 15 categories enriched in the trigonal epithelium, including RHO GTPase effectors, cornified envelope formation, and neutrophil degranulation. Five bacterial taxa in urine differed significantly in patients and healthy adolescent controls. The evaluation of their transcriptomes indicated that the bladder body and trigonal urothelia were functionally different tissues. The molecular differences between the body and trigonal urothelia responsible for clinical symptoms in adolescents with bladder pain syndrome/interstitial cystitis remain unclear.

Prospective randomized controlled trial comparing fulguration versus fulguration and hydrodistension for Hunner-type interstitial cystitis/bladder pain syndrome

PURPOSE

In Hunner-type interstitial cystitis/bladder pain syndrome (IC/BPS), it is unclear whether suburothelial afferents underlying normal-appearing background areas contribute to symptom development. We examined whether adding hydrodistension (HD) to transurethral fulguration (TUF) of Hunner lesions, for the purpose of treating the background areas, is superior to TUF alone.

METHODS

This randomized controlled trial included 52 patients with Hunner-type IC/BPS allocated at a 1:1 (TUF:TUF+HD) ratio. HD was performed at 80 cmH₂O for 8 min before TUF in the TUF+HD group. Thirty-three patients remained until the end of the 6-month observational period. The primary endpoint was the visual analogue scale (VAS) pain score at 1 month. Major secondary endpoints were the treatment-failure rate, VAS pain scores at ≥ 2 months, and frequency-volume chart parameters.

RESULTS

Both TUF and TUF+HD showed significant improvement in VAS pain score at 1 month (95% confidence interval [CI]: - 1.62 to 0.16, P = 0.106). VAS pain scores were significantly lower in TUF+HD than TUF at 2 (95% CI: - 1.97 to - 0.28, P = 0.011), 4 (95% CI: - 2.83 to - 0.72, P = 0.002), and 6 (95% CI: - 3.11 to - 0.07, P = 0.040) months. Treatment-failure rate was higher in TUF (36.4%) than TUF+HD (17.4%), without significance (odds ratio: 2.714, 95% CI: 0.68 to 10.84, P = 0.189). Functional capacity and urgency were not significantly different between groups.

CONCLUSION

The addition of HD to TUF tended to be superior to TUF monotherapy for controlling pain in Hunner-type IC/BPS. This indicates that not only Hunner lesions but also normal-appearing background areas may have a role in the pain of IC/BPS.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03987594, date of registration: 2019-06-17 (retrospectively registered).

Functional and histologic imaging of urinary bladder wall after exposure to psychological stress and protamine sulfate

To quantify the urinary bladder wall T1 relaxation time (T1) before and after the instillation contrast mixture in rats previously subjected to water avoidance stress (WAS) and/or acute exposure to protamine sulfate (PS). Female Wistar rats were randomized to receive either sham (control) or 1 h of WAS for ten consecutive days before the evaluation of nocturnal urination pattern in metabolic cages. T1 mapping of urinary bladder wall at 9.4 T was performed pre- and post- instillation of 4 mM Gadobutrol in a mixture with 5 mM Ferumoxytol. Subsequently, either T1 mapping was repeated after brief intravesical PS exposure or the animals were sacrificed for histology and analyzing the mucosal levels of mRNA. Compared to the control group, WAS exposure decreased the single void urine volume and shortened the post-contrast T1 relaxation time of mucosa- used to compute relatively higher ingress of instilled Gadobutrol. Compromised permeability in WAS group was corroborated by the urothelial denudation, edema and ZO-1 downregulation. PS exposure doubled the baseline ingress of Gadobutrol in both groups. These findings confirm that psychological stress compromises the paracellular permeability of bladder mucosa and its non-invasive assay with MRI was validated by PS exposure.

Single-cell transcriptomes of mouse bladder urothelium uncover novel cell type markers and urothelial differentiation characteristics

Objectives

Much of the information to date in terms of subtypes and function of bladder urothelial cells were derived from anatomical location or by the expression of a small number of marker genes. To have a comprehensive map of the cellular anatomy of bladder urothelial cells, we performed single‐cell RNA sequencing to thoroughly characterize mouse bladder urothelium.

Materials and methods

A total of 18,917 single cells from mouse bladder urothelium were analysed by unbiased single‐cell RNA sequencing. The expression of the novel cell marker was confirmed by immunofluorescence using urinary tract infection models.

Results

Unsupervised clustering analysis identified 8 transcriptionally distinct cell subpopulations from mouse bladder urothelial cells. We discovered a novel type of bladder urothelial cells marked by Plxna4 that may be involved with host response and wound healing. We also found a group of basal‐like cells labelled by ASPM that could be the progenitor cells of adult bladder urothelium. ASPM⁺ urothelial cells are significantly increased after injury by UPEC. In addition, specific transcription factors were found to be associated with urothelial cell differentiation. At the last, a number of interstitial cystitis/bladder pain syndrome–regulating genes were found differentially expressed among different urothelial cell subpopulations.

Conclusions

Our study provides a comprehensive characterization of bladder urothelial cells, which is fundamental to understanding the biology of bladder urothelium and associated bladder disease.

Effect of Glycosaminoglycan Replacement on Markers of Interstitial Cystitis In Vitro

Aims: To examine the effect of three commercial intravesical formulations of glycosaminoglycan on in vitro inflammatory models of IC/BPS to better understand there effect on specific markers of disease.

Methods: Human urothelial cells (HTB-4) were cultured under four conditions in the presence or absence of commercial GAG formulations. Cells were cultured under a basal condition or pre-treated with protamine sulfate (100 ng/ml) (damages the endogenous glycosaminoglycan layer), hydrogen peroxide (1%) (a metabolic stressor) or TNFα (10 ng/ml) (creating an inflammatory environment). Each of these four culture conditions was then treated with one of three GAG formulations, CystistatⓇ, iAluRilⓇ and HyacystⓇ. Assays were then performed to examine the effect of the exogenous GAGs on cell viability, cell migration, sGAG production, cytokine and gene expression.

Results: All GAG formulations were well tolerated by the HTB-4 cells and supported cell growth and migration. iAluRilⓇ was most effective at stimulating endogenous sGAG production under all conditions, increasing sGAGs by up to 15-fold. All GAG formulations significantly reduced the production of the pro-inflammatory cytokine IL-8 under basal conditions, while no GAG treatment suppressed cytokine production under any other condition. Only Cystistat^Ⓡ had a significant effect on HA receptor expression, significantly increasing ICAM-1 expression at 3 h that returned to basal levels at 24 h. No GAG treatment significantly changed the expression of GAG synthesis enzymes (CSGALNACT1, CSGALNACT2) or markers of tissue remodeling (MMP2, TIMP1) and pain (COX-1/PTGS-1, NGF).

Conclusions: The data presented in this study reveal that commercial intravesical formulation support cell viability and migration. In addition, the commercial GAG formulations have a mild anti-inflammatory effect in the in vitro model of interstitial cystitis/bladder pain syndrome.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Antagonism of proNGF or its receptor p75NTR reverses remodelling and improves bladder function in a mouse model of diabetic voiding dysfunction

AIMS/HYPOTHESIS

Although 80% of diabetic patients will suffer from voiding difficulties and urinary symptoms, defined as diabetic voiding dysfunction (DVD), therapeutic targets and treatment options are limited. We hypothesise that the blockade of the pro-nerve growth factor (NGF)/p75 neurotrophin receptor (p75NTR) axis by an anti-proNGF monoclonal antibody or by a small molecule p75NTR antagonist (THX-B) can restore bladder remodelling (represented by bladder weight) in an animal model of DVD. Secondary outcomes of the study include improvements in bladder compliance, contractility and morphology, as well as in voiding behaviour, proNGF/NGF balance and TNF-α expression.

METHODS

In a streptozotocin-induced mouse model of diabetes, diabetic mice received either a blocking anti-proNGF monoclonal antibody or a p75NTR antagonist small molecule as weekly systemic injections for 4 weeks. Animals were tested at baseline (at 2 weeks of diabetes induction), and after 2 and 4 weeks of treatment. Outcomes measured were voiding function with voiding spot assays and cystometry. Bladders were assessed by histological, contractility and protein expression assays.

RESULTS

Diabetic mice showed features of DVD as early as 2 weeks after diabetes diagnosis (baseline) presented by hypertrophy, reduced contractility and abnormal cystometric parameters. Following treatment initiation, a twofold increase (p < 0.05) in untreated diabetic mouse bladder weight and thickness compared with non-diabetic controls was observed, and this change was reversed by p75NTR antagonism (37% reduction in bladder weight compared with untreated diabetic mice [95% CI 14%, 60%]) after 4 weeks of treatment. However, blocking proNGF did not help to reverse bladder hypertrophy. While diabetic mice had significantly worse cystometric parameters and contractile responses than non-diabetic controls, proNGF antagonism normalised bladder compliance (0.007 [Q1-Q3; 0.006-0.009] vs 0.015 [Q1-Q3; 0.014-0.029] ml/cmH2O in untreated diabetic mice, representing 62% reduction [95% CI 8%, 110%], p < 0.05) and contractility to KCl, carbachol and electrical field stimulation (p < 0.05 compared with the diabetic group) after 2 weeks of treatment. These effects were not observed after 4 weeks of treatment with proNGF antagonist. p75NTR antagonism did not show important improvements in cystometric parameters after 2 weeks of treatment. Slightly improved bladder compliance (0.01 [Q1-Q3; 0.009-0.012] vs 0.013 [Q1-Q3; 0.011-0.016] ml/cmH2O for untreated diabetic mice) was seen in the p75NTR antagonist-treated group after 4 weeks of treatment with significantly stabilised contractile responses to KCl, carbachol and electric field stimulation (p < 0.05 for each) compared with diabetic mice. Bladder dysfunction observed in diabetic mice was associated with a significant increase in bladder proNGF/NGF ratio (3.1 [±1.2] vs 0.26 [±0.04] ng/pg in control group, p < 0.05 at week 2 of treatment) and TNF-α (p < 0.05). The proNGF/NGF ratio was partially reduced (about 60% reduction) with both treatments (1.03 [±0.6] ng/pg for proNGF antibody-treated group and 1.4 [±0.76] ng/pg for p75NTR blocker-treated group after 2 weeks of treatment), concomitant with a significant decrease in the bladder levels of TNF-α (p < 0.05), despite persistent hyperglycaemia.

CONCLUSIONS/INTERPRETATION

Our findings indicate that blockade of proNGF and the p75NTR receptor in diabetes can impede the development and progression of DVD. The reported improvements in morphological and functional features in our DVD model validates the proNGF/p75NTR axis as a potential therapeutic target in this pathology. Graphical abstract.

A non-enzymatic method for dissection of mouse bladder urothelial tissue

Urothelial cells contribute to bladder functions, including urine storage, urine emptying, and innate immune response. Functional studies of urothelial cells usually use either freshly isolated cells or cultured cells. Most methods of isolating urothelial cells require enzymes; however, these techniques remove proteins that connect the cells and disrupt the orientation of the cells within the multilayered urothelium. In addition, PCR or immunoblot results obtained from homogenates of bladder mucosa or whole bladder do not represent pure urothelial cells. We describe a dissection process that does not require enzymes and is able to obtain pure urothelial tissues from mice and humans. This method can isolate single urothelial cells for electrophysiology in situ and can also isolate pure urothelial tissue for PCR, microarray, and immunoblot procedures. The time required to obtain urothelial tissue from one mouse bladder is 15-20 min. This method is simple and time efficient as compared with alternative methods and therefore facilitates our understanding of urothelial biology.

Lipopolysaccharide stimulates BK channel activity in bladder umbrella cells

Bladder urothelium plays an active role in response to bacterial infection. There is little known about the electrophysiological activity in urothelial cells in this process. We used a nonenzymatic method to isolate bladder urothelial tissue and to patch clamp umbrella cells in situ. A 200 pS conductance potassium (K⁺) channel was detected from female C57BL6 mice. Of 58 total patches, 17.2% patches displayed the 200 pS K⁺ conductance channel. This K⁺ conductance channel showed Ca²⁺ sensitivity and voltage dependence. Specific big-conductance potassium channel (BK) inhibitors (paxilline, iberiotoxin) blocked the 200 pS K⁺ conductance channel activity. RT-PCR and immunoblot confirmed BK channel pore-forming α-subunit (BK-α) mRNA and protein in urothelium. Immunohistochemistry also showed the BK-α located in urothelium. The above data provided evidence that the 200 pS K⁺ conductance channel was a BK channel. Lipopolysaccharide (LPS), a component of uropathogenic Escherichia coli, was used to investigate the role of BK channel in the pathogenesis of urinary tract infection. BK channel activity as NP_o increased threefold within 30 min of exposure to LPS. mRNAs for LPS receptors (TLR4, CD14, MD-2) were expressed in the urothelium but not in lamina propria or detrusor. Blockade of the receptors by an antagonist (polymyxin B) abrogated LPS's effect on BK channel. The involvement of protein kinase A (PKA) on BK channel activity was demonstrated by applying PKA blockers (H89 and PKI). Both PKA inhibitors abolished the BK channel activity induced by LPS. In conclusion, BK channel was identified in bladder umbrella cells, and its activity was significantly increased by LPS.

The urinary microbiota: a paradigm shift for bladder disorders?

PURPOSE OF REVIEW

A resident microbial community [the female urinary microbiota (FUM)] exists within the female bladder of many adult women. Information about the FUM is likely to modify the diagnosis, prevention and treatment of adult women with urinary disorders. This review highlights key findings from recent literature relevant to adult, nonpregnant women.

RECENT FINDINGS

Similar to other human microbial communities, the FUM varies in its characteristics, including organism diversity and predominant organism identity. Recent literature reveals previously undetected organisms and community characteristics that appear associated with certain urinary symptoms, including urinary tract infection and urgency urinary incontinence. The role of individual organisms may range from beneficial to pathogenic and may vary on the basis of an individual's FUM characteristics. The simple dichotomy of 'infected' or 'sterile' no longer sufficiently captures the microbiological complexity of the female bladder.

SUMMARY

Deeper understanding of the FUM should yield better methods to restore the microbiota to a healthy state, providing symptom relief. Opportunities to modify the FUM without antibiotic use are exciting possibilities for future research; stand-alone antibiotic use may be reevaluated to improve treatment precision. Long-standing nomenclature for conditions such as asymptomatic bacteriuria and urinary tract infection will likely require modification.

Urothelial MaxiK-activity regulates mucosal and detrusor metabolism

There is increasing evidence for a role of MaxiK potassium channel-activity in regulating the metabolism and intracellular signaling of non-contractile bladder mucosal tissues. At present however no studies have determined the impact of urothelial MaxiK-activity on overall bladder metabolism. To address this we have investigated the effect of bladder lumen instillation of the MaxiK inhibitor, iberiotoxin (IBTX), on mucosal and detrusor metabolism using metabolomics. Since IBTX does not cross plasma membranes, when instilled into the bladder lumen it would only effect urothelially expressed MaxiK-activity. Surprisingly IBTX treatment caused more effect on the metabolome of the detrusor than mucosa (the levels of 17% of detected detrusor metabolites were changed in comparison to 6% of metabolites in mucosal tissue following IBTX treatment). In mucosal tissues, the major effects can be linked to mitochondrial-associated metabolism whereas in detrusor there were additional changes in energy generating pathways (such as glycolysis and the TCA cycle). In the detrusor, changes in metabolism are potentially a result of IBTX effecting MaxiK-linked signaling pathways between the mucosa and detrusor, secondary to changes in physiological activity or a combination of both. Overall we demonstrate that urothelial MaxiK-activity plays a significant role in determining mitochondrially-associated metabolism in mucosal tissues, which effects the metabolism of detrusor tissue. Our work adds further evidence that the urothelium plays a major role in determining overall bladder physiology. Since decreased MaxiK-activity is associated with several bladder pathophysiology's, the changes in mucosal metabolism reported here may represent novel downstream targets for therapeutic interventions.

New therapeutic directions to treat underactive bladder

Underactive bladder (UAB) is a term used to describe a constellation of symptoms that is perceived by patients suggesting bladder hypocontractility. Urodynamic measurement that suggest decreased contractility of the bladder is termed detrusor underactivity (DUA). Regulatory approved specific management options with clinically proven ability to increase bladder contractility do not currently exist. While DUA specific treatments presumably will focus on methods to increase efficiency of bladder emptying capability relying on augmenting the motor pathway in the micturition reflex, other approaches include methods to augment the sensory (afferent) contribution to the micturition reflex which could result in increased detrusor contractility. Another method to induce more efficient bladder emptying could be to induce relaxation of the bladder outlet. Using cellular regenerative techniques, the detrusor smooth muscle can be targeted so the result is to increase detrusor smooth muscle function. In this review, we will cover areas of potential new therapies for DUA including: drug therapy, stem cells and regenerative therapies, neuromodulation, and urethral flow assist device. Paralleling development of new therapies, there also needs to be clinical studies performed that address how DUA relates to UAB.

Stem Cells in Functional Bladder Engineering

Conditions impairing bladder function in children and adults, such as myelomeningocele, posterior urethral valves, bladder exstrophy or spinal cord injury, often need urinary diversion or augmentation cystoplasty as when untreated they may cause severe bladder dysfunction and kidney failure. Currently, the gold standard therapy of end-stage bladder disease refractory to conservative management is enterocystoplasty, a surgical enlargement of the bladder with intestinal tissue. Despite providing functional improvement, enterocystoplasty is associated with significant long-term complications, such as recurrent urinary tract infections, metabolic abnormalities, stone formation, and malignancies. Therefore, there is a strong clinical need for alternative therapies for these reconstructive procedures, of which stem cell-based tissue engineering (TE) is considered to be the most promising future strategy. This review is focused on the recent progress in bladder stem cell research and therapy and the challenges that remain for the development of a functional bladder wall.