Cellular sterol trafficking and metabolism: spotlight on structure

Cholesterol is the main but not the only sterol in cell membranes of higher eukaryotes. Currently, there is an increasing interest toward structurally different sterols, because their membrane partitioning, trafficking, and metabolic properties may differ considerably from those of cholesterol. There is also growing information on specific sterol-protein interactions and their functional consequences, as exemplified by NPC proteins and select ABC-transporters. Several aspects of sterol trafficking and homeostasis are conserved between eukaryotes, and novel, unanticipated findings in this area have recently been made, particularly from genetic screens in yeast. This includes a novel, reversible modification of the sterol structure that affects the choice of transport route.     

Effects of habitat quality and landscape structure on saproxylic species dwelling in boreal spruce-swamp forests

Intensive forest management has caused loss and fragmentation of old‐growth forests and reduced the amount of dead wood throughout northwest Europe. Changes in habitat availability are reflected in occurrence patterns of habitat‐specialist species only after a certain time lag. Here we analyse the responses of wood‐decomposing fungi and saproxylic beetles inhabiting patches of spruce‐swamp forest to habitat quality, loss and isolation at three different spatial scales in eastern Finland and adjacent Russian Karelia, where forestry has been very marginal until recently. Both rare specialist species and common generalist species were included in the study to reveal whether their occurrence patterns differ. Variables describing habitat quality (density and continuity of host trees, patch area) turned out significant in explaining species' incidences (proportion of occupied host trees) in only a few cases, probably because of the relatively high quality of all study patches. Despite this fact, and consistent with our hypothesis, incidences of all the eight specialist species were higher in Russia than Finland, and the difference was significant in the two most strict habitat specialists, Pytho kolwensis and Phlebia centrifuga. In contrast, incidences of three out of four generalist species were higher in Finland than in Russia, and the difference was significant in Rhagium inquisitor. In a subset of 21 patches in Finland, we used a metapopulation model to predict the probability of each patch to be currently occupied by a species given the known spatiotemporal distribution of suitable forest stands during the last 50 years. The degree of isolation alone explained significantly the incidences of five species. However, including habitat variables into the models altered some of the effects. Moreover, inconsistent with our hypothesis, isolation appeared to also negatively affect some very common generalist species. Inclusion of these species in the study disclosed that apparently significant effects of spatiotemporal isolation should be interpreted cautiously.     

Species‐specific limitation of vole population growth by least weasel predation: facilitation of coexistence?

Interspecific competition is usually understood as different species competing directly with each other for limited resources. However, predators can alter such competitive interactions substantially. Predation can promote the coexistence of species in a situation where it would otherwise be impossible, for example if a tradeoff between the competitive abilities and predation resistance of the prey species exists. The field vole Microtus agrestis and the sibling vole M. rossiaemeridionalis are sympatric grassland species, which compete for the same resources. At the population level sibling voles are suggested to be superior competitors to field voles, yet more vulnerable to predation. We tested the effects of predation on the two species in 0.5 ha outdoor enclosures by exposing vole populations to radio-collared freely-hunting least weasels Mustela nivalis nivalis for three weeks. Lethal and non-lethal impacts of predation limited population densities of both species during and after the experimental period, but the effect was more pronounced in sibling voles in which population densities decreased markedly during the treatment period and even after that. Field vole population densities remained stable under weasel predation, while densities increased in controls. Survival in both species was lower in treatment populations compared to controls, but the effect tended to be more pronounced in sibling voles and in females of both species. The average mass of adults in both species declined in the treatment populations. These results suggest that predation by least weasels can limit vole populations locally, even during favourable summer conditions, and have extended negative effects on the dynamics of vole populations. In addition, predation alleviated interspecific competition between the vole species and is, therefore, a potential factor enabling the coexistence of them.     

Use of BODIPY‐Cholesterol (TF‐Chol) for Visualizing Lysosomal Cholesterol Accumulation

Dipyrromethene difluoride‐cholesterol (TopFluor‐Cholesterol, TF‐Chol) is a widely used cholesterol analogue due to its excellent fluorescence properties and considerable similarity with natural cholesterol in terms of membrane partitioning. However, the suitability of TF‐Chol for detecting lysosomal cholesterol deposition has recently been questioned. Here, we highlight the fact that the method of lipid delivery and the analysis of time‐point both affect the membrane distribution and labeling pattern of TF‐Chol, similarly as with radiolabeled cholesterol. Lysosomal sterol accumulation characteristic to a lysosomal storage disease is most readily detected when the probe is introduced via the physiological route, i.e. as a sterol fatty acid ester in low‐density lipoprotein particles. When administered to cells from solvent, lysosomal sterol sequestration becomes evident after an overnight equilibration between membranes.      

Are nociceptin(1‐13)NH2 and its structural analogue [ORN9]nociceptin(1‐13)NH2 able to affect brain antioxidant status in control and kainic acid‐treated rats?

In‐vivo effects of nociceptin (N/OFQ(1‐13)NH₂) on the levels of lipid peroxidation and cell enzyme (superoxide dismutase, glutathione peroxidase and glutathione reductase) and non‐enzyme (glutathione) antioxidants in brain of control and kainic acid‐treated rats were studied. N/OFQ(1‐13)NH₂ effects were compared with those of its structural analogue [Orn⁹]N/OFQ(1‐13)NH₂. Kainic acid (25 µg, i.c.v) increased the lipid peroxidation (4 and 24 h after kainic acid treatment) and decreased the glutathione level (1 h after kainic acid injection). We failed to find, any changes in antioxidant enzyme activities, independently of the time of kainic acid treatment. At the background of kainic acid‐effects, N/OFQ(1‐13)NH₂ and [Orn⁹] N/OFQ(1‐13)NH₂, injected 30 min before kainic acid, had no effects on all parameters, tested in brain. In addition, the neuropeptides did not change the antioxidant status in brain of control animals. It might be concluded that N/OFQ(1‐13)NH₂ and [Orn⁹]N/OFQ(1‐13)NH₂ have neither pro‐ nor anti‐oxidant activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Neural and mechanical responses of the triceps surae muscle group after 1 h of repeated fast passive stretches.

Experiments were carried out to examine interaction between mechanical changes of the muscle-tendon unit and reduced reflex sensitivity after repeated and prolonged passive muscle stretching (RPS). There is some evidence that this interaction might be relevant also during active stretch-shortening cycle type of fatigue tasks. The results demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions after RPS. Maximal voluntary contraction (MVC), average electromyographic activities of the gastrocnemius and soleus muscles, and maximal twitch contraction decreased on average by 13.8, 10.4, 7.6, and 16.8%, respectively. In addition, there was a 14% lengthening in the total duration of the twitch. MVCs measured at different ankle joint angles revealed a downward and rightward shift in the torque-fascicle length curve after RPS. Interestingly, there was a crossing in the torque-fascicle length curves while measured at different activation levels but at the same joint angle before and after RPS. Even though no changes were observed in the activation level during MVCs, all the reflex parameters showed a clear reduction after RPS. This study presents evidence that repeated and prolonged passive muscle stretching can lead to some modification of material behavior of the aponeurosis-tendon system, such as stress relaxation and/or plastic deformation. In addition, altered material properties seem to affect proprioceptive feedback and, therefore, the motor unit activation in proportion to the contractile failure.