The role of c-kit-positive interstitial cells in mediating phasic contractions of bladder strips from streptozotocin-induced diabetic rats

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.

Therapeutic effect of integrin-linked kinase gene-modified bone marrow-derived mesenchymal stem cells for streptozotocin-induced diabetic cystopathy in a rat model

Background

Diabetic cystopathy (DCP) is a chronic complication of diabetes mainly within the submucosal and muscular layers of the bladder due to the hyperglycemia-induced ischemia. As no effective therapies are currently available, the administration of optimized mesenchymal stem cells (MSCs) provides a potential treatment of DCP. Thus far, new strategy, such as genetic modification of MSCs, has been developed and has shown promising outcomes of various disorders.

Methods

This study was conducted using integrin-linked kinase (ILK) gene-modified bone marrow-derived stem cells (BMSCs) for streptozotocin (STZ)-induced diabetic cystopathy in a rat model. In total, 68 male Sprague-Dawley rats were randomized into five groups: sham control (control group, n = 10); DCP model alone (DM group, n = 10); DCP rats intravenously treated with BMSCs (BMSC group, n = 16); DCP rats accepted adenoviral vector-infected BMSCs (Ad-null-BMSC group, n = 16) and DCP rats accepted ILK adenoviral vector-infected BMSCs (Ad-ILK-BMSC group, n = 16). Diabetic rats accepted cell transplantation in the experimental group (2 rats per group) were sacrificed for the bladder tissue on the third day, 7th day, and 14th day of treatment respectively ahead of schedule. At 4 weeks after treatment, all rats in five groups accepted urodynamic studies to evaluate bladder function and were sacrificed for bladder tissue.

Results

Our data showed that the underactive bladder function was significantly improved in DCP rats intravenously treated with ILK gene-modified BMSCs compared to those in the DM, BMSCs, and Ad-null-BMSC group. Meanwhile, we found that gene-modified BMSC treatment significantly promoted the activation of the AKT/GSK-3β pathway by increasing phosphorylation and led to the enhancement of survival. In addition, the expression levels of angiogenesis-related protein vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and stromal cell-derived factor-1 (SDF-1) were significantly higher in the Ad-ILK-BMSC group than that in the DM, BMSCs, and Ad-null-BMSC group as assessed by enzyme-linked immunosorbent assay and western blot. As two indicators of vascular endothelial cell markers, the expression of von Willebrand factor (vWF) and CD31 by western blot and immunofluorescent staining revealed that the percentage of the vascular area of the bladder tissue significantly increased in Ad-ILK-BMSC group compared with the BMSCs and Ad-null-BMSC group on the 14th day of treatment. Histological and immunohistochemical staining (hematoxylin and eosin (HE), vWF, Ki67, and TUNNEL) on the bladder tissue revealed statistically different results between groups.

Conclusion

ILK gene-modified BMSCs restored the bladder function and histological construction via promoting the process of angiogenesis and protecting cells from high glucose-associated apoptosis in STZ-induced DCP rat model, which provides a potential for the treatment of patients with DCP.

Cyclic Stretch Promotes Proliferation and Contraction of Human Bladder Smooth Muscle Cells by Cajal-Mediated c-kit Expression in Interstitial Cells

Background

The present study was performed to assess the effect of mechanical stretch on the proliferation and contractile function of hBSMCs.

Material/Methods

hBSMCs and ICCs were seeded at 8×10⁴ cells/well in 6-well silicone elastomer-bottomed culture plates coated with type I collagen, and grown to 80% confluence in DMEM/10% FBS and a 5% CO₂ humidified atmosphere at 37°C. Cells of hBSMCs and hBSMCs/ICCs of co-culture were then subjected to continuous cycles of stretch-relaxation using a computer-driven, stretch-inducing device. The treated concentration of imatinib was 10 μM. Mechanisms underlying observed hBSMCs contraction were examined using Western blotting and RT-PCR. The 0.1 μM carbachol was separately added to the experimental groups, and 300 s was recorded by laser scanning confocal microscope.

Results

We found that mechanical stretch increased contraction and proliferation of hBSMCs. Calcium ion activity increased significantly after mechanical stretch. The number of hBSMCs was significantly increased after the combination mechanical stretch with ICCs treatment. After combination mechanical stretch with hBSMCs/ICCs treatment, the mRNA and protein level of M2, M3, and c-kit were significantly increased. After combination of mechanical stretch with no imatinib treatment, the proliferation of hBSMCs was higher than others, and the mRNA and protein level of M2 and M3 were significantly increased.

Conclusions

We revealed that ICCs could promote hBSMC proliferation and contraction, and cyclic stretch could promote acetylcholine receptor M2 and M3 caused by c-kit in the ICCs, which promoted the contraction of hBSMCs.

Urothelial Senescence in the Pathophysiology of Diabetic Bladder Dysfunction-A Novel Hypothesis

Diabetic bladder dysfunction (DBD) is a well-recognized and common symptom affecting up to 50% of all diabetic patients. DBD has a broad range of clinical presentations ranging from overactive to underactive bladder symptoms that develops in middle-aged to elderly patients with long standing and poorly controlled diabetes. Low efficacy of current therapeutics and lifestyle interventions combined with high national healthcare costs highlight the need for more research into bladder dysfunction pathophysiology and novel treatment options. Cellular senescence is an age-related physiologic process in which cells undergo irreversible growth arrest induced by replicative exhaustion and damaging insults. While controlled senescence negatively regulates cell proliferation and promotes tissue regeneration, uncontrolled senescence is known to result in tissue dysfunction through enhanced secretion of inflammatory factors. This review presents previous scientific findings and current hypotheses that characterize diabetic bladder dysfunction. Further, we propose the novel hypothesis that cellular senescence within the urothelial layer of the bladder contributes to the pro-inflammatory/pro-oxidant environment and symptoms of diabetic bladder dysfunction. Our results show increased cellular senescence in the urothelial layer of the bladder; however, whether this phenomenon is the cause or effect of DBD is unknown. The urothelial layer of the bladder is made up of transitional epithelia specialized to contract and expand with demand and plays an active role in transmission by modulating afferent activity. Transition from normal functioning urothelial cells to secretory senescence cells would not only disrupt the barrier function of this layer but may result in altered signaling and sensation of bladder fullness; dysfunction of this layer is known to result in symptoms of frequency and urgency. Future DBD therapeutics may benefit from targeting and preventing early transition of urothelial cells to senescent cells.

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

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

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.

Increased Piezo1 channel activity in interstitial Cajal-like cells induces bladder hyperactivity by functionally interacting with NCX1 in rats with cyclophosphamide-induced cystitis

The Piezo1 channel is a mechanotransduction mediator, and Piezo1 abnormalities have been linked to several clinical disorders. However, the role of the Piezo1 channel in cystitis-associated bladder dysfunction has not been documented. The current study aimed to discover the functional role of this channel in regulating bladder activity during cyclophosphamide (CYP)-induced cystitis. One hundred four female rats were randomly assigned to the control, CYP-4h, CYP-48h and CYP-8d groups. CYP successfully induced acute or chronic cystitis in these rats. CYP treatment for 48h or 8d significantly increased Piezo1 channel expression in bladder interstitial Cajal-like cells (ICC-LCs), and the increase in CYP-8d rats was more prominent. In addition, 2.5 μM Grammostola spatulata mechanotoxin 4 (GsMTx4) significantly attenuated bladder hyperactivity in CYP-8d rats by inhibiting the Piezo1 channel in bladder ICC-LCs. Furthermore, by using GsMTx4 and siRNA targeting the Piezo1 channel, we demonstrated that hypotonic stress-induced Piezo1 channel activation significantly triggered Ca²⁺ and Na⁺ influx into bladder ICC-LCs during CYP-induced chronic cystitis. In addition, the Piezo1 channel functionally interacted with the relatively activated reverse mode of Na⁺/Ca²⁺ exchanger 1 (NCX1) in bladder ICC-LCs from CYP-8d rats. In conclusion, we suggest that the functional role of the Piezo1 channel in CYP-induced chronic cystitis is based on its synergistic effects with NCX1, which can significantly enhance [Ca²⁺]_i and result in Ca²⁺ overload in bladder ICC-LCs, indicating that the Piezo1 channel and NCX1 are potential novel therapeutic targets for chronic cystitis-associated bladder hyperactivity.

A protein that controls the passage of ions through cell membranes is implicated in interstitial cystitis/painful bladder syndrome (IC/PBS). This condition causes chronic pelvic pain and increased urinary frequency and urgency. Current treatment options are unsatisfactory. Researchers led by Longkun Li at the Third Military Medical University in Chongqing, China, and Mingjia Tan at the University of Michigan, Ann Arbor, USA, studied the role of this membrane channel protein, called Piezo1. Increased activity of Piezo1 was linked to bladder hyperactivity in rats with drug-induced cystitis. The research also identified a synergistic interaction between Piezo1 and a second membrane channel protein. A drug that inhibits Piezo1 activity reduced bladder hyperactivity in the rats. Drugs targeting these two proteins might help to treat the chronic cystitis of patients with IC/PBS.

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.

Proliferation of Interstitial Cells in the Cyclophosphamide-Induced Cystitis and the Preventive Effect of Imatinib

Cyclophosphamide- (CYP-) induced cystitis in the rat is a well-known model of bladder inflammation that leads to an overactive bladder, a process that appears to involve enhanced nitric oxide (NO) production. We investigated the changes in the number and distribution of interstitial cells (ICs) and in the expression of endothelial NO synthase (eNOS) in the bladder and urethra of rats subjected to either intermediate or chronic CYP treatment. Pronounced hyperplasia and hypertrophy of ICs were evident within the lamina propria and in the muscle layer. IC immunolabeling with CD34, PDGFRα, and vimentin was enhanced, as reflected by higher colocalization indexes of the distinct pairs of markers. Moreover, de novo expression of eNOS was evident in vimentin and CD34 positive ICs. Pretreatment with the receptor tyrosine kinase inhibitor Imatinib prevented eNOS expression and ICs proliferation, as well as the increased voiding frequency and urinary tract weight provoked by CYP. As similar results were obtained in the urethra, urethritis may contribute to the uropathology of CYP-induced cystitis.

Cyclophosphamide-induced HCN1 channel upregulation in interstitial Cajal-like cells leads to bladder hyperactivity in mice

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are confirmed to be expressed in bladder interstitial Cajal-like cells (ICC-LCs), but little is known about their possible role in cystitis-associated bladder dysfunction. The present study aimed to determine the functional role of HCN channels in regulating bladder function under inflammatory conditions. Sixty female wild-type C57BL/6J mice and sixty female HCN1-knockout mice were randomly assigned to experimental and control groups, respectively. Cyclophosphamide (CYP)-induced cystitis models were successfully established in these mice. CYP treatment significantly enhanced HCN channel protein expression and I_h density and significantly altered bladder HCN1 channel regulatory proteins. Carbachol (CCH) and forskolin (FSK) exerted significant effects on bladder ICC-LC [Ca²⁺]_i in CYP-treated wild-type (WT) mice, and HCN1 channel ablation significantly decreased the effects of CCH and FSK on bladder ICC-LC [Ca²⁺]_i in both naive and CYP-treated mice. CYP treatment significantly potentiated the spontaneous contractions and CCH (0.001–10 μM)-induced phasic contractions of detrusor strips, and HCN1 channel deletion significantly abated such effects. Finally, we demonstrated that the development of CYP-induced bladder overactivity was reversed in HCN1−/− mice. Taken together, our results suggest that CYP-induced enhancements of HCN1 channel expression and function in bladder ICC-LCs are essential for cystitis-associated bladder hyperactivity development, indicating that the HCN1 channel may be a novel therapeutic target for managing bladder hyperactivity.

Diabetes Mellitus Type 2: A Driving Force for Urological Complications

Type 2 diabetes mellitus (T2DM) is a growing epidemic associated with many adverse complications. Urological complications of diabetes mellitus in men are gaining recognition. Previously unknown associations between T2DM and risk for prostate cancer, bladder cancer, renal cell carcinomas, urinary tract infections, nephrolithiasis, penile lesions, androgen deficiency, and erectile dysfunction have been discovered. Significantly, metformin could play a role in the management of urological malignancies, and therapies used for management of these cancers could in return lead to increased risk for diabetes. In this review, we aim to bridge the gap between T2DM and urological complications by discussing the latest findings in these fields, with the ultimate goal being improved patient care on both fronts.

Interaction of Caveolin-3 and HCN is involved in the pathogenesis of diabetic cystopathy

A growing body of research suggests that impaired bladder Cajal-like interstitial cells (ICCs) are a important component in the pathogenesis of diabetes-induced bladder dysfunction, although the molecular mechanisms have not been illustrated completely. The purpose of this study was to examine whether the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in ICCs-DM were responsible for the detrusor weak contractility of Diabetic cystopathy (DCP) and to study the possible mechanism of regulating the expression and function of HCN channels. HCN channels expression were decreased at the mRNA and protein levels. Forskolin (FSK), which can elevate intracellular cAMP levels, increased the density of the hyperpolarization-activated current and intracellular calcium concentration in both normal control (NC) rats and DCP rats, but the sensitivity of FSK on HCN channels was clearly down-regulated in DCP rats. The loss of caveolae and caveolin was in accordance with the decrease in HCN channels. Caveolin-3 co-localizes with and affects the expression and function of HCN. Taken together, these results indicate that the loss of caveolae and HCN channels in ICCs-DM is important in the pathogenesis of DCP. Increasing the number of caveolae to enhance the function of HCN channels may represent a viable target for the pharmacological treatment of DCP.

Research Findings on Overactive Bladder

Several physiopathologic conditions lead to the manifestation of overactive bladder (OAB). These conditions include ageing, diabetes mellitus, bladder outlet obstruction, spinal cord injury, stroke and brain injury, Parkinson's disease, multiple sclerosis, interstitial cystitis, stress and depression. This review has discussed research findings in human and animal studies conducted on the above conditions. Several structural and functional changes under these conditions have not only been observed in the lower urinary tract, but also in the brain and spinal cord. Significant changes were observed in the following areas: neurotransmitters, prostaglandins, nerve growth factor, Rho-kinase, interstitial cells of Cajal, and ion and transient receptor potential channels. Interestingly, alterations in these areas showed great variation in each of the conditions of the OAB, suggesting that the pathophysiology of the OAB might be different in each condition of the disease. It is anticipated that this review will be helpful for further research on new and specific drug development against OAB.

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.

Does diabetes affect the distribution and number of interstitial cells and neuronal tissue in the ureter, bladder, prostate, and urethra of humans?

INTRODUCTION

The aim of this study was to investigate and compare the distribution and number of interstitial cells (ICs) and neuronal tissue in the ureter, bladder, prostate, and urethra of human patients with and without diabetes.

MATERIAL AND METHODS

Human tissue was obtained from patients who had undergone radical cystectomy for bladder cancer (10 diabetic and 11 non-diabetic males). Interstitial cells were stained immunohistochemically with anti-human CD117 (c-kit) rabbit polyclonal antibody, Vimentin, and Connexin-43. Neural tissue was stained with synaptophysin. The number of ICs and neurons was evaluated and compared between the groups (diabetic versus non-diabetic).

RESULTS

The mean number of c-kit (+) ICs in bladder lamina propria was significantly decreased in diabetics (32.40 ±12.96 versus 57.18 ±25.37, p = 0.036). The mean number of ICs in the detrusor muscle was significantly decreased in diabetics (40.50 ±16.79 versus 64.55 ±22.08, p = 0.013). Between the groups, no significant differences were detected regarding the number of ICs at the level of the ureter, urethra, and prostate. No significant differences were detected regarding the number of nerves in the ureter, bladder, prostate, and urethra of both groups.

CONCLUSIONS

The number of ICs may be decreased in the lamina propria and detrusor muscle of the human bladder in diabetes. This can be an underlying cause of lower urinary tract (LUT) dysfunction in diabetics. Research into the development of drugs targeting or stimulating IC function in order to prevent diabetic LUT dysfunction is warranted.

Interstitial cells: regulators of smooth muscle function

Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.

Anoctamin-1 in the juvenile rat urinary bladder

Purpose

To investigate presence, location and functional role of calcium-activated chloride channel (CaCC) Anoctamin-1 (Ano1) in rat urinary bladder.

Materials and Methods

Bladders from 3 week old Wistar rats were studied. End-point PCR on total mRNA was used to assess the expression of Ano1. Immunofluorescent labelling of whole mount bladder tissue imaged with confocal microscope allowed localization of Ano1 and vimentin immunopositive cells. The effects of CaCC blockers: niflumic acid (NFA) (3,10,30 µM) and 5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) (10, 30 µM) on spontaneous phasic contractile activity of intact (with mucosa) and denuded (without mucosa) detrusor strips were measured under isometric tension in organ baths (n = 141, N = 60).

Results

Ano1 expression was found at mRNA level in mucosa and detrusor layers. Confocal microscopy revealed presence of Ano1 immunopositive cells in mucosa and in detrusor layers; a subpopulation of vimentin positive cells expressed Ano1. Both chloride channel blockers reduced the amplitude and frequency of phasic contractions in denuded and intact strips.

Conclusions

Ano1 is expressed in rat urinary bladder and is present in cells sharing markers with interstitial cells. CaCC blockers reduced phasic activity of the bladder tissue. Ano1 is expressed in the bladder and plays a role in its spontaneous phasic contractile activity.

Diabetes attenuates urothelial modulation of detrusor contractility and spontaneous activity

OBJECTIVES

To investigate the effect of diabetes on urothelial modulation of bladder contractility.

METHODS

Bladder strips (urothelium intact or denuded) were prepared from 8-week-old streptozotocin-induced diabetic (n = 19) and non-diabetic control rats (n = 10). The effect of modulators of MaxiK (iberiotoxin and tetraethylammonium) and Kv7 (XE991 and retigabine) potassium channel activity were investigated for their effects on both carbachol-induced force generation and spontaneous contractile activity.

RESULTS

In bladder strips from non-diabetic animals, the presence of the urothelium resulted in marked sensitivity to carbachol-induced force generation by modulators of MaxiK and Kv7 channel activity, whereas in the diabetic animal urothelial sensitivity to these agents was significantly diminished. Urothelial-intact bladder strips from non-diabetic animals were more sensitive to modulators of Kv7 activity in reducing the amplitude of spontaneous phasic contractions than urothelial-denuded bladder strips, whereas in diabetic animals the presence or absence of the urothelium did not alter the sensitivity to modulators of Kv7 activity. Spontaneous activity in the presence of tetraethylammonium was not affected by the urothelium in bladder strips from either diabetic or non-diabetic animals.

CONCLUSIONS

The presence of the urothelium in bladders from non-diabetic animals modulates the activity of potassium blockers to affect bladder contractility, whereas in the diabetic bladder this effect is attenuated. These findings could help to explain the lack of success of pharmaceutical treatments targeting potassium channels to treat bladder pathology in patients with diseases imparing urothelial function.

Cajal-like interstitial cells as a novel target in detrusor overactivity treatment: true or myth?

Introduction

The Cajal–like intestitial cells (ICCs) act as a pacemaker and are responsible for generating smooth muscle activity in the gastrointestinal tract (GI). Interstitial cells that resemble ICCs in the GI have been identified in the urinary bladder.

Materials and methods

This review is based on a systemic literature research. The medline/pubmed, scopus, embase, and Web of Science databases were browsed in order to identify original and review articles, as well as editorials relating to cajal–like cells, urinary bladder, detrusor overactivity, overactive bladder, glivec, etc. The controlled vocabulary of the Medical Subject Headings (MeSH) database was used to ensure the sensitivity of the searches. 40 papers met the criteria and were used for this review.

Results

Cajal cells lie in close proximity to the muscle cells, autonomic nerve endings, and urothelial cells. There is increasing evidence that ICCs play role in urinary tract dysfunction development (e.g. detrusor overactivity, primary obstructive megaureter, congenital ureteropelvic junction obstruction, etc.). ICCs may be responsible for generating electrical potentials and induction of detrusor muscle contractions. Novel pathomechanisms of detrusor overactivity development have been postulated, as follows: 1) the disturbance of spontaneous contractility caused by altered signal transduction of ICCs between nerves and detrusor muscle cells, and 2). the alteration in signal transduction between urothelium and afferent nerve endings via suburothelial ICCs. The c–kit receptor is not only a detection marker of these cells, but may also play a crucial role in the control of bladder function.

Conclusions

Cajal cells in urinary bladder suggest that the c–kit receptor may provide a novel target for treating detrusor overactivity. The review presents the current knowledge of ICCs, its role in urinary bladder function, and potential novel therapeutic strategy.

Spontaneous electrical activity of cultured interstitial cells of cajal from mouse urinary bladder

Interstitial cells of Cajal (ICCs) from the urinary bladder regulate detrusor smooth muscle activities. We cultured ICCs from the urinary bladder of mice and performed patch clamp and intracellular Ca²⁺ ([Ca²⁺]_i) imaging to investigate whether cultured ICCs can be a valuable tool for cellular functional studies. The cultured ICCs displayed two types of spontaneous electrical activities which are similar to those recorded in intact bladder tissues. Spontaneous electrical activities of cultured ICCs were nifedipine-sensitive. Carbachol and ATP, both excitatory neurotransmitters in the urinary bladder, depolarized the membrane and increased the frequency of spike potentials. Carbachol increased [Ca²⁺]_i oscillations and basal Ca²⁺ levels, which were blocked by atropine. These results suggest that cultured ICCs from the urinary bladder retain rhythmic phenotypes similar to the spontaneous electrical activities recorded from the intact urinary bladder. Therefore, we suggest that cultured ICCs from the urinary bladder may be useful for cellular and molecular studies of ICCs.

Phasic contractions in urinary bladder from juvenile versus adult pigs

Aims

Alterations in properties of the bladder with maturation are relevant physiologically and pathophysiologically. The aim of this study was to investigate alterations in bladder properties with maturation in juvenile vs. adult pig, focussing on differences between layers of the bladder wall (mucosa vs. detrusor) and the presence and functional contribution of interstitial cells (ICs).

Methods

Basal and cholinergic-induced phasic contractions (PCs) in mucosal and denuded-detrusor strips from juvenile and adult pigs were assessed. Expression of c-kit, a marker of ICs, was investigated in the mucosa and the detrusor layers of the pig bladder. The functional role of ICs in mediating PCs was examined using imatinib.

Results

Mucosal strips from juvenile and adult pig bladders demonstrated basal PCs whilst denuded-detrusor strips did not. PCs of mucosal strips from juvenile pigs were significantly greater than those from adult bladders. Immunoreactivity for c-kit was detected in mucosa and detrusor layers of pig bladder. Histological studies demonstrated a distinct layer of smooth muscle between the urothelium and bladder detrusor, termed the muscularis mucosa. Imatinib was only effective in inhibiting PCs in mucosal strips from juvenile pigs. Imatinib inhibited the carbachol-induced PCs of both juvenile and adult denuded-detrusor strips, although strips from juvenile bladders demonstrated a trend towards being more sensitive to this inhibition.

Conclusions

We confirm the presence of c-kit positive ICs in pig urinary bladder. The enhanced PCs of mucosal strips from juvenile animals could be due to altered properties of ICs or the muscularis mucosa in the bladders of these animals.

Bladder interstitial cells: an updated review of current knowledge

The field of bladder research has been energized by the study of novel interstitial cells (IC) over the last decade. Several subgroups of IC are located within the bladder wall and make structural interactions with nerves and smooth muscle, indicating integration with intercellular communication and key physiological functions. Significant progress has been made in the study of bladder ICs' cellular markers, ion channels and receptor expression, electrical and calcium signalling, yet their specific functions in normal bladder filling and emptying remain elusive. There is increasing evidence that the distribution of IC is altered in bladder pathophysiologies suggesting that changes in IC may be linked with the development of bladder dysfunction. This article summarizes the current state of the art of our knowledge of IC in normal bladder and reviews the literature on IC in dysfunctional bladder.

Cellular expression profile for interstitial cells of cajal in bladder - a cell often misidentified as myocyte or myofibroblast

BACKGROUND

Interstitial cells of Cajal (ICC) have been identified in urinary bladder of several species, but their presence in mice remains uncertain. Meanwhile, dozens of reports indicate that dysregulation of connexin 43 plays an important role in bladder overactivity, but its localization has not been clearly defined, with reports of expression in either the smooth muscle or in myofibroblasts. We recently identified a population of ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) positive cells that resemble ICC and are distinct from smooth muscle, fibroblasts, myofibroblasts and neurons. Thus we sought to define more clearly the molecular signature of ICC and in doing so resolve some of these uncertainties.

PRINCIPLE FINDINGS

Immunofluorescent localization revealed that NTPDase2-positive cells lie closely adjacent to smooth muscle but are separate from them. NTPDase2 positive cells exhibited co-localization with the widely accepted ICC marker - c-kit. They were further shown to co-localize with other ICC markers CD34 and Ano1, but not with mast cell marker tryptase. Significantly, they show convincing co-localization with connexin 43, which was not present in smooth muscle. The identity of these cells as ICC was further confirmed by the presence of three mesenchymal markers - vimentin, desmin, and PDGFβ receptor, which indicates their mesenchymal origin. Finally, we observed for the first time, the presence of merlin/neurofibromin 2 in ICC. Normally considered a neuronal protein, the presence of merlin suggests ICC in bladder may have a role in neurotransmission.

CONCLUSIONS

NTPDase2 positive cells in mice bladder are ICC, which can be defined by the presence of c-Kit, CD34, Ano1, NTPDase2, connexin 43, vimentin, desmin, PDGFβ receptor and merlin/NF2. These data establish a definitive molecular expression profile, which can be used to assist in explorations of their functional roles, and the presence of NTPDase2 suggests that purinergic signaling plays a role in regulation of ICC function.

Identification of T-type calcium channels in the interstitial cells of Cajal in rat bladder

OBJECTIVE

To investigate the expression and function of T-type calcium channels in the interstitial cells of Cajal in rat bladders.

METHODS

Bladders were harvested from Sprague-Dawley rats. The expression of T-type calcium channels subtypes (α1G, α1H, and α1I) in interstitial cells of Cajal were identified by double-labeled immunofluorescence analysis and reverse transcription-polymerase chain reaction analysis in whole mount preparations of rat bladders. The function of T-type calcium channels in freshly isolated interstitial cells of Cajal was assessed by detecting the changes of intracellular calcium ([Ca(2+)](i)) with preloading fluo-3 AM, and by evaluating the changes of the phasic contractions of rat bladder strips after treating with mibefradil and glivec.

RESULTS

Three T-type calcium channels subtypes, α1G, α1H, and α1I, colocalized with c-kit in bladder interstitial cells of Cajal by double-labeled immunofluorescence analysis, and this was confirmed using reverse transcription-polymerase chain reaction. The T-type calcium channels selective blocker, mibefradil (1 μM), significantly decreased the intracellular calcium concentration ([Ca(2+)](i)) in isolated interstitial cells of Cajal (P < .01) and inhibited the spontaneous phasic contraction of bladder strips (P < .01). Moreover, the c-kit receptor blocker, glivec, significantly decreased the [Ca(2+)](i) of interstitial cells of Cajal further (P < .01) and the spontaneous phasic contraction of bladder strips.

CONCLUSION

T-type calcium channel subtypes were confirmed to colocalize in interstitial cells of Cajal in rats bladders, which might participate in the spontaneous activity of interstitial cells of Cajal and phasic contractions of bladder strips by modulating [Ca(2+)](i) in interstitial cells of Cajal.

Identification of PDGFRα positive populations of interstitial cells in human and guinea pig bladders

PURPOSE

The bladder wall comprises a complex array of cells, including urothelium, smooth muscle, nerves and interstitial cells. Interstitial cells have several subtypes based on site, morphology and differential expression of markers such as anti-vimentin and anti-KIT. We examined whether a subpopulation of interstitial cells immunopositive for PDGFRα exists in human and guinea pig bladders.

MATERIALS AND METHODS

Human and guinea pig bladder tissues were processed for immunohistochemistry and examined by bright field or confocal microscopy. Whole mount tissues and paraffin sections were labeled with antibodies to PDGFRα, vimentin, KIT and PGP9.5. Protein expression was assessed by Western blot.

RESULTS

PDGFRα(+) cells were present in human and guinea pig bladders. In the guinea pig PDGFRα(+) cells had a branched stellate morphology and formed networks in the lamina propria. In human and guinea pig detrusors PDGFRα(+) cells were elongated on the boundary of smooth muscle bundles or were seen as groups of stellate cells in the interbundle spaces. PDGFRα(+) cells were located close to nerves labeled by PGP9.5. Double labeling revealed that PDGFRα(+) cells were a subgroup of the vimentin(+) population. A significant proportion of PDGFRα(+) cells were also KIT(+). Bands corresponding to PDGFRα, KIT and vimentin proteins were detected on Western blot.

CONCLUSIONS

To our knowledge this study is the first to identify PDGFRα(+)/KIT(+) cells in the bladder lamina propria and detrusor layers. These cells are a subgroup of the vimentin(+) population, showing the complexity of bladder interstitial cells. PDGFRα(+) cells are apparently structurally associated with intramural nerves, indicating integration with bladder control mechanisms.

The effects of the c-kit blocker glivec on the contractile response of urinary bladder

OBJECTIVES

To investigate the effects of imatinib (Glivec) on the urinary bladder contraction and excitation induced by neurostimulation, therefore to clarify the relationships between the bladder interstitial cell of Cajal (ICC) and the neural signals.

METHODS

In in vivo experiments, pelvic nerves of rats were stimulated by square-wave pulses. The contractile response was recorded before and 40 min after the administration of medications (atropine, Glivec, and ketotifen). In in vitro experiments, the bladder contractile response induced by acetylcholine with or without Glivec was evaluated. The space relationship between ICC and neural fibers were observed with double-labeled fluorescence using primary antibodies (anti-c-kit and anti-vesicular acetylcholine transferase) and secondary fluorescent antibodies (Alexa 488 and Alexa 594; Molecular Probes, Eugene, OR).

RESULTS

Atropine and Glivec could significantly inhibit the bladder contractile response induced by the electrical stimulation in a dose-dependent manner, while ketotifen did not obviously affect bladder contractile response. In in vitro experiments, Glivec did not affect acetylcholine-induced bladder contractile response. The location of ICC in close proximity to cholinergic nerve fibers was confirmed by double-labeled fluorescence.

CONCLUSIONS

Bladder ICC play an important role as intermediaries in the transmission of cholinergic signals from nerve to smooth muscle cells.

Role of KIT-Positive Interstitial Cells of Cajal in the Urinary Bladder and Possible Therapeutic Target for Overactive Bladder

In the gastrointestinal tract, interstitial cells of Cajal (ICCs) act as pacemaker cells to generate slow wave activity. Interstitial cells that resemble ICCs in the gastrointestinal tract have been identified by their morphological characteristics in the bladder. KIT is used as an identification marker of ICCs. ICCs in the bladder may be involved in signal transmission between smooth muscle bundles, from efferent nerves to smooth muscles, and from the urothelium to afferent nerves. Recent research has suggested that not only the disturbance of spontaneous contractility caused by altered detrusor ICC signal transduction between nerves and smooth muscle cells but also the disturbance of signal transduction between urothelial cells and sensory nerves via suburothelial ICC may induce overactive bladder (OAB). Recent reports have suggested that KIT is not only a detection marker of these cells, but also may play a crucial role in the control of bladder function. Research into the effect of a c-kit receptor inhibitor, imatinib mesylate, on bladder function implies that KIT-positive ICCs may be therapeutic target cells to reduce bladder overactivity and that the blockage of c-kit receptor may offer a new therapeutic strategy for OAB treatment, although further study will be needed.