Contractile and cytoskeletal proteins in smooth muscle during hypertrophy and its reversal

Differential transcriptomic changes in the central nervous system and urinary bladders of mice infected with a coronavirus

Multiple sclerosis (MS) often leads to the development of neurogenic lower urinary tract symptoms (LUTS). We previously characterized neurogenic bladder dysfunction in a mouse model of MS induced by a coronavirus, mouse hepatitis virus (MHV). The aim of the study was to identify genes and pathways linking neuroinflammation in the central nervous system with urinary bladder (UB) dysfunction to enhance our understanding of the mechanisms underlying LUTS in demyelinating diseases. Adult C57BL/6 male mice (N = 12) received either an intracranial injection of MHV (coronavirus-induced encephalomyelitis, CIE group), or sterile saline (control group). Spinal cord (SC) and urinary bladders (UB) were collected from CIE mice at 1 wk and 4 wks, followed by RNA isolation and NanoString nCounter Neuroinflammation assay. Transcriptome analysis of SC identified a significantly changed expression of >150 genes in CIE mice known to regulate astrocyte, microglia and oligodendrocyte functions, neuroinflammation and immune responses. Two genes were significantly upregulated (Ttr and Ms4a4a), and two were downregulated (Asb2 and Myct1) only in the UB of CIE mice. Siglec1 and Zbp1 were the only genes significantly upregulated in both tissues, suggesting a common transcriptomic link between neuroinflammation in the CNS and neurogenic changes in the UB of CIE mice.

Molecular and Morphological Characteristics of the De-Obstructed Rat Urinary Bladder—An Update

Many patients with outlet obstruction secondary to prostatic enlargement have lower urinary tract symptoms (LUTSs) and an increased frequency of micturition. The standard treatment is transurethral resection of the prostate (TURP), which alleviates obstruction and symptoms. However, after TURP, 20–40 percent of patients continue to experience LUTSs. The aim of the present study in rats was to identify the mechanisms that do not normalize after the removal of the obstruction and that could explain the persisting symptoms. We had microarray data from control, obstructed, and de-obstructed female rat bladders, which made it possible to study 14,553 mRNA expressions. We also had a bank of electron micrographs from similar detrusors. Microarrays: There were significant differences between the control and obstructed bladders for 1111 mRNAs. The obstructed and de-obstructed bladders differed significantly for 1059 mRNAs. The controls and the de-obstructed bladders differed significantly for 798 mRNAs. We observed many mRNAs that were increased in the obstructed bladder and then decreased to control levels after de-obstruction, and many mRNAs that were decreased in the obstructed bladder and then increased following de-obstruction. mRNAs that were significantly higher or lower in the de-obstructed bladder than in the control bladder were also found. Ultrastructure: The detrusor cells in the obstructed bladders had cross-sectional areas that were much larger than those in the controls. The control cells had smooth outlines and similar cross-sectional areas. The de-obstructed detrusor cells had larger cross-sectional areas than the controls, as well as corrugated surfaces. The cell areas varied, suggesting that the shrinkage of the de-obstructed cells was not even. We did not find any points of contact of the gap junction plaque type between the detrusor cells. There were abundant finger-like processes between the detrusor cells in the obstructed and in de-obstructed bladders, which were only occasionally found in the control detrusors. They are the only possible localization for gap junction channels. The de-obstructed rat bladder is not an organ with properties intermediate between those of the control and obstructed bladders. Instead, de-obstructed bladders have gene expressions, morphologies, and functional properties of the individual cells and their organization, which make them distinctly different from both control and obstructed bladders.

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.

Identification of the intermediate filament protein synemin/SYNM as a target of myocardin family coactivators

Myocardin (MYOCD) is a critical regulator of smooth muscle cell (SMC) differentiation, but its transcriptional targets remain to be exhaustively characterized, especially at the protein level. Here we leveraged human RNA and protein expression data to identify novel potential MYOCD targets. Using correlation analyses we found several targets that we could confirm at the protein level, including SORBS1, SLMAP, SYNM, and MCAM. We focused on SYNM, which encodes the intermediate filament protein synemin. SYNM rivalled smooth muscle myosin (MYH11) for SMC specificity and was controlled at the mRNA and protein levels by all myocardin-related transcription factors (MRTFs: MYOCD, MRTF-A/MKL1, and MRTF-B/MKL2). MRTF activity is regulated by the ratio of filamentous to globular actin, and SYNM was accordingly reduced by interventions that depolymerize actin, such as latrunculin treatment and overexpression of constitutively active cofilin. Many MRTF target genes depend on serum response factor (SRF), but SYNM lacked SRF-binding motifs in its proximal promoter, which was not directly regulated by MYOCD. Furthermore, SYNM resisted SRF silencing, yet the time course of induction closely paralleled that of the SRF-dependent target gene ACTA2. SYNM was repressed by the ternary complex factor (TCF) FLI1 and was increased in mouse embryonic fibroblasts lacking three classical TCFs (ELK1, ELK3, and ELK4). Imaging showed colocalization of SYNM with the intermediate filament proteins desmin and vimentin, and MRTF-A/MKL1 increased SYNM-containing intermediate filaments in SMCs. These studies identify SYNM as a novel SRF-independent target of myocardin that is abundantly expressed in all SMCs.

Array profiling reveals contribution of Cthrc1 to growth of the denervated rat urinary bladder

Bladder denervation and bladder outlet obstruction are urological conditions that cause bladder growth. Transcriptomic surveys in outlet obstruction have identified differentially expressed genes, but similar studies following denervation have not been done. This was addressed using a rat model in which the pelvic ganglia were cryo-ablated followed by bladder microarray analyses. At 10 days following denervation, bladder weight had increased 5.6-fold, and 2,890 mRNAs and 135 micro-RNAs (miRNAs) were differentially expressed. Comparison with array data from obstructed bladders demonstrated overlap between the conditions, and 10% of mRNAs changed significantly and in the same direction. Many mRNAs, including collagen triple helix repeat containing 1 ( Cthrc1), Prc1, Plod2, and Dkk3, and miRNAs, such as miR-212 and miR-29, resided in the shared signature. Discordantly regulated transcripts in the two models were rare, making up for <0.07% of all changes, and the gene products in this category localized to the urothelium of normal bladders. These transcripts may potentially be used to diagnose sensory denervation. Western blotting demonstrated directionally consistent changes at the protein level, with increases of, e.g., Cthrc1, Prc1, Plod2, and Dkk3. We chose Cthrc1 for further studies and found that Cthrc1 was induced in the smooth muscle cell (SMC) layer following denervation. TGF-β1 stimulation and miR-30d-5p inhibition increased Cthrc1 in bladder SMCs, and knockdown and overexpression of Cthrc1 reduced and increased SMC proliferation. This work defines common and distinguishing features of bladder denervation and obstruction and suggests a role for Cthrc1 in bladder growth following denervation.

Bladder wall thickness in the assessment of neurogenic bladder: a translational discussion of current clinical applications

The prospective trial by Kim et al. "Can Bladder Wall Thickness Predict Videourodynamic Findings in Children with Spina Bifida?" published in Journal of Urology investigated the measurement of bladder wall thickness (BWT) as a non-invasive assessment tool for lower urinary tract changes in neurogenic bladder (NGB). In this study, no significant association was observed between BWT and high-risk urodynamic parameters. This editorial discusses the basic science of bladder wall thickening as well as prior studies relating wall thickness to clinical parameters. Although Kim et al. provide a unique literature contribution in terms of assessment of BWT at defined percent cystometric capacity, specific aspects of study methodology and population may have contributed to a lack of correlation with high-risk urodynamic findings. The application of non-invasive modalities to lower urinary tract assessment of NGB remains a promising and relevant area of future research to prevent progression to end stage lower urinary tract changes for all individuals with spina bifida.

[Physiopathology of overactive bladder syndrome]

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

Protein kinase C activation of a blebbistatin sensitive contractile component in the wall of hypertrophying mouse urinary bladder

AIM

To examine the role of protein kinase C (PKC) and non-muscle myosin in regulation of wall tension in the hypertrophied urinary bladder.

METHODS

A partial urinary outflow obstruction was induced in the mouse. Tissue strips from sham operated controls and obstructed bladders were examined in vitro with quantitative gel electrophoresis, immunohistochemistry, and in vitro force recordings.

RESULTS

Outlet obstruction (14-18 days) induced a significant growth of the bladder, 73 ± 6.13 mg compared to 19 ± 1 13 mg in sham operated controls. The hypertrophying bladder tissue had increased expression of non-muscle myosin B (SMemb) mainly localized to serosa and suburothelium. Direct activation of PKC with PDBu did not alter force in the control urinary bladder. In contrast, PDBu initiated a prominent and sustained contraction which had an increased sensitivity to the myosin type II inhibitor blebbistatin.

CONCLUSIONS

PKC activates a significant contractile response in the wall of the hypertrophying urinary bladder, possibly supported by non-muscle myosin. This contractile component is not contributing to the physiological response to muscarinic stimulation, but might be separately regulated by other, yet unknown, mechanisms.

Phenotypic switching induced by damaged matrix is associated with DNA methyltransferase 3A (DNMT3A) activity and nuclear localization in smooth muscle cells (SMC)

Extracellular matrix changes are often crucial inciting events for fibroproliferative disease. Epigenetic changes, specifically DNA methylation, are critical factors underlying differentiated phenotypes. We examined the dependency of matrix-induced fibroproliferation and SMC phenotype on DNA methyltransferases. The cooperativity of matrix with growth factors, cell density and hypoxia was also examined. Primary rat visceral SMC of early passage (0–2) were plated on native collagen or damaged/heat-denatured collagen. Hypoxia was induced with 3% O₂ (balanced 5% CO₂ and 95% N₂) over 48 hours. Inhibitors were applied 2–3 hours after cells were plated on matrix, or immediately before hypoxia. Cells were fixed and stained for DNMT3A and smooth muscle actin (SMA) or smooth muscle myosin heavy chain. Illumina 450 K array of CpG sites was performed on bisulfite-converted DNA from smooth muscle cells on damaged matrix vs native collagen. Matrix exquisitely regulates DNMT3A localization and expression, and influences differentiation in SMCs exposed to denatured matrix +/− hypoxia. Analysis of DNA methylation signatures showed that Matrix caused significant DNA methylation alterations in a discrete number of CpG sites proximal to genes related to SMC differentiation. Matrix has a profound effect on the regulation of SMC phenotype, which is associated with altered expression, localization of DNMTs and discrete changes DNA methylation.

A nonhuman primate model for urinary bladder regeneration using autologous sources of bone marrow-derived mesenchymal stem cells

Animal models that have been used to examine the regenerative capacity of cell-seeded scaffolds in a urinary bladder augmentation model have ultimately translated poorly in the clinical setting. This may be due to a number of factors including cell types used for regeneration and anatomical/physiological differences between lower primate species and their human counterparts. We postulated that mesenchymal stem cells (MSCs) could provide a cell source for partial bladder regeneration in a newly described nonhuman primate bladder (baboon) augmentation model. Cell-sorted CD105(+) /CD73(+) /CD34(-) /CD45(-) baboon MSCs transduced with green fluorescent protein (GFP) were seeded onto small intestinal submucosa (SIS) scaffolds. Baboons underwent an approximate 40%-50% cystectomy followed by augmentation cystoplasty with the aforementioned scaffolds or controls and finally enveloped with omentum. Bladders from sham, unseeded SIS, and MSC/SIS scaffolds were subjected to trichrome, H&E, and immunofluorescent staining 10 weeks postaugmentation. Immunofluorescence staining for muscle markers combined with an anti-GFP antibody revealed that >90% of the cells were GFP(+) /muscle marker(+) and >70% were GFP(+) /Ki-67(+) demonstrating grafted cells were present and actively proliferating within the grafted region. Trichrome staining of MSC/SIS-augmented bladders exhibited typical bladder architecture and quantitative morphometry analyses revealed an approximate 32% and 52% muscle to collagen ratio in unseeded versus seeded animals, respectively. H&E staining revealed a lack of infiltration of inflammatory cells in grafted animals and in corresponding kidneys and ureters. Simple cystometry indicated recovery between 28% and 40% of native bladder capacity. Data demonstrate MSC/SIS composites support regeneration of bladder tissue and validate this new bladder augmentation model.

Blebbistain, a myosin II inhibitor, as a novel strategy to regulate detrusor contractility in a rat model of partial bladder outlet obstruction

Partial bladder outlet obstruction (PBOO), a common urologic pathology mostly caused by benign prostatic hyperplasia, can coexist in 40–45% of patients with overactive bladder (OAB) and is associated with detrusor overactivity (DO). PBOO that induces DO results in alteration in bladder myosin II type and isoform composition. Blebbistatin (BLEB) is a myosin II inhibitor we recently demonstrated potently relaxed normal detrusor smooth muscle (SM) and reports suggest varied BLEB efficacy for different SM myosin (SMM) isoforms and/or SMM vs nonmuscle myosin (NMM). We hypothesize BLEB inhibition of myosin II as a novel contraction protein targeted strategy to regulate DO. Using a surgically-induced male rat PBOO model, organ bath contractility, competitive and Real-Time-RT-PCR were performed. It was found that obstructed-bladder weight significantly increased 2.74-fold while in vitro contractility of detrusor to various stimuli was impaired ∼50% along with decreased shortening velocity. Obstruction also altered detrusor spontaneous activities with significantly increased amplitude but depressed frequency. PBOO switched bladder from a phasic-type to a more tonic-type SM. Expression of 5’ myosin heavy chain (MHC) alternatively spliced isoform SM-A (associated with tonic-type SM) increased 3-fold while 3’ MHC SM1 and essential light chain isoform MLC_17b also exhibited increased relative expression. Total SMMHC expression was decreased by 25% while the expression of NMM IIB (SMemb) was greatly increased by 4.5-fold. BLEB was found to completely relax detrusor strips from both sham-operated and PBOO rats pre-contracted with KCl, carbachol or electrical field stimulation although sensitivity was slightly decreased (20%) only at lower doses for PBOO. Thus we provide the first thorough characterization of the response of rat bladder myosin to PBOO and demonstrate complete BLEB-induced PBOO bladder SM relaxation. Furthermore, the present study provides valuable evidence that BLEB may be a novel type of potential therapeutic agent for regulation of myogenic and nerve-evoked DO in OAB.

In vitro and in vivo relaxation of urinary bladder smooth muscle by the selective myosin II inhibitor, blebbistatin

OBJECTIVE To investigate the in vitro and in vivo effects of blebbistatin (a small cell-permeable molecule with high affinity and selectivity toward the myosin II contractile molecule) on bladder smooth muscle (SM) contractility, as antimuscarinic therapy is only 65-75% effective in treating overactive bladder (OAB) and is associated with considerable side-effects, with a < 25% continuation rate at 1 year. MATERIALS AND METHODS Bladder and aortic strips from adult male rats, and human bladder strips obtained from open prostatectomy, were used for organ-bath studies of blebbistatin. Awake cystometry was also used in rats in both the presence and absence of intravesically delivered blebbistatin. RESULTS Blebbistatin dose-dependently and completely relaxed both KCl- and carbachol-induced rat detrusor and endothelin-1-induced human bladder contraction. Pre-incubation with 10 µm blebbistatin attenuated carbachol responsiveness by ≈ 65% while blocking electrical field stimulation-induced bladder contraction reaching 50% inhibition at 32 Hz. The basal tone and amplitude of spontaneous contraction were also significantly diminished. Urodynamic variables were obviously altered by intravesical infusion with blebbistatin. CONCLUSION Our novel data show that blebbistatin strongly relaxes both rat and human bladder contraction induced by various physiological stimuli. Coupled with our in vivo data showing that nanomole doses of blebbistatin significantly alter urodynamic variables to produce a less active bladder, our results suggest the possibility of intravesically administered blebbistatin binding at myosin II being developed as a therapeutic treatment for OAB via a novel targeting of the SM contractile apparatus.

Partial urethral obstruction: ATF3 and p-c-Jun are involved in the growth of the detrusor muscle and its motor innervation

OBJECTIVE

Infravesical obstruction leads to growth of urinary bladder smooth-muscle cells. The ganglion cells innervating the bladder muscle also increase in size. Stretch of detrusor muscle cells rapidly activates c-Jun NH₂-terminal kinase (JNK), which phosphorylates the transcription factor c-Jun, and stimulates the synthesis of the cotranscription factor ATF3. The aim of the study was to determine whether ATF3 and p-c-Jun were involved in growth of bladder smooth-muscle and ganglion cells.

MATERIAL AND METHODS

The urethra was partially obstructed in female rats. After 3 days or 10 weeks bladders were weighed, fixated and cut for immunohistochemistry to demonstrate ATF3 and p-c-Jun. Ganglia were processed separately. Unoperated and sham-operated rats were used as controls.

RESULTS

There was no ATF3 or p-c-Jun in control detrusor muscle. After 3 days of obstruction bladder weight had nearly doubled. Almost all nuclei in the detrusor showed immunofluorescence for ATF3 and p-c-Jun. After 10 weeks bladder weight had increased 10-fold. Almost all detrusor nuclei still showed p-c-Jun, but few had ATF3 activity. In control ganglia there was no ATF3 and only faint nuclear p-c-Jun activity. After 3 days of obstruction the ganglion cells had increased in size and many nuclei showed intense immunofluorescence for ATF3 and p-c-Jun. After 10 weeks the ganglion cell size had increased further. There was no ATF3 activity and no more p-c-Jun than in control ganglia.

CONCLUSION

ATF3 and p-c-Jun seem to be involved in the growth of the detrusor muscle and its motor innervation following infravesical outlet obstruction.

Temporal morphological and functional impact of complete urinary diversion on the bladder: a model of bladder disuse in rats

PURPOSE

Urinary diversion has been used as a surgical option for some bladder diseases. We developed a urinary diversion model in the rat and examined the effects of urinary diversion on the bladder.

MATERIALS AND METHODS

We distributed female Sprague-Dawley® rats into age matched control, sham urinary diversion and urinary diversion groups. Each group was subsequently evaluated 1 or 8 weeks after urinary diversion or sham operation. Diversion was done by surgical disconnection of the ureters from the bladder and implantation to the uterine cervix. Conscious cystometry was examined. Bladders were harvested for histological examination and quantification of smooth muscle, urothelium and collagen. Vaginal histology was assessed. Bladder muscarinic and purinergic receptor expression was examined.

RESULTS

All rats survived the urinary diversion procedure. Bladder weight decreased in the diversion group. Cystometry showed decreased intercontractile interval and voided volume in the urinary diversion group compared to those in the control and sham operated groups. Compliance was decreased in diverted rats. Smooth muscle and urothelium were decreased as a percent of total bladder cross-sectional area. Collagen increased in 1 and 8-week diverted rats vs controls. Histological examination of the vaginal wall revealed mild swelling in 2 rats. Urinary diversion caused decreased muscarinic 3 and ligand gated purinergic 1 receptor expression but no change in muscarinic 2 or ligand gated purinergic 2 receptors.

CONCLUSIONS

Creating a urinary diversion model by ureterovaginostomy in the rat is feasible. Urinary diversion causes distinct functional and morphometric bladder alterations.

Alterations in caveolin expression and ultrastructure after bladder smooth muscle hypertrophy

PURPOSE

Partial bladder outlet obstruction in male rabbits causes detrusor smooth muscle hypertrophy and voiding dysfunction similar to that observed in men with benign prostate hyperplasia. Using this model, we analyzed the protein expression and ultrastructure of caveolae and the intermediate size filament in detrusor smooth muscle following partial bladder outlet obstruction induced hypertrophy.

MATERIALS AND METHODS

Detrusor smooth muscle sections from bladder body were processed for immunofluorescence and electron microscopy. Western analysis was performed to determine the expression of caveolin isoform-1, 2 and 3, and intermediate size filament proteins.

RESULTS

Detrusor smooth muscle cells from both normal and hypertrophied bladders contain orderly arrays of thick and thin myofilaments, interspersed with dense bodies. In addition, there was an increase in intermediate size filaments in the hypertrophic detrusor smooth muscle cells. The dense plaques in the inner membrane of hypertrophied detrusor smooth muscle were longer than those of the control. Detrusor smooth muscle from hypertrophied bladder revealed a decreased number of caveolae and a lack of their orderly distribution at the plasma membrane. Western blotting showed decreased expression of caveolin-1, 2 and 3 in hypertrophied detrusor smooth muscle.

CONCLUSIONS

Caveolae serve as platforms for proteins and receptors that have a role in signal transduction. The decreased number of caveolae and caveolin protein expression in hypertrophied detrusor smooth muscle might contribute to alterations in signal transduction pathways that regulate the downstream effects of agonist induced contraction, including calcium sensitization, observed in obstructed bladder. In addition, the increased number of intermediate size filaments in the hypertrophied detrusor smooth muscle is likely to alter the cytoskeletal structure and affect the cellular transmission of passive and/or active force.

Role of desmin in active force transmission and maintenance of structure during growth of urinary bladder

Role of the intermediate filament protein desmin in hypertrophy of smooth muscle was examined in desmin-deficient mice (Des(-/-)). A partial obstruction of the urethra was created, and after 9-19 days bladder weight increased approximately threefold in both Des(-/-) and wild type (Des(+/+)) animals. Bladder growth was associated with the synthesis of actin and myosin. In the hypertrophic Des(+/+) bladder, the relative content of desmin increased. In Des(-/-)mice, desmin was absent. No alterations in the amount of vimentin were observed. Although Des(-/-) obstructed bladders were capable of growth, they had structural changes with a partial disruption of the wall. Des(-/-)bladders had slightly lower passive stress and significantly lower active stress compared with Des(+/+). Des(-/-)preparations had lower shortening velocity. During hypertrophy, these structural and mechanical alterations in the Des(-/-)urinary bladder became more pronounced. In conclusion, desmin in the bladder smooth muscle is not needed for growth but has a role in active force transmission and maintenance of wall structure.

Intracellular calcium in hypertrophic smooth muscle from rat urinary bladder

OBJECTIVE

To explore whether infravesical outlet obstruction is associated with alterations in calcium activation of detrusor smooth muscle.

MATERIAL AND METHODS

Outlet obstruction was created by partial ligature of the urethra in female rats. Western blotting was performed using an antibody against the cytoplasmatic region of the alpha1c subunit of the L-type Ca2+ channel. Intracellular calcium was measured using Fura-2 in detrusors that had been obstructed for 10 days and activated by high K+ concentrations at different extracellular Ca2+ concentrations. The rate of force development after rapid opening of L-type Ca2+ channels was measured in contractions initiated by flash photolysis of nifedipine in Ca2(+)-containing depolarizing solution.

RESULTS

Bladder weight increased from 62 +/- 3 to 254 +/- 43 mg after 10 days of obstruction. Expression of the alpha1c subunit increased after 3 days and continued to increase until it was about fourfold greater after 10 days; however, it had not increased further at 6 weeks. This change was reversible after removal of obstruction. Activation with K+ produced a stable force at different extracellular Ca2+ concentrations, with no difference in response between controls and rats that had been obstructed for 10 days. Intracellular Ca2+ concentrations were lower in the obstructed group, showing that the calcium sensitivity of the contraction force had increased. The delay between the opening of L-type channels and the onset of contraction was longer in obstructed detrusors.

CONCLUSIONS

Growth of detrusor muscle following obstruction is accompanied by attenuated calcium transients following activation, despite upregulation of L-type Ca2+ channels. The Ca2+ sensitivity of contraction was increased in obstructed detrusors. We suggest that the decreased surface: volume ratio in hypertrophic smooth muscle cells is partly involved in the lowered Ca2+ transients. The increases in L-type calcium channels and in calcium sensitivity may be compensatory mechanisms.

Novel biomarkers of bladder decompensation after partial bladder obstruction

AIMS

Partial bladder outlet obstruction (PBOO) results in marked contractile, biochemical, and histological alterations in the bladder. Our aim was to determine the time course of progressive PBOO in the rabbit and to find parameters that marked the shift to decompensation.

MATERIALS AND METHODS

Twenty-four rabbits were subjected to 1, 2, 4, and 8 weeks of PBOO. Sham operated rabbits served as controls. At each time period, cystometry was performed and individual bladder strips were used for contractility studies. Full-thickness sections of bladder body from each rabbit were fixed in formalin and used to determine the vascular density and nerve density. The balance of the bladder body was separated between muscle and mucosa and was analyzed for superoxide dismutase (SOD) and catalase (CAT) activities.

RESULTS

Bladder weight increased progressively and all contractile responses were reduced significantly over the course of obstruction. Markedly increased bladder weight and very large bladder volumes indicated decompensation. Nerve density was marked decreased in decompensated bladders. Similarly, SOD activity in muscle decreased progressively and was markedly lower in decompensated bladders. Although CAT activity of the muscle increased after 2-4 weeks of obstruction, it decreased markedly in decompensated bladders.

CONCLUSION

This study shows that prolonged PBOO causes progressive deterioration in the rabbit bladder with decompensation after 8 weeks. Markedly decreased nerve density and severely reduced SOD and CAT activities are associated with the shift from compensated to decompensated function of the bladder. They may be excellent biomarkers of decompensation.

Plasticity of rat small intestine after removal of a chronic mechanical obstruction

Chronic intestinal obstruction is associated with morphological changes and functional disorders clinically reported and experimentally documented in laboratory animals. In contrast, little is known about the properties of the hypertrophied intestine after removal of the obstruction. In the present study, we removed the ileal obstruction previously applied to the ileum of rats and, after 1 or 2 weeks, studied in vitro the motor responses of de-obstructed segments of intestine to pharmacological or electrical field stimulation (EFS). By 2 weeks after de-obstruction, maximal contractile responses to receptor (acetylcholine) and non-receptor (K(+)) mediated stimuli were comparable in operated and control tissues; furthermore, the loss of sensitivity to nitric oxide (NO) unmasked in obstructed tissues was, after de-obstruction, replaced by supersensitivity to exogenous NO and vasoactive intestinal polypeptide, probably acting through cyclic nucleotide-independent pathways. Despite the complete recovery of smooth muscle responses, neurogenic contractions remained impaired in de-obstructed tissue; however, the equal contribution of cholinergic/peptidergic components to EFS responses could represent a sign of gradual but delayed recovery of enteric neurotransmission.

The detrusor muscle: an innocent victim of bladder outlet obstruction

OBJECTIVES

Benign prostatic hyperplasia (BPH) is considered a frequent cause of bladder outlet obstruction (BOO) and lower urinary tract symptoms (LUTS), although the physiopathologic mechanism through which BPH causes LUTS is not clear. Several morphologic and functional modifications of the bladder detrusor have been described in patients with BPH and could play a direct role in determining symptoms. The opinion is spreading that the enlarged prostates in patients with LUTS is nothing more than a mere bystander. Evidence has accumulated, however, supporting the role of BPH-related BOO as the direct cause determining bladder dysfunction and indirectly causing urinary symptoms. The present review addresses the bladder response to BOO, particularly focusing on the physiopathologic cascade that links obstructive BPH to bladder dysfunction.

METHODS

A literature review of peer-reviewed articles has been performed, including both in vivo and in vitro studies on human tissue and animal model experiments.

RESULTS

Epithelial and smooth muscle cells in the bladder wall are mechanosensitive, and in response to mechanical stretch stress caused by BOO, undergo modifications of gene expression and protein synthesis. This process involves several transduction mechanisms and finally alter the ultrastructure and physiology of cell membranes, cytoskeleton, contractile proteins, mitochondria, extracellular matrix, and neuronal networks.

CONCLUSIONS

BOO is the initiator of a physiopathologic cascade leading to deep changing of bladder structure and function. Before being a direct cause of storing-phase urinary symptoms, the bladder is the first innocent victim of prostatic obstruction.

Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

A major development in smooth muscle research in recent years is the recognition that the myofilament lattice of the muscle is malleable. The malleability appears to stem from plastic rearrangement of contractile and cytoskeletal filaments in response to stress and strain exerted on the muscle cell, and it allows the muscle to adapt to a wide range of cell lengths and maintain optimal contractility. Although much is still poorly understood, we have begun to comprehend some of the basic mechanisms underlying the assembly and disassembly of contractile and cytoskeletal filaments in smooth muscle during the process of adaptation to large changes in cell geometry. One factor that likely facilitates the plastic length adaptation is the ability of myosin filaments to form and dissolve at the right place and the right time within the myofilament lattice. It is proposed herein that formation of myosin filaments in vivo is aided by the various filament-stabilizing proteins, such as caldesmon, and that the thick filament length is determined by the dimension of the actin filament lattice. It is still an open question as to how the dimension of the dynamic filament lattice is regulated. In light of the new perspective of malleable myofilament lattice in smooth muscle, the roles of many smooth muscle proteins could be assigned or reassigned in the context of plastic reorganization of the contractile apparatus and cytoskeleton.

Altered expression of thin filament-associated proteins in hypertrophied urinary bladder smooth muscle

AIMS

Obstruction of the urinary bladder outlet induces detrusor smooth muscle (DSM) hypertrophy. The goal of this study was to determine whether the composition of thin filament-associated proteins, known to play important roles in cytoskeletal structure and/or the regulation of contraction, is altered in DSM during hypertrophy.

METHODS

DSM hypertrophy was induced in male rabbits by partial ligation of the urethra. Sham-operated rabbits served as a control. Reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time PCR revealed a significant increase in the expression of mRNAs for basic (h1) calponin (CaP), and alpha-isoform of tropomyosin (Tm) in hypertrophied DSM compared to controls. Western blotting and two-dimensional (2-D) gel electrophoresis showed enhanced expression of these proteins and also a significant increase in the expression of beta-non muscle and gamma-smooth muscle actin in the DSM from obstructed bladders, while alpha-actin remained constant.

RESULTS

Enhanced expression of these proteins in the DSM from obstructed bladders was confirmed by immunofluorescence microscopy. Double immunostaining with Cap/Tm and alpha/beta-actin-specific antibodies showed co-localization of these proteins in myocytes. Colocalization of smooth muscle specific myosin and CaP to cytoplasmic filaments in cells dissociated from the hypertrophied DSM indicated that these cells are differentiated smooth muscle cells.

CONCLUSIONS

The change in the isoforms of actin, Cap, and Tm may be part of the molecular mechanism for bladder compensation in increased urethral resistance.

Smooth muscle membrane organization in the normal and dysfunctional human urinary bladder: a structural analysis

PURPOSE

The decline in contractile properties is a characteristic feature of the dysfunctional bladder as a result of infravesical outlet obstruction. During clinical progression of the disease, smooth muscle cells undergo structural modifications. Since adaptations to constant changes in length require a high degree of structural organization within the sarcolemma, we have investigated the expression of several proteins, which are involved in smooth muscle membrane organization, in specimens derived from normal and dysfunctional organs.

MATERIALS AND METHODS

Specimen from patients with urodynamically normal/equivocal (n = 4), obstructed (n = 2), and acontractile (n = 2) bladders were analyzed relative to their structural features and sarcolemmal protein profile.

RESULTS

Smooth muscle cells within the normal urinary bladder display a distinct sarcolemmal domain structure, characterized by firm actin-attachment sites, alternating with flexible "hinge" regions. In obstructed bladders, foci of cells displaying degenerative sarcolemmal changes alternate with areas of hypertrophic cells in which the membrane appears unaffected. In acontractile organs, the overall membrane structure remains intact, however annexin 6, a protein belonging to a family of Ca2+-dependent, "membrane-organizers," is downregulated.

CONCLUSION

Degenerative changes in smooth muscle cells, which are chronically working against high resistance, are preferentially located within the actin-attachment sites. In acontractile bladders, the downregulation of annexin 6 might have a bearing on the fine-tuning of the plasma membrane during contraction/relaxation cycles.

Decreased expression of smooth muscle alpha-actin results in decreased contractile function of the mouse bladder

PURPOSE

Smooth muscle alpha-actin (SMalphaA) is an important actin isoform for functional contractility in the mouse bladder. Alterations in the expression of SMalphaA have been associated with a variety of bladder pathological conditions. Recently, a SMalphaA-null mouse was generated and differences in vascular tone and contractility were observed between wild-type and SMalphaA-null mice suggesting alterations in function of vascular smooth muscle. We used SMalphaA-null mice to explore the hypothesis that SMalphaA is necessary for normal bladder function.

MATERIALS AND METHODS

Reverse transcriptase polymerase chain reaction, Western blotting and immunohistochemical staining were used to confirm the absence of SMalphaA transcript and protein in the bladder of SMalphaA-null mice. In vitro bladder contractility compared between bladder rings harvested from wild-type and SMalphaA-null mice was determined by force measurement following electrical field stimulation (EFS), and exposure to chemical agonists and antagonists including KCl, carbachol, atropine and tetrodotoxin. Resulting force generation profiles for each tissue and agent were analyzed.

RESULTS

There was no detectable SMalphaA transcript and protein expression in the bladder of SMalphaA-null mice. Nine wild-type and 9 SMalphaA-null mice were used in the contractility study. Bladders from SMalphaA-null mice generated significantly less force than wild-type mice in response to EFS after KCl. Similarly, bladders from SMalphaA-null mice generated less force than wild-type mice in response to pretreatment EFS, and EFS after carbachol and atropine, although the difference was not significant. Surprisingly, the bladders in SMalphaA-null mice appeared to function normally and showed no gross or histological abnormalities.

CONCLUSIONS

SMalphaA appears to be necessary for the bladder to be able to generate normal levels of contractile force. No functional deficits were observed in the bladders of these animals but no stress was placed on these bladders. To our knowledge this study represents the first report to demonstrate the importance of expression of SMalphaA in force generation in the bladder.

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.

Smooth, slow and smart muscle motors

Smooth muscle is a slow and economical muscle with a large variability in contractile properties. This review describes results regarding the relation between expression of myosin isoforms and the contraction of smooth muscle. The focus of the review is on studies of the organised contractile system in the smooth muscle tissue. The role of the myosin heavy chain variants formed by alternative splicing in the myosin heavy chain tail (SM1, SM2 isoforms) and head (SM-A SM-B isoforms) regions, as well as the role of essential light chains (LC17a, LC17b isoforms) for the variability of contractile properties are discussed. Smooth muscle also has the ability to alter its contractile properties in response to altered functional demands in vivo, e.g. during hypertrophic growth of urinary bladder, intestine, uterus and vessels and in response to altered hormone levels. These alterations involve changes in myosin expression and altered contractile kinetics. Non-muscle myosin has been shown to have a contractile function in some smooth muscle tissues and recent data on the kinetic properties of non-muscle myosin filaments in smooth muscle tissue are described.

Response of bladder smooth muscle cells to obstruction: signal transduction and the role of mechanosensors

Bladder hypertrophy and detrusor overactivity are well-known bladder responses to outlet obstruction. Mechanical stretch stress is considered the trigger inducing these responses in the urodynamically overloaded bladder. Several studies using an in vitro model of mechanical stress demonstrate that repetitive stretch stimulation of bladder smooth muscle cells results in increased expression of a variety of growth factors and other specific proteins. In the bladder smooth muscle cell, stretch-activated ion channels (SACs) and protein kinase C (PKC) sarcolemmal proteins may function as sensors for external mechanical forces. In particular, SACs couple mechanical stress to activation of c-jun NH2-terminal kinase, which leads to a rapid induction of nuclear transcription factors. PKC also may involve an indirect or direct regulation of nuclear events. In addition, mechanical stress may induce the release of angiotensin II in an autocrine fashion. These factors in turn stimulate expression of specific gene-encoding proteins, such as heparin-binding epidermal growth factor-like growth factor, nerve growth factor, and an isomer of cyclooxygenase-2, all of which have the potential to contribute to structural and functional alterations in the bladder after obstruction.

Smooth muscle hypertrophy following partial bladder outlet obstruction is associated with overexpression of non-muscle caldesmon

Partial bladder outlet obstruction (PBOO) induces remodeling of urinary bladder smooth muscle (detrusor). We demonstrate an increase in bladder wall mass, muscle bundle size, and a threefold increase in the cross-sectional area of detrusor myocytes following PBOO in male New Zealand White rabbits compared to that of controls. Some bladders with detrusor hypertrophy function close to normal (compensated), whereas others were dysfunctional (decompensated), showing high intravesical pressure, large residual urine volume, and voiding difficulty. We analyzed the expression of smooth muscle-specific caldesmon (h-CaD) and non-muscle (l-CaD) by Western blotting, RT-PCR, and real-time PCR. The expression of l-CaD is increased significantly at the mRNA and protein levels in the decompensated bladders compared to that of normal and compensated bladders. The CaD was also co-localized with myosin containing cytoplasmic fibrils in cells dissociated from obstructed bladders and cultured overnight. Our data show that the inability of decompensated bladders to empty, despite detrusor hypertrophy, is associated with an overexpression of l-CaD. The level of l-CaD overexpression might be a useful marker to estimate the degree of detrusor remodeling and contractile dysfunction in PBOO.

Storage and voiding symptoms: pathophysiologic aspects

Lower urinary tract symptoms (LUTS) can be categorized as storage, voiding, and postmicturition symptoms. Although often associated with benign prostatic hyperplasia (BPH), they may also occur in women. This observation, the beneficial effects of alpha-adrenoceptor (AR) antagonists in men with BPH and LUTS, and the frail correlation between LUTS, and prostatic enlargement and/or outflow obstruction have focused interest on the role of extraprostatic alpha-ARs in the pathogenesis of LUTS. It has been suggested that an upregulation of contraction-mediating alpha-ARs and a downregulation of relaxation-mediating beta-ARs can contribute to LUTS generation. However, recent investigations on human bladder tissue could not confirm such a change. Antimuscarinic agents are effective for treatment of the overactive bladder, which is characterized by urge, frequency, urge incontinence, and nocturia (ie, LUTS). This suggests that muscarinic receptors are involved in the pathogenesis of LUTS, and there is recent evidence implicating purinergic receptors. Structural changes in the bladder, such as smooth muscle hypertrophy and connective tissue infiltration, are associated with detrusor overactivity in about 50% to 66% of patients with BPH. However, it is unclear whether this is caused by bladder outlet obstruction because the symptoms may remain in up to 33% of the patients after surgical removal of the obstruction. When outflow obstruction is reversed in rats, there is a subset (20%) that continues to have overactive voiding, despite a reversal of the bladder hypertrophy, suggesting that changes within the central nervous system may be a contributing factor. LUTS can be caused by many, often overlapping, pathophysiologic mechanisms, which may contribute to individual variation in response to treatment.

Estudio experimental de la expresión de las proteínas de la pared vesical en la obstrucción del tracto urinario inferior en el conejo

OBJECTIVES

To determine the relationship of the bladder wall levels of the contractile proteins: whole actin, beta-actin, alpha-sarcomeric-actina caldesmon and of the Heat Stress Protein HSP-70, with the partial bladder outlet obstruction.

MATERIAL AND METHODS

It was carried out an experimental study on 43 New-Zealand rabbits. These animals were divided into a control group and six experimental groups with partial bladder outlet obstruction induced by an incomplete tie around the urethra. The experimental groups were defined according the day when the animals were sacrified: at 24 hours, 7 days, 15 days, 1 month, 3 months and 6 months of the obstruction. It was determined in all animals the muscular bladder wall concentration of whole actin, beta-actin, alpha-sarcomeric-actin, caldesmon and HSP-70 protein, according to Western Blotting technique. The results were analyzed by means of ANOVA, using the Scheffe post hoc method.

RESULTS

The bladder weight of the obstructed animals increased significantly in two stages: until the day 15 and between the day 15 and the end of the study, corresponding to theoretical phases of initial hypertrophy and compensation. The level of whole actin showed a significant decrease at the beginning of compensation phase, while the beta-actin level increased in the phase of initial hypertrophy and the alpha-sarcomeric-actin level increased at the end of the compensation phase, while the caldesmon and the HSP-70 made it at the end of the initial hypertrophy phase.

CONCLUSIONS

Analysing our data we conclued that the determination of the caldesmon levels is the marker that better adjusts to the changes associated with partial bladder outlet obstruction in the rabbit.

Local infusion of the nitric oxide donor Sin-1 after angioplasty. Effects on intimal hyperplasia in porcine coronary arteries

PURPOSE

To investigate the development of intimal hyperplasia in response to percutaneous transluminal coronary angioplasty (PTCA) followed by local delivery of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1).

MATERIAL AND METHODS

Overdilation PTCA was performed in coronary arteries in 20 healthy pigs. One of the dilated segments was additionally treated with local delivery of SIN-1 for 10 min. Segments distal to the treated part of the arteries served as controls. Arteries were radiographically depicted and analyzed after 1 and 8 weeks for actin, myosin and intermediate filaments (IF), nitric oxide synthetase (NOS) and histological evaluation.

RESULTS

Segments treated with PTCA+SIN-1 showed a significantly (p=0.03) larger luminal diameter compared with PTCA only treated segments. The luminal loss after SIN-1 was not significant compared with the diameter prior to treatment. Endothelial NOS content was significantly lower in the PTCA+SIN-1 group compared with the PTCA group after 1 (p=0.03) and 8 weeks (p=0.013). IF/actin ratio after 1 week was significantly increased in PTCA-treated segments compared with untreated controls (p=0.004), and compared with PTCA+SIN-1-treated segments (p=0.004).

CONCLUSION

PTCA-induced intimal hyperplasia was potently inhibited by local delivery of the NO donor SIN-1. Momentary events at the time of injury play a significant role in the development of intimal hyperplasia and long-lasting down-regulation of the endothelial NOS expression after SIN-1 exposure is suggested. The IF/actin ratio can be useful as an early marker of intimal hyperplasia.

Decreased shortening velocity and altered myosin isoforms in guinea-pig hypertrophic intestinal smooth muscle

The aims of this study were to investigate whether hypertrophy of the small intestinal smooth muscle leads to alterations of myosin isoform composition and shortening velocity and whether possible changes correlate with a change in the sensitivity to ADP of shortening velocity in this tissue. A partial occlusion was introduced in the distal part of the ileum of guinea-pigs. After 2 weeks, the part of the small intestine just proximal of the stenosis was hypertrophied (indicated by a significantly increased cross-sectional area). The most proximal part of the small intestine was used as control, thus enabling comparisons between hypertrophic and normal tissue from the same animal. The outer longitudinal layer of the intestinal wall was gently peeled off and used for biochemistry, RT-PCR and mechanical experiments. The desmin/actin ratio was significantly increased following hypertrophy, although myosin and actin expression were similar in control and hypertrophic tissue. In hypertrophic tissue, the myosin heavy chain mRNA with a 21 base pair insert decreased significantly. The composition of the mRNA encoding the myosin essential light chains changed towards more of the basic type (LC17b). No change in the expression of non-muscle myosin heavy chains A and B was detected. The maximal shortening velocity (V(max)) of maximally activated skinned preparations was significantly lower in the hypertrophic tissue (~50 % of control). The sensitivity of V(max) to ADP was increased in the hypertrophic smooth muscle tissue. We conclude that myosin expression is altered following intestinal hypertrophy and that these alterations affect reactions in the cross-bridge interaction, leading to a slower and more economical contractile function.

Altered cytoskeleton in smooth muscle of aganglionic bowel

CONTEXT

Intestinal motility is under the control of smooth muscle cells, enteric plexus, and hormonal factors. In Hirschsprung disease (HD), the aganglionic colon remains spastic or tonically enhanced and unable to relax. The smooth muscle cell's cytoskeleton consists of proteins or structures whose primary function is to link or connect protein filaments to each other or to the anchoring sites. Dystrophin is a subsarcolemmal protein with a double adhesion property, one between the membrane elements and the contractile filaments of the cytoskeleton and the other between the cytoskeletal proteins and the extracellular matrix. Desmin and vinculin are functionally related proteins that are present in the membrane-associated dense bodies in the sarcolemma of the smooth muscle cells.

OBJECTIVE

To examine the distribution of the cytoskeletal proteins in the smooth muscle of the aganglionic bowel.

DESIGN

Bowel specimens from ganglionic and aganglionic sections of the colon were collected at the time of pull-through surgery from 8 patients with HD. Colon specimens collected from 4 patients at the time of bladder augmentation acted as controls. Anti-dystrophin, anti-desmin, and anti-vinculin antibodies were used for fluorescein immunostaining using confocal laser scanning microscopy.

RESULTS

Moderate to strong dystrophin immunoreactivity was observed at the periphery of smooth muscle fibers in normal bowel and ganglionic bowel from patients with HD, whereas dystrophin immunoreactivity was either absent or weak in the smooth muscle of aganglionic colon. Moderate to strong cytoplasmic immunostaining for vinculin and desmin was seen in the smooth muscle of normal bowel and ganglionic bowel from patients with HD, whereas vinculin and desmin staining in the aganglionic colon was absent or weak.

CONCLUSION

This study demonstrates that the cytoskeletal proteins are abundant in the smooth muscle of normal bowel, but are absent or markedly reduced in the aganglionic bowel of HD. As cytoskeletal proteins are required for the coordinated contraction of muscle cells, their absence may be responsible for the motility dysfunction in the aganglionic segment.

Regeneration of detrusor muscle after subtotal cystectomy in the rat: effects on contractile proteins and bladder mechanics

The aim of the present study was to determine to what extent adult rats can produce new contracting bladder muscle and to see if such newly formed bladder tissue possesses characteristic mechanical properties or whether the ability to recover mechanically is so pronounced that the prehistory of the bladder is unimportant. Subtotal cystectomy was performed in adult female rats, leading to a pronounced decrease in total bladder weight. At 10 weeks, bladder weight had normalized. The histological appearance of such bladders was similar to that of the controls. Active and passive length-tension relations for the detrusor muscle were determined in controls and up to 10 weeks after surgery. Immediately after surgery active and passive forces showed a leftward shift and maximum active force decreased markedly. With time the length-tension curves shifted back to normal, but a decreased active force still remained at 10 weeks. Detrusor actin concentration and detrusor myosin/actin ratio were unaffected by the subtotal cystectomy. Intermediate filament protein/actin ratio showed a significant but transitory increase. We conclude that there is a remarkable recovery of detrusor muscle function after subtotal cystectomy, leading to a normalization of optimum length for active force and a net synthesis of contractile and cytoskeletal proteins. The ability to produce active force does, however, not fully recover.

Bladder instability: a re-appraisal of classical experimental approaches and development of new therapeutic strategies

1 Despite the growing social interest in human urinary tract disorders, the aetiology of detrusor instability remains poorly understood. Myogenic and neural impairment of detrusor activity caused by CNS or autonomic injuries can results in dysfunctions of normal voiding of the bladder such as urinary incontinence. 2 The contractility of human detrusor smooth muscle is critically dependent on acetylcholine-induced muscarinic receptor activation. Biochemical and functional in vivo and in vitro studies suggest the presence of an heterogeneous population of muscarinic receptor subtypes (M1-M4) localized at muscular and neutral sites. There is increasing evidence on the prejunctional auto- and hetero-regulation of acetylcholine release from parasympathetic nerve endings in modulating detrusor muscle contraction during micturition. 3 Activation of P2X purinoreceptors closely associated with the parasympathetic varicosities seems to be implicated to varying extent in the contractility in normal or instable human detrusor. Interestingly, P2X(1) subtype expression on smooth muscle increases considerably in the symptomatically obstructed bladder. A striking absence of P2X(3) and P2X(5) subtypes was observed in the cholinergic innervation of detrusor from patients with urgent incontinence. Thus, it is likely that alteration of the neural acetylcholine control can play a critical role in pathological states. 4 If the failures in storage and voiding can be recognized urodynamically, considerable difficulties remain in investigating the underlying functional changes especially because the study of the pathophysiology requires techniques that can be justified in animals but not in humans. 5 Recently, to solve this problem an alternative technique using human smooth muscle cells in culture has been developed. Human cell lines may be relevant in investigating the molecular pathways in physiological and pathological conditions. 6 The potential development of novel molecular therapeutic strategies such as gene therapy and tissue engineering is also discussed.

Myosin isoforms in female human detrusor

The aim of this study was to document the relative proportions of two isoforms of myosin heavy chain in detrusor smooth muscle of women with detrusor overactivity and in asymptomatic controls. Women aged 35-65 with documented detrusor overactivity and without a history of neurologic disease, prior incontinence surgery, elevated post-void residual urine volume, or indwelling urinary catheter were eligible for the study. Full-thickness biopsies of extraperitoneal bladder dome were obtained at the time of laparotomy in six patients with documented detrusor overactivity and in a control group of eight continent patients. Biopsies were frozen in liquid nitrogen, crushed with a frozen mortar and pestle at -80 degrees C, and homogenized in buffer, and the extracts were electrophoresed on 6% polyacrylamide sodium dodecyl sulfate gels and stained with Coomassie blue. The gels were de-stained and then the protein bands were scanned with a densitometer. The mean patient age was 48 years (range, 36-59). Seven patients were Caucasian and seven patients were African American. Detrusor smooth muscle contains a mean of 34% (range, 27-43%) SM1 and 66% (range, 57-73%) SM2 isoforms. There was no difference in isoform composition when patients were compared according to urogynecologic diagnosis or according to race. In detrusor biopsies from women, approximately 34% of myosin is of the SM1 isoform and approximately 66% is of the SM2 isoform. This ratio is relatively constant in the two races studied and unchanged in women with detrusor overactivity. Animal models utilizing outlet obstruction of the bladder to provoke detrusor instability and detrusor hypertrophy are known to alter myosin isoform distribution and may not be appropriate models of detrusor instability in human females.

Effects of partial bladder outlet obstruction and its relief on types I and III collagen and detrusor contractility in the rat

Bladder outlet obstruction induces a rapid hypertrophy characterized by increased bladder mass and collagen deposition. An increase in collagen is likely to reduce the contractility and compliance of bladder wall. This study was undertaken to investigate the effects of partial bladder outlet obstruction and its relief on types I and III collagen, and the relationship between detrusor contractility and collagen types. A total of 40 female rats was used for experiment and divided into one control, one obstruction, and three recovery groups. The contractility to field stimulation was recorded; total collagen and collagen concentration were quantified. The localization of types I and III collagen and the expression of pro-alpha1(I) and alpha1(III) collagen mRNA were determined by immunohistochemical staining and Northern blot hybridization, respectively. Contractile response to field stimulation was reduced after obstruction and recovered following relief. The total amount of collagen increased after obstruction and decreased after relief; however, collagen concentration decreased after obstruction and increased following relief. Contractility correlated negatively with total collagen but positively with collagen concentration. The protein deposition of types I and III collagen was localized in lamina propria and muscle bundles in all groups. The expression of types I and III collagen gene was up regulated after obstruction, but down regulated after relief. Negative correlation between contractility and gene expressions of collagen types was significant. These data suggest that the change in localization and quantity of collagen types leads to morphologic changes of bladder and can have an impact on the contractility of detrusor. Neurourol. Urodynam. 19:29-42, 2000.

Filling mechanics of obstructed and de-obstructed rat urinary bladders

Chronic bladder distension occurs after partial outlet obstruction and can lead to decompensation and impaired function. To quantify the degree of chronic bladder distension, we previously defined the zero pressure volume (ZPV), the largest contained volume at zero transmural pressure. In the current study, we investigated the short- and long-term effects of outlet obstruction and de-obstruction on chronic distension and passive bladder filling mechanics. Voiding patterns were measured 10 days (short term) or 6 weeks (long term) after partial bladder outlet obstruction and the bladders were tested in vitro at that time. De-obstructed bladders were obstructed for 6 weeks, and voiding patterns were measured 10 days or 6 weeks after de-obstruction, followed by in vitro testing. Mean voided volume was increased in de-obstructed bladders but not obstructed bladders. The volume of urine in the bladder at euthanasia was greater than mean voided volume in obstructed bladders and less than mean voided volume in de-obstructed bladders, indicating large residual urine in the obstructed bladders. ZPV was significantly increased only after long-term obstruction or de-obstruction. Similarly, intravesical pressure and mean bladder wall stress were increased only after long-term obstruction or de-obstruction. We conclude that tissue remodeling occurs in the bladder wall after long-term obstruction, possibly both as a result of and leading to chronic overdistension and high residual urine. Tissue remodeling occurs in the bladder wall after long-term de-obstruction, possibly due to large voided volumes. Neurourol. Urodynam. 18:659-671, 1999.

Targeted expression of SV40 large T-antigen to visceral smooth muscle induces proliferation of contractile smooth muscle cells and results in megacolon

Many pathological conditions result from the proliferation and de-differentiation of smooth muscle cells leading to impaired contractility of the muscle. Here we show that targeted expression of SV40 large T-antigen to visceral smooth muscle cells in vivo results in increased smooth muscle cell proliferation without de-differentiation or decreased contractility. These data suggest that the de-differentiation and proliferation of smooth muscle cells, seen in many pathological states, may be independently regulated. In the T-antigen transgenic mice the increased smooth muscle cell proliferation results in thickening of the distal colon. Consequently the distal colon becomes hyper-contractile and impedes the flow of digesta through the colon resulting in enlargement of the colon oral to the obstruction. These transgenic mice thus represent a novel model of megacolon that results from increased smooth muscle cell proliferation rather than altered neuronal innervation.