Effect of streptozotocin-induced maternal diabetes on fetal rat brain glucose transporters

Nociceptor-derived Reg3γ prevents endotoxic death by targeting kynurenine pathway in microglia

Nociceptors can fine-tune local or systemic immunity, but the mechanisms of nociceptive modulation in endotoxic death remain largely unknown. Here, we identified C-type lectin Reg3γ as a nociceptor-enriched hormone that protects the host from endotoxic death. During endotoxemia, nociceptor-derived Reg3γ penetrates the brain and suppresses the expression of microglial indoleamine dioxygenase 1, a critical enzyme of the kynurenine pathway, via the Extl3-Bcl10 axis. Endotoxin-administered nociceptor-null mice and nociceptor-specific Reg3γ-deficient mice exhibit a high mortality rate accompanied by decreased brain HK1 phosphorylation and ATP production despite normal peripheral inflammation. Such metabolic arrest is only observed in the brain, and aberrant production of brain quinolinic acid, a neurotoxic metabolite of the kynurenine pathway, causes HK1 suppression. Strikingly, the central administration of Reg3γ protects mice from endotoxic death by enhancing brain ATP production. By identifying nociceptor-derived Reg3γ as a microglia-targeted hormone, this study provides insights into the understanding of tolerance to endotoxic death.

Chronic maternal hyperglycemia induced during mid-pregnancy in rats increases RAGE expression, augments hippocampal excitability, and alters behavior of the offspring

Maternal diabetes during pregnancy may increase the risk of neurodevelopmental disorders in the offspring by increasing inflammation. A major source of inflammatory signaling observed in diabetes is activation of the receptor for advanced glycation end-products (RAGE), and increased RAGE expression has been reported in psychiatric disorders. Thus, we sought to examine whether maternal diabetes creates a proinflammatory state, triggered largely by RAGE signaling, that alters normal brain development and behavior of the offspring. We tested this hypothesis in rats using the streptozotocin (STZ; 50mg/kg; i.p.) model of diabetes induced during mid-pregnancy. Following STZ treatment, we observed a significant increase in RAGE protein expression in the forebrain of the offspring (postnatal day 1). Data obtained from whole-cell patch clamping of hippocampal neurons in cultures from the offspring of STZ-treated dams revealed a striking increase in excitability. When tested in a battery of behavioral tasks in early adulthood, the offspring of STZ-treated dams had significantly lower prepulse inhibition, reduced anxiety-like behavior, and altered object-place preference when compared to control offspring. In an operant-based strategy set-shifting task, STZ offspring did not differ from controls on an initial visual discrimination or reversal learning but took significantly longer to shift to a new strategy (i.e., set-shift). Insulin replacement with an implantable pellet in the dams reversed the effects of maternal diabetes on RAGE expression, hippocampal excitability, prepulse inhibition and object-place memory, but not anxiety-like behavior or set-shifting. Taken together, these results suggest that chronic maternal hyperglycemia alters normal hippocampal development and behavior of the offspring, effects that may be mediated by increased RAGE signaling in the fetal brain.

Gestational diabetes affects postnatal development of transport and enzyme functions in rat intestine

The effect of alloxan-induced gestational diabetes on the postnatal development of brush border disaccharidases and D-glucose transport in rat intestine was studied. Pups born to diabetic mothers showed 92-22% increase in blood sugar levels compared with the controls. Western blot and RT-PCR analyses revealed that the activities of brush border sucrase, lactase and Sodium Glucose Co-transporter 1 (SGLT1) correlates with protein and mRNA levels in intestine of pups born to diabetic rat mothers after 5-45 days of birth. Intestinal histology in pups born to diabetic mothers at day 10 and 45 after birth showed distorted cellular organization of mucosa with a decrease in the number of secretary goblet cells and regression of tubular mass. These findings suggest that the genetic switch in utero regulates the postnatal expression of enzyme and transport functions in intestine of pups born to diabetic rat mothers. This may influence the growth and development of offsprings later in life.

Exposure to maternal diabetes is associated with altered fetal growth patterns: A hypothesis regarding metabolic allocation to growth under hyperglycemic-hypoxemic conditions

The prevalence of diabetes is rising worldwide, including women who grew poorly in early life, presenting intergenerational health problems for their offspring. It is well documented that fetuses exposed to maternal diabetes during pregnancy experience both macrosomia and poor growth outcomes in birth size. Less is known about the in utero growth patterns that precede these risk factor expressions. Fetal growth patterns and the effects of clinical class and glycemic control were investigated in 37 diabetic pregnant women and their fetuses and compared to 29 nondiabetic, nonsmoking maternal/fetal pairs who were participants in a biweekly longitudinal ultrasound study with measurements of the head, limb, and trunk dimensions. White clinical class of the diabetic women was recorded (A2-FR) and glycosylated hemoglobin levels taken at the time of measurement assessed glycemic control (median 6.9%, interquartile range 5.6-9.2%). No significant difference in fetal weight was found by exposure. The exposed sample had greater abdominal circumferences from 21 weeks (P < or = 0.05) and shorter legs, but greater upper arm and thigh circumferences accompanied increasing glycemia in the second trimester. In the third trimester, exposed fetuses had a smaller slope for the occipital frontal diameter (P = 0.00) and were brachycephalic. They experienced a proximal/distal growth gradient in limb proportionality with higher humerus / femur ratios (P = 0.04) and arms relatively long by comparison with legs (P = 0.02). HbA1c levels above 7.5% accompanied shorter femur length for thigh circumference after 30 gestational weeks of age. Significant effects of diabetic clinical class and glycemic control were identified in growth rate timing. These growth patterns suggest that hypoxemic and hyperglycemic signals cross-talk with their target receptors in a developmentally regulated, hierarchical sequence. The increase in fetal fat often documented with diabetic pregnancy may reflect altered growth at the level of cell differentiation and proximate mechanisms controlling body composition. These data suggest that the maternal-fetal interchange circuit, designed to share and capture resources on the fetal side, may not have had a long evolutionary history of overabundance as a selective force, and modern health problems drive postnatal sequelae that become exacerbated by increasing longevity.

Intrauterine hyperglycemia increases insulin binding sites but not glucose transporter expression in discrete brain areas in term rat fetuses

Diabetic pregnancy results in several metabolic and hormonal disorders, both in the embryo and the fetus of different species, including humans. Insulin is a potent modulator of brain development and is suggested to promote the differentiation and maturation of hypothalamic or related extrahypothalamic structures, which are directly involved in neural inputs to the pancreas. Because these structures are known to be specifically responsive both to insulin and glucose, we examined the effects of 48-h hyperglycemic clamps in unrestrained pregnant rats on insulin binding and glucose transporter expression in hypothalamic and extrahypothalamic-related areas of their fetal offspring. The main result was an increase in insulin binding in the ventromedial hypothalamic nucleus (VMH), the arcuate nucleus (AN), and the lateral hypothalamus (LH), and in the nucleus of the tractus solitarius (NTS) for extrahypothalamic areas (+30% in the VMH, +37% in the AN, +25.8% in the LH, and +37.3% in the NTS). The deleterious effect of brain hyperinsulinism during the late gestational stage does not seem to act through glucose transporter (GLUT) expression, inasmuch as no relationship between GLUT level and hyperinsulinism in brain areas could be observed. The specific increase in insulin binding in areas involved in the nervous control of metabolism could be a factor in the increased glucose intolerance and impairment of insulin secretion that was previously observed in the adult rats from hyperglycemic mothers.

Postnatal hypoxic-ischemic brain injury alters mechanisms mediating neuronal glucose transport

We examined the effect of hypoxic ischemia and hypoxia vs. normoxia on postnatal murine brain substrate transporter concentrations and function. We detected a transient increase in the neuronal brain glucose transporter isoform (GLUT-3) in response to hypoxic ischemia after 4 h of reoxygenation. This increase was associated with no change in GLUT-1 (blood-brain barrier/glial isoform), monocarboxylate transporter isoforms 1 and 2, synapsin I (neuronal marker), or Bax (proapoptotic protein) but with a modest increase in Bcl-2 (antiapoptotic mitochondrial protein) protein concentrations. At 24 h of reoxygenation, the increase in GLUT-3 disappeared but was associated with a decline in Bcl-2 protein concentrations and the Bcl2:Bax ratio, an increase in caspase-3 enzyme activity (apoptotic effector enzyme), and extensive DNA fragmentation, which persisted later in time (48 h) only in the hippocampus. Hypoxia alone in the absence of ischemia was associated with a transient but modest increase in GLUT-3 and synapsin I protein concentrations, which did not cause significant apoptosis and/or necrosis. Assessment of glucose transporter function by 2-deoxyglucose (2-DG) uptake using two distinct techniques, namely positron emission tomography (PET) and the modified Sokoloff method, revealed a discrepancy due to glucose uptake by extracranial Harderian glands that masked the accurate detection of intracranial brain glucose uptake by PET scanning. The modified Sokoloff method assessing 2-DG uptake revealed that the transient increase in GLUT-3 was critical in protecting against a decline in brain glucose uptake. We conclude that hypoxic-ischemic brain injury is associated with transient compensatory changes targeted at protecting glucose delivery to fuel cellular energy metabolism, which then may delay the processes of apoptosis and cell necrosis.

Time-dependent physiological regulation of ovine placental GLUT-3 glucose transporter protein

We immunolocalized the GLUT-3 glucose transporter isoform versus GLUT-1 in the late-gestation epitheliochorial ovine placenta, and we examined the effect of chronic maternal hyperglycemia and hypoglycemia on placental GLUT-3 concentrations. GLUT-3 was limited to the apical surface of the trophoectoderm, whereas GLUT-1 was on the basolateral and apical surfaces of this cell layer and in the epithelial cells lining the placental uterine glands. GLUT-3 concentrations declined at 17-20 days of chronic hyperglycemia (P < 0.05), associated with increased uterine and uteroplacental net glucose uptake rate, but a normal fetal glucose uptake rate was observed. Chronic hypoglycemia did not change GLUT-3 concentrations, although uterine, uteroplacental, and fetal net glucose uptake rates were decreased. Thus maternal hyperglycemia causes a time-dependent decline in the entire placental glucose transporter pool (GLUT-1 and GLUT-3). In contrast, maternal hypoglycemia decreases GLUT-1 but not GLUT-3, resulting in a relatively increased GLUT-3 contribution to the placental glucose transporter pool, which could maintain glucose delivery to the placenta relative to the fetus when maternal glucose is low.

Glucose transporters, hexokinase, and phosphofructokinase in brain of rats with perinatal asphyxia

Transport by glucose transporters from blood to the brain during hypoxic-ischemic conditions is well studied. However, the recent availability of a clinically related animal model of perinatal asphyxia and the fact that no concomitant determination of glucose transporters, parameters for glucose utilization, brain glucose, and cerebral blood flow (CBF) have been reported and the early phase of perinatal asphyxia has never been studied led us to perform the following study. Cesarean section was performed on full-term pregnant rats. The obtained pups within patent uterus horns were placed into a water bath at 37 degrees C from which they were subsequently removed after 5-20 min of graded asphyxia. Brain pH, brain tissue glucose, CBF, mRNA and activity of hexokinase and phosphofructokinase, and mRNA and protein of the glucose transporters GLUTI and GLUT3 were determined. Brain pH decreased and brain tissue glucose and CBF increased with the length of the asphyctic period; hexokinase and phosphofructokinase mRNA and activity were unchanged during the observation period. The mRNA and protein of both glucose transporters were comparable between normoxic and asphyctic groups. We show that glucose transport and utilization are unchanged in the early phase of perinatal asphyxia at a time point when CBF and brain glucose are already significantly increased and severe acidosis is present.

Effect of primary congenital hypothyroidism upon expression of genes mediating murine brain glucose uptake

Using hyt/hyt mice that exhibit naturally occurring primary hypothyroidism (n = 72) and Balb/c controls (n = 66), we examined the mRNA, protein, and activity of brain glucose transporters (Glut 1 and Glut 3) and hexokinase I enzyme at various postnatal ages (d 1, 7, 14, 21, 35, and 60). The hyt/hyt mice showed an age-dependent decline in body weight (p < 0.04) and an increase in serum TSH levels (p < 0.001) at all ages. An age-dependent translational/posttranslational 40% decline in Glut 1 (p = 0.02) with no change in Glut 3 levels was observed. These changes were predominant during the immediate neonatal period (d 1). A posttranslational 70% increase in hexokinase enzyme activity was noted at d 1 alone (p < 0.05) with no concomitant change in brain 2-deoxy-glucose uptake. This was despite a decline in the hyt/hyt glucose production rate. We conclude that primary hypothyroidism causes a decline in brain Glut 1 associated with no change in Glut 3 levels and a compensatory increase in hexokinase enzyme activity. These changes are pronounced only during the immediate neonatal period and disappear in the postweaned stages of development. These hypothyroid-induced compensatory changes in gene products mediating glucose transport and phosphorylation ensure an adequate supply of glucose to the developing brain during transition from fetal to neonatal life.

Effect of development and hypoxic-ischemia upon rabbit brain glucose transporter expression

We have cloned and sequenced a full length rabbit GLUT 1 and partial rabbit GLUT 3 cDNAs. The derived rabbit GLUT 3 peptide revealed 84% homology to the mouse, 82% to the rat, human, dog, and sheep, and 69% to the chicken GLUT 3 peptides. Using Northern blot analysis, we investigated the tissue and brain cellular distribution of GLUT 1 and GLUT 3 expression. In addition, we examined the effect of development and hypoxic-ischemia upon brain GLUT 1 and GLUT 3 mRNA levels. While GLUT 1 mRNA was observed in most tissues, GLUT 3 was expressed predominantly in the brain, placenta, stomach, and lung with minor amounts in the heart, kidney and skeletal muscle. In the brain, both GLUT 1 and GLUT 3 were noted in neuron- and glial-enriched cultures. Both GLUT 1 and GLUT 3 mRNA levels demonstrated a similar developmental progression (p<0.05) secondary to post-transcriptional mechanisms. Further, while hypoxic-ischemia did not significantly affect brain GLUT 1 mRNA and protein, it altered GLUT 3 mRNA levels in a region-specific manner, with a three-fold increase in the cerebral cortex, a two-fold increase in the hippocampus, and a 50% increase in the caudate nucleus (p<0.05). We conclude, that the rabbit GLUT 3 peptide sequence exhibits 82-84% homology to that of other species in the coding region with a 62-89% sequence identity in the 3'-untranslated region. The tissue-specific expression of rabbit GLUT 3 mimics that of the human closely. Postnatal development and hypoxic-ischemia with reperfusion injury cause an increase in brain GLUT 3 expression, as a response to synaptogenesis and substrate deprivation, respectively.

Time-dependent and tissue-specific effects of circulating glucose on fetal ovine glucose transporters

To determine the cellular adaptations to fetal hyperglycemia and hypoglycemia, we examined the time-dependent effects on basal (GLUT-1 and GLUT-3) and insulin-responsive (GLUT-4) glucose transporter proteins by quantitative Western blot analysis in fetal ovine insulin-insensitive (brain and liver) and insulin-sensitive (myocardium, skeletal muscle, and adipose) tissues. Maternal glucose infusions causing fetal hyperglycemia resulted in a transient 30% increase in brain GLUT-1 but not GLUT-3 levels and a decline in liver and adipose GLUT-1 and myocardial and skeletal muscle GLUT-1 and GLUT-4 levels compared with gestational age-matched controls. Maternal insulin infusions leading to fetal hypoglycemia caused a decline in brain GLUT-3, an increase in brain GLUT-1, and a subsequent decline in liver GLUT-1, with no significant change in insulin-sensitive myocardium, skeletal muscle, and adipose tissue GLUT-1 or GLUT-4 concentrations, compared with gestational age-matched sham controls. We conclude that fetal glucose transporters are subject to a time-dependent and tissue- and isoform-specific differential regulation in response to altered circulating glucose and/or insulin concentrations. These cellular adaptations in GLUT-1 (and GLUT-3) are geared toward protecting the conceptus from perturbations in substrate availability, and the adaptations in GLUT-4 are geared toward development of fetal insulin resistance.

Developmental regulation of genes mediating murine brain glucose uptake

We examined the molecular mechanisms that mediate the developmental increase in murine whole brain 2-deoxyglucose uptake. Northern and Western blot analyses revealed an age-dependent increase in brain GLUT-1 (endothelial cell and glial) and GLUT-3 (neuronal) membrane-spanning facilitative glucose transporter mRNA and protein concentrations. Nuclear run-on experiments revealed that these developmental changes in GLUT-1 and -3 were regulated posttranscriptionally. In contrast, the mRNA and protein levels of the mitochondrially bound glucose phosphorylating hexokinase I enzyme were unaltered. However, hexokinase I enzyme activity increased in an age-dependent manner suggestive of a posttranslational modification that is necessary for enzymatic activation. Together, the postnatal increase in GLUT-1 and -3 concentrations and hexokinase I enzymatic activity led to a parallel increase in murine brain 2-deoxyglucose uptake. Whereas the molecular mechanisms regulating the increase in the three different gene products may vary, the age-dependent increase of all three constituents appears essential for meeting the increasing demand of the maturing brain to fuel the processes of cellular growth, differentiation, and neurotransmission.