Collagen and elastin in the obstructed fetal bladder

Temporal expression of elastic fiber components in bladder development

Fetal and postnatal bovine bladders were examined for expression of elastic fiber components by immunohistochemistry as well as by measurement of steady state mRNA levels. Expression of fibrillin-1, microfibril-associated glycoprotein (MAGP) and elastin during the fetal period were compared with that of postnatal two year old animals (heifers) and adults. Each bladder was separated into two distinct tissue samples: 1) the outer smooth muscle layer (detrusor) and 2) the inner epithelium (urothelium) lined lamina propria (urotherial-lamina propria). Each of these samples was analyzed separately. Distribution of the elastic fiber components, determined by immunohistochemistry with matrix-specific antibodies, was different depending upon the region of the bladder wall examined and its developmental stage. In particular, MAGP and fibrillin-1 were conspicuously present in the urothelium during the later fetal stages. RNA products of elastic fiber genes were detectable both in the detrusor smooth muscle and urothelial-lamina propria fractions. The highest level of expression occurred in the urothelial-lamina propria fraction during the late second-early third trimester. Elastin expression was different from that of MAGP and fibrillin-1. The highest levels of steady-state elastin mRNA occurred at the earliest developmental stages examined and then progressively decreased through term. A high level of elastin expression occurred within the inner or lamina propria layer of the bladder. Since this layer is the functional capacitance layer within the bladder, its flexibility is likely related to the structural integration of elastin and associated microfibrillar components.

The effect of angiotensin converting enzyme inhibition and angiotensin II receptor antagonism on obstructed rat bladder

PURPOSE

Others have demonstrated that inhibition of angiotensin II production partially ameliorates obstructive changes in the neonatal rabbit bladder. We examined the effect of angiotensin II converting enzyme inhibition and receptor antagonism on the obstructed rat bladder.

MATERIALS AND METHODS

Three groups of animals were investigated. Partial bladder neck obstruction was created in 23 rats by placing a 2-zero silk ligature around the vesicourethral junction. Eight rats were given untreated tap water, 9 were given water supplemented with 50 mg./kg. of the angiotensin-converting enzyme inhibitor captopril and 6 were given water with 30 mg./kg. of the angiotensin II subtype AT1 receptor antagonist losartan potassium. Eight unobstructed rats served as controls. After 2 weeks of partial outlet obstruction the animals were sacrificed and bladders were harvested. Routine histological evaluation and assays for total protein, deoxyribonucleic acid and collagen content were performed.

RESULTS

Histological evaluation revealed that administration of captopril or losartan potassium resulted in a mild decrease in the degree of obstructive bladder changes. Biochemically neither captopril nor losartan potassium caused a significant decrease in the amount of total deoxyribonucleic acid, protein or collagen content per bladder compared to untreated obstructed bladders.

CONCLUSIONS

In contrast to previous studies in neonatal rabbits, neither captopril nor losartan potassium significantly ameliorated the histological or biochemical features of partial bladder outlet obstruction in the rat. Further investigation is necessary into species specific differences to understand better the role that angiotensin II may have in mediating the bladder changes of experimentally induced obstruction.

Captopril (an inhibitor of angiotensin converting enzyme) inhibits obstructive changes in the neonatal rabbit bladder

OBJECTIVES

To investigate whether angiotensin II has a role in the regulation of bladder smooth muscle growth and function, we developed a model of bladder neck obstruction (BNO) in the neonatal rabbit and investigated the effect of captopril (angiotensin converting enzyme inhibitor) on the obstructive changes in the developing bladder.

METHODS

Partial BNO was induced in a group of 2-day-old rabbits (n = 8) by placing a loose 2-0 silk ligature around the vesicourethral junction. A second group of rabbits subjected to the identical partial BNO procedure (n = 8) was given captopril (1 mg/kg/day). Twelve days postobstruction, bladders from these animals, along with paired controls (n = 8), were harvested and assayed for total protein, DNA, and collagen content.

RESULTS

Partial BNO resulted in a 170% increase in wet weight (P < 0.05), 132% increase in protein/deoxyribonucleic acid (DNA) ratio (P < 0.05), 75% increase in total DNA (P < 0.05), and 115% increase in total collagen (P < 0.05). When compared with obstructed animals, captopril administration significantly inhibited the increase in total DNA (P < 0.05) and reduced the amount of total collagen (P = 0.054). Examination of histology specimens demonstrated that captopril inhibited the serosal hyperplasia and collagen deposition associated with obstruction.

CONCLUSIONS

These data demonstrate that captopril partially inhibits the changes in the neonatal rabbit bladder associated with obstruction, supporting the hypothesis that angiotensin II is involved in the regulation of bladder smooth muscle growth and collagen production.

Smooth muscle development in the obstructed fetal bladder

OBJECTIVES

To evaluate changes in the smooth muscle and connective tissue development in the obstructed and normal fetal bladder.

METHODS

The smooth muscle and connective tissue composition of 19 fetal urinary bladders, including those of 9 fetuses with anatomic obstruction and 10 controls free of urologic disease, were analyzed by light microscopy and computer-assisted color image analysis.

RESULTS

The bladder wall thickness was markedly increased in obstructed fetuses throughout gestation as compared with that in controls. The disparity in bladder wall thickness increased rapidly during gestation. The percent area density of smooth muscle and connective tissue as well as the ratio of smooth muscle to connective tissue remained the same in the obstructed and normal control fetal bladders.

CONCLUSIONS

Although bladder outlet obstruction is associated with a marked increase in bladder wall thickness, the percent of smooth muscle and connective tissue comprising the mural histology remains relatively constant as compared with that of normal fetal controls. This study suggests that bladder outlet obstruction in the fetus is not associated with excess collagen deposition but rather with an increased amount of bladder with normal cellular content and a concomitant increase in smooth muscle development.

Mesenchymal-epithelial interactions in the bladder

During bladder development, undifferentiated mesenchymal and epithelial cells undergo an orderly sequence of differentiation defined by the expression of smooth-muscle (alpha-actin, myosin, vinculin, desmin, vimentin, and laminin) and epithelial (cytokeratins 5, 7, 8, 14, 18 and 19) protein markers. This process requires mesenchymal-epithelial interactions with bladder epithelium (urothelium) necessary for the differentiation of bladder smooth muscle. Peptide growth factors such as keratinocyte growth factor (KGF) and transforming growth factors (TGF) alpha and beta are likely candidates as mediators of these mesenchymal-epithelial interactions. Transcripts for KGF, TGF alpha, and TGF beta are regulated during bladder development and during smooth-muscle hypertrophy secondary to bladder-outlet obstruction. Finally, two experimental bladder models--(1) partial outlet obstruction and (2) regeneration of bladder smooth muscle into an acellular tissue matrix--are described in the context of mesenchymal-epithelial interactions in the bladder.

Angiotensin II and basic fibroblast growth factor induce neonatal bladder stromal cell mitogenesis

PURPOSE

Our aims were to establish primary stromal cell cultures from the neonatal rabbit bladder and investigate the potential mitogenic effects of angiotensin II and basic fibroblast growth factor on these cells.

MATERIALS AND METHODS

Primary bladder stromal cell cultures were obtained from 3-day-old rabbits, plated at a density of 3 x 10(4) cells per ml. and allowed to grow for 24 hours. Subconfluent cells were growth arrested in serum deficient (0.25% newborn calf serum) or serum-free media for 24 hours and then stimulated with 10(-7) M. angiotensin II or 10 ng./ml. basic fibroblast growth factor for an additional 48 hours. Cell counts and [3H] thymidine incorporation were done to measure cellular proliferation and deoxyribonucleic acid synthesis.

RESULTS

Angiotensin II and basic fibroblast growth factor each stimulated neonatal bladder stromal cell proliferation and [3H] thymidine incorporation under serum deficient conditions. Angiotensin II provoked an average 26% increase in cell number (p < 0.01) and 35% increase in [3H] thymidine incorporation (p < 0.01) compared to control values. Basic fibroblast growth factor was an even more potent mitogen with a 47% increase in cell number (p < 0.01) and 180% increase in [3H] thymidine incorporation (p < 0.01) compared to controls. In contrast, angiotensin II and basic fibroblast growth factor each failed to have significant stimulatory effects under serum-free conditions.

CONCLUSIONS

Angiotensin II and basic fibroblast growth factor induce a mitogenic response to neonatal bladder stromal cells in vitro. These mitogenic effects require the presence of serum factors. Whether angiotensin II and basic fibroblast growth factor are involved in the in vivo regulation of bladder growth associated with obstructive uropathy requires further investigation.

Effects of ovariectomy on mechanical properties and collagen content in rabbit lower urinary tract smooth muscle

Fourteen female rabbits underwent ovariectomy or were sham-operated six weeks before investigation. Detrusor and urethral strips (longitudinal and circular urethral muscle fibers were studied separately) were prepared and length-tension relations studied in organ baths experiments. In addition, the specimens were examined for collagen content. Maximal active tension in the detrusor, longitudinal and circular urethral preparations, determined as the response to K+ (124mM), was reached when the length of the strips was 178 +/- 8% (n = 7), 153 +/- 9% (n = 5), and 127 +/- 5% (n = 7) of the resting length, respectively. Ovariectomy did not alter the length for development of maximal active tension. In detrusor strips, ovariectomy caused a significant increase in maximal active tension from 39 +/- 7 mN (sham-operated rabbits) to 79 +/- 11 mN (p < 0.01), despite an unchanged relative amount of smooth muscle. The maximal active tension produced in the urethra was lower (15-25 mN) than in the detrusor, and not significantly affected by ovariectomy. Approximately 40% of the dry defatted tissue weight of the detrusor consisted of collagen, whereas corresponding value in the urethra was 50-60%. Ovariectomy had no effect on tissue collagen concentrations. In conclusion, ovariectomy for six weeks did not affect the passive mechanical properties or the collagen concentration in rabbit lower urinary tract smooth muscle, but increased the responsiveness of the detrusor muscle to K+ (124 mM).

Urinary tract reconstruction in children undergoing renal transplantation

In children, congenital urinary tract anomalies contribute to end-stage renal disease in 20% to 30% of cases. As more and more children with myelomeningocele, posterior urethral valves, prune belly syndrome, and other serious congenital anomalies of the urinary tract survive early infancy, more of these patients will be in need of renal transplantation. Of these, a significant proportion will have persisting abnormal anatomic and physiological characteristics of the urinary tract requiring reconstructive surgery before transplantation. Before undertaking these procedures, urologic evaluation should be performed in all such children. Comprehensive evaluation includes a careful history and physical examination with radiological imaging of the urinary tract (renal ultrasonography and voiding cystourethrography). In selected instances, further evaluation of bladder function and urethral anatomy may require urodynamic evaluation or cystourethroscopy. The goal of these investigations is to ensure that the bladder will hold urine at a low intravesical pressure during the storage phase and that it can be evacuated with certainty. This presentation focuses on the pretransplantation evaluation and the various possible urinary tract reconstructions that may be performed in children destined for renal transplantation.

Morphological, stereological, and biochemical analysis of the mini-pig urinary bladder after chronic outflow obstruction and after recovery from obstruction

Chronic partial bladder outlet obstruction was created in nine mini-pigs by implanting a 6-7 mm ring around the proximal urethra. After a median obstruction period of 63 days, the ring was removed and after a recovery period of median 60 days the animals were sacrificed. Changes in muscle and connective tissue were assessed by unbiased, modern morphometry and biochemical analysis. After obstruction the results were as follows: (1) a 6-fold increase in bladder weight, (2) a 2.5-fold increase in smooth muscle cell size, (3) a 3-fold increase in smooth muscle cell number, (4) unchanged proportions between muscle and connective tissue, (5) unchanged hydroxyproline concentrations, (6) an 8-fold increase in total collagen content, (7) an increase in the ratio of type I/III collagen, and (8) a 7-8-fold increase in total content of type I and III collagen. All changes were markedly, though incompletely, reversed after recovery, except smooth muscle cell number and the ratio of type I/III collagen.

Congenital bladder obstruction: research strategies and directions

The clinical significance of congenital bladder obstruction is evident to those who deal with children suffering from severe bladder dysfunction and renal failure. It is a lifelong effect often requiring complex surgical reconstruction and renal transplantation. CBO also represents an important pathophysiologic process with relevance to other organ systems in which hypertrophic and fibrotic processes occur. CBO occurs in a dynamic and developing organ in which function and development are interdependent. Alterations of one will induce alterations in the other which then affect the first. Multiple levels of organization are involved and relevant, from the cell to the whole bladder as a part of the organism. Functional and developmental changes have been demonstrated in models of CBO. Much attention has been focused on the connective tissue compartment of the bladder due to its important role in determining bladder compliance characteristics. Preliminary findings suggest that connective tissue remodeling may be affected by alterations in the balance of the regulatory mechanisms of collagen degradation. Further studies should be able to define these alterations and may permit specific modulation of these mechanisms.

The effect of vesical outlet obstruction on the protein secondary structure of the mucosa and serosa in rabbit bladder wall

The biochemical composition of physiologically moist mucosa and serosa of rabbit bladder before and after bladder outlet obstruction was determined by means of FT-IR spectroscopy with the ATR method and second-derivative analysis. A predominantly beta-sheet structure was found in the amide I band for mucosa and serosa before and after obstruction, but the random coil structure increased in both obstructed bladder samples. However, the major beta-sheet structure associated with some alpha-helical structure in the amide II band of mucosa and serosa for non-obstructed bladder changed into a predominantly alpha-helical structure after bladder obstruction. The obstructed bladder serosa was more pronounced. The amount of glycoproteins doubled in the obstructed bladder serosa, but did not change in the bladder mucosa.

Effect of physical forces on bladder smooth muscle and urothelium

Abnormalities in bladder physiology may be due to obstruction (pressure) and/or neurological impairment. Clinically they can result in an increase in connective tissue and a decrease in bladder compliance. To study the effects of physical forces on the bladder without the influence of the nerves we developed a cellular model system by isolating the 2 major cell types in the bladder: smooth muscle and urothelial cells. Extracellular matrix protein biosynthesis by these 2 cell types in vitro has been characterized by metabolic labeling of proteins with [14C] radiolabeled proline and analysis by gel electrophoresis. These studies demonstrate that fetal bovine bladder smooth muscle and urothelial cells synthesize fibronectin and types I and III interstitial collagen. Since bladder cells exist in an active physical environment, we have attempted to simulate this at the cellular level. Using a device developed in our laboratory, we applied a precise and reproducible mechanical strain (physical force) to these 2 cell types. By enzyme linked immunosorbent assay we quantitated collagen types I and III and fibronectin synthesized by fetal bovine bladder smooth muscle and urothelial cells undergoing mechanical strain (4.9%). These cells were compared to unstrained control cells that were exposed to the same experimental conditions. For bladder smooth muscle cells we found a significant increase in collagen type III and fibronectin synthesis when compared to unstrained cells. In contrast, collagen type I synthesis decreased with mechanical strain. For bladder urothelial cells we found an increase in collagen type I and fibronectin while collagen type III remained unchanged. These studies demonstrate that extracellular matrix synthesis by urothelial and smooth muscle cells can be modulated by stretch (strain) in the absence of neurological input. It is likely that bladder function may be impaired as a result of abnormal synthesis of connective tissue.

Bladder smooth muscle cells in culture: I. Identification and characterization

This report documents the growth and culture characteristics of human and fetal bovine bladder smooth muscle cells in vitro. Bladder smooth muscle cell strains have been identified by their spindle shaped morphology, noncontact inhibited growth characteristics and the expression of smooth muscle cell specific alpha-actin. Extracellular matrix protein biosynthesis by these cells in vitro has been characterized by metabolic labeling of proteins with [14C] radiolabeled proline and analysis by SDS gel electrophoresis. These studies demonstrate that bladder smooth muscle cells synthesize predominantly types I and III collagen, and fibronectin. In addition type III collagen exists in both a partially processed (pN alpha 1[III]) form and processed form. Complementary immunohistochemical studies show localization of type I, III, and IV collagens, and fibronectin to bladder smooth muscle cell extracellular matrix. We conclude that both fetal bovine and human smooth muscle bladder cells are capable of secreting the classic components of the surrounding connective tissue.

Urinary bladder function in the tight-skin mouse

Tight-skin mice develop hypertrophy of connective tissue and tendons, associated with increases in collagen concentration in skin, heart, lungs, and tail. The bladders from these mice have not previously been examined. Because of the purported importance of collagen in bladder wall structure and compliance, we examined collagen content, micturition characteristics, and length-tension relationships in bladders from tight-skin mice. Bladder collagen content and concentration were approximately 70% greater in 5-6 month tight-skin mice than age-matched controls, but bladder mass, protein content, and protein concentration were similar. Tight-skin mice urinated larger volumes more frequently during the light cycle, and the functional bladder capacity appeared to be greater than that of controls. There was a small shift to the right of the passive length-tension curves of bladder strips from tight-skin mice, but the shift was not statistically significant. The magnitude of active tension development was the same. The data suggest that bladder collagen concentration does not necessarily determine bladder capacity or compliance. It is suggested that other factors, such as the ratio of collagen subtypes or the collagen:elastin ratio may have more importance for the maintenance of bladder distension.

The effect of obstruction on the developing bladder

Congenital bladder obstruction causes significant immediate and long-term consequences yet its pathophysiology remains poorly understood. A model of early fetal bladder obstruction in sheep has been developed to study the response of the developing bladder to high grade obstruction, with particular emphasis on the regulation of growth and development. Congenital bladder obstruction was produced in fetal sheep at 60 days of gestation and studied at 95 days of gestation (14 sheep) or term (12 sheep). A total of 24 age-matched normal sheep served as controls. Bladders were analyzed by total weight, stereological estimation of smooth muscle cell size, number and total mass, deoxyribonucleic acid concentration, muscarinic cholinergic receptor density, myosin isoform analysis and/or passive cystometrics. Congenital bladder obstruction caused a 4.6 times increase in bladder weight at term reflecting a 5.8 times increase in smooth muscle mass. This increase was predominantly that of cellular hypertrophy and less so of hyperplasia, based upon increased cell volume, increased protein-to-deoxyribonucleic acid ratio, and no significant increase in total cell number. Muscarinic cholinergic receptor number per smooth muscle cell increased 3.2 times but it did not change relative to myosin content. The ratio of myosin heavy chain isoforms SM1:SM2 is developmentally regulated and was seen to change from 1.6 at 100 days of gestation to 1.13 at term in normals. After 5 weeks of obstruction SM1:SM2 was 1.27 and it was 1.25 at term, indicating an effect on the developmental regulation of smooth muscle. Rapid fill cystometry in vivo measured the rate of stress relaxation to assess accommodative properties. The half-decay time was increased in all 3 obstructed bladders tested to greater than 15 seconds at 50% capacity (normal less than 5 seconds), suggesting reduced compliance. This study shows that an in utero model of bladder obstruction is feasible. Congenital bladder obstruction produces a variety of structural, biochemical and functional changes in the developing bladder indicative of alterations in the regulation of growth and differentiation.

Microanatomy and morphometry of the hydronephrotic "obstructed" renal pelvis in asymptomatic infants

There has been limited histological study of the obstructed ureteropelvic junction in patients less than 1 year old. We present our prospective studies on the histomorphometry of the ureteropelvic junction complexes of 35 infants, of whom 23 underwent pyeloplasty for obstruction and 12 were age matched autopsy normals. Qualitatively, the major abnormalities of the pelvic microanatomy in the hydronephrotic obstructed kidneys included a lamina muscularis that was significantly thicker than normal and the presence of collagen fibers between muscle fascicles. Additionally, variable amounts of elastin were present in the adventitia and lamina muscularis. At the ureteropelvic junction the abnormalities were an increase in the number of inner longitudinal muscle bundles, collagen between muscle bundles (p less than 0.016) and elastin in the adventitia. Quantitatively, for the pelvis the lamina muscularis was significantly thicker in 18 obstructed kidneys compared to 7 controls (1,075 +/- 79 mu. versus 420 +/- 63 mu., mean +/- standard error of mean, p less than 0.001). The percentage area density of smooth muscle in the obstructed versus normals was increased (45.1% versus 35.2%, p less than 0.039). The percentage area density of collagen in the obstructed specimens versus normal showed an upward trend (38.6% versus 27.6%), which was not significant. In conclusion, the obstructed ureteropelvic junction complexes of kidneys in asymptomatic infants show significant qualitative and quantitative differences from normal.

Is lamina propria matrix responsible for normal bladder compliance?

Immunohistochemistry using monoclonal and polyclonal antibodies to extracellular matrix proteins is a highly sensitive tool for the characterization of matrix components. For the first time in the normal and noncompliant human bladder we have used antibodies to collagen types I, III and IV, and elastin to provide morphological correlation with mechanical properties noted clinically. In the normal bladder elastin and collagen types I and III showed intense localization in the lamina propria with modest localization in the detrusor layer. In contrast, lamina propria staining in the noncompliant bladder was essentially unchanged, while there was intense localization within the detrusor layer. Significantly, this intense localization consisted of collagen type III and elastin with little increase in type I. Type IV collagen is associated with basement membranes and individual smooth muscle cells, and shows commensurate increase in specimens with muscle hypertrophy and/or hyperplasia. These observations suggest that in the normal bladder the lamina propria may be a major structural capacitance layer with the smooth muscle covering it. The collagen fibers of the lamina propria may gradually unfold during filling, thus, accounting for normal compliance while in the noncompliant bladder the capacitance layer shifts outward to the infiltrated smooth muscle, thus, preventing the normal expansion of the lamina propria. The smooth muscle infiltration consists of a deposition of collagen type III and elastin with little increase of collagen type I, and it results in a loss of compliance. The pattern of localization would suggest that the smooth muscle is responsible for this accumulation.