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Nonalcoholic fatty liver disease (NAFLD) and impaired glycemic control are closely linked; however, the pathophysiological mechanisms underpinning this bidirectional relationship remain unresolved. The high secretory capacity of the liver and impairments in protein secretion in NAFLD suggest that endocrine changes in the liver are likely to contribute to glycemic defects. We identify hexosaminidase A (HEXA) as an NAFLD-induced hepatokine in both mice and humans. HEXA regulates sphingolipid metabolism, converting GM2 to GM3 gangliosides—sphingolipids that are primarily localized to cell-surface lipid rafts. Using recombinant murine HEXA protein, an enzymatically inactive HEXA(R178H) mutant, or adeno-associated virus vectors to induce hepatocyte-specific overexpression of HEXA, we show that HEXA improves blood glucose control by increasing skeletal muscle glucose uptake in mouse models of insulin resistance and type 2 diabetes, with these effects being dependent on HEXA's enzymatic action. Mechanistically, HEXA remodels muscle lipid raft ganglioside composition, thereby increasing IGF-1 signaling and GLUT4 localization to the cell surface. Disrupting lipid rafts reverses these HEXA-mediated effects. In this study, we identify a pathway for intertissue communication between liver and skeletal muscle in the regulation of systemic glycemic control. [ABSTRACT FROM AUTHOR]

The article presents the discussion on sphingolipids, including ceramide, glucosylceramide, and gangliosides gaining traction as cell-autonomous inducers of insulin resistance. Topics include working as a hepatokine to restructure signaling platforms within detergent-resistant lipid domains in muscle; and GM3 gangliosides have all shown glycemic benefit in mouse models of obesity and diabetes.

Insulin-like growth factors (IGFs), specifically IGF1 and IGF2, promote glucose metabolism, with their availability regulated by IGF-binding proteins (IGFBPs). We hypothesized that IGF1 and IGF2 levels, or their bioavailability, are reduced during type 1 diabetes development. Total serum IGF1, IGF2, and IGFBP1-7 levels were measured in an age-matched, cross-sectional cohort at varying stages of progression to type 1 diabetes. IGF1 and IGF2 levels were significantly lower in autoantibody (AAb)+ compared with AAb- relatives of subjects with type 1 diabetes. Most high-affinity IGFBPs were unchanged in individuals with pre-type 1 diabetes, suggesting that total IGF levels may reflect bioactivity. We also measured serum IGFs from a cohort of fasted subjects with type 1 diabetes. IGF1 levels significantly decreased with disease duration, in parallel with declining β-cell function. Additionally, plasma IGF levels were assessed in an AAb+ cohort monthly for a year. IGF1 and IGF2 showed longitudinal stability in single AAb+ subjects, but IGF1 levels decreased over time in subjects with multiple AAb and those who progressed to type 1 diabetes, particularly postdiagnosis. In sum, IGFs are dysregulated both before and after the clinical diagnosis of type 1 diabetes and may serve as novel biomarkers to improve disease prediction. [ABSTRACT FROM AUTHOR]

Although endoplasmic reticulum (ER) chaperone binding to mutant proinsulin has been reported, the role of protein chaperones in the handling of wild-type proinsulin is underinvestigated. Here, we have explored the importance of glucose-regulated protein 94 (GRP94), a prominent ER chaperone known to fold insulin-like growth factors, in proinsulin handling within β-cells. We found that GRP94 coimmunoprecipitated with proinsulin and that inhibition of GRP94 function and/or expression reduced glucose-dependent insulin secretion, shortened proinsulin half-life, and lowered intracellular proinsulin and insulin levels. This phenotype was accompanied by post-ER proinsulin misprocessing and higher numbers of enlarged insulin granules that contained amorphic material with reduced immunogold staining for mature insulin. Insulin granule exocytosis was accelerated twofold, but the secreted insulin had diminished bioactivity. Moreover, GRP94 knockdown or knockout in β-cells selectively activated protein kinase R-like endoplasmic reticulum kinase (PERK), without increasing apoptosis levels. Finally, GRP94 mRNA was overexpressed in islets from patients with type 2 diabetes. We conclude that GRP94 is a chaperone crucial for proinsulin handling and insulin secretion. [ABSTRACT FROM AUTHOR]

Type 2 diabetes (T2D) affects more than 415 million people worldwide, and its costs to the health care system continue to rise. To identify common or rare genetic variation with potential therapeutic implications for T2D, we analyzed and replicated genome-wide protein coding variation in a total of 8,227 individuals with T2D and 12,966 individuals without T2D of Latino descent. We identified a novel genetic variant in the IGF2 gene associated with ∼20% reduced risk for T2D. This variant, which has an allele frequency of 17% in the Mexican population but is rare in Europe, prevents splicing between IGF2 exons 1 and 2. We show in vitro and in human liver and adipose tissue that the variant is associated with a specific, allele-dosage-dependent reduction in the expression of IGF2 isoform 2. In individuals who do not carry the protective allele, expression of IGF2 isoform 2 in adipose is positively correlated with both incidence of T2D and increased plasma glycated hemoglobin in individuals without T2D, providing support that the protective effects are mediated by reductions in IGF2 isoform 2. Broad phenotypic examination of carriers of the protective variant revealed no association with other disease states or impaired reproductive health. These findings suggest that reducing IGF2 isoform 2 expression in relevant tissues has potential as a new therapeutic strategy for T2D, even beyond the Latin American population, with no major adverse effects on health or reproduction. [ABSTRACT FROM AUTHOR]

Brain activity requires a flux of glucose to active regions to sustain increased metabolic demands. Insulin, the main regulator of glucose handling in the body, has been traditionally considered not to intervene in this process. However, we now report that insulin modulates brain glucose metabolism by acting on astrocytes in concert with IGF-I. The cooperation of insulin and IGF-I is needed to recover neuronal activity after hypoglycemia. Analysis of underlying mechanisms show that the combined action of IGF-I and insulin synergistically stimulates a mitogen-activated protein kinase/protein kinase D pathway resulting in translocation of GLUT1 to the cell membrane through multiple protein-protein interactions involving the scaffolding protein GAIP-interacting protein C terminus and the GTPase RAC1. Our observations identify insulin-like peptides as physiological modulators of brain glucose handling, providing further support to consider the brain as a target organ in diabetes. [ABSTRACT FROM AUTHOR]

The insulin-like growth factor (IGF) axis may be implicated in glucose homeostasis, but its longitudinal profile across gestation in relation to the development of gestational diabetes mellitus (GDM) is largely unknown. We prospectively investigated IGF axis biomarkers in early-to-midpregnancy in relation to subsequent GDM risk in a case-control study of 107 case subjects with GDM and 214 control subjects without GDM, with blood sample collection at gestational weeks 10-14, 15-26, 23-31, and 33-39. Conditional logistic regression was used, adjusting for major risk factors including prepregnancy BMI. Plasma IGF-I and IGF binding protein 3 (IGFBP-3) concentrations and molar ratio of IGF-I to IGFBP-3 increased, whereas IGFBP-2 decreased throughout pregnancy. At gestational weeks 10-14, both IGF-I and IGF-I/IGFBP-3 were positively associated with GDM risk; adjusted odds ratio (OR) comparing the highest versus lowest quartile (ORQ4-Q1) was 2.93 (95% CI 1.18, 7.30) for IGF-I and 3.31 (1.10, 9.98) for IGF-I/IGFBP-3. In contrast, higher IGFBP-2 levels were related to a substantially lower risk of GDM (ORQ4-Q1 0.04 [0.01, 0.06]). Similar results were observed at gestational weeks 15-26. In sum, the IGF axis, IGFBP-2 in particular, may be implicated in the pathogenesis of GDM, with significant associations and incremental predictive value detected as early as gestational weeks 10-14, ∼10-18 weeks earlier before GDM is typically screened for. [ABSTRACT FROM AUTHOR]

Ectopic lipid accumulation in the liver is an almost universal feature of human and rodent models of generalized lipodystrophy and is also a common feature of type 2 diabetes, obesity, and metabolic syndrome. Here we explore the progression of fatty liver disease using a mouse model of lipodystrophy created by a fat-specific knockout of the insulin receptor (F-IRKO) or both IR and insulin-like growth factor 1 receptor (F-IR/IGFRKO). These mice develop severe lipodystrophy, diabetes, hyperlipidemia, and fatty liver disease within the first weeks of life. By 12 weeks of age, liver demonstrated increased reactive oxygen species, lipid peroxidation, histological evidence of balloon degeneration, and elevated serum alanine aminotransferase and aspartate aminotransferase levels. In these lipodystrophic mice, stored liver lipids can be used for energy production, as indicated by a marked decrease in liver weight with fasting and increased liver fibroblast growth factor 21 expression and intact ketogenesis. By 52 weeks of age, liver accounted for 25% of body weight and showed continued balloon degeneration in addition to inflammation, fibrosis, and highly dysplastic liver nodules. Progression of liver disease was associated with improvement in blood glucose levels, with evidence of altered expression of gluconeogenic and glycolytic enzymes. However, these mice were able to mobilize stored glycogen in response to glucagon. Feeding F-IRKO and F-IR/IGFRKO mice a high-fat diet for 12 weeks accelerated the liver injury and normalization of blood glucose levels. Thus, severe fatty liver disease develops early in lipodystrophic mice and progresses to advanced nonalcoholic steatohepatitis with highly dysplastic liver nodules. The liver injury is propagated by lipotoxicity and is associated with improved blood glucose levels. [ABSTRACT FROM AUTHOR]

The article presents abstracts on medical topics, which include such studies as the association of genetic determinants of fasting glucose and insulin with other metabolic traits in African-American glucose and insulin genetic epidemiology (AAGILE), the genome-wide association studies of renal diabetes complications in patients with type 2 diabetes, and the link of the genetic variant (R27S) in insulin-like peptide 5 with increased insulin sensitivity.

The author discusses the study on the longitudinal characterization of insulin-like growth factor (IGF) across pregnancy in women with and without gestational diabetes mellitus (GDM). He mentions the importance of the study given the pathophysiologic and clinical relationship between GDM and type 2 diabetes (T2D). He also notes the feature of the study which he deemed as not valuable regarding the measurement of multiple elements of the IGF axis across trimesters.

IGF-1 and insulin promote β-cell expansion by inhibiting β-cell death and stimulating β-cell proliferation, and the phosphatidylinositol (PI) 3-kinase/Akt pathway mediates insulin and IGF-1 action. Impaired β-cell expansion is a risk factor for type 2 diabetes. Here, we identified SH2B1, which is highly expressed in β-cells, as a novel regulator of β-cell expansion. Silencing of SH2B1 in INS-1 832/13 β-cells attenuated insulin- and IGF-1--stimulated activation of the PI 3-kinase/Akt pathway and increased streptozotocin (STZ)-induced apoptosis; conversely, overexpression of SH2B1 had the opposite effects. Activation of the PI 3-kinase/Akt pathway in β-cells was impaired in pancreas-specific SH2B1 knockout (PKO) mice fed a high-fat diet (HFD). HFDfed PKO mice also had increased β-cell apoptosis, decreased β-cell proliferation, decreased β-cell mass, decreased pancreatic insulin content, impaired insulin secretion, and exacerbated glucose intolerance. Furthermore, PKO mice were more susceptible to STZ-induced β-cell destruction, insulin deficiency, and hyperglycemia. These data indicate that SH2B1 in β-cells is an important prosurvival and proproliferative protein and promotes compensatory β-cell expansion in the insulin-resistant state and in response to β-cell stress. [ABSTRACT FROM AUTHOR]

Aging is characterized by a deterioration in the maintenance of homeostatic processes over time, leading to functional decline and increased risk for disease and death. The aging process is characterized metabolically by insulin resistance, changes in body composition, and physiological declines in growth hormone (GH), insulin-like growth factor-1 (IGF-1), and sex steroids. Some interventions designed to address features of aging, such as caloric restriction or visceral fat depletion, have succeeded in improving insulin action and life span in rodents. Meanwhile, pharmacologic interventions and hormonal perturbations have increased the life span of several mammalian species without necessarily addressing features of age-related metabolic decline. These interventions include inhibition of the mammalian target of rapamycin and lifetime deficiency in GH/IGF-1 signaling. However, strategies to treat aging in humans, such as hormone replacement, have mostly failed to achieve their desired response. We will briefly discuss recent advances in our understanding of the complex role of metabolic pathways in the aging process and highlight important paradoxes that have emerged from these discoveries. Although life span has been the major outcome of interest in the laboratory, a special focus is made in this study on healthspan, as improved quality of life is the goal when translated to humans [ABSTRACT FROM AUTHOR]

OBJECTIVE--In mice, haploinsufficiency of the IGF-1 receptor (IGF-1R+/-), at a wholebody level, increases resistance to inflammation and oxidative stress, but the underlying mechanisms are unclear. We hypothesized that by forming insulin-resistant heterodimers composed of one IGF-1Rαβ and one insulin receptor (IR), IRαβ complex in endothelial cells (ECs), IGF-1R reduces free IR, which reduces EC insulin sensitivity and generation of the antioxidant/anti-inflammatory signaling radical nitric oxide (NO). RESEARCH DESIGN AND METHODS--Using a number of complementary gene-modified mice with reduced IGF-1R at a whole-body level and specifically in EC, and complementary studies in EC in vitro, we examined the effect of changing IGF-1R/IR stoichiometry on EC insulin sensitivity and NO bioavailability. RESULTS--IGF-1R+/- mice had enhanced insulin-mediated glucose lowering. Aortas from these mice were hypocontractile to phenylephrine (PE) and had increased basal NO generation and augmented insulin-mediated NO release from EC. To dissect EC from whole-body effects we generated mice with EC-specific knockdown of IGF-1R. Aortas from these mice were also hypo-contractile to PE and had increased basal NO generation. Whole-body and EC deletion of IGF-1R reduced hybrid receptor formation. By reducing IGF-1R in IR-haploinsufficient mice we reduced hybrid formation, restored insulin-mediated vasorelaxation in aorta, and insulin stimulated NO release in EC. Complementary studies in human umbilical vein EC in which IGF-1R was reduced using siRNA confirmed that reducing IGF-1R has favorable effects on NO bioavailability and EC insulin sensitivity. CONCLUSIONS--These data demonstrate that IGF-1R is a critical negative regulator of insulin sensitivity and NO bioavailability in the endothelium. [ABSTRACT FROM AUTHOR]

OBJECTIVE--To understand the relationships between maternal glycemia during pregnancy and prenatal and early postnatal growth by evaluating cord C-peptide and IGF-I as mediating biomarkers in boys and girls separately. RESEARCH DESIGN AND METHODS--We evaluated 342 neonates within the EDEN mother-child cohort study born to mothers without diabetes diagnosis before pregnancy. We measured maternal glycemia at 24-28 weeks of gestation and neonates' cord blood C-peptide (used as a proxy for fetal insulin) and IGF-I at birth. Reported maternal prepregnancy BMI and all measured infant weights and lengths in the 1st year were recorded. Growth modeling was used to obtain an individual growth curve for each infant in the 1st year. Path models, a type of structural equation modeling, were used for statistical analysis. Path analysis is a multivariate method associated with a graphical display that allows evaluation of mediating factors and distinguishes direct, indirect, and total effects. RESULTS--Cord C-peptide at birth was positively correlated with maternal prepregnancy BMI and maternal glycemia and was higher in girls. In a path model that represented prenatal growth, there was no significant direct effect of maternal glycemia on birth weight, but the effect of maternal glycemia on birth weight was mediated by fetal insulin and IGF-I in both girls and boys. However, in girls only, higher concentrations of cord C-peptide (but not cord IGF-I or maternal glucose) were associated with slower weight growth in the first 3 months of life. CONCLUSIONS--Our study underlines the role of the fetal insulin-IGF-I axis in the relationship between maternal glycemia during pregnancy and birth weight. We also show for the first time that high insulin concentration in female fetuses is associated with slower early postnatal growth. This slow, early growth pattern may be programmed by fetal hyperinsulinemia, and girls may be more susceptible than boys to its consequences. [ABSTRACT FROM AUTHOR]

OBJECTIVE--Compelling epidemiological and clinical evidence has identified a specific cardiomyopathy in diabetes, characterized by early diastolic dysfunction and adverse structural remodeling. Activation of the insulin-like growth factor 1 (IGF-1) receptor (IGF-1R) promotes physiological cardiac growth and enhances contractile function. The aim of the present study was to examine whether cardiac-specific overexpression of IGF-1R prevents diabetes-induced myocardial remodeling and dysfunction associated with a murine model of diabetes. RESEARCH DESIGN AND METHODS--Type 1 diabetes was induced in 7-week-old male IGF-1R transgenic mice using streptozotocin and followed for 8 weeks. Diastolic and systolic function was assessed using Doppler and M-mode echocardiography, respectively, in addition to cardiac catheterization. Cardiac fibrosis and cardiomyocyte width, heart weight index, gene expression, Akt activity, and IGF-1R protein content were also assessed. RESULTS--Nontransgenic (Ntg) diabetic mice had reduced initial (E)-to-second (A) blood flow velocity ratio (E:A ratio) and prolonged deceleration times on Doppler echocardiography compared with nondiabetic counterparts, indicative markers of diastolic dysfunction. Diabetes also increased cardiomyocyte width, collagen deposition, and prohypertrophic and profibrotic gene expression compared with Ntg nondiabetic littermates. Overexpression of the IGF-1R transgene markedly reduced collagen deposition, accompanied by a reduction in the incidence of diastolic dysfunction. Akt phosphorylation was elevated = 15-fold in IGF-1R nondiabetic mice compared with Ntg, and this was maintained in a setting of diabetes. CONCLUSIONS--The current study suggests that cardiac overexpression of IGF-1R prevented diabetes-induced cardiac fibrosis and diastolic dysfunction. Targeting IGF-1R-Akt signaling may represent a therapeutic target for the treatment of diabetic cardiac disease. Diabetes 59:1512-1520, 2010 [ABSTRACT FROM AUTHOR]

OBJECTIVE--There is a complex relationship between IGF-I, IGF binding proteins, growth hormone, and insulin. The IGF-I kinase receptor activation assay (KIRA) is a novel method for measuring IGF-I bioactivity in human serum. We speculated that determination of IGF-I bioactivity might broaden our understanding of the IGF-I system in subjects with the metabolic syndrome. The purpose of our study was to investigate whether IGF-I bioactivity was related to insulin sensitivity and the metabolic syndrome. RESEARCH DESIGN AND METHODS--We conducted a cross-sectional study embedded in a random sample (1,036 elderly subjects) of a prospective population-based cohort study. IGF-I bioactivity was determined by the IGF-I KIRA. Categories of glucose (in)tolerance were defined by the 2003 American Diabetes Association criteria. Insulin sensitivity was assessed by homeostasis model assessment. The Adult Treatment Panel III definition of the metabolic syndrome was used. RESULTS--In subjects with normal fasting glucose and impaired fasting glucose, IGF-I bioactivity progressively increased with increasing insulin resistance, peaked at fasting glucose levels just below 7.0 mmol/l, and dropped at higher glucose levels. Mean IGF-I bioactivity peaked when three criteria of the metabolic syndrome were present and then declined significantly when five criteria of the metabolic syndrome were present. CONCLUSIONS--We observed that IGF-I bioactivity was related to insulin sensitivity, insulin levels, and the metabolic syndrome. Our study suggests that there exists an inverse U-shaped relationship between IGF-I bioactivity and number of components of the metabolic syndrome. This observation contrasts with previous results reporting an inverse relationship between total IGF-I and components of the metabolic syndrome. Diabetes 59:505-508, 2010 [ABSTRACT FROM AUTHOR]

OBJECTIVE--Alteration of placental structure may influence fetal overgrowth and complications of maternal diabetes. We examined the placenta in a cohort of offspring of mothers with type 1 diabetes (OT1DM) to assess structural changes and determine whether these were related to maternal A1C, fetal hematocrit, fetal hormonal, or metabolic axes. RESEARCH DESIGN AND METHODS--Placental samples were analyzed using stereological techniques to quantify volumes and surface areas of key placental components in 88 OT1DM and 39 control subjects, and results related to maternal A1C and umbilical cord analytes (insulin, leptin, adiponectin, IGF-I, hematocrit, lipids, C-reactive protein, and interleukin-6). RESULTS--Intervillous space volume was increased in OT1DM (OT1DM 250 ± 81 cm³ vs. control 217 ± 65 cm³ P = 0.02) with anisomorphic growth of villi (P = 0.025). The placentas showed a trend to increased weight (OT1DM 690 ± 19 g; control 641 ± 22 g; P = 0.08), but villous, nonparenchymal, trophoblast, and capillary volumes did not differ. Villous surface area, capillary surface area, membrane thickness, and calculated morphometric diffusing capacity were also similar in type 1 diabetic and control subjects. A1C at 26-34 weeks associated with birth weight (r = 0.27, P = 0.03), placental weight (r = 0.41, P = 0.0009), and intervillous space volume (r = 0.38, P = 0.0024). In multivariate analysis of cord parameters in OT1DM, fetal IGF-I emerged as a significant correlate of most components (intervillous space, villous, trophoblast, and capillary volumes, all P < 0.01). By contrast, fetal insulin was only independently associated with capillary surface area (positive, r² = 6.7%; P = 0.02). CONCLUSIONS--There are minimal placental structural differences between OT1DM and control subjects. Fetal IGF-I but not fetal insulin emerges as a key correlate of placental substructural volumes, thereby facilitating feedback to the placenta regarding fetal metabolic demand. Diabetes 58:2634-2641, 2009 [ABSTRACT FROM AUTHOR]

OBJECTIVE--The gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect β-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect. RESEARCH DESIGN AND METHODS--We performed comparative transcriptomic analysis of islets from control and GipR[sup -/-],Glp-1-R[sup -/-] mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis. RESULTS--We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1-induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary β-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis. CONCLUSIONS--An IGF-2/IGF-1 receptor autocrine loop operates in β-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1-induced protection against apoptosis. These findings may lead to novel ways of preventing β-cell loss in the pathogenesis of diabetes. Diabetes 58:1816-1825, 2009 [ABSTRACT FROM AUTHOR]

OBJECTIVE--Smooth muscle cell (SMC) maintained in medium containing normal levels of glucose do not proliferate in response to IGF-I, whereas cells maintained in medium containing 25 mmol/l glucose can respond. The aim of this study was to determine whether signaling events that have been shown to be required for stimulation of SMC growth were regulated by glucose concentrations in vivo. RESEARCH DESIGN AND METHODS--We compared IGF-I-stimulated signaling events and growth in the aortic smooth muscle cells from normal and hyperglycemic mice. RESULTS--We determined that, in mice, hyperglycemia was associated with an increase in formation of the integrin-associated protein (IAP)/Src homology 2 domaine containing tyrosine phosphatase substrate 1 (SHPS-1) complex. There was a corresponding increase in Shc recruitment to SHPS-1 and Shc phosphorylation in response to IGF-I. There was also an increase in mitogen-activated protein kinase activation and SMC proliferation. The increase in IAP association with SHPS-1 in hyperglycemia appeared to be due to the protection of IAP from cleavage that occurred during exposure to normal glucose. In addition, we demonstrated that the protease responsible for IAP cleavage was matrix metalloprotease-2. An anti-IAP antibody that disrupted the IAP-SHPS-1 association resulted in complete inhibition of IGF-I-stimulated proliferation. CONCLUSIONS--Taken together, our results support a model in which hyperglycemia is associated with a reduction in IAP cleavage, thus allowing the formation of the IAP-SHPS-1 signaling complex that is required for IGF-I-stimulated proliferation of SMC. Diabetes 57:2637-2643, 2008 [ABSTRACT FROM AUTHOR]

OBJECTIVE--IGF-1 and the IGF-1 receptor (IGF-1R) have been implicated in the regulation of adipocyte differentiation and lipid accumulation in vitro. RESEARCH DESIGN AND METHODS--To investigate the role of IGF-1 receptor in vivo, we have inactivated the Igf-1r gene in adipose tissue (IGF-1R[sup aP2Cre] mice) using conditional gene targeting strategies. RESULTS--Conditional IGF-1R inactivation resulted in increased adipose tissue mass with a predominantly increased lipid accumulation in epigonadal fat pads. However, insulin-stimulated glucose uptake into adipocytes was unaffected by the deletion of the IGF-1R. Surprisingly, IGF-1R[sup aP2Cre] mice exhibited markedly increased somatic growth in the presence of elevated IGF-1 serum concentrations, and IGF-1 mRNA expression was significantly increased in liver and adipose tissue. IGF-1 stimulation of wild-type adipocytes significantly decreased IGF-1 mRNA expression, whereas the opposite effect was observed in IGF-1R deficient adipocytes. CONCLUSIONS--IGF-1R signaling in adipocytes does not appear to be crucial for the development and differentiation of adipose tissue in vivo, but we identified a negative IGF-1R-mediated feedback mechanism of IGF-1 on its own gene expression in adipocytes, indicating an unexpected role for adipose tissue IGF-1 signaling in the regulation of IGF-1 serum concentrations in control of somatic growth. Diabetes 57:2074-2082, 2008 [ABSTRACT FROM AUTHOR]

OBJECTIVE Offspring of mothers with type 1 diabetes (OT1DM) demonstrate increased fat deposition, hyperinsulinemia, and hyperleptinemia in utero. We examined the influence of maternal diabetes on cord lipids at birth and relationship to body composition, cord insulin, leptin, and other hormonal measures. RESEARCH DESIGN AND METHODS We performed an observational study measuring fetal, HDL, and LDL cholesterol; triglycerides; and nonesterified fatty acids (NEFAs) in a total of 139 OT1DM and 48 control subjects at birth and assessed cross-sectional relationships with birth weight, fetal insulin, leptin, adiponectin, and IGF-1. RESULTS Concentrations of total cholesterol (male OT1DM [mean ± SD] 1.49 ± 0.45 mmol/l and male control subjects 1.74 ± 0.33 mmol/l; P < 0.001), HDL cholesterol (0.53 ± 0.21 and 0.74 ± 0.19 mmol/l, respectively; P < 0.001), and NEFA (median 0.17 [interquartile range 2.30-2.95] and 0.21 [0.18-0.36], respectively; P < 0.001) were significantly lower in male OT1DM, with no significant differences in female subjects. Differences in male subjects were independent of mode of delivery. Cord lipids were unrelated to birth weight in OT1DM and did not show consistent relationships with fetal insulin. Unexpectedly, IGF-1 was a strong correlate of HDL cholesterol in control subjects (r = 0.40, P = 0.002) and OT1DM (r = 0.32, P < 0.001) but a negative correlate of triglycerides in control subjects (r = -0.48, P < 0.001) and OT1DM (r = -0.21, P = 0.004), with these relationships present in both sexes. In OT1DM, leptin was also independently correlated (negatively, P < 0.001) with HDL cholesterol in male and female subjects. CONCLUSIONS Maternal diabetes is associated with significant alterations in lipid levels in male fetuses. IGF-1, leptin, and male sex rather than insulin may be the major determinants of HDL cholesterol and triglycerides in utero. Diabetes 56:2705-2709, 2007 [ABSTRACT FROM AUTHOR]

Women with polycystic ovarian syndrome are at increased risk of miscarriage. Although evidence exists that metformin reduces this risk, the mechanism is unknown. This study tests the hypothesis that AMP kinase (AMPK) activation with metformin directly improves insulin signaling within the blastocyst, leading to improved pregnancy outcomes. Murine embryos were exposed to 200 nmol/l IGF-I, similar to the concentrations that can occur during polycystic ovary syndrome (PCOS). Resulting blastocysts were compared with embryos cocultured with excess IGF-I plus metformin and embryos cultured in control medium for the following: AMPK phosphorylation, insulin-stimulated glucose uptake, and apoptosis. Study and control blastocysts were also transferred into control animals. On embryonic day (E) 14.5, resulting fetuses were examined for size and rates of fetal implantation and resorption. Compared with control blastocysts, blastocysts exposed to high concentrations of IGF-I showed a decrease in AMPK activation and insulin-stimulated glucose uptake and an increase in the number of apoptotic nuclei. Blastocysts cocultured in metformin and excess IGF-I performed as well as controls in all studies. 5-Aminoimidazole-4-carboxamide 1-β-D-ribofuranoside, another AMPK activator, also prevented the effects of excess IGF-I on blastocysts. Implantation rates and fetal size at day 14.5 were significantly lower among IGF-I-exposed embryos transferred into control mothers compared with control embryos transferred into control mothers. Both of these parameters were reversed by coincubation with metformin and IGF-I before transfer. Activation of embryonic AMPK may be the mechanism responsible for the improved pregnancy outcomes seen in PCOS patients taking metformin. Diabetes 56:2228-2234, 2007 [ABSTRACT FROM AUTHOR]

The dysregulation of the IGF system has been implicated in the pathogenesis of obesity, diabetes, and diabetes complications such as nephropathy, but little is known about the genomics of the IGF system in health and disease. We genotyped 13 single nucleotide polymorphisms (SNPs) in IGFBP1 gene in 732 representative type 2 diabetic patients from the Salford Diabetes Register. Of the 13 SNPs, 8 were polymorphic and 7 of those had minor allele frequencies >0.1, one of which was in the gene promoter and one of which was nonsynonymous in exon 4. The minor alleles of these SNPs and two others were associated with a reduced prevalence of diabetic nephropathy. Haplotype analysis revealed that 97% of the genetic variation for IGFBP1 in the population sample could be accounted for using two of the "reno-protective" SNPs, with other SNPs adding little extra information. One of these two SNPs was the nonsynonymous mutation in exon 4, lying close to the integrin-binding RGD motif, which is thought to affect tissue delivery of IGF-I by IGF-binding protein 1 (IGFBP-1), possibly suggesting a "reno-protective" effect via altered IGFBP-1 binding. In conclusion, we have described the first genomic markers to be associated with diabetic microvascular complications within the human IGFBP1 gene. [ABSTRACT FROM AUTHOR]

Damage to interstitial cells of Cajal (ICC), pacemakers, and mediators of neuromuscular neurotransmission in the gastrointestinal tract contributes to the pathogenesis of diabetic gastroenteropathy in both patients and animal models. ICC depletion in diabetes may result from chronic hyperglycemia or lost/ineffective insulin signaling. Because independent control of insulin and glucose concentrations is difficult in chronic in vivo studies, we used long-term organotypic cultures to address this problem. Murine gastric muscles were cultured in normoglycemic or hyperglycemic basal media with or without insulin or IGF-I for 1-3 months, the time required for gastroparesis and ICC damage to develop in diabetic mice. ICC were assessed by c-Kit immunohistochemistry and quantitative analysis of c-kit expression. Electrical pacemaking was studied by intracellular recording of slow waves. ICC survived for at least 34 days in unsupplemented normoglycemic media, but their networks, c-kit expression, and slow waves were profoundly reduced after 68 days. These changes could be entirely prevented by insulin or IGF-I supplementation. ICC networks were completely resistant to hyperglycemia for at least 72 days. Thus, hyperglycemia is unlikely to be responsible for the diabetes-associated depletion of ICC. In contrast, maintenance of ICC requires insulin or IGF-I, which are reduced or ineffective in diabetes. [ABSTRACT FROM AUTHOR]

Heat shock protein (Hsp)60 and IGF-1 receptor signaling protect cardiac muscle against injury. The abundance of cardiac IGF-1 receptor can be upregulated by Hsp60, but how diabetes modulates cardiac muscle Hsp60 has not yet been defined. We investigated the changes of Hsp60 and IGF-1 receptor signaling in the diabetic myocardium and studied how diabetes modulates Hsp60 and IGF-1 receptor in diabetic myocardium. In the streptozotocin (STZ)-induced diabetic rat, downregulation of Hsp60 and IGF-1 receptor occurred 4 days after induction of diabetes. IGF-1 activation of IGF-1 receptor, Mek, and Akt were reduced accordingly in the diabetic myocardium. The independent effect of insulin and hyperglycemia on Hsp60 was investigated in primary cardiomyocytes. Incubating cardiomyocytes with insulin was associated with dose-dependent increase of Hsp60 protein. In contrast, the abundance of Hsp60 was not affected by high concentration of glucose in these cells. To further determine the independent effects of hyperglycemia and insulin deficiency on the changes of myocardial Hsp60 and IGF-1 receptor, we used phlorizin to normalize blood glucose in diabetic rats. In the phlorizin-treated diabetic rats, myocardial Hsp60 was lower than that of the normal controls. In contrast, insulin treatment normalized myocardial Hsp60 in the diabetic rats. Because phlorizin does not alter insulin secretion, Hsp60 expression was modulated by insulin and not by hyperglycemia. Similar changes of Hsp60 and IGF-1 receptor were observed in the skeletal muscle of STZ-induced diabetic rats. These findings suggest that insulin deficiency is a novel mechanism that leads to downregulation of Hsp60 in diabetic muscle tissues. The development of diabetic cardiomyopathy might have involved downregulation of Hsp60 and subsequent reduction of IGF-1 receptor signaling. [ABSTRACT FROM AUTHOR]

The dogma that IGF-I stimulates pancreatic islet growth has been challenged by combinational targeting of IGF or IGF-IR (IGF receptor) genes as well as beta-cell-specific IGF-IR gene deficiency, which caused no defect in islet cell growth. To assess the physiological role of locally produced IGF-I, we have developed pancreatic-specific IGF-I gene deficiency (PID) by crossing Pdx1-Cre and IGF-I/loxP mice. PID mice are normal except for decreased blood glucose level and a 2.3-fold enlarged islet cell mass. When challenged with low doses of streptozotocin, control mice developed hyperglycemia after 6 days that was maintained at high levels for at least 2 months. In contrast, PID mice only exhibited marginal hyperglycemia after 12 days, maintained throughout the experiment. Fifteen days after streptozotocin, PID mice demonstrated significantly higher levels of insulin production. Furthermore, streptozotocin-induced beta-cell apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL] assay) was significantly prevented in PID mice. Finally, PID mice exhibited a delayed onset of type 2 diabetes induced by a high-fat diet, accompanied by super enlarged pancreatic islets, increased insulin mRNA levels, and preserved sensitivity to insulin. Our results suggest that locally produced IGF-I within the pancreas inhibits islet cell growth; its deficiency provides a protective environment to the beta-cells and potential in combating diabetes. [ABSTRACT FROM AUTHOR]

Müller cells, the principal glia of the retina, generate tractional forces in response to IGF-I and platelet-derived growth factor and are present in diabetic fibro-vascular scar tissues causing traction retinal detachment. While diabetes-associated increases in vitreous IGFs have been reported, paradoxically high concentrations of these same growth factors in normal vitreous suggest the presence of more complex mechanisms regulating growth factor bioavailability. To define diabetes-associated changes in vitreous biological activity, the stimulatory effects of 68 samples were evaluated using Müller cell tractional force generation as a target bioassay. Dose-response profiles were used to calculate vitreous specific activity (per unit protein) and total vitreous activity (per unit volume). Vitreous samples from patients lacking diabetes or other retinal pathology had undetectable or low activities, whereas diabetic retinopathy was associated with 6.9- and 8.7-fold increases in vitreous specific and total activities, respectively. Secondary analyses revealed no activity differences associated with patient sex, age, or the presence of vitreous hemorrhage. However, compared with diabetes alone, the presence of proliferative diabetic retinopathy was associated with additional 2.3-fold increases in vitreous specific and total activities. Vitreous dose-response assays performed with and without growth factor-neutralizing antibodies enable attribution of vitreous activity to IGFs (53.9%) and, to a lesser extent, platelet-derived growth factors (14.5%). Because the observed increases in vitreous growth factor activity grossly exceed the reported increases in growth factor concentration, these data indicate that diabetes-associated changes in vitreous biological activity involve more complex biochemical changes that ultimately yield increased growth factor bioavailability and/or Müller cell responsiveness. [ABSTRACT FROM AUTHOR]

IGFs are important regulators of pancreatic beta-cell development, growth, and maintenance. Mutations in the IGF genes have been found to be associated with type 2 diabetes, myocardial infarction, birth weight, and obesity. These associations could result from changes in insulin secretion. We have analyzed glucose-stimulated insulin secretion using hyperglycemic clamps in carriers of a CA repeat in the IGF-I promoter and an ApaI polymorphism in the IGF-II gene. Normal and impaired glucose-tolerant subjects (n = 237) were independently recruited from three different populations in the Netherlands and Germany to allow independent replication of associations. Both first- and second-phase insulin secretion were not significantly different between the various IGF-I or IGF-II genotypes. Remarkably, noncarriers of the IGF-I CA repeat allele had both a reduced insulin sensitivity index (ISI) and disposition index (DI), suggesting an altered balance between insulin secretion and insulin action. Other diabetes-related parameters were not significantly different for both the IGF-I and IGF-II gene variant. We conclude that gene variants in the IGF-I and IGF-II genes are not associated with detectable variations in glucose-stimulated insulin secretion in these three independent populations. Further studies are needed to examine the exact contributions of the IGF-I CA repeat alleles to variations in ISI and DI. [ABSTRACT FROM AUTHOR]

Tubulointerstitial fibrosis is an important component in the development of diabetic nephropathy. Various renal cell types, including fibroblasts, contribute to the excessive matrix deposition in the kidney. Although transforming growth factor-beta (TGF-beta) has been thought to play a major role during fibrosis, other growth factors are also involved. Here we examined the effects of connective tissue growth factor (CTGF) and IGF-I on collagen type I and III production by human renal fibroblasts and their involvement in glucose-induced matrix accumulation. We have demonstrated that both CTGF and IGF-I expressions were increased in renal fibroblasts under hyperglycemic conditions, also in the absence of TGF-beta signaling. Although CTGF alone had no effect on collagen secretion, combined stimulation with IGF-I enhanced collagen accumulation. Furthermore, IGF-I also had a synergistic effect with glucose on the induction of collagens. Moreover, we observed a partial inhibition in glucose-induced collagen secretion with neutralizing anti-CTGF antibodies, thereby demonstrating for the first time the involvement of endogenous CTGF in glucose-induced effects in human renal fibroblasts. Therefore, the cooperation between CTGF and IGF-I might be involved in glucose-induced matrix accumulation in tubulointerstitial fibrosis and might contribute to the pathogenesis of diabetic nephropathy. [ABSTRACT FROM AUTHOR]

IGFs and their binding proteins (IGFBPs) play a significant role in metabolic regulation, and there is growing evidence that they also exert important vascular effects. IGFBP-1 contributes to glucose counterregulation, and observational studies demonstrate an inverse association between circulating IGFBP-1 levels and cardiovascular risk factors. Furthermore, IGFBP-1 levels are lower in subjects with overt macrovascular disease. We therefore hypothesized that IGFBP-1 exerts potentially beneficial effects, either directly or indirectly, on blood pressure regulation and vascular function. We tested this hypothesis using a unique transgenic mouse, which overexpresses human IGFBP-1, and explored the effect of this protein on metabolic, blood pressure, and vascular homeostasis. IGFBP-1-overexpressing mice exhibited postprandial hyperinsulinemia with preservation of glucocompetence and insulin sensitivity. Blood pressure was unchanged in the fasting state but was significantly lower in transgenic mice after a carbohydrate load. Aortic rings from IGFBP-1-overexpressing mice were hypocontractile in response to vasoconstrictors, and relaxation responses were unimpaired. Basal nitric oxide production was increased and endothelial nitric oxide synthase mRNA expression upregulated in aortae of these mice. Our data suggest that IGFBP-1 plays an important and potentially beneficial role in regulating metabolic and vascular homeostasis. [ABSTRACT FROM AUTHOR]

Results from experimental and gene-association studies suggest that IGF-II may influence body weight regulation and that individuals with low IGF-II levels may be more susceptible to weight gain and obesity. We therefore assessed the association between circulating concentrations of IGF-II and subsequent weight gain and progression to obesity. Participants in this study were 463 nonobese men and women aged between 45 and 60 years with normal glucose tolerance and with metabolic and anthropometric assessments at baseline and follow-up clinic visits. We examined the association between baseline concentrations of fasting serum IGF-II and risk of gaining > or =2.5 kg body wt or developing obesity using unconditional logistic regression. A total of 217 participants gained > or =2.5 kg body wt, and 29 developed obesity after >4 years of follow-up. In multivariate analysis, baseline IGF-II levels were significantly lower in participants who subsequently gained weight compared with individuals who remained stable or lost weight (P = 0.010). Similarly, individuals who developed obesity had lower baseline IGF-II levels (P = 0.006). Relatively higher IGF-II levels were also associated with a reduced risk of gaining weight (P for trend across quintiles of IGF-II = 0.006). Our data suggest that circulating IGF-II levels may play a role in body weight regulation and development of obesity in men and women with normal glucose tolerance. [ABSTRACT FROM AUTHOR]

IGF-I has a critical role in growth and metabolism. A microsatellite polymorphism 1 kb upstream to the IGF-I gene has recently been associated with several adult phenotypes. In a large Dutch cohort, the absence of the commonest allele (Z) was associated with reduced serum IGF-I levels, reduced height, and an increased risk of type 2 diabetes and myocardial infarction. This result has not been replicated, and the role of this polymorphism in these traits in U.K. subjects is not known. We sought further evidence for the involvement of this variant in type 2 diabetes using a case-control study and IGF-I and diabetes-related traits in a population cohort of 640 U.K. individuals aged 25 years. Absence of the common allele was not associated with type 2 diabetes (odds ratio 0.70, 95% CI 0.47–1.04 for X/X versus Z/Z genotype, 2 test for trend across genotypes, P = 0.018). In the population cohort, the common allele (Z) was associated with decreased IGF-I levels (P = 0.01), contrary to the Dutch study, but not with adult height (P = 0.23), glucose tolerance (P = 0.84), oral glucose tolerance test-derived values of β-cell function (P = 0.90), or insulin resistance (P = 0.66). There was no association with measures of fetal growth, including birth weight (P = 0.17). Our results do not support the previous associations and suggest that the promoter microsatellite is unlikely to be functionally important. [ABSTRACT FROM AUTHOR]

Maturity-onset diabetes of the young type 3 (MODY3) is characterized by impaired insulin secretion. Heterozygous mutations in the gene encoding hepatocyte nuclear factor (HNF)-1alpha are the cause of MODY3. Transgenic mice overexpressing dominant-negative HNF-1alpha mutant in pancreatic beta-cells and HNF-1alpha knockout mice are animal models of MODY3. These mice exhibit defective glucose-stimulated insulin secretion and have reduced beta-cell mass and beta-cell proliferation rate. Here we examined the effect of HNF-1alpha on beta-cell proliferation by overexpressing a human naturally occurring dominant- negative mutation P291fsinsC in INS-1 cells under the control of doxycycline-induction system. INS-1 cells overexpressing P291fsinsC showed apparent growth impairment. The proliferation rate estimated by [(3)H]thymidine incorporation was significantly reduced in P291fsinsC-expressing INS-1 cells compared with noninduced or wild-type HNF-1alpha-overexpressing INS-1 cells. Growth inhibition occurred at the transition from G1 to S cell cycle phase, with reduced expression of cyclin E and upregulation of p27. cDNA array analysis revealed that the expression levels of IGF-1, a major growth factor for beta-cells, and macrophage migration inhibitory factor (MIF), a cytokine expressed in pancreatic beta-cells, were reduced in P291fsinsC-HNF-1alpha-expressing INS-1 cells. Although MIF seemed to have proliferative function, blockade of MIF action by anti-MIF antibody stimulated INS-1 cell proliferation, excluding its direct role in the growth impairment. However, addition of IGF-1 to P291fsinsC-expressing INS-1 cells rescued the growth inhibition. Our data suggest that HNF-1alpha is critical for modulating pancreatic beta-cell growth by regulating IGF-1 expression. IGF-1 might be a potential therapeutic target for the treatment of MODY3. [ABSTRACT FROM AUTHOR]

Transforming growth factor (TGF)-alpha- and epidermal growth factor (EGF)-induced signal transduction was directly compared with that of glucose and insulin-like growth factor-1 (IGF-1) in INS-1 cells. TGF-alpha/EGF transiently (<20 min) induced phosphorylation of extracellular-regulated kinase (Erk)-1/2 (>20-fold), glycogen synthase kinase (GSK)-3 (>10-fold), and protein kinase B (PKB) (Ser(473) and Thr(308)), but did not increase [(3)H]thymidine incorporation. In contrast, phosphorylation of Erk1/2, GSK-3, and PKB in response to glucose and IGF-1 was more prolonged (>24 h) and, though not as robust as TGF-alpha/EGF, did increase beta-cell proliferation. Phosphorylation of p70(S6K) was also increased by IGF-1/glucose, but not by TGF-alpha/EGF, despite upstream PKB activation. It was found that IGF-1 induced phosphatidylinositol 3-kinase (PI3K) association with insulin receptor substrate (IRS)-1 and -2 in a glucose-dependent manner, whereas TGF-alpha/EGF did not. The importance of specific IRS-2-mediated signaling events was emphasized in that adenoviral-mediated overexpression of IRS-2 further increased glucose/IGF-1-induced beta-cell proliferation (more than twofold; P < 0.05) compared with control or adenoviral-mediated IRS-1 overexpressing INS-1 cells. Neither IRS-1 nor IRS-2 overexpression induced a beta-cell proliferative response to TGF-alpha/EGF. Thus, a prolonged activation of Erk1/2 and PI3K signaling pathways is important in committing a beta-cell to a mitogenic event, and it is likely that this sustained activation is instigated by signal transduction occurring specifically through IRS-2. [ABSTRACT FROM AUTHOR]

Examines the activation of insulin receptor substrate-2 mediated signal transduction by insulin-like growth factor. Augmentation of pancreatic β-cell proliferation; Induction of phosphorylation of extracellular-regulated kinase; Increment of β-cell proliferation.

Immortalized brown adipocyte cell lines have been generated from fetuses of mice deficient in the insulin-like growth factor I receptor gene (IGF-IR[sup -/-]), as well as from fetuses of wild-type mice (IGF-IR[sup +/+]). These cell lines maintained the expression of adipogenic- and thermogenic-differentiation markers and show a multilocular fat droplets phenotype. IGF-IR[sup -/-] brown adipocytes lacked IGF-IR protein expression; insulin receptor (IR) expression remained unchanged as compared with wild-type cells. Insulin-induced tyrosine autophosphorylation of the IR β-chain was augmented in IGF-IR–deficient cells. Upon insulin stimulation, tyrosine phosphorylation of (insulin receptor substrate-1) IRS-1 was much higher in IGF-IR[sup -/-] brown adipocytes, although IRS-1 protein content was reduced. In contrast, tyrosine phosphorylation of IRS-2 decreased in IGF-IR–deficient cells; its protein content was unchanged as compared with wild-type cells. Downstream, the association IRS-1/growth factor receptor binding protein-2 (Grb-2) was augmented in the IGF-IR[sup -/-] brown adipocyte cell line. However, SHC expression and SHC tyrosine phosphorylation and its association with Grb-2 were unaltered in response to insulin in IGF-IR–deficient brown adipocytes. These cells also showed an enhanced activation of mitogen-activated protein kinase (MAPK) kinase (MEK1/2) and p42/p44 mitogen-activated protein kinase (MAPK) upon insulin stimulation. In addition, the lack of IGF-IR in brown adipocytes resulted in a higher mitogenic response (DNA synthesis, cell number, and proliferating cell nuclear antigen expression) to insulin than wild-type cells. Finally, cells lacking IGF-IR showed a much lower association between IR or IRS-1 and phosphotyrosine phosphatase 1B (PTP1B) and also a decreased PTP1B activity upon insulin stimulation. However, PTP1B/Grb-2 association remained unchanged in both cell types, regardless of insulin stimulation. Data presented here provide strong evidence that IGF-IR–deficient brown adipocytes show an increased insulin sensitivity via IRS-1/Grb-2/MAPK, resulting in an increased mitogenesis in response to insulin. [ABSTRACT FROM AUTHOR]

Investigates the role of liver-derived insulin-like growth factor (IGF)-I for carbohydrate and lipid metabolism by using mice with liver-specific IGF-I gene inactivation. Importance of IGF-I in glucose metabolism; Increase in serum leptin concentrations noted in the mice with concomitant decrease in fat mass.

Insulin and insulin-like growth factors (IGFs) mediate a variety of signals involved in mammalian development and metabolism. To study the metabolic consequences of IGF-I deficiency, we used the liver IGF-I-deficient (LID) mouse model. The LID mice show a marked reduction (approximately 75%) in circulating IGF-I and elevated growth hormone (GH) levels. Interestingly, LID mice show a fourfold increase in serum insulin levels (2.2 vs. 0.6 ng/ml in control mice) and abnormal glucose clearance after insulin injection. Fasting blood glucose levels and those after a glucose tolerance test were similar between the LID mice and their control littermates. Thus, the high levels of circulating insulin enable the LID mice to maintain normoglycemia in the presence of apparent insulin insensitivity. Insulin-induced autophosphorylation of the insulin receptor and tyrosine phosphorylation of insulin receptor substrate (IRS)-1 were absent in muscle, but were normal in liver and white adipose tissue of the LID mice. In contrast, IGF-I-induced autophosphorylation of its cognate receptor and phosphorylation of IRS-1 were normal in muscle of LID mice. Thus, the insulin insensitivity seen in the LID mice is muscle specific. Recombinant human IGF-I treatment of the LID mice caused a reduction in insulin levels and an increase in insulin sensitivity. Treatment of the LID mice with GH-releasing hormone antagonist, which reduces GH levels, also increased insulin sensitivity. These data provide evidence of the role of circulating IGF-I as an important component of overall insulin action in peripheral tissues. [ABSTRACT FROM AUTHOR]

We have recently demonstrated that the exposure to hyperglycemia in utero impairs nephrogenesis in rat fetuses (Amri K et al., Diabetes 48:2240-2245, 1999). Diabetic pregnancy is commonly associated with alterations in the IGF system in fetal tissues. It has also been shown that both IGF-I and IGF-II are produced within developing metanephros and promote renal organogenesis. Therefore, we investigated the effect of maternal diabetes on IGFs and their receptors in developing fetal rat kidney. Diabetes was induced in pregnant rats by a single injection of streptozotocin on day 0 of gestation. We measured the amounts of IGF and their receptors, both proteins and mRNAs, in the metanephroi of fetuses issued from diabetic subjects and in age-matched fetuses from control subjects (14-20 days of gestation). IGF-II was produced throughout fetal nephrogenesis, whereas IGF-I protein was not detected, suggesting a critical role of IGF-II in kidney development. Fetal exposure to maternal diabetes caused no change in IGF production in the early stages of nephrogenesis. Similarly, the amounts of IGF-I receptor and insulin receptor were not altered. By contrast, there was an increase in production of IGF-II/mannose-6-phosphate receptor throughout nephrogenesis. Because this receptor plays an essential role in regulating the action of IGF-II, the altered nephrogenesis in fetuses exposed to maternal diabetes may be linked to a decrease in IGF-II bioavailability. [ABSTRACT FROM AUTHOR]

Evidence is accumulating that low levels of IGF-I play a role in the pathogenesis of type 2 diabetes and cardiovascular diseases. We examined the role of a genetic polymorphism in the promoter region of the IGF-I gene in relation to circulating IGF-I levels and growth measured as body height, and we studied the relationship of this polymorphism with type 2 diabetes and myocardial infarction. The relation between the IGF-I polymorphism and body height was assessed in a population-based sample of 900 subjects from the Rotterdam Study. Within each genotype stratum, 50 subjects were randomly selected for a study of the relation of this polymorphism with serum IGF-I levels. To assess the risk for type 2 diabetes, we studied 220 patients and 596 normoglycemic control subjects. For myocardial infarction, 477 patients with evidence of myocardial infarction on electrocardiogram and 808 control subjects were studied. A 192-bp allele was present in 88% of the population, suggesting that this is the wild-type allele from which all other alleles originated. Body height was, on average, 2.7 cm lower (95% CI for difference -4.6 to -0.8 cm, P = 0.004), and serum IGF-I concentrations were 18% lower (95% CI for difference -6.0 to -1.3 mmol/l, P = 0.003) in subjects who did not carry the 192-bp allele. In noncarriers of the 192-bp allele, an increased relative risk for type 2 diabetes (1.7 [95% CI 1.1-2.7]) and for myocardial infarction (1.7 [95% CI 1.1-2.5]) was found. In patients with type 2 diabetes, the relative risk for myocardial infarction in subjects without the 192-bp allele was 3.4 (95% CI 1.1-11.3). Our study suggests that a genetically determined exposure to relatively low IGF-I levels is associated with an increased risk for type 2 diabetes and myocardial infarction. [ABSTRACT FROM AUTHOR]

Insulin and insulin-like growth factor-1 (IGF-1) are members of the family of the insulin family of growth factors, which activate similar cellular downstream pathways. In this study, we analyzed the effects of insulin and IGF-1 on the proliferation of murine skin keratinocytes in an attempt to determine whether these hormones trigger the same signaling pathways. Increasing doses of insulin and IGF-1 promote keratinocyte proliferation in an additive manner. We identified downstream pathways specifically involved in insulin signaling that are known to play a role in skin physiology; these include activation of the Na+/K+ pump and protein kinase C (PKC). Insulin, but not IGF-1, stimulated Na+/K+ pump activity. Furthermore, ouabain, a specific Na+/K+ pump inhibitor, abolished the proliferative effect of insulin but not that of IGF-1. Insulin and IGF-1 also differentially regulated PKC activation. Insulin, but not IGF-1, specifically activated and translocated the PKCB isoform to the membrane fraction. There was no effect on PKC isoforms alpha, eta, epsilon, and zeta, which are expressed in skin. PKC8 overexpression increased keratinocyte proliferation and Na+/K+ pump activity to a degree similar to that induced by insulin but had no affect on IGF-1-induced proliferation. Furthermore, a dominant negative form of PKCdelta abolished the effects of insulin on both proliferation and Na+/K+ pump activity but did not abrogate induction of keratinocyte proliferation induced by other growth factors. These data indicate that though insulin or IGF-1 stimulation induce keratinocyte proliferation, only insulin action is specifically mediated via PKC8 and involves activation of the Na+/K+ pump. [ABSTRACT FROM AUTHOR]

IGF-I promotes the survival of multiple cell types by activating the IGF-I receptor (IGF-IR), which signals downstream to a serine/threonine kinase termed Akt. Because in diabetes vascular and neural cells of the retina undergo accelerated apoptosis, we examined IGF-I synthesis and signaling in the human and rat diabetic retina. In retinas obtained postmortem from six donors aged 64 +/- 8 years with a diabetes duration of 7 +/- 5 years, IGF-I mRNA levels were threefold lower than in the retinas of six age-matched nondiabetic donors (P = 0.005). In the retinas of rats with 2 months' duration of streptozotocin-induced diabetes, IGF-I mRNA levels were similar to those of control rats, but after 5 months of diabetes they failed to increase to the levels recorded in age-matched controls (P < 0.02). Retinal IGF-I expression was not altered by hypophysectomy, proving to be growth-hormone independent. IGF-IR levels were modestly increased in the human diabetic retinas (P = 0.02 vs. nondiabetic retinas) and were unchanged in the diabetic rats. Phosphorylation of the IGF-IR could be measured only in the rat retina, and was not decreased in the diabetic rats (94 +/- 18% of control values). In the same diabetic rats, phosphorylation of Akt was 123 +/- 21% of control values. There was not yet evidence of increased apoptosis of retinal microvascular cells after 5 months of streptozotocin-induced diabetes. Hence, in the retina of diabetic rats, as in the retina of diabetic human donors, IGF-I mRNA levels are substantially lower than in age-matched nondiabetic controls, whereas IGF-IR activation and signaling are not affected, at least for some time. This finding suggests that in the diabetic retina, the activation of the IGF-IR is modulated by influences that compensate for, or are compensated by, decreased IGF-I synthesis. [ABSTRACT FROM AUTHOR]

Insulin-like growth factor binding protein (IGFBP)-1 has been shown to alter cellular responses to insulin-like growth factor 1 (IGF-1). Human IGFBP-1 undergoes serine phosphorylation, and this enhances both its affinity for IGF-1 by six- to eightfold and its capacity to inhibit IGF-1 actions. To investigate the physiological role of IGFBP-1 in vivo, transgenic mice have been generated using either the human IGFBP-1 or rat IGFBP-1 transgene. Both lines of mice expressed high concentrations of IGFBP-1 in serum and tissues; however, human IGFBP-1 transgenic mice did not show glucose intolerance and exhibited no significant intrauterine growth retardation, whereas rat IGFBP-1 transgenic mice showed fasting hyperglycemia and intrauterine growth restriction. The aim of this study was to investigate the physiological differences in the phosphorylation state of human IGFBP-1 and rat IGFBP-1 in these transgenic mice. The phosphorylation status of IGFBP-1 in transgenic mouse serum was analyzed by nondenaturing PAGE. Almost all of the IGFBP-1 in serum from the human IGFBP-1 transgenic mice was present as a nonphosphorylated form. Most of the rat IGFBP-1 in the serum of the mice expressing the rat IGFBP-1 was phosphorylated. Immunoprecipitation showed that mouse hepatoma (Hepa 1-6) cells (exposed to [32P]H3PO4) secrete 32P-labeled IGFBP-1. When the human IGFBP-1 transgene was transfected into Hepa 1-6 cells, all of the IGFBP-1 was secreted in the nonphosphorylated form. However, when the rat IGFBP-1 transgene was transfected into these cells, phosphorylated forms of IGFBP-1 were secreted. To confirm this result, the mouse hepatoma cell protein kinase was partially purified. This kinase activity phosphorylated mouse and rat IGFBP-1 in vitro, but it did not phosphorylate human IGFBP-1. Scatchard analysis showed that the affinity of phosphorylated rat IGFBP-1 for IGF-1 was 3.9-fold higher than that of nonphosphorylated human IGFBP-1. We conclude that the mouse IGFBP-1 kinase activity cannot phosphorylate human IGFBP-1, whereas it can phosphorylate rat IGFBP-1. The phosphorylation state of human IGFBP-1 may account for part of the phenotypic differences noted in the two studies of transgenic mice, and it is an important determinant of the capacity of human IGFBP-1 to inhibit IGF-1 actions in vivo. [ABSTRACT FROM AUTHOR]

Challenge of Ins-1 cells, a rat beta-pancreatic cell line, with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) promoted the expression of type 2 nitric oxide synthase (NOS-2) in a cooperative way. Treatment of Ins-1 cells with IGF-I significantly inhibited the expression of NOS-2, especially at subsaturating concentrations of LPS and IFN-gamma. The inhibitory effect of IGF-I on NOS-2 expression was abrogated when cells were incubated with wortmannin or LY294002, two inhibitors of phosphatidylinositol 3-kinase. Transient expression of the p110 subunit of phosphatidylinositol 3-kinase impaired the LPS and IFN-gamma-dependent NOS-2 promoter activity in cells transfected with a 1-kb fragment corresponding to the 5'-flanking region of the NOS-2 gene. However, expression of a dominant negative form of p85 abolished the inhibitory action of IGF-I on the NOS-2 promoter activity. Analysis of the decreased NOS-2 promoter activity in cells incubated with IGF-I showed a lower nuclear factor KB binding as determined by electrophoretic mobility shift assays. The synthesis of NO, produced after LPS and IFN-gamma challenge, triggered an apoptotic response in these cells. IGF-I reduced apoptosis mainly through the decreased synthesis of NO. However, in activated cells treated with N-[3-(aminomethyl)benzyl]acetamidine, a specific NOS-2 inhibitor, IGF-I completely abolished the NO-independent apoptosis. This protection from apoptosis was dependent on phosphatidylinositol 3-kinase activity. These results suggest an important anti-inflammatory and anti-apoptotic role for IGF-I in beta-pancreatic cells, with both actions depending on the activation of phosphatidylinositol 3-kinase. [ABSTRACT FROM AUTHOR]

Discusses the implication of insulin-like growth factor (IGF)-I in the regulation of physiological and pathological functions of cell types such as pancreatic beta-cells. Expression of type two nitric oxide synthesase (NOS-2) in a cooperative way; Abrogation of NOS-2 expression under pro-inflammatory conditions; Pro-inflammatory stimuli.

Expression of the genes encoding several matrix proteins, including the laminin gamma1 and beta1 subunits, is increased in glomeruli or renal cortex from diabetic animals or in mesangial cells cultured in high concentrations of glucose. Transforming growth factor (TGF)-beta1 and IGF-1 have been implicated as mediators of this response. In the present study, we assessed the influence of high glucose concentrations and the roles of TGF-beta1 and IGF-1 in the regulation of laminin C1 gene expression in cultured mesangial cells. Culture of normal rat mesangial cells (RMC) or SV40-transformed mouse mesangial (MES-13) cells in 500 mg/dl D-glucose for 2 days to 3 weeks significantly increased laminin C1 mRNA abundance compared with cells cultured in 100 mg/dl D-glucose. IGF-1 also increased laminin C1 mRNA abundance in RMC or MES-13 cells, whereas TGF-beta1 was without effect. The influence of raising the medium glucose concentration on laminin C1 promoter activity was further studied in MES-13 cells that had been stably transfected with a reporter gene containing the promoter linked to luciferase. Culture in 500 mg/dl D-glucose for 4 h to at least 1 week increased laminin C1 promoter activity compared with cells maintained in 100 mg/dl glucose. In contrast, culture of cells in medium that contained 400 mg/dl mannitol or 400 mg/dl L-glucose in addition to 100 mg/dl D-glucose did not increase laminin C1 promoter activity. The ability of high glucose to increase laminin C1 promoter activity was absolutely dependent on the presence of serum. Consistent with results obtained with mRNA, TGF-beta1 had no influence on promoter activity in stable integrants. Whereas IGF-1 transiently increased promoter activity in stable integrants, the increase was not sustained (6 h). Moreover, neutralizing antibody to TGF-beta or to IGF-1 receptor did not suppress increases in laminin C1 promoter activity induced by culture of stable integrants in high glucose. Several inhibitors of protein kinase C, including bisindolylmaleimide (GFX), myristoylated PKC inhibitor peptide, and LY333531, were also without effect on increases in laminin C1 promoter activity induced by culture in high glucose. Exposure to the NO donor (+/-)-s-nitroso-n-acetylpenicillamine (SNAP) blocked increases in laminin C1 promoter activity induced by serum and by culture in high glucose without influencing promoter activity in cells cultured in the absence of serum and in 100 mg/dl glucose. The ability of high glucose concentrations and IGF-1 to increase laminin C1 promoter activity in cultured mesangial cells, and the suppression of glucose actions by the NO donor SNAP, provide potential mechanisms whereby the synthesis of the laminin gamma1 chain may be regulated in the glomerulus in diabetes. Of note, the mechanism by which high glucose increases laminin C1 promoter activity appears to differ from mechanisms previously described for some other glucose actions on matrix protein synthesis. In this regard, TGF-beta and protein kinase C were not implicated as mediators of the effect of high glucose on laminin C1 promoter activity. [ABSTRACT FROM AUTHOR]

During pregnancy, IGFs and their binding proteins (IGFBPs) are important for the growth of fetal and maternal tissues. IGFBP-1 normally circulates as a single, highly phosphorylated species (hpIGFBP-1). However, in pregnancy there are lesser phosphorylated isoforms (lpIGFBP-1) with decreased affinity for IGF-I, allowing for increased IGF bioavailability. Because regulation of IGFBP-1 is abnormal in type 1 diabetes, we examined the impact of this on IGFBP-1 and its phosphorylation status in diabetic pregnancy. We assessed IGFBP-1 in relation to birth weight, maternal weight gain, duration of diabetes, glycemic control, and the presence or absence of retinopathy in 44 diabetic and 11 nondiabetic subjects. We found that in type 1 diabetic patients there was a significant negative relationship between hpIGFBP-1 and birth weight (r = -0.42, P < 0.01) and between the ratio of hpIGFBP-1 to lpIGFBP-1 and birth weight (r = -0.38, P = 0.02) by week 18 of gestation. Multiple regression analysis confirmed that hpIGFBP-1 was the best single predictor of birth weight (R2 = 0.3, P = 0.001) in diabetic subjects using models including other parameters known to influence fetal size. In contrast to hpIGFBP-1 levels, lpIGFBP-1 levels were not associated with birth weight, but were significantly related to initial maternal BMI and maternal weight throughout gestation in diabetic subjects (r = -0.57, P < 0.001). hpIGFBP-1 levels were positively related to duration of diabetes (r = 0.38, P < 0.01). Diabetic subjects had significantly higher hpIGFBP-1 and lpIGFBP-1 levels than nondiabetic subjects (hpIGFBP-1: 215 +/- 21 vs. 108 +/- 13 microg/l, P = 0.01; lpIGFBP-1: 139 +/- 12 vs. 66 +/- 5 microg/l, P < 0.001), but the ratio of hpIGFBP-1 to lpIGFBP-1 was similar in both groups (2.1 +/- 0.3 [diabetic] vs. 1.7 +/- 0.2 [nondiabetic], NS). In summary, maternal IGFBP-1 levels were higher in diabetic than in normal pregnancies. Diabetic subjects with prolonged duration of diabetes and retinopathy had higher total IGFBP-1 levels than those with shorter disease duration. Thus hpIGFBP-1 in diabetic pregnancy is positively related to the duration of diabetes and inversely related to fetal growth, with lpIGFBP-1 being related to maternal weight and BMI. The ratio of hpIGFBP-1 to lpIGFBP-1 may be a more robust indicator of fetal outcome, since it was consistent between diabetic and nondiabetic subjects. Measurement of the different phosphorylated isoforms of IGFBP-1 may increase the usefulness of IGFBP-1 as a predictor of fetal growth in both normal and diabetic pregnancy. [ABSTRACT FROM AUTHOR]

The early renal growth in streptozotocin (STZ)-induced diabetic rats is preceded by a transient rise in renal tissue insulin-like growth factor (IGF)-I concentration. Administration of the long-acting somatostatin analog octreotide to STZ diabetic rats inhibits the early increase in kidney IGF-I and the increase in kidney size without affecting metabolic control. We studied the effects of octreotide treatment on the intrarenal IGF axis at 2 and at 7 days after the induction of STZ diabetes. Two days after induction of diabetes, kidney IGF-I was increased from 850 +/- 43 ng/g tissue in controls to 1,648 +/- 165 ng/g tissue (P < 0.001) in diabetic animals. The diabetes-associated increase in renal IGF-I 48 h after STZ injection was totally prevented by octreotide (IGF = 780 +/- 57 ng/g tissue). However, 7 days after the induction of diabetes, kidney IGF-I was similar to that of control and was not affected by octreotide. No difference in serum IGF-I was observed between controls and diabetic rats after 2 days of diabetes; however, octreotide treatment resulted in a significant decrease of serum IGF-I after 2 days when compared with control rats (P < 0.05). Renal IGF-I mRNA was significantly decreased to the same extent in both diabetic groups 2 and 7 days after the induction of diabetes, while renal IGF-I receptor (IGF-IR) mRNA was unchanged in rats from either group. Two days after induction of diabetes, renal insulin-like growth factor binding protein (IGFBP)-1 mRNA and 30-kDa IGFBPs (containing IGFBP-1) increased by 186 and 192%, respectively, in untreated diabetic animals compared with controls. Octreotide treatment prevented the diabetes-associated rise in renal IGFBP-1 mRNA and protein. However, 7 days after the induction of diabetes, renal IGFBP-1 mRNA and protein were similarly increased in both octreotide-treated or untreated diabetic rats. Renal IGFBP-3 gene expression and protein and IGFPB-5 mRNA remained unchanged after 2 and 7 days of diabetes when treated or untreated with octreotide. We conclude that the well-known inhibitory effect of octreotide on the early increase in renal IGF-I concentration and renal size in diabetes may be mediated through a direct effect on renal IGFBP-1 levels. [ABSTRACT FROM AUTHOR]

Genetic studies have identified a number of loci demonstrating linkage to type 1 diabetes. One of the largest single contributors to genetic susceptibility, after the major histocompatability complex, is the IDDM2 locus, which maps to a nontranscribed variable number of tandem repeats (VNTR) minisatellite upstream of the insulin (INS) and insulin-like growth factor 2 (IGF2) genes. In a progression from population to functional studies, recent reports have shown that VNTR susceptibility alleles (class I) have different transcriptional effects on INS than protective VNTR alleles (class III) in thymus and pancreas, two tissues important in the pathogenesis of the disease. Similar VNTR transcriptional effects on IGF2 have also been proposed as a mechanism by which the IDDM2 locus confers susceptibility in addition to, or instead of, effects on INS. We evaluated this hypothesis by comparing IGF2 expression levels from chromosomes with the protective class III alleles to those with class I alleles in tissues relevant to type 1 diabetes pathogenesis. In thymus, class III alleles were associated with an IGF2 mRNA level of 4.7 +/- 0.9 (mean +/- SE, arbitrary units, n = 12) compared with 4.7 +/- 1.3 for class I alleles (n = 17). The same absence of a significant difference was found in pancreas, where class III alleles were associated with a level of 28.4 +/- 4.2 (n = 7) and class I alleles with a level of 29.5 +/- 5.2 (n = 6). There was a significant correlation between fetal age and IGF2 in both tissues, but fetal ages were not different in the genotype groups compared. We therefore did not detect any significant difference in IGF2 mRNA levels associated with the protective class of VNTR alleles as compared with the predisposing class. This is evidence against the hypotheses that have suggested IGF2 is a mediator of IDDM2-encoded susceptibility and corroborates previous studies suggesting insulin is the gene involved. [ABSTRACT FROM AUTHOR]