Changes of gap junctional cell-cell communication in overactive detrusor in rats

Novel phenotype characterization utilizing electrical impedance myography signatures in murine spinal cord injury neurogenic bladder models

Neurogenic bladder (NB) affects people of all ages. Electric impedance myography (EIM) assesses localized muscle abnormalities. Here, we sought to investigate whether unique detrusor EIM signatures are present in NB due to spinal cord injury (SCI). Twenty-eight, 8-10 weeks old, C57BL/6J female mice were studied. Twenty underwent spinal cord transection; 8 served as controls. Cohorts were euthanized at 4 and 6 weeks after spinal cord transection. Each bladder was measured in-situ with EIM with applied frequencies of 1 kHz to 10 MHz, and then processed for molecular and histologic study. SCI mice had greater bladder-to-body weight ratio (p < 0.0001), greater collagen deposition (p = 0.009), and greater smooth-muscle-myosin-heavy-chain isoform A/B ratio (p < 0.0001). Compared with the control group, the SCI group was associated with lower phase, reactance, and resistance values (p < 0.01). Significant correlations (p < 0.001) between bladder-to-body weight ratios and EIM measurements were observed across the entire frequency spectrum. A severely hypertrophied phenotype was characterized by even greater bladder-to-body weight ratios and more depressed EIM values. Our study demonstrated distinct EIM alterations in the detrusor muscle of mice with NB due to SCI. With further refinement, EIM may offer a potential point-of-care tool for the assessment of NB and its response to treatment.

Increased transient receptor potential canonical 3 activity is involved in the pathogenesis of detrusor overactivity by dynamic interaction with Na+/Ca2+ exchanger 1

Transient receptor potential canonical 3 (TRPC3) is a nonselective cation channel, and its dysfunction is the basis of many clinical diseases. However, little is known about its possible role in the bladder. The purpose of this study was to explore the function and mechanism of TRPC3 in partial bladder outlet obstruction (PBOO)-induced detrusor overactivity (DO). We studied 31 adult female rats with DO induced by PBOO (the DO group) and 40 sham-operated rats (the control group). Here we report that the expression of TRPC3 in the bladder of DO rats increased significantly. Furthermore, PYR10, which can selectively inhibit the TRPC3 channel, significantly reduced bladder excitability in DO and control rats, but the decrease of the bladder excitability of DO rats was more obvious. PYR10 significantly reduced the intracellular calcium concentration in smooth muscle cells (SMCs) in DO and control rats. Finally, Na+/Ca2+ exchanger 1 (NCX1) colocalizes with TRPC3 and affects its expression and function. Collectively, these results indicate that TRPC3 plays an important role in the pathogenesis of DO through a synergistic effect with NCX1. TRPC3 and NCX1 may be new therapeutic targets for DO.

Electrophysiology of Syncytial Smooth Muscle

As in other excitable tissues, two classes of electrical signals are of fundamental importance to the functioning of smooth muscles: junction potentials, which arise from neurotransmission and represent the initiation of excitation (or in some instances inhibition) of the tissue, and spikes or action potentials, which represent the accomplishment of excitation and lead on to contractile activity. Unlike the case in skeletal muscle and in neurons, junction potentials and spikes in smooth muscle have been poorly understood in relation to the electrical properties of the tissue and in terms of their spatiotemporal spread within it. This owes principally to the experimental difficulties involved in making precise electrical recordings from smooth muscles and also to two inherent features of this class of muscle, ie, the syncytial organization of its cells and the distributed innervation they receive, which renders their biophysical analysis problematic. In this review, we outline the development of hypotheses and knowledge on junction potentials and spikes in syncytial smooth muscle, showing how our concepts have frequently undergone radical changes and how recent developments hold promise in unraveling some of the many puzzles that remain. We focus especially on computational models and signal analysis approaches. We take as illustrative examples the smooth muscles of two organs with distinct functional characteristics, the vas deferens and urinary bladder, while also touching on features of electrical functioning in the smooth muscles of other organs.

TGF-β1 and connexin-43 expression in neurogenic bladder from rats with sacral spinal cord injury

AIMS

Sacral spinal cord injury (SCI) could induce underactive bladder (UAB). Malfunction of connexin 43 (CX43) regulated by TGF-β1 might involve in urinary bladder dysfunction. We studied the changes of CX43 and TGF-β1/Smad3 signaling in detrusor of neurogenic bladder (NB) in sacral SCI rats.

METHODS

Sacral SCI was produced by hemisection (SSCH) or transection (SSCT) of spinal cord between L4 and L5 in female Wistar rats. BBB scores, residual urine volume and bladder weight as well as characteristic cystometric parameters at 6th week were used to confirm the successful establishment of NB. Western blotting and qRT-PCR were used to exam the protein and mRNA expression levels of CX43, CX45, TGF-β1, and Smad3 in detrusor.

RESULTS

BBB scores were significantly decreased, with the lowest in SSCT rats (P < 0.01). The residual urine volume, mean bladder weight, and cystometric parameters were increased, with the highest in SSCT rats. CX43 and phospho-CX43 protein levels were significantly decreased, but those of TGF-β1, Smad3, and phospho-Smad3 were significantly increased. It was the protein and mRNA levels of CX43 but not those of CX45 which were decreased in negative accordance with those of TGF-β1 and Smad3. Those changes were more significant in SSCT than in SSCH rats.

CONCLUSIONS

This study indicates that voiding dysfunction is related to the decreased CX43 function in detrusor from NB. TGF-β1/Smad3 signaling might be involved in the down-regulation of CX43 in SCI rats. Early regulation of CX43 might be beneficial to patients with voiding dysfunction.

Original Research: Combined model of bladder detrusor smooth muscle and interstitial cells

Although patients with lower urinary tract symptoms constitute a large and still growing population, understanding of bladder detrusor muscle physiology remains limited. Understanding the interactions between the detrusor smooth muscle cells and other bladder cell types (e.g. interstitial cells, IC) that may significantly contribute to coordinating and modulating detrusor contractions represents a considerable challenge. Computer modeling could help to elucidate some properties that are difficult to address experimentally; therefore, we developed in silico models of detrusor smooth muscle cell and interstitial cells, coupled through gap junctions. The models include all of the major ion conductances and transporters described in smooth muscle cell and interstitial cells in the literature. The model of normal detrusor muscle (smooth muscle cell and interstitial cells coupled through gap junctions) completely reproduced the experimental results obtained with detrusor strips in the presence of several pharmacological interventions (ryanodine, caffeine, nimodipine), whereas the model of smooth muscle cell alone (without interstitial cells) failed to reproduce the experimental results. Next, a model of overactive bladder, a highly prevalent clinical condition in both men and women with increasing incidence at older ages, was produced by modifying several processes as reported previously: a reduction of Ca(2+)-release through ryanodine receptors and a reduction of Ca(2+)-dependent K(+)-conductance with augmented gap junctional coupling. This model was also able to reproduce the pharmacological modulation of overactive bladder. In conclusion, a model of bladder detrusor muscle was developed that reproduced experimental results obtained in both normal and overactive bladder preparations. The results indicate that the non-smooth muscle cells of the detrusor (interstitial cells) contribute significantly to the contractile behavior of bladder detrusor muscle and should not be neglected. The model suggests that reduced Ca(2+)-release through ryanodine receptors and Ca(2+)-dependent K(+)-conductance together with augmented gap junctional coupling might play a major role in overactive bladder pathogenesis.

Structural and functional changes in gap junctional intercellular communication in a rat model of overactive bladder syndrome induced by partial bladder outlet obstruction

The aim of the present study was to investigate the association between connexin (Cx)43 levels and alterations in gap junctional mediation of intercellular communication in overactive bladder syndrome (OAB), and to examine the effects of connexin inhibitor on this condition. Adult female Wistar rats with OAB following partial bladder outlet obstruction (PBBO) (OAB group, n=37) and sham-operated rats (control group, n=17) were studied. The ultrastructure of the rat detrusor was observed by transmission electron microscopy and the protein expression levels of Cx43 were analyzed using western blot analysis. Furthermore, bladder detrusor cells in both groups were cultured and cells in the OAB group were randomly divided into ten groups. In nine of these groups, 18-β glycyrrhetinic acid (18β-GA) was administered at various doses and durations. All groups were compared using fluorescence redistribution after photobleaching and a laser scanning confocal microscope. Cystometry demonstrated that gap junctions were an abundant mechanism among adjacent cells, and Cx43 protein expression levels were increased in the OAB group following 6 weeks of obstruction, as compared with the control group. Mean fluorescence recovery rates in the OAB group were significantly increased, as compared with the control group (P<0.01). Mean fluorescence recovery rates were noted following 18β-GA administration. These results suggested that upregulation of Cx43 induces structural and functional alterations in gap junctional intercellular communication following PBOO, and connexin inhibitors may be a novel therapeutic strategy for the clinical treatment of OAB.

Gap junction blockage promotes cadmium-induced apoptosis in BRL 3A derived from Buffalo rat liver cells

Gap junctions mediate direct communication between cells; however, toxicological cascade triggered by nonessential metals can abrogate cellular signaling mediated by gap junctions. Although cadmium (Cd) is known to induce apoptosis in organs and tissues, the mechanisms that underlie gap junction activity in Cd-induced apoptosis in BRL 3A rat liver cells has yet to be established. In this study, we showed that Cd treatment decreased the cell index (a measure of cellular electrical impedance) in BRL 3A cells. Mechanistically, we found that Cd exposure decreased expression of connexin 43 (Cx43), increased expression of p-Cx43 and elevated intracellular free Ca²⁺ concentration, corresponding to a decrease in gap junctional intercellular communication. Gap junction blockage pretreatment with 18β-glycyrrhizic acid (GA) promoted Cd-induced apoptosis, involving changes in expression of Bax, Bcl-2, caspase-3 and the mitochondrial transmembrane electrical potential (Δψm). Additionally, GA was found to enhance ERK and p38 activation during Cd-induced activation of mitogen-activated protein kinases, but had no significant effect on JNK activation. Our results indicated the apoptosis-related proteins and the ERK and p38 signaling pathways may participate in gap junction blockage promoting Cd-induced apoptosis in BRL 3A cells.

The c-Jun N-terminal kinase (JNK) pathway is activated in human interstitial cystitis (IC) and rat protamine sulfate induced cystitis

The pathogenesis of bladder pain syndrome/interstitial cystitis (BPS/IC) is currently unclear. However, inflammation has been suggested to play an important role in BPS/IC. JNK downstream signaling plays an important role in numerous chronic inflammatory diseases. However, studies of the JNK pathway in BPS/IC are limited. In this study, we investigated the role of the JNK pathway in human BPS/IC and rat protamine sulfate (PS)-induced cystitis and examined the effect of the selective JNK inhibitor SP600125 on rat bladder cystitis. In our study, we demonstrated that the JNK signaling pathway was activated (the expression of JNK, c-Jun, p-JNK, p-c-Jun, IL-6 and TNF-α were significantly increasing in BPS/IC compared to the non-BPS/IC patients) and resulted in inflammation in human BPS/IC. Further animal models showed that the JNK pathway played an important role in the pathogenesis of cystitis. JNK inhibitors, SP600125, effectively inhibited the expression of p-JNK, p-c-Jun, IL-6 and TNF-α. The inhibition of these pathways had a protective effect on PS-induced rat cystitis by significantly decreasing histological score and mast cell count and improving bladder micturition function (micturition frequency significantly decreasing and bladder capacity significantly increasing). Therefore, JNK inhibition could be used as a potential treatment for BPS/IC.

AMPK Suppresses Connexin43 Expression in the Bladder and Ameliorates Voiding Dysfunction in Cyclophosphamide-induced Mouse Cystitis

Bladder voiding dysfunction is closely related to local oxidation, inflammation, and enhanced channel activities. Given that the AMP-activated protein kinase (AMPK) has anti-oxidative, anti-inflammatory and channel-inhibiting properties, we examined whether and how AMPK affected bladder activity. AMPK activation in rat bladder smooth muscle cells (BSMCs) using three different AMPK agonists resulted in a decrease in connexin43 (Cx43) expression and function, which was associated with reduced CREB phosphorylation, Cx43 promoter activity and mRNA expression, but not Cx43 degradation. Downregulation of CREB with siRNA increased Cx43 expression. A functional analysis revealed that AMPK weakened BSMC contraction and bladder capacity. AMPK also counteracted the IL-1β- and TNFα-induced increase in Cx43 in BSMCs. In vivo administration of the AMPK agonist AICAR attenuated cyclophosphamide-initiated bladder oxidation, inflammation, Cx43 expression and voiding dysfunction. Further analysis comparing the responses of the wild-type (Cx43(+/+)) and heterozygous (Cx43(+/-)) Cx43 mice to cyclophosphamide revealed that the Cx43(+/-) mice retained a relatively normal micturition pattern compared to the Cx43(+/+) mice. Taken together, our results indicate that AMPK inhibits Cx43 in BSMCs and improves bladder activity under pathological conditions. We propose that strategies that target AMPK can be developed as novel therapeutic approaches for treating bladder dysfunction.

Spontaneous Contractile Activity of the Detrusor Muscle and Its Role in the Pathogenesis of Overactive Bladder Syndrome

There is accumulated evidence that spontaneous contractions (SCs) in the bladder wall are associated with afferent nerve firing in the bladder. The role of the urothelium in bladder sensation might be restricted to pathological conditions, such as interstitial cystitis or chemical cystitis in which the release of urothelium-derived mediators such as adenosine triphosphate is increased. Recent publications imply that SCs in bladders with detrusor overactivity due to spinal cord injury or bladder outlet obstruction are modulated by intracellular signal transduction mechanisms such as the RhoA/Rho-kinase pathway, denervation-supersensitivity to acetylcholine, changes in ion channel activity, enhanced gap-junctional intercellular communication, alterations in interstitial cells of Cajal, the actions of local mediators in the detrusor and the influence of the urothelium. Spontaneous contractions and possible consequent afferent nerve firing might participate in the generation of overactive bladder syndrome.

Enhanced expression of TWIK-related arachidonic acid-activated K+ channel in the spinal cord of detrusor overactivity rats after partial bladder outlet obstruction

Background

Detrusor overactivity (DO) secondary to partial bladder outlet obstruction (PBOO) is closely associated with alteration of ion channels. The objective of this study is to investigate the expression of the TWIK-related arachidonic acid-activated K⁺ channel (TRAAK) in the L6-S1 spinal cord of DO rats after PBOO.

Methods

Female Sprague–Dawley rats undergoing PBOO surgery were screened for DO by cystometry. Sham-operated rats served as controls. The expression of TRAAK in the L6-S1 spinal cord was detected by real-time polymerase chain reaction, western blotting and immunohistochemistry.

Results

DO was successfully induced after chronic PBOO in rats, with an incidence rate of 62.5 %. Compared with sham-operated rats, the expression of TRAAK in the L6-S1 spinal cord of DO rats was significantly increased at the mRNA (1.886 ± 0.710 versus 0.790 ± 0.679, P < 0.05) and protein level (0.510 ± 0.087 versus 0.255 ± 0.107, P < 0.05). Immunohistochemical staining showed increased expression of TRAAK in the dorsal horn and ventral horn of the spinal cord.

Conclusions

Upregulation of TRAAK was observed in the spinal cord of DO rats after chronic PBOO, which may exert a protective effect against DO by suppressing the excitability of neurons.

[Physiopathology of overactive bladder syndrome]

The pathophysiology of OAB is complex, multifactorial and still largely unknown. Several pathophysiological mechanisms have been highlighted that may play a different role in different patient groups. There are now experimental evidences that support both the myogenic and neurogenic hypothesis, but in recent years the "integrative" hypothesis has been gaining more and more acceptance, where a disruption in the multiple interactions between different cell types (neurons, urothelium, interstitial cells, myocytes) and network functions represent a central element of lower urinary tract dysfunctions. Of utmost importance, a disorder in the urothelial sensory function and in the urothelial/suburothelial non-neural cholinergic system, favored by age and comorbidities, appears to be crucial for the development of the OAB. Neuroplastic and detrusor changes in OAB are broadly similar to those observed in bladders exposed to outlet obstruction, neuropathies, inflammation or aging, and may be driven by a common urothelial dysfunction. Several signaling substances and their receptors were found to be involved in central pathways of bidirectional communication between the different cell types in the bladder, and were shown to be modified in several animal models of OAB as well as in human models, indicating new potential therapeutic targets.

Detrusor myocyte autophagy protects the bladder function via inhibiting the inflammation in cyclophosphamide-induced cystitis in rats

Autophagy, a highly conserved homeostatic cellular process that removes and recycles damaged proteins and organelles in response to cellular stress, is believed to play a crucial role in the immune response and inflammation. The role of autophagy in bladder cystitis, however, has not well been clarified. Here we investigate the role of detrusor myocytes autophagy (DMA) in cyclophosphamide-induced cystitis animal model. 164 female Sprague-Dawley rats were randomized into three experimental groups and compared to three control groups, respectively. The expressions of microtubule-associated protein 1 light chain 3 (LC3), p-p70s6k (the phosphorylated form of ribosomal protein S6), SOD2 (superoxide dismutase 2) in the bladder muscular layer were measured using western blot. The co-location of LC3, alpha-smooth muscle actin (α-SMA), and autophagic vacuoles were investigated with double-labeled immunofluorescence and transmission electron microscopy (TEM). The expression of lL-1β, IL-6, IL-8, malondialdehyde (MDA), and glutathione (GSH) in the detrusor layer were analyzed using ELISA. The bladder inflammation and the number of mast cells in the muscular layer were analyzed by histology. The bladder function was evaluated using cystometry. In cyclophosphamide-induced cystitis, autophagy was detected in detrusor myocytes by increased LC3, p-p70s6k expression, and autophagosomes. However, the presence of enhanced inflammation and oxidative stress in the cyclophosphamide-treated group suggest autophagy of detrusor myocytes may not be sufficiently activated. Inflammation and oxidative stress were significantly decreased and the bladder histology and micturition function were significantly improved with rapamycin (RAPA, autophagy agonist) pre-treatment. In contrast, inflammation and oxidative stress were dramatically increased and the bladder histology and function were negatively affected with chloroquine (CQ, autophagy blocker) pre-treated. These findings preferentially provide evidence of the association between DMA and cyclophosphamide-induced cystitis in rats. The autophagy agonist RAPA significantly decreased the inflammation and protected the bladder function, which might be considered as a potential treatment for interstitial cystitis.

Altered detrusor gap junction communications induce storage symptoms in bladder inflammation: a mouse cyclophosphamide-induced model of cystitis

Lower urinary tract symptoms (LUTS) include storage, voiding and post-micturition symptoms, featuring many urological diseases. Storage symptoms are the most frequent among these and associated with overactive bladder and non-bacterial bladder inflammation such as interstitial cystitis/bladder pain syndrome (IC/BPS). Gap junction, a key regulator of hyperactive conditions in the bladder, has been reported to be involved in pathological bladder inflammation. Here we report involvement of gap junction in the etiology of storage symptoms in bladder inflammation. In this study, cyclophosphamide-induced cystitis was adapted as a model of bladder inflammation. Cyclophosphamide-treated mice showed typical storage symptoms including increased urinary frequency and reduced bladder capacity, with concurrent up-regulation of connexin 43 (GJA1), one of the major gap junction proteins in the bladder. In isometric tension study, bladder smooth muscle strips taken from the treated mice showed more pronounced spontaneous contraction than controls, which was attenuated by carbenoxolone, a gap junction inhibitor. In voiding behavior studies, the storage symptoms in the treated mice characterized by frequent voiding were alleviated by 18α-glycyrrhetinic acid, another gap junction inhibitor. These results demonstrate that cyclophosphamide-induced mouse model of cystitis shows clinical storage symptoms related with bladder inflammation and that gap junction in the bladder may be a key molecule of these storage symptoms. Therefore, gap junction in the bladder might be an alternative therapeutic target for storage symptoms in bladder inflammation.

Changes in store-operated calcium channels in rat bladders with detrusor overactivity

OBJECTIVE

To investigate the regulation of intracellular store-operated calcium channels (SOCCs) in detrusor overactivity (DO) during detrusor function changes in Sprague-Dawley rats.

METHODS

Sixty female Sprague-Dawley rats were randomized into control and DO groups. The contraction of the smooth muscle of the bladder was evaluated in vivo using smooth muscle strips. Changes in intracellular calcium ions were observed using confocal microscopy with preload fluo-4 AM, the SOCC agonist cyclopiazonic acid (CPA; 10 μM) and inhibitor SKF-96365 (10 μM). Cell currents were recorded with the whole-cell patch-clamp technique.

RESULTS

The in vitro frequencies of bladder smooth muscle contraction were significantly different (P <.05) between the DO and control groups, and the amplitudes were not significantly different (P >.05). The changes in intracellular calcium ions and current density were significantly different between the 2 groups (P <.05).

CONCLUSION

SOCCs were involved in DO and caused variations in muscle contraction.

Myogenic bladder defects in mouse models of human oculodentodigital dysplasia

To date, over 65 mutations in the gene encoding Cx43 (connexin43) have been linked to the autosomal-dominant disease ODDD (oculodentodigital dysplasia). A subset of these patients experience bladder incontinence which could be due to underlying neurogenic deterioration or aberrant myogenic regulation. BSMCs (bladder smooth muscle cells) from wild-type and two Cx43 mutant lines (Cx43(G60S) and Cx43(I130T)) that mimic ODDD exhibit a significant reduction in total Cx43. Dye transfer studies revealed that the G60S mutant was a potent dominant-negative inhibitor of co-expressed Cx43, a property not equally shared by the I130T mutant. BSMCs from both mutant mouse strains were defective in their ability to contract, which is indicative of phenotype changes due to harbouring the Cx43 mutants. Upon stretching, Cx43 levels were significantly elevated in controls and mutants containing BSMCs, but the non-muscle myosin heavy chain A levels were only reduced in cells from control mice. Although the Cx43(G60S) mutant mice showed no difference in voided urine volume or frequency, the Cx43(I130T) mice voided less frequently. Thus, similar to the diversity of morbidities seen in ODDD patients, genetically modified mice also display mutation-specific changes in bladder function. Furthermore, although mutant mice have compromised smooth muscle contraction and response to stretch, overriding bladder defects in Cx43(I130T) mice are likely to be complemented by neurogenic changes.

Changes in the function and expression of T-type and N-type calcium channels in the rat bladder after bladder outlet obstruction

PURPOSE

We evaluated possible changes in the function and expression of T-type and N-type Ca(2+) channels in the bladder of rats with bladder outlet obstruction.

MATERIALS AND METHODS

Female Sprague Dawley® rats were divided into a group with bladder outlet obstruction created by partial urethral ligation and a sham operated group. Six weeks postoperatively we determined the mRNA expression of T-type and N-type Ca(2+) channels in the bladder, dorsal root ganglion and spinal cord. We also cystometrically investigated expression by intravenous administration of the T-Ca blocker RQ-00311610 or the N-type Ca(2+) channel blocker ω-conotoxin GVIA. We then performed in vitro functional studies of detrusor strips using these blockers.

RESULTS

mRNA expression of T-type Ca(2+) channels in the bladder detrusor and mucosa layers, and the spinal cord dorsal horn, and N-type Ca(2+) channels in the whole bladder and detrusor layer, and the spinal cord dorsal horn was greater in the obstructed group than the sham operated group. In obstructed rats bladder capacity and voided volume increased after RQ-00311610 administration but the number of nonvoiding contractions decreased after ω-conotoxin GVIA administration. Detrusor strips from obstructed rats showed weaker contractile responses to electrical field stimulation, particularly in regard to the purinergic component. ω-Conotoxin GVIA suppressed electrical field stimulation induced contractions only in the detrusor of obstructed rats, especially the cholinergic component.

CONCLUSIONS

Blocking T-type Ca(2+) channels increased bladder capacity while N-type Ca(2+) channel blockade inhibited nonvoiding contractions in rats with bladder outlet obstruction. Decreased bladder efferent neurotransmission occurred after bladder outlet obstruction, predominantly in its purinergic component and detrusor contractions via cholinergic neurotransmission were activated in a compensatory manner, probably via N-type Ca(2+) channel up-regulation.

Myocardin and microRNA-1 modulate bladder activity through connexin 43 expression during post-natal development

Overactive bladder (OAB) is a pervasive clinical problem involving alterations in both neurogenic and myogenic activity. While there has been some progress in understanding neurogenic inputs to OAB, the mechanisms controlling myogenic bladder activity are unclear. We report the involvement of myocardin (MYOCD) and microRNA-1 (miR-1) in the regulation of connexin 43 (GJA1), a major gap junction in bladder smooth muscle, and the collective role of these molecules during post-natal bladder development. Wild-type (WT) mouse bladders showed normal development from early post-natal to adult including increases in bladder capacity and maintenance of normal sensitivity to cholinergic agents concurrent with down-regulation of MYOCD and several smooth muscle cell (SMC) contractile genes. Myocardin heterozygous-knockout mice exhibited reduced expression of Myocd mRNA and several SMC contractile genes concurrent with bladder SMC hypersensitivity that was mediated by gap junctions. In both cultured rat bladder SMC and in vivo bladders, MYOCD down-regulated GJA1 expression through miR-1 up-regulation. Interestingly, adult myocardin heterozygous-knockout mice showed normal increases in bladder and body weight but lower bladder capacity compared to WT mice. These results suggest that MYOCD down-regulates GJA1 expression via miR-1 up-regulation, thereby contributing to maintenance of normal sensitivity and development of bladder capacity.

Gap junction expression and the effects of gap junction inhibitors in overactive bladder models: does ovariectomy have a role?

PURPOSE

In this study, gap junction expression and the effects of estrogen deficiency and gap junction inhibitors were investigated in overactive bladder models which were created by bladder outlet obstruction.

METHODS

In our study, we created four groups as control, ovariectomy, bladder outlet obstruction (BOO), and ovariectomy + BOO. We investigated the effects of oxybutynin and 18-alpha glycyrrhetinic acid (18-α-GA) which is a gap junction blocker on isolated detrusor strips. Western blot method was used to measure the level of connexin-43 in detrusor.

RESULTS

Bladder weights were significantly increased in the BOO and ovariectomy + BOO groups (p < 0.05). There was no statistically significant difference in the maximal contraction responses to carbachol between ovariectomy and control groups. In BOO and ovariectomy + BOO groups, contractile responses were significantly prominent with higher doses of carbachol. Oxybutynin-induced relaxant responses of BOO and ovariectomy + BOO groups were significantly higher than control group (p < 0.05). The relaxation effect of 18-a-GA was more effective in the obstruction groups. Among those two groups, the relaxation observed in BOO group was higher than ovariectomy + BOO group in higher doses of 18-a-GA. Connexin-43 expression was increased in BOO group compared with the control group (p = 0.006). Ovariectomy did not change connexin-43 expression alone; however, when combined with BOO, connexin-43 expression decreased significantly (p = 0.023).

CONCLUSIONS

Ovariectomy had no effect on the gap junctions in the bladder and bladder overactivity alone. Therefore, obstruction is the main factor that increases the amount of gap junctions, and gap junction blockers are thus more effective in obstruction. However, ovariectomy was shown to decrease the expression of gap junctions and relaxation effect of gap junction blockers, when combined with BOO.

Remodeling of the muscle layer (detrusor muscle) of hyperactive bladder disease in patients with benign prostatic hyperplasia

We studied remodeling of the detrusor of hyperactive bladder in patients with benign prostatic hyperplasia. Detrusor remodeling was caused by degenerative and atrophic changes and elimination of smooth muscle cells, compensatory hypertrophy of remaining cells, and diffuse or focal-diffuse replacement fibrosis. Focal or diffuse infiltration of all layers of the detrusor with lymphocytes and plasma cells is an important pathologic feature of hyperactive bladder. These changes correlated with pronounced remodeling of the glandular and fibrotic-muscular layers in the prostate gland. We have identified stereotyped patterns of the intracellular reorganization of smooth muscle cells in the detrusor of hyperactive bladder and in the prostate with benign prostatic hyperplasia, which represent both the compensatory and adaptive reactions (hypertrophied cells with minor ultrastructural changes) and the types of smooth muscle cell injury ("dark" electron-dense cells and "light" cells with pronounced lysis of myofilaments and discomplexation of organelles).

Reciprocal regulation between proinflammatory cytokine-induced inducible NO synthase (iNOS) and connexin43 in bladder smooth muscle cells

Gap junctions (GJs) play an important role in the control of bladder contractile response and in the regulation of various immune inflammatory processes. Here, we investigated the possible interaction between inflammation and GJs in bladder smooth muscle cells (BSMCs). Stimulation of BSMCs with IL1β and TNFα increased connexin43 (Cx43) expression and function, which was associated with increased phosphorylation of vasodilator-stimulated phosphoprotein. Inhibition of PKA with H89 or down-regulation of CREB with specific siRNAs largely abolished the Cx43-elevating effect. Further analysis revealed that IL1β/TNFα induced NFκB-dependent inducible NO synthase (iNOS) expression. Inhibition of iNOS with G-nitro-l-arginine methyl ester abrogated and an exogenous NO donor mimicked the effect of the cytokines on Cx43. Intraperitoneal injection of LPS into mice also induced bladder Cx43 expression, which was largely blocked by an iNOS inhibitor. Finally, the elevated Cx43 was found to negatively regulate iNOS expression. Dysfunction of GJs with various blockers or down-regulation of Cx43 with siRNA significantly potentiated the expression of iNOS. Fibroblasts from Cx43 knock-out (Cx43(-/-)) mice also displayed a significantly higher response to the cytokine-induced iNOS expression than cells from Cx43 wild-type (Cx43(+/+)) littermates. Collectively, our study revealed a previously unrecognized reciprocal regulation loop between cytokine-induced NO and GJs. Our findings may provide an important molecular mechanism for the symptoms of bladder infection. In addition, it may further our understanding of the roles of GJs in inflammatory diseases.

Regulation of connexin 43 by basic fibroblast growth factor in the bladder: transcriptional and behavioral implications

PURPOSE

Basic fibroblast growth factor is a candidate causative factor of detrusor overactivity in bladder outlet obstruction cases through up-regulation of the gap junction protein connexin 43. We addressed the transcriptional and behavioral implications of this axis.

MATERIALS AND METHODS

Cx43 and Cx45 mRNA expression was assessed by real-time reverse transcriptase-polymerase chain reaction in the bladder of a rat bladder outlet obstruction model and in cultured rat bladder smooth muscle cells with and without basic fibroblast growth factor treatment. Involvement of the extracellular signal regulated kinase 1/2-activator protein-1 pathway was evaluated by immunofluorescence study and a promoter-reporter assay in bladder smooth muscle cells. The effect of basic fibroblast growth factor on micturition behavior was measured in unrestrained rats under a 12-hour light/dark cycle using a controlled release system from gelatin hydrogels fixed on the bladder. The expression of extracellular signal regulated kinase 1/2 and connexin 43 protein was assessed by Western blotting of rat bladder protein.

RESULTS

Cx43 but not Cx45 mRNA expression was increased in the bladder of the obstruction model and in bladder smooth muscle cells treated with basic fibroblast growth factor. The mitogen-activated and extracellular signal-regulated kinase kinase inhibitor PD98059 blocked the stimulatory effect of basic fibroblast growth factor on connexin 43 protein expression and promoter activity, which was also decreased by mutation or deletion of an activator protein-1 cis-element of the connexin 43 promoter. In vivo application of basic fibroblast growth factor on the bladder increased urinary frequency during the latter half of the dark phase, ie the late active phase of rats (F = 5.1, 2-way ANOVA p <0.05). The expression of phospho-extracellular signal regulated kinase 1/2 and connexin 43 protein was increased in the bladder.

CONCLUSIONS

The extracellular signal regulated kinase 1/2-activator protein-1-connexin 43 axis could be a potential therapeutic target for increased urinary frequency.

Direct coupling through gap junctions is not involved in urethral neurotransmission

Interstitial cells of Cajal (ICC) are believed to participate in urethral neurotransmission and it was proposed that direct coupling of ICC and smooth muscle cells (SMC) through gap junctions (GJ) is involved, although this still remains unclear. Hence, we investigated the distribution of different connexins (Cx 43, Cx40, and Cx37) in the sheep and rat urethra, as well as their possible role in neurotransmission. Conventional PCR confirmed that three Cxs are expressed in the urethra. Moreover, both Cx43 and Cx37-immunoreactivity (-ir) were present in SMC, ICC, and the urothelium, although Cx37-ir was significantly weaker and Cx40-ir was limited to the endothelium. While these results indicate that GJ intercellular communication could occur between SMC and ICC, neither the contractile (noradrenergic) nor the relaxant (nitrergic) responses of the rat and sheep urethra to electrical field stimulation were significantly modified by two different GJ inhibitors: 18α-glycyrrhetinic acid and a cocktail of Cx mimetic peptides (Cx43Gap 26,Cx37, Cx43Gap 27, andCx40Gap 27). By contrast, contractions induced by high K+were effectively reduced by both blockers, evidence that they effectively inhibit intercellular communication. These results indicate that GJ are not implicated in urethral neurotransmission, although the question of whether ICC modulate neurotransmission through some other mechanism remains to be determined.

Dietary soy isoflavone replacement improves detrusor overactivity of ovariectomized rats with altered connexin-43 expression in the urinary bladder

To evaluate the effects of dietary soy isoflavone on detrusor overactivity (DO) in ovariectomized (Ovx) rats and the association between these effects and expression of the gap junction protein, connexin-43, in the urinary bladder, and to discuss the usefulness of soy isoflavones for overactive bladder (OAB).

MATERIALS AND METHODS

In all, 24 (8-week-old) virgin female Sprague-Dawley rats were divided equally into four groups: sham operation with control diet (with no dietary soy isoflavones; Sham-CD), bilateral Ovx with CD (Ovx-CD), sham operation with soy isoflavone diet (Sham-ID), bilateral Ovx with soy ID (Ovx-ID). Cystometry was performed after the 4-week CD or ID in each group while awake. Quantitative reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemical and Western blot analyses were also performed to examine the expression of connexin-43 in each group.

RESULTS

In Ovx-CD rats, there were some significant changes in cystometry variables, including shortening of the intercontraction interval and an increased number of non-voiding contractions compared with Sham-CD rats (P < 0.05). These changes were significantly improved by 4-week soy isoflavone administration (Ovx-ID; P < 0.05). Quantitative RT-PCR, immunohistochemical and Western blot analyses showed that the expression level of connexin-43 mRNA and protein was significantly greater in the urinary bladder of Ovx-CD rats compared with Sham-CD rats. Soy isoflavone administration significantly reduced this increased expression (Ovx-ID).

CONCLUSIONS

Soy isoflavone replacement improved DO with alteration of the connexin-43 expression pattern in the urinary bladder of Ovx rats. Routine consumption of diet soy isoflavones may be a useful treatment to prevent and improve OAB.

Basic fibroblast growth factor causes urinary bladder overactivity through gap junction generation in the smooth muscle

Overactive bladder is a highly prevalent clinical condition that is often caused by bladder outlet obstruction (BOO). Increased coupling of bladder smooth muscle cells (BSMC) via gap junctions has been hypothesized as a mechanism for myogenic bladder overactivity in BOO, although little is known about the regulatory system underlying such changes. Here, we report the involvement of basic fibroblast growth factor (bFGF) and connexin 43, a bladder gap junction protein, in bladder overactivity. BOO created by urethral constriction in rats resulted in elevated bFGF and connexin 43 levels in the bladder urothelium and muscle layer, respectively, and muscle strips from these bladders were more sensitive than those from sham-operated controls to a cholinergic agonist. In vitro bFGF treatment increased connexin 43 expression in cultured rat BSMC via the ERK 1/2 pathway. This finding was supported by another in vivo model, where bFGF released from gelatin hydrogels fixed on rat bladder walls caused connexin 43 upregulation and gap junction formation in the muscle layer. Bladder muscle strips in this model showed increased sensitivity to a cholinergic agonist that was blocked by inhibition of gap junction function with alpha-glycyrrhetinic acid. Cystometric analyses of this model showed typical features of detrusor overactivity such as significantly increased micturition frequency and decreased bladder capacity. These findings suggest that bFGF from the urothelium could induce bladder hypersensitivity to acetylcholine via gap junction generation in the smooth muscle, thereby contributing to the myogenic overactivity of obstructed bladders.