Insulin potentiates platelet-derived growth factor action in vascular smooth muscle cells

Cardiovascular complications in insulin resistance and endocrine diseases

Cerebrovascular diseases, such as stroke and cardiovascular disease, are one of the leading causes of death in Japan. Type 2 diabetes is the most common form of diabetes and an important risk factor for these diseases. Among various pathological conditions associated with type 2 diabetes, insulin resistance has already been reported to be an important risk factor for diabetic complications. The major sites of insulin action in glucose metabolism in the body include the liver, skeletal muscle, and adipose tissue. However, insulin signaling molecules are also constitutively expressed in vascular endothelial cells, vascular smooth muscle, and monocytes/macrophages. Forkhead box class O family member proteins (FoxOs) of transcription factors play important roles in regulating glucose and lipid metabolism, oxidative stress response and redox signaling, and cell cycle progression and apoptosis. FoxOs in vascular endothelial cells strongly promote arteriosclerosis by suppressing nitric oxide production, enhancing inflammatory response, and promoting cellular senescence. In addition, primary aldosteronism and Cushing's syndrome are known to have adverse effects on the cardiovascular system, apart from hypertension, diabetes, and dyslipidemia. In the treatment of endocrine disorders, hormonal normalization by surgical treatment and receptor antagonists play an important role in preventing cardiovascular complications.

Role of insulin action in the pathogenesis of diabetic complications

Among the various pathological conditions associated with type 2 diabetes, insulin resistance has long been reported to be a potent risk factor for diabetic complications. The liver, skeletal muscle, and adipose tissue are the major organs of action of insulin in systemic glucose metabolism, but insulin receptors and their downstream insulin signaling molecules are also constitutively expressed in vascular endothelial cells, vascular smooth muscle, and monocytes/macrophages. Forkhead box class O family member proteins (FoxOs) of transcription factors are essential regulators of cellular homeostasis, including glucose and lipid metabolism, oxidative stress response and redox signaling, cell cycle progression and apoptosis. In vascular endothelial cells, FoxOs strongly promote atherosclerosis via suppressing nitric oxide production and enhancing inflammatory responses. In liver sinusoidal endothelial cells, FoxOs induces hepatic insulin resistance by inducing nitration of insulin receptor in hepatocytes. Insulin resistance in adipose tissue limits capacity of lipid accumulation in adipose tissue, which promotes ectopic lipid accumulation and organ dysfunction in liver, vascular, and kidney. Modulation of insulin sensitivity in adipose tissue to induce healthy adipose expansion is expected to be a promising strategy for diabetic complications.

Pseudoacromegaly

Individuals with acromegaloid physical appearance or tall stature may be referred to endocrinologists to exclude growth hormone (GH) excess. While some of these subjects could be healthy individuals with normal variants of growth or physical traits, others will have acromegaly or pituitary gigantism, which are, in general, straightforward diagnoses upon assessment of the GH/IGF-1 axis. However, some patients with physical features resembling acromegaly - usually affecting the face and extremities -, or gigantism - accelerated growth/tall stature - will have no abnormalities in the GH axis. This scenario is termed pseudoacromegaly, and its correct diagnosis can be challenging due to the rarity and variability of these conditions, as well as due to significant overlap in their characteristics. In this review we aim to provide a comprehensive overview of pseudoacromegaly conditions, highlighting their similarities and differences with acromegaly and pituitary gigantism, to aid physicians with the diagnosis of patients with pseudoacromegaly.

Insulin augments tumor necrosis factor-alpha stimulated expression of vascular cell adhesion molecule-1 in vascular endothelial cells

BACKGROUND

Atherosclerosis is an inflammatory disease that is marked by increased presence of Tumor Necrosis Factor-alpha (TNFα), increased expression of Vascular Cell Adhesion Molecule-1 (VCAM-1), increased presence of serum monocytes and activation of the canonical inflammatory molecule, Nuclear Factor Kappa-B (NFκB). Hyperinsulinemia is a hallmark of insulin resistance and may play a key role in this inflammatory process.

METHODS

Using Western blot analysis, immunocytochemistry, flow cytometry and biochemical inhibitors, we measured changes in VCAM-1 protein expression and NFκB translocation in vascular endothelial cells in the presence of TNFα and/or hyperinsulinemia and in the absence or presence of kinase pathway inhibitors.

RESULTS

We report that hyperinsulinemia augmented TNFα stimulated increases in VCAM-1 protein greater than seen with TNFα alone and decreased the time in which VCAM-1 translocated to the cell surface. We also observed that in the presence of Wortmannin, a biochemical inhibitor of phosphatidylinositol 3-kinase (a hallmark of insulin resistance), VCAM-1 expression was greater in the presence of TNFα plus insulin as compared to that seen with insulin or TNFα alone. Additionally, nuclear import of NFκB occurred sooner in the presence of insulin and TNFα together as compared to each alone, and in the presence of Wortmannin, nuclear import of NFκB was greater than that seen with insulin and TNFα alone.

CONCLUSIONS

hyperinsulinemia and insulin resistance appear to augment the inflammatory effects of TNFα on VCAM-1 expression and NFκB translocation, both of which are markers of inflammation in the vasculature.

ERK5: a novel IKKα-kinase in rat hippocampal neurons

BACKGROUND

Alzheimer's Disease (AD) is characterized in part by the increased presence of neurofibrillary tangles and amyloid beta (Aβ) plaques. Alzheimer's Disease is considered an inflammatory disease and, as such, nuclear factor-kappaB (NFκB) plays an important role in the pathophysiology of AD. Insulin acts as a neurotrophic factor. Yet, in the context of insulin resistance, concomitant hyperinsulinemia may contribute to the pathogenesis of AD.

METHODS

Rat Primmary Hippocampal Neurons (RPHN) were treated with insulin in the absence and presence of Wortmannin and ERK5 small inhibitory RNA and assayed for downstream effectors of activated ERK5.

RESULTS

Here we demonstrate that genetic inhibition of ERK5 blocks insulin stimulated (1) activation and translocation of ERK5 and NFκB, (2) phosphorylation of IKKα via association with ERK5, (3) increases in Aβ1-40 and Aβ1-42 soluble proteins 3-fold and 2.2-fold, respectively, and (4) increases in tau phosphorylation in RPHN.

CONCLUSIONS

ERK5 plays an active role in insulin signaling in neurons and may be a potential therapeutic target for neurodegenerative diseases.

Childhood obesity and cardiovascular disease: links and prevention strategies

The prevalence and severity of pediatric obesity have dramatically increased since the late 1980s, raising concerns about a subsequent increase in cardiovascular outcomes. Strong evidence, particularly from autopsy studies, supports the concept that precursors of adult cardiovascular disease (CVD) begin in childhood, and that pediatric obesity has an important influence on overall CVD risk. Lifestyle patterns also begin early and impact CVD risk. In addition, obesity and other CVD risk factors tend to persist over time. However, whether childhood obesity causes adult CVD directly, or does so by persisting as adult obesity, or both, is less clear. Regardless, sufficient data exist to warrant early implementation of both obesity prevention and treatment in youth and adults. In this Review, we examine the evidence supporting the impact of childhood obesity on adult obesity, surrogate markers of CVD, components of the metabolic syndrome, and the development of CVD. We also evaluate how obesity treatment strategies can improve risk factors and, ultimately, adverse clinical outcomes.

Metabolic syndrome and cardiovascular risk in survivors after hematopoietic cell transplantation

Increasing numbers of hematopoietic cell transplantations (HCTs) are being performed annually with a greater number of long-term survivors. There is increasing concern regarding the late complications and long-term effects that are secondary to treatment exposures before HCT as well as during the HCT conditioning therapy. In both the autologous as well as allogeneic transplant setting, transplant survivors experience mortality rates higher than the general population and the risk of premature cardiovascular (CV)-related death is increased 2.3-fold compared with the general population. The etiology of CV-related deaths in HCT survivors is multifactorial; however, increasing evidence suggests that HCT survivors are at higher risk of developing adverse CV risk factors leading to the development of the metabolic syndrome (a constellation high triglyceride levels, low high-density lipoprotein-cholesterol, hypertension, high fasting blood sugars and increased waist circumference), which then predisposes individuals to risk for early CV-related death. Resistance to insulin is the primary underlying pathophysiologic mechanism that contributes to the development of metabolic syndrome and HCT survivors have been shown to be more likely to develop hypertension, hyperlipidemia and to be insulin resistant. However, the relationship between HCT-related treatment exposures (total body irradiation, high dose chemotherapy, calcineurin inhibitors, steroids, etc) and transplant-related complications (such as GVHD) with the development of CV risk factors and insulin resistance is still in the early stages of investigation. Greater knowledge of the concern regarding CV risk in HCT survivors among both patients and care providers will provide the opportunity for appropriate screening as well as interventions for modifiable risk factors.

Nontraditional risk factors and biomarkers for cardiovascular disease: mechanistic, research, and clinical considerations for youth: a scientific statement from the American Heart Association

The rapid increase in the prevalence and severity of obesity in children is likely to lower the age of onset and increase the incidence of cardiovascular disease worldwide. Understanding the pathophysiology and improving the clinical management of cardiovascular disease involve a knowledge of novel risk factors and biomarkers. The clinical and mechanistic roles of these novel biological factors during childhood are currently being investigated. The goals of this scientific statement are to present the existing knowledge and theoretical framework of nontraditional risk factors for cardiovascular disease as they relate to children and adolescents, to describe the relevance and weight of available experimental and clinical evidence and the therapeutic implications pertaining to nontraditional risk factors in the pediatric population, and to stimulate further research with a goal of developing valid and reliable approaches to identify and validate novel risk factors that will aid in the clinical evaluation and perhaps prediction of cardiovascular disease in the pediatric population. Although several biomarkers are promising, substantial research is required before nontraditional risk factors can be used to identify and reduce cardiovascular disease risk in children and adolescents.

Insulin resistance and hyperinsulinaemia in the development and progression of cancer

Experimental, epidemiological and clinical evidence implicates insulin resistance and its accompanying hyperinsulinaemia in the development of cancer, but the relative importance of these disturbances in cancer remains unclear. There are, however, theoretical mechanisms by which hyperinsulinaemia could amplify such growth-promoting effects as insulin may have, as well as the growth-promoting effects of other, more potent, growth factors. Hyperinsulinaemia may also induce other changes, particularly in the IGF (insulin-like growth factor) system, that could promote cell proliferation and survival. Several factors can independently modify both cancer risk and insulin resistance, including subclinical inflammation and obesity. The possibility that some of the effects of hyperinsulinaemia might then augment pro-carcinogenic changes associated with disturbances in these factors emphasizes how, rather than being a single causative factor, insulin resistance may be most usefully viewed as one strand in a network of interacting disturbances that promote the development and progression of cancer.

Chronic insulin treatment suppresses PTP1B function, induces increased PDGF signaling, and amplifies neointima formation in the balloon-injured rat artery

We tested the hypothesis that hyperinsulinemia induces the suppression of protein tyrosine phosphatase 1B (PTP1B) function, leading to enhanced PDGF receptor (PDGFR) signaling and neointimal hyperplasia. Rats were implanted with insulin-releasing pellets or sham pellets. Blood glucose levels, insulin levels, food and water intake, body weights, and blood pressures were measured. Neointimal hyperplasia was assessed by computerized morphometry 14 days after carotid balloon injury. PTP1B protein expression in injured arteries was determined via Western blot analysis, whereas PTP1B activity was determined via an immunophosphatase assay. Serum insulin levels were two- to threefold greater in hyperinsulinemic rats, whereas systolic blood pressures, food and water intake, serum triglyceride levels, plasma cortisol levels, and urinary catecholamine levels were not affected. Fourteen days after injury, neointima-to-media area ratios were 0.89 +/- 0.23 and 1.35 +/- 0.22 in control and hyperinsulinemic rats, respectively (P < 0.01). PTP1B protein levels and total PTP1B activity in injured carotid arteries from the insulin-treated group were significantly decreased 7 or 14 days after injury, whereas PTP1B specific activity was decreased only 14 days after injury. These findings were associated with decreased PTP1B mRNA levels and increased PDGFR tyrosyl phosphorylation in insulin-treated rats. These observations support the hypothesis that hyperinsulinemia induces the suppression of PTP1B function, leading to enhanced PDGFR signaling and neointimal hyperplasia.

Chronic insulin treatment amplifies PDGF-induced motility in differentiated aortic smooth muscle cells by suppressing the expression and function of PTP1B

Hyperinsulinemia plays a major role in the pathogenesis of vascular disease. Restenosis occurs at an accelerated rate in hyperinsulinemia and is dependent on increased vascular smooth muscle cell movement from media to neointima. PDGF plays a critical role in mediating neointima formation in models of vascular injury. We have reported that PDGF increases the levels of protein tyrosine phosphatase PTP1B and that PTP1B suppresses PDGF-induced motility in cultured cells and that it attenuates neointima formation in injured carotid arteries. Others have reported that insulin enhances the mitogenic and motogenic effects of PDGF in cultured smooth muscle cells and that hyperinsulinemia promotes vascular remodeling. In the present study, we tested the hypothesis that insulin amplifies PDGF-induced cell motility by suppressing the expression and function of PTP1B. We found that chronic but not acute treatment of cells with insulin enhances PDGF-induced motility in differentiated cultured primary rat aortic smooth muscle cells and that it suppresses PDGF-induced upregulation of PTP1B protein. Moreover, insulin suppresses PDGF-induced upregulation of PTP1B mRNA levels, PTP1B enzyme activity, and binding of PTP1B to the PDGF receptor-beta, and it enhances PDGF-induced PDGF receptor phosphotyrosylation. Treatment with insulin induces time-dependent upregulation of phosphatidylinositol 3-kinase (PI3-kinase)-delta and activation of Akt, an enzyme downstream of PI3-kinase. Finally, inhibition of PI3-kinase activity, or its function, by pharmacological or genetic means rescues PTP1B activity in insulin-treated cells. These observations uncover novel mechanisms that explain how insulin amplifies the motogenic capacity of the pivotal growth factor PDGF.

Effects of insulin dependence on inflammatory process, thrombotic mechanisms and endothelial function, in patients with type 2 diabetes mellitus and coronary atherosclerosis

BACKGROUND

Type 2 diabetes mellitus (T2DM) is characterized by endothelial dysfunction, increased thrombogenicity and abnormal inflammatory response.

HYPOTHESIS

We hypothesizsed that insulin dependence/exogenous insulin administration may affect thrombotic/inflammatory status and endothelial function in patients with T2DM and coronary artery disease (CAD).

METHODS

Fifty-five patients with T2DM + CAD (26 insulin-treated (INS) and 29 under oral biguanide + sulphonylurea (TABL)) were recruited. Endothelial function was assessed by gauge-strain plethysmography, and serum levels of inflammatory and thrombotic markers were determined by enzyme linked immunosorbent assay.

RESULTS

There was no significant difference in endothelium-dependent dilation (EDD) between the study groups, while EDD was correlated with fasting glucose levels in both INS (r = - 0.776, p = 0.0001) and TABL (r = - 0.702, p = 0.0001). Patients in INS group had higher levels of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), monocyte chemoattractant protein (MCP-1) and vascular cell adhesion molecule (sVCAM-1), compared to TABL. However, TNF-alpha was negatively correlated with protein C (PrtC) only in INS (r = - 0.726, p = 0.01) but not in TABL group (r = - 0.066, p = 0.738). Similarly, sVCAM-1 was correlated with PrtC only among INS patients (r = - 0.451, p = 0.046) but not in TABL (r = 0.069, p = 0.727). In multivariate analysis, insulin dependence was a predictor of IL-6, TNF-alpha, MCP-1 and sVCAM-1 levels independently from the patients' demographic characteristics, the angiographic extend of CAD or the duration of diabetes.

CONCLUSIONS

Insulin treatment in patients with type 2 diabetes mellitus affects the expression of inflammatory cytokines and subsequently modifies the thrombotic mechanisms in patients with coronary atherosclerosis, independently from the duration of diabetes and the extend of coronary artery disease.

Regulation of ERK5 by insulin and angiotensin-II in vascular smooth muscle cells

ERK5 is involved in proliferation of vascular smooth muscle cells (VSMC). The proliferative actions of insulin and angiotensin-II (A-II) in VSMC are mediated in part by ERK1/2. We hypothesized that insulin and A-II also regulate ERK5 activity in VSMC. Acute treatment (<60min) with insulin or A-II increased phosphorylation of ERK1/2 at 15min and ERK5 at 5min. Chronic treatment (< or = 8h) with insulin increased ERK1/2 phosphorylation by 4h and ERK5 by 8h. A-II-stimulated phosphorylation of ERK1/2 by 8h and ERK5 by 4h. The EC(50) for insulin treatment effecting ERK1/2 and ERK5 phosphorylation was 1.5 and 0.1nM, whereas the EC(50) for A-II was 2nM, each. Insulin plus A-II induced an additive effect only on ERK5 phosphorylation. Inhibition of insulin- and A-II-stimulated phosphorylation of ERK5 and ERK1/2 by PD98059 and Wortmannin exhibited differential and time-dependent effects. Taken together, these data indicate that insulin and A-II regulate the activity of ERK5, but different from that seen for ERK1/2.

Key role of the achievement of an appropriate ribosomal RNA complement for G1-S phase transition in H4-II-E-C3 rat hepatoma cells

Cell growth is closely related to cell proliferation and an adequate ribosome biogenesis appears to be necessary for cell duplication. In the present study, we have investigated the relationship between rRNA synthesis and cell cycle progression. For this purpose, in a first set of experiments, we evaluated the effect of rRNA synthesis variation on cycle duration in asynchronously growing H4-II-E-C3 rat hepatoma cells. Cells were either treated with insulin or insulin plus actinomycin D (AMD). The hormone stimulated ribosome biogenesis, which was later followed by an increased synthesis of DNA and a shortening of cell doubling time (DT). Bivariate flow cytometry indicated that the reduced length of the cell cycle was mainly due to the shorter G1-phase. AMD, at the concentration of 0.04 microg/ml, hindered ribosome biogenesis without affecting heterogeneous RNA production. A 12-h reduction in ribosome biogenesis level by AMD caused a lowering of DNA synthesis and a lengthening of cell DT with a longer G1-phase. In a second set of experiments, we analyzed the cell content variations of 28S and 18S rRNA transcripts during G1 phase in H4-II-E-C3 cells, synchronized by serum deprivation, and then stimulated by serum, serum plus insulin, and serum plus insulin and AMD. In control cells, a progressive increase in rRNA content occurred until the highest value of rRNA content was reached 21 h after serum stimulation. In insulin-treated cells, the highest rRNA value was reached at 12 h whereas in AMD-treated cells, the rRNA quantity was constantly low until 18 h and then sharply increased at 21 h. In the three experimental conditions, the highest values of rRNA amount were reached at the end of G1 phase and were quite similar to one another. We also evaluated, by real-time RT-PCR, cyclin E mRNA expression, which appeared to sharply increase at those times in which the maximum increase in the rRNA content was observed. Our results indicated that the achievement of an appropriate amount of rRNA allows G1/S phase transition, probably by modulating the expression of cyclin E mRNA.

Inhibition of endogenous SHIP2 ameliorates insulin resistance caused by chronic insulin treatment in 3T3-L1 adipocytes

AIMS/HYPOTHESIS

SHIP2 is a physiologically important negative regulator of insulin signalling hydrolysing the PI3-kinase product, PI(3,4,5)P3, which also has an impact on insulin resistance. In the present study, we examined the effect of inhibiting the endogenous SHIP2 function on the insulin resistance caused by chronic insulin treatment.

METHODS

The endogenous function of SHIP2 was inhibited by expressing a catalytically inactive SHIP2 (DeltaIP-SHIP), and compared with the effect of treatments designed to restore the levels of IRS-1 in insulin signalling systems of 3T3-L1 adipocytes.

RESULTS

Chronic insulin treatment induced the large (86%) down-regulation of IRS-1 and the modest (36%) up-regulation of SHIP2. Subsequent stimulation by insulin of Akt phosphorylation, PKClambda activity, and 2-deoxyglucose (2-DOG) uptake was markedly decreased by the chronic insulin treatment. Coincubation with the mTOR inhibitor, rapamycin, effectively inhibited the proteosomal degradation of IRS-1 caused by the chronic insulin treatment. Although the coincubation with rapamycin and advanced overexpression of IRS-1 effectively ameliorated subsequent insulin-induced phosphorylation of Akt, insulin stimulation of PKClambda activity and 2-DOG uptake was partly restored by these treatments. Similarly, expression of DeltaIP-SHIP2 effectively ameliorated the insulin-induced phosphorylation of Akt without affecting the amount of IRS-1. Furthermore, the decreased insulin-induced PKClambda activity and 2-DOG uptake following chronic insulin treatment were ameliorated by the expression of DeltaIP-SHIP2 more effectively than by the treatment with rapamycin.

CONCLUSIONS/INTERPRETATION

Our results indicate that the inhibition of endogenous SHIP2 is effective in improving the state of insulin resistance caused by chronic insulin treatment.

Molecular mechanisms of insulin resistance that impact cardiovascular biology

Insulin resistance is concomitant with type 2 diabetes, obesity, hypertension, and other features of the metabolic syndrome. Because insulin resistance is associated with cardiovascular disease, both scientists and physicians have taken great interest in this disorder. Insulin resistance is associated with compensatory hyperinsulinemia, but individual contributions of either of these two conditions remain incompletely understood and a subject of intense investigation. One possibility is that in an attempt to overcome the inhibition within the metabolic insulin-signaling pathway, hyperinsulinemia may continue to stimulate the mitogenic insulin-signaling pathway, thus exerting its detrimental influence. Here we discuss some of the effects of insulin resistance and mechanisms of potentially detrimental influence of hyperinsulinemia in the presence of metabolic insulin resistance.

Novel actions of thiazolidinediones on vascular function and exercise capacity

The endothelium is the first line of defense for maintaining normal vascular function in the vessel wall; however, the endothelium is sensitive to metabolic stress. In patients with insulin resistance or type 2 diabetes mellitus, a set of metabolic insults--namely high plasma levels of glucose and free fatty acids, increased inflammation, dyslipidemia, and hypertension--cause endothelial dysfunction and a transition from an antiatherogenic endothelium to a proatherogenic endothelium. Disruption of endothelial function leads to activation of platelets and macrophages, increased thrombotic potential, transition of macrophages to foam cells, stimulation of cytokine secretion, and proliferation of vascular smooth muscle cells. Insulin-sensitizing agents, such as the thiazolidinediones (TZDs), improve flow-mediated vasodilation, decrease macrophage and smooth muscle cell activation, proliferation, and migration, and decrease plaque formation. The TZDs exert multifaceted effects on the vasculature by regulating the expression of transcription factors and orchestrating whole-gene programs that restore vascular physiology to the healthy state. Exercise training and increased levels of habitual physical activity have therapeutic benefit in terms of both preventing and treating insulin resistance and diabetes. However, this benefit of exercise training and increased physical activity is complicated by the fact that individuals with insulin resistance or type 2 diabetes have decreased maximal exercise capacity or maximal oxygen consumption and have slower oxygen uptake kinetics at the beginning of exercise. Both of these abnormalities contribute to the decreased levels of habitual physical activity observed in patients with diabetes. Preliminary data suggest that TZDs improve measures of cardiac function and exercise capacity, and investigators are assessing the impact of treatment with rosiglitazone on exercise capacity in an ongoing clinical trial.

The roles of insulin resistance, hyperinsulinemia, and thiazolidinediones in cardiovascular disease

Although it is difficult to distinguish between the relative effects of insulin resistance and hyperinsulinemia, insulin resistance is clearly associated with significantly increased cardiovascular and cerebrovascular risk. This effect is consistent across the spectrum of worsening glycemic control, from the onset of impaired glucose tolerance to the development of clinical diabetes. It is more difficult to discriminate between the roles of elevated circulating insulin and proinsulin levels; the association between insulin levels and cardiovascular risk is weak. The thiazolidinediones (TZDs) significantly improve insulin sensitivity and exert numerous effects on the vascular bed, including improved endothelial function, decreased vascular inflammation, decreased plasma free fatty acid levels, improved dyslipidemic profiles, and inhibition of vascular smooth muscle proliferation. These findings provide increasing evidence to suggest that the TZDs may have a beneficial effect on atherosclerosis and may reduce the incidence and severity of adverse cardiovascular outcomes. These effects remain to be substantiated by the results of large outcomes studies to evaluate the impact of glycemic control and reversal of insulin resistance on cardiovascular events.

Dual role of SRC homology domain 2-containing inositol phosphatase 2 in the regulation of platelet-derived growth factor and insulin-like growth factor I signaling in rat vascular smooth muscle cells

Src homology domain 2 (SH2)-containing inositol phosphatase 2 (SHIP2) possesses 5-phosphatase activity and an SH2 domain. The role of SHIP2 in platelet-derived growth factor (PDGF) and IGF-I signaling was studied by expressing wild-type (WT-) and a catalytically defective (Delta IP-) SHIP2 into rat aortic smooth muscle cells by adenovirus-mediated gene transfer. PDGF- and IGF-I-induced tyrosine phosphorylation of their respective receptors and phosphatidylinositol 3-kinase (PI3-kinase) activity were not affected by the expression of either WT- or Delta IP-SHIP2. SHIP2 possessed 5'-phosphatase activity to hydrolyze the PI3-kinase product phosphatidylinositol 3,4,5-trisphosphate in vivo. Akt and glycogen synthase kinase 3beta are known to be downstream molecules of PI3-kinase, leading to the antiapoptotic effect. Overexpression of WT-SHIP2 inhibited PDGF- and IGF-I-induced phosphorylation of these molecules and the protective effect of poly(ADP-ribose) polymerase degradation, whereas these phosphorylations and the protective effect were enhanced by the expression of Delta IP-SHIP2, which functions in a dominant negative fashion. Regarding the Ras-MAPK pathway, PDGF- and IGF-I-induced tyrosine phosphorylation of Shc was not affected by the expression of either WT- or Delta IP-SHIP2, whereas both expressed SHIP2 associated with Shc. Importantly, PDGF and IGF-I stimulation of Shc/Grb2 binding, MAPK activation, and 5-bromo-2'-deoxyuridine incorporation were all decreased in both WT- and Delta IP-SHIP2 expression. These results indicate that SHIP2 plays a negative regulatory role in PDGF and IGF-I signaling in vascular smooth muscle cells. As the bifunctional role, our results suggest that SHIP2 regulates PDGF- and IGF-I-mediated signaling downstream of PI3-kinase, leading to the antiapoptotic effect via 5-phosphatase activity, and that SHIP2 regulates the growth factor-induced Ras-MAPK pathway mainly via the SH2 domain.

Dominant negative alpha-subunit of farnesyl- and geranylgeranyl-transferase I inhibits insulin-induced differentiation of 3T3-L1 pre-adipocytes

OBJECTIVE

To investigate whether the expression of a dominant negative (DN) farnesyl- and geranygeranyl-transferase I (FTase/GGTase I) alpha-subunit in 3T3-L1 pre-adipocytes can inhibit insulin's ability to induce differentiation.

DESIGN

3T3-L1 pre-adipocytes were stably transfected with vector alone or vector expressing a mutated DN FTase/GGTase I alpha-subunit (S60A)(S62A) and incubated in serum-free medium in the absence and presence of insulin.

MEASUREMENTS

Various assays were performed to determine the effect of DN FTase/GGTase I alpha-subunit expression in 3T3-L1 pre-adipocyte on insulin-induced DNA synthesis, cell count, phosphorylation of the FTase/GGTase I alpha-subunit, FTase and GGTase I activity, amounts of prenylated p21Ras and RhoA, phosphorylation of MAP kinase and Akt, and differentiation to mature fat cells.

RESULTS

Expression of DN FTase/GGTase I alpha-subunit inhibited insulin's ability to increase DNA synthesis, cell count, FTase and GGTase I activity, amounts of prenylated p21Ras and RhoA, and magnitude of phosphorylation of MAP kinase. Expression of DN FTase/GGTase I alpha-subunit in 3T3-L1 pre-adipocytes was without effect on insulin-induced Akt phosphorylation.

CONCLUSION

Expression of DN FTase/GGTase I alpha-subunit inhibits insulin-induced differentiation of 3T3-L1 pre-adipocytes to mature adipocytes, and thus could indicate potential therapeutic avenues to assuage the deleterious effects of obesity and type 2 diabetes.

Dominant negative alpha-subunit of FTase inhibits effects of insulin and IGF-I in MCF-7 cells

We recently designed a dominant negative (DN) farnesyltransferase (FTase)/geranyl-gerahyltransferase I (GGTase I) alpha-subunit that when expressed in vascular smooth muscle cells decreased insulin-stimulated phosphorylation of FTase, FTase activity, amounts of farnesylated p21Ras, DNA synthesis, and cell migration. Currently, we explored the inhibitory effects of DN FTase/GGTase I alpha-subunit in MCF-7 cells on IGF-1- and insulin-stimulated DNA synthesis and cell proliferation. Expression of the DN FTase/GGTase I alpha-subunit completely blocked IGF-1- and insulin-stimulated BrdU incorporation and cell count. DN FTase/GGTase I alpha-subunit inhibited insulin-stimulated phosphorylation of FTase/GGTase I alpha-subunit, FTase and GGTase I activity, and prenylation of p21Ras and RhoA. Expression of DN FTase/GGTase I alpha-subunit diminished IGF-1- and insulin-stimulated phosphorylation of ERK (extracellular signal-regulated kinase), but had no effect on IGF-1- and insulin-stimulated phosphorylation of Akt. Taken together, these data suggest that DN FTase/GGTase I alpha-subunit can assuage the mitogenic effects of IGF-1 and insulin on MCF-7 breast cancer cells.

Inhibition of phosphatidylinositol 3-kinase enhances mitogenic actions of insulin in endothelial cells

The concept of "selective insulin resistance" has emerged as a unifying hypothesis in attempts to reconcile the influence of insulin resistance with that of hyperinsulinemia in the pathogenesis of macrovascular complications of diabetes. To explore this hypothesis in endothelial cells, we designed a set of experiments to mimic the "typical metabolic insulin resistance" by blocking the phosphatidylinositol 3-kinase pathway and exposing the cells to increasing concentrations of insulin ("compensatory hyperinsulinemia"). Inhibition of phosphatidylinositol 3-kinase with wortmannin blocked the ability of insulin to stimulate increased expression of endothelial nitric-oxide synthase, did not affect insulin-induced activation of MAP kinase, and increased the effects of insulin on prenylation of Ras and Rho proteins. At the same time, this experimental paradigm resulted in increased expression of vascular cellular adhesion molecules-1 and E-selectin, as well as increased rolling interactions of monocytes with endothelial cells. We conclude that inhibition of the metabolic branch of insulin signaling leads to an enhanced mitogenic action of insulin in endothelial cells.

Effect of insulin on cell cycle progression in MCF-7 breast cancer cells. Direct and potentiating influence

We recently demonstrated that in MCF-7 breast cancer cells, insulin promoted the phosphorylation and activation of geranylgeranyltransferase I (GGTI-I), increased the amounts of geranylgeranylated Rho-A and potentiated the transactivating activity of lysophosphatidic acid (LPA) (Chappell, J., Golovchenko, I., Wall, K., Stjernholm, R., Leitner, J., Goalstone, M., and Draznin, B. (2000) J. Biol. Chem. 275, 31792-31797). In the present study, we explored the mechanism of this potentiating effect of insulin on LPA. Insulin (10 nm) potentiated the ability of LPA to stimulate cell cycle progression and DNA synthesis in MCF-7 cells. The potentiating effect of insulin appears to involve increases in the expression of cyclin E and decreases in the expression of the cyclin-dependent kinase inhibitor p27Kip1. All potentiating effects of insulin were inhibited in the presence of an inhibitor of GGTase I, GGTI-286 (3 microm) or by an expression of a dominant negative mutant of Rho-A. In contrast to its potentiating action, a direct mitogenic effect of insulin in MCF-7 cells involves activation of phosphatidylinositol 3-kinase and increased expression of cyclin D1. We conclude that the ability of insulin to increase the cellular amounts of geranylgeranylated Rho-A results in potentiation of the LPA effect on cyclin E expression and degradation of p27Kip1 and cell cycle progression in MCF-7 breast cancer cells.

TZDs inhibit vascular smooth muscle cell growth independently of the cyclin kinase inhibitors p21 and p27

The thiazolidenediones (TZDs) are commonly used to treat hyperglycemia in type 2 diabetes. Diabetes is associated with macrovascular disease, leading to accelerated atherosclerosis caused by aberrant vascular smooth muscle (VSM) cell proliferation. Although VSM cell proliferation is inhibited by the TZDs, the mechanism of this effect has not been established. Because of reports that the cyclin kinase inhibitors (CKIs) p21(Waf1/Cip1) and p27(Kip1) can exhibit both growth-inhibitory and growth-permissive effects in VSM cells, we asked whether alterations in these cell cycle regulatory proteins are the mechanism by which the TZDs inhibit VSM cell growth. We show that platelet-derived growth factor-BB increases p21 and p27 and that this increase is attenuated by TZDs. Surprisingly, when VSM cells were transfected with antisense oligodeoxynucleotides to p21 and p27, inhibition of DNA synthesis by TZDs occurred to the same degree as in control cells. Furthermore, the TZDs have inhibitory effects on cyclin D1 and cyclin E levels, suggesting another mechanism by which these drugs decrease VSM cell growth. These data suggest that the TZD-mediated reduction in CKI levels is not the sole mechanism for their antiproliferative effects. The observed decrease in levels of the G1 cyclins by the TZDs suggests a possible mechanism of VSM cell growth inhibition.

Fetal hyperinsulinemia increases farnesylation of p21 Ras in fetal tissues

Even though the role of fetal hyperinsulinemia in the pathogenesis of fetal macrosomia in patients with overt diabetes and gestational diabetes mellitus seems plausible, the molecular mechanisms of action of hyperinsulinemia remain largely enigmatic. Recent indications that hyperinsulinemia "primes" various tissues to the mitogenic influence of growth factors by increasing the pool of prenylated Ras proteins prompted us to investigate the effect of fetal hyperinsulinemia on the activitiy of farnesyltransferase (FTase) and the amounts of farnesylated p21 Ras in fetal tissues in the ovine experimental model. Induction of fetal hyperinsulinemia by direct infusion of insulin into the fetus and by either fetal or maternal infusions of glucose resulted in significant increases in the activity of FTase and the amounts of farnesylated p21 Ras in fetal liver, skeletal muscle, fat, and white blood cells. An additional infusion of somatostatin into hyperglycemic fetuses blocked fetal hyperinsulinemia and completely prevented these increases, specifying insulin as the causative factor. We conclude that the ability of fetal hyperinsulinemia to increase the size of the pool of farnesylated p21 Ras may prime fetal tissues to the action of other growth factors and thereby constitute one mechanism by which fetal hyperinsulinemia could induce macrosomia in diabetic pregnancies.

Dominant negative farnesyltransferase alpha-subunit inhibits insulin mitogenic effects

Farnesylation of p21Ras is required for translocation to the plasma membrane and subsequent activation by growth factors. Previously we demonstrated that insulin stimulates the phosphorylation of farnesyltransferase (FTase) and its activity, whereby the amount of farnesylated p21Ras anchored at the plasma membrane is increased. Herein we report that substitution of alanine for two serine residues (S60A)(S62A) of the alpha-subunit of FTase creates a dominant negative (DN) mutant. VSMC expressing the FTase alpha-subunit (S60A)(S62A) clone showed a 30% decreased basal FTase activity concurrent with a 15% decrease in the amount of farnesylated p21Ras compared to controls. Expression of alpha-subunit (S60A,S62A) blunted FTase phosphorylation and activity in the presence of hyperinsulinemia, and inhibited insulin-stimulated increases in farnesylated p21Ras. Insulin-stimulated VSMC expressing the FTase alpha-subunit (S60A,S62A) showed decreased (i) phosphorylation of FTase, (ii) FTase activity, (iii) amounts of farnesylated p21Ras, (iv) DNA synthesis, and (v) migration. Thus, down-regulation of FTase activity appears to mitigate the potentially detrimental mitogenic effects of hyperinsulinemia on VSMC.

Insulin signals to prenyltransferases via the Shc branch of intracellular signaling

We assessed the roles of insulin receptor substrate-1 (IRS-1) and Shc in insulin action on farnesyltransferase (FTase) and geranylgeranyltransferase I (GGTase I) using Chinese hamster ovary (CHO) cells that overexpress wild-type human insulin receptors (CHO-hIR-WT) or mutant insulin receptors lacking the NPEY domain (CHO-DeltaNPEY) or 3T3-L1 fibroblasts transfected with adenoviruses that express the PTB or SAIN domain of IRS-1 and Shc, the pleckstrin homology (PH) domain of IRS-1, or the Src homology 2 (SH2) domain of Shc. Insulin promoted phosphorylation of the alpha-subunit of FTase and GGTase I in CHO-hIR-WT cells, but was without effect in CHO-DeltaNPEY cells. Insulin increased FTase and GGTase I activities and the amounts of prenylated Ras and RhoA proteins in CHO-hIR-WT (but not CHO-DeltaNPEY) cells. Overexpression of the PTB or SAIN domain of IRS-1 (which blocked both IRS-1 and Shc signaling) prevented insulin-stimulated phosphorylation of the FTase and GGTase I alpha-subunit activation of FTase and GGTase I and subsequent increases in prenylated Ras and RhoA proteins. In contrast, overexpression of the IRS-1 PH domain, which impairs IRS-1 (but not Shc) signaling, did not alter insulin action on the prenyltransferases, but completely inhibited the insulin effect on the phosphorylation of IRS-1 and on the activation of phosphatidylinositol 3-kinase and Akt. Finally, overexpression of the Shc SH2 domain completely blocked the insulin effect on FTase and GGTase I activities without interfering with insulin signaling to MAPK. These data suggest that insulin signaling from its receptor to the prenyltransferases FTase and GGTase I is mediated by the Shc pathway, but not the IRS-1/phosphatidylinositol 3-kinase pathway. Shc-mediated insulin signaling to MAPK may be necessary (but not sufficient) for activation of prenyltransferase activity. An additional pathway involving the Shc SH2 domain may be necessary to mediate the insulin effect on FTase and GGTase I.

Portal venous and enteric exocrine drainage versus systemic venous and bladder exocrine drainage of pancreas grafts: clinical outcome of 40 consecutive transplant recipients

OBJECTIVE

To test the hypothesis that pancreas transplantation using the more physiologic method of portal venous-enteric (PE) drainage could be performed without compromising patient and graft outcome, compared with the standard method of systemic venous-bladder (SB) drainage.

METHODS

Between November 1995 and November 1998, the authors prospectively followed up 20 consecutive patients with SB drainage followed by 20 consecutive patients with PE drainage. All patients underwent simultaneous pancreas-kidney transplantation, and all were immunosuppressed with antilymphocyte serum, cyclosporin, azathioprine, and steroids.

RESULTS

The actuarial patient survival rate at 1 year was 95% in the SB group and 100% in the PE group. Death-censored kidney graft survival was 100% in both groups; pancreas graft survival was 95% in the SB group and 100% in the PE group. The mean initial hospital stay was 15 days for both groups. However, during the first 6 months after transplantation, the SB group required more medical day-unit visits, mostly for treatment of metabolic acidosis and dehydration. The incidence of urinary tract infections was similar in both groups. The incidence of cytomegalovirus infections was significantly less in the PE group. The incidence of acute rejection was 37% in the SB group and 15% in the PE group. Mean serum creatinine levels 6 months after transplantation were significantly lower in the PE group than in the SB group. Glycemic control was excellent in both groups, but fasting serum insulin levels were significantly lower in the PE group.

CONCLUSIONS

The PE method of pancreas transplantation can be performed with excellent patient and graft outcomes.

Hyperinsulinemia enhances transcriptional activity of nuclear factor-kappaB induced by angiotensin II, hyperglycemia, and advanced glycosylation end products in vascular smooth muscle cells

Pathogenesis of macrovascular complications of diabetes may involve an activation of the transcription factor nuclear factor-kappaB (NF-kappaB) by hyperglycemia and advanced glycosylation end products (AGEs). Activation of NF-kappaB is believed to be dependent on activation of the Rho family of GTPases. Although the precise mechanism of the Rho-mediated action is not completely understood, posttranslational modification of the Rho proteins by geranylgeranylation is required for their subsequent activation. We observed that in cultured vascular smooth muscle cells (VSMCs), insulin stimulated the activity of geranylgeranyltransferase (GGTase) I and increased the amounts of geranylgeranylated Rho-A from 47% to 60% (P:<0.05). GGTI-286, an inhibitor of GGTase I, blocked both effects of insulin. Increased availability of prenylated Rho-A significantly augmented the abilities of angiotensin II (Ang II), hyperglycemia, and AGEs to activate NF-kappaB, as measured by NF-kappaB response-element luciferase reporter activity. Preincubations of VSMCs with insulin for 24 hours doubled NF-kappaB transactivation by Ang II, hyperglycemia, and AGEs. This priming effect of insulin was completely inhibited by GGTI-286. We demonstrate for the first time, to our knowledge, that insulin potentiates NF-kappaB-dependent transcriptional activity induced by hyperglycemia, AGEs, and Ang II in VSMCs by increasing the activity of GGTase I and the availability of geranylgeranylated Rho-A.

Potentiation of Rho-A-mediated lysophosphatidic acid activity by hyperinsulinemia

We have shown previously that insulin promotes phosphorylation and activation of farnesyltransferase and geranylgeranyltransferase (GGTase) II. We have now examined the effect of insulin on geranylgeranyltransferase I in MCF-7 breast cancer cells. Insulin increased GGTase I activity 3-fold and augmented the amounts of geranylgeranylated Rho-A by 18%. Both effects of the insulin were blocked by an inhibitor of GGTase I, GGTI-286. The insulin-induced increases in the amounts of geranylgeranylated Rho-A resulted in potentiation of the Rho-A-mediated effects of lysophosphatidic acid (LPA) on a serum response element-luciferase construct. Preincubation of cells with insulin augmented the LPA-stimulated serum response element-luciferase activation to 12-fold, compared with just 6-fold for LPA alone (p < 0.05). The potentiating effect of insulin was dose-dependent, inhibited by GGTI-286 and not mimicked by insulin-like growth factor-1. We conclude that insulin activates GGTase I, increases the amounts of geranylgeranylated Rho-A protein, and potentiates the Rho-A-dependent nuclear effects of LPA in MCF-7 breast cancer cells.

Effects of laparoscopic ovarian drilling on serum vascular endothelial growth factor and on insulin responses to the oral glucose tolerance test in women with polycystic ovary syndrome

OBJECTIVE

To evaluate the serum vascular endothelial growth factor concentrations and insulin responses to the oral glucose tolerance test before and after laparoscopic ovarian drilling in women with PCOS.

DESIGN

Prospective study.

SETTING

University teaching center.

PATIENT(S)

Twenty-seven women with clomiphene citrate-resistant polycystic ovary syndrome.

INTERVENTION(S)

Laparoscopic ovarian drilling.

MAIN OUTCOME MEASURE(S)

VEGF levels and insulin responses to OGTT before and after ovarian drilling.

RESULT(S)

No difference was found in VEGF levels in women with PCOS before (6.0 +/- 1.2 ng/mL) and after ovarian drilling (5.5 +/- 1.2 ng/mL). VEGF levels before and after ovarian drilling in women who conceived were, respectively, 5.9 +/- 1.0 and 5.1 +/- 0.9 ng/mL and in those who did not conceive were 6.0 +/- 1.3 and 5.7 +/- 1.2 ng/mL. No correlation was found between baseline serum insulin and VEGF levels. VEGF concentrations in women with normal ovaries (4.5 +/- 1.7 ng/mL) were significantly lower than in women with PCOS. There was no difference in glucose and insulin responses to OGTT before and after ovarian drilling.

CONCLUSION(S)

VEGF levels in women with PCOS are higher than in normal women, and ovarian drilling does not affect these levels. The procedure does not change insulin responses to OGTT.

Peroxisome proliferator-activated receptor gamma ligands inhibit retinoblastoma phosphorylation and G1--> S transition in vascular smooth muscle cells

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily that is activated by binding certain fatty acids, eicosanoids, and insulin-sensitizing thiazolidinediones (TZD). The TZD troglitazone (TRO) inhibits vascular smooth muscle cell proliferation and migration both in vitro and in vivo. The precise mechanism of its antiproliferative activity, however, has not been elucidated. We report here that PPARgamma ligands inhibit rat aortic vascular smooth muscle cell proliferation by blocking the events critical for G(1) --> S progression. Flow cytometry demonstrated that both TRO and another TZD, rosiglitazone, prevented G(1) --> S progression induced by platelet-derived growth factor and insulin. Movement of cells from G(1) --> S was also inhibited by the non-TZD, natural PPARgamma ligand 15-deoxy-(12,14)Delta prostaglandin J(2) (15d-PGJ(2)), and the mitogen-activated protein kinase pathway inhibitor PD98059. Inhibition of G(1) --> S exit by these compounds was accompanied by a substantial blockade of retinoblastoma protein phosphorylation. TRO and rosiglitazone attenuated both the mitogen-induced degradation of p27(kip1) and the mitogenic induction of p21(cip1). 15d-PGJ(2) and PD98059 inhibited both the degradation of p27(kip1) and the induction of cyclin D1 in response to mitogens. These effects resulted in the inhibition of mitogenic stimulation of cyclin-dependent kinases activated by cyclins D1 and E. These data demonstrate that PPARgamma ligands are antiproliferative drugs that act by modulating cyclin-dependent kinase inhibitors; they may provide a new therapeutic approach for proliferative vascular diseases.

Effects of insulin on prenylation as a mechanism of potentially detrimental influence of hyperinsulinemia

To investigate the cause and effect relationship between hyperinsulinemia and the increased amounts of farnesylated p21Ras, we performed hyperinsulinemic euglycemic clamps in normal weight volunteers as well as in normal mice and dogs. Insulin infusions significantly raised the amounts of farnesylated p21Ras in the white blood cells of humans, in liver samples of mice and dogs, and in aorta samples of mice. Obese hyperinsulinemic individuals and dogs (made hyperinsulinemic by surgical diversion of the pancreatic outflow from the portal vein into the vena cava) displayed increased amounts of farnesylated p21Ras before the hyperinsulinemic clamps. Infusions of insulin did not alter the already increased levels of farnesylated p21Ras in these experimental models. To further investigate the role of acquired insulin resistance in modulating insulin's effect on p21Ras prenylation, we induced insulin resistance in rats by glucosamine infusion. Insulin-resistant glucosamine-treated animals displayed significantly increased farnesylated p21Ras in response to insulin infusion compared to that in control saline-treated animals. Transgenic models of insulin resistance (heterozygous insulin receptor substrate-1 knockout mice, A-ZIP/F-1 fatless mice, and animals overexpressing glutamine:fructose-6-phosphate amidotransferase) contained increased amounts of farnesylated p21Ras. We conclude that hyperinsulinemia, either endogenous (a prominent feature of insulin resistance) or produced by infusions of insulin, increases the amounts of farnesylated p21Ras in humans, mice, and dogs. This aspect of insulin action may represent one facet of the molecular mechanism of the potentially detrimental influence of hyperinsulinemia.

High glucose and insulin inhibit VSMC MKP-1 expression by blocking iNOS via p38 MAPK activation

Our laboratory has recently demonstrated a role for the phosphatidylinositol 3-kinase-mediated inducible NO synthase (iNOS) signaling pathway in acute regulation of insulin-induced mitogen-activated protein phosphatase-1 (MKP-1) expression in primary cultures of rat aortic vascular smooth muscle cells (VSMCs) (N. Begum, L. Ragolia, M. McCarthy, and N. Duddy. J. Biol. Chem. 273: 25164-25170, 1998). We now show that prolonged treatment of VSMCs with 100 nM insulin and high glucose (25 mM) for 12-24 h, to mimic hyperinsulinemia and hyperglycemia, completely blocked MKP-1 mRNA and protein expression in response to subsequent acute insulin treatment. To understand the mechanism of insulin resistance induced by high glucose and insulin, we studied the regulation of iNOS protein induction in these cells. Both high glucose and chronic insulin treatment caused a marked impairment of iNOS induction in response to acute insulin. Blocking of signaling via the p38 mitogen-activated protein kinase (MAPK) pathway by prior treatment for 1 h with SB-203580, a synthetic p38 MAPK inhibitor, completely prevented the inhibition of iNOS induced by high glucose and insulin and restored MKP-1 induction to levels observed with acute insulin treatment. In contrast, PD-98059, a MEK inhibitor, had no effect. Furthermore, high glucose and chronic insulin treatment caused sustained p38 MAPK activation. We conclude 1) that chronic insulin and high glucose-induced insulin resistance is accompanied by marked reductions in both iNOS and MKP-1 inductions due to p38 MAPK activation that leads to excessive cell growth and 2) that p38 MAPK/extracellular signal-regulated kinase pathways regulate iNOS induction, thereby controlling MKP-1 expression, which in turn inactivates MAPKs as a feedback mechanism and inhibits cell growth.