From urgency to frequency: facts and controversies of TRPs in the lower urinary tract

From cause to relief: Vitamin D plays a crucial role in overactive bladder via the RhoA/ROCK signaling pathway

Overactive bladder (OAB) is a common urological disorder, characterized by urinary urgency and frequency. However, the etiology and pathogenesis of OAB remain unclear. The objective of this study was to construct a Vitamin D-deficient rat model with the aim of clarifying the relationship between Vitamin D deficiency and the development of OAB, as well as investigating the potential mechanisms involved. The findings revealed that rats with vitamin D deficiency exhibited indications of OAB, including increased urinary frequency and urgency, as evidenced by void spot assay and cystometry. Furthermore, supplementation with vitamin D proved to be an effective intervention in alleviating these symptoms. The activation of RhoA/ROCK pathway was found in the bladder tissues and urine of rats with vitamin D deficiency. Moreover, supplementation with vitamin D led to a significant decrease in the expression levels of RhoA/ROCK pathway in both bladder tissue and urine. In conclusion, our study was the first to demonstrate that vitamin D deficiency is one of the etiological factors of OAB through the activation of the RhoA/ROCK signaling pathway, and that vitamin D supplementation has been shown to effectively alleviate OAB symptoms by inhibiting this pathway. Meanwhile, urinary RhoA may be a biomarker of OAB. Our present work makes a significant contribution to the clarification of the etiology and mechanism of OAB, as well as to the refinement of OAB treatment strategies.

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.

Novel pharmacotherapeutic avenues for bladder storage dysfunction in men

INTRODUCTION

Bladder storage dysfunction is associated with low quality of life in men and remains a challenging field in pharmacotherapy because of low persistence followed by patient-perceived lack of efficacy and adverse effects. The persistent desire for the development of novel pharmacotherapy is evident, leading to numerous research efforts based on its pathophysiology.

AREAS COVERED

This review describes the pathophysiology, current pharmacotherapeutic strategies, and emerging novel drugs for male bladder storage dysfunction. The section on emerging pharmacotherapy provides an overview of current research, focusing on high-potential target molecules, particularly those being evaluated in ongoing clinical trials.

EXPERT OPINION

As pharmacotherapies targeting alpha-adrenergic, beta-adrenergic, and muscarinic receptors - the current primary targets for treating male bladder storage dysfunction - have demonstrated insufficient efficacy and side effects, researchers are exploring various alternative molecular targets. Numerous targets have been identified as central to regulating bladder afferent nerve activity, and their pharmacological effects and potential have been evaluated in animal-based experiments. However, there is a limited number of clinical trials for these new pharmacotherapies, and they have not demonstrated clear superiority over current treatments. Further research is needed to develop new effective pharmacotherapies for bladder storage dysfunction in men.

Inflammation-the role of TRPA1 channel

Recently, increasing numbers of studies have demonstrated that transient receptor potential ankyrin 1 (TRPA1) can be used as a potential target for the treatment of inflammatory diseases. TRPA1 is expressed in both neuronal and non-neuronal cells and is involved in diverse physiological activities, such as stabilizing of cell membrane potential, maintaining cellular humoral balance, and regulating intercellular signal transduction. TRPA1 is a multi-modal cell membrane receptor that can sense different stimuli, and generate action potential signals after activation via osmotic pressure, temperature, and inflammatory factors. In this study, we introduced the latest research progress on TRPA1 in inflammatory diseases from three different aspects. First, the inflammatory factors released after inflammation interacts with TRPA1 to promote inflammatory response; second, TRPA1 regulates the function of immune cells such as macrophages and T cells, In addition, it has anti-inflammatory and antioxidant effects in some inflammatory diseases. Third, we have summarized the application of antagonists and agonists targeting TRPA1 in the treatment of some inflammatory diseases.

TRPV1 and TRPM8 antagonists reduce cystitis-induced bladder hypersensitivity via inhibition of different sensitised classes of bladder afferents in guinea pigs

BACKGROUND AND PURPOSE

Interstitial cystitis (=painful bladder syndrome) is a chronic bladder syndrome characterised by pelvic and bladder pain, urinary frequency and urgency, and nocturia. Transient receptor potential (TRP) channels are an attractive target in reducing the pain associated with interstitial cystitis. The current study aims to determine the efficacy of combination of TRP vanilloid 1 (TRPV1) and TRP melastatin 8 (TRPM8) channel inhibition in reducing the pain associated with experimental cystitis in guinea pigs.

EXPERIMENTAL APPROACH

A novel animal model of non-ulcerative interstitial cystitis has been developed using protamine sulfate/zymosan in female guinea pigs. Continuous voiding cystometry was performed in conscious guinea pigs. Ex vivo "close-to-target" single unit extracellular recordings were made from fine branches of pelvic nerves entering the guinea pig bladder. Visceromotor responses in vivo were used to determine the effects of TRP channel antagonists on cystitis-induced bladder hypersensitivity.

KEY RESULTS

Protamine sulfate/zymosan treatment evoked mild inflammation in the bladder and increased micturition frequency in conscious animals. In cystitis, high threshold muscular afferents were sensitised via up-regulation of TRPV1 channels, high threshold muscular-mucosal afferents were sensitised via TRPM8 channels, and mucosal afferents by both. Visceromotor responses evoked by noxious bladder distension were significantly enhanced in cystitis and were returned to control levels upon administration of combination of low doses of TRPV1 and TRPM8 antagonists.

CONCLUSIONS AND IMPLICATIONS

The data demonstrate the therapeutic promises of combination of TRPV1 and TRPM8 antagonists for the treatment of bladder hypersensitivity in cystitis.

The urothelium: a multi-faceted barrier against a harsh environment

All mucosal surfaces must deal with the challenge of exposure to the outside world. The urothelium is a highly specialized layer of stratified epithelial cells lining the inner surface of the urinary bladder, a gruelling environment involving significant stretch forces, osmotic and hydrostatic pressures, toxic substances, and microbial invasion. The urinary bladder plays an important barrier role and allows the accommodation and expulsion of large volumes of urine without permitting urine components to diffuse across. The urothelium is made up of three cell types, basal, intermediate, and umbrella cells, whose specialized functions aid in the bladder's mission. In this review, we summarize the recent insights into urothelial structure, function, development, regeneration, and in particular the role of umbrella cells in barrier formation and maintenance. We briefly review diseases which involve the bladder and discuss current human urothelial in vitro models as a complement to traditional animal studies.

KPR-5714, a selective transient receptor potential melastatin 8 antagonist, improves voiding dysfunction in rats with bladder overactivity but does not affect voiding behavior in normal rats

AIMS

Transient receptor potential melastatin 8 (TRPM8) has a role in the abnormal sensory transduction of the bladder and is involved in the pathophysiology of hyperactivity bladder disorders. The aim of this study is to examine the effects of KPR-5714, a novel and selective TRPM8 antagonist, on voiding dysfunction induced by bladder afferent hyperactivity via mechanosensitive C-fibers in rats.

METHODS

The effects of intragastric administration of KPR-5714 on bladder overactivity induced by intravesical instillation of 10 mM ATP were investigated using cystometry in conscious female rats. We examined the effects of oral administration of KPR-5714 on voiding behavior using a metabolic cage in normal male rats and rats with an intratesticular injection of 3% acetic acid.

RESULTS

In cystometry measurements, the intercontraction interval was decreased by intravesical ATP instillation. KPR-5714 (0.1, 0.3, and 1 mg/kg) dose-dependently prolonged the shortened intercontraction interval provoked by ATP. In voiding behavior measurements, intratesticular injection of acetic acid decreased the mean voided volume and increased voiding frequency. KPR-5714 (0.1 and 0.3 mg/kg) dose-dependently increased the mean voided volume and decreased voiding frequency without affecting the total voided volume in these rats. However, KPR-5714 (1 and 10 mg/kg) did not influence the voiding behavior in normal rats.

CONCLUSION

The present results suggest that KPR-5714 improves voiding dysfunction by inhibiting the enhanced activity of mechanosensitive bladder C-fibers in rats with bladder overactivity and shows no significant change in voiding behavior in normal rats.

Posterior tibial nerve stimulation improves neurogenic bladder in rats with spinal cord injury through transient receptor potential/P2X signaling pathway

BACKGROUND

To study the influences of posterior tibial nerve stimulation (PTNS) on neurogenic bladder and the expression of transient receptor potential (TRP) channels and P2X receptors in rats with spinal cord injury (SCI) and explore the possible mechanism.

METHODS

SCI model was established by modified Allen's method and PTNS was performed. Urodynamic indexes and Haematoxylin and Eosine staining of bladder tissue were used to evaluate the therapeutic effect. The expression of TRP channels and P2X receptors in the bladder and dorsal root ganglia (DRG) was detected by real-time PCR and Western blot.

RESULTS

The low compliance of bladder in treatment group was significantly improved compared with SCI group, and the infiltration of inflammatory cells in bladder tissue was significantly reduced. At the same time, the expression of TRP and P2X in bladder and DRG was partially restored after the treatment of PTNS.

CONCLUSIONS

PTNS is an effective therapy for SCI-induced neurogenic bladder via the TRP/P2X signaling pathway.

Suppression of Inflammatory and Fibrotic Signals by Cinnamon (Cinnamomum cassia) and Cinnamaldehyde in Cyclophosphamide-Induced Overactive Bladder in Mice

Cinnamon (Cinnamomum cassia) is a well-known traditional Chinese medicine used to treat nocturia by tonifying and warming the kidney. Our recent clinical study found that overactive bladder (OAB) patients treated with cinnamon powder (CNP) patches exhibited significantly ameliorated OAB symptoms without significant side effects, but the mechanism of action is unclear. To explore the beneficial effects and action mechanisms of CNP and its major active component cinnamaldehyde (CNA) in an OAB-related murine model, cyclophosphamide- (CYP-) induced OAB injury was performed on male ICR mice in the presence or absence of CNP and CNA, as well as solifenacin, a clinical drug for OAB as a reference. Twenty-four-hour micturition patterns (frequency of urination and volume of urine per time), as well as histopathological examination, immunohistochemistry (IHC), and Western blotting of the bladder, were analyzed for mechanism elucidation. Administration of CYP (300 mg/kg, i.p.) induced typical OAB pathophysiological changes, including increased frequency of urination and reduced volume of urine. CYP-induced mice displayed strong edema of the bladder and hemorrhagic cystitis, accompanied by loss of normal corrugated folds and decreased muscarinic receptors (M2/M3) in the urothelium, and disordered/broken structures of the lamina propria and detrusor. These changes were correlated with increased leukocyte (CD11b) infiltration colocalized with inflammatory (pp65 NFκB, macrophage migration inhibitory factor (MIF)/Toll-like receptor 4 (TLR4)) and fibrotic (stem cell factor (SCF)/c-Kit, α-smooth muscle actin (α-SMA)/β-catenin) signals. Treatment with CNP (600 mg/kg, p.o.) and CNA (10–50 mg/kg, p.o.), but not solifenacin (50 mg/kg), 30 min after CYP induction significantly ameliorated CYP-induced dysfunction in micturition patterns and pathophysiological changes. CNP and CNA further suppressed MIF/TLR4-associated inflammatory and SCF/c-Kit-related fibrotic signaling pathways. Our findings indicate that suppression of inflammatory and fibrotic signals contributes to the crucial mechanism in the improvement of CYP-induced OAB by CNP and CNA.

Emerging role of transient receptor potential (TRP) channels in cancer progression

Transient receptor potential (TRP) channels comprise a diverse family of ion channels, the majority of which are calcium permeable and show sophisticated regulatory patterns in response to various environmental cues. Early studies led to the recognition of TRP channels as environmental and chemical sensors. Later studies revealed that TRP channels mediated the regulation of intracellular calcium. Mutations in TRP channel genes result in abnormal regulation of TRP channel function or expression, and interfere with normal spatial and temporal patterns of intracellular local Ca2+ distribution. The resulting dysregulation of multiple downstream effectors, depending on Ca2+ homeostasis, is associated with hallmarks of cancer pathophysiology, including enhanced proliferation, survival and invasion of cancer cells. These findings indicate that TRP channels affect multiple events that control cellular fate and play a key role in cancer progression. This review discusses the accumulating evidence supporting the role of TRP channels in tumorigenesis, with emphasis on prostate cancer. [BMB Reports 2020; 53(3): 125-132].

Alterations in detrusor contractility in rat model of bladder cancer

Urinary incontinence of idiopathic nature is a common complication of bladder cancer, yet, the mechanisms underlying changes in bladder contractility associated with cancer are not known. Here by using tensiometry on detrusor smooth muscle (DSM) strips from normal rats and rats with bladder cancer induced by known urothelial carcinogen, N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), we show that bladder cancer is associated with considerable changes in DSM contractility. These changes include: (1) decrease in the amplitude and frequency of spontaneous contractions, consistent with the decline of luminal pressures during filling, and detrusor underactivity; (2) diminution of parasympathetic DSM stimulation mainly at the expense of m-cholinergic excitatory transmission, suggestive of difficulty in bladder emptying and weakening of urine stream; (3) strengthening of TRPV1-dependent afferent limb of micturition reflex and TRPV1-mediated local contractility, promoting urge incontinence; (4) attenuation of stretch-dependent, TRPV4-mediated spontaneous contractility leading to overflow incontinence. These changes are consistent with the symptomatic of bladder dysfunction in bladder cancer patients. Considering that BBN-induced urothelial lesions in rodents largely resemble human urothelial lesions at least in their morphology, our studies establish for the first time underlying reasons for bladder dysfunction in bladder cancer.

TRP Channels Role in Pain Associated With Neurodegenerative Diseases

Transient receptor potential (TRP) are cation channels expressed in both non-excitable and excitable cells from diverse tissues, including heart, lung, and brain. The TRP channel family includes 28 isoforms activated by physical and chemical stimuli, such as temperature, pH, osmotic pressure, and noxious stimuli. Recently, it has been shown that TRP channels are also directly or indirectly activated by reactive oxygen species. Oxidative stress plays an essential role in neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, and TRP channels are involved in the progression of those diseases by mechanisms involving changes in the crosstalk between Ca2+ regulation, oxidative stress, and production of inflammatory mediators. TRP channels involved in nociception include members of the TRPV, TRPM, TRPA, and TRPC subfamilies that transduce physical and chemical noxious stimuli. It has also been reported that pain is a complex issue in patients with Alzheimer's and Parkinson's diseases, and adequate management of pain in those conditions is still in discussion. TRPV1 has a role in neuroinflammation, a critical mechanism involved in neurodegeneration. Therefore, some studies have considered TRPV1 as a target for both pain treatment and neurodegenerative disorders. Thus, this review aimed to describe the TRP-dependent mechanism that can mediate pain sensation in neurodegenerative diseases and the therapeutic approach available to palliate pain and neurodegenerative symptoms throughout the regulation of these channels.

Urinary bladder smooth muscle ion channels: expression, function, and regulation in health and disease

Urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, forms the bladder wall and ultimately determines the two main attributes of the organ: urine storage and voiding. The two functions are facilitated by UBSM relaxation and contraction, respectively, which depend on UBSM excitability shaped by multiple ion channels. In this review, we summarize the current understanding of key ion channels establishing and regulating UBSM excitability and contractility. They include excitation-enhancing voltage-gated Ca2+ (Cav) and transient receptor potential channels, excitation-reducing K+ channels, and still poorly understood Cl- channels. Dynamic interplay among UBSM ion channels determines the overall level of Cav channel activity. The net Ca2+ influx via Cav channels increases global intracellular Ca2+ concentration, which subsequently triggers UBSM contractility. Here, for each ion channel type, we describe UBSM tissue/cell expression (mRNA and protein) profiles and their role in regulating excitability and contractility of UBSM in various animal species, including the mouse, rat, and guinea pig, and, most importantly, humans. The currently available data reveal certain interspecies differences, which complicate the translational value of published animal research results to humans. This review highlights recent developments, findings on genetic knockout models, pharmacological data, reports on UBSM ion channel dysfunction in animal bladder disease models, and the very limited human studies currently available. Among all gaps in present-day knowledge, the unknowns on expression and functional roles for ion channels determined directly in human UBSM tissues and cells under both normal and disease conditions remain key hurdles in the field.

KPR-5714, a Novel Transient Receptor Potential Melastatin 8 Antagonist, Improves Overactive Bladder via Inhibition of Bladder Afferent Hyperactivity in Rats

Transient receptor potential (TRP) melastatin 8 (TRPM8) is a temperature-sensing ion channel mainly expressed in primary sensory neurons (Aδ-fibers and C-fibers in the dorsal root ganglion). In this report, we characterized KPR-5714 (N-[(R)-3,3-difluoro-4-hydroxy-1-(2H-1,2,3-triazol-2-yl)butan-2-yl]-3-fluoro-2-[5-(4-fluorophenyl)-1H-pyrazol-3-yl]benzamide), a novel and selective TRPM8 antagonist, to assess its therapeutic potential against frequent urination in rat models with overactive bladder (OAB). In calcium influx assays with HEK293T cells transiently expressing various TRP channels, KPR-5714 showed a potent TRPM8 antagonistic effect and high selectivity against other TRP channels. Intravenously administered KPR-5714 inhibited the hyperactivity of mechanosensitive C-fibers of bladder afferents and dose-dependently increased the intercontraction interval shortened by intravesical instillation of acetic acid in anesthetized rats. Furthermore, we examined the effects of KPR-5714 on voiding behavior in conscious rats with cerebral infarction and in those exposed to cold in metabolic cage experiments. Cerebral infarction and cold exposure induced a significant decrease in the mean voided volume and increase in voiding frequency in rats. Orally administered KPR-5714 dose-dependently increased the mean voided volume and decreased voiding frequency without affecting total voided volume in these models. This study demonstrates that KPR-5714 improves OAB in three different models by inhibiting exaggerated activity of mechanosensitive bladder C-fibers and suggests that KPR-5714 may provide a new and useful approach to the treatment of OAB. SIGNIFICANCE STATEMENT: TRPM8 is involved in bladder sensory transduction and plays a role in the abnormal activation in hypersensitive bladder disorders. KPR-5714, as a novel and selective TRPM8 antagonist, may provide a useful treatment for the disorders related to the hyperactivity of bladder afferent nerves, particularly in overactive bladder.

Identification of a Sacral, Visceral Sensory Transcriptome in Embryonic and Adult Mice

Visceral sensory neurons encode distinct sensations from healthy organs and initiate pain states that are resistant to common analgesics. Transcriptome analysis is transforming our understanding of sensory neuron subtypes but has generally focused on somatic sensory neurons or the total population of neurons in which visceral neurons form the minority. Our aim was to define transcripts specifically expressed by sacral visceral sensory neurons, as a step towards understanding the unique biology of these neurons and potentially leading to identification of new analgesic targets for pelvic visceral pain. Our strategy was to identify genes differentially expressed between sacral dorsal root ganglia (DRG) that include somatic neurons and sacral visceral neurons, and adjacent lumbar DRG that comprise exclusively of somatic sensory neurons. This was performed in adult and E18.5 male and female mice. By developing a method to restrict analyses to nociceptive Trpv1 neurons, a larger group of genes were detected as differentially expressed between spinal levels. We identified many novel genes that had not previously been associated with pelvic visceral sensation or nociception. Limited sex differences were detected across the transcriptome of sensory ganglia, but more were revealed in sacral levels and especially in Trpv1 nociceptive neurons. These data will facilitate development of new tools to modify mature and developing sensory neurons and nociceptive pathways.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

TRP Channels as Lower Urinary Tract Sensory Targets

Several members of the transient receptor potential (TRP) superfamily, including TRPV1, TRPV2, TRPV4, TRM4, TRPM8 and TRPA1, are expressed in the lower urinary tract (LUT), not only in neuronal fibers innervating the bladder and urethra, but also in the urothelial and muscular layers of the bladder and urethral walls. In the LUT, TRP channels are mainly involved in nociception and mechanosensory transduction. Animal studies have suggested the therapeutic potential of several TRP channels for the treatment of both bladder over- and underactivity and bladder pain disorders,; however translation of this finding to clinical application has been slow and the involvement of these channels in normal human bladder function, and in various pathologic states have not been established. The development of selective TRP channel agonists and antagonists is ongoing and the use of such agents can be expected to offer new and important information concerning both normal physiological functions and possible therapeutic applications.

Potential therapeutic value of transient receptor potential channels in male urogenital system

Transient receptor potential (TRP) channels comprise a family of cation channels implicated in a variety of cellular processes including light, mechanical or chemical stimuli, temperature, pH, or osmolarity. TRP channel proteins are a diverse family of proteins that are expressed in many tissues. We debated our recent knowledge about the expression, function, and regulation of TRP channels in the different parts of the male urogenital system in health and disease. Emerging evidence suggests that dysfunction of TRP channels significantly contributes to the pathophysiology of urogenital diseases. So far, there are many efforts underway to determine if these channels can be used as drug targets to reverse declines in male urogenital function. Furthermore, developing safe and efficacious TRP channel modulators is warranted for male urogenital disorders in a clinical setting.

Rhythmic Calcium Events in the Lamina Propria Network of the Urinary Bladder of Rat Pups

The lamina propria contains a dense network of cells, including interstitial cells (ICs), that may play a role in bladder function by modulating communication between urothelium, nerve fibers and smooth muscle or acting as pacemakers. Transient receptor potential vanilloid 4 (TRPV4) channels allow cation influx and may be involved in sensing stretch or chemical irritation in urinary bladder. Urothelium was removed from rats (P0-Adult), cut into strips, and loaded with a Ca²⁺ fluorescent dye (Fluo-2 AM leak resistant or Cal 520) for 90 min (35-37°C) to measure Ca²⁺ events. Ca²⁺ events were recorded for a period of 60 seconds (s) in control and after drug treatment. A heterogeneous network of cells was identified at the interface of the urothelium and lamina propria of postnatal rat pups, aged ≤ postnatal (P) day 21, with diverse morphology (round, fusiform, stellate with numerous projections) and expressing platelet-derived growth factor receptor alpha (PDGFRα)- and TRPV4-immunoreactivity (IR). Ca²⁺ transients occurred at a slow frequency with an average interval of 30 ± 8.6 s. Waveform analyses of Ca²⁺ transients in cells in the lamina propria network revealed long duration Ca²⁺ events with slow upstrokes. We observed slow propagating waves of activity in the lamina propria network that displayed varying degrees of coupling. Application of the TRPV4 agonist, GSK1016790 (100 nM), increased the duration of Ca²⁺ events, the number of cells with Ca²⁺ events and the integrated Ca²⁺ activity corresponding to propagation of activity among cells in the lamina propria network. However, GSK2193874 (1 μM), a potent antagonist of TRPV4 channels, was without effect. ATP (1 μM) perfusion increased the number of cells in the lamina propria exhibiting Ca²⁺ events and produced tightly coupled network activity. These findings indicate that ATP and TRPV4 can activate cells in the laminar propria network, leading to the appearance of organized propagating wavefronts.

PACAP/Receptor System in Urinary Bladder Dysfunction and Pelvic Pain Following Urinary Bladder Inflammation or Stress

Complex organization of CNS and PNS pathways is necessary for the coordinated and reciprocal functions of the urinary bladder, urethra and urethral sphincters. Injury, inflammation, psychogenic stress or diseases that affect these nerve pathways and target organs can produce lower urinary tract (LUT) dysfunction. Numerous neuropeptide/receptor systems are expressed in the neural pathways of the LUT and non-neural components of the LUT (e.g., urothelium) also express peptides. One such neuropeptide receptor system, pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1) and its cognate receptor, PAC1 (Adcyap1r1), have tissue-specific distributions in the LUT. Mice with a genetic deletion of PACAP exhibit bladder dysfunction and altered somatic sensation. PACAP and associated receptors are expressed in the LUT and exhibit neuroplastic changes with neural injury, inflammation, and diseases of the LUT as well as psychogenic stress. Blockade of the PACAP/PAC1 receptor system reduces voiding frequency in preclinical animal models and transgenic mouse models that mirror some clinical symptoms of bladder dysfunction. A change in the balance of the expression and resulting function of the PACAP/receptor system in CNS and PNS bladder reflex pathways may underlie LUT dysfunction including symptoms of urinary urgency, increased voiding frequency, and visceral pain. The PACAP/receptor system in micturition pathways may represent a potential target for therapeutic intervention to reduce LUT dysfunction.

TRPA1-dependent regulation of bladder detrusor smooth muscle contractility in normal and type I diabetic rats

TRPA1 is a Ca²⁺-permeable cation channel that is activated by painful low temperatures (˂17 °C), irritating chemicals, reactive metabolites and mediators of inflammation. In the bladder TRPA1 is predominantly expressed in sensory afferent nerve endings, where it mediates sensory transduction. The contractile effect of its activation on detrusor smooth muscle (DSM) is explained by the release from sensory afferents of inflammatory factors – tachykinins and prostaglandins, which cause smooth muscle cell contraction. Diabetes is a systemic disease, with common complications being diabetic cystopathies and urinary incontinence. However, data on how diabetes affects bladder contractility associated with TRPA1 activation are not available. In this study, by using a rat model with streptozotocin-induced type I diabetes, contractility measurements of DSM strips in response to TRPA1-activating and modulating pharmacological agents and assessment of TRPA1 mRNA expression in bladder-innervating dorsal root ganglia, we have shown that diabetes enhances the TRPA1-dependent mechanism involved in bladder DSM contractility. This is not due to changes in TRPA1 expression, but mainly due to the general inflammatory reaction caused by diabetes. The latter leads to an increase in cyclooxygenase-2-dependent prostaglandin synthesis through the mechanisms associated with substance P activity. This results in the enhanced functional coupling between the tachykinin and prostanoid systems, and the concomitant increase of their impact on DSM contractility in response to TRPA1 activation.

Hydrogen peroxide preferentially activates capsaicin-sensitive high threshold afferents via TRPA1 channels in the guinea pig bladder

BACKGROUND AND PURPOSE

There is increasing evidence suggesting that ROS play a major pathological role in bladder dysfunction induced by bladder inflammation and/or obstruction. The aim of this study was to determine the effect of H₂ O₂ on different types of bladder afferents and its mechanism of action on sensory neurons in the guinea pig bladder.

EXPERIMENTAL APPROACH

'Close-to-target' single unit extracellular recordings were made from fine branches of pelvic nerves entering the guinea pig bladder, in flat sheet preparations, in vitro.

KEY RESULTS

H₂ O₂ (300-1000 μM) preferentially and potently activated capsaicin-sensitive high threshold afferents but not low threshold stretch-sensitive afferents, which were only activated by significantly higher concentrations of hydrogen peroxide. The TRPV1 channel agonist, capsaicin, excited 86% of high threshold afferents. The TRPA1 channel agonist, allyl isothiocyanate and the TRPM8 channel agonist, icilin activated 72% and 47% of capsaicin-sensitive high threshold afferents respectively. The TRPA1 channel antagonist, HC-030031, but not the TRPV1 channel antagonist, capsazepine or the TRPM8 channel antagonist, N-(2-aminoethyl)-N-[[3-methoxy-4-(phenylmethoxy)phenyl]methyl]thiophene-2-carboxamide, significantly inhibited the H₂ O₂ -induced activation of high threshold afferents. Dimethylthiourea and deferoxamine did not significantly change the effect of H₂ O₂ on high threshold afferents.

CONCLUSIONS AND IMPLICATIONS

The findings show that H₂ O₂ , in the concentration range detected in inflammation or reperfusion after ischaemia, evoked long-lasting activation of the majority of capsaicin-sensitive high threshold afferents, but not low threshold stretch-sensitive afferents. The data suggest that the TRPA1 channels located on these capsaicin-sensitive afferent fibres are probable targets of ROS released during oxidative stress.

Piezo1 expression increases in rat bladder after partial bladder outlet obstruction

AIMS

For patients with benign prostatic hyperplasia (BPH), storage symptoms due to bladder dysfunction are bothersome, and that mechanism elucidation is needed. Piezo1, a mechanically activated ion channel, is believed to play a role in sensing bladder distension. To investigate the involvement of Piezo1 in bladder dysfunction, we examined the expression and distribution of Piezo1 and neurofilament (NF-L) to understand pathological alterations in rat bladders with partial bladder outlet obstruction (pBOO), an animal model of BPH.

MAIN METHODS

Female Sprague-Dawley rats were subjected to sham or pBOO operations. On days 3, 7, and 14 after pBOO, Piezo1 mRNA levels in the bladder were examined by quantitative real-time PCR. The expression of light NF-L was also examined by western blotting. On day 7, the distributions of Piezo1 were examined by in situ hybridization.

KEY FINDINGS

The expression levels of Piezo1 mRNA in whole bladder were significantly increased from days 3 to 14 after pBOO. On day 7 in pBOO rats, significant increases in Piezo1 mRNA were observed in the detrusor layer as well as the suburothelial layer, while the predominant distribution was observed in the urothelium of sham rats. Coinciding with the increase in Piezo1, the decreases in NF-L expression were observed in the bladder from pBOO rats.

SIGNIFICANCE

The increase in Piezo1 in pBOO rat bladders might be involved in the compensatory mechanism associated with bladder denervation including the decrease in NF-L. Inhibition of Piezo-1 may be a new therapeutic approach to ameliorate the storage dysfunction shown in pBOO.

Receptors, channels, and signalling in the urothelial sensory system in the bladder

The storage and periodic elimination of urine, termed micturition, requires a complex neural control system to coordinate the activities of the urinary bladder, urethra, and urethral sphincters. At the level of the lumbosacral spinal cord, lower urinary tract reflex mechanisms are modulated by supraspinal controls with mechanosensory input from the urothelium, resulting in regulation of bladder contractile activity. The specific identity of the mechanical sensor is not yet known, but considerable interest exists in the contribution of transient receptor potential (TRP) channels to the mechanosensory functions of the urothelium. The sensory, transduction, and signalling properties of the urothelium can influence adjacent urinary bladder tissues including the suburothelial nerve plexus, interstitial cells of Cajal, and detrusor smooth muscle cells. Diverse stimuli, including those that activate TRP channels expressed by the urothelium, can influence urothelial release of chemical mediators (such as ATP). Changes to the urothelium are associated with a number of bladder pathologies that underlie urinary bladder dysfunction. Urothelial receptor and/or ion channel expression and the release of signalling molecules (such as ATP and nitric oxide) can be altered with bladder disease, neural injury, target organ inflammation, or psychogenic stress. Urothelial receptors and channels represent novel targets for potential therapies that are intended to modulate micturition function or bladder sensation.

Drug therapy of overactive bladder--what is coming next?

After the approval and introduction of mirabegron, tadalafil, and botulinum toxin A for treatment of lower urinary tract symptoms/overactive bladder, focus of interest has been on their place in therapy versus the previous gold standard, antimuscarinics. However, since these agents also have limitations there has been increasing interest in what is coming next - what is in the pipeline? Despite progress in our knowledge of different factors involved in both peripheral and central modulation of lower urinary tract dysfunction, there are few innovations in the pipe-line. Most developments concern modifications of existing principles (antimuscarinics, β₃-receptor agonists, botulinum toxin A). However, there are several new and old targets/drugs of potential interest for further development, such as the purinergic and cannabinoid systems and the different members of the transient receptor potential channel family. However, even if there seems to be good rationale for further development of these principles, further exploration of their involvement in lower urinary tract function/dysfunction is necessary.

Developing a functional urinary bladder: a neuronal context

The development of organs occurs in parallel with the formation of their nerve supply. The innervation of pelvic organs (lower urinary tract, hindgut, and sexual organs) is complex and we know remarkably little about the mechanisms that form these neural pathways. The goal of this short review is to use the urinary bladder as an example to stimulate interest in this question. The bladder requires a healthy mature nervous system to store urine and release it at behaviorally appropriate times. Understanding the mechanisms underlying the construction of these neural circuits is not only relevant to defining the basis of developmental problems but may also suggest strategies to restore connectivity and function following injury or disease in adults. The bladder nerve supply comprises multiple classes of sensory, and parasympathetic or sympathetic autonomic effector (motor) neurons. First, we define the developmental endpoint by describing this circuitry in adult rodents. Next we discuss the innervation of the developing bladder, identifying challenges posed by this area of research. Last we provide examples of genetically modified mice with bladder dysfunction and suggest potential neural contributors to this state.

Pirt reduces bladder overactivity by inhibiting purinergic receptor P2X3

Pirt is a transmembrane protein predominantly expressed in peripheral neurons. However, the physiological and pathological roles of Pirt in hollow viscus are largely unknown. Here we show that Pirt deficiency in mice causes bladder overactivity. The density of α,β-meATP-induced currents is significantly reinforced in Pirt-deficient dorsal root ganglion (DRG) neurons. Pirt and P2X3 receptor co-localize in bladder nerve fibres and heterologous Pirt expression significantly reduces P2X3-mediated currents. Pirt interacts with P2X3 through the N-terminal 14 amino-acid residues. TAT-conjugated Pirt(N14) peptide (Pirt(N14)) is sufficient to inhibit P2X3 activation in bladder DRG neurons and to alleviate bladder overactivity in Pirt(-/-) mice. Pirt expression is decreased in the bladder of cyclophosphamide (CYP)-treated mice, a commonly used model of bladder overactivity. Importantly, Pirt(N14) administration reduces the frequency of bladder voiding and restores the voided volume of CYP-treated mice. Therefore, our results demonstrate that Pirt is an endogenous regulator of P2X3 in bladder function.

Mechanisms of pain from urinary tract infection

The pain response to urinary tract infection is largely uncharacterized, but the symptomatic response to urinary tract infection contrasts with the lack of pain response among individuals with asymptomatic bacteriuria. Quantifying pelvic pain in a murine urinary tract infection model, uropathogenic Escerichia coli induces transient pelvic pain, whereas an asymptomatic bacteriuria E. coli isolate causes no pain, thus recapitulating the spectrum of clinical responses to intravesical E. coli. These differential pain responses are not correlated with bladder colonization or inflammation, but instead are intrinsic to E. coli lipopolysaccharide and dependent on the lipopolysaccharide receptor, TLR4. Epidemiological data suggest a link between interstitial cystitis and a history of urinary tract infection, so it was evaluated whether repetitive uropathogenic E. coli instillation would result in chronic pain through central sensitization. Although repeated infection with wild type uropathogenic E. coli results in only transient episodes of acute pain, a uropathogenic E. coli mutant lacking O-antigen causes chronic, post-urinary tract infection pelvic pain. Similarly, a K-12 E. coli strain lacking O-antigen induces chronic pain that persisted long after bacterial clearance, and expressing O-antigen nullified the pain phenotype. Spinal cords isolated from mice with post-urinary tract infection chronic pain showed deficits in short-term depression consistent with central sensitization. Deleting O-antigen gene complex from a uropathogenic E. coli strain and subsequent heterologous expression of O-antigen gene clusters shows that a single bacterial isolate can exhibit pain phenotypes ranging from a null phenotype, an acute pain phenotype, to a chronic pain phenotype. Post-urinary tract infection chronic pain is also associated with voiding dysfunction and anxious/depressive behavior. These effects are also mediated by TRPV1 at the level of pain establishment and CCR2 at the level of pain maintenance. Together, these findings show that transient infection with E. coli might result in chronic visceral pain with the hallmarks of neuropathic pain. This pattern of behaviors mimics the spectrum of interstitial cystitis symptoms, thus supporting the possibility of an infectious etiology of interstitial cystitis.

Pulmonary epithelial barrier function: some new players and mechanisms

The pulmonary epithelium serves as a barrier to prevent access of the inspired luminal contents to the subepithelium. In addition, the epithelium dictates the initial responses of the lung to both infectious and noninfectious stimuli. One mechanism by which the epithelium does this is by coordinating transport of diffusible molecules across the epithelial barrier, both through the cell and between cells. In this review, we will discuss a few emerging paradigms of permeability changes through altered ion transport and paracellular regulation by which the epithelium gates its response to potentially detrimental luminal stimuli. This review is a summary of talks presented during a symposium in Experimental Biology geared toward novel and less recognized methods of epithelial barrier regulation. First, we will discuss mechanisms of dynamic regulation of cell-cell contacts in the context of repetitive exposure to inhaled infectious and noninfectious insults. In the second section, we will briefly discuss mechanisms of transcellular ion homeostasis specifically focused on the role of claudins and paracellular ion-channel regulation in chronic barrier dysfunction. In the next section, we will address transcellular ion transport and highlight the role of Trek-1 in epithelial responses to lung injury. In the final section, we will outline the role of epithelial growth receptor in barrier regulation in baseline, acute lung injury, and airway disease. We will then end with a summary of mechanisms of epithelial control as well as discuss emerging paradigms of the epithelium role in shifting between a structural element that maintains tight cell-cell adhesion to a cell that initiates and participates in immune responses.

Transient receptor potential channels as drug targets: from the science of basic research to the art of medicine

The large Trp gene family encodes transient receptor potential (TRP) proteins that form novel cation-selective ion channels. In mammals, 28 Trp channel genes have been identified. TRP proteins exhibit diverse permeation and gating properties and are involved in a plethora of physiologic functions with a strong impact on cellular sensing and signaling pathways. Indeed, mutations in human genes encoding TRP channels, the so-called "TRP channelopathies," are responsible for a number of hereditary diseases that affect the musculoskeletal, cardiovascular, genitourinary, and nervous systems. This review gives an overview of the functional properties of mammalian TRP channels, describes their roles in acquired and hereditary diseases, and discusses their potential as drug targets for therapeutic intervention.

Urinary nerve growth factor correlates with the severity of urgency and pain

INTRODUCTION AND HYPOTHESIS

Urinary nerve-growth-factor (NGF) level reflected the severity of urgency in patients with lower urinary tract symptoms (LUTS) and pain in patients with Bladder pain syndrome/interstitial cystitis (BPS/IC). The aim of this study was to investigate the levels of biomarkers, nerve growth factor (NGF), and prostaglandin E2 (PGE2) among disease groups sharing similar urinary symptoms and to elucidate which symptoms are related to individual biomarker levels.

METHODS

We studied 83 patients with LUTS who visited our outpatient clinic from May 2011 to December 2012. On the basis of clinical symptoms and a 3-day voiding diary, patients were classified into three groups: those with frequency (n = 13), overactive bladder (OAB) (n = 35), and BPS/IC (n = 35). Patients with stress urinary incontinence (SUI) or microscopic hematuria served as controls (n = 24). Storage symptoms were evaluated based on OAB symptom score (OAB-SS).

RESULTS

Mean patient age was 62.08 ± 11.47 (range, 23-84). Urinary NGF and creatinine-normalized NGF levels were significantly increased in those with OAB (201.90 and 4.08, respectively) and BPS/IC (173.71 and 2.72) compared with controls (77.77 and 1.29) and those with frequency (67.76 and 1.23). Neither value significantly differed between OAB and BPS/IC patients or between controls and frequency patients. Urinary PGE2 and creatinine-normalized PGE2 levels were not significantly different among groups. On linear regression analysis, urinary NGF levels were significantly correlated with urgency severity overall (R = 0.222) and also pain in BPS/IC patients (R = 0.409).

CONCLUSIONS

The levels of urinary NGF were elevated in patients with OAB and BPS/IC but not those with frequency and reflected the severity of urgency. In BPS/IC patients, urinary NGF increased with pain severity.

Bladder cancer and urothelial impairment: the role of TRPV1 as potential drug target

Urothelium, in addition to its primary function of barrier, is now understood to act as a complex system of cell communication that exhibits specialized sensory properties in the regulation of physiological or pathological stimuli. Furthermore, it has been hypothesized that bladder inflammation and neoplastic cell growth, the two most representative pathological conditions of the lower urinary tract, may arise from a primary defective urothelial lining. Transient receptor potential vanilloid channel 1 (TRPV1), a receptor widely distributed in lower urinary tract structures and involved in the physiological micturition reflex, was described to have a pathophysiological role in inflammatory conditions and in the genesis and development of urothelial cancer. In our opinion new compounds, such as curcumin, the major component of turmeric Curcuma longa, reported to potentiate the effects of the chemotherapeutic agents used in the management of recurrent urothelial cancer in vitro and also identified as one of several compounds to own the vanillyl structure required to work like a TRPV1 agonist, could be thought as complementary in the clinical management of both the recurrences and the inflammatory effects caused by the endoscopic resection or intravesical chemotherapy administration or could be combined with adjuvant agents to potentiate their antitumoral effect.

Transient receptor potential (TRP) channels: a clinical perspective

Transient receptor potential (TRP) channels are important mediators of sensory signals with marked effects on cellular functions and signalling pathways. Indeed, mutations in genes encoding TRP channels are the cause of several inherited diseases in humans (the so-called 'TRP channelopathies') that affect the cardiovascular, renal, skeletal and nervous systems. TRP channels are also promising targets for drug discovery. The initial focus of research was on TRP channels that are expressed on nociceptive neurons. Indeed, a number of potent, small-molecule TRPV1, TRPV3 and TRPA1 antagonists have already entered clinical trials as novel analgesic agents. There has been a recent upsurge in the amount of work that expands TRP channel drug discovery efforts into new disease areas such as asthma, cancer, anxiety, cardiac hypertrophy, as well as obesity and metabolic disorders. A better understanding of TRP channel functions in health and disease should lead to the discovery of first-in-class drugs for these intractable diseases. With this review, we hope to capture the current state of this rapidly expanding and changing field.

Characterization of bladder sensory neurons in the context of myelination, receptors for pain modulators, and acute responses to bladder inflammation

Bladder sensation is mediated by lumbosacral dorsal root ganglion neurons and is essential for normal voiding and nociception. Numerous electrophysiological, structural, and molecular changes occur in these neurons following inflammation. Defining which neurons undergo these changes is critical for understanding the mechanism underlying bladder pain and dysfunction. Our first aim was to define the chemical classes of bladder sensory neurons that express receptors for the endogenous modulators of nociceptor sensitivity, glial cell line-derived neurotrophic factor (GDNF), the related neurotrophic factor, artemin, and estrogens. Bladder sensory neurons of adult female Sprague-Dawley rats were identified with retrograde tracer. Diverse groups of neurons express these receptors, and some neurons express receptors for both neurotrophic factors and estrogens. Lumbar and sacral sensory neurons showed some distinct differences in their expression profile. We also distinguished the chemical profile of myelinated and unmyelinated bladder sensory neurons. Our second aim was to identify bladder sensory neurons likely to be undergoing structural remodeling during inflammation. Following systemic administration of cyclophosphamide (CYP), its renal metabolite acrolein causes transient urothelial loss, exposing local afferent terminals to a toxic environment. CYP induced expression of the injury-related immediate-early gene product, activating transcription factor-3 (ATF-3), in a small population of sacral nitrergic bladder sensory neurons. In conclusion, we have defined the bladder sensory neurons that express receptors for GDNF, artemin and estrogens. Our study has also identified a sub-population of sacral sensory neurons that are likely to be undergoing structural remodeling during acute inflammation of the bladder. Together these results contribute to increased understanding of the neurons that are known to be involved in pain modulation and hyperreflexia during inflammation.

Pannexin 1 involvement in bladder dysfunction in a multiple sclerosis model

Bladder dysfunction is common in Multiple Sclerosis (MS) but little is known of its pathophysiology. We show that mice with experimental autoimmune encephalomyelitis (EAE), a MS model, have micturition dysfunction and altered expression of genes associated with bladder mechanosensory, transduction and signaling systems including pannexin 1 (Panx1) and Gja1 (encoding connexin43, referred to here as Cx43). EAE mice with Panx1 depletion (Panx1^−/−) displayed similar neurological deficits but lesser micturition dysfunction compared to Panx1^+/+ EAE. Cx43 and IL-1β upregulation in Panx1^+/+ EAE bladder mucosa was not observed in Panx1^−/− EAE. In urothelial cells, IL-1β stimulation increased Cx43 expression, dye-coupling, and p38 MAPK phosphorylation but not ERK1/2 phosphorylation. SB203580 (p38 MAPK inhibitor) prevented IL-1β-induced Cx43 upregulation. IL-1β also increased IL-1β, IL-1R-1, PANX1 and CASP1 expression. Mefloquine (Panx1 blocker) reduced these IL-1β responses. We propose that Panx1 signaling provides a positive feedback loop for inflammatory responses involved in bladder dysfunction in MS.

Control of urinary bladder smooth muscle excitability by the TRPM4 channel modulator 9-phenanthrol

The Ca (2+)-activated monovalent cation selective transient receptor potential melastatin 4 (TRPM4) channel has been recently identified in detrusor smooth muscle (DSM) of the urinary bladder. Two recent publications by our research group provide evidence in support of the novel hypothesis that TRPM4 channels enhance DSM excitability and contractility. This is a critical question as prior studies have primarily targeted hyperpolarizing currents facilitated by K(+) channels, but the depolarizing component in DSM cells is not well understood. For the first time, we utilized the selective TRPM4 channel inhibitor, 9-phenanthrol, to investigate TRPM4 channel functional effects in DSM at both cellular and tissue levels in rodents. Our new data presented here showed that in rat DSM cells, 9-phenanthrol attenuates spontaneous inward currents in the presence of the muscarinic receptor agonist, carbachol, thus reducing DSM cell excitability. In support of our original hypothesis, we found that TRPM4 channel mRNA levels are much higher in DSM vs. vascular smooth muscle and that inhibition of TRPM4 channels can potentially attenuate DSM excitability. Thus, we postulate the novel concept that selective pharmacological inhibition of TRPM4 channels can limit both excitability and contractility of DSM.

TRPV2 mediates adrenomedullin stimulation of prostate and urothelial cancer cell adhesion, migration and invasion

Adrenomedullin (AM) is a 52-amino acid peptide initially isolated from human pheochromocytoma. AM is expressed in a variety of malignant tissues and cancer cell lines and was shown to be a mitogenic factor capable of stimulating growth of several cancer cell types. In addition, AM is a survival factor for certain cancer cells. Some data suggest that AM might be involved in the progression cancer metastasis via angiogenesis and cell migration and invasion control. The Transient Receptor Potential channel TRPV2 is known to promote in prostate cancer cell migration and invasive phenotype and is correlated with the stage and grade of bladder cancer. In this work we show that AM induces prostate and urothelial cancer cell migration and invasion through TRPV2 translocation to plasma membrane and the subsequent increase in resting calcium level.

Co-cultures provide a new tool to probe communication between adult sensory neurons and urothelium

PURPOSE

Recent evidence suggests that the urothelium functions as a sensory transducer of chemical, mechanical or thermal stimuli and signals to nerve terminals and other cells in the bladder wall. The cellular and molecular basis of neuro-urothelial communication is not easily studied in the intact bladder. This led us to establish a method of co-culturing dorsal root ganglion sensory neurons and bladder urothelial cells.

MATERIALS AND METHODS

Sensory neurons and urothelial cells obtained from dorsal root ganglia and bladders dissected from adult female Sprague-Dawley® rats were isolated by enzyme treatment and mechanical dissociation. They were plated together or separately on collagen coated substrate and cultured in keratinocyte medium for 48 to 72 hours. Retrograde tracer labeling was performed to identify bladder afferents used for functional testing.

RESULTS

Neurite growth and complexity in neurons co-cultured with urothelial cells was increased relative to that in neuronal monocultures. The growth promoting effect of urothelial cells was reduced by the tyrosine kinase inhibitor K252a but upstream inhibition of nerve growth factor signaling with TrkA-Fc had no effect. Fura-2 calcium imaging of urothelial cells showed responses to adenosine triphosphate (100 μM) and activation of TRPV4 (4α-PDD, 10 μM) but not TRPV1 (capsaicin, 1 μM), TRPV3 (farnesyl pyrophosphate, 1 μM) or TRPA1 (mustard oil, 100 μM). In contrast, co-cultured neurons were activated by all agonists except farnesyl pyrophosphate.

CONCLUSIONS

Co-culturing provides a new methodology for investigating neuro-urothelial interactions in animal models of urological conditions. Results suggest that neuronal properties are maintained in the presence of urothelium and neurite growth is potentiated by a nerve growth factor independent mechanism.

Modulation of TRPV1-dependent contractility of normal and diabetic bladder smooth muscle by analgesic toxins from sea anemone Heteractis crispa

AIMS

TRPV1-expressing, capsaicin (CAP)-sensitive afferent fibers innervating bladder in addition to sensory function also exhibit "efferent" features consisting in TRPV1-dependent release of tachykinins (TAC) affecting detrusor smooth muscle (DSM) contractions. Our aim was to investigate the effects of two novel polypeptide inhibitors of TRPV1 from the venom of tropical sea anemone Heteractis crispa, APHC1 and APHC3, on the contractions of DSM from bladders of normal and diabetic rats.

MAIN METHODS

Experiments were conducted on urothelium-devoid DSM strips from normal rats and rats 8weeks after streptozotocin-induced diabetes by means of contraction force measurements.

KEY FINDINGS

Pre-exposure of DSM strips to APHC1 or APHC3 (200nM) specifically inhibited CAP-induced, TRPV1-dependent contractions. Both peptides also transiently enhanced basal tone and spontaneous contractions of DSM strips followed by delayed suppression of electric field stimulation (EFS)-evoked nonadrenergic-noncholinergic (NANC) contractions. The decrease of the amplitude of EFS-evoked NANC contractions by АРНС1 or АРНС3 reached 38.5±3.4% and 25.1±1.6%, respectively, in normal DSM strips and 46.3±3.3% and 43.9±1.8%, respectively, in diabetic ones. APHC-peptide-induced transient enhancement of basal tone could be mimicked by serine protease inhibitor, 4-(2-aminoethyl)bezenesulfonyl fluoride (300 μM).

SIGNIFICANCE

Our results demonstrate that АРНС1 and АРНС3 may be considered as effective inhibitors of bladder contractility especially during diabetic cystopathy. Modality of action of APHC-polypeptides via the mechanisms involving decreased TRPV1-dependent release of TAC from bladder afferents and suppression of TAC degradation due to their activity as endogenous proteases inhibitors is proposed.

Plasticity of TRPV1-Expressing Sensory Neurons Mediating Autonomic Dysreflexia Following Spinal Cord Injury

Spinal cord injury (SCI) triggers profound changes in visceral and somatic targets of sensory neurons below the level of injury. Despite this, little is known about the influence of injury to the spinal cord on sensory ganglia. One of the defining characteristics of sensory neurons is the size of their cell body: for example, nociceptors are smaller in size than mechanoreceptors or proprioceptors. In these experiments, we first used a comprehensive immunohistochemical approach to characterize the size distribution of sensory neurons after high- and low-thoracic SCI. Male Wistar rats (300 g) received a spinal cord transection (T3 or T10) or sham-injury. At 30 days post-injury, dorsal root ganglia (DRGs) and spinal cords were harvested and analyzed immunohistochemically. In a wide survey of primary afferents, only those expressing the capsaicin receptor (TRPV1) exhibited somal hypertrophy after T3 SCI. Hypertrophy only occurred caudal to SCI and was pronounced in ganglia far distal to SCI (i.e., in L4-S1 DRGs). Injury-induced hypertrophy was accompanied by a small expansion of central territory in the lumbar spinal dorsal horn and by evidence of TRPV1 upregulation. Importantly, hypertrophy of TRPV1-positive neurons was modest after T10 SCI. Given the specific effects of T3 SCI on TRPV1-positive afferents, we hypothesized that these afferents contribute to autonomic dysreflexia (AD). Rats with T3 SCI received vehicle or capsaicin via intrathecal injection at 2 or 28 days post-SCI; at 30 days, AD was assessed by recording intra-arterial blood pressure during colo-rectal distension (CRD). In both groups of capsaicin-treated animals, the severity of AD was dramatically reduced. While AD is multi-factorial in origin, TRPV1-positive afferents are clearly involved in AD elicited by CRD. These findings implicate TRPV1-positive afferents in the initiation of AD and suggest that TRPV1 may be a therapeutic target for amelioration or prevention of AD after high SCI.

Function of the Cold Receptor (TRPM8) Associated with Voiding Dysfunction in Bladder Outlet Obstruction in Rats

Purpose

Bladder outlet obstruction (BOO) causes storage and voiding dysfunction in the lower urinary tract. We investigated the expression of transient receptor potential cation channel subfamily M member 8 (TRPM8) to evaluate the relationship between TRPM8 expression and overactive bladder (OAB) in a rat model of BOO.

Methods

Fifty female Sprague-Dawley rats were divided into 4 groups; normal (n=10), normal-menthol (n=10), BOO (n=15), BOO-menthol (n=15). After 3 weeks, cystometry was performed by infusing physiological saline and menthol (3 mM) into the bladder at a slow infusion rate. The histological changes and expression of TRPM8 in the bladder were investigated by Masson's trichrome staining, immunofluorescence and reverse transcription-polymerase chain reaction.

Results

Cystometry showed that the intercontraction interval (ICI; 428.2±23.4 vs. 880.4±51.2, P<0.001), micturition pressure (MP; 25.7±1.01 vs. 71.80±3.01, P<0.001), and threshold pressure (2.9±0.25 vs. 9.2±1.58, P<0.01) were significantly increased in BOO rats. The bladder wall was significantly dilated compared with the control. Detrusor muscle hypertrophy and a thick mucosa layer were observed in BOO bladder. After menthol treatment, ICIs were decreased and MPs were increased in the menthol treatment groups. TRPM8-positive cells and mRNA were predominantly increased in the bladder and dorsal root ganglia of all groups compared with the normal group.

Conclusions

Increased bladder wall thickness and proportion of collagen probably affect voiding dysfunction. Furthermore, an increase of TRPM8 expression in BOO may induce entry of Ca²⁺ from the extracellular space or stores. The increase of Ca²⁺ probably causes contraction of smooth muscle in BOO. However, OAB symptoms were not observed after menthol treatment although the expression of TRPM8 was abundant in the bladder epithelium after menthol treatment. Although OAB in BOO models may be caused by complex pathways, regulation of TRPM8 presents possibilities for OAB treatment.

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

The urothelium is a multifunctional tissue that not only acts as a barrier between the vesical contents of the lower urinary tract and the underlying tissues but also acts as a sensory organ by transducing physical and chemical stresses to the attendant afferent nervous system and underlying smooth muscle. This review will consider the nature of the stresses that the urothelium can transduce; the transmitters that mediate the transduction process; and how lower urinary pathologies, including overactive bladder syndrome, painful bladder syndrome and bacterial infections, are associated with alterations to this sensory system. In particular, the role of muscarinic receptors and the TRPV channels system will be discussed in this context. The urothelium also influences the contractile state of detrusor smooth muscle, both through modifying its contractility and the extent of spontaneous activity; potential pathways are discussed. The potential role that the urothelium may play in bladder underactivity is introduced, as well as potential biomarkers for the condition that may cross the urothelium to the urine. Finally, consideration is given to vesical administration of therapeutic agents that influence urinary tract function and how the properties of the urothelium may determine the effectiveness of this mode of delivery.