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Find video protocols related to scientific articles indexed in Pubmed.
The effect of the dual PI3K and mTOR inhibitor BEZ235 on tumour growth and osteolytic bone disease in multiple myeloma.
Eur. J. Haematol.
PUBLISHED: 09-02-2014
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The plasma cell malignancy multiple myeloma (MM) is unique among haematological malignancies in its capacity to cause osteoclast-mediated skeletal destruction. The PI3K/Akt/mTOR pathway mediates proliferation, survival and drug resistance in MM plasma cells and is also involved in regulating the formation and activity of bone-forming osteoblasts and bone-resorbing osteoclasts. NVP-BEZ235 is a dual pan class I PI3K and mTOR inhibitor that is currently undergoing clinical evaluation in several tumour settings. In this study, we examined the anti-tumorigenic effects of BEZ235 in an immunocompetent mouse model of MM and assessed the effects of BEZ235 on osteoblast and osteoclast formation and function. BEZ235 treatment (50 mg/kg) resulted in a significant decrease in serum paraprotein and tumour burden, and ?CT analysis of the proximal tibia revealed a significant reduction in the number of osteolytic bone lesions in BEZ235-treated animals. Levels of the serum osteoblast marker P1NP were significantly higher in BEZ235-treated animals, while levels of the osteoclast marker TRAcP5 were reduced. In vitro, BEZ235 decreased MM plasma cell proliferation, osteoclast formation and function and promoted osteoblast formation and function. These findings suggest that, in addition to its anti-tumour properties, BEZ235 could be useful in treating osteolytic bone disease in MM patients.
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Effects of neonatal treatment with the TRPV1 agonist, capsaicin, on adult rat brain and behaviour.
Behav. Brain Res.
PUBLISHED: 05-05-2014
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Treatment of neonatal rats with the transient receptor potential vanilloid 1 (TRPV1) channel agonist, capsaicin, produces life-long loss of sensory neurons expressing TRPV1 channels. Previously it was shown that rats treated on day 2 of life with capsaicin had behavioural hyperactivity in a novel environment at 5-7 weeks of age and brain changes reminiscent of those found in subjects with schizophrenia. The objective of the present study was to investigate brain and behavioural responses of adult rats treated as neonates with capsaicin. It was found that the brain changes found at 5-7 weeks in rats treated as neonates with capsaicin persisted into adulthood (12 weeks) but were less in older rats (16-18 weeks). Increased prepulse inhibition (PPI) of acoustic startle was found in these rats at 8 and 12 weeks of age rather than the deficit commonly found in animal models of schizophrenia. Subjects with schizophrenia also have reduced flare responses to niacin and methylnicotinate proposed to be mediated by prostaglandin D2 (PGD2). Flare responses are accompanied by cutaneous plasma extravasation. It was found that the cutaneous plasma extravasation responses to methylnicotinate and PGD2 were reduced in capsaicin-treated rats. In conclusion, several neuroanatomical changes observed in capsaicin-treated rats, as well as the reduced cutaneous plasma extravasation responses, indicate that the role of TRPV1 channels in schizophrenia is worthy of investigation.
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Increased polyubiquitination and proteasomal degradation of a munc18-1 disease-linked mutant causes temperature-sensitive defect in exocytosis.
Cell Rep
PUBLISHED: 02-27-2014
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Munc18-1 is a critical component of the core machinery controlling neuroexocytosis. Recently, mutations in Munc18-1 leading to the development of early infantile epileptic encephalopathy have been discovered. However, which degradative pathway controls Munc18-1 levels and how it impacts on neuroexocytosis in this pathology is unknown. Using neurosecretory cells deficient in Munc18, we show that a disease-linked mutation, C180Y, renders the protein unstable at 37°C. Although the mutated protein retains its function as t-SNARE chaperone, neuroexocytosis is impaired, a defect that can be rescued at a lower permissive temperature. We reveal that Munc18-1 undergoes K48-linked polyubiquitination, which is highly increased by the mutation, leading to proteasomal, but not lysosomal, degradation. Our data demonstrate that functional Munc18-1 levels are controlled through polyubiquitination and proteasomal degradation. The C180Y disease-causing mutation greatly potentiates this degradative pathway, rendering Munc18-1 unable to facilitate neuroexocytosis, a phenotype that is reversed at a permissive temperature.
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Secretagogue stimulation of neurosecretory cells elicits filopodial extensions uncovering new functional release sites.
J. Neurosci.
PUBLISHED: 12-06-2013
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Regulated exocytosis in neurosecretory cells relies on the timely fusion of secretory granules (SGs) with the plasma membrane. Secretagogue stimulation leads to an enlargement of the cell footprint (surface area in contact with the coverslip), an effect previously attributed to exocytic fusion of SGs with the plasma membrane. Using total internal reflection fluorescence microscopy, we reveal the formation of filopodia-like structures in bovine chromaffin and PC12 cells driving the footprint expansion, suggesting the involvement of cortical actin network remodeling in this process. Using exocytosis-incompetent PC12 cells, we demonstrate that footprint enlargement is largely independent of SG fusion, suggesting that vesicular exocytic fusion plays a relatively minor role in filopodial expansion. The footprint periphery, including filopodia, undergoes extensive F-actin remodeling, an effect abolished by the actomyosin inhibitors cytochalasin D and blebbistatin. Imaging of both Lifeact-GFP and the SG marker protein neuropeptide Y-mCherry reveals that SGs actively translocate along newly forming actin tracks before undergoing fusion. Together, these data demonstrate that neurosecretory cells regulate the number of SGs undergoing exocytosis during sustained stimulation by controlling vesicular mobilization and translocation to the plasma membrane through actin remodeling. Such remodeling facilitates the de novo formation of fusion sites.
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How do people understand their neuropathic pain? A Q-study.
Pain
PUBLISHED: 07-01-2013
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Neuropathic pain (NP) is not easy to understand for those with the diagnosis. Even in specialist medical services, explanation may not be given or may not be integrated with patients existing beliefs about their conditions. We were curious about how people with NP conceptualised the problem. Web sites relevant to NP were used to recruit 79 people with NP. They were sampled using Q-methodology, which requires sorting according to degree of agreement or disagreement with diverse statements about NP, derived from the widest possible range of sources. The sets of sorted statements are analysed for factors which represent shared constructions. The four factors that we found differed in important ways: (1) identification of nerve damage as cause; (2) the necessity of identifying cause; (3) the acceptability of symptomatic treatment; (4) the existence or not of psychological influences; and (5) the usefulness of psychological treatment. The meaning of these factors was extended by participants free comments: certain viewpoints showed associations with their medical and treatment histories and with the interference of pain with daily life. Overall, a biopsychosocial model of pain was only weakly represented, and no integrated model of pain emerged across the four different accounts. There was little reference to NP having been explained when the diagnosis was made. This study highlights the need for more accessible explanations of NP within and outside medical services if people with NP are to use their understanding of NP to help them manage their pain and reduce its impact on their lives.
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The Munc18-1 domain 3a loop is essential for neuroexocytosis but not for syntaxin-1A transport to the plasma membrane.
J. Cell. Sci.
PUBLISHED: 06-14-2013
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Munc18-1 plays a dual role in transporting syntaxin-1A (Sx1a) to the plasma membrane and regulating SNARE-mediated membrane fusion. As impairment of either function leads to a common exocytic defect, assigning specific roles for various Munc18-1 domains has proved difficult. Structural analyses predict that a loop region in Munc18-1 domain 3a could catalyse the conversion of Sx1a from a closed, fusion-incompetent to an open, fusion-competent conformation. As this conversion occurs at the plasma membrane, mutations in this loop could potentially separate the chaperone and exocytic functions of Munc18-1. Expression of a Munc18-1 deletion mutant lacking 17 residues of the domain 3a loop (Munc18-1(?317-333)) in PC12 cells deficient in endogenous Munc18 (DKD-PC12 cells) fully rescued transport of Sx1a to the plasma membrane, but not exocytic secretory granule fusion. In vitro binding of Munc18-1(?317-333) to Sx1a was indistinguishable from that of full-length Munc18-1, consistent with the critical role of the closed conformation in Sx1a transport. However, in DKD-PC12 cells, Munc18-1(?317-333) binding to Sx1a was greatly reduced compared to that of full-length Munc18-1, suggesting that closed conformation binding contributes little to the overall interaction at the cell surface. Furthermore, we found that Munc18-1(?317-333) could bind SNARE complexes in vitro, suggesting that additional regulatory factors underpin the exocytic function of Munc18-1 in vivo. Together, these results point to a defined role for Munc18-1 in facilitating exocytosis linked to the loop region of domain 3a that is clearly distinct from its function in Sx1a transport.
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Caveolin-1 is necessary for hepatic oxidative lipid metabolism: evidence for crosstalk between caveolin-1 and bile acid signaling.
Cell Rep
PUBLISHED: 03-04-2013
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Caveolae and caveolin-1 (CAV1) have been linked to several cellular functions. However, a model explaining their roles in mammalian tissues in vivo is lacking. Unbiased expression profiling in several tissues and cell types identified lipid metabolism as the main target affected by CAV1 deficiency. CAV1-/- mice exhibited impaired hepatic peroxisome proliferator-activated receptor ? (PPAR?)-dependent oxidative fatty acid metabolism and ketogenesis. Similar results were recapitulated in CAV1-deficient AML12 hepatocytes, suggesting at least a partial cell-autonomous role of hepatocyte CAV1 in metabolic adaptation to fasting. Finally, our experiments suggest that the hepatic phenotypes observed in CAV1-/- mice involve impaired PPAR? ligand signaling and attenuated bile acid and FXR? signaling. These results demonstrate the significance of CAV1 in (1) hepatic lipid homeostasis and (2) nuclear hormone receptor (PPAR?, FXR?, and SHP) and bile acid signaling.
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Inhibition of PIKfyve by YM-201636 dysregulates autophagy and leads to apoptosis-independent neuronal cell death.
PLoS ONE
PUBLISHED: 02-21-2013
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The lipid phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P 2), synthesised by PIKfyve, regulates a number of intracellular membrane trafficking pathways. Genetic alteration of the PIKfyve complex, leading to even a mild reduction in PtdIns(3,5)P 2, results in marked neurodegeneration via an uncharacterised mechanism. In the present study we have shown that selectively inhibiting PIKfyve activity, using YM-201636, significantly reduces the survival of primary mouse hippocampal neurons in culture. YM-201636 treatment promoted vacuolation of endolysosomal membranes followed by apoptosis-independent cell death. Many vacuoles contained intravacuolar membranes and inclusions reminiscent of autolysosomes. Accordingly, YM-201636 treatment increased the level of the autophagosomal marker protein LC3-II, an effect that was potentiated by inhibition of lysosomal proteases, suggesting that alterations in autophagy could be a contributing factor to neuronal cell death.
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Myosin VI small insert isoform maintains exocytosis by tethering secretory granules to the cortical actin.
J. Cell Biol.
PUBLISHED: 02-06-2013
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Before undergoing neuroexocytosis, secretory granules (SGs) are mobilized and tethered to the cortical actin network by an unknown mechanism. Using an SG pull-down assay and mass spectrometry, we found that myosin VI was recruited to SGs in a Ca(2+)-dependent manner. Interfering with myosin VI function in PC12 cells reduced the density of SGs near the plasma membrane without affecting their biogenesis. Myosin VI knockdown selectively impaired a late phase of exocytosis, consistent with a replenishment defect. This exocytic defect was selectively rescued by expression of the myosin VI small insert (SI) isoform, which efficiently tethered SGs to the cortical actin network. These myosin VI SI-specific effects were prevented by deletion of a c-Src kinase phosphorylation DYD motif, identified in silico. Myosin VI SI thus recruits SGs to the cortical actin network, potentially via c-Src phosphorylation, thereby maintaining an active pool of SGs near the plasma membrane.
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Dynamin inhibition blocks botulinum neurotoxin type A endocytosis in neurons and delays botulism.
J. Biol. Chem.
PUBLISHED: 08-05-2011
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The botulinum neurotoxins (BoNTs) are di-chain bacterial proteins responsible for the paralytic disease botulism. Following binding to the plasma membrane of cholinergic motor nerve terminals, BoNTs are internalized into an endocytic compartment. Although several endocytic pathways have been characterized in neurons, the molecular mechanism underpinning the uptake of BoNTs at the presynaptic nerve terminal is still unclear. Here, a recombinant BoNT/A heavy chain binding domain (Hc) was used to unravel the internalization pathway by fluorescence and electron microscopy. BoNT/A-Hc initially enters cultured hippocampal neurons in an activity-dependent manner into synaptic vesicles and clathrin-coated vesicles before also entering endosomal structures and multivesicular bodies. We found that inhibiting dynamin with the novel potent Dynasore analog, Dyngo-4a(TM), was sufficient to abolish BoNT/A-Hc internalization and BoNT/A-induced SNAP25 cleavage in hippocampal neurons. Dyngo-4a also interfered with BoNT/A-Hc internalization into motor nerve terminals. Furthermore, Dyngo-4a afforded protection against BoNT/A-induced paralysis at the rat hemidiaphragm. A significant delay of >30% in the onset of botulism was observed in mice injected with Dyngo-4a. Dynamin inhibition therefore provides a therapeutic avenue for the treatment of botulism and other diseases caused by pathogens sharing dynamin-dependent uptake mechanisms.
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High-throughput screening of Australian marine organism extracts for bioactive molecules affecting the cellular storage of neutral lipids.
PLoS ONE
PUBLISHED: 07-08-2011
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Mammalian cells store excess fatty acids as neutral lipids in specialised organelles called lipid droplets (LDs). Using a simple cell-based assay and open-source software we established a high throughput screen for LD formation in A431 cells in order to identify small bioactive molecules affecting lipid storage. Screening an n-butanol extract library from Australian marine organisms we identified 114 extracts that produced either an increase or a decrease in LD formation in fatty acid-treated A431 cells with varying degrees of cytotoxicity. We selected for further analysis a non-cytotoxic extract derived from the genus Spongia (Heterofibria). Solvent partitioning, HPLC fractionation and spectroscopic analysis (NMR, MS) identified a family of related molecules within this extract with unique structural features, a subset of which reduced LD formation. We selected one of these molecules, heterofibrin A1, for more detailed cellular analysis. Inhibition of LD biogenesis by heterofibrin A1 was observed in both A431 cells and AML12 hepatocytes. The activity of heterofibrin A1 was dose dependent with 20 µM inhibiting LD formation and triglyceride accumulation by ?50% in the presence of 50 µM oleic acid. Using a fluorescent fatty acid analogue we found that heterofibrin A1 significantly reduces the intracellular accumulation of fatty acids and results in the formation of distinct fatty acid metabolites in both cultured cells and in embryos of the zebrafish Danio rerio. In summary we have shown using readily accessible software and a relatively simple assay system that we can identify and isolate bioactive molecules from marine extracts, which affect the formation of LDs and the metabolism of fatty acids both in vitro and in vivo.
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Disruption of prepulse inhibition by 3,4-methylenedioxymethamphetamine (MDMA): comparison between male and female wild-type and 5-HT(1A) receptor knockout mice.
Int. J. Neuropsychopharmacol.
PUBLISHED: 02-18-2011
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The aim of this study was to investigate the involvement of serotonin-1A (5-HT(1A)) receptors in the effects of 3,4-methylenedioxymetamphetamine (MDMA) on prepulse inhibition of acoustic startle (PPI) by comparing male and female wild-type (WT) mice and 5-HT(1A) receptor knockout (1AKO) mice. MDMA dose-dependently decreased PPI in male and female mice although female mice were more sensitive at the 100-ms inter-stimulus interval (ISI). In male mice, 10 mg/kg MDMA disrupted PPI in 1AKO but not in WT controls. There was no genotype difference at higher or lower doses of MDMA. In female mice, there was no difference between genotypes at any dose of MDMA. Average startle was reduced by 10 mg/kg and 20 mg/kg MDMA similarly in male and female mice and all genotypes. These results show an involvement of 5-HT(1A) receptors in the effect of MDMA on PPI in male, but not female mice.
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Enhanced effects of amphetamine but reduced effects of the hallucinogen, 5-MeO-DMT, on locomotor activity in 5-HT(1A) receptor knockout mice: implications for schizophrenia.
Neuropharmacology
PUBLISHED: 01-11-2011
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Serotonin-1A (5-HT(1A)) receptors may play a role in schizophrenia and the effects of certain antipsychotic drugs. However, the mechanism of interaction of 5-HT(1A) receptors with brain systems involved in schizophrenia, remains unclear. Here we show that 5-HT(1A) receptor knockout mice display enhanced locomotor hyperactivity to acute treatment with amphetamine, a widely used animal model of hyperdopaminergic mechanisms in psychosis. In contrast, the effect of MK-801 on locomotor activity, modeling NMDA receptor hypoactivity, was unchanged in the knockouts. The effect of the hallucinogen 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) was markedly reduced in 5-HT(1A) receptor knockout mice. There were no changes in apomorphine-induced disruption of PPI, a model of sensory gating deficits seen in schizophrenia. Similarly, there were no major changes in density of dopamine transporters (DAT) or dopamine D(1) or D(2) receptors which could explain the behavioural changes observed in 5-HT(1A) receptor knockout mice. These results extend our insight into the possible role of these receptors in aspects of schizophrenia. As also suggested by previous studies using agonist and antagonist drugs, 5-HT(1A) receptors may play an important role in hallucinations and to modulate dopaminergic activity in the brain.
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Quantitative analysis of lipid droplet fusion: inefficient steady state fusion but rapid stimulation by chemical fusogens.
PLoS ONE
PUBLISHED: 08-23-2010
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Lipid droplets (LDs) are dynamic cytoplasmic organelles containing neutral lipids and bounded by a phospholipid monolayer. Previous studies have suggested that LDs can undergo constitutive homotypic fusion, a process linked to the inhibitory effects of fatty acids on glucose transporter trafficking. Using strict quantitative criteria for LD fusion together with refined light microscopic methods and real-time analysis, we now show that LDs in diverse cell types show low constitutive fusogenic activity under normal growth conditions. To investigate the possible modulation of LD fusion, we screened for agents that can trigger fusion. A number of pharmacological agents caused homotypic fusion of lipid droplets in a variety of cell types. This provided a novel cell system to study rapid regulated fusion between homotypic phospholipid monolayers. LD fusion involved an initial step in which the two adjacent membranes became continuous (<10 s), followed by the slower merging (100 s) of the neutral lipid cores to produce a single spherical LD. These fusion events were accompanied by changes to the LD surface organization. Measurements of LDs undergoing homotypic fusion showed that fused LDs maintained their initial volume, with a corresponding decrease in surface area suggesting rapid removal of membrane from the fused LD. This study provides estimates for the level of constitutive LD fusion in cells and questions the role of LD fusion in vivo. In addition, it highlights the extent of LD restructuring which occurs when homotypic LD fusion is triggered in a variety of cell types.
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Heterofibrins: inhibitors of lipid droplet formation from a deep-water southern Australian marine sponge, Spongia (Heterofibria) sp.
Org. Biomol. Chem.
PUBLISHED: 07-14-2010
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A bioassay-guided search for inhibitors of lipid droplet formation in a deep-water southern Australian marine sponge, Spongia (Heterofibria) sp., yielded six new compounds, fatty acids heterofibrins A1 (1) and B1 (4), along with related monolactyl and dilactyl esters, heterofibrins A2 (2), B2 (5), A3 (3) and B3 (6). Heterofibrin structures were assigned on the basis of detailed spectroscopic analysis, with comparison to chiral synthetic model compounds. All heterofibrins possess a diyne-ene moiety, while the monolactyl and dilactyl moiety featured in selected heterofibrins is unprecedented in the natural products literature. SAR by co-metabolite studies on the heterofibrins confirmed them to be non-cytotoxic, with the carboxylic acids 1 and 4 inhibiting lipid droplet formation in A431 fibroblast cell lines. Such inhibitors have potential application in the management of obesity, diabetes and atherosclerosis
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NVP-BEZ235, a dual pan class I PI3 kinase and mTOR inhibitor, promotes osteogenic differentiation in human mesenchymal stromal cells.
J. Bone Miner. Res.
PUBLISHED: 05-26-2010
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Osteoblasts are bone-forming cells derived from mesenchymal stromal cells (MSCs) that reside within the bone marrow. In response to a variety of factors, MSCs proliferate and differentiate into mature, functional osteoblasts. Several studies have shown previously that suppression of the PI3K and mTOR signaling pathways in these cells strongly promotes osteogenic differentiation, which suggests that inhibitors of these pathways may be useful as anabolic bone agents. In this study we examined the effect of BEZ235, a newly developed dual PI3K and mTOR inhibitor currently in phase I-II clinical trials for advanced solid tumors, on osteogenic differentiation and function using primary MSC cultures. Under osteoinductive conditions, BEZ235 strongly promotes osteogenic differentiation, as evidenced by an increase in mineralized matrix production, an upregulation of genes involved in osteogenesis, including bone morphogenetic proteins (BMP2, -4, and -6) and transforming growth factor ?1 (TGF-?1) superfamily members (TGFB1, TGFB2, and INHBE), and increased activation of SMAD signaling molecules. In addition, BEZ235 enhances de novo bone formation in calvarial organotypic cultures. Using pharmacologic inhibitors to delineate mechanism, our studies reveal that suppression of mTOR and, to a much lesser extent PI3K p110?, mediates the osteogenic effects of BEZ235. As confirmation, shRNA-mediated knockdown of mTOR enhances osteogenic differentiation and function in SAOS-2 osteoblast-like cells. Taken together, our findings suggest that BEZ235 may be useful in treating PI3K/mTOR-dependent tumors associated with bone loss, such as the hematologic malignancy multiple myeloma.
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A genetic epilepsy rat model displays endophenotypes of psychosis.
Neurobiol. Dis.
PUBLISHED: 02-03-2010
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The incidence of psychosis is increased in people with epilepsy, including idiopathic generalized epilepsies. To study the biological basis for this co-morbidity, we compared GAERS, a genetic rat model of absence epilepsy, to non-epileptic control rats (NEC). Mature, 14-week old GAERS showed enhanced amphetamine-induced locomotor hyperactivity - a feature also present in young (6-week old) GAERS prior to epilepsy onset. Prepulse inhibition and its disruption by psychotropic drugs did not differ between strains, although GAERS displayed elevated startle responses at both epileptic and pre-epileptic ages. The frontoparietal cortex of GAERS displayed a twofold increase in the power of gamma (30-80 Hz) oscillations, a proposed neurophysiological correlate of psychosis. Radioligand binding autoradiography demonstrated reduced densities of dopamine transporters in the caudate nucleus and nucleus accumbens core and of dopamine D2 receptors in the caudate nucleus. GAERS provide an opportunity to study the neurodevelopmental, genetic and therapeutic aspects of psychiatric comorbidities associated with epilepsy.
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Behavioural phenotype of APPC100.V717F transgenic mice over-expressing a mutant Abeta-bearing fragment is associated with reduced NMDA receptor density.
Behav. Brain Res.
PUBLISHED: 01-07-2010
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The aim of this study was to characterize APPC100.V717F transgenic (TgC100.V717F) mice which over-express a mutant C100 fragment of the amyloid precursor protein. The mice were compared to TgC100 wild type mice (TgC100.WT) and non-transgenic controls at 4-9 and 16-22 months of age. TgC100.V717F mice showed behavioural hyperactivity, particularly at a younger age, as shown by increased numbers of elevated plus maze arm entries and Y-maze arm entries, enhanced baseline locomotor activity in the open field, and enhanced amphetamine-induced hyperlocomotion. This hyperactivity was less pronounced in TgC100.WT which only displayed significant differences to non-transgenic controls at a younger age for the number of Y-maze arm entries and baseline locomotor activity in the open field. In addition, TgC100.V717F mice, but not TgC100.WT, demonstrated cognitive deficits, as shown by reduced spontaneous alternation in the Y-maze and markedly reduced retention in a passive avoidance test. At an older age, TgC100.V717F mice showed enhanced startle and increased immobility time in the forced swim test. In the TgC100.V717F mice, but not TgC100.WT, the behavioural changes were paralleled by a significant reduction in the expression of hippocampal NMDA receptor subunits types 1 and 2A. Concomitantly, we detected axonal disruption and apoptosis in the hippocampus of TgC100.V717F mice. In conclusion, these data demonstrate that the mutant C100 fragment is an effector of biochemical and both cognitive and non-cognitive behaviours. These transgenic mice may be a model for the psychotic features associated with early Alzheimers disease.
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Hypoxia-inducible factor-2 is a novel regulator of aberrant CXCL12 expression in multiple myeloma plasma cells.
Haematologica
PUBLISHED: 12-16-2009
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Multiple myeloma is an incurable malignancy of bone marrow plasma cells. Progression of multiple myeloma is accompanied by an increase in bone marrow angiogenesis. Studies from our laboratory suggest a role for the CXCL12 chemokine in this process, with circulating levels of CXCL12 correlating with bone marrow angiogenesis in patients with multiple myeloma. While the mechanisms responsible for aberrant plasma cell expression of CXCL12 remain to be determined, studies in other systems suggest a role for hypoxia and hypoxia-inducible transcription factors.
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Spatiotemporal regulation of early lipolytic signaling in adipocytes.
J. Biol. Chem.
PUBLISHED: 09-15-2009
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Hormone-sensitive lipase (HSL) is a key enzyme regulating the acute activation of lipolysis. HSL functionality is controlled by multiple phosphorylation events, which regulate its association with the surface of lipid droplets (LDs). We determined the progression and stability of HSL phosphorylation on individual serine residues both spatially and temporally in adipocytes using phospho-specific antibodies. Within seconds of beta-adrenergic receptor activation, HSL was phosphorylated on Ser-660, the phosphorylated form appearing in the peripheral cytosol prior to rapid translocation to, and stable association with, LDs. In contrast, phosphorylation of HSL on Ser-563 was delayed, the phosphorylated protein was predominantly detected on LDs, and mutation of the Ser-659/Ser-660 site to Ala significantly reduced subsequent phosphorylation on Ser-563. Phosphorylation of HSL on Ser-565 was observed in control cells; the phosphorylated protein was translocated to LDs with similar kinetics to total HSL, and the degree of phosphorylation was inversely related to phospho-HSL(Ser-563). These results describe the remarkably rapid, sequential phosphorylation of specific serine residues in HSL at spatially distinct intracellular locales, providing new insight into the complex regulation of lipolysis.
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Lipid droplet-organelle interactions; sharing the fats.
Biochim. Biophys. Acta
PUBLISHED: 09-11-2009
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Lipid droplets (LDs) are key cellular organelles involved in lipid storage and mobilisation. While the major signalling cascades and many of the regulators of lipolysis have been identified, the cellular interactions involved in lipid mobilisation and release remain largely undefined. In non-adipocytes, LDs are small, mobile and interact with other cellular compartments. In contrast, adipocytes primarily contain very large, immotile LDs. The striking morphological differences between LDs in adipocytes and non-adipocytes suggest that key differences must exist in the manner in which LDs in different cell types interact with other organelles. Recent studies have highlighted the complexity of LD interactions, which can be both homotypic, with each other, and heterotypic, with other organelles. The molecules involved in these interactions are also now emerging, including Rab proteins, key regulators of membrane traffic, and caveolin, an integral membrane protein providing a functional link between the cell surface and LDs. Here we summarise recent insights into the cell biology of the LD particularly focussing on the homotypic and heterotypic interactions in both adipocytes and non-adipocytes. We speculate that these interactions may involve inter-organelle membrane contact sites or a hemi-fusion type mechanism to facilitate lipid transfer.
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Nucleophosmin and nucleolin regulate K-Ras plasma membrane interactions and MAPK signal transduction.
J. Biol. Chem.
PUBLISHED: 08-06-2009
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The spatial organization of Ras proteins into nanoclusters on the inner leaflet of the plasma membrane is essential for high fidelity signaling through the MAPK pathway. Here we identify two selective regulators of K-Ras nanoclustering from a proteomic screen for K-Ras interacting proteins. Nucleophosmin (NPM) and nucleolin are predominantly localized to the nucleolus but also have extranuclear functions. We show that a subset of NPM and nucleolin localizes to the inner leaflet of plasma membrane and forms specific complexes with K-Ras but not other Ras isoforms. Active GTP-loaded and inactive GDP-loaded K-Ras both interact with NPM, although NPM-K-Ras binding is increased by growth factor receptor activation. NPM and nucleolin both stabilize K-Ras levels on the plasma membrane, but NPM concurrently increases the clustered fraction of GTP-K-Ras. The increase in nanoclustered GTP-K-Ras in turn enhances signal gain in the MAPK pathway. In summary these results reveal novel extranucleolar functions for NPM and nucleolin as regulators of K-Ras nanocluster formation and activation of the MAPK pathway. The study also identifies a new class of K-Ras nanocluster regulator that operates independently of the structural scaffold galectin-3.
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Neuregulin 1 hypomorphic mutant mice: enhanced baseline locomotor activity but normal psychotropic drug-induced hyperlocomotion and prepulse inhibition regulation.
Int. J. Neuropsychopharmacol.
PUBLISHED: 04-29-2009
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Neuregulin 1 (Nrg1) has been widely recognized as a candidate gene for schizophrenia. This study therefore investigated mice heterozygous for a mutation in the transmembrane domain of this trophic factor (Nrg1+/- mice) in a number of behavioural test systems with relevance to schizophrenia, including psychotropic drug-induced locomotor hyperactivity and prepulse inhibition (PPI) of startle. Baseline locomotor activity in the open field or in photocell cages was slightly, but significantly enhanced in Nrg1+/- mice compared to wild-type littermate controls at age 12-16 wk, but not at age 6 months. The ability of amphetamine, phencyclidine (PCP) or MK-801 to induce locomotor hyperactivity was not significantly different between the genotypes. There was no difference in baseline PPI, startle or startle habituation and there was no difference in the effect of apomorphine, amphetamine or MK-801 on any of these parameters. Only treatment with the 5-HT1A receptor agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) showed a differential effect between genotypes, with a disruption of PPI occurring in Nrg1+/- mice compared to no effect in wild-type controls. This treatment also induced a significant reduction of startle which could have influenced the result. The density of dopamine D2 receptors in the forebrain and of 5-HT1A receptors in the hippocampus and raphe nuclei was not different between Nrg1+/- mice and controls. These studies add to the knowledge about behavioural effects in this mouse model of impaired Nrg1 function and suggest that a number of the behavioural tests with relevance to schizophrenia are normal in these mice.
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Targeted disruption of the CXCL12/CXCR4 axis inhibits osteolysis in a murine model of myeloma-associated bone loss.
J. Bone Miner. Res.
PUBLISHED: 04-02-2009
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The plasma cell (PC) malignancy, multiple myeloma (MM), is unique among hematological malignancies in its capacity to cause osteoclast (OC)-mediated skeletal destruction. We have previously shown that elevated plasma levels of PC-derived CXCL12 are associated with presence of X-ray detectable osteolytic lesions in MM patients. To further investigate this relationship, plasma levels of CXCL12 and betaCrossLaps, a marker of bone loss, were measured. A strong correlation between levels of CXCL12 and OC-mediated bone resorption was identified. To confirm the OC-activating potential of MM PC-derived CXCL12 in vivo, we established a model of MM-mediated focal osteolysis, wherein MM PC lines, such as RPMI-8226, were injected into the tibias of nude mice. Implanting RPMI-8226 gave rise to osteolytic lesions proximal to the tumor, resulting in a 5% decrease in bone volume (BV) compared with vehicle control. Importantly, bone loss was significantly inhibited with systemic administration of the CXCL12/CXCR4 antagonist T140. Furthermore, implanting CXCL12-overexpressing RPMI-8226 cells resulted in a 13% decrease in BV and was associated with increased OC recruitment proximal to the tumor, increased serum matrix metalloproteinase activity, and increased levels of collagen I degradation products. These findings confirm our hypothesis that MM PC-derived CXCL12 stimulates the recruitment and activity of OC, thereby contributing to the formation of MM osteolytic lesions.
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Apo2L/TRAIL inhibits tumor growth and bone destruction in a murine model of multiple myeloma.
Clin. Cancer Res.
PUBLISHED: 03-10-2009
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Multiple myeloma is an incurable disease, for which the development of new therapeutic approaches is required. Here, we report on the efficacy of recombinant soluble Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to inhibit tumor progression and bone destruction in a xenogeneic model of human multiple myeloma.
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Caveolin-1 deficiency leads to increased susceptibility to cell death and fibrosis in white adipose tissue: characterization of a lipodystrophic model.
PLoS ONE
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Caveolin-1 (CAV1) is an important regulator of adipose tissue homeostasis. In the present study we examined the impact of CAV1 deficiency on the properties of mouse adipose tissue both in vivo and in explant cultures during conditions of metabolic stress. In CAV1(-/-) mice fasting caused loss of adipose tissue mass despite a lack of hormone-sensitive lipase (HSL) phosphorylation. In addition, fasting resulted in increased macrophage infiltration, enhanced deposition of collagen, and a reduction in the level of the lipid droplet protein perilipin A (PLIN1a). Explant cultures of CAV1(-/-) adipose tissue also showed a loss of PLIN1a during culture, enhanced secretion of IL-6, increased release of lactate dehydrogenase, and demonstrated increased susceptibility to cell death upon collagenase treatment. Attenuated PKA-mediated signaling to HSL, loss of PLIN1a and increased secretion of IL-6 were also observed in adipose tissue explants of CAV1(+/+) mice with diet-induced obesity. Together these results suggest that while alterations in adipocyte lipid droplet biology support adipose tissue metabolism in the absence of PKA-mediated pro-lipolytic signaling in CAV1(-/-) mice, the tissue is intrinsically unstable resulting in increased susceptibility to cell death, which we suggest underlies the development of fibrosis and inflammation during periods of metabolic stress.
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Co-regulation of cell polarization and migration by caveolar proteins PTRF/Cavin-1 and caveolin-1.
PLoS ONE
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Caveolin-1 and caveolae are differentially polarized in migrating cells in various models, and caveolin-1 expression has been shown to quantitatively modulate cell migration. PTRF/cavin-1 is a cytoplasmic protein now established to be also necessary for caveola formation. Here we tested the effect of PTRF expression on cell migration. Using fluorescence imaging, quantitative proteomics, and cell migration assays we show that PTRF/cavin-1 modulates cellular polarization, and the subcellular localization of Rac1 and caveolin-1 in migrating cells as well as PKC? caveola recruitment. PTRF/cavin-1 quantitatively reduced cell migration, and induced mesenchymal epithelial reversion. Similar to caveolin-1, the polarization of PTRF/cavin-1 was dependent on the migration mode. By selectively manipulating PTRF/cavin-1 and caveolin-1 expression (and therefore caveola formation) in multiple cell systems, we unveil caveola-independent functions for both proteins in cell migration.
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Postlipolytic insulin-dependent remodeling of micro lipid droplets in adipocytes.
Mol. Biol. Cell
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Despite the lipolysis-lipogenesis cycle being a fundamental process in adipocyte biology, very little is known about the morphological changes that occur during this process. The remodeling of lipid droplets to form micro lipid droplets (mLDs) is a striking feature of lipolysis in adipocytes, but once lipolysis ceases, the cell must regain its basal morphology. We characterized mLD formation in cultured adipocytes, and in primary adipocytes isolated from mouse epididymal fat pads, in response to acute activation of lipolysis. Using real-time quantitative imaging and electron tomography, we show that formation of mLDs in cultured adipocytes occurs throughout the cell to increase total LD surface area by ~30% but does not involve detectable fission from large LDs. Peripheral mLDs are monolayered structures with a neutral lipid core and are sites of active lipolysis. Electron tomography reveals preferential association of mLDs with the endoplasmic reticulum. Treatment with insulin and fatty acids results in the reformation of macroLDs and return to the basal state. Insulin-dependent reformation of large LDs involves two distinct processes: microtubule-dependent homotypic fusion of mLDs and expansion of individual mLDs. We identify a physiologically important role for LD fusion that is involved in a reversible lipolytic cycle in adipocytes.
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Altered N-methyl-D-aspartate receptor function in reelin heterozygous mice: male-female differences and comparison with dopaminergic activity.
Prog. Neuropsychopharmacol. Biol. Psychiatry
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The aim of this study was to investigate the in vivo relationship between reelin and NMDA receptor function in schizophrenia. We assessed the effect of reelin deficiency in behavioral models of aspects of this illness, NMDA receptor subunit levels, and NMDA receptor, dopamine D? receptor, and dopamine transporter density. Male, but not female, reelin heterozygous mice showed significantly enhanced MK-801-induced locomotor hyperactivity compared to wildtype controls (7.4-fold vs. 5.2-fold effect of MK-801 over saline, respectively) but there were no genotype differences in the response to amphetamine. Both male and female reelin heterozygous mice showed enhanced effects of MK-801 on startle, but not prepulse inhibition (PPI) of startle. There were no group differences in the effect of apomorphine on startle or PPI. The levels of NMDA receptor subunits were not altered in the striatum. In the frontal cortex, male and female reelin heterozygous mice showed significant up-regulation of NR1 subunits, but down-regulation of NR2C subunits, which was associated with significantly elevated NR1/NR2A and NR1/NR2C ratios. However, there were no differences in [³H]MK-801 binding density in the nucleus accumbens or caudate nucleus, nor in the density of [³H]YM-09151 or [³H]GBR12935 in these brain regions. The enhanced effects of MK-801 in reelin heterozygous mice in this study could be reflective of the role of reelin deficiency in schizophrenia. This genotype effect was male-specific for locomotor hyperactivity, a model of psychosis, but was seen in male and female mice for startle, which could be an indication of changes in anxiety. Changes in NMDA receptor subunit levels and ratios were also seen in both male and female mice. These results suggest that the role of reelin deficiency in schizophrenia may be particularly mediated by altered NMDA receptor responses, with some of these effects being strictly sex-specific.
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