Asynchrony among local communities stabilises ecosystem function of metacommunities

Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land management and policy decisions. We used species‐level abundance data from 62 plant communities across five continents to assess mechanisms of temporal stability across spatial scales. We assessed how asynchrony (i.e. different units responding dissimilarly through time) of species and local communities stabilised metacommunity ecosystem function. Asynchrony of species increased stability of local communities, and asynchrony among local communities enhanced metacommunity stability by a wide range of magnitudes (1–315%); this range was positively correlated with the size of the metacommunity. Additionally, asynchronous responses among local communities were linked with species’ populations fluctuating asynchronously across space, perhaps stemming from physical and/or competitive differences among local communities. Accordingly, we suggest spatial heterogeneity should be a major focus for maintaining the stability of ecosystem services at larger spatial scales.     

Regulation of proteasome-mediated protein degradation during oxidative stress and aging

Protein degradation is a physiological process required to maintain cellular functions. There are distinct proteolytic systems for different physiological tasks under changing environmental and pathophysiological conditions. The proteasome is responsible for the removal of oxidatively damaged proteins in the cytosol and nucleus. It has been demonstrated that proteasomal degradation increases due to mild oxidation, whereas at higher oxidant levels proteasomal degradation decreases. Moreover, the proteasome itself is affected by oxidative stress to varying degrees. The ATP-stimulated 26S proteasome is sensitive to oxidative stress, whereas the 20S form seems to be resistant. Non-degradable protein aggregates and cross-linked proteins are able to bind to the proteasome, which makes the degradation of other misfolded and damaged proteins less efficient. Consequently, inhibition of the proteasome has dramatic effects on cellular aging processes and cell viability. It seems likely that during oxidative stress cells are able to keep the nuclear protein pool free of damage, while cytosolic proteins may accumulate. This is because of the high proteasome content in the nucleus, which protects the nucleus from the formation and accumulation of non-degradable proteins. In this review we highlight the regulation of the proteasome during oxidative stress and aging.     

Lack of efficacy of a partial adenosine A1 receptor agonist in neuropathic pain models in mice

Previous studies suggest that adenosine A₁ receptors (A₁R) modulate the processing of pain. The aim of this study was to characterize the distribution of A₁R in nociceptive tissues and to evaluate whether targeting A₁R with the partial agonist capadenoson may reduce neuropathic pain in mice. The cellular distribution of A₁R in dorsal root ganglia (DRG) and the spinal cord was analyzed using fluorescent in situ hybridization. In behavioral experiments, neuropathic pain was induced by spared nerve injury or intraperitoneal injection of paclitaxel, and tactile hypersensitivities were determined using a dynamic plantar aesthesiometer. Whole-cell patch-clamp recordings were performed to assess electrophysiological properties of dissociated DRG neurons. We found A₁R to be expressed in populations of DRG neurons and dorsal horn neurons involved in the processing of pain. However, administration of capadenoson at established in vivo doses (0.03–1.0 mg/kg) did not alter mechanical hypersensitivity in the spared nerve injury and paclitaxel models of neuropathic pain, whereas the standard analgesic pregabalin significantly inhibited the pain behavior. Moreover, capadenoson failed to affect potassium currents in DRG neurons, in contrast to a full A₁R agonist. Despite expression of A₁R in nociceptive neurons, our data do not support the hypothesis that pharmacological intervention with partial A₁R agonists might be a valuable approach for the treatment of neuropathic pain.     

Biodiversity and decomposition in experimental grassland ecosystems

We examined the impact of biodiversity on litter decomposition in an experiment that manipulated plant species richness. Using biomass originating from the experimental species richness gradient and from a species used as a common substrate, we measured rates of decomposition in litterbags in two locations: in situ in the experiment plots and in an adjacent common garden. This allowed us to separate the effects of litter quality and decomposition location on decomposition. We found that plant species richness had a significant, but minor negative effect on the quality (nitrogen concentration) of the biomass. Neither litter type nor location had a consistent effect on the rate of carbon and nitrogen loss over a 1-year period. Thus, the increased productivity and corresponding lower soil available nitrogen levels observed in high diversity plots do not lead to faster litter decomposition or faster nitrogen turnover. This supports the hypothesis that increased productivity corresponding with higher species richness results in increased litter production, higher standing litter pools and a negative feedback on productivity, because of an increased standing nitrogen pool in the litter.     

Lack of effector cell function and altered tetramer binding of tumor-infiltrating lymphocytes

Tumor-specific CD8 T cell responses to MCA102 fibrosarcoma cells expressing the cytotoxic T cell epitope gp33 from lymphocytic choriomeningitis virus were studied. MCA102(gp33) tumors grew progressively in C57BL/6 mice, despite induction of peripheral gp33-tetramer(+) T cells that were capable of mediating antiviral protection, specific cell rejection, and concomitant tumor immunity. MCA102(gp33) tumors were infiltrated with a high number ( approximately 20%) of CD11b(+)CD11c(-) macrophage-phenotype cells that were able to cross-present the gp33 epitope to T cells. Tumor-infiltrating CD8 T cells exhibited a highly activated phenotype but lacked effector cell function. Strikingly, a significant portion of tumor-infiltrating lymphocytes expressed TCRs specific for gp33 but bound MHC tetramers only after cell purification and a 24-h resting period in vitro. The phenomenon of "tetramer-negative T cells" was not restricted to tumor-infiltrating lymphocytes from MCA102(gp33) tumors, but was also observed when Ag-specific T cells derived from an environment with high Ag load were analyzed ex vivo. Thus, using a novel tumor model, allowing us to trace tumor-specific T cells at the single cell level in vivo, we demonstrate that the tumor microenvironment is able to alter the functional activity of T cells infiltrating the tumor mass.     

Increased proteolysis after single-dose exposure with hepatotoxins in HepG2 cells

Chronic ethanol consumption is associated with increased protein oxidation and decreased proteolysis in the liver. We tested the hypothesis that even single-dose treatment with ethanol or bromotrichloromethane causes increased protein oxidation and a distinct proteolytic response in cultured hepatocytes. HepG2 cells were treated for 30 min with ethanol, H(2)O(2) and bromotrichloromethane at various nontoxic concentrations. Protein degradation was measured in living cells using [35S]-methionine labeling. Protein oxidation, and 20S proteasome activity were measured in cell lysates. Oxidized proteins increased immediately after ethanol, H(2)O(2), and bromotrichloromethane exposure, but a further significant increase 24-h after exposure was observed only following ethanol and bromotrichloromethane treatment. All three reagents caused a significant increase of the overall intracellular proteolysis at rather low concentrations, which could be suppressed by the proteasome inhibitor lactacystin. A decline of proteolysis observed at higher-subtoxic-concentrations was not related to decreased proteasome activity. Preincubation with ketoconazole or 4-methylpyrazole completely prevented the ethanol- and bromotrichloromethane-induced but not the H(2)O(2)-induced protein oxidation and proteolysis, suggesting strongly an enzyme-mediated generation of reactive oxygen species. In conclusion single-dose exposure with ethanol or haloalkanes causes increased protein oxidation followed by an increased proteasome-dependent protein degradation in human liver cells.     

Iron oxide particles for molecular magnetic resonance imaging cause transient oxidative stress in rat macrophages

Iron oxide particles are a promising marker in molecular magnetic resonance imaging. They are used to label distinct cell populations either in vitro or in vivo. We investigated for the first time whether small citrate-coated very small superparamagnetic iron oxide particles (VSOPs) can lead to an increase in cellular oxidative stress. We incubated rat macrophages (RAW) in vitro with iron oxide particles. We observed a massive uptake of VSOPs measured both with atomic absorption spectroscopy and with NMR, which could be visualized by confocal laser scanning microscopy. After incubation, cells were lysed and the levels of malonyldialdehyde (MDA) and protein carbonyls were determined. We found a significant increase in both MDA and protein carbonyl levels after incubation with the particles. Surprisingly, 24 h after incubation, a significant indication of oxidative stress could no longer be observed. The increase in oxidative stress seems to be transient and closely linked to the incubation procedure. The iron chelator desferal and the intracellular spin trap PBN caused a significant reduction in oxidative stress to almost control levels. This indicates that the augmentation of oxidative stress is closely linked to the free iron during incubation. Proliferation assays showed that incorporation of VSOPs did not lead to long-term cytotoxic effects even though the iron oxide particles remained in the cell. Magnetic labeling of cells with VSOPs seems to cause transient oxidative conditions not affecting cellular viability and seems to be a usable approach for molecular magnetic resonance imaging.     

Immunodominance of an antiviral cytotoxic T cell response is shaped by the kinetics of viral protein expression

Lymphocytic choriomeningitis virus (LCMV) infection induces a protective CTL response consisting of gp- and nucleoprotein (NP)-specific CTL. We find that a small load of LCMV led to immunodominance of NP-CTL, whereas a large viral load resulted in dominance of gp-CTL. This is the first study describing that immunodominance is not fixed after infection with a given pathogen, but varies with the viral load instead. We assumed higher Ag sensitivity for NP-CTL, which would explain their preferential priming at low viral load, as well as their overstimulation resulting in selective exhaustion at high viral load. The higher Ag sensitivity of NP-CTL was due to faster kinetics of NP-epitope presentation. Thus, we uncover a novel factor that impinges upon immunodominance and is related to the kinetics of virus protein expression. We propose that CTL against early viral proteins swiftly interfere with virus replication, resulting in efficient protection. If these "early" CTL fail in immediate virus control, they are activated in the face of higher viral load compared with "late" CTL and are therefore prone to be exhausted. Thus, the observed absence of early CTL in persistent infections might not be the cause, but rather the consequence of viral persistence.