Structural and functional insights into tRNA binding and adenosine N1-methylation by an archaeal Trm10 homologue.

Purine nucleosides on position 9 of eukaryal and archaeal tRNAs are frequently modified in vivo by the post-transcriptional addition of a methyl group on their N1 atom. The methyltransferase Trm10 is responsible for this modification in both these domains of life. While certain Trm10 orthologues specifically methylate either guanosine or adenosine at position 9 of tRNA, others have a dual specificity. Until now structural information about this enzyme family was only available for the catalytic SPOUT domain of Trm10 proteins that show specificity toward guanosine. Here, we present the first crystal structure of a full length Trm10 orthologue specific for adenosine, revealing next to the catalytic SPOUT domain also N- and C-terminal domains. This structure hence provides crucial insights in the tRNA binding mechanism of this unique monomeric family of SPOUT methyltransferases. Moreover, structural comparison of this adenosine-specific Trm10 orthologue with guanosine-specific Trm10 orthologues suggests that the N1 methylation of adenosine relies on additional catalytic residues.

Membrane associated complexes in calcium dynamics modelling.

Mitochondria not only govern energy production, but are also involved in crucial cellular signalling processes. They are one of the most important organelles determining the Ca(2+) regulatory pathway in the cell. Several mathematical models explaining these mechanisms were constructed, but only few of them describe interplay between calcium concentrations in endoplasmic reticulum (ER), cytoplasm and mitochondria. Experiments measuring calcium concentrations in mitochondria and ER suggested the existence of cytosolic microdomains with locally elevated calcium concentration in the nearest vicinity of the outer mitochondrial membrane. These intermediate physical connections between ER and mitochondria are called MAM (mitochondria-associated ER membrane) complexes. We propose a model with a direct calcium flow from ER to mitochondria, which may be justified by the existence of MAMs, and perform detailed numerical analysis of the effect of this flow on the type and shape of calcium oscillations. The model is partially based on the Marhl et al model. We have numerically found that the stable oscillations exist for a considerable set of parameter values. However, for some parameter sets the oscillations disappear and the trajectories of the model tend to a steady state with very high calcium level in mitochondria. This can be interpreted as an early step in an apoptotic pathway.

Benefits of napping and an extended duration of recovery sleep on alertness and immune cells after acute sleep restriction.

Understanding the interactions between sleep and the immune system may offer insight into why short sleep duration has been linked to negative health outcomes. We, therefore, investigated the effects of napping and extended recovery sleep after sleep restriction on the immune and inflammatory systems and sleepiness. After a baseline night, healthy young men slept for a 2-h night followed by either a standard 8-h recovery night (n=12), a 30-min nap (at 1 p.m.) in addition to an 8-h recovery night (n=10), or a 10-h extended recovery night (n=9). A control group slept 3 consecutive 8-h nights (n=9). Subjects underwent continuous electroencephalogram polysomnography and blood was sampled every day at 7 a.m. Leukocytes, inflammatory and atherogenesis biomarkers (high-sensitivity C-reactive protein, interleukin-8, myeloperoxidase, fibrinogen and apolipoproteins ApoB/ApoA), sleep patterns and sleepiness were investigated. All parameters remained unchanged in the control group. After sleep restriction, leukocyte and - among leukocyte subsets - neutrophil counts were increased, an effect that persisted after the 8-h recovery sleep, but, in subjects who had a nap or a 10-h recovery sleep, these values returned nearly to baseline. Inflammatory and atherogenesis biomarkers were unchanged except for higher myeloperoxidase levels after sleep restriction. The increased sleepiness after sleep restriction was reversed better in the nap and extended sleep recovery conditions. Saliva cortisol decreased immediately after the nap. Our results indicate that additional recovery sleep after sleep restriction provided by a midday nap prior to recovery sleep or a sleep extended night can improve alertness and return leukocyte counts to baseline values.

Organic solvents and the dopaminergic system.

Organic solvents pose a considerable health risk for humans. It is due to their ability to cross biological barriers and indisputable toxicity on the one hand, and the wealth of applications and large production and consumption volumes on the other. The primary target of the toxic action of organic solvents is the nervous system. In this paper, some literature data showing that dopaminergic neurons and their projections are particularly susceptible to the toxic solvent action are presented.

Temporal dissociation between myeloperoxidase (MPO)-modified LDL and MPO elevations during chronic sleep restriction and recovery in healthy young men.

OBJECTIVES: Many studies have evaluated the ways in which sleep disturbances may influence inflammation and the possible links of this effect to cardiovascular risk. Our objective was to investigate the effects of chronic sleep restriction and recovery on several blood cardiovascular biomarkers. METHODS AND RESULTS: Nine healthy male non-smokers, aged 22-29 years, were admitted to the Sleep Laboratory for 11 days and nights under continuous electroencephalogram polysomnography. The study consisted of three baseline nights of 8 hours sleep (from 11 pm to 7 am), five sleep-restricted nights, during which sleep was allowed only between 1 am and 6 am, and three recovery nights of 8 hours sleep (11 pm to 7 am). Myeloperoxidase-modified low-density lipoprotein levels increased during the sleep-restricted period indicating an oxidative stress. A significant increase in the quantity of slow-wave sleep was measured during the first recovery night. After this first recovery night, insulin-like growth factor-1 levels increased and myeloperoxidase concentration peaked. CONCLUSIONS: We observed for the first time that sleep restriction and the recovery process are associated with differential changes in blood biomarkers of cardiovascular disease.

Neuropeptide Y and sleep.

Neuropeptide Y (NPY), a 36-amino-acid peptide from the pancreatic polypeptide family, is one of the more abundant peptides in the central nervous system. It acts as a neurohormone and as a neuromodulator. NPY is widely distributed in the brain, particularly the hypothalamus, the amygdala, the locus coeruleus and the cerebral cortex. At least six NPY receptors subtypes have been identified. NPY is involved in the regulation of several physiological functions such as food intake, hormonal release, circadian rhythms, cardiovascular disease, thermoregulation, stress response, anxiety and sleep. Sleep promoting effects of NPY as well as wakefulness effects of NPY were found in animals, depending on the site of injection as well as on the functional state of the structure. In humans, NPY was found to have hypnotic properties, possibly acting as a physiological antagonist of corticotropin-releasing hormone (CRH). In conclusion, NPY participates in sleep regulation in humans, particularly in the timing of sleep onset and may as such play a role in the integration of sleep regulation, food intake and metabolism.

Sleep restriction increases white blood cells, mainly neutrophil count, in young healthy men: a pilot study.

OBJECTIVES: This study examines the effects of sleep restricted to four hours for three consecutive nights on blood parameters, known to be associated with cardiovascular risk, in young healthy men. MATERIAL AND METHODS: Eight young healthy men (age 24.5 +/- 3.3 years) were studied in the sleep restricted group. Nine young healthy men (age 24 +/- 2 years) were included in the control group and spent the days and nights in the sleep lab, while sleeping eight hours/night. One baseline night was followed by three nights of sleep restriction to four hours and by one recovery night of eight hours. Blood samplings were performed after the baseline night and after the third night of sleep restriction or without restriction for the control group. RESULTS: A significant increase in white blood cells (WBC) (5.79 +/- 1.05 vs. 6.89 +/- 1.31 10(3) cell/microl, p = 0.03), and neutrophils (3.17 +/- 0.69 vs 4.24 +/- 0.97 10(3) cell/microl, p = 0.01) was observed after the third night of sleep restriction. Other blood parameters were not affected. No significant variation was observed in the control group. CONCLUSION: Sleep restriction affected WBC count, mainly neutrophils, considered as risk factor for cardiovascular disease. Stress induced by the short term sleep restriction could be involved in this observation.