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1.  Hepatic Insulin Resistance is Sufficient to Produce Dyslipidemia and Susceptibility to Atherosclerosis 
Cell metabolism  2008;7(2):125-134.
Insulin resistance plays a central role in the development of the metabolic syndrome, but how it relates to cardiovascular disease remains controversial. Liver insulin receptor knockout (LIRKO) mice have pure hepatic insulin resistance. On a chow diet, LIRKO mice have a proatherogenic lipoprotein profile with reduced HDL cholesterol and VLDL particles that are markedly enriched in cholesterol. This is due to increased secretion and decreased clearance of apoB-containing lipoproteins, coupled with decreased triglyceride secretion secondary to increased expression of PGC-1β, which promotes VLDL secretion, but decreased expression of SREBP-1c, SREBP-2 and their targets, the lipogenic enzymes and the LDL receptor. Within twelve weeks on an atherogenic diet, LIRKO mice show marked hypercholesterolemia, and 100% of LIRKO mice, but 0% of controls, develop severe atherosclerosis. Thus, insulin resistance at the level of the liver is sufficient to produce the dyslipidemia and increased risk of atherosclerosis associated with the metabolic syndrome.
PMCID: PMC4251554  PMID: 18249172
2.  Induction of Vascular Insulin Resistance, Endothelin-1 Expression and Acceleration of Atherosclerosis by the Overexpression of Protein Kinase C β Isoform in the Endothelium 
Circulation research  2013;113(4):418-427.
Loss of insulin action on the endothelium can cause endothelial dysfunction and atherosclerosis. Hyperglycemia and elevated fatty acids induced by diabetes can activate protein kinase C (PKC) β isoforms and selectively inhibit insulin signaling via phosphatidylinositol 3-kinase (PI3K)/Akt pathway to inhibit the activation of endothelial nitric oxide synthase (eNOS) and metabolic actions.
To demonstrate that overexpressing PKCβ2 isoform in endothelial cells can cause selective insulin resistance and exacerbate atherosclerosis in the aorta.
Methods and Results
PKCβ2 isoform was overexpressed in endothelial cells using a promoter of vascular endothelial cell-cadherin (VE-Cadherin). These mice were cross-bred with ApoE-/- mice (Tg (Prkcb)ApoE-/-). On a Western diet, Tg(Prkcb)ApoE-/- and ApoE-/- mice did not differ in systemic insulin sensitivity, glucose tolerance, plasma lipid or blood pressure. Insulin action in endothelial cells and femoral artery from Tg(Prkcb)ApoE-/- mice were impaired by ∼40% with respect to Akt/eNOS activation and leukocyte-endothelial cell binding increased in cultured lung endothelial cells from Tg(Prkcb)ApoE-/-mice compared to ApoE-/- mice. Basal and angiotensin stimulated big endothelin-1 (ET-1) levels were elevated in Tg(Prkcb)ApoE-/- mice compared to ApoE-/- mice. The severity of atherosclerosis in the aorta from Tg(Prkcb)ApoE-/- mice increased by ∼70% as measured by en face fat staining and plaque content of the number of smooth muscle cells, macrophages and extracellular matrix.
Specific PKCβ2 activation in the endothelial cells caused dysfunction and accelerated atherosclerosis due to loss of insulin-stimulated Akt/eNOS activation and angiotensin induced increases in ET-1 expression.
PMCID: PMC3893704  PMID: 23759514
Endothelium; endothelial dysfunction; protein kinase C; insulin resistance; atherosclerosis
3.  Serine Phosphorylation Sites on IRS2 Activated by Angiotensin II and Protein Kinase C To Induce Selective Insulin Resistance in Endothelial Cells 
Molecular and Cellular Biology  2013;33(16):3227-3241.
Protein kinase C (PKC) activation, induced by hyperglycemia and angiotensin II (AngII), inhibited insulin-induced phosphorylation of Akt/endothelial nitric oxide (eNOS) by decreasing tyrosine phosphorylation of IRS2 (p-Tyr-IRS2) in endothelial cells. PKC activation by phorbol ester (phorbol myristate acetate [PMA]) reduced insulin-induced p-Tyr-IRS2 by 46% ± 13% and, similarly, phosphorylation of Akt/eNOS. Site-specific mutational analysis showed that PMA increased serine phosphorylation at three sites on IRS2 (positions 303, 343, and 675), which affected insulin-induced tyrosine phosphorylation of IRS2 at positions 653, 671, and 911 (p-Tyr-IRS2) and p-Akt/eNOS. Specific PKCβ2 activation decreased p-Tyr-IRS2 and increased the phosphorylation of two serines (Ser303 and Ser675) on IRS2 that were confirmed in cells overexpressing single point mutants of IRS2 (S303A or S675A) containing a PKCβ2-dominant negative or selective PKCβ inhibitor. AngII induced phosphorylation only on Ser303 of IRS2 and inhibited insulin-induced p-Tyr911 of IRS2 and p-Akt/eNOS, which were blocked by an antagonist of AngII receptor I, losartan, or overexpression of single mutant S303A of IRS2. Increases in p-Ser303 and p-Ser675 and decreases in p-Tyr911 of IRS2 were observed in vessels of insulin-resistant Zucker fatty rats versus lean rats. Thus, AngII or PKCβ activation can phosphorylate Ser303 and Ser675 in IRS2 to inhibit insulin-induced p-Tyr911 and its anti-atherogenic actions (p-Akt/eNOS) in endothelial cells.
PMCID: PMC3753901  PMID: 23775122
4.  Vascular complications of diabetes: mechanisms of injury and protective factors 
Cell metabolism  2013;17(1):20-33.
In patients with diabetes, atherosclerosis is the main reason for impaired life expectancy, and diabetic nephropathy and retinopathy are the largest contributors to end-stage renal disease and blindness, respectively. An improved therapeutic approach to combat diabetic vascular complications might include blocking mechanisms of injury as well as promoting protective or regenerating factors, for example by enhancing the action of insulin-regulated genes in endothelial cells, promoting gene programs leading to induction of antioxidant or anti-inflammatory factors, or improving the sensitivity to vascular cell survival factors. Such strategies could help prevent complications despite suboptimal metabolic control.
PMCID: PMC3546345  PMID: 23312281
5.  Protective Effects of GLP-1 on Glomerular Endothelium and Its Inhibition by PKCβ Activation in Diabetes 
Diabetes  2012;61(11):2967-2979.
To characterize glucagon-like peptide (GLP)-1 signaling and its effect on renal endothelial dysfunction and glomerulopathy. We studied the expression and signaling of GLP-1 receptor (GLP-1R) on glomerular endothelial cells and the novel finding of protein kinase A–dependent phosphorylation of c-Raf at Ser259 and its inhibition of angiotensin II (Ang II) phospho–c-Raf(Ser338) and Erk1/2 phosphorylation. Mice overexpressing protein kinase C (PKC)β2 in endothelial cells (EC-PKCβ2Tg) were established. Ang II and GLP-1 actions in glomerular endothelial cells were analyzed with small interfering RNA of GLP-1R. PKCβ isoform activation induced by diabetes decreased GLP-1R expression and protective action on the renal endothelium by increasing its degradation via ubiquitination and enhancing phospho–c-Raf(Ser338) and Ang II activation of phospho-Erk1/2. EC-PKCβ2Tg mice exhibited decreased GLP-1R expression and increased phospho–c-Raf(Ser338), leading to enhanced effects of Ang II. Diabetic EC-PKCβ2Tg mice exhibited greater loss of endothelial GLP-1R expression and exendin-4–protective actions and exhibited more albuminuria and mesangial expansion than diabetic controls. These results showed that the renal protective effects of GLP-1 were mediated via the inhibition of Ang II actions on cRaf(Ser259) and diminished by diabetes because of PKCβ activation and the increased degradation of GLP-1R in the glomerular endothelial cells.
PMCID: PMC3478518  PMID: 22826029
6.  Tissue-specific insulin signaling, metabolic syndrome and cardiovascular disease 
Impaired insulin signaling is central to the development of the metabolic syndrome and can promote cardiovascular disease indirectly through development of abnormal glucose and lipid metabolism, hypertension and a proinflammatory state. However, insulin action directly on vascular endothelium, atherosclerotic plaque macrophages, and in the heart, kidney, and retina has now been described, and impaired insulin signaling in these locations can alter progression of cardiovascular disease in the metabolic syndrome and affect development of microvascular complications of diabetes. Recent advances in our understanding of the complex pathophysiology of insulin’s effects on vascular tissues offer new opportunities for preventing these cardiovascular disorders.
PMCID: PMC3511859  PMID: 22895666
7.  Retinal Not Systemic Oxidative and Inflammatory Stress Correlated with VEGF Expression in Rodent Models of Insulin Resistance and Diabetes 
To correlate changes between VEGF expression with systemic and retinal oxidative stress and inflammation in rodent models of obesity induced insulin resistance and diabetes.
Retinal VEGF mRNA and protein levels were assessed by RT-PCR and VEGF ELISA, respectively. Urinary 8-hydroxydeoxyguanosine (8-OHdG), blood levels of C-reactive protein (CRP), malondialdehyde (MDA), and CD11b/c positive cell ratio were used as systemic inflammatory markers. Retinal expression of Nox2, Nox4, and p47phox mRNA levels were measured as oxidative stress markers. TNF-α, inter-cellular adhesion molecule-1 (ICAM-1), IL1β, and activation of nuclear factor κB (NF-κB) were used as retinal inflammatory markers.
Retinal VEGF mRNA and protein expression increased in Zucker diabetic fatty (ZDFfa/fa) rats and streptozotosin (STZ) induced diabetic Sprague-Dawley rats, after two months of disease, but not in Zucker fatty (ZF) rats. Systemic markers of oxidative stress and inflammation were elevated in insulin resistant and diabetic rats. Some oxidative stress and inflammatory markers (TNF-α, IL-6, ICAM-1, and IL1-β) were upregulated in the retina of ZDFfa/fa and STZ diabetic rats after 4 months of disease. In contrast, activation of NF-κB in the retina was observed in high fat fed nondiabetic and diabetic cis-NF-κBEGFP mice, ZF, ZDFfa/fa, and STZ-induced diabetic rats.
Only persistent hyperglycemia and diabetes increased retinal VEGF expression. Some markers of inflammation and oxidative stress were elevated in the retina and systemic circulation of obese and insulin resistant rodents with and without diabetes. Induction of VEGF and its associated retinal pathologies by diabetes requires chronic hyperglycemia and factors in addition to inflammation and oxidative stress.
Only chronic diabetes induced late markers of inflammation and oxidative stress in the retina correlated with increased VEGF expression, but insulin resistance alone caused systemic and retinal inflammation and no increase in VEGF elevation.
PMCID: PMC3753893  PMID: 23197686
8.  PKCβ-induced Selective IRS1 Dysfunction and Insulin Resistance in Renal Glomeruli of Rodent Models of Diabetes and Obesity 
Kidney international  2011;79(8):883-896.
Insulin resistance has been associated with the progression of chronic kidney disease in both diabetes and obesity. This study characterizes insulin signaling in renal tubules and glomeruli in insulin resistant and diabetic states.
Insulin-induced phosphorylation of insulin receptor substrate-1 (IRS1), Akt, endothelial nitric oxide (eNOS), and glycogen synthase kinase 3α (GSK3α) were selectively inhibited in the glomeruli but not in the renal tubules of both streptozotocin (STZ)-diabetic and Zucker fatty, insulin resistant rats compared to non-diabetic and Zucker lean rats. Protein levels, but not the mRNA expression, of IRS1 were decreased only in the glomeruli of STZ-diabetic rats and increased its association with ubiquitination. Protein kinase C (PKC) β isoform inhibitor, ruboxistaurin (RBX), treatment enhanced insulin actions and elevated IRS1 expression. In glomerular endothelial cells, high glucose inhibited phosphorylation of Akt, eNOS and GSK3α, decreased IRS1 protein expression and increased association with ubiquitination. Overexpression of IRS1 or the addition of RBX reversed the inhibitory effects of high glucose.
Selective inhibition of the IRS1/PI3K/Akt pathway and insulin activation of eNOS and GSK3α in the glomeruli in diabetes and insulin resistance is partly due to increased IRS1 degradation and PKCβ activation. The loss of insulin's effect on endothelial eNOS and GSK3α activation may contribute to the glomeropathy observed in diabetes and obesity.
PMCID: PMC3612886  PMID: 21228767
diabetic nephropathy; insulin resistance; obesity; insulin receptor substrate-1; protein kinase C β
9.  Differential regulation of VEGF signaling by PKCα and PKCε in endothelial cells 
Vascular endothelial growth factor (VEGF) stimulates pro-angiogenic signal transduction and cell function in part through activation of protein kinase C (PKC). Our aim was to examine how individual isoforms of PKC affect VEGF action.
Methods and Results
Transfection of bovine aortic endothelial cells with small interfering RNA (siRNA) targeting either PKCα, δ, or ε caused a reduction in the cognate PKC protein by 76–89% without changing expression of non-targeted isoforms. Downregulation of PKCε abrogated VEGF-stimulated phosphorylation of Akt at Ser473 and eNOS at Ser1179 and decreased VEGF-stimulated NO synthase activity in intact cells. In contrast, PKCα knockdown increased Akt and eNOS phosphorylation, while PKCδ knockdown had no significant effect. PKCε knockdown also decreased VEGF-stimulated Erk1/2 phosphorylation and abolished VEGF-stimulated DNA synthesis. Consistent with an effect on several pathways of VEGF signaling, VEGF receptor-2 (VEGFR2) tyrosine phosphorylation and expression of VEGFR2 protein and mRNA was decreased by 81, 90, and 84%, respectively, during knockdown of PKCε, but increased during PKCα knockdown.
By regulating VEGFR2 expression and activation, PKCε expression is critical for activation of Akt and eNOS by VEGF and contributes to VEGF-stimulated Erk activation, whereas PKCα has opposite effects.
PMCID: PMC3340425  PMID: 18323518
10.  Endothelium-dependent delivery of insulin to muscle interstitium 
Cell metabolism  2011;13(3):236-238.
Insulin contributes to skeletal muscle glucose uptake by increasing blood flow and recruiting perfused capillaries. In this issue, Kubota et al. (2011) show that deletion of IRS-2 in endothelial cells in mice causes impaired transcapillary insulin transport, decreased insulin-stimulated glucose uptake in muscle, and mild glucose intolerance.
PMCID: PMC3232062  PMID: 21356512
11.  The effect of chronic heart failure and type 2 diabetes on insulin-stimulated endothelial function is similar and additive 
Chronic heart failure is associated with endothelial dysfunction and insulin resistance. The aim of this investigation was to study insulin-stimulated endothelial function and glucose uptake in skeletal muscles in patients with heart failure in comparison to patients with type 2 diabetes.
Twenty-three patients with systolic heart failure and no history of diabetes, seven patients with both systolic heart failure and type 2 diabetes, 19 patients with type 2 diabetes, and ten healthy controls were included in the study. Endothelial function was studied by venous occlusion plethysmography. Insulin-stimulated endothelial function was assessed after intra-arterial infusion of insulin followed by co-infusion with serotonin in three different dosages. Forearm glucose uptake was measured during the insulin infusion.
Patients with systolic heart failure had impaired insulin-stimulated endothelial function. The percentage increase in blood flow during co-infusion with insulin and serotonin dose response study was 24.74% ± 6.16%, 23.50% ± 8.32%, and 22.29% ± 10.77% at the three doses respectively, compared to the healthy control group 45.96% ± 11.56%, 67.40% ± 18.11% and 84.57% ± 25.73% (P = 0.01). Insulin-stimulated endothelial function was similar in heart failure patients and patients with type 2 diabetes, while it was further deteriorated in patients suffering from both heart failure and diabetes with a percentage increase in blood flow of 19.15% ± 7.81%, −2.35% ± 11.76%, and 5.82% ± 17.70% at the three doses of serotonin, respectively. Forearm glucose uptake was impaired in patients with heart failure compared to healthy controls (P = 0.03) and tended to be further impaired by co-existence of diabetes (P = 0.08).
Systolic heart failure and type 2 diabetes result in similar vascular insulin resistance and reduced muscular insulin-stimulated glucose uptake. The effects of systolic heart failure and type 2 diabetes appear to be additive.
PMCID: PMC3253770  PMID: 22241951
insulin resistance; diabetes; heart failure; endothelial function
13.  Modulating Notch Signaling to Enhance Neovascularization and Reperfusion in Diabetic Mice 
Biomaterials  2010;31(34):9048-9056.
Diabetes can diminish the responsiveness to angiogenic factors (e.g., VEGF) important for wound healing and the treatment of ischemic diseases, and this study investigated the hypothesis that this effect can be reversed by altering Notch signaling. Aortic endothelial cells (ECs) isolated from diabetic mice demonstrated reduced sprouting capability in vitro, but adding a Notch inhibitor (DAPT) led to cell-density and VEGF-dose dependent enhancement of proliferation, migration and sprouting, in both 2-D and 3-D cultures, as compared to VEGF alone. The in vivo effects of VEGF and DAPT were tested in the ischemic hindlimbs of diabetic mice. Combining VEGF and DAPT delivery resulted in increased blood vessel density (~150%) and improved tissue perfusion (~160%), as compared to VEGF alone. To examine if DAPT would interfere with vessel maturation, DAPT was also delivered with a combination of VEGF and platelet derived growth factor (PDGF). DAPT and PDGF did not interfere with the effects of the other, and highly functional and mature networks of vessels could be formed with appropriate delivery. In summary, modulating Notch signaling enhances neovascularization and perfusion recovery in diabetic mice suffering from ischemia, suggesting this approach could have utility for human diabetics.
PMCID: PMC2949444  PMID: 20800279
14.  Endothelial function is unaffected by changing between carvedilol and metoprolol in patients with heart failure-a randomized study 
Carvedilol has been shown to be superior to metoprolol tartrate to improve clinical outcomes in patients with heart failure (HF), yet the mechanisms responsible for these differences remain unclear. We examined if there were differences in endothelial function, insulin stimulated endothelial function, 24 hour ambulatory blood pressure and heart rate during treatment with carvedilol, metoprolol tartrate and metoprolol succinate in patients with HF.
Twenty-seven patients with mild HF, all initially treated with carvedilol, were randomized to a two-month treatment with carvedilol, metoprolol tartrate or metoprolol succinate. Venous occlusion plethysmography, 24-hour blood pressure and heart rate measurements were done before and after a two-month treatment period.
Endothelium-dependent vasodilatation was not affected by changing from carvedilol to either metoprolol tartrate or metoprolol succinate. The relative forearm blood flow at the highest dose of serotonin was 2.42 ± 0.33 in the carvedilol group at baseline and 2.14 ± 0.24 after two months continuation of carvedilol (P = 0.34); 2.57 ± 0.33 before metoprolol tartrate treatment and 2.42 ± 0.55 after treatment (p = 0.74) and in the metoprolol succinate group 1.82 ± 0.29 and 2.10 ± 0.37 before and after treatment, respectively (p = 0.27). Diurnal blood pressures as well as heart rate were also unchanged by changing from carvedilol to metoprolol tartrate or metoprolol succinate.
Endothelial function remained unchanged when switching the beta blocker treatment from carvedilol to either metoprolol tartrate or metoprolol succinate in this study, where blood pressure and heart rate also remained unchanged in patients with mild HF.
Trial registration
Current Controlled Trials NCT00497003
PMCID: PMC3212926  PMID: 21999413
Heart failure; Endothelial function; Beta blocker
15.  Loss of insulin signaling in vascular endothelial cells accelerates atherosclerosis in apolipoprotein E null mice 
Cell metabolism  2010;11(5):379-389.
To determine whether insulin action on endothelial cells promotes or protects against atherosclerosis, we generated apolipoprotein E null mice in which the insulin receptor gene was intact or conditionally deleted in vascular endothelial cells. Insulin sensitivity, glucose tolerance, plasma lipids, and blood pressure were not different between the two groups, but atherosclerotic lesion size was more than 2-fold higher in mice lacking endothelial insulin signaling. Endothelium-dependent vasodilation was impaired and endothelial cell VCAM-1 expression was increased in these animals. Adhesion of mononuclear cells to endothelium in vivo was increased 4-fold compared with controls, but reduced to below control values by a VCAM-1 blocking antibody. These results provide definitive evidence that loss of insulin signaling in endothelium, in the absence of competing systemic risk factors, accelerates atherosclerosis. Therefore, improving insulin sensitivity in the endothelium of patients with insulin resistance or type 2 diabetes may prevent cardiovascular complications.
PMCID: PMC3020149  PMID: 20444418
16.  Metoprolol compared to carvedilol deteriorates insulin-stimulated endothelial function in patients with type 2 diabetes - a randomized study 
Studies of beta blockade in patients with type 2 diabetes have shown inferiority of metoprolol treatment compared to carvedilol on indices of insulin resistance. The aim of this study was to examine the effect of metoprolol versus carvedilol on endothelial function and insulin-stimulated endothelial function in patients with type 2 diabetes.
24 patients with type 2 diabetes were randomized to receive either 200 mg metoprolol succinate or 50 mg carvedilol daily. Endothelium-dependent vasodilation was assessed by using venous occlusion plethysmography with increasing doses of intra-arterial infusions of the agonist serotonin. Insulin-stimulated endothelial function was assessed after co-infusion of insulin for sixty minutes. Vaso-reactivity studies were done before and after the two-month treatment period.
Insulin-stimulated endothelial function was deteriorated after treatment with metoprolol, the percentage change in forearm blood-flow was 60.19% ± 17.89 (at the highest serotonin dosages) before treatment and -33.80% ± 23.38 after treatment (p = 0.007). Treatment with carvedilol did not change insulin-stimulated endothelial function. Endothelium-dependent vasodilation without insulin was not changed in either of the two treatment groups.
This study shows that vascular insulin sensitivity was preserved during treatment with carvedilol while blunted during treatment with metoprolol in patients with type 2 diabetes.
Trial registration
Current Controlled Trials NCT00497003
PMCID: PMC2893119  PMID: 20500877

Results 1-16 (16)