[Glucagon-like peptide-1 regulates lipid metabolism in hepatocytes through Foxo1/3].

Objective: Glucagon-like peptide-1 (GLP-1) has been reported to be effective in the treatment of nonalcoholic fatty liver disease (NAFLD). However, the molecular mechanism of GLP-1 on NAFLD is remained unclear. The present study was to detect whether the effect of GLP-1 on triglyceride (TG) content in hepatocytes is dependent on Foxos. Methods: HepG2 cells were treated with palmitic/oleic acid for 24 h. The knockdown of Foxo1, Foxo3 was conducted through small interfering RNA (siRNA). Real time PCT (RT-PCR) was used to detect the changes of the SREBP1c and Acox2 genes in HepG2 cells after Foxo1/3 knockdown. Results: As expected, palmitic/oleic acid increased TG concentration in HepG2 cells [(12.65 ± 1.32) µg/mg vs. (4.32±0.54) µg/mg, P<0.05]. Addition of GLP-1 dose (10, 50, 100nmol/L) dependently lowered the TG content and reached plateau at 100 nmol/L of GLP-1 [TG(8.38±1.47) µg/mg]. The GLP-1 effect on TG remained after knocking down either Foxo1 [(9.09±1.34)µg/mg] or Foxo3 [(8.90±1.60) µg/mg] alone, but not when knocking down Foxo1 and Foxo3 (Foxo1/3) together [(14.66±1.77)µg/mg]. Moreover, knocking down Foxo1/3 also abolished GLP-1 effect on SREBP1c and Acox2 expression. Conclusion: GLP-1 can inhibit the synthesis of TG in hepatocytes depending on Foxo1 and Foxo3. Further studies are needed to explore the specific mechanisms.

Rosiglitazone attenuates tumor necrosis factor-α-induced protein-tyrosine phosphatase-1B production in HepG2 cells.

Tumor necrosis factor (TNF)-α impairs insulin signaling and plays an important role in the development of insulin resistance. The underlying molecular mechanism by which TNF-α regulates hepatic protein-tyrosine phosphatase (PTP)-1B expression is not well understood. Rosiglitazone is used as a drug to improve insulin sensitivity in vivo. However, its effect on TNF-α-induced PTP-1B expression remains to be explored. In the present study, we sought to identify the mechanism of TNF-α-regulated hepatic PTP-1B expression and evaluate the effect of rosiglitazone on TNF-α-induced hepatic PTP-1B upregulation. TNF-α up-regulates PTP- 1B expression in a dose-dependent manner and decreases insulin-stimulated phosphorylation of IR and insulin receptor substrate-1 in HepG2 cells. TNF-α increases p65 protein level and nuclear factor κB (NF-κB) activity. Inhibition of NF-κB activation by pyrrolidine dithiocarbamate impairs TNF-α-induced PTP-1B upregulation. Rosiglitazone significantly blocks TNF-α-induced PTP-1B upregulation and NF-κB activation. Our data strongly suggest that TNF-α-induced PTP-1B overexpression may contribute to hepatic IR in obesity and diabetes, and NF-κB is involved in rosiglitazone attenuated PTP- 1B upregulation by TNF-α.

Active immunization with glucose-dependent insulinotropic polypeptide vaccine influences brain function and behaviour in rats.

Glucose-dependent insulinotropic polypeptide (GIP) is involved in the aetiology of obesity induced by overnutrition, and blocking GIP activity may be valuable to anti-obesity treatment. However, GIP and GIP receptor are closely related to various brain functions which have caused very little data to be published concerning this cerebral functionality after blocking GIP activity. Here, we showed that active vaccination of mature rats with GIP immunoconjugates [GIP-keyhole limpet haemocyanin (KLH)] was associated with changes in body weight. Furthermore, we also observed significant changes in brain function and behaviour. Data indicated that GIP-KLH-immunized rats showed decreased spontaneous activity in the open field test, decreased cerebral glucose utilization assessed by 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT), and increased apoptosis and proliferation of hippocampal granule cells marked by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) or proliferating cell nuclear antigen method. In conclusion, we have shown that vaccine-induced antibodies inhibited GIP activity in vivo and led to significant changes in brain function and behaviour, which underscore the need to address any potential problems GIP-targeted immunotherapy may involve in further research.

Serum resistin level in essential hypertension patients with different glucose tolerance.

AIMS: To investigate resistin concentrations in patients with essential hypertension and different glucose tolerance and the relationship between serum resistin level and blood glucose. METHODS: Sixty-five patients with essential hypertension [13 with Type 2 diabetes mellitus (DM), 26 with impaired glucose tolerance (IGT), and 26 with normal glucose tolerance (NGT); 30 males, 35 females] were studied. Fasting serum resistin concentrations were measured by enzyme immunoassay (EIA). Oral glucose tolerance tests and insulin release tests were used to calculate glucose area under the curve (AUCG), the ratio of insulin to glucose (DeltaI30/DeltaG30), and insulin sensitivity index (ISI) according to Cederholm's formula. RESULTS: Fasting serum resistin concentrations (microg/l) in DM (34.9 +/- 10.2) patients were significantly higher than those in IGT (25.1 +/- 10.4) (P < 0.05) and in NGT (21.5 +/- 7.9) (P < 0.05) patients. Pearson correlation showed that fasting serum resistin concentration was correlated with AUCG (r = 0.445, P < 0.001), ISI (r = -0.322, P < 0.01) and DeltaI30/DeltaG30 (r = -0.366, P < 0.01), but not body mass index and waist-hip ratio. After adjustment for gender, age and body mass index (BMI), partial correlation analysis showed that the fasting serum resistin concentrations were still correlated with AUCG (r = 0.327, P < 0.01) and DeltaI30/DeltaG30 (r = -0.348, P < 0.01), but ISI. CONCLUSION: Resistin may be involved in the development of diabetes in humans.

Postsynaptic calcium/calmodulin-dependent protein kinase II is required to limit elaboration of presynaptic and postsynaptic neuronal arbors.

Neuronal dendritic and axonal arbors grow to a characteristic size and then stabilize their structures. Activity-dependent stop-growing signals may limit neuronal process elaboration. We tested whether endogenous calcium/calmodulin-dependent protein kinase II (CaMKII) activity in postsynaptic optic tectal cells is required to restrict the elaboration of neuronal processes in the Xenopus tadpole retinotectal projection. Optic tectal cells were infected with vaccinia viruses that express CaMKII-specific inhibitory peptides. In vivo time-lapse imaging revealed that expression of CaMKII inhibitors blocked the growth restriction that normally occurs during maturation of tectal cell dendritic arbors. Postsynaptic CaMKII inhibition also increased the growth of presynaptic retinotectal axon arbors. The results indicate that endogenous postsynaptic CaMKII activity is required to limit the growth of presynaptic and postsynaptic arbor structures in vivo.

Dendritic dynamics in vivo change during neuronal maturation.

In vivo imaging of optic tectal neurons in the intact Xenopus tadpole permits direct observation of the structural dynamics that occur during dendritic arbor formation. Based on images of single DiI-labeled neurons collected at daily intervals over a period of 6 d, we divided tectal cell development into three phases according to the total length of the dendritic arbor. During phase 1, the cell differentiates from a neuroepithelial cell type and extends an axon out of the tectum. The total dendritic branch length (TDBL) is <100 micrometers. During phase 2, when TDBL is 100-400 micrometers, the dendritic arbor grows rapidly. During phase 3, when TDBL is >400 micrometers, the dendritic arbor grows slowly and appears stable. Neurons at different positions along the rostrocaudal developmental axis of the tectum were imaged at 2 hr intervals over 6 hr and at 24 hr intervals over several days. Images collected at 2 hr intervals were analyzed to determine rates of branch additions and retractions. Morphologically complex, phase 3 neurons show half the rate of branch additions and retractions as phase 2 neurons. Therefore, rapidly growing neurons have dynamic dendritic arbors, and slower-growing neurons are structurally stable. The change in growth rate and dendritic arbor dynamics from phase 2 to phase 3 correlates with the developmental increase in synaptic strength in neurons located along the rostrocaudal tectal axis. The data are consistent with the idea that strong synaptic inputs stabilize dendritic arbor structures and that weaker synaptic inputs are permissive for a greater degree of dynamic rearrangements and a faster growth rate in the dendritic arbor.

Expression of constitutively active CaMKII in target tissue modifies presynaptic axon arbor growth.

Calcium/calmodulin-dependent protein kinase II (CaMKII) can be regulated by synaptic activity and could therefore be involved in activity-dependent control of neuronal growth. We tested whether increased CaMKII activity in postsynaptic optic tectal neurons can modify the development of retinotectal axons in Xenopus. The elaboration of individual presynaptic retinal axons was observed in vivo before and up to 3 days after infecting the tectal cells with vaccinia virus carrying the gene for constitutively active truncated CaMKII (tCaMKII). Elevated postsynaptic CaMKII activity prevented the axons from developing the complexity of normal arbors by increasing the normal rate of branch retractions. Some effects of tCaMKII on arbor morphology were seen 1 day after infection, but they became more dramatic by the third day. The results suggest that postsynaptic CaMKII plays a role in the development of presynaptic arbor structure.

Infection of frog neurons with vaccinia virus permits in vivo expression of foreign proteins.

Vaccinia virus can be used to infect cells in the CNS of frogs, Xenopus laevis, and Rana pipiens, both in vivo and in vitro. In vivo infections were accomplished by injection of viral solution into the tectal ventricle of stage 40-48 tadpoles or by local injections into distinct neural regions. Infections with high titer of virus injected into the ventricle resulted in the majority of cells in the brain expressing foreign protein, while cells in the retina and optic nerve showed no expression. Infection with lower viral titers resulted in fewer infected cells that were distributed throughout the otherwise normal tissue. Intense expression of foreign protein in the brain was observed 36 hr after injection and remained high for at least 4 days. Infected animals developed normally and had the same number of cells in the optic tectum as control animals. Infection with a recombinant virus carrying the gene for Green Fluorescent Protein labels neurons, so that infected cells can be observed in vivo. Vaccinia virus provides a versatile means to alter proteins in distinct populations of neurons in amphibia.

Respiratory rhythm in the isolated central nervous system of newborn opossum.

1. Respiratory activity was recorded from spinal ventral roots in the isolated intact central nervous system (CNS) of newborn opossum, Monodelphis domestica. These signals occurred in synchrony with movements of the ribs and the electromyogram (EMG) recorded from the intercostal muscles during inspiration. Rhythmical activity could be recorded for more than 6 h in acute preparations. 2. The rhythm-generating region was shown to be located in the lower brain stem by perfusing different CNS regions with medium containing 20 mmoll-1 Mg2+, which blocks synaptic transmission reversibly in the opossum CNS. The conclusion that respiration was generated by neurones in the lower brain stem was further confirmed by selective ablation of part of the CNS. 3. Recordings were made from 128 neurones in the respiratory region of the lower brain stem with activity related to the respiratory rhythm. They consisted of two inspiratory groups and two expiratory groups. In the groups of inspiratory units, recordings were made from 69 early inspiratory and 38 inspiratory units. In the groups of expiratory units, recordings were made from 17 post-inspiratory and 4 expiratory units. The sites of 22 respiratory neurones were marked in 4-day-old animals by injecting Pontamine Sky Blue. These neurones were distributed from 175 microns anterior to 525 microns posterior to the obex, from 225 to 450 microns lateral to the midline and from 175 to 425 microns deep to the ventral surface of the brain stem. 4. The respiratory rhythm recorded in the isolated CNS was influenced by pH and neurotransmitters. The respiratory rate decreased by about 26% at high pH (7.7) and increased by about 33% at low pH (7.1). Bath application of noradrenaline (30-100 mumol l-1) decreased the respiratory rate and increased the amplitude of the rhythmic bursts significantly. All these effects were reversible. 5. The results presented here indicate that the isolated intact CNS of newborn opossum offers advantages for exploring mechanisms responsible for generating the respiratory rhythm.

The intact central nervous system of the newborn opossum in long-term culture: fine structure and GABA-mediated inhibition of electrical activity.

1. The entire central nervous system (CNS) of the newly born, South American opossum (Monodelphis domestica) was isolated and maintained in basal medium, Eagle's (BME) with 0.2% foetal calf serum and antibiotics. Isolated CNS preparations remained electrically excitable for up to 10 days. The fine structure of the spinal cord was normal after 5 days in culture: axons, synapses, dendrites and glia were virtually unchanged. Signs of degeneration were evident only in dorsal areas of the spinal cord, which had been denervated by removal of the dorsal root ganglia during dissection. 2. Amino acid transmitters such as glycine, glutamate, N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid (GABA), applied to the bathing fluid, rapidly and reversibly inhibited synaptic transmission in cervical segments of the spinal cord. GABA (10-100 mumol l-1) produced a dose-dependent reduction in the magnitude of ventral root responses evoked by dorsal root stimulation. GABA also inhibited synaptically activated compound action potentials produced by spinal cord stimulation. Dose-response curves for GABA obtained in different preparations were highly reproducible. 3. Both GABAA and GABAB receptors were reversibly activated by selective agonists and inhibited by specific antagonists. The actions of GABA were potentiated by benzodiazepines, competitively antagonised by bicuculline (a selective GABAA antagonist) and mimicked by muscimol (a GABAA agonist). Baclofen (a specific GABAB agonist) also inhibited electrical activity and was competitively antagonised by the GABAB antagonist, CGP 35348. 4. After 5 days of culture in BME or minimal essential medium (MEM), GABA dose-response curves were unchanged from those observed immediately after removal of the CNS. The inhibitory potency of baclofen was also unaffected by culture in BME. By contrast, after 5 days of culture in MEM, baclofen no longer inhibited electrical activity. This difference between BME and MEM could be attributed to the higher content of L-histidine in MEM. Thus, addition of 150 mumol l-1 L-histidine to BME produced similar results to culture in MEM: the inhibitory action of baclofen was virtually abolished after 3-5 days. L-Histidine had no effect on freshly dissected preparations. Chronic application of L-histidine did not affect glycine or glutamate responses after 5 days. Addition of D-histidine or other amino acids, such as arginine, to BME did not abolish the responses to baclofen. 5. These results show that the isolated CNS of the newborn opossum survives well in long-term culture and that it provides a useful preparation to study receptor development and plasticity of an intact mammalian CNS in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of GABAB receptors by histamine and neuronal activity in the isolated spinal cord of neonatal opossum in culture.

The aim of these experiments has been to analyse the properties of receptors for the transmitter gamma-aminobutyric acid (GABA) in developing mammalian nervous system. Changes in responses of GABAB receptors have been measured after alterations of the chemical environment and the level of electrical activity. We have previously shown that when the central nervous system (CNS) of the new-born opossum, Monodelphis domestica, is cultured for three to five days in the presence of histidine, inhibition by baclofen, a GABAB agonist, disappears (Stewart et al. 1991). We have now investigated whether histidine acts indirectly by way of conversion to histamine. As with histidine, culture with 150 microM histamine for five days virtually abolished the inhibition by baclofen. The effects of histidine, as well as histamine, were blocked by mepyramine, a histamine H1-receptor antagonist, and by ranitidine, an H2-antagonist. Tetrodotoxin (TTX), which blocks all electrical activity, protected preparations from the action of histidine but not histamine. Our results suggest that histidine is converted to histamine, which reduces the efficacy of GABAB agonists. We conclude that, in the developing mammalian CNS, transmitter levels and electrical activity can selectively influence the properties of receptors.