Aberrant insulin receptor expression is associated with insulin resistance and skeletal muscle atrophy in myotonic dystrophies

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are autosomal dominant multisystemic disorders linked to two different genetic loci and characterized by several features including myotonia, muscle atrophy and insulin resistance. The aberrant alternative splicing of insulin receptor (IR) gene and post-receptor signalling abnormalities have been associated with insulin resistance, however the precise molecular defects that cause metabolic dysfunctions are still unknown. Thus, the aims of this study were to investigate in DM skeletal muscle biopsies if beyond INSR missplicing, altered IR protein expression could play a role in insulin resistance and to verify if the lack of insulin pathway activation could contribute to skeletal muscle wasting. Our analysis showed that DM skeletal muscle exhibits a lower expression of the insulin receptor in type 1 fibers which can contribute to the defective activation of the insulin pathway. Moreover, the aberrant insulin signalling activation leads to a lower activation of mTOR and to an increase in MuRF1 and Atrogin-1/MAFbx expression, possible explaining DM skeletal muscle fiber atrophy. Taken together our data indicate that the defective insulin signalling activation can contribute to skeletal muscle features in DM patients and are probably linked to an aberrant specific-fiber type expression of the insulin receptor.

Branched-Chain Amino Acid-Rich Supplements Containing Microelements Have Antioxidant Effects on Nonalcoholic Steatohepatitis in Mice

BACKGROUND

The aim of the present study was to elucidate whether the administration of antioxidant-rich nutrients, including branched-chain amino acids (BCAAs), microelements, and vitamins, both alone and in combination, has a positive impact on liver function in a nonalcoholic steatohepatitis (NASH) mouse model and identify the mechanisms underlying these effects.

METHODS

Seven-week-old male KKAy mice fed a methionine- and choline-deficient diet (MCD) for 4 weeks were divided into 7 groups and fed the following planned diets for another 4 weeks: group A (normal diet), group B (MCD; control), group C (MCD with rich microelements), group D (MCD with rich BCAAs), group E (MCD with rich microelements and BCAAs), and group F (MCD with rich microelements, BCAAs, and vitamins). We then conducted biochemical assays, histological analyses, immunohistochemistry for 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxy-2'-nonenal (4-HNE), and Western blotting for insulin glucose signaling, lipid metabolism, and endoplasmic reticulum (ER) stress-related signaling in liver specimens obtained from mice in each group.

RESULTS

The morphometric grades of all NASH-related findings and the mean degree of 8-OHdG immunolocalization in groups D-F were significantly lower than those observed in group B. The expression levels of insulin receptor β subunit (IRβ) and p-elF in groups E and F and those of phosphatidyl-inositol 3 kinase (PI3K85), p-AcelCoA, and PERK in group F were similar to those noted in group A.

CONCLUSIONS

The administration of a combination of antioxidant-rich nutrients, including BCAAs and microelements, is likely to suppress the progression of NASH by reducing oxidative stress, primarily via the downregulation of the ER stress pathway.

Aptamer-based single-molecule imaging of insulin receptors in living cells

We present a single-molecule imaging platform that quantitatively explores the spatiotemporal dynamics of individual insulin receptors in living cells. Modified DNA aptamers that specifically recognize insulin receptors (IRs) with a high affinity were selected through the SELEX process. Using quantum dot-labeled aptamers, we successfully imaged and analyzed the diffusive motions of individual IRs in the plasma membranes of a variety of cell lines (HIR, HEK293, HepG2). We further explored the cholesterol-dependent movement of IRs to address whether cholesterol depletion interferes with IRs and found that cholesterol depletion of the plasma membrane by methyl-β-cyclodextrin reduces the mobility of IRs. The aptamer-based single-molecule imaging of IRs will provide better understanding of insulin signal transduction through the dynamics study of IRs in the plasma membrane.

Chronic insulin exposure does not cause insulin resistance but is associated with chemo-resistance in colon cancer cells

Insulin resistance is an adaptive process in insulin-sensitive tissues characterised by reduced insulin receptor (IR) and insulin-receptor substrate (IRS)-1 expression, increased IRS-1 serine phosphorylation and attenuated downstream signalling. We tested whether this molecular phenotype prevails in cancer cells after long-term exposure to insulin. We characterised expression of IR-related molecules, IRS-1 phosphorylation and downstream signalling in a panel of 5 colon cancer cell lines at different insulin exposures: 15 min (100 nM), approximating to acute stimulation; 48 h (100 nM), used to demonstrate adaptive changes; and 12 weeks (20 nM; chronic insulin exposure, CIE), approximating to chronic hyperinsulinaemia. To assess clinical relevance, we determined IC50 values (increased indicating chemo-resistance) in the CIE-treated cells using oxaliplatin, SN38 (irinotecan) and 5-fluorouracil (5-FU). All colon cancer cell lines (HCT 116, HT-29, C32, CaCo2, LoVo) were sensitive to 15 min insulin exposure with increased phosphorylation of Akt, PRAS40 and p70-S6K. At 48 h, there was incomplete or absent features of insulin resistance. In CIE-treated cells, there was reduced IR expression, incomplete IRS-1 adaptation, lack of signalling pathway attenuation and contra-adaptive increases in IRS-1 tyrosine phosphorylation in several cell types. In CIE cells, there were multiple examples of increased IC50 values (2- to 100-fold) following 24-h treatment with oxaliplatin and SN38, but not with 5-FU. We concluded that CIE in colon cancer cells does not completely induce an insulin resistance molecular phenotype but is associated with chemo-resistance. Adaptive changes seen in insulin-sensitive non-neoplastic cells in response to long-term insulin may not extrapolate to neoplastic cells.

Improvement of insulin sensitivity promotes extravillous trophoblast cell migration stimulated by insulin-like growth factor-I

Insulin-like growth factor-I (IGF-I) has been shown to stimulate extravillous trophoblast (EVT) cell migration and invasion, and to play a crucial role in placental function, thereby, influencing placental development and fetal growth. Insufficient invasion of EVT cells into the uterine endometrium leads to pregnancy-related complications, including spontaneous abortion, fetal growth restriction (FGR), and pregnancy-induced hypertension (PIH). Insulin-resistant conditions such as polycystic ovary syndrome (PCOS) and gestational diabetes mellitus (GDM) have also been associated with abortion and PIH. However, the effects of IGF-I on EVT cells under insulin-resistant conditions have not been elucidated yet. The current study was undertaken to analyze the effects of IGF-I under insulin-resistant conditions and to determine whether improvement in insulin sensitivity alters IGF signaling and cell migration in the EVT. Incubation with pioglitazone, an insulin sensitizer, increased peroxisome proliferator-activated receptor-γ (PPARγ) expression after 48 h. A 48-h pre-incubation with insulin reduced the phosphorylation and concentration of the insulin receptors, which were increased by insulin treatment. Long-term exposure to insulin reduced phosphorylation of the IGF-I receptor, insulin receptor substrate-1 (IRS-1), and Akt, and also reduced EVT cell migration. However, when the cells were incubated with pioglitazone in addition to insulin for 48 h, the phosphorylation of these proteins was restored. This combination partially reversed the inhibitory effect of insulin on EVT cell migration. These results suggest that abnormalities in pregnancy that are induced by loss of insulin sensitivity can be treated by improving insulin sensitivity.

PTPIP51: a new interaction partner of the insulin receptor and PKA in adipose tissue

AIMS

Our previous experiments revealed an association of PTPIP51 (protein tyrosine phosphatase interacting protein 51) with the insulin signalling pathway through PTP1B and 14-3-3beta. We aimed to clarify the role of PTPIP51 in adipocyte metabolism.

METHODS

Four groups of ten C57Bl/6 mice each were used. Two groups were fed a standard diet; two groups were fed a high-fat diet. Two groups (one high-fat diet and one standard diet) were submitted to endurance training, while the remaining two groups served as untrained control groups. After ten weeks, we measured glucose tolerance of the mice. Adipose tissue samples were analyzed by immunofluorescence and Duolink proximity ligation assay to quantify interactions of PTPIP51 with either insulin receptor (IR) or PKA.

RESULTS

PTPIP51 and the IR and PTPIP51 and PKA, respectively, were colocalized in all groups. Standard diet animals that were submitted to endurance training showed low PTPIP51-IR and PTPIP51-PKA interactions. The interaction levels of both the IR and PKA differed between the feeding and training groups.

CONCLUSION

PTPIP51 might serve as a linking protein in adipocyte metabolism by connecting the IR-triggered lipogenesis with the PKA-dependent lipolysis. PTPIP51 interacts with both proteins, therefore being a potential gateway for the cooperation of both pathways.

Association of placental insulin, total and activated insulin receptor contents, cortisol and IL-6 concentrations with human birth weight and length: pilot study

We followed-up, from pregnancy to birth, a group of newborns both IUGR and AGA and we aimed at establishing placental biochemical determinants of birth weight and length. Insulin, total and activated insulin receptor contents (IR), cortisol and IL-6 placental concentrations were assayed in 23 IUGR and 37 AGA subjects at birth, and a multiple regression model was designed and applied to assess the significant biochemical determinants of birth size. IL-6 and activated insulin receptor content were significantly increased in IUGR, whereas insulin, total insulin receptor content, and cortisol placental concentrations were similar in IUGR and AGA. Placental cortisol concentration was found to be significantly and negatively related with both birth length (0.778, P<0.001) and weight (0.508, P<0.008). A negative effect of IL-6 placental concentration was found on birth length (P<0.002). For the first time we provide evidence of a negative association of placental cortisol and IL-6 concentrations on birth size.

Insulin receptor and IRS-1 co-immunoprecipitation with SOCS-3, and IKKα/β phosphorylation are increased in obese Zucker rat skeletal muscle

AIMS

We evaluated if selected pro-inflammatory cytokines and/or the protein suppressor of cytokine signaling 3 (SOCS-3) could account for decreased insulin-stimulated phosphatidylinositol 3-kinase (PI3-K) activity in the skeletal muscle of the obese Zucker rat.

MAIN METHODS

Eight lean and eight obese Zucker rats ~4weeks of age were obtained and allowed to feed ad libitum for 4weeks before undergoing hind limb perfusion in the presence of 500μU/ml insulin.

KEY FINDINGS

Insulin-stimulated skeletal muscle PI3-K activity and 3-O-methylglucose transport rates were reduced (P<0.05) in obese compared to lean animals. IRS-1 concentration remained unchanged although IRS-1 tyrosine phosphorylation was decreased (P<0.05), and IRS-1 serine phosphorylation (pS) was increased (P<0.05) in obese animals compared to lean animals. IKKα/β pS and JNK theronine/tyrosine phosphorylation was increased (P<0.05) in the obese animals. IκBα concentration was decreased (P<0.05) and IκBα pS was increased (P<0.05) in the obese compared to lean Zucker animals. SOCS-3 concentration and SOCS-3 co-immunoprecipitation with both insulin receptor β-subunit (IR-β) and IRS-1 were elevated (P<0.05) in obese compared to lean animals. IRS-1 co-immunoprecipitation with IR-β was reduced 56% in the obese animals.

SIGNIFICANCE

Increased IKKα/β and JNK serine phosphorylation may contribute to increasing IRS-1 serine phosphorylation, while concurrent co-localization of SOCS-3 with both IR-β and IRS-1 may prevent IRS-1 from interacting with IR-β. These two mechanisms thusly may independently contribute to impairing insulin-stimulated PI3-K activation in the skeletal muscle of the obese Zucker rat.

Ciliary neurotrophic factor (CNTF) protects non-obese Swiss mice against type 2 diabetes by increasing beta cell mass and reducing insulin clearance

AIMS/HYPOTHESIS

Ciliary neurotrophic factor (CNTF) improves metabolic variables of obese animals with characteristics of type 2 diabetes, mainly by reducing insulin resistance. We evaluated whether CNTF was able to improve other metabolic variables in mouse models of type 2 diabetes, such as beta cell mass and insulin clearance, and whether CNTF has any effect on non-obese mice with characteristics of type 2 diabetes.

METHODS

Neonatal mice were treated with 0.1 mg/kg CNTF or citrate buffer via intraperitoneal injections, before injection of 250 mg/kg alloxan. HEPG2 cells were cultured for 3 days in the presence of citrate buffer, 1 nmol/l CNTF or 50 mmol/l alloxan or a combination of CNTF and alloxan. Twenty-one days after treatment, we determined body weight, epididymal fat weight, blood glucose, plasma insulin, NEFA, glucose tolerance, insulin resistance, insulin clearance and beta cell mass. Finally, we assessed insulin receptor and protein kinase B phosphorylation in peripheral organs, as well as insulin-degrading enzyme (IDE) protein production and alternative splicing in the liver and HEPG2 cells.

RESULTS

CNTF improved insulin sensitivity and beta cell mass, while reducing glucose-stimulated insulin secretion and insulin clearance in Swiss mice, improving glucose handling in a non-obese type 2 diabetes model. This effect was associated with lower IDE production and activity in liver cells. All these effects were observed even at 21 days after CNTF treatment.

CONCLUSIONS/INTERPRETATION

CNTF protection against type 2 diabetes is partially independent of the anti-obesity actions of CNTF, requiring a reduction in insulin clearance and increased beta cell mass, besides increased insulin sensitivity. Furthermore, knowledge of the long-term effects of CNTF expands its pharmacological relevance.

Berberine lowers blood glucose in type 2 diabetes mellitus patients through increasing insulin receptor expression

Our previous work demonstrated that berberine (BBR) increases insulin receptor (InsR) expression and improves glucose utility both in vitro and in animal models. Here, we study the InsR-up-regulating and glucose-lowering activities of BBR in humans. Our results showed that BBR increased InsR messenger RNA and protein expression in a variety of human cell lines, including CEM, HCT-116, SW1990, HT1080, 293T, and hepatitis B virus-transfected human liver cells. Accordingly, insulin-stimulated phosphorylations of InsR beta-subunit and Akt were increased after BBR treatment in cultured cells. In the clinical study, BBR significantly lowered fasting blood glucose (FBG), hemoglobin A(1c), triglyceride, and insulin levels in patients with type 2 diabetes mellitus (T2DM). The FBG- and hemoglobin A(1c)-lowering efficacies of BBR were similar to those of metformin and rosiglitazone. In the BBR-treated patients, the percentages of peripheral blood lymphocytes that express InsR were significantly elevated after therapy. Berberine also lowered FBG effectively in chronic hepatitis B and hepatitis C patients with T2DM or impaired fasting glucose. Liver function was improved greatly in these patients by showing reduction of liver enzymes. Our results confirmed the activity of BBR on InsR in humans and its relationship with the glucose-lowering effect. Together with our previous report, we strongly suggest BBR as an ideal medicine for T2DM with a mechanism different from metformin and rosiglitazone.

Effects of caffeic acid and cinnamic acid on glucose uptake in insulin-resistant mouse hepatocytes

Tumor necrosis factor-alpha was used to induce insulin resistance of mouse liver FL83B cells. Two phenolic acids, caffeic acid and cinnamic acid, were then added separately to investigate their effects on glucose uptake of the insulin-resistant cells. The results suggest that these two phenolic acids may promote insulin receptor tyrosyl phosphorylation, up-regulate the expression of insulin signal associated proteins, including insulin receptor, phosphatidylinositol-3 kinase, glycogen synthase, and glucose transporter-2, increase the uptake of glucose, and alleviate insulin resistance in cells as a consequence.

IGF-I and insulin receptors in bovine skeletal muscle: comparisons of different developmental ages, two different genotypes and various individual muscles

To investigate the regulation of the IGF-I and the insulin receptor in bovine skeletal muscle, we determined their concentrations and their affinity constants in animals of different age, muscle type and breed. Receptors were solubilized and measured by an enzyme-immunoassay. During ontogenesis the concentration of IGF-I receptors decreased from 1650 /+- 600 fmol/mg protein in 3-5-month old fetuses to 105 /+- 20 fmol/mg protein in 16-month old heifers (p < or = 0.01). The insulin receptor concentrations also decreased with age from 136 /+- 28 fmol/mg protein in 3-5-month old fetuses to 50 /+- 11 fmol/mg protein (p < or = 0.05) in 16-month old heifers. In order to compare different muscle types, seven muscles, which represent large differences in fibre type composition and growth impetus, were selected from 6 month old female Jersey calves and were assayed for IGF-I and insulin receptors. We observed significant differences of the IGF-I as well as the insulin receptor concentrations between distinct muscles. However, no relationship could be established between receptor concentration and fibre type composition or growth impetus. In muscle of two cattle breeds, differing markedly with regard to muscle growth intensity, the Jersey and the German Fleckvieh breed, we observed no divergence in IGF-I nor insulin receptor concentrations. We found no differences in IGF-I and in insulin receptor affinities in any of the adult animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin inhibition of platelet-endothelial interaction is mediated by insulin effects on endothelial cells without direct effects on platelets

OBJECTIVES

Platelet hyperreactivity contributes to adverse vascular events in diabetes mellitus. It is unclear whether platelet hyperreactivity is due to impaired insulin effects directly on platelets and /or originates from endothelial cells. Here, acute effects of insulin on platelet activation and platelet-endothelial cell interactions were analyzed.

METHODS AND RESULTS

Washed human platelets were treated with insulin alone or in combinations with thrombin, collagen and ADP. Insulin signaling was analyzed by intracellular phosphorylation markers of platelet activation (ERK, p38 MAPK, PKB) or inhibition (VASP), platelet aggregation, intracellular Ca(2+) levels, and platelet adhesion to collagen coated surfaces and endothelial cells under flow. Insulin up to 100 nm for 5 min did not change phosphorylation status of VASP, p38, ERK or PKB in platelets. Integrin alpha(IIb)beta(3) activation, P-selectin expression, aggregation, and platelet adhesion to collagen coated surfaces and endothelial cells under flow were not altered by insulin. An insulin receptor was detected on endothelial cells but not on human platelets. Insulin treatment decreased platelet adhesion to endothelial cells through insulin stimulation of endothelial NO production and NOS inhibition interfered with this process.

CONCLUSIONS

Insulin exerts no direct acute effects on platelet function but inhibits platelet-endothelial interaction by insulin stimulation of endothelial NO production.

Characterization of ScAP-23, a new cell line from murine subcutaneous adipose tissue, identifies genes for the molecular definition of preadipocytes

The 3T3-L1 model of in vitro adipogenesis has provided key insights into the molecular nature of this process. However, given that 3T3-L1 are of an embryonic origin, it is not clear to what extent they represent adipogenesis as it occurs in white adipose tissue (WAT). With the goal of better defining preadipocytes and adipogenesis in WAT, we have generated a new cell culture model from adipocyte precursors present in C57BL/6 mouse subcutaneous WAT. ScAP-23 preadipocytes show fibroblastic morphology, and on treatment with dexamethasone, 3-methylisobutylxanthine, insulin, and indomethacin, convert to nearly 100% adipocyte morphology. ScAP-23 adipocytes contain abundant lipid droplets and express transcripts for PPARγ, C/EBP family, and SREBP-1c transcription factors, SCD1, aFABP, ATGL, GLUT4, FAS, LDL, and GPDH, and are insulin responsive. Differential screening of 1,176 genes using nylon DNA arrays identified 10 transcripts enriched in ScAP-23 adipocytes vs. preadipocytes and 26 transcripts enriched in ScAP-23 preadipocytes vs. adipocytes. Semiquantitative or real-time PCR analyses identified a common cohort of 14 transcripts markedly downregulated in both ScAP-23 and 3T3-L1 adipogenesis. These included catenin-β1, chemokine ligand-2, serine or cysteine peptidase inhibitor f1, aurora kinase B, thrombospondin2, and solute carrier-7a5. Five of these transcripts (Ccl2, Serpinf1, Aurkb, Thbs2, and Slc7a5) demonstrated at least a twofold increase in WAT from obese ( ob/ob) mice compared with that of wild-type mice. This suggests that comparative gene expression studies of ScAP-23 and 3T3-L1 adipogenesis may be particularly fruitful in identifying preadipocyte-expressed genes that play a role in adipose tissue physiology and/or pathophysiology.

Insulin signaling in mouse oocytes

Continuous exposure of follicles/oocytes to elevated levels of insulin compromises embryonic developmental competence, although the underlying cellular mechanisms are unknown. The objectives of the present study were to determine whether mouse oocytes have insulin receptors and a functional insulin signaling cascade, and whether insulin exposure during oocyte growth or maturation influences meiotic progression and chromatin remodeling. Immunoblot and immunocytochemical analyses of germinal vesicle-intact (GVI) oocytes demonstrated the presence of insulin receptor-beta. Insulin receptor expression in oocytes was increased by gonadotropin stimulation, and remained elevated throughout meiotic maturation. Fully grown GVI oocytes contained 3-phosphoinositide-dependent protein kinase-1 (PDPK1), thymoma viral proto-oncogene 1 (AKT1), and glycogen synthase kinase 3 (GSK3). In vitro maturation of GVI oocytes in 5 microg/ml insulin had no influence on meiotic progression or the incidence of normal metaphase II (MII) chromosome condensation. Treatment of oocytes during maturation had no effect on GSK3A/B protein expression or phosphorylation of S21/9. However, the culturing of preantral follicles for 10 days with 5 microg/ml insulin increased the phosphorylation of oocyte GSK3B, indicating GSK3 inactivation. The rates of development to metaphase I (MI) were similar for oocytes obtained from insulin-treated follicles and controls, whereas the incidence of abnormal MI chromatin condensation was significantly higher in oocytes obtained from follicles cultured with insulin compared to those cultured without insulin. These results demonstrate that oocytes contain a functional insulin signaling pathway, and that insulin exposure during oocyte growth results in chromatin remodeling aberrations. These findings begin to elucidate the mechanisms by which chronic elevated insulin influences oocyte meiosis, chromatin remodeling, and embryonic developmental competence.

Effect of type-1 diabetes mellitus on the regulation of insulin and endothelin-1 receptors in rat hearts

This project assesses the treatment role with insulin and (or) angiotensin II receptor subtype-1 (AT1-R) blocker (ARB) on insulin receptor and endothelin-1 receptor subtype (ETA-R and ETB-R) regulation in rat hearts suffering from insulin-dependent diabetes mellitus (IDDM). Animals were divided into 6 groups: groups 1, 3, and 5 were controls consisting of normal, diabetic (streptozotocin-treated, once at 0 time), and diabetic supplemented daily with insulin, respectively, whereas groups 2, 4, and 6 were the controls treated daily with losartan. One month after enrollment, rats were sacrificed and samples of cardiac tissue were snapped frozen for immunostaining and Western blotting. Insulin receptor density was observed to be upregulated in the cardiomyocytes of diabetic animals, but downregulated with insulin supplementation alone. Cotreatment with insulin and an ARB resulted in drastic increase in insulin-receptor density in the diabetic rats. In addition, expression of ETA-R in cardiomyocytes was upregulated and was consistently maintained within the various treatment modalities. However, ETB-R expression was significantly reduced in the diabetic group treated with both insulin and an ARB. The changes in the expression of the insulin, the ETA-Rs, and the ETB-Rs at the various sites of the myocardium and the effect of both insulin treatment and blockade of the AT1-R explain the new benefits related to the halting of myocardial remodeling in IDDM rats.

Phosphopeptide enrichment by IEF

In our efforts to improve the identification of phosphopeptides by MS we have used peptide IEF on IPG strips. Phosphopeptides derived from trypsin digests of single proteins as well as complex cellular protein mixtures can be enriched by IEF and recovered in excellent yields at the acidic end of an IPG strip. IPG peptide fractionation in combination with MS/MS analysis has allowed us to identify phosphopeptides from tryptic digests of a cellular protein extract.

Insulin receptor is an independent predictor of a favorable outcome in early stage breast cancer

Fasting insulin is related to outcome in early breast cancer. We evaluated the expression of insulin receptor (IR) and its prognostic significance in patients with early stage breast cancer. Tumors from 191 patients with T1-3, N0-1, M0 breast cancer who were enrolled at a single center of a multicenter cohort study were used to construct microarrays with subsequent immunohistochemical evaluation of IR, IGF-IR, ER, PgR and HER2/neu. Correlation of biomarker expression with traditional prognostic factors, serum biochemistry (notably insulin) and clinical outcome was assessed. IR was strongly positive (Allred score = 8) in 54% of tumors. High IR expression significantly correlated with favorable prognostic markers (low tumor grade, lymph node negativity and progesterone receptor positivity) but not with fasting levels of circulating insulin. At a median follow-up of 9.1 years, high vs. low IR expression (an Allred score of 8 vs. 0-7) was associated with statistically significant improved distant disease-free survival (multivariate hazard ratio (HR) = 0.4; P = 0.027) and overall survival (multivariate HR = 0.26; P = 0.005). IR is highly expressed in the majority of early stage breast cancers but this expression is not clearly down-regulated in the presence of high insulin levels. Furthermore, high expression of IR is independently and significantly associated with more favorable clinical outcomes. Follow-up intervention research is recommended.

Adiposity associated rise in leptin impairs ovarian activity during winter dormancy in Vespertilionid bat, Scotophilus heathi

The aim of the study was to evaluate the seasonal variation in serum leptin levels in a natural population of the female bat,Scotophilus heathiand their relationship to the changes in the body mass, serum insulin level, and ovarian activity. Circulating leptin level varied significantly over the season and correlated positively with the changes in body mass, and circulating insulin and androstenedione (A4) levels. Circulating leptin concentrations showed two peaks; one coincides with the maximum fat accumulation prior to winter dormancy, whereas the second shorter peak coincides with late pregnancy. Thein vivostudy inS. heathishowed that the increased circulating leptin level during winter dormancy coincides with the decreased expression of ovarian steroidogenic acute regulatory (StAR) protein, and low circulating estradiol (E2) level. At the same time, increased circulating leptin level coincides with increased expression of ovarian insulin receptor and high circulating A4 level. The low circulating leptin level during preovulatory period coincides with the increase in StAR protein but decrease in insulin receptor protein. Thein vitrostudy confirmed thein vivoobservations of inhibitory effect of leptin on LH induced StAR expression and E2production, whereas the stimulatory effect of leptin (high dose) on LH induced expression of insulin receptor protein and A4 production. However, pharmacological dose of leptin produced inhibitory effect on the expression of insulin receptor protein. The results of the present study thus suggest that high circulating leptin level during winter dormancy promotes adiposity and impairs ovarian activity by suppressing StAR-mediated E2production as well as by enhancing insulin receptor-mediated A4 synthesis thereby contributing anovulatory condition of delayed ovulation inS. heathi.

Degeneration of the Golgi and neuronal loss in dorsal root ganglia in diabetic BioBreeding/Worcester rats

AIMS/HYPOTHESIS

The aim of this study was to evaluate the nature and extent of neuronal loss in dorsal root ganglia (DRG) in diabetic polyneuropathy.

MATERIALS AND METHODS

We examined 10-month diabetic BioBreeding/Worcester (BB/Wor) rats with respect to DRG ultrastructure and morphometry, sural nerve morphometry, pro- and anti-apoptotic proteins, the expression of neurotrophic factors and their receptors, and sensory nerve functions.

RESULTS

In diabetic rats, DRG neurons decreased to 73% of normal, owing to loss of substance P and calcitonin gene-related peptide-positive neurons. Levels of pro-apoptotic active caspase-3, Bax and low-affinity nerve growth factor (NGF) were increased in DRG. The concentration of anti-apoptotic heat shock protein (HSP) 70 in DRG was decreased, whereas concentrations of Bcl-xl and HSP27 were unaltered. Levels of poly(ADP-ribose) polymerase (PARP) and cleaved PARP were unaltered. Levels of NGF in sciatic nerve and concentrations of the high-affinity NGF receptor, insulin receptor and IGF-I receptor in DRG were significantly decreased. Sensory nerve conduction velocity decreased to 78% of normal. Hyperalgesia increased up to 6 months. Myelinated and unmyelinated fibre numbers of the sural nerve were significantly decreased in diabetic rats. DRG examinations revealed no evidence of apoptosis, mitochondrial changes or abnormalities of the endoplasmic reticulum. Instead, neurons demonstrated progressive vacuolar degenerative changes of the Golgi apparatus, with fragmentation and formation of large cytoplasmic vacuoles. These data show that sustained apoptotic stress is present in DRG of chronically diabetic BB/Wor rats, but fails to proceed to apoptotic cell death.

CONCLUSIONS/INTERPRETATION

Progressive DRG neuronal loss, particularly of small neurons, occurs in the type 1 diabetic BB/Wor rat. This is associated with neurotrophic withdrawal and progressive degeneration of the Golgi apparatus.

Insulin resistance and increased pancreatic beta-cell proliferation in mice expressing a mutant insulin receptor (P1195L)

Several mutations of the tyrosine kinase domain of insulin receptor (IR) have been clinically reported to lead insulin resistance and insulin hypersecretion in humans. However, it has not been completely clarified how insulin resistance and pancreatic beta-cell function affect each other under the expression of mutant IR. We investigated the response of pancreatic beta-cells in mice carrying a mutation (P1195L) in the tyrosine kinase domain of IR beta-subunit. Homozygous (Ir(P1195L/P1195L)) mice showed severe ketoacidosis and died within 2 days after birth, and heterozygous (Ir(P1195L/wt)) mice showed normal levels of plasma glucose, but high levels of plasma insulin in the fasted state and after glucose loading, and a reduced response of plasma glucose lowering effect to exogenously administered insulin compared with wild type (Ir(wt/wt)) mice. There were no differences in the insulin receptor substrate (IRS)-2 expression and its phosphorylation levels in the liver between Ir(P1195L/wt) and Ir(wt/wt) mice, both before and after insulin injection. This result may indicate that IRS-2 signaling is not changed in Ir(P1195L/wt) mice. The beta-cell mass increased due to the increased numbers of beta-cells in Ir(P1195L/wt) mice. More proliferative beta-cells were observed in Ir(P1195L/wt) mice, but the number of apoptotic beta-cells was almost the same as that in Ir(wt/wt) mice, even after streptozotocin treatment. These data suggest that, in Ir(P1195L/wt) mice, normal levels of plasma glucose were maintained due to high levels of plasma insulin resulting from increased numbers of beta-cells, which in turn was due to increased beta-cell proliferation rather than decreased beta-cell apoptosis.

Up-regulation of the phosphatidylinositol 3-kinase/protein kinase B pathway in the ovary of rats by chronic treatment with hCG and insulin

Polycystic ovary syndrome (PCOS) manifests as chronic anovulation, ovarian hyperandrogenism, and follicular cysts, which are amplified by insulin as well as the inability of the hormone to stimulate glucose uptake in classic target tissues such as muscle and fat. In the present study, we evaluated the regulation of the insulin-signaling pathways by using immunoprecipitation and immunoblotting in whole extracts of ovaries from non-pregnant human chorionic gonadotropin (hCG)-treated rats, hyperinsulinemic-induced rats and hyperinsulinemic-induced rats, treated with hCG for 22 consecutive days. There were increased associations of insulin receptor substrate (IRS)-1 and IRS-2 with phosphatidylinositol (PI) 3-kinase, followed by enhanced protein kinase B (Akt) serine and threonine phosphorylation, in the ovaries of rats that were treated with hCG, either alone or with insulin. In contrast, the skeletal muscle demonstrated a reduced IRS-1/PI 3-kinase/Akt pathway in hyperinsulinemic-induced rats. These intracellular modifications were accompanied by follicular cysts, detected by optical microscopy, and increased androstenedione serum levels. In summary, our data show that chronic treatment with hCG or hCG plus insulin can induce changes in ovaries that simulate PCOS. In these situations, an increase in the insulin-induced IRS/PI 3-kinase/Akt pathway occurs in the ovary, suggesting that the activation of this pathway may have a role in the development of PCOS.

A miniaturized cell-based fluorescence resonance energy transfer assay for insulin-receptor activation

This report describes the development, optimization, and implementation of a miniaturized cell-based assay for the identification of small-molecule insulin mimetics and potentiators. Cell-based assays are attractive formats for compound screening because they present the molecular targets in their cellular environment. A fluorescence resonance energy transfer (FRET) cell-based assay that measures the insulin-dependent colocalization of Akt2 fused with either cyan fluorescent protein or yellow fluorescent protein to the cellular membrane was developed. This ratiometric FRET assay was miniaturized into a robust, yet sensitive 3456-well nanoplate assay with Z' factors of approximately 0.6 despite a very small assay window (less than twofold full activation with insulin). The FRET assay was used for primary screening of a large compound collection for insulin-receptor agonists and potentiators. To prioritize compounds for further development, primary hits were tested in two additional assays, a biochemical time-resolved fluorescence resonance energy transfer assay to measure insulin-receptor phosphorylation and a translocation-based imaging assay. Results from the three assays were combined to yield 11 compounds as potential leads for the development of insulin mimetics or potentiators.

Insulin differentially regulates monocyte and polymorphonuclear neutrophil functions in healthy young and elderly humans

CONTEXT

Insulin can regulate immune cell function. Aging is associated with various degrees of insulin resistance together with reduced immune cell activity.

OBJECTIVE

We investigated the hypothesis that blood monocytes and polymorphonuclear neutrophils (PMNs) are less responsive to the action of insulin in elderly subjects. DESIGN-INTERVENTION: We evaluated the effect of hyperinsulinemia (0.7 mU/kg(-1) fat-free mass per minute(-1)) on monocyte and PMN activity using a 4-h euglycemic clamp technique.

PARTICIPANTS

Eight young (24 +/- 6 yr old) and nine elderly (69 +/- 4 yr old) healthy volunteers participated in the study.

MAIN OUTCOME MEASURES

Monocyte and PMN receptor expression and density were measured using flow cytometric detection. PMN chemotaxis toward formyl-Met-Leu-Phe (fMLP) was evaluated using a two-compartment chamber. PMN and monocyte phagocytosis was determined by measuring the engulfment of opsonized particles. Microbicidal functions were determined based on the production of reactive oxygen species (ROS) and bactericidal protein by stimulated cells.

RESULTS

The density of PMN and monocyte insulin receptors was not affected by age or insulin clamp treatment regardless of the age. Insulin was able to regulate the expression of receptors involved in PMN action in the young-adult group only. PMN chemotaxis was up-regulated by insulin in both groups. In contrast, although insulin stimulated phagocytosis and bactericidal activity in young-adult subjects, the ability of PMN to adapt to physiological hyperinsulinemia was blunted in the older group. The effect of insulin on monocyte bactericidal properties seemed to be limited, although a suppressive action on fMLP-induced ROS production was detected in young adults.

CONCLUSIONS

We confirmed the presence of the insulin receptor on monocyte and PMN membranes. We revealed that insulin has a limited action on monocyte function. Insulin has a priming effect on the main PMN functions. Immune cell function adapted poorly to insulin infusion in the elderly subjects.

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.

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.

Severely impaired insulin signaling in chronic wounds of diabetic ob/ob mice: a potential role of tumor necrosis factor-alpha

Wound-healing disorders are major complications of diabetes mellitus. Here, we investigated insulin-mediated signaling in nonwounded skin and in cutaneous tissue regeneration of healthy C57BL/6 and diabetes-impaired leptin-deficient obese/obese (ob/ob) mice. The insulin receptor (InsR) was abundantly expressed in wound margins and granulation tissue during acute healing in healthy mice. Remarkably, active signaling from the InsR, as assessed by phosphorylation of downstream targets such as protein tyrosine phosphatase-1B, glycogen synthase (GS), and GS kinase, was nearly absent in nonwounded and acutely healing skin from ob/ob mice. Systemic leptin administration to ob/ob mice reverted the diabetic phenotype and improved tissue regeneration as well as the impaired expression of InsR, insulin receptor substrate-1 and insulin receptor substrate-2, and downstream signaling (phosphorylation of GS kinase and GS) in late wounds and nonwounded skin of ob/ob mice. Importantly, tumor necrosis factor (TNF)-alpha was a mediator of insulin resistance in keratinocytes in vitro and in ob/ob wound tissue in vivo. Systemic administration of a monoclonal anti-TNF-alpha antibody (V1q) in wounded ob/ob mice attenuated wound inflammation, improved re-epithelialization, and restored InsR expression and signaling in wound tissue of ob/ob mice. These data suggest that InsR signaling in diabetes-impaired wounds is sensitive to inflammatory conditions and that anti-inflammatory approaches, such as anti-TNF-alpha strategies, improve diabetic wound healing.

Monkey Embryonic Stem Cells Differentiate into AdipocytesIn Vitro

Production of functional adipocytes is important in adipocyte research and regenerative medicine. In this paper, we describe the differentiation of monkey embryonic stem (ES) cells into insulin-responsive adipocytes. Treatment of embryoid body (EB) outgrowth with adipogenic hormones induced the expression of adipocyte-specific genes, such as PPARgamma, C/EBPalpha, aP2, insulin receptor, and GLUT4. Expression of adipocytokines, leptin and adiponectin, was also detected. Furthermore, translocation of GLUT4 was observed by insulin stimulation in differentiated adipocytes. These results suggested that monkey ES cells can be a useful tool for studying adipogenesis in primate.

Effect of insulin on the brain activity obtained during visual and memory tasks in healthy human subjects

Insulin receptors are found throughout the brain, particularly in the hippocampus, although the impact of insulin on memory is unclear. The purpose of this study was to examine the effect of insulin on event-related potentials in response to a standard memory task and visual evoked potentials (VEPs) during exposure to a reversing checkerboard. We hypothesized that insulin would decrease P300 magnitude and latency during the presentation of previously observed stimuli, but would have no effect on VEPs. Sixteen humans participated in two euglycemic clamp studies with somatostatin performed in random order in which serum insulin levels were either suppressed (14 +/- 1 pmol/l) or increased by insulin infusion (433 +/- 40 pmol/l). At steady state, event-related potentials and then VEPs were collected using a 32-electrode cap. The major finding was that the P300 amplitude measured during the identification of an object as old was significantly smaller over parietal regions when insulin was infused than when no insulin was provided. Insulin was without effect on the VEPs. We conclude that insulin has region- and task-specific effects on neuronal activation. While the P300 amplitude measured during the presentation of an old object was reduced during insulin infusion, the hormone was without effect on VEPs.

Bone formation is impaired in a model of type 1 diabetes

The effects of type 1 diabetes on de novo bone formation during tibial distraction osteogenesis (DO) and on intact trabecular and cortical bone were studied using nonobese diabetic (NOD) mice and comparably aged nondiabetic NOD mice. Diabetic mice received treatment with insulin, vehicle, or no treatment during a 14-day DO procedure. Distracted tibiae were analyzed radiographically, histologically, and by microcomputed tomography (microCT). Contralateral tibiae were analyzed using microCT. Serum levels of insulin, osteocalcin, and cross-linked C-telopeptide of type I collagen were measured. Total new bone in the DO gap was reduced histologically (P < or = 0.001) and radiographically (P < or = 0.05) in diabetic mice compared with nondiabetic mice but preserved by insulin treatment. Serum osteocalcin concentrations were also reduced in diabetic mice (P < or = 0.001) and normalized with insulin treatment. Evaluation of the contralateral tibiae by microCT and mechanical testing demonstrated reductions in trabecular bone volume and thickness, cortical thickness, cortical strength, and an increase in endosteal perimeter in diabetic animals, which were prevented by insulin treatment. These studies demonstrate that bone formation during DO is impaired in a model of type 1 diabetes and preserved by systemic insulin administration.

Effect of every other day feeding diet on gene expression in normal and in long-lived Ames dwarf mice

Ames dwarf mutant mice are long-lived, hypoinsulinemic and hypoglycemic and exhibit enhanced sensitivity to injected insulin. Their phenotypic characteristics show many similarities to animals subjected to caloric restriction (CR) but Ames dwarf mice are not CR mimetics. Reducing daily food intake by 30% prolongs longevity in both normal and Ames dwarf mice. In the present study, the animals were subjected to a different type of CR, every other day feeding (EOD). Using real-time PCR, we have examined the expression of genes related to insulin signaling in the liver of normal and dwarf mice after 9 months of EOD. The results indicate that EOD produces some changes in the insulin and IGF1 signaling pathways, and that these changes are consistent with EOD increasing insulin sensitivity.

Optical mapping of propagation changes induced by elevated extracellular potassium ion concentration in genetically altered mouse hearts

Diabetes is associated with high rates of cardiovascular disease and sudden death. Therefore, dissecting specific mechanisms, such as the effects of impaired insulin signaling on cardiac electrophysiology may lead to better diagnosis and treatment. Lack of insulin receptors in mouse myocytes has been shown to reduce repolarizing potassium currents and prolong action potential duration. We hypothesized that these changes would manifest as rate-related effects on electrical propagation in the intact heart. This study employed optical mapping to characterize propagation changes in intact mouse hearts with cardiomyocyte-restricted knock out of insulin receptors (CIRKO).

METHODS

Fluorescent signals emitted from excited Di-4-ANEPPS in isolated Langendorff perfused mouse hearts were recorded from the left ventricular epicardium using an 8 by 8 photo diode array. The study included hearts from 8 CIRKO mice and 8 wild type (WT) littermate controls. Hearts were stimulated from the right atrium or the left ventricle at basic cycle lengths ranging from 160 to 280 ms under normal conditions and then after 5 minutes of perfusion with elevated potassium ion concentration (9.4 mM).

RESULTS

None of the 8 CIRKO hearts maintained regular responses to atrial stimulation at the 160 ms cycle length under normal conditions; however, all of the WT hearts were captured at this rate. Total activation time for a 4 mm by 4 mm area was longer for CIRKO hearts when compared with WT. Average epicardial conduction velocity was slower for the CIRKO when compared to WT. Propagation delay due to the presence of high [K+]e was significant in both CIRKO and WT mice, but significantly longer for the CIRKO hearts.

CONCLUSIONS

These results show that in addition to reducing repolarization currents, impaired myocardial insulin signaling leads to impaired electrical impulse propagation particularly at increased heart rates. These data suggest a link between impaired myocardial insulin signaling and the increased risk of arrhythmia and sudden death in patients with diabetes.

Insulin receptor, insulin receptor substrate-1, Raf-1, and Mek-1 during hormonal hepatocarcinogenesis by intrahepatic pancreatic islet transplantation in diabetic rats

Low-number transplantation of pancreatic islets into the livers of diabetic rats leads to transformation of the downstream liver acini into clear-cell foci of altered hepatocytes (FAHs). These FAHs correspond to the glycogen-storing (clear-cell) phenotype of hepatocellular preneoplasias and develop into hepatocellular adenomas (HCAs) and hepatocellular carcinomas (HCCs) within 6 to 24 months. In addition, they show metabolic alterations that resemble well-known insulin effects, most likely constituting the result of the local hyperinsulinemia. Thus, we investigated FAHs, HCAs, and HCCs for altered expression of insulin receptor, insulin receptor substrate-1 (IRS-1), Raf-1 and Mek-1. Light and electron microscopic immunohistochemistry revealed a translocation of insulin receptor from the plasma membrane (normal tissue) into the cytoplasm in clear-cell FAHs and an increase in insulin receptor expression in HCAs and HCCs. FAHs also showed an increase in IRS-1 gene expression, investigated by in situ hybridization and quantitative reverse transcription-PCR. IRS-1, Raf-1, and Mek-1 proteins were strongly overexpressed in FAHs and tumors, as compared with the unaltered liver tissue. These overexpressions were closely linked to the clear-cell phenotype of preneoplastic and neoplastic hepatocytes, because basophilic FAHs (later stages) and basophilic tumors showed no overexpressions. In this endocrine model of hepatocarcinogenesis, severe alterations of insulin signaling were induced by the pathological local action of islet hormones in the livers and may substantially contribute to the carcinogenic process.

Pinitol supplementation does not affect insulin-mediated glucose metabolism and muscle insulin receptor content and phosphorylation in older humans

This study assessed the effect of oral pinitol supplementation on oral and intravenous glucose tolerances and on skeletal muscle insulin receptor content and phosphorylation in older people. Fifteen people (6 men, 9 women; age 66 +/- 8 y; BMI 27.9 +/- 3.3 kg/m(2); hemoglobin A1c 5.39 +/- 0.46%, mean +/- SD) completed a 7-wk protocol. Subjects were randomly assigned to groups that during wk 2-7 consumed twice daily either a non-nutritive beverage (Placebo group, n = 8) or the same beverage with 1000 mg pinitol dissolved into it (Pinitol group, n = 7, total dose = 2000 mg pinitol/d). Testing was done at wk 1 and wk 7. In the Pinitol group with supplementation, 24-h urinary pinitol excretion increased 17-fold. The fasting concentrations of glucose, insulin, and C-peptide, and the 180-min area under the curve for these compounds, in response to oral (75 g) and intravenous (300 mg/kg) glucose tolerance challenges, were unchanged from wk 1 to wk 7 and were not influenced by pinitol. Also, pinitol did not affect indices of hepatic and whole-body insulin sensitivity from the oral glucose tolerance test and indices of insulin sensitivity, acute insulin response to glucose, and glucose effectiveness from the intravenous glucose tolerance test, estimated using minimal modeling. Pinitol did not differentially affect total insulin receptor content and insulin receptor phosphotyrosine 1158 and insulin receptor phosphotyrosine 1162/1163 activation in vastus lateralis samples taken during an oral-glucose-induced hyperglycemic and hyperinsulinemic state. These data suggest that pinitol supplementation does not influence whole-body insulin-mediated glucose metabolism and muscle insulin receptor content and phosphorylation in nondiabetic, older people.

The insulin resistant subphenotype of polycystic ovary syndrome: clinical parameters and pathogenesis

OBJECTIVE

This study was undertaken to compare clinical and biochemical characteristics of the insulin resistant (IR) and non-IR subphenotypes of polycystic ovary syndrome (PCOS).

STUDY DESIGN

Infertile PCOS women were classified as IR (n=32) or non-IR (n=46) on the basis of fasting glucose and insulin levels. The incidence of acanthosis nigricans (AN), hirsutism, and ovulation in response to clomiphene citrate (CC) was compared between the 2 groups, along with serum levels of gonadotropins, and sex steroids. Blood samples from 28 PCOS patients and 8 controls were analyzed by enzymatic immunoassay for autophosphorylated insulin receptor (APIR) and total insulin receptor (TIR) content.

RESULTS

Insulin resistance was associated with obesity (odds ratio [OR]=3.5, P <.05), AN (OR=6.0, P <.05), hirsutism (OR=3.1, P <.05), and resistance to CC (OR=5.0, P <.05). Mean levels of LH, LH/FSH ratios, and testosterone were lower in women with IR (11.5 +/- 6.8 mIU/mL, 2.0 +/- 1.0, and 56.6 +/- 29.0 ng/dL, respectively) compared with women without IR (15.0 +/- 13.4 mIU/mL, 2.4 +/- 1.5, and 72.5 +/- 29.8 ng/dL, respectively) (P <.05). Mean APIR/TIR ratios in IR women were lower than in non-IR women (P <.05 at 100 nmol/L of insulin) and controls (P <.01 at 1, 10 and 100 nmol/L insulin).

CONCLUSION

Patients with IR are more likely to be obese and have AN, hirsutism, resistance to CC, and lower LH, LH/FSH ratios, and testosterone levels. Furthermore, IR patients appear to have defective autophosphorylation of the insulin receptor, a key element in insulin action, and a possible mechanism for IR in PCOS.

Proreceptor Dimerization Is Required for Insulin Receptor Post-translational Processing

The insulin receptor is a transmembrane protein dimer composed of two alphabeta monomers held together by inter-alpha-chain disulfide bonds. In a previous report we described a monomeric insulin receptor obtained by replacing Cys-524, -682, -683, and -685 with serine. The membrane-bound monomeric insulin receptors could be cross-linked to dimers in the presence of insulin, indicating that although covalent interactions had been abolished, noncovalent dimerization could still occur in the membrane. To eliminate noncovalent dimerization, we replaced all or some of Cys-524, -682, -683, and -685 with arginine or aspartic acid with the expectation that the electrostatic repulsion at these contact sites would prevent noncovalent dimerization. The results indicate that mutant insulin receptors that are able to form covalent dimers are expressed at the wild type level; mutants that can form noncovalent dimers are expressed at half the level of the wild type receptor, whereas insulin receptor mutants that cannot dimerize are expressed at less than 10% of the wild type level. To elucidate the mechanism of the decrease in expression of the mutant insulin receptors, we examined their subcellular localization and biosynthesis. The results suggest that the extent of expression of these mutant receptors is related to their ability to form covalent or noncovalent dimers at the proreceptor stage.

Response of hexokinase enzymes and the insulin system to dietary carbohydrates in the common carp,Cyprinus carpio

The response of the common carp to diets with varying amounts of digestible starch, provided either as pea meal (LP, HP, 30 and 46% peas, respectively) or as cereal (LW, HW, 30 and 46% wheat, respectively), was studied and compared with the response to a carbohydrate-free protein-rich diet (CF). Here we focused on the utilisation of dietary carbohydrates by examining the relationship between dietary starch intake, hepatic hexokinase activities, circulating insulin and muscle insulin receptor system. Plasma glucose concentration and hepatic high Km hexokinase (glucokinase, GK) activity were not affected by the content of digestible starch, but 6 h after feeding enzyme activity was higher in the fish fed carbohydrate diets. Similarly, low Km hexokinase (HK) activity was also higher in the fish 24 h after feeding. Fat gain and protein retention were significantly improved by increased digestible starch intake, especially in the HP group, which in turn, presented the highest plasma insulin levels. Glycogen stores were moderately increased by the ingestion of digestible starch. The number of insulin receptors was greater in the CF group than in fish on carbohydrates, except the HP group. Our results confirmed that the common carp uses dietary carbohydrates efficiently, especially when there are provided by peas. This efficiency might be related to the enhanced response of postprandial insulin observed in the HP group.

Human skeletal muscle cell differentiation is associated with changes in myogenic markers and enhanced insulin-mediated MAPK and PKB phosphorylation

AIM

We hypothesized that myogenic differentiation of HSMC would yield a more insulin responsive phenotype.

METHODS

We assessed expression of several proteins involved in insulin action or myogenesis during differentiation of primary human skeletal muscle cultures (HSMC).

RESULTS

Differentiation increased creatine kinase activity and expression of desmin and myocyte enhancer factor (MEF)2C. No change in expression was observed for big mitogen-activated protein kinase (BMK1/ERK5), MEF2A, insulin receptor (IR), hexokinase II, and IR substrates 1 and 2, while expression of glycogen synthase, extracellular signal-regulated kinase 1 and 2 (ERK1/2 MAP kinase) and the insulin responsive aminopeptidase increased after differentiation. In contrast to protein kinase B (PKB)a, expression of (PKB)b increased, with differentiation. Both basal and insulin-stimulated PI 3-kinase activity increased with differentiation. Insulin-mediated phosphorylation of PKB and ERK1/2 MAP kinase increased after differentiation.

CONCLUSION

Components of the insulin-signalling machinery are expressed in myoblast and myotube HSMC; however, insulin responsiveness to PKB and ERK MAP kinase phosphorylation increases with differentiation.

Expression of insulin-like growth factors (IGF)-1 and -2, IGF-binding proteins-2 and -3, and receptors for growth hormone, IGF type-1 and -2 and insulin in the gastrointestinal tract of neonatal calves

Growth hormone (GH), insulin-like growth factors (IGFs) and insulin influence post-natal gastrointestinal development and function. We have measured by real-time PCR the mRNA levels of IGF-1 and -2, IGF-binding proteins (IGFBPs)-2 and -3, and receptors for GH, IGF type-1 and -2, and insulin in esophagus, rumen, fundus, pylorus, duodenum, jejunum, ileum and colon of calves on days 1 and 5 of life. Levels of mRNA of measured traits were different (P < 0.05) at different gastrointestinal sites. Furthermore, mRNA levels of IGFs, IGFBPs and of receptors for GH and IGF type-1 and -2 and insulin differed (P < 0.05) on days 1 and 5. Differences in mRNA abundance of IGFs, IGFBPs and of receptors for GH, IGFs, and insulin among gastrointestinal sites on days 1 and 5 of life suggest site-specific functional importance and demonstrate that changes are the consequence of ontogenetic development and/or due to feeding.

De novo emergence of growth factor receptors in activated human CD4+ and CD8+ T lymphocytes

Using phytohemagglutinin (PHA)-activated human T lymphocytes, we have demonstrated de novo emergence of growth factor receptors (insulin, insulin-like growth factor-1 [IGF-1], and interleukin-2 [IL-2]) in the CD4(+) and CD8(+) subsets determined by flow cytometry. This activation was also associated with development of insulin-degrading activity (IDA) in a time-dependent fashion. These events, which are actinomycin- and cycloheximide-sensitive, occur only in activated, but not nonactivated, CD4(+) and CD8(+) lymphocytes. The emergence of these receptors, as well as IDA, which is preceded by CD69 emergence, reaches a plateau by 72 hours and is comparable in both subsets. The IDA is localized in the cytosol, and insulin binding is limited to the cell membrane. T-lymphocyte activation also initiates expression of the IL-2 gene with the transcription of IL-2 mRNA, the level of which is further enhanced by 38% with the addition of insulin. In these activated lymphocytes, insulin binding to its receptor also caused an 83% upregulation of phosphorylated insulin receptor substrate-1 (IRS-1). In situ development of these growth factor receptors and signal transduction mechanisms in T lymphocytes upon activation, such as by proinflammatory cytokines or oxidative stress, could be an important defense mechanism in various disease states in man.

Insulin stimulates movement of sorting nexin 9 between cellular compartments: a putative role mediating cell surface receptor expression and insulin action

SNX9 (sorting nexin 9) is one member of a family of proteins implicated in protein trafficking. This family is characterized by a unique PX (Phox homology) domain that includes a proline-rich sequence and an upstream phospholipid binding domain. Many sorting nexins, including SNX9, also have a C-terminal coiled region. SNX9 additionally has an N-terminal SH3 (Src homology 3) domain. Here we have investigated the cellular localization of SNX9 and the potential role it plays in insulin action. SNX9 had a cytosolic and punctate distribution, consistent with endosomal and cytosolic localization, in 3T3L1 adipocytes. It was excluded from the nucleus. The SH3 domain was responsible, at least in part, for the membrane localization of SNX9, since expression of an SH3-domain-deleted GFP (green fluorescent protein)-SNX9 fusion protein in HEK293T cells rendered the protein cytosolic. Membrane localization may also be attributed in part to the PX domain, since in vitro phospholipid binding studies demonstrated SNX9 binding to polyphosphoinositides. Insulin induced movement of SNX9 to membrane fractions from the cytosol. A GST (glutathione S-transferase)-SNX9 fusion protein was associated with IGF1 (insulin-like growth factor 1) and insulin receptors in vitro. A GFP-SNX9 fusion protein, overexpressed in 3T3L1 adipocytes, co-immunoprecipitated with insulin receptors. Furthermore, overexpression of this GFP-SNX9 fusion protein in CHOT cells decreased insulin binding, consistent with a role for SNX9 in the trafficking of insulin receptors. Microinjection of 3T3L1 cells with an antibody against SNX9 inhibited stimulation by insulin of GLUT4 translocation. These results support the involvement of SNX9 in insulin action, via an influence on the processing/trafficking of insulin receptors. A secondary role in regulation of the cellular processing, transport and/or subcellular localization of GLUT4 is also suggested.

Insulin induces cobalt uptake in a subpopulation of rat cultured primary sensory neurons

Previous findings show that both the vanilloid receptor 1 and the insulin receptor are expressed on small primary sensory neurons. As insulin evokes activity in second messengers which could induce opening of the vanilloid receptor 1, we examined, by using the cobalt-uptake technique, whether or not insulin can activate cultured rat primary sensory neurons through activating the vanilloid receptor 1. Capsaicin (50, 100 and 500 nm) induced concentration-dependent labelling in primary sensory neurons. Preincubation of cells in insulin (10 micromoles) for 10 min followed by a 2-min wash did not produce significant change in the capsaicin-induced labelling. Coapplication of insulin (10 micromoles) with capsaicin, however, potentiated the 50 and 100 nm capsaicin-evoked staining. Insulin itself also produced cobalt labelling in a concentration-dependent manner. The size-frequency distributions of neurons showing capsaicin- or insulin-induced cobalt accumulation were similar. The insulin-induced cobalt labelling was significantly reduced by the tyrosine kinase inhibitor, tyrphostin AG1024, the vanilloid receptor 1 antagonists, ruthenium red and capsazepine, the protein kinase inhibitor, staurosporine and the phospholipase C inhibitor neomycin. Double immunostaining of cultured primary sensory neurons and sections from dorsal root ganglia revealed that about one-third of the cells coexpress the insulin receptor and vanilloid receptor 1. These findings suggest that insulin activates a subpopulation of primary sensory neurons, probably through phosphorylation- and/or phosphatidylinositol(4,5)biphosphate hydrolysis-evoked activation of the vanilloid receptor 1. Although the insulin-induced activation of vanilloid receptor 1 seems to be a short-lived effect in vitro, in vivo it might play a role in the development of burning pain sensation in hyperinsulinism.

Between-gel reproducibility of the human cerebrospinal fluid proteome

This manuscript describes the between-gel reproducibility of the two-dimensional gel electrophoresis analysis of the human lumbar cerebrospinal fluid (CSF) proteome. This reproducibility study is a necessary component for our long-term research program that uses comparative proteomics to analyze lumbar CSF samples in a study of human idiopathic low back pain. A Protein-Plus Dodeca Cell electrophoresis apparatus and PDQuest software were used to measure the level of between-gel reproducibility of the CSF proteome. One pooled CSF sample was used to evaluate the level of within-sample, between-gel reproducibility, and a set of seven different CSF samples (CSF-1 to 7) was used to test the level of within-group and between-group variability. Differentially expressed proteins (six CSF samples versus the designated control, CSF-3) were characterized with mass spectrometry. The number of spots found in the pooled CSF sample was 490 +/- 30 (n = 10 gels); the percentage of protein spots found in those 10 gels was 92 +/- 6%, with a coefficient of variation of 6%; and a positive coefficient of correlation (r = 0.82) was found. In order to test the proof-of-principle, that set of seven CSF samples served as a test of our ability to perform reproducibility comparative proteomics, and to detect differentially expressed proteins within that set of test samples. One sample (CSF-3) served as the control for the other six to locate the differentially expressed proteins. A comparison of fifteen differentially expressed proteins found in that set of test CSF samples correlated with pathology. Matrix-assisted laser desorption/ionization-time-of-flight and electrospray ionization quadrupole ion trap mass spectrometry were used to characterize thirteen of those fifteen differentially expressed proteins. These results (reproducibility, protein characterization, set of test samples, and proof-of-principle) suggest that the analysis of human CSF two-dimensional gels can achieve a high level of within-sample and between-sample reproducibility, and that PDQuest software can measure the relative protein abundance in the human CSF proteome.

Abundance of message for insulin-like growth factors-I and -II and for receptors for growth hormone, insulin-like growth factors-I and -II, and insulin in the intestine and liver of pre- and full-term calves

The somatotropic axis and insulin are involved in pre- and postnatal development. In pre- and full-term calves (GrP0 and GrN0; born after 277 and 290 d of pregnancy, respectively) and in preterm calves on d 8 of life after being fed for 7 d (GrP8), we studied whether there are differences in the abundance of messenger RNA (mRNA) of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II, and insulin among different intestinal sites (duodenum, jejunum, ileum, and colon) and whether there are ontogenetic differences during the perinatal period in intestine and liver. Intestinal site differences (P < 0.05) existed in mRNA levels of IGF-I and IGF-II and receptors for GH, IGF-I, IGF-II, and insulin. Abundance of mRNA of IGF-I and -II and of receptors for IGF-I and GH was highest (P < 0.05) in the colon, abundance of the receptor for IGF-II was comparably high in the colon and ileum, and that of the receptor for insulin was similarly high in colon, ileum, and jejunum. Among GrP0, GrN0, and GrP8 groups, there were differences (P < 0.05) in mRNA levels of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II and insulin. Abundance of mRNA of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II and insulin was highest (P < 0.05) in GrP0 calves immediately after birth and was primarily seen in the ileum. In liver, the mRNA levels differed (P < 0.05) among groups for IGF-II and receptors for IGF-I, IGF-II, and insulin, and were highest (P < 0.05) for IGF-II in GrP0, for receptors of IGF-I in GrN0, and were higher (P < 0.05) in GrP0 than GrP8 for receptors of IGF-II. In conclusion, mRNA levels of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II, and insulin were different at different intestinal sites and in intestine and liver and changed during the perinatal period.

Increased hepatic insulin sensitivity together with decreased hepatic triglyceride stores in hormone-sensitive lipase-deficient mice

Hormone-sensitive lipase (HSL) is a major enzyme for triglyceride (TG) lipolysis in adipose tissue. In HSL-knockout mice, plasma free fatty acid and TG levels are low, associated with low liver TG content. Because a decreased hepatic insulin sensitivity has been reported to be associated with high liver TG levels, our aim was to determine whether a hepatic TG content lower than normal, as observed in HSL-knockout mice, leads to increased hepatic insulin sensitivity. Therefore, hyperinsulinemic clamp experiments in combination with D-(3)H-glucose were used. Furthermore, hepatic insulin receptor and phosphorylated protein kinase B (PKB-P)/akt were analyzed by Western blotting. No significant differences where observed in insulin-mediated whole-body glucose uptake between HSL-knockout and control mice. Interestingly, hepatic insulin sensitivity of HSL-knockout mice was increased, because insulin caused a greater reduction in endogenous glucose production ( approximately 71% compared with approximately 31% in control mice; P < 0.05), despite decreased plasma adiponectin levels. PKB/akt phosphorylation and phosphatidylinositol-3-kinase activity was significantly higher in livers of HSL-knockout mice after insulin stimulation. In HSL-knockout mice, reduced hepatic TG stores result in an increased suppressive effect of insulin on hepatic glucose production, in line with an increased hepatic PKB-P/akt and phosphatidylinositol-3 kinase activity. Thus, hepatic insulin sensitivity is indeed increased after reducing hepatic TG stores below normal.

Insulin signaling through insulin receptor substrate 1 and 2 in normal liver development

BACKGROUND & AIMS

The insulin growth factor signal transduction pathway is an important regulator of adult hepatocyte proliferation. The purpose of this study was to determine the roles of the insulin receptor substrate (IRS-1 and IRS-2)-mediated growth cascades in rapidly growing fetal rat liver.

METHODS

We determined the expression and tyrosyl phosphorylation of the insulin receptor beta subunit (IRbeta), IRS-1 and IRS-2, the binding of phosphatidylinositol 3-kinase (PI3K), and activation of the mitogen-activated protein kinase (MAPK) pathway in the presence or absence of insulin stimulation in vivo during development and in the adult liver. In addition, activation of other downstream components including PI3K, Akt, GSK3beta, Bad, and p70S6 kinase was studied.

RESULTS

We observed reduced expression and tyrosyl phosphorylation of IRS-1 in the fetal liver compared with the adult liver. These developmental changes resulted in a lack of sensitivity to insulin stimulation and subsequent downstream activation of the PI3K and MAPK cascades until the postneonatal period. In contrast, there was a high level of IRS-2 expression and insulin-stimulated tyrosyl phosphorylation as early as embryonic day 15 with robust PI3K binding and activation, which may enhance hepatocyte survival during the rapid growth phase of the liver.

CONCLUSIONS

The IRS-1 signal transduction pathway does not play a major role in fetal liver growth because IRS-2 functions as the major insulin responsive molecule in early development. However, insulin-mediated IRS-1/MAPK cascade activation contributes to growth in the adult.

Chronic hyperglycemia impairs insulin secretion by affecting insulin receptor expression, splicing, and signaling in RIN beta cell line and human islets of Langerhans

Recent evidence suggests that insulin signaling through the insulin receptor A type (Ex11-), regulates insulin gene transcription. Because chronic hyperglycemia negatively affects insulin receptor function and regulates alternative splicing of the insulin receptor, we inquired whether chronic exposure of pancreatic beta-cells to high glucose results in alterations in insulin signaling due to changes in insulin receptor expression and relative abundance of its spliced isoforms. Our results demonstrate that the insulin receptor is localized in insulin secretory vescicles in human pancreatic beta-cells. Furthermore, we find that alterations in insulin expression and secretion caused by chronic exposure to high glucose are paralleled by decreased insulin receptor expression and increased relative abundance of the Ex11+ isoform in both human islets and RIN beta-cells. PDX-1 and HMGI(Y) transcription factors are down-regulated by high glucose. These changes are associated with defects in insulin signaling involving insulin receptor-associated PI 3-kinase/Akt/PHAS-I pathway in RIN beta-cells. Re-expression in RIN beta-cells chronically exposed to high glucose of the Ex11-, but not the Ex11+, isoform restored insulin mRNA expression. These data suggest that changes in early steps of insulin receptor signaling may play a role in determining beta-cell dysfunction caused by chronic hyperglycemia.