Localization of increased insulin-like growth factor binding protein-3 in diabetic rat penis: implications for erectile dysfunction

Short hairpin rna targeting insulin-like growth fator binding protein-3 restores the bioavailability of insulin-like growth factor-1 in diabetic rats

Purpose

To investigate whether intracavernosal injection of short hairpin RNA for IGFBP-3 could improve erectile function in streptozotocin-induced diabetic rats.

Materials and methods

After 12 weeks of IGFBP-3 short hairpin RNA injection treatment, intracavernous pressure responses to electrical stimulation of cavernous nerves were evaluated. The expression of IGFBP-3 and IGF-1 at mRNA and protein levels were detected by quantitative real-time PCR analysis and Western blot, respectively. The concentration of cavernous cyclic guanosine monophosphate was detected by enzyme-linked immunosorbent assay.

Results

At 12 weeks after intracavernous administration of IGFBP-3 shRNA, the cavernosal pressure was significantly increased in response to the cavernous nerves stimulation compared to the diabetic group (P<0.05). Cavernous IGFBP-3 expression at both mRNA and protein levels was significantly inhibited. At the same time, cavernous IGF-1 expression was significantly increased in the IGFBP-3 shRNA treatment group compared to the diabetic group (P<0.01). Cavernous cyclic guanosine monophosphate concentration was significantly increased in the IGFBP-3 shRNA treatment group compared to the diabetic group (P<0.01).

Conclusions

Gene transfer of IGFBP-3 shRNA could improve erectile function via the restoration of cavernous IGF-1 bioavailability and an increase of cavernous cGMP concentration in the pathogenesis of erectile dysfunction in streptozotocin-induced diabetic rats.

Low serum insulin-like growth factor-1 in patients with erectile dysfunction

OBJECTIVE

Endothelial dysfunction and microvascular damage play a crurical role in the pathogenesis of erectile dysfunction (ED). Insulin-like growth factor-1 (IGF-1) is one of the growth factors that have a wide range of biologic effects. IGF-1 is an important mediator of cell growth, differentiation and transformation in various tissues. The purpose of the current study was to determine the association between IGF-1 levels and ED.

MATERIALS AND METHODS

All men were evaluated for ED and divided into two groups: 80 patients suffering from ED for > 1 year and 80 subjects without ED were enrolled as a control group in this study. Diagnosis of ED was based on the International Index of Erectile Function Score-5. IGF-1 levels were measured in serum by an automated chemiluminescence immunoassay. The relationship between IGF-1 levels and ED scores in patients was statistically evaluated.

RESULTS

The mean age of patients in ED group was 60.4 ± 11.3 years and 55.4 ± 9.6 in control group. The plasma IGF-1 levels were significantly lower in ED than in control group (96.5 ± 38.3 and 132.5 ± 53.3 ng/ mL, respectively, P < 0.001). The IGF-1 levels were positively correlated with ED score (r = 0.623, P < 0.01).

CONCLUSION

In this study serum IGF-1 levels were found to be associated with endothelial dysfunction that predicts ED. Serum IGF-1 level appears to be a specific predictor of ED, and it might be used in early prediction of ED in male population.

Effects of insulin-like growth factor-1 on the relaxation responses of the cavernous smooth muscle from aged rats

OBJECTIVE

The aim of this study was determine whether intracavernosal injection (ICI) of insulin-like growth factor-1 (IGF-1) protein can improve corpus cavernosal smooth muscle relaxation in aging rats.

MATERIALS AND METHODS

Ten young (4-month-old) and 30 old (24-month-old) Sprague-Dawley male rats were enrolled in the study. The old rats were divided into three groups: vehicle-only (n = 10), IGF-1 1 µg/kg (n = 10) and IGF-1 10 µg/kg treatment groups (n = 10). After 4 weeks of single IGF-1 injection treatment, strips of corporal tissue were precontracted with phenylephrine, and dose-response curves were generated to evaluate endothelial-dependent [acetylcholine (ACh)], endothelial-independent [sodium nitroprusside (SNP)] and electrical field stimulation (EFS) vasoreactivity. The changes in percentage of cavernosal smooth muscle and the concentration of nitric oxide (NO) in penile tissue were also evaluated.

RESULTS

After IGF-1 treatment, the vasoreactivity was significantly improved in both the 1 µg/kg and the 10 µg/kg treatment groups compared with the vehicle-only group at 4 weeks in response to ACh, SNP and EFS (all p < 0.05). The percentage of cavernosal smooth muscle was increased in the IGF-1 treatment groups. The NO concentrations were increased after IGF-1 treatment.

CONCLUSIONS

These data demonstrate that ICI of IGF-1 can improve vasoreactivity via endothelium-dependent and endothelial-independent mechanisms in the corpus cavernosum of the aging rat.

Short hairpin ribonucleic acid constructs targeting insulin-like growth factor binding protein-3 rehabilitated decreased testosterone concentrations in diabetic rats

Background

The aim of this study was to determine if shRNA constructs targeting insulin-like growth factor binding protein-3 can rehabilitate decreased serum testosterone concentrations in streptozotocin-induced diabetic rats.

Material/Methods

After 12 weeks of intracavernous administration of IGFBP-3 shRNA, intracavernous pressure responses to electrical stimulation of cavernous nerves were evaluated. The expression of IGFBP-3 at mRNA and protein levels was detected by quantitative real-time PCR analysis and Western blot, respectively. The concentrations of serum testosterone and cavernous cyclic guanosine monophosphate were detected by enzyme-linked immunosorbent assay.

Results

After 12 weeks of intracavernous administration of IGFBP-3 shRNA, the cavernosal pressure was significantly increased in response to the cavernous nerves stimulation compared to the diabetic control group (p<0.01). Cavernous IGFBP-3 expression at both mRNA and protein levels was significantly inhibited. Both serum testosterone and cavernous cyclic guanosine monophosphate concentrations were significantly increased in the IGFBP-3 shRNA treatment group compared to the diabetic control group (p<0.01).

Conclusions

These results suggest that IGFBP-3 shRNA may rehabilitate erectile function via increases of concentrations of serum testosterone and cavernous cyclic guanosine monophosphate in streptozotocin-induced diabetic rats.

shRNA constructs targeting IGFBP-3 alleviate age related erectile dysfunction in the rat

PURPOSE

We investigated whether injecting shRNA constructs targeting IGFBP-3 in the penis of old rats would improve erectile function.

MATERIALS AND METHODS

The most validated IGFBP-3 shRNA plasmid vector (pGPU6/GFP/Neo-shIGFBP-3) was prepared and injected in penile corpus cavernosum tissue. A total of 30 old (age 24 months) male Sprague Dawley® rats were randomly divided into 3 groups, including 10 each that received phosphate buffered saline only (100 μl), pGPU6/GFP/Neo-shNC (100 μg) and the most validated plasmid constructs pGPU6/GFP/Neo-shIGFBP-3 (100 μg). At 4 weeks the erectile response was measured as intracavernous pressure. The percent of smooth muscle in corpus cavernosum tissue was evaluated. Nitric oxide synthase activity and the cGMP concentration in penile tissue were also analyzed. IGFBP-3 was estimated in penile tissue by Western blot, real-time reverse transcriptase-polymerase chain reaction and immunohistochemistry.

RESULTS

pGPU6/GFP/Neo-shIGFBP-3 corrected the impaired erectile response in aged rats compared with the response in those injected with phosphate buffered saline and pGPU6/GFP/Neo-shNC (each p <0.01). The percent of cavernous smooth muscle was increased in the pGPU6/GFP/Neo-shIGFBP-3 group. Nitric oxide synthase activity and the cGMP concentration were also significantly increased in rats treated with pGPU6/GFP/Neo-shIGFBP-3. IGFBP-3 shRNA effectively reduced IGFBP-3 mRNA and protein expression in penile corpus cavernosum tissue.

CONCLUSIONS

Decreasing IGFBP-3 expression by plasmid expressed shRNA improved erectile function in aged rats. The therapy may modulate smooth muscle integrity and increase the cGMP concentration. This may be a new direction for treating erectile dysfunction in clinical practice.

The influence of promoter -202 A/C polymorphism (rs2854744) of the IGFBP-3 gene on erectile dysfunction risk and serum levels of IGF-I and IGFBP-3

PURPOSE

We studied whether the IGFBP-3 gene polymorphism rs2854744 is associated with erectile dysfunction.

MATERIALS AND METHODS

We investigated the association of this polymorphism with erectile dysfunction in 176 cases and 352 controls. We genotyped rs2854744 using polymerase chain reaction-restriction fragment length polymorphism. Circulating concentrations of IGF-I and IGFBP-3 were also measured.

RESULTS

Allelic frequencies were 0.474 (A allele) and 0.526 (C allele) in men with erectile dysfunction, and 0.457 (A allele) and 0.543 (C allele) in normal controls (adjusted OR 1.74, 95% CI 0.82-2.43, p = 0.08). The frequency of the IGFBP-3 A-202C polymorphism genotype was 0.273 (CC), 0.506 (AC) and 0.221 (AA) in the case group, and 0.296 (CC), 0.494 (AC) and 0.210 (AA) in the control group (chi-square test p = 0.08). Neither the IGFBP-3 A-202C polymorphism nor serum IGF-I and IGFBP-3 levels were significantly associated with the risk of erectile dysfunction. Carriers of the AA genotype had the highest age adjusted serum IGFBP-3. This demonstrated a stepwise decrease in the presence of 1 or 2 copies of the C allele (mean ± SD 4,541 ± 796.2, 3,552 ± 642.4 and 3,314 ± 669.3 ng/ml, respectively). There was a positive correlation between serum IGFBP-3 and serum IGF-I concentrations (Spearman correlation coefficient r = 0.34, p for trend = 0.001).

CONCLUSIONS

The IGFBP-3 gene A-202C polymorphism does not modulate the risk of erectile dysfunction.

Increased expression of insulin-like growth factor-binding protein-3 is implicated in erectile dysfunction in two-kidney one-clip hypertensive rats after propranolol treatment

This study aimed to investigate the role of insulin-like growth factor-binding protein-3 (IGFBP-3) in erectile dysfunction (ED) in two-kidney one-clip (2K-1C) hypertensive rats treated with the β-blocking agent propranolol. Adult male Wistar rats were randomly divided into three groups: a normal control group, a hypertensive control group and a propranolol treatment group (n=9). After 4 weeks of propranolol treatment, intracavernous pressure (ICP) responses to electrical stimulation of the cavernous nerves were evaluated. The expression of IGFBP-3 and insulin-like growth factor-1 (IGF-1) mRNA and protein in the rat cavernous tissue were detected by quantitative real-time PCR and Western blot, respectively. The concentration of cyclic guanosine monophosphate (cGMP) in the cavernous tissue was determined by enzyme-linked immunosorbent assay (ELISA). Cavernosal pressure in response to cavernous nerve stimulation was decreased 4 weeks after propranolol treatment (P<0.01, compared to the hypertensive control group). IGFBP-3 mRNA and protein expression was increased in the propranolol treatment group compared to the hypertensive control group (P<0.01), whereas IGF-1 expression was decreased in the propranolol treatment group compared to the hypertensive control group (P<0.01). In addition, cavernous cGMP concentration was decreased in the propranolol treatment group compared to the hypertensive control group (P<0.01). Taken together, these results suggest that the upregulation of IGFBP-3 may play a role in the development of ED in hypertensive rats.

Abnormal protein expression in the corpus cavernosum impairs erectile function in type 2 diabetes

OBJECTIVE

To investigate the changes in corporal relaxation, intracavernous pressure (ICP) and associated protein expression that control normal erectile function in rats with type 2 diabetes (T2D), as this disease is part of the 'metabolic syndrome' associated with a high rate of erectile dysfunction (ED) in men, resulting from failure of corpus cavernosum-mediated processes.

MATERIALS AND METHODS

T2D was induced in rats by feeding them with a high-fat diet (HFD) followed by an injection with low-dose streptozotocin (STZ); they were then compared with rats that received a normal diet (ND).

RESULTS

Hyperglycaemia and dyslipidaemia were induced in HFD + STZ rats, suggesting that T2D was established. The rats with T2D had associated ED, as both nonadrenergic noncholinergic-mediated corporal relaxation and increased ICP by cavernous nerve stimulation were significantly attenuated compared to the ND group. Western blot analysis revealed diabetes-associated lower expression of endothelial and neuronal nitric oxide synthase (e and nNOS), and cGMP-dependent protein kinase (PKG)-1alpha/beta expression in penile tissue than in the ND group. Contrary to the proteins that regulate corporal relaxation, there were relatively high levels of RhoA/Rho kinase receptor 1 (ROCK1) and ET-A receptor (ETAR) in T2D rats. However, the expressed level of phosphodiesterase-5 and insulin-like growth factor binding protein 3 was not altered significantly in response to T2D.

CONCLUSION

Decreased expression of certain proteins that mediate the relaxant mechanism, associated with increased expression of certain proteins that mediate contractile mechanisms, might be important in the development of T2D-associated ED. In particular, down-regulated eNOS/nNOS/PKG1 as well as up-regulated ETAR/RhoA/ROCK1 might participate in the aetiology of ED in T2D.

Perspectives in mammalian IGFBP-3 biology: local vs. systemic action

Insulin-like growth factor (IGF) binding protein (IGFBP)-3 has traditionally been defined by its role as a binding protein and its association with IGF delivery and availability. Development of non-IGF binding IGFBP-3 analogs and the use of cell lines devoid of type 1 IGF receptors (IGF-R) have led to critical advances in the field of IGFBP-3 biology. These studies show that IGFBP-3 has IGF-independent roles in inhibiting cell proliferation in cancer cell lines. Nuclear transcription factor, retinoid X receptor (RXR)-alpha, and IGFBP-3 functionally interact to reduce prostate tumor growth and prostate-specific antigen in vivo. Moreover, IGFBP-3 inhibits insulin-stimulated glucose uptake into adipocytes independent of IGF. The purpose of this review is to highlight IGFBP-3 as a novel effector molecule and not just another "binding protein" by discussing its IGF-independent actions on metabolism and cell growth. Although this review presents studies that assume the role of IGFBP-3 as either an endocrine or autocrine/paracrine molecule, these systems may not exist as distinct entities, justifying the examination of IGFBP-3 in an integrated model. Also, we provide an overview of factors that regulate IGFBP-3 availability, including its production, methylation, and ubiquitination. We conclude with the role of IGFBP-3 in whole body systems and possible future applications of IGFBP-3 in physiology.

Insulin-like growth factor-1 restores erectile function in aged rats: modulation the integrity of smooth muscle and nitric oxide-cyclic guanosine monophosphate signaling activity

INTRODUCTION

Insulin-like growth factor-1 (IGF-1) is one of the growth factors that have a wide range of biologic effects. We have confirmed that gene transfer of IGF-1 to the penis could improve erectile capacity. However, there are some limitations in gene therapies, such as toxicity or a risk of insertional mutagenesis. Protein treatment may be another choice for decreasing these risks.

AIM

To investigate whether intracavernosal injection of IGF-1 protein can restore erectile function in the aging rat.

MAIN OUTCOME MEASURES

Erectile responses, morphological changes, and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) signaling pathways-related marker were determined.

METHODS

Ten young (4 months) and 30 old (24 months) Sprague-Dawley male rats were enrolled in this study. The old rats were divided into three groups: vehicle-only (N = 10), IGF-1 1 microg/kg (N = 10) and IGF-1 10 microg/kg treatment group (N = 10). After 4 and 8 weeks of single IGF-1 injection treatment, intracavernous pressure (ICP) responses with electrical stimulation to the cavernous nerve were evaluated. The percent of smooth muscle in corpus cavernosum tissue, the expression of mRNA and protein of endothelial nitric oxide synthase (eNOS) were also evaluated. The activity of nitric oxide synthase (NOS) and concentration of guanosine 3',5'-cyclic-monophosphate (cGMP) that act upon the major NO-cGMP signaling pathways in penile tissue were also analyzed.

RESULTS

After IGF-1 treatment, the ICP responses was significantly increased as the young control group in both the IGF-1 1 microg/kg and the IGF-1 10 microg/kg group compared with the vehicle-only group at 4 and 8 weeks (P < 0.05). Masson's trichrom staining showed the percentage of cavernosal smooth muscle was increased in IGF-1 treatment group. IGF-1 increased e-NOS expression. NOS activities and cGMP concentrations were also significantly increased in IGF-1 treatment rats.

CONCLUSIONS

IGF-1 improved erectile function in aged rats via restoration the integrity of smooth muscle of corpus cavernosum and modulation of NO-cGMP pathways.