Intrauterine growth restriction (IUGR) leads to obesity, glucose intolerance, and type 2 diabetes mellitus in the adult. To determine the mechanism(s) behind this “metabolic imprinting” phenomenon, we examined the effect of total calorie restriction during mid- to late gestation modified by postnatal ad libitum access to nutrients (CM/SP) or nutrient restriction (SM/SP) vs. postnatal nutrient restriction alone (SM/CP) on skeletal muscle and white adipose tissue (WAT) insulin-responsive glucose transporter isoform (GLUT4) expression and insulin-responsive translocation. A decline in skeletal muscle GLUT4 expression and protein concentrations was noted only in the SM/SP and SM/CP groups. In contrast, WAT demonstrated no change in GLUT4 expression and protein concentrations in all experimental groups. The altered in utero hormonal/metabolic milieu was associated with a compensatory adaptation that persisted in the adult and consisted of an increase in the skeletal muscle basal plasma membrane-associated GLUT4 concentrations. This perturbation led to no further exogenous insulin-induced GLUT4 translocation, thereby disabling the insulin responsiveness of the skeletal muscle but retaining it in WAT. These changes, which present at birth, collectively maximize basal glucose transport to the compromised skeletal muscle with a relative resistance to exogenous/postprandial insulin. Preservation of insulin responsiveness in WAT may serve as a sink that absorbs postprandial nutrients that can no longer efficiently access skeletal muscle. We speculate that, in utero, GLUT4 aberrations may predict type 2 diabetes mellitus, whereas postnatal nutrient intake may predict obesity, thereby explaining the heterogeneous phenotype of the IUGR adult offspring.

Neuronal glucose transporter (GLUT) isoform 3 deficiency in null heterozygous mice led to abnormal spatial learning and working memory but normal acquisition and retrieval during contextual conditioning, abnormal cognitive flexibility with intact gross motor ability, electroencephalographic seizures, perturbed social behavior with reduced vocalization and stereotypies at low frequency. This phenotypic expression is unique as it combines the neurobehavioral with the epileptiform characteristics of autism spectrum disorders. This clinical presentation occurred despite metabolic adaptations consisting of an increase in microvascular/glial GLUT1, neuronal GLUT8 and monocarboxylate transporter (MCT) isoform 2 concentrations, with minimal to no change in brain glucose uptake but an increase in lactate uptake. Neuron-specific glucose deficiency has a negative impact on neurodevelopment interfering with functional competence. This is the first description of GLUT3 deficiency that forms a possible novel genetic mechanism for pervasive developmental disorders, such as the neuropsychiatric autism spectrum disorders, requiring further investigation in humans.

Newborn rat pups artificially raised on a high-carbohydrate (HC) milk formula are chronically hyperinsulinemic and develop adult-onset obesity. As HC rats display aberrations in body weight regulation, hypothalamic adaptations predisposing to obesity have been investigated in this study. The artificial rearing of neonatal rat pups on the HC milk formula resulted in significant increases in the mRNA levels of neuropeptide Y, agouti-related polypeptide, and galanin in the hypothalamus of 12-day-old HC rats. Simultaneously, decreases in the mRNA levels of POMC, melanocortin receptor-4, cocaine- and amphetamine-regulated transcript, and corticotrophin-releasing factor were observed in the hypothalamus of these rats. These changes persisted in 100-day-old HC rats despite weaning onto a rodent diet on postnatal day 24. Marked hyperphagia and increased body weight gain were observed in the post-weaning period. The mRNA levels and protein content of insulin receptor beta (IR-beta) and leptin receptor (long form) showed significant decreases in the hypothalamus of both 12- and 100-day-old HC rats. Further investigation of insulin signaling in the hypothalamus of HC rats indicated significant decreases in the proximal signaling components (insulin receptor substrate proteins 1 and 2 and phosphotidylinositol 3-kinase) in 100-day-old HC rats. These results suggest that hypothalamic neuropeptides respond to the increased carbohydrate availability with associated hormonal alterations during the period of dietary modulation and that these adaptations by persisting in the post-weaning period predispose the HC rats for adult-onset obesity.

The murine facilitative glucose transporter isoform 3 (Glut 3) is developmentally regulated and is predominantly expressed in neurons and trophoblasts. Employing the primer extension and RNase protection assays, the transcription start site (denoted as ؉1) of the murine

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The murine facilitative glucose transporter isoform 3 is developmentally regulated and is predominantly expressed in neurons. By employing the primer extension assay, the transcription start site of the murine Glut 3 gene in the brain was localized to ؊305 bp 5 to the ATG translation start codon. Transient transfection assays in N2A neuroblasts using murine GLUT3-luciferase reporter constructs mapped enhancer activities to two regions located at ؊203 to ؊177 and ؊104 to ؊29 bp flanking a previously described repressor element (؊137 to ؊130 bp). Dephosphorylated Sp1 and Sp3 proteins from the 1-and 21-day-old mouse brain nuclear extracts bound the repressor elements, whereas both dephosphorylated and phosphorylated cAMP-response element-binding protein (CREB) in N2A, 1-and 21-dayold mouse brain nuclear extracts bound the 5-enhancer cis-elements (؊187 to ؊180 bp) of the Glut 3 gene, and the Y box protein MSY-1 bound the sense strand of the ؊83-to ؊69-bp region. Sp3, CREB, and MSY-1 binding to the GLUT 3 DNA was confirmed by the chromatin immunoprecipitation assay, whereas CREB and MSY-1 interaction was detected by the co-immunoprecipitation assay. Furthermore, small interference RNA targeted at CREB in N2A cells decreased endogenous CREB concentrations, and CREB mediated GLUT 3 transcription. Thus, in the murine brain similar to the N2A cells, phosphorylated CREB and MSY-1 bound the Glut 3 gene trans-activating the expression in neurons, whereas Sp1/Sp3 bound the repressor elements. We speculate that phosphorylated CREB and Sp3 also interacted to bring about GLUT 3 expression in response to development/cell differentiation and neurotransmission.Glucose, an essential substrate for brain oxidative metabolism, is transported across the blood-brain barrier and into neurons and glia by a family of structurally related membranespanning glycoproteins termed the facilitative glucose transporters (1, 2). Of the 14 major isoforms cloned to date (1-9), GLUT 1 and GLUT 3 are the isoforms predominantly expressed in the brain (10, 11). Whereas GLUT 1 is expressed by endothelial cells lining the microvasculature and glial cells, which are components of the blood-brain barrier (10), GLUT 3 is the predominant neuronal isoform (11). We and others have reported previously that although the spatial distribution of GLUT 3 in brain is not age-dependent (12), a temporal distribution exists with low amounts noted during the embryonic/ fetal and early postnatal stages and peak amounts at day 14 -21 (13), which coincides with the timing of synaptogenesis (14 -16). In addition, GLUT 3 localization to the synaptic region and its vesicular trafficking, which involves SNAP-25 and syntaxin-1, proteins of the SNARE complex present in synaptic vesicles, supports a role for GLUT 3 in neurotransmission (17). Brain 2-deoxyglucose uptake serves as a surrogate marker for neuronal activity (18); thus GLUT 3, which mediates this glucose uptake, must play a major role in fueling neurotransmission (19). Depolarization of neurons in vitro by the presence of...

We examined the long-term effect of in utero exposure to streptozotocin-induced maternal diabetes on the progeny that postnatally received either ad libitum access to milk by being fed by control mothers (CM/DP) or were subjected to relative nutrient restriction by being fed by diabetic mothers (DM/DP) compared with the control progeny fed by control mothers (CM/CP). There was increased food intake, glucose intolerance, and obesity in the CM/DP group and diminished food intake, glucose tolerance, and postnatal growth restriction in the DM/DP group, persisting in the adult. These changes were associated with aberrations in hormonal and metabolic profiles and alterations in hypothalamic neuropeptide Y concentrations. By use of subfractionation and Western blot analysis techniques, the CM/DP group demonstrated a higher skeletal muscle sarcolemma-associated (days 1 and 60) and white adipose tissue plasma membrane-associated (day 60) GLUT4 in the basal state with a lack of insulin-induced translocation. The DM/DP group demonstrated a partial amelioration of this change observed in the CM/DP group. We conclude that the offspring of a diabetic mother with ad libitum postnatal nutrition demonstrates increased food intake and resistance to insulin-induced translocation of GLUT4 in skeletal muscle and white adipose tissue. This in turn leads to glucose intolerance and obesity at a later stage (day 180). Postnatal nutrient restriction results in reversal of this adult phenotype, thereby explaining the phenotypic heterogeneity that exists in this population.

The cellular and molecular basis of growth hormone (GH) actions on the heart remain poorly defined, and it is unclear whether GH effects on the myocardium are direct or mediated at least in part via insulin-like growth factor (IGF-1). Here, we demonstrate that the cultured neonatal cardiomyocyte is not an appropriate model to study the effects of GH because of artifactual loss of GH receptors (GHRs). To circumvent this problem, rat neonatal cardiomyocytes were infected with a recombinant adenovirus expressing the murine GHR. Functional integrity of GHR was suggested by GH-induced activation of the cognate JAK2/STAT5, MAPK, and Akt intracellular pathways in the cells expressing GHR. Although exposure to GH resulted in a significant increase in the size of the cardiomyocyte and increased expression of c-fos, myosin light chain 2, and skeletal ␣-actin mRNAs, there were no significant changes in IGF-1 or atrial natriuretic factor mRNA levels in response to GH stimulation. In this model, GH increased incorporation of leucine, uptake of palmitic acid, and abundance of fatty acid transport protein mRNA. In contrast, GH decreased uptake of 2-deoxy-D-glucose and levels of Glut1 protein. Thus, in isolated rat neonatal cardiomyocytes expressing GHR, GH induces hypertrophy and causes alterations in cellular metabolic profile in the absence of demonstrable changes in IGF-1 mRNA, suggesting that these effects may be independent of IGF-1.Several observations implicate a role for growth hormone (GH) 1 in modulation of cardiac structure and function (1). Patients with excess endogenous GH (i.e. acromegaly) suffer from cardiac complications including biventricular hypertrophy, impaired diastolic filling, and decreased cardiac performance on effort due to diastolic and systolic dysfunction (2). Patients with chronic GH deficiency also show cardiac abnormalities; in general, the data support the presence of a hypokinetic cardiac syndrome in patients with GH deficiency that can be reversed with GH replacement therapy (3-5). Fazio et al. (6) reported that GH therapy in patients with idiopathic dilated cardiomyopathy was associated with significant improvement in left ventricular ejection fraction, isovolumic relaxation time, and efficiency of myocardial energy utilization. Subsequent to these landmark findings, some studies have supported a beneficial effect of exogenous GH on cardiac function (7), whereas other investigators were unable to demonstrate salutary effects of GH on cardiac function in patients with heart failure (8).A particularly well studied animal model is that of the transplanted GH-secreting pituitary tumor cell line, GH 3. In this model of GH excess, there is increased myocardial contractility and calcium sensitivity of myocardial contractile proteins (1). Similarly, normal rats given recombinant GH show an increase in left ventricular mass, as well as an increase in several aspects of cardiac performance (9). In the rodent model of myocardial infarction, administration of GH results in improvements in myocardial ...