Alterations in the contractile phenotype of the bladder: lessons for understanding physiological and pathological remodelling of smooth muscle

Astragaloside IV Protects Detrusor from Partial Bladder Outlet Obstruction-Induced Oxidative Stress by Activating Mitophagy through AMPK-ULK1 Pathway

Aims

Bladder outlet obstruction (BOO) and the consequent low contractility of detrusor are the leading causes of voiding dysfunction. In this study, we aimed to evaluate the pharmacological activity of astragaloside IV (AS-IV), an antioxidant biomolecule that possess beneficial effect in many organs, on detrusor contractility and bladder wall remodeling process.

Methods

Partial BOO (pBOO) was created by urethral occlusion in female rats, followed by oral gavage of different dose of AS-IV or vehicle. Cystometric evaluation and contractility test were performed. Bladder wall sections were used in morphology staining, and bladder tissue lysate was used for ELISA assay. Primary smooth muscle cells (SMCs) derived from detrusor were used for mechanism studies.

Results

Seven weeks after pBOO, the bladder compensatory enlarged, and the contractility in response to electrical or chemical stimuli was reduced, while AS-IV treatment reversed this effect dose-dependently. AS-IV also showed beneficial effect on reversing the bladder wall remodeling process, as well as reducing ROS level. In mechanism study, AS-IV activated mitophagy and alleviated oxidative stress via an AMPK-dependent pathway.

Conclusion

Out data suggested that AS-IV enhanced the contractility of detrusor and protected the bladder from obstruction induced damage, via enhancing the mitophagy and restoring mitochondria function trough an AMPK-dependent way.

Partial inhibition of activin receptor-like kinase 4 alleviates bladder fibrosis caused by bladder outlet obstruction

The bladder undergoes profound structural alterations after bladder outlet obstruction (BOO), characterized by hypertrophy of the bladder wall and accumulation of extracellular matrix (ECM). Transforming growth factor-β (TGF-β) has been found to promote fibrosis of the bladder induced by partial bladder outlet obstruction (pBOO). Activin receptor-like kinase 4 (ALK4) is a downstream receptor of the TGF-β superfamily. However, the role of the ALK4-Smad2/3 pathway in the pathogenesis of bladder fibrosis caused by pBOO remains unknown. This study focused on learning the role of ALK4 in the process of bladder fibrosis caused by pBOO. The pBOO mice models showed that ALK4 expression was found to upregulate in the wild-type bladder 6 weeks after pBOO compared to control group. Then, mice with heterozygous knockout of the ALK4 gene (ALK4+/-) were generated. Histological analysis and Western blot (WB) results showed significant suppression of collagen expression in the bladders of ALK4+/- mice after pBOO compared with WT mice. WB also showed that ALK4+/- mice demonstrated significant suppression of phosphorylated Smad2/3 (p-Smad2/3) expression in the bladder 6 weeks after pBOO but not of phosphorylated extracellular signal-regulated kinase, c-Jun N-terminal kinase or protein 38 (p-ERK, p-JNK, p-P38) expression. This effect might have occurred through partial inactivation of the Smad2/3 signaling pathway. In vitro, ALK4 overexpression promoted collagen production in cultured BSMCs and activated the Smad2/3 signaling pathway. Taken together, our results demonstrated that ALK4 insufficiency alleviated bladder fibrosis in a mouse model of pBOO partly by suppressing Smad2/3 activity.

Dietary reversal reverts diet-induced alterations in obstructed bladders of Wistar rats

OBJECTIVES

The aim of this study was to investigate the effects of diet reversal to standard chow on diet-induced changes in structure and function of normal and obstructed bladders in male Wistar rats.

METHODS

Eighty animals were equally divided into sham-surgery and bladder outlet obstruction (BOO) dietary groups and fed standard chow (control), high-carbohydrate, high-fat, and high-protein diets. BOO groups had surgically induced BOO, whereas sham surgery was performed on sham groups at the end of week 8. Animals were continued on the treatment diets for 4 wk after surgery, then the diets were all changed to standard chow for the remainder of the study period. Bladder weight, detrusor contractility, Rho-associated protein kinase (Rho-kinase), and myosin light chain kinase were determined. Polymerase chain reaction was used to assay for transforming growth factor-β, connecting tissue growth factor, hypoxia-inducible factor-1α, and platelet-derived growth factor subunit A levels in the bladder. C-reactive protein, insulin-like growth factor-1, nerve growth factor, and C-X-C motif chemokine ligand 12 concentrations were determined by enzyme-linked immunosorbent assay. The collagen content of the bladder was estimated by liquid chromatography/mass spectrometry.

RESULTS

Reversal of diet to standard chow resulted in reversal of diet-induced changes in all variables measured in obstructed bladders. High-fat-diet-induced alterations in normal bladders were also reversed.

CONCLUSION

The results suggested that in obstructed bladders of animals, reversal of the diet could reverse all diet-associated changes that increase inflammation and fibrosis in obstructed bladders. This is especially important in changes related to high consumption of fatty diets and associated lower urinary tract symptoms.

The role of interleukin-6/interleukin-6 receptor signaling in the mechanical stress-induced extracellular matrix remodeling of bladder smooth muscle

Extracellular matrix (ECM) remodeling is strongly associated with pathological changes induced by bladder outlet obstruction (BOO). In this study, we investigated the role of interleukin-6 (IL-6) in mechanical stretch-induced ECM remodeling of bladder smooth muscle. To construct a BOO animal model, the urethras of female Sprague-Dawley rats were partially ligated. In addition, increased hydrostatic pressure and mechanical stretching were applied to human bladder smooth muscle cells (HBSMCs) as an in vitro model. The expression of rat inflammatory genes was analyzed using DNA microarrays. We used quantitative RT-PCR (qRT-PCR) and immunohistochemical staining to detect IL-6 in the bladder smooth muscle of rats. To determine the specificity of IL-6, small interfering ribonucleic acid (siRNA) transfection and IL-6 receptor inhibitor (SC144) were applied to HBSMCs. qRT-PCR with siRNA transfection was also used to determine the specificity of downstream signaling. Moreover, western blotting was conducted to verify the expression results. In the animal model, the expression of ECM components and inflammatory genes was significantly upregulated. The expression of IL-6 was increased at both the mRNA level and the protein level in BOO rats. In vitro, hydrostatic pressure, and mechanical stretching both promoted MMP7 and MMP11 expression. Additionally, downregulation of collagen III occurred in both the hydrostatic pressure group and the mechanical stretch group. However, the expression of fibronectin exhibited opposing patterns between the hydrostatic pressure and mechanical stretch groups. The application of targeted siRNA transfection and an inhibitor (SC144) that targeted IL-6 significantly reversed the changes in MMP7 and MMP11 under mechanical stress and partially increased the expression of collagen III and fibronectin. In summary, IL-6 participated in the ECM remodeling of HBSMCs under mechanical stress, indicating that IL-6 may play an essential role in BOO.
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A multilayered scaffold for regeneration of smooth muscle and connective tissue layers

Tissue regeneration often requires recruitment of different cell types and rebuilding of two or more tissue layers to restore function. Here, we describe the creation of a novel multilayered scaffold with distinct fiber organizations-aligned to unaligned and dense to porous-to template common architectures found in adjacent tissue layers. Electrospun scaffolds were fabricated using a biodegradable, tyrosine-derived terpolymer, yielding densely-packed, aligned fibers that transition into randomly-oriented fibers of increasing diameter and porosity. We demonstrate that differently-oriented scaffold fibers direct cell and extracellular matrix (ECM) organization, and that scaffold fibers and ECM protein networks are maintained after decellularization. Smooth muscle and connective tissue layers are frequently adjacent in vivo; we show that within a single scaffold, the architecture supports alignment of contractile smooth muscle cells and deposition by fibroblasts of a meshwork of ECM fibrils. We rolled a flat scaffold into a tubular construct and, after culture, showed cell viability, orientation, and tissue-specific protein expression in the tube were similar to the flat-sheet scaffold. This scaffold design not only has translational potential for reparation of flat and tubular tissue layers but can also be customized for alternative applications by introducing two or more cell types in different combinations.

Systems analysis of benign bladder disorders: insights from omics analysis

The signaling pathways and effectors that drive the response of the bladder to nonmalignant insults or injury are incompletely defined. Interrogation of biological systems has been revolutionized by the ability to generate high-content data sets that capture information on a variety of biomolecules in cells and tissues, from DNA to RNA to proteins. In oncology, such an approach has led to the identification of cancer subtypes, improved prognostic capability, and has provided a basis for precision treatment of patients. In contrast, systematic molecular characterization of benign bladder disorders has lagged behind, such that our ability to uncover novel therapeutic interventions or increase our mechanistic understanding of such conditions is limited. Here, we discuss existing literature on the application of omics approaches, including transcriptomics and proteomics, to urinary tract conditions characterized by pathological tissue remodeling. We discuss molecular pathways implicated in remodeling, challenges in the field, and aspirations for omics-based research in the future.

Responses of bladder smooth muscle to the stretch go through extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 protein kinase (p90RSK)/Nuclear factor-κB (NF-κB) Pathway

AIMS

The present study was designed to study changes and its potential mechanisms in human bladder smooth muscle subjected to stretch.

METHODS

Bioinformatics analyses including differential expression analysis, overrepresentation enrichment analysis, principal component analysis, and weighted gene coexpression network analysis were used to analyze a microarray dataset (GSE47080) of partial bladder outlet obstruction (pBOO) in rat to find the potential changes of gene expressions. Bladder from pBOO model and human bladder smooth muscle cells (HBSMCs) subjected to sustained prolonged stretch were collected for Western blot analysis, real-time polymerase chain reaction, and fluorescence analysis to verify the changes of gene expressions and preliminarily study the potential role of signaling pathway regulation in treatment of pBOO.

RESULTS

The bioinformatics analysis showed that chronic obstruction activated mitogen-activated protein kinase pathway and changed cytoskeleton structure in bladder smooth muscle. In in vivo experiments in mice, pBOO was verified by cystometry. Partial BOO activated the extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 protein kinase (p90RSK)/nuclear factor-κB (NF-κB) signaling pathway in DM. The messenger RNA (mRNA) expressions of contractile phenotypic proteins increased after pBOO. In in vitro experiments of HBSMCs, mechanical stretch activated ERK/p90RSK/NF-κB in HBSMCs in a time-dependent manner. The mRNA expressions of α-smooth muscle actin and SM22 also increased and filamentous actin (F-actin) polymerization was enhanced as well. Inhibition of ERK/p90RSK/NF-κB pathway reversed mechanical stretch-induced changes of contractile phenotypic expression and F-action polymerization.

CONCLUSIONS

Continuous stretch increases expressions of contractile phenotypic proteins and promotes the polymerization of F-actin. This process partially goes through ERK/p90RSK/NF-κB pathway.

Nerve sprouting and neurogenic inflammation characterize the neurogenic detrusor overactive bladder of patients no longer responsive to drug therapies

Urothelium and Lamina Propria (LP) are considered an integrate sensory system which is able to control the detrusor activity. Complete supra-sacral spinal cord lesions cause Neurogenic Detrusor Overactivity (NDO) whose main symptoms are urgency and incontinence. NDO therapy at first consists in anti-muscarinic drugs; secondly, in intra-vesical injection of botulinum toxin. However, with time, all the patients become insensitive to the drugs and decide for cystoplastic surgery. With the aim to get deeper in both NDO and drug's efficacy lack pathogenesis, we investigated the innervation, muscular and connective changes in NDO bladders after surgery by using morphological and quantitative methodologies. Bladder innervation showed a significant global loss associated with an increase in the nerve endings located in the upper LP where a neurogenic inflammation was also present. Smooth muscle cells (SMC) anomalies and fibrosis were found in the detrusor. The increased innervation in the ULP is suggestive for a sprouting and could condition NDO evolution and drug efficacy length. Denervation might cause the SMC anomalies responsible for the detrusor altered contractile activity and intra-cellular traffic and favour the appearance of fibrosis. Inflammation might accelerate these damages. From the clinical point of view, an early anti-inflammatory treatment could positively influence the disease fate.

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.

Concordant miRNA and mRNA expression profiles in humans and mice with bladder outlet obstruction

Bladder outlet obstruction (BOO) leads to lower urinary tract symptoms (LUTS) and urodynamic changes of the bladder function. Previously we identified microRNA (miRNA) and mRNA expression profiles associated with different states of BOO-induced LUTD in human patients. Bladder wall remodeling resulting from obstruction is widely studied in animal models of experimentally-induced partial BOO (pBOO). Here we determined the expression profiles of miRNAs and selected mRNAs in pBOO mice and compared the observed changes to human patients. Similar to results from human patients, we observed a down-regulation of smooth muscle-associated miRNAs mmu-miR-1, mmu-miR-143, mmu-miR-145, mmu-miR-486 and mmu-miR-133a in pBOO mouse bladders. Pro-fibrotic miRNAs mmu-miR-142-3p and mmu-miR-21 were up-regulated, and anti-fibrotic miRNA mmu-miR-29c was down-regulated. Pathway analysis in human BOO patients identified TNF-alpha as the top upstream regulator. Although there was evidence of hypertrophic changes in pBOO mice, contrary to human data, we observed no regulation of TNF-responsive genes in the mouse model. Experimentally-induced pBOO in mice led to significant gene expression changes, including alteration of pro-fibrotic mRNAs and miRNAs resembling human BOO patients. Gene expression changes were also validated in a mouse model of bladder inflammation. Lack of evidence of TNF-alpha-induced miRNA and mRNA regulation might indicate a different pathophysiological mechanism of organ remodeling in pBOO model compared to the human disease.

Developmental changes in contractile responses to cholinergic stimuli: role of calcium sensitization and related pathways

This study was performed to analyze the developmental changes in bladder response to cholinergic stimulation in detail, highlighting calcium sensitization (CS) and its related pathways. Rats were divided into three groups in accordance with reported time of developmental milestones (newborns, days 1–4; youngsters, days 5–14; and grown-ups, days 15–28). Following cholinergic stimulation (carbachol, 5 µM), the contractile response to detrusor was analyzed with respect to three phases (initial phasic, tonic, and superimposed phasic contractions). Contractile responses were analyzed by their dynamic and kinetic aspects. The responses were further compared in varying external calcium concentrations and in the presence of inhibitors of protein kinase C (PKC) and Rho kinase (ROCK), which are involved in CS. The responses of newborns contrasted with the others by their short and brisk initial phasic contractions, prominent tonic contractions, and delayed participation of irregular superimposed phasic contractions. With development, phasic contractions became prominent, and tonic contractions diminished. These developmental changes in phasic contractions were reproduced when exposed to increasing calcium concentrations. Application of specific inhibitors and molecular phasic analysis revealed that PKC was functional in tonic contractions of the newborns, whereas ROCK took over its role with development. Within a few days of birth, rats’ bladders experienced drastic changes in contractile mechanisms. This included dominance of phasic contractions over tonic contractions due to increased calcium dependence and the maturational shift of the calcium sensitivity mechanism from PKC to ROCK.

Non-neurogenic Chronic Urinary Retention: What Are We Treating?

PURPOSE OF REVIEW

This review examines current terminology used to define non-neurogenic chronic urinary retention (CUR), describes the pathophysiology of urinary retention, and highlights contemporary diagnostic and treatment algorithms.

RECENT FINDINGS

There is no standardized definition for the condition, but volumes >300 ml are commonly used to describe CUR. It is a clinical diagnosis which does not require urodynamics. Pathophysiologic causes of CUR be from myogenic, neurogenic, bladder outlet obstruction, or a combination of these sources. Treatment algorithms recommend stratifying patients with chronic urinary retention by risk and by symptoms before initiating treatment. Common CUR outcome endpoints need to be better utilized so that treatment modalities can be compared. Non-neurogenic CUR is a heterogeneous condition that has multiple definitions, underlying physiologies, and possible endpoints. Standardization is needed to better understand and treat CUR.

Deletion of neuropilin 2 enhances detrusor contractility following bladder outlet obstruction

Chronic urethral obstruction and the ensuing bladder wall remodeling can lead to diminished bladder smooth muscle (BSM) contractility and debilitating lower urinary tract symptoms. No effective pharmacotherapy exists to restore BSM contractile function. Neuropilin 2 (Nrp2) is a transmembrane protein that is highly expressed in BSM. Nrp2 deletion in mice leads to increased BSM contraction. We determined whether genetic ablation of Nrp2 could restore BSM contractility following obstruction. Partial bladder outlet obstruction (pBOO) was created by urethral occlusion in mice with either constitutive and ubiquitous, or inducible smooth muscle-specific deletion of Nrp2, and Nrp2-intact littermates. Mice without obstruction served as additional controls. Contractility was measured by isometric tension testing. Nrp2 deletion prior to pBOO increased force generation in BSM 4 weeks following surgery. Deletion of Nrp2 in mice already subjected to pBOO for 4 weeks showed increased contractility of tissues tested 6 weeks after surgery compared with nondeleted controls. Assessment of tissues from patients with urodynamically defined bladder outlet obstruction revealed reduced NRP2 levels in obstructed bladders with compensated compared with decompensated function, relative to asymptomatic controls. We conclude that downregulation of Nrp2 promotes BSM force generation. Neuropilin 2 may represent a novel target to restore contractility following obstruction.

Assessing the contribution of thrombospondin-4 induction and ATF6α activation to endoplasmic reticulum expansion and phenotypic modulation in bladder outlet obstruction

Phenotypic modulation of smooth muscle cells is a hallmark of disease. The associated expansion of endoplasmic reticulum (ER) volume remains unexplained. Thrombospondin-4 was recently found to promote ATF6α activation leading to ER expansion. Using bladder outlet obstruction as a paradigm for phenotypic modulation, we tested if thrombospondin-4 is induced in association with ATF6α activation and ER expansion. Thrombospondin-4 was induced and ATF6α was activated after outlet obstruction in rodents. Increased abundance of spliced of Xbp1, another ER-stress sensor, and induction of Atf4 and Creb3l2 was also seen. Downstream of ATF6α, Calr, Manf, Sdf2l1 and Pdi increased as did ER size, whereas contractile markers were reduced. Overexpression of ATF6α, but not of thrombospondin-4, increased Calr, Manf, Sdf2l1 and Pdi and caused ER expansion, but the contractile markers were inert. Knockout of thrombospondin-4 neither affected bladder growth nor expression of ATF6α target genes, and repression of contractile markers was the same, even if ATF6α activation was curtailed. Increases of Xbp1s, Atf4 and Creb3l2 were similar. Our findings demonstrate reciprocal regulation of the unfolded protein response, including ATF6α activation and ER expansion, and reduced contractile differentiation in bladder outlet obstruction occurring independently of thrombospondin-4, which however is a sensitive indicator of obstruction.

Carbachol-induced signaling through Thr696-phosphorylation of myosin phosphatase-targeting subunit 1 (MYPT1) in rat bladder smooth muscle cells

PURPOSE

Lines of evidence suggest that Rho-associated protein kinase (ROCK)-mediated myosin phosphatase-targeting subunit 1 (MYPT1) phosphorylation plays a central role in smooth muscle contraction. However, the physiological significance of MYPT1 phosphorylation at Thr696 catalyzed by ROCK in bladder smooth muscle remains controversial. We attempt to directly observe the quantitative protein expression of Rho A/ROCK and phosphorylation of MYPT1 at Thr696 after carbachol administration in rat bladder smooth muscle cells (RBMSCs).

MATERIALS AND METHODS

Primary cultured smooth muscle cells were obtained from rat bladders. The effects of both concentration and time-course induced by the muscarinic agonist carbachol were investigated by assessing the expression of Rho A/ROCK and MYPT1 phosphorylation at Thr696 using Western blot.

RESULTS

In the dose-course studies, carbachol showed significant increase in phosphorylation of MYPT1 at Thr696 (p-MYPT1) from concentrations of 15-100 μM based on Western blot results (p < 0.05, ANOVA test). In the time-course studies, treatment of cells with 15 μM of carbachol significantly enhanced the expression of p-MYPT1 from 3 to 15 h (p < 0.05, ANOVA test) and induced the expression of Rho A from 10 to 120 min (p < 0.05, ANOVA test).

CONCLUSIONS

Carbachol can induce the expression of ROCK pathway, leading to MYPT1 phosphorylation at Thr696 and thereby sustained RBSMCs contraction.

A Novel Selectable Islet 1 Positive Progenitor Cell Reprogrammed to Expandable and Functional Smooth Muscle Cells

Disorders affecting smooth muscle structure/function may require technologies that can generate large scale, differentiated and contractile smooth muscle cells (SMC) suitable for cell therapy. To date no clonal precursor population that provides large numbers of differentiated SMC in culture has been identified in a rodent. Identification of such cells may also enhance insight into progenitor cell fate decisions and the relationship between smooth muscle precursors and disease states that implicate differentiated SMC.  In this study, we used classic clonal expansion techniques to identify novel self-renewing Islet 1 (Isl-1) positive primitive progenitor cells (PPC) within rat bone marrow that exhibited canonical stem cell markers and preferential differentiation towards a smooth muscle-like fate. We subsequently used molecular tagging to select Isl-1 positive clonal populations from expanded and de novo marrow cell populations. We refer to these previously undescribed cells as the PPC given its stem cell marker profile, and robust self-renewal capacity. PPC could be directly converted into induced smooth muscle cells (iSMC) using single transcription factor (Kruppel-like factor 4) knockdown or transactivator (myocardin) overexpression in contrast to three control cells (HEK 293, endothelial cells and mesenchymal stem cells) where such induction was not possible. iSMC exhibited immuno- and cytoskeletal-phenotype, calcium signaling profile and contractile responses similar to bona fide SMC. Passaged iSMC could be expanded to a scale sufficient for large scale tissue replacement.  PPC and reprogramed iSMC so derived may offer future opportunities to investigate molecular, structure/function and cell-based replacement therapy approaches to diverse cardiovascular, respiratory, gastrointestinal, and genitourinary diseases that have as their basis smooth muscle cell functional aberrancy or numerical loss. Stem Cells 2016;34:1354-1368.

Activation of common signaling pathways during remodeling of the heart and the bladder

The heart and the urinary bladder are hollow muscular organs, which can be afflicted by pressure overload injury due to pathological conditions such as hypertension and bladder outlet obstruction. This increased outflow resistance induces hypertrophy, marked by dramatic changes in the organs' phenotype and function. The end result in both the heart and the bladder can be acute organ failure due to advanced fibrosis and the subsequent loss of contractility. There is emerging evidence that microRNAs (miRNAs) play an important role in the pathogenesis of heart failure and bladder dysfunction. MiRNAs are endogenous non-coding single-stranded RNAs, which regulate gene expression and control adaptive and maladaptive organ remodeling processes. This Review summarizes the current knowledge of molecular alterations in the heart and the bladder and highlights common signaling pathways and regulatory events. The miRNA expression analysis and experimental target validation done in the heart provide a valuable source of information for investigators working on the bladder and other organs undergoing the process of fibrotic remodeling. Aberrantly expressed miRNA are amendable to pharmacological manipulation, offering an opportunity for development of new therapies for cardiac and bladder hypertrophy and failure.

Research Findings on Overactive Bladder

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

Biomatrices for bladder reconstruction

There is a demand for tissue engineering of the bladder needed by patients who experience a neurogenic bladder or idiopathic detrusor overactivity. To avoid complications from augmentation cystoplasty, the field of tissue engineering seeks optimal scaffolds for bladder reconstruction. Naturally derived biomaterials as well as synthetic and natural polymers have been explored as bladder substitutes. To improve regenerative properties, these biomaterials have been conjugated with functional molecules, combined with nanotechology, or seeded with exogenous cells. Although most studies reported complete and functional bladder regeneration in small-animal models, results from large-animal models and human clinical trials varied. For functional bladder regeneration, procedures for biomaterial fabrication, incorporation of biologically active agents, introduction of nanotechnology, and application of stem-cell technology need to be standardized. Advanced molecular and medical technologies such as next generation sequencing and magnetic resonance imaging can be introduced for mechanistic understanding and non-invasive monitoring of regeneration processes, respectively.

In vivo roles for myosin phosphatase targeting subunit-1 phosphorylation sites T694 and T852 in bladder smooth muscle contraction

KEY POINTS

Force production and maintenance in smooth muscle is largely controlled by myosin regulatory light chain (RLC) phosphorylation, which relies on a balance between Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) activities. MYPT1 is the regulatory subunit of MLCP that biochemically inhibits MLCP activity via T694 or T852 phosphorylation in vitro. Here we separately investigated the contribution of these two phosphorylation sites in bladder smooth muscles by establishing two single point mutation mouse lines, T694A and T852A, and found that phosphorylation of MYPT1 T694, but not T852, mediates force maintenance via inhibition of MLCP activity and enhancement of RLC phosphorylation in vivo. Our findings reveal the role of MYPT1 T694/T852 phosphorylation in vivo in regulation of smooth muscle contraction.

ABSTRACT

Force production and maintenance in smooth muscle is largely controlled by different signalling modules that fine tune myosin regulatory light chain (RLC) phosphorylation, which relies on a balance between Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) activities. To investigate the regulation of MLCP activity in vivo, we analysed the role of two phosphorylation sites on MYPT1 (regulatory subunit of MLCP) that biochemically inhibit MLCP activity in vitro. MYPT1 is constitutively phosphorylated at T694 by unidentified kinases in vivo, whereas the T852 site is phosphorylated by RhoA-associated protein kinase (ROCK). We established two mouse lines with alanine substitution of T694 or T852. Isolated bladder smooth muscle from T852A mice displayed no significant changes in RLC phosphorylation or force responses, but force was inhibited with a ROCK inhibitor. In contrast, smooth muscles containing the T694A mutation showed a significant reduction of force along with reduced RLC phosphorylation. The contractile responses of T694A mutant smooth muscle were also independent of ROCK activation. Thus, phosphorylation of MYPT1 T694, but not T852, is a primary mechanism contributing to inhibition of MLCP activity and enhancement of RLC phosphorylation in vivo. The constitutive phosphorylation of MYPT1 T694 may provide a mechanism for regulating force maintenance of smooth muscle.

Control of urinary drainage and voiding

Urine differs greatly in ion and solute composition from plasma and contains harmful and noxious substances that must be stored for hours and then eliminated when it is socially convenient to do so. The urinary tract that handles this output is composed of a series of pressurizable muscular compartments separated by sphincteric structures. With neural input, these structures coordinate the delivery, collection, and, ultimately, expulsion of urine. Despite large osmotic and chemical gradients in this waste fluid, the bladder maintains a highly impermeable surface in the face of a physically demanding biomechanical environment, which mandates recurring cycles of surface area expansion and increased wall tension during filling, followed by rapid wall compression during voiding. Afferent neuronal inflow from mucosa and submucosa communicates sensory information about bladder fullness, and voiding is initiated consciously through coordinated central and spinal efferent outflow to the detrusor, trigonal internal sphincter, and external urethral sphincter after periods of relative quiescence. Provocative new findings suggest that in some cases, lower urinary tract symptoms, such as incontinence, urgency, frequency, overactivity, and pain may be viewed as a consequence of urothelial defects (either urothelial barrier breakdown or inappropriate signaling from urothelial cells to underlying sensory afferents and potentially interstitial cells). This review describes the physiologic and anatomic mechanisms by which urine is moved from the kidney to the bladder, stored, and then released. Relevant clinical examples of urinary tract dysfunction are also discussed.

JunB mediates basal- and TGFβ1-induced smooth muscle cell contractility

Smooth muscle contraction is a dynamic process driven by acto-myosin interactions that are controlled by multiple regulatory proteins. Our studies have shown that members of the AP-1 transcription factor family control discrete behaviors of smooth muscle cells (SMC) such as growth, migration and fibrosis. However, the role of AP-1 in regulation of smooth muscle contractility is incompletely understood. In this study we show that the AP-1 family member JunB regulates contractility in visceral SMC by altering actin polymerization and myosin light chain phosphorylation. JunB levels are robustly upregulated downstream of transforming growth factor beta-1 (TGFβ1), a known inducer of SMC contractility. RNAi-mediated silencing of JunB in primary human bladder SMC (pBSMC) inhibited cell contractility under both basal and TGFβ1-stimulated conditions, as determined using gel contraction and traction force microscopy assays. JunB knockdown did not alter expression of the contractile proteins α-SMA, calponin or SM22α. However, JunB silencing decreased levels of Rho kinase (ROCK) and myosin light chain (MLC20). Moreover, JunB silencing attenuated phosphorylation of the MLC20 regulatory phosphatase subunit MYPT1 and the actin severing protein cofilin. Consistent with these changes, cells in which JunB was knocked down showed a reduction in the F:G actin ratio in response to TGFβ1. Together these findings demonstrate a novel function for JunB in regulating visceral smooth muscle cell contractility through effects on both myosin and the actin cytoskeleton.