Increase in insulin-like growth factor I in hypertrophying smooth muscle

Therapeutic strategies based on non-ionizing radiation to prevent venous neointimal hyperplasia: the relevance for stenosed arteriovenous fistula, and the role of vascular compliance

We have reviewed the development and current status of therapies based on exposure to non-ionizing radiation (with a photon energy less than 10 eV) aimed at suppressing the venous neointimal hyperplasia, and consequentially at avoiding stenosis in arteriovenous grafts. Due to the drawbacks associated with the medical use of ionizing radiation, prominently the radiation-induced cardiovascular disease, the availability of procedures using non-ionizing radiation is becoming a noteworthy objective for the current research. Further, the focus of the review was the use of such procedures for improving the vascular access function and assuring the clinical success of arteriovenous fistulae in hemodialysis patients. Following a brief discussion of the physical principles underlying radiotherapy, the current methods based on non-ionizing radiation, either in use or under development, were described in detail. There are currently five such techniques, including photodynamic therapy (PDT), far-infrared therapy, photochemical tissue passivation (PTP), Alucent vascular scaffolding, and adventitial photocrosslinking. The last three are contingent on the mechanical stiffening achievable by the exogenous photochemical crosslinking of tissular collagen, a process that leads to the decrease of venous compliance. As there are conflicting opinions on the role of compliance mismatch between arterial and venous conduits in a graft, this aspect was also considered in our review.

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.

Increased bladder wall thickness in diabetic and nondiabetic women with overactive bladder

Purpose

Bladder wall thickness has been reported to be associated with overactive bladder (OAB) in women. Diabetic women have an increased risk for OAB syndrome and may have an increased risk for bladder wall thickness.

Methods

A total of 235 female patients aged 40 to 75 years were categorized into four groups. The first group consisted of women free of urgency or urge urinary incontinence. The second group included nondiabetic women with idiopathic OAB. The third group consisted of women with diabetes and clinical OAB, and women with diabetes but without OAB constituted the fourth group. Bladder wall thickness at the anterior wall was measured by ultrasound by the suprapubic approach with bladder filling over 250 mL.

Results

The diabetic (third group) and nondiabetic (second group) women with OAB had significantly greater bladder wall thickness at the anterior bladder wall than did the controls. However, the difference was not significant between the diabetic (third group) and the nondiabetic (second group) women with OAB. Women with diabetes but without OAB (fourth group) had greater bladder wall thickness than did the controls but this difference was not significant. Additionally, the difference in bladder wall thickness between diabetic women with (third group) and without (fourth group) OAB was not significant.

Conclusions

This is the first study to show that bladder wall thickness is increased in diabetic women with and without OAB. Additionally, nondiabetic women with OAB had increased bladder wall thickness. Further studies may provide additional information for diabetic and nondiabetic women with OAB, in whom the etiopathogenesis of the disease may be similar.

Association of insulin resistance with overactive bladder in female patients

PURPOSE

Metabolic syndrome and obesity have been advocated to be risk factors for the development of overactive bladder (OAB). Additionally, insulin resistance is the underlying mechanism of metabolic syndrome. We aimed to investigate the association of insulin resistance with overactive bladder in female patients.

METHODS

We prospectively conducted the study in our urology department. Female patients aged between 30 and 76 years old applied to our policlinics with or without OAB symptoms were enrolled. One hundred and twenty-two patients with OAB and 62 age-matched controls without OAB were included into the study. Fasting serum insulin, glucose, high-density lipoprotein (HDL-c), and triglycerides levels were measured. Insulin resistance value was obtained via the homeostasis model assessment of insulin resistance (HOMA-IR) calculator. The chi-square and Mann-Whitney U tests were used to compare differences in variables.

RESULTS

Serum insulin level was found higher in female patients with OAB (11.5±6.2 µU/mL) relative to controls (6.4±2.1 µU/mL), statistically significant (P=0.036). In addition, HOMA-IR was significantly found higher in the OAB group, 2.86 (0.76 to 17.04) in comparison to controls, 1.32 (0.67 to 224), P=0.018. High-density lipoprotein cholesterol levels (HDL-c) were significantly found lower in females with OAB.

CONCLUSIONS

Insulin resistance can be associated to overactive bladder and may play significant role in pathogenesis.

Intravenous IGF-I receptor antisense reduces IGF-IR expression and diminishes pressor responses to angiotensin II in conscious normotensive rats

Given the variety of cardiovascular effects of insulin-like growth factor-I (IGF-I), we investigated the effects of a functional deficit in IGF-I signalling in the conscious rat cardiovascular system using intravenous IGF-I receptor antisense (AS, 0.5 nmol) treatment.Insulin-like growth factor-I receptor (IGF-IR) immunoreactivity was reduced in IGF-IR AS-treated tail arteries. Western immunoblot analysis demonstrated a decrease in cardiac IGF-IR in IGF-IR AS-treated rats; treatment reduced the expression of IGF-IR to 83+/-6% of that in samples from vehicle-treated rats, compared to 99+/-3% for a control, full-mismatch oligonucleotide (MM-18) or 100% (vehicle).IGF-IR AS treatment had no effect on resting blood pressure during the 14-day treatment period. Pressor responses (as measured by increase in systolic arterial pressure) to angiotensin II (AngII) gradually decreased over 2 weeks treatment with IGF-IR AS (5 x 0.5 nmol per intravenous injection, 2 weeks), and were significantly reduced at treatment day 14 compared to day 7 (2.7-fold rightward shift). IGF-IR AS treatment caused a significant rightward shift in the angiotensin II (AngII) dose-response compared to both vehicle and full-mismatch treated rats (4.0-fold shift compared to vehicle, P<0.01, n=6-14). There was a significant decrease in cardiac angiotensin II type 1 receptor (AT(1)R) expression in AS-treated rats compared to vehicle-treated rats; cardiac AT(1)R was decreased to 80+/-6% in comparison to 100%. AT(1)R immunoreactivity was also reduced in IGF-IR AS-treated tail arteries.IGF-IR AS treatment resulted in structural changes in both the heart and aortae, with small but significant differences observed between left ventricle/bodyweight ratios of AS and both vehicle- and MM-18-treated rats (n=8, P<0.05). Aortic cross-sectional areas of AS-treated rats were significantly lower than MM-18- and vehicle-treated rats (27.4+/-5.7% reduction of vehicle-treated samples, n=8, P<0.01). The results of this study suggest that an induced loss of IGF-IR, while not affecting resting blood pressure, has a predominantly inhibitory effect on vascular response to vasoconstrictor agents including angiotensin II. This may occur through downstream effects on AT1R expression, via modulation of the expression of receptors for other vasoactive signalling molecules, or via changes in myocyte proliferation.

Mechanical stretch is a highly selective regulator of gene expression in human bladder smooth muscle cells

Application of mechanical stimuli has been shown to alter gene expression in bladder smooth muscle cells (SMC). To date, only a limited number of "stretch-responsive" genes in this cell type have been reported. We employed oligonucleotide arrays to identify stretch-sensitive genes in primary culture human bladder SMC subjected to repetitive mechanical stimulation for 4 h. Differential gene expression between stretched and nonstretched cells was assessed using Significance Analysis of Microarrays (SAM). Expression of 20 out of 11,731 expressed genes ( approximately 0.17%) was altered >2-fold following stretch, with 19 genes induced and one gene (FGF-9) repressed. Using real-time RT-PCR, we tested independently the responsiveness of 15 genes to stretch and to platelet-derived growth factor-BB (PDGF-BB), another hypertrophic stimulus for bladder SMC. In response to both stimuli, expression of 13 genes increased, 1 gene (FGF-9) decreased, and 1 gene was unchanged. Six transcripts (HB-EGF, BMP-2, COX-2, LIF, PAR-2, and FGF-9) were evaluated using an ex vivo rat model of bladder distension. HB-EGF, BMP-2, COX-2, LIF, and PAR-2 increased with bladder stretch ex vivo, whereas FGF-9 decreased, consistent with expression changes observed in vitro. In silico analysis of microarray data using the FIRED algorithm identified c-jun, AP-1, ATF-2, and neurofibromin-1 (NF-1) as potential transcriptional mediators of stretch signals. Furthermore, the promoters of 9 of 13 stretch-responsive genes contained AP-1 binding sites. These observations identify stretch as a highly selective regulator of gene expression in bladder SMC. Moreover, they suggest that mechanical and growth factor signals converge on common transcriptional regulators that include members of the AP-1 family.

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.

Mechanical stretch regulates cell survival in human bladder smooth muscle cells in vitro

Our understanding of the pathophysiology of the overactive bladder is poor. It has been proposed that localized contractions result in the abnormal stretching of bladder smooth muscle. We hypothesize that stretch regulates the cellular processes that determine tissue size. The purpose of this study was to investigate the effect of stretch on apoptosis, proliferation, cell hypertrophy, and growth factor production in human bladder smooth muscle cells in vitro. Normal human detrusor muscle was obtained from patients undergoing radical cystectomy for invasive bladder cancer, and primary cultures were established. Cells were mechanically stretched on flexible plates at a range of pressures and times. Apoptosis was assessed by propidium iodide incorporation and flow cytometry. Radiolabeled thymidine and amino acid incorporation were used to assess proliferation and cell hypertrophy. ELISA and RT-PCR were used to assess growth factor production. Mechanical stretch inhibits apoptosis in a time- and dose-dependent manner and was associated with increases in the antiapoptotic proteins heat shock protein-70 and cIAP-1. Stretch also increases smooth muscle cell proliferation and hypertrophy, but hypertrophy is the more dominant response. These changes were associated with increases in IGF-1 and basic FGF and a decrease in transforming growth factor-beta1. Mechanical stretch regulates apoptosis, proliferation, and cell hypertrophy in human bladder smooth muscle cells.

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.

Activation of mitogenic and antimitogenic pathways in cyclically stretched arterial smooth muscle

Biophysical forces regulate vascular smooth muscle cell (VSMC) physiology and evoke vascular remodeling. Two VSMC autocrine molecules, insulin-like growth factor I (IGF-I) and nitric oxide (NO), are implicated in remodeling attributable to VSMC hyperplasia. We investigated the role of in vitro cyclic stretch on rat VSMC IGF-I, NO, and cellular growth. Cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated VSMC proliferation 2.5-fold vs. unstretched cells and was accompanied by a 1.8-fold increase in VSMC IGF-I secretion. Despite activation of this proliferative pathway, cyclic stretch induced inducible (i) nitric oxide synthase (NOS) expression and a twofold increase in NO secretion, a molecule with documented antiproliferative effects. Cytokine treatment enhanced iNOS expression and NO secretion while inhibiting vascular growth by approximately 50% in static cells. Cytokine treatment of stretched VSMC enhanced NO secretion 2.5-fold while inhibiting growth by approximately 80%. Exogenous IGF-I increased NOS activity 1.5-fold and NO secretion 8.5-fold in static cells. In turn, iNOS inhibition increased IGF-I secretion 1.6-fold and enhanced VSMC growth 1.6-fold in stretched cells. An NO donor (sodium nitroprusside) similarly inhibited VSMC proliferation in static (24%) and stretched (50%) VSMC while also inhibiting IGF-I secretion from stretched cells by approximately 35%. Thus cyclic stretch stimulates mitogenic (IGF-I) and antimitogenic (NO) pathways in VSMC. These two molecules regulate each other's secretory rates, providing tight regulation of VSMC proliferation. These data may have profound implications in understanding vascular growth alterations in vascular injury and hypertension.

Pathogenesis and prevalence of hypertension in acromegaly

Hypertension is an important complication of acromegaly, contributing to the increased morbidity and mortality of this condition. Prevalence of hypertension in acromegalic patients is about 35%, ranging from 18 to 60% in different clinical series, and the incidence is higher than in the general population. The lowering of blood pressure observed concomitantly with the reduction in GH levels after successful therapy for acromegaly suggests a relationship between GH and/or IGF-I excess and hypertension. The exact mechanisms underlying the development of hypertension in acromegaly are still not clear but may include several factors depending on the chronic exposure to GH and/or IGF-I excess. Experimental and clinical studies suggest that the anti-natriuretic action of GH (due to direct renal action of GH or IGF-I and/or to indirect, systemic GH or IGF-I-mediated mechanisms) may play a role in the pathogenesis of hypertension. Acromegaly is frequently associated with insulin resistance and hyperinsulinaemia which may induce hypertension by stimulating renal sodium absorption and sympathetic nervous activity. Whether sympathetic tone is altered in acromegalic hypertensive patients remains a matter of debate. Recent studies indicate that an increased sympathetic tone and/or abnormalities in the circadian activity of sympathetic system could play an important role in development and/or maintenance of elevated blood pressure in acromegaly, and may partially account for the increased risk of cardiovascular complications. Acromegalic cardiomiopathy may also concur to elevate blood pressure and can be aggravated by the coexistence of hypertension. Finally, a role of GH and IGF-I as vascular growth factors cannot be excluded. In conclusion, acromegaly is associated with hypertension, but there is still no real consensus in the literature on the mechanisms behind the development of the high blood pressure.

Diffusable growth factors induce bladder smooth muscle differentiation

Bladder smooth muscle differentiation is dependent on the presence of bladder epithelium. Previously, we have shown that direct contact between the epithelium and bladder mesenchyme (BLM) is necessary for this interaction. In this study, we tested the hypothesis that bladder smooth muscle can be induced via diffusable growth factors. Fourteen-day embryonic rat bladders were separated into bladder mesenchyme (prior to smooth muscle differentiation) and epithelium by enzymatic digestion and microdissection. Six in vitro experiments were performed with either direct cellular contact or no contact (1) 14-d embryonic bladder mesenchyme (BLM) alone (control), (Contact) (2) 14-d embryonic bladders intact (control), (3) 14-d embryonic bladder mesenchyme combined with BPH-1 cells (an epithelial prostate cell line) in direct contact, (4) 14-d embryonic bladder mesenchyme with recombined bladder epithelium (BLE) in direct contact, (No Contact) (5) 14-d embryonic bladder mesenchyme with BPH-1 prostatic epithelial cells cocultured in type 1 collagen gel on the bottom of the well, and (6) 14-d embryonic bladder mesenchyme with BPH-1 epithelium cultured in a monolayer on a transwell filter. In each case the bladder tissue was cultured on Millicell-CM 0.4-microm membranes for 7 d in plastic wells using serum free medium. Growth was assessed by observing the size of the bladder organoids in histologic cross section as well as the vertical height obtained in vitro. Immunohistochemical analysis of the tissue explants was performed to assess cellular differentiation with markers for smooth muscle alpha-actin and pancytokeratin to detect epithelial cells. Control (1) bladder mesenchyme grown alone did not exhibit growth or smooth muscle and epithelial differentiation. Contact experiments (2) intact embryonic bladder, (3) embryonic bladder mesenchyme recombined with BPH-1 cells, and (4) embryonic bladder mesenchyme recombined with urothelium each exhibited excellent growth and bladder smooth muscle and epithelial differentiation. Both noncontact experiments (5) and (6) exhibited growth as well as bladder smooth muscle and epithelial differentiation but to a subjectively lesser degree than the contact experiments. Direct contact of the epithelium with bladder mesenchyme provides the optimal environment for growth and smooth muscle differentiation. Smooth muscle growth and differentiation can also occur without direct cell to cell contact and is not specific to urothelium. This data supports the hypothesis that epithelium produces diffusable growth factors that induce bladder smooth muscle.

Targeted overexpression of IGF-I evokes distinct patterns of organ remodeling in smooth muscle cell tissue beds of transgenic mice

Smooth muscle cells (SMC) of the vascular wall, bladder, myometrium, and gastrointestinal and respiratory tracts retain the ability to proliferate postnatally, which enables adaptive responses to injury, hormonal, or mechanical stimulation. SMC growth is regulated by a number of mesenchymal growth factors, including insulin-like growth factor I (IGF-I). To explore the function of IGF-I on SMC in vivo, the mouse SMC alpha-actin promoter fragment SMP8 (-1074 bp, 63 bp of 5'UT and 2.5 kb of intron 1) was cloned upstream of rat IGF-I cDNA, and the fusion gene microinjected to fertilized eggs of the FVB-N mouse strain. Mating of hemizygous mice with controls produced about 50% transgenic offspring, with equal sex distribution. Transgenic IGF-I mRNA expression was confined to SMC-containing tissues, with the following hierarchy: bladder > stomach > aorta = uterus > intestine. There was no transgene expression in skeletal muscle, heart, or liver. Radioimmunoassayable IGF-I content was increased by 3.5- to 4-fold in aorta, and by almost 10-fold in bladder of transgenic mice at 5 and 10 wk, with no change in plasma IGF-I levels. Wet weight of bladder, stomach, intestine, uterus, and aorta was selectively increased, with no change in total body or carcass weight of transgenic animals. In situ hybridization showed that transgene expression was exquisitely targeted to the smooth muscle layers of the arteries, veins, bladder, ureter, stomach, intestine, and uterus. Paracrine overproduction of IGF-I resulted in hyperplasia of the muscular layers of these tissues, manifesting in remarkably different phenotypes in the various SMC beds. Whereas the muscular layer of the bladder and stomach exhibited a concentric thickening, the SMC of the intestine and uterus grew in a longitudinal fashion, resulting in a marked lengthening of the small bowel and of the uterine horns. This report describes the first successful targeting of expression of any functional protein capable of modifying the phenotype of SMC in transgenic mice. IGF-I stimulates SMC hyperplasia, leading to distinct patterns of organ remodeling in the different tissue environments.

Proliferation precedes differentiation in IGF-I-stimulated myogenesis

The insulin-like growth factors (IGFs) have dramatic and complex effects on the growth of many tissues and have been implicated in both the proliferation and differentiation of skeletal muscle cells. A detailed analysis of gene expression was performed in L6E9 myoblast cultures treated with IGF-I to dissect the early events leading to the stimulation of myogenic differentiation by this growth factor. A time course of transcript accumulation in confluent L6E9 myoblasts treated with defined media containing IGF-I revealed an initial transient decrease in myogenic factors, accompanied by an increase in cell cycle markers and cell proliferation. This pattern was reversed at later time points, when the subsequent activation of myogenic factors resulted in a net increase in structural gene expression and larger myotubes. The data presented here support the hypothesis that IGF-I activates proliferation first, and subsequently stimulates events leading to the expression of muscle-specific genes in myogenic cell cultures.