Urinary outflow obstruction increases apoptosis and deregulates Bcl-2 and Bax expression in the fetal ovine bladder

METTL3-dependent m6A modification mediates bladder remodeling after partial bladder outlet obstruction through CCN2 activation

AIMS

N6-methyladenosine (m6A) modification is a critical posttranscriptional event in gene regulation. Thus, identifying methyltransferase, demethylase, or m6A binding protein-mediated m6A modifications in cancer or noncancer transcriptomes has become a promising novel strategy for disease therapy development. However, novel insights into m6A modification in partial bladder outlet obstruction (pBOO) and detailed information about the drivers of bladder remodeling remain to be elucidated. Here, we first characterized the m6A modification landscape in pBOO and investigated potential actionable pharmaceutical targets for future therapies.

METHODS

We generated an improved animal model of pBOO in SD rats with urethral meatus stricture induced by suturing. Urodynamic investigations and cystometry were carried out to evaluate the physiologic changes elicited by pBOO. Whole-transcriptome sequencing (RNA-seq) and m6A-modified RNA immunoprecipitation sequencing (MeRIP-seq) were subsequently performed to analyze the expression pattern associated with bladder remodeling in pBOO.

RESULTS

The cystometric evaluation of bladder function demonstrated obvious increases in pressure-related parameters in the pBOO group. Hematoxylin and eosin staining and Masson's trichrome staining validated the occurrence of bladder remodeling. A global elevation in m6A RNA methylation levels was observed in parallel to a increased expression of METTL3 in the pBOO group. High-throughput sequencing revealed the differences in expression patterns between the pBOO and sham-operated groups. Furthermore, potential m6A-modified genes, including CCN2, may serve as new pharmaceutical targets to reverse bladder remodeling.

CONCLUSIONS

Exploring the roles of m6A-modified genes identified as associated with bladder remodeling by integrating RNA-seq and MeRIP-seq data can offer new insights for developing promising treatments for pBOO patients.

Envisioning treating genetically-defined urinary tract malformations with viral vector-mediated gene therapy

Human urinary tract malformations can cause dysfunctional voiding, urosepsis and kidney failure. Other affected individuals, with severe phenotypes on fetal ultrasound screening, undergo elective termination. Currently, there exist no specific treatments that target the primary biological disease mechanisms that generate these urinary tract malformations. Historically, the pathogenesis of human urinary tract malformations has been obscure. It is now established that some such individuals have defined monogenic causes for their disease. In health, the implicated genes are expressed in either differentiating urinary tract smooth muscle cells, urothelial cells or peripheral nerve cells supplying the bladder. The phenotypes arising from mutations of these genes include megabladder, congenital functional bladder outflow obstruction, and vesicoureteric reflux. We contend that these genetic and molecular insights can now inform the design of novel therapies involving viral vector-mediated gene transfer. Indeed, this technology is being used to treat individuals with early onset monogenic disease outside the urinary tract, such as spinal muscular atrophy. Moreover, it has been contended that human fetal gene therapy, which may be necessary to ameliorate developmental defects, could become a reality in the coming decades. We suggest that viral vector-mediated gene therapies should first be tested in existing mouse models with similar monogenic and anatomical aberrations as found in people with urinary tract malformations. Indeed, gene transfer protocols have been successfully pioneered in newborn and fetal mice to treat non-urinary tract diseases. If similar strategies were successful in animals with urinary tract malformations, this would pave the way for personalized and potentially curative treatments for people with urinary tract malformations.

Antenatal biological models in the characterization and research of congenital lower urinary tract disorders

Congenital lower urinary tract disorders are a family of diseases affecting both urinary storage and voiding as well as upstream kidney function. Current treatments include surgical reconstruction but many children still fail to achieve urethral continence or progress to chronic kidney disease. New therapies can only be achieved through undertaking research studies to enhance our understanding of congenital lower urinary tract disorders. Animal models form a critical component of this research, a corner of the triangle composed of human in-vitro studies and clinical research. We describe the current animal models for two rare congenital bladder disorders, posterior urethral valves (PUV) and bladder exstrophy (BE). We highlight important areas for researchers to consider when deciding which animal model to use to address particular research questions and outline the strengths and weaknesses of current models available for PUV and BE. Finally, we present ideas for refining animal models for PUV and BE in the future to stimulate future researchers and help them formulate their thinking when working in this field.

Contractile function of detrusor smooth muscle from children with posterior urethral valves - The role of fibrosis

INTRODUCTION

Posterior urethral valves (PUV) is the most common cause of congenital bladder outflow obstruction with persistent lower urinary tract and renal morbidities. There is a spectrum of functional bladder disorders ranging from hypertonia to bladder underactivity, but the aetiology of these clinical conditions remains unclear.

AIMS AND OBJECTIVES

We tested the hypothesis that replacement of detrusor muscle with non-muscle cells and excessive deposition of connective tissue is an important factor in bladder dysfunction with PUV. We used isolated detrusor samples from children with PUV and undergoing primary or secondary procedures in comparison to age-matched data from children with functionally normal bladders. In vitro contractile properties, as well as passive stiffness, were measured and matched to histological assessment of muscle and connective tissue. We examined if a major pathway for fibrosis was altered in PUV tissue samples.

METHODS

Isometric contractions were measured in vitro in response to either stimulation of motor nerves to detrusor or exposure to cholinergic and purinergic receptor agonists. Passive mechanical stiffness was measured by rapid stretching of the tissue and recording changes to muscle tension. Histology measured the relative amounts of detrusor muscle and connective tissue. Multiplex quantitative immunofluorescence labelling using five epitope markers was designed to determine cellular pathways, in particular the Wnt-signalling pathway, responsible for any changes to excessive deposition of connective tissue.

RESULTS AND DISCUSSION

PUV tissue showed equally reduced contractile function to efferent nerve stimulation or exposure to contractile agonists. Passive muscle stiffness was increased in PUV tissue samples. The smooth muscle:connective tissue ratio was also diminished and mirrored the reduction of contractile function and the increase of passive stiffness. Immunofluorescence labelling showed in PUV samples increased expression of the matrix metalloproteinase, MMP-7; as well as cyclin-D1 expression suggesting cellular remodelling. However, elements of a fibrosis pathway associated with Wnt-signalling were either reduced (β-catenin) or unchanged (c-Myc). The accumulation of extracellular matrix, containing collagen, will contribute to the reduced contractile performance of the bladder wall. It will also increase tissue stiffness that in vivo would lead to reduced filling compliance.

CONCLUSIONS

Replacement of smooth muscle with fibrosis is a major contributory factor in contractile dysfunction in the hypertonic PUV bladder. This suggests that a potential strategy to restore normal contractile and filling properties is development of the effective use of antifibrotic agents.

Effects of Qianlie Tongqiao Capsule on Bladder Weight and Growth Factors in Bladder Tissue of Rats with Testosterone-Induced Benign Prostatic Hyperplasia

Qianlie Tongqiao Capsule (QTC) is clinically confirmed to be efficacious and safe in treating lower urinary tract syndromes and bladder dysfunction that are induced by benign prostatic hyperplasia (BPH). However, the functional mechanisms of QTC remain unclear. We aim to investigate the effects of QTC on both bladder weight and several growth factors in the bladder tissue of rats with testosterone-induced BPH. BPH in the rats was established through bilateral orchiectomy and subcutaneous administration of testosterone propionate (5 mg/kg) dissolved in corn oil. At the end of the study, all bladder tissues were collected and weighed, and a histological examination was conducted using H&E staining. Immunohistochemistry and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were applied to detect the expression of nerve growth factor (NGF), basic fibroblast growth factor (bFGF), and transformation growth factor-β1 (TGF-β1) in the bladder tissue. The expression of Bcl-2 and Bax in the bladder tissue was tested by Western Blot and qRT-PCR. We found that QTC, especially when administered in high-dosages, had a significant inhibitory effect on bladder weight gain and overexpression of NGF, bFGF, and TGF-β1 in rats with BPH. In addition, QTC downregulated and upregulated protein and mRNA expression of Bcl-2 and Bax in the bladder after prostatic obstruction, respectively. Furthermore, QTC balanced the Bcl-2/Bax ratio. Overall, these results reveal possible functional mechanisms of QTC in treating BPH-caused bladder dysfunction, and further studies are needed.

Evaluation of the effects of omega-3 & interferon alpha-2b administration on partial bladder outlet obstruction in a rat model

BACKGROUND & OBJECTIVES

In bladder outlet obstruction-induced rat models, the transforming growth factor-beta (TGF-β) and collagen ratios have been shown to be increased. Increased TGF-β leads to fibrosis. In this study, the effect of omega-3 and interferon alpha-2b (IFN α-2b) was investigated on oxidative stress, inflammation and fibrosis in bladder structure in a partial bladder outlet obstruction (PBOO) rat model.

METHODS

A total of 35 male Wistar albino rats, weighing 300-350 g, were used in the study. The rats were randomly divided into five groups. At the end of the experimental period, bladders were harvested from all the rats, and pathological analysis of the rat bladder tissues was performed. In addition, investigations were carried out with enzymatic and non-enzymatic antioxidant systems to study the antioxidant properties of omega-3 fatty acid and IFN alpha-2b.

RESULTS

Increased bladder weight in the PBOO group, in comparison to the control group, was decreased by the administration of omega-3 and IFN α-2b (P=0.002). Significantly higher superoxide dismutase (SOD) levels were detected in group 2 in comparison to the control group. It was also detected that serum SOD, glutathione peroxidase and nitric oxide (NO) levels were significantly higher in group 2 when compared to the control group (P<0.05). In the pathologic evaluation, group 2 showed significantly increased inflammation and fibrosis compared to the control group. Omega-3 treatment significantly decreased inflammation. It was shown that IFN α-2b application partially decreased inflammation.

INTERPRETATION & CONCLUSIONS

The results of the present study showed that in addition to the standard primary approaches to prevent the damage to the upper urinary tract secondary to PBOO, omega-3 fatty acid and IFN α-2b could be beneficial as adjunct treatment in clinical practice. However, this needs to be further investigated with prospective, randomized clinical trials with larger sample sizes.

Effects of transforming growth factor on the developing embryonic ureter: An in-vitro megaureter model in mice

INTRODUCTION

It is generally agreed that the cause of a megaureter is narrowing at the vesicoureteral junction, with a functional obstruction arising from an aperistaltic, juxtavesical segment that is unable to transport urine at an acceptable rate. Histological examinations of megaureter specimens have reported several histological analyses, and the pathogenic role of transforming growth factor is still a matter of speculation.

OBJECTIVE

To evaluate whether transforming growth factor-beta (TGF-β) and its receptors (TGFRs) are expressed during ureterovesical junction (UVJ) and lower ureter development in mice, and whether exogenous TGF-β might postpone the maturation of smooth muscle cells, in the pathogenesis of megaureter using an embryonic organ-culture model.

METHODS

Expression of TGF-β and TGFRs on the lower ureter and UVJ were determined at different embryonic days (E) (E16, 18, 20 and postnatal day 1). The functional studies were performed by harvesting ureters from wild-type mice at embryonic day 16 (E16), which were grown in serum-free organ-culture; some cultures were supplemented with TGF-β (2 and 20 ng/ml) and/or with soluble TGFR, which blocks bioactivity. Organs were harvested after 6 days and the expression of CD31 and Ki67 were assessed using immunohistochemistry. The muscle content of the UVJ and ureter were analyzed by flowcytometry.

RESULTS

The TGF-β and TGFR positive cells were immune detected in embryonic ureters. The TGF-β expression was highest on E18 and decreased postnatally. Exogenous TGF-β decreased ureterovesical (UV) muscle differentiation and proliferation. The longitudinal muscle fibers were significantly less in TGF-β explants. The TGF-β also decreased the proportions of cells expressing α smooth muscle actin (α-SMA). Soluble TGFR blocked the effects of exogenous TGF-β.

CONCLUSIONS

In organ culture, exogenous TGF-β postpones the UV smooth muscle proliferation and affects the muscular structure. Whether the effects of TGF-β are direct or indirect, these form an in-vitro megaureter model. The finding that TGF-β is highest in embryonic ureters in vivo and decreased postnatally suggests that a pathological persistence might potentially explain the pathogenesis of primary megaureters.

From gene discovery to new biological mechanisms: heparanases and congenital urinary bladder disease

We present a scientific investigation into the pathogenesis of a urinary bladder disease. The disease in question is called urofacial syndrome (UFS), a congenital condition inherited in an autosomal recessive manner. UFS features incomplete urinary bladder emptying and vesicoureteric reflux, with a high risk of recurrent urosepsis and end-stage renal disease. The story starts from a human genomic perspective, then proceeds through experiments that seek to determine the roles of the implicated molecules in embryonic frogs and newborn mice. A future aim would be to use such biological knowledge to intelligently choose novel therapies for UFS. We focus on heparanase proteins and the peripheral nervous system, molecules and tissues that appear to be key players in the pathogenesis of UFS and therefore must also be critical for functional differentiation of healthy bladders. These considerations allow the envisioning of novel biological treatments, although the potential difficulties of targeting the developing bladder in vivo should not be underestimated.

Genetics of human congenital urinary bladder disease

Lower urinary tract and/or kidney malformations are collectively the most common cause of end-stage renal disease in children, and they are also likely to account for a major subset of young adults requiring renal replacement therapy. Advances have been made regarding the discovery of the genetic causes of human kidney malformations. Indeed, testing for mutations of key nephrogenesis genes is now feasible for patients seen in nephrology clinics. Unfortunately, less is known about defined genetic bases of human lower urinary tract anomalies. The focus of this review is the genetic bases of congenital structural and functional disorders of the urinary bladder. Three are highlighted. First, prune belly syndrome, where mutations of CHRM3, encoding an acetylcholine receptor, HNF1B, encoding a transcription factor, and ACTA2, encoding a cytoskeletal protein, have been reported. Second, the urofacial syndrome, where mutations of LRIG2 and HPSE2, encoding proteins localised in nerves invading the fetal bladder, have been defined. Finally, we review emerging evidence that bladder exstrophy may have genetic bases, including variants in the TP63 promoter. These genetic discoveries provide a new perspective on a group of otherwise poorly understood diseases.

Cell proliferation and apoptosis in urinary bladder urothelium of rats following ovariectomy and chronic estrogen replacement therapy

AIMS

In this study we followed the effect of menopause and estrogenic replacement therapy on the proliferative and apoptotic activity of the bladder urothelial cells.

METHODS

The experimental model of menopause was reproduced using a standard protocol of bilateral ovariectomy in rats, estrogen replacement therapy being achieved by systemic administration of hexestrol diacetate for six weeks. Proliferative and apoptotic activity was monitored by quantifying the urothelium imunoexpression for PCNA antigen as a marker of S phase of the cell cycle and Cleaved Caspase 3 for monitoring apoptotic activity.

RESULTS

Following ovariectomy, the main changes were urothelial atrophy associated with intensification of the apoptotic activity at these level. Estrogen therapy managed to improve the urothelium activity by reducing the Apoptotic Index and by increasing urothelial proliferative activity.

CONCLUSIONS

The results show the important role of estrogens in maintaining urothelial activities, highlighting their potential use in the treatment of urothelium atrophic and degenerative processes associated with menopause.

Oxidative stress status accompanying diabetic bladder cystopathy results in the activation of protein degradation pathways

OBJECTIVE

• To investigate the role that oxidative stress plays in the development of diabetic cystopathy.

MATERIALS AND METHODS

• Comparative gene expression in the bladder of non-diabetic and streptozotocin (STZ)-induced 2-month- old diabetic rats was carried out using microarray analysis. • Evidence of oxidative stress was investigated in the bladder by analyzing glutathione S-transferase activity, lipid peroxidation, and carbonylation and nitrosylation of proteins. • The activity of protein degradation pathways was assessed using Western blot analysis.

RESULTS

• Analysis of global gene expression showed that detrusor smooth muscle tissue of STZ-induced diabetes undergoes significant enrichment in targets involved in the production or regulation of reactive oxygen species (P = 1.27 × 10(-10)). The microarray analysis was confirmed by showing that markers of oxidative stress were all significantly increased in the diabetic bladder. • It was hypothesized that the sequelae to oxidative stress would be increased protein damage and apoptosis. • This was confirmed by showing that two key proteins involved in protein degradation (Nedd4 and LC3B) were greatly up-regulated in diabetic bladders compared to controls by 12.2 ± 0.76 and 4.4 ± 1.0-fold, respectively, and the apoptosis inducing protein, BAX, was up-regulated by 6.76 ± 0.76-fold.

CONCLUSION

• Overall, the findings obtained in the present study add to the growing body of evidence showing that diabetic cystopathy is associated with oxidative damage of smooth muscle cells, and results in protein damage and activation of apoptotic pathways that may contribute to a deterioration in bladder function.

CONGENITAL URINARY BLADDER OUTLET OBSTRUCTION

The term congenital ‘bladder outlet obstruction (BOO)’ describes the collection of conditions in which the normal, urethral egress of urine from the fetal bladder is impaired. The term is interchangeable with fetal ‘lower urinary tract obstruction’, as used by other authors. After considering normal urinary tract embryology, we describe the epidemiology of congenital BOO and the primary anatomical disorders associated with it. We then proceed to describe its fetal and postnatal clinical manifestations and then consider therapies and interventions which have been used to manage the condition. We not only focus on urethral and bladder disease with constitutes BOO itself, but also describe associated kidney disorders which, via chronic renal excretory failure, are important causes of morbidity. Rather than provide an exhaustive review, we emphasise studies published in the last decade, and therefore readers are referred to other reviews citing numerous earlier references.

Involvement of hypoxia-triggered endoplasmic reticulum stress in outlet obstruction-induced apoptosis in the urinary bladder

In bladder outlet obstruction (BOO), mechanical stress and ischemia/hypoxia are implicated in structural and functional alterations of the urinary bladder. Because mechanical stress and hypoxia may trigger endoplasmic reticulum (ER) stress, we examined involvement of ER stress in the damage of the bladder caused by BOO. An experimental model of BOO was established in rats by complete ligature of the urethra for 24 h, and bladders were subjected to northern blot analysis and assessment of apoptosis. Isolated urinary bladders and bladder-derived smooth muscle cells (BSMCs) were also exposed to mechanical strain and hypoxia and used for analyses. To examine involvement of ER stress in the damage of the bladder, the effects of a chemical chaperone 4-phenylbutyrate (4-PBA) were evaluated in vitro and in vivo. Outlet obstruction for 24 h induced expression of ER stress markers, GRP78 and CCAAT/enhancer-binding protein-homologous protein (CHOP), in the bladder. It was associated with induction of markers for mechanical stress (cyclooxygenases 2) and hypoxia (vascular endothelial growth factor and glyceraldehyde-3-phosphate dehydrogenase). When isolated bladders and BSMCs were subjected to mechanical strain, induction of GRP78 and CHOP was not observed. In contrast, when BSMCs were exposed to hypoxic stress caused by CoCl2 or thenoyltrifluoroacetone (TTFA), substantial upregulation of GRP78 and CHOP was observed, suggesting involvement of hypoxia in the induction of ER stress. In the bladder subjected to BOO, the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells increased in the epithelial cells and BSMCs. Similarly, treatment with TTFA or CoCl2 induced apoptosis of BSMCs, and 4-PBA significantly attenuated ER stress and apoptosis triggered by these agents. Furthermore, in vivo administration with 4-PBA significantly reduced apoptosis in the bladder subjected to BOO. These results suggested that outlet obstruction caused ER stress via hypoxic stress in the bladder and that hypoxia-triggered ER stress may be involved in the induction of apoptosis in BOO.

Experimental congenital vesicoureteral reflux in sheep is associated with reduced renal expression levels of aquaporin 1 and 2

PURPOSE

Impaired concentrating capacity has been demonstrated in human refluxing kidneys and in kidneys of growing animals with experimental congenital vesicoureteral reflux. Aquaporin water channel proteins are the principal mediators of water homeostasis in the kidney. We examined the impact of experimental congenital vesicoureteral reflux on renal aquaporin protein expression.

MATERIALS AND METHODS

Vesicoureteral reflux was surgically induced bilaterally in male fetal sheep at 95 days of gestation (term 140 days). Following birth animals received antibiotic prophylaxis, and reflux grades were assessed by fluoroscopic voiding cystogram. After sacrifice at age 6 months 1 kidney of each animal (5 refluxing kidneys, and 3 from normal age and sex matched controls) was retrieved, frozen in liquid nitrogen and used for immunoblotting. The second kidney was perfusion fixed and processed for immunohistochemical analysis.

RESULTS

Semiquantitative immunoblotting of inner medulla showed that vesicoureteral reflux was associated with a marked down-regulation in expression of aquaporin 1 (arbitrary units 7.0 +/- 4.3 vs 22.5 +/- 2.8, p <0.05) and aquaporin 2 (5.7 +/- 5.1 vs 24.8 +/- 3.8, p <0.05), which was confirmed by immunocytochemical analysis. Dot blot analysis revealed a homogeneous down-regulation of aquaporin 2 expression throughout the refluxing kidney to 0.029 vs 0.1 in normal kidneys (p = 0.026).

CONCLUSIONS

Progressively impaired renal concentrating capacity induced by experimental fetal reflux is associated with decreased levels of renal aquaporin 1 and 2 expression. This long-term down-regulation of aquaporin 1 and 2 provides important molecular evidence for a defect in resorptive capacity of water induced by vesicoureteral reflux.

Altered extracellular matrix expression in the diverted fetal sheep bladder

PURPOSE

It is unclear whether filling and emptying are important to bladder development. We tested this in an experimental preparation.

MATERIAL AND METHODS

Urinary diversion was performed in 7 fetal lambs at 90 days of gestation and 6 unoperated fetal lambs served as controls. Transmural sections were analyzed for changes in tissue layer thickness and/or composition after 14 days of urinary diversion. Matrix mRNA levels (collagen I and III, and FN) as well as the cytokines/growth factors IGF-1, EGR-1, WT-1 and BCL-2 were quantified by real-time polymerase chain reaction. Hydroxyproline measurements of total collagen and collagen subtype quantification were done by enzyme-linked immunosorbent assay.

RESULTS

Diverted fetal bladders showed a 27% and 57% decrease in mucosal and detrusor muscle layer thickness, respectively. In contrast, there was a 270% increase in serosal layer thickness in diverted bladders. The mRNA levels of COL1A1, COL3A1, IGF-1, EGR-1 and the anti-apoptotic gene BCL-2 were increased significantly in the serosal/detrusor layer of diverted bladders. In the mucosa levels of these mRNAs remained unchanged except for those of FN and WT-1, which were significantly decreased and increased, respectively. Total collagen, and type I and III collagen protein levels were significantly increased in diverted bladders.

CONCLUSIONS

The lack of mechanical loading in diverted bladders leads to the arrest of detrusor smooth muscle growth, and concurrent fibrosis and thickening of the serosal layer. Changes in the levels of IGF-1, BCL-2 and EGR-1 likely have regulatory roles that affect the smooth muscle phenotype in the detrusor layer.

Ca 2+ Regulation in Detrusor Smooth Muscle From Ovine Fetal Bladder After In Utero Bladder Outflow Obstruction

PURPOSE

We characterized intracellular Ca(2+) regulation in fetal bladders following outflow obstruction by examining the Ca(2+) response to agonists in smooth muscle cells.

MATERIALS AND METHODS

Severe bladder outflow obstruction was induced in male fetal sheep by placing a urethral ring and urachal ligation midway through gestation at 75 days. Fetuses were examined 30 days after surgery. Intracellular Ca(2+) in single smooth muscle cells isolated from the bladder wall was measured with epifluorescence microscopy using fura-2(AM) during exposure to agonists, such as carbachol and adenosine triphosphate, and to other activators, such as caffeine and KCl.

RESULTS

Detrusor smooth muscle cells from obstructed bladders had resting intracellular Ca(2+) similar to that in sham operated controls. The maximal response to carbachol was decreased following obstruction (p <0.05). Construction of dose-response curves also demonstrated higher EC(50) (p <0.05). However, these changes were not mirrored by caffeine evoked Ca(2+) release, which was not significantly different between the obstruction group and sham operated controls. Kinetic analysis of carbachol transients further revealed an attenuated maximal rate of increase in obstructed bladders (p <0.01). The magnitude of intracellular Ca(2+) to purinergic neurotransmitter adenosine triphosphate was also found to be smaller in cells from obstructed bladders (p <0.05), although transmembrane influx by high K depolarization was not significantly affected.

CONCLUSIONS

Muscarinic and purinergic pathways were down-regulated in fetal detrusor muscle following outflow obstruction. These major functional receptors appeared to be more susceptible to obstruction than other Ca(2+) regulators. Their impairment may contribute to the compromised contractile function seen in in utero bladder outflow obstruction.

Uroplakins: new molecular players in the biology of urinary tract malformations

The uroplakins (UPs) are a family of proteins which associate with each other and form plaques on the apical surface of the urothelium. These plaques contribute to a permeability barrier, preventing the influx of urine from the urinary tract lumen. Urinary tract malformations associated with human and mouse UP mutations, the human fetal expression patterns of UPs and experiments in Xenopus oocytes are collectively revealing new functions for the UPs, forcing us to view these proteins in a new light. Rather than simply being products of the urothelial differentiation program, they may be a group of proteins central to the process of urinary tract differentiation itself.

Null mutation in macrophage migration inhibitory factor prevents muscle cell loss and fibrosis in partial bladder outlet obstruction

Idiopathic detrusor underactivity (DU) and detrusor decompensation which develops following partial bladder outlet obstruction (pBOO) are both associated with smooth muscle degeneration and fibrosis. Macrophage migration inhibitory factor (MIF), an important mediator of bladder inflammation, has been shown to promote fibroblast survival and muscle death in other tissues. We evaluated the hypothesis that MIF has similar actions in the bladder by studying detrusor responses to pBOO or sham surgery in anesthetized female mice rendered null for the mif gene (MIF KO) and in wild-type (WT) controls, all killed 3 wk after surgery. WT mice revealed intense MIF immunoreactivity in urothelial cells which decreased, without change in overall mif mRNA levels. Stereologically sound quantitative morphometric measurements were performed in the middetrusor region of each bladder. MIF KO bladders were normal in appearance, yet were 30–40% heavier, with increased middetrusor collagen and muscle, compared with WT controls. In WT mice, pBOO increased the collagen-to-muscle ratio 1.9-fold and middetrusor collagen 1.8-fold, while nucleated muscle counts were 22% lower. In MIF KO mice, by contrast, pBOO had no significant effect on any of these parameters. In primary bladder muscle cultures, treatment with rMIF protein increased TUNEL staining, raising the proportion of early and late apoptotic cells on flow cytometry. Our studies implicate MIF in the sequence of events leading to detrusor muscle loss and fibrosis in obstruction. They raise the possibility that strategies designed to antagonize MIF synthesis, release, or biological activity could prevent or delay DU and urinary retention.

Experimental short-term fetal bladder outflow obstruction: I. Morphology and cell biology associated with urinary flow impairment

PURPOSE

In fetal sheep, combined urethral and urachal obstruction initiated at 75 days' gestation and maintained for 30 days led to dysmorphic bladders, similar to those found in humans with prune belly syndrome, and uniformly disrupted kidney development. We aimed to create a less severe model of fetal bladder outlet obstruction, more closely resembling infants with posterior urethral valves, and additionally to further our understanding on the role of the urachus. We hypothesized that milder morphological renal tract changes would occur after shorter term experimental obstruction.

MATERIALS AND METHODS

Male fetal lambs were assigned to urachal and urethral ligation, urachal ligation only or sham operations. Analyses were performed after 9 days.

RESULTS

Concurrent urachal and urethral obstruction resulted in increased bladder weight, and protein and DNA content. Detrusor smooth muscle was well maintained, as assessed by light and electron microscopy, although urothelia showed basal apoptosis. Bladder obstruction led to hydronephrosis but failed to produce significant perturbations in urine osmolality. The nephrogenic cortex was either well preserved or was replaced by glomerular cysts; the latter group tended to have heavier bladders. Urachal obstruction alone produced similar changes suggesting that the male sheep fetal urethra is a high-resistance conduit in mid-gestation.

CONCLUSIONS

Concurrent urachal and urethral obstruction, or urachal obstruction alone, initiated in mid-gestation and maintained for 9 days leads to bladder overgrowth but preserved renal tubular function. In future, it will be interesting to determine whether bladder decompression around this stage leads to reversal of bladder overgrowth and/or ameliorates severe renal tract damage described after longer term fetal bladder outflow obstruction.

Experimental short-term partial fetal bladder outflow obstruction: II. Compliance and contractility associated with urinary flow impairment

PURPOSE

Posterior urethral valves (PUV) is the commonest cause of congenital bladder outlet obstruction. Despite valve ablation in the neonatal period, up to 70% of patients develop renal failure by their teenage years, and progressive bladder dysfunction. This study forms part of a continuing project examining the relationship between severity and duration of obstruction and urinary tract dysfunction. Here is the assessed result of short-term (9-day) obstruction.

MATERIALS AND METHODS

Fourteen male fetal lambs at 75 days' gestation were assigned to one of three groups: urachal ligation, urachal ligation with partial urethral obstruction, sham-operated controls. Pregnancy proceeded for 9 days. At autopsy, filling cystometry was performed with the urinary tract in situ and the bladder harvested for nerve counts using PGP 9.5 immunohistochemistry, or in vitro measurement of contractile function.

RESULTS

Obstruction was associated with an increase in bladder:fetal weight ratio. Compliance was variable in the obstructed bladders, but the calculated wall stress per unit strain was either similar or less than controls. Nerve-mediated or agonist-induced contraction magnitude in tissue from obstructed bladders and nerve counts did not differ from controls.

CONCLUSIONS

Nine days of outflow obstruction at mid-gestation generated a bladder of increased weight but without evidence of contractile failure. An increase in bladder compliance as a function of bladder growth was observed even at this stage, and represents one of the initial responses to outflow tract obstruction.

Vascular endothelial growth factor stimulates embryonic urinary bladder development in organ culture

OBJECTIVES

To determine whether vascular endothelial growth factor A (VEGF) and its receptors are expressed during bladder development in mice when capillaries are forming, and whether exogenous VEGF might enhance the growth of endothelia and other types of bladder cells, using an embryonic organ-culture model.

MATERIALS AND METHODS

Whole bladders from wild-type mice, at embryonic day (E) 14, were grown in serum-free organ culture in an air/5% CO2 atmosphere; some cultures were supplemented with VEGF and/or with VEGF receptor 1/Fc chimera (VEGFR1/Fc), which blocks VEGF bioactivity. Organs were harvested after 6 days and the expression of VEGF and related molecules assessed using immunohistochemistry.

RESULTS

VEGF, VEGFR1 and VEGFR2 positive cells were immunodetected in E14 and E18 bladders. Exogenous VEGF increased whole-organ growth, as assessed by explant areas, total cell numbers, DNA and protein content; proliferation was enhanced, and apoptosis decreased, in urothelium and surrounding tissues. VEGF also increased the proportions of cells expressing endothelial (CD31) and smooth muscle (alpha smooth muscle actin) markers. VEGFR1/Fc blocked the growth-enhancing effects of exogenous VEGF.

CONCLUSIONS

In organ culture, exogenous VEGF not only stimulated embryonic bladder endothelial cells but also strikingly enhanced the growth of the whole organ. Whether the effects of VEGF on diverse bladder cell populations are direct or indirect requires further investigation. The finding that VEGF protein is present in embryonic bladders in vivo raises the possibility that it has similar actions during normal development. The results also illuminate the pathobiology of certain bladder diseases in which VEGF levels have been shown to be increased.

Ca2+ regulation in detrusor smooth muscle from developing fetal sheep bladders

Sheep fetus is a useful model to study in utero bladder outflow obstruction but little is known about cell physiology of fetal bladders. To remedy this defect we have characterised intracellular Ca(2+) regulation in fetal sheep myocytes of different developmental ages. Fetal detrusor myocytes had a similar resting [Ca(2+)](i) to adult cells and exhibited transient [Ca(2+)](i) increases in response to carbachol, ATP, high-K, caffeine and low-Na. The carbachol transients were abolished by atropine and caffeine; the ATP response was blocked by alpha,beta-methylene ATP; high-K-evoked [Ca(2+)](i) rises were antagonised by verapamil. The maximal responses to carbachol, high-K, caffeine and low-Na in fetal cells were similar to those of adult counterparts, whilst the ATP response was smaller (p < 0.05). These variables were largely similar between the three gestational groups with the exception of ATP-induced response between early fetal and adult bladders (p < 0.05). Dose-response curves to carbachol demonstrated an increase of potency between mid-gestation and early adulthood (p < 0.05). These data show that muscarinic receptors coupled to intracellular Ca(2+) release, P2X receptor-linked Ca(2+) entry, depolarisation-induced Ca(2+) rise via L-type Ca(2+) channels, Na(+)/Ca(2+) exchange and functional intracellular Ca(2+) stores are all operational in fetal bladder myocytes. Whilst most of Ca(2+) regulators are substantially developed and occur at an early fetal age, a further functional maturation for cholinergic sensitivity and purinergic efficacy continues throughout to adulthood.

Contractile properties of the developing fetal sheep bladder

AIM

To characterise the developmental changes to the normal bladder by examining the in vitro contractile properties of the fetal sheep detrusor smooth muscle bladder at different gestational ages.

METHODS

Three groups of normally developing fetal sheep bladders were investigated: (1) 65-70 days gestation (2nd trimester); (2) 105-110 days (3rd trimester); (3) 135-140 days (term). Isometric contractions in isolated detrusor strips were measured during either electrical field stimulation (EFS) or exposure to agonists: carbachol, alpha-beta methylene-ATP (ABMA) and KCl.

RESULTS

There was a significant increase of absolute force elicited by EFS with fetal age. Contractures elicited by carbachol, ABMA and KCl increased between Groups 1 and 2, but not thereafter. The proportional increase of contractions elicited by carbachol and ABMA was also greater between Groups 1 and 2, than for EFS and KCl.

CONCLUSIONS

Fetal development between 65 and 140 days in the sheep is associated with increased contractile activation. The data are consistent with an increase of muscle development in the earlier stages (65-110 days). In the later stage (110-140 days) muscle development is complete but functional innervation of the tissue continues.

Effects of early vesicostomy in obstructive uropathy on bladder development

PURPOSE

Creation of a vesico-amniotic shunt for obstructive uropathy removes the normal fetal urination cycle. It is unclear how this affects bladder function at term. The authors measured the bladder volume and reviewed the bladder histology after fetal vesicostomy.

METHODS

The authors created an obstructive uropathy in fetal lambs at 60 days' gestation by ligating the urethra and urachus. Vesicostomy (female) or urethrostomy (male) were performed 21 days after obstruction to release the obstruction. The fetuses were killed at term (145 days).

RESULTS

Thirteen fetuses were shunted. Seven fetuses miscarried after shunting. Six survived, and 3 had a successful shunt with a very small bladder (5 to 7 mL). Two had incomplete shunts that failed some time after shunting. These both had huge bladders (399 mL). In one, the obstruction was unsuccessful. Histologic examination showed that the obstruction caused bladder muscle hypertrophy. Shunted lambs had severe fibrosis of the bladder wall and very poor bladder compliance.

CONCLUSIONS

Shunt operations after obstructive uropathy may salvage the kidney but fail to preserve bladder function. The fetus needs a normal urination cycle for normal bladder development. This requirement exists even when the obstruction is successfully bypassed.

The P2X7 ATP receptor modulates renal cyst development in vitro

P2X(7), a purinergic receptor, is expressed in renal collecting ducts as they undergo fulminant cystogenesis in the cpk/cpk mouse model of autosomal recessive polycystic kidney disease (ARPKD). Dissociated cpk/cpk kidneys generate cysts from cell aggregates within 24h of suspension culture and we demonstrate that BzATP, a P2X(7) agonist, reduces cystogenesis. This effect is P2X(7)-specific, because: (i) equimolar concentrations of other purinergic agonists, ATP and UTP, had lesser effects and (ii) the P2X(7) inhibitor, oxidized ATP, abrogated the BzATP-mediated reduction in cystogenesis. BzATP did not significantly affect total cell number, proliferation, LDH release or caspase 3 activity, and zVAD-fmk, a caspase blocker, failed to modulate BzATP effects. In addition, this P2X(7) agonist did not significantly alter cyst size, probably excluding altered vectorial transport. In vivo, ATP was detected in cyst fluid from cpk/cpk kidneys; moreover, P2X(7) protein was also upregulated in human fetal ARPKD epithelia versus normal fetal collecting ducts. Thus, ATP may inhibit pathological renal cyst growth through P2X(7) signaling.

Experimental models to study the physiology, pathophysiology, and pharmacology of the lower urinary tract

The lower urinary tract is subject to a number of functional disorders, the most common of which, in humans, is bladder overactivity. To understand its pathophysiological basis, several in vitro and in vivo methodologies have been developed. In vitro tension recording from multicellular strips is in widespread use, and alternative experimental arrangements to a conventional organ bath are described, the relative merits are discussed, and the different experimentally derived variables are evaluated. Other methodologies, such as skinned fibres and whole bladder preparations, are also described. Electromyography in the isolated bladder is now feasible, and its potential uses discussed. The use of isolated smooth muscle cells is presented, especially with respect to the measurement of intracellular ion concentrations and electrophysiological parameters. The development of methods to prepare other cell types from the lower urinary tract is also introduced. A large-scale culture of urothelial and smooth muscle cells is possible, and their use as experimental tools, as well as a substrate for the development of surgical implants, is presented. Finally, different in vivo models of the lower urinary tract are presented, with reference to their investigation of clinical problems. These include models of bladder outflow obstruction, bladder ischaemia, bladder denervation, and congenital abnormalities and their influence on foetal development of the lower urinary tract.

A preliminary study of natural-fill radiotelemetered ovine fetal cystometry

OBJECTIVE

To determine whether fetal cystometric studies by radiotelemetry are feasible in the fetal lamb, and potentially suitable for chronically monitoring fetal bladder pressures in an experimental fetal model of bladder outlet obstruction (BOO), as in utero BOO (e.g. caused by posterior urethral valves) results in significant postnatal bladder dysfunction but the pathophysiological progression of fetal bladder maldevelopment remains poorly understood.

MATERIALS AND METHODS

The procedure required fetal sheep surgery and anaesthesia. Radiotelemetry implants comprised catheters that transmitted pressure fluctuations to an implant body; data were then transmitted using radio frequency to a receiver that passed this information to a computer. Four fetuses were used with different methods of catheter placement to optimize the technique.

RESULTS

Recordings were possible in three of the four sheep; during observation there were: (i) quiet periods with no abdominal or bladder pressure rises; (ii) synchronous activity in the bladder and abdomen; and (iii) discriminate activity, associated with intravesical activity only. Four patterns of discriminate bladder activity were observed, defined as void, immature void, staccato activity and 'unstable' type activity.

CONCLUSIONS

Radiotelemetry cystometry for long-term monitoring is feasible in the experimental fetus without causing death or morbidity, or inhibiting growth. The method can discriminate reproducible patterns of detrusor activity. Recorded 'voiding' types were consistent between experiments and as reported in other fetal animal studies.

Uteroplacental insufficiency increases apoptosis and alters p53 gene methylation in the full-term IUGR rat kidney

Uteroplacental insufficiency causes intrauterine growth retardation (IUGR), which is associated with adult onset diseases such as hypertension. Previous studies demonstrate that growth retardation in humans and rats decreases glomeruli number; however, the molecular mechanisms responsible for this reduction are unknown. Apoptosis plays a key role in renal organogenesis. We therefore hypothesized that the in utero deprivation associated with uteroplacental insufficiency decreases glomeruli, increases apoptosis, and alters the mRNA levels of key apoptosis-related proteins in full-term IUGR kidneys. To prove this hypothesis, we induced asymmetric IUGR through bilateral uterine artery ligation of the pregnant rat. We found that uteroplacental insufficiency significantly reduced glomeruli number while increasing TUNEL staining and caspase-3 activity in the IUGR kidney. A significant decrease in Bcl-2 mRNA and a significant increase in Bax and p53 mRNA further characterized the IUGR kidney. Because altered p53 CpG methylation affects p53 expression, we analyzed p53 promoter CpG methylation using methylation-sensitive restriction enzymes and real-time PCR. Uteroplacental insufficiency specifically decreased CpG methylation of the renal p53 BstU I site promoter without affecting the Hha I or the Aci I sites. Uteroplacental insufficiency also induced a relative hypomethylation from exon 5 to exon 8, which was associated with deceased mRNA levels of DNMT1. We conclude that uteroplacental insufficiency alters p53 DNA CpG methylation, affects mRNA levels of key apoptosis-related proteins, increases renal apoptosis, and reduces glomeruli number in the IUGR kidney. We speculate that these changes represent mechanisms that contribute to the fetal origins of adult disease.