The iron-dopamine D1 coupling modulates neural signatures of working memory across adult lifespan

Brain iron overload and decreased integrity of the dopaminergic system have been independently reported as brain substrates of cognitive decline in aging. Dopamine (DA), and iron are co-localized in high concentrations in the striatum and prefrontal cortex (PFC), but follow opposing age-related trajectories across the lifespan. DA contributes to cellular iron homeostasis and the activation of D1-like DA receptors (D1DR) alleviates oxidative stress-induced inflammatory responses, suggesting a mutual interaction between these two fundamental components. Still, a direct in-vivo study testing the iron-D1DR relationship and their interactions on brain function and cognition across the lifespan is rare. Using PET and MRI data from the DyNAMiC study (n=180, age=20-79, %50 female), we showed that elevated iron content was related to lower D1DRs in DLPFC, but not in striatum, suggesting that dopamine-rich regions are less susceptible to elevated iron. Critically, older individuals with elevated iron and lower D1DR exhibited less frontoparietal activations during the most demanding task, which in turn was related to poorer working-memory performance. Together, our findings suggest that the combination of elevated iron load and reduced D1DR contribute to disturbed PFC-related circuits in older age, and thus may be targeted as two modifiable factors for future intervention.

Contributions of the Catechol-O-Methyltransferase Val158Met Polymorphism to Changes in Brain Iron Across Adulthood and Their Relationships to Working Memory

Ageing is associated with excessive free brain iron, which may induce oxidative stress and neuroinflammation, likely causing cognitive deficits. Lack of dopamine may be a factor behind the increase of iron with advancing age, as it has an important role in cellular iron homoeostasis. We investigated the effect of COMT Val 158 Met (rs4680), a polymorphism crucial for dopamine degradation and proxy for endogenous dopamine, on iron accumulation and working memory in a longitudinal lifespan sample (n = 208, age 20–79 at baseline, mean follow-up time = 2.75 years) using structural equation modelling. Approximation of iron content was assessed using quantitative susceptibility mapping in striatum and dorsolateral prefrontal cortex (DLPFC). Iron accumulated in both striatum and DLPFC during the follow-up period. Greater iron accumulation in DLPFC was associated with more deleterious change in working memory. Older (age 50–79) Val homozygotes (with presumably lower endogenous dopamine) accumulated more iron than older Met carriers in both striatum and DLPFC, no such differences were observed among younger adults (age 20–49). In conclusion, individual differences in genetic predisposition related to low dopamine levels increase iron accumulation, which in turn may trigger deleterious change in working memory. Future studies are needed to better understand how dopamine may modulate iron accumulation across the human lifespan.

Osteoblast-like cellular response to dynamic changes in the ionic extracellular environment produced by calcium-deficient hydroxyapatite

Solution-mediated reactions due to ionic substitutions are increasingly explored as a strategy to improve the biological performance of calcium phosphate-based materials. Yet, cellular response to well-defined dynamic changes of the ionic extracellular environment has so far not been carefully studied in a biomaterials context. In this work, we present kinetic data on how osteoblast-like SAOS-2 cellular activity and calcium-deficient hydroxyapatite (CDHA) influenced extracellular pH as well as extracellular concentrations of calcium and phosphate in standard in vitro conditions. Since cells were grown on membranes permeable to ions and proteins, they could share the same aqueous environment with CDHA, but still be physically separated from the material. In such culture conditions, it was observed that gradual material-induced adsorption of calcium and phosphate from the medium had only minor influence on cellular proliferation and alkaline phosphatase activity, but that competition for calcium and phosphate between cells and the biomaterial delayed and reduced significantly the cellular capacity to deposit calcium in the extracellular matrix. The presented work thus gives insights into how and to what extent solution-mediated reactions can influence cellular response, and this will be necessary to take into account when interpreting CDHA performance both in vitro and in vivo.

Ion reactivity of calcium-deficient hydroxyapatite in standard cell culture media

Solution-mediated surface reactions occur for most calcium phosphate-based biomaterials and may influence cellular response. A reasonable extrapolation of such processes observed in vitro to in vivo performance requires a deep understanding of the underlying mechanisms. We therefore systematically investigated the nature of ion reactivity of calcium-deficient hydroxyapatite (CDHA) by exposing it for different periods of time to standard cell culture media of different chemical composition (DMEM and McCoy medium, with and without osteogenic supplements and serum proteins). Kinetic ion interaction studies of principal extracellular ions revealed non-linear sorption of Ca²⁺ (∼50% sorption) and K⁺ (∼8%) as well as acidification of all media during initial contact with CDHA (48h). Interestingly, inorganic phosphorus (P(i)) was sorbed from McCoy medium (∼50%) or when using osteogenic media containing β-glycerophosphate, but not from DMEM medium. Non-linear sorption data could be perfectly described by pseudo-first-order and pseudo-second-order sorption models. At longer contact time (21 days), and with frequent renewal of culture medium, sorption of Ca²⁺ remained constant throughout the experiment, while sorption of P(i) gradually decreased in McCoy medium. In great contrast, CDHA began to release P(i) slowly with time when using DMEM medium. Infrared spectra showed that CDHA exposed to culture media had a carbonated surface chemistry, suggesting that carbonate plays a key role in the ion reactivity of CDHA. Our data show that different compositions of the aqueous environment may provoke opposite ion reactivity of CDHA, and this must be carefully considered when evaluating the osteoinductive potential of the material.

Comprehensive analysis of electrically-pumped GaSb-based VCSELs

This paper discusses several performance-related aspects of electrically-pumped GaSb-based buried tunnel junction VCSELs with an emission wavelength of 2.6 μm based on theoretical and experimental results. These results allow a deeper insight into the internal device physics, such as radial diffusion of carriers, maximum continuous-wave operating temperature, diffraction loss, internal temperature, gain and loss parameters, internal quantum efficiency of the active region etc. These parameters can be taken into account while designing mid-infrared lasers which leads to an improved device performance. A simple thermal model of the devices based on the two-dimensional (2-D) finite element method using the material data from the literature is also presented. In addition, an application-based result utilizing these lasers for the measurement of absolute water vapor concentration by wavelength modulation spectroscopy (WMS) method are also described, hinting that devices are well-suited for the targeted sensing applications.

The feasibility of trace element supplementation for stable operation of wheat stillage-fed biogas tank reactors

The aim of this study was to investigate the effect of trace element supplementation on operation of wheat stillage-fed biogas tank reactors. The stillage used was a residue from bio-ethanol production, containing high levels of sulfate. In biogas production, high sulfate content has been associated with poor process stability in terms of low methane production and accumulation of process intermediates. However, the results of the present study show that this problem can be overcome by trace element supplementations. Four lab-scale wheat stillage-fed biogas tank reactors were operated for 345 days at a hydraulic retention time of 20 days (37 degrees C). It was concluded that daily supplementation with Co (0.5 mg L(-1)), Ni (0.2 mg L(-1)) and Fe (0.5 g L(-1)) were required for maintaining process stability at the organic loading rate of 4.0 g volatile solids L(-1) day(-1).

Characterisation of STREAMLINE phenyl

STREAMLINE Phenyl is a new hydrophobic interaction chromatography support designed for use in expanded bed adsorption. The phenyl groups are linked to STREAMLINE matrix via highly stable ether linkages. Within this development project the chemical and chromatographic stability as well as the breakthrough capacity for human IgG has been studied. The chemical stability was monitored as the carbon leakage from the matrix to the storage solution, pH 1-14 at 20 and 40 degrees C. The carbon content in the supernatant was determined with Total Organic Carbon (TOC) technique. In the chromatographic stability study STREAMLINE Phenyl was stored in eight different storage solutions under ambient conditions for 12 weeks and then tested in a chromatographic function test. The results show that the adsorbent is chemically stable and that the chromatographic properties are retained under the tested conditions. The breakthrough capacity study demonstrates the importance of the bed height for obtaining maximal dynamic capacity. Further, there is a good correlation between breakthrough data generated from packed bed and expanded bed runs.

Localization of the insulin receptor in caveolae of adipocyte plasma membrane

The insulin receptor is a transmembrane protein of the plasma membrane, where it recognizes extracellular insulin and transmits signals into the cellular signaling network. We report that insulin receptors are localized and signal in caveolae microdomains of adipocyte plasma membrane. Immunogold electron microscopy and immunofluorescence microscopy show that insulin receptors are restricted to caveolae and are colocalized with caveolin over the plasma membrane. Insulin receptor was enriched in a caveolae-enriched fraction of plasma membrane. By extraction with beta-cyclodextrin or destruction with cholesterol oxidase, cholesterol reduction attenuated insulin receptor signaling to protein phosphorylation or glucose transport. Insulin signaling was regained by spontaneous recovery or by exogenous replenishment of cholesterol. beta-Cyclodextrin treatment caused a nearly complete annihilation of caveolae invaginations as examined by electron microscopy. This suggests that the receptor is dependent on the caveolae environment for signaling. Insulin stimulation of cells prior to isolation of caveolae or insulin stimulation of the isolated caveolae fraction increased tyrosine phosphorylation of the insulin receptor in caveolae, demonstrating that insulin receptors in caveolae are functional. Our results indicate that insulin receptors are localized to caveolae in the plasma membrane of adipocytes, are signaling in caveolae, and are dependent on caveolae for signaling.

Characterisation of ANX Sepharose 4 Fast Flow media

ANX Sepharose 4 Fast Flow (low sub) and ANX Sepharose 4 Fast Flow (high sub) are two new media developed at Amersham Pharmacia Biotech. They are weak anion exchangers with different amounts of tertiary amine groups attached via a spacer arm to Sepharose 4 Fast Flow. They have been characterised by the separation of some model proteins under different conditions and by determination of breakthrough capacities for proteins of different molecular masses. Functional performance after storage in different solutions at ambient temperature has been monitored. Carbon release after storage at different pH and temperatures has been measured using the total organic carbon technique. The selectivity results show that these new media are interesting complements to already existing Fast Flow anion exchangers. They are very stable and can be especially useful in applications involving the purification of high-molecular-mass proteins.

Rapid detection of a mutation hot-spot in the human androgen receptor

Mutations of the human androgen receptor gene may disturb sexual development in males, and are inherited as an X-linked recessive trait. The vast majority of the mutations are familial. We have identified a large kindred with complete androgen insensitivity syndrome (CAIS) without detectable androgen-binding in genital skin fibroblasts. A single nucleotide substitution (C-to-T transition) was identified, resulting in an Arg855 to Cys in the androgen binding domain. To date, four independent CAIS families have been reported with this specific mutation that coincides with the propensity of cytosines at CpG dinucleotides to methylate. An allele-specific oligo-nucleotide assay was developed that allowed for the rapid and specific identification of this mutation hot-spot in individuals with androgen receptor insensitivity syndromes.

Cytoplasmic CREB alpha-like antigens in specific regions of the rat brain

We have investigated the expression of the alpha-region of CREB (amino acids 88-101) in the rat brain. This region is encoded by a separate exon and has been reported to enhance the transcriptional efficiency of CREB. Light microscopic immunohistochemistry showed labeled neurons in several brain regions, such as the spinal cord, pontine reticular formation, cerebellum, hypothalamus, hippocampus and olfactory cortex. The labeling was exclusively cytoplasmic, and electron microscopy revealed that the CREB alpha-immunoreactivity was localized to the Golgi apparatus and axon terminals. Immunoblotting after SDS-PAGE showed specifically detected proteins of 21 and 160 kD. We suggest that neuronal CREB alpha-proteins represent alternatively spliced isoforms of CREB that lack the nuclear translocation signal. These isoforms may be involved in the regulation of CREB-mediated transcription.

Insulin-stimulated glucose uptake involves the transition of glucose transporters to a caveolae-rich fraction within the plasma membrane: implications for type II diabetes

BACKGROUND

Adipose and muscle tissues express an insulin-sensitive glucose transporter (GLUT4). This transporter has been shown to translocate from intracellular stores to the plasma membrane following insulin stimulation. The molecular mechanisms signalling this event and the details of the translocation pathway remain unknown. In type II diabetes, the cellular transport of glucose in response to insulin is impaired, partly explaining why blood-glucose levels in patients are not lowered by insulin as in normal individuals.

MATERIALS AND METHODS

Isolated rat epididymal adipocytes were stimulated with insulin and subjected to subcellular fractionation and to measurement of glucose uptake. A caveolae-rich fraction was isolated from the plasma membranes after detergent solubilization and ultracentrifugal floatation in a sucrose gradient. Presence of GLUT4 and caveolin was determined by immunoblotting after SDS-PAGE.

RESULTS

In freshly isolated adipocytes, insulin induced a rapid translocation of GLUT4 to the plasma membrane fraction, which was followed by a slower transition of the transporter into a detergent resistant caveolae-rich region of the plasma membrane. The insulin-stimulated appearance of transporters in the caveolae-rich fraction occurred in parallel with enhanced glucose uptake by cells. Treatment with isoproterenol plus adenosine deaminase rapidly inhibited insulin-stimulated glucose transport by 40%, and at the same time GLUT4 disappeared from the caveolae-rich fraction and from plasma membranes as a whole.

CONCLUSIONS

Insulin stimulates glucose uptake in adipocytes by rapidly translocating GLUT4 from intracellular stores to the plasma membrane. This is followed by a slower transition of GLUT4 to the caveolae-rich regions of the plasma membrane, where glucose transport appears to take place. These results have implications for an understanding of the defect in glucose transport involved in type II diabetes.

Translocation of insulin-regulated glucose transporter is stimulated by long-chain 1,2-diacylglycerol in rat adipocytes

The long-chain diacylglycerol 1,2-dimyristoylglycerol emulsified with taurodeoxycholate has been shown to potently stimulate glucose transport in isolated rat adipocytes (Stråfors, Nature 335, 554-556 (1988)). We now report that this 1,2-diacylglycerol in the presence of taurodeoxycholate, similarly to insulin, induced translocation of the insulin-regulated glucose transporter (GLUT-4) from a microsomal membrane compartment to the plasma membrane. H4IIE hepatoma cells expressed mRNA for GLUT-1, but not for GLUT-4. In these, otherwise insulin-responsive, cells diacylglycerol or insulin had only a marginal effect on glucose transport.

Uptake and metabolism of long-chain 1,2-diacylglycerols by rat adipocytes and H4IIE hepatoma cells

The physiological long-chain diacylglycerols 1,2-dioleoylglycerol and 1,2-dimyristoylglycerol were taken up and metabolized, both by adipocytes and by hepatoma cells, in amounts sufficient to elicit biological responses, without use of emulsifier or any special cell treatment. In adipocytes the only metabolic lipid product of either diacylglycerol was triacylglycerol. In hepatoma cells both diacylglycerols were converted to a number of identified products, mainly phosphatidylcholine and triacylglycerol. This has implications for the interpretation of reports in which long-chain diacylglycerols have been found ineffective in stimulation of cells.

Isolation of phosphooligosaccharide/phosphoinositol glycan from caveolae and cytosol of insulin-stimulated cells

A phosphooligosaccharide has been proposed as a second messenger of insulin. It is believed to be structurally related to the carbohydrate moiety of phosphatidylinositol glycan anchors of many cell surface proteins. Herein we demonstrate that [32]phosphate in freshly isolated adipocytes and [3H]galactose in cultured hepatoma cells (H4IIE) labeled the same set of three different glycolipids. With all three, the radiolabel was made water soluble by phosphatidylinositol(glycan)-specific phospholipase C or D catalyzed hydrolysis. We isolated the three phospholipase C-released substances. One of them was susceptible to nitrous acid deamination, indicative of a hexosamine with a free amino group. This phosphooligosaccharide structure had an apparent molecular mass between tetra- and pentaglucose by gel filtration. By anion-exchange chromatography it was separated into two differently charged and interconvertible species. Adipocytes stimulated with insulin accumulated the nitrous acid sensitive phosphooligosaccharide: after stimulation the intracellular level of free phosphooligosaccharide increased threefold within 5 min, fell off during the next few minutes and then remained at a slightly elevated level. After insulin stimulation the intracellular concentration of free phosphooligosaccharide was > 1,000-fold higher than in the incubation medium. When prepared from rat livers on a preparative scale, the oligosaccharide was also found to exhibit insulinomimetic effects on protein phosphorylation of insulin target proteins in intact adipocytes. After subcellular fractionation of adipocytes the lipid-bound [32P]phosphooligosaccharide of the plasma membrane was found to be localized in plasma membrane domains apparently corresponding to caveolae. Lipid-bound [32P]phosphooligosaccharide was found also in the microsomal fraction.

Inhibition of Raf-1 kinase expression abolishes insulin stimulation of DNA synthesis in H4IIE hepatoma cells

The involvement of Raf-1 kinase in the insulin signal transduction chain leading to control of cell proliferation was studied in the H4IIE rat hepatoma cell line by inhibiting expression of the kinase with antisense oligodeoxyribonucleotide directed against Raf-1 mRNA. Antisense oligonucleotide was found to reduce (at 2 microM) or completely block (at 15 microM) the stimulation by insulin of DNA synthesis, measured as thymidine incorporation. The residual DNA synthesis seen in the absence of insulin stimulation was also inhibited by the Raf-1 kinase antisense oligonucleotide.

Regulation of calcium influx across the plasma membrane of the human T-leukemic cell line, JURKAT: dependence on a rise in cytosolic free calcium can be dissociated from formation of inositol phosphates

A rise in the cytosolic free Ca2+ concentration due to both mobilization of Ca2+ from internal stores and influx of extracellular Ca2+ across the plasma membrane through 'second messenger-operated Ca2+ channels' is one of the first transmembrane signals detected following activation of CD2 or CD3 receptors on T-cells. In this study, we have further elucidated the regulation of these channels in the human T-leukemic cell line, JURKAT. Stimulation with either OKT3 or PHA induced a prompt influx of Ca2+ as assessed by MN2+ quenching of intracellular fura-2 fluorescence. When cytosolic free Ca2+ transient was partially buffered by loading the cells with BAPTA, neither agonist could induce Ca2+ entry into the cells as depicted by the lack of quenching of the fluorescence signal by Mn2+. This is in good agreement with our previous data on agonist-induced 45Ca2+ influx demonstrating that a rise in cytosolic free Ca2+ due to agonist-induced mobilization of Ca2+ from intracellular stores, could, directly or indirectly via the inositol cycle, initiate Ca2+ influx in these cells. Further support of this idea comes from the data demonstrating that agonist-induced mobilization of Ca2+ precedes the influx of Ca2+ across the plasma membrane. The present findings show that agonist-stimulation significantly increased the levels of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 after only 5 s, indicating that one or both of these substances could play a role in the regulation of Ca2+ influx. However, when agonist-induced Mn2+ influx was totally abolished, by partially buffering the cytosolic free Ca2+ rise, the formation of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 was not affected. Consequently, the dependence of an initial rise in cytosolic free Ca2+ for the subsequent regulation of Ca2+ influx across the plasma membrane, can be dissociated from the formation of both Ins(1,4,5)P3 and Ins(1,3,4,5)P4.

Association of ligand-receptor complexes with actin filaments in human neutrophils: a possible regulatory role for a G-protein

Most ligand-receptor interactions result in an immediate generation of various second messengers and a subsequent association of the ligand-receptor complex to the cytoskeleton. Depending on the receptor involved, this linkage to the cytoskeleton has been suggested to play a role in the termination of second messenger generation and/or the endocytic process whereby the ligand-receptor complex is internalized. We have studied how the binding of chemotactic peptide-receptor complexes to the cytoskeleton of human neutrophils is accomplished. As much as 76% of the tritiated formylmethionyl-leucyl-phenylalanine (fMet-Leu-[3H]Phe) specifically bound to intact cells, obtained by a 30-s stimulation with 20 nM fMet-Leu-[3H]Phe, still remained after Triton X-100 extraction. Preincubating intact cells with dihydrocytochalasin B (dhCB) or washing the cytoskeletal preparation with a high concentration of potassium, reduced the binding of ligand-receptor complexes to the cytoskeleton by 46% or more. Inhibition of fMet-Leu-Phe-induced generation of second messengers by ADP-ribosylating the alpha-subunit of the receptor-coupled G-protein with pertussis toxin, did not reduce the binding of ligand-receptor complexes to the cytoskeleton. However, using guanosine-5'-O-(2-thiodiphosphate) (GDP beta S) to prevent the dissociation of the fMet-Leu-Phe-associated G-protein within electrically permeabilized cells, led to a pronounced reduction (62%) of the binding between ligand-receptor complexes and the cytoskeleton. In summary, in human neutrophils the rapid association between chemotactic peptide-receptor complexes and the cytoskeleton is dependent on filamentous actin. This association is most likely regulated by the activation and dissociation of the fMet-Leu-Phe-associated G-protein.

Elution behaviour of some proteins on fresh, acid- or base-treated Sephacryl S-200 HR

The influence of sodium chloride concentration and the pH of the mobile phase on the distribution coefficient of proteins with different pI values was studied on Sephacryl S-200 HR. The non-size-related behaviour of this gel filtration packing is mainly attributed to small amounts of groups that are negatively charged within the pH range investigated (4.2-10.0). These anionic groups on the packing gave rise to ion-exchange or ion-exclusion interactions depending on the charge characteristics of the protein. Hydrophobic interactions at high ionic strength and intramolecular electrostatic repulsive interactions at low ionic strength were also observed for some proteins. The chemical stability of Sephacryl S-200 HR was studied by comparing the chromatographic results with Sephacryl S-200 HR that had been treated in acidic or basic solutions with those with fresh Sephacryl. After Sephacryl S-200 HR had been stored for 2 weeks in 0.10 M sodium hydroxide the chromatographic results at low ionic strengths clearly showed that groups that are positively charged at pH 4.2 had been formed. However, storage for 2 weeks in 0.01 M hydrochloric acid did not change the chromatographic behaviour of the proteins from that observed when injected on fresh Sephacryl S-200 HR.

Skiing safety in children: a prospective study of downhill skiing injuries and their relation to the skier and his equipment

A prospective analysis was made of 31 children who sustained an injury of the lower extremity during downhill skiing. They were compared with a control population of 183 skiers. The injured children were to a large extent less skillful skiers and tended to be injured at the start of their skiing season. In general, the risk of having an injury did not seem to be influenced by the question of where or by whom the bindings were adjusted. Nevertheless, beginners predominantly had had their bindings adjusted in ski shops. The heel mechanism functioned well in most cases, while the function of the toe mechanism was poor in the control population and even poorer in the injury group. The results indicate that many of the present release bindings used by children are of poor quality and should be improved. At present, a reasonable recommendation for children should be to set the heel mechanism according to the standard scale and the toe mechanism as loosely as possible without having a release during ordinary skiing. Increased use of testing devices is advocated. In Sweden, improved education of personnel in ski shops, with the children in focus, seems important, and training and supervision of the beginners should be intensified.

Skiing safety in children: adjustment and reliability of the bindings

One-hundred children were picked at random from ski lift queues and were questioned as regards their skiing ability, experience, and ski equipment. Around 40% of the skiers had not made any adjustment and/or setting of the bindings. The lateral toe release and recentering forces were recorded. We found, irrespective of to which reference system our results were correlated, a very low percentage of bindings with acceptable setting, lower than has been reported for adults. Sixty percent of the bindings did not have any space between the sole of the boot and the slip plate. After correction of the space, the lateral toe release torque decreased significantly. Only 20% of the bindings displayed a recentering force. Our results indicate the need for several improvements regarding children's release bindings, including factors such as mechanical function, adjustment, and testing. The IAS reference system is recommended as the best of the existing reference systems.

Release and retention in Alpine ski bindings

Six different designs of alpine ski bindings were semistatically tested in a MTS machine, and measurements of release forces were performed at the toe and at the heel, perpendicularly, and at 30 degrees backward and 30 degrees forward from the normal of the ski, respectively. In the conventional, two-part bindings examined, there was no difference between the forces acting in perpendicular and oblique planes. The release resistance in oblique directions was lower than the retention force perpendicularly to the ski in two binding designs with a spring-loaded, moveable toe unit (Besser, "Jack" prototype). A low release resistance obliquely forward is important for the prevention of injury to the lower extremity when a skier falls forward. On analysis of the injury-preventing properties of a release binding, consideration should also be paid to release resistance in oblique planes.