Dominant negative insulin-like growth factor-1 receptor inhibits neointimal formation through suppression of vascular smooth muscle cell migration and proliferation, and induction of apoptosis

Cell-Specific Effects of Insulin in a Murine Model of Restenosis Under Insulin-Sensitive and Insulin-Resistant Conditions

Restenosis following percutaneous revascularization is a major challenge in patients with insulin resistance and diabetes. Currently, the vascular effects of insulin are not fully understood. In vitro, insulin's effects on endothelial cells (ECs) are beneficial, whereas on vascular smooth muscle cells (SMCs), they are mitogenic. We previously demonstrated a suppressive effect of insulin on neointimal growth under insulin-sensitive conditions that was abolished in insulin-resistant conditions. Here, we aimed to determine the cell-specific effects of insulin on neointimal growth in a model of restenosis under insulin-sensitive and insulin-resistant conditions. Vascular cell-specific insulin receptor (IR)-deficient mice were fed a low-fat diet (LFD) or a high-fat, high-sucrose diet (HFSD) and implanted with an insulin pellet or vehicle prior to femoral artery wire injury. In insulin-sensitive conditions, insulin decreased neointimal growth only in controls. However, under insulin-resistant conditions, insulin had no effect in either control, EC-specific or SMC-specific IR-deficient mice. These data demonstrate that EC and SMC IRs are required for the anti-restenotic effect of insulin in insulin-sensitive conditions and that, in insulin resistance, insulin has no adverse effect on vascular SMCs in vivo.

Vascular Smooth Muscle Cell Subpopulations and Neointimal Formation in Mouse Models of Elastin Insufficiency

OBJECTIVE

Using a mouse model of Eln (elastin) insufficiency that spontaneously develops neointima in the ascending aorta, we sought to understand the origin and phenotypic heterogeneity of smooth muscle cells (SMCs) contributing to intimal hyperplasia. We were also interested in exploring how vascular cells adapt to the absence of Eln. Approach and Results: We used single-cell sequencing together with lineage-specific cell labeling to identify neointimal cell populations in a noninjury, genetic model of neointimal formation. Inactivating Eln production in vascular SMCs results in rapid intimal hyperplasia around breaks in the ascending aorta's internal elastic lamina. Using lineage-specific Cre drivers to both lineage mark and inactivate Eln expression in the secondary heart field and neural crest aortic SMCs, we found that cells with a secondary heart field lineage are significant contributors to neointima formation. We also identified a small population of secondary heart field-derived SMCs underneath and adjacent to the internal elastic lamina. Within the neointima of SMC-Eln knockout mice, 2 unique SMC populations were identified that are transcriptionally different from other SMCs. While these cells had a distinct gene signature, they expressed several genes identified in other studies of neointimal lesions, suggesting that some mechanisms underlying neointima formation in Eln insufficiency are shared with adult vessel injury models.

CONCLUSIONS

These results highlight the unique developmental origin and transcriptional signature of cells contributing to neointima in the ascending aorta. Our findings also show that the absence of Eln, or changes in elastic fiber integrity, influences the SMC biological niche in ways that lead to altered cell phenotypes.

Whole Body Vibration Retards Progression of Atherosclerosis via Insulin-Like Growth Factor 1 in Apolipoprotein E-Deficient Mice

Whole body vibration (WBV) has a marked impact on lipid metabolism and the endocrine system, which is related to the progression of atherosclerosis (AS). To investigate the effects of WBV, we measured the atherosclerotic plaque area of apolipoprotein E-knockout (ApoE^−/−) AS mice, which were trained by WBV (15 Hz, 30 min) for 12 weeks. Simultaneously, serum levels of lipids, insulin-like growth factor 1 (IGF-1), insulin-like growth factor 1 receptor (IGF-1R), interleukin 6 (IL-6), and the mRNA and protein levels of the same in the aorta were compared between the control and WBV groups. The results indicated that WBV significantly reduced the atherosclerotic plaque area with lower very low-density lipoprotein (VLDL) and oxidized low-density lipoprotein (ox-LDL) in the blood. Moreover, the levels of IGF-1 in serum and expression of IL-6, IGF-1R, and p-IGF-1R protein in the mice aorta decreased significantly in the WBV group. In addition, we found that serum IGF-1 in mice increased to the highest concentration in 30 min after WBV for 10, 30, 60, and 120 minutes. These results suggested that appropriate WBV may delay the progression of AS, which was associated with acutely elevated serum IGF-1 and lower levels of IGF-1 and IL-6 in the aorta for long-term treatment.

MicroRNA-99a inhibits insulin-induced proliferation, migration, dedifferentiation, and rapamycin resistance of vascular smooth muscle cells by inhibiting insulin-like growth factor-1 receptor and mammalian target of rapamycin

Patients with type 2 diabetes mellitus (T2DM) are characterized by insulin resistance and are subsequently at high risk for atherosclerosis. Hyperinsulinemia has been associated with proliferation, migration, and dedifferentiation of vascular smooth muscle cells (VSMCs) during the pathogenesis of atherosclerosis. Moreover, insulin-like growth factor-1 receptor (IGF-1R) and mammalian target of rapamycin (mTOR) have been demonstrated to be the underlying signaling pathways. Recently, microRNA-99a (miR-99a) has been suggested to regulate the phenotypic changes of VSMCs in cancer cells. However, whether it is involved in insulin-induced changes of VSCMs has not been determined. In this study, we found that insulin induced proliferation, migration, and dedifferentiation of mouse VSMCs in a dose-dependent manner. Furthermore, the stimulating effects of high-dose insulin on proliferation, migration, and dedifferentiation of mouse VSMCs were found to be associated with the attenuation of the inhibitory effects of miR-99a on IGF-1R and mTOR signaling activities. Finally, we found that the inducing effect of high-dose insulin on proliferation, migration, and dedifferentiation of VSMCs was partially inhibited by an active mimic of miR-99a. Taken together, these results suggest that miR-99a plays a key regulatory role in the pathogenesis of insulin-induced proliferation, migration, and phenotype conversion of VSMCs at least partly via inhibition of IGF-1R and mTOR signaling. Our results provide evidence that miR-99a may be a novel target for the treatment of hyperinsulinemia-induced atherosclerosis.

Insulin-like growth factor-1 inhibits colonic smooth muscle cell apoptosis in diabetic rats with colonic dysmotility

Cellular apoptosis and colonic dysmotility are involved in diabetes mellitus (DM) complications. Insulin-like growth factor-1 (IGF-1) is known to affect apoptosis and proliferation. Here, we demonstrated that the treatment of 1500 ng/kg IGF-1 partly recovers the decrease of the muscle thickness, body weight and gastrointestinal transit rate in DM rats. The gastrointestinal transit rate is positively correlated with the IGF-I level, but negatively correlated with the level of colonic cellular apoptosis. The DM-induced colonic apoptosis is also attenuated by the IGF-1 stimulation. Moreover, IGF-1 inhibits the apoptosis of the isolated colonic SMCs in vitro via the activation of PI3K/Akt and ERK1/2 signaling pathways. Taken together, our data indicated that IGF-1 inhibits the DM-induced colonic SMC apoptosis and might be involved in the alleviation of colonic dysmotility in diabetic rats.

Local insulin application on the carotid artery inhibits neointima formation

Anti-mitogenic agents currently used to prevent restenosis in drug-eluting stents delay re-endothelialization. Delayed re-endothelialization is now considered as the main cause of late stent thrombosis with drug-eluting stents, which emphasizes the need for new treatments. We have shown that systemic insulin treatment decreases neointimal growth and accelerates re-endothelialization after arterial injury in a rat model of restenosis. However, systemic insulin treatment cannot be given to non-diabetic individuals because of the risk of hypoglycemia. Thus, we investigated whether local insulin treatment is also effective in reducing neointimal growth after arterial injury. Rats were given local vehicle or local insulin delivered via Pluronic gel applied around the carotid artery immediately following balloon injury. Plasma glucose and systemic insulin levels were not affected by local insulin treatment. Insulin decreased intimal area at 28 days (P < 0.05) and also inhibited vascular smooth muscle cell migration by 60% at 4 days (P < 0.05). NPH (a longer-lasting insulin) also decreased neointimal area. These results indicate that local insulin treatment can lead to decreased restenosis, suggesting a protective vascular effect of insulin in vivo and that local insulin treatment, possibly via insulin-eluting stents, may be clinically relevant.

MicroRNA-133a regulates insulin-like growth factor-1 receptor expression and vascular smooth muscle cell proliferation in murine atherosclerosis

OBJECTIVE

MicroRNA-133a (miR-133a) and insulin-like growth factor-1 (IGF-1) are two different molecules known to regulate cardiovascular cell proliferation. This study tested whether miR-133a affects expression of IGF-1 receptor (IGF-1R) and proliferation of IGF-1-stimulated vascular smooth muscle cells (VSMC) in a murine model of atherosclerosis.

METHODS AND RESULTS

Expression of IGF-1R was analyzed by immuno-fluorescence and immuno-blotting, and miR-133a by qRT-PCR in the aortas of wild-type C57BL/6J (WT) and apolipoprotein-E deficient (ApoE(-/-)) mice. Compared to those in WT aortas, the IGF-1R and miR-133a levels were lower in ApoE(-/-) aortas. ApoE(-/-) VSMC grew slower than WT cells in the cultures with IGF-1-containing medium. MiR-133a-specific inhibitor decreased miR-133a, IGF-1R expression, IGF-1-stimulated VSMC growth in lipoprotein deficient media. By contrast, miR-133a precursor increased IGF-1R levels and promoted IGF-1-induced VSMC proliferation. In the luciferase-IGF-1R 3'UTR reporter system, the reporter luciferase activity was not inhibited in VSMC with miR-133a overexpression. IGF-1R mRNA half-life in ApoE(-/-) VSMC was shorter than that in WT VSMC. MiR-133a inhibitor reduced but precursor increased the mRNA half-life, although the effects appeared less striking in ApoE(-/-) VSMC than in WT cells.

CONCLUSION

MiR-133a serves as a stimulatory factor for IGF-1R expression through prolonging IGF-1R mRNA half-life. In atherosclerosis induced by ApoE deficiency, reduced miR-133a expression is associated with lower IGF-1R levels and suppressive VSMC growth. Administration of miR-133a precursor may potentiate IGF-1-stimulated VSMC survival and growth.

Dopamine d(1)-like receptors suppress proliferation of vascular smooth muscle cell induced by insulin-like growth factor-1

OBJECTIVE

Proliferation of vascular smooth muscle cells (VSMCs) participates in the pathogenesis and development of cardiovascular diseases, including essential hypertension and atherosclerosis. Our previous study found that stimulation of D1-like dopamine receptors inhibited insulin-induced proliferation of VSMCs. Insulin-like growth factor-1 (IGF-1) and insulin share similar structure and biological effect. However, whether or not there is any effect of D1-like receptors on IGF-1-induced proliferation of VSMCs is not known. Therefore, we investigated the inhibitory effect of D1-like dopamine receptors on the IGF-1-induced VSMCs proliferation in this study.

METHOD

VSMC proliferation was determined by [(3)H]-thymidine incorporation, the uptake of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and cell number. Phosphorylated/non-phosphorylated IGF-1 receptor, Akt, mTOR and p70S6K expressions were determined by immunoblotting. The oligodeoxynucleotides were transfected to A10 cells to identify the effect of D1 and D5 receptors, respectively.

RESULTS

IGF-1 increased the proliferation of VSMCs, while in the presence of fenoldopam, IGF-1-mediated stimulatory effect was reduced. Use of either antisense for D1 or D5 receptor partially inhibited the fenoldopam-induced antiproliferation effect of VSMCs. Use of both D1 and D5 receptor antisenses completely blocked the inhibitory effect of fenoldopam. In the presence of PI3k and mTOR inhibitors, the IGF-1-mediated proliferation of VSMCs was blocked. Moreover, IGF-1 increased the phosphorylation of PI3k and mTOR. The inhibitory effect of fenoldopam on VSMC proliferation might be due to the inhibition of IGF-1 receptor expression and IGF-1 phosphorylation, because in the presence of fenoldopam, the stimulatory effect of IGF-1 on phosphorylation of IGF-1 receptor, PI3k and mTOR is reduced, the IGF-1 receptor expression was reduced in A10 cells.

CONCLUSION

Activation of the D1-like receptors suppressed the proliferative effect of IGF-1 in A10 cells via the inhibition of the IGF-1R/Akt/mTOR/p70S6K pathway and downregulated the expression of IGF-1 receptor.

Insulin-like growth-factor-1-induced PKB signaling and Egr-1 expression is inhibited by curcumin in A-10 vascular smooth muscle cells

Insulin-like growth factor 1 (IGF-1) is a mitogenic factor that stimulates the signaling pathways responsible for inducing hypertrophic and proliferative responses in vascular smooth muscle cells (VSMC). We have previously demonstrated that IGF-1 receptor (IGF-1R) plays a key role in transducing the hypertrophic and proliferative responses of angiotensin II (Ang-II) and endothelin-1 (ET-1). Curcumin, a polyphenolic compound derived from the spice turmeric is known to possess antiproliferative properties and exerts vasculoprotective effects. However, the ability of curcumin to modulate IGF-1-induced signaling responses in VSMC remains to be investigated. In this study, we determined the effect of curcumin on IGF-1-induced phosphorylation of protein kinase B (PKB), glycogen synthase kinase-3β (GSK-3β), and IGF-1R in VSMC. Curcumin inhibited IGF-1-induced phosphorylation of PKB and GSK-3β as well as the IGF-1R β subunit in a dose-dependent fashion. In addition, IGF-1-induced expression of early growth response protein 1 (Egr-1) which plays a pathogenic role in vascular dysfunctions, was also attenuated by curcumin. In conclusion, these results indicate that curcumin is a potent inhibitor of key components of the IGF-1-induced mitogenic and proliferative signaling system in VSMC, and suggest that curcumin-induced attenuation of these signaling components may constitute a potential mechanism for its vasculoprotective effects.

Transfection with siRNA against ERK1/2 inhibits IGF-1-induced stem cell factor expression in colonic smooth muscle cells

AIM: To investigate how insulin-like growth factor-1 (IGF-1) regulates the expression of stem cell factor (SCF) in colonic smooth muscle cells (SMCs).

METHODS: After rat colonic SMCs were treated with different concentrations of IGF-1 (0, 50, 100, 150 μg/L) for different durations (0, 5, 15, 30, 45, 60 min), the levels of phosphorylated ERK1/2 and SCF were determined by RT-PCR and Western blot. Rat colonic SMCs were then transfected with siRNA against ERK1/2 to examine the impact of ERK1/2 down-regulation on IGF-1-induced SCF expression.

RESULTS: After treatment with IGF-1, the level of phosphorylated ERK1/2 in colonic SMCs reached a peak at about 15 min (0.417 ± 0.036 vs 0.101 ± 0.015; P < 0.05). The optimal concentration of IGF-1 to induce the expression of phosphorylated ERK1/2 and SCF was 100 μg/L (0.790 ± 0.051 vs 0.336 ± 0.013; 0.765 ± 0.061 vs 0.289 ± 0.021, both P < 0.05). After treatment with IGF-1, the expression levels of phosphorylated ERK1/2, total ERK1/2, and SCF in colonic SMCs transfected with siRNA against ERK1/2 were lower than those in the control group (0.284 ± 0.021 vs 0.732 ± 0.005; 0.256 ± 0.015 vs 0.712 ± 0.023; 0.219 ± 0.020 vs 0.673 ± 0.013; 0.621 ± 0.027 vs 1.725 ± 0.012; 0.821 ± 0.019 vs 1.751 ± 0.043; 0.275 ± 0.061 vs 0.531 ± 0.047; all P < 0.05).

CONCLUSION: IGF-1 treatment up-regulated the expression of phosphorylated ERK1/2 and SCF in colonic SMCs, while transfection with siRNA against ERK1/2 down-regulated IGF-1-induced expression of phosphorylated ERK1/2 and SCF, suggesting that the ERK/MAPK pathway may be involved in IGF-1-induced expression of phosphorylated ERK1/2 and SCF.

Changes in proteomic features induced by insulin on vascular smooth muscle cells from spontaneous hypertensive rats in vitro

Hyperinsulinemia is a risk factor in atherosclerosis formation that it stimulated vascular smooth muscle cells (VSMCs) proliferation and migration. To understand the underlying molecular mechanism involved in the processes of cellular response to insulin, VSMCs from Wistar-Kyoto rat (WKY) and spontaneous hypertensive rat (SHR) were isolated and cultured, and its proteome was comparatively analyzed with normal control by two-dimensional gel electrophoresis (2-DE). Results showed that the proliferation of VSMCs from SHR be more sensitive to insulin stimulation than that VSMCs from WKY. The detectable spots ranged from 537 to 608 on the gels in VSMCs of SHR, and 413 ± 31 spots in VSMCs of WKY. The different expressed protein spots in VSMCs of SHR were then isolated and measured by matrix-assisted desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS). A total of 18 spots showed a sharp clear spectrum, and 13 spots matched with the known proteins from database. These proteins were mainly involved in cytoskeleton, glycometabolism, and post-translational processes. Among these proteins, OPN and matrix gla protein were up-regulated expression proteins, while α-SM actin was down-regulated. Furthermore, these preliminarily identified proteins confirmed by RT-PCR and western blotting analysis were coincident with the changes in 2-DE check. In addition, the cytoskeleton changes and migration rate of VSMCs from SHR treated by insulin increased significantly. The results showed that insulin plays a crucial role in activating proliferation and migration of VSMCs, by regulating the phenotype switch of VSMCs.

Involvement of insulin-like growth factor 1 receptor transactivation in endothelin-1-induced signaling in vascular smooth muscle cells

Endothelin-1 (ET-1) is a potent vasoactive peptide that exerts hypertrophic, migratory, and mitogenic effects in vascular smooth muscle cells. ET-1-induced activation of several signaling events has been shown to mediate the cellular effects of ET-1. In the past several years, transactivation of growth factor receptor has gained much recognition in transducing the signaling responses of ET-1. Among various growth factor receptors studied, the involvement of epidermal growth factor receptor transactivation in triggering ET-1-induced responses has been studied in some detail. However, recent studies have implicated insulin-like growth factor 1 receptor transactivation in this process. There are also some suggestions for a role of the Src family of nonreceptor protein tyrosine kinases, such as c-Src, in transducing the signaling responses of vasoactive peptides. In this review, we will examine the contribution of both insulin-like growth factor 1 receptor and c-Src in mediating ET-1-induced signaling responses in vascular smooth muscle cells.

Insulin-like growth factor-1 upregulates the expression of stem cell factor in rat colonic smooth muscle cells

AIM: To investigate the effects of insulin-like growth factor-1 (IGF-1) on the expression of stem cell factor (SCF) in rat colonic smooth muscle cells (SMCs).

METHODS: Rat colonic SMCs were separated, cultured, and identified by immunofluorescence staining of α-actin. Cultured colonic SMCs were divided into IGF-1 treatment group and IGF-1 receptor antibody intervention group. Cells in the IGF-1 treatment group incubated with different concentrations (0, 5, 10, 50, 100 and 150 μg/L) of IGF-1 for different durations (0, 8, 16, 24 and 48 hours), while those in the IGF-1 receptor antibody intervention group were treated with IGF-1 and different concentrations of IGF-1 receptor monoclonal antibody (0, 50, 100 and 150 μg/L). The expression of SCF in colonic SMCs was examined by Western blot and quantitative reverse transcription-polymerase chain reaction.

RESULTS: Although IGF-1 at low concentrations (5 and 10 μg/L) had no significant impact on the expression of SCF mRNA and protein in SMCs (all P > 0.05), IGF-1 at moderate or high concentrations (50, 100 and 150 μg/L) significantly upregulated the expression of SCF mRNA and protein (all P < 0.05). The optimum concentration of IGF-1 to upregulate SCF expression in vitro was 100 μg/L (0.820 ± 0.061 vs 0.167 ± 0.015 and 1.269 ± 0.219 vs 0.560 ± 0.023, respectively; both P < 0.05), and the peak expression of SCF occurred 16 hours after incubation with IGF-1 (0.420 ± 0.034 vs 0.209 ± 0.001 and 1.407 ± 0.133 vs 0.477 ± 0.041, respectively; both P < 0.05). IGF-1 receptor monoclonal antibody could inhibit the expression of SCF in SMCs in a dose-dependent manner (all P < 0.05).

CONCLUSION: IGF-1 can upregulate the expression of SCF in colonic SMCs perhaps in an IGF-1 receptor-dependent manner.

Mechano-sensitive transcriptional factor Egr-1 regulates insulin-like growth factor-1 receptor expression and contributes to neointima formation in vein grafts

OBJECTIVE

Vein grafts in a coronary bypass or a hemodialysis access often develop obliterative growth of the neointima. We previously reported that the mechanical stretch-activated insulin-like growth factor-1 receptor (IGF-1/IGF-1R) pathway plays an important role in this remodeling. However, the transcriptional mechanism(s) regulating IGF-1R expression and neointima formation have not been identified.

METHODS AND RESULTS

Deletion and site-specific mutagenesis analysis of IGF-1R promoter identified that the minimal mechano-responsive promoter element (-270--130) contains 2 consensus sequences for binding of early growth reponse-1 (Egr-1) transcriptional factor. Mechanical stretch stimulated both Egr-1 mRNA (4.6-fold) and protein (5.2-fold) in vascular smooth muscle cells. Interposition of a vein into an artery increased Egr-1 mRNA (7.8+/-2.6-fold vs sham). In vascular smooth muscle cells isolated from Egr-1 knockout mice, mechanical stretch could not increase IGF-1R, and vascular smooth muscle cells proliferation was decreased by 47% compared to wild-type cells. Importantly, the neointima area was reduced by at least 50%, and the lumen-to-media ratio increased by 55% in vein grafts of Egr-1 knockout mice compared with results of wild-type mice.

CONCLUSIONS

Egr-1 is a mechano-sensitive transcriptional factor that stimulates IGF-1R transcription, resulting in vascular remodeling of vein grafts.

Insulin-like growth factor-1 protects from vascular stenosis and accelerates re-endothelialization in a rat model of carotid artery injury

BACKGROUND

IGF-1 is a potent mitogen for vascular smooth muscle cells, but exerts protective effects on endothelial cells that may trigger antiatherogenic mechanisms.

OBJECTIVES

This study was designed to test the hypothesis that an IGF-1 excess following arterial injury prevents neointima formation and vascular stenosis.

METHODS

Rats were subjected to carotid balloon injury and treated with IGF-1 (1.2 mg kg(-1) per die) or saline for 10 days.

RESULTS

In IGF-1 treated animals, high tissue levels of eNOS, Akt and its phosphorylated form were found, confirming activation of IGF-1-dependent signaling pathways. IGF-1 markedly reduced neointima formation and post-injury arterial stenosis. IGF-1 exerted proliferative and anti-apoptotic effects in the media of injured carotids, but inhibited mitotic activity and induced apoptosis in the neointima. Furthermore, IGF-1 stimulated mobilization of progenitor endothelial cells and re-endothelialization of the injured arteries. L-NAME administration inhibited IGF-1 vasculoprotective effects.

CONCLUSIONS

IGF-1 attenuates post-injury carotid stenosis by exerting differential effects in the neointima and tunica media with regard to the key components of the response to injury. The data point to a novel role of IGF-1 as a potent vasculoprotective factor.

Adiponectin inhibits insulin-like growth factor-1-induced cell migration by the suppression of extracellular signal-regulated kinase 1/2 activation, but not Akt in vascular smooth muscle cells

Adiponectin, an adipocyte-derived hormone, has been proposed to show antiatherogenic properties through the inhibitory effects against various growth factors. Insulin-like growth factor-1 (IGF-1) is one of the potent mitogens, which has been considered to play important roles in both atherogenesis and plaque stabilization in accordance to the phase of atherosclerosis. The aim of this study is to elucidate the adiponectin effects on IGF-1-induced cell migration and its intracellular signaling pathways in vascular smooth muscle cells (VSMCs). In this study, we assessed cell migration and several kinase activities in cultured rat aortic smooth muscle cells (RASMCs). Adiponectin pretreatment suppressed IGF-1-induced cell migration and extracellular signal-regulated kinase (ERK)1/2 activation, which is one of the major mediators for IGF-1-induced cell migration. In RASMCs, adiponectin and 5-aminoimidazole-4-carboxamide riboside (AICAR), a 5'-AMP-activated protein kinase (AMPK) activator, stimulated AMPK activation. AMPK activation by AICAR inhibited IGF-1-induced ERK1/2 activation and cell migration in RASMCs. On the other hand, phosphorylation of Akt and Bad, proapoptotic molecules of the Bcl-2 family, which were increased by IGF-1 stimulation, was not diminished by the pretreatment with adiponectin. It was shown that adiponectin inhibited IGF-1-induced VSMC migration through suppression of ERK1/2 activation, which might be implicated in AMPK activation. Furthermore, adiponectin selectively inhibited ERK1/2 pathway, not Akt-Bad pathway, stimulated by IGF-1. From these findings, it was implied that adiponectin suppressed IGF-1-induced VSMC migration and its signaling selectivity.

Age-related differences in insulin-like growth factor-1 receptor signaling regulates Akt/FOXO3a and ERK/Fos pathways in vascular smooth muscle cells

Advanced age is a major risk factor for atherosclerosis, but how aging per se influences pathogenesis is not clear. Insulin-like growth factor-1 receptor (IGF-1R) promotes aortic vascular smooth muscle cell (VSMC) growth, migration, and extracellular matrix formation, but how IGF-1R signaling changes with age in VSMC is not known. We previously found age-related differences in the activation of Akt/FOXO3a and ERK1/2 pathways in VSMC, but the upstream signaling remains unclear. Using explanted VSMC from Fischer 344/Brown Norway F1 hybrid rats shown to display age-related vascular pathology similar to humans, we compared IGF-1R expression in early passages of VSMC and found a constitutive activation of IGF-1R in VSMC from old compared to young rats, including IGF-1R expression and its tyrosine kinase activity. The link between IGF-1R activation and the Akt/FOXO3a and ERK pathways was confirmed through the induction of IGF-1R with IGF-1 in young cells and attenuation of IGF-1R with an inhibitor in old cells. The effects of three kinase inhibitors: AG1024, LY294002, and TCN, were compared in VSMC from old rats to differentiate IGF-1R from other upstream signaling that could also regulate the Akt/FOXO and ERK pathways. Genes for p27kip-1, catalase and MnSOD, which play important roles in the control of cell cycle arrest and stress resistance, were found to be FOXO3a-targets based on FOXO3a-siRNA treatment. Furthermore, IGF-1R signaling modulated these genes through activation of the Akt/FOXO3a pathway. Therefore, activation of IGF-1R signaling influences VSMC function in old rats and may contribute to the increased risk for atherosclerosis.

TRAIL stimulates proliferation of vascular smooth muscle cells via activation of NF-kappaB and induction of insulin-like growth factor-1 receptor

TRAIL/Apo2L (tumor necrosis factor-related apoptosis-inducing ligand) is a multifunctional protein regulating homeostasis of the immune system, infection, autoimmune diseases, and apoptosis. However, its function in normal, nontransformed tissues is not clear. Here we show that TRAIL increases vascular smooth muscle cell (VSMC) proliferation in vitro, effects that can be blocked with neutralizing antibodies to TRAIL receptors DR4 and DcR1. In aortocoronary saphenous vein bypass grafts in vivo, TRAIL co-localizes with VSMC, proliferating cell nuclear antigen, and insulin-like growth factor type 1 receptor (IGF1R) expression but not active caspase-3. TRAIL is required for serum-inducible IGF1R expression, and antisense IGF1R inhibits TRAIL-induced VSMC proliferation. At 1 ng/ml, TRAIL stimulates IGF1R mRNA expression greater than insulin-like growth factor-1 and also activates the IGF1R promoter 7-fold. TRAIL-inducible IGF1R expression requires NF-kappaB activation. Consistent with this, ammonium pyrrolidine dithiocarbamate, a pharmacological inhibitor of NF-kappaB, blocks TRAIL-induced IGF1R expression, and p65 overexpression increases IGF1R protein levels. In addition, NF-kappaB binds a novel TRAIL-responsive element on the IGF1R promoter. Our findings suggest that the biological functions of TRAIL in VSMC extend beyond its role in promoting apoptosis. Thus, TRAIL may play an important role in atherosclerosis by regulating IGF1R expression in VSMC in an NF-kappaB-dependent manner.

The cyclolignan picropodophyllin attenuates intimal hyperplasia after rat carotid balloon injury by blocking insulin-like growth factor-1 receptor signaling

OBJECTIVE

Smooth muscle cell proliferation (SMC) is a pivotal factor in the development of intimal hyperplasia after vascular injury. A number of growth factors, including insulin-like growth factor-1 (IGF-1), have been shown to be involved in SMC proliferation. We evaluated the effect of picropodophyllin (PPP), a new IGF-1 receptor inhibitor, in the prevention of SMC proliferation and development of intimal hyperplasia after vascular injury.

METHODS

The effects of systemic administration of PPP on intimal hyperplasia were studied in a balloon rat carotid injury model. Lesions were quantified by morphometry and SMC proliferation and apoptosis was studied by immunohistochemical staining for proliferating cell nuclear antigen (PCNA) and activated caspase 3, respectively. The effect of PPP on rat aortic SMC proliferation and apoptosis was studied in vitro by using cell counting, 3[H]-thymidine incorporation, and a flow cytometry assay for annexin V. Phosphorylation of the IGF-1 receptor, protein kinase B (Akt), and extracellular signal-regulated kinase 1/2 (ERK1/2) in vitro and in vivo were analyzed by using Western blotting.

RESULTS

PPP inhibited IGF-1-mediated SMC proliferation in vitro but no significant increase in apoptosis was detected. In rats treated with PPP, a more than a twofold reduction in carotid intima area was observed 2 weeks after balloon injury, a significant decrease in PCNA staining was demonstrated in early lesions, but activated caspase 3 was not detected. In addition, PPP attenuated phosphorylation of the IGF-1 receptor, Akt, and ERK1/2 in IGF-1-stimulated SMCs in vitro, and a reduced phosphorylation of the IGF-1 receptor and Akt was found in balloon-injured carotid arteries in rats treated with PPP.

CONCLUSION

These results show that PPP potently blocks IGF-1-mediated phosphorylation of the IGF-1 receptor in SMCs, decreases downstream Akt and ERK1/2 activation, inhibits SMC replication, and subsequently attenuates intimal hyperplasia after balloon injury of rat carotid arteries.