Hyperglycemia alters the responsiveness of smooth muscle cells to insulin-like growth factor-I

Triglyceride-Glucose Index: A Candidate Prognostic Marker in HR-Positive/HER2-Negative Metastatic Breast Cancer Patients Treated With CDK4/6 Inhibitors

AIMS AND OBJECTIVES

Although cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i) are a vital part of the treatment of hormone receptor (HR)-positive/HER-2-negative metastatic breast cancer (BC), individuals have different sensitivities to CDK4/6i, indicating the need for biomarkers. The fasting triglyceride glucose (TyG) index is an easily accessible surrogate marker of insulin resistance (IR). Herein, we investigated the prognostic significance of the fasting triglyceride glucose (TyG) index in HR+/HER2- metastatic BC patients treated with CDK4/6i plus endocrine therapy (ET).

METHODS

About 333 patients with HR+/HER2-metastatic BC treated with CDK4/6i plus ET were analyzed retrospectively. The TyG index was calculated within 3 months before the initiation of CDK4/6i plus ET. The median value of 8.43 was taken as the cutoff for the TyG index.

RESULTS

The median overall survival (OS) was 73.6 months (95% CI, 66.0-81.1) in the whole cohort. The progression-free survival (PFS) was significantly longer in the low-TyG subgroup than in the high-TyG subgroup (30.1 vs. 21.3 months, multivariate adjusted [HR] = 0.666, 95% CI, 0.450-0.987, P = .043). While the median OS was not reached in the low TyG subgroup, it was 69.0 months in the high TyG subgroup (multivariate-adjusted HR = 0.513, 95% CI, 0.281-0.936, P = .030). Although the ORR and DCR were numerically greater in the low-TyG subgroup, no significant differences were observed between the low-TyG subgroup and high-TyG subgroup (28.1% vs. 24.7%, P = .476; 83.2% vs. 80.1%, P = .463, respectively).

CONCLUSIONS

These data imply that the TyG index could be a predictive biomarker for the therapeutic efficacy of CDK4/6is. Extensive prospective studies are needed to confirm these findings.

Buddleja officinalis Maxim.: A review of its botany, ethnopharmacology, phytochemistry, pharmacology, and therapeutic potential for ophthalmic diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Buddleja officinalis Maxim. (B. officinalis), commonly known as "Menghua" "Yangerduo" is a widely recognized traditional herbal medicine in China, Korea, and Vietnam. For thousands of years, it has been used to treat dry eye disease, conjunctivitis, keratitis, eye ulcers, eye pain, cough, asthma, hemoptysis, and other medical conditions.

AIM OF THE REVIEW

This review article aims to provide a concise summary of the botany, ethnopharmacology, phytochemistry, pharmacology, medicinal potential, and application of B. officinalis in treating ophthalmic diseases and critically evaluates the existing literature to establish a scientific basis for its reasonable utilization and further investigation.

MATERIALS AND METHODS

The information reviewed in this study was collected from various electronic resources, including the Web of Science, PubMed, and Google Scholar.

RESULTS

To date, 80 structurally diverse compounds have been isolated and characterized from B. officinalis, primarily flavonoids, phenylethanoids, triterpenoids, and monoterpenes. Extracts and compounds derived from B. officinalis have been reported to possess broad pharmacological effects including anti-dry eye disease, anti-inflammation, anti-oxidation, anti-diabetes, anti-obesity, improving osteoporosis and treatment of skin diseases. This review provides a reference for the future studies on of B. officinalis.

CONCLUSIONS

As a natural medicinal plant, B. officinalis is worthy of further development in botany, ethnopharmacology, phytochemistry, pharmacology, and therapeutic potential for ophthalmic diseases. Although some components have demonstrated multiple pharmacological activities, their mechanisms of action remain unclear. Further studies on the underlying molecular basis and mechanism of action are warranted.

Mechano-Redox Control of Integrins in Thromboinflammation

Significance: How mechanical forces and biochemical cues are coupled remains a miracle for many biological processes. Integrins, well-known adhesion receptors, sense changes in mechanical forces and reduction-oxidation reactions (redox) in their environment to mediate their adhesive function. The coupling of mechanical and redox function is a new area of investigation. Disturbance of normal mechanical forces and the redox balance occurs in thromboinflammatory conditions; atherosclerotic plaques create changes to the mechanical forces in the circulation. Diabetes induces redox changes in the circulation by the production of reactive oxygen species and vascular inflammation. Recent Advances: Integrins sense changes in the blood flow shear stress at the level of focal adhesions and respond to flow and traction forces by increased signaling. Talin, the integrin-actin linker, is a traction force sensor and adaptor. Oxidation and reduction of integrin disulfide bonds regulate their adhesion. A conserved disulfide bond in integrin αlpha IIb beta 3 (αIIbβ3) is directly reduced by the thiol oxidoreductase endoplasmic reticulum protein 5 (ERp5) under shear stress. Critical Issues: The coordination of mechano-redox events between the extracellular and intracellular compartments is an active area of investigation. Another fundamental issue is to determine the spatiotemporal arrangement of key regulators of integrins' mechanical and redox interactions. How thromboinflammatory conditions lead to mechanoredox uncoupling is relatively unexplored. Future Directions: Integrated approaches, involving disulfide bond biochemistry, microfluidic assays, and dynamic force spectroscopy, will aid in showing that cell adhesion constitutes a crossroad of mechano- and redox biology, within the same molecule, the integrin. Antioxid. Redox Signal. 37, 1072-1093.

Association between triglyceride glucose index and risk of cancer: A meta-analysis

BACKGROUND

Triglyceride glucose (TyG) index as a more convenient and reliable predictor of insulin resistance (IR) is thought to be associated with many diseases, but its relationship with cancer remains unclear.

METHODS

The meta-analysis was conducted to evaluate the effects of TyG index on cancer risk utilizing the available evidence. PubMed, EMBASE, Medline, Cochrane Library and Web of Science were searched from their inception up to July 2022. A random-effects model was used to calculate the effect estimates and 95% confidence intervals (CIs).

RESULTS

A total of 6 observational studies met our inclusion criteria, which including 992292 participants. The meta-analysis indicated that the higher TyG index increased cancer risk compared to the lower TyG index group (total effect size =1.14, 95% CI [1.08, 1.20], P<0.001).

CONCLUSIONS

Our meta-analysis found that higher TyG index may increase the risk of cancer. More prospective cohort studies and basic research are warranted to verify the relationship.

Salvia miltiorrhiza bunge exerts anti-oxidative effects through inhibiting KLF10 expression in vascular smooth muscle cells exposed to high glucose

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicinal herb Salvia miltiorrhiza Bunge(Danshen) and its components have been widely used to treat cardiovascular diseases for hundreds of years in China, including hypertension, diabetes, atherosclerosis, and chronic heart failure. Salvia miltiorrhiza injection (SMI), an aqueous extracts of Salvia miltiorrhiza Bunge, is one of most widely used traditional Chinese medicine injections. SMI is widely used in the treatment of diabetic vascular complications, However, the mechanisms remain to be defined.

AIM OF THE STUDY

To investigate protective mechanism of Salvia miltiorrhiza Bunge against ROS generation in VSMCs of diabetic mice and patients.

MATERIALS AND METHODS

Salvia miltiorrhiza injection (hereinafter referred to as SMI, 1.5 g mL^-1), which was approved by the State Food and Drug Administration (approval number: Z32020161), was obtained from Shenlong Pharmaceutical Co., Ltd. (batch number: 11040314). SMI or vehicle were intraperitoneally administrated to the HFD-fed db/db mice, artery was harvested after 24weeks later. qRT-PCR and Western blot analysis were used to detect the expression of KLF6, KLF5, KLF4, KLF10, KLF12, and HO-1. DCFH-DA staining detected intracellular ROS production. Loss- and gain-of-function experiments of KLF10 were used to investigate the effect of KLF10 on the expression of HO-1. Dual-luciferase reporter assay evaluated the effect of KLF10 on the activity of the HO-1 promoter.

RESULTS

KLF10 expression and ROS generation are significantly increased in the arteries of HFD-fed db/db mice, VSMCs of diabetic patients, as well as in high glucose-treated VSMCs. KLF10 overexpression suppresses, while its knockdown facilitates the expression of heme oxygenase (HO-1) mRNA and protein. Further, Salvia miltiorrhiza injection (SMI) abrogates KLF10 upregulation and reduces ROS generation induced by high glucose in VSMCs. Mechanistically, KLF10 negatively regulates the HO-1 gene transcription via directly binding to its promoter. Accordingly, SMI treatment of VSMCs reduces ROS generation through inhibiting KLF10 expression and thus relieving KLF10 repression of the expression of HO-1 gene, subsequently contributing to upregulation of HO-1.

CONCLUSION

SMI exerts anti-oxidative effects on VSMCs exposed to high glucose through inhibiting KLF10 expression and thus upregulating HO-1.

Triglyceride-glucose index (TyG index) is a predictor of incident colorectal cancer: a population-based longitudinal study

BACKGROUND

Colorectal cancer (CRC), which is related with insulin resistance, is a one of the most common cancers. Triglyceride-glucose index (TyG index) was made for a marker of insulin resistance. We conducted the investigation of association between TyG index and incident CRC.

METHODS

We examined the affect of TyG index on incident CRC in this historical cohort study of 27,944 (16,454 men and 11,490 women) participants. TyG index was calculated as ln [fasting triglycerides (mg/dL) × fasting plasma glucose (mg/dL)/2]. The impact of TyG index on incident CRC was investigated using Cox proportional hazard models, adjusting for sex, age, body mass index, smoking status, alcohol consumption, exercise, systolic blood pressure and creatinine. The covariate-adjusted receiver operating characteristic (ROC) curve calculated the area under the curve (AUC) and cut-off value of TyG index for the incidence of CRC.

RESULTS

During the median 4.4-year follow-up, 116 participants were diagnosed as CRC. The cumulative incidence rate of CRC were 0.4%. In Cox proportional hazard model, the HRs of TyG index were 1.38 (95% Confidence interval (CI), 1.00-1.91, p = 0.049) after adjusting for covariates. In the covariate-adjusted ROC curve analysis, the cut-off value of TyG index for incident CRC was 8.272 (AUC 0.687 (95%CI, 0.637-737, sensitivity = 0.620, specificity = 0.668, p < 0.001)).

CONCLUSIONS

TyG index can predict the onset of CRC. For early detection of CRC, we should encourage people with high TyG index to undergo screening for CRC.

Regulatory Effects of O-GlcNAcylation in Vascular Smooth Muscle Cells on Diabetic Vasculopathy

Vascular complications from uncontrolled hyperglycemia are the leading cause of death in patients with diabetes mellitus. Previous reports have shown a strong correlation between hyperglycemia and vascular calcification, which increases mortality and morbidity in individuals with diabetes. However, the precise underlying molecular mechanisms of hyperglycemia-induced vascular calcification remain largely unknown. Transdifferentiation of vascular smooth muscle cells (VSMC) into osteoblast-like cells is a known culprit underlying the development of vascular calcification in the diabetic vasculature. Pathological conditions such as high glucose levels and oxidative stress are linked to enhanced osteogenic differentiation of VSMC both in vivo and in vitro. It has been demonstrated that increased expression of runt-related transcription factor 2 (Runx2), a bone-related transcription factor, in VSMC is necessary and sufficient for the induction of VSMC calcification. Addition of a single O-linked β-N-acetylglucosamine (O-GlcNAc) moiety to the serine/threonine residues of target proteins (O-GlcNAcylation) has been observed in the arteries of diabetic patients, as well as in animal models in association with the enhanced expression of Runx2 and aggravated vascular calcification. O-GlcNAcylation is a dynamic and tightly regulated process, that is mediated by 2 enzymes, O-GlcNAc transferase and O-GlcNAcase. Glucose is metabolized into UDP-β-D-N-acetylglucosamine, an active sugar donor of O-GlcNAcylation via the hexosamine biosynthetic pathway. Overall increases in the O-GlcNAcylation of cellular proteins have been closely associated with cardiovascular complications of diabetes. In this review, the authors provide molecular insights into cardiovascular complications, including diabetic vasculopathy, that feature increased O-GlcNAcylation in people with diabetes.

Hyperglycemia induces vascular smooth muscle cell dedifferentiation by suppressing insulin receptor substrate-1-mediated p53/KLF4 complex stabilization

Hyperglycemia and insulin resistance accelerate atherosclerosis by an unclear mechanism. The two factors down-regulate insulin receptor substrate-1 (IRS-1), an intermediary of the insulin/IGF-I signaling system. We previously reported that IRS-1 down-regulation leads to vascular smooth muscle cell (VSMC) dedifferentiation and that IRS-1 deletion from VSMCs in normoglycemic mice replicates this response. However, we did not determine IRS-1's role in mediating differentiation. Here, we sought to define the mechanism by which IRS-1 maintains VSMC differentiation. High glucose or IRS-1 knockdown decreased p53 levels by enhancing MDM2 proto-oncogene (MDM2)-mediated ubiquitination, resulting in decreased binding of p53 to Krüppel-like factor 4 (KLF4). Exposure to nutlin-3, which dissociates MDM2/p53, decreased p53 ubiquitination and enhanced the p53/KLF4 association and differentiation marker protein expression. IRS-1 overexpression in high glucose inhibited the MDM2/p53 association, leading to increased p53 and p53/KLF4 levels, thereby increasing differentiation. Nutlin-3 treatment of diabetic or Irs1 ^-/- mice enhanced p53/KLF4 and the expression of p21, smooth muscle protein 22 (SM22), and myocardin and inhibited aortic VSMC proliferation. Injecting normoglycemic mice with a peptide disrupting the IRS-1/p53 association reduced p53, p53/KLF4, and differentiation. Analyzing atherosclerotic lesions in hypercholesterolemic, diabetic pigs, we found that p53, IRS-1, SM22, myocardin, and KLF4/p53 levels are significantly decreased compared with their expression in nondiabetic pigs. We conclude that IRS-1 is critical for maintaining VSMC differentiation. Hyperglycemia- or insulin resistance-induced IRS-1 down-regulation decreases the p53/KLF4 association and enhances dedifferentiation and proliferation. Our results suggest that enhancing IRS-1-dependent p53 stabilization could attenuate the progression of atherosclerotic lesions in hyperglycemia and insulin-resistance states.

An anti-αVβ3 antibody inhibits coronary artery atherosclerosis in diabetic pigs

BACKGROUND AND AIMS

Diabetes is a major risk factor for the development of atherosclerosis. Hyperglycemia stimulates vascular smooth muscle cells (VSMC) to secrete ligands that bind to the αVβ3 integrin, a receptor that regulates VSMC proliferation and migration. This study determined whether an antibody that had previously been shown to block αVβ3 activation and to inhibit VSMC proliferation and migration in vitro, inhibited the development of atherosclerosis in diabetic pigs.

METHODS

Twenty diabetic pigs were maintained on a high fat diet for 22 weeks. Ten received injections of anti-β3 F(ab)₂ and ten received control F(ab)₂ for 18 weeks.

RESULTS

The active antibody group showed reduction of atherosclerosis of 91 ± 9% in the left main, 71 ± 11%, in left anterior descending, 80 ± 10.2% in circumflex, and 76 ± 25% in right coronary artery, (p < 0.01 compared to lesions areas from corresponding control treated arteries). There were significant reductions in both cell number and extracellular matrix. Histologic analysis showed neointimal hyperplasia with macrophage infiltration, calcifications and cholesterol clefts. Antibody treatment significantly reduced number of macrophages contained within lesions, suggesting that this change contributed to the decrease in lesion cellularity. Analysis of the biochemical changes within the femoral arteries that received the active antibody showed a 46 ± 12% (p < 0.05) reduction in the tyrosine phosphorylation of the β3 subunit of αVβ3 and a 40 ± 14% (p < 0.05) reduction in MAP kinase activation.

CONCLUSIONS

Blocking ligand binding to the αVβ3 integrin inhibits its activation and attenuates increased VSMC proliferation that is induced by chronic hyperglycemia. These changes result in significant decreases in atherosclerotic lesion size in the coronary arteries. The results suggest that this approach may have efficacy in treating the proliferative phase of atherosclerosis in patients with diabetes.

Soluble Urokinase Receptor and the Kidney Response in Diabetes Mellitus

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD) worldwide. DN typically manifests by glomerular hyperfiltration and microalbuminuria; then, the disease progresses to impaired glomerular filtration rate, which leads to ESRD. Treatment options for DN include the strict control of blood glucose levels and pressure (e.g., intraglomerular hypertension). However, the search for novel therapeutic strategies is ongoing. These include seeking specific molecules that contribute to the development and progression of DN to potentially interfere with these "molecular targets" as well as with the cellular targets within the kidney such as podocytes, which play a major role in the pathogenesis of DN. Recently, podocyte membrane protein urokinase receptor (uPAR) and its circulating form (suPAR) are found to be significantly induced in glomeruli and sera of DN patients, respectively, and elevated suPAR levels predicted diabetic kidney disease years before the occurrence of microalbuminuria. The intent of this review is to summarize the emerging evidence of uPAR and suPAR in the clinical manifestations of DN. The identification of specific pathways that govern DN will help us build a more comprehensive molecular model for the pathogenesis of the disease that can inform new opportunities for treatment.

Down-regulation of Insulin Receptor Substrate 1 during Hyperglycemia Induces Vascular Smooth Muscle Cell Dedifferentiation

Diabetes is a major risk factor for the development of atherosclerosis, but the mechanism by which hyperglycemia accelerates lesion development is not well defined. Insulin and insulin-like growth factor I (IGF-I) signal through the scaffold protein insulin receptor substrate 1 (IRS-1). In diabetes, IRS-1 is down-regulated, and cells become resistant to insulin. Under these conditions, the IGF-I receptor signals through an alternate scaffold protein, SHPS-1, resulting in pathophysiologic stimulation of vascular smooth muscle cell (VSMC) migration and proliferation. These studies were undertaken to determine whether IRS-1 is functioning constitutively to maintain VSMCs in their differentiated state and, thereby, inhibit aberrant signaling. Here we show that deletion of IRS-1 expression in VSMCs in non-diabetic mice results in dedifferentiation, SHPS-1 activation, and aberrant signaling and that these changes parallel those that occur in response to hyperglycemia. The mice showed enhanced sensitivity to IGF-I stimulation of VSMC proliferation and a hyperproliferative response to vascular injury. KLF4, a transcription factor that induces VSMC dedifferentiation, was up-regulated in IRS-1^-/- mice, and the differentiation inducer myocardin was undetectable. Importantly, these changes were replicated in wild-type mice during hyperglycemia. These findings illuminate a new function of IRS-1: that of maintaining cells in their normal, differentiated state. Because IRS-1 is down-regulated in states of insulin resistance that occur in response to metabolic stresses such as obesity and cytokine stimulation, the findings provide a mechanism for understanding how patients with metabolic stress and/or diabetes are predisposed to developing vascular complications.

Increased diet-induced fatty streak formation in female mice with deficiency of liver-derived insulin-like growth factor-I

The role of endocrine IGF-I for atherosclerosis is unclear. We determined the importance of circulating, liver-derived IGF-I for fatty streak formation in mice. Mice with adult, liver-specific IGF-I inactivation (LI-IGF-I(-/-) mice, serum IGF-I reduced by approximately 80 %) and control mice received an atherogenic (modified Paigen) diet between 6 and 12 months of age. At study end, Oil Red O staining of aortic root cryosections showed increased fatty streak area and lipid deposition in female but not in male LI-IGF-I(-/-) mice compared to controls. Mac-2 staining of aortic root and measurements of CD68 mRNA level in femoral artery revealed increased macrophage accumulation in proportion to the increased fatty streak area in female LI-IGF-I(-/-) mice. Moreover, female LI-IGF-I(-/-) mice displayed increased serum cholesterol and interleukin-6 as well as increased vascular cell-adhesion molecule 1 (VCAM1) mRNA levels in the femoral artery and elevated VCAM1 protein expression in the aortic root. Thus, increased diet-induced fatty streak formation in female LI-IGF-I(-/-) mice was associated with increased serum cholesterol and signs of systemic inflammation, endothelial activation, lipid deposition, and macrophage infiltration in the vascular wall.

Blocking ligand occupancy of the αVβ3 integrin inhibits the development of nephropathy in diabetic pigs

Hyperglycemia stimulates secretion of αVβ3 ligands from vascular cells, including endothelial cells, resulting in activation of the αVβ3 integrin. This study determined whether blocking ligand occupancy of αVβ3 would inhibit the development of diabetic nephropathy. Ten diabetic pigs received an F(ab)2 fragment of an antibody directed against the extracellular domain of the β3-subunit, and 10 received a control IgG F(ab)2 for 18 weeks. Nondiabetic pigs excreted 115 ± 50 μg of protein/mg creatinine compared with control F(ab)2-treated diabetic animals (218 ± 57 μg/mg), whereas diabetic animals treated with the anti-β3 F(ab)2 excreted 119 ± 55 μg/mg (P < .05). Mesangial volume/glomerular volume increased to 21 ± 2.4% in control-treated diabetic animals compared with 14 ± 2.8% (P < .01) in animals treated with active antibody. Diabetic animals treated with control F(ab)2 had significantly less glomerular podocin staining compared with nondiabetic animals, and this decrease was attenuated by treatment with anti-β3 F(ab)2. Glomerular basement membrane thickness was increased in the control, F(ab)2-treated diabetic animals (212 ± 14 nm) compared with nondiabetic animals (170 ± 8.8 nm), but it was unchanged (159.9 ± 16.4 nm) in animals receiving anti-β3 F(ab)2. Podocyte foot process width was greater in control, F(ab)2-treated, animals (502 ± 34 nm) compared with animals treated with the anti-β3 F(ab)2 (357 ± 47 nm, P < .05). Renal β3 tyrosine phosphorylation decreased from 13 934 ± 6437 to 6730 ± 1524 (P < .01) scanning units in the anti-β3-treated group. We conclude that administration of an antibody that inhibits activation of the β3-subunit of αVβ3 that is induced by hyperglycemia attenuates proteinuria and early histologic changes of diabetic nephropathy, suggesting that it may have utility in preventing the progression of this disease complication.

Interaction between insulin-like growth factor-1 and atherosclerosis and vascular aging

The process of vascular aging encompasses alterations in the function of endothelial (ECs) and vascular smooth muscle cells (VSMCs) via oxidation, inflammation, cell senescence and epigenetic modifications, increasing the probability of atherosclerosis. Aged vessels exhibit decreased endothelial antithrombogenic properties, increased reactive oxygen species generation, inflammatory signaling and migration of VSMCs to the subintimal space, impaired angiogenesis and increased elastin degradation. The key initiating step in atherogenesis is subendothelial accumulation of apolipoprotein B-containing low-density lipoproteins resulting in activation of ECs and recruitment of monocytes. Activated ECs secrete 'chemokines' that interact with cognate chemokine receptors on monocytes and promote directional migration. Recruitment of immune cells establishes a proinflammatory status, further causing elevated oxidative stress, which in turn triggers a series of events including apoptotic or necrotic death of vascular and nonvascular cells. Increased oxidative stress is also considered to be a key factor in mechanisms of aging-associated changes in tissue integrity and function. Experimental evidence indicates that insulin-like growth factor-1 exerts antioxidant, anti-inflammatory and pro-survival effects on the vasculature, reducing atherosclerotic plaque burden and promoting features of atherosclerotic plaque stability.

Blocking αVβ3 integrin ligand occupancy inhibits the progression of albuminuria in diabetic rats

This study determined if blocking ligand occupancy of the αVβ3 integrin could inhibit the pathophysiologic changes that occur in the early stages of diabetic nephropathy (DN). Diabetic rats were treated with either vehicle or a monoclonal antibody that binds the β3 subunit of the αVβ3 integrin. After 4 weeks of diabetes the urinary albumin to creatinine ratio (UACR) increased in both diabetic animals that subsequently received vehicle and in the animals that subsequently received the anti-β3 antibody compared with control nondiabetic rats. After 8 weeks of treatment the UACR continued to rise in the vehicle-treated rats; however it returned to levels comparable to control nondiabetic rats in rats treated with the anti-β3 antibody. Treatment with the antibody prevented the increase of several profibrotic proteins that have been implicated in the development of DN. Diabetes was associated with an increase in phosphorylation of the β3 subunit in kidney homogenates from diabetic animals, but this was prevented by the antibody treatment. This study demonstrates that, when administered after establishment of early pathophysiologic changes in renal function, the anti-β3 antibody reversed the effects of diabetes normalizing albuminuria and profibrotic proteins in the kidney to the levels observed in nondiabetic control animals.

Dysregulation of the Mammalian Target of Rapamycin and p27Kip1 Promotes Intimal Hyperplasia in Diabetes Mellitus

The proliferation and migration of vascular smooth muscle cells (VSMCs) in the intima of an artery, known as intimal hyperplasia, is an important component of cardiovascular diseases. This is seen most clearly in the case of in-stent restenosis, where drug eluting stents are used to deliver agents that prevent VSMC proliferation and migration. One class of agents that are highly effective in the prevention of in-stent restenosis is the mammalian Target of Rapamycin (mTOR) inhibitors. Inhibition of mTOR blocks protein synthesis, cell cycle progression, and cell migration. Key to the effects on cell cycle progression and cell migration is the inhibition of mTOR-mediated degradation of p27Kip1 protein. p27Kip1 is a cyclin dependent kinase inhibitor that is elevated in quiescent VSMCs and inhibits the G1 to S phase transition and cell migration. Under normal conditions, vascular injury promotes degradation of p27Kip1 protein in an mTOR dependent manner. Recent reports from our lab suggest that in the presence of diabetes mellitus, elevation of extracellular signal response kinase activity may promote decreased p27Kip1 mRNA and produce a relative resistance to mTOR inhibition. Here we review these findings and their relevance to designing treatments for cardiovascular disease in the presence of diabetes mellitus.

Enhanced platelet activity and thrombosis in a murine model of type I diabetes are partially insulin-like growth factor 1-dependent and phosphoinositide 3-kinase-dependent

OBJECTIVES

To determine whether dysregulation of platelet signaling mechanisms contributes to the increased risk of thrombosis associated with diabetes, using a type I diabetes mouse model.

METHODS AND RESULTS

Type I diabetes was induced in C57Bl6 mice following streptozotocin injection. Arterial thrombosis, platelet signaling and function were assessed 4 weeks later in comparison with non-diabetic control mice. Fifty-seven per cent of diabetic mice (glucose level of > 250 mg dL(-1) ) developed stable occlusive thrombi after FeCl3 injury, as compared with 5% of their non-diabetic counterparts, suggesting that diabetic mice are more sensitive to arterial injury (P ≤ 0.02). Platelets from diabetic mice were more sensitive to protease-activated receptor 4 (PAR4) agonist-induced fibrinogen binding than platelets from non-diabetic mice, and the average Akt phosphorylation induced by PAR4 agonist peptide was greater (P ≤ 0.01) in platelets from diabetic mice. Recent studies suggest that insulin-like growth factor 1 (IGF-1) potentiates Akt phosphorylation in platelets. To determine whether IGF-1 signaling contributes to the increase in PAR4 sensitivity in platelets from diabetic mice, platelet signaling and function were evaluated in the presence of inhibitors of the IGF-1 receptor. IGF-1 receptor inhibition reduced Akt phosphorylation and fibrinogen binding in platelets from diabetic mice to levels consistent with those seen in normoglycemic platelets, but had no significant effect on platelets from non-diabetic mice.

CONCLUSIONS

The results suggest that platelets from mice with streptozotocin-induced diabetes show enhanced platelet Akt phosphorylation and activity resulting from IGF-1-dependent mechanisms. Increases in platelet Akt activation may explain the enhanced sensitivity to thrombotic insult seen in diabetic mice.

Aging, atherosclerosis, and IGF-1

Insulin-like growth factor 1 (IGF-1) is an endocrine and autocrine/paracrine growth factor that circulates at high levels in the plasma and is expressed in most cell types. IGF-1 has major effects on development, cell growth and differentiation, and tissue repair. Recent evidence indicates that IGF-1 reduces atherosclerosis burden and improves features of atherosclerotic plaque stability in animal models. Potential mechanisms for this atheroprotective effect include IGF-1-induced reduction in oxidative stress, cell apoptosis, proinflammatory signaling, and endothelial dysfunction. Aging is associated with increased vascular oxidative stress and vascular disease, suggesting that IGF-1 may exert salutary effects on vascular aging processes. In this review, we will provide a comprehensive update on IGF-1's ability to modulate vascular oxidative stress and to limit atherogenesis and the vascular complications of aging.

Disruption of the association of integrin-associated protein (IAP) with tyrosine phosphatase non-receptor type substrate-1 (SHPS)-1 inhibits pathophysiological changes in retinal endothelial function in a rat model of diabetes

AIMS/HYPOTHESIS

We have previously shown that the association of integrin-associated protein (IAP) with tyrosine phosphatase non-receptor type substrate-1 (SHPS-1) regulates the response of cells, including osteoclasts, osteoblasts, smooth muscle and retinal endothelial cells, to IGF-I. Here we sought to: (1) determine whether the regulation of IGF-I responsiveness by the association of IAP with SHPS-1 is a generalised response of endothelial cells; (2) identify the mechanism by which this association contributes to changes in endothelial cell responses to IGF-I; and (3) determine whether inhibition of this association alters pathophysiological changes occurring in vivo.

METHODS

Endothelial cells were maintained in 5 mmol/l glucose and at hyperglycaemic levels, and exposed to an anti-IAP antibody that disrupts the association between IAP and SHPS-1. A rodent model of diabetes with endothelial cell dysfunction was used to investigate the role of the association of IAP with SHPS-1 in endothelial cell function in vivo.

RESULTS

Endothelial cells maintained in 5 mmol/l glucose showed constitutive cleavage of the extracellular domain of IAP (which contains the SHPS-1 binding site), with no association between IAP and SHPS-1 being detected. In contrast, hyperglycaemia inhibited IAP cleavage, allowing IAP to associate with SHPS-1 and IGF-I to stimulate SHPS-1 tyrosine phosphorylation. Exposure to the anti-IAP antibody inhibited IGF-I-stimulated tube formation and increased permeability. In the rodent model, basal IAP-SHPS-1 association was not detected in retinal extracts from normal rats, but was fully restored in rats with diabetes. The anti-IAP antibody inhibited the association of IAP with SHPS-1, and reduced retinal vascular permeability and leucocyte adherence to levels similar to those in non-diabetic rats. The antibody also significantly inhibited the aberrant neovascularisation induced by hypoxia.

CONCLUSIONS/INTERPRETATION

Our results demonstrate that the increased association of IAP with SHPS-1 contributes to the pathophysiological changes in the endothelium that are induced by hyperglycaemia and hypoxia.

Hyperglycemia enhances IGF-I-stimulated Src activation via increasing Nox4-derived reactive oxygen species in a PKCζ-dependent manner in vascular smooth muscle cells

IGF-I-stimulated sarcoma viral oncogene (Src) activation during hyperglycemia is required for propagating downstream signaling. The aim of the current study was to determine the mechanism by which hyperglycemia enhances IGF-I-stimulated Src activation and the role of NADPH oxidase 4 (Nox4) and protein kinase C ζ (PKCζ) in mediating this response in vascular smooth muscle cells (VSMCs). Nox4 expression was analyzed in VSMCs exposed to hyperglycemia. The role of Nox4-derived reactive oxygen species (ROS) in IGF-I-stimulated Src activation was investigated via knockdown of Nox4. Different isoforms of PKC were screened to investigate their role in hyperglycemia-induced Nox4. The oxidation of Src was shown to be a prerequisite for its activation in response to IGF-I during hyperglycemia. Hyperglycemia induced Nox4, but not Nox1, and p22 phagocyte oxidase (p22phox) expression and IGF-I stimulated Nox4/p22phox complex formation, leading to increased ROS generation. Knockdown of Nox4 prevented ROS generation and impaired the oxidation and activation of Src in response to IGF-I, whereas knockdown of Nox1 had no effect. PKCζ was shown to mediate the hyperglycemia-induced increase in Nox4 expression. The key observations in cultured VSMCs were confirmed in the diabetic mice. Nox4-derived ROS is responsible for the enhancing effect of hyperglycemia on IGF-I-stimulated Src activation, which in turn amplifies IGF-I-linked downstream signaling and biological actions.

Suppression of AMPK activation via S485 phosphorylation by IGF-I during hyperglycemia is mediated by AKT activation in vascular smooth muscle cells

As a metabolic sensor, the serine/threonine protein kinase AMP-activated protein kinase (AMPK) promotes the adaptation of cells to signals arising from nutrients, hormones, and growth factors. The ability of IGF-I to stimulate protein synthesis is suppressed by AMPK, therefore, these studies were undertaken to determine whether IGF-I modulates AMPK activity. IGF-I dose-dependently suppressed phosphorylation of AMPK T172, and it stimulated AMPK S485 phosphorylation in vascular smooth muscle cells (VSMC). To determine whether stimulation of AMPK S485 phosphorylation was mediating this response, VSMC were transduced with a mutant AMPKα (AMPK S485A). Expression of this altered form inhibited the ability of IGF-I to suppress AMPK T172 activation, which resulted in inhibition of IGF-I-stimulated phosphorylation of P70S6 kinase. In contrast, expression of an AMPK S485D mutant resulted in constitutive suppression of AMPK activity and was associated with increased IGF-I-stimulated P70S6K phosphorylation and protein synthesis. The addition of a specific AKT inhibitor or expression of an AKT1 short hairpin RNA inhibited AMPK S485 phosphorylation, and it attenuated the IGF-I-induced decrease in AMPK T172 phosphorylation. Exposure to high glucose concentrations suppressed AMPK activity and stimulated S485 phosphorylation, and IGF-I stimulated a further increase in S485 phosphorylation and AMPK T172 suppression. We conclude that AMPK S485 phosphorylation negatively regulates AMPK activity by modulating the T172 phosphorylation response to high glucose and IGF-I. IGF-I stimulates S485 phosphorylation through AKT1. The results suggest that AMPK plays an inhibitory role in modulating IGF-I-stimulated protein synthesis and that IGF-I must down-regulate AMPK activity to induce an optimal anabolic response.

IGF-I stimulates cooperative interaction between the IGF-I receptor and CSK homologous kinase that regulates SHPS-1 phosphorylation in vascular smooth muscle cells

IGF-I plays an important role in smooth muscle cell proliferation and migration. In vascular smooth muscle cells cultured in 25 mm glucose, IGF-I stimulated a significant increase in Src homology 2 domain containing protein tyrosine phosphatase substrate-1 (SHPS-1) phosphorylation compared with 5 mm glucose and this increase was required for smooth muscle cell proliferation. A proteome-wide screen revealed that carboxyl-terminal SRC kinase homologous kinase (CTK) bound directly to phosphotyrosines in the SHPS-1 cytoplasmic domain. Because the kinase(s) that phosphorylates these tyrosines in response to IGF-I is unknown, we determined the roles of IGF-I receptor (IGF-IR) and CTK in mediating SHPS-1 phosphorylation. After IGF-I stimulation, CTK was recruited to IGF-IR and subsequently to phospho-SHPS-1. Expression of an IGF-IR mutant that eliminated CTK binding reduced CTK transfer to SHPS-1, SHPS-1 phosphorylation, and cell proliferation. IGF-IR phosphorylated SHPS-1, which provided a binding site for CTK. CTK recruitment to SHPS-1 resulted in a further enhancement of SHPS-1 phosphorylation. CTK knockdown also impaired IGF-I-stimulated SHPS-1 phosphorylation and downstream signaling. Analysis of specific tyrosines showed that mutation of tyrosines 428/452 in SHPS-1 to phenylalanine reduced SHPS-1 phosphorylation but allowed CTK binding. In contrast, the mutation of tyrosines 469/495 inhibited IGF-IR-mediated the phosphorylation of SHPS-1 and CTK binding, suggesting that IGF-IR phosphorylated Y469/495, allowing CTK binding, and that CTK subsequently phosphorylated Y428/452. Based on the above findings, we conclude that after IGF-I stimulation, CTK is recruited to IGF-IR and its recruitment facilitates CTK's subsequent association with phospho-SHPS-1. This results in the enhanced CTK transfer to SHPS-1, and the two kinases then fully phosphorylate SHPS-1, which is necessary for IGF-I stimulated cellular proliferation.

Betulinic acid inhibits high glucose-induced vascular smooth muscle cells proliferation and migration

The proliferation of vascular smooth muscle cells may perform a crucial role in the pathogenesis of diabetic vascular disease. The principal objective of this study was to determine the effects of betulinic acid (BA) on human aortic smooth muscle cell (HASMC) proliferation induced by high glucose (HG). In this study, [(3) H]-thymidine incorporation under 25 mM HG was accelerated significantly as compared with 5.5 mM glucose, and this increase was inhibited significantly by BA treatment. We utilized Western blotting analysis to evaluate the effects of BA on cell-cycle regulatory proteins. HG induced the expression of cyclins/CDKs and reduced the expression of p21(waf1/cip1) /p27(kip1). However, BA also attenuated the expression of HG-induced cell-cycle regulatory proteins. The results of gelatin zymography demonstrated that the HG-treated HASMC secreted gelatinases, probably including MMP-2/-9, which may be involved in the invasion and migration of HASMC. Additionally, BA suppressed the protein and mRNA expression levels of MMP-2/-9 in a dose-dependent manner. BA inhibited the production of HG-induced hydrogen peroxide (H(2)O(2)) and the formation of DCF-sensitive intracellular reactive oxygen species (ROS). Further, BA suppressed the nuclear translocation and phosphorylation of IκB-α of NF-κB under HG conditions. Our results showed that BA exerts multiple effects on HG-induced HASMC proliferation and migration, including the inhibition of both MMP-2 and MMP-9 transcription, protein activity, and the downregulation of ROS/NF-κB signaling, thereby suggesting that BA may be a possible therapeutic approach to the inhibition of diabetic vascular disease.

Loss of canonical insulin signaling accelerates vascular smooth muscle cell proliferation and migration through changes in p27Kip1 regulation

Insulin resistance is associated with an accelerated rate of atherosclerosis. Vascular smooth muscle cell (VSMC) migration and proliferation are important components of atherosclerosis. To elucidate the effects of the loss of normal insulin receptor (IR) signaling on VSMC function, we compared the proliferation and migration of murine VSMCs lacking the IR (L2-VSMCs) with wild type (WT-VSMCs). We also examined changes in the response of L2-VSMCs to insulin stimulation and to inhibition of the mammalian target of rapamycin (mTOR), a kinase critical in VSMC proliferation and migration. The L2-VSMCs exhibit greater proliferation and migration rates compared with WT-VSMCs. L2-VSMCs also exhibit a resistance to the effects of rapamycin, an mTOR inhibitor, on proliferation, migration, and cell cycle progression. The resistance to mTOR inhibition is coupled with a loss of effect on the cyclin-dependent kinase inhibitor p27(Kip1), an inhibitor of cell cycle progression and VSMC migration. In response to stimulation with physiological insulin, the L2-VSMCs exhibit a loss of Akt phosphorylation and a significantly increased activation of the ERK-1/2 compared with WT-VSMCs. Insulin stimulation also decreased p27(Kip1) mRNA in L2-VSMCs but not in WT-VSMCs. The effect of insulin on p27(Kip1) mRNA was blocked by pretreatment with an ERK-1/2 pathway inhibitor. We conclude that loss of canonical insulin signaling results in increased ERK-1/2 activation in response to physiological insulin that decreases p27(Kip1) mRNA. These data demonstrate a potential mechanism where changes in IR signaling could lead to a decrease in p27(Kip1), accelerating VSMC proliferation and migration.

SDF-1α/CXCR4 axis is involved in glucose-potentiated proliferation and chemotaxis in rat vascular smooth muscle cells

Excessive proliferation of vascular smooth muscle cells (VSMCs), which migrate from the tunica media to the subendothelial region, is one of the primary lesions involved in atherogenesis in diabetes. Here, we investigated whether high glucose potentiated the proliferation and chemotaxis of VSMCs by activating SDF-1α/CXCR4/PI-3K/Akt signalling. The expression of SDF-1α, CXCR4 and PCNA was up-regulated in tunica media of thoracic aortas by streptozotocin-induced hyperglycaemic Sprague-Dawley rats. Exposure of primary VSMCs to high glucose (25 mM) led to the up-regulated expression of SDF-1α and CXCR4, activated PI-3K/Akt signalling, and consequently promoted the proliferation and chemotaxis of VSMCs. Interestingly, the administration of SDF-1 siRNA or neutralizing antibody against SDF-1α abolished high glucose-induced up-regulation of CXCR4. Moreover, pretreatment with SDF-1α neutralizing antibody, CXCR4 specific inhibitor (AMD3100) or PI-3K inhibitor (LY294002) attenuated the high glucose-potentiated proliferation and chemotaxis in VSMCs. These results suggested that high glucose activated the SDF-1α/CXCR4/PI-3K/Akt signalling pathway in VSMCs in an autocrine manner, which enhanced the proliferation and chemotaxis of VSMCs.

Aldosterone enhances IGF-I-mediated signaling and biological function in vascular smooth muscle cells

The IGF-I pathway and renin-angiotensin-aldosterone axis are both involved in the pathogenesis of hypertension and atherosclerosis, but no information is available about IGF-I and aldosterone interaction or their potential synergistic effects in vascular smooth muscle cells (VSMCs). The aims of this study were to investigate whether aldosterone influences IGF-I signaling and to determine the mechanism(s) by which aldosterone affects IGF-I function. Aldosterone resulted in significant increases in the Akt (1.87 ± 0.24, P < 0.001), MAPK (1.78 ± 0.13, P < 0.001), p70S6kinase (1.92 ± 0.15, P < 0.001), IGF-I receptor (1.69 ± 0.05, P < 0.01), and insulin receptor substrate-1 (1.7 ± 0.04, P < 0.01) (fold increase, mean ± SEM, n = 3) phosphorylation responses to IGF-I compared with IGF-I treatment alone. There were also significant increases in VSMC proliferation, migration, and protein synthesis (1.63 ± 0.03-, 1.56 ± 0.08-, and 1.51 ± 0.04-fold increases compared with IGF-I alone, respectively, n = 3, P < 0.001). Aldosterone induced osteopontin (OPN) mRNA expression and activation of αVβ3-integrin as well as an increase in the synthesis of IGF-I receptor. The enhancing effects of aldosterone were inhibited by eplerenone (10 μmol/liter), actinomycin-D (20 nmol/liter), and an anti-αVβ3-integrin antibody that blocks OPN binding. The antioxidant N-acetylcysteine (2 mmol/liter) completely inhibited the ability of aldosterone to induce any of these changes. In conclusion, our results show that aldosterone enhances IGF-I signaling and biological actions in VSMCs through induction of OPN followed by its subsequent activation of the αVβ3-integrin and by increasing IGF-I receptor. These changes are mediated in part through increased oxidative stress. The findings suggest a new mechanism by which aldosterone could accelerate the development of atherosclerosis.

Recruitment of Pyk2 to SHPS-1 signaling complex is required for IGF-I-dependent mitogenic signaling in vascular smooth muscle cells

In vascular smooth muscle cells, IGF-I stimulates SHPS-1/SHP2/Src complex formation which is required for IGF-I-stimulated cell proliferation. Using SHP2/Src silencing and a Pyk2/Y402F mutant, we showed that Pyk2 was also recruited to the SHPS-1 complex. Pyk2 recruitment to SHPS-1 is mediated via the interaction of Pyk2 Tyr402 and the Src in response to IGF-I. Following Src/Pyk2 association, Src phosphorylates Pyk2 on Tyr881 providing a binding site for Grb2. Cells expressing Pyk2/Y881F showed decreased Grb2 recruitment to SHPS-1 and impaired Shc/Grb2 association. This change led to reduced Erk1/2 (MAP kinase) activation and cell proliferation in response to IGF-I. Our results show that, following its recruitment to the SHPS-1 signaling complex, Pyk2 localizes Grb2 in close proximity to Shc thereby facilitating Shc/Grb2 association which leads to Erk1/2 activation in response to IGF-I. Thus, Pyk2 recruitment to SHPS-1 plays an important role in regulating the IGF-I-stimulated mitogenic response.

PDK1 recruitment to the SHPS-1 signaling complex enhances insulin-like growth factor-i-stimulated AKT activation and vascular smooth muscle cell survival

In vascular smooth muscle cells, exposed to hyperglycemia and insulin-like growth factor-I (IGF-I), SHPS-1 functions as a scaffold protein, and a signaling complex is assembled that leads to AKT activation. However, the underlying mechanism by which formation of this complex activates the kinase that phosphorylates AKT (Thr(308)) is unknown. Therefore, we investigated the mechanism of PDK1 recruitment to the SHPS-1 signaling complex and the consequences of disrupting PDK1 recruitment for downstream signaling. Our results show that following IGF-I stimulation, PDK1 is recruited to SHPS-1, and its recruitment is mediated by Grb2, which associates with SHPS-1 via its interaction with Pyk2, a component of the SHPS-1-associated complex. A proline-rich sequence in PDK1 bound to an Src homology 3 domain in Grb2 in response to IGF-I. Disruption of Grb2-PDK1 by expression of either a Grb2 Src homology 3 domain or a PDK1 proline to alanine mutant inhibited PDK1 recruitment to SHPS-1, leading to impaired IGF-I-stimulated AKT Thr(308) phosphorylation. Following its recruitment to SHPS-1, PDK1 was further activated via Tyr(373/376) phosphorylation, and this was required for a maximal increase in PDK1 kinase activity and AKT-mediated FOXO3a Thr(32) phosphorylation. PDK1 recruitment was also required for IGF-I to prevent apoptosis that occurred in response to hyperglycemia. Assembly of the Grb2-PDK1 complex on SHPS-1 was specific for IGF-I signaling because inhibiting PDK1 recruitment to SHPS-1 had no effect on EGF-stimulated AKT Thr(308) phosphorylation. These findings reveal a novel mechanism for recruitment of PDK1 to the SHPS-1 signaling complex, which is required for IGF-I-stimulated AKT Thr(308) phosphorylation and inhibition of apoptosis.

A monoclonal antibody against alphaVbeta3 integrin inhibits development of atherosclerotic lesions in diabetic pigs

Atherosclerotic lesions develop and progress more rapidly in diabetic patients than in nondiabetic individuals. This may be caused by accelerated lesion formation in the high-glucose environment of diabetes. Smooth muscle cells (SMCs) cultured in high glucose are more responsive to growth factors such as insulin-like growth factor-1 (IGF-1). This enhanced response to IGF-1 is due in part to increased activation of the alpha(V)beta(3) integrin. We tested whether alpha(V)beta(3) integrin activation was increased in diabetic animals and whether an antibody to beta(3) would inhibit IGF-1 action and development of atherosclerosis. Eight male pigs were made diabetic with streptozotocin and fed a high-fat diet. A F(ab)(2) antibody fragment directed at beta(3) was infused into one femoral artery, whereas the other artery received control F(ab)(2) for 3.5 months. There was a 65 +/- 8% reduction in atherosclerotic lesion area in the arteries treated with F(ab)(2) antibody to beta(3). Phosphorylation of beta(3) was reduced by 75 +/- 18% in vessels treated with the antibody. Shc and mitogen-activated protein kinase phosphorylation, which are required for IGF-1-stimulated SMC proliferation, were also significantly reduced. We conclude that activation of IGF-1 receptor and alpha(V)beta(3)-linked signaling pathways accelerates atherosclerosis in diabetes and that administration of an antibody to beta(3) to diabetic pigs inhibits alpha(V)beta(3) activation, IGF-1-stimulated signaling, and atherosclerotic lesion development. This approach offers a potential therapeutic approach to the treatment of this disorder.

Hyperglycemia-induced p66shc inhibits insulin-like growth factor I-dependent cell survival via impairment of Src kinase-mediated phosphoinositide-3 kinase/AKT activation in vascular smooth muscle cells

Hyperglycemia has been shown to induce the p66shc expression leading to increased reactive oxygen species (ROS) generation and apoptosis. In the present study, we demonstrated that hyperglycemia induced p66shc expression in vascular smooth muscle cells. This induction was associated with an increase in apoptosis as assessed by the increase of capspase-3 enzymatic activity, cleaved caspase-3 protein, and the number of dead cells. The ability of IGF-I to inhibit apoptosis was also attenuated. Further studies showed that hyperglycemia-induced p66shc inhibited IGF-I-stimulated phosphoinositide (PI)-3 kinase and AKT activation. Mechanistic studies showed that knockdown of p66shc enhanced IGF-I-stimulated SHPS-1/p85, p85/SHP-2, and p85/Grb2 association, all of which are required for PI-3 kinase/AKT activation. These responses were attenuated by overexpression of p66shc. IGF-I-stimulated p85 and AKT recruitment to the cell membrane fraction was altered in the same manner. Disruption of p66shc-Src interaction using either a blocking peptide or by expressing a p66shc mutant that did not bind to Src rescued IGF-I-stimulated PI-3 kinase/AKT activation as well as IGF-I-dependent cell survival. Although the highest absolute level of ROS was detected in p66shc-overexpressing cells, the relative increase in ROS induced by hyperglycemia was independent of p66shc expression. Taken together, our data suggest that the increase in p66shc that occurs in response to hyperglycemia is functioning to inhibit IGF-I-stimulated signaling and that the incremental increase in SMC sensitivity to IGF-I stimulation that occurs in response to p66shc induction of ROS is not sufficient to overcome the inhibitory effect of p66shc on Src kinase activation.

Smooth muscle cell-specific insulin-like growth factor-1 overexpression in Apoe-/- mice does not alter atherosclerotic plaque burden but increases features of plaque stability

OBJECTIVE

Growth factors may play a permissive role in atherosclerosis initiation and progression, in part via their promotion of vascular smooth muscle cell (VSMC) accumulation in plaques. However, unstable human plaques often have a relative paucity of VSMC, which has been suggested to contribute to plaque rupture and erosion and to clinical events. Insulin-like growth factor-1 (IGF-1) is an endocrine and autocrine/paracrine growth factor that is a mitogen for VSMC, but when infused into Apoe(-/-) mice it paradoxically reduces atherosclerosis burden.

METHODS AND RESULTS

To determine the effect of stimulation of VSMC growth on atherosclerotic plaque development and to understand mechanisms of IGF-1's atheroprotective effect, we assessed atherosclerotic plaques in mice overexpressing IGF-1 in smooth muscle cells (SMC) under the control of the α-smooth muscle actin promoter, after backcrossing to the Apoe(-/-) background (SMP8/Apoe(-/-)). Compared with Apoe(-/-) mice, these SMP8/Apoe(-/-) mice developed a comparable plaque burden after 12 weeks on a Western diet, suggesting that the ability of increased circulating IGF-1 to reduce plaque burden was mediated in large part via non-SMC target cells. However, advanced plaques in SMP8/Apoe(-/-) mice displayed several features of plaque stability, including increased fibrous cap area, α-smooth muscle actin-positive SMC and collagen content, and reduced necrotic cores.

CONCLUSIONS

These findings indicate that stimulation of VSMC IGF-1 signaling does not alter total atherosclerotic plaque burden and may improve atherosclerotic plaque stability.

Glucose regulation of thrombospondin and its role in the modulation of smooth muscle cell proliferation

Smooth muscle cells (SMC) maintained in high glucose are more responsive to IGF-I than those in normal glucose. There is significantly more thrombospondin-1 (TSP-1) in extracellular matrix surrounding SMC grown in 25 mM glucose. In this study we investigated 1) the mechanism by which glucose regulates TSP-1 levels and 2) the mechanism by which TS-1 enhances IGF-I signaling. The addition of TSP-1 to primary SMC was sufficient to enhance IGF-I responsiveness in normal glucose. Reducing TSP-1 protein levels inhibited IGF-I signaling in SMC maintained in high glucose. We determined that TSP-1 protected IAP/CD47 from cleavage and thereby facilitated its association with SHP substrate-1 (SHPS-1). We have shown previously that the hyperglycemia induced protection of IAP from cleavage is an important component of the ability of hyperglycemia to enhance IGF-I signaling. Furthermore we determined that TSP-1 also enhanced phosphorylation of the beta3 subunit of the alphaVbeta3 integrin, another molecular event that we have shown are critical for SMC response to IGF-I in high glucose. Our studies also revealed that the difference in the amount of TSP-1 in the two different glucose conditions was due, at least in part, to a difference in the cellular uptake and degradation of TSP-1.

Buddleja officinalis suppresses high glucose-induced vascular smooth muscle cell proliferation: role of mitogen-activated protein kinases, nuclear factor-kappaB and matrix metalloproteinases

Diabetes mellitus is a well-established risk factor for vascular diseases caused by atherosclerosis. In the development of diabetic atherogenesis, vascular smooth muscle cell proliferation is recognized as a key event. Thus, we aimed to investigate whether an ethanol extract of Buddleja officinalis (EBO) suppresses high glucose-induced proliferation in primary cultured human aortic smooth muscle cells (HASMC). [(3)H]-thymidine incorporation revealed that incubation of HASMC with a high concentration of glucose (25 mmol/L) increased cell proliferation. The expression levels of cell cycle protein were also increased by treatment with high glucose concentration. Pretreatment of HASMC with EBO significantly attenuated the increase of high glucose-induced cell proliferation as well as p38 mitogen-activated protein kinases (MAPK) and JNK phosphorylation. EBO suppressed high glucose-induced matrix metalloproteinase (MMP)-9 activity in a dose-dependent manner. In addition, EBO suppressed nuclear factor-kappaB (NF-kappaB) nuclear translocation and transcriptional activity in high glucose conditions. Taken together, the present data suggest that EBO could suppress high glucose-induced atherosclerotic processes through inhibition of p38, JNK, NF-kappaB and MMP signal pathways in HASMC.

IGF-1, oxidative stress and atheroprotection

Atherosclerosis is a chronic inflammatory disease in which early endothelial dysfunction and subintimal modified lipoprotein deposition progress to complex, advanced lesions that are predisposed to erosion, rupture and thrombosis. Oxidative stress plays a crucial role not only in initial lesion formation but also in lesion progression and destabilization. Although most growth factors are thought to promote vascular smooth muscle cell proliferation and migration, thereby increasing neointima, recent animal studies indicate that insulin-like growth factor (IGF)-1 exerts both pleiotropic anti-oxidant effects and anti-inflammatory effects, which together reduce atherosclerotic burden. This review discusses the effects of IGF-1 in models of vascular injury and atherosclerosis, emphasizing the relationship between oxidative stress and potential atheroprotective actions of IGF-1.

Insulin-like growth factor-I-stimulated insulin receptor substrate-1 negatively regulates Src homology 2 domain-containing protein-tyrosine phosphatase substrate-1 function in vascular smooth muscle cells

Vascular smooth muscle cells maintained in normal (5.6 mm) glucose respond to insulin-like growth factor-I (IGF-I) with increased protein synthesis but do not proliferate. In contrast, hyperglycemia alters responsiveness to IGF-I, resulting in increased SHPS-1 phosphorylation and assembly of a signaling complex that enhances MAPK and phosphatidylinositol 3-kinase pathways. Hyperglycemia also reduces the basal IRS-1 concentration and IGF-I-stimulated IRS-1-linked signaling. To determine if failure to down-regulate IRS-1 alters vascular smooth muscle cell (VSMC) responses to IGF-I, we overexpressed IRS-1 in VSMCs maintained in high glucose. These cultures showed reduced SHPS-1 phosphorylation, transfer of SHP-2 to SHPS-1, and impaired Shc and MAPK phosphorylation and cell proliferation in response to IGF-I. In vitro studies demonstrated that SHPS-1 was a substrate for type I IGF receptor (IGF-IR) and that IRS-1 competitively inhibited SHPS-1 phosphorylation. Exposure of VSMC cultures to a peptide that inhibited IRS-1/IGF-IR interaction showed that IRS-1 binding to IGF-IR impairs SHPS-1 phosphorylation in vivo. IRS-1 also sequestered SHP-2. Expression of an IRS-1 mutant (Y1179F/Y1229F) reduced IRS-1/SHP-2 association, and exposure of cells expressing the mutant to the inhibitory peptide enhanced SHPS-1 phosphorylation and SHP-2 transfer. This result was confirmed by expressing an IRS-1 mutant that had both impaired binding to IGF-IR and to SHP-2 IGF-I increased SHPS-1 phosphorylation, SHP-2 association with SHPS-1, Shc MAPK phosphorylation, and proliferation in cells expressing the mutant. We conclude that IRS-1 is an important factor for maintaining VSMCs in the non-proliferative state and that its down-regulation is a component of the VSMC response to hyperglycemic stress that results in an enhanced response to IGF-I.

Enhanced proliferation and migration of vascular smooth muscle cells in response to vascular injury under hyperglycemic conditions is controlled by beta3 integrin signaling

Atheroma formation and restenosis following percutaneous vascular intervention involve the growth and migration of vascular smooth muscle cells (SMCs) into neointimal lesions, in part due to changes in the extracellular matrix. While some clinical studies have suggested that, in comparison to non-diabetics, beta3 integrin inhibition in diabetic patients confers protection from restenosis, little is known regarding the role of beta3 integrin inhibition on SMC responses in this context. To understand the molecular mechanisms underlying integrin-mediated regulation of SMC function in diabetes, we examined SMC responses in diabetic mice deficient in integrin beta3 and observed that the integrin was required for enhanced proliferation, migration and extracellular regulated kinase (ERK) activation. Hyperglycemia-enhanced membrane recruitment and catalytic activity of PKCbeta in an integrin beta3-dependent manner. Hyperglycemia also promoted SMC filopodia formation and cell migration, both of which required alphaVbeta3, PKCbeta, and ERK activity. Furthermore, the integrin-kinase association was regulated by the alphaVbeta3 integrin ligand thrombospondin and the integrin modulator Rap1 under conditions of hyperglycemia. These results suggest that there are differences in SMC responses to vascular injury depending on the presence or absence of hyperglycemia and that SMC response under hyperglycemic conditions is largely mediated through beta3 integrin signaling.

Identification of compounds that inhibit IGF-I signaling in hyperglycemia

Increased responsiveness of vascular cells to the growth factor IGF-I has been implicated in complications associated with diabetes. Here we describe the development of an assay and screening of a library of compounds for their ability to accelerate cleavage of the transmembrane protein integrin-associated protein (IAP) thereby disrupting the association between IAP and SHPS-1 which we have shown as critical for the enhanced response of vascular cells to IGF-I. The cell-based ELISA utilizes an antibody that specifically detects cleaved, but not intact, IAP. Of the 1040 compounds tested, 14 were considered active by virtue of their ability to stimulate an increase in antibody-binding indicative of IAP cleavage. In experiments with smooth muscle and retinal endothelial cell cultures in hyperglycemic conditions, each active compound was shown to accelerate the cleavage of IAP, and this was associated with a decrease in IAP association with SHPS-1 as determined by coimmunoprecipitation of the proteins from cell lysates. As a consequence of the acceleration in IAP cleavage, the compounds were shown to inhibit IGF-I-stimulated phosphorylation of key signaling molecules including Shc and ERK1/2, and this in turn was associated with a decrease in IGF-I-stimulated cell proliferation. Identification of these compounds that utilize this mechanism has the potential to yield novel therapeutic approaches for the prevention and treatment of vascular complications associated with diabetes.

p66shc inhibits insulin-like growth factor-I signaling via direct binding to Src through its polyproline and Src homology 2 domains, resulting in impairment of Src kinase activation

p66(shc) is increased in response to cell stress, and these increases regulate growth factor actions. These studies were conducted to determine how p66(shc) alters IGF-I-stimulated Src activation, leading to decreased IGF-I actions. Our results show that p66(shc) binds to Src through a polyproline sequence motif contained in the CH2 domain, a unique domain in p66(shc), and IGF-I stimulates this interaction. Disruption of this interaction using a synthetic peptide containing the p66(shc) polyproline domain or expression of a p66(shc) mutant containing substitutions for the proline residues (P47A/P48A/P50A) resulted in enhanced Src kinase activity, p52(shc) phosphorylation, MAPK activation, and cell proliferation in response to IGF-I. To determine the mechanism of inhibition, the full-length CH2 domain and intact p66(shc) were tested for their ability to directly inhibit Src kinase activation in vitro. The CH2 domain peptide was clearly inhibitory, but full-length p66(shc) had a greater effect. Deletion of the C-terminal Src homology 2 domain in p66(shc) reduced its ability to inhibit Src kinase activation. These findings demonstrate that p66(shc) utilizes a novel mechanism for modulating Src kinase activation and that this interaction is mediated through both its collagen homologous region 2 and Src homology 2 domains.

Identification of novel SHPS-1-associated proteins and their roles in regulation of insulin-like growth factor-dependent responses in vascular smooth muscle cells

Tyrosine phosphatase non-receptor type substrate-1 (SHPS-1), a transmembrane protein, plays a vital role in cell migration and proliferation. Our previous studies have shown that insulin-like growth factor-I (IGF-I) stimulates SHPS-1 phosphorylation, leading to recruitment of SHP-2, c-Src, Shc, and Grb2.p85 to phosphorylated SHPS-1. Assembly of this signaling complex is required for optimal stimulation of both mitogen-activated protein and phosphatidylinositol 3-kinase pathways. The main aim of the present study was to identify novel proteins that interacted with the cytoplasmic domain of SHPS-1 (SHPS-1/CD) in response to IGF-I stimulation and define the role of these interactions in mediating specific biological functions. We performed a functional proteomic screening to identify SHPS-1 binding partners using combination of mRNA display and the tandem affinity purification-tag methods. Screening identified a number of proteins not previously known to interact with phosphorylated SHPS-1/CD. These novel SHPS-1 binding partners represent several functional categories including heat shock proteins, protein kinases and phosphatases, and proteins that regulate transcription or translation. In Vivo and in vitro studies suggested that most of the proteins bound to SHPS-1 via binding to one of the four SH2 domain containing proteins, SHP-2, CTK, SUPT6H, and STAT1, that directly bound to SHPS-1. Although the binding of most of these proteins to SHPS-1 was positively regulated by IGF-I, a few were negatively regulated, suggesting differential regulation of protein complexes assembled on SHPS-1/CD in response to IGF-I. Further studies showed that truncation of SHPS-1/CD significantly impaired IGF-I-dependent AKT signal transduction and subsequent biological functions including cell survival, protein synthesis, protein aggregation, and prevention of apoptosis. The results emphasize the importance of formation of SHPS-1 signaling complex induced by IGF-I and provide novel insights into our knowledge of the role of this molecular scaffold in regulation of IGF-I-stimulated signal transduction and biological actions.

Glucose-oxidized low-density lipoproteins enhance insulin-like growth factor I-stimulated smooth muscle cell proliferation by inhibiting integrin-associated protein cleavage

Prior published reports have demonstrated that glucose-oxidized low-density lipoproteins (g-OxLDL) enhance the proliferative response of vascular smooth muscle cells (SMC) to IGF-I. Our previous studies have determined that the regulation of cleavage of integrin-associated protein (IAP) by matrix-metalloprotease-2 (MMP-2) in diabetic mice in response to hyperglycemia is a key regulator of the response of SMC to IGF-I. Because chronic hyperglycemia enhances glucose-induced LDL oxidation, these studies were conducted to determine whether g-OxLDL modulates the response of SMC to IGF-I by regulating MMP-2-mediated cleavage of IAP. We determined that exposure of SMC to g-OxLDL, but not native LDL, was sufficient to facilitate an increase in cell proliferation in response to IGF-I. Exposure to an anti-CD36 antibody, which has been shown to inhibit g-OxLDL-mediated signaling, inhibited the effects of g-OxLDL on IGF-I-stimulated SMC proliferation. The effect of g-OxLDL could be attributed, in part, to an associated decrease in proteolytic cleavage of IAP leading to increase in the basal association between IAP and Src homology 2 domain-containing protein tyrosine phosphatase substrate-1, which is required for IGF-I-stimulated proliferation. The inhibitory effect of g-OxLDL on IAP cleavage appeared to be due to its ability to decrease the amount of activated MMP-2, the protease responsible for IAP cleavage. In conclusion, these data provide a molecular mechanism to explain previous studies that have reported an enhancing effect of g-OxLDL on IGF-I-stimulated SMC proliferation.

Integrin-associated protein association with SRC homology 2 domain containing tyrosine phosphatase substrate 1 regulates igf-I signaling in vivo

OBJECTIVE

Smooth muscle cell (SMC) maintained in medium containing normal levels of glucose do not proliferate in response to IGF-I, whereas cells maintained in medium containing 25 mmol/l glucose can respond. The aim of this study was to determine whether signaling events that have been shown to be required for stimulation of SMC growth were regulated by glucose concentrations in vivo.

RESEARCH DESIGN AND METHODS

We compared IGF-I-stimulated signaling events and growth in the aortic smooth muscle cells from normal and hyperglycemic mice.

RESULTS

We determined that, in mice, hyperglycemia was associated with an increase in formation of the integrin-associated protein (IAP)/Src homology 2 domaine containing tyrosine phosphatase substrate 1 (SHPS-1) complex. There was a corresponding increase in Shc recruitment to SHPS-1 and Shc phosphorylation in response to IGF-I. There was also an increase in mitogen-activated protein kinase activation and SMC proliferation. The increase in IAP association with SHPS-1 in hyperglycemia appeared to be due to the protection of IAP from cleavage that occurred during exposure to normal glucose. In addition, we demonstrated that the protease responsible for IAP cleavage was matrix metalloprotease-2. An anti-IAP antibody that disrupted the IAP-SHPS-1 association resulted in complete inhibition of IGF-I-stimulated proliferation.

CONCLUSIONS

Taken together, our results support a model in which hyperglycemia is associated with a reduction in IAP cleavage, thus allowing the formation of the IAP-SHPS-1 signaling complex that is required for IGF-I-stimulated proliferation of SMC.

p66shc negatively regulates insulin-like growth factor I signal transduction via inhibition of p52shc binding to Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 leading to impaired growth factor receptor-bound protein-2 membrane recruitment

Our previous studies have indicated an essential role of p52shc in mediating IGF-I activation of MAPK in smooth muscle cells (SMC). However, the role of the p66 isoform of shc in IGF-I signal transduction is unclear. In the current study, two approaches were employed to investigate the role of p66shc in mediating IGF-I signaling. Knockdown p66shc by small interfering RNA enhanced IGF-I-stimulated p52shc tyrosine phosphorylation and growth factor receptor-bound protein-2 (Grb2) association, resulting in increased IGF-I-dependent MAPK activation. This was associated with enhanced IGF-I-stimulated cell proliferation. In contrast, knockdown of p66shc did not affect IGF-I-stimulated IGF-I receptor tyrosine phosphorylation. Overexpression of p66shc impaired IGF-I-stimulated p52shc tyrosine phosphorylation and p52shc-Grb2 association. In addition, IGF-I-dependent MAPK activation was also impaired, and SMC proliferation in response to IGF-I was inhibited. IGF-I-dependent cell migration was enhanced by p66shc knockdown and attenuated by p66shc overexpression. Mechanistic studies indicated that p66shc inhibited IGF-I signal transduction via competitively inhibiting the binding of Src homology 2 domain-containing protein tyrosine phosphatase-2 (SHP-2) to SHP substrate-1 (SHPS-1), leading to the disruption of SHPS-1/SHP-2/Src/p52shc complex formation, an event that has been shown previously to be essential for p52shc phosphorylation and Grb2 recruitment. These findings indicate that p66shc functions to negatively regulate the formation of a signaling complex that is required for p52shc activation in response to IGF-I, thus leading to attenuation of IGF-I-stimulated cell proliferation and migration.

Glucose regulation of integrin-associated protein cleavage controls the response of vascular smooth muscle cells to insulin-like growth factor-I

Vascular smooth muscle cells (SMC) maintained in high glucose are more responsive to IGF-I than SMC maintained in normal glucose due to a difference in the Shc phosphorylation response. In this study we aimed to determine the mechanism by which glucose regulates the sensitivity of SMC to IGF-I. For Shc to be phosphorylated in response to IGF-I it must be recruited to tyrosine-phosphorylated sites on Src homology 2 domain-containing phosphatase (SHP) substrate-1 (SHPS-1). The association of integrin-associated protein (IAP) with SHPS-1 is required for SHPS-1 tyrosine phosphorylation. When SMC were grown in 5 mm glucose, the amount of intact IAP was reduced, compared with SMC grown in 25 mm glucose. This reduction was due to proteolytic cleavage of IAP. Proteolysis of IAP resulted in loss of its SHPS-1 binding site, which led to loss of SHPS-1 phosphorylation. Analysis of the conditioned medium showed that there was more protease activity in the medium from SMC cultured in 5 mm glucose as compared with 25 mm. Inhibition of matrix metalloprotease-2 synthesis using RNA interference or its activity using a specific protease inhibitor protected IAP from cleavage. This protection was associated with an increase in IAP-SHPS-1 association, increased recruitment and phosphorylation of Shc, and increased cell growth in response to IGF-I. Our results show that the enhanced response of SMC in 25 mm glucose to IGF-I is due to the protection of IAP from proteolytic degradation, thereby increasing its association with SHPS-1 and allowing the formation of the SHPS-1-Shc signaling complex.

Insulin-like growth factor-I stimulates Shc-dependent phosphatidylinositol 3-kinase activation via Grb2-associated p85 in vascular smooth muscle cells

Insulin-like growth factor-I (IGF-I) stimulates vascular smooth muscle cell proliferation and migration by activating both MAPK and phosphatidylinositol 3-kinase (PI3K). Vascular smooth muscle cells (VSMCs) maintained in 25 mm glucose sustain MAPK activation via increased Shc phosphorylation and Grb2 association resulting in an enhanced mitogenic response compared with cells grown in 5 mm glucose. PI3K plays a major role in IGF-I-stimulated VSMC migration, and hyperglycemia augments this response. In contrast to MAPK activation the role of Shc in modulating PI3K in response to IGF-I has not been determined. In this study we show that impaired Shc association with Grb2 results in decreased Grb2-p85 association, SHPS-1-p85 recruitment, and PI3K activation in response to IGF-I. Exposure of VSMCs to cell-permeable peptides, which contained polyproline sequences from p85 proposed to mediate Grb2 association, resulted in inhibition of Grb2-p85 binding and AKT phosphorylation. Transfected cells that expressed p85 mutant that had specific prolines mutated to alanines resulted in less Grb2-p85 association, and a Grb2 mutant (W36A/W193A) that attenuated p85 binding showed decreased association of p85 with SHPS-1, PI3K activation, AKT phosphorylation, cell proliferation, and migration in response to IGF-I. Cellular exposure to 25 mm glucose, which is required for Shc phosphorylation in response to IGF-I, resulted in enhanced Grb2 binding to p85, activation of PI3K activity, and increased AKT phosphorylation as compared with cells exposed to 5 mm glucose. We conclude that in VSMCs exposed to hyperglycemia, IGF-I stimulation of Shc facilitates the transfer of Grb2 to p85 resulting in enhanced PI3K activation and AKT phosphorylation leading to enhanced cell proliferation and migration.

Arterial smooth muscle cells dysfunction in hyperglycaemia and hyperglycaemia associated with hyperlipidaemia: from causes to effects

Given the important role of smooth muscle cells in arterial wall dysfunction in diabetes, as well as in diabetes associated with accelerated atherosclerosis, we provide a brief review of the recent achievements in identification of signalling molecules underlying their altered cellular responses, and examine the consequences of these pathological insults on smooth muscle cells properties. The original results emerging from the Golden Syrian hamster model (rendered diabetic or simultaneously hyperlipidaemic-diabetic) and from human aortic smooth muscle cells cultured in 25 mM glucose (to mimic diabetic condition) or sera of obese type 2 diabetic patients (to mimic the metabolic syndrome condition) are presented in this context. We conclude this review with several open issues disclosed by the most recent literature that deserve essential attention for targeting the translational medicine.

Expression of the human beta3 integrin subunit in mouse smooth muscle cells enhances IGF-I-stimulated signaling and proliferation

Optimal stimulation of signal transduction and biological functions by IGF-I in porcine smooth muscle cells (pSMC) requires ligand occupancy of the alphaVbeta3 integrin. Binding of heparin-binding domain (HBD) of vitronectin (VN) to the cysteine loop (C-loop) region of beta3 is required for pSMC to respond optimally to IGF-I stimulation. Mouse smooth muscle cells (mSMC), which express a form of beta3 whose sequence within the C-loop region is different than porcine or human beta3, do not respond optimally to IGF-I, and IGF-I stimulated beta3 and SHPS-1 phosphorylation which are necessary for optimal IGF-I signaling were undetectable. VN also had no effect on IGF-I stimulated the cell proliferation. In contrast, when human beta3 (hbeta3) was introduced into mSMC, there was an enhanced VN binding in spite of an equivalent amount of total beta3 expression, and IGF-I-dependent beta3, and SHPS-1 phosphorylation were detected. In addition, there was enhanced IGF-I-stimulated Shc association with SHPS-1, Shc tyrosine phosphorylation, Shc and Grb2 association, and MAP kinase activation leading to increased cell proliferation. These enhancements could be further augmented by adding a peptide containing the HBD of VN. To determine if these changes were mediated by the C-loop region of beta3, an antibody that reacts with that region of beta3 was utilized. The addition of the hbeta3 C-loop antibody abolished VN-induced enhancement of IGF-I signaling and IGF-I-stimulated cell proliferation. These results strongly support the conclusion that optimal SMC responsiveness to IGF-I requires ligand interaction with the C-loop domain of hbeta3.