Phosphoinositide-specific inositol polyphosphate 5-phosphatase IV inhibits inositide trisphosphate accumulation in hypothalamus and regulates food intake and body weight

The enzyme phosphatidylinositol 3-kinase (PI3-kinase) exerts an important role in the transduction of the anorexigenic and thermogenic signals delivered by insulin and leptin to first-order neurons of the arcuate nucleus in the hypothalamus. The termination of the intracellular signals generated by the activation of PI3-kinase depends on the coordinated activity of specific inositol phosphatases. Here we show that phosphoinositide-specific inositol polyphosphate 5-phosphatase IV (5ptase IV) is highly expressed in neurons of the arcuate and lateral nuclei of the hypothalamus. Upon intracerebroventricular (ICV) treatment with insulin, 5ptase IV undergoes a time-dependent tyrosine phosphorylation, which follows the same patterns of canonical insulin signaling through the insulin receptor, insulin receptor substrate-2, and PI3-kinase. To evaluate the participation of 5ptase IV in insulin action in hypothalamus, we used a phosphorthioate-modified antisense oligonucleotide specific for this enzyme. The treatment of rats with this oligonucleotide for 4 d reduced the hypothalamic expression of 5ptase IV by approximately 80%. This was accompanied by an approximately 70% reduction of insulin-induced tyrosine phosphorylation of 5ptase IV and an increase in basal accumulation of phosphorylated inositols in the hypothalamus. Finally, inhibition of hypothalamic 5ptase IV expression by the antisense approach resulted in reduced daily food intake and body weight loss. Thus, 5ptase IV is a powerful regulator of signaling through PI3-kinase in hypothalamus and may become an interesting target for therapeutics of obesity and related disorders.

The Cbl family proteins: ring leaders in regulation of cell signaling

The proto-oncogenic protein c-Cbl was discovered as the cellular form of v-Cbl, a retroviral transforming protein. This was followed over the years by important discoveries, which identified c-Cbl and other Cbl-family proteins as key players in several signaling pathways. c-Cbl has donned the role of a multivalent adaptor protein, capable of interacting with a plethora of proteins, and has been shown to positively influence certain biological processes. The identity of c-Cbl as an E3 ubiquitin ligase unveiled the existence of an important negative regulatory pathway involved in maintaining homeostasis in protein tyrosine kinase (PTK) signaling. Recent years have also seen the emergence of novel regulators of Cbl, which have provided further insights into the complexity of Cbl-influenced pathways. This review will endeavor to provide a summary of current studies focused on the effects of Cbl proteins on various biological processes and the mechanism of these effects. The major sections of the review are as follows: Structure and genomic organization of Cbl proteins; Phosphorylation of Cbl; Interactions of Cbl; Localization of Cbl; Mechanism of effects of Cbl: (a) Ubiquitylation-dependent events: This section elucidates the mechanism of Cbl-mediated downregulation of EGFR and details the PTK and non-PTKs targeted by Cbl. In addition, it addresses the functional requirements for E3 Ubiquitin ligase activity of Cbl and negative regulation of Cbl-mediated downregulation of PTKs, (b) Adaptor functions: This section discusses the mechanisms of adaptor functions of Cbl in mitogen-activated protein kinase (MAPK) activation, insulin signaling, regulation of Ras-related protein 1 (Rap1), PI-3' kinase signaling, and regulation of Rho-family GTPases and cytoskeleton; Biological functions: This section gives an account of the diverse biological functions of Cbl and includes the role of Cbl in transformation, T-cell signaling and thymus development, B-cell signaling, mast-cell degranulation, macrophage functions, bone development, neurite growth, platelet activation, muscle degeneration, and bacterial invasion; Conclusions and perspectives.

Circulating ghrelin concentrations are lowered by intracerebroventricular insulin

AIMS/HYPOTHESIS

Ghrelin is a peptide that is mainly produced by the stomach and stimulates food intake, adiposity and weight gain. Previous studies have documented that plasma levels of ghrelin are reduced by insulin, but the mechanisms that mediate this effect are unclear.

METHODS

To determine whether phosphatidylinositol 3-kinase (PI(3)K) and/or mitogen-activated protein kinase (MAPK) are involved in this insulin action, we tested the intracerebroventricular (i.c.v.) effect of specific inhibitors of PI(3)K (LY294002 and wortmannin) and MAPK (PD98059 and UO126) on the insulin-mediated reduction of ghrelin levels in rats.

RESULTS

Intracerebroventricular treatment with insulin reduced ghrelin levels. Inhibition of PI(3)K specifically blocked the insulin-induced reduction in ghrelin concentration, whereas inhibition of MAPK had no effect on insulin-mediated actions. Moreover, pretreatment with i.c.v. PI(3)K inhibitors blocked the reduction of ghrelin levels after OGTT-induced hyperglycaemia and hyperinsulinaemia.

CONCLUSIONS/INTERPRETATION

These data demonstrate that changes in insulin action in the central nervous system regulate circulating ghrelin levels and that PI(3)K is a specific mediator of this action.

Effects of swimming training on bone mass and the GH/IGF-1 axis in diabetic rats

The aim of this study was to examine the influence of moderate swimming training on the GH/IGF-1 growth axis and tibial mass in diabetic rats. Male Wistar rats were allocated to one of four groups: sedentary control (SC), trained control (TC), sedentary diabetic (SD) and trained diabetic (TD). Diabetes was induced with alloxan (35 mg/kg b.w.). The training program consisted of a 1h swimming session/day with a load corresponding to 5% of the b.w., five days/week for six weeks. At the end of the training period, the rats were sacrificed and blood was collected for quantification of the serum glucose, insulin, GH, and IGF-1 concentrations. Samples of skeletal muscle were used to quantify the IGF-1 peptide content. The tibias were collected to determine their total area, length and bone mineral content. The results were analyzed by ANOVA with P<0.05 indicating significance. Diabetes decreased the serum levels of GH and IGF-1, as well as the tibial length, total area and bone mineral content in the SD group (P<0.05). Physical training increased the serum IGF-1 level in the TC and TD groups when compared to the sedentary groups (SC and SD), and the tibial length, total area and bone mineral content were higher in the TD group than in the SD group (P<0.05). Exercise did not alter the level of IGF-1 in gastrocnemius muscle in nondiabetic rats, but the muscle IGF-1 content was higher in the TD group than in the SD group. These results indicate that swimming training stimulates bone mass and the GH/IGF-1 axis in diabetic rats.

Pancreatic islets from hypothalamic obese rats maintain K+ATP channel-dependent but not -independent pathways on glucose-induced insulin release process

One of the main features of obesity is hyperinsulinemia, which is related to insulin oversecretion. Glucose is by far the major physiological stimulator of insulin secretion. Glucose promotes an increase in the ATP/ADP ratio, which inactivates ATP-sensitive K+ channels (K+ATP) and induces beta cell depolarization with consequent calcium influx. Increased intracellular calcium concentration triggers insulin exocytosis. K+ATP channel function is important for K+ATP channel-dependent pathways involved in glucose-stimulated insulin secretion (GSIS). However, K+ATP channel-independent pathway has been identified and it has been found that this pathway sustains GSIS. Both pathways are critical to better GSIS control. GSIS was studied in pancreatic islets from hyperinsulinemic adult obese rats obtained by monosodium L-glutamate (MSG) neonatal treatment. Islets from MSG-obese rats were more glucose responsive than control ones. Diazoxide, a drug which maintains the K+ATP channels open without interfering with cell metabolism, blocked GSIS in islets from both groups. High extracellular potassium concentration plus diazoxide was used to study an alternative to the K+ATP channel pathway; in these conditions islets from MSG-obese rats did not respond, while islets from control animals showed enhanced GSIS. Results indicate that MSG-obese rats oversecreted insulin, even though the K+ATP channel-independent pathway is impaired in their beta cells.

Central insulin action in energy and glucose homeostasis

Insulin has pleiotropic biological effects in virtually all tissues. However, the relevance of insulin signaling in peripheral tissues has been studied far more extensively than its role in the brain. An evolving body of evidence indicates that in the brain, insulin is involved in multiple regulatory mechanisms including neuronal survival, learning, and memory, as well as in regulation of energy homeostasis and reproductive endocrinology. Here we review insulin's role as a central homeostatic signal with regard to energy and glucose homeostasis and discuss the mechanisms by which insulin communicates information about the body's energy status to the brain. Particular emphasis is placed on the controversial current debate about the similarities and differences between hypothalamic insulin and leptin signaling at the molecular level.

Selective modulation of the CAP/Cbl pathway in the adipose tissue of high fat diet treated rats

A high-fat diet (HFD) is associated with reduced glucose uptake in muscle, but not in adipose tissue. In the present study, we investigated whether a HFD can modulate glucose uptake in adipose tissue by increasing signal transduction through the CAP/Cbl pathway, independently of the PI3-K/Akt pathway. Our results suggest that, in HFD, the differential regulation of insulin-induced glucose uptake between skeletal muscle and adipose tissue may, in part, be a consequence of the CAP/Cbl/C3G pathway, since the expression of CAP and Cbl, and also the activation of this pathway were increased in adipose tissue but not in muscle.

Targeted disruption of iNOS prevents LPS-induced S-nitrosation of IRbeta/IRS-1 and Akt and insulin resistance in muscle of mice

We have previously demonstrated that the insulin resistance associated with inducible nitric oxide synthase (iNOS) induction in two different models of obesity, diet-induced obesity and the ob/ob mice, is mediated by S-nitrosation of proteins involved in insulin signal transduction: insulin receptor beta-subunit (IRbeta), insulin receptor substrate 1(IRS-1), and Akt. S-nitrosation of IRbeta and Akt impairs their kinase activities, and S-nitrosation of IRS-1 reduces its tissue expression. In this study, we observed that LPS-induced insulin resistance in the muscle of wild-type mice, as demonstrated by reduced insulin-induced tyrosine phosphorylation of IRbeta and IRS-1, reduced IRS-1 expression and reduced insulin-induced serine phosphorylation of Akt. This resistance occurred in parallel with enhanced iNOS expression, which was accompanied by S-nitrosation of IRbeta/IRS-1 and Akt. In the muscle of iNOS(-/-) mice, we did not observe enhanced iNOS expression or any S-nitrosation of IRbeta/IRS-1 and Akt after LPS treatment. Moreover, insulin resistance was not present. The preservation of insulin-induced tyrosine phosphorylation of IRbeta and IRS-1, of IRS-1 protein expression, and of insulin-induced serine phosphorylation of Akt observed in LPS-treated iNOS(-/-) mice strongly suggests that the insulin resistance induced by LPS is iNOS mediated, probably through S-nitrosation of proteins of early steps of insulin signaling.

The redox regulation of PI 3-kinase-dependent signaling

Signal transduction via PI 3-kinases plays an important role in regulating the cellular processes of cell growth, survival, proliferation, and motility. The stimulated generation of reactive oxygen species is a necessary component of the signal transduction mechanisms by which many growth factors and cytokines activate this signaling pathway and elicit their cellular responses. Evidence now supports the oxidative inactivation of both tyrosine phosphatases acting upstream of PI 3-kinase, and of the lipid phosphatase PTEN as components of the normal stimulated regulation of PI 3-kinase signaling. However, the effects of chronic oxidative stress appear rather different, particularly a proposed role for nitrosylation of Akt and other targets leading to inhibition of PI 3-kinase signaling during diabetic insulin resistance in muscle. Recently, evidence has also begun to emerge, indicating that physiological redox signaling may display the same tight spatial and temporal specificity as seen with many other signal transduction systems in terms of targeting individual proteins for modification, and of enzymatic reversal mechanisms. This review will focus upon the details of these and other roles for reactive oxygen and nitrogen species in the regulation of PI 3-kinase signaling, both during acute stimulation and chronic oxidative stress, and the evidence for their significance.

Comparison of clinical, ultrasonographic, and biochemical differences at the beginning of puberty in healthy girls born either small for gestational age or appropriate for gestational age: preliminary results

CONTEXT

There are limited and controversial data concerning puberty characteristics in girls born small for gestational age (SGA).

OBJECTIVE

The objective of the study was to document clinical, ultrasonographic, and biochemical characteristics at the beginning of puberty in matched healthy girls born either SGA or appropriate for gestational age (AGA) recruited from the community.

PATIENTS

Inclusion criteria were breast Tanner stage II and a body mass index between the 10th and 95th percentiles.

INTERVENTIONS

Recruited subjects underwent a complete physical exam, bone age, and ultrasound measurements of the internal genitalia. Hormonal assessment included fasting early morning dehydroepiandrosterone sulfate, androstenedione, SHBG, inhibin-B, FSH, LH, estradiol (E2), 17-hydroxyprogesterone (17OH Prog), and testosterone. Thereafter, a GnRH agonist test (leuprolide 500 microg, sc) was performed with FSH and LH at time 3 and 24 h for E2, 17OH Prog, and testosterone.

RESULTS

Sixty-five girls (35 AGA, 30 SGA) with a mean age of 9.9 +/- 1.03 (7.8-12.5) yr, similar bone age/chronological age (1.02 +/- 0.8 in AGA and 1 +/- 0.76 in SGA), median height of 1.35 +/- 0.06 cm, and similar waist to hip ratio were included. No differences in the presence of pubic hair, axillary hair, apocrine odor, or ultrasound measurements were found. SGA girls had increased baseline E2 as well as stimulated E2 and 17OH Prog.

CONCLUSIONS

In a preliminary sample of lean, healthy girls recruited from the community born either SGA or AGA, we observed slight hormonal differences at the beginning of puberty. Longitudinal follow-up of this cohort will allow us to understand whether these differences are maintained and have a clinical impact in their pubertal development.

Exercise improves insulin and leptin sensitivity in hypothalamus of Wistar rats

Prolonged exercise of medium to high intensity is known to promote a substantial effect on the energy balance of rats. In male rats, moderately to severely intense programs lead to a reduction in food intake. However, the exact causes for the appetite-suppressive effects of exercise are not known. Here, we show that intracerebroventricular insulin or leptin infusion reduced food intake in exercised rats to a greater extent than that observed in control animals. Exercise was associated with a markedly increased phosphorylation/activity of several proteins involved in leptin and insulin signal transduction in the hypothalamus. The regulatory role of interleukin (IL)-6 in mediating the increase in leptin and insulin sensitivity in hypothalamus was also investigated. Treatment with insulin or leptin markedly reduced food intake in exercised rats that were pretreated with vehicle, although no increase in sensitivity to leptin- and insulin-induced anorexia after pretreatment with anti-IL-6 antibody was detected. The current study provides direct measurements of leptin and insulin signaling in the hypothalamus and documents increased sensitivity to these hormones in the hypothalamus of exercised rats in an IL-6-dependent manner. These findings provide support for the hypothesis that the appetite-suppressive actions of exercise may be mediated by the hypothalamus.

Photoperiodic regulation of insulin receptor mRNA and intracellular insulin signaling in the arcuate nucleus of the Siberian hamster,Phodopus sungorus

During the last 5 years it has been well established that photoperiod-induced changes in body weight in the seasonal hamster, Phodopus sungorus, are accompanied by a marked seasonal cycle in leptin sensitivity. In the present study, we investigated the possible involvement of insulin signaling in seasonal body weight regulation. We analyzed the expression pattern and relative intensity of insulin receptor (IR), phosphatidylinositol 3-kinase (PI3-kinase), and protein tyrosine phosphatase 1B (PTP1B) mRNAs by in situ hybridization in the brains of juvenile female hamsters acclimated to either long- (LD) or short-day length (SD) for 8 wk, with or without superimposed food deprivation for 48 h. Furthermore, the hypothalamic concentration and distribution of phospho-AKT, a marker of PI3-kinase activity was determined by immunoblotting and immunohistochemistry. Eight weeks of acclimation to SD led to a substantial downregulation of IR, PTP1B gene expression, and phospho-AKT concentration in this brain region, whereas PI3-kinase mRNA was unchanged. Food deprivation induced a decrease in PTP1B and a trend toward lowered IR gene expression in LD but not in SD. Additionally, a striking increase in PTP1B gene expression in the thalamus was observed after food deprivation in both photoperiods. The direction of change in neuronal insulin signaling contrasts to the central catabolic nature of this pathway described in other species. SD-induced reduction in insulin signaling may be due to decline in body fat stores mediated by enhanced central leptin sensitivity. Increased anorexigenic tone of leptin may overwrite central insulin signaling to prevent catabolic overdrive.

Selective PPAR modulators, dual and pan PPAR agonists: multimodal drugs for the treatment of Type 2 diabetes and atherosclerosis

More than 70% of patients with Type 2 diabetes mellitus (T2DM) die because of cardiovascular diseases. Current therapeutic strategies are based on separate treatment of insulin resistance and dyslipidaemia. Development of drugs with multimodal activities should improve management of the global cardiovascular risk of T2DM patients and result in better patient compliance. New therapeutic strategies are aimed at targeting the entire spectrum of dysfunctioning organs, cells and regulatory pathways implicated in the pathogenesis of T2DM, dyslipidaemia and atherosclerosis. PPAR family members play major roles in the regulation of lipid metabolism, glucose homeostasis and inflammatory processes, making these transcription factors ideal targets for therapeutic strategies against these diseases. This review discusses why PPARs and development of novel selective PPAR modulators, dual and pan PPAR agonists constitute promising approaches for the treatment of diabetes, dyslipidaemia and atherosclerosis.

The metabolic syndrome

The metabolic syndrome (MS) is a cluster of metabolic abnormalities leading to increased risk for cardiovascular diseases and diabetes type 2. Its prevalence is increasing with aging. There exists actually an epidemic of MS. Visceral obesity and the resulting insulin resistance (IR) are the major determinant in the development of the MS. Abdominal obesity results in a low grade inflammation via the adipose tissue and macrophages secreted adipokines. This inflammation, via the generated pro-inflammatory molecules, interferes with the normal insulin signalling and thus contributes to the etiopathogenesis of the MS. Large clinical studies showed that CRP is increased in obese subjects and concomitantly to the number of existing component of the MS. Treatment of the MS is aimed to improve the IR by lifestyle changes including exercise and diet alone or in combination with medication targeting the individual components but having also anti-inflammatory actions. More research is needed to bring new therapies to be able to decrease the incidence and prevalence of the MS among the population and thus increasing their quality of life.

Irbesartan restores the in-vivo insulin signaling pathway leading to Akt activation in obese Zucker rats

BACKGROUND

Angiotensin II (AII) has been shown to contribute to the pathogenesis of hypertension and insulin resistance. In addition, the administration of selective AII type 1 receptor blockers has been shown to improve insulin sensitivity. However, only a few studies have addressed the molecular mechanisms involved in this association. Furthermore, in a previous study we illustrated that obese Zucker rats (OZR) present increased serine 994 (Ser994) phosphorylation of hepatic insulin receptor, and this event seems to be implicated in the regulation of the intrinsic IRK in this model of insulin resistance.

OBJECTIVE AND DESIGN

We examined the effects of chronic treatment with irbesartan (50 mg/kg a day for 6 months) on the hepatic insulin signaling system of OZR.

METHODS

The extent of phosphorylation of several components of the insulin signaling system was assessed by immunoprecipitation, followed by immunoblotting with phosphospecific antibodies. In addition, liver AII levels and fat deposits were determined by immunohistochemistry and Oil red O, respectively.

RESULTS

OZR displayed a marked attenuation in the in-vivo phosphorylation of several components of the insulin signaling pathways in the liver, together with significantly higher hepatic AII levels and hepatic steatosis when compared with lean Zucker rats. We found that in the livers of OZR long-term administration of irbesartan is associated with: (i) increased insulin-stimulated insulin receptor tyrosine phosphorylation; (ii) decreased insulin receptor Ser994 phosphorylation; (iii) augmented insulin receptor substrate (IRS) 1 and 2 abundance and tyrosine phosphorylation; (iv) augmented association between IRS and the p85 regulatory subunit of phosphatidylinositol 3-kinase; (v) increased insulin-induced Akt phosphorylation; and (vi) decreased hepatic steatosis.

CONCLUSION

The present study provides substantial information that demonstrates that long-term selective AII blockade by irbesartan improves insulin signaling and is associated with decreased insulin receptor Ser994 phosphorylation in the liver of a representative animal model of the human metabolic syndrome.

Activated FOXO-mediated insulin resistance is blocked by reduction of TOR activity

Reducing insulin/IGF signaling allows for organismal survival during periods of inhospitable conditions by regulating the diapause state, whereby the organism stockpiles lipids, reduces fertility, increases stress resistance, and has an increased lifespan. The Target of Rapamycin (TOR) responds to changes in growth factors, amino acids, oxygen tension, and energy status; however, it is unclear how TOR contributes to physiological homeostasis and disease conditions. Here, we show that reducing the function of Drosophila TOR results in decreased lipid stores and glucose levels. Importantly, this reduction of dTOR activity blocks the insulin resistance and metabolic syndrome phenotypes associated with increased activity of the insulin responsive transcription factor, dFOXO. Reduction in dTOR function also protects against age-dependent decline in heart function and increases longevity. Thus, the regulation of dTOR activity may be an ancient "systems biological" means of regulating metabolism and senescence, that has important evolutionary, physiological, and clinical implications.

Molecular mechanisms of insulin resistance: serine phosphorylation of insulin receptor substrate-1 and increased expression of p85alpha: the two sides of a coin

Initial attempts to unravel the molecular mechanism of insulin resistance have strongly suggested that a defect responsible for insulin resistance in the majority of patients lies at the postreceptor level of insulin signaling. Subsequent studies in insulin-resistant animal models and humans have consistently demonstrated a reduced strength of insulin signaling via the insulin receptor substrate (IRS)-1/phosphatidylinositol (PI) 3-kinase pathway, resulting in diminished glucose uptake and utilization in insulin target tissues. However, the nature of the triggering event(s) remains largely enigmatic. Two separate, but likely, complementary mechanisms have recently emerged as a potential explanation. First, it became apparent that serine phosphorylation of IRS proteins can reduce their ability to attract PI 3-kinase, thereby minimizing its activation. A number of serine kinases that phosphorylate serine residues of IRS-1 and weaken insulin signal transduction have been identified. Additionally, mitochondrial dysfunction has been suggested to trigger activation of several serine kinases, leading to a serine phosphorylation of IRS-1. Second, a distinct mechanism involving increased expression of p85alpha has also been found to play an important role in the pathogenesis of insulin resistance. Conceivably, a combination of both increased expression of p85alpha and increased serine phosphorylation of IRS-1 is needed to induce clinically apparent insulin resistance.

The JAK/STAT pathway is essential for opioid-induced cardioprotection: JAK2 as a mediator of STAT3, Akt, and GSK-3β

We examined the role for the JAK/STAT signaling pathway in acute opioid-induced cardioprotection (OIC) and whether opioid-induced glycogen synthase kinase-3β (GSK-3β) inhibition is mediated by the JAK/STAT pathway. Rats underwent 30 min of ischemia and either 5 min or 2 h of reperfusion, followed by tissue isolation for molecular analysis or infarct size assessment, respectively. Rats were treated with vehicle, morphine (300 μg/kg), the δ-opioid agonist fentanyl isothiocynate (FIT, 10 μg/kg), or the GSK inhibitor SB-216763 (SB21, 600 μg/kg) 10 min before ischemia. Five minutes before opioid or SB21 treatment, some rats received the putative JAK2 inhibitor AG-490 (3 mg/kg) or the putative JAK3 inhibitor ZM-449829 (3 mg/kg). H9C2 cardiomyoblast cells were also used to investigate FIT-induced signaling (1 μM) in vitro via molecular analysis. Morphine induced the phosphorylation of JAK2, yet not JAK1, in the area at risk. Morphine, FIT, and SB21 also reduced infarct size compared with vehicle (water) when administered before ischemia [43.0 ± 2.8, 39.1 ± 3.1, and 42.1 ± 2.5 (* P < 0.001, respectively) vs. 58.1 ± 1.3%, respectively]. AG-490 abrogated OIC, whereas ZM-449829 had no effect on OIC. Cardioprotection was afforded by SB21 even in the presence of AG-490. Morphine phosphorylated STAT3, Akt, and GSK-3β, and phosphorylation was abrogated by AG-490. FIT stimulation of H9C2 cells also caused a time-dependent phosphorylation of STAT3, Akt, and GSK-3β, and this effect was abrogated by AG-490. STAT3 phosphorylation was also dependent on phosphatidylinositol 3-kinase (PI3K) activation in both tissue and H9C2 cells. These data suggest that OIC occurs via the JAK2 regulation of PI3K pathway-dependent STAT3, Akt, and GSK-3β, with GSK-3β contributing a central role in acute OIC.

Pancreatic signals controlling food intake; insulin, glucagon and amylin

The control of food intake and body weight by the brain relies upon the detection and integration of signals reflecting energy stores and fluxes, and their interaction with many different inputs related to food palatability and gastrointestinal handling as well as social, emotional, circadian, habitual and other situational factors. This review focuses upon the role of hormones secreted by the endocrine pancreas: hormones, which individually and collectively influence food intake, with an emphasis upon insulin, glucagon and amylin. Insulin and amylin are co-secreted by B-cells and provide a signal that reflects both circulating energy in the form of glucose and stored energy in the form of visceral adipose tissue. Insulin acts directly at the liver to suppress the synthesis and secretion of glucose, and some plasma insulin is transported into the brain and especially the mediobasal hypothalamus where it elicits a net catabolic response, particularly reduced food intake and loss of body weight. Amylin reduces meal size by stimulating neurons in the hindbrain, and there is evidence that amylin additionally functions as an adiposity signal controlling body weight as well as meal size. Glucagon is secreted from A-cells and increases glucose secretion from the liver. Glucagon acts in the liver to reduce meal size, the signal being relayed to the brain via the vagus nerves. To summarize, hormones of the endocrine pancreas are collectively at the crossroads of many aspects of energy homeostasis. Glucagon and amylin act in the short term to reduce meal size, and insulin sensitizes the brain to short-term meal-generated satiety signals; and insulin and perhaps amylin as well act over longer intervals to modulate the amount of fat maintained and defended by the brain. Hormones of the endocrine pancreas interact with receptors at many points along the gut-brain axis, from the liver to the sensory vagus nerve to the hindbrain to the hypothalamus; and their signals are conveyed both neurally and humorally. Finally, their actions include gastrointestinal and metabolic as well as behavioural effects.

Inducible-NOS but not neuronal-NOS participate in the acute effect of TNF-α on hypothalamic insulin-dependent inhibition of food intake

TNF-alpha acts on the hypothalamus modulating food intake and energy expenditure through mechanisms incompletely elucidated. Here, we explore the hypothesis that, to modulate insulin-induced anorexigenic signaling in hypothalamus, TNF-alpha requires the synthesis of NO. TNF-alpha activates signal transduction through JNK and p38 in hypothalamus, peaking at 10(-8) M. This is accompanied by the induction of expression of the inducible and neuronal forms of NOS, in both cases peaking at 10(-12) M. In addition, TNF-alpha stimulates NOS catalytic activity. Pre-treatment with TNF-alpha at a low dose (10(-12) M) inhibits insulin-dependent anorexigenic signaling, and this effect is abolished in iNOS but not in nNOS knockout mice.

Inhibition of cardiac PGC-1alpha expression abolishes ERbeta agonist-mediated cardioprotection following trauma-hemorrhage

PGC-1alpha (peroxisome proliferator-activated receptor [PPARgamma] coactivator-1alpha) activates PPARalpha and mitochondrial transcription factor A (Tfam), which regulate proteins, fatty acid and ATP metabolism (i.e., FAT/CD36, MCAD, and COX I). Recently we found that the salutary effects of estradiol (E2) on cardiac function following trauma-hemorrhage (T-H) are mediated via estrogen receptor (ER)beta. In this study we tested the hypothesis that ERbeta-mediated cardioprotection is induced via up-regulation of PGC-1alpha through PPARalpha or Tfam-dependent pathway. Male rats underwent T-H and received ERalpha agonist propylpyrazole-triol (PPT), ERbeta agonist diarylpropionitrile (DPN), E2, or vehicle. Another group was treated with antisense PGC-1alpha oligonucleotides prior to administration of DPN. E2 and DPN treatments attenuated the decrease in cardiac mitochondrial ATP, abrogated the T-H-induced lipid accumulation, and normalized PGC-1alpha, PPARalpha, FAT/CD36, MCAD, Tfam, and COX I after T-H. In contrast, PPT administration did not abrogate lipid accumulation. Moreover, in PPT-treated animals mitochondrial ATP remained significantly lower than those observed in DPN- or E2-treated animals. Prior administration of antisense PGC-1alpha prevented DPN-mediated cardioprotection and increase in ATP levels and Tfam but not in PPARalpha following T-H. These findings suggest that the salutary effects of E2 on cardiac function following T-H are mediated via ERbeta up-regulation of PGC-1alpha through Tfam-dependent pathway.

Intake of trans fatty acid–rich hydrogenated fat during pregnancy and lactation inhibits the hypophagic effect of central insulin in the adult offspring

OBJECTIVE

Using rats we examined whether maternal intake of hydrogenated fat rich in trans fatty acids affects brain fatty acid profile, hypothalamic content of insulin receptor and insulin receptor substrate-1 proteins, and the hypophagic effect of centrally administered insulin in 3-mo-old male progeny.

METHODS

Throughout pregnancy and lactation, Wistar rats ate isocaloric/normolipidic diets with soybean oil (control) or soybean oil-derived hydrogenated fat (trans diet) as a fat source. Upon weaning, the trans offspring continued on the trans diet (trans group) or were switched to a control diet (trans-control group).

RESULTS

Compared with control rats, trans rats had lower brain levels of eicosapentaenoic acid. Compared with trans rats, trans-control rats had increased levels of total polyunsaturated fatty acids and arachidonic acid and decreased levels of trans fatty acids, saturated fatty acids, and monounsaturated fatty acids. Insulin receptor and insulin receptor substrate-1 levels were significantly lower (44% and 38%, respectively) in trans than in control rats. In trans-control rats, insulin receptor was 26% lower (P < 0.05), whereas insulin receptor substrate-1 was 50% lower, than in control rats. Insulin decreased 24-h feeding in control (27%) and trans (38%) rats but failed to do so in trans-control rats. The latter group had increased serum glucose levels.

CONCLUSIONS

The data suggest that the early (intrauterine/perinatal) exposure to hydrogenated fat rich in trans fatty acids programmed the hypothalamic feeding control mechanisms. As young adults, only trans-control animals showed loss of insulin-induced hypophagia, indicating that the mismatch between early and later nutritional environments was relevant. However, the trans group also showed signs of altered appetite signaling mechanisms, suggesting that the early adaptations may have deleterious consequences later in life.

Activation of the lutropin/choriogonadotropin receptor in MA-10 cells stimulates tyrosine kinase cascades that activate ras and the extracellular signal regulated kinases (ERK1/2)

We show that activation of the recombinant lutropin/choriogonadotropin receptor (LHR) in mouse Leydig tumor cells (MA-10 cells) leads to the tyrosine phosphorylation of Shc (Src homology and collagen homology) and the formation of complexes containing Shc and Sos (Son of sevenless), a guanine nucleotide exchange factor for Ras. Because a dominant-negative mutant of Shc inhibits the LHR-mediated activation of Ras and the phosphorylation of ERK1/2, we conclude that the LHR-mediated phosphorylation of ERK1/2 is mediated, at least partially, by the classical pathway used by growth factor receptors. We also show that the endogenous epidermal growth factor receptor (EGFR) present in MA-10 cells is phosphorylated upon activation of the LHR. The LHR-mediated phosphorylation of the EGFR and Shc, the activation of Ras, and the phosphorylation of ERK1/2 are inhibited by expression of a dominant-negative mutant of Fyn, a member of the Src family kinases (SFKs) expressed in MA-10 cells and by PP2, a pharmacological inhibitor of the SFKs. These are also inhibited, but to a lesser extent, by AG1478, an inhibitor of the EGFR kinase. We conclude that the SFKs are responsible for the LHR-mediated phosphorylation of the EGFR and Shc, the formation of complexes containing Shc and Sos, the activation of Ras, and the phosphorylation of ERK1/2.

Tumor necrosis factor-alpha activates signal transduction in hypothalamus and modulates the expression of pro-inflammatory proteins and orexigenic/anorexigenic neurotransmitters

Tumor necrosis factor-alpha (TNF-alpha) is known to participate in the wastage syndrome that accompanies cancer and severe infectious diseases. More recently, a role for TNF-alpha in the pathogenesis of type 2 diabetes mellitus and obesity has been shown. Much of the regulatory action exerted by TNF-alpha upon the control of energy stores depends on its action on the hypothalamus. In this study, we show that TNF-alpha activates canonical pro-inflammatory signal transduction pathways in the hypothalamus of rats. These signaling events lead to the transcriptional activation of an early responsive gene and to the induction of expression of cytokines and a cytokine responsive protein such as interleukin-1beta, interleukin-6, interleukin-10 and suppressor of cytokine signalling-3, respectively. In addition, TNF-alpha induces the expression of neurotransmitters involved in the control of feeding and thermogenesis. Thus, TNF-alpha may act directly in the hypothalamus inducing a pro-inflammatory response and the modulation of expression of neurotransmitters involved in energy homeostasis.

Overfeeding during lactation modulates insulin and leptin signaling cascade in rats' hearts

Insulin has been described as a potential mediator of intrinsic responses to the nutritional state in the heart due to its effects on cardiac metabolism, mainly on glucose transport. It has been demonstrated that leptin can act through some components of the insulin-signaling cascade. We investigated the association between overfeeding during lactation and alterations of insulin and leptin signaling in the heart. In summary, we analyzed a feasible cross-talk between insulin and leptin through the study of some key proteins of their cascades in the heart. In order to study the effect of overfeeding on these cascades, Wistar rats were overfed through litter size reduction to only three pups. At 10 and 21 days of life, key proteins such as insulin receptor, leptin receptor, PI3-kinase, JAK2, STAT3, and GLUT4 were measured by Western blotting. Furthermore, the pups' weight and the plasma levels of insulin, leptin and glucose were determined. Overfed animals were overweight, had high insulin and leptin plasma levels, and displayed an activation of insulin and leptin cascade, leading to an increased translocation of GLUT4. We suggest that overfeeding during lactation probably alters cardiac metabolism, through the activation of a modulated cross-talk between leptin and insulin cascades.

Role of mitochondria in the immune response to cancer: a central role for Ca2+

This study demonstrates that Ca2+ stimulates mitochondrial energy metabolism during spleen lymphocyte activation in response to the ascitic Walker 256 tumor in rats. Intracellular Ca2+ concentrations, phosphorylated protein kinase C (pPKC) levels, Bcl-2 protein contents, interleukin-2 (IL-2) levels, mitochondrial uncoupling protein-2 (UCP-2) contents and reactive oxygen species (ROS) were significantly elevated in these activated lymphocytes. Mitochondria of activated lymphocytes exhibited high free Ca2+ concentrations in the matrix and enhanced oligomycin-sensitive oxygen consumption, indicating an increased rate of oxidative phosphorylation. The production of ROS was largely decreased by diphenylene iodinium in the activated lymphocytes, suggesting that NADPH oxidase is the prevalent source of these species. Accumulation of UCP-2 and the anti-apoptotic protein Bcl-2 is probably important to prevent mitochondrial dysfunction and cell death elicited by the sustained high levels of intracellular Ca2+ and ROS and may explain the observed higher resistance from activated lymphocytes against the opening of the mitochondrial membrane permeability pore (MPT). All these changes were blocked by pretreatment of the rats with verapamil, an L-type Ca2+ channel antagonist. These data demonstrate a central role of Ca2+ in the control of mitochondrial bioenergetics in spleen lymphocytes during the immune response to cancer.

Altered renal sodium handling in spontaneously hypertensive rats (SHR) after hypertonic saline intracerebroventricular injection: role of renal nerves

The mechanism by which blood pressure rises in the SHR strain remains to be elucidated. Also, there is a surprising lack of experimental data on the natriuretic mechanisms induced by intracerebroventricular (ICV) injection of hyperosmotic saline (HoS) in SHR. In normotensive animals ICV injection of HoS causes coordinated responses including natriuresis and inhibition of renal sympathetic nerve activity. In the present study, we hypothesized that presumable blunting of the sympathoinhibitory response to centrally injected HoS may contribute to a lack of suppression of efferent renal nerve outflow in SHR. To test this hypothesis, the present study evaluates the influence of renal denervation after central HoS injection at increasing concentration on urinary sodium handling in SHR compared with age-matched normotensive WKy rats. The study confirmed previous data showing pronounced natriuretic response to centrally HoS stimuli but also demonstrated that the creatinine clearance (C(Cr)) and fractional sodium excretion responses diminished as graded NaCl concentrations were increased in WKy rats but not in SHR. In SHR, increased FE(Na) obtained by central administration of 0.90 M NaCl was produced by increases in proximal (FEP(Na)) and post-proximal fractional urinary sodium rejection without changes in C(Cr), indicating a direct tubular effect. Renal denervation caused significant antinatriuresis by decreased C(Cr) and increased FEP(Na) reabsorption in WKy but not in SHR. This study suggests that natriuresis observed only after higher centrally HoS stimuli with a rightward shift of dose-response curve provides evidence of a down-regulation of target organ responsiveness of periventricular areas of genetic hypertensive rats.

Nutrient overload, insulin resistance, and ribosomal protein S6 kinase 1, S6K1

Nutrient overload leads to obesity, insulin resistance, and often type 2 diabetes. Whereas increased fat intake is commonly cited as the major factor in diet-induced dysmetabolic states, increased protein consumption also contributes, through elevated circulating amino acids. Recent studies have revealed that ribosomal protein S6 kinase 1, S6K1, an effector of mTOR, is sensitive to both insulin and nutrients, including amino acids. Although S6K1 is an effector of growth, recent reports show that amino acids also negatively affect insulin signaling through mTOR/S6K1 phosphorylation of IRS1. Moreover, rather than signaling through the class 1 PI3K pathway, amino acids appear to mediate mTOR activation through class 3 PI3K, or hVps34. Consistent with this, infusion of amino acids into humans leads to S6K1 activation, inhibition of insulin-induced class 1 PI3K activation, and insulin resistance. Thus, S6K1 may mediate deleterious effects, like insulin resistance, and potentially type 2 diabetes in the face of nutrient excess.

Angiotensin II regulates phosphoinositide 3 kinase/Akt cascade via a negative crosstalk between AT1 and AT2 receptors in skin fibroblasts of human hypertrophic scars

Angiotensin II (Ang II) stimulation has been shown to regulate proliferation of skin fibroblasts and production of extracellular matrix, which are very important process in skin wound healing and scarring; however, the signaling pathways involved in this process, especially in humans, are less explored. In the present study, we used skin fibroblasts of human hypertrophic scar, which expressed both AT1 and AT2 receptors, and observed that Ang II increased Akt phosphorylation and phosphoinositide 3 kinase (PI 3-K) activity. In addition, the Ang II-induced Akt phosphorylation was blocked by wortmannin, a PI 3-K inhibitor. This Ang II-activated PI 3-K/Akt cascade was markedly inhibited by valsartan, an AT(1) receptor-specific blocker, whereas it was enhanced by PD123319, an AT(2) receptor antagonist. On the other hand, the Ang II- or EGF-induced activation of PI 3-K/Akt was strongly attenuated by AG1478, an inhibitor of epidermal growth factor (EGF) receptor kinase. Moreover, Ang II stimulated tyrosine phosphorylation of EGF receptor and p85alpha subunit of PI 3-K accompanied by an increase in their association, which was inhibited by valsartan, and enhanced by PD123319. The Ang II-induced transactivation of EGF receptor resulted in activation of extracellular signal-regulated kinase (ERK) that was also inhibited by valsartan, and enhanced by PD123319. Taken together, our results showed that AT(1) receptor-mediated activation of PI 3-K/Akt cascades occurs at least partially via the transactivation of EGF receptor, which is under a negative control by AT(2) receptor in hypertrophic scar fibroblasts. These findings contribute to understanding the molecular mechanism of human hypertrophic scar formation.

Effect of antihypertensive agents on the development of type 2 diabetes mellitus

People with hypertension have a high prevalence of insulin resistance and are at relatively high risk of developing type 2 diabetes mellitus. It is becoming increasingly evident that antihypertensive agents have disparate metabolic effects. For example, recent clinical trials indicate that agents that interrupt the renin-angiotensin axis reduce the risk of developing diabetes compared with other classes of antihypertensive agents. Blockade of the effects of angiotensin II might improve blood flow to insulin-sensitive tissues. Furthermore, interruption of the renin-angiotensin system might provide metabolic benefit through such mechanisms as reduced oxidative stress and restored nitric oxide production, which could lead to improved insulin signaling. Alternatively, collective trials suggest that both diuretics and beta-blockers accelerate the appearance of new-onset type 2 diabetes mellitus in patients with hypertension. Therefore, the risk of new-onset diabetes-associated cardiovascular risks should be factored into future treatment recommendations for patients who require antihypertensive therapy. This will become even more important as the number of insulin-resistant patients with hypertension increases in parallel with the steady growth in the number of sedentary, obese, and aged persons in our population.

Nitric oxide agents impair insulin-mediated signal transduction in rat skeletal muscle

Background

Evidence demonstrates that exogenously administered nitric oxide (NO) can induce insulin resistance in skeletal muscle. We have investigated the modulatory effects of two NO donors, S-nitroso-N-acetyl-D, L-penicillamine (SNAP) and S-nitrosoglutathione (GSNO) on the early events in insulin signaling in rat skeletal myocytes.

Results

Skeletal muscle cells from 6–8 week old Sprague-Dawley rats were treated with SNAP or GSNO (25 ng/ml) in the presence or absence of glucose (25 mM) and insulin (100 nM). Cellular insulin receptor-β levels and tyrosine phosphorylation in IRS-1 were significantly reduced, while serine phosphorylation in IRS-1 was significantly increased in these cells, when compared to the insulin-stimulated control. Reversal to near normal levels was achieved using the NO scavenger, 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl 3-oxide (carboxy-PTIO).

Conclusion

These data suggest that NO is a potent modulator of insulin-mediated signal transduction and may play a significant role in the pathogenesis of type 2 diabetes mellitus.

[The hypothalamic control of feeding and thermogenesis: implications on the development of obesity]

The worldwide increase in the prevalence of obesity is becoming one of the most important clinical-epidemiological phenomena of the present days. Environmental factors such as changes in life-style and feeding behavior associated with poorly characterized genetic determinants are though to play the most important roles in the pathogenesis of this disease. During the last ten years, since the discovery of leptin, great advances were obtained in the characterization of the hypothalamic mechanisms involved in the control of food intake and thermogenesis. Such advances are unveiling a complex and integrated system and are opening a wide perspective for the finding of novel therapeutic targets for the treatment of this harming condition. This review will present some of the most recent findings in this field. It will be focused on the actions of leptin and insulin in the hypothalamus and will explore the hypothesis that hypothalamic resistance to the action of these hormones may play a role in the development of obesity and may act as a molecular link between obesity, type 2 diabetes mellitus and other clinical conditions on which insulin resistance plays an important pathogenetic role.

Gonadotropins activate proteolysis and increase invasion through protein kinase A and phosphatidylinositol 3-kinase pathways in human epithelial ovarian cancer cells

Despite evidence that gonadotropins may facilitate peritoneal metastasis of ovarian cancer by increasing cell adhesion, the action and molecular mechanism of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in ovarian cancer invasion is not well characterized. In the present study, we investigated the effects of FSH and LH on the invasive activity and the expression of metastasis-related proteinases in human epithelial ovarian cancer by Western blot, zymography, reverse transcription-PCR (RT-PCR), ELISA, and Boyden chamber assay. Treatment with FSH or LH (10, 100, or 1,000 ng/mL) significantly increased the invasion of ovarian cancer cell lines, including BG-1, CaOV-3, and SKOV-3 cells but not OVCAR-3 cells. In addition, treatment of SKOV-3 cells with FSH or LH (100 or 1,000 ng/mL) enhanced the expression and activation of matrix metalloproteinases (MMP-2 and MMP-9) as shown by RT-PCR, gelatin zymography, and ELISA. Pretreatment with [(2R)-2-(hydroxamido-carbonylmethyl)-4-methylpentanoyl]-l-tryptophan methylamide (10 micromol/L), a total MMP inhibitor, and 3-(4-phenoxyphenylsulfonyl)-propylthiirane (20 micromol/L), a specific gelatinase inhibitor, neutralized the proinvasive effect of gonadotropins in SKOV-3 cells. In addition, the secretion of tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) and plasminogen activator inhibitor-1 was significantly decreased by FSH and LH (100 or 1,000 ng/mL). We further showed that gonadotropins induced an increase in SKOV-3 invasiveness via the activation of protein kinase A (PKA) and phosphatidylinositol 3-kinase (PI3K) signaling pathways. Taken together, these results suggest that gonadotropins may contribute to ovarian cancer metastasis via activation of proteolysis and increase in invasion through the PKA and PI3K pathways.

Stimulation of the intestinal phosphate transporter SLC34A2 by the protein kinase mTOR

Adequate phosphate homeostasis is of critical importance for a wide variety of functions including bone mineralization and energy metabolism. Phosphate balance is a function of intestinal absorption and renal elimination, which are both under tight hormonal control. Intestinal phosphate absorption is accomplished by the Na(+), phosphate cotransporter NaPi IIb (SLC34A2). Signaling mechanisms mediating hormonal regulation of SLC34A2 are incompletely understood. The mammalian target of rapamycin (mTOR) is a kinase regulating a variety of nutrient transporters. The present experiments explored whether mTOR regulates the activity of SLC34A2. In Xenopus oocytes expressing SLC34A2 but not in water injected oocytes phosphate (1 mM) induced a current (Ip) which was significantly enhanced by coexpression of mTOR. Preincubation of the oocytes for 24 h with rapamycin (50 nM) did not significantly affect Ip in the absence of mTOR but virtually abolished the increase of Ip following coexpression of mTOR. The wild type serum and glucocorticoid inducible kinase SGK1 and the constitutively active (S422D)SGK1 similarly stimulated Ip, an effect again reversed by rapamycin. Coexpression of the inactive mutant of the serum and glucocorticoid inducible kinase (K119N)SGK1 significantly decreased Ip and abrogated the stimulating effect of mTOR on Ip. In conclusion, mTOR and SGK1 cooperate in the stimulation of the intestinal phosphate transporter SLC34A2.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.

Lipid phosphatases as drug discovery targets for type 2 diabetes

The soaring incidence of type 2 diabetes has created pressure for new pharmaceutical strategies to treat this devastating disease. With much of the focus on overcoming insulin resistance, investigation has focused on finding ways to restore activation of the phosphatidylinositol 3'-kinase pathway, which is diminished in many patients with type 2 diabetes. Here we review the evidence that lipid phosphatases, specifically PTEN and SHIP2, attenuate this important insulin signalling pathway. Both in vivo and in vitro studies indicate their role in regulating whole-body energy metabolism, and possibly weight gain as well. The promise and challenges presented by this new class of drug discovery targets will also be discussed.

Luteinizing hormone-induced RUNX1 regulates the expression of genes in granulosa cells of rat periovulatory follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Insulin activates hypoxia-inducible factor-1alpha in human and rat vascular smooth muscle cells via phosphatidylinositol-3 kinase and mitogen-activated protein kinase pathways: impairment in insulin resistance owing to defects in insulin signalling

AIMS/HYPOTHESIS

We previously demonstrated that insulin stimulates vascular endothelial growth factor (VEGF) synthesis and secretion via phosphatidylinositol-3 kinase (PI3-K) and mitogen-activated protein kinase (MAPK) pathways in vascular smooth muscle cells (VSMC) from humans and from insulin-sensitive lean Zucker fa/+ rats. We also showed that this effect is attenuated in VSMC from insulin-resistant obese Zucker fa/fa rats. As it is not known whether the effects of insulin on VEGF involve activation of hypoxia-inducible factor-1 (HIF-1), we aimed to evaluate: (1) whether insulin modulates HIF-1alpha protein synthesis and activity; (2) the insulin signalling pathways involved; and (3) the role of insulin resistance.

METHODS

Using aortic VSMC taken from humans and Zucker rats and cultured in normoxia, the following were evaluated: (1) dose-dependent (0.5, 1, 2 nmol/l) and time-dependent (2, 4, 6 h) effects exerted by insulin on HIF-1alpha content in both nucleus and cytosol, measured by Western blots; (2) insulin effects on HIF-1 DNA-binding activity on the VEGF gene, measured by electrophoretic mobility shift assay; and (3) involvement of the insulin signalling molecules in these insulin actions, by using the following inhibitors: LY294002 (PI3-K), PD98059 (extracellular signal regulated kinase [ERK]), SP600125 (Jun N terminal kinase [JNK]), SB203580 (p38 mitogen-activated protein kinase) and rapamycin (mammalian target of rapamycin), and by detecting the insulin signalling molecules by Western blots.

RESULTS

In aortic VSMC from humans and Zucker fa/+ rats cultured in normoxia insulin increases the HIF-1alpha content in cytosol and nucleus via dose- and time-dependent mechanisms, and HIF-1 DNA-binding activity on the VEGF gene. The insulin-induced increase of HIF-1alpha is blunted by the translation inhibitor cycloheximide, LY294002, PD98059, SP600125 and rapamycin, but not by SB203580. It is also reduced in Zucker fa/fa rats, which present an impaired ability of insulin to induce Akt, ERK-1/2 and JNK-1/2 phosphorylation.

CONCLUSIONS/INTERPRETATION

These results provide a biological mechanism for the impaired collateral vessel formation in obesity.

Leptin down-regulates insulin action through phosphorylation of serine-318 in insulin receptor substrate 1

Insulin resistance in skeletal muscle is found in obesity and type 2 diabetes. A mechanism for impaired insulin signaling in peripheral tissues is the inhibition of insulin action through serine phosphorylation of insulin receptor substrate (Irs) proteins that abolish the coupling of Irs proteins to the activated insulin receptor. Recently, we described serine-318 as a protein kinase C (PKC)-dependent phosphorylation site in Irs1 (Ser-318) activated by hyperinsulinemia. Here we show in various cell models that the adipose hormone leptin, a putative mediator in obesity-related insulin resistance, promotes phosphorylation of Ser-318 in Irs1 by a janus kinase 2, Irs2, and PKC-dependent pathway. Mutation of Ser-318 to alanine abrogates the inhibitory effect of leptin on insulin-induced Irs1 tyrosine phosphorylation and glucose uptake in L6 myoblasts. In C57Bl/6 mice, Ser-318 phosphorylation levels in muscle tissue were enhanced by leptin and insulin administration in lean animals while in diet-induced obesity Ser-318 phosphorylation levels were already up-regulated in the basal state, and further stimulation was diminished. In analogy, in lymphocytes of obese hyperleptinemic human subjects basal Ser-318 phosphorylation levels were increased compared to lean individuals. During a hyperinsulinemic euglycemic clamp, the increment in Ser-318 phosphorylation observed in lean individuals was absent in obese. In summary, these data suggest that phosphorylation of Ser-318 in Irs1 mediates the inhibitory signal of leptin on the insulin-signaling cascade in obese subjects.

Hypothalamic huntingtin-associated protein 1 as a mediator of feeding behavior

The hypothalamus responds to circulating leptin and insulin in the control of food intake and body weight. A number of neurotransmitters in the hypothalamus, including gamma-aminobutyric acid (GABA), also have key roles in feeding. Huntingtin-associated protein 1 (Hap1) is expressed more abundantly in the hypothalamus than in other brain regions, and lack of Hap1 in mice leads to early postnatal death. Hap1 is also involved in intracellular trafficking of the GABA(A) receptor. Here, we report that fasting upregulates the expression of Hap1 in the rodent hypothalamus, whereas intracerebroventricular administration of insulin downregulates Hap1 by increasing its degradation through ubiquitination. Decreasing the expression of mouse hypothalamic Hap1 by siRNA reduces the level and activity of hypothalamic GABA(A) receptors and causes a decrease in food intake and body weight. These findings provide evidence linking hypothalamic Hap1 to GABA in the stimulation of feeding and suggest that this mechanism is involved in the feeding-inhibitory actions of insulin in the brain.

PTEN and SHIP2 phosphoinositide phosphatases as negative regulators of insulin signalling

Insulin resistance in peripheral tissues is the primary cause responsible for onset of type II diabetes mellitus. Recently, the genetic and biochemical dissection of intracellular signalling pathways transducing the metabolic and mitogenic effects of insulin has contributed to the understanding of the molecular causes of this insulin resistance. In particular, important efforts have been developed to comprehend the role of negative regulators of insulin signalling, since they might represent future therapeutical targets to reduce insulin resistance in peripheral tissues. Herein, we will briefly review major intracellular signalling pathways activated by insulin and how they are negatively regulated by distinct mechanisms. In particular, the role of PTEN and SHIP2, two phosphoinositide phosphatases recently implicated as negative modulators of insulin signalling, is in focus. Current knowledge on the role of PTEN and SHIP2 in insulin resistance, type II diabetes and related disorders will also be discussed.

Activation of the Cbl insulin signaling pathway in cardiac muscle; Dysregulation in obesity and diabetes

In adipocytes, the Cbl/CAP dependent signaling pathway has been involved in regulating insulin-stimulated glucose uptake. We investigated activation of Cbl and its downstream effector TC10 in cardiac and skeletal muscle of Balb/C mice. Insulin administration resulted in Cbl phosphorylation in cardiac, skeletal muscle, and adipose tissue. Subsequent TC10 activation was detected only in heart and adipose tissue. c-Cbl and CAP gene expression was significantly reduced in the heart tissue of streptozotocin-induced diabetic animals, whereas no change was observed for other components of the pathway. No changes in Cbl expression were detected in hindlimb muscle. In leptin-/- obese mice Cbl expression in heart and adipose tissue was maintained, although insulin-mediated Cbl phosphorylation and subsequent TC10 activation were significantly reduced. In conclusion, our data demonstrate that Cbl/CAP/TC10 insulin signaling pathway is active in cardiac muscle and impaired during obesity and insulin deficiency.

[Insulin resistance/hyperinsulinemia associated diseases not included in the metabolic syndrome]

In the past years, in Brazil and in developed countries, obesity has become a major public health problem. It was identified that besides DM2 and metabolic syndrome other clinical entities were associated with insulin resistance. In this review we describe some of these alterations emphasizing nonalcoholic fatty liver disease, but also including polycistic ovary disease, hyperuricemia, chronic renal failure, heart failure, cognitive decline and cancer.

Physiological changes in glucose differentially modulate the excitability of hypothalamic melanin-concentrating hormone and orexin neurons in situ

The physiological signaling mechanisms that link normal variations in body energy status to the activity of arousal- and metabolism-regulating brain centers are not well understood. The melanin-concentrating hormone (MCH) and orexin/hypocretin types of neurons of the lateral hypothalamus (LH) exert opposing effects on arousal and metabolism. We examined whether shifts in brain extracellular glucose that correspond to physiological changes in blood glucose can alter the electrical output of neurochemically and biophysically defined LH cells in mouse brain slices. Here, we show that physiologically relevant concentrations of glucose dose-dependently enhance the electrical excitability of MCH neurons by inducing depolarization and increasing membrane resistance. We also demonstrate that the same physiological shifts in glucose have the opposite effects on the electrical activity of orexin neurons. We propose that these direct actions of glucose on the arousal- and metabolism-regulating LH neurons play a key role in the translation of normal variations in body energy resources into appropriate changes in arousal and metabolism.

Oral administration of S-nitroso-N-acetylcysteine prevents the onset of non alcoholic fatty liver disease in rats

AIM: To evaluate the potential of S-nitroso-N-acetylcysteine (SNAC) in inhibition of lipid peroxidation and the effect of oral SNAC administration in the prevention of nonalcoholic fatty liver disease (NAFLD) in an animal model.

METHODS: NAFLD was induced in Wistar male rats by choline-deficient diet for 4 wk. SNAC-treated animals (n=6) (1.4 mg/kg/day of SNAC, orally) were compared to 2 control groups: one (n=6) received PBS solution and the other (n=6) received NAC solution (7 mg/kg/d). Histological variables were semiquantitated with respect to macro and microvacuolar fat changes, its zonal distribution, foci of necrosis, portal and perivenular fibrosis, and inflammatory infiltrate with zonal distribution. LOOHs from samples of liver homogenates were quantified by HPLC. Nitrate levels in plasma of portal vein were assessed by chemiluminescence. Aqueous low-density lipoprotein (LDL) suspensions (200 µg protein/mL) were incubated with CuCl₂ (300 µmol/L) in the absence and presence of SNAC (300 µmol/L) for 15 h at 37 °C. Extent of LDL oxidation was assessed by fluorimetry. Linoleic acid (LA) (18.8 µmol/L) oxidation was induced by soybean lipoxygenase (SLO) (0.056 µmol/L) at 37 °C in the presence and absence of N-acetylcysteine (NAC) and SNAC (56 and 560 µmol/L) and monitored at 234 nm.

RESULTS: Animals in the control group developed moderate macro and microvesicular fatty changes in periportal area. SNAC-treated animals displayed only discrete histological alterations with absence of fatty changes and did not develop liver steatosis. The absence of NAFLD in the SNAC-treated group was positively correlated with a decrease in the concentration of LOOH in liver homogenate, compared to the control group (0.7±0.2 nmol/mg vs 3.2±0.4 nmol/mg protein, respectively, P<0.05), while serum levels of aminotransferases were unaltered. The ability of SNAC in preventing lipid peroxidation was confirmed in in vitro experiments using LA and LDL as model substrates.

CONCLUSION: Oral administration of SNAC prevents the onset of NAFLD in Wistar rats fed with choline-deficient diet. This effect is correlated with the ability of SNAC to block the propagation of lipid peroxidation in vitro and in vitro.

Hyperinsulinemia: effect on cardiac mass/function, angiotensin II receptor expression, and insulin signaling pathways

To investigate the association between hyperinsulinemia and cardiac hypertrophy, we treated rats with insulin for 7 wk and assessed effects on myocardial growth, vascularization, and fibrosis in relation to the expression of angiotensin II receptors (AT-R). We also characterized insulin signaling pathways believed to promote myocyte growth and interact with proliferative responses mediated by G protein-coupled receptors, and we assessed myocardial insulin receptor substrate-1 (IRS-1) and p110 alpha catalytic and p85 regulatory subunits of phospatidylinositol 3 kinase (PI3K), Akt, MEK, ERK1/2, and S6 kinase-1 (S6K1). Left ventricular (LV) geometry and performance were evaluated echocardiographically. Insulin decreased AT1a-R mRNA expression but increased protein levels and increased AT2-R mRNA and protein levels and phosphorylation of IRS-1 (Ser374/Tyr989), MEK1/2 (Ser218/Ser222), ERK1/2 (Thr202/Tyr204), S6K1 (Thr421/Ser424/Thr389), Akt (Thr308/Thr308), and PI3K p110 alpha but not of p85 (Tyr508). Insulin increased LV mass and relative wall thickness and reduced stroke volume and cardiac output. Histochemical examination demonstrated myocyte hypertrophy and increases in interstitial fibrosis. Metoprolol plus insulin prevented the increase in relative wall thickness, decreased fibrosis, increased LV mass, and improved function seen with insulin alone. Thus our data demonstrate that chronic hyperinsulinemia decreases AT1a-to-AT2 ratio and increases MEK-ERK1/2 and S6K1 pathway activity related to hypertrophy. These changes might be crucial for increased cardiovascular growth and fibrosis and signs of impaired LV function.

Further insights into the neurobiology of melanin-concentrating hormone in energy and mood balances

Melanin-concentrating hormone (MCH) is a critical hypothalamic anabolic neuropeptide, with key central and peripheral actions on energy balance regulation. The actions of MCH are, so far, known to be transduced through two seven-transmembrane-like receptor paralogues, named MCH1R and MCH2R. MCH2R is not functional in rodents. MCH1R is an important receptor involved in mediating feeding behaviour modulation by MCH in rodents. Pharmacological antagonism at MCH1R in rodents diminishes food intake and results in significant and sustained weight loss in fat tissues, particularly in obese animals. Additionally, MCH1R antagonists have been shown to have anxiolytic and antidepressant properties. The purpose of this review is to highlight the recent numerous pieces of evidence showing that pharmacological blockade at MCH1R could be a potential treatment for obesity and its related metabolic syndrome, as well as for various psychiatric disorders.

Leishmanicidal activity of primary S-nitrosothiols against Leishmania major and Leishmania amazonensis: implications for the treatment of cutaneous leishmaniasis

Nitric oxide (NO) is considered a key molecule in the defense against intracellular pathogens, particularly Leishmania. The expression of inducible nitric oxide synthase and consequent production of NO by infected macrophages has been shown to correlate with leishmaniasis resistance in the murine model as well as in human patients. Nitric oxide donors have been used successfully in the treatment of cutaneous leishmaniasis in humans, although their mechanisms of action are not fully understood. In the present work, the dose-dependent cytotoxic effects of the NO-donors S-nitroso-N-acetyl-l-cysteine (SNAC) and S-nitrosoglutathione (GSNO) against Leishmania were evaluated. GSNO inhibited the growth of Leishmania major and Leishmania amazonensis with in vitro 50% inhibitory concentrations (IC(50)) of 68.8+/-22.86 and 68.9+/-7.9 micromol L(-1), respectively. The IC(50) for SNAC against L. major and L. amazonensis were, respectively, 54.6+/-8.3 and 181.6+/-12.5 micromol L(-1). The leishmanicidal activity of GSNO, but not of SNAC, was reversed by ascorbic acid (AA) and dithiothreitol (DTT), suggesting that the mechanism of action of GSNO is related to the transnitrosation of parasite proteins. These results demonstrate that SNAC and GSNO have leishmanicidal activity, and are thus potential therapeutic agents against cutaneous leishmaniasis.