Epidermal growth factor and transforming growth factor alpha mimic the effects of insulin in human fat cells and augment downstream signaling in insulin resistance

Heparin impairs skeletal muscle glucose uptake by inhibiting insulin binding to insulin receptor

Aim

Heparin, a widely used antithrombotic drug has many other anticoagulant-independent physiological functions. Here, we elucidate a novel role of heparin in glucose homeostasis, suggesting an approach for developing heparin-targeted therapies for diabetes.

Methods

For serum heparin levels and correlation analysis, 122 volunteer's plasma, DIO (4 weeks HFD) and db/db mice serums were collected and used for spectrophotometric determination. OGTT, ITT, 2-NBDG uptake and muscle GLUT4 immunofluorescence were detected in chronic intraperitoneal injection of heparin or heparinase (16 days) and muscle-specific loss-of-function mice. In 293T cells, the binding of insulin to its receptor was detected by fluorescence resonance energy transfer (FRET), Myc-GLUT4-mCherry plasmid was used in GLUT4 translocation. In vitro, C2C12 cells as mouse myoblast cells were further verified the effects of heparin on glucose homeostasis through 2-NBDG uptake, Western blot and co-immunoprecipitation.

Results

Serum concentrations of heparin are positively associated with blood glucose levels in humans and are significantly increased in diet-induced and db/db obesity mouse models. Consistently, a chronic intraperitoneal injection of heparin results in hyperglycaemia, glucose intolerance and insulin resistance. These effects are independent of heparin's anticoagulant function and associated with decreases in glucose uptake and translocation of glucose transporter type 4 (GLUT4) in skeletal muscle. By using a muscle-specific loss-of-function mouse model, we further demonstrated that muscle GLUT4 is required for the detrimental effects of heparin on glucose homeostasis.

Conclusions

Heparin reduced insulin binding to its receptor by interacting with insulin and inhibited insulin-mediated activation of the PI3K/Akt signalling pathway in skeletal muscle, which leads to impaired glucose uptake and hyperglycaemia.

A multidimensional functional fitness score has a stronger association with type 2 diabetes than obesity parameters in cross sectional data

Objectives

We examine here the association of multidimensional functional fitness with type 2 diabetes mellitus (T2DM) as compared to anthropometric indices of obesity such as body mass index (BMI) and waist to hip ratio (WHR) in a sample of Indian population.

Research design and method

We analysed retrospective data of 663 volunteer participants (285 males and 378 females between age 28 and 84), from an exercise clinic in which every participant was required to undergo a health related physical fitness (HRPF) assessment consisting of 15 different tasks examining 8 different aspects of functional fitness.

Results

The odds of being diabetic in the highest quartile of BMI were not significantly higher than that in the lowest quartile in either of the sexes. The odds of being a diabetic in the highest WHR quartile were significantly greater than the lowest quartile in females (OR = 4.54 (1.95, 10.61) as well as in males (OR = 3.81 (1.75, 8.3). In both sexes the odds of being a diabetic were significantly greater in the lowest quartile of HRPF score than the highest (males OR = 10.52 (4.21, 26.13); females OR = 10.50 (3.53, 31.35)). After removing confounding, the predictive power of HRPF was significantly greater than that of WHR. HRPF was negatively correlated with WHR, however for individuals that had contradicting HRPF and WHR based predictions, HRPF was the stronger predictor of T2DM.

Conclusion

The association of multidimensional functional fitness score with type 2 diabetes was significantly stronger than obesity parameters in a cross sectional self-selected sample from an Indian city.

Underlying Mechanism of Insulin Resistance: A Bioinformatics Analysis Based on Validated Related-Genes from Public Disease Databases

Background

The underlying mechanism of insulin resistance is complex; bioinformatics analysis is used to explore the mechanism based differential expression genes (DEGs) obtained from omics analysis. However, the expression and role of most DEGs involved in bioinformatics analysis are invalidated. This study aimed to disclose the mechanism of insulin resistance via bioinformatics analysis based on validated insulin resistance-related genes (IRRGs) collected from public disease-gene databases.

Material/Methods

IRRGs were collected from 4 disease databases including NCBI-Gene, CTD, RGD, and Phenopedia. GO and KEGG analysis of IRRGs were performed by DAVID. Then, the STRING database was employed to construct a protein–protein interaction (PPI) network of IRRGs. The module analysis and hub genes identification were carried out by MCODE and cytoHubba plugin of Cytoscape based on the primary PPI network, respectively.

Results

A total of 1195 IRRGs were identified. Response to drug, hypoxia, insulin, positive regulation of transcription from RNA polymerase II promoter, cell proliferation, inflammatory response, negative regulation of apoptotic process, glucose homeostasis, cellular response to insulin stimulus, and aging were proposed as the crucial functions related to insulin resistance. Ten insulin resistance-related pathways included the pathways of insulin resistance, pathways in cancer, adipocytokine, prostate cancer, PI3K-Akt, insulin, AMPK, HIF-1, prolactin, and pancreatic cancer signaling pathway were revealed. INS, AKT1, IL-6, TP53, TNF, VEGFA, MAPK3, EGFR, EGF, and SRC were identified as the top 10 hub genes.

Conclusions

The current study presented a landscape view of possible underlying mechanism of insulin resistance by bioinformatics analysis based on validated IRRGs.

Exercise Training in Obese Rats Does Not Induce Browning at Thermoneutrality and Induces a Muscle-Like Signature in Brown Adipose Tissue

Aim: Exercise training elicits diverse effects on brown (BAT) and white adipose tissue (WAT) physiology in rodents housed below their thermoneutral zone (i.e., 28-32°C). In these conditions, BAT is chronically hyperactive and, unlike human residence, closer to thermoneutrality. Therefore, we set out to determine the effects of exercise training in obese animals at 28°C (i.e., thermoneutrality) on BAT and WAT in its basal (i.e., inactive) state. Methods: Sprague-Dawley rats (n = 12) were housed at thermoneutrality from 3 weeks of age and fed a high-fat diet. At 12 weeks of age half these animals were randomized to 4-weeks of swim-training (1 h/day, 5 days per week). Following a metabolic assessment interscapular and perivascular BAT and inguinal (I)WAT were taken for analysis of thermogenic genes and the proteome. Results: Exercise attenuated weight gain but did not affect total fat mass or thermogenic gene expression. Proteomics revealed an impact of exercise training on 2-oxoglutarate metabolic process, mitochondrial respiratory chain complex IV, carbon metabolism, and oxidative phosphorylation. This was accompanied by an upregulation of multiple proteins involved in skeletal muscle physiology in BAT and an upregulation of muscle specific markers (i.e., Myod1, CkM, Mb, and MyoG). UCP1 mRNA was undetectable in IWAT with proteomics highlighting changes to DNA binding, the positive regulation of apoptosis, HIF-1 signaling and cytokine-cytokine receptor interaction. Conclusion: Exercise training reduced weight gain in obese animals at thermoneutrality and is accompanied by an oxidative signature in BAT which is accompanied by a muscle-like signature rather than induction of thermogenic genes. This may represent a new, UCP1-independent pathway through which BAT physiology is regulated by exercise training.

Kinin B1 Receptor Acts in Adipose Tissue to Control Fat Distribution in a Cell-Nonautonomous Manner

The kinin B₁ receptor (B₁R) plays a role in inflammatory and metabolic processes. B₁R deletion (B₁ ^-/-) protects mice from diet-induced obesity and improves insulin and leptin sensitivity. In contrast, genetic reconstitution of B₁R exclusively in adipose tissue reverses the lean phenotype of B₁ ^-/- mice. To study the cell-nonautonomous nature of these effects, we transplanted epididymal white adipose tissue (eWAT) from wild-type donors (B₁ ^+/+) into B₁ ^-/- mice (B₁ ^+/+→B₁ ^-/-) and compared them with autologous controls (B₁ ^+/+→B₁ ^+/+ or B₁ ^-/-→B₁ ^-/-). We then fed these mice a high-fat diet for 16 weeks and investigated their metabolic phenotypes. B₁ ^+/+→B₁ ^-/- mice became obese but not glucose intolerant or insulin resistant, unlike B₁ ^-/-→B₁ ^-/- mice. Moreover, the endogenous adipose tissue of B₁ ^+/+→B₁ ^-/- mice exhibited higher expression of adipocyte markers (e.g., Fabp4 and Adipoq) and changes in the immune cell pool. These mice also developed fatty liver. Wild-type eWAT transplanted into B₁ ^-/- mice normalized circulating insulin, leptin, and epidermal growth factor levels. In conclusion, we demonstrated that B₁R in adipose tissue controls the response to diet-induced obesity by promoting adipose tissue expansion and hepatic lipid accumulation in cell-nonautonomous manners.

Insulin-signaling Pathway Regulates the Degradation of Amyloid β-protein via Astrocytes

Alzheimer's disease (AD) has been considered as a metabolic dysfunction disease associated with impaired insulin signaling. Determining the mechanisms underlying insulin signaling dysfunction and resistance in AD will be important for its treatment. Impaired clearance of amyloid-β peptide (Aβ) significantly contributes to amyloid accumulation, which is typically observed in the brain of AD patients. Reduced expression of important Aβ-degrading enzymes in the brain, such as neprilysin (NEP) and insulin-degrading enzyme (IDE), can promote Aβ deposition in sporadic late-onset AD patients. Here, we investigated whether insulin regulates the degradation of Aβ by inducing expression of NEP and IDE in cultured astrocytes. Treatment of astrocytes with insulin significantly reduced cellular NEP levels, but increased IDE expression. The effects of insulin on the expression of NEP and IDE involved activation of an extracellular signal-regulated kinase (ERK)-mediated pathway. The reduction in cellular NEP levels was associated with NEP secretion into the culture medium, whereas IDE was increased in the cell membranes. Moreover, insulin-treated astrocytes significantly facilitated the degradation of exogenous Aβ within the culture medium. Interestingly, pretreatment of astrocytes with an ERK inhibitor prior to insulin exposure markedly inhibited insulin-induced degradation of Aβ. These results suggest that insulin exposure enhanced Aβ degradation via an increase in NEP secretion and IDE expression in astrocytes, via activation of the ERK-mediated pathway. The inhibition of insulin signaling pathways delayed Aβ degradation by attenuating alterations in NEP and IDE levels and competition with insulin and Aβ. Our results provide further insight into the pathological relevance of insulin resistance in AD development.

How much variance in insulin resistance is explained by obesity?

Background: Obesity is believed to be the major cause of insulin resistance, although many other obesity-independent signals are shown to affect insulin sensitivity.Aim: We address the degree to which variation in insulin resistance is explained by morphometric and biochemical measures of obesity.Methods: PubMed and Google Scholar were searched for epidemiological studies published between 1994 and 2015 that report correlations between at least one measure of obesity and that of insulin resistance.Results: A total of 63 studies satisfied inclusion criteria. Frequency distribution of coefficients of determination between morphometric measures of obesity and insulin resistance was skewed with the mode being less than 10%, class and median being 17.3%. Plasma leptin concentration, but not plasma non-esterified fatty acid level, was better correlated with insulin resistance, the median variance explained being 33.29%. Morphometric measures alone had a median variance explained of 16%. Ethnicity explained part of the variance across studies with the correlation being significantly poorer in Asians.Conclusion: The extremely limited predictive power of morphometric and biochemical measures of obesity suggests that more research needs to focus on the obesity-independent signals that affect insulin sensitivity as well as leptin expression.

Beta Cell Mass Restoration in Alloxan-Diabetic Mice Treated with EGF and Gastrin

One week of treatment with EGF and gastrin (EGF/G) was shown to restore normoglycemia and to induce islet regeneration in mice treated with the diabetogenic agent alloxan. The mechanisms underlying this regeneration are not fully understood. We performed genetic lineage tracing experiments to evaluate the contribution of beta cell neogenesis in this model. One day after alloxan administration, mice received EGF/G treatment for one week. The treatment could not prevent the initial alloxan-induced beta cell mass destruction, however it did reverse glycemia to control levels within one day, suggesting improved peripheral glucose uptake. In vitro experiments with C2C12 cell line showed that EGF could stimulate glucose uptake with an efficacy comparable to that of insulin. Subsequently, EGF/G treatment stimulated a 3-fold increase in beta cell mass, which was partially driven by neogenesis and beta cell proliferation as assessed by beta cell lineage tracing and BrdU-labeling experiments, respectively. Acinar cell lineage tracing failed to show an important contribution of acinar cells to the newly formed beta cells. No appearance of transitional cells co-expressing insulin and glucagon, a hallmark for alpha-to-beta cell conversion, was found, suggesting that alpha cells did not significantly contribute to the regeneration. An important fraction of the beta cells significantly lost insulin positivity after alloxan administration, which was restored to normal after one week of EGF/G treatment. Alloxan-only mice showed more pronounced beta cell neogenesis and proliferation, even though beta cell mass remained significantly depleted, suggesting ongoing beta cell death in that group. After one week, macrophage infiltration was significantly reduced in EGF/G-treated group compared to the alloxan-only group. Our results suggest that EGF/G-induced beta cell regeneration in alloxan-diabetic mice is driven by beta cell neogenesis, proliferation and recovery of insulin. The glucose-lowering effect of the treatment might play an important role in the regeneration process.

I(f) current channel inhibitor (ivabradine) deserves cardioprotective effect via down-regulating the expression of matrix metalloproteinase (MMP)-2 and attenuating apoptosis in diabetic mice

Background

Ivabradine (IVBD), a novel I(f)-channel inhibitor and specific heart rate-lowering agent, is known to have anti-oxidative activity that promotes endothelial function. However, the molecular mechanism through which IVBD acts on cardiac function has yet to be elucidated, especially in experimental diabetic animals.

Methods

For this reason, twenty diabetic mice were randomly assigned to IVBD-treated (10 mg/kg/day) and control (saline) groups. After a 3-month treatment, microarray assay was performed to identify differentia expressed genes, and cardiac function was measured by echocardiography, with subsequent immunohistochemistry analysis and western blotting.

Results

Our results showed that ivabradine treatment attenuated the expression and staining score of matrix metalloproteinase (MMP)-2, induced the dephosphorylation of caspase 3, BAX and MMP-2, and enhanced the phosphorylation of NF-κB. Ivabradine treatment led to a significant improvement in cardiac function.

Conclusion

Ivabradine significantly improved cardiac function by attenuating apoptosis and inhibiting the expression and activity of MMP-2 in diabetic mice, which underscored the novel clinical implications of ivabradine for diabetic patients.

A single mechanism can explain network-wide insulin resistance in adipocytes from obese patients with type 2 diabetes

The response to insulin is impaired in type 2 diabetes. Much information is available about insulin signaling, but understanding of the cellular mechanisms causing impaired signaling and insulin resistance is hampered by fragmented data, mainly obtained from different cell lines and animals. We have collected quantitative and systems-wide dynamic data on insulin signaling in primary adipocytes and compared cells isolated from healthy and diabetic individuals. Mathematical modeling and experimental verification identified mechanisms of insulin control of the MAPKs ERK1/2. We found that in human adipocytes, insulin stimulates phosphorylation of the ribosomal protein S6 and hence protein synthesis about equally via ERK1/2 and mTORC1. Using mathematical modeling, we examined the signaling network as a whole and show that a single mechanism can explain the insulin resistance of type 2 diabetes throughout the network, involving signaling both through IRS1, PKB, and mTOR and via ERK1/2 to the nuclear transcription factor Elk1. The most important part of the insulin resistance mechanism is an attenuated feedback from the protein kinase mTORC1 to IRS1, which spreads signal attenuation to all parts of the insulin signaling network. Experimental inhibition of mTORC1 using rapamycin in adipocytes from non-diabetic individuals induced and thus confirmed the predicted network-wide insulin resistance.

TGF-β stimulation in human and murine cells reveals commonly affected biological processes and pathways at transcription level

Background

The TGF-β signaling pathway is a fundamental pathway in the living cell, which plays a key role in many central cellular processes. The complex and sometimes contradicting mechanisms by which TGF-β yields phenotypic effects are not yet completely understood. In this study we investigated and compared the transcriptional response profile of TGF-β1 stimulation in different cell types. For this purpose, extensive experiments are performed and time-course microarray data are generated in human and mouse parenchymal liver cells, human mesenchymal stromal cells and mouse hematopoietic progenitor cells at different time points. We applied a panel of bioinformatics methods on our data to uncover common patterns in the dynamic gene expression response in respective cells.

Results

Our analysis revealed a quite variable and multifaceted transcriptional response profile of TGF-β1 stimulation, which goes far beyond the well-characterized classical TGF-β1 signaling pathway. Nonetheless, we could identify several commonly affected processes and signaling pathways across cell types and species. In addition our analysis suggested an important role of the transcription factor EGR1, which appeared to have a conserved influence across cell-types and species. Validation via an independent dataset on A549 lung adenocarcinoma cells largely confirmed our findings. Network analysis suggested explanations, how TGF-β1 stimulation could lead to the observed effects.

Conclusions

The analysis of dynamical transcriptional response to TGF-β treatment experiments in different human and murine cell systems revealed commonly affected biological processes and pathways, which could be linked to TGF-β1 via network analysis. This helps to gain insights about TGF-β pathway activities in these cell systems and its conserved interactions between the species and tissue types.

Early effects of a hypocaloric, Mediterranean diet on laboratory parameters in obese individuals

Calorie restriction is a common strategy for weight loss in obese individuals. However, little is known about the impact of moderate hypocaloric diets on obesity-related laboratory parameters in a short-term period. Aim of this study was to evaluate the variation of laboratory biomarkers in obese individuals following a Mediterranean, hypocaloric (1400-1600 Kcal/die) diet. 23 obese, pharmacologically untreated patients were enrolled and subjected to the determination of anthropometric variables and blood collection at baseline, 1 and 4 months after diet initiation. After 4 months of calorie restriction, we observed a significant decrease in body weight and BMI (both P < 0.0001), insulin (P = 0.037), HOMA-IR (P = 0.026), leptin (P = 0.008), and LDH (P = 0.023) and an increase in EGF (P = 0.013). All these parameters, except LDH, varied significantly already at 1 month after diet initiation. Also, lower levels of insulin (P = 0.025), leptin (P = 0.023), and EGF (P = 0.035) were associated with a greater (>5%) weight loss. Collectively, our data support a precocious improvement of insulin and leptin sensitivity after a modest calorie restriction and weight reduction. Moreover, EGF and LDH may represent novel markers of obesity, which deserve further investigations.

From signal transduction to signal interpretation: an alternative model for the molecular function of insulin receptor substrates

The insulin receptor (IR) recruits adaptor proteins, so-called insulin receptor substrates (IRS), to connect with downstream signalling pathways. A family of IRS proteins was defined based on three major common structural elements: Amino-terminal PH and PTB domains that mediate protein-lipid or protein-protein interactions, mostly carboxy-terminal multiple tyrosine residues that serve as binding sites for proteins that contain one or more SH2 domains and serine/threonine-rich regions which may be recognized by negative regulators of insulin action. The current model for the role of IRS proteins therefore combines an adaptor function with the integration of mostly negative input from other signal transduction cascades allowing for modulation of signalling amplitude. In this review we propose an extended version of the adaptor model that can explain how signalling specificity could be implemented at the level of IRS proteins.

Erlotinib appears to produce prolonged remission of insulin-requiring type 2 diabetes associated with metabolic syndrome and chronic kidney disease

Patients with metabolic syndrome are at higher risk for type 2 diabetes and for chronic kidney disease. Metformin is the oral medication of choice for the treatment of type 2 diabetes in the absence of chronic kidney disease. There is a need for another oral glucose lowering agent for use in metabolic syndrome with type 2 diabetes and chronic kidney disease. We submit the first report of erlotinib, a once-daily oral medication for the treatment of non-small-cell lung cancer associated with specific genetic mutations, appearing to eliminate the need for insulin in insulin-requiring type 2 diabetes associated with metabolic syndrome and chronic kidney disease. The mechanism by which erlotinib, a tyrosine kinase inhibitor of the epidermal growth factor receptor may improve glycaemic control is unknown. Potential possibilities are explored.

Growth factor concentrations and their placental mRNA expression are modulated in gestational diabetes mellitus: possible interactions with macrosomia

Background

Gestational diabetes mellitus (GDM) is a form of diabetes that occurs during pregnancy. GDM is a well known risk factor for foetal overgrowth, termed macrosomia which is influenced by maternal hypergycemia and endocrine status through placental circulation. The study was undertaken to investigate the implication of growth factors and their receptors in GDM and macrosomia, and to discuss the role of the materno-foeto-placental axis in the in-utero regulation of foetal growth.

Methods

30 women with GDM and their 30 macrosomic babies (4.75 ± 0.15 kg), and 30 healthy age-matched pregnant women and their 30 newborns (3.50 ± 0.10 kg) were recruited in the present study. Serum concentrations of GH and growth factors, i.e., IGF-I, IGF-BP3, FGF-2, EGF and PDGF-B were determined by ELISA. The expression of mRNA encoding for GH, IGF-I, IGF-BP3, FGF-2, PDGF-B and EGF, and their receptors, i.e., GHR, IGF-IR, FGF-2R, EGFR and PDGFR-β were quantified by using RT-qPCR.

Results

The serum concentrations of IGF-I, IGF-BP3, EGF, FGF-2 and PDGF-B were higher in GDM women and their macrosomic babies as compared to their respective controls. The placental mRNA expression of the growth factors was either upregulated (FGF-2 or PDGF-B) or remained unaltered (IGF-I and EGF) in the placenta of GDM women. The mRNA expression of three growth factor receptors, i.e., IGF-IR, EGFR and PDGFR-β, was upregulated in the placenta of GDM women. Interestingly, serum concentrations of GH were downregulated in the GDM women and their macrosomic offspring. Besides, the expression of mRNAs encoding for GHR was higher, but that encoding for GH was lower, in the placenta of GDM women than control women.

Conclusions

Our results demonstrate that growth factors might be implicated in GDM and, in part, in the pathology of macrosomia via materno-foeto-placental axis.

Expression-based network biology identifies alteration in key regulatory pathways of type 2 diabetes and associated risk/complications

Type 2 diabetes mellitus (T2D) is a multifactorial and genetically heterogeneous disease which leads to impaired glucose homeostasis and insulin resistance. The advanced form of disease causes acute cardiovascular, renal, neurological and microvascular complications. Thus there is a constant need to discover new and efficient treatment against the disease by seeking to uncover various novel alternate signalling mechanisms that can lead to diabetes and its associated complications. The present study allows detection of molecular targets by unravelling their role in altered biological pathways during diabetes and its associated risk factors and complications. We have used an integrated functional networks concept by merging co-expression network and interaction network to detect the transcriptionally altered pathways and regulations involved in the disease. Our analysis reports four novel significant networks which could lead to the development of diabetes and other associated dysfunctions. (a) The first network illustrates the up regulation of TGFBRII facilitating oxidative stress and causing the expression of early transcription genes via MAPK pathway leading to cardiovascular and kidney related complications. (b) The second network demonstrates novel interactions between GAPDH and inflammatory and proliferation candidate genes i.e., SUMO4 and EGFR indicating a new link between obesity and diabetes. (c) The third network portrays unique interactions PTPN1 with EGFR and CAV1 which could lead to an impaired vascular function in diabetic nephropathy condition. (d) Lastly, from our fourth network we have inferred that the interaction of β-catenin with CDH5 and TGFBR1 through Smad molecules could contribute to endothelial dysfunction. A probability of emergence of kidney complication might be suggested in T2D condition. An experimental investigation on this aspect may further provide more decisive observation in drug target identification and better understanding of the pathophysiology of T2D and its complications.

Gene expression and muscle fiber function in a porcine ICU model

Skeletal muscle wasting and impaired muscle function in response to mechanical ventilation and immobilization in intensive care unit (ICU) patients are clinically challenging partly due to 1) the poorly understood intricate cellular and molecular networks and 2) the unavailability of an animal model mimicking this condition. By employing a unique porcine model mimicking the conditions in the ICU with long-term mechanical ventilation and immobilization, we have analyzed the expression profile of skeletal muscle biopsies taken at three time points during a 5-day period. Among the differentially regulated transcripts, extracellular matrix, energy metabolism, sarcomeric and LIM protein mRNA levels were downregulated, while ubiquitin proteasome system, cathepsins, oxidative stress responsive genes and heat shock proteins (HSP) mRNAs were upregulated. Despite 5 days of immobilization and mechanical ventilation single muscle fiber cross-sectional areas as well as the maximum force generating capacity at the single muscle fiber level were preserved. It is proposed that HSP induction in skeletal muscle is an inherent, primary, but temporary protective mechanism against protein degradation. To our knowledge, this is the first study that isolates the effect of immobilization and mechanical ventilation in an ICU condition from various other cofactors.

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

OBJECTIVE

To establish a method for isolation and culture of subcutaneous microvascular endothelial cells (MVEC) from small human tissue biopsies to compare gene and protein expression of insulin signaling molecules in MVEC from insulin-resistant and healthy control subjects.

RESEARCH DESIGN AND METHODS

Stromavascular cells from subcutaneous needle biopsies of type 2 diabetic and control subjects were expanded in culture and the endothelial cells selected with magnetic immune separation. Western blots and RT-PCR were used for protein and gene expression assays.

RESULTS

At least 99% of the expanded primary MVEC could be characterized as endothelial cells. The expression of insulin receptors was low, but insulin increased tyrosine phosphorylation of both the insulin receptor and insulin receptor substrate (IRS)-1 and activated protein kinase B (PKB). The IRS-1 protein expression was reduced and the serine phosphorylation of PKB in response to insulin attenuated whereas basal and insulin-stimulated phosphorylation of extracellular signal-related kinase (ERK)1/2 was increased in type 2 diabetes MVEC. Endothelin (ET)-1 mRNA levels were significantly higher in type 2 diabetes cells. The addition of ET-1 increased the phosphorylation of mitogen-activated protein kinase (MAPK), an effect antagonized by the MEK-1 inhibitor PD98059. Furthermore, the endothelin ET(A) and ET(B) receptor antagonists BQ123 and BQ788 decreased basal MAPK activity in type 2 diabetes MVEC and prevented the ET-1-induced activation.

CONCLUSIONS

We developed a system for isolation and culture of human MVEC from small needle biopsies. Our observations support the concept of "selective" insulin resistance, involving IRS-1 and the PI3kinase pathway, as an underlying factor for a dysregulated microvascular endothelium in type 2 diabetes. Our data also support a role of ET-1 for the increased MAPK activity seen in nonstimulated type 2 diabetes MVEC.

In-depth qualitative and quantitative profiling of tyrosine phosphorylation using a combination of phosphopeptide immunoaffinity purification and stable isotope dimethyl labeling

Several mass spectrometry-based assays have emerged for the quantitative profiling of cellular tyrosine phosphorylation. Ideally, these methods should reveal the exact sites of tyrosine phosphorylation, be quantitative, and not be cost-prohibitive. The latter is often an issue as typically several milligrams of (stable isotope-labeled) starting protein material are required to enable the detection of low abundance phosphotyrosine peptides. Here, we adopted and refined a peptidecentric immunoaffinity purification approach for the quantitative analysis of tyrosine phosphorylation by combining it with a cost-effective stable isotope dimethyl labeling method. We were able to identify by mass spectrometry, using just two LC-MS/MS runs, more than 1100 unique non-redundant phosphopeptides in HeLa cells from about 4 mg of starting material without requiring any further affinity enrichment as close to 80% of the identified peptides were tyrosine phosphorylated peptides. Stable isotope dimethyl labeling could be incorporated prior to the immunoaffinity purification, even for the large quantities (mg) of peptide material used, enabling the quantification of differences in tyrosine phosphorylation upon pervanadate treatment or epidermal growth factor stimulation. Analysis of the epidermal growth factor-stimulated HeLa cells, a frequently used model system for tyrosine phosphorylation, resulted in the quantification of 73 regulated unique phosphotyrosine peptides. The quantitative data were found to be exceptionally consistent with the literature, evidencing that such a targeted quantitative phosphoproteomics approach can provide reproducible results. In general, the combination of immunoaffinity purification of tyrosine phosphorylated peptides with large scale stable isotope dimethyl labeling provides a cost-effective approach that can alleviate variation in sample preparation and analysis as samples can be combined early on. Using this approach, a rather complete qualitative and quantitative picture of tyrosine phosphorylation signaling events can be generated.

Systems-level interactions between insulin-EGF networks amplify mitogenic signaling

Crosstalk mechanisms have not been studied as thoroughly as individual signaling pathways. We exploit experimental and computational approaches to reveal how a concordant interplay between the insulin and epidermal growth factor (EGF) signaling networks can potentiate mitogenic signaling. In HEK293 cells, insulin is a poor activator of the Ras/ERK (extracellular signal-regulated kinase) cascade, yet it enhances ERK activation by low EGF doses. We find that major crosstalk mechanisms that amplify ERK signaling are localized upstream of Ras and at the Ras/Raf level. Computational modeling unveils how critical network nodes, the adaptor proteins GAB1 and insulin receptor substrate (IRS), Src kinase, and phosphatase SHP2, convert insulin-induced increase in the phosphatidylinositol-3,4,5-triphosphate (PIP₃) concentration into enhanced Ras/ERK activity. The model predicts and experiments confirm that insulin-induced amplification of mitogenic signaling is abolished by disrupting PIP₃-mediated positive feedback via GAB1 and IRS. We demonstrate that GAB1 behaves as a non-linear amplifier of mitogenic responses and insulin endows EGF signaling with robustness to GAB1 suppression. Our results show the feasibility of using computational models to identify key target combinations and predict complex cellular responses to a mixture of external cues.

Biological determinants of and reference values for plasma interleukin-8, monocyte chemoattractant protein-1, epidermal growth factor, and vascular endothelial growth factor: Results from the STANISLAS cohort

BACKGROUND

Interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF) are known to be involved in various diseases related to inflammation, vascular remodeling, or growth deregulation. In addition, increases in plasma concentrations of these cytokines appear to provide useful diagnostic and prognostic information. We therefore investigated which factors most strongly influence the biological variations of plasma IL-8, MCP-1, EGF, and VEGF concentrations.

METHODS

We used the Evidence biochip array analyzer to quantify plasma IL-8, MCP-1, EGF, and VEGF concentrations in a subsample of 304 children (age range, 4-17 years) and 540 adults (age range, 18-55 years) from the STANISLAS family study. We also calculated reference intervals for the 4 cytokines.

RESULTS

We found the following associations with plasma marker concentrations: Age, neutrophil count, and glucose concentration were positively associated with IL-8 concentrations in children and adults, as were smoking and platelet count in adults. MCP-1 concentrations were associated with age and smoking in both children and adults, monocyte count in children, and sex and hematocrit in adults. EGF concentrations were associated with platelet count in children and monocyte count and glucose in adults. VEGF concentrations were associated with age in children and adults and platelet count and alanine aminotransferase activity in adults.

CONCLUSION

Our results for IL-8, MCP-1, EGF, and VEGF may be useful for interpretation of patients' laboratory results and for understanding the regulation of concentrations of these cytokines in physiologic conditions.

Insulin receptor substrate is a mediator of phosphoinositide 3-kinase activation in quiescent pancreatic cancer cells

Phosphoinositide 3-kinase (PI3K) is activated in pancreatic cancer cells and plays a central role in their proliferation, survival, and drug resistance. Although the mechanism is unclear, PI3K activation in these cells could be due to physical interaction between its regulatory subunit (p85) and specific tyrosine kinases or their mediators. Consistent with this possibility, PI3K was precipitated with anti-phosphotyrosine antibodies and Akt phosphorylation was blocked by the tyrosine kinase inhibitors SU6656 and PD158780 in quiescent pancreatic cancer cells. Pull-down assays with a fusion protein (GST-p85NC-SH2), and coimmunoprecipitation studies, indicated that the insulin receptor substrate (IRS), and not the epidermal growth factor and insulin-like growth factor receptors or the Src tyrosine kinase, was physically associated with PI3K in these cells. Our data also indicated that SU6656 and PD158780 inhibited Akt activation in pancreatic cancer cells by interfering with the ability of IRS-1 to recruit PI3K. Furthermore, IRS-1 was phosphorylated on a p85-binding site (Y(612)), and IRS-specific small interfering RNA potently inhibited activation of PI3K and Akt in transfected cells. Taken together, these observations indicate that IRS is a mediator of PI3K activation in quiescent pancreatic cancer cells.

A Compendium of Signals and Responses Triggered by Prodeath and Prosurvival Cytokines

Cell-signaling networks consist of proteins with a variety of functions (receptors, adaptor proteins, GTPases, kinases, proteases, and transcription factors) working together to control cell fate. Although much is known about the identities and biochemical activities of these signaling proteins, the ways in which they are combined into networks to process and transduce signals are poorly understood. Network-level understanding of signaling requires data on a wide variety of biochemical processes such as posttranslational modification, assembly of macromolecular complexes, enzymatic activity, and localization. No single method can gather such heterogeneous data in high throughput, and most studies of signal transduction therefore rely on series of small, discrete experiments. Inspired by the power of systematic datasets in genomics, we set out to build a systematic signaling dataset that would enable the construction of predictive models of cell-signaling networks. Here we describe the compilation and fusion of approximately 10,000 signal and response measurements acquired from HT-29 cells treated with tumor necrosis factor-alpha, a proapoptotic cytokine, in combination with epidermal growth factor or insulin, two prosurvival growth factors. Nineteen protein signals were measured over a 24-h period using kinase activity assays, quantitative immunoblotting, and antibody microarrays. Four different measurements of apoptotic response were also collected by flow cytometry for each time course. Partial least squares regression models that relate signaling data to apoptotic response data reveal which aspects of compendium construction and analysis were important for the reproducibility, internal consistency, and accuracy of the fused set of signaling measurements. We conclude that it is possible to build self-consistent compendia of cell-signaling data that can be mined computationally to yield important insights into the control of mammalian cell responses.

Diabetic pregnancy associated with increased epidermal growth factor in cord serum at term

OBJECTIVE

Epidermal growth factor is a ubiquitous mitogen that also possesses insulin-like properties. Fetal mal-growth is associated with altered epidermal growth factor levels. Maternal diabetes is frequently complicated by macrosomia, but the effect of maternal diabetes on fetal epidermal growth factor levels is not known. We studied cord serum epidermal growth factor concentrations in pregnancies complicated by diabetes and in normal pregnancies.

METHODS

Cord serum epidermal growth factor concentrations were measured at birth by a sandwich-type time-resolved immunofluorometric assay in 63 pregnancies complicated by insulin-dependent diabetes mellitus, in 25 pregnancies complicated by insulin-treated gestational diabetes, and in 56 normal pregnancies.

RESULTS

Cord serum epidermal growth factor correlated positively with the duration of pregnancy in diabetic and normal pregnancies. In a subgroup of women at similar gestational ages (38-39 weeks), cord serum epidermal growth factor concentrations were higher in pregnancies complicated by insulin-dependent diabetes mellitus (962 +/- 211 ng/L, P =.047; n = 9) and in pregnancies complicated by gestational diabetes (1133 +/- 115 ng/L, P =.001; n = 9) than in controls (564 +/- 75 ng/L; n = 22). In multiple regression analysis, only umbilical artery hemoglobin in diabetic pregnancies and vaginal delivery in normal pregnancies were associated with cord serum epidermal growth factor.

CONCLUSION

Epidermal growth factor concentrations are higher than normal in fetuses of diabetic mothers at term. Pregnancy complications, such as hypertensive disorders, fetal hypoxia and fetal malgrowth, may not explain the rise in epidermal growth factor levels. We hypothesize that the rise in epidermal growth factor levels is a metabolic response of the fetoplacental unit to diabetes-related hyperglycemia.

LEVEL OF EVIDENCE

III

Positive and negative regulation of glucose uptake by hyperosmotic stress

This review will provide insight on the current understanding of the intracellular signaling mechanisms by which hyperosmolarity mimics insulin responses such as Glut 4 translocation and glucose transport but also antagonizes insulin effects. Glucose uptake induced by insulin is largely dependent on the PI 3-kinase/PKB pathway. In both adipocyte and muscle cells, hyperosmolarity promotes glucose uptake by multiple mechanisms which do not require PI 3-kinase/PKB pathway but are dependent on the cell type. In muscle, osmotic stress induces glucose uptake by stimulation of AMP-Kinase and/or inhibition of Glut 4 endocytosis. In adipocytes, activation of Gab1-dependent signaling pathway plays an important role in osmotic stress-mediated glucose uptake. Apart of its insulin-like effects, hyperosmolarity can lead to cellular insulin resistance mediated by both prevention of PKB activation and inhibition of the Insulin Receptor Substrate-1 (IRS1) function. Serine phosphorylation and degradation of IRS1 negatively regulate its functions. Understanding how osmotic stress induces glucose transport or mediates insulin resistance may provide novel targets for strategies to enhance glucose transport or to prevent insulin resistance.

Defective signaling through Akt-2 and -3 but not Akt-1 in insulin-resistant human skeletal muscle: potential role in insulin resistance

Recent evidence has shown that activation of phosphatidyinositol-3-kinase (PI3K) and Akt, necessary for insulin stimulation of glucose transport, is impaired in insulin resistance. It is unknown, however, which Akt isoform shows impaired activation in insulin resistance. Additionally, related growth factors (epidermal or platelet-derived vascular) also stimulate PI3K, but it is unknown whether production of 3,4,5 phosphatidyinositol is sufficient to stimulate glucose transport in insulin-resistant muscle. Moreover, these studies were performed in rodents, and little data exists from humans. Hence, we investigated the stimulation of PI3K and Akt-1, -2, and -3 by insulin and epidermal growth factors (EGFs) in skeletal muscles from lean and obese insulin-resistant humans. Insulin activated all Akt isoforms in lean muscles, whereas only Akt-1 was activated in obese muscles. Insulin receptor substrate (IRS)-1 was associated with PI3K activity, which is necessary for Akt activation by insulin, and was reduced in obese muscles, and this was accompanied by decreased IRS-1 expression. In contrast, insulin- or EGF-stimulated phosphotyrosine-associated PI3K activity was not different between lean and obese muscles. These results show that a defect in the ability of insulin to activate Akt-2 and -3 may explain the impaired insulin-stimulated glucose transport in insulin resistance. Additionally, these data also show that different upstream or downstream signals may regulate the activity of the various Akt isoforms.