Changes in nascent chromatin structure regulate activation of the pro-fibrotic transcriptome and myofibroblast emergence in organ fibrosis

Cell reprogramming to a myofibroblast responsible for the pathological accumulation of extracellular matrix is fundamental to the onset of fibrosis. Here, we explored how condensed chromatin structure marked by H3K72me3 becomes modified to allow for activation of repressed genes to drive emergence of myofibroblasts. In the early stages of myofibroblast precursor cell differentiation, we discovered that H3K27me3 demethylase enzymes UTX/KDM6B creates a delay in the accumulation of H3K27me3 on nascent DNA revealing a period of decondensed chromatin structure. This period of decondensed nascent chromatin structure allows for binding of pro-fibrotic transcription factor, Myocardin-related transcription factor A (MRTF-A) to nascent DNA. Inhibition of UTX/KDM6B enzymatic activity condenses chromatin structure, prevents MRTF-A binding, blocks activation of the pro-fibrotic transcriptome, and results in an inhibition of fibrosis in lens and lung fibrosis models. Our work reveals UTX/KDM6B as central coordinators of fibrosis, highlighting the potential to target its demethylase activity to prevent organ fibrosis.

Human Fibrotic Diseases: Current Challenges in Fibrosis Research

Human fibrotic diseases constitute a major health problem worldwide owing to the large number of affected individuals, the incomplete knowledge of the fibrotic process pathogenesis, the marked heterogeneity in their etiology and clinical manifestations, the absence of appropriate and fully validated biomarkers, and, most importantly, the current void of effective disease-modifying therapeutic agents. The fibrotic disorders encompass a wide spectrum of clinical entities including systemic fibrotic diseases such as systemic sclerosis (SSc), sclerodermatous graft vs. host disease, and nephrogenic systemic fibrosis, as well as numerous organ-specific disorders including radiation-induced fibrosis and cardiac, pulmonary, liver, and kidney fibrosis. Although their causative mechanisms are quite diverse and in several instances have remained elusive, these diseases share the common feature of an uncontrolled and progressive accumulation of fibrotic tissue in affected organs causing their dysfunction and ultimate failure. Despite the remarkable heterogeneity in the etiologic mechanisms responsible for the development of fibrotic diseases and in their clinical manifestations, numerous studies have identified activated myofibroblasts as the common cellular element ultimately responsible for the replacement of normal tissues with nonfunctional fibrotic tissue. Critical signaling cascades, initiated primarily by transforming growth factor-β (TGF-β), but also involving numerous cytokines and signaling molecules which stimulate profibrotic reactions in myofibroblasts, offer potential therapeutic targets. Here, we briefly review the current knowledge of the molecular mechanisms involved in the development of tissue fibrosis and point out some of the most important challenges to research in the fibrotic diseases and to the development of effective therapeutic approaches for this often fatal group of disorders. Efforts to further clarify the complex pathogenetic mechanisms of the fibrotic process should be encouraged to attain the elusive goal of developing effective therapies for these serious, untreatable, and often fatal disorders.

Keloids: The paradigm of skin fibrosis - Pathomechanisms and treatment

Keloids, fibroproliferative dermal tumors with effusive accumulation of extracellular matrix (ECM) components, particularly collagen, result from excessive expression of growth factors and cytokines. The etiology of keloids is unknown but they occur after dermal injury in genetically susceptible individuals, and they cause both physical and psychological distress for the affected individuals. Several treatment methods for keloids exist, including the combination therapy of surgical excision followed by intralesional steroid therapy, however, they have high recurrence rate regardless of the current treatment method. Improved understanding of the pathomechanisms leading to keloid formation will hopefully identify pathways that serve as specific targets to improve therapy for this devastating, currently intractable, disorder.

Pathobiological mechanisms of peritoneal adhesions: The mesenchymal transition of rat peritoneal mesothelial cells induced by TGF-β1 and IL-6 requires activation of Erk1/2 and Smad2 linker region phosphorylation

Peritoneal adhesions, primarily caused by surgical procedures, are the leading cause of pelvic pain, bowel obstruction, and infertility. TGF-β1 and IL-6 have been found to be elevated in the peritoneal fluid of patients during/after abdominal surgery. However, it remains to be determined whether these cytokines interact and facilitate adhesion formation by promoting mesothelial to mesenchymal transition (MMT). In the present study, isolated rat peritoneal mesothelial cells were treated with TGF-β1 and/or IL-6 which elicited MMT as determined by morphologic and biochemical techniques. During this transition, cellular morphology changed from that of cobblestone polygonal cells to elongated/spindle-shaped fibroblast-like cells. There was decreased expression of genes characteristic of mesothelial cells, such as E-cadherin, and increased expression of genes characteristic of the myofibroblast phenotype, including α-smooth muscle actin and the EDA form of fibronectin, both of which appear to mediate the transfer of force to the extracellular matrix. Partial characterization of relevant signaling pathways identified Erk1/2 activation, which was enhanced by combined TGF-β1/IL-6 administration, as a crucial necessary factor in the transition. Erk1/2 activation as well as the phosphorylation of the linker region of Smad2 and MMT could be blocked by the MEK inhibitor, U0126, suggesting that such activation may be a potential pharmaceutical target to prevent MMT. In addition, the phenotypic transition could be prevented by hydrocortisone.

New frontiers in fibrotic disease therapies: The focus of the Joan and Joel Rosenbloom Center for Fibrotic Diseases at Thomas Jefferson University

Fibrotic diseases constitute a world-wide major health problem, but research support remains inadequate in comparison to the need. Although considerable understanding of the pathogenesis of fibrotic reactions has been attained, no completely effective therapies exist. Although fibrotic disorders are diverse, it is universally appreciated that a particular cell type with unique characteristics, the myofibroblast, is responsible for replacement of functioning tissue with non-functional scar tissue. Understanding the cellular and molecular mechanisms responsible for the creation of myofibroblasts and their activities is central to the development of therapies. Critical signaling cascades, initiated primarily by TGF-β, but also involving other cytokines which stimulate pro-fibrotic reactions in the myofibroblast, offer potential therapeutic targets. However, because of the multiplicity and complex interactions of these signaling pathways, it is very unlikely that any single drug will be successful in modifying a major fibrotic disease. Therefore, we have chosen to examine the effectiveness of administration of several drug combinations in a mouse pneumoconiosis model. Such treatment proved to be effective. Because fibrotic diseases that tend to be chronic, are difficult to monitor, and are patient variable, implementation of clinical trials is difficult and expensive. Therefore, we have made efforts to identify and validate non-invasive biomarkers found in urine and blood. We describe the potential utility of five such markers: (i) the EDA form of fibronectin (Fn(EDA)), (ii) lysyl oxidase (LOX), (iii) lysyl oxidase-like protein 2 (LoxL2), (iv) connective tissue growth factor (CTGF, CCNII), and (v) the N-terminal propeptide of type III procollagen (PIIINP).

Regulation of Cyr61/CCN1 gene expression through RhoA GTPase and p38MAPK signaling pathways

Cysteine-rich protein 61 (Cyr61/CCN1) is an angiogenic factor and a member of a family of growth factor-inducible immediate-early genes with functions in cell adhesion, proliferation and differentiation. We investigated the regulatory mechanisms and signaling pathways involved in Cyr61/CCN1gene activation in smooth muscle cells. Treatment of these cells with sphingosine 1-phosphate (S1P), a bioactive lysolipid, increased rapidly but transiently the expression of the Cyr61/CCN1 gene at both the mRNA and protein levels. Cyr61/CCN1 mRNA stability was not altered but the transcription rate of the Cyr61/CCN1 gene was increased fivefold in isolated nuclei from S1P-stimulated cells indicating that the level of control is primarily transcriptional. Transfection experiments showed that a 936-bp promoter fragment of the human Cyr61/CCN1 gene is functional and induces a reporter gene activity in S1P-treated cells. Using a combination of cis-element mutagenesis and expression of dominant negative inhibitors of transcription factors, we showed that both a CRE and AP-1 site and their cognate transcription factors, cAMP response element binding protein (CREB) and AP-1, were responsible for the promoter activity in S1P-stimulated cells. Furthermore, by using either pharmacological inhibitors or active forms of known signaling molecules, we showed that inducible Cyr61/CCN1 gene expression occurs through RhoA GTPase and that additional signaling through the p38 pathway is required. In particular, p38 seems to regulate Cyr61/CCN1 promoter activity through modulation of phosphorylation of CREB and the CREB kinase, MSK1. These findings demonstrate the transcriptional regulation of the Cyr61/CCN1 gene and provide clues to the signaling molecules and transcription factors involved in such regulation.

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

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

Beta-cyclodextrin tetradecasulfate, a novel cyclic oligosaccharide, inhibits thrombus and neointimal formation after coronary vascular injury

BACKGROUND

Neointimal formation is a major cause of restenosis after interventional vascular procedures. Beta-cyclodextrin tetradecasulfate (beta-CDT) has been shown to inhibit fibroblast growth factor activity and we hypothesized that beta-CDT would reduce intimal formation.

DESIGN

Three studies were performed: (1) pharmacokinetics of oral and intravenous beta-CDT and determination of optimal dose, (2) determination of efficacy of oral and intravenous beta-CDT in reducing neointimal formation after balloon-overstretch injury and (3) determination of the effect of beta-CDT on cellular proliferation, factor Xa activity, activated clotting time, activated partial thromboplastin time and thrombus formation.

METHODS

Pharmacokinetics were determined in eight domestic swine following administration of oral beta-CDT and intravenous beta-CDT at three doses each. In the efficacy study, balloon-overstretch injury of 37 pigs (69 arteries) was performed and randomized into three groups (n = 23 arteries/group): control, oral administration of 300 mg beta-CDT/kg per day or intravenous infusion of 100 mg beta-CDT/kg per day. Animals were sacrificed 14 days later. Cellular proliferation and mural thrombus were determined in six arteries/group at 5 days and endothelial coverage was evaluated at 5 and 14 days.

RESULTS

Oral and intravenous beta-CDT reduced the intimal hyperplasia area normalized to injury index by 24 and 48%, respectively: control, 3.03 +/- 0.75 mm2, oral, 2.31 +/- 0.83 mm2 (P = 0.004) and intravenous, 1.67 +/- 0.73 mm2 (P = 0.0000002). beta-CDT reduced cellular proliferation (control, 55 +/- 18%, oral, 35 +/- 7%, P = 0.03 and intravenous, 30 +/- 12%, P = 0.01) and mural thrombus formation (control, 0.84 +/- 0.4 mm2, oral, 0.44 +/- 0.14 mm2, P = 0.04, intravenous, 0.42 +/- 0.09 mm2, P = 0.03). Endothelial coverage was increased in the experimental groups (P = 0.008, oral versus control, P < 0.0001, intravenous versus control). Factor Xa activity was inhibited 9-10 fold following intravenous administration while oral administration demonstrated no effect.

CONCLUSIONS

Both oral and intravenous formation of beta-CDT reduced intimal hyperplasia with the greatest reduction in the intravenous group. We postulate that beta-CDT was effective by the combination of increasing endothelial coverage, reducing mural thrombus formation, inhibiting factor Xa activity and reducing cellular proliferation.

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

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

Regulation of Cyr61 gene expression by mechanical stretch through multiple signaling pathways

The cysteine-rich protein 61 (Cyr61) is a signaling molecule with functions in cell migration, adhesion, and proliferation. This protein is encoded by an immediate early gene whose expression is mainly induced by serum growth factors. Here we show that Cyr61 mRNA levels increase sharply in response to cyclic mechanical stretch applied to cultured bladder smooth muscle cells. Stretch-induced changes of Cyr61 transcripts were transient and accompanied by an increase of the encoded protein that localized mainly to the cytoplasm and nucleus of the cells. With the use of pharmacological agents that interfere with known signaling pathways, we show that transduction mechanisms involving protein kinase C and phosphatidylinositol 3-kinase activation partly blocked stretch-induced Cyr61 gene expression. Selective inhibition of Rho kinase pathways altered this stretch effect as well. Meanwhile, using inhibitors of the actin cytoskeleton, we show that Cyr61 gene expression is sensitive to mechanisms that sense actin dynamics. These results establish the regulation of Cyr61 gene by mechanical stretch and provide clues to the key signaling molecules involved in this process.

The response of fetal sheep bladder tissue to partial outlet obstruction

PURPOSE

We characterized the response of fetal ovine bladder strips to stimulated contraction and relaxation, and compared this response to that of strips from the pregnant mother and those obtained after a short duration of fetal bladder outlet obstruction.

MATERIALS AND METHODS

Sham surgery or bladder obstruction was performed in fetal sheep at 90 days of gestation (term 147 days). Bladder tissue was obtained 3 and 5 days later. Isolated strips of full-thickness bladders from fetuses and pregnant females were mounted individually in Tyrode's solution containing glucose. The strips were subjected to electrical field stimulation. Alternate strips were stimulated by adding carbachol, adenosine triphosphate and KCl. Each strip stimulated by carbachol also underwent field stimulation in the presence of carbachol. Relaxation was also tested using isoproterenol and nitroprusside.

RESULTS

The response of isolated strips to field stimulation showed phasic contraction or biphasic response, consisting of initial phasic contraction followed by phasic relaxation and a return to control tension after the end of stimulation. In fetal bladder strips field stimulation at all frequencies after carbachol stimulation produced phasic relaxation or a biphasic response with an initial relaxation phase followed by phasic contraction. This field stimulated relaxant response was not present in adult female bladder strips. In addition, field stimulation stimulated relaxation was completely eliminated by pretreatment with N-nitro-L-arginine-methyl ester, indicating that relaxation was nitric oxide mediated. The fetal responses to all forms of stimulation and relaxation were significantly greater than those of pregnant females. After 5 days or greater of obstruction the responses to field stimulation were reduced significantly. In contrast, there were no significant differences in contractile responses to adenosine triphosphate, carbachol or KCl, or the relaxant response to field stimulation after obstruction. However, there was a significant reduction in relaxant responses to isoproterenol and nitroprusside.

CONCLUSIONS

In mid gestation sheep fetus contractile responses to field stimulation, adenosine triphosphate, carbachol and isoproterenol are well developed. The fetal ovine bladder shows a strong neuronal nitric oxide response that is not present in the pregnant mother and is maintained after short-term obstruction.

Active and passive compliance of the fetal bovine bladder

PURPOSE

Others have shown that the fetal bovine bladder is relatively noncompliant. Previous studies on compliance of fetal bovine bladders have demonstrated that the youngest fetal bladders had lowest and the oldest fetal bladders (near full-term) had greatest compliance. Our study was designed to determine the level of participation of active tension in the compliance of fetal bladders during gestation.

MATERIALS AND METHODS

Fetal bovine bladders were obtained immediately after maternal harvest and crown-to-rump length was measured to determine gestational age. The fetus was inspected for genitourinary anomalies and the bladder was immediately placed in chilled M199 media. Strips (1 x 0.5 cm.) were excised from the anterior sagittal plane of the bladder and subjected to length-tension analysis in oxygenated Tyrode's buffer at 37C. Tension was measured using a force transducer and length was increased using a micropositioner. Compliance refers to the length-tension studies performed in normal Tyrode's solution and consists of a combination of active (smooth muscle tone) and passive properties. Passive compliance refers to length-tension studies performed after inactivation of bladder smooth muscle tone. Compliance with muscle tone intact was determined by incrementally stretching the strips to twice resting length in physiological buffer and then permitting them to return to resting length. Passive compliance with muscle tone ablated was determined in the same fashion after overnight incubation in calcium-free Tyrode's buffer in the presence of 5 mM. egtazic acid and 10 mM. sodium azide. An exponential function was fit to the normalized length-tension curves, where the exponential coefficient (EC) is numerically inversely proportional to compliance.

RESULTS

Passive compliance was greatest in the youngest bladders (EC = 0.5 in the first trimester) and gradually decreased with increasing fetal age (EC = 1.2 in the third trimester). Active compliance demonstrated the opposite pattern, since the younger bladders were more stiff (EC = 2.1 in the first and 1.6 in the third trimesters).

CONCLUSIONS

These studies demonstrate that passive compliance is greatest in the youngest bladders and progressively decreases with gestation. However, active smooth muscle tone is greatest in the youngest bladders and decreases with gestation. Thus, high active smooth muscle tone in the youngest fetal bladders results in relatively poor compliance of the early stage fetal bladder.

A basic compositional requirement of agents having heparin-like cell-modulating activities

Heparin has been recognized as possessing a large variety of cell-modulating activities. Using compositionally simple, structurally rigid, and low molecular weight saccharide molecules (cyclodextrins), we demonstrated that these activities depend primarily on a single, gross compositional parameter: a minimum intramolecular density of neighboring anionic (sulfate) groups. This same critical parameter is shown to be involved in achieving cell-modulating behavior as diverse as angiogenesis, endothelial proliferation, inhibition of smooth muscle cell growth, and cell protection against virus invasion. Physical chemical evidence is presented that associates this property with multi-ionic complex formation between the clusters of anionic and cationic sites on the complexing partners. These observations revive early suggestions of the decisive role of electrostatic complexation capabilities of glycosaminoglycans like heparin; taken together with numerous observations on heparinoids and other agents reported in diverse specialized fields of cell biology and medicine, they provide evidence that molecular agents of critical anionic (sulfate) density (MACADs) represent a broad class of molecules that, in contrast to proteins, do not rely on structural detail for their cell biological activities, but function by ionic complexation with proteinic agents (e.g. growth factors), thereby modifying their structure-specific activities.

Expression of microfibrillar proteins by bovine bladder urothelium

OBJECTIVES

To determine the occurrence and potential function of proteins composing elastic microfibrils in the developing bovine bladder.

METHODS

Monospecific antibodies, generated against two well-characterized microfibrillar proteins, microfibril-associated glycoprotein (MAGP) and fibrillin-1 (FBN1), were used in immunohistochemical analysis of full-thickness frozen sections of fetal bovine bladder. The localization of these two antibodies was compared with that of anti-type IV collagen antibody. Adjacent serial sections were stained for routine light microscopy. Cultured urothelial cells were fixed in 3.7% formaldehyde and permeabilized with 0.5% Triton X-100 before immunoanalysis. Control reactions used either preimmune serum or a monoclonal antibody to a nonmatrix protein. Poly(A+) ribonucleic acid was isolated from cultured urothelial cells and subjected to Northern analysis using specific complementary deoxyribonucleic acid probes for MAGP and FBN1.

RESULTS

Both MAGP and FBN1 are expressed by the urothelium and are found in association with the underlying basement membrane, as visualized by their co-localization with type IV collagen. Furthermore, urothelial cells in culture continue to express both microfibrillar proteins.

CONCLUSIONS

The developing bovine urothelium expresses major microfibrillar protein components. The role of these microfibrils in the urothelium remains to be determined, but they may have an important anchoring function.

Type III collagen decreases in normal fetal bovine bladder development

In normal fetal bovine bladder development we have shown that compliance increases at approximately the same time that urine production first occurs. The late first trimester fetal bladders are relatively stiff with a progressive increase in bladder compliance peaking in the newborn period. From the newborn period through adulthood, we documented a relatively modest decrease in bladder compliance, which may result from the normal aging process. To account for these changes, we have used the bovine model to perform biochemical analyses of the major structural collagens that are found in the bladder (types I and III). These results show that the per cent of type III collagen decreases in the developing bladder from the end of the first trimester until the newborn period. Comparing the newborn bladder to that of a mature adult, we documented a relatively modest increase in the amount of type III collagen. We demonstrated that the ratio of type III-to-type I collagen parallels the normal compliance changes in the developing fetal and mature bovine bladder.

Bovine bladder compliance increases with normal fetal development

In this study we characterized the elastic properties of the normal bovine bladder throughout fetal life, the newborn period and into adulthood. The elasticity of the bladder was measured with a novel circularly clamped bladder testing system. Pressurization of a circularly clamped bladder tissue sample caused the tissue to deflect upward repetitively in the shape of a spherical cap. If the centerline deflection is much larger than the tissue thickness, the elastic modulus, considered the inverse of compliance, can be determined using linear regression techniques. The results of our analyses showed that the elastic modulus decreases in direct proportion with increasing gestational age. These data suggest that during normal development of the bovine fetal bladder there is a progressive change from a rather stiff noncompliant bladder characterized by a high elastic modulus to a compliant bladder with a lower elastic modulus. Moreover, the increase in compliance appears in the developmental period when urine production first occurs. These observations suggest that volume work may be a significant event in the normal development process of the bovine bladder and results in an increase in bladder compliance. Conversely, the poorly compliant fetal bladder may explain some of the transient dilatations of the upper urinary tract which have been documented in utero. Finally, from the newborn period to the mature adult bovine we documented a relatively modest increase in the elastic modulus or decrease in bladder compliance which may reflect the normal aging process.

Comparative studies on the ontogeny and autonomic responses of the fetal calf bladder at different stages of development: involvement of nitric oxide on field stimulated relaxation

This initial study correlates the passive length-tension relationship, contractile and relaxant responses to field stimulation and contractile responses to specific autonomic agonists and antagonists with gestational age. Fetal bovine bladders were separated into three groups based on the head-rump length (FL): 30 to 45 cm. (early gestation), 50 to 65 cm. (middle gestation) and 70 to 85 cm. (late gestation). Each bladder was separated into upper and lower bladder segments; longitudinal strips of smooth muscle were isolated and placed in individual muscle baths. Passive length-tension studies demonstrated that compliance was greatest in the bladder of late gestation and lowest in the bladder of early gestation period. Field stimulation (FS) elicited frequency-dependent contractile responses in all strips. In the upper bladder, the maximal response and maximal rate of tension generation to FS was lowest in the youngest fetuses and increased in proportion to the gestational age. In the lower bladders, there were no gestational age-related differences in the maximal response or maximal rate of tension generation in response to field stimulation. The maximal response of the upper bladder to bethanechol increased significantly from the youngest gestational age to mid-gestation, with no further changes between mid- and late gestation. The maximal response to field stimulation and bethanechol were equal between upper and lower bladder segments for the youngest gestational bladders, whereas for the oldest gestational ages, the maximal response of the upper bladder to FS and bethanechol were significantly greater than the responses of the lower bladder. In the presence of maximal precontraction with bethanechol, FS induced a rapid and marked decrease in tension. The magnitude of the relaxation was substantially greater for the strips of lower bladder than for the strips of upper bladder at late gestation. In lower bladders, the magnitude of the field stimulated relaxation was greater in the strips from the older fetuses than in the strips from younger fetuses. In all strips, field stimulated relaxations were completely inhibited by pretreatment with L-NAME (an inhibitor of nitric oxide synthesis), indicating that the FS-induced relaxation was due to nitric oxide. In addition to nitric oxide-induced relaxation, beta adrenergic stimulation also induced a significant relaxation of the isolated strips. In summary, these data suggest that, in the tubular shaped fetal bovine bladder, there were distinct differences in the autonomic responses between the upper bladder segment and the lower bladder segment in the late gestation period.

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.

Effect of mechanical forces on extracellular matrix synthesis by bovine urethral fibroblasts in vitro

The role of mechanical forces in normal physiological processes is just beginning to be elucidated. Using a system developed in our laboratory, we can apply precise and reproducible mechanical deformations (biaxial strain) to cells. These deformations alter cell activities in a reproducible fashion and may mimic the physical environment found in portions of the urinary tract. At a low strain of 1.8% no change in the synthesis of types I and III collagen by urethral fibroblasts was found. However, at a high strain (4.9%) types I and III collagen showed a significant increase in synthesis compared to controls (type I, 1.4 +/- 0.25 microgram. versus 0.9 +/- 0.27 microgram., p = 0.053; type III, 110 +/- 7 ng. versus 88 +/- 10 ng., p = 0.036). In addition, fibronectin synthesis was increased at low and high strains when compared to controls (low strain 3.20 +/- 1.03 micrograms. versus 1.46 +/- 0.15 microgram., p = 0.042; high strain 8.90 +/- 1.09 micrograms. versus 3.12 +/- 0.69 microgram., p = 0.001). We have shown at the cellular level that mechanical force applied to fetal bovine urethral fibroblasts results in an increase in the amount of collagen synthesis and fibronectin synthesis. These findings suggest that alterations in the physical environment of cells found in the urethral wall can affect biochemical processes including those that govern the synthesis of structural macromolecules such as collagen.

Distribution and function of the adrenergic and cholinergic receptors in the fetal calf bladder during mid-gestational age

Previous studies on the developing fetal bovine bladder demonstrate that compliance is low during early stages of fetal development and increases with fetal age. In addition, the pharmacological response of isolated fetal bovine bladder smooth muscle strips to field stimulation and bethanechol increased in proportion with the gestational age. In the adult bladder (rabbit), the contractile response to autonomic receptor stimulation and the autonomic receptor density showed a parallel gradation in the the bladder between bladder dome and the urethra. The present studies were designed to determine the distribution of the cholinergic and adrenergic receptors in the urinary bladder of the fetal calf at mid-gestational age, and to correlate the receptor density with the magnitude of the response to receptor stimulation. Each bladder body was separated into upper, middle, and lower segments. For the functional studies, circular and longitudinal strips were cut from each bladder segment and stimulated with field stimulation (FS), bethanechol, methoxamine, isoproterenol, and KCl. Autonomic receptor assays were performed using 3H-QNB (muscarinic cholinergic), 3H-DHE (alpha adrenergic), and 3H-DHA (beta adrenergic) as ligands. In general, there were no significant differences in receptor density among the three bladder segments. However, the density of muscarinic receptors was significantly greater than the density of alpha- or beta-adrenergic receptors for all bladder segments. The receptor densities correlated very well with the functional response of isolated bladder strips to the specific autonomic agonists. The contractile response of isolated bladder strips to the specific autonomic agonists. The contractile responses of the strips to FS, bethanechol, and methoxamine were not significantly different among the three different bladder segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum fibronectin is elevated during normobaric and hyperbaric oxygen exposure in rats

Serum fibronectin concentration was measured by immunoelectrophoresis in rats exposed to 1 atmosphere absolute (ata) of oxygen for 24 to 72 h and at 30-min intervals during 1 to 5 h of exposure to 4 ata O2. At 1 ata O2, there was a progressive increase in serum fibronectin, which became significant at 48 h and was 2.5 times the control value by 72 h (p less than 0.01). At 4 ata O2, the rise in serum fibronectin was significant at 2 h, and was followed by an accelerated rate of increase to 5 h, at which time serum fibronectin concentration was 1.75 times the control value (p less than 0.05). By SDS-polyacrylamide gel electrophoresis and crossed immunoelectrophoresis, there was no evidence of fragmentation of fibronectin. This study demonstrated a progressive increase in serum fibronectin in the oxygen-exposed rat. The magnitude and course of the increase suggest increased synthesis and secretion of intact fibronectin molecules.

Bovine endothelial cells in culture produce thromboxane as well as prostacyclin

Bovine aortic endothelial and smooth muscle cells in culture were incubated with arachidonic acid or prostaglandin H2. The amount of prostacyclin nd thromboxane A2 synthesized ws then determined by specific radioimmunoassay for 6-keto-prostaglandin F1 alpha and thromboxane B2. Although smooth muscle cells produced only 6-keto-prostaglandin F1 alpha and thromboxane B2 in a ratio of 5:1 to 10:1. The same ratio of these metabolites of arachidonic acid ws also found when prostaglandin production from endogenous arachidonic acid was stimulated in endothelial cells by the ionophore A23187. Cyclooxygenase inhibitors inhibited the production of both metabolites equally, whereas thromboxane synthetase inhibitors selectively inhibited the production of thromboxane B2. Cells in culture were also incubated with [1-14C]arachidonic acid and the extracted products were identified by two-dimensional thin-layer chromatography. 6-Keto-prostaglandin F1 alpha was the only metabolite produced by smooth muscle cells, but endothelial cells synthesized 6-keto prostaglandin F1 alpha, thromboxane B2, prostaglandin E2, and prostaglandin F2 alpha.

Production of 5-hydroxyindoleacetic acid from serotonin by cultured endothelial cells

Endothelial cells cells from bovine aorta and human umbilical vein and fibroblasts from human foreskin were cultured and subsequently evaluated for ability to metabolize serotonin (5-HT) to 5-hydroxyindoleacetic acid (5-HIAA). Cells were incubated for three hours with 4 X 10(-6) M [14C] 5-HT creatinine sulfate. [14C] 5-HIAA was separated from labeled 5-HT by column chromatography and measured for scintillation counting. Production of 5-HIAA by bovine aorta cells was 39.0+/-7.5 (S.E.M., n=6) nmoles per 10(9) cells per hour. Production of 5-HIAA was markedly inhibited by the presence of 10(-4) M iproniazid (an inhibitor of monoamine oxidase) or 10(-4) M imipramine (an inhibitor of amine transport). 5-HIAA was the only product of 5-HT metabolism detected by thin layer chromatography. Production of 5-HIAA by human umbilical vein endothelial cells was 5.4+/-2.0 nmoles per 10(9) cells per hour (n=5) and by human foreskin fibroblasts was 3.9+/-1.4 nmoles per 10(9) cells per hour (n=5). The results obtained during incubation in the presence and absence of inhibitors indicate that bovine aorta endothelial cells maintained in tissue culture are able to transport serotonin with subsequent production of 5-HIAA. By contrast, human umbilical vein endothelial cells and fibroblasts exhibited relatively low rates of 5-HT uptake and metabolism.