Endothelial Insulin Signaling Research Articles

Neuraminidase causes endothelial phosphatidylserine externalization and ADAM17 activation: implications for shedding of insulin receptor and endothelial insulin resistance

Endothelial insulin resistance represents a causal factor in the pathogenesis of type 2 diabetes (T2D) and vascular disease, thus underscoring the need to identify molecular mechanisms underlying defects in endothelial insulin signaling. We previously showed that a disintegrin and metalloproteinase-17 (ADAM17) is increased while insulin receptor α-subunit (IRα) is decreased in the vasculature of patients with T2D, leading to impaired insulin-induced vasodilation. We also showed that ADAM17 is a sheddase that targets IRα. Externalization of phosphatidylserine (PS) from the inner to the outer leaflet of cell membranes has been proposed as a pivotal step in the activation of ADAM17. However, whether PS externalization increases ADAM17 sheddase activity and, consequently, shedding of endothelial IRα in T2D is not known. Herein, we hypothesized that neuraminidase (Neu), an enzyme we showed is upregulated in diabetes, leads to PS externalization via activation of Ca2+ influx and subsequent induction of ADAM17 sheddase activity. All reported differences are significant at P<0.05. In support of this hypothesis, we report that Neu and ADAM17 activities are increased in plasma of individuals with T2D, relative to non-T2D subjects. In experiments using cultured endothelial cells, we show that exposure to Neu increases Ca2+ influx and ADAM17 activity. We also find that augmenting endothelial Ca 2+ influx using a calcium ionophore (A23187) increases adhesion of lactadherin (a peptide that binds externalized PS) to the surface of endothelial cells, as does treatment with the ADAM17 activator, PMA, which also reduces IRα on the cells. Importantly, overexpression of ADAM17 in endothelial cells reduces IRα in cell lysates and this coincides with a tendency towards increased IRα in the cell culture supernatant, indicative of protein shedding. Collectively, these findings suggest that Neu causes Ca 2+ influx in endothelial cells, favoring PS externalization and, consequently, increased ADAM17 activity and shedding of IRα. Hence, inhibition of Neu and ADAM17 sheddase activities should be considered as novel potential strategies to improve endothelial insulin signaling in T2D. R01HL151384 (to LAML and JP), R01HL153264 (to LAML and JP), and R01HL137769 (to JP). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

ADAM17 cleaves the insulin receptor ectodomain on endothelial cells and causes vascular insulin resistance.

Inflammation and vascular insulin resistance are hallmarks of type 2 diabetes (T2D). However, several potential mechanisms causing abnormal endothelial insulin signaling in T2D need further investigation. Evidence indicates that the activity of ADAM17 (a disintegrin and metalloproteinase-17) and the presence of insulin receptor (IR) in plasma are increased in subjects with T2D. Accordingly, we hypothesized that in T2D, increased ADAM17 activity sheds the IR ectodomain from endothelial cells and impairs insulin-induced vasodilation. We used small visceral arteries isolated from a cross-sectional study of subjects with and without T2D undergoing bariatric surgery, human cultured endothelial cells, and recombinant proteins to test our hypothesis. Here, we demonstrate that arteries from subjects with T2D had increased ADAM17 expression, reduced presence of tissue inhibitor of metalloproteinase-3 (TIMP3), decreased extracellular IRα, and impaired insulin-induced vasodilation versus those from subjects without T2D. In vitro, active ADAM17 cleaved the ectodomain of the IRβ subunit. Endothelial cells with ADAM17 overexpression or exposed to the protein kinase-C activator, PMA, had increased ADAM17 activity, decreased IRα presence on the cell surface, and increased IR shedding. Moreover, pharmacological inhibition of ADAM17 with TAPI-0 rescued PMA-induced IR shedding and insulin-signaling impairments in endothelial cells and insulin-stimulated vasodilation in human arteries. In aggregate, our findings suggest that ADAM17-mediated shedding of IR from the endothelial surface impairs insulin-mediated vasodilation. Thus, we propose that inhibition of ADAM17 sheddase activity should be considered a strategy to restore vascular insulin sensitivity in T2D.NEW & NOTEWORTHY To our knowledge, this is the first study to investigate the involvement of ADAM17 in causing impaired insulin-induced vasodilation in T2D. We provide evidence that ADAM17 activity is increased in the vasculature of patients with T2D and support the notion that ADAM17-mediated shedding of endothelial IRα ectodomains is a novel mechanism causing vascular insulin resistance. Our results highlight that targeting ADAM17 activity may be a potential therapeutic strategy to correct vascular insulin resistance in T2D.

Endothelial Cell Insulin Signaling Regulates CXCR4 (C-X-C Motif Chemokine Receptor 4) and Limits Leukocyte Adhesion to Endothelium.

An activated, proinflammatory endothelium is a key feature in the development of complications of obesity and type 2 diabetes and can be caused by insulin resistance in endothelial cells. We analyzed primary human endothelial cells by RNA sequencing to discover novel insulin-regulated genes and used endothelial cell culture and animal models to characterize signaling through CXCR4 (C-X-C motif chemokine receptor 4) in endothelial cells. CXCR4 was one of the genes most potently regulated by insulin, and this was mediated by PI3K (phosphatidylinositol 3-kinase), likely through FoxO1, which bound to the CXCR4 promoter. CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared with lean controls and 37% higher in db/db mice than db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. SDF-1 (stromal cell-derived factor-1)-the ligand for CXCR4-increased leukocyte adhesion to cultured endothelial cells. This effect was lost after deletion of CXCR4 by gene editing while 80% of the increase was prevented by treatment of endothelial cells with insulin. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling after intravenous injection of SDF-1, but most of this response was prevented in transgenic mice with endothelial overexpression of IRS-1 (insulin receptor substrate-1). Endothelial cell insulin signaling limits leukocyte/endothelial cell interaction induced by SDF-1 through downregulation of CXCR4. Improving insulin signaling in endothelial cells or inhibiting endothelial CXCR4 may reduce immune cell recruitment to the vascular wall or tissue parenchyma in insulin resistance and thereby help prevent several vascular complications.

A Nine-Strain Bacterial Consortium Improves Portal Hypertension and Insulin Signaling and Delays NAFLD Progression In Vivo.

The gut microbiome has a recognized role in Non-alcoholic fatty liver disease (NAFLD) and associated comorbidities such as Type-2 diabetes and obesity. Stool transplantation has been shown to improve disease by restoring endothelial function and insulin signaling. However, more patient-friendly treatments are required. The present study aimed to test the effect of a defined bacterial consortium of nine gut commensal strains in two in vivo rodent models of Non-alcoholic steatohepatitis (NASH): a rat model of NASH and portal hypertension (PHT), and the Stelic animal (mouse) model (STAM™). In both studies the consortium was administered orally q.d. after disease induction. In the NASH rats, the consortium was administered for 2 weeks and compared to stool transplant. In the STAM™ study administration was performed for 4 weeks, and the effects compared to vehicle or Telmisartan at the stage of NASH/early fibrosis. A second group of animals was followed for another 3 weeks to assess later-stage fibrosis. In the NASH rats, an improvement in PHT and endothelial function was observed. Gut microbial compositional changes also revealed that the consortium achieved a more defined and richer replacement of the gut microbiome than stool transplantation. Moreover, liver transcriptomics suggested a beneficial modulation of pro-fibrogenic pathways. An improvement in liver fibrosis was then confirmed in the STAM™ study. In this study, the bacterial consortium improved the NAFLD activity score, consistent with a decrease in steatosis and ballooning. Serum cytokeratin-18 levels were also reduced. Therefore, administration of a specific bacterial consortium of defined composition can ameliorate NASH, PHT, and fibrosis, and delay disease progression.

Endothelial HSP72 is not reduced in type 2 diabetes nor is it a key determinant of endothelial insulin sensitivity.

Impaired endothelial insulin signaling and consequent blunting of insulin-induced vasodilation is a feature of type 2 diabetes (T2D) that contributes to vascular disease and glycemic dysregulation. However, the molecular mechanisms underlying endothelial insulin resistance remain poorly known. Herein, we tested the hypothesis that endothelial insulin resistance in T2D is attributed to reduced expression of heat shock protein 72 (HSP72). HSP72 is a cytoprotective chaperone protein that can be upregulated with heating and is reported to promote insulin sensitivity in metabolically active tissues, in part via inhibition of JNK activity. Accordingly, we further hypothesized that, in individuals with T2D, 7 days of passive heat treatment via hot water immersion to waist level would improve leg blood flow responses to an oral glucose load (i.e., endogenous insulin stimulation) via induction of endothelial HSP72. In contrast, we found that: 1) endothelial insulin resistance in T2D mice and humans was not associated with reduced HSP72 in aortas and venous endothelial cells, respectively; 2) after passive heat treatment, improved leg blood flow responses to an oral glucose load did not parallel with increased endothelial HSP72; and 3) downregulation of HSP72 (via small-interfering RNA) or upregulation of HSP72 (via heating) in cultured endothelial cells did not impair or enhance insulin signaling, respectively, nor was JNK activity altered. Collectively, these findings do not support the hypothesis that reduced HSP72 is a key driver of endothelial insulin resistance in T2D but provide novel evidence that lower-body heating may be an effective strategy for improving leg blood flow responses to glucose ingestion-induced hyperinsulinemia.

The transcriptional coregulator CITED2 suppresses expression of IRS-2 and impairs insulin signaling in endothelial cells.

Endothelial cell insulin resistance contributes to the development of vascular complications in diabetes. Hypoxia-inducible factors (HIFs) modulate insulin sensitivity, and we have previously shown that a negative regulator of HIF activity, CREB-binding protein/p300 (CBP/p300) interacting transactivator-2 (CITED2), is increased in the vasculature of people with type 2 diabetes. Therefore, we examined whether CITED2 regulates endothelial insulin sensitivity. In endothelial cells isolated from mice with a "floxed" mutation in the Cited2 gene, loss of CITED2 markedly enhanced insulin-stimulated Akt phosphorylation without altering extracellular signal-related kinase 1/2 (ERK1/2) phosphorylation. Similarly, insulin-stimulated Akt phosphorylation was increased in aortas of mice with endothelial-specific deletion of CITED2. Consistent with these observations, loss of CITED2 in endothelial cells increased insulin-stimulated endothelial nitric oxide synthase phosphorylation, Vegfa expression, and cell proliferation. Endothelial cells lacking CITED2 exhibited an increase in insulin receptor substrate (IRS)-2 protein, a key mediator of the insulin signaling cascade, whereas IRS-1 was unchanged. Conversely, overexpression of CITED2 in endothelial cells decreased IRS-2 protein by 55% without altering IRS-1, resulting in impaired insulin-stimulated Akt phosphorylation and Vegfa expression. Overexpression of HIF-2α significantly increased activity of the Irs2 promoter, and coexpression of CITED2 abolished this increase. Moreover, chromatin immunoprecipitation (ChIP) showed that loss of CITED2 increased occupancy of p300, a key component of the HIF transcriptional complex, on the Irs2 promoter. Together, these results show that CITED2 selectively inhibits endothelial insulin signaling and action through the phosphoinositide 3-kinase (PI3K)/Akt pathway via repression of HIF-dependent IRS-2 expression. CITED2 is thus a promising target to improve endothelial insulin sensitivity and prevent the vascular complications of diabetes.NEW & NOTEWORTHY Endothelial cell insulin resistance is a major contributor to the development of diabetic complications. In this study, we have shown that CITED2, a transcriptional coregulator, inhibits endothelial insulin signaling through the PI3K/Akt pathway via repression of HIF-dependent IRS-2 expression, and that deletion of CITED2 enhances insulin signaling. Thus, CITED2 represents a novel and promising target to improve insulin sensitivity in endothelial cells and prevent vascular complications in diabetes.

Macrophage Depletion Improves Endothelial Insulin Resistance and Protects against Cardiovascular Injury in Salt-Sensitive Hypertension.

Vascular endothelial insulin signaling is critical for the maintenance of vascular and metabolic homeostasis. We have previously shown that in hypertensive Dahl rats, impaired vascular insulin action is linked to angiotensin II activation of the NFκB inflammatory pathway. Macrophage polarization (M1) has implicated in hypertensive and metabolic diseases. Here, we investigated the effect of macrophage depletion using liposome-encapsulated clodronate (LEC) on endothelial insulin resistance and cardiovascular remodeling in Dahl salt-sensitive (DS) rats. High salt intake (HS) for 5 weeks increased systolic blood pressure (SBP: 192 ± 5 vs. 144 ± 4 mmHg in NS, p < 0.05), aortic and cardiac hypertrophy, cardiac fibrosis, and impaired acetylcholine- and insulin-induced vasorelaxation, accompanied by impaired insulin activation of endothelial nitric oxide synthases (eNOS)/NO signaling. HS rats had a significant increase in CD68 (a monocyte/macrophage marker) expression in the aorta and the heart. LEC reduced SBP (168 ± 5 mmHg, p < 0.05) and cardiovascular injury and improved acetylcholine- and insulin-mediated vasorelaxation and insulin signaling molecules with a reduction in the macrophage infiltration in the aorta and the heart. HS rats also manifested an increase in the aortic expressions of inflammatory cytokines, including the ratio of phosphorylated inhibitory kappa B (Iκb)/Iκb, tumor necrosis factor α, and phosphorylated c-Jun N-terminal kinase (JNK) and oxidative stress, which were reduced in HS/LEC rats. Our results suggest that in salt-sensitive hypertension, macrophage may importantly contribute to endothelial insulin resistance, vascular inflammation, and injury. These findings support the idea that macrophages may be a new target for immunotherapy of vasculopathy in hypertensive and metabolic disorders.

Endothelial dysfunction due to selective insulin resistance in vascular endothelium: insights from mechanistic modeling.

Previously, we have used mathematical modeling to gain mechanistic insights into insulin-stimulated glucose uptake. Phosphatidylinositol 3-kinase (PI3K)-dependent insulin signaling required for metabolic actions of insulin also regulates endothelium-dependent production of the vasodilator nitric oxide (NO). Vasodilation increases blood flow that augments direct metabolic actions of insulin in skeletal muscle. This is counterbalanced by mitogen-activated protein kinase (MAPK)-dependent insulin signaling in endothelium that promotes secretion of the vasoconstrictor endothelin-1 (ET-1). In the present study, we extended our model of metabolic insulin signaling into a dynamic model of insulin signaling in vascular endothelium that explicitly represents opposing PI3K/NO and MAPK/ET-1 pathways. Novel NO and ET-1 subsystems were developed using published and new experimental data to generate model structures/parameters. The signal-response relationships of our model with respect to insulin-stimulated NO production, ET-1 secretion, and resultant vascular tone, agree with published experimental data, independent of those used for model development. Simulations of pathological stimuli directly impairing only insulin-stimulated PI3K/Akt activity predict altered dynamics of NO and ET-1 consistent with endothelial dysfunction in insulin-resistant states. Indeed, modeling pathway-selective impairment of PI3K/Akt pathways consistent with insulin resistance caused by glucotoxicity, lipotoxicity, or inflammation predict diminished NO production and increased ET-1 secretion characteristic of diabetes and endothelial dysfunction. We conclude that our mathematical model of insulin signaling in vascular endothelium supports the hypothesis that pathway-selective insulin resistance accounts, in part, for relationships between insulin resistance and endothelial dysfunction. This may be relevant for developing novel approaches for the treatment of diabetes and its cardiovascular complications.

Endothelial Dysfunction in Diabetes.

Diabetes is a worldwide health issue closely associated with cardiovascular events. Given the pandemic of obesity, the identification of the basic underpinnings of vascular disease is strongly needed. Emerging evidence has suggested that endothelial dysfunction is a critical step in the progression of atherosclerosis. However, how diabetes affects the endothelium is poorly understood. Experimental and clinical studies have illuminated the tight link between insulin resistance and endothelial dysfunction. In addition, macrophage polarization from M2 towards M1 contributes to the process of endothelial damage. The possibility that novel classes of anti-hyperglycemic agents exert beneficial effects on the endothelial function and macrophage polarization has been raised. In this review, we discuss the current status of knowledge regarding the pathological significance of insulin signaling in endothelium. Finally, we summarize recent therapeutic strategies against endothelial dysfunction with an emphasis on macrophage polarity.

300-OR: The Transcriptional Coregulator CITED2 Suppresses Expression of IRS-2 in Endothelial Cells and Impairs Vascular Insulin Signaling In Vivo

Endothelial insulin signaling regulates perfusion, leukocyte adhesion, and angiogenesis, and its impairment may contribute to the development of vascular complications in diabetes. Hypoxia-inducible factors (HIF) are known modulators of insulin signaling and we have recently shown that a negative regulator of HIF activity, CBP/p300 interacting transactivator-2 (CITED2), is increased in the vasculature of people with type 2 diabetes. Therefore, we examined the role of CITED2 in endothelial insulin signaling by generating a mouse model with endothelial-specific loss of Cited2. We found that in the aorta and isolated endothelial cells, loss of Cited2 markedly enhanced insulin-stimulated Akt phosphorylation at Ser473 without altering ERK1/2 phosphorylation. Consistent with this observation, Cited2 deletion in endothelial cells increased insulin-stimulated Vegfa expression, endothelial nitric oxide synthase phosphorylation, and cell proliferation. Endothelial cells lacking CITED2 exhibited a 3.6-fold increase in insulin receptor substrate (IRS)-2 protein, a key mediator of the insulin signaling cascade, and 66% increase in Irs2 mRNA expression while IRS-1 was unchanged. Similarly, overexpression of CITED2 in endothelial cells decreased IRS-2 levels by 55% without altering IRS-1. Expression of HIF-2α significantly increased transcription of the Irs2 promoter and co-expression of CITED2 abolished this increase. Moreover, ChIP showed that loss of CITED2 increases occupancy of p300, a key component of the HIF transcriptional complex, on the Irs2 promoter. Together, these results suggest that loss of CITED2 enhances endothelial insulin signaling through de-repression of HIF-dependent Irs2 expression. The CITED2-p300 interaction can likely be interrupted by a small-molecule drug, and is thus a potential target to improve insulin action on endothelial cells in order to prevent vascular complications of diabetes. Disclosure B. Kunkemoeller: None. K. Chen: None. X. Wang: None. C. Rask-Madsen: None. Funding National Institutes of Health (5T32DK007260)

92-OR: EMC10, a Novel Serum Predictor for Coronary Artery Disease, Exerts an Impact on the Development of Atherosclerosis via Negatively Modulating Endothelial Insulin Signaling

Cardiovascular disease is the leading cause of global mortality, accounting for about one third of deaths worldwide. Secreted proteins from metabolically regulated organs are released into circulation and exert impacts on the pathogenesis of cardiovascular disease. In this study, we identified a novel secreted protein, EMC10, that might influence the development of atherosclerosis. We initially observed that serum EMC10 is significantly decreased in patients with coronary artery diseases evidenced by coronary artery stenosis over 50 percent, compared with those suffering stenosis less than 50%. In addition, we found that the levels of serum Emc10 are even lower in patients who meanwhile suffered from hypertension. After adjusted for age, BMI, hypertension, and diabetes, the regression analysis revealed that serum EMC10 is an independent predictor for coronary artery diseases. To determine the role of EMC10 in cardiovascular disease, we established Emc10 whole body knockout mice and found that both the systolic and diastolic blood pressure are significantly decreased in EMC10 KO mice in comparison to wild type ones. Furthermore, in vitro experiments showed that EMC10 significantly decreases the insulin-stimulated phosphorylations of both Akt and eNOS, and conversely, significantly increases VCAM-1 mRNA in endothelial cells. Collectively, these preliminary data suggest EMC10 leads to endothelial insulin resistance and plays a role in the development of atherosclerosis, by which EMC10 is involved in the pathogenesis of cardiovascular disease. Our findings establish Emc10 as a novel modulator of endothelial insulin signaling and a potential target for the intervention of diabetic vascular diseases. Disclosure Y. Jing: None. X. Wang: None. Y. Yu: None. K. Chen: None. S. Jin: None. Y. Li: None. X. Wang: None. Funding National Natural Science Foundation of China (81370936); Science and Technology Commission of Shanghai Municipality (18140902100)

273-LB: Leukocyte-Endothelial Interaction Is Reduced by Insulin-Induced Downregulation of Endothelial CXCR4

An activated, pro-inflammatory endothelium is a key feature of obesity and type 2 diabetes and may contribute to adipose tissue inflammation, atherosclerosis and tumor formation. We have previously published a striking 4-fold increase in leukocyte adhesion to endothelium in mice with endothelial cell knockout of the insulin receptor. Here, we searched for insulin-regulated genes involved in leukocyte-endothelial cell interaction by performing RNA sequencing in primary human endothelial cells. Among genes with the largest change in expression after insulin treatment was C-X-C motif chemokine receptor 4 (CXCR4), which was downregulated by 54%. This reduction was completely prevented by pretreatment with wortmannin but not by U0126, an inhibitor of MAPK signaling. In CD31+ cells isolated by fluorescence-activated cell sorting of enzymatically dissociated tissue, CXCR4 mRNA in was 77% higher in mice with diet-induced obesity compared to lean controls and 37% higher in db/db mice compared to db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. Stromal-derived factor-1 (SDF-1), the ligand for CXCR4, increased leukocyte adhesion to cultured endothelial cells. Insulin treatment of endothelial cells prevented 80% of this increase which in turn was abrogated by plerixafor, a clinically approved CXCR4 antagonist, or deletion of CXCR4 by gene editing. To study gain of endothelial cell insulin signaling in vivo, we examined transgenic mice with endothelial overexpression of insulin receptor substrate-1 (IRS-1). In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling and adhesion after intravenous injection of SDF-1 in wildtype mice which was reduced by 83% in transgenic mice. We conclude that endothelial cell insulin signaling limits leukocyte-endothelial cell interaction through downregulation of CXCR4 and that targeting endothelial CXCR4 may protect against inflammation in insulin resistant states. Disclosure B. Kunkemoeller: None. T. Rathjen: Employee; Self; Bayer AG. J.C. Patti: None. Q. Li: None. K. Park: None. G.L. King: Research Support; Self; Sanofi. C. Rask-Madsen: None.

Corrigendum: Resistin-Induced Endoplasmic Reticulum Stress Contributes to the Impairment of Insulin Signaling in Endothelium.

[This corrects the article DOI: 10.3389/fphar.2018.01226.].

Resistin-Induced Endoplasmic Reticulum Stress Contributes to the Impairment of Insulin Signaling in Endothelium.

Background: Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of obesity, insulin resistance and cardiovascular diseases (CVDs). Impairment of insulin vascular action may represent a mechanism linking insulin resistance and CVDs. The present study tested the hypothesis that adipocyte-derived resistin inhibits insulin-stimulated endothelial NO production through the induction of ER stress.Methods and Results: Human umbilical vein endothelial cells (HUVC) were incubated with tunicamycin (an inducer of ER stress, 1–20 μg/mL) or resistin (10–100 ng/mL) for 1 h. Either tunicamycin or resistin increased GRP78 (an ER stress marker) expression associated with the impairment of insulin-stimulated Akt/eNOS phosphorylation, which were prevented by TUDCA (an ER stress suppressor). Resistin increased reactive oxygen species (ROS) production, antioxidant treatment inhibited resistin-induced GRP78 expression and impairment of insulin Akt/eNOS signaling, suggesting that ROS may involve resistin-induced ER stress. Resistin also increased JNK phosphorylation, which was prevented by TUDCA. JNK inhibitor SP600125 relieved the resistin inhibitory effects on endothelial insulin Akt/eNOS signaling. In ex vivo experiments, the incubation of aortic rings with resistin impaired insulin- but not acetylcholine-induced vasodilation, which was restored by TUDCA. LNAME (a NOS inhibitor) abolished insulin-induced vasorelaxation in the control or the resistin-treated aortic rings. In addition, resistin increased the mRNA expressions of proinflammatory cytokines tumor nuclear factor (TNF)α and interleukin (IL)-1β, which were also prevented by TUDCA.Conclusion: Our results support the ideal that ER stress may play an important role for resistin impairment of vascular insulin signaling and insulin action. The mitigation of ER stress may represent a new strategy for prevention and treatment of CVDs in obesity and insulin resistant-related diseases.

Insulin Action on Endothelial Cells Limits Leukocyte-Endothelial Interaction through CXCR4 and Counteracts Intestinal Tumor Formation in Obesity

An activated, pro-inflammatory endothelium is a key feature of obesity and type 2 diabetes but little is known about its contribution to the increased cancer risk in these conditions. We recently published that insulin resistance in endothelial cells increases VCAM-1 expression, increases recruitment of tumor-associated neutrophils and promotes intestinal tumor formation. Here, we report that tumor-prone Apc(Min/+) mice have 2.1-fold more intestinal tumors during high-fat feeding. However, gain of insulin signaling specifically in endothelial cells by overexpression of IRS1 prevented 44% of tumors in diet-induced obesity. RNA sequencing in primary human endothelial cells identified 17 genes changed by insulin treatment with a log(2) change of at least ±0.5, among them C-X-C motif chemokine receptor 4 (CXCR4), which was downregulated by 54%. Downregulation of CXCR4 after insulin treatment was completely prevented by pretreatment with wortmannin but not by U0126, an inhibitor of MAPK signaling. Using FACS of enzymatically dissociated tissue, CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared to lean controls and 37% higher in db/db mice compared to db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. CXCL12, the ligand for CXCR4, increased leukocyte adhesion to cultured endothelial cells and this was completely prevented by plerixafor, a clinically approved CXCR4 antagonist. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling and adhesion after intravenous injection of CXCL12 and this change was abrogated in transgenic mice with endothelial overexpression of IRS1. We conclude that endothelial cell insulin signaling limit leukocyte-endothelial cell interaction through downregulation of CXCR4 and that improving insulin signaling in endothelial cells may protect against tumor development in obesity. Disclosure T. Rathjen: Employee; Self; Novo Nordisk A/S, Bayer AG. Q. Li: None. K. Park: None. G. Povlsen: Employee; Self; Novo Nordisk A/S. G.S. Olsen: Employee; Self; Novo Nordisk A/S. G.L. King: Research Support; Self; Sanofi-Aventis. C. Rask-Madsen: Research Support; Self; Novo Nordisk A/S.

Abstract 427: Chronic Intermittent Hypoxia Induces Endothelial Insulin Resistance in vivo and in vitro

Introduction: Obstructive sleep apnea, a condition leading to chronic intermittent hypoxia (CIH), is an independent risk factor for cardiovascular disease and type 2 diabetes and is correlated with insulin resistance. Insulin stimulates production of nitric oxide (NO) in vascular endothelial cells through the IRS-1/PI3K/Akt/eNOS pathway (IRS-1, insulin receptor substrate 1; PI3K, phosphatidylinositol 3-kinase; eNOS, endothelial NO synthase). Endothelial cells directly expose to blood flow and respond to oxygen concentration change in flow. We wondered if and how CIH would affect insulin signalling/action in endothelial cells. Methods and Results: C57BL/6J mice were exposed to CIH (21%-5%, 90 s/cycle, 10 h/day) or intermittent air for 7 weeks. HUVECs were exposed to CIH (21%-5%, 1 h/cycle) for 24 h or 48 h with or without insulin. We observed that CIH increased systolic blood pressure and impaired endothelium-dependent relaxation of aortas in C57BL/6J mice. CIH increased IRS-1 phosphorylation at Ser307 and Ser612 and impaired insulin-stimulated phosphorylation of IRS-1 at Tyr896 and Akt/eNOS pathway in aortas. Furthermore, CIH activated hypoxia-inducible factor 1α (HIF-1α) and nuclear factor kappa B (NF-κB) in aortas. In vitro, CIH activated endothelial HIF-1α signaling, impaired endothelial insulin signaling and reduced insulin-mediated NO production. In addition, CIH resulted in mitochondria proton leak and elevated oxygen consumption in HUVECs. Increased oxygen consumption further leaded to endothelial hypoxia and HIF-1α induction. Pharmacological inhibition of proton leak ameliorated CIH-induced endothelial insulin resistance in HUVECs. Conclusion: Our data suggest that CIH induces insulin resistant endothelial dysfunction, which may be associated with HIF-1α induction and proton leak.

Propranolol treatment lowers blood pressure, reduces vascular inflammatory markers and improves endothelial function in obese mice

Obesity-associated hypertension is accompanied by a number of cardiovascular risk factors including vascular insulin resistance (IR) and higher sympathetic nervous activity. Therefore, autonomic blockade was demonstrated to reverse hypertension, endothelial dysfunction and IR in obese individuals. We hypothesized that β-AR blockade with propranolol would restore endothelial function and vascular insulin signaling in obesity, associated with an anti-inflammatory effect. Body weight, systolic blood pressure (SBP), plasma biochemical parameters and aortic endothelial function were analyzed in mice fed standard diet (control group) or a high fat diet (HFD) that were treated with vehicle (water) or propranolol (10mg/kg/day) for 8weeks. Propranolol treatment did not modify obesogenic effect of HFD feeding. However, propranolol was effective in preventing the rise in SBP, the hyperinsulinemia and the impaired endothelium-dependent relaxation to acetylcholine and to insulin in obese mice. Protective effect of propranolol administration in endothelial function was associated with increased nitric oxide (NO) production and phosphorylation of Akt (Ser473) and eNOS (Ser1177), but with reduced phospho-IRS-1(Ser307) and phospho-ERK1/2 (Thr202/Tyr204). In addition, β-blocker propranolol prevented the NF-kB nuclear translocation and the increase in phospho-IκB-α (Ser32) and in interleukin(IL)-6 expression in aorta of obese mice, without significant changes in either aortic reactive oxygen species production or in circulating IL-6 and TNF-α levels. In β2-AR knockout mice, despite increasing body weight and visceral fat, HFD did not increase SBP and showed a partial improvement of endothelial function, revealing a role of β2-AR in cardiovascular effects of obesity. In conclusion, our results suggest that β-AR blockade with propranolol is effective to prevent the endothelial dysfunction, vascular IR and pro-inflammatory state displayed in HFD-induced obesity, independent of changes in body weight.

S-nitrosylation of endogenous protein tyrosine phosphatases in endothelial insulin signaling

Nitric oxide (NO) exerts its biological function through S-nitrosylation of cellular proteins. Due to the labile nature of this modification under physiological condition, identification of S-nitrosylated residue in enzymes involved in signaling regulation remains technically challenging. The present study investigated whether intrinsic NO produced in endothelium-derived MS-1 cells response to insulin stimulation might target endogenous protein tyrosine phosphatases (PTPs). For this, we have developed an approach using a synthetic reagent that introduces a phenylacetamidyl moiety on S-nitrosylated Cys, followed by detection with anti-phenylacetamidyl Cys (PAC) antibody. Coupling with sequential blocking of free thiols with multiple iodoacetyl-based Cys-reactive chemicals, we employed this PAC-switch method to show that endogenous SHP-2 and PTP1B were S-nitrosylated in MS-1 cells exposed to insulin. The mass spectrometry detected a phenylacetamidyl moiety specifically present on the active-site Cys463 of SHP-2. Focusing on the regulatory role of PTP1B, we showed S-nitrosylation to be the principal Cys reversible redox modification in endothelial insulin signaling. The PAC-switch method in an imaging format illustrated that a pool of S-nitrosylated PTP1B was colocalized with activated insulin receptor to the cell periphery, and that such event was endothelial NO synthase (eNOS)-dependent. Moreover, ectopic expression of the C215S mutant of PTP1B that mimics the active-site Cys215 S-nitrosylated form restored insulin responsiveness in eNOS-ablated cells, which was otherwise insensitive to insulin stimulation. This work not only introduces a new method that explores the role of physiological NO in regulating signal transduction, but also highlights a positive NO effect on promoting insulin responsiveness through S-nitrosylation of PTP1B's active-site Cys215.

Effects of vitamin D supplementation on endothelial function: a systematic review and meta-analysis of randomised clinical trials.

In addition to regulating calcium homoeostasis and bone health, vitamin D influences vascular and metabolic processes including endothelial function (EF) and insulin signalling. This systematic review and meta-analysis of randomised clinical trials (RCTs) were conducted to investigate the effect of vitamin D supplementation on EF and to examine whether the effect size was modified by health status, study duration, dose, route of vitamin D administration, vitamin D status (baseline and post-intervention), body mass index (BMI), age and type of vitamin D. We searched the Medline, Embase, Cochrane Library and Scopus databases from inception until March 2015 for studies meeting the following criteria: (1) RCT with adult participants, (2) vitamin D administration alone, (3) studies that quantified EF using commonly applied methods including ultrasound, plethysmography, applanation tonometry and laser Doppler. Sixteen articles reporting data for 1177 participants were included. Study duration ranged from 4 to 52weeks. The effect of vitamin D on EF was not significant (SMD: 0.08, 95% CI -0.06, 0.22, p=0.28). Subgroup analysis showed a significant improvement of EF in diabetic subjects (SMD: 0.31, 95% CI 0.05, 0.57, p=0.02). A non-significant trend was found for diastolic blood pressure (β=0.02; p=0.07) and BMI (β=0.05; p=0.06). Vitamin D supplementation did not improve EF. The significant effect of vitamin D in diabetics and a tendency for an association with BMI may indicate a role of excess adiposity and insulin resistance in modulating the effects of vitamin D on vascular function. This remains to be tested in future studies.

Abstract 13492: Increasing Endothelial Insulin Sensitivity Rescues Vascular Function and Repair in Systemic Insulin Resistance by Restoring Nitric Oxide Bioavailability and Improving Endothelial Cell Migration

Introduction: Insulin resistance is independently associated with vascular disease. Insulin receptor haploinsufficient (IRKO) mice are hypertensive and exhibit endothelial dysfunction and impaired vascular repair despite normal glucoregulation. We hypothesise that endothelial insulin signalling is crucial for vascular function and that selectively restoring endothelial cell (EC) insulin signalling may rescue these vascular derangements. Methods: Transgenic mice with Tie-2-driven human IR expression in the endothelium (HIRECO) were bred with IRKO, providing HIRECOxIRKO (HxI) offspring. Metabolic assessment included glucose and insulin tolerance tests, ELISA for plasma insulin concentration and non-invasive blood pressure measurement. Femoral artery injury was performed with angioplasty wires; repair was quantified in Evans Blue-perfused vessels at day 4. Circulating endothelial progenitor cells (EPC) were counted using FACS and cultured from blood. Explanted aortic rings were exposed to phenylephrine (PE) before and after incubation with the NOS inhibitor L-NMMA in organ baths to assess vasomotor function. Boyden chamber assays were used to assess migration of cultured lung ECs to VEGF. Data are expressed as mean(SE) and compared using t-tests;*=p&lt;0.05. Results: HxI and IRKO had similar glucocompetence and basal insulin [0.8(0.1)ng/mL vs 0.7(0.2);p=0.8]. Systolic BP was lower in HxI [97(2)mmHg vs 106(3)*]. Vascular repair was improved in HxI [57(4)% vs 46(2)%*]. There was no recovery in EPC numbers by FACS [99(10) vs 105(15);p=0.74], nor in culture [0.4(0.1)/HPF vs 0.4(0.2);p=0.99]. HxI aortic rings showed less PE-induced constriction than IRKO [EC50 8.9(0.8)x10 7 nM vs 6.3(0.9)x10 7 *], with greater NO bioavailability [Post-L-NMMA PE EC50 4.1(0.8)x10 7 nM vs IRKO 6.1(1.8)x10 7 *]. ECs from HxI showed greater net migration to VEGF [6.3(1.3) vs 1.9(1.2)*]. Conclusion: HIRECOxIRKO show rescue of vascular function despite global insulin resistance. This is not associated with improved glucoregulation or EPC abundance; rather, it may relate to increased NO availability and enhanced EC migration. Our data support endothelial insulin sensitisation as a potential therapeutic target for vascular dysfunction in insulin resistance.