Phasic contractions in urinary bladder from juvenile versus adult pigs

Imatinib Mesylate Reduces Neurotrophic Factors and pERK and pAKT Expression in Urinary Bladder of Female Mice With Cyclophosphamide-Induced Cystitis

Imatinib mesylate is a tyrosine kinase inhibitor that inhibits platelet-derived growth factor receptor (PDGFR)-α, -β, stem cell factor receptor (c-KIT), and BCR-ABL. PDGFRα is expressed in a subset of interstitial cells in the lamina propria (LP) and detrusor muscle of the urinary bladder. PDGFRα + interstitial cells may contribute to bladder dysfunction conditions such as interstitial cystitis/bladder pain syndrome (IC/BPS) or overactive bladder (OAB). We have previously demonstrated that imatinib prevention via oral gavage or treatment via intravesical infusion improves urinary bladder function in mice with acute (4 hour, h) cyclophosphamide (CYP)-induced cystitis. Here, we investigate potential underlying mechanisms mediating the bladder functional improvement by imatinib using a prevention or treatment experimental design. Using qRT-PCR and ELISAs, we examined inflammatory mediators (NGF, VEGF, BDNF, CCL2, IL-6) previously shown to affect bladder function in CYP-induced cystitis. We also examined the distribution of phosphorylated (p) ERK and pAKT expression in the LP with immunohistochemistry. Imatinib prevention significantly (0.0001 ≤ p ≤ 0.05) reduced expression for all mediators examined except NGF, whereas imatinib treatment was without effect. Imatinib prevention and treatment significantly (0.0001 ≤ p ≤ 0.05) reduced pERK and pAKT expression in the upper LP (U. LP) and deeper LP (D. LP) in female mice with 4 h CYP-induced cystitis. Although we have previously demonstrated that imatinib prevention or treatment improves bladder function in mice with cystitis, the current studies suggest that reductions in inflammatory mediators contribute to prevention benefits of imatinib but not the treatment benefits of imatinib. Differential effects of imatinib prevention or treatment on inflammatory mediators may be influenced by the route and frequency of imatinib administration and may also suggest other mechanisms (e.g., changes in transepithelial resistance of the urothelium) through which imatinib may affect urinary bladder function following CYP-induced cystitis.

Partial recovery of voiding function in female mice following repeated psychological stress exposure

Psychological stress causes bladder dysfunction in humans and in rodent models, with increased urinary frequency and altered contractile responses evident following repeated environmental stress exposure. However, whether these changes persist after removal of the stressor is unknown, and the aim of this study was to determine if stress-induced changes in voiding behaviour and bladder function recover following removal of the stressor. Adult female mice were allocated to three groups: Unstressed, Stressed or Stressed + Recovery. Animals in the stressed groups were exposed to water avoidance stress for 1h/day for 10-days, with unstressed animals age-matched and housed under normal conditions. For recovery studies, animals were housed without stress exposure for an additional 10-days. Voiding behaviour was assessed periodically and animals sacrificed on day 10 (Unstressed and Stressed) or day 20 (Unstressed and Stressed + Recovery). Isolated whole bladder studies were used to assess compliance, urothelial mediator release and contractile responses. Exposure to stress increased plasma corticosterone levels almost three-fold (P<0.05) but this returned to baseline during the recovery period. Contractile responses of the bladder to carbachol and KCl were also increased following stress, and again fully recovered after a 10-day stress-free period. In contrast, stress increased urinary frequency four-fold (P<0.001), but this did not return fully to baseline during the recovery period. Bladder compliance was unchanged by stress; however, it was increased in the stressed + recovery group (P<0.05). Thus, following a stress-free period there is partial recovery of voiding behaviour, with an increase in bladder compliance possibly contributing to the compensatory mechanisms.

The anxiolytic sertraline reduces the impact of psychological stress on bladder function in mice

AIMS

To determine if treatment with the selective serotonin reuptake inhibitor (SSRI) sertraline reduces the bladder dysfunction caused by water avoidance stress in mice.

MAIN METHODS

Adult female mice were randomly allocated to (1) Unstressed, (2) Stressed or (3) Stress + Sertraline experimental groups. Stressed mice were subjected to water avoidance for 1 h/day for 10 days and received sertraline or vehicle in drinking water, starting 10-days prior to the first stress exposure. Age matched control/unstressed mice were house under normal conditions without stress exposure. Voiding behaviour was assessed throughout the experimental protocol. After the final stress exposure, a blood sample was taken to measure plasma corticosterone levels and bladders were removed, catheterised and intravesical pressure responses recorded during distension and in response to pharmacological agents.

KEY FINDINGS

Plasma corticosterone levels in sertraline-treated animals were equivalent to unstressed controls and significantly decreased compared to the stressed group. Voiding frequency was significantly increased in the stressed group, and treatment with sertraline significantly decreased voiding frequency, however, this remained elevated compared to unstressed control animals. Bladders from stressed mice displayed enhanced maximal contractile response to the muscarinic agonist carbachol and greater release of ACh in the serosal fluid, which was reduced to control levels by sertraline treatment. Spontaneous phasic contractions were not altered by stress but were significantly reduced in bladders from sertraline treated animals, relative to controls.

SIGNIFICANCE

These results indicate that management of voiding dysfunction caused by psychological stress may be aided by the addition of an SSRI such as sertraline.

Contractile elements and their sympathetic regulations in the pig urinary bladder: a species and regional comparative study

Contractile behaviour of the urinary bladder and its sympathetic inhibition during storage phases are not well understood. Here, we explore muscularis mucosae (MM) as a predominant mucosal contractile element and the capability of sympathetic nerves to relax detrusor smooth muscle (DSM) or MM. Distribution of α-smooth muscle actin (α-SMA)-immunoreactive cells was compared in pig, human, guinea pig, rat and mouse bladders by immunohistochemistry, while contractility of the bladder mucosa was compared in these species by isometric tension recordings. In pig, human and guinea pig bladders, DSM and MM located in the lamina propria expressed α-SMA immunoreactivity, while both rat and mouse bladders lacked a MM. Consistent with this presence or absence of MM, bladder mucosa of pig, human and guinea pig but not rat and mouse developed spontaneous phasic contractions (SPCs). Distribution of tyrosine hydroxylase (TH)-immunoreactive sympathetic nerve fibres was compared in pig DSM, MM, trigone and urethra, as were their sympathetic nerve-evoked contractile/relaxing responses examined. In pig DSM or MM, where TH-immunoreactive sympathetic fibres exclusively projected to the vasculature, sympathetic relaxations were difficult to demonstrate. In contrast, sympathetic contractions were invariably evoked in pig trigone and urethra where the smooth muscle cells receive TH-immunoreactive sympathetic innervations. Thus, SPCs of bladder mucosa appear to predominantly arise from the MM displaying species differences. Despite the currently accepted concept of sympathetic nerve-mediated DSM relaxation during the storage phase, it is unlikely that neurally released noradrenaline acts on β-adrenoceptors to relax either DSM or MM due to the anatomical lack of sympathetic innervation.

Spontaneous Activity and the Urinary Bladder

The urinary bladder has two functions: to store urine, when it is relaxed and highly compliant; and void its contents, when intravesical pressure rises due to co-ordinated contraction of detrusor smooth muscle in the bladder wall. Superimposed on this description are two observations: (1) the normal, relaxed bladder develops small transient increases of intravesical pressure, mirrored by local bladder wall movements; (2) pathological, larger pressure variations (detrusor overactivity) can occur that may cause involuntary urine loss and/or detrusor overactivity. Characterisation of these spontaneous contractions is important to understand: how normal bladder compliance is maintained during filling; and the pathophysiology of detrusor overactivity. Consideration of how spontaneous contractions originate should include the structural complexity of the bladder wall. Detrusor smooth muscle layer is overlain by a mucosa, itself a complex structure of urothelium and a lamina propria containing sensory nerves, micro-vasculature, interstitial cells and diffuse muscular elements.Several theories, not mutually exclusive, have been advanced for the origin of spontaneous contractions. These include intrinsic rhythmicity of detrusor muscle; modulation by non-muscular pacemaking cells in the bladder wall; motor input to detrusor by autonomic nerves; regulation of detrusor muscle excitability and contractility by the adjacent mucosa and spontaneous contraction of elements of the lamina propria. This chapter will consider evidence for each theory in both normal and overactive bladder and how their significance may vary during ageing and development. Further understanding of these mechanisms may also identify novel drug targets to ameliorate the clinical consequences of large contractions associated with detrusor overactivity.

Expression of components of the urothelial cholinergic system in bladder and cultivated primary urothelial cells of the pig

BACKGROUND

Porcine urinary bladders are widely used for uro-pharmacological examinations due to their resemblance to the human organ. However, characterisations of the porcine urothelium at the molecular level are scarce up to now. As it has become clear over the last years that this tissue plays an important role in the signaling-pathways of the bladder, we examined whether the transporter and receptor pattern (with focus on the transmitter acetylcholine) is comparable to the human urothelium. With regard to in vitro studies, we also investigated if there is a difference between the native tissue and cultivated primary urothelial cells in culture.

METHODS

Urothelium from German Landrace and Göttingen Minipig bladders was collected. One part of the German Landrace tissue was used for cultivation, and different passages of the urothelial cells were collected. The actual mRNA expression of different transporters and receptors was examined via quantitative real-time PCR. These included the vesicular acetylcholine transporter (VAChT), the choline acetyl transferase (ChAT), organic cation transporters 1-3 (OCT1-3), organic anion transporting polypeptide 1A2 (OATP1A2), P-glycoprotein (ABCB1), the carnitine acetyl-transferase (CarAT), as well as the muscarinic receptors 1-5 (M1-5).

RESULTS

There is a strong qualitative resemblance between the human and the porcine urothelium with regard to the investigated cholinergic receptors, enzymes and transporters. CarAT, OCT1-3, OATP1A2 and ABCB1 could be detected in the urothelium of both pig races. Moreover, all 5 M-receptors were prominent with an emphasis on M2 and M3. VAChT and ChAT could not be detected at all. Cultures of the derived urothelial cells showed decreased expression of all targets apart from ABCB1 and CarAT.

CONCLUSIONS

Based on the expression pattern of receptors, transporters and enzymes of the cholinergic system, the porcine urinary bladder can be regarded as a good model for pharmacological studies. However, cultivation of primary urothelial cells resulted in a significant drop in mRNA expression of the targets. Therefore, it can be concluded that the intact porcine urothelium, or the whole pig bladder, may be appropriate models for studies with anticholinergic drugs, whereas cultivated urothelial cells have some limitation due to significant changes in the expression levels of relevant targets.

Modulation of Bladder Wall Micromotions Alters Intravesical Pressure Activity in the Isolated Bladder

Micromotions are phasic contractions of the bladder wall. During urine storage, such phasic activity has little effect on intravesical pressure, however, changed motile activity may underlie urodynamic observations such as detrusor overactivity. The potential for bladder motility to affect pressure reflects a summation of the overall movements, comprising the initiation, propagation, and dissipation components of micromotions. In this study, the influence of initiation of micromotions was investigated using calcium activated chloride channel blocker niflumic acid, and the effect of propagation using blockers of gap junctions. The overall bladder tone was modulated using isoprenaline. Isolated tissue strips and whole bladder preparations from juvenile rats were used. 18β-glycyrrhetinic acid was used to block gap junctions, reducing the amplitude and frequency of micromotions in in vitro and ex vivo preparations. Niflumic acid reduced the frequency of micromotions but had no effect on the amplitude of pressure fluctuations. Isoprenaline resulted in a reduction in pressure fluctuations and a decrease in pressure baseline. Using visual video data analysis, bladder movement was visible, irrespective of lack of pressure changes, which persisted during bladder relaxation. However, micromotions propagated over shorter distances and the overall bladder tone was reduced. All these results suggest that phasic activity of the bladder can be characterised by a combination of initiation and propagation of movement, and overall bladder tone. At any given moment, intravesical pressure recordings are an integration of these parameters. This synthesis gives insight into the limitations of clinical urodynamics, where intravesical pressure is the key indicator of detrusor activity.

NKA enhances bladder-afferent mechanosensitivity via urothelial and detrusor activation

Tachykinins are expressed within bladder-innervating sensory afferents and have been shown to generate detrusor contraction and trigger micturition. The release of tachykinins from these sensory afferents may also activate tachykinin receptors on the urothelium or sensory afferents directly. Here, we investigated the direct and indirect influence of tachykinins on mechanosensation by recording sensory signaling from the bladder during distension, urothelial transmitter release ex vivo, and direct responses to neurokinin A (NKA) on isolated mouse urothelial cells and bladder-innervating DRG neurons. Bath application of NKA induced concentration-dependent increases in bladder-afferent firing and intravesical pressure that were attenuated by nifedipine and by the NK2 receptor antagonist GR159897 (100 nM). Intravesical NKA significantly decreased bladder compliance but had no direct effect on mechanosensitivity to bladder distension (30 µl/min). GR159897 alone enhanced bladder compliance but had no effect on mechanosensation. Intravesical NKA enhanced both the amplitude and frequency of bladder micromotions during distension, which induced significant transient increases in afferent firing, and were abolished by GR159897. NKA increased intracellular calcium levels in primary urothelial cells but not bladder-innervating DRG neurons. Urothelial ATP release during bladder distention was unchanged in the presence of NKA, whereas acetylcholine levels were reduced. NKA-mediated activation of urothelial cells and enhancement of bladder micromotions are novel mechanisms for NK2 receptor-mediated modulation of bladder mechanosensation. These results suggest that NKA influences bladder afferent activity indirectly via changes in detrusor contraction and urothelial mediator release. Direct actions on sensory nerves are unlikely to contribute to the effects of NKA.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

The Role of the Mucosa in Normal and Abnormal Bladder Function

The internal face of the detrusor smooth muscle wall of the urinary bladder is covered by a mucosa, separating muscle from the hostile environment of urine. However, the mucosa is more than a very low permeability structure and offers a sensory function that monitors the extent of bladder filling and composition of the urine. The mucosa may be considered as a single functional structure and comprises a tight epithelial layer under which is a basement membrane and lamina propria. The latter region itself is a complex of afferent nerves, blood vessels, interstitial cells and in some species including human beings a muscularis mucosae. Stress on the bladder wall through physical or chemical stressors elicits release of chemicals, such as ATP, acetylcholine, prostaglandins and nitric oxide that modulate the activity of either afferent nerves or the muscular components of the bladder wall. The release and responses are graded so that the mucosa forms a dynamic sensory structure, and there is evidence that the gain of this system is increased in pathologies such as overactive bladder and bladder pain syndrome. This system therefore potentially provides a number of drug targets against these conditions, once a number of fundamental questions are answered. These include how is mediator release regulated; what are the intermediate roles of interstitial cells that surround afferent nerves and blood vessels; and what is the mode of communication between urothelium and muscle - by diffusion of mediators or by cell-to-cell communication?

Potential in two types of collagen scaffolds for urological tissue engineering applications – Are there differences in growth behaviour of juvenile and adult vesical cells?

The aging society has a deep impact on patient care in urology. The number of patients in need of partial or whole bladder wall replacement is increasing simultaneously with the number of cancer incidents. Therefore, urological research requires a model of bladder wall replacement in adult and elderly people. Two types of porcine collagen I/III scaffolds were used in vitro for comparison of cell growth of two different pig breeds at different growth stages. Scaffolds were characterised with scanning electron and laser scanning microscopy. Urothelial and detrusor smooth muscle cells were isolated from 15 adult Göttingen minipigs and 15 juvenile German Landrace pigs. Growth behaviour was examined in cell culture and seeded onto the collagen scaffolds via immunohistochemistry, two-photon laser scanning microscopy and a viability assay. The collagen scaffolds showed different structured surfaces which are appropriate for seeding of the two different cell types. Moisturisation of the scaffolds resulted in a change of the structure. Cell growth of German Landrace urothelial cells and smooth muscle cells was significantly higher than cell growth of the Göttingen minipig cells. Seeding of scaffolds with both cell types from both pig races was possible which could be shown by immunohistochemistry and two-photon laser scanning microscopy. Growth behaviour on the scaffolds was significantly increased for the German Landrace compared to Göttingen minipig. Nevertheless, seeding with the adult Göttingen minipig cells resulted in a closed layer on the surface and urothelial cells and smooth muscle cells showed increasing growth until day 14. The results show that these collagen scaffolds are adequate for the seeding with vesical cells. Moreover, they seem appropriate for the use as an in vitro model for the adult or elderly as the cells of the adult Göttingen minipig too, show good growth behaviour.

Physiological and pathophysiological implications of micromotion activity in urinary bladder function

'Micromotions' is a term signifying the presence of localized microcontractions and microelongations, alongside non-motile areas. The motile areas tend to shift over the bladder surface with time, and the intravesical pressure reflects moment-by-moment summation of the interplay between net contractile force generated by micromotions and general bladder tone. Functionally, the bladder structure may comprise modules with variable linkage, which supports presence of localized micromotions (no functional linkage between modules), propagating contractions (where emergence of linkage allows sequential activation) and the shifting of micromotions over time. Detrusor muscle, interstitial cells and intramural innervation have properties potentially relevant for initiating, coordinating and modulating micromotions. Conceptually, such activity could facilitate the generation of afferent activity (filling state reporting) in the absence of intravesical pressure change and the ability to transition to voiding at any bladder volume. This autonomous activity is an intrinsic property, seen in various experimental contexts including the clinical setting of human (female) overactive bladder. 'Disinhibited autonomy' may explain the obvious micromotions in isolated bladders and perhaps contribute clinically in neurological disease causing detrusor overactivity. Furthermore, any process that could increase the initiation or propagation of microcontractions might be anticipated to have a functional effect, increasing the likelihood of urinary urgency and detrusor overactivity respectively. Thus, models of bladder outlet obstruction, neurological trauma and ageing provide a useful framework for detecting cellular changes in smooth muscle, interstitial cells and innervation, and the consequent effects on micromotions.

Infantile hypertrophic pyloric stenosis (IHPS): a study of its pathophysiology utilizing the newborn hph-1 mouse model of the disease

Infantile hypertrophic pyloric stenosis (IHPS) is a common disease of unknown etiology. The tetrahydrobiopterin (BH4)-deficient hyperphenylalaninemia-1 (hph-1) newborn mouse has a similar phenotype to the human condition. For hph-1 and wild-type control animals, pyloric tissue agonist-induced contractile properties, reactive oxygen species (ROS) generation, cGMP, neuronal nitric oxide synthase (nNOS) content, and Rho-associated protein kinase 2 (ROCK-2) expression and activity were evaluated. Primary pyloric smooth muscle cells from wild-type newborn animals were utilized to evaluate the effect of BH4 deficiency. One-week-old hph-1 mice exhibited a fourfold increase (P < 0.01) in the pyloric sphincter muscle contraction magnitude but similar relaxation values when compared with wild-type animals. The pyloric tissue nNOS expression and cGMP content were decreased, whereas the rate of nNOS uncoupling increased (P < 0.01) in 1-wk-old hph-1 mice when compared with wild-type animals. These changes were associated with increased pyloric tissue ROS generation and elevated ROCK-2 expression/activity (P < 0.05). At 1-3 days of age and during adulthood, the gastric emptying rate of the hph-1 mice was not altered, and there were no genotype differences in pyloric tissue ROS generation, nNOS expression, or ROCK-2 activity. BH4 inhibition in pyloric smooth muscle cells resulted in increased ROS generation (P < 0.01) and ROCK-2 activity (P < 0.05). Oxidative stress upregulated ROCK-2 activity in pyloric tissue, but no changes were observed in newborn fundal tissue in vitro. We conclude that ROS-induced upregulation of ROCK-2 expression accounts for the increased pyloric sphincter tone and nNOS downregulation in the newborn hph-1 mice. The role of ROCK-2 activation in the pathogenesis of IHPS warrants further study.

Calcium signalling in Cajal-like interstitial cells of the lower urinary tract

Interstitial cells of Cajal (ICC) serve several critical physiological roles in visceral smooth muscle organs, including acting as electrical pacemakers to modulate phasic contractile activity and as intermediaries in motor neurotransmission. The major roles of ICC have been described in the gastrointestinal tract, however, ICC-like cells (ICC-LC) can also be found in other visceral organs, including those of the lower urinary tract (LUT), where they provide similar functions, acting as electrical pacemakers and as intermediary cells involved in the modulation of neurotransmission to adjacent smooth muscle cells. The physiological functions of ICC-LC, in particular their role as pacemakers, relies on their ability to generate transient and propagating intracellular Ca(2+) events. The role of ICC-LC as pacemakers and neuromodulators in the LUT is increasingly apparent and the study of their intracellular Ca(2+) dynamics will provide a better understanding of their role in LUT excitability.

Do we understand any more about bladder interstitial cells?-ICI-RS 2013

AIMS

To present a brief review on discussions from "Do we understand any more about lower urinary tract interstitial cells?" session at the 2013 International Consultation on Incontinence-Research Society (ICI-RS) meeting in Bristol, UK.

METHODS

Discussion focused on bladder interstitial cell (IC) subtypes, their localization and characterization, and communication between themselves, the urothelium, and detrusor smooth muscle. The role of ICs in bladder pathologies and new methods for studying ICs were also addressed.

RESULTS

ICs have been studied extensively in the lower urinary tract and have been characterized based on comparisons with ICs of Cajal in the gastro-intestinal tract. In fetal bladders it is believed that ICs drive intrinsic contractions to expel urine through the urachus. These contractions diminish postpartum as bladder innervation develops. Voiding in human neonates occurs when filling triggers a spinal cord reflex that contracts the detrusor; in rodents, maternal stimulation of the perineum triggers voiding. Following spinal cord injury, intrinsic contractions, and spinal micturition reflexes develop, similar to those seen during neonatal development. These enhanced contractions may stimulate nociceptive and mechanosensitive afferents contributing to neurogenic detrusor overactivity and incontinence. The IC-mediated activity is believed to be initiated in the lamina propria by responding to urothelial factors. These IC may act syncytially through gap junction coupling and modulate detrusor activity through unknown mechanisms.

CONCLUSION

There has been a great deal of information discovered regarding bladder ICs, however, many of their (patho)physiological functions and mechanisms are still unclear and necessitates further research. Neurourol. Urodynam. 33:573-576, 2014. © 2014 Wiley Periodicals, Inc.