Loss of caveolin-1 expression is associated with disruption of muscarinic cholinergic activities in the urinary bladder

Decreased Expression of Urethral Caveolin-1, -2, and -3 in the Rat Model of Overactive Bladder: Potential Mediator of Functional Interaction of Urethra and Urinary Bladder

Purpose: To investigate the effect of detrusor overactivity (DO) on the urethral expression of caveolin (CAV)-1, -2, and -3 of urethra in an animal model of cyclophosphamide (CYP)-induced cystitis rat.Methods: Female Sprague-Dawley rats were divided into the control group (n=20) and the cystitis group (n=20). Cystitis was induced by intraperitoneal injection of CYP (200 mg/kg). An urodynamic study was done 3 days after the CYP injection to measure functional change of the urinary bladder and urethra. Cellular localization and expression of CAV-1, -2, and -3 in the rat urethra were determined by immunohistochemistry (IHC) and Western blot.Results: Urodynamic experiments demonstrated a decreased contraction interval in the cystitis group compared to the control (3.9±1.0 minutes vs. 6.6±1.2 minutes, P<0.05). Conversely, contraction pressure increased significantly in the cystitis group compared to the control (22.4±0.7 mmHg vs. 11.5±0.4 mmHg, P<0.05). The urethral pressure was decreased in the cystitis group compared to the control (4.05 ±2.5 mmHg vs. 5.8 ±2.8 mmHg, P <0.05). The IHC and Western blot data showed that CAV-1, -2, and -3 expression decreased significantly in the cystitis group compared control group (P<0.05).Conclusions: The decreased urethral CAV-1, -2, and -3 in the DO rats suggests that CAVs might be related with the functional change of urethra in association with DO of urinay bladder.

Decreased urothelial expression of caveolin 1 and 2 in aging rats showing detrusor overactivity: Potential association with aging bladder

PURPOSE

The purpose of this study was to investigate the effect of aging on bladder function and caveolin protein expression in rat urothelium.

MATERIALS AND METHODS

Female Sprague-Dawley rats were divided into the following two groups: young age control group (12 weeks) and old-aged group of rats (80 weeks). Urodynamic measurements were taken to compare the contraction interval and the contraction pressure between the two groups. The expression and cellular localization of caveolin 1 and 2 in the urothelium of the rat urinary bladder were determined by Western blot and immunofluorescence microscopy.

RESULTS

In cystometrograms, the contraction interval (min) was significantly shorter in the old-aged group (3.7±0.5 min) than in the young age control group (6.2±0.8 min). Also, the average contraction pressure (mmHg) was lower in the old-aged group (8.4±0.6 mmHg) than in the young age control group (13.2±1.3 mmHg). Caveolin 1 and 2 were expressed in the subepithelial area in the urothelium. The protein expression of both caveolin 1 and 2 was significantly lower in the old-aged group than in the young age control group.

CONCLUSIONS

Aging caused a significant change in the expression of caveolin 1 and 2 in the urothelium of the rat urinary bladder. These findings suggest that these molecules might have specific roles in the functional change of the urinary bladder that occurs in association with aging.

NF-κB and GATA-Binding Factor 6 Repress Transcription of Caveolins in Bladder Smooth Muscle Hypertrophy

Caveolins (CAVs) are structural proteins of caveolae that function as signaling platforms to regulate smooth muscle contraction. Loss of CAV protein expression is associated with impaired contraction in obstruction-induced bladder smooth muscle (BSM) hypertrophy. In this study, microarray analysis of bladder RNA revealed down-regulation of CAV1, CAV2, and CAV3 gene transcription in BSM from models of obstructive bladder disease in mice and humans. We identified and characterized regulatory regions responsible for CAV1, CAV2, and CAV3 gene expression in mice with obstruction-induced BSM hypertrophy, and in men with benign prostatic hyperplasia. DNA affinity chromatography and chromatin immunoprecipitation assays revealed a greater increase in binding of GATA-binding factor 6 (GATA-6) and NF-κB to their cognate binding motifs on CAV1, CAV2, and CAV3 promoters in obstructed BSM relative to that observed in control BSM. Knockout of NF-κB subunits, shRNA-mediated knockdown of GATA-6, or pharmacologic inhibition of GATA-6 and NF-κB in BSM increased CAV1, CAV2, and CAV3 transcription and promoter activity. Conversely, overexpression of GATA-6 decreased CAV2 and CAV3 transcription and promoter activity. Collectively, these data provide new insight into the mechanisms by which CAV gene expression is repressed in hypertrophied BSM in obstructive bladder disease.

Caveolin1 Identifies a Specific Subpopulation of Cerebral Cortex Callosal Projection Neurons (CPN) Including Dual Projecting Cortical Callosal/Frontal Projection Neurons (CPN/FPN)

The neocortex is composed of many distinct subtypes of neurons that must form precise subtype-specific connections to enable the cortex to perform complex functions. Callosal projection neurons (CPN) are the broad population of commissural neurons that connect the cerebral hemispheres via the corpus callosum (CC). Currently, how the remarkable diversity of CPN subtypes and connectivity is specified, and how they differentiate to form highly precise and specific circuits, are largely unknown. We identify in mouse that the lipid-bound scaffolding domain protein Caveolin 1 (CAV1) is specifically expressed by a unique subpopulation of Layer V CPN that maintain dual ipsilateral frontal projections to premotor cortex. CAV1 is expressed by over 80% of these dual projecting callosal/frontal projection neurons (CPN/FPN), with expression peaking early postnatally as axonal and dendritic targets are being reached and refined. CAV1 is localized to the soma and dendrites of CPN/FPN, a unique population of neurons that shares information both between hemispheres and with premotor cortex, suggesting function during postmitotic development and refinement of these neurons, rather than in their specification. Consistent with this, we find that Cav1 function is not necessary for the early specification of CPN/FPN, or for projecting to their dual axonal targets. CPN subtype-specific expression of Cav1 identifies and characterizes a first molecular component that distinguishes this functionally unique projection neuron population, a population that expands in primates, and is prototypical of additional dual and higher-order projection neuron subtypes.

Similar regulatory mechanisms of caveolins and cavins by myocardin family coactivators in arterial and bladder smooth muscle

Caveolae are membrane invaginations present at high densities in muscle and fat. Recent work has demonstrated that myocardin family coactivators (MYOCD, MKL1), which are important for contractile differentiation and cell motility, increase caveolin (CAV1, CAV2, CAV3) and cavin (CAVIN1, CAVIN2, CAVIN3) transcription, but several aspects of this control mechanism remain to be investigated. Here, using promoter reporter assays we found that both MKL1/MRTF-A and MKL2/MRTF-B control caveolins and cavins via their proximal promoter sequences. Silencing of MKL1 and MKL2 in smooth muscle cells moreover reduced CAV1 and CAVIN1 mRNA levels by well over 50%, as did treatment with second generation inhibitors of MKL activity. GATA6, which modulates expression of smooth muscle-specific genes, reduced CAV1 and CAV2, whereas the cavins were unaffected or increased. Viral overexpression of MKL1 and myocardin induced caveolin and cavin expression in bladder smooth muscle cells from rats and humans and MYOCD correlated tightly with CAV1 and CAVIN1 in human bladder specimens. A recently described activator of MKL-driven transcription (ISX) failed to induce CAV1/CAVIN1 which may be due to an unusual transactivation mechanism. In all, these findings further support the view that myocardin family coactivators are important transcriptional drivers of caveolins and cavins in smooth muscle.

Altered expression and modulation of the two-pore-domain (K2P) mechanogated potassium channel TREK-1 in overactive human detrusor

Detrusor overactivity (DO) is the abnormal response of the urinary bladder to physiological stretch during the filling phase of the micturition cycle. The mechanisms of bladder smooth muscle compliance upon the wall stretch are poorly understood. We previously reported that the function of normal detrusor is regulated by TREK-1, a member of the mechanogated subfamily of two-pore-domain potassium (K_2P) channels. In the present study, we aimed to identify the changes in expression and function of TREK-1 channels under pathological conditions associated with DO, evaluate the potential relationship between TREK-1 channels and cytoskeletal proteins in the human bladder, and test the possibility of modulation of TREK-1 channel expression by small RNAs. Expression of TREK-1 channels in DO specimens was 2.7-fold decreased compared with control bladders and was associated with a significant reduction of the recorded TREK-1 currents. Isolated DO muscle strips failed to relax when exposed to a TREK-1 channel opener. Immunocytochemical labeling revealed close association of TREK-1 channels with cell cytoskeletal proteins and caveolins, with caveolae microdomains being severely disrupted in DO specimens. Small activating RNA (saRNA) tested in vitro provided evidence that expression of TREK-1 protein could be partially upregulated. Our data confirmed a significant downregulation of TREK-1 expression in human DO specimens and provided evidence of close association between the channel, cell cytoskeleton, and caveolins. Upregulation of TREK-1 expression by saRNA could be a future step for the development of in vivo pharmacological and genetic approaches to treat DO in humans.

Effects of sacral nerve stimulation on postpartum urinary retention-related changes in rat bladder

OBJECTIVE

To examine the effect of sacral nerve stimulation (SNS) on the urodynamic function and molecular structure of bladders in rats following acute urinary retention (AUR) after parturition.

MATERIAL AND METHODS

Thirty primiparous rats were divided into three groups: postpartum, postpartum+AUR, and postpartum+AUR+SNS. AUR was achieved by clamping the distal urethra of a rat for 60 minutes. The postpartum+AUR+SNS group received electrical stimulation 60 minutes daily for 3 days after AUR. In addition to cystometric studies and external urethral sphincter electromyography, the expression of caveolins and nerve growth factor (NGF) and caveolae number in bladder muscle were analyzed.

RESULTS

The postpartum+AUR group has significantly greater residual volume than the postpartum group, but the residual volume decreased significantly after SNS treatment. The postpartum+AUR group had significantly lower peak voiding pressure, a longer bursting period and lower amplitude of electromyograms of external urethral sphincter activity than the postpartum and postpartum+AUR+SNS groups. The postpartum+AUR rats had higher NGF expression, lower caveolin-1 expression, and fewer caveolae in bladder muscle compared with the postpartum rats. Conversely, the caveolin-1 expression and caveolae number increased, and the NGF expression decreased after SNS treatment.

CONCLUSION

Bladder dysfunction after parturition in a rat model caused by AUR may be restored to the non-AUR structural and functional level after SNS treatment.

Caveolae - mechanosensitive membrane invaginations linked to actin filaments

An essential property of the plasma membrane of mammalian cells is its plasticity, which is required for sensing and transmitting of signals, and for accommodating the tensional changes imposed by its environment or its own biomechanics. Caveolae are unique invaginated membrane nanodomains that play a major role in organizing signaling, lipid homeostasis and adaptation to membrane tension. Caveolae are frequently associated with stress fibers, a major regulator of membrane tension and cell shape. In this Commentary, we discuss recent studies that have provided new insights into the function of caveolae and have shown that trafficking and organization of caveolae are tightly regulated by stress-fiber regulators, providing a functional link between caveolae and stress fibers. Furthermore, the tension in the plasma membrane determines the curvature of caveolae because they flatten at high tension and invaginate at low tension, thus providing a tension-buffering system. Caveolae also regulate multiple cellular pathways, including RhoA-driven actomyosin contractility and other mechanosensitive pathways, suggesting that caveolae could couple mechanotransduction pathways to actin-controlled changes in tension through their association with stress fibers. Therefore, we argue here that the association of caveolae with stress fibers could provide an important strategy for cells to deal with mechanical stress.

Loss of Caveolin 1 is Associated With the Expression of Aquaporin 1 and Bladder Dysfunction in Mice

Purpose:

It is suggested that caveolin and aquaporin might be closely associated with bladder signal activity. We investigated the effect of the deletion of caveolin 1, using caveolin 1 knockout mice, on the expression of aquaporin 1 in order to identify their relation in the urothelium of the urinary bladder.

Methods:

The cellular localization and expressions of aquaporin 1 and caveolin 1, in the wild type and caveolin 1 knockout mice urinary bladder, were examined by Western blot and immunofluorescence techniques.

Results:

Aquaporin 1 and caveolin 1 were coexpressed in the arterioles, venules, and capillaries of the suburothelial layer in the wild type controls. Aquaporin 1 protein expression was significantly higher in the caveolin 1 knockout mice than in the wild type controls (P <0.05).

Conclusions:

The results imply that aquaporin 1 and caveolin 1 may share a distinct relation with the bladder signal activity. This might play a specific role in bladder dysfunction.

Vasopressin-induced mouse urethral contraction is modulated by caveolin-1

Caveolae are 50-100nm large invaginations in the cell membrane that are considered to play roles in receptor signaling. Here we aimed to investigate the expression and distribution of the arginine-vasopressin (AVP) V1a receptor and its functional dependence on caveolin-1 (Cav1) in the mouse urethra. Female Cav1 knockout (KO) and wild type (WT) mice were used, and urethral preparations were micro-dissected for mechanical experiments. Methyl-β-cyclodextrin (mβcd) was used to deplete cholesterol and to disrupt caveolae. Protein expression and localization was determined using immunofluorescence and western blotting and transcript expression was determined by qRT-PCR. We found that Cav1 and AVP V1a receptors were expressed in urethral smooth muscle cells with apparent co-localization at the cell membrane. AVP caused urethral contraction that was inhibited by the V1a receptor antagonist SR49059. Concentration-response curves for AVP were right-shifted and maximal contraction was reduced in Cav1 KO mice and after mβcd treatment. In addition to caveolin-1 we also detected caveolin-2, cavin-1 and cavin-3 in the mouse urethra by western blotting. Caveolin-2, cavin-1 and cavin-3 as well as V1a receptor expression was reduced in KO urethra. We conclude that AVP regulates urethral contractility via the V1a receptor through a Cav1-dependent mechanism involving, in part, altered V1a receptor expression.

Atherosclerosis differentially affects calcium signalling in endothelial cells from aortic arch and thoracic aorta in Apolipoprotein E knockout mice

Apolipoprotein‐E knockout (ApoE^−/−) mice develop hypercholesterolemia and are a useful model of atherosclerosis. Hypercholesterolemia alters intracellular Ca²⁺ signalling in vascular endothelial cells but our understanding of these changes, especially in the early stages of the disease process, is limited. We therefore determined whether carbachol‐mediated endothelial Ca²⁺ signals differ in plaque‐prone aortic arch compared to plaque‐resistant thoracic aorta, of wild‐type and ApoE^−/− mice, and how this is affected by age and the presence of hypercholesterolemia. The extent of plaque development was determined using en‐face staining with Sudan IV. Tissues were obtained from wild‐type and ApoE^−/− mice at 10 weeks (pre‐plaques) and 24 weeks (established plaques). We found that even before development of plaques, significantly increased Ca²⁺ responses were observed in arch endothelial cells. Even with aging and plaque formation, ApoE^−/− thoracic responses were little changed, however a significantly enhanced Ca²⁺ response was observed in arch, both adjacent to and away from lesions. In wild‐type mice of any age, 1–2% of cells had oscillatory Ca²⁺ responses. In young ApoE^−/− and plaque‐free regions of older ApoE^−/−, this is unchanged. However a significant increase in oscillations (~13–15%) occurred in thoracic and arch cells adjacent to lesions in older mice. Our data suggest that Ca²⁺ signals in endothelial cells show specific changes both before and with plaque formation, that these changes are greatest in plaque‐prone aortic arch cells, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

We have investigated aortic endothelial cell calcium signalling changes in the Apolipoprotein E knockout mouse model of atherosclerosis. Our data show that calcium signals in endothelial cells undergo specific changes both before and with plaque formation, that these changes are greater in plaque‐prone aortic arch than in plaque‐resistant thoracic aorta, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

Contemporary concepts in the aetiopathogenesis of detrusor underactivity

Detrusor underactivity (DUA) is a poorly understood, yet common, bladder dysfunction, referred to as underactive bladder, which is observed in both men and women undergoing urodynamic studies. Despite its prevalence, no effective therapeutic approaches exist for DUA. Exactly how the contractile function of the detrusor muscle changes with ageing is unclear. Data from physiological studies in animal and human bladders are contradictory, as are the results of the limited number of clinical studies assessing changes in urodynamic parameters with ageing. The prevalence of DUA in different patient groups suggests that multiple aetiologies are involved in DUA pathogenesis. Traditional concepts focused on either efferent innervation or myogenic dysfunction. By contrast, contemporary views emphasize the importance of the neural control mechanisms, particularly the afferent system, which can fail to potentiate detrusor contraction, leading to premature termination of the voiding reflex. In conclusion, the contemporary understanding of the aetiology and pathophysiology of DUA is limited. Further elucidation of the underlying mechanisms is needed to enable the development of new and effective treatment approaches.

Overexpression of aquaporin-1 and caveolin-1 in the rat urinary bladder urothelium following bladder outlet obstruction

PURPOSE

This study was designed to investigate the effect of detrusor overactivity induced by partial bladder outlet obstruction (BOO) on the expression of aquaporin 1 (AQP1) and caveolin 1 (CAV1) in the rat urinary bladder, and to determine the role of these molecules in detrusor overactivity.

METHODS

Female Sprague-Dawley rats were divided into control (n=30) and experimental (n=30) groups. The BOO group underwent partial BOO, and the control group underwent a sham operation. After 4 weeks, an urodynamic study was performed to measure the contraction interval and contraction pressure. The expression and cellular localization of AQP1 and CAV1 were determined by western blot and immunofluorescence experiments in the rat urinary bladder.

RESULTS

In cystometrograms, the contraction interval was significantly lower in the BOO group (2.9±1.5 minutes) than in the control group (6.7±1.0 minutes) (P<0.05). Conversely, the average contraction pressure was significantly higher in the BOO group (21.2±3.3 mmHg) than in the control group (13.0±2.5 mmHg) (P<0.05). AQP1 and CAV1 were coexpressed in the capillaries, arterioles, and venules of the suburothelial layer. AQP1 and CAV1 protein expression was significantly increased in the BOO rats compared to the control rats (P<0.05).

CONCLUSIONS

Detrusor overactivity induced by BOO causes a significant increase in the expression of AQP1 and CAV1, which were coexpressed in the suburothelial microvasculature. This finding suggests that AQP1 and CAV1 might be closely related to bladder signal activity and may have a functional role in BOO-associated detrusor overactivity.

Altered expression of caveolin 2 and 3 in smooth muscle of rat urinary bladder by 17β-estradiol

Background

The purpose of this study was to investigate the effect of estrogen alteration on the expression of caveolin 2 and 3 in rat smooth muscle of urinary bladder.

Methods

Female Sprague–Dawley rats were divided into three groups: control, bilateral ovariectomy (Ovx), and bilateral ovariectomy followed by subcutaneous injections of 17β-estradiol (Ovx?+?Est). After 4 weeks, urodynamic measurements were taken to ascertain the contraction interval and contraction pressure. The expression and cellular localization of caveolin 2 and 3 were determined by Western blot and immunohistochemistry in rat urinary bladder smooth muscle.

Results

In cystometrograms, the contraction interval (min) was significantly lower in the Ovx group (3.1?±?1.5) than in the control group (5.6?±?1.2), but was increased after estrogen treatment (9.3?±?1.0). Conversely, the average contraction pressure (mmHg) was higher in the Ovx group (26.2?±?2.3) than in the control group (21.9?±?3.1), and was decreased after estrogen treatment (23.8?±?3.5). Caveolin 2 and 3 expression was localized in the cell membrane of the smooth muscle. The protein expression of both caveolin 2 and 3 was significantly lower after ovariectomy and was restored to the control levels after 17β-estradiol treatment.

Conclusions

Hormonal alteration causes a significant change in the expression of caveolin 2 and 3 in smooth muscle of rat urinary bladder. These findings suggest that these molecules might have functional roles in the detrusor overactivity that occurs in association with hormonal alteration.

Expression of caveolin-1 in rat urinary bladder with cyclophosphamide-induced cystitis

Purpose

The purposes of this study were to investigate the effect of cyclophosphamide (CYP)-induced inflammatory cystitis on caveolin 1 in rat urinary bladder and to determine the role of these molecules in the bladder dysfunction that occurs in inflammatory change in rat urinary bladder.

Methods

Female Sprague-Dawley rats were divided into control (n=30) and experimental (n=30) groups. Cystitis in experimental group was induced by intraperitoneal injection of CYP (200 mg/kg). The control group underwent an intraperitoneal saline injection. After 3 days, urodynamic studies were done to measure the contraction interval and contraction pressure. The expression and cellular localization of caveolin 1 were determined by Western blot and immunofluorescent study in rat urinary bladder.

Results

In cystometrograms, the contraction interval (minute) was significantly increased in the CYP-induced cystitis rats (15.8±1.5) than in the control group (6.3±0.5) (P<0.05). Conversely, the average contraction pressure (mmHg) was significantly higher in the CYP-induced cystitis rats (15.6±1.7) than in the control group (11.3±0.5) (P<0.05). Caveolin 1 was expressed in the capillaries, arteriols and venules. The protein expression of caveolin 1 was significantly decreased in the CYP-induced cystitis rats (P<0.05).

Conclusions

Inflammatory change of urinary bladder maybe causes a significant change in the expression of caveolin 1. These findings suggest that caveolin 1 might have a functional role in the bladder dysfunction related with cystitis in rat urinary bladder.

Impaired contractility and detrusor hypertrophy in cavin-1-deficient mice

Caveolae are membrane invaginations present in a variety of cell types. Formation of caveolae depends on caveolins and on the more recently discovered family of proteins known as the cavins. Genetic ablation of caveolin-1 was previously shown to give rise to a number of urogenital alterations, but the effects of cavin-1 deletion on urogenital function remain unknown. Here we characterised detrusor contractility and structure in cavin-1-deficient mice. Electron microscopy demonstrated essentially complete lack of caveolae in the knock-out detrusor, and immunoblotting disclosed reduced levels of cavin-3 and of all caveolin proteins. Bladder weight was increased in male knock-out mice, and length-tension relationships demonstrated a reduction in depolarisation-induced contraction. Contractility in response to muscarinic receptor activation was similarly reduced. Despite these functional changes, micturition patterns were similar in conscious and freely moving animals and diuresis was unchanged. Our breeding additionally disclosed that the number of knock-out mice generated in heterozygous crosses was lower than expected, suggesting embryonic/perinatal lethality. In conclusion, this is the first study to show that cavin-1 is critical for detrusor caveolae and for the overall contractility and structure of the urinary bladder.

Metabotropic glutamate receptor 5 (mGluR5) regulates bladder nociception

BACKGROUND

Interstitial cystitis/painful bladder syndrome (IC/PBS), is a severely debilitating chronic condition that is frequently unresponsive to conventional pain medications. The etiology is unknown, however evidence suggests that nervous system sensitization contributes to enhanced pain in IC/PBS. In particular, central nervous system plasticity of glutamatergic signaling involving NMDA and metabotropic glutamate receptors (mGluRs) has been implicated in a variety of chronic pain conditions. Here, we test the hypothesis that mGluR5 mediates both non-inflammatory and inflammatory bladder pain or nociception in a mouse model by monitoring the visceromotor response (VMR) during graded bladder distention.

RESULTS

Using a combination of genetic and pharmacologic approaches, we provide evidence indicating that mGluR5 is necessary for the full expression of VMR in response to bladder distention in the absence of inflammation. Furthermore, we observed that mice infected with a uropathogenic strain of Escherichia coli (UPEC) develop inflammatory hyperalgesia to bladder distention, and that the selective mGluR5 antagonist fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl) urea], reduces the VMR to bladder distention in UPEC-infected mice.

CONCLUSIONS

Taken together, these data suggest that mGluR5 modulates both inflammatory and non-inflammatory bladder nociception, and highlight the therapeutic potential for mGluR5 antagonists in the alleviation of bladder pain.

Loss of bladder smooth muscle caveolae in the aging bladder

AIMS

Caveolae are specialized regions of the cell membrane that modulate signal transduction and alterations in these structures affect bladder smooth muscle (BSM) contraction. Since bladder dysfunctions are common in the elderly, we evaluated the effect of aging on the morphology of caveolae and caveolin protein expression in BSM.

METHODS

Caveolar morphology (number, size, and depth) in BSM was determined from electron microscopy images of young (10 weeks), adult (6-month old), and old (12-month old) rat urinary bladders. Changes in expression levels of caveolin proteins with age were investigated by Western blot and immunofluorescence microscopy. Caveolin-3 gene expression was determined by real-time RT-PCR in young and 19-month-old rat bladders.

RESULTS

Twelve-month-old animals exhibited 50% fewer BSM caveolae compared to young (P < 0.01). The area of caveolae was significantly decreased at 6 and 12 months. Despite a decrease in the number of BSM caveolae at 12 months, the expression of caveolin-1 and cavin-1 were unaltered with age. In contrast, caveolin-2 and caveolin-3 protein expression and immunoreactivity were reduced in BSM at 6 and 12 months of age. Caveolin-3 gene expression was also downregulated at 19 months compared to young animals.

CONCLUSION

Biological aging significantly decreases BSM caveolae number and morphology with associated selective alteration in caveolin protein expression. Since caveolae are protected membrane regions that regulate signal transduction, age-related alterations in caveolae and caveolin protein expression could alter BSM contractility resulting in bladder dysfunctions of the elderly.

Biomechanical properties and innervation of the female caveolin-1-deficient detrusor

BACKGROUND AND PURPOSE

Caveolin-1-deficiency is associated with substantial urogenital alterations. Here, a mechanical, histological and biochemical characterization of female detrusors from wild-type and caveolin-1-deficient (KO) mice was made to increase the understanding of detrusor changes caused by lack of caveolae.

EXPERIMENTAL APPROACH

Length-tension relationships were generated, and we recorded responses to electrical field stimulation, the muscarinic receptor agonist carbachol and the purinoceptor agonist ATP. Tyrosine nitration and the contents of caveolin-1, cavin-1, muscarinic M₃ receptors, phospholipase C(β1), muscle-specific kinase (MuSK) and L-type Ca(2+) channels were determined by immunoblotting. Innervation was assessed by immunohistochemistry.

KEY RESULTS

Bladder to body weight ratio was not changed, nor was there any change in the optimum circumference for force development. Depolarization- and ATP-induced stress was reduced, as was carbachol-induced stress between 0.1 and 3 µM, but the supramaximal relative (% K(+)) response to carbachol was increased, as was M₃ expression. The scopolamine-sensitive component of the electrical field stimulation response was impaired, and yet bladder nerves contained little caveolin-1. The density of cholinergic nerves was unchanged, whereas CART- and CGRP-positive nerves were reduced. Immunoblotting revealed loss of MuSK.

CONCLUSIONS AND IMPLICATIONS

Ablation of caveolae in the female detrusor leads to generalized impairment of contractility, ruling out prostate hypertrophy as a contributing factor. Cholinergic neuroeffector transmission is impaired without conspicuous changes in the density of cholinergic nerves or morphology of their terminals, but correlating with reduced expression of MuSK.

Effects of estrogens on the expression of caveolin-1 in the urinary bladders of female rats

PURPOSE

The purposes of this study were to investigate the effect of hormonal alterations on the expression of caveolin-1 in the urinary bladders of ovariectomized rats and to determine the role of caveolin-1 in the overactivity of the detrusor muscle that occurs with hormonal alterations in rats.

METHODS

Female Sprague-Dawley rats were divided into three groups: a control group, a group that underwent bilateral ovariectomy (Ovx), and a group that underwent bilateral ovariectomy followed by subcutaneous injections of 17β-estradiol (Ovx+Est). After 4 weeks, urodynamic studies were done to measure the contraction interval and contraction pressure. The expression and cellular localization of caveolin-1 were determined by Western blot and immunofluorescence in the urinary bladders of rats.

RESULTS

On cystometrograms, the contraction interval was significantly shorter in the Ovx group (3.0±0.3 minute) than in the control group (5.6±0.5 minute) but was longer in the Ovx+Est group (9.2±0.4 minute) (P<0.05). Conversely, the average contraction pressure was higher in the Ovx group (26.4±0.48 mmHg) than in the control group (21.8±0.37 mmHg) but was lower in the Ovx+Est group (23.9±0.76 mmHg) (P<0.05). Caveolin-1 was expressed in the capillaries, arterioles, and venules. Expression of the protein caveolin-1 was significantly lower after ovariectomy and was restored to control levels after treatment with 17β-estradiol (P<0.05).

CONCLUSIONS

Hormonal alterations cause a significant change in the expression of caveolin-1, which suggests that caveolin-1 might have a functional role in the overactivity of the detrusor muscle related to hormonal alterations in the urinary bladders of rats.

The physiological significance of p27(KIP1) expression in detrusor function

PURPOSE

Bladder outlet obstruction results in smooth muscle cell hyperplasia, decreased bladder wall compliance, and lower and upper urinary tract pathology. The cyclin-dependent kinase inhibitor p27(KIP1) regulates bladder smooth muscle cell proliferation in response to bladder outlet obstruction but little is known about its physiological role in the bladder. We investigated the role of p27(KIP1) in the structure and function of the detrusor layer of the bladder wall.

MATERIALS AND METHODS

We used immunoblotting and reverse transcriptase-polymerase chain reaction to examine cell cycle regulation in response to increased mechanical tension in an in vitro model of tension induced smooth muscle cell proliferation and an in vivo model of bladder outlet obstruction. We compared unobstructed bladders of p27(+/+) and p27(-/-) mice (Jackson Laboratory, Bar Harbor, Maine) structurally by histological staining and functionally by in vivo cystometric measurements of bladder capacity, detrusor compliance and detrusor leak point pressure.

RESULTS

Increased tension decreased p27(KIP1) at the protein level in human bladder smooth muscle cells and in intact murine bladder smooth muscle. p27(-/-) mice had bladder smooth muscle cell hyperplasia even in the absence of bladder outlet obstruction. While p27 loss had little effect on detrusor leak point pressure, p27(-/-) mice had significantly decreased bladder capacity and detrusor compliance.

CONCLUSIONS

To our knowledge we provide the first report of the in vivo significance of p27(KIP1) in the regulation of detrusor function using a cystometric approach. We identified a role for p27(KIP1) in protecting against dysregulated smooth muscle cell proliferation, bladder capacity and detrusor compliance under normotensive conditions.

A complex of Ca(V)1.2/PKC is involved in muscarinic signaling in smooth muscle

Here we present functional and biochemical evidence for a Ca(2+) channel (Ca(V)1.2)/protein kinase C (PKC) signaling complex being a key player in muscarinic regulation of urinary bladder smooth muscle. Muscarinic stimulation induced Ca(2+) signals and concomitant contractions in detrusor muscle from mice that were dependent on functional Ca(2+) channels. These signals were still present in muscles being depolarized by 85 mM extracellular K(+). Muscarinic-induced contractions were reduced by a PKC inhibitor [bisindolylmaleimide I (BIM-I)] and a phospholipase D (PLD) inhibitor (1-butanol). A phorbol ester (PDBu) enlarged muscarinic-induced Ca(2+) signals and contractions. The effects of BIM-I and PDBu were inhibited by isradipine and/or absent in muscles from Ca(V)1.2-deficient mice. Both carbachol and PDBu increased Ca(V)1.2 channel currents in isolated bladder myocytes. Blue native-PAGE electrophoresis revealed that Ca(V)1.2, PKC, and PLD are closely associated in muscles being previously stimulated by carbachol. Immunoprecipitation using anti-Ca(V)1.2 followed by Western blotting demonstrated that Ca(V)1.2 and PKC are coupled in stimulated muscles from wild-type mice. Autoradiography on immunoprecipitates showed that Ca(V)1.2 is a substrate for PKC-mediated phosphorylation. These findings suggest that a signaling complex consisting of Ca(V)1.2, PKC, and, probably, PLD controls muscarinic-mediated phasic contraction of urinary bladder smooth muscle.

Human urinary bladder smooth muscle is dependent on membrane cholesterol for cholinergic activation

Voiding is mediated by muscarinic receptors in urinary bladder smooth muscle cells. Lipid rafts and caveolae are cholesterol enriched membrane domains that modulate the activity of G protein-coupled receptors and second messenger systems. Conflicting findings regarding sensitivity of muscarinic signalling to cholesterol desorption, which perturbs lipid rafts and caveolae, have been reported, and no study has used human urinary bladder. Here, the dependence of human bladder muscarinic receptor signalling on plasma membrane cholesterol was examined. Nerve-mediated contraction, elicited by electrical field stimulation of human bladder strips, was impaired by desorption of cholesterol using methyl-beta-cyclodextrin, and the concentration-response curve for the muscarinic agonist carbachol was right-shifted. No effect of cholesterol desorption was observed in rat, and in mouse increased maximum contraction was seen. Expression of caveolin-1, PLCbeta1 and M3 muscarinic receptors did not differ between species in a manner that would explain the differential sensitivity to cholesterol desorption. In human bladder, threshold depolarisation eliminated the difference between cyclodextrin-treated and control preparations. Contraction elicited by depolarisation per se was not affected. M3 muscarinic receptors appeared clustered along plasma membrane profiles as shown by immunohistochemical staining of human bladder, but no redistribution in association with cholesterol reduction was seen. Thus, muscarinic receptor-induced contraction of the urinary bladder exhibits species-specific differences in its sensitivity to cholesterol desorption suggesting differential roles of lipid rafts/caveolae in muscarinic receptor signalling between species.

Muscarinic receptor-mediated bronchoconstriction is coupled to caveolae in murine airways

Cholinergic bronchoconstriction is mediated by M(2) and M(3) muscarinic receptors (MR). In heart and urinary bladder, MR are linked to caveolin-1 or -3, the structural proteins of caveolae. Caveolae are cholesterol-rich, omega-shaped invaginations of the plasma membrane. They provide a scaffold for multiple G protein receptors and membrane-bound enzymes, thereby orchestrating signaling into the cell interior. Hence, we hypothesized that airway MR signaling pathways are coupled to caveolae as well. To address this issue, we determined the distribution of caveolin isoforms and MR subtype M2R in murine and human airways and investigated protein-protein associations by fluorescence resonance energy transfer (FRET)-confocal laser scanning microscopy (CLSM) analysis in immunolabeled murine tissue sections. Bronchoconstrictor responses of murine bronchi were recorded in lung-slice preparations before and after caveolae disruption by methyl-β-cyclodextrin, with efficiency of this treatment being validated by electron microscopy. KCl-induced bronchoconstriction was unaffected after treatment, demonstrating functional integrity of the smooth muscle. Caveolae disruption decreased muscarine-induced bronchoconstriction in wild-type and abolished it in M2R(-/-) and M3R(-/-) mice. Thus M2R and M3R signaling pathways require intact caveolae. Furthermore, we identified a presumed skeletal and cardiac myocyte-specific caveolin isoform, caveolin-3, in human and murine bronchial smooth muscle and found it to be associated with M2R in situ. In contrast, M2R was not associated with caveolin-1, despite an in situ association of caveolin-1 and caveolin-3 that was detected. Here, we demonstrated that M2R- and M3R-mediated bronchoconstriction is caveolae-dependent. Since caveolin-3 is directly associated with M2R, we suggest caveolin-3 as novel regulator of M2R-mediated signaling.

Catecholamines relax detrusor through beta 2-adrenoceptors in mouse and beta 3-adrenoceptors in man

(-)-Isoproterenol [4-[1-hydroxy-2-[(1-methylethyl)amino]ethyl]-1,2-benzene diol hydrochloride] relaxes murine detrusor through beta-adrenoceptors (ARs); however, the beta-AR subtypes involved are unknown. beta(2)-ARs have been associated with caveolae, plasma-lemmal scaffolding domains that are absent in caveolin-1 (cav-1) knockout (KO) mice. Here, we studied detrusor responses in the absence and presence of beta-AR subtype-selective antagonists in wild-type (WT) and cav-1 KO mice. To inquire whether the murine detrusor model is relevant to man, beta-AR subtypes that mediate (-)-isoproterenol-evoked human detrusor relaxation were investigated. In WT mice, (-)-isoproterenol concentration-dependently relaxed the KCl (40 mM)-precontracted detrusor (-logEC(50)M = 8.04, E(max) = 62%). The effects of (-)-isoproterenol were surmountably antagonized by the beta(2)-AR-selective antagonist ICI 118,551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol] (pK(B) = 9.28) but not affected by the beta(1)-AR-selective antagonist CGP 20712 [1-[2-((3-carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol] and beta(3)-AR-selective L-748,337 [(S)-M-[4-[2-[3-[3-[acetamidomethyl)phenoxy)-2-hydroxypropyl]-amino]-ethyl]-phenylbenzsulfonamide)], suggesting involvement of beta(2)-AR only. The cav-1 KO detrusor displayed significant contractile dysfunction. (-)-Isoproterenol was less potent and efficient in relaxing detrusor from cav-1 KO (-logEC(50)M, 7.76; E(max) = 44%), but ICI 118,551 caused similar antagonism (pK(B) = 9.15), suggesting that beta(2)-AR function persisted in cav-1 KO. The beta(3)-AR-selective antagonist L-748,337 in the presence of ICI 118,551 and CGP 20712 caused additional blockade of (-)-isoproterenol effects in cav-1 KO, consistent with a beta(3)-AR involvement during relaxation and suppression of this effect in WT. (-)-Isoproterenol relaxed human detrusor muscle precontracted with carbachol (-logEC(50)M = 6.39, E(max) = 52%). However, the effects of (-)-isoproterenol in human detrusor were not blocked by CGP 20712 or ICI 118,551 but antagonized by L-748,337 (pK(B) = 7.65). We conclude that murine detrusor relaxation occurs via beta(2)-AR, and loss of caveolae does not perturb beta(2)-AR function but unmasks an additional activation of beta(3)-AR. In contrast, detrusor relaxation in man is mediated exclusively via beta(3)-AR.

Caveolae as organizers of pharmacologically relevant signal transduction molecules

Caveolae, a subset of membrane (lipid) rafts, are flask-like invaginations of the plasma membrane that contain caveolin proteins, which serve as organizing centers for cellular signal transduction. Caveolins (-1, -2, and -3) have cytoplasmic N and C termini, palmitolylation sites, and a scaffolding domain that facilitates interaction and organization of signaling molecules so as to help provide coordinated and efficient signal transduction. Such signaling components include upstream entities (e.g., G protein-coupled receptors (GPCRs), receptor tyrosine kinases, and steroid hormone receptors) and downstream components (e.g., heterotrimeric and low-molecular-weight G proteins, effector enzymes, and ion channels). Diseases associated with aberrant signaling may result in altered localization or expression of signaling proteins in caveolae. Caveolin-knockout mice have numerous abnormalities, some of which may reflect the impact of total body knockout throughout the life span. This review provides a general overview of caveolins and caveolae, signaling molecules that localize to caveolae, the role of caveolae/caveolin in cardiac and pulmonary pathophysiology, pharmacologic implications of caveolar localization of signaling molecules, and the possibility that caveolae might serve as a therapeutic target.

Caveolae facilitate muscarinic receptor-mediated intracellular Ca2+ mobilization and contraction in airway smooth muscle

Contractile responses of airway smooth muscle (ASM) determine airway resistance in health and disease. Caveolae microdomains in the plasma membrane are marked by caveolin proteins and are abundant in contractile smooth muscle in association with nanospaces involved in Ca(2+) homeostasis. Caveolin-1 can modulate localization and activity of signaling proteins, including trimeric G proteins, via a scaffolding domain. We investigated the role of caveolae in contraction and intracellular Ca(2+) ([Ca(2+)](i)) mobilization of ASM induced by the physiological muscarinic receptor agonist, acetylcholine (ACh). Human and canine ASM tissues and cells predominantly express caveolin-1. Muscarinic M(3) receptors (M(3)R) and Galpha(q/11) cofractionate with caveolin-1-rich membranes of ASM tissue. Caveolae disruption with beta-cyclodextrin in canine tracheal strips reduced sensitivity but not maximum isometric force induced by ACh. In fura-2-loaded canine and human ASM cells, exposure to methyl-beta-cyclodextrin (mbetaCD) reduced sensitivity but not maximum [Ca(2+)](i) induced by ACh. In contrast, both parameters were reduced for the partial muscarinic agonist, pilocarpine. Fluorescence microscopy revealed that mbetaCD disrupted the colocalization of caveolae-1 and M(3)R, but [N-methyl-(3)H]scopolamine receptor-binding assay revealed no effect on muscarinic receptor availability or affinity. To dissect the role of caveolin-1 in ACh-induced [Ca(2+)](i) flux, we disrupted its binding to signaling proteins using either a cell-permeable caveolin-1 scaffolding domain peptide mimetic or by small interfering RNA knockdown. Similar to the effects of mbetaCD, direct targeting of caveolin-1 reduced sensitivity to ACh, but maximum [Ca(2+)](i) mobilization was unaffected. These results indicate caveolae and caveolin-1 facilitate [Ca(2+)](i) mobilization leading to ASM contraction induced by submaximal concentrations of ACh.

Neuronally released acetylcholine acts on the M2 muscarinic receptor to oppose the relaxant effect of isoproterenol on cholinergic contractions in mouse urinary bladder

We investigated whether M(2) muscarinic receptor activation opposes isoproterenol-induced relaxation in mouse urinary bladder and whether endogenous acetylcholine acts through a similar M(2) mechanism. When measured in urinary bladder from M(3) receptor knockout mice, the muscarinic agonist oxotremorine-M elicited only very weak contractions. In the presence of alpha,beta-methylene ATP (30 microM) and isoproterenol (1 microM), however, oxotremorine-M elicited a robust contractile response. This response was completely absent in bladder from M(2)/M(3) double knockout mice, indicating that activation of the M(2) receptor inhibits the relaxant effect of isoproterenol on the contraction to alpha,beta-methylene ATP. Similar results were obtained when prostaglandin F(2alpha) (5 microM) was used as the contractile agent but not when serotonin was used. Electrical field stimulation of the urinary bladder from wild-type mouse elicited contractions that were inhibited 20% by atropine and 40% by desensitization with alpha,beta-methylene ATP. When measured in the presence of alpha,beta-methylene ATP to desensitize the purinergic component of contraction, isoproterenol exhibited moderately greater relaxant activity in field-stimulated bladder from the M(2) knockout mouse compared with that observed in wild-type bladder. This differential relaxant effect of isoproterenol was greatly increased in the presence of physostigmine. In contrast, no differential effects were noted for isoproterenol in similar experiments on bladders from M(3) knockout and M(2)/M(3) double knockout mice in the presence of physostigmine. Our results suggest that neuronally released acetylcholine acts on the M(2) muscarinic receptor to inhibit the relaxant effect of isoproterenol on the minor, cholinergic component of contraction in the field-stimulated mouse urinary bladder.

Smooth muscle caveolae differentially regulate specific agonist induced bladder contractions

AIMS

Caveolae are cholesterol-rich plasmalemmal microdomains that serve as sites for sequestration of signaling proteins and thus may facilitate, organize, and integrate responses to extracellular stimuli. While previous studies in the bladder have demonstrated alterations in caveolae with particular physiologic or pathologic conditions, little attention has been focused on the functional significance of these organelles. Therefore, the purpose of this study was to investigate the role of caveolae in the modulation of receptor-mediated signal transduction and determine the presence and localization of caveolin proteins in bladder tissue.

METHODS

Contractile responses to physiologic agonists were measured in rat bladder tissue before and after disruption of caveolae achieved by depleting membrane cholesterol with methyl-beta-cyclodextrin. Stimulation with agonists was repeated after caveolae were restored as a result of cholesterol replenishment. RT-PCR, immmunohistochemistry, and Western blotting were used to determine the expression and localization of caveolin mRNA and proteins.

RESULTS

Following caveolae disruption, contractile responses to angiotensin II and serotonin were attenuated, whereas responses to bradykinin and phenylephrine were augmented. Cholesterol replenishment restored responses towards baseline. Carbachol and KCl induced contractions were not affected by caveolae disruption. Ultrastructure analysis confirmed loss of caveolae following cholesterol depletion with cyclodextrin and caveolae restoration following cholesterol replacement. Gene and protein expression of caveolin-1, -2, and -3 was detected in bladder tissue. Immunoreactivity for all three caveolins was observed in smooth muscle cells throughout the bladder.

CONCLUSIONS

The functional effects of cholesterol depletion on specific agonist-induced contractile events and the expression of all three caveolins in bladder smooth muscle support a central role for caveolae in regulation of selective G-protein-coupled receptor signaling pathways in bladder smooth muscle. Thus, caveolae serve to differentially regulate bladder smooth muscle by a stimulus-dependent potentiation or inhibition of bladder contraction.

Using Caveolin-1 Knockout Mouse to Study Impaired Detrusor Contractility and Disrupted Muscarinic Activity in the Aging Bladder

OBJECTIVES

The caveolin-1 knockout mouse has been proposed as an animal model to study impaired bladder contractility and detrusor overactivity. This study investigated the effects of aging on detrusor contraction in wild type and caveolin-1 knockout mice.

METHODS

Young (3-month-old) and old (1-year-old) male caveolin-1 knockout mice and their age-matched male wild type littermates (controls) were used. Longitudinal bladder strips were stimulated electrically (20 Hz) and pharmacologically using 1 to 10 microM carbachol (a nonsubtype selective cholinergic receptor agonist), 10 microM alpha,beta-methylene adenosine triphosphate (a purinergic receptor agonist), and 100 mM potassium (a depolarizing agent). Isometric bladder strip contractions were compared between the young wild type and knockout groups and between the old wild type and knockout groups.

RESULTS

The bladder strips from the 1-year-old knockout mice exhibited a 40% to 42% decrease in electrical neural contractions and carbachol-evoked contractions compared with the 1-year-old wild type controls (P <0.05). Even though the bladder strips from the 3-month-old knockout mice demonstrated a smaller decrease (29% to 32%) in electrical neural contractions and carbachol-evoked contractions compared with their age-matched controls, the trend did not reach statistical significance (P >0.05). The postjunctional cholinergic pathway was specifically disrupted in caveolin-1 knockout animals because no difference was found in contractility between the knockout and wild type mice (young or old) when the bladders were stimulated by alpha,beta-methylene adenosine triphosphate or potassium. The differences in cholinergic contractility between the knockout and wild type mice became significantly greater as the animals aged from 3 months old (young bladders) to 1 year old (aged bladders).

CONCLUSIONS

The male caveolin-1 knockout mouse provides a much-needed animal model for the study of impaired detrusor contractility in the aging bladder.

Lipid raft microdomains and neurotransmitter signalling

Lipid rafts are specialized structures on the plasma membrane that have an altered lipid composition as well as links to the cytoskeleton. It has been proposed that these structures are membrane domains in which neurotransmitter signalling might occur through a clustering of receptors and components of receptor-activated signalling cascades. The localization of these proteins in lipid rafts, which is affected by the cytoskeleton, also influences the potency and efficacy of neurotransmitter receptors and transporters. The effect of lipid rafts on neurotransmitter signalling has also been implicated in neurological and psychiatric diseases.

Increased Rho activation and PKC-mediated smooth muscle contractility in the absence of caveolin-1

Caveolae are omega-shaped membrane invaginations that are abundant in smooth muscle cells. Since many receptors and signaling proteins co-localize with caveolae, these have been proposed to integrate important signaling pathways. The aim of this study was to test whether RhoA/Rho-kinase and protein kinase C (PKC)-mediated Ca2+sensitization depends on caveolae using caveolin (Cav)-1-deficient (KO) and wild-type (WT) mice. In WT smooth muscle, caveolae were detected and Cav-1, -2 and -3 proteins were expressed. Relative mRNA expression levels were ∼15:1:1 for Cav-1, -2, and -3, respectively. Caveolae were absent in KO and reduced levels of Cav-2 and Cav-3 proteins were seen. In intact ileum longitudinal muscle, no differences in the responses to 5-HT or the muscarinic agonist carbachol were found, whereas contraction elicited by endothelin-1 was reduced. Rho activation by GTPγS was increased in KO compared with WT as shown using a pull-down assay. Following α-toxin permeabilization, no difference in Ca2+sensitivity or in Ca2+sensitization was detected. In KO femoral arteries, phorbol 12,13-dibutyrate (PDBu)-induced and PKC-mediated contraction was increased. This was associated with increased α1-adrenergic contraction. Following inhibition of PKC, α1-adrenergic contraction was normalized. PDBu-induced Ca2+sensitization was not increased in permeabilized femoral arteries. In conclusion, Rho activation, but not Ca2+sensitization, depends on caveolae in the ileum. Moreover, PKC driven arterial contraction is increased in the absence of caveolin-1. This depends on an intact plasma membrane and is not associated with altered Ca2+sensitivity.

Detrusor Underactivity: Clinical Features and Pathogenesis of an Underdiagnosed Geriatric Condition

Urinary incontinence and other lower urinary tract symptoms exert a major influence on the health and independence of frail older people. Detrusor underactivity (DU) is defined as a contraction of reduced strength and/or duration, resulting in prolonged bladder emptying and/or a failure to achieve complete bladder emptying within a normal time span. DU may influence the clinical presentation and impede the therapy of disorders as common and as disparate as detrusor overactivity, urinary retention, and benign prostatic hyperplasia. Urodynamically, nearly two-thirds of incontinent nursing home residents exhibit DU. The clinical diagnosis of DU when present alone or in association with other bladder conditions such as detrusor overactivity (detrusor hyperactivity with impaired contractility (DHIC)) is challenging, because symptoms lack adequate precision. A catheterized and increasingly noninvasive ultrasound-based postvoid residual assessment allows a bedside diagnosis of retention and may suggest the presence of DU in individuals (mostly women) with a low likelihood of bladder outlet obstruction (BOO). Nevertheless, it cannot differentiate primary DU from retention secondary to BOO. The management of individuals with DHIC remains unsatisfactory, because antispasmodic anticholinergic medications may worsen retention, whereas bethanechol does not improve bladder emptying. Human detrusor biopsies reveal axonal degeneration, muscle loss, and fibrosis in DU. Animal studies suggest that multiple risk factors, including retention itself, lack of estrogen, infection, inflammation, and aging, may contribute to DU. Priority areas for future research include efforts to facilitate clinical nonurodynamic diagnosis of probable DU plus translational research designed to address the pathogenesis of this complex multifactorial geriatric syndrome.

Functional changes in bladder tissue from type III collagen-deficient mice

OBJECTIVE

Collagen fibers impart tensile strength and transfer tension from bladder smooth muscle cells. We have previously shown that fibrotic bladders are characterized by an increased type III:type I collagen ratio. To determine the effect of decreased type III collagen on bladder function, type III collagen-deficient mice (COL3A1) were studied physiologically.

METHODS

Bladders from wild-type (+/+) and heterozygous (+/-) COL3A1 mice were biochemically characterized to determine total collagen (hydroxyproline analysis) and collagen subtype concentration (cyanogen bromide digestion and ELISA). Alterations in collagen fiber diameter were assessed by electron microscopy. Bladder muscle strips were used to assess physiologic function.

RESULTS

Hydroxyproline content decreased in heterozygous bladders, which had 50% less type III collagen. Wild-type bladders had a biphasic distribution of collagen fiber sizes, whereas heterozygous bladder collagen fibers spanned a broad range. Physiologically, there were no differences in contractile responses between wild-type and heterozygotes when stimulated with ATP, carbachol or KCl, indicating normal contraction via purinergic and muscarinic receptors, and in response to direct membrane depolarization. In contrast, tension generation in heterozygotes was decreased after field stimulation (FS), indicating decreased synaptic transmission. Length-tension studies showed that the heterozygote muscle strips generated less tension per unit length, indicating that they were more compliant than wild-type controls.

CONCLUSIONS

Critical levels of type III collagen appear to be a requirement for normal bladder tension development and contraction. Our data show that a decrease in the type III:type I collagen ratio, and altered fiber size, results in a more compliant bladder with altered neurotransmitter function.

Getting rid of caveolins: phenotypes of caveolin-deficient animals

The elucidation of the role of caveolae has been the topic of many investigations which were greatly enhanced after the discovery of caveolin, the protein marker of these flask-shaped plasma membrane invaginations. The generation of mice deficient in the various caveolin genes (cav-1, cav-2 and cav-3) has provided physiological models to unravel the role of caveolins or caveolae at the whole organism level. Remarkably, despite the essential role of caveolins in caveolae biogenesis, all knockout mice are viable and fertile. However, lack of caveolae or caveolins leads to a wide range of phenotypes including muscle, pulmonary or lipid disorders, suggesting their implication in many cellular processes. The aim of this review is to give a broad overview of the phenotypes described for the caveolin-deficient mice and to link them to the numerous functions so far assigned to caveolins/caveolae.