A tale of two neurotransmitters.

Amacrine cells are a diverse set of local circuit neurons of the inner retina, and they all release either GABA or glycine, amino acid neurotransmitters that are generally inhibitory. But some types of amacrine cells have another function besides inhibiting other neurons. One glycinergic amacrine cell, the Aii type, excites a subset of bipolar cells via extensive gap junctions while inhibiting others at chemical synapses. Many types of GABAergic amacrine cells also release monoamines, acetylcholine, or neuropeptides. There is now good evidence that another type of amacrine cell releases glycine at some of its synapses and releases the excitatory amino acid glutamate at others. The glutamatergic synapses are made onto a subset of retinal ganglion cells and amacrine cells and have the asymmetric postsynaptic densities characteristic of central excitatory synapses. The glycinergic synapses are made onto other types of ganglion cells and have the symmetric postsynaptic densities characteristic of central inhibitory synapses. These amacrine cells, which contain vesicular glutamate transporter 3, will be the focus of this brief review.

Immunoexpression of Glucose Transporters 1 and 3 and Macrophage Colony-Stimulating Factor in Central and Peripheral Giant Cell Lesions of the Jaws.

PURPOSE: The peripheral giant cell lesion (PGCL) is a reactive process associated with a local irritating factor that shows low recurrence after treatment, especially if the irritating factor is eliminated. In contrast, the central giant cell lesion (CGCL) presents variable clinical behavior ranging from slow and asymptomatic growth without recurrence to rapid, painful, and recurrent growth. The immunoexpression of glucose transporter (GLUT)-1, GLUT-3, and macrophage colony-stimulating factor (M-CSF) was compared in CGCL and PGCL. MATERIALS AND METHODS: Twenty nonaggressive CGCLs, 20 aggressive CGCLs, and 20 PGCLs were selected for analysis of the immunoexpression of GLUT-1, GLUT-3, and M-CSF in multinuclear giant cells (MGCs) and mononuclear cells (MCs). RESULTS: There was a difference in the percentage of immunoreactive cells of GLUT-1 and GLUT-3 in MC components among lesions and in the intensity of GLUT-1 in MCG and MC components, GLUT-3 in MGC components, and M-CSF in MC components. CONCLUSIONS: These results suggest that GLUT-1, GLUT-3, and M-CSF could play a role in the pathogenesis of the lesions studied. The stronger immunostaining of these proteins in MCs shows that these cells have greater metabolic activity and osteoclastogenesis, especially in aggressive CGCL. The MCs showed a stronger relation than the MGCs to the pathogenesis of the studied lesions.

Comparative intrauterine development and placental function of ART concepti: implications for human reproductive medicine and animal breeding.

BACKGROUND: The number of children conceived using assisted reproductive technologies (ART) has reached >5 million worldwide and continues to increase. Although the great majority of ART children are healthy, many reports suggest a forthcoming risk of metabolic complications, which is further supported by the Developmental Origins of Health and Disease hypothesis of suboptimal embryo/fetal conditions predisposing adult cardiometabolic pathologies. Accumulating evidence suggests that fetal and placental growth kinetics are important features predicting post-natal health, but the relationship between ART and intrauterine growth has not been systematically reviewed. METHODS: Relevant studies describing fetoplacental intrauterine phenotypes of concepti generated by in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) and somatic cell nuclear transfer (SCNT) in the mouse, bovine and human were comprehensively researched using PubMed and Google Scholar. Intrauterine growth plots were created from tabular formatted data available in selected reports. RESULTS: ART pregnancies display minor but noticeable alterations in fetal and placental growth curves across mammalian species. In all species, there is evidence of fetal growth restriction in the earlier stages of pregnancy, followed by significant increases in placental size and accelerated fetal growth toward the end of gestation. However, there is a species-specific effect of ART on birthweights, that additionally vary in a culture condition-, strain-, and/or stage at transfer-specific manner. We discuss the potential mechanisms that underlie these changes, and how they are affected by specific components of ART procedures. CONCLUSIONS: ART may promote measurable alterations to intrauterine growth trajectory and placental function. Key findings include evidence that birthweight is not a reliable marker of fetal stress, and that increases in embryo manipulation result in more deviant fetal growth curves. Because growth kinetics in early life are particularly relevant to adult metabolic physiology, we advise more rigorous assessment of fetal growth and placental function in human ART pregnancies, as well as continued follow-up of ART offspring throughout post-natal life. Finally, strategies to minimize embryo manipulations should be adopted whenever possible.

Creb1-Mecp2-(m)CpG complex transactivates postnatal murine neuronal glucose transporter isoform 3 expression.

The murine neuronal facilitative glucose transporter isoform 3 (Glut3) is developmentally regulated, peaking in expression at postnatal day (PN)14. In the present study, we characterized a canonical CpG island spanning the 5'-flanking region of the glut3 gene. Methylation-specific PCR and bisulfite sequencing identified methylation of this CpG ((m)CpG) island of the glut3 gene, frequency of methylation increasing 2.5-fold with a 1.6-fold increase in DNA methyl transferase 3a concentrations noted with advancing postnatal age (PN14 vs PN3). 5'-flanking region of glut3-luciferase reporter transient transfection in HT22 hippocampal neurons demonstrated that (m)CpGs inhibit glut3 transcription. Contrary to this biological function, glut3 expression rises synchronously with (m)CpGs in PN14 vs PN3 neurons. Chromatin immunoprecipitation (IP) revealed that methyl-CpG binding protein 2 (Mecp2) bound the glut3-(m)CpGs. Depending on association with specific coregulators, Mecp2, a dual regulator of gene transcription, may repress or activate a downstream gene. Sequential chromatin IP uncovered the glut3-(m)CpGs to bind Mecp2 exponentially upon recruitment of Creb1 rather than histone deacetylase 1. Co-IP and coimmunolocalization confirmed that Creb1 associated with Mecp2 and cotransfection with glut3-(m)CpG in HT22 cells enhanced glut3 transcription. Separate 5-aza-2'-deoxycytidine pretreatment or in combination with trichostatin A reduced (m)CpG and specific small interference RNAs targeting Mecp2 and Creb1 separately or together depleting Mecp2 and/or Creb1 binding of glut3-(m)CpGs reduced glut3 expression in HT22 cells. We conclude that Glut3 is a methylation-sensitive neuronal gene that recruits Mecp2. Recruitment of Creb1-Mecp2 by glut3-(m)CpG contributes towards transactivation, formulating an escape from (m)CpG-induced gene suppression, and thereby promoting developmental neuronal glut3 gene transcription and expression.

Changes in glucose transporter expression in monocytes of periparturient dairy cows.

The transition period of dairy cows is characterized by dramatic changes in metabolism and immune cell function that contributes to increased susceptibility to several economically important diseases. Monocyte and macrophage populations increase in blood and tissues of cows during the transition period and have enhanced inflammatory responses that may contribute to increased severity of disease. Glucose is a major energy source for activated monocytes and glucose uptake is facilitated by glucose transporters (GLUT). The objective of this study was to determine how bovine monocyte GLUT expression changes during lactogenesis and in response to proinflammatory stimulation. Blood samples were collected from 10 dairy cows approximately 5 wk before calving and during the first week of lactation. Monocytes were isolated from total peripheral blood mononuclear cells, and expression of GLUT1, GLUT3, and GLUT4 isoforms was assessed in resting cells and following endotoxin stimulation. In general, the onset of lactation served to decrease overall GLUT expression. Gene and protein expression of GLUT1 was significantly decreased after parturition, and GLUT3 and GLUT4 cell surface expression was also significantly decreased postcalving. Endotoxin stimulation, however, increased gene expression of GLUT3 and GLUT4, and gene expression for all GLUT isoforms was positively correlated to production of tumor necrosis factor-α. This study identified, for the first time, the presence of GLUT isoforms in bovine monocytes. Alterations in monocyte GLUT expression at the onset of lactation warrant further investigation to ascertain how changes in glucose uptake may contribute to periparturient inflammatory dysfunction.

Antidiabetic pharmacology: a link between metabolic syndrome and neuro-oncology?

One of the main topics of the annual meeting of the American Society for Clinical Oncology in 2011 were the results presented on breast cancer chemotherapy and concomitant administration of the oral antidiabetic metformin. The overall agreement was that current evidence is just enough to dramatically change the clinical practice of oncology, and in our case, brain cancer treatment, and that further research is needed to address the relationship between diabetes, metabolism, insulin analogues and neoplasia. Still, it is very interesting to explore the potentially beneficial effects of metformin in glioma chemo/immunotherapy and wait for results in the clinic. In the current paper we present the cell and molecular aspects of the metabolic syndrome, metformin administration and cancer chemotherapy, with a special emphasis in neuro-oncology, since brain tumors are usually devastating diseases with an extremely high mortality within two years of diagnosis even when surgical, radiotherapeutic and chemotherapeutic interventions are applied.

Does the association with diabetes say more about schizophrenia and its treatment?--the GLUT hypothesis.

All effective anti psychotic drugs block glucose transporter proteins (GLUTs), peripherally and in the brain. These drugs are implicated in hyperglycaemia as demonstrated in mouse and human studies. Clozapine is the strongest blocker, with Haloperidol the weakest. The GLUT hypothesis suggests that schizophrenia is partly due to poor functioning of brain glucose transporters (GLUT 1 and 3). Neuronal glucose malnutrition could result in excessive neuronal pruning (so called Crow's Type 2 with a predominance of negative symptoms) or result in recurrent/ineffective pruning (Type 1 with positive symptoms). GLUT blockade by anti psychotic agents could assist Type 1 patients to complete the pruning process by deactivating already damaged neurones and circuits, but will make Type 2 patients more cognitively impaired. Future treatment options are discussed in line with the above formulation.

The protein family of glucose transport facilitators: It's not only about glucose after all.

The protein family of facilitative glucose transporters comprises 14 isoforms that share common structural features such as 12 transmembrane domains, N- and C-termini facing the cytoplasm of the cell, and a N-glycosylation side either within the first or fifth extracellular loop. Based on their sequence homology, three classes can be distinguished: class I includes GLUT1-4 and GLUT14, class II the "odd transporters" GLUT5, 7, 9, 11, and class III the "even transporters" GLUT6, 8, 10, 12 and the proton driven myoinositol transporter HMIT (or GLUT13). With the cloning and characterization of the more recent class II and III isoforms, it became apparent that despite their structural similarities, the different isoforms not only show a distinct tissue-specific expression pattern but also show distinct characteristics such as alternative splicing, specific (sub)cellular localization, and affinities for a spectrum of substrates. This review summarizes the current understanding of the physiological role for the various transport facilitators based on human genetically inherited disorders or single-nucleotide polymorphisms and knockout mice models. The emphasis of the review will be on the potential functional role of the more recent isoforms.

Involvement of the p66Shc protein in glucose transport regulation in skeletal muscle myoblasts.

The p66(Shc) protein isoform regulates MAP kinase activity and the actin cytoskeleton turnover, which are both required for normal glucose transport responses. To investigate the role of p66(Shc) in glucose transport regulation in skeletal muscle cells, L6 myoblasts with antisense-mediated reduction (L6/p66(Shc)as) or adenovirus-mediated overexpression (L6/p66(Shc)adv) of the p66(Shc) protein were examined. L6/(Shc)as myoblasts showed constitutive activation of ERK-1/2 and disruption of the actin network, associated with an 11-fold increase in basal glucose transport. GLUT1 and GLUT3 transporter proteins were sevenfold and fourfold more abundant, respectively, and were localized throughout the cytoplasm. Conversely, in L6 myoblasts overexpressing p66(Shc), basal glucose uptake rates were reduced by 30% in parallel with a approximately 50% reduction in total GLUT1 and GLUT3 transporter levels. Inhibition of the increased ERK-1/2 activity with PD98059 in L6/(Shc)as cells had a minimal effect on increased GLUT1 and GLUT3 protein levels, but restored the actin cytoskeleton, and reduced the abnormally high basal glucose uptake by 70%. In conclusion, p66(Shc) appears to regulate the glucose transport system in skeletal muscle myoblasts by controlling, via MAP kinase, the integrity of the actin cytoskeleton and by modulating cellular expression of GLUT1 and GLUT3 transporter proteins via ERK-independent pathways.

Neuronal functions, feeding behavior, and energy balance in Slc2a3+/- mice.

Homozygous deletion of the gene of the neuronal glucose transporter GLUT3 (Slc2a3) in mice results in embryonic lethality, whereas heterozygotes (Slc2a3+/-) are viable. Here, we describe the characterization of heterozygous mice with regard to neuronal function, glucose homeostasis, and, since GLUT3 might be a component of the neuronal glucose-sensing mechanism, food intake and energy balance. Levels of GLUT3 mRNA and protein in brain were reduced by 50% in Slc2a3+/- mice. Electrographic features examined by electroencephalographic recordings give evidence for slightly but significantly enhanced cerebrocortical activity in Slc2a3+/- mice. In addition, Slc2a3+/- mice were slightly more sensitive to an acoustic startle stimulus (elevated startle amplitude and reduced prepulse inhibition). However, systemic behavioral testing revealed no other functional abnormalities, e.g., in coordination, reflexes, motor abilities, anxiety, learning, and memory. Furthermore, no differences in body weight, blood glucose, and insulin levels were detected between wild-type and Slc2a3+/- littermates. Food intake as monitored randomly or after intracerebroventricular administration of 2-deoxyglucose or d-glucose, or food choice for carbohydrates/fat was not affected in Slc2a3+/- mice. Taken together, our data indicate that, in contrast to Slc2a1, a single allele of Slc2a3 is sufficient for maintenance of neuronal energy supply, motor abilities, learning and memory, and feeding behavior.

Glucose transporter isoform-3-null heterozygous mutation causes sexually dimorphic adiposity with insulin resistance.

We examined male and female glucose transporter isoform-3 (GLUT3; placenta)-null heterozygous(+/-) mutation-carrying mice and compared them with age- and sex-matched wild-type(+/+) littermates. No difference in postnatal (1-2 days, 6-7 days, 12-13 days, 20-21 days), postsuckling (1-2 mo), and adult (3-6 mo) growth pattern was seen except for an increase in body weight of 9- to 11-mo-old male but not female GLUT3(+/-) mice. This change in male mutant mice was associated with increased total body fat mass, perirenal and epididymal white adipose tissue weight, and hepatic lipid infiltration. These minimally glucose-intolerant male mutant mice demonstrated no change in caloric intake but a decline in basal metabolic rate and insulin resistance. No perturbation in basal circulating glucose concentrations but an increase in insulin concentrations, triglycerides, and total cholesterol was observed in GLUT3(+/-) male mice. Tissue analysis in males and females demonstrated diminished GLUT3 protein in GLUT3(+/-) brain and skeletal muscle with no change in brain and adipose tissue GLUT1 protein concentrations. Furthermore, the male GLUT3(+/-) mice expressed decreased insulin-responsive GLUT4 in white adipose tissue and skeletal muscle sarcolemma. We conclude that the GLUT3(+/-) male mice develop adult-onset adiposity with insulin resistance.

Hypoxic regulation of glucose transport, anaerobic metabolism and angiogenesis in cancer: novel pathways and targets for anticancer therapeutics.

Cancer cells require a steady source of metabolic energy in order to continue their uncontrolled growth and proliferation. Accelerated glycolysis is one of the biochemical characteristics of cancer cells. Recent work indicates that glucose transport and metabolism are essential for the posttreatment survival of tumor cells, leading to poor prognosis. Glycolytic breakdown of glucose is preceded by the transport of glucose across the cell membrane, a rate-limiting process mediated by facilitative glucose transporter proteins belonging to the facilitative glucose transporter/solute carrier GLUT/SLC2A family. Tumors frequently show overexpression of GLUTs, especially the hypoxia-responsive GLUT1 and GLUT3 proteins. There are also studies that have reported associations between GLUT expression and proliferative indices, whilst others suggest that GLUT expression may be of prognostic significance. In this article we revisit Warburg's original hypothesis and review the recent clinical and basic research on the expression of GLUT family members in human cancers and in cell lines derived from human tumors. We also explore the links between hypoxia-induced genes, glucose transporters and angiogenic factors. Hypoxic tumors are significantly more malignant, metastatic, radio- and chemoresistant and have a poor prognosis. With the discovery the oxygen-sensitive transcription factor hypoxia-inducible factor (HIF-1) has come a new understanding of the molecular link between hypoxia and deregulated glucose metabolism. HIF-1 induces a number of genes integral to angiogenesis, e.g. vascular endothelial growth factor (VEGF), a process intimately involved with metastatic spread. This knowledge may enhance existing chemotherapeutic strategies so that treatment can be more rationally applied and personalized for cancer patients.

Adaptation of nutrient supply to fetal demand in the mouse involves interaction between the Igf2 gene and placental transporter systems.

The mammalian fetus is unique in its dependence during gestation on the supply of maternal nutrients through the placenta. Maternal supply and fetal demand for nutrients need to be fine tuned for healthy growth and development of the fetus along its genetic trajectory. An altered balance between supply and demand can lead to deviations from this trajectory with long-term consequences for health. We have previously shown that in a knockout lacking the imprinted placental-specific Igf2 transcript (P0), growth of the placenta is compromised from early gestation but fetal growth is normal until late gestation, suggesting functional adaptation of the placenta to meet the fetal demands. Here, we show that placental transport of glucose and amino acids are increased in the Igf2 P0(+/-) null and that this up-regulation of transport occurs, at least in part, through increased expression of the transporter genes Slc2a3 and Slc38a4, the imprinted member of the System A amino acid transporter gene family. Decreasing fetal demand genetically by removal of fetal Igf2 abolished up-regulation of both transport systems and reduced placental System A amino acid transport activity and expression of Slc38a2 in late gestation. Our results provide direct evidence that the placenta can respond to fetal demand signals through regulation of expression of specific placental transport systems. Thus, crosstalk between an imprinted growth demand gene (Igf2) and placental supply transporter genes (Slc38a4, Slc38a2, and Slc2a3) may be a component of the genetic control of nutrient supply and demand during mammalian development.

Hypoxia inducible factor-1 and facilitative glucose transporters GLUT1 and GLUT3: putative molecular components of the oxygen and glucose sensing apparatus in articular chondrocytes.

Articular cartilage is an avascular connective tissue in which the availability of oxygen and glucose is significantly lower than synovial fluid and plasma. Glucose is an important metabolic fuel and structural precursor that plays a key role in the synthesis of extracellular matrix macromolecules in articular cartilage. However, glucose concentrations in cartilage can fluctuate depending on age, physical activity and endocrine status. Chondrocytes are glycolytic cells and must be able to sense the quantities of oxygen and glucose available to them in the extracellular matrix and respond appropriately by adjusting cellular metabolism. Consequently chondrocytes must have the capacity to survive in an extracellular matrix with limited nutrients and low oxygen tensions. The molecular mechanisms responsible for allowing chondrocytes to adapt to these harsh environmental conditions are poorly understood. In this article we present a novel "dual" model of oxygen and glucose sensing in chondrocytes based on recent experimental data. This model incorporates the hypoxia-inducible factor alpha (HIF-1alpha) as an oxygen sensor and the hypoxia responsive facilitative glucose transporters, GLUT1 and GLUT3 as putative components of the glucose sensing apparatus in chondrocytes. Recent studies have shown that GLUT1 and GLUT3 are both expressed in chondrocytes and their HIF-1alpha-mediated transcription may be dually stimulated in response to hypoxia and low glucose conditions which in turn promote anaerobic glycolysis in favor of oxidative phosphorylation. This working model provides, for the first time, a unifying hypothesis to explain how chondrocytes might sense and respond to low oxygen tensions and alterations in extracellular glucose.