Insulin resistance and a diabetes mellitus-like syndrome in mice lacking the protein kinase Akt2 (PKB beta)

Glucose homeostasis depends on insulin responsiveness in target tissues, most importantly, muscle and liver. The critical initial steps in insulin action include phosphorylation of scaffolding proteins and activation of phosphatidylinositol 3-kinase. These early events lead to activation of the serine-threonine protein kinase Akt, also known as protein kinase B. We show that mice deficient in Akt2 are impaired in the ability of insulin to lower blood glucose because of defects in the action of the hormone on liver and skeletal muscle. These data establish Akt2 as an essential gene in the maintenance of normal glucose homeostasis.

A role for AMP-activated protein kinase in contraction- and hypoxia-regulated glucose transport in skeletal muscle

Eukaryotic cells possess systems for sensing nutritional stress and inducing compensatory mechanisms that minimize the consumption of ATP while utilizing alternative energy sources. Such stress can also be imposed by increased energy needs, such as in skeletal muscle of exercising animals. In these studies, we consider the role of the metabolic sensor, AMP-activated protein kinase (AMPK), in the regulation of glucose transport in skeletal muscle. Expression in mouse muscle of a dominant inhibitory mutant of AMPK completely blocked the ability of hypoxia or AICAR to activate hexose uptake, while only partially reducing contraction-stimulated hexose uptake. These data indicate that AMPK transmits a portion of the signal by which muscle contraction increases glucose uptake, but other AMPK-independent pathways also contribute to the response.

Exercise induces isoform-specific increase in 5'AMP-activated protein kinase activity in human skeletal muscle

The 5'AMP-activated protein kinase (AMPK) is stimulated by contractile activity in rat skeletal muscle. AMPK has emerged as an important signaling intermediary in the regulation of cell metabolism being linked to exercise-induced changes in muscle glucose and fatty acid metabolism. In the present study, we determined the effects of exercise on isoform-specific AMPK activity (alpha1 and alpha2) in human skeletal muscle. Needle biopsies of vastus lateralis muscle were obtained from seven healthy subjects at rest, after 20 and 60 min of cycle ergometer exercise at 70% of VO(2)max, and 30 min following the 60 min exercise bout. In comparison to the resting state, AMPK alpha2 activity significantly increased at 20 and 60 min of exercise, and remained at a higher level with 30 min of recovery. AMPK alpha1 activity tended to slightly decrease with 20 min of exercise at 70%VO(2)max; however, the change was not statistically significant. AMPK alpha1 activities were at basal levels at 60 min of exercise and 30 min of recovery. On a separate day, the same subjects exercised for 20 min at 50% of VO(2)max. Exercise at this intensity did not change alpha2 activity, and similar to exercise at 70% of VO(2)max, there was no significant change in alpha1 activity. In conclusion, exercise at a higher intensity for only 20 min leads to increases in AMPK alpha2 activity but not alpha1 activity. These results suggest that the alpha2-containing AMPK complex, rather than alpha1, may be involved in the metabolic responses to exercise in human skeletal muscle.

The regulation of AMP-activated protein kinase by H(2)O(2)

AMP-activated protein kinase (AMPK), a heterotrimeric serine/threonine kinase, is activated by conditions leading to an increase of the intracellular AMP:ATP ratio. However, how AMPK is regulated under the oxidative stress is completely unknown. In the present study, we examined effects of the oxidative agent H(2)O(2) on AMPK. AMPK was transiently and concentration-dependently activated by H(2)O(2) in NIH-3T3 cells. This activation was tightly associated with an increased AMP:ATP ratio, an electrophoretic mobility shift of AMPK alpha1 catalytic subunit, and an increased phosphorylation level of AMPK alpha1 threonine 172, which is a major in vitro phosphorylation site by the upstream AMPK kinase. All of these events were significantly blocked by the pretreatment of 0.5% dimethyl sulfoxide, a potent hydroxyl radical scavenger, indicating that AMPK cascades are highly sensitive to the oxidative stress. Interestingly, a specific tyrosine kinase inhibitor, genistein, further stimulated the H(2)O(2)-induced AMPK activity by 70% without altering the AMP:ATP. Taken together, our results suggest that AMP:ATP ratio is the major parameter to which AMPK responds under the oxidative stress, but AMPK may be regulated in part by a tyrosine kinase-dependent pathway, which is independent of the cellular adenosine nucleotides level.

Physiological role of AMP-activated protein kinase (AMPK): insights from knockout mouse models

AMP-activated protein kinase (AMPK) is viewed as a fuel sensor for glucose and lipid metabolism. To understand better the physiological role of the catalytic AMPK subunit isoforms, we generated two knockout mouse models with the alpha1 (AMPK alpha 1(-/-)) and alpha 2 (AMPK alpha 2(-/-)) catalytic subunit genes deleted. No defect in glucose homoeostasis was observed in AMPK alpha 1(-/-) mice. On the other hand, AMPK alpha 2(-/-) mice presented high plasma glucose levels and low plasma insulin concentrations in the fed period and during the glucose tolerance test. Nevertheless, in isolated AMPK alpha 2(-/-) pancreatic islets, glucose-stimulated insulin secretion was not affected. Surprisingly, AMPK alpha 2(-/-) mice were insulin-resistant and had reduced muscle glycogen synthesis as assessed in vivo by the hyperinsulinaemic euglycaemic clamp procedure. Reduction of insulin sensitivity and glycogen synthesis were not dependent on the lack of AMPK in skeletal muscle, since mice expressing a dominant inhibitory mutant of AMPK in skeletal muscle were not affected and since insulin-stimulated glucose transport in incubated muscles in vitro was normal in AMPK alpha 2(-/-) muscles. Furthermore, AMPK alpha 2(-/-) mice have a higher sympathetic tone, as shown by increased catecholamine urinary excretion. Increased adrenergic tone could explain both decreased insulin secretion and insulin resistance observed in vivo in AMPK alpha 2(-/-) mice. We suggest that the alpha2 catalytic subunit of AMPK plays a major role as a fuel sensor by modulating the activity of the autonomous nervous system in vivo.

Glucagon receptor knockout mice are resistant to diet-induced obesity and streptozotocin-mediated beta cell loss and hyperglycaemia

AIMS/HYPOTHESIS

Under normal physiological conditions, glucagon signalling is important in glucose homeostasis. Hyperglucagonaemia or altered insulin:glucagon ratio plays a role in maintaining hyperglycaemia in subjects with type 2 diabetes. It has been reported that glucagon receptor knockout (Gcgr (-/-)) mice develop normally and have lower plasma glucose on a normal diet. The goal of the current research was to further investigate the role of glucagon signalling in metabolic control and glucose homeostasis.

METHODS

Gcgr (-/-) mice were challenged with a high-fat diet (HFD) and with streptozotocin, which induces beta cell damage. They were then analysed for whole-body and serum metabolic phenotypes as well as pancreatic islet morphology.

RESULTS

In comparison with wild-type mice, Gcgr (-/-) mice exhibited decreased body weight and food intake, reduced plasma glucose levels, and improved oral and intraperitoneal glucose tolerance. Elevated glucagon-like peptide-1 levels and reduced gastric emptying were also observed in Gcgr (-/-) mice, which also had reduced HFD-induced hyperinsulinaemia and hyperleptinaemia, and were resistant to the development of hepatic steatosis. In addition, Gcgr (-/-) mice were resistant to STZ-induced hyperglycaemia and pancreatic beta cell destruction.

CONCLUSIONS/INTERPRETATION

This study demonstrates that blocking glucagon signalling by targeted Gcgr gene deletion leads to an improvement in metabolic control in this mouse model.

Anisotropy and Corotation of Galactic Cosmic Rays

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.

A Phototheranostic Strategy to Continuously Deliver Singlet Oxygen in the Dark and Hypoxic Tumor Microenvironment

Continuous irradiation during photodynamic therapy (PDT) inevitably induces tumor hypoxia, thereby weakening the PDT effect. In PDT-induced hypoxia, providing singlet oxygen from stored chemical energy may enhance the cell-killing effect and boost the therapeutic effect. Herein, we present a phototheranostic (DPPTPE@PEG-Py NPs) prepared by using a 2-pyridone-based diblock polymer (PEG-Py) to encapsulate a semiconducting, heavy-atom-free pyrrolopyrrolidone-tetraphenylethylene (DPPTPE) with high singlet-oxygen-generation ability both in dichloromethane and water. The PEG-Py can trap the 1 O2 generated from DPPTPE under laser irradiation and form a stable intermediate of endoperoxide, which can then release 1 O2 in the dark, hypoxic tumor microenvironment. Furthermore, fluorescence-imaging-guided phototherapy demonstrates that this phototheranostic could completely inhibit tumor growth with the help of laser irradiation.

Characterization of a pollen-expressed receptor-like kinase gene of Petunia inflata and the activity of its encoded kinase

From a pollen tube cDNA library of Petunia inflata, we isolated clones encoding a protein with structural features and biochemical properties characteristic of receptor-like kinases. It was designated PRK1 for pollen receptor-like kinase 1. The cytoplasmic domain of PRK1 is highly similar to the kinase domains of other plant receptor-like kinases and contains nearly all of the conserved amino acids for serine/threonine kinases. The extracellular domain of PRK1 contains leucine-rich repeats as found in some other plant receptor-like kinases, but overall its sequence in this region does not share significant similarity. Characterization of a gene encoding PRK1 revealed the presence of two introns. During pollen development, PRK1 mRNA was first detected in anthers containing mostly binucleate microspores; it reached the highest level of mature pollen and remained at a high level in in vitro-germinated pollen tubes. The recombinant cytoplasmic domain of PRK1 autophosphorylated on serine and tyrosine, suggesting that PRK1 may be a dual-specificity kinase. Monospecific immune serum to the recombinant extracellular domain of PRK1 detected a 69-kD protein in microsomal membranes of pollen and pollen tubes. The characteristics of PRK1 suggest that it may play a role in signal transduction events during pollen development and/or pollination.

Selective suppression of AMP-activated protein kinase in skeletal muscle: update on 'lazy mice'

AMP-activated protein kinase (AMPK) is becoming recognized as a critical regulator of energy metabolism in cells. Using a mouse model in which we specifically blocked AMPK activity in muscles, we have demonstrated that activation of AMPK is necessary for the effects of 5-aminoimidazole-4-carboxamide riboside ('AICAR') and hypoxia, and is possibly required for a portion of exercise-induced glucose uptake. These same mice could not maintain sufficient glycogen in their skeletal muscle and it was rapidly depleted when the animals were subjected to mild exercise. Using isolated strips, we observed muscle hypertrophy and increased tiredness in the AMPK-deficient muscle. We also performed microarray analysis and showed dramatic changes of transcription profile in muscles of the lazy mice. These could have a significant impact on muscle function and may contribute to the observed phenotype.

Requirement of the self-glucosylating initiator proteins Glg1p and Glg2p for glycogen accumulation in Saccharomyces cerevisiae

Glycogen, a branched polymer of glucose, is a storage molecule whose accumulation is under rigorous nutritional control in many cells. We report the identification of two Saccharomyces cerevisiae genes, GLG1 and GLG2, whose products are implicated in the biogenesis of glycogen. These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase. Over a region of 258 residues, the Glg proteins have 55% sequence identify to each other and approximately 33% identity to glycogenin, a mammalian protein postulated to have a role in the initiation of glycogen biosynthesis. Yeast cells defective in either GLG1 or GLG2 are similar to the wild type in their ability to accumulate glycogen. Disruption of both genes results in the inability of the cells to synthesize glycogen despite normal levels of glycogen synthase. These results suggest that a self-glucosylating protein is required for glycogen biosynthesis in a eukaryotic cell. The activation state of glycogen synthase in glg1 glg2 cells is suppressed, suggesting that the Glg proteins may additionally influence the phosphorylation state of glycogen synthase.

Cannabinoid and kappa opioid receptors reduce potassium K current via activation of G(s) proteins in cultured hippocampal neurons

The current study showed that potassium K current (I(K)), which is evoked at depolarizing potentials between -30 and +40 mV in cultured hippocampal neurons, was significantly reduced by exposure to the CB1 cannabinoid receptor agonist WIN 55,212-2 (WIN-2). WIN-2 (20-40 nM) produced an average 45% decrease in I(K) amplitude across all voltage steps, which was prevented by SR141716A, the CB1 receptor antagonist. The cannabinoid receptor has previously been shown to be G(i/o) protein-linked to several cellular processes; however, the decrease in I(K) was unaffected by modulators of G(i/o) proteins and agents that alter levels of protein kinase A. In contrast, CB1 receptor-mediated or direct activation of G(s) proteins with cholera toxin (CTX) produced the same decrease in I(K) amplitude as WIN-2, and the latter was blocked in CTX-treated cells. G(s) protein inhibition via GDPbetaS also eliminated the effects of WIN-2 on I(K). Consistent with this outcome, activation of protein kinase C (PKC) by arachidonic acid produced similar effects to WIN-2 and CTX. Kappa opioid receptor agonists, which also reduce I(K) amplitude via G(s) proteins, were compared with WIN-2 actions on I(K.) The kappa receptor agonist U50,488 reduced I(K) amplitude in the same manner as WIN-2, while the kappa receptor antagonist, nor-binaltorphimine, actually increased I(K) amplitude and significantly reduced the effect of co-administered WIN-2. The results indicate that CB1 and kappa receptor activation is additive with respect to I(K) amplitude, suggesting that CB1 and kappa receptors share a common G(s) protein signaling pathway involving PKC.

Causes of death among people with convulsive epilepsy in rural West China: a prospective study

BACKGROUND

Epilepsy is a serious health problem associated with an increased risk of premature mortality. Few studies have investigated risk factors for this. Understanding these risks may enable the implementation of preventative measures to reduce premature mortality.

METHODS

A management program for convulsive forms of epilepsy has been in place at the primary health care level in rural West China since May 2005. Demographic data and putative causes of death of attendees of the program since inception to the end of December 2009 have been recorded. Case fatality (CF), the proportional mortality ratios (PMRs) for each cause, and standardized mortality ratios (SMRs) for each age and cause were estimated based on the 2007 Chinese rural population.

RESULTS

There were 106 reported deaths (70 male) among 3,568 people. CF was 2.97% during a median of 28 months' follow-up. The highest PMRs were for accidental death (59%) including drowning (45.1%); probable sudden unexpected death in epilepsy (SUDEP) (14.7%); status epilepticus (6.9%), and neoplasm (6.9%). The overall SMR was 4.92 (95% confidence interval 4.0-6.1); the risks were high in young people. The risk of drowning was 82-fold higher in the cohort than the general population.

CONCLUSION

In rural West China, the risk of premature death is nearly 5 times higher in people with convulsive epilepsy than in the general Chinese population and especially high among young people. Accidental death, including drowning, and probable SUDEP are the leading putative causes of death in people with convulsive epilepsy in rural West China.

Brain magnetic resonance imaging abnormalities in neuromyelitis optica

OBJECTIVE

Brain abnormalities in neuromyelitis optica (NMO) attracted much attention. Our study was to identify the brain magnetic resonance imaging (MRI) abnormalities in Chinese NMO patients.

METHODS

Patients who fulfilled the latest diagnostic criteria of NMO proposed by Wingerchuk et al. [Neurology 66 (2006) 1485] and whose brain MRI did not meet the multiple sclerosis (MS) criteria of McDonald et al. [Ann Neurol 50 (2001) 121] were selected to perform MRI scanning of the brain, spinal cord and optic nerves.

RESULTS

Twenty-eight of 33 patients (84.8%) had abnormal MRI findings. Twenty-two patients (66.7%) presented with well-defined brain parenchymal lesions and the other six patients (18.2%) with macroscopic symmetrical diffuse hyperintensities in deep white matter. Fifteen of 22 patients had more than one lesion (> or =2 lesions) and the other seven patients had single lesion. In the supratentorium, most lesions were punctate or small round dot and non-specific in juxtacortical, subcortical and deep white matter regions, a few were patchy atypical confluent lesions. Brainstem was easily involved (14/33, 42.4%) especially in medulla (7/33, 21.2%).

CONCLUSIONS

This study demonstrates the characteristics of brain MRI abnormalities in Chinese NMO patients, which are helpful to the revision of diagnostic criteria for NMO.

Molecular mechanisms underlying IFN-gamma-mediated tumor growth inhibition induced during tumor immunotherapy with rIL-12

The present study investigates the molecular mechanisms by which IFN-gamma produced as a result of in vivo IL-12 administration exerts its anti-tumor effects. rIL-12 was administered three or five times into mice bearing CSA1M fibrosarcoma, OV-HM ovarian carcinoma or MCH-1-A1 fibrosarcoma. This regimen induced complete regression of CSA1M and OV-HM tumors but only transient growth inhibition of MCH-1-A1 tumors. The anti-tumor effects of IL-12 were associated with enhanced induction of IFN-gamma because these effects were abrogated by pretreatment of hosts with anti-IFN-gamma antibody. Exposure in vitro of the three types of tumor cells to rRFN-gamma resulted in moderate to potent inhibition of tumor cell growth. IFN-gamma stimulated the expression of mRNAs for an inducible type of NO synthase (iNOS) in CSA1M cells and indoleamine 2,3-dioxygenase (IDO), an enzyme capable of degrading tryptophan, in OH-HM cells, but induced only marginal levels of these mRNAs in MCH-1-A1 cells. In association with iNOS gene expression, IFN-gamma-stimulated CSA1M cells produced a large amount of NO which functioned to inhibit their own growth in vitro. Although OV-HM and MCH-1A1 cells did not produce NO, they also exhibited NO susceptibility. Whereas the tumor masses from IL-12-treated CSA1M-bearing or OV-HM-bearing mice induced higher levels of iNOS (for CSA1M) or IDO and iNOS (for OV-HM) mRNAs, the MCH-1-A1 tumor mass expressed lower levels of iNOS mRNA alone. Moreover, massive infiltration of CD4(+) and CD8(+) T cells and Mac-1(+) cells was seen only in the CSA1M and OV-HM tumors. Thus, these results indicate that IFN-gamma produced after IL-12 treatment induces the expression of various genes with potential to modulate tumor cell growth by acting directly on tumor cells or stimulating tumor-infiltrating lymphoid cells and that the effectiveness of IL-12 therapy is associated with the operation of these mechanisms.

Role of cyclic AMP dependent protein kinase in cannabinoid receptor modulation of potassium "A-current" in cultured rat hippocampal neurons

Cannabinoid receptor agonists have been previously shown to enhance a potassium A-current (IA) in cultured rat hippocampal neurons. This effect has been further demonstrated to be dependent on G-protein linkage to adenylyl cyclase and levels of intracellular cyclic AMP (cAMP). The present study extends this analysis to the involvement of cAMP-dependent protein kinase (PKA) in this cascade. Specific activators and inhibitors of PKA were shown to have differential effects on the voltage dependence of IA. Specific activators of PKA produced a negative shift in voltage dependence of IA, whereas PKA inhibitors produced a positive shift in IA voltage dependence, the latter similar to that effected by the cannabinoid agonist WIN 55,212-2. Although the negative shift in IA induced by PKA stimulation could be reversed by PKA inhibitors, the positive shift produced by the PKA inhibitors alone was only 50-60% of the cannabinoid-produced shift in IA voltage dependence. This partial effect of PKA inhibition was confirmed by biochemical assays in the same cultured neurons that showed a similar 50-60% decrement in in vitro protein phosphorylation produced by PKA inhibitors. Results are discussed in terms of a diffusible second messenger linkage of the cannabinoid receptor to the A-current channel via the role of protein phosphorylation in modulation of IA.

Chronic treatment with a glucagon receptor antagonist lowers glucose and moderately raises circulating glucagon and glucagon-like peptide 1 without severe alpha cell hypertrophy in diet-induced obese mice

AIMS/HYPOTHESIS

Antagonism of the glucagon receptor (GCGR) represents a potential approach for treating diabetes. Cpd-A, a potent and selective GCGR antagonist (GRA) was studied in preclinical models to assess its effects on alpha cells.

METHODS

Studies were conducted with Cpd-A to examine the effects on glucose-lowering efficacy, its effects in combination with a dipeptidyl peptidase-4 (DPP-4) inhibitor, and the extent and reversibility of alpha cell hypertrophy associated with GCGR antagonism in mouse models.

RESULTS

Chronic treatment with Cpd-A resulted in effective and sustained glucose lowering in mouse models in which endogenous murine Gcgr was replaced with human GCGR (hGCGR). Treatment with Cpd-A also led to stable, moderate elevations in both glucagon and glucagon-like peptide 1 (GLP-1) levels, which were completely reversible and not associated with a hyperglycaemic overshoot following termination of treatment. When combined with a DPP-4 inhibitor, Cpd-A led to additional improvement of glycaemic control correlated with elevated active GLP-1 levels after glucose challenge. In contrast to Gcgr-knockout mice in which alpha cell hypertrophy was detected, chronic treatment with Cpd-A in obese hGCGR mice did not result in gross morphological changes in pancreatic tissue.

CONCLUSIONS/INTERPRETATION

A GRA lowered glucose effectively in diabetic models without significant alpha cell hypertrophy during or following chronic treatment. Treatment with a GRA may represent an effective approach for glycaemic control in patients with type 2 diabetes, which could be further enhanced when combined with DPP-4 inhibitors.

Cloning and sequencing of cDNAs encoding two self-incompatibility associated proteins in Solanum chacoense

We have isolated and sequenced cDNAs for S2- and S3-alleles of the self-incompatibility locus (S-locus) in Solanum chacoense Bitt., a wild potato species displaying gametophytic self-incompatibility. The S2- and S3-alleles encode pistil-specific proteins of 30 kDa and 31 kDa, respectively, which were previously identified based on cosegregation with their respective alleles in genetic crosses. The amino acid sequence homology between the S2- and S3-proteins is 41.5%. This high degree of sequence variability between alleles is a distinctive feature of the S-gene system. Of the 31 amino acid residues which were previously found to be conserved among three Nicotiana alata S-proteins (S2, S3, and S6) and two fungal ribonucleases (RNase T2 and RNase Rh), 27 are also conserved in the S2- and S3-proteins of S. chacoense. These residues include two histidines implicated in the active site of the RNase T2, six cysteines, four of which form disulfide bonds in RNase T2, and hydrophobic residues which might form the core structure of the protein. The finding that these residues are conserved among S-proteins with very divergent sequences suggests a functional role for the ribonuclease activity of the S-protein in gametophytic self-incompatibility.

IL-12-induced tumor regression correlates with in situ activity of IFN-gamma produced by tumor-infiltrating cells and its secondary induction of anti-tumor pathways

Administration of recombinant interleukin-12 (rIL-12) into CSA1M fibrosarcoma-bearing mice results in complete regression of growing tumors. This tumor regression is associated with massive lymphoid cell infiltration to tumor sites and is completely blocked by injection of anti-interferon-gamma (IFN-gamma) monoclonal antibody (mAb). We investigated whether anti-IFN-gamma mAb exerts its suppressive effect on tumor regression by blocking the IL-12-induced lymphoid cell migration to tumor sites or by inhibiting the secondary effects of IFN-gamma produced by infiltrating cells. Injection of anti-IFN-gamma mAb to CSA1M-bearing mice before IL-12 treatment prevented the induction of tumor regression, whereas this treatment affected only marginally the infiltration of lymphoid cells to tumor masses. In accordance with this, IFN-gamma mRNA was expressed inside tumor masses by infiltrating cells after IL-12 therapy irrespective of whether anti-IFN-gamma mAb was injected. However, anti-IFN-gamma mAb treatment almost completely abrogated the in situ expression of inducible nitric oxide synthase (iNOS) as well as IFN-inducible protein-10 (IP-10) genes as examples of IFN-gamma-inducible genes. Immunohistochemical analyses also revealed that the expression of iNOS protein was completely inhibited by anti-IFN-gamma injection. These results suggest that the implementation of in situ IFN-gamma activity and its secondary induction of anti-tumor pathways such as iNOS and IP-10 expression are important processes in the IL-12-induced tumor regression.

Plasma-based proteomics reveals lipid metabolic and immunoregulatory dysregulation in post-stroke depression

BACKGROUND

Post-stroke depression (PSD) is the most common psychiatric complication facing stroke survivors and has been associated with increased distress, physical disability, poor rehabilitation, and suicidal ideation. However, the pathophysiological mechanisms underlying PSD remain unknown, and no objective laboratory-based test is available to aid PSD diagnosis or monitor progression.

METHODS

Here, an isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic approach was performed to identify differentially expressed proteins in plasma samples obtained from PSD, stroke, and healthy control subjects.

RESULTS

The significantly differentiated proteins were primarily involved in lipid metabolism and immunoregulation. Six proteins associated with these processes--apolipoprotein A-IV (ApoA-IV), apolipoprotein C-II (ApoC-II), C-reactive protein (CRP), gelsolin, haptoglobin, and leucine-rich alpha-2-glycoprotein (LRG)--were selected for Western blotting validation. ApoA-IV expression was significantly upregulated in PSD as compared to stroke subjects. ApoC-II, LRG, and CRP expression were significantly downregulated in both PSD and HC subjects relative to stroke subjects. Gelsolin and haptoglobin expression were significantly dysregulated across all three groups with the following expression profiles: gelsolin, healthy control>PSD>stroke subjects; haptoglobin, stroke>PSD>healthy control.

CONCLUSIONS

Early perturbation of lipid metabolism and immunoregulation may be involved in the pathophysiology of PSD. The combination of increased gelsolin levels accompanied by decreased haptoglobin levels shows promise as a plasma-based diagnostic biomarker panel for detecting increased PSD risk in post-stroke patients.

Glycogenin-2, a novel self-glucosylating protein involved in liver glycogen biosynthesis

Glycogenin is a self-glucosylating protein involved in the initiation phase of glycogen biosynthesis. A single mammalian gene had been reported to account for glycogen biogenesis in liver and muscle, the two major repositories of glycogen. We describe the characterization of novel forms of glycogenin, designated glycogenin-2 (GN-2), encoded by a second gene that is expressed preferentially in certain tissues, including liver, heart, and pancreas. Cloning of cDNAs encoding glycogenin-2 indicated the existence of multiple species, including three liver forms (GN-2alpha, GN-2beta, and GN-2gamma) generated in part by alternative splicing. Overall, GN-2 has 40-45% identity to muscle glycogenin but is 72% identical over a 200-residue segment thought to contain the catalytic domain. GN-2 expressed in Escherichia coli or COS cells is active in self-glucosylation assays, and self-glucosylated GN-2 can be elongated by skeletal muscle glycogen synthase. Antibodies raised against GN-2 produced in E. coli recognized proteins of Mr approximately 66,000 present in extracts of rat liver and in cultured H4IIEC3 hepatoma cells. In H4IIEC3 cells, most of the GN-2 was present as a free protein but some was covalently associated with glycogen fractions and was only released by treatment with alpha-amylase. H4IIEC3 cells also expressed the muscle form of glycogenin (glycogenin-1), which was attached to a chromatographically separable glycogen fraction.

Novel aspects of the regulation of glycogen storage

The storage polysaccharide glycogen is widely distributed in nature, from bacteria to mammals. Study of its regulated accumulation has resulted in the discovery or elaboration of several important biochemical principles. Many aspects of the control of glycogen storage still remain poorly understood and glycogen metabolism continues to provide interesting models of more general relevance.

Inhibition of growth and metastasis of ovarian carcinoma by administering a drug capable of interfering with vascular endothelial growth factor activity

The present study investigates the relationship between in vivo growth/metastasis of tumor cells and their capacity to produce the vascular endothelial growth factor (VEGF), as well as the regulation of tumor growth/metastasis using an angiogenesis-inhibitory drug. Two cloned tumor cell lines designated OV-LM and OV-HM were isolated from a murine ovarian carcinoma OV2944. OV-LM and OV-HM cells grew in cultures at comparable rates. However, when transplanted s.c. into syngeneic mice, OV-HM exhibited a faster growth rate and a much higher incidence of metastasis to lymph nodes and lung. Histologically, intense neovascularization was detected in sections of OV-HM but not of OV-LM tumor. OV-HM and OV-LM tumor cells obtained from in vitro cultures expressed high and low levels of VEGF mRNA, respectively. A difference in VEGF mRNA expression was much more clearly observed between RNAs prepared from fresh OV-HM and OV-LM tumor masses: RNA from OV-HM contained larger amounts of VEGF mRNA, whereas RNA from OV-LM exhibited only marginal levels of VEGF mRNA. An angiogenesis-inhibitory drug, FR118487 inhibited the VEGF-mediated in vitro growth of endothelial cells but did not affect the expression in vitro of VEGF mRNA by OV-HM tumor cells. Intraperitoneal injections of FR118487 into mice bearing OV-HM tumors resulted in: (i) a subsequent growth inhibition of primary tumors; (ii) a marked decrease in neovascularization inside tumor masses expressing comparable levels of VEGF mRNA to those detected in control OV-HM masses; and (iii) almost complete inhibition of metastasis to lymph nodes and lung. These results indicate that growth/metastasis of tumor cells correlates with their VEGF-producing capacity and that an angiogenesis inhibitor, FR118487, inhibits tumor growth and metastasis through mechanism(s) including the suppression of VEGF function in vivo.

Self-glucosylation of glycogenin, the initiator of glycogen biosynthesis, involves an inter-subunit reaction

Glycogenin is a dimeric self-glucosylating protein involved in the initiation phase of glycogen biosynthesis. As an enzyme, glycogenin has the unusual property of transferring glucose residues from UDP-glucose to itself, forming an alpha-1,4-glycan of around 10 residues attached to Tyr194. Whether this self-glucosylation reaction is inter- or intramolecular has been debated. We used site-directed mutagenesis of recombinant rabbit muscle glycogenin-1 to address this question. Mutation of highly conserved Lys85 to Gln generated a glycogenin mutant (K85Q) that had only 1-2% of the self-glucosylating activity of wild-type enzyme. Consistent with previous work, mutation of Tyr194 to Phe in a GST-fusion protein yielded a mutant, Y194F, that was catalytically active but incapable of self-glucosylation. The Y194F mutant was able to glucosylate the K85Q mutant. However, there was an initial lag in the self-glucosylation reaction that was abolished by preincubation of the two mutant proteins. The interaction between glycogenin subunits was relatively weak, with a dissociation constant inferred from kinetic experiments of around 2 microM. We propose a model for the glucosylation of K85Q by Y194F in which mixing of the proteins is followed by rate-limiting formation of a species containing both subunit types. The results provide the most direct evidence to date that the self-glucosylation of glycogenin involves an inter-subunit reaction.