Glucose-induced dissociation of glucokinase from its regulatory protein in the nucleus of hepatocytes prior to nuclear export

The glucose phosphorylating enzyme glucokinase regulates glucose metabolism in the liver. Glucokinase activity is modulated by a liver-specific competitive inhibitor, the glucokinase regulatory protein (GRP), which mediates sequestration of glucokinase to the nucleus at low glucose concentrations. However, the mechanism of glucokinase nuclear export is not fully understood. In this study we investigated the dynamics of glucose-dependent interaction and translocation of glucokinase and GRP in primary hepatocytes using fluorescence resonance energy transfer, selective photoconversion and fluorescence recovery after photobleaching. The formation of the glucokinase:GRP complex in the nucleus of primary hepatocytes at 5 mmol/l glucose was significantly reduced after a 2 h incubation at 20 mmol/l glucose. The GRP was predominantly localized in the nucleus, but a mobile fraction moved between the nucleus and the cytoplasm. The glucose concentration only marginally affected GRP shuttling. In contrast, the nuclear export rate of glucokinase was significantly higher at 20 than at 5 mmol/l glucose. Thus, glucose was proven to be the driving-force for nuclear export of glucokinase in hepatocytes. Using the FLII12Pglu-700μ-δ6 glucose nanosensor it could be shown that in hepatocytes the kinetics of nuclear glucose influx, metabolism or efflux were significantly faster compared to insulin-secreting cells. The rapid equilibration kinetics of glucose flux into the nucleus facilitates dissociation of the glucokinase:GRP complex and also nuclear glucose metabolism by free glucokinase enzyme. In conclusion, we could show that a rise of glucose in the nucleus of hepatocytes releases active glucokinase from the glucokinase:GRP complex and promotes the subsequent nuclear export of glucokinase.     

Prodromal Huntington Disease as a Model for Functional Compensation of Early Neurodegeneration

Functional compensation demonstrated as mechanism to offset neuronal loss in early Alzheimer disease may also occur in other adult-onset neurodegenerative diseases, particularly Huntington disease (HD) with its genetic determination and gradual changes in structural integrity. In HD, neurodegeneration typically initiates in the dorsal striatum, successively affecting ventral striatal areas. Investigating carriers of the HD mutation with evident dorsal, but only minimal or no ventral striatal atrophy, we expected to find evidence for compensation of ventral striatal functioning. We investigated 14 pre- or early symptomatic carriers of the mutation leading to HD and 18 matched healthy controls. Participants underwent structural T1 magnetic resonance imaging (MRI) and functional MRI during a reward task that probes ventral striatal functioning. Motor functioning and attention were assessed with reaction time (RT) tasks. Structural images confirmed a specific decrease of dorsal striatal but only marginal ventral striatal volume in HD relative to control subjects, paralleling prolonged RT in the motor response tasks. While behavioral performance in the reward task during fMRI scanning was unimpaired, reward-related fMRI signaling in the HD group was differentially enhanced in the bilateral ventral striatum and in bilateral orbitofrontal cortex/anterior insula, as another region sensitive to reward processing. We provide evidence for the concept of functional compensation in premanifest HD which may suggest a defense mechanism in neurodegeneration. Given the so far inevitable course of HD with its genetically determined endpoint, this disease may provide another model to study the different aspects of the concept of functional compensation.     

Cardio-Respiratory Reference Data in 4631 Healthy Men and Women 20-90 Years: The HUNT 3 Fitness Study

Purpose

To provide a large reference material on key cardio-respiratory variables in a healthy population of Norwegian men and women aged 20–90 years.

Methods

Sub maximal and peak levels of cardio-respiratory variables were measured using cardiopulmonary exercise testing during treadmill running.

Results

The highest peak ventilation among men (141.9±24.5 L·min⁻¹) and women (92.0±16.5 L·min⁻¹) was observed in the youngest age group (20–29 years, sex differences p<0.001) with an average 7% reduction per decade. The highest tidal volumes were observed in the 30–39 and 40–49 year age groups among men (2.94±0.46 L) and women (2.06±0.32 L) (sex differences p<0.001), with a subsequent average 6% reduction per decade. Ventilatory threshold and respiratory compensation point were observed at approximately 77% and 87% of peak oxygen uptake (VO_2peak) among men and women, respectively. The best ventilatory efficiency (EqVCO_2Than) was observed in the youngest age group (20–29 years) in both men (26.2±2.8) and woman (27.5±2.7) (sex differences p<0.001) with an average 3% deterioration in ventilatory efficiency per decade.

Conclusion

This is the largest European reference material of cardio-respiratory variables in healthy men and women aged 20–90 years, establishing normal values for, and associations between key cardio-respiratory parameters. This will be useful in clinical decision making when evaluating cardiopulmonary health in similar populations.     

Synthesis and pharmacological activity of fluorescent histamine H2 receptor antagonists related to potentidine

Fluorescently labeled histamine H(2) receptor antagonists were synthesized starting from N-cyano-N'-[3-(3-piperidin-1-ylmethylphenoxy)propyl]guanidines with an additional N"-omega-aminoalkyl substituent (chain lengths 2-8 methylene groups) or from 3-(3-piperidin-1-ylmethylphenoxy)propylamine. The primary amino group was derivatized with various fluorophores (fluorescein, acridine, dansyl, nitrobenzoxadiazole (NBD), indolo[2,3-a]quinolizine). On the isolated spontaneously beating guinea pig right atrium most of the fluorescent probes were only weakly active, however, the NBD-labeled substances proved to be potent histamine H(2) receptor antagonists achieving pA(2) values in the range of 7.5-8.0, comparable to the activity of famotidine.     

A comprehensive strategy enabling high-resolution functional analysis of the yeast genome

Functional genomic studies in Saccharomyces cerevisiae have contributed enormously to our understanding of cellular processes. Their full potential, however, has been hampered by the limited availability of reagents to systematically study essential genes and the inability to quantify the small effects of most gene deletions on growth. Here we describe the construction of a library of hypomorphic alleles of essential genes and a high-throughput growth competition assay to measure fitness with unprecedented sensitivity. These tools dramatically increase the breadth and precision with which quantitative genetic analysis can be performed in yeast. We illustrate the value of these approaches by using genetic interactions to reveal new relationships between chromatin-modifying factors and to create a functional map of the proteasome. Finally, by measuring the fitness of strains in the yeast deletion library, we addressed an enigma regarding the apparent prevalence of gene dispensability and found that most genes do contribute to growth.     

Plasma insulin-like growth factor-I concentrations and growth in juvenile halibut (Hippoglossus hippoglossus): effects of photoperiods and feeding regimes

The effects of photoperiod and feeding regimes on plasma IGF-I levels and their relationship with growth rate of juvenile halibut (initial mean weight 364 g) were investigated by rearing fish under five different photoperiod regimes and two feeding regimes for 14 months. The entire photoperiod experiment was divided into 3 phases where the fish in each phase were exposed to either natural photoperiod (N), stimulated photoperiod with long day and short night (S) or continuous light (L). Thus, the following five photoperiod combinations were tested: a) Control group (NNN) b) Group 2A (NLN) c) Group 2B (NNL) d) Long day-natural group (SNN) e) Production group (LNN). In addition, the Control group was split into two parts and fed according to two different feeding regimes: a) Continuous fed group: Fish fed every day. b) Starvation/re-fed group: Fish were starved for 5 weeks and then re-fed for 10 weeks, and the treatment repeated during the whole experimental period. The analyses of IGF-I were performed from individually tagged fish in all groups in September 2005 and March 2006. In order to test how rapidly starvation affects circulating IGF-I levels samples were taken from the Starvation/re-fed group after a 10 days starvation (September) and immediately after 10 weeks of feeding (March). A significant relationship between IGF-I levels and individual growth in the preceding period and photoperiod and starvation treatment was found on both occasions. In conclusion, the present study indicates that plasma IGF-I levels are correlated to growth in Atlantic halibut, and affected by photoperiod treatment or compensatory growth during re-feeding. Correlation between individual growth rate and IGF-I levels was low, but significant, highlighting the complexity of how environmental factors affect the endocrine and physiological regulation of growth in fish.     

ApoB100-LDL Acts as a Metabolic Signal from Liver to Peripheral Fat Causing Inhibition of Lipolysis in Adipocytes

Background

Free fatty acids released from adipose tissue affect the synthesis of apolipoprotein B-containing lipoproteins and glucose metabolism in the liver. Whether there also exists a reciprocal metabolic arm affecting energy metabolism in white adipose tissue is unknown.

Methods and Findings

We investigated the effects of apoB-containing lipoproteins on catecholamine-induced lipolysis in adipocytes from subcutaneous fat cells of obese but otherwise healthy men, fat pads from mice with plasma lipoproteins containing high or intermediate levels of apoB100 or no apoB100, primary cultured adipocytes, and 3T3-L1 cells. In subcutaneous fat cells, the rate of lipolysis was inversely related to plasma apoB levels. In human primary adipocytes, LDL inhibited lipolysis in a concentration-dependent fashion. In contrast, VLDL had no effect. Lipolysis was increased in fat pads from mice lacking plasma apoB100, reduced in apoB100-only mice, and intermediate in wild-type mice. Mice lacking apoB100 also had higher oxygen consumption and lipid oxidation. In 3T3-L1 cells, apoB100-containing lipoproteins inhibited lipolysis in a dose-dependent fashion, but lipoproteins containing apoB48 had no effect. ApoB100-LDL mediated inhibition of lipolysis was abolished in fat pads of mice deficient in the LDL receptor (Ldlr^−/−Apob ^100/100).

Conclusions

Our results show that the binding of apoB100-LDL to adipocytes via the LDL receptor inhibits intracellular noradrenaline-induced lipolysis in adipocytes. Thus, apoB100-LDL is a novel signaling molecule from the liver to peripheral fat deposits that may be an important link between atherogenic dyslipidemias and facets of the metabolic syndrome.     

Soluble expression and purification of tumor suppressor WT1 and its zinc finger domain

Full length murine WT1 and its zinc finger domain were separately inserted into Escherichia coli expression vectors with various fusion tags on either terminus by Gateway technology (Invitrogen) and expression of soluble protein was assessed. Fusion proteins including the four zinc finger domains of WT1 were used to optimize expression and purification conditions and to characterize WT1:DNA interactions in the absence of WT1:WT1 interactions. Zinc finger protein for in vitro characterization was prepared by IMAC purification of WT1 residues 321-443 with a thioredoxin-hexahistidine N-terminal fusion, followed by 3C protease cleavage to liberate the zinc fingers and cation exchange chromatography to isolate the zinc fingers and reduce the level of the truncated forms. Titration of zinc finger domain with a binding site from the PDGFA promoter gave a K(d) of 100±30nM for the -KTS isoform and 130±40nM for the +KTS isoform. The zinc finger domain was also co-crystallized with a double-stranded DNA oligonucleotide, yielding crystals that diffract to 5.5?. Using protocols established for the zinc finger domain, we expressed soluble full-length WT1 with an N-terminal thioredoxin domain and purified the fusion protein by IMAC. In electro-mobility shift assays, purified full-length WT1 bound double-stranded oligonucleotides containing known WT1 binding sites, but not control oligonucleotides. Two molecules of WT1 bind an oligonucleotide presenting the full PDGFA promoter, demonstrating that active full-length WT1 can be produced in E. coli and used to investigate WT1 dimerization in complex with DNA in vitro.     

Habitat use and diet of sympatric Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and whitefish (<Emphasis Type="Italic">Coregonus lavaretus</Emphasis>) in five lakes in southern Norway: not only interspecific population dominance?

Stable coexistence of Arctic charr and whitefish does occur in a number of native lake fish communities in Scandinavia. Even so, whitefish introductions into Arctic charr lakes have resulted in serious decline and possibly local extinction of Arctic charr. In this article, we analyze the habitat use and diet of the two species in five Norwegian lakes differing in basin shape and environmental conditions. In two of the lakes, both species are native, and appear to live in a relatively stable coexistence. Here, whitefish mainly occupy the littoral and upper pelagic zone, while Arctic charr live in the deeper habitats. Diets are generally quite different in terms of the zooplankton species eaten. In the three other lakes, either whitefish or both species have been introduced. In the shallowest lake, habitat segregation is similar to that seen in the pristine lakes, although Arctic charr appears to be on the brink of extinction. In the remaining two lakes, however, Arctic charr dominates, and occurs in higher numbers than whitefish in all the habitats. Our observations indicate that coexistence of the two species in oligotrophic and relatively pristine lakes requires an extensive profundal zone to serve as a refugium for Arctic charr. If the littoral zone is rendered inaccessible or unprofitable for whitefish due to dominance of a third competitor or predator, or as a result of lake regulation, then Arctic charr may be the dominant species.