Tau haplotypes regulate transcription and are associated with Parkinson's disease

A primary haplotype (H1) of the microtubule-associated protein Tau (MAPT) gene is associated with Parkinson's disease (PD). However, the mechanism for disease susceptibility remains unknown. We examined the promoter region of MAPT and identified single nucleotide polymorphisms and insertions of 1 to 11 nucleotides. These polymorphisms corresponded to the previously characterized haplotypes, H1 and H2, as well as a novel variant of the H1 haplotype, H1'. As observed in other studies, we demonstrated a significant association with the H1/H1 promoter genotype and PD in a cohort of 206 idiopathic late-onset cases. This is in contrast with a panel of 13 early-onset PD patients, for whom we did not detect any mutations in MAPT. By examining single nucleotide polymorphisms in adjacent genes, we showed that linkage disequilibrium does not extend beyond the MAPT haplotype to neighboring genes. To define the mechanism of disease susceptibility, we examined the transcriptional activity of the promoter haplotypes using a luciferase reporter assay. We demonstrated in two human cell lines, SK-N-MC and 293, that the H1 haplotype was more efficient at driving gene expression than the H2 haplotype. Our data suggest that an increase in expression of the MAPT gene is a susceptibility factor in idiopathic PD.

Tyrosine 394 is phosphorylated in Alzheimer's paired helical filament tau and in fetal tau with c-Abl as the candidate tyrosine kinase

Tau is a major microtubule-associated protein of axons and is also the principal component of the paired helical filaments (PHFs) that comprise the neurofibrillary tangles found in Alzheimer's disease and other tauopathies. Besides phosphorylation of tau on serine and threonine residues in both normal tau and tau from neurofibrillary tangles, Tyr-18 was reported to be a site of phosphorylation by the Src-family kinase Fyn. We examined whether tyrosine residues other than Tyr-18 are phosphorylated in tau and whether other tyrosine kinases might phosphorylate tau. Using mass spectrometry, we positively identified phosphorylated Tyr-394 in PHF-tau from an Alzheimer brain and in human fetal brain tau. When wild-type human tau was transfected into fibroblasts or neuroblastoma cells, treatment with pervanadate caused tau to become phosphorylated on tyrosine by endogenous kinases. By replacing each of the five tyrosines in tau with phenylalanine, we identified Tyr-394 as the major site of tyrosine phosphorylation in tau. Tyrosine phosphorylation of tau was inhibited by PP2 (4-amino-5-(4-chlorophenyl-7-(t-butyl) pyrazolo[3,4-d] pyrimidine), which is known to inhibit Src-family kinases and c-Abl. Cotransfection of tau and kinases showed that Tyr-18 was the major site for Fyn phosphorylation, but Tyr-394 was the main residue for Abl. In vitro, Abl phosphorylated tau directly. Abl could be coprecipitated with tau and was present in pretangle neurons in brain sections from Alzheimer cases. These results show that phosphorylation of tau on Tyr-394 is a physiological event that is potentially part of a signal relay and suggest that Abl could have a pathogenic role in Alzheimer's disease.

Walking performance, oxygen uptake kinetics and resting muscle pyruvate dehydrogenase complex activity in peripheral arterial disease

In the present study, we tested the hypothesis that walking intolerance in intermittent claudication (IC) is related to both slowed whole body oxygen uptake (Vo(2)) kinetics and altered activity of the active fraction of the pyruvate dehydrogenase complex (PDCa) in skeletal muscle. Ten patients with IC and peripheral arterial disease [ankle/brachial index (ABI) = 0.73 +/- 0.13] and eight healthy controls (ABI = 1. 17 +/- 0.13) completed three maximal walking tests. From these tests, averaged estimates of walking time, peak Vo(2) and the time constant of Vo(2) (tau) during submaximal walking were obtained. A muscle sample was taken from the gastrocnemius medialis muscle at rest and analysed for PDCa and several other biochemical variables. Walking time and peak Vo(2) were approx. 50 % lower in patients with IC than controls, and tau was 2-fold higher (P < 0.05). r was significantly correlated with walking time (r = -0.72) and peak Vo(2) (r = -0.66) in patients with IC, but not in controls. PDCa was not significantly lower in patients with IC than controls; however, PDCa tended to be correlated with tau (r = -0.56, P = 0.09) in patients with IC, but not in controls (r = -0.14). A similar correlation was observed between resting ABI and tau (r = -0.63, P = 0.05) in patients with IC. These data suggest that the impaired Vo(2) kinetics contributes to walking intolerance in IC and that, within a group of patients with IC, differences in Vo(2) kinetics might be partly linked to differences in muscle carbohydrate oxidation.

Binomial leap methods for simulating stochastic chemical kinetics

This paper discusses efficient simulation methods for stochastic chemical kinetics. Based on the tau-leap and midpoint tau-leap methods of Gillespie [D. T. Gillespie, J. Chem. Phys. 115, 1716 (2001)], binomial random variables are used in these leap methods rather than Poisson random variables. The motivation for this approach is to improve the efficiency of the Poisson leap methods by using larger stepsizes. Unlike Poisson random variables whose range of sample values is from zero to infinity, binomial random variables have a finite range of sample values. This probabilistic property has been used to restrict possible reaction numbers and to avoid negative molecular numbers in stochastic simulations when larger stepsize is used. In this approach a binomial random variable is defined for a single reaction channel in order to keep the reaction number of this channel below the numbers of molecules that undergo this reaction channel. A sampling technique is also designed for the total reaction number of a reactant species that undergoes two or more reaction channels. Samples for the total reaction number are not greater than the molecular number of this species. In addition, probability properties of the binomial random variables provide stepsize conditions for restricting reaction numbers in a chosen time interval. These stepsize conditions are important properties of robust leap control strategies. Numerical results indicate that the proposed binomial leap methods can be applied to a wide range of chemical reaction systems with very good accuracy and significant improvement on efficiency over existing approaches. (C) 2004 American Institute of Physics.

The origin and evolution of the surfactant system in fish: Insights into the evolution of lungs and swim bladders

Several times throughout their radiation fish have evolved either lungs or swim bladders as gas-holding structures. Lungs and swim bladders have different ontogenetic origins and can be used either for buoyancy or as an accessory respiratory organ. Therefore, the presence of air-filled bladders or lungs in different groups of fishes is an example of convergent evolution. We propose that air breathing could not occur without the presence of a surfactant system and suggest that this system may have originated in epithelial cells lining the pharynx. Here we present new data on the surfactant system in swim bladders of three teleost fish ( the air-breathing pirarucu Arapaima gigas and tarpon Megalops cyprinoides and the non-air-breathing New Zealand snapper Pagrus auratus). We determined the presence of surfactant using biochemical, biophysical, and morphological analyses and determined homology using immunohistochemical analysis of the surfactant proteins (SPs). We relate the presence and structure of the surfactant system to those previously described in the swim bladders of another teleost, the goldfish, and those of the air-breathing organs of the other members of the Osteichthyes, the more primitive air-breathing Actinopterygii and the Sarcopterygii. Snapper and tarpon swim bladders are lined with squamous and cuboidal epithelial cells, respectively, containing membrane-bound lamellar bodies. Phosphatidylcholine dominates the phospholipid (PL) profile of lavage material from all fish analyzed to date. The presence of the characteristic surfactant lipids in pirarucu and tarpon, lamellar bodies in tarpon and snapper, SP-B in tarpon and pirarucu lavage, and SPs ( A, B, and D) in swim bladder tissue of the tarpon provide strong evidence that the surfactant system of teleosts is homologous with that of other fish and of tetrapods. This study is the first demonstration of the presence of SP-D in the air-breathing organs of nonmammalian species and SP-B in actinopterygian fishes. The extremely high cholesterol/disaturated PL and cholesterol/PL ratios of surfactant extracted from tarpon and pirarucu bladders and the poor surface activity of tarpon surfactant are characteristics of the surfactant system in other fishes. Despite the paraphyletic phylogeny of the Osteichthyes, their surfactant is uniform in composition and may represent the vertebrate protosurfactant.

Protein utilisation and turnover in lines of chickens selected for different aspects of body composition

1. Protein utilisation and turnover were measured in male chickens sampled from a line selected for high breast yield and a randombred control line (lines QL and CL, experiment 1) and in male chickens sampled from lines selected for either high or low abdominal fatness (lines FL and LL, experiment 2). In each experiment, 18 birds per line were given iso-energetic (12.9 MJ ME/kg) diets containing either 120 or 220 g CP/kg from 21 to 29 d (experiment 1) and 33 to 43 d (experiment 2). 2. Measurements were made of growth rate, food intake, body composition, excreta production and N-tau-methylhistidine excretion as a measure of myofibrillar protein breakdown, and fractional rates (%/d) of protein deposition, breakdown and synthesis were calculated. 3. In experiment 1, there were no significant differences between the line means for the fractional measures of protein turnover, but there was marked differential response in the two lines in the fractional rates of protein deposition, breakdown and synthesis, to increase in protein intake. The positive slope of the regressions of fractional (%/d) protein deposition and synthesis rates on protein intake (g/d/kg BW) were approximately 1.4- and 2.0-fold higher respectively in the QL than the CL line birds, and the negative slope of the regression of fractional breakdown rate on protein intake was approximately threefold greater in the CL than the QL line birds. 4. In experiment 2, fractional deposition rate was 6.2% lower, but fractional breakdown rate 9.4% higher in the LL than the FL birds, whilst there was essentially no difference in response of the FL and LL birds in the components of protein turnover to increase in protein intake. Line differences in deposition and breakdown rates were thus a reflection of the considerably higher (20%) food and hence protein intake in the FL than the LL birds. 5. The differential line responses in protein turnover in the two experiments suggest that selection for increased breast muscle yield and for reduced body fatness manipulate different physiological pathways in relation to protein turnover, but neither selection strategy results in an improvement in net protein utilisation at typical levels of protein intake by birds on commercial broiler diets, through a reduction in protein breakdown rate.

Changes in neuronal protein 22 expression and cytoskeletal association in the alcohol-dependent and withdrawn rat brain

The action of alcohol on neuronal pathways has been an issue of increasing research focus, with numerous findings contradicting the previously accepted idea that its effect is nonspecific. The human NP22 (hNP22) gene was revealed by its elevated expression in the frontal cortex of the human alcoholic. The sequences of hNP22 and the rat orthologue rNP22 contain a number of domains consistent with those of cytoskeletal-interacting proteins. Localization of rNP22 is restricted to the cytoplasm and processes of neurons and it colocalizes with elements of the microfilament and microtubule matrices including filamentous actin (F-actin), alpha-tubulin, tau, and microtubule-associated protein 2 (MAP2). Withdrawal of Wistar rats after alcohol dependence induced by alcohol vapor produced elevated levels of rNP22 mRNA and protein in the cortex, CA2, and dentate gyrus regions of the hippocampus. In contrast, there was decreased rNP22 expression in the striatum after chronic ethanol exposure. Chronic ethanol exposure did not markedly alter rNP22 colocalization with F-actin, alpha-tubulin, or MAP2, although colocalization at the periphery of the neuronal soma with F-actin was observed only after chronic ethanol exposure and withdrawal. Rat NP22 colocalization with MAP2 was reduced during withdrawal, whereas association with alpha-tubulin and actin was maintained. These findings suggest that the effect of chronic ethanol exposure and withdrawal on rNP22 expression is region selective. Rat NP22 may affect microtubule or microfilament function, thereby regulating the neuroplastic changes associated with the development of alcohol dependence and physical withdrawal.

Olfactory marker protein modulates primary olfactory axon overshooting in the olfactory bulb

Olfactory marker protein (OMP) is expressed by mature primary olfactory sensory neurons during development and in adult mice. In mice that lack OMP, olfactory sensory neurons have perturbed electrophysiological activity, and the mice exhibit altered responses and behavior to odor stimulation. To date, defects in axon guidance in mice that lack OMP have not been investigated. During development of the olfactory system in mouse, primary olfactory axons often overshoot their target glomerular layer and project into the deeper external plexiform layer. These aberrant axonal projections are normally detected within the external plexiform layer up to postnatal day 12. We have examined the projections of primary olfactory axons in OMP-tau:LacZ mice and OMP-GFP mice, two independent lines in which the OMP coding region has been replaced by reporter molecules. We found that axons overshoot their target layer and grow into the external plexiform layer in these OMP null mice as they do in wild-type animals. However, in the absence of OMP, overshooting axons are more persistent and remain prominent until 5 weeks postnatally, after which their numbers decrease. Overshooting axons are still present in these mice even at 8 months of age. In heterozygous mice, axons also overshoot into the external plexiform layer; however, there are fewer axons, and they project for shorter distances, compared with those in a homozygous environment. Our results suggest that perturbed electrophysiological responses, caused by loss of OMP in primary olfactory neurons, reduce the ability of primary olfactory axons to recognize their glomerular target. © 2005 Wiley-Liss, Inc.

Motorcycle accident risk could be inflated by a time to arrival illusion

Purpose. Drivers adopt smaller safety margins when pulling out in front of motorcycles compared with cars. This could partly account for why the most common motorcycle/car accident involves a car violating a motorcyclist's right of way. One possible explanation is the size-arrival effect in which smaller objects are perceived to arrive later than larger objects. That is, drivers may estimate the time to arrival of motorcycles to be later than cars because motorcycles are smaller. Methods. We investigated arrival time judgments using a temporal occlusion paradigm. Drivers recruited from the student population (n = 28 and n = 33) saw video footage of oncoming vehicles and had to press a response button when they judged that vehicles would reach them. Results. In experiment 1, the time to arrival of motorcycles was estimated to be significantly later than larger vehicles (a car and a van) for different approach speeds and viewing times. In experiment 2, we investigated an alternative explanation to the size-arrival effect: that the smaller size of motorcycles places them below the threshold needed for observers to make an accurate time to arrival judgment using tau. We found that the motorcycle/car difference in arrival time estimates was maintained for very short occlusion durations when tau could be estimated for both motorcycles and cars. Conclusions. Results are consistent with the size-arrival effect and are inconsistent with the tau threshold explanation. Drivers estimate motorcycles will reach them later than cars across a range of conditions. This could have safety implications.

Sheet flow sediment transport under waves with acceleration skewness and boundary layer streaming

The effect of acceleration skewness on sheet flow sediment transport rates (q) over bar (s) is analysed using new data which have acceleration skewness and superimposed currents but no boundary layer streaming. Sediment mobilizing forces due to drag and to acceleration (similar to pressure gradients) are weighted by cosine and sine, respectively, of the angle phi(.)(tau)phi(tau) = 0 thus corresponds to drag dominated sediment transport, (q) over bar (s)similar to vertical bar u(infinity)vertical bar u(infinity), while phi(tau) = 90 degrees corresponds to total domination by the pressure gradients, (q) over bar similar to du(infinity)/dt. Using the optimal angle, phi = 51 degrees based on that data, good agreement is subsequently found with data that have strong influence from boundary layer streaming. Good agreement is also maintained with the large body of U-tube data simulating sine waves with superimposed currents and second-order Stokes waves, all of which have zero acceleration skewness. The recommended model can be applied to irregular waves with arbitrary shape as long as the assumption negligible time lag between forcing and sediment transport rate is valid. With respect to irregular waves, the model is much easier to apply than the competing wave-by-wave models. Issues for further model developments are identified through a comprehensive data review.

Selective loss of synaptic proteins in Alzheimer's disease: Evidence for an increased severity with APOE epsilon 4

A pathological feature of Alzheimer's disease (AD) is an area-specific neuronal loss that may be caused by excitotoxicity-related synaptic dysfunction. Relative expression levels of synaptopbysin, dynamin I, complexins I and II, N-cadherin, and alpha CaMKII were analysed in human brain tissue from AD cases and controls in hippocampus, and inferior temporal and occipital cortices. Synaptophysin and dynamin I are presynaptic terminal proteins not specific to any neurotransmitter system whereas complexin II, N-cadherin, and alpha CaMKII are specific for excitatory synapses. Complexin I is a presynaptic protein localised to inhibitory synapses. There were no significant differences in synaptophysin, dynamin I, N-cadherin, or alpha CaMKII protein levels between AD cases and controls. The complexin proteins were both markedly lower in AD cases than in controls (P < 0.01). Cases were also categorised by APOE genotype. Averaged across areas there was a 36% lowering of presynaptic proteins in AD cases carrying at least one epsilon 4 allele compared with in AD cases lacking the epsilon 4 allele. We infer that synaptic protein level is not indicative of neuronal loss, but the synaptic dysfunction may result from the marked relative loss of the complexins in AD, and lower levels of presynaptic proteins in AD cases with the APOE epsilon 4 allele. (c) 2006 Elsevier Ltd. All rights reserved.

Implantation of a scaffold following bulbectomy induces laminar organization of regenerating olfactory axons

Primary olfactory axons expressing different odorant receptors are interspersed within the olfactory nerve. However, upon reaching the outer nerve fiber layer of the olfactory bulb they defasciculate, sort out, and refasciculate prior to targeting glomeruli in fixed topographic positions. While odorant receptors are crucial for the final targeting of axons to glomeruli, it is unclear what directs the formation of the nerve fiber and glomerular layers of the olfactory bulb. While the olfactory bulb itself may provide instructive cues for the development of these layers, it is also possible that the incoming axons may simply require the presence of a physical scaffold to establish the outer laminar cytoarchitecture. In order to begin to understand the underlying role of the olfactory bulb in development of the outer layers of the olfactory bulb, we physically ablated the olfactory bulbs in OMP-IRES-LacZ and P2-IRES-tau-LacZ neonatal mice and replaced them with artificial biological scaffolds molded into the shape of an olfactory bulb. Regenerating axons projected around the edge of the cranial cavity at the periphery of the artificial scaffold and were able to form an olfactory nerve fiber layer and, to some extent, a glomerular layer. Our results reveal that olfactory axons are able to form rudimentary cytoarchitectonic layers if they are provided with an appropriately shaped biological scaffold. Thus, the olfactory bulb does not appear to provide any tropic substance that either attracts regenerating olfactory axons into the cranial cavity or induces these axons to form a plexus around its outer surface. (c) 2006 Elsevier B.V. All rights reserved.

EAAT2 splice variants in Alzheimer disease

Regional atrophy caused by neuronal loss is a characteristic of Alzheimer Disease (AD). Excitatory amino acid transporter-2 (EAAT2) is the major carrier responsible for clearing glutamate from the synaptic cleft in mammalian CNS. A localized attenuation of glutamate transport via reduced expression of functional forms of EAAT2 might contribute to regional excitotoxicity. The EAAT2 gene spans over 100 kb and encodes a 12-kb message. Several groups have identified alternative splice variants of EAAT2 in human brain tissue. These variants can affect transport by altering wild-type EAAT2 protein expression, localization, or transport efficiency. Alternative EAAT2 mRNA transcripts reportedly elicit a dominant-negative effect on glutamate uptake in cell culture. A 50% reduction in the expression in AD cortex of the truncated EAAT2 C-terminal isoform, EAAT2b, has been reported. We obtained cerebral cortex tissue, under informed written consent from the next of kin, from pathologically confirmed control, AD, and non-AD dementia cases. We aimed to determine the distribution and expression patterns of EAAT2 subtypes in susceptible and spared brain regions. We detected five alternate transcripts of EAAT2, two of which had not previously been reported. The relative contributions of novel variants, wild-type EAAT2, and previously discovered splice variants was investigated using Real-time PCR in AD, non-AD dementia, and age-matched control cortex. Our aim is to survey the relationship between these expression patterns and those of markers such as tau, GFAP, and b-amyloid, and to assess the correlation between variant-transporter expression and the level of cell loss.