In-situ spectroscopic investigation of ultrasonic assisted unfolding and aggregation of insulin

It is well-known that fibrillogenesis of proteins can be influenced by diverse external parameters, such as temperature, pressure, agitation or chemical agents. The present preliminary study suggests that ultrasonic excitation at moderate intensities has a significant influence on the unfolding and aggregation behaviour of insulin. Irradiation with an average sound intensity of even as low as 70 mW/cm² leads to a lowering of the unfolding and aggregation temperature up to 7 K. The effect could be explained by an increase of the aggregation kinetics due to ultrasonically induced acoustic micro-streaming in the insulin solution that most probably enhances the aggregation rate. The clear and remarkable effect at relatively low sound intensities offers interesting options for further applications of ultrasound in biophysics and biochemistry. On the other hand, a process that causes a change of kinetics equivalent to 7 K also gives a warning signal concerning the safety of those medical ultrasonic devices that work in this intensity range.     

Tree mineral nutrition is deteriorating in Europe

The response of forest ecosystems to increased atmospheric CO₂ is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂ emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.     

Drivers of temporal changes in temperate forest plant diversity vary across spatial scales

Global biodiversity is affected by numerous environmental drivers. Yet, the extent to which global environmental changes contribute to changes in local diversity is poorly understood. We investigated biodiversity changes in a meta‐analysis of 39 resurvey studies in European temperate forests (3988 vegetation records in total, 17–75 years between the two surveys) by assessing the importance of (i) coarse‐resolution (i.e., among sites) vs. fine‐resolution (i.e., within sites) environmental differences and (ii) changing environmental conditions between surveys. Our results clarify the mechanisms underlying the direction and magnitude of local‐scale biodiversity changes. While not detecting any net local diversity loss, we observed considerable among‐site variation, partly explained by temporal changes in light availability (a local driver) and density of large herbivores (a regional driver). Furthermore, strong evidence was found that presurvey levels of nitrogen deposition determined subsequent diversity changes. We conclude that models forecasting future biodiversity changes should consider coarse‐resolution environmental changes, account for differences in baseline environmental conditions and for local changes in fine‐resolution environmental conditions.     

Former land use affects the nitrogen and phosphorus concentrations and biomass of forest herbs

The colonization rates of understorey plants into forests growing on former agricultural land differ remarkably among species. Different dispersal and recruitment largely account for the contrasting colonization rates, but different effects of the soil legacies of former agricultural land use on plant performance may also play a role. Seven herbaceous forest species were sampled in paired post-agricultural and ancient forest stands to study whether land-use history has an effect on the aboveground nutrient concentrations (N, P and N:P ratios) and biomass of forest herbs and, if so, whether slow and fast colonizing species respond differently. Results showed that P concentrations were significantly affected by former land use with higher concentrations in the post-agricultural stands. N concentrations were unaffected and N:P ratios were significantly higher in the ancient stands. Nutrient concentrations varied considerably among species, but the variation was unrelated to their colonization capacity. Six out of the seven species had higher biomass in the post-agricultural stands relative to the ancient stands, and the degree to which the species increased biomass was positively related to their colonization capacity, i.e., the fast colonizing species showed the strongest increase. Such differential responses to past land use may contribute to the contrasting colonization capacity of forest plants. Land-use history thus affected both the nutrient concentrations and biomass of forest herbs, and only the biomass response was related to colonization capacity.     

Cytoplasmic localization of PML particles in laminopathies

There is growing evidence that laminopathies, diseases associated with mutations in the LMNA gene, are caused by a combination of mechanical and gene regulatory distortions. Strikingly, there is a large variability in disease symptoms between individual patients carrying an identical LMNA mutation. This is why classical genetic screens for mutations appear to have limited predictive value for disease development. Recently, the widespread occurrence of repetitive nuclear ruptures has been described in fibroblast cultures from various laminopathy patients. Since this phenomenon was strongly correlated with disease severity, the identification of biomarkers that report on these rupture events could have diagnostic relevance. One such candidate marker is the PML nuclear body, a structure that is normally confined to the nuclear interior, but leaks out of the nucleus upon nuclear rupture. Here, we show that a variety of laminopathies shows the presence of these cytoplasmic PML particles (PML CPs), and that the amount of these protein aggregates increases with severity of the disease. In addition, between clinically healthy individuals, carrying LMNA mutations, significant differences can be found. Therefore, we postulate that detection of PML CPs in patient fibroblasts could become a valuable marker for diagnosis of disease development.     

Procyanidins can interact with Caco-2 cell membrane lipid rafts: Involvement of cholesterol

Large procyanidins (more than three subunits) are not absorbed at the gastrointestinal tract but could exert local effects through their interactions with membranes. We previously showed that hexameric procyanidins (Hex), although not entering cells, interact with membranes modulating cell signaling and fate. This paper investigated if Hex, as an example of large procyanidins, can selectively interact with lipid rafts which could in part explain its biological actions. This mechanism was studied in both synthetic membranes (liposomes) and Caco-2 cells. Hex promoted Caco-2 cell membrane rigidification and dehydration, effects that were abolished upon cholesterol depletion with methyl-β-cyclodextrin (MCD). Hex prevented lipid raft structure disruption induced by cholesterol depletion/redistribution by MCD or sodium deoxycholate. Supporting the involvement of cholesterol–Hex bonding in Hex interaction with lipid rafts, the absence of cholesterol markedly decreased the capacity of Hex to prevent deoxycholate- and Triton X-100-mediated disruption of lipid raft-like liposomes. Stressing the functional relevance of this interaction, Hex mitigated lipid raft-associated activation of the extracellular signal-regulated kinases (ERK) 1/2. Results support the capacity of a large procyanidin (Hex) to interact with membrane lipid rafts mainly through Hex–cholesterol bondings. Procyanidin–lipid raft interactions can in part explain the capacity of large procyanidins to modulate cell physiology.     

In vitro Interactions of Thallium with Components of the Glutathione-dependent Antioxidant Defence System

We investigated the hypothesis that thallium (Tl) interactions with the glutathione-dependent antioxidant defence system could contribute to the oxidative stress associated with Tl toxicity. Working in vitro with reduced glutathione (GSH), glutathione reductase (GR) or glutathione peroxidase (GPx) in solution, we studied the effects of Tl⁺ and Tl³⁺ (1-25 μM) on: (a) the amount of free GSH, investigating whether the metal binds to GSH and/or oxidizes it; (b) the activity of the enzyme GR, that catalyzes GSH regeneration; and (c) the enzyme GPx, that reduces hydroperoxide at expense of GSH oxidation. We found that, while Tl⁺ had no effect on GSH concentration, Tl³⁺ oxidized it. Both cations inhibited the reduction of GSSG by GR and the diaphorase activity of this enzyme. In addition, Tl³⁺per se oxidized NADPH, the cofactor of GR. The effects of Tl on GPx activity depended on the metal charge: Tl⁺ inhibited GPx when cumene hydroperoxide (CuOOH) was the substrate, while Tl³⁺-mediated GPx inhibition occurred with both substrates. The present results show that Tl interacts with all the components of GSH/GSSG antioxidant defence system. Alterations of this protective pathway could be partially responsible for the oxidative stress associated with Tl toxicity.     

Increased mechanosensitivity and nuclear stiffness in Hutchinson-Gilford progeria cells: effects of farnesyltransferase inhibitors

Hutchinson-Gilford progeria syndrome (HGPS), reportedly a model for normal aging, is a genetic disorder in children marked by dramatic signs suggestive for premature aging. It is usually caused by de novo mutations in the nuclear envelope protein lamin A. Lamins are essential to maintaining nuclear integrity, and loss of lamin A/C results in increased cellular sensitivity to mechanical strain and defective mechanotransduction signaling. Since increased mechanical sensitivity in vascular cells could contribute to loss of smooth muscle cells and the development of arteriosclerosis--the leading cause of death in HGPS patients--we investigated the effect of mechanical stress on cells from HGPS patients. We found that skin fibroblasts from HGPS patients developed progressively stiffer nuclei with increasing passage number. Importantly, fibroblasts from HGPS patients had decreased viability and increased apoptosis under repetitive mechanical strain, as well as attenuated wound healing, and these defects preceded changes in nuclear stiffness. Treating fibroblasts with farnesyltransferase inhibitors restored nuclear stiffness in HGPS cells and accelerated the wound healing response in HGPS and healthy control cells by increasing the directional persistence of migrating cells. However, farnesyltransferase inhibitors did not improve cellular sensitivity to mechanical strain. These data suggest that increased mechanical sensitivity in HGPS cells is unrelated to changes in nuclear stiffness and that increased biomechanical sensitivity could provide a potential mechanism for the progressive loss of vascular smooth muscle cells under physiological strain in HGPS patients.     

Living on a surface: swarming and biofilm formation

Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colonization of a nutrient-rich environment and host tissues. This complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria into swarmer cells. Here, we provide a review of recent advances in the study of the regulatory pathways that lead to swarming behavior of different model bacteria. It has now become clear that many of these pathways also affect the formation of biofilms, surface-attached bacterial colonies. Decision-making between rapidly colonizing a surface and biofilm formation is central to bacterial survival among competitors. In the second part of this article, we review recent developments in the understanding of the transition between motile and sessile lifestyles of bacteria.