Insulin receptor/IRS-1/PI 3-kinase signaling system in corticosteroid-induced insulin resistance

Oleic Acid Protects Against Insulin Resistance by Regulating the Genes Related to the PI3K Signaling Pathway

BACKGROUND

The effects of different types of fatty acids on the gene expression of key players in the IRS1/PI3K signaling pathway have been poorly studied.

MATERIAL AND METHODS

We analyzed IRS1, p85α, and p110β mRNA expression and the fatty acid composition of phospholipids in visceral adipose tissue from patients with morbid obesity and from non-obese patients. Moreover, we analyzed the expression of those genes in visceral adipocytes incubated with oleic, linoleic, palmitic and dosahexaenoic acids.

RESULTS

We found a reduced IRS1 expression in patients with morbid obesity, independent of insulin resistance, and a reduced p110β expression in those with lower insulin resistance. A positive correlation was found between p85α and stearic acid, and between IRS1 and p110β with palmitic and dosahexaenoic acid. In contrast, a negative correlation was found between p85α and oleic acid, and between IRS1 and p110β with linoleic, arachidonic and adrenic acid. Incubation with palmitic acid decreased IRS1 expression. p85α was down-regulated after incubation with oleic and dosahexaenoic acid and up-regulated with palmitic acid. p110β expression was increased and decreased after incubation with oleic and palmitic acid, respectively. The ratio p85α/p110β was decreased by oleic and dosahexaenoic acid and increased by palmitic acid.

CONCLUSIONS

Our in vitro results suggest a detrimental role of palmitic acid on the expression of gene related to insulin signaling pathway, with oleic acid being the one with the higher and more beneficial effects. DHA had a slight beneficial effect. Fatty acid-induced regulation of genes related to the IRS1/PI3K pathway may be a novel mechanism by which fatty acids regulate insulin sensitivity in visceral adipocytes.

Potent therapeutic effects of shouwu jiangqi decoction on polycystic ovary syndrome with insulin resistance in rats

OBJECTIVE

To investigate the effect of Shouwu Jiangqi Decoction (SJD) on polycystic ovary syndrome (PCOS) with insulin resistance (IR) in rats and to explore the underlining molecular mechanisms.

METHODS

A total of 51 female Sprague-Dawley rats were randomly divided into 6 groups: control group (n=7), model group (n=8), SJD high-dose group (n=9), SJD medium-dose group (n=9), SJD low-dose group (n=9) and DMBG group (n=9). Radioimmunoassay was used to measure serum follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone concentrations and qRT-PCR and western blot were used to examine the expression levels of mRNA and protein respectively of insulin receptor substrate 1 (IRS-1) and phosphatidylinositide 3-kinases (PI3K) p85α in different groups.

RESULTS

FSH level significantly decreased in the model group compared with the normal control (P<0.01), and high-dose SJD and DMBG can significantly increase FSH level (P<0.01). LH level showed a mild increase without statistic significance in the model group compared with the control and different dosages of SJD had no significance effect on LH level, while DMBG can significantly decrease LH level (P<0.01). Testosterone level significantly increased in the model group compared with the control group (P<0.01), and high-dose SJD and DMBG can significantly decrease testosterone level (P<0.01). The expression of IRS-1 as well as PI3Kp85α were significantly decreased in the model group compared with the normal control group at both mRNA (P<0.001) and protein (P<0.01) level, and both high-dose SJD and DMBG can enhance IRS-1 and PI3K expression (P<0.05).

CONCLUSIONS

SJD has potent therapeutic effects on PCOS with IR in rats. The therapeutic effects of SJD on IR and ovulatory dysfunction are probably achieved through correcting the defective insulin signaling transduction.

Dexamethasone-induced insulin resistance: kinetic modeling using novel PET radiopharmaceutical 6-deoxy-6-[(18)F]fluoro-D-glucose

PURPOSE

An insulin-resistant rat model, induced by dexamethasone, was used to evaluate a Michaelis-Menten-based kinetic model using 6-deoxy-6-[(18)F]fluoro-D-glucose (6-[(18)F]FDG) to quantify glucose transport with PET.

PROCEDURES

Seventeen, male, Sprague-Dawley rats were studied in three groups: control (Ctrl), control + insulin (Ctrl + I), and dexamethasone + insulin (Dex + I). PET scans were acquired for 2 h under euglycemic conditions in the Ctrl group and under hyperinsulinemic-euglycemic conditions in the Ctrl + I and Dex + I groups.

RESULTS

Glucose transport, assessed according to the 6-[(18)F]FDG concentration, was highest in skeletal muscle in the Ctrl + I, intermediate in the Dex + I, and lowest in the Ctrl group, while that in the brain was similar among the groups. Modeling analysis applied to the skeletal muscle uptake curves yielded values of parameters related to glucose transport that were greatest in the Ctrl + I group and increased to a lesser degree in the Dex + I group, compared to the Ctrl group.

CONCLUSION

6-[(18)F]FDG and the Michaelis-Menten-based model can be used to measure insulin-stimulated glucose transport under basal and an insulin resistant state in vivo.

The role of hypothalamic estrogen receptors in metabolic regulation

Estrogens regulate key features of metabolism, including food intake, body weight, energy expenditure, insulin sensitivity, leptin sensitivity, and body fat distribution. There are two 'classical' estrogen receptors (ERs): estrogen receptor alpha (ERS1) and estrogen receptor beta (ERS2). Human and murine data indicate ERS1 contributes to metabolic regulation more so than ESR2. For example, there are human inactivating mutations of ERS1 which recapitulate aspects of the metabolic syndrome in both men and women. Much of our understanding of the metabolic roles of ERS1 was initially uncovered in estrogen receptor α-null mice (ERS1(-/-)); these mice display aspects of the metabolic syndrome, including increased body weight, increased visceral fat deposition and dysregulated glucose intolerance. Recent data further implicate ERS1 in specific tissues and neuronal populations as being critical for regulating food intake, energy expenditure, body fat distribution and adipose tissue function. This review will focus predominantly on the role of hypothalamic ERs and their critical role in regulating all aspects of energy homeostasis and metabolism.

Mechanisms of muscle wasting in chronic kidney disease

In patients with chronic kidney disease (CKD), loss of cellular proteins increases the risks of morbidity and mortality. Persistence of muscle protein catabolism in CKD results in striking losses of muscle proteins as whole-body protein turnover is great; even small but persistent imbalances between protein synthesis and degradation cause substantial protein loss. No reliable methods to prevent CKD-induced muscle wasting currently exist, but mechanisms that control cellular protein turnover have been identified, suggesting that therapeutic strategies will be developed to suppress or block protein loss. Catabolic pathways that cause protein wasting include activation of the ubiquitin-proteasome system (UPS), caspase-3, lysosomes and myostatin (a negative regulator of skeletal muscle growth). These pathways can be initiated by complications associated with CKD, such as metabolic acidosis, defective insulin signalling, inflammation, increased angiotensin II levels, abnormal appetite regulation and impaired microRNA responses. Inflammation stimulates cellular signalling pathways that activate myostatin, which accelerates UPS-mediated catabolism. Blocking this pathway can prevent loss of muscle proteins. Myostatin inhibition could yield new therapeutic directions for blocking muscle protein wasting in CKD or disorders associated with its complications.

Evidence of selection at insulin receptor substrate-1 gene loci

Type 2 diabetes mellitus (T2DM) is a complex disease characterized by insulin resistance and defect of insulin secretion. The worldwide prevalence of T2DM is steadily increasing. T2DM is also significantly associated with obesity, coronary artery disease (CAD), and metabolic syndrome. There is a clear difference in the prevalence of T2DM among populations, and T2DM is highly heritable. Human adaptations to environmental changes in food supply, lifestyle, and geography may have pressured the selection of genes associated with the metabolism of glucose, lipids, carbohydrates, and energy. The insulin receptor substrate-1 (IRS1) gene is considered a major T2DM gene, and common genetic variations near the IRS1 gene were found to be associated with T2DM, insulin resistance, adiposity, and CAD. Here, we aimed to find evidence of selection at the IRS1 gene loci using the HapMap population data. We investigated a 3-step test procedure-Wright's F statistics (Fst), the long-range haplotype (LRH) test, and the integrated haplotype score (iHS) test-to detect selection at the IRS1 gene loci using the HapMap population data. We observed that 1 CAD-associated SNP (rs2943634) and 1 adiposity- and insulin resistance-associated SNP (rs2943650) exhibited high Fst values. We also found selection at the IRS1 gene loci by the LRH test and the iHS test. These findings suggest evidence of selection at the IRS1 gene loci and that further studies should examine the adaptive evolution of T2DM genes.

The endocrine disrupting chemical tolylfluanid alters adipocyte metabolism via glucocorticoid receptor activation

Glucocorticoid signaling plays a critical role in regulating energy metabolism. Emerging data implicate environmental endocrine-disrupting chemicals as contributors to the obesity and diabetes epidemics. Previous studies have shown that the phenylsulfamide fungicide tolylfluanid (TF) augments glucocorticoid receptor (GR)-dependent luciferase expression in 3T3-L1 preadipocytes while modulating insulin action in primary murine and human adipocytes. Studies were performed to interrogate glucocorticoid signaling in primary adipocytes exposed to TF. TF mimicked the gene transcription profile of the murine glucocorticoid corticosterone (Cort). Cellular fractionation assays demonstrated that TF treatment promoted the activating serine phosphorylation of GR, augmenting its cytoplasmic-to-nuclear translocation as well as its enrichment at glucocorticoid response elements on the glucocorticoid-induced leucine zipper gene promoter. After acute treatment, Cort or TF promoted insulin receptor substrate-1 (IRS-1) gene and protein expression. Either treatment also enriched GR binding at an identified glucocorticoid response element in the IRS-1 gene. TF or Cort each increased insulin-stimulated lipogenesis, an effect resulting from increased lipogenic gene expression and enhanced insulin-stimulated dephosphorylation of acetyl-coenzyme A carboxylase. The augmentation of insulin-stimulated lipogenesis was mediated through a specific enhancement of Akt phosphorylation at T308. These findings support modulation of IRS-1 levels as a mechanism for glucocorticoid-mediated changes in insulin action in primary adipocytes. Albeit with less affinity than Cort, in silico analysis suggests that TF can interact with the ligand binding pocket of GR. Collectively, these studies identify TF as a structurally unique environmental glucocorticoid. Glucocorticoid signaling may thus represent a novel pathway by which environmental toxicants promote the development of metabolic diseases.

[Corticosteroids and diabetes mellitus]

During corticosteroid prescriptions, diabetes mellitus may be completely deregulated or may be revealed as such. Predisposition to diabetes mellitus could be because of latent β Langerhans cell deregulation or because enhancement of tissue sensitivity by glucocorticosteroids. However, epidemiologic data concerning predisposing factors and frequency of cortico-induced diabetes are not well known. Detection, treatment and prevention are the same as for type II diabetes. Glycemia should be monitored throughout long-term treatments.

Sustained Impairments in Brain Insulin/IGF Signaling in Adolescent Rats Subjected to Binge Alcohol Exposures during Development

Background

Chronic or binge ethanol exposures during development can cause fetal alcohol spectrum disorder (FASD) which consists of an array of neurobehavioral deficits, together with structural, molecular, biochemical, and neurotransmitter abnormalities in the brain. Previous studies showed that perinatal neurodevelopmental defects in FASD are associated with inhibition of brain insulin and insulin-like growth factor (IGF) signaling. However, it is not known whether sustained abnormalities in adolescent brain structure and function are mediated by the same phenomena.

Aims

Using an early postnatal (3^rd trimester equivalent) binge ethanol exposure model, we assessed neurobehavioral function, structure, and the integrity of insulin/IGF signaling in young adolescent cerebella.

Methods

Long Evans male rats were treated with 50 µl of saline (vehicle) or 2 mg/kg of ethanol by i.p. injection on postnatal days (P) 2, 4, 6, and 8. On P19–20, rats were subjected to rotarod testing of motor function, and on P30, they were sacrificed to harvest cerebella for histological, molecular, and biochemical studies.

Results

Binge ethanol exposures impaired motor function, caused sustained cerebellar hypocellularity, and reduced neuronal and oligodendrocyte gene expression. These effects were associated with significant deficits in insulin and IGF signaling, including impaired receptor binding, reduced Akt, and increased GSK-3β activation.

Conclusions

FASD-associated neurobehavioral, structural, and functional abnormalities in young adolescent brains may be mediated by sustained inhibition of insulin/IGF-1 signaling needed for cell survival, neuronal plasticity, and myelin maintenance.

Central effects of estradiol in the regulation of food intake, body weight, and adiposity

In recent years, obesity and its associated health disorders and costs have increased. Accumulation of adipose tissue, or fat, in the intra-abdominal adipose depot is associated with an increased risk of developing cardiovascular problems, type-2 diabetes mellitus, certain cancers, and other disorders like the metabolic syndrome. Males and females differ in terms of how and where their body fat is stored, in their hormonal secretions, and in their neural responses to signals regulating weight and body fat distribution. Men and post-menopausal women accumulate more fat in their intra-abdominal depots than pre-menopausal women, resulting in a greater risk of developing complications associated with obesity. The goal of this review is to discuss the current literature on sexual dimorphisms in body weight regulation, adipose tissue accrual and deposition.

Effects of dexamethasone on insulin receptor in aging

The aim of this study was to examine the effects of dexamethasone (Dex) on functional properties of the rat insulin receptor (IR). Male Mill Hill hooded rats, 3, 6, 12, 18 and 21 months old, were injected with Dex (4 mg/kg) and rat liver and erythrocytes were used for experiments 18 h after Dex administration. Treatment with Dex lowered the specific binding (SB) of insulin (INS) in the liver of 3- and 18-month-old rats and concentration of INS binding sites (N1, N2) and the dissociation constant of low-affinity binding sites (Kd2) in the liver of 6- and 18-month-old rats. In addition, Dex treatment lowered the liver IR protein level in all analyzed groups, except 21-month-old rats where it remained unchanged, but raised the IR mRNA level in 18-month-old rats. In erythrocytes, treatment with Dex decreased SB and Kd2 (in animals 3 and 6 months old) and N1 (in ones 3 and 18 months old). Following Dex treatment, the INS plasma level increased (in rats 3, 18 and 21 months old), while glucose (Glu) concentration increased in 3 and 12 months old, but decreased in 6- and 21-month-old rats. In summary, Dex exerts the strongest effect on the erythrocyte IR of 3- and 6-month-old rats and the hepatic IR of 18-month-old rats. IR in both tissues is almost insensitive to Dex in 12- and 21-month-old rats. The pattern of age-related changes of IR induced by Dex does not correlate with changes of plasma Glu and INS.

Insulin resistance is associated with hypercortisolemia in Polynesian patients treated with antipsychotic medication

OBJECTIVE

Type 2 diabetes is more prevalent in the indigenous Polynesian population of New Zealand (Maori) than in Europeans. The aim of this study was to determine whether insulin resistance in Maori psychiatric patients was associated with antipsychotic treatment and to investigate the mechanism of an association.

RESEARCH DESIGN AND METHODS

Thirty adult Maori psychiatric patients receiving antipsychotic medication for >6 months and 30 healthy, age-, sex-, and BMI-matched control subjects were enrolled. Early morning fasting blood samples were analyzed for plasma levels of glucose, insulin, A1C, triglycerides, total cholesterol, IGF-1, cortisol, cortisol-binding globulin (CBG), and adiponectin.

RESULTS

The patient group had significantly higher median fasting insulin plasma levels than the control group (P = 0.002), which were independent of BMI, age, and sex. In addition, the patient group had significantly higher total cortisol (P = 0.03) and lower CBG levels (P = 0.004) than the control group, resulting in significantly higher levels of free cortisol (P = 0.004). The patient group was also significantly more hypoglycemic (P = 0.026) and hypertriglyceridemic (P = 0.028) than the control group. There was no significant difference in BMI, waist circumference, A1C, total cholesterol, IGF-1, or adiponectin levels between the two groups.

CONCLUSIONS

An increase in insulin resistance is seen in Maori psychiatric patients treated with antipsychotic medication. Therefore, Polynesian ethnicity should be considered in prescribing practice and general care of this group. In addition, the hypothalamic-pituitary-adrenal axis may have an important role in the mechanism by which this insulin resistance develops.

Gonadal hormones determine sensitivity to central leptin and insulin

Males have proportionally more visceral fat and are more likely to develop complications associated with obesity than females, and the male brain is relatively more sensitive to the catabolic action of insulin and less sensitive to that of leptin than the female brain. To understand the underlying mechanism, we manipulated estrogen through ovariectomy (OVX) and estradiol administration. Rats with relatively high systemic estrogen (intact females and OVX females and males administered estrogen subcutaneously) were significantly more sensitive to leptin's anorexic action in the brain (i3vt), as well as significantly less sensitive to insulin's i3vt action, than intact males. Administering estradiol directly into the brain of our females increased i3vt leptin sensitivity while decreasing i3vt insulin sensitivity and changed the body fat distribution of our females to resemble that of intact females. These data indicate that estrogen acts within the brain to increase leptin sensitivity, decrease insulin sensitivity, and favor subcutaneous over visceral fat.

Mitogen-Activated Protein Kinase (MAPK) Phosphatase-1 and -4 Attenuate p38 MAPK during Dexamethasone-Induced Insulin Resistance in 3T3-L1 Adipocytes

Prolonged use of glucocorticoids induces pronounced insulin resistance in vivo. In vitro, treatment of 3T3-L1 adipocytes with dexamethasone for 48 h reduces the maximal level of insulin- and stress (arsenite)-induced glucose uptake by approximately 50%. Although phosphatidylinositol 3-kinase signaling was slightly attenuated, phosphorylation of its downstream effectors such as protein kinase B and protein kinase C-lambda remained intact. Nor was any effect of dexamethasone treatment observed on insulin- or arsenite-induced translocation of glucose transporter 4 (GLUT4) toward the plasma membrane. However, for a maximal response to either arsenite- or insulin-induced glucose uptake in these cells, functional p38 MAPK signaling is required. Dexamethasone treatment markedly attenuated p38 MAPK phosphorylation coincident with an up-regulation of the MAPK phosphatases MKP-1 and MKP-4. Employing lentivirus-mediated ectopic expression in fully differentiated 3T3-L1 adipocytes demonstrated a differential effect of these phosphatases: whereas MKP-1 was a more potent inhibitor of insulin-induced glucose uptake, MKP-4 more efficiently inhibited arsenite-induced glucose uptake. This coincided with the effects of these phosphatases on p38 MAPK phosphorylation, i.e. MKP-1 and MKP-4 attenuated p38 MAPK phosphorylation by insulin and arsenite, respectively. Taken together, these data provide evidence that in 3T3-L1 adipocytes dexamethasone inhibits the activation of the GLUT4 in the plasma membrane by a p38 MAPK-dependent process, rather than in a defect in GLUT4 translocation per se.

Transcriptional regulation through glutamate receptors: Involvement of tyrosine kinases

Glutamate receptors play a key role in neuronal plasticity, learning and memory, and in several neuropathologies. Short-term and long-term changes in synaptic efficacy are triggered by glutamate. Although an enhanced glutamate-dependent tyrosine phosphorylation has been described in several systems, its role in membrane-to-nuclei signaling is unclear. Taking advantage of the fact that the gene encoding the chick kainate-binding protein undergoes a glutamate-dependent transcriptional regulation via an activator protein-1 (AP-1) site, we evaluated the involvement of tyrosine kinases in this process. We describe here the participation of receptor and non-receptor tyrosine kinases in the signaling cascade triggered by glutamate. Our results suggest that in Bergmann glia cells, glutamate receptors transactivate receptor tyrosine kinases, favoring the idea of a complex network of signals activated by this excitatory neurotransmitter that results in regulation of gene expression.

Disturbances in leptin metabolism are related to energy imbalance during acute exacerbations of chronic obstructive pulmonary disease

Previously we reported an impaired energy balance in patients with chronic obstructive pulmonary disease (COPD) during an acute disease exacerbation, but limited data are available on the underlying mechanisms. Experimental and clinical research supports the hypothesis of involvement of the hormone leptin in body weight and energy balance homeostasis. The aim of this study was to investigate the course of the energy balance in relation to leptin and the soluble tumor necrosis factor (TNF) receptors (sTNF-R) 55 and 75, plasma glucose, and serum insulin in patients with severe COPD during the first 7 d of hospitalization for an acute exacerbation (n = 17, 11 men, age mean [SD] 66 [10] yr, FEV(1) 36 [12] %pred). For reference values of the laboratory parameters, blood was collected from 23 (16 men) healthy, elderly subjects. On admission, the dietary intake/resting energy expenditure (REE) ratio was severely depressed (1.28 [0.57]), but gradually restored until Day 7 (1.65 [0. 45], p = 0.005 versus Day 1). Glucose and insulin concentrations were elevated on admission, but on Day 7 only plasma glucose was decreased. The sTNF-Rs were not different from healthy subjects and did not change. Plasma leptin, adjusted for fat mass expressed as percentage of body weight (%FM), was elevated on Day 1 compared with healthy subjects (1.82 [3.85] versus 0.32 [0.72] ng%/ml, p = 0.008), but decreased significantly until Day 7 (1.46 [3.77] ng%/ml, p = 0. 015 versus Day 1). On Day 7, sTNF-R55 was, independently of %FM, correlated with the natural logarithm (LN) of leptin (r = 0.65, p = 0.041) and with plasma glucose (r = 0.81, p = 0.015). In addition, the dietary intake/REE ratio was not only inversely related with LN leptin (-0.74, p = 0.037), but also with sTNF-R55 (r = -0.93, p = 0. 001) on day seven. In conclusion, temporary disturbances in the energy balance were seen during an acute exacerbation of COPD, related to increased leptin concentrations as well as to the systemic inflammatory response. Evidence was found that the elevated leptin concentrations were in turn under control of the systemic inflammatory response, and, presumably, the high-dose systemic glucocorticosteroid treatment.