Role of angiotensin II in bladder smooth muscle growth and function

Insights into the associative role of hypertension and angiotensin II receptor in lower urinary tract dysfunction

In men, the lower urinary tract comprises the urinary bladder, urethra, and prostate, and its primary functions include urine storage and voiding. Hypertension is a condition that causes multi-organ damage and an age-dependent condition. Hypertension and the renin-angiotensin system activation are associated with the development of lower urinary tract dysfunction. Hypertensive animal models show bladder dysfunction, urethral dysfunction, and prostatic hyperplasia. In the renin-angiotensin system, angiotensin II and the angiotensin II type 1 receptor, which are expressed in the lower urinary tract, have been implicated in the pathogenesis of lower urinary tract dysfunction. Moreover, among the several antihypertensives, renin-angiotensin system inhibitors have proven effective in human and animal models of lower urinary tract dysfunction. This review aimed to elucidate the hitherto known mechanisms underlying the development of lower urinary tract dysfunction in relation to hypertension and the angiotensin II/angiotensin II type 1 receptor axis and the effect of renin-angiotensin system inhibitors on lower urinary tract dysfunction. Possible mechanisms through which hypertension or activation of Ang II/AT1 receptor axis causes LUTD such as bladder dysfunction, urethral dysfunction, and prostatic hyperplasia. LUT: lower urinary tract, LUTD: lower urinary tract dysfunction, AT1: angiotensin II type 1, ACE: angiotensin-converting enzyme.

Hypertension and urologic chronic pelvic pain syndrome: An analysis of MAPP-I data

BACKGROUND

Urologic chronic pelvic pain syndrome (UCPPS), which includes interstitial cystitis/bladder pain syndrome (IC/BPS) and chronic prostatitis (CP/CPPS), is associated with increased voiding frequency, nocturia, and chronic pelvic pain. The cause of these diseases is unknown and likely involves many different mechanisms. Dysregulated renin-angiotensin-aldosterone-system (RAAS) signaling is a potential pathologic mechanism for IC/BPS and CP/CPPS. Many angiotensin receptor downstream signaling factors, including oxidative stress, fibrosis, mast cell recruitment, and increased inflammatory mediators, are present in the bladders of IC/BPS patients and prostates of CP/CPPS patients. Therefore, we aimed to test the hypothesis that UCPPS patients have dysregulated angiotensin signaling, resulting in increased hypertension compared to controls. Secondly, we evaluated symptom severity in patients with and without hypertension and antihypertensive medication use.

METHODS

Data from UCPPS patients (n = 424), fibromyalgia or irritable bowel syndrome (positive controls, n = 200), and healthy controls (n = 415) were obtained from the NIDDK Multidisciplinary Approach to the Study of Chronic Pelvic Pain I (MAPP-I). Diagnosis of hypertension, current antihypertensive medications, pain severity, and urinary symptom severity were analyzed using chi-square test and t-test.

RESULTS

The combination of diagnosis and antihypertensive medications use was highest in the UCPPS group (n = 74, 18%), followed by positive (n = 34, 17%) and healthy controls (n = 48, 12%, p = 0.04). There were no differences in symptom severity based on hypertension in UCPPS and CP/CPPS; however, IC/BPS had worse ICSI (p = 0.031), AUA-SI (p = 0.04), and BPI pain severity (0.02). Patients (n = 7) with a hypertension diagnosis not on antihypertensive medications reported the greatest severity of pain and urinary symptoms.

CONCLUSION

This pattern of findings suggests that there may be a relationship between hypertension and UCPPS. Treating hypertension among these patients may result in reduced pain and symptom severity. Further investigation on the relationship between hypertension, antihypertensive medication use, and UCPPS and the role of angiotensin signaling in UCPPS conditions is needed.

Mechanisms involved in nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox)-derived reactive oxygen species (ROS) modulation of muscle function in human and dog bladders

Roles of redox signaling in bladder function is still under investigation. We explored the physiological role of reactive oxygen species (ROS) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) in regulating bladder function in humans and dogs. Mucosa-denuded bladder smooth muscle strips obtained from 7 human organ donors and 4 normal dogs were mounted in muscle baths, and trains of electrical field stimulation (EFS) applied for 20 minutes at 90-second intervals. Subsets of strips were incubated with hydrogen peroxide (H2O2), angiotensin II (Ang II; Nox activator), apocynin (inhibitor of Noxs and ROS scavenger), or ZD7155 (specific inhibitor of angiotensin type 1 (AT1) receptor) for 20 minutes in continued EFS trains. Subsets treated with inhibitors were then treated with H2O2 or Ang II. In human and dog bladders, the ROS, H2O2 (100μM), caused contractions and enhanced EFS-induced contractions. Apocynin (100μM) attenuated EFS-induced strip contractions in both species; subsequent treatment with H2O2 restored strip activity. In human bladders, Ang II (1μM) did not enhance EFS-induced contractions yet caused direct strip contractions. In dog bladders, Ang II enhanced both EFS-induced and direct contractions. Ang II also partially restored EFS-induced contractions attenuated by prior apocynin treatment. In both species, treatment with ZD7155 (10μM) inhibited EFS-induced activity; subsequent treatment with Ang II did not restore strip activity. Collectively, these data provide evidence that ROS can modulate bladder function without exogenous stimuli. Since inflammation is associated with oxidative damage, the effects of Ang II on bladder smooth muscle function may have pathologic implications.

Copy number variations in a population with prune belly syndrome

Prune Belly Syndrome (PBS) is a congenital multisystem myopathy with mild to lethal severity. While of uncertain etiology, 95% male predominance and familial occurrence suggest a genetic basis. As copy number variations (CNVs) can cause unexplained genetic disorders, we tested for novel CNVs in a large PBS population. We genotyped 21 unrelated PBS patients by high-resolution array comparative genomic hybridization (aCGH) and phenotyped using a novel PBS severity scoring system. Available parents were screened for detected CNV via quantitative PCR (qPCR). We additionally screened for recurrence of identified novel candidate CNVs on 106 PBS probands by qPCR. We identified 10 CNVs in 8 of 21 PBS patients tested (38%). Testing confirmed inheritance from an unaffected biological parent in six patients; parental samples were unavailable in two probands. One candidate CNV includes duplication of the X-chromosome AGTR2 gene, known to function in urinary tract development. Subsequent screening of the larger PBS cohort did not identify any recurrent CNVs. Presence of CNV did not correlate with PBS severity scoring. CNVs were uncommon in this large PBS population, but analysis of identified variants may inform disease pathogenesis and reveal targets for therapeutic intervention for this rare, severe disorder.

Effect of the Renin-Angiotensin System on the Obstructed Bladder

Bladder hypertrophy and dysfunction are well-known bladder responses to outlet obstruction (i.e. urodynamic overload). Cardiac hypertrophy and heart failure are also caused by hemodynamic overload, and many basic and clinical studies suggest that the local renin-angiotensin system (RAS) has a crucial role in load-induced cardiac pathogenesis. The similarity of the response of the heart and the bladder to overload suggests that angiotensin II (AngII) may have a similar regulatory role in pathological remodeling, such as muscle growth and collagen production of the obstructed bladder. Previous in vitro studies show that angiotensin I is converted to AngII by angiotensin converting enzyme (ACE) or chymase, which exists in the human bladder. In addition, many studies using contractile responses to AngII, autoradiography, radioreceptor assay and mRNA expression demonstrate the presence of AngII receptor in the bladder from various animals and the human. Recent evidence indicates that AngII is released from bladder smooth muscle cells (SMCs) in response to a repetitive stretch stimulus, and subsequently activates AT1 in an autocrine fashion. This AT1 activation has been shown to mediate heparin-binding epidermal growth factor-like growth factor gene expression and to increase the DNA synthesis rate of bladder SMCs. Consistent with this in vitro study, previous studies and our preliminary data suggest the usefulness of AT1 antagonists or ACE inhibitor in bladder outlet obstruction of the rabbit and rat. Taken together, the local RAS contributes to structural and functional alterations in the bladder after obstruction.

The effects of Ins2(Akita) diabetes and chronic angiotensin II infusion on cystometric properties in mice

AIMS

Diabetes is associated with both dysfunction of the lower urinary tract (LUT) and overactivity of the renin-angiotensin system (RAS). Although it is well known that the RAS affects normal LUT function, very little is known about RAS effects on the diabetic LUT. Accordingly, we investigated the effects of chronic angiotensin II (AngII) treatment on the LUT in a model of type 1 diabetes.

METHODS

Ins2(Akita) diabetic mice (20 weeks old) and their age-matched background controls underwent conscious cystometric evaluation after 4 weeks of chronic AngII treatment (700 ng/kg/min by osmotic pump) or vehicle (saline).

RESULTS

Diabetic mice had compensated LUT function with bladder hypertrophy. Specifically, micturition volume, residual volume, and bladder capacity were all increased, while voiding efficiency and pressure generation were unchanged as bladder mass, contraction duration, and phasic urethral function were increased. AngII significantly increased voiding efficiency and peak voiding pressure and decreased phasic frequency irrespective of diabetic state and, in diabetic but not normoglycemic control mice, significantly decreased residual volume and increased contraction duration and nonphasic contraction duration.

CONCLUSIONS

The Ins2(Akita) diabetic mice had compensated LUT function at 20 weeks of age. Even under these conditions, AngII had beneficial effects on LUT function, resulting in increased voiding efficiency. Future studies should therefore be conducted to determine whether AngII can rescue the decompensated LUT function occurring in end-stage diabetic uropathy.

Metabolic syndrome and lower urinary tract symptoms

Recently, clinical and epidemiologic data indicating the involvement of metabolic syndrome (MetS) in the pathogenesis and progression of lower urinary tract symptom (LUTS)/benign prostatic hyperplasia (BPH) are reported. This review evaluates the reports on the influence of MetS in the development and progression of LUTS/BPH, and discusses possible clinical implications for the management and treatment of this disease. Recent studies on the epidemiological relationship between MetS and LUTS hypothesize that MetS may be associated with an overactivity of the autonomic nervous system for which hyperinsulinemia, a key element of the MetS, might be responsible. An alternative explanation is that LUTS are associated with chronic ischemia of pelvis resulting from atherosclerotic changes in blood vessels, which leads the production of reactive oxygen species, which can damage the bladder detrusor. Control of autonomic nervous system overactivity and control of chronic bladder ischemia have potential as new targets for LUTS treatment. Studies suggest an association of MetS with LUTS/BPH, although further research is needed to understand how MetS influences LUTS/BPH. MetS should be considered a new domain in basic and clinical research in patients with LUTS/BPH and as a target for treatment.

Expression of Angiotensin II Type 1 Receptor in Rat Bladder Smooth Muscle Cells in Response to a Streptzotocin Induced Diabetes Mellitus Model

INTRODUCTION

The aim of this study was to investigate angiotensin II type 1 (AT1) receptors in rat bladder smooth muscle cells and alterations of AT1 receptors by diabetes mellitus and diuretic states.

MATERIALS AND METHODS

Diabetes and diuresis were induced in adult female rats by a single intraperitoneal injection of streptozotocin and feeding 5% sucrose in water. Cystometry was performed on control, diuretic, and diabetic rats at 2 and 8 weeks after treatment. Immunohistochemical staining was used to detect expression of AT1 receptors in the bladder smooth muscle cell membrane.

RESULTS AND CONCLUSIONS

In diabetic rats, expression of AT1 receptors in the bladder smooth muscle cell membrane increased at 2 weeks and further increased at 8 weeks. The local renin-angiotensin system in the rat bladder might be activated by the continuous hyperglycemia caused by intraperitoneal injection of streptozotocin administration.

Characterization of the urinary bladder dysfunction in renovascular hypertensive rats

AIMS

Association between arterial hypertension and urinary bladder dysfunction has been reported in humans and spontaneously hypertensive rats. However, no study exists evaluating the bladder dysfunction in conditions of renovascular hypertension. The purpose of this study was to characterize the bladder dysfunction in two kidney-one clip (2K-1C) hypertensive rats.

METHODS

A silver clip was placed around the renal artery of male Wistar rats. After 8 weeks, cystometric study, concentration-response curves to contractile and relaxant agents, frequency-dependent contractions, histomorphometry, muscarinic M(2) /M(3) mRNA expression and cyclic AMP measurements were performed.

RESULTS

2K-1C rats showed enhanced bladder volume, wall thickness and smooth muscle density. 2K-1C rats also exhibited increases in bladder capacity and non-void contractions, and decreases in the inter-contraction intervals. In isolated detrusor smooth muscle (DSM), contractions to carbachol and electrical-field stimulation (EFS) were significantly greater in 2K-1C rats. The Rho-kinase inhibitor Y27632 (10 µM) significantly reduced the carbachol-induced contractions in SHAM and 2K-1C rats, but DSM remained overactive in 2K-1C rats in presence of Y27632. Concentration-dependent contractions to the P2X receptor agonist α,β-methylene ATP, KCl and extracellular Ca(2+) did not change between SHAM and 2K-1C groups. In 2K-1C rats, isoproterenol, metaproterenol and BRL 37-344 (non-selective, β(2) - and β(3) -selective adrenoceptor agonists, respectively) produced significantly lower relaxations and decreased cAMP levels, whereas relaxant responses to sodium nitroprusside and BAY 41-2272 remained unchanged. Muscarinic M(3) mRNA expression receptors were higher in 2K-1C group.

CONCLUSIONS

Renovascular hypertensive rats exhibit bladder dysfunction that involves tissue remodeling and enhanced muscarinic M(3) -mediated contractions associated with reduced β-adrenoceptor-mediated signal transduction.

Basic fibroblast growth factor modulates proliferation and collagen expression in urinary bladder smooth muscle cells

Bladder hypertrophy is a general consequence of bladder outlet obstruction (BOO) and a typical phenomenon observed in clinical urologic diseases such as benign prostatic hyperplasia and neurogenic bladder. It is characterized by smooth muscle hyperplasia, altered extracellular matrix composition, and increased contractile function. Various growth factors are likely involved in hypertrophic pathophysiology, but their functions remain unknown. In this report, the role of basic fibroblast growth factor (bFGF) was investigated using a rat bladder smooth muscle cell (BSMC) culture system and an original animal model, in which bFGF was released from a gelatin hydrogel directly onto rat bladders. bFGF treatment promoted BSMC proliferation both in vitro and in vivo. In vitro, bFGF downregulated the expression of type I collagen, but upregulated type III collagen. ERK1/2, but not p38MAPK, was activated by bFGF, whereas inhibition of ERK1/2 by PD98059 reversed bFGF-induced BSMC proliferation, type I collagen downregulation, and type III collagen upregulation. In the in vivo release model, bFGF upregulated type III collagen and increased the contractile force of treated bladders. In parallel with these findings, hypertrophied rat bladders created by urethral constriction showed increased urothelial bFGF expression, BSMC proliferation, and increased type III collagen expression compared with sham-operated rats. These data suggest that bFGF from the urothelium could act as a paracrine signal that stimulates the proliferation and matrix production of BSMC, thereby contributing to the hypertrophic remodeling of the smooth muscle layer.

Angiotensin II plays a role in acute murine experimental autoimmune cystitis

OBJECTIVES

To investigate whether angiotensin II (AII) receptor antagonism decreases the inflammation and oedema in acute murine experimental autoimmune cystitis (EAC), as interstitial cystitis (IC) might have an autoimmune component and AII has been implicated in autoimmune-mediated vascular congestion, oedema and scarring.

MATERIALS AND METHODS

Female Balb/cAN mice were divided into three treatment groups (eight in each group) that were autoimmunized with bladder homogenate to induce EAC. One group received an AII type 1 receptor (AT(1)) antagonist, one group an AII type 2 receptor (AT(2)) antagonist, and one group remained untreated (EAC). A control and sham-injected group were also included. After 10 weeks, bladders were removed, sectioned, and stained with haematoxylin and eosin.

RESULTS

Grossly, there was no thickening or adhesions in the bladders of the control or sham-injected mice. In five of seven surviving EAC bladders, there were dense adhesions to surrounding peritoneal structures. There were also adhesions and bladder thickening in all of the AT(2) antagonist-treated mice (though in a milder form) but in only two of seven surviving AT(1) antagonist-treated mice. There was no inflammation or oedema in the sham and control groups. All the EAC bladders were inflamed, with submucosal oedema and urothelial detachment from the lamina propria. In the AT(1) antagonist-treated mice there was no inflammation or oedema. By contrast, all AT(2) antagonist-treated mice had moderate inflammation and minor detachment of the urothelium from the lamina propria.

CONCLUSIONS

AT(1) receptor blockade ameliorated the inflammatory infiltration, submucosal oedema, and urothelial detachment associated with EAC in mice. This was achieved to a lesser extent by AT(2) receptor blockade. If some patients with IC have a pathophysiology similar to that of EAC mice, there might be potential benefit from AII receptor blockade.

The role of angiotensin II in stress urinary incontinence: A rat model

AIMS

Pharmacological treatment for stress urinary incontinence (SUI) is limited to the use of non-selective alpha-agonists, which are often ineffective. Non-adrenergic mechanisms have also been implicated in urethral closure, including angiotensin II (Ang-II), which has been demonstrated throughout the urinary tract. We investigate the role of Ang-II in urethral tone in a rat model of SUI.

METHODS

Abdominal leak point pressure (ALPP) and retrograde urethral pressure profilometry (RLPP) were measured in 70 female virgin rats. Thirty rats underwent pudendal nerve injury (PNT), 30 had circumferential urethrolysis (U-Lys), and 10 had sham surgery. Rats received daily doses of Angiotensin Type 1 (AT-1) receptor inhibitor (20 mg/kg), Angiotensin Type 2 (AT-2) receptor antagonist (10 mg/kg), or Ang-II (2 mg/kg).

RESULTS

Following U-Lys, RLPP and ALPP decreased from 21.4 +/- 2.0 and 39.2 +/- 3.3 mm Hg, to 13.1 +/- 1.5 and 21.6 +/- 1.9 mmHg, respectively (P < 0.01). After PNT, RLPP, and ALPP decreased from 21.0 +/- 1.6 and 41.9 +/- 3.0 mmHg to 13.1 +/- 1.5 and 24.7 +/- 3.3 mmHg, respectively (P < 0.01). AT-1 inhibitor caused significant decrease in RLPP and ALPP from 21.0 +/- 6.2 and 41.8 +/- 9.4 mmHg, to 12.0 +/- 3.8 and 25.6 +/- 6.6 mmHg, respectively (P < 0.01). Likewise, AT-2 treatment reduced RLPP and ALPP from 21.4 +/- 6.3 and 40.1 +/- 1.7 mmHg, to 13.5 +/- 5.7 and 31.0 +/- 7.2 mmHg, respectively (P < 0.01). Following surgery, Ang-II administration restored RLPP and ALPP to baseline presurgical values.

CONCLUSIONS

AT-1 and AT-2 receptor inhibition significantly lowers urethral resistance, comparable to either neurogenic or urethrolytic injury. Ang-II treatment restored urethral tone in rats with intrinsic sphincter dysfunction. Ang II appears to serve a functional role in the maintenance of urethral tone and stress continence.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Cyr61 and CTGF are molecular markers of bladder wall remodeling after outlet obstruction

Cysteine-rich protein (Cyr61) and connective tissue growth factor (CTGF) are key immediate early growth factors with functions in cell proliferation, differentiation, and extracellular matrix synthesis. Studies were performed to assess the gene expression profile of Cyr61 and CTGF in rat urinary bladder during growth in response to partial outlet obstruction. The mRNA levels of Cyr61 as determined by ribonuclease protection assay increased sharply after 1 day and remained elevated throughout the time period of the obstruction. This correlates well with increased bladder weight. The CTGF mRNA levels seemed to peak within the second week of the urethral obstruction and correlate well with increased type I collagen mRNA. The expression pattern of either Cyr61 or CTGF proteins corroborated that of their respective mRNAs. Immunohistochemical analyses showed that immunoreactivity of Cyr61 was confined to detrusor smooth muscle and that of CTGF was detected within both detrusor muscle and lamina propria layers. These data strongly indicate the involvement of Cyr61 and CTGF in bladder wall remodeling as a result of the outlet obstruction.

Mechanical regulation of IGF-I and IGF-binding protein gene transcription in bladder smooth muscle cells

Mechanical forces are well known to modulate smooth muscle cell growth and synthetic phenotype. The signals controlling this process are complex and potentially involve changes in the expression of peptide growth factor genes such as those of the insulin-like growth factor (IGF) system. This study was designed to investigate the mechanical regulation of IGF-I and the binding proteins for IGF (IGFBPs) in smooth muscle cells cultured on a deformable surface and subjected to cyclic stretch. Using the RNase protection assay, we found that the application of a cyclic biaxial strain to cells induced a 2.5- to 4-fold increase in IGF-I mRNA levels after 8 h and an even greater increase after 16-24 h of stretch. This change was not affected by variations in the magnitude of the applied strain but was attenuated ( approximately 40%) when cells were treated with antagonists for angiotensin II receptors. Furthermore, the transcript levels of the three major IGF binding proteins produced in smooth muscle cells, e.g., IGFBP-2, IGFBP-4, and IGFBP-5, varied between stretched and control cells. Both IGFBP-2 and IGFBP-4 mRNA levels were consistently reduced in stretched cells but remained comparable to those of the control cells when the angiotensin II transducing pathway was blocked by inhibitors prior to the application of mechanical strain. Conversely, the gene expression of IGFBP-5 was upregulated in stretched cells, and neutralizing antibodies to IGF-I blocked this activation. Similarly, pharmacologic inhibition of the phosphatidylinositol 3-kinase, an important component of the IGF receptor transduction pathway, inhibited IGFBP-5 gene expression in stretched cells. These results suggest that the downstream effects of mechanical strain on IGF-I and IGFBP transcript levels are mediated, to greater or lesser extent, either through an angiotensin II tranducing pathway or via a feedback loop involving the autocrine secretion of IGF-I itself.