Increased MAPK activation and impaired insulin signaling in subcutaneous microvascular endothelial cells in type 2 diabetes: the role of endothelin-1

Metabolic and vascular insulin resistance: partners in the pathogenesis of cardiovascular disease in diabetes

Vascular insulin resistance has emerged as a pivotal factor in the genesis of cardiovascular disease (CVD) in people with diabetes. It forms a complex pathogenic partnership with metabolic insulin resistance to significantly amplify the CVD risk of diabetes and other affected populations. Metabolic insulin resistance (characterized by quantitatively diminished insulin action on glucose metabolism in skeletal muscle, liver, and adipose tissue) is a hallmark of diabetes, obesity, and related conditions. In contrast, vascular insulin resistance is a less appreciated and not well-quantified complication of these conditions. Importantly, an impaired vascular response to insulin contributes directly to vascular dysfunction and over 40 years of research has convincingly shown that vascular and metabolic insulin resistance synergize to create an environment that predisposes individuals to CVD. In this review, we examine the multifaceted vascular actions of insulin, including its roles in regulating blood pressure, blood flow, endothelial health, and arterial stiffness. We also examine how these processes become disrupted in the setting of vascular insulin resistance, which subsequently undermines endothelial function, compromises tissue microvascular perfusion, and promotes vascular rigidity and atherosclerosis. We then highlight potential therapeutic strategies with demonstrated efficacy to improve vascular insulin sensitivity in people with diabetes and suggest that targeting disordered vascular insulin signaling holds promise not only for refining the functional understanding of vascular insulin resistance but also for developing innovative treatments with potential to reduce CVD risk and improve cardiovascular outcomes in people with diabetes.

Causal network perturbation analysis identifies known and novel type-2 diabetes driver genes

The molecular pathogenesis of diabetes is multifactorial, involving genetic predisposition and environmental factors that are not yet fully understood. However, pancreatic β-cell failure remains among the primary reasons underlying the progression of type-2 diabetes (T2D) making targeting β-cell dysfunction an attractive pathway for diabetes treatment. To identify genetic contributors to β-cell dysfunction, we investigated single-cell gene expression changes in β-cells from healthy (C57BL/6J) and diabetic (NZO/HlLtJ) mice fed with normal or high-fat, high-sugar diet (HFHS). Our study presents an innovative integration of the causal network perturbation assessment (ssNPA) framework with meta-cell transcriptome analysis to explore the genetic underpinnings of type-2 diabetes (T2D). By generating a reference causal network and in silico perturbation, we identified novel genes implicated in T2D and validated our candidates using the Knockout Mouse Phenotyping (KOMP) Project database.

Integrated investigation and discovery of therapeutic targets for 3-hydroxybakuchiol against diabetes based on molecular docking studies and cell experiments

BACKGROUND

Diabetes mellitus is a prevalent endocrine condition. We aimed to investigate the anti-diabetic effects of 3-hydroxybakuchiol (HYD) by exploring its potential targets and molecular mechanisms through bioinformatics analysis and cell experiments.

METHODS

We performed an extensive search and screening of HYD and its potential targets for diabetes mellitus across various databases. Enrichment analyses were conducted using the ClusterProfiler package. PPI networks of the identified genes were constructed using STRING, and topological analysis was performed to identify core targets. The results were further confirmed through molecular docking. To validate the findings of our bioinformatics analysis, we conducted cell experiments using insulin resistance-induced HepG2 cells and C2C12 cells.

RESULTS

We discovered 260 common targets of HYD and diabetes mellitus, which were primarily related to the MAPK signaling pathway, PI3K-Akt signaling pathway, and endocrine resistance. A topological analysis of the PPI network identified four core targets (HSP90AA1, AKT1, SRC, and MAPK1). Molecular docking studies further confirmed the strong binding ability between HYD and these core targets. In cell experiments, we observed that HYD enhanced glucose uptake and suppressed gluconeogenesis in HepG2 cells and C2C12 cells. This resulted in an improvement in glucose metabolism, potentially through the regulation of the PI3K-Akt pathway.

CONCLUSIONS

This study provides valuable insights into the pharmacological effects of HYD on diabetes mellitus, suggesting its potential as a promising treatment option for the disease.

Differentially Expressed Genes Regulating Glutathione Metabolism, Protein-Folding, and Unfolded Protein Response in Pancreatic β-Cells in Type 2 Diabetes Mellitus

Impaired redox homeostasis in the endoplasmic reticulum (ER) may contribute to proinsulin misfolding and thus to activate the unfolded protein response (UPR) and apoptotic pathways, culminating in pancreatic β-cell loss and type 2 diabetes (T2D). The present study was designed to identify differentially expressed genes (DEGs) encoding enzymes for glutathione metabolism and their impact on the expression levels of genes regulating protein folding and UPR in β-cells of T2D patients. The GEO transcriptome datasets of β-cells of diabetics and non-diabetics, GSE20966 and GSE81608, were analyzed for 142 genes of interest using limma and GREIN software, respectively. Diabetic β-cells showed dataset-specific patterns of DEGs (FDR ≤ 0.05) implicated in the regulation of glutathione metabolism (ANPEP, PGD, IDH2, and CTH), protein-folding (HSP90AB1, HSP90AA1, HSPA1B, HSPA8, BAG3, NDC1, NUP160, RLN1, and RPS19BP1), and unfolded protein response (CREB3L4, ERP27, and BID). The GCLC gene, encoding the catalytic subunit of glutamate-cysteine ligase, the first rate-limiting enzyme of glutathione biosynthesis, was moderately down-regulated in diabetic β-cells from both datasets (p ≤ 0.05). Regression analysis established that genes involved in the de novo synthesis of glutathione, GCLC, GCLM, and GSS affect the expression levels of genes encoding molecular chaperones and those involved in the UPR pathway. This study showed for the first time that diabetic β-cells exhibit alterations in the expression of genes regulating glutathione metabolism, protein-folding, and UPR and provided evidence for the molecular crosstalk between impaired redox homeostasis and abnormal protein folding, underlying ER stress in type 2 diabetes.

Effects of sesame (Sesamum indicum L.) and bioactive compounds (sesamin and sesamolin) on inflammation and atherosclerosis: A review

Inflammation, oxidative stress, obesity, infection, hyperlipidemia, hypertension, and diabetes are the main causes of atherosclerosis, which in the long term lead to hardening of the arteries. In the current study, we reviewed recent findings of the mechanism of sesame and its active compounds of sesamin and sesamolin regulates on atherosclerosis. Sesame can decrease the lipid peroxidation and affect the enzymes, which control the balance of oxidative status in the body. Besides modulating the inflammatory cytokines, sesame regulates the main mediators of the signaling pathways in the process of inflammation, such as prostaglandin E2 (PGE2), nuclear factor kappa light-chain enhancer of activated B cells (NF-kB) and peroxisome proliferator-activated receptor gamma (PPAR-γ). Sesame decreases the growth of different pathogens. It fights against obesity and helps to reduce weight, body mass index (BMI), waist circumference, and lipid count of serum and liver. In addition to lowering fasting blood sugar (FBS), it decreases the hemoglobin A1c (HbA1c) and glucose levels and improves insulin function. With high content of linoleic acid, α-linolenic acid, and total polyunsaturated fatty acid (PUFA), sesame efficiently controls the blood plasma lipids and changes the lipid profile. In the case of hypertension, it maintains the health of endothelium through multiple mechanisms and conserves the response of the arteries to vasodilation. PUFA in sesame suppresses blood clotting and fibrinogen activity. All the mentioned properties combat atherosclerosis and hardening of blood vessels, which are detailed in the present review for sesame.

Adipose Tissue Paracrine-, Autocrine-, and Matrix-Dependent Signaling during the Development and Progression of Obesity

Obesity is an ever-increasing phenomenon, with 42% of Americans being considered obese (BMI ≥ 30) and 9.2% being considered morbidly obese (BMI ≥ 40) as of 2016. With obesity being characterized by an abundance of adipose tissue expansion, abnormal tissue remodeling is a typical consequence. Importantly, this pathological tissue expansion is associated with many alterations in the cellular populations and phenotypes within the tissue, lending to cellular, paracrine, mechanical, and metabolic alterations that have local and systemic effects, including diabetes and cardiovascular disease. In particular, vascular dynamics shift during the progression of obesity, providing signaling cues that drive metabolic dysfunction. In this review, paracrine-, autocrine-, and matrix-dependent signaling between adipocytes and endothelial cells is discussed in the context of the development and progression of obesity and its consequential diseases, including adipose fibrosis, diabetes, and cardiovascular disease.

New insights into mechanisms of endothelial insulin resistance in type 2 diabetes

Insulin resistance in the vasculature is a hallmark of type 2 diabetes (T2D), and blunting of insulin-induced vasodilation is its primary consequence. Individuals with T2D exhibit a marked impairment in insulin-induced dilation in resistance arteries across vascular beds. Importantly, reduced insulin-stimulated vasodilation and blood flow to skeletal muscle limits glucose uptake and contributes to impaired glucose control in T2D. The study of mechanisms responsible for the suppressed vasodilatory effects of insulin has been a growing topic of interest for not only its association with glucose control and extension to T2D but also its relationship with cardiovascular disease development and progression. In this mini-review, we integrate findings from recent studies by our group with the existing literature focused on the mechanisms underlying endothelial insulin resistance in T2D.

Skin Microhemodynamics and Mechanisms of Its Regulation in Type 2 Diabetes Mellitus

The review presents modern ideas about peripheral microhemodynamics, approaches to the ana-lysis of skin blood flow oscillations and their diagnostic significance. Disorders of skin microhemodynamics in type 2 diabetes mellitus (DM) and the possibility of their interpretation from the standpoint of external and internal interactions between systems of skin blood flow regulation, based on a comparison of couplings in normal and pathological conditions, including models of pathologies on animals, are considered. The factors and mechanisms of vasomotor regulation, among them receptors and signaling events in endothelial and smooth muscle cells considered as models of microvessels are discussed. Attention was drawn to the disturbance of Ca2+-dependent regulation of coupling between vascular cells and NO-dependent regulation of vasodilation in diabetes mellitus. The main mechanisms of insulin resistance in type 2 DM are considered to be a defect in the number of insulin receptors and impaired signal transduction from the receptor to phosphatidylinositol-3-kinase and downstream targets. Reactive oxygen species plays an important role in vascular dysfunction in hyperglycemia. It is assumed that the considered molecular and cellular mechanisms of microhemodynamics regulation are involved in the formation of skin blood flow oscillations. Parameters of skin blood microcirculation can be used as diagnostic and prognostic markers for assessing the state of the body.

Pathophysiological Association between Diabetes Mellitus and Endothelial Dysfunction

Endothelial dysfunction plays a critical role in atherosclerosis progression, leading to cardiovascular complications. There are significant associations between diabetes mellitus, oxidative stress, and endothelial dysfunction. Oxidative stress is increased by chronic hyperglycemia and acute glucose fluctuations induced by postprandial hyperglycemia in patients with diabetes mellitus. In addition, selective insulin resistance in the phosphoinositide 3-kinase/Akt/endothelial nitric oxide (NO) synthase pathway in endothelial cells is involved in decreased NO production and increased endothelin-1 production from the endothelium, resulting in endothelial dysfunction. In a clinical setting, selecting an appropriate therapeutic intervention that improves or augments endothelial function is important for preventing diabetic vascular complications. Hypoglycemic drugs that reduce glucose fluctuations by decreasing the postprandial rise in blood glucose levels, such as glinides, α-glucosidase inhibitors and dipeptidyl peptidase 4 inhibitors, and hypoglycemic drugs that ameliorate insulin sensitivity, such as thiazolidinediones and metformin, are expected to improve or augment endothelial function in patients with diabetes. Glucagon-like peptide 1 receptor agonists, metformin, and sodium-glucose cotransporter 2 inhibitors may improve endothelial function through multiple mechanisms, some of which are independent of glucose control or insulin signaling. Oral administration of antioxidants is not recommended in patients with diabetes due to the lack of evidence for the efficacy against diabetic complications.

Anti-inflammatory and anti-proliferative action of adiponectin mediated by insulin signaling cascade in human vascular smooth muscle cells

After confirmation of the presence of adiponectin (ADPN) receptors and intra-cellular binding proteins in coronary artery smooth muscle cells (VSMC), we tested the hypotheses that, in acute insulin resistance: (i) the activation/inactivation of metabolic and mitogenic insulin signaling pathways are inversely affected by ADPN and, (ii) changes in VSMC migration/proliferation rates correlate with signal activity/inactivity. In primary cultures of VSMC exposed to high glucose and palmitate plus insulin, the expression of PI-3 kinase (Akt and m-TOR), MAP-Kinase (Erk and p-38) molecules, and inflammatory markers (TLR-4 and IkB-α) were assessed with Western blot, in the absence/presence of AdipoRon (AR). Migration and proliferation rates were measured in similar experimental conditions. There were decreases of ~ 25% (p-Akt) and 40-60% (p-mTOR) expressions with high glucose/palmitate, which reversed when AR was added were. Elevations in p-Erk and p-p38 expressions were obliterated by AR. Although, no changes were detected with high glucose and palmitate, when AR was added, a decline in inflammatory activity was substantiated by a ~ 50% decrease in TLR-4 and 40-60% increase in IkBα expression. Functional assays showed 10-20% rise in VSMC proliferation with high glucose and palmitate, but addition of AR lead to 15-25% decline. The degree of VSMC migration was reduced with AR addition by ~ 15%, ~ 35% and 55%, in VSMC exposed to 5 mM, 25 mM glucose and 25 mM + 200 µM palmitate, respectively. Changes in intracellular molecular messaging in experiments mimicking acute insulin resistance suggest that anti-inflammatory and anti-atherogenic actions of ADPN in VSMC are mediated via insulin signaling pathways.

SCUBE2, vascular endothelium, and vascular complications: A systematic review

The vascular endothelium plays a vital role in regulating normal vascular function. Endothelial lining maintains the balance of thrombolytic and fibrinolytic microenvironment in the vasculature. Alterations of vascular endothelium referred to as endothelial dysfunction, caused the pathological changes in vessel wall such activation of proinflammatory and procoagulatory that initiate atherosclerosis. The concept that endothelial dysfunction plays a critical role in the initiation of atherosclerosis due to vascular inflammation gained tremendous attention. Diabetes mellitus is a metabolic-related disease that caused high mortality and morbidity, leading to its cardiovascular complication over the past decade. Atherosclerosis is the leading cardiovascular complication in diabetes mellitus. Despite metabolic and glycemic control, atherosclerotic plaque progression remains an enormous problem in diabetes mellitus complications. Thus, new inroads therapeutic approach in preventing complications that induced inflammation in endothelial cells could help prevent the disease progression. Signal peptide-CUB-EGF like domain-containing protein 2 (SCUBE2) expressed in vascular endothelium and reported to involve in inflammation. A recent study reported an increased SCUBE2 expression in diabetes mellitus and correlated with high expression of endothelin-1 (ET-1), a proinflammatory endothelial cell-derived peptide. Moreover, this gene showed to increase during atherosclerosis development. The present systematic review will summarize the involvement of SCUBE2 in vascular endothelium function changes and vascular complication, particularly in diabetes mellitus and atherosclerosis.

Metabolic Syndrome, Brain Insulin Resistance, and Alzheimer's Disease: Thioredoxin Interacting Protein (TXNIP) and Inflammasome as Core Amplifiers

Empirical evidence indicates a strong association between insulin resistance and pathological alterations related to Alzheimer's disease (AD) in different cerebral regions. While cerebral insulin resistance is not essentially parallel with systemic metabolic derangements, type 2 diabetes mellitus (T2DM) has been established as a risk factor for AD. The circulating "toxic metabolites" emerging in metabolic syndrome may engage several biochemical pathways to promote oxidative stress and neuroinflammation leading to impair insulin function in the brain or "type 3 diabetes". Thioredoxin-interacting protein (TXNIP) as an intracellular amplifier of oxidative stress and inflammasome activation may presumably mediate central insulin resistance. Emerging data including those from our recent studies has demonstrated a sharp TXNIP upregulation in stroke, aging and AD and well underlining the significance of this hypothesis. With the main interest to illustrate TXNIP place in type 3 diabetes, the present review primarily briefs the potential mechanisms contributing to cerebral insulin resistance in a metabolically deranged environment. Then with a particular focus on plausible TXNIP functions to drive and associate with AD pathology, we present the most recent evidence supporting TXNIP as a promising therapeutic target in AD as an age-associated dementia.

Persistent insulin signaling coupled with restricted PI3K activation causes insulin-induced vasoconstriction

Insulin modulates vasomotor tone through vasodilator and vasoconstrictor signaling pathways. The purpose of the present work was to determine whether insulin-stimulated vasoconstriction is a pathophysiological phenomenon that can result from a combination of persistent insulin signaling, suppressed phosphatidylinositol-3 kinase (PI3K) activation, and an ensuing relative increase in MAPK/endothelin-1 (ET-1) activity. First, we examined previously published work from our group where we assessed changes in lower-limb blood flow in response to an oral glucose tolerance test (endogenous insulin stimulation) in lean and obese subjects. The new analyses showed that the peak rise in vascular resistance during the postprandial state was greater in obese compared with lean subjects. We next extended on these findings by demonstrating that insulin-induced vasoconstriction in isolated resistance arteries from obese subjects was attenuated with ET-1 receptor antagonism, thus implicating ET-1 signaling in this constriction response. Last, we examined in isolated resistance arteries from pigs the dual roles of persistent insulin signaling and blunted PI3K activation in modulating vasomotor responses to insulin. We found that prolonged insulin stimulation did not alter vasomotor responses to insulin when insulin-signaling pathways remained unrestricted. However, prolonged insulinization along with pharmacological suppression of PI3K activity resulted in insulin-induced vasoconstriction, rather than vasodilation. Notably, such aberrant vascular response was rescued with either MAPK inhibition or ET-1 receptor antagonism. In summary, we demonstrate that insulin-induced vasoconstriction is a pathophysiological phenomenon that can be recapitulated when sustained insulin signaling is coupled with depressed PI3K activation and the concomitant relative increase in MAPK/ET-1 activity.NEW & NOTEWORTHY This study reveals that insulin-induced vasoconstriction is a pathophysiological phenomenon. We also provide evidence that in the setting of persistent insulin signaling, impaired phosphatidylinositol-3 kinase activation appears to be a requisite feature precipitating MAPK/endothelin 1-dependent insulin-induced vasoconstriction.

Overproduction of endothelin-1 impairs glucose tolerance but does not promote visceral adipose tissue inflammation or limit metabolic adaptations to exercise

Endothelin-1 (ET-1) is a potent vasoconstrictor and proinflammatory peptide that is upregulated in obesity. Herein, we tested the hypothesis that ET-1 signaling promotes visceral adipose tissue (AT) inflammation and disrupts glucose homeostasis. We also tested if reduced ET-1 is a required mechanism by which exercise ameliorates AT inflammation and improves glycemic control in obesity. We found that 1) diet-induced obesity, AT inflammation, and glycemic dysregulation were not accompanied by significantly increased levels of ET-1 in AT or circulation in wild-type mice and that endothelial overexpression of ET-1 and consequently increased ET-1 levels did not cause AT inflammation yet impaired glucose tolerance; 2) reduced AT inflammation and improved glucose tolerance with voluntary wheel running was not associated with decreased levels of ET-1 in AT or circulation in obese mice nor did endothelial overexpression of ET-1 impede such exercise-induced metabolic adaptations; 3) chronic pharmacological blockade of ET-1 receptors did not suppress AT inflammation in obese mice but improved glucose tolerance; and 4) in a cohort of human subjects with a wide range of body mass indexes, ET-1 levels in AT, or circulation were not correlated with markers of inflammation in AT. In aggregate, we conclude that ET-1 signaling is not implicated in the development of visceral AT inflammation but promotes glucose intolerance, thus representing an important therapeutic target for glycemic dysregulation in conditions characterized by hyperendothelinemia. Furthermore, we show that the salutary effects of exercise on AT and systemic metabolic function are not contingent on the suppression of ET-1 signaling.

Endothelial adenosine kinase deficiency ameliorates diet-induced insulin resistance

Insulin resistance-related disorders are associated with endothelial dysfunction. Accumulating evidence has suggested a role for adenosine signaling in the regulation of endothelial function. Here, we identified a crucial role of endothelial adenosine kinase (ADK) in the regulation of insulin resistance. Feeding mice with a high-fat diet (HFD) markedly enhanced the expression of endothelial Adk. Ablation of endothelial Adk in HFD-fed mice improved glucose tolerance and insulin sensitivity and decreased hepatic steatosis, adipose inflammation and adiposity, which were associated with improved arteriole vasodilation, decreased inflammation and increased adipose angiogenesis. Mechanistically, ADK inhibition or knockdown in human umbilical vein endothelial cells (HUVECs) elevated intracellular adenosine level and increased endothelial nitric oxide synthase (NOS3) activity, resulting in an increase in nitric oxide (NO) production. Antagonism of adenosine receptor A2b abolished ADK-knockdown-enhanced NOS3 expression in HUVECs. Additionally, increased phosphorylation of NOS3 in ADK-knockdown HUVECs was regulated by an adenosine receptor-independent mechanism. These data suggest that Adk-deficiency-elevated intracellular adenosine in endothelial cells ameliorates diet-induced insulin resistance and metabolic disorders, and this is associated with an enhancement of NO production caused by increased NOS3 expression and activation. Therefore, ADK is a potential target for the prevention and treatment of metabolic disorders associated with insulin resistance.

Activation of cancer-related and mitogen-activated protein kinase signaling pathways in human mature osteoblasts isolated from patients with type 2 diabetes

Diabetes mellitus is a disease of glucose metabolism, and it adversely affects bone metabolism and increases the risk of cancer development. Previously, we reported a method for the direct isolation of human mature osteoblasts and indicated that osteoblasts were associated with type 2 diabetes mellitus-related signaling pathways. In addition, a recent report suggested that osteoblasts are involved in glucose metabolism. Thus, we sought to examine the effects of diabetes on osteoblast signaling in vivo. We recruited eight patients with type 2 diabetes and eight non-diabetic individuals. We isolated human mature osteoblasts from the resected femoral heads during orthopaedic surgery and extracted their RNA. We compared the gene expression between the two groups by RNA microarray and pathway analyses. Microarray analysis showed significant differences in 885 of 19,463 genes between the two groups (p < 0.05), and pathway analysis revealed that pathways related to cancer and the mitogen-activated protein kinase signaling pathway were significantly activated in the diabetes group (p < 0.01). These preliminary findings suggest that diabetes affects intracellular signaling in human mature osteoblasts and that osteoblasts might not only play a key role in the regulation of bone and glucose metabolism, but might also be related to cancer metabolism. We plan to conduct further studies to examine signaling in diabetic osteoblasts and to further investigate the genes and pathways identified here.

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Compared microarray data from in vivo DM and healthy control osteoblasts

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MAPK and cancer-related signaling genes were enriched in DM osteoblasts.

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DM may increase cancer risk by activating cancer-related pathways in osteoblasts.

Serum microRNAs and chronic periodontitis: A case-control study

OBJECTIVE

An association is present between periodontitis and rates of expression of certain microRNAs (miRNAs) in periodontal tissue. However, the association between periodontitis and miRNA levels in human serum is unknown. We performed a case-control study in patients with chronic periodontitis to investigate serum miRNA levels.

DESIGN

We enrolled 30 healthy patients without periodontitis and 30 patients with chronic periodontitis. Participants underwent clinical examination, case selection, and a blood draw from the antecubital vein. Serum miRNA profiles were compared in samples from participants with and without chronic periodontitis using microarray and real-time PCR.

RESULTS

Microarray demonstrated seven miRNAs that were expressed <1/1.5 or >1.5 in the control group compared to the periodontitis group (p < 0.05). Real-time PCR showed that hsa-miR-664a-3p, hsa-miR-501-5p, and hsa-miR-21-3p were higher in the periodontitis group than the control group (p < 0.05).

CONCLUSION

Hsa-miR-664a-3p, hsa-miR-501-5p, and hsa-miR-21-3p are candidate serum biomarkers for chronic periodontitis.

Human adipose tissue microvascular endothelial cells secrete PPARγ ligands and regulate adipose tissue lipid uptake

Human adipose cells cannot secrete endogenous PPARγ ligands and are dependent on unknown exogenous sources. We postulated that the adipose tissue microvascular endothelial cells (aMVECs) cross-talk with the adipose cells for fatty acid (FA) transport and storage and also may secrete PPARγ ligands. We isolated aMVECs from human subcutaneous adipose tissue and showed that in these cells, but not in (pre)adipocytes from the same donors, exogenous FAs increased cellular PPARγ activation and markedly increased FA transport and the transporters FABP4 and CD36. Importantly, aMVECs only accumulated small lipid droplets and could not be differentiated to adipose cells and are not adipose precursor cells. FA exchange between aMVECs and adipose cells was bidirectional, and FA-induced PPARγ activation in aMVECs was dependent on functional adipose triglyceride lipase (ATGL) protein while deleting hormone-sensitive lipase in aMVECs had no effect. aMVECs also released lipids to the medium, which activated PPARγ in reporter cells as well as in adipose cells in coculture experiments, and this positive cross-talk was also dependent on functional ATGL in aMVECs. In sum, aMVECs are highly specialized endothelial cells, cannot be differentiated to adipose cells, are adapted to regulating lipid transport and secreting lipids that activate PPARγ, and thus, regulate adipose cell function.

Insulin and Insulin Receptors in Adipose Tissue Development

Insulin is a major endocrine hormone also involved in the regulation of energy and lipid metabolism via the activation of an intracellular signaling cascade involving the insulin receptor (INSR), insulin receptor substrate (IRS) proteins, phosphoinositol 3-kinase (PI3K) and protein kinase B (AKT). Specifically, insulin regulates several aspects of the development and function of adipose tissue and stimulates the differentiation program of adipose cells. Insulin can activate its responses in adipose tissue through two INSR splicing variants: INSR-A, which is predominantly expressed in mesenchymal and less-differentiated cells and mainly linked to cell proliferation, and INSR-B, which is more expressed in terminally differentiated cells and coupled to metabolic effects. Recent findings have revealed that different distributions of INSR and an altered INSR-A:INSR-B ratio may contribute to metabolic abnormalities during the onset of insulin resistance and the progression to type 2 diabetes. In this review, we discuss the role of insulin and the INSR in the development and endocrine activity of adipose tissue and the pharmacological implications for the management of obesity and type 2 diabetes.

Carnosine improves diabetic retinopathy via the MAPK/ERK pathway

Diabetic retinopathy (DR) is one of the most common causes of blindness in developed countries. Due to its asymptomatic onset and progressive disease course, DR is typically diagnosed at a late stage when treatment options are limited and therefore often results in irreversible blindness. Studies have demonstrated that carnosine may prevent and treat DR. In a previous study, the positive effect of carnosine on DR was determined and it was revealed that there may be an association between carnosine and the mitogen-activated protein kinase (MAPK)/extracellular signal related kinase (ERK) signaling pathway. To assess the interaction between carnosine and the MAPK/ERK signaling pathway, changes in PKC, ERK and p-ERK expression was assessed in diabetic rats following treatment with carnosine, PD98059 or U46619 via reverse transcription-quantitative polymerase chain reaction and western blotting. The results demonstrated that the expression of ERK and p-ERK were significantly suppressed following treatment with carnosine, but no significant effect on the expression of PKC was identified, which indicates that suppressing the activation of the MAPK/ERK signaling pathway may serve an important role in carnosine-induced DR prevention and treatment.

Visual Defects and Ageing

Many diseases are related to age, among these neurodegeneration is particularly important. Alzheimer's disease Parkinson's and Glaucoma have many common pathogenic events including oxidative damage, Mitochondrial dysfunction, endothelial alterations and changes in the visual field. These are well known in the case of glaucoma, less in the case of neurodegeneration of the brain. Many other molecular aspects are common, such as the role of endoplasmic reticulum autophagy and neuronal apoptosis while others have been neglected due to lack of space such as inflammatory cytokine or miRNA. Moreover, the loss of specific neuronal populations, the induction of similar mechanisms of cell injury and the deposition of protein aggregates in specific anatomical areas are very similar events between these diseases. Intracellular and/or extracellular accumulation of protein aggregates is a key feature of many neurodegenerative disorders. The existence of abnormal protein aggregates has been documented in the RGCs of glaucomatous patients such as the anomalous Tau protein or the β-amyloid accumulations. Intra-cell catabolic processes also appear to be common in both glaucoma and neurodegeneration. They also help us to understand how the basis between these diseases is common and how the visual aspects can be a serious problem for those who are affected.

Prenatal retinoic acid exposure reveals candidate genes for craniofacial disorders

Syndromes that display craniofacial anomalies comprise a major class of birth defects. Both genetic and environmental factors, including prenatal retinoic acid (RA) exposure, have been associated with these syndromes. While next generation sequencing has allowed the discovery of new genes implicated in these syndromes, some are still poorly characterized such as Oculo-Auriculo-Vertebral Spectrum (OAVS). Due to the lack of clear diagnosis for patients, developing new strategies to identify novel genes involved in these syndromes is warranted. Thus, our study aimed to explore the link between genetic and environmental factors. Owing to a similar phenotype of OAVS reported after gestational RA exposures in humans and animals, we explored RA targets in a craniofacial developmental context to reveal new candidate genes for these related disorders. Using a proteomics approach, we detected 553 dysregulated proteins in the head region of mouse embryos following their exposure to prenatal RA treatment. This novel proteomic approach implicates changes in proteins that are critical for cell survival/apoptosis and cellular metabolism which could ultimately lead to the observed phenotype. We also identified potential molecular links between three major environmental factors known to contribute to craniofacial defects including maternal diabetes, prenatal hypoxia and RA exposure. Understanding these links could help reveal common key pathogenic mechanisms leading to craniofacial disorders. Using both in vitro and in vivo approaches, this work identified two new RA targets, Gnai3 and Eftud2, proteins known to be involved in craniofacial disorders, highlighting the power of this proteomic approach to uncover new genes whose dysregulation leads to craniofacial defects.

[Type 2 Diabetes and Vascular Endothelial Dysfunction]

Vascular endothelial function is important for maintaining the homeostasis of the living body. Especially, nitric oxide (NO) produced in vascular endothelial cells regulates blood vessel tone and has an antiatherosclerotic effect. Type 2 diabetes is a typical disease that causes impaired vascular endothelial function, resulting in various vascular complications and damage to organs. Cardiovascular disease associated with type 2 diabetes is a chronic inflammatory disease that starts with endothelial dysfunction (ED), and vascular ED is important as an initial change in arteriosclerotic lesions. Vascular ED in type 2 diabetes is thought to be caused by hyperglycemia, hyperinsulinemia associated with insulin resistance, and hypoglycemia, in which elevated oxidative stress accompanying postprandial hyperglycemia and blood glucose fluctuation are involved. Vascular ED is also caused by postprandial metabolic abnormalities, so correcting postprandial metabolic abnormalities is also important. Meanwhile, Glucagon-like peptide-1 (GLP-1) receptor agonist, thiazolidine, biguanide and Dipeptidyl peptidase-4 (DPP-4) inhibitor have an effect of protecting vascular endothelial function beyond glycemic control. In order to promote a healthy lifestyle for diabetes patients, it is important not only to lower HbA1c but also to avoid postprandial hyperglycemia, blood glucose fluctuation, and hypoglycemia. It is also important to conduct treatment with a view to suppressing vascular complications, such as the selection of antiarteriosclerosis medications.

Insulin uptake and action in microvascular endothelial cells of lymphatic and blood origin

Whereas the blood microvasculature constitutes a biological barrier to the action of blood-borne insulin on target tissues, the lymphatic microvasculature might act as a barrier to subcutaneously administrated insulin reaching the circulation. Here, we evaluate the interaction of insulin with primary microvascular endothelial cells of lymphatic [human dermal lymphatic endothelial cells (HDLEC)] and blood [human adipose microvascular endothelial cells (HAMEC)] origin, derived from human dermal and adipose tissues, respectively. HDLEC express higher levels of insulin receptor and signal in response to insulin as low as 2.5 nM, while HAMEC only activate signaling at 100 nM (a dose that blood vessels do not normally encounter). Low insulin acts specifically through the insulin receptor, while supraphysiological insulin acts through both the IR and insulin growth factor-1 receptor. At supraphysiological or injection site-compatible doses pertinent to lymphatic microvessels, insulin enters HAMEC and HDLEC via fluid-phase endocytosis. Conversely, at physiologically circulating doses (0.2 nM) pertinent to blood microvessels, insulin enters HAMEC through a receptor-mediated process requiring IR autophosphorylation but not downstream insulin signaling. At physiological doses, internalized insulin is barely degraded and is instead released intact to the extracellular medium. In conclusion, we document for the first time the mechanism of interaction of insulin with lymphatic endothelial cells, which may be relevant to insulin absorption during therapeutic injections. Furthermore, we describe distinct action and uptake routes for insulin at physiological and supraphysiological doses in blood microvascular endothelial cells, providing a potential explanation for previously conflicting studies on endothelial insulin uptake.

Gelidium elegans Extract Ameliorates Type 2 Diabetes via Regulation of MAPK and PI3K/Akt Signaling

Gelidium elegans, a red alga native to the Asia Pacific region, contains biologically active polyphenols. We conducted a molecular biological study of the anti-diabetic effect of Gelidium elegans extract (GEE) in C57BL/KsJ-db/db mice. Mice that had been administered GEE had significantly lower body mass, water consumption, and fasting blood glucose than db/db controls. Moreover, hemoglobin A1c (HbA1c), an indicator of the glycemic status of people with diabetes, was significantly lower in mice that had been administered GEE. We also found that 200 mg/kg/day GEE upregulates the insulin signaling pathway by activating insulin receptor substrate-1 (IRS-1) and phosphoinositide 3-kinase (PI3K), and increasing the expression of glucose transporter type 4 (GLUT4). In parallel, mitogen-activated protein kinase (MAPK) activity was lower in GEE-treated groups. In summary, these findings indicate that GEE regulates glucose metabolism by activating the insulin signaling pathway and downregulating the MAPK signaling pathway.

TRAF3IP2 mediates high glucose-induced endothelin-1 production as well as endothelin-1-induced inflammation in endothelial cells

Hyperglycemia-induced production of endothelin (ET)-1 is a hallmark of endothelial dysfunction in diabetes. Although the detrimental vascular effects of increased ET-1 are well known, the molecular mechanisms regulating endothelial synthesis of ET-1 in the setting of diabetes remain largely unidentified. Here, we show that adapter molecule TRAF3 interacting protein 2 (TRAF3IP2) mediates high glucose-induced ET-1 production in endothelial cells and ET-1-mediated endothelial cell inflammation. Specifically, we found that high glucose upregulated TRAF3IP2 in human aortic endothelial cells, which subsequently led to activation of JNK and IKKβ. shRNA-mediated silencing of TRAF3IP2, JNK1, or IKKβ abrogated high-glucose-induced ET-converting enzyme 1 expression and ET-1 production. Likewise, overexpression of TRAF3IP2, in the absence of high glucose, led to activation of JNK and IKKβ as well as increased ET-1 production. Furthermore, ET-1 transcriptionally upregulated TRAF3IP2, and this upregulation was prevented by pharmacological inhibition of ET-1 receptor B using BQ-788, or inhibition of NADPH oxidase-derived reactive oxygen species using gp91ds-tat and GKT137831. Notably, we found that knockdown of TRAF3IP2 abolished ET-1-induced proinflammatory and adhesion molecule (IL-1β, TNF-α, monocyte chemoattractant protein 1, ICAM-1, VCAM-1, and E-selectin) expression and monocyte adhesion to endothelial cells. Finally, we report that TRAF3IP2 is upregulated and colocalized with CD31, an endothelial marker, in the aorta of diabetic mice. Collectively, findings from the present study identify endothelial TRAF3IP2 as a potential new therapeutic target to suppress ET-1 production and associated vascular complications in diabetes. NEW & NOTEWORTHY This study provides the first evidence that the adapter molecule TRAF3 interacting protein 2 mediates high glucose-induced production of endothelin-1 by endothelial cells as well as endothelin-1-mediated endothelial cell inflammation. The findings presented herein suggest that TRAF3 interacting protein 2 may be an important therapeutic target in diabetic vasculopathy characterized by excess endothelin-1 production.

A genome-wide association study suggests that MAPK14 is associated with diabetic foot ulcers

BACKGROUND

Diabetic foot ulcers (DFUs) are a devastating complication of diabetes.

OBJECTIVES

To identify genetic contributors to the development of DFUs in the presence of peripheral neuropathy in a Scottish cohort with diabetes using a genome-wide association study.

METHODS

A genome-wide association approach was applied. A case was defined as a person with diabetes (type 1 or type 2) who had ever had a foot ulcer (current or previous) in at least one foot, as well as a positive monofilament test result (i.e. evidence of peripheral neuropathy) recorded in their longitudinal e-health records. A control was defined as an individual with diabetes (type 1 or type 2) who has never been recorded as having a foot ulcer in either foot but who had a positive monofilament test result recorded in either foot in their longitudinal e-health records.

RESULTS

There were 699 DFU cases and 2695 controls in the Genetics of Diabetes Audit and Research in Tayside Scotland (GoDARTS) dataset. The single-nucleotide polymorphism rs80028505 (Chr6p21·31) in MAPK14 reached genome-wide significance with a lowest P-value of 2·45 × 10-8 . The narrow-sense heritability of this phenotype is 0·06.

CONCLUSIONS

We suggest that MAPK14 is associated with DFUs.

Prolonged sitting leg vasculopathy: contributing factors and clinical implications

Atherosclerotic peripheral artery disease primarily manifests in the medium- to large-sized conduit arteries of the lower extremities. However, the factors underlying this increased vulnerability of leg macrovasculature to disease are largely unidentified. On the basis of recent studies, we propose that excessive time spent in the sitting position and the ensuing reduction in leg blood flow-induced shear stress cause endothelial cell dysfunction, a key predisposing factor to peripheral artery disease. In particular, this review summarizes the findings from laboratory-based sitting studies revealing acute leg vascular dysfunction with prolonged sitting in young healthy subjects, discusses the primary physiological mechanisms and the potential long-term implications of such leg vasculopathy with repeated exposure to prolonged sitting, as well as identifies strategies that may be effective at evading it.

Imbalanced Insulin Actions in Obesity and Type 2 Diabetes: Key Mouse Models of Insulin Signaling Pathway

Since the discovery of the tyrosine kinase activity of the insulin receptor (IR), researchers have been engaged in intensive efforts to resolve physiological functions of IR and its major downstream targets, insulin receptor substrate 1 (Irs1) and Irs2. Studies conducted using systemic and tissue-specific gene-knockout mice of IR, Irs1, and Irs2 have revealed the physiological roles of these molecules in each tissue and interactions among multiple tissues. In obesity and type 2 diabetes, selective downregulation of Irs2 and its downstream actions to cause reduced insulin actions was associated with increased insulin actions through Irs1 in variety tissues. Thus, we propose the novel concept of "organ- and pathway-specific imbalanced insulin action" in obesity and type 2 diabetes, which includes and extends "selective insulin resistance." This Review focuses on recent progress in understanding insulin signaling and insulin resistance using key mouse models for elucidating pathophysiology of human obesity and type 2 diabetes.

Role of Insulin-Stimulated Adipose Tissue Perfusion in the Development of Whole-Body Insulin Resistance

After food ingestion, macronutrients are transported to and stored in the skeletal muscle and adipose tissue. They can be subsequently used as an energy source in times of energy deprivation. Uptake of these nutrients in myocytes and adipocytes depends largely on adequate tissue perfusion. Interestingly, insulin is able to dilate skeletal muscle arterioles, which facilitates the delivery of macronutrients and insulin itself to muscle tissue. Insulin-stimulated skeletal muscle perfusion is impaired in several insulin-resistant states and is believed to contribute to impaired skeletal muscle glucose uptake and consequently impaired whole-body glucose disposal. Insulin-resistant individuals also exhibit blunted postprandial adipose tissue perfusion. However, the relevance of this impairment to metabolic dysregulation is less clear. In this review, we provide an overview of adipose tissue perfusion in healthy and insulin-resistant individuals, its regulation among others by insulin, and the possible influences of impaired adipose tissue perfusion on whole-body insulin sensitivity. Finally, we propose a novel hypothesis that acute overfeeding impacts distribution of macronutrients by reducing skeletal muscle perfusion, while adipose tissue perfusion remains intact.

VISUAL OVERVIEW

An online visual overview is available for this article.

High fructose-mediated attenuation of insulin receptor signaling does not affect PDGF-induced proliferative signaling in vascular smooth muscle cells

Insulin resistance is associated with accelerated atherosclerosis. Although high fructose is known to induce insulin resistance, it remains unclear as to how fructose regulates insulin receptor signaling and proliferative phenotype in vascular smooth muscle cells (VSMCs), which play a major role in atherosclerosis. Using human aortic VSMCs, we investigated the effects of high fructose treatment on insulin receptor substrate-1 (IRS-1) serine phosphorylation, insulin versus platelet-derived growth factor (PDGF)-induced phosphorylation of Akt, S6 ribosomal protein, and extracellular signal-regulated kinase (ERK), and cell cycle proteins. In comparison with PDGF (a potent mitogen), neither fructose nor insulin enhanced VSMC proliferation and cyclin D1 expression. d-[¹⁴C(U)]fructose uptake studies revealed a progressive increase in fructose uptake in a time-dependent manner. Concentration-dependent studies with high fructose (5-25mM) showed marked increases in IRS-1 serine phosphorylation, a key adapter protein in insulin receptor signaling. Accordingly, high fructose treatment led to significant diminutions in insulin-induced phosphorylation of downstream signaling components including Akt and S6. In addition, high fructose significantly diminished insulin-induced ERK phosphorylation. Nevertheless, high fructose did not affect PDGF-induced key proliferative signaling events including phosphorylation of Akt, S6, and ERK and expression of cyclin D1 protein. Together, high fructose dysregulates IRS-1 phosphorylation state and proximal insulin receptor signaling in VSMCs, but does not affect PDGF-induced proliferative signaling. These findings suggest that systemic insulin resistance rather than VSMC-specific dysregulation of insulin receptor signaling by high fructose may play a major role in enhancing atherosclerosis and neointimal hyperplasia.

From DNA damage to functional changes of the trabecular meshwork in aging and glaucoma

Glaucoma is a degenerative disease of the eye. Both the anterior and posterior segments of the eye are affected, extensive damage being detectable in the trabecular meshwork and the inner retina-central visual pathway complex. Oxidative stress is claimed to be mainly responsible for molecular damage in the anterior chamber. Indeed, oxidation harms the trabecular meshwork, leading eventually to endothelial cell decay, tissue malfunction, subclinical inflammation, changes in the extracellular matrix and cytoskeleton, altered motility, reduced outflow facility and (ultimately) increased IOP. Moreover, free radicals are involved in aging and can be produced in the brain (as well as in the eye) as a result of ischemia, leading to oxidation of the surrounding neurons. Glaucoma-related cell death occurs by means of apoptosis, and apoptosis is triggered by oxidative stress via (a) mitochondrial damage, (b) inflammation, (c) endothelial dysregulation and dysfunction, and (d) hypoxia. The proteomics of the aqueous humor is significantly altered in glaucoma as a result of oxidation-induced trabecular damage. Those proteins whose aqueous humor levels are increased in glaucoma are biomarkers of trabecular meshwork impairment. Their diffusion from the anterior to the posterior segment of the eye may be relevant in the cascade of events triggering apoptosis in the inner retinal layers, including the ganglion cells.

Reversibility of endothelial dysfunction in diabetes: role of polyphenols

The endothelium, a thin single sheet of endothelial cells, is a metabolically active layer that coats the inner surface of blood vessels and acts as an interface between the circulating blood and the vessel wall. The endothelium through the secretion of vasodilators and vasoconstrictors serves as a critical mediator of vascular homeostasis. During the development of the vascular system, it regulates cellular adhesion and vessel wall inflammation in addition to maintaining vasculogenesis and angiogenesis. A shift in the functions of the endothelium towards vasoconstriction, proinflammatory and prothrombic states characterise improper functioning of these cells, leading to endothelial dysfunction (ED), implicated in the pathogenesis of many diseases including diabetes. Major mechanisms of ED include the down-regulation of endothelial nitric oxide synthase levels, differential expression of vascular endothelial growth factor, endoplasmic reticulum stress, inflammatory pathways and oxidative stress. ED tends to be the initial event in macrovascular complications such as coronary artery disease, peripheral arterial disease, stroke and microvascular complications such as nephropathy, neuropathy and retinopathy. Numerous strategies have been developed to protect endothelial cells against various stimuli, of which the role of polyphenolic compounds in modulating the differentially regulated pathways and thus maintaining vascular homeostasis has been proven to be beneficial. This review addresses the factors stimulating ED in diabetes and the molecular mechanisms of natural polyphenol antioxidants in maintaining vascular homeostasis.

Microvascular endothelial cells from preeclamptic women exhibit altered expression of angiogenic and vasopressor factors

Preeclampsia (PE) is a severe complication of pregnancy associated with maternal and fetal morbidity and mortality. The underlying pathophysiology involves maternal systemic vascular and endothelial dysfunction associated with circulating antiangiogenic factors, although the specific etiology of the disease remains elusive. Our aim was to investigate the maternal endothelium in PE by exploring the expression of genes involved with endothelial function in a novel platform of maternal primary endothelial cells. Adipose tissue was sampled at the time of caesarean section from both normal and preeclamptic patients. Maternal microvascular endothelial cells were isolated by tissue digestion and CD31 magnetic Dynabeads. Cell purity was confirmed by immunofluorescence microscopy and flow cytometry. Western analyses revealed VEGF activation of VEGF receptor 2 (VEGFR2) and ERK in primary cells. Quantitative PCR analyses revealed significantly altered mRNA levels of various genes involved with angiogenesis and blood pressure control in preeclamptic cells, including soluble fms-like tyrosine kinase-1, endoglin, VEGFR2, angiotensin receptor 1, and endothelin compared with cells isolated from normal pregnancies. Overall, maternal endothelial cells from preeclamptic patients exhibit extensive alteration of expression of factors associated with antiangiogenic and vasoconstrictive phenotypes, shedding light on the underlying mechanisms associated with the vascular dysfunction characteristic of PE.

Sex and Gender Differences in Risk, Pathophysiology and Complications of Type 2 Diabetes Mellitus

The steep rise of type 2 diabetes mellitus (T2DM) and associated complications go along with mounting evidence of clinically important sex and gender differences. T2DM is more frequently diagnosed at lower age and body mass index in men; however, the most prominent risk factor, which is obesity, is more common in women. Generally, large sex-ratio differences across countries are observed. Diversities in biology, culture, lifestyle, environment, and socioeconomic status impact differences between males and females in predisposition, development, and clinical presentation. Genetic effects and epigenetic mechanisms, nutritional factors and sedentary lifestyle affect risk and complications differently in both sexes. Furthermore, sex hormones have a great impact on energy metabolism, body composition, vascular function, and inflammatory responses. Thus, endocrine imbalances relate to unfavorable cardiometabolic traits, observable in women with androgen excess or men with hypogonadism. Both biological and psychosocial factors are responsible for sex and gender differences in diabetes risk and outcome. Overall, psychosocial stress appears to have greater impact on women rather than on men. In addition, women have greater increases of cardiovascular risk, myocardial infarction, and stroke mortality than men, compared with nondiabetic subjects. However, when dialysis therapy is initiated, mortality is comparable in both males and females. Diabetes appears to attenuate the protective effect of the female sex in the development of cardiac diseases and nephropathy. Endocrine and behavioral factors are involved in gender inequalities and affect the outcome. More research regarding sex-dimorphic pathophysiological mechanisms of T2DM and its complications could contribute to more personalized diabetes care in the future and would thus promote more awareness in terms of sex- and gender-specific risk factors.

Modulation of the cellular content of metabolites in adipocytes by insulin

Although the insulin-mediated cell signaling pathway has been extensively examined, changes in the cellular content of metabolites currently remain unclear. We herein examined metabolite contents in 3T3-L1 adipocytes treated with insulin using a metabolomic analysis. Fifty-four compounds were detected, and the contents of metabolites from the citric acid cycle increased in response to the insulin treatment for 4 h, which was sensitive to U0126 and LY294002, inhibitors for mitogen-activated protein kinase kinase-1 and phosphoinositide 3-kinase, respectively. The cellular contents of fumaric acid and malic acid were increased more by insulin than those of citric acid and succinic acid. Time-course changes in metabolites from the citric acid cycle exhibited oscillations with a 2-h cycle. A metabolic pathway analysis also indicated that insulin affected the metabolism of alanine, aspartate and glutamate, as well as that of arginine and proline. The contents of free amino acids were slightly decreased by the insulin treatment, while the co-treatment with U0126 and LY294002 abrogated these insulin-mediated decreases. The present study revealed the unexpected accumulation of citric acid cycle metabolites in adipocytes by insulin. Our results indicate the usefulness of metabolomic analyses for obtaining a more comprehensive understanding of the regulation of metabolic pathways in cell-culture systems.

The Activation of ERK1/2 and JNK MAPK Signaling by Insulin/IGF-1 Is Responsible for the Development of Colon Cancer with Type 2 Diabetes Mellitus

Previous studies showed that type 2 diabetes mellitus (T2DM) is linked to increased risk of developing colon cancer. Insulin and insulin-like growth factor 1 (IGF-1) are increased in patients with T2DM. The increased insulin and IGF-1 may be responsible for the developing of colon cancer. In this study, we investigated the effects and mechanisms of insulin and IGF-1 in colon cancer development in vitro and in vivo. Insulin and IGF-1 alone or together elevated proliferation and reduced apoptosis in colon cancer MC38 cells. Meanwhile, insulin and IGF-1 promoted the phosphorylation of extracellular-signal regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK). Treatment with ERK1/2 or JNK inhibitor in the presence of insulin and IGF-1 significantly decreased B-cell lymphoma 2 (Bcl-2) and increased Bcl-2-associated X protein (Bax) expression and finally increased apoptosis and inhibited the proliferation. Accelerative colon tumor growth was found in a mouse model of T2DM with db/db mice which got high level of endogenous insulin and IGF-1. Furthermore, the inhibition of ERK1/2 or JNK suppressed the development of colon tumor in vivo. These results suggest that the activation of ERK1/2 and JNK signaling by insulin and IGF-1, at least in part, is responsible for the development of colon cancer with T2DM.

Metabolic, anabolic, and mitogenic insulin responses: A tissue-specific perspective for insulin receptor activators

Insulin acts as the major regulator of the fasting-to-fed metabolic transition by altering substrate metabolism, promoting energy storage, and helping activate protein synthesis. In addition to its glucoregulatory and other metabolic properties, insulin can also act as a growth factor. The metabolic and mitogenic responses to insulin are regulated by divergent post-receptor signaling mechanisms downstream from the activated insulin receptor (IR). However, the anabolic and growth-promoting properties of insulin require tissue-specific inter-relationships between the two pathways, and the nature and scope of insulin-regulated processes vary greatly across tissues. Understanding the nuances of this interplay between metabolic and growth-regulating properties of insulin would have important implications for development of novel insulin and IR modulator therapies that stimulate insulin receptor activation in both pathway- and tissue-specific manners. This review will provide a unique perspective focusing on the roles of "metabolic" and "mitogenic" actions of insulin signaling in various tissues, and how these networks should be considered when evaluating selective pharmacologic approaches to prevent or treat metabolic disease.

Does bosentan protect diabetic brain alterations in rats? The role of endothelin-1 in the diabetic brain

Diabetes mellitus (DM) is a major problem all over the world, affecting more people in recent years. Individuals with diabetes are more prone to disease than non-diabetics, especially vascular complications. The aim of this study was to examine the roles of the endothelin (ET)-1 in brain damage formed in a streptozocin (STZ)-induced diabetes model, and the effect of bosentan, which is the non-specific ET1 receptor blocker in the prevention of the diabetes-induced brain damage. To examine the effects of bosentan (50 mg/kg and 100 mg/kg) in this study, the rats were given the drug for 3 months. The rats were divided into four groups: the sham group (n = 10), the diabetic control group (n = 10), the group of diabetic rats given bosentan 50 mg/kg (n = 10) and the group of diabetic rats given bosentan 100 mg/kg (n = 10). Diabetes was induced in the rats by STZ (60 mg/kg i.p.). On day 91, all rats were killed. Brain tissues of the rats were measured by molecular, biochemical and histopathological methods. Antioxidant levels in the therapy groups were observed as quite near to the values in the healthy group. In this study, while the brain eNOS levels in the diabetic groups decreased, the ET1 and iNOS levels were found to be increased. However, in the diabetes group, hippocampus and cerebellum, pericellular oedema and a number of neuronal cytoretraction were increased in neuropiles, whereas these results were decreased in the therapy group. Based on all of these results, ET1 will not be ignored in diabetes-induced cerebral complications.

The effects of apelin treatment on a rat model of type 2 diabetes

PURPOSE

Apelin is an adipokine that plays a role in the regulation of many biological functions in mammals including the neuroendocrine, cardiovascular, immune systems, glucose homeostasis and obesity. It can act via autocrine, paracrine, endocrine, and exocrine signaling. We aimed to identify the role of apelin pathophysiology of diabetes.

MATERIAL/METHODS

37 male Wistar Albino rats aged 8-10 weeks were divided in four experimental groups as: control group (C) control+apelin group (C+A), diabetic group (D) diabetic+apelin group (D+A). Apelin and apelin receptor mRNA gene expressions in heart and aorta tissue were determined by real-time polymerase chain reaction. The plasma levels of insulin and plasma apelin were determined by ELISA.

RESULTS

Plasma levels of insulin, glucose, blood pressure levels were significantly lower in D+A group. There was no statistically significant difference for level of apelin between diabetic groups. On the other hand, differences for apelin and APJ mRNA expression in heart and vascular tissue were found significant between groups.

CONCLUSIONS

Apelin can be used as a therapeutic agent in the treatment of type II diabetes in the future.

MicroRNAs and cardiovascular diseases

Coronary artery diseases (CAD) and heart failure have high mortality rate in the world, although much progress has been made in this field in last two decades. There is still a clinical need for a novel diagnostic approach and a therapeutic strategy to decrease the incidence of CAD. MicroRNAs (miRNAs) are highly conserved noncoding small RNA molecules that regulate a large fraction of the genome by binding to complementary messenger RNA sequences, resulting in posttranscriptional gene silencing. Recent studies have shown that specific miRNAs are involved in whole stage of atherosclerosis, from endothelium dysfunction to plaque rupture. These findings suggest that miRNAs are potential biomarkers in early diagnosis and therapeutic targets in CAD. In the present review, we highlight the role of miRNAs in every stage of atherosclerosis, and discuss the prospects of miRNAs in the near future.

Endothelial dysfunction as a nexus for endothelial cell-cardiomyocyte miscommunication

Most studies of the heart focus on cardiomyocytes (CM) at the exclusion of other cell types such as myocardial endothelial cells (EC). Such mono-cellular approaches propagate the presumption that EC provide a mere “passive lining” or supportive role. In fact, EC contribute to a dynamic network regulating vascular tone, cardiac development, and repair. Two distinct EC types, vascular EC and epicardial EC, possess important structural and signaling properties within both the healthy and diseased myocardium. In this review, we address EC-CM interactions in mature, healthy myocardium, followed by a discussion of diseases characterized by EC dysfunction. Finally, we consider strategies to reverse EC-CM “miscommunication” to improve patients' outcomes in various cardiovascular diseases.

Crucial roles of Nox2-derived oxidative stress in deteriorating the function of insulin receptors and endothelium in dietary obesity of middle-aged mice

BACKGROUND AND PURPOSE

Systemic oxidative stress associated with dietary calorie overload plays an important role in the deterioration of vascular function in middle-aged patients suffering from obesity and insulin resistance. However, effective therapy is still lacking.

EXPERIMENTAL APPROACH

In this study, we used a mouse model of middle-aged obesity to investigate the therapeutic potential of pharmaceutical inhibition (apocynin, 5 mM supplied in the drinking water) or knockout of Nox2, an enzyme generating reactive oxygen species (ROS), in high-fat diet (HFD)-induced obesity, oxidative stress, insulin resistance and endothelial dysfunction. Littermates of C57BL/6J wild-type (WT) and Nox2 knockout (KO) mice (7 months old) were fed with a HFD (45% kcal fat) or normal chow diet (NCD, 12% kcal fat) for 16 weeks and used at 11 months of age.

KEY RESULTS

Compared to NCD WT mice, HFD WT mice developed obesity, insulin resistance, dyslipidaemia and hypertension. Aortic vessels from these mice showed significantly increased Nox2 expression and ROS production, accompanied by significantly increased ERK1/2 activation, reduced insulin receptor expression, decreased Akt and eNOS phosphorylation and impaired endothelium-dependent vessel relaxation to acetylcholine. All these HFD-induced abnormalities (except the hyperinsulinaemia) were absent in apocynin-treated WT or Nox2 KO mice given the same HFD.

CONCLUSIONS AND IMPLICATIONS

In conclusion, Nox2-derived ROS played a key role in damaging insulin receptor and endothelial function in dietary obesity after middle-age. Targeting Nox2 could represent a valuable therapeutic strategy in the metabolic syndrome.

Acute insulin resistance stimulates and insulin sensitization attenuates vascular smooth muscle cell migration and proliferation

Differential activation/deactivation of insulin signaling, PI-3K and MAP-K pathways by high glucose and palmitate, with/out the insulin sensitizer pioglitazone (PIO), have been previously shown in vascular smooth muscle cells (VSMCs). To determine the biological impact of these molecular changes, we examined VSMC migration and proliferation ("M"&"P") patterns in similar conditions. VSMCs from healthy human coronary arteries were incubated in growth medium and "M"&"P" were analyzed after exposure to high glucose (25 mmol/L) ± palmitate (200 μmol/L) and ± PIO (8 μmol/L) for 5 h. "M"&"P" were assessed by: (1) polycarbonate membrane barrier with chemo-attractants and extended cell protrusions quantified by optical density (OD595 nm); (2) % change in radius area (2D Assay) using inverted microscopy images; and (3) cell viability assay expressed as cell absorbance (ABS) in media. "M" in 25 mmol/L glucose media increased by ~25% from baseline and % change in radius area rose from ~20% to ~30%. The addition of PIO was accompanied by a significant decrease in "M" from 0.25 ± 0.02 to 0.19 ± 0.02; a comparable decline from 0.25 ± 0.02 to 0.18 ± 0.02 was also seen with 25 mmol/L of glucose +200 μmol/L of palmitate. When PIO was coincubated with high glucose plus palmitate there was a 50% reduction in % change in radius. A ~10% increase in ABS, reflecting augmented "P" in media with 25 mmol/L glucose versus control was documented. The addition of PIO reduced ABS from 0.208 ± 0.03 to 0.183 ± 0.06. Both high glucose and palmitate showed ABS of ~0.140 ± 0.02, which decreased with PIO to ~0.120 ± 0.02, indicating "P" was reduced.

CONCLUSION

These results confirm that high glucose and palmitate stimulate VSMCs migration and proliferation in vitro, which is attenuated by coincubation with the insulin sensitizer PIO. Although, we cannot ascertain whether these functional changes are coincident with the activation/deactivation of signal molecules, our findings are consistent with the theory that differential regulation of insulin signaling pathways in VSMCs in insulin-resistant states plays an important role in inflammation, arterial wall thickening, and plaque formation during development of atherosclerosis.

Human biliverdin reductase-based peptides activate and inhibit glucose uptake through direct interaction with the kinase domain of insulin receptor

Insulin binding changes conformation of the insulin receptor kinase (IRK) domain and initiates glucose uptake through the insulin, IGF-1, phosphatidyl inositol 3-kinase (PI3K), and MAPK pathways; human biliverdin reductase (hBVR) is an IRK substrate and pathway effector. This is the first report on hBVR peptide-mediated IRK activation and conformational change. (290)KYCCSRK, which increased IRK V(max) without changing K(m), stimulated glucose uptake and potentiated insulin and IGF-1 stimulation in 4 cell lines. KYCCSRK in native hBVR was necessary for the hBVR and IRK cross-activation. Peptide treatment also activated PI3K downstream effectors, Akt and ERK, phosphorylation, and Elk transcriptional activity. In cells transfected with CMV-regulated EGFP-VP-peptide plasmid, C(292)→A mutant did not stimulate glucose uptake; K(296)→A decreased uptake and kinase activity. KEDQYMKMTV, corresponding to hBVR's SH2-binding domain, was a potent inhibitor of glucose uptake and IRK. The mechanism of action of peptides was examined using cells expressing IRK (aa 988-1263) activated by coexpressed KYCCSRK. Three active cys-mutants of IRK, with fluorophore coupled to cysteines, C(1056), C(1138), or C(1234), were examined for changes in fluorescence emission spectra in the presence of peptides. KYCCSRK and KEDQYMKMTV bound to different sites in IRK. The findings identify novel agents for activating or inhibiting insulin signaling and offer a new approach for treatment of type 2 diabetes and hypoglycemia.