Effects of Fluctuating Glucose Levels on Neuronal Cells In Vitro

There is increasing evidence for glucose fluctuation playing a role in the damaging effects of diabetes on various organs, including the brain. We aimed to study the effects of glycaemic variation (GV) upon mitochondrial activity using an in vitro human neuronal model. The metabolic disturbance of GV in neuronal cells, was mimicked via exposure of neuroblastoma cells SH-SY5Y to constant glucose or fluctuating (i.e. 6 h cycles) for 24 and 48 h. Mitochondrial dehydrogenase activity was determined via MTT assay. Cell mitochondrial activity (MTT) was moderately decreased in constant high glucose, but markedly decreased following 24 and 48 h of cyclical glucose fluctuations. Glucose transport determined via 2-deoxy-D-[1-(14)C] glucose uptake was regulated in an exaggerated manner in response to glucose variance, accompanied by modest changes in GLUT 1 mRNA abundance. Osmotic components of these glucose effects were investigated in the presence of the osmotic-mimics mannitol and L: -glucose. Both treatments showed that fluctuating osmolality did not result in a significant change in mitochondrial activity and had no effects on (14)Cglucose uptake, suggesting that adverse effects on mitochondrial function were specifically related to metabolically active glucose fluctuations. Apoptosis gene expression showed that both intrinsic and extrinsic apoptotic pathways were modulated by glucose variance, with two major response clusters corresponding to (i) glucose stress-modulated genes, (ii) glucose mediated osmotic stress-modulated genes. Gene clustering analysis by STRING showed that most of the glucose stress-modulated genes were components of the intrinsic/mitochondrial apoptotic pathway including Bcl-2, Caspases and apoptosis executors. On the other hand the glucose mediated osmotic stress-modulated genes were mostly within the extrinsic apoptotic pathway, including TNF receptor and their ligands and adaptors/activators/initiators of apoptosis. Fluctuating glucose levels have a greater adverse effect on neuronal cell energy regulation mechanisms than either sustained high or low glucose levels.     

The application of muscle wrapping to voxel-based finite element models of skeletal structures

Finite elements analysis (FEA) is now used routinely to interpret skeletal form in terms of function in both medical and biological applications. To produce accurate predictions from FEA models, it is essential that the loading due to muscle action is applied in a physiologically reasonable manner. However, it is common for muscle forces to be represented as simple force vectors applied at a few nodes on the model’s surface. It is certainly rare for any wrapping of the muscles to be considered, and yet wrapping not only alters the directions of muscle forces but also applies an additional compressive load from the muscle belly directly to the underlying bone surface. This paper presents a method of applying muscle wrapping to high-resolution voxel-based finite element (FE) models. Such voxel-based models have a number of advantages over standard (geometry-based) FE models, but the increased resolution with which the load can be distributed over a model’s surface is particularly advantageous, reflecting more closely how muscle fibre attachments are distributed. In this paper, the development, application and validation of a muscle wrapping method is illustrated using a simple cylinder. The algorithm: (1) calculates the shortest path over the surface of a bone given the points of origin and ultimate attachment of the muscle fibres; (2) fits a Non-Uniform Rational B-Spline (NURBS) curve from the shortest path and calculates its tangent, normal vectors and curvatures so that normal and tangential components of the muscle force can be calculated and applied along the fibre; and (3) automatically distributes the loads between adjacent fibres to cover the bone surface with a fully distributed muscle force, as is observed in vivo. Finally, we present a practical application of this approach to the wrapping of the temporalis muscle around the cranium of a macaque skull.     

Molecular basis for phosphospecific recognition of histone H3 tails by Survivin paralogues at inner centromeres

Survivin, a subunit of the chromosome passenger complex (CPC), binds the N-terminal tail of histone H3, which is phosphorylated on T3 by Haspin kinase, and localizes the complex to the inner centromeres. We used x-ray crystallography to determine the residues of Survivin that are important in binding phosphomodified histone H3. Mutation of amino acids that interact with the histone N-terminus lowered in vitro tail binding affinity and reduced CPC recruitment to the inner centromere in cells, validating our solved structures. Phylogenetic analysis shows that nonmammalian vertebrates have two Survivin paralogues, which we name class A and B. A distinguishing feature of these paralogues is an H-to-R change in an amino acid that interacts with the histone T3 phosphate. The binding to histone tails of the human class A paralogue, which has a histidine at this position, is sensitive to changes around physiological pH, whereas Xenopus Survivin class B is less so. Our data demonstrate that Survivin paralogues have different characteristics of phosphospecific binding to threonine-3 of histone H3, providing new insight into the biology of the inner centromere.     

Is there a temporal niche separation in the leaf phenology of savanna trees and grasses?

Aim It has been proposed that, in tropical savannas, trees deploy their leaves earlier in the growing season and grasses deploy their leaves later. This hypothesis implies a mechanism that facilitates the coexistence of trees and grasses in savannas. If true, this hypothesis would also allow algorithms to use differences in the phenological timing of grass and tree leaves to partition the relative contribution of grasses and trees to net primary production. In this study we examine whether a temporal niche separation between grasses and trees exists in savanna. Location A semi‐arid, subtropical savanna, Kruger National Park, South Africa. Methods We use a multi‐spectral camera to track through an entire growing season the normalized difference vegetation index (NDVI) of individual canopies of grasses and trees at eight sites arranged along a precipitation and temperature gradient. Results Among trees, we identified two distinct phenological syndromes: an early flushing syndrome and a late‐flushing syndrome. Leaf flush in the tree strategies appears to pre‐empt rainfall, whereas grass leaf flush follows the rain. The growing season of trees is 20 (late‐flushing trees) to 27 (early flushing trees) days longer than that of the grasses. Main conclusions We show that grasses and trees have different leaf deployment strategies. Trees deployed leaves at lower temperatures than grasses and retained them for longer at the end of the growing season. The timing of the increase in NDVI is, however, similar between grasses and late‐flushing trees and this complicates the separation of grass and tree signals from multi‐spectral satellite imagery.     

Reaction of selenium with immunoglobulin molecules.

Radioactive selenite reacts with purified human and goat immunoglobulins at acidic and neutral pH. The antigenic properties of the immunoglobulins are retained during the selenium labelling as shown by immunoelectrophoresis and autoradiography. Pepsin digests of 75Se-labelled IgG possess 75Se both in the (Fab')2 fraction and in the low molecular weight peptides derived from the Fc domains. Alpha-1-acid glycoprotein, ribonuclease, and lysozyme are also labelled by this procedure. Enhancement of 75Se incorporation by urea, guanidinium chloride, mercaptoethanol, sodium sulfite and carrier selenite is interpreted as an effect of destabilization of IgG disulfide bonds. Up to 1.4 g atoms Se per mol IgG have been incorporated. We assume that selenite is cleaving disulfides by a process akin to sulfitolysis. The lability of the isolated 75Se-labelled IgG to high concentrations of mercaptans and sulfite is consistent with this idea. These 75Se-labelled proteins may be useful in structure studies and radioimmunoassay.     

Changes in urinary dinor dihydro F2-isoprostane metabolite concentrations,a marker of oxidative stress,during and following asthma exacerbations

To investigate changes in oxidant stress during and following acute asthma exacerbations, this stidy measured 2,3-dinor-5,6-dihydro-15-F_2t-IsoP (F₂-IsoP-M), the major urinary metabolite of 15-F_2t-IsoP, in eight asthmatic adults, during and following an asthma hospitalization. F₂-IsoP-M concentrations at admission and follow-up were significantly higher than discharge (admission median: 4.12 ng/Cr mg, range 1.89–7.8; follow-up: 2.47 ng/Cr mg (1.56–6.86); discharge: 1.42 ng/Cr mg (0.7–4.44); both p<0.01), but not significantly different between admission and follow-up. F₂-IsoP-M concentrations at follow-up were higher than a control group with stable asthma (0.68 ng/Cr mg (0.31–1.5), p=0.0008). In conclusion, asthma exacerbations requiring hospitalization are associated with 6-fold higher urinary F₂-IsoP-M concentrations compared to stable asthmatics. F₂-IsoP-M concentrations decreased significantly during hospitalization, but significant elevations 3 months following hospitalization suggest ongoing oxidative stress despite clinical improvement. Urinary F₂-IsoP-M may be a clinically useful, simple non-invasive systemic measure of oxidative stress in asthmatics, providing information not captured by spirometry or symptoms.