The uroepithelial-associated sensory web

In situ characterization of glycans in the urothelium of donkey bladder: evidence of secretion of sialomucins

The glycoprotein pattern was investigated by lectin histochemistry in the urothelium lining the urinary bladder of the donkey Equus asinus. Tissue sections were stained with a panel of twelve lectins, in combination with saponification and sialidase digestion (K-s). The urinary bladder urothelium has three distinct layers from the basal zone to the lumen consisting of basal, intermediate and superficial cells (umbrella cells). Cytoplasm of basal cells reacted with SNA, PNA, K-s-PNA, GSA I-B4 and Con A showing glycans ending with Neu5Acα2,6Gal/GalNAc, Neu5AcGalβ1,3GalNAc, αGal and with terminal/internal αMan. The cytoplasm of umbrella cells displayed an increase of Neu5AcGalβ1,3GalNAc and the appearance of Neu5AcGalβ1,3GalNAc, Neu5acα2,3Galβ1,4GlcNAc and Neu5AcGalNAc residues (MAL II, K-s-SBA and K-s-HPA staining). Scattered umbrella cells were characterized by glycans terminating with GalNAc binding DBA, SBA and HPA. The mucosa forms folds with a crypt-like appearance where the urothelium shows a different pattern of glycans. The bladder luminal surface stained with K-s-PNA, K-s-DBA, KOH-s-SBA, and K-s-HPA displaying a coating of sialoglycoproteins belonging to O-linked glycans (typical secretory moieties). These findings show that different glycosylation patterns exist along the donkey bladder urothelium, and different sub-populations of umbrella cells are present secreting the sialoglycans which constitute the protective gel layer lining the bladder.

The concept of peripheral modulation of bladder sensation

It is recognized that, as the bladder fills, there is a corresponding increase in sensation. This awareness of the volume in the bladder is then used in a complex decision making process to determine if there is a need to void. It is also part of everyday experience that, when the bladder is full and sensations strong, these sensations can be suppressed and the desire to void postponed. The obvious explanation for such altered perceptions is that they occur centrally. However, this may not be the only mechanism. There are data to suggest that descending neural influences and local factors might regulate the sensitivity of the systems within the bladder wall generating afferent activity. Specifically, evidence is accumulating to suggest that the motor-sensory system within the bladder wall is influenced in this way. The motor-sensory system, first described over 100 years ago, appears to be a key component in the afferent outflow, the afferent "noise," generated within the bladder wall. However, the presence and possible importance of this complex system in the generation of bladder sensation has been overlooked in recent years. As the bladder fills the motor activity increases, driven by cholinergic inputs and modulated, possibly, by sympathetic inputs. In this way information on bladder volume can be transmitted to the CNS. It can be argued that the ability to alter the sensitivity of the mechanisms generating the motor component of this motor-sensory system represents a possible indirect way to influence afferent activity and so the perception of bladder volume centrally. Furthermore, it is emerging that the apparent modulation of sensation by drugs to alleviate the symptoms of overactive bladder (OAB), the anti-cholinergics and the new generation of drugs the β 3 sympathomimetics, may be the result of their ability to modulate the motor component of the motor sensory system. The possibility of controlling sensation, physiologically and pharmacologically, by influencing afferent firing at its point of origin is a "new" concept in bladder physiology. It is one that deserves careful consideration as it might have wider implications for our understanding of bladder pathology and in the development of new therapeutic drugs. In this overview, evidence for the concept peripheral modulation of bladder afferent outflow is explored.

Expression and function of CCL2/CCR2 in rat micturition reflexes and somatic sensitivity with urinary bladder inflammation

Chemokines are proinflammatory mediators of the immune response, and there is growing evidence for chemokine/receptor signaling involvement in pronociception. Bladder pain syndrome (BPS)/interstitial cystitis (IC) is a chronic pain syndrome characterized by pain, pressure, or discomfort perceived to be bladder-related with at least one urinary symptom. We have explored the expression and functional roles of CCL2 (monocyte chemoattractant protein-1) and its high-affinity receptor, CCR2, in micturition reflex function and somatic sensitivity in rats with urinary bladder inflammation induced by cyclophosphamide (CYP) treatment of varying duration (4 h, 48 h, chronic). Real-time quantitative RT-PCR, ELISAs, and immunohistochemistry demonstrated significant (P ≤ 0.01) increases in CCL2 and CCR2 expression in the urothelium and in Fast Blue-labeled bladder afferent neurons in lumbosacral dorsal root ganglia with CYP-induced cystitis. Intravesical infusion of RS504393 (5 μM), a specific CCR2 antagonist, reduced voiding frequency and increased bladder capacity and void volume in rats with CYP-induced cystitis (4 h), as determined with open outlet, conscious cystometry. In addition, CCR2 blockade, at the level of the urinary bladder, reduced referred somatic sensitivity of the hindpaw and pelvic region in rats with CYP treatment, as determined with von Frey filament testing. We provide evidence of functional roles for CCL2/CCR2 signaling at the level of the urinary bladder in reducing voiding frequency and somatic sensitivity following CYP-induced cystitis (4 h). These studies suggest that chemokines/receptors may be novel targets with therapeutic potential in the context of urinary bladder inflammation.

Urothelial signaling

The urothelium, which lines the inner surface of the renal pelvis, the ureters, and the urinary bladder, not only forms a high-resistance barrier to ion, solute and water flux, and pathogens, but also functions as an integral part of a sensory web which receives, amplifies, and transmits information about its external milieu. Urothelial cells have the ability to sense changes in their extracellular environment, and respond to chemical, mechanical and thermal stimuli by releasing various factors such as ATP, nitric oxide, and acetylcholine. They express a variety of receptors and ion channels, including P2X3 purinergic receptors, nicotinic and muscarinic receptors, and TRP channels, which all have been implicated in urothelial-neuronal interactions, and involved in signals that via components in the underlying lamina propria, such as interstitial cells, can be amplified and conveyed to nerves, detrusor muscle cells, and ultimately the central nervous system. The specialized anatomy of the urothelium and underlying structures, and the possible communication mechanisms from urothelial cells to various cell types within the bladder wall are described. Changes in the urothelium/lamina propria ("mucosa") produced by different bladder disorders are discussed, as well as the mucosa as a target for therapeutic interventions.

Loss of β1-integrin from urothelium results in overactive bladder and incontinence in mice: a mechanosensory rather than structural phenotype

Bladder urothelium senses and communicates information about bladder fullness. However, the mechanoreceptors that respond to tissue stretch are poorly defined. Integrins are mechanotransducers in other tissues. Therefore, we eliminated β1-integrin selectively in urothelium of mice using Cre-LoxP targeted gene deletion. β1-Integrin localized to basal/intermediate urothelial cells by confocal microscopy. β1-Integrin conditional-knockout (β1-cKO) mice lacking urothelial β1-integrin exhibited down-regulation and mislocalization of α3- and α5-integrins by immunohistochemistry but, surprisingly, had normal morphology, permeability, and transepithelial resistance when compared with Cre-negative littermate controls. β1-cKO mice were incontinent, as judged by random urine leakage on filter paper (4-fold higher spotting, P<0.01; 2.5-fold higher urine area percentage, P<0.05). Urodynamic function assessed by cystometry revealed bladder overfilling with 80% longer intercontractile intervals (P<0.05) and detrusor hyperactivity (3-fold more prevoid contractions, P<0.05), but smooth muscle contractility remained intact. ATP secretion into the lumen was elevated (49 vs. 22 nM, P<0.05), indicating abnormal filling-induced purinergic signaling, and short-circuit currents (measured in Ussing chambers) revealed 2-fold higher stretch-activated ion channel conductances in response to hydrostatic pressure of 1 cmH2O (P<0.05). We conclude that loss of integrin signaling from urothelium results in incontinence and overactive bladder due to abnormal mechanotransduction; more broadly, our findings indicate that urothelium itself directly modulates voiding.

Bradykinin modulates spontaneous nerve growth factor production and stretch-induced ATP release in human urothelium

The urothelium plays a crucial role in integrating urinary bladder sensory outputs, responding to mechanical stress and chemical stimulation by producing several diffusible mediators, including ATP and, possibly, neurotrophin nerve growth factor (NGF). Such urothelial mediators activate underlying afferents and thus may contribute to normal bladder sensation and possibly to the development of bladder overactivity. The muscle-contracting and pain-inducing peptide bradykinin is produced in various inflammatory and non-inflammatory pathologies associated with bladder overactivity, but the effect of bradykinin on human urothelial function has not yet been characterized. The human urothelial cell line UROtsa expresses mRNA for both B1 and B2 subtypes of bradykinin receptors, as determined by real-time PCR. Bradykinin concentration-dependently (pEC50=8.3, Emax 4434±277nM) increased urothelial intracellular calcium levels and induced phosphorylation of the mitogen-activated protein kinase (MAPK) ERK1/2. Activation of both bradykinin-induced signaling pathways was completely abolished by the B2 antagonist icatibant (1μM), but not the B1 antagonist R715 (1μM). Bradykinin-induced (100nM) B2 receptor activation markedly increased (192±13% of control levels) stretch-induced ATP release from UROtsa in hypotonic medium, the effect being dependent on intracellular calcium elevations. UROtsa cells also expressed mRNA and protein for NGF and spontaneously released NGF to the medium in the course of hours (11.5±1.4pgNGF/mgprotein/h). Bradykinin increased NGF mRNA expression and accelerated urothelial NGF release to 127±5% in a protein kinase C- and ERK1/2-dependent manner. Finally, bradykinin up-regulated mRNA for transient-receptor potential vanilloid (TRPV1) sensory ion channel in UROtsa. In conclusion, we show that bradykinin represents a versatile modulator of human urothelial phenotype, accelerating stretch-induced ATP release, spontaneous release of NGF, as well as expression of sensory ion channel TRPV1. Bradykinin-induced changes in urothelial sensory function might contribute to the development of bladder dysfunction.

Autonomic nervous control of the urinary bladder

The autonomic nervous system plays an important role in the regulation of the urinary bladder function. Under physiological circumstances, noradrenaline, acting mainly on β(3) -adrenoceptors in the detrusor and on α(1) (A) -adrenoceptors in the bladder outflow tract, promotes urine storage, whereas neuronally released acetylcholine acting mainly on M(3) receptors promotes bladder emptying. Under pathophysiological conditions, however, this system may change in several ways. Firstly, there may be plasticity at the levels of innervation and receptor expression and function. Secondly, non-neuronal acetylcholine synthesis and release from the urothelium may occur during the storage phase, leading to a concomitant exposure of detrusor smooth muscle, urothelium and afferent nerves to acetylcholine and noradrenaline. This can cause interactions between the adrenergic and cholinergic system, which have been studied mostly at the post-junctional smooth muscle level until now. The implications of such plasticity are being discussed.

From urothelial signalling to experiencing a sensation related to the urinary bladder

The mechanisms underlying bladder sensation and the way we experience sensations during normal voiding and in pathology is complex and not well understood. During storage and emptying, mechanical changes occurring in number of cell types within the bladder wall (i.e. the uroepithelium and bladder afferents) can have a major influence on our sensory systems. In this review, we discuss bladder sensation with a focus on coding events in the periphery.

Alteration in TRPV1 and Muscarinic (M3) receptor expression and function in idiopathic overactive bladder urothelial cells

AIM

To examine function of both cholinergic (muscarinic) and TRPV1 receptors in human bladder urothelial (HBUC) from non-neurogenic overactive bladder (OAB) patients as compared to control subjects.

METHODS

Primary HBUC cultures were derived from cystoscopic biopsies from OAB and control subjects. Muscarinic and TRPV1 function was assessed by acetylcholine (5 μm) or capsaicin (0.5 μm) evoked ATP release, measured by luciferase assay. Overall, expression of TRPV1 and muscarinic M3 receptors in bladder urothelial cells was accomplished using western immunoblotting.

RESULTS

Our findings revealed that the response to acetylcholine in OAB HBUC cultures (which was blocked by the nonselective muscarinic antagonist, atropine methyl nitrate or AMN) was not significantly different than from controls. The acetylcholine M3 receptor was slightly decreased as compared to control. In contrast, OAB HBUC cultures exhibited a capsaicin hypersensitivity and augmented release of ATP (3.2 fold higher), which was blocked by the antagonist capsazepine. The increase in capsaicin sensitivity correlated with increased urothelial TRPV1 expression.

CONCLUSION

Though characterized in a small number of subjects, augmented release of urothelial-derived transmitters such as ATP could 'amplify' signalling between and within urothelial cells and nearby afferent nerves.

Nervous network for lower urinary tract function

Traditionally, sensory signaling in the urinary bladder has been largely attributed to direct activation of bladder afferents. There is substantive evidence that sensory systems can be influenced by non-neuronal cells, such as the urothelium, which are able to respond to various types of stimuli that can include physiological, psychological and disease-related factors. The corresponding release of chemical mediators (through activation of a number of receptors/ion channels) can initiate signaling mechanisms between and within urothelial cells, as well as other cell types within the bladder wall including bladder nerves. However, the mechanisms underlying how various cell types in the bladder wall respond to normal filling and emptying, and are challenged by a variety of stressors (physical and chemical) are still not well understood. Alterations or defects in signaling mechanisms are likely to contribute to the pathophysiology of bladder disease with symptoms including urinary urgency, increased voiding frequency and pain. This review will discuss some of the components involved in control of lower urinary tract function, with an emphasis on the sensor and transducer roles of the urothelium.

Intravesical Botulinum Toxin for Overactive Bladder Syndrome without Detrusor Overactivity

Objective:

To report our experience of intravesical botulinum toxin for idiopathic overactive bladder syndrome (OAB) without detrusor overactivity (DOA) on urodynamic assessment.

Patients and methods:

Data regarding presentation, diagnosis, urodynamic findings, date and dose of treatment, and outcomes were recorded prospectively for 94 patients undergoing intravesical botulinum toxin injection for idiopathic overactive bladder syndrome at our institution. The cohort included 19 patients without DOA on urodynamics. A positive response to treatment was defined as patient-reported improvement without the need for further treatment. ICIQ-OAB and UI scores, and bladder diary parameters were also recorded. Rates of urinary retention requiring intermittent or indwelling catheterisation were noted.

Results:

The overall response rate to treatment was 82% ( n = 94). Patients without DOA ( n = 19) had a response rate of 89%, which compared favourably with a response rate of 81% in patients with DOA ( n = 75). Overall, 29% of patients who were voiding normally prior to treatment required intermittent self-catheterisation after the procedure. The requirement for self-catheterisation did not appear to be influenced by urodynamic findings.

Conclusion:

These preliminary, non-randomised data suggest that intravesical botulinum toxin injection may be efficacious in patients with OAB symptoms without DOA. Further evaluation by means of a randomised, controlled trial is suggested.

Expression profiling of G-protein-coupled receptors in human urothelium and related cell lines

What's known on the subject? and What does the study add? Urothelium emerged as a crucial integrator of sensory inputs and outputs in the bladder wall, and urothelial G-protein-coupled receptors (GPCRs) may represent plausible targets for treatment of various bladder pathologies. Urothelial cell lines provide a useful tool to study urothelial receptor function, but their validity as models for native human urothelium remains unclear. We characterize the mRNA expression of genes coding for GPCRs in human freshly isolated urothelium and compare the expression pattern with those in human urothelial cell lines.

OBJECTIVES

To characterize the mRNA expression pattern of genes coding for G-protein-coupled receptors (GPCRs) in human freshly isolated urothelium. To compare GPCR expression in human urothelium-derived cell lines to explore the suitability of these cell lines as model systems to study urothelial function.

MATERIALS AND METHODS

Native human urothelium (commercially sourced) and human urothelium-derived non-cancer (UROtsa and TERT-NHUC) and cancer (J82) cell lines were used. For mRNA expression profiling we used custom-designed real-time polymerase chain reaction array for 40 receptors and several related genes.

RESULTS

Native urothelium expressed a wide variety of GPCRs, including α(1A), α(1D) and all subtypes of α(2) and β adrenoceptors. In addition, M(2) and M(3) cholinergic muscarinic receptors, angiotensin II AT(1) receptor, serotonin 5-HT(2A) receptor and all subtypes of bradykinin, endothelin, cannabinoid, tachykinin and sphingosine-1-phosphate receptors were detected. Nerve growth factor and both its low- and high-affinity receptors were also expressed in urothelium. In all cell lines expression of most GPCRs was markedly downregulated, with few exceptions. In UROtsa cells, but much less in other cell lines, the expression of β(2) adrenoceptors, M(3) muscarinic receptors, B(1) and B(2) bradykinin receptors, ET(B) endothelin receptors and several subtypes of sphingosine-1-phosphate receptors was largely retained.

CONCLUSIONS

Human urothelium expresses a wide range of receptors which enables sensing and integration of various extracellular signals. Human urothelium-derived cell lines, especially UROtsa cells, show comparable mRNA expression to native tissue for several physiologically relevant GPCRs, but lose expression of many other receptors. The use of cell lines as model systems of human urothelium requires careful validation of suitability for the genes of interest.

Modulation of bladder function by luminal adenosine turnover and A1 receptor activation

The bladder uroepithelium transmits information to the underlying nervous and musculature systems, is under constant cyclical strain, expresses all four adenosine receptors (A(1), A(2A), A(2B), and A(3)), and is a site of adenosine production. Although adenosine has a well-described protective effect in several organs, there is a lack of information about adenosine turnover in the uroepithelium or whether altering luminal adenosine concentrations impacts bladder function or overactivity. We observed that the concentration of extracellular adenosine at the mucosal surface of the uroepithelium was regulated by ecto-adenosine deaminase and by equilibrative nucleoside transporters, whereas adenosine kinase and equilibrative nucleoside transporters modulated serosal levels. We further observed that enriching endogenous adenosine by blocking its routes of metabolism or direct activation of mucosal A(1) receptors with 2-chloro-N(6)-cyclopentyladenosine (CCPA), a selective agonist, stimulated bladder activity by lowering the threshold pressure for voiding. Finally, CCPA did not quell bladder hyperactivity in animals with acute cyclophosphamide-induced cystitis but instead exacerbated their irritated bladder phenotype. In conclusion, we find that adenosine levels at both surfaces of the uroepithelium are modulated by turnover, that blocking these pathways or stimulating A(1) receptors directly at the luminal surface promotes bladder contractions, and that adenosine further stimulates voiding in animals with cyclophosphamide-induced cystitis.

Differential expression and function of nicotinic acetylcholine receptors in the urinary bladder epithelium of the rat

It has been previously determined that the epithelial lining of the urinary bladder, or urothelium, expresses two subtypes of nicotinic acetylcholine receptors (nAChRs) that mediate distinct physiological effects in vivo. These effects include inhibition of bladder reflexes through α7 receptors and an excitation of bladder reflexes through α3-containing (α3*) receptors. It is believed that urothelial receptors mediate their effects through modulating the release of neurotransmitters such as ATP that subsequently influence bladder afferent nerve excitability. Therefore, we examined the distribution of nAChRs in the urothelium, as well as their ability to influence the release of the neurotransmitter ATP. Immunofluorescent staining of both whole bladder tissue and primary urothelial cultures from the rat demonstrated that the urothelium contains both α3* and α7 receptors. In primary urothelial cultures, α7 stimulation with choline (10 μM to 1 mM) caused a decrease in basal ATP release while α3* stimulation with cytisine (1–100 μM) caused a concentration-dependent, biphasic response, with low concentrations (1–10 μM) inhibiting release and higher concentrations (50–100 μM) increasing release. These responses were mirrored in an in vitro, whole bladder preparation. In vivo, excitation of bladder reflexes in response to intravesical cytisine (100 μM) is blocked by systemic administration of the purinergic antagonist PPADS (1 or 3 μg kg(−1)). We also examined how each receptor subtype influenced intracellular Ca2+ levels in cultured urothelial cells. nAChR stimulation increased [Ca2+]i through distinct mechanisms: α7 through a ryanodine-sensitive intracellular mechanism and α3* through extracellular influx. In addition, our findings suggest interactions between nAChR subtypes whereby activation of α7 receptors inhibited the response to a subsequent activation of α3* receptors, preventing the increase in [Ca2+]i previously observed. This inhibitory effect appears to be mediated through protein kinase A- or protein kinase C-mediated pathways.

Loss of adenosine A2B receptor mediated relaxant responses in the aged female rat bladder; effects of dietary phytoestrogens

This study examined the effect of age, ovariectomy and dietary phytoestrogen ingestion on adenosine A(2B) receptor mediated relaxant responses and mRNA expression of adenosine receptor subtypes in the rat isolated bladder. Female Wistar rats (8 weeks) were anaesthetised and the ovaries were removed (ovx) or left intact (sham). Rats were fed either normal rat chow (soy, phytoestrogens) or a non-soy (phytoestrogen free) diet. Isolated bladder from rats aged 12, 24 or 52 weeks were pre-contracted with 3 μM carbachol prior to a concentration response curve to 5'-(N-ethylcarboxamido) adenosine (NECA) being obtained. In 12-week-old rats, the bladder exhibited enhanced relaxant responses to NECA in soy-fed rats (P < 0.05), whilst at 24 weeks of age, the relaxant responses to NECA were attenuated in all the groups studied except soy-treated sham rat bladders in which the relaxant responses were enhanced. At 52 weeks of age, no relaxant effects were observed in any of the treatment groups and NECA-induced contractile responses occurred. In all bladders, the adenosine A(2B) receptor was the most abundantly expressed. In bladders from young and mature female rats, the mRNA expression of adenosine receptors (A(1), A(2A) and A(2B)) was lowest in the bladder from non-soy-fed ovariectomised animals and the use of phytoestrogens in the diet increased the mRNA expression of these receptors (P < 0.05). While a soy diet improves the relaxant effects to the adenosine analogue via adenosine A(2B) receptors in bladders from younger rats, the benefits are lost with advancing age.

Interactions between cholinergic and prostaglandin signaling elements in the urothelium: role for muscarinic type 2 receptors

OBJECTIVE

To characterize the interactions between the cholinergic and prostaglandin signaling systems within the urothelium-lamina propria of the guinea pig and elucidate the role of muscarinic receptors in these interactions.

METHODS

The urothelium-lamina propria was isolated from guinea pig bladders, cut into strips (5×10 mm), and maintained in vitro. The tissue was either stretched or left unstretched but exposed to 2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate tri(triethylammonium) salt, arecaidine, and prostaglandin E2 (PGE2). Acetylcholine and PGE2 release was measured using a GeneBLAzer M3 CHO-K1-bla cell reporter assay and an enzyme immunoassay, respectively. The role of the muscarinic type 2 and 3 (M2 and M3, respectively) receptors and nitric oxide in mediating PGE2 release was determined in the presence of the muscarinic antagonists 11-[(2-[(diethylamino)methyl]-1-piperidinyl)acetyl]-5,11-dihydro-6H-pyrido[2,3b][1,4] benzodiazepin-6-one and darafenicin and a nitric oxide donor (NONOate).

RESULTS

Acetylcholine release was detected in response to stretch and in the unstretched preparations exposed to PGE2 or the adenosine triphosphate analog 2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate tri(triethylammonium) salt. The cholinergic agonist arecaidine induced a concentration-dependent production of PGE2 (half-maximal concentration 75 nM). The arecaidine stimulation of PGE2 production was inhibited in a dose-dependent manner by the antagonist AFDX-116 (M2>M3; half-maximal inhibition 110 nM) but not darifenacin (M3>>M2). Finally, in the presence of the nitric oxide donor, NONOate, arecaidine-stimulated PGE2 production was inhibited.

CONCLUSION

These observations demonstrate that complex signal interactions occur within the urothelium involving acetylcholine, adenosine triphosphate, nitric oxide, and PGE2. In addition, the data have demonstrated a role for muscarinic M2 receptors and nitric oxide in the cholinergic regulation of PGE2 production in the bladder wall.

Defining protein expression in the urothelium: a problem of more than transitional interest

The transitional epithelium of the bladder, the urothelium, is a challenging tissue to study due to its fragility, complex cellular makeup, stratified composition, and intimate connections to both neural and connective tissue elements. With the increasing focus on the urothelium as a mechanosensory tissue with complex autocrine and paracrine signaling activities, there have arisen a number of unresolved controversies in the urothelial literature regarding whether certain important sensory and signaling proteins are expressed by the urothelium. Prominent examples of this include the transient receptor potential (TRP) family member TRPV1 and the purinergic receptor P2X(3). The problem is more than one of scientific bookkeeping since studies utilizing genetic models (primarily knockout mice) claim additional credibility for urothelial functions when phenotypes are discovered. Furthermore, both of the above-mentioned receptors are important therapeutic targets for various bladder disorders including inflammatory and neuropathic pain. The reasons for the confusion about urothelial expression are manifold, but they likely include low expression levels in some cases, poor specificity of antibodies (sometimes lacking adequate controls), the presence of nonurothelial cells resident within the urothelium, and the fact that the urothelium is particularly prone to aspecific adsorption of antibodies. In this review, we attempt to summarize some of the pitfalls with currently accepted practices in this regard, as well as to describe a set of guidelines which will improve the reliability of conclusions related to urothelial expression. It is hoped that this will be of value to investigators studying the urothelium, to those attempting to interpret conflicts in the literature, and hopefully also those charged with reviewing unpublished work. These recommendations will outline a set of "baseline" and "best practice" guidelines by which both researchers and reviewers will be able to evaluate the evidence presented.

Role for pAKT in rat urinary bladder with cyclophosphamide (CYP)-induced cystitis

AKT phosphorylation following peripheral nerve injury or inflammation may play a role in somatic pain processes and visceral inflammation. To examine such a role in micturition reflexes with bladder inflammation, we induced bladder inflammation in adult female Wistar rats (200-300 g) by injecting cyclophosphamide (CYP) intraperitoneally at acute (150 mg/kg; 4 h), intermediate (150 mg/kg; 48 h), and chronic (75 mg/kg; every third day for 10 days) time points. Western blot analyses of whole urinary bladders showed significant increases (P ≤ 0.01) in phosphorylated (p) AKT at all time points; however, the magnitude of AKT phosphorylation varied with duration of CYP treatment. Immunohistochemical analyses of pAKT immunoreactivity (pAKT-IR) in cryostat bladder sections demonstrated duration-dependent, significant (P ≤ 0.01) increases in pAKT-IR in both the urothelium and detrusor smooth muscle of CYP-inflamed bladders. Additionally, a suburothelial population of pAKT-IR macrophages (CD68-, MAC2-, and F4/80-positive) was present in chronic CYP-treated bladders. The functional role of pAKT in micturition was evaluated using open, conscious cystometry with continuous instillation of saline in conjunction with administration of an inhibitor of AKT phosphorylation, deguelin (1.0 μg/10 μl), or vehicle (1% DMSO in saline) in control (no inflammation) and CYP (48 h)-treated rats. Bladder capacity, void volume, and intercontraction void interval increased significantly (P ≤ 0.05) following intravesical instillation of deguelin in CYP (48 h)-treated rats. These results demonstrate increased AKT phosphorylation in the urinary bladder with urinary bladder inflammation and that blockade of AKT phosphorylation in the urothelium improves overall bladder function.

Expression and distribution of ectonucleotidases in mouse urinary bladder

Background

Normal urinary bladder function requires bidirectional molecular communication between urothelium, detrusor smooth muscle and sensory neurons and one of the key mediators involved in this intercellular signaling is ATP. Ectonucleotidases dephosphorylate nucleotides and thus regulate ligand exposure to P2X and P2Y purinergic receptors. Little is known about the role of these enzymes in mammalian bladder despite substantial literature linking bladder diseases to aberrant purinergic signaling. We therefore examined the expression and distribution of ectonucleotidases in the mouse bladder since mice offer the advantage of straightforward genetic modification for future studies.

Principal Findings

RT-PCR demonstrated that eight members of the ectonucleoside triphosphate diphosphohydrolase (NTPD) family, as well as 5′-nucleotidase (NT5E) are expressed in mouse bladder. NTPD1, NTPD2, NTPD3, NTPD8 and NT5E all catalyze extracellular nucleotide dephosphorylation and in concert achieve stepwise conversion of extracellular ATP to adenosine. Immunofluorescent localization with confocal microscopy revealed NTPD1 in endothelium of blood vessels in the lamina propria and in detrusor smooth muscle cells, while NTPD2 was expressed in cells localized to a region of the lamina propria adjacent to detrusor and surrounding muscle bundles in the detrusor. NTPD3 was urothelial-specific, occurring on membranes of intermediate and basal epithelial cells but did not appear to be present in umbrella cells. Immunoblotting confirmed NTPD8 protein in bladder and immunofluorescence suggested a primary localization to the urothelium. NT5E was present exclusively in detrusor smooth muscle in a pattern complementary with that of NTPD1 suggesting a mechanism for providing adenosine to P1 receptors on the surface of myocytes.

Conclusions

Ectonucleotidases exhibit highly cell-specific expression patterns in bladder and therefore likely act in a coordinated manner to regulate ligand availability to purinergic receptors. This is the first study to determine the expression and location of ectonucleotidases within the mammalian urinary bladder.

Increased expression of interleukin-6 family members and receptors in urinary bladder with cyclophosphamide-induced bladder inflammation in female rats

Recent studies suggest that janus-activated kinases-signal transducer and activator of transcription signaling pathways contribute to increased voiding frequency and referred pain of cyclophosphamide (CYP)-induced cystitis in rats. Potential upstream chemical mediator(s) that may be activated by CYP-induced cystitis to stimulate JAK/STAT signaling are not known in detail. In these studies, members of the interleukin (IL)-6 family of cytokines including, leukemia inhibitory factor (LIF), IL-6, and ciliary neurotrophic factor (CNTF) and associated receptors, IL-6 receptor (R) α, LIFR, and gp130 were examined in the urinary bladder in control and CYP-treated rats. Cytokine and receptor transcript and protein expression and distribution were determined in urinary bladder after CYP-induced cystitis using quantitative, real-time polymerase chain reaction (Q-PCR), western blotting, and immunohistochemistry. Acute (4 h; 150 mg/kg; i.p.), intermediate (48 h; 150 mg/kg; i.p.), or chronic (75 mg/kg; i.p., once every 3 days for 10 days) cystitis was induced in adult, female Wistar rats with CYP treatment. Q-PCR analyses revealed significant (p ≤ 0.01) CYP duration- and tissue- (e.g., urothelium, detrusor) dependent increases in LIF, IL-6, IL-6Rα, LIFR, and gp130 mRNA expression. Western blotting demonstrated significant (p ≤ 0.01) increases in IL-6, LIF, and gp130 protein expression in whole urinary bladder with CYP treatment. CYP-induced cystitis significantly (p ≤ 0.01) increased LIF-immunoreactivity (IR) in urothelium, detrusor, and suburothelial plexus whereas increased gp130-IR was only observed in urothelium and detrusor. These studies suggest that IL-6 and LIF may be potential upstream chemical mediators that activate JAK/STAT signaling in urinary bladder pathways.

Cannabinoids: potential targets for bladder dysfunction

Cannabinoids are the active chemical components of Cannabis sativa (marijuana). The medical use of cannabis goes back over 5,000 years. Cannabinoids produce a very wide array of central and peripheral effects, some of which may have beneficial clinical applications. The discovery of cannabinoid receptors has spawned great interest within the pharmaceutical industry with the hopes of capitalizing on the beneficial effects of cannabis without the unwanted psychotropic effects on the central and peripheral nervous system. This chapter presents an overview of the pharmacology of cannabinoids and their derivatives. It reviews the current literature on central and peripheral cannabinoid receptors as related to effects on the lower urinary tract and the role of these receptors in normal and abnormal urinary tract function. An objective evaluation of the published results of clinical trials of cannabis extracts for the treatment of bladder dysfunction resulting from multiple sclerosis is also presented. It is clear that cannabinoid receptors are present in the lower urinary tract as well as spinal and higher centers involved in lower urinary tract control. Systemic cannabinoids have effects on the lower urinary tract that may be able to become clinically useful; however, a much greater understanding of the mechanisms of cannabinoid receptors in control of the human lower urinary tract is necessary to facilitate development of novel cannabinoid drugs for treatment of pelvic disorders.

Neuroanatomy of the lower urinary tract

The lower urinary tract (LUT), which consists of the urinary bladder and its outlet, the urethra, is responsible for the storage and periodic elimination of bodily waste in the form of urine. The LUT is controlled by a complex set of peripheral autonomic and somatic nerves, which in turn are controlled through neural pathways in the spinal cord and brain. This influence of the central nervous system allows for the conscious control of the bladder, allowing the individual to choose an appropriate place to urinate. Defects in the CNS pathways that control the LUT can lead to incontinence, an embarrassing condition that affects over 200 million people worldwide. As a first step in understanding the neural control of the bladder, we will discuss the neuroanatomy of the LUT, focusing first on the peripheral neural pathways, including the sensory pathways that transmit information on bladder filling and the motoneurons that control LUT muscle contractility. We will also discuss the organization of the central pathways in the spinal cord and brainstem that are responsible for coordinating bladder activity, promoting continuous storage of urine except for a few short minutes per day when micturition takes place. To conclude, we will discuss current studies underway that aim to elucidate the higher areas of the brain that control the voluntary nature of micturition in higher organisms.

Urothelial signaling

The urinary bladder "mucosa" or innermost portion of the bladder is composed of transitional epithelium, basement membrane, and the lamina propria. This chapter reviews the specialized anatomy of the bladder epithelium (urothelium) and speculates on possible communication mechanisms from urothelial cells to various cell types within the bladder wall. For example, beyond serving as a simple barrier, there is growing evidence that the urinary bladder urothelium exhibits specialized sensory properties and plays a key role in the detection and transmission of both physiological and nociceptive stimuli. Findings from a number of studies suggest that the urothelium exhibits both "sensor" (expressing receptors/ion channels capable of responding to thermal, mechanical, and chemical stimuli) and "transducer" (ability to release chemicals) properties. Thus, urothelial cells exhibit the ability to sense changes in their extracellular environment including the ability to respond to chemical, mechanical, and thermal stimuli that may communicate the state of the urothelial environment to the underlying nervous and muscular systems.

Afferent mechanism in the urinary tract

Much of the current research on lower urinary tract dysfunction is focused on afferent mechanisms. The main goals are to define and modulate the signaling pathways by which afferent information is generated and conveyed to the central nervous system. Alterations in bladder afferent mechanisms are a potential source of voiding dysfunction and an emerging source of drug targets. Even some established drug therapies such as muscarinic receptor antagonists, as well as emerging therapies such as botulinum toxin type-A, may act partly through afferent mechanisms. This review presents up-to-date findings on the localization of afferent fiber types within the bladder wall, afferent receptors and transmitters, and how these may communicate with the urothelium, interstitial cells, and detrusor smooth muscle to regulate micturition in normal and pathological bladders. Peripheral and central mechanisms of afferent sensitization and myogenic mechanisms that lead to detrusor overactivity, overactive bladder symptoms, and urgency sensations are also covered as well as new therapeutic approaches and new and established methods of measuring afferent activity.

Expression and distribution of transient receptor potential (TRP) channels in bladder epithelium

The urothelium is proposed to be a sensory tissue that responds to mechanical stress by undergoing dynamic membrane trafficking and neurotransmitter release; however, the molecular basis of this function is poorly understood. Transient receptor potential (TRP) channels are ideal candidates to fulfill such a role as they can sense changes in temperature, osmolarity, and mechanical stimuli, and several are reported to be expressed in the bladder epithelium. However, their complete expression profile is unknown and their cellular localization is largely undefined. We analyzed expression of all 33 TRP family members in mouse bladder and urothelium by RT-PCR and found 22 specifically expressed in the urothelium. Of the latter, 10 were chosen for closer investigation based on their known mechanosensory or membrane trafficking functions in other cell types. Western blots confirmed urothelial expression of TRPC1, TRPC4, TRPV1, TRPV2, TRPV4, TRPM4, TRPM7, TRPML1, and polycystins 1 and 2 (PKD1 and PKD2) proteins. We further defined the cellular and subcellular localization of all 10 TRP channels. TRPV2 and TRPM4 were prominently localized to the umbrella cell apical membrane, while TRPC4 and TRPV4 were identified on their abluminal surfaces. TRPC1, TRPM7, and TRPML1 were localized to the cytoplasm, while PKD1 and PKD2 were expressed on the apical and basolateral membranes of umbrella cells as well as in the cytoplasm. The cellular location of TRPV1 in the bladder has been debated, but colocalization with neuronal marker calcitonin gene-related peptide indicated clearly that it is present on afferent neurons that extend into the urothelium, but may not be expressed by the urothelium itself. These findings are consistent with the hypothesis that the urothelium acts as a sentinel and by expressing multiple TRP channels it is likely it can detect and presumably respond to a diversity of external stimuli and suggest that it plays an important role in urothelial signal transduction.

Formation and maintenance of blood-urine barrier in urothelium

Blood-urine barrier, which is formed during differentiation of superficial urothelial cells, is the tightest and most impermeable barrier in the body. In the urinary bladder, the barrier must accommodate large changes in the surface area during distensions and contractions of the organ. Tight junctions and unique apical plasma membrane of superficial urothelial cells play a critical role in the barrier maintenance. Alterations in the blood-urine barrier function accompany most of the urinary tract diseases. In this review, we discuss recent discoveries on the role of tight junctions, dynamics of Golgi apparatus and post-Golgi compartments, and intracellular membrane traffic during the biogenesis and maintenance of blood-urine barrier.

Exploring the mechanisms of intravesical electrical stimulation in the in vitro rat whole bladder after treatment with atropine, α,β-methylATP and tetrodotoxin

AIMS

In a previous study, we showed that the working mechanism of intravesical electrical stimulation (IVES) is probably mainly nerve mediated. But even after bladder decentralization, IVES can induce detrusor contraction. This study explores the effect of IVES in decentralized bladders and the importance of receptors in the bladder wall for a response on IVES.

METHODS

IVES (10 Hz square wave pulses, 20 msec pulse duration, 6 mA) was used in the bladder of 16 female Sprague-Dawley rats. After repeating IVES after consecutive bilateral bladder nerves section (L6-roots, pelvic nerves, and major pelvic ganglion (MPG)), the bladders were mounted in a tissue bath. IVES was performed in the control (n=16), after administration of tetrodotoxin (TTX) (n=6), after atropine and atropine with α,β-methylATP (n=6), and after α,β-methylATP and α,β-methylATP with atropine (n=4). The IVES-induced pressure rise (ΔP) was recorded.

RESULTS

Maximum ΔP (maxΔP) after transection of the MPG was significantly lower than after pelvic nerves transection. Treatment with TTX and with α,β-methylATP plus atropine abolished ΔP. Atropine alone gave an insignificant decrease of maxΔP. Treatment with α,β-methylATP alone reduced maxΔP significantly.

CONCLUSIONS

IVES can evoke contractions in a decentralized bladder. IVES-induced contractions are not a result of direct muscle stimulation, but are nerve mediated, involving intramural innervation and several parts of the bladder innervation. IVES-evoked contraction can be divided in a, contraction duration determining, cholinergic part and a, contraction strength determining, purinergic part. The peripheral innervation could play a role in IVES treatment in patients with interrupted central reflex pathway.

Excitatory cholinergic and purinergic signaling in bladder are equally susceptible to botulinum neurotoxin a consistent with co-release of transmitters from efferent fibers

Mediators of neuromuscular transmission in rat bladder strips were dissected pharmacologically to examine their susceptibilities to inhibition by botulinum neurotoxins (BoNTs) and elucidate a basis for the clinical effectiveness of BoNT/A in alleviating smooth muscle spasms associated with overactive bladder. BoNT/A, BoNT/C1, or BoNT/E reduced peak and average force of muscle contractions induced by electric field stimulation (EFS) in dose-dependent manners by acting only on neurogenic, tetrodotoxin-sensitive responses. BoNTs that cleaved vesicle-associated membrane protein proved to be much less effective. Acetylcholine (ACh) and ATP were found to provide virtually all excitatory input, because EFS-evoked contractions were abolished by the muscarinic receptor antagonist, atropine, combined with either a desensitizing agonist of P2X(1) and P2X(3) or a nonselective ATP receptor antagonist. Both transmitters were released in the innervated muscle layer and, thus, persisted after removal of urothelium. Atropine or a desensitizer of the P2X(1) or P2X(3) receptors did not alter the rate at which muscle contractions were weakened by BoNT/A. Moreover, although cholinergic and purinergic signaling could be partially delineated by using high-frequency EFS (which intensified a transient, largely atropine-resistant spike in muscle contractions that was reduced after P2X receptor desensitization), they proved equally susceptible to BoNT/A. Thus, equi-potent blockade of ATP co-released with ACh from muscle efferents probably contributes to the effectiveness of BoNT/A in treating bladder overactivity, including nonresponders to anticholinergic drugs. Because purinergic receptors are known mediators of sensory afferent excitation, inhibition of efferent ATP release by BoNT/A could also help to ameliorate acute pain and urgency sensation reported by some recipients.

Temporally and spatially controllable gene expression and knockout in mouse urothelium

Urothelium that lines almost the entire urinary tract performs important functions and is prone to assaults by urinary microbials, metabolites, and carcinogens. To improve our understanding of urothelial physiology and disease pathogenesis, we sought to develop two novel transgenic systems, one that would allow inducible and urothelium-specific gene expression, and another that would allow inducible and urothelium-specific knockout. Toward this end, we combined the ability of the mouse uroplakin II promoter (mUPII) to drive urothelium-specific gene expression with a versatile tetracycline-mediated inducible system. We found that, when constructed under the control of mUPII, only a modified, reverse tetracycline trans-activator (rtTA-M2), but not its original version (rtTA), could efficiently trans-activate reporter gene expression in mouse urothelium on doxycycline (Dox) induction. The mUPII/rtTA-M2-inducible system retained its strict urothelial specificity, had no background activity in the absence of Dox, and responded rapidly to Dox administration. Using a reporter gene whose expression was secondarily controlled by histone remodeling, we were able to identify, colocalize with 5-bromo-2-deoxyuridine incorporation, and semiquantify newly divided urothelial cells. Finally, we established that, when combined with a Cre recombinase under the control of the tetracycline operon, the mUPII-driven rtTA-M2 could inducibly inactivate any gene of interest in mouse urothelium. The establishment of these two new transgenic mouse systems enables the manipulation of gene expression and/or inactivation in adult mouse urothelium at any given time, thus minimizing potential compensatory effects due to gene overexpression or loss and allowing more accurate modeling of urothelial diseases than previously reported constitutive systems.

Beyond neurons: Involvement of urothelial and glial cells in bladder function

AIM

The urothelium, or epithelial lining of the lower urinary tract (LUT), is likely to play an important role in bladder function by actively communicating with bladder nerves, smooth muscle, and cells of the immune and inflammatory systems. Recent evidence supports the importance of non-neuronal cells that may extend to both the peripheral and central processes of the neurons that transmit normal and nociceptive signals from the urinary bladder. Using cats diagnosed with a naturally occurring syndrome termed feline interstitial cystitis (FIC), we investigated whether changes in physiologic parameters occur within 3 cell types associated with sensory transduction in the urinary bladder: 1) the urothelium, 2) identified bladder dorsal root ganglion (DRG) neurons and 3) grey matter astrocytes in the lumbosacral (S1) spinal cord. As estrogen fluctuations may modulate the severity of many chronic pelvic pain syndromes, we also examined whether 17beta-estradiol (E2) alters cell signaling in rat urothelial cells.

RESULTS

We have identified an increase in nerve growth factor (NGF) and substance P (SP) in urothelium from FIC cats over that seen in urothelium from unaffected (control) bladders. The elevated NGF expression by FIC urothelium is a possible cause for the increased cell body size of DRG neurons from cats with FIC, reported in this study. At the level of the spinal cord, astrocytic GFAP immuno-intensity was significantly elevated and there was evidence for co-expression of the primitive intermediate filament, nestin (both indicative of a reactive state) in regions of the FIC S1 cord (superficial and deep dorsal horn, central canal and laminae V-VIl) that receive input from pelvic afferents. Finally, we find that E2 triggers an estrus-modifiable activation of p38 MAPK in rat urothelial cells. There were cyclic variations with E2-mediated elevation of p38 MAPK at both diestrus and estrus, and inhibition of p38 MAPK in proestrous urothelial cells.

CONCLUSION

Though urothelial cells are often viewed as bystanders in the processing of visceral sensation, these and other findings support the view that these cells function as primary transducers of some physical and chemical stimuli. In addition, the pronounced activation of spinal cord astrocytes in an animal model for bladder pain syndrome (BPS) may play an important role in the pain syndrome and open up new potential approaches for drug intervention.

Bladder urothelial cells from patients with interstitial cystitis have an increased sensitivity to carbachol

AIMS

The presence of muscarinic receptors on bladder urothelial cells (BUC), suggests BUC may be a target for antimuscarinics. This study determined whether human BUC are responsive to a muscarinic agonist and if so, whether responses are altered in interstitial cystitis (IC) BUC.

METHODS

Primary urothelial cell cultures were established from cystoscopic biopsies. Normal (NB) and IC BUC were studied using calcium imaging techniques as a means to monitor the response to muscarinic receptor activation with the agonist, carbachol (CCh). Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured with fura-2 ratiometric microfluorimetry. Dose-response curves (CCh dose vs. [Ca(2+)](i)) were measured in IC and NB BUC. Tolterodine was used to confirm the specificity (muscarinic versus nicotinic) of CCh evoked increases in [Ca(2+)](i).

RESULTS

CCh induced a dose-dependent increase in [Ca(2+)](i). Potency and efficacy of CCh was significantly greater in IC BUC. The maximal increase in [Ca(2+)](i) was 136.3 +/- 5.1% over baseline in 78 cells from 4 IC patients versus 92.4 +/- 4.8% over baseline in 67 cells from 4 NB subjects (P < 0.01). The EC50 of the evoked increase was 1.10 +/- 0.14 microM versus 3.36 +/- 0.72 microM (P < 0.01) in BUC from IC and NB controls, respectively. Removal of extracellular calcium or application of tolterodine, abolished CCh evoked increase in [Ca(2+)](i) in IC and NB BUC.

CONCLUSIONS

The greater sensitivity of IC BUC to CCh suggests that IC patholobiology may also include alterations muscarinic signaling. The physiologic sequelae of muscarinic activation in BUC need to be further investigated.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Expression and function of CXCL12/CXCR4 in rat urinary bladder with cyclophosphamide-induced cystitis

Chemokines, otherwise known as chemotactic cytokines, are proinflammatory mediators of the immune response and have been implicated in altered sensory processing, hyperalgesia, and central sensitization following tissue injury or inflammation. To address the role of CXCL12/CXCR4 signaling in normal micturition and inflammation-induced bladder hyperreflexia, bladder inflammation in adult female Wistar rats (175-250 g) was induced by injecting cyclophosphamide (CYP) intraperitoneally at acute (150 mg/kg; 4 h), intermediate (150 mg/kg; 48 h), and chronic (75 mg/kg; every 3rd day for 10 days) time points. CXCL12, and its receptor, CXCR4, were examined in the whole urinary bladder of control and CYP-treated rats using enzyme-linked immunosorbent assays (ELISAs), quantitative PCR (qRT-PCR), and immunostaining techniques. ELISAs, qRT-PCR, and immunostaining experiments revealed a significant (P < or = 0.01) increase in CXCL12 and CXCR4 expression in the whole urinary bladder, and particularly in the urothelium, with CYP treatment. The functional role of CXCL12/CXCR4 signaling in micturition was evaluated using conscious cystometry with continuous instillation of saline and CXCR4 receptor antagonist (AMD-3100; 5 microM) administration in control and CYP (48 h)-treated rats. Receptor blockade of CXCR4 using AMD-3100 increased bladder capacity in control (no CYP) rats and reduced CYP-induced bladder hyperexcitability as demonstrated by significant (P < or = 0.01) increases in intercontraction interval, bladder capacity, and void volume. These results suggest a role for CXCL12/CXCR4 signaling in both normal micturition and with bladder hyperreflexia following bladder inflammation.

Augmented bladder urothelial polyamine signaling and block of BK channel in the pathophysiology of overactive bladder syndrome

Overactive bladder syndrome (OAB) is an idiopathic condition characterized by urinary urgency and urge incontinence. Detrusor overactivity has been traditionally described as the physiologic mechanism for OAB. However, the bladder urothelium (BU) may also be involved in the pathophysiology. This study measured polyamine signaling and its downstream effects on membrane conductivity in bladder urothelial cells (BUC) obtained from asymptomatic and OAB subjects. Immunohistofluorescence was used to measure ornithine decarboxylase (ODC) expression in BU. BUC, cultured from BU biopsies, were used for electrophysiologic studies. dl-alpha-Difluoromethylornithine (DFMO), spermine, or spermidine was used to modulate polyamine signaling in BUC. Results showed ODC overexpression in OAB BU. In OAB BUC, whole cell and cell-attached configuration showed significantly decreased currents. Using inside-out patches, outward currents increased significantly, suggesting a cytoplasmic source of the outward current block in OAB BUC. In control BUC, outward currents were mediated by the large-conductance calcium-activated potassium (BK) channel due to calcium dose-dependence and block by iberiotoxin. Spermidine and spermine blocked the outward current in normal BUC in dose-dependent fashion. Conversely, DFMO significantly increased (P < 0.01) outward currents in OAB BUC both in cell-attached and in whole cell configuration. The outward currents in DFMO-treated-OAB BUC could be significantly reduced (P < 0.05) by adding back spermidine and spermine. These data suggest that polyamine signaling is upregulated in OAB urothelium and OAB BUC. Furthermore, polyamines in BUC block the BK channel. Targeting of bladder urothelial polyamine signaling may represent a novel approach for OAB treatment based on pathophysiologic mechanisms.

Stretch independent regulation of prostaglandin E(2) production within the isolated guinea-pig lamina propria

OBJECTIVE

To use an isolated preparation of the guinea-pig bladder lamina propria (LP) to investigate the effects of adenosine tri-phosphate (ATP) and nitric oxide (NO) on the release of prostaglandin E(2) (PGE(2)).

MATERIALS AND METHODS

The bladders of female guinea-pigs (200-400 g) were isolated and opened to expose the urothelial surface. The LP was dissected free of the underlying detrusor muscle and cut into strips from the dome to base. Strips were then incubated in Krebs buffer at 37 degrees C. Each tissue piece was then exposed to the stable ATP analogue, BzATP, and a NO donor, diethylamine-NONOate (DEANO), and the effect on PGE(2) output into the supernatant determined using the Parameter(TM) PGE(2) enzyme immunoassay kit (R & D Systems, Abingdon, UK). Experiments were repeated in the presence of purinergic receptor and cyclooxygenase (COX) enzymes, COX I and COX II, antagonists. The cellular location of COX I, COX II and neuronal NO synthase (nNOS) within the bladder LP was also determined by immunohistochemistry.

RESULTS

PGE(2) production was significantly increased by BzATP. Antagonist studies showed the purinergic stimulation involved both P(2)X and P(2)Y receptors. The BzATP response was inhibited by the COX inhibitor indomethacin (COX I >COX II) but not by DUP 697 (COX II >COX I). Thus, BzATP stimulation occurs because of COX I stimulation. NO had no effect on PGE(2) production over the initial 10 min of an exposure. However, PGE(2) output was increased 100 min after exposure to the NO donor. In the presence of NO, the BzATP stimulation was abolished. Immunohistochemistry was used to confirm the location of COX I to the basal and inner intermediate urothelial layers and to cells within the diffuse layer of LP interstitial cells. In addition, nNOS was also located in the basal urothelial layers whilst COX II was found in the interstitial cell layers.

CONCLUSIONS

There is complex interaction between ATP and NO to modulate PGE(2) release from the bladder LP in the un-stretched preparation. Such interactions suggest a complex interrelationship of signals derived from this region of the bladder wall. The importance of these interactions in relation to the physiology of the LP remains to be determined.

Urothelial signaling

Beyond serving as a simple barrier, there is growing evidence that the urinary bladder urothelium exhibits specialized sensory properties and play a key role in the detection and transmission of both physiological and nociceptive stimuli. These urothelial cells exhibit the ability to sense changes in their extracellular environment including the ability to respond to chemical, mechanical and thermal stimuli that may communicate the state of the urothelial environment to the underlying nervous and muscular systems. Here, we review the specialized anatomy of the urothelium and speculate on possible communication mechanisms from urothelial cells to various cell types within the bladder wall.

Cell biology and physiology of the uroepithelium

The uroepithelium sits at the interface between the urinary space and underlying tissues, where it forms a high-resistance barrier to ion, solute, and water flux, as well as pathogens. However, the uroepithelium is not simply a passive barrier; it can modulate the composition of the urine, and it functions as an integral part of a sensory web in which it receives, amplifies, and transmits information about its external milieu to the underlying nervous and muscular systems. This review examines our understanding of uroepithelial regeneration and how specializations of the outermost umbrella cell layer, including tight junctions, surface uroplakins, and dynamic apical membrane exocytosis/endocytosis, contribute to barrier function and how they are co-opted by uropathogenic bacteria to infect the uroepithelium. Furthermore, we discuss the presence and possible functions of aquaporins, urea transporters, and multiple ion channels in the uroepithelium. Finally, we describe potential mechanisms by which the uroepithelium can transmit information about the urinary space to the other tissues in the bladder proper.

Defects in muscarinic receptor cell signaling in bladder urothelial cancer cell lines

INTRODUCTION

To explore muscarinic receptor signaling in 4 bladder cancer cell lines, bladder urothelial cells (BUC) have been shown to release and respond to various putative neurotransmitters.

METHODS

Reverse transcription-polymerase chain reaction was used to detect the presence of m1-m5 transcripts in the J82, RT4, T24, and 5637 lines of cancer BUC. Immunofluorescence was used to detect expression of m3 protein. Cancer and normal BUC were stimulated with carbachol (100 microM), a muscarinic agonist. Carbachol-evoked changes in intracellular calcium ([Ca(2+)](i)) levels were measured using fura-2 ratiometric microfluorimetry. Transfection of J82 cells with m3 plasmid was performed, and changes in carbachol-evoked [Ca(2+)](i) were re-examined.

RESULTS

None of the cancer cell lines expressed m3 transcripts, unlike normal BUC, which expressed m3. None of the 4 bladder cancer cell lines responded to carbachol. However, 47% of normal BUC responded to carbachol. The m3-transfected J82 cells expressed both m3 transcript and protein. Thirteen percent of m3-transfected J82 cells responded to carbachol.

CONCLUSIONS

This is the first description of altered muscarinic signaling in cancer BUC. Unlike normal BUC, bladder urothelial cancer cells neither expressed m3 transcript nor responded to carbachol, as measured by changes in [Ca(2+)](i). We could partially reverse this defect in one of the cancer cell lines, J82, by transfecting these cells with the m3 plasmid. Although the effects of muscarinic receptor signaling on urothelial cell are unknown, this signaling pathway may play a role in urothelial cell adhesion similar to that in keratinocytes.

Uroplakins in urothelial biology, function, and disease

Urothelium covers the inner surfaces of the renal pelvis, ureter, bladder, and prostatic urethra. Although morphologically similar, the urothelia in these anatomic locations differ in their embryonic origin and lineages of cellular differentiation, as reflected in their different uroplakin content, expandability during micturition, and susceptibility to chemical carcinogens. Previously thought to be an inert tissue forming a passive barrier between the urine and blood, urothelia have recently been shown to have a secretory activity that actively modifies urine composition. Urothelial cells express a number of ion channels, receptors, and ligands, enabling them to receive and send signals and communicate with adjoining cells and their broader environment. The urothelial surface bears specific receptors that not only allow uropathogenic E. coli to attach to and invade the bladder mucosa, but also provide a route by which the bacteria ascend through the ureters to the kidney to cause pyelonephritis. Genetic ablation of one or more uroplakin genes in mice causes severe retrograde vesicoureteral reflux, hydronephrosis, and renal failure, conditions that mirror certain human congenital diseases. Clearly, abnormalities of the lower urinary tract can impact the upper tract, and vice versa, through the urothelial connection. In this review, we highlight recent advances in the field of urothelial biology by focusing on the uroplakins, a group of urothelium-specific and differentiation-dependent integral membrane proteins. We discuss these proteins' biochemistry, structure, assembly, intracellular trafficking, and their emerging roles in urothelial biology, function, and pathological processes. We also call attention to important areas where greater investigative efforts are warranted.

Substance P increases cell-surface expression of CD74 (receptor for macrophage migration inhibitory factor): in vivo biotinylation of urothelial cell-surface proteins

Macrophage migration inhibitory factor (MIF), an inflammatory cytokine, and its receptor CD74 are upregulated by bladder inflammation. MIF-mediated signal transduction involves binding to cell-surface CD74, this study documents, in vivo, MIF-CD74 interactions at the urothelial cell surface. N-hydroxysulfosuccinimide biotin ester-labeled surface urothelial proteins in rats treated either with saline or substance P (SP, 40 microg/kg). The bladder was examined by histology and confocal microscopy. Biotinylated proteins were purified by avidin agarose, immunoprecipitated with anti-MIF or anti-CD74 antibodies, and detected with strepavidin-HRP. Only superficial urothelial cells were biotinylated. These cells contained a biotinylated MIF/CD74 cell-surface complex that was increased in SP-treated animals. SP treatment increased MIF and CD74 mRNA in urothelial cells. Our data indicate that intraluminal MIF, released from urothelial cells as a consequence of SP treatment, interacts with urothelial cell-surface CD74. These results document that our previously described MIF-CD74 interaction occurs at the urothelial cell surface.

Cannabinoid CB1 receptors are expressed in the mouse urinary bladder and their activation modulates afferent bladder activity

Pharmacological studies have indirectly shown the possible presence of cannabinoid receptors in the urinary bladder and their potential role in reducing bladder inflammatory pain. However, the localization of cannabinoid receptors in the urinary bladder remains unknown and there are no published data on the effects of cannabinoids on the sensory system of the bladder. The present study was performed to evaluate the expression of the cannabinoid CB(1) receptors in the mouse urinary bladder and to assess their co-localization with the purinergic P2X(3) receptor, a major player in the transduction of sensory events in the bladder. Also, the effect of intravesical administration of a cannabinoid agonist on the electrical activity of bladder afferent fibers was studied. The expression of mRNA coding for CB(1) receptor was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). Immunofluorescence experiments were performed to study CB(1) and P2X(3) protein expression in the bladder. The electrical activity of bladder afferent fibers was recorded using an ex vivo bladder-nerve preparation. Mechanical stimulation of the bladder was performed by a controlled slow inflation with an external pump. A bolus of a cannabinoid agonist (AZ12646915) was administered intravesically prior to a second inflation. Afferent activity was measured before and after administration of the cannabinoid compound or its vehicle. The effects of CB(1) receptor antagonist (AM251) on the AZ12646915 response were also analyzed. Cannabinoid receptor CB(1) mRNA was detected in the urinary bladder of the mouse. The protein was found in the urothelium, as well as in nerve fibers. CB(1) and P2X(3) receptors were found to be co-expressed in urothelial cells and in some nerve fibers. In addition, intravesical administration of a cannabinoid receptor agonist reduced the mechanically-evoked activity of bladder afferents in the pelvic nerve. This effect was abolished by the previous administration of the CB(1) antagonist AM251. These data demonstrate the presence of cannabinoid CB(1) receptor mRNA and the protein in the mouse urinary bladder. CB(1) and P2X(3) protein co-localization supports the hypothesis of an interaction between the cannabinoid and the purinergic systems in the transduction of sensory information in the urinary bladder. Finally, the reduction of nerve activity induced by cannabinoid-receptor activation implicates CB(1) receptors in the peripheral modulation of bladder afferent information.

Surgical implantation of avulsed lumbosacral ventral roots promotes restoration of bladder morphology in rats

Injuries to the cauda equina and conus medullaris of the spinal cord commonly result in paraplegia, sensory deficits, neuropathic pain, as well as bladder, bowel, and reproductive dysfunctions. In a recently developed lower motoneuron model for cauda equina injury and repair, we have demonstrated that an acute surgical implantation of avulsed lumbosacral ventral roots into the conus medullaris is neuroprotective, promotes regeneration of efferent spinal cord axons into the implanted roots, and may result in functional reinnervation of the lower urinary tract. Here, we investigated the effects of a bilateral lumbosacral ventral root avulsion (VRA) injury and re-implantation on the morphology of the rat bladder at twelve weeks post-operatively. We demonstrated a VRA-induced overall thinning of the bladder wall, which exhibited reduced thickness of both the lamina propria and smooth muscle. In contrast, the bladder epithelium markedly increased its thickness in the injured series. Quantitative immunohistochemical studies showed a selective increase in CGRP immunoreactivity in the lamina propria after the VRA injury. Interestingly, the injury-induced changes in bladder wall morphology were ameliorated by an acute implantation of the lesioned roots into the conus medullaris. Specifically, bladders of the implanted group showed a partial restoration of the thickness of the lamina propria and epithelium as well as a return of CGRP immunoreactivity to baseline levels in the lamina propria. Our results support the notion that surgical implantation of severed ventral roots into the spinal cord may promote the recovery of a normal morphological phenotype in peripheral end organs.