Regulation of arginase I activity and expression by both PD-1 and CTLA-4 on the myeloid-derived suppressor cells

An elevated number of Gr-1⁺CD11b⁺ myeloid-derived suppression cells (MDSCs) has been described in mice and human bearing tumor and associated with immune suppression. Arginase I production by MDSCs in the tumor environment may be a central mechanism for immunosuppression and tumor evasion. In this study and before, we found that Gr-1⁺CD11b⁺ MDSCs from ascites and spleen of mice bearing ovarian 18D carcinoma express a high level of PD-1, CTLA-4, B7-H1 and CD80 while other co-stimulatory molecules, namely CD40, B7-DC and CD86 are not detected. Further studies showed that PD-1 and CTLA-4 on the Gr-1⁺CD11b⁺ MDSCs regulated the activity and expression of arginase I. The blockage and silencing of PD-1, CTLA-4 or both PD-1 and CTLA4 molecules could significantly reduce arginase I activity and expression induced with tumor-associated factor. Similar results were also observed while their ligands B7-H1 and/or CD80 were blocked or silenced. Furthermore, CD80 deficiency also decreased the arginase I expression and activity. Antibody blockade or silencing of PD-1, CTLA-4 or both reduced the suppressive potential of PD-1+CTLA-4+MDSCs. Blockade of PD-1, CTLA-4 or both also slowed tumor growth and improved the survival rate of tumor-bearing mice. Thus, there may exist a coinhibitory and costimulatory molecules-based immuno-regulating wet among MDSCs. This research was supported by Nankai University grant, NSFC grant “30771967”, “985” grant,The Ministry of Science and Technology grant “2006AA020502”“06C26211200695”, Tianjin Grant “07JCZDJC03300” and “06ZHCXSH04800”.     

Biosynthesis and biotechnological production of serotonin derivatives

Serotonin derivatives belong to a class of phenylpropanoid amides found at low levels in a wide range of plant species. Representative serotonin derivatives include feruloylserotonin (FS) and 4-coumaroylserotonin (CS). Since the first identification of serotonin derivatives in safflower seeds, their occurrence, biological significance, and pharmacological properties have been reported. Recently, serotonin N-hydroxycinnamoyl transferase (SHT), which is responsible for the synthesis of serotonin derivatives, was cloned from pepper (Capsicum annuum) and characterized in terms of its enzyme kinetics. Using the SHT gene, many attempts have been made to either increase the level of serotonin derivatives in transgenic plants or produce serotonin derivatives de novo in microbes by dual expression of key genes such as SHT and 4-coumarate-CoA ligase (4CL). Due to the strong antioxidant activity and other therapeutic properties of serotonin derivatives, these compounds may have high potential in treatment and prophylaxis, as cosmetic ingredients, and as major components of functional foods or feeds that have health-improving effects. This review examines the biosynthesis of serotonin derivatives, corresponding enzymes, heterologous production in plants or microbes, and their applications.     

Mycorrhizal synthesis of four ectomycorrhizal fungi in potted <Emphasis Type="Italic">Populus maximowiczii</Emphasis> seedlings

Ectomycorrhizal (ECM) syntheses between four ECM fungi, Laccaria amethystina, Hebeloma mesophaeum, Thelephora terrestris, and Tomentella sp., and Populus maximowiczii seedlings that are known to form ECM at a denuded area of Mt. Usu were performed in volcanic debris in a controlled growth chamber. The percentage of ECM colonization and seedling growth were determined 3 months after inoculation. Seedlings were successfully colonized by the inoculated ECM fungi with low contamination ratios. Seedling height and biomass were larger in the inoculated seedlings than in the control, although the effects of inoculation on seedling growth varied with the ECM fungus.     

Model for fluorescence quenching in light harvesting complex II in different aggregation states

Low-temperature (77 K) steady-state fluorescence emission spectroscopy and dynamic light scattering were applied to the main chlorophyll a/b protein light harvesting complex of photosystem II (LHC II) in different aggregation states to elucidate the mechanism of fluorescence quenching within LHC II oligomers. Evidences presented that LHC II oligomers are heterogeneous and consist of large and small particles with different fluorescence yield. At intermediate detergent concentrations the mean size of the small particles is similar to that of trimers, while the size of large particles is comparable to that of aggregated trimers without added detergent. It is suggested that in small particles and trimers the emitter is monomeric chlorophyll, whereas in large aggregates there is also another emitter, which is a poorly fluorescing chlorophyll associate. A model, describing populations of antenna chlorophyll molecules in small and large aggregates in their ground and first singlet excited states, is considered. The model enables us to obtain the ratio of the singlet excited-state lifetimes in small and large particles, the relative amount of chlorophyll molecules in large particles, and the amount of quenchers as a function of the degree of aggregation. These dependencies reveal that the quenching of the chl a fluorescence upon aggregation is due to the formation of large aggregates and the increasing of the amount of chlorophyll molecules forming these aggregates. As a consequence, the amount of quenchers, located in large aggregates, is increased, and their singlet excited-state lifetimes steeply decrease.     

Structural and functional regeneration after spinal cord injury in the weakly electric teleost fish, <Emphasis Type="Italic">Apteronotus</Emphasis><Emphasis Type="Italic">leptorhynchus</Emphasis>

In contrast to mammals, teleost fish exhibit an enormous potential to regenerate adult spinal cord tissue after injury. However, the mechanisms mediating this ability are largely unknown. Here, we analyzed the major processes underlying structural and functional regeneration after amputation of the caudal portion of the spinal cord in Apteronotus leptorhynchus, a weakly electric teleost. After a transient wave of apoptotic cell death, cell proliferation started to increase 5 days after the lesion and persisted at high levels for at least 50 days. New cells differentiated into neurons, glia, and ependymal cells. Retrograde tract tracing revealed axonal re-growth and innervation of the regenerate. Functional regeneration was demonstrated by recovery of the amplitude of the electric organ discharge, a behavior generated by spinal motoneurons. Computer simulations indicated that the observed rates of apoptotic cell death and cell proliferation can adequately explain the re-growth of the spinal cord. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Resource-dependent reproductive adjustment and the stability of consumer-resource dynamics

This study explored a consumer-resource model including reproductive and nonreproductive subpopulations of the consumer to consider whether resource-dependent reproductive adjustment by the consumer would stabilize consumer-resource dynamics. The model assumed that decreasing (increasing) resource availability caused reproductive suppression (facilitation), and that the reproductive consumer had a higher mortality rate than the nonreproductive one (i.e., a trade-off between reproduction and survival). The model predicted that the variability would be reduced when the consumer had a strong tendency to suppress reproduction in response to low resource availability or when the cost of reproduction was high, although consumer extinction became more likely. Furthermore, when the consumer-resource dynamics converged to limit cycles, reproductive adjustment enhanced the long-term average of the consumer density. It was also predicted that if reproductive suppression enhanced resource consumption efficiency (i.e., a trade-off between reproduction and foraging), then it would destabilize the system by canceling the stabilizing effect of the reproductive adjustment itself. These results suggest that it is necessary not only to identify the costs of reproduction, but also to quantify the changes in individual-level performances due to reproduction in order to understand the ecological consequences of reproductive adjustment.     

Directed evolution of aniline dioxygenase for enhanced bioremediation of aromatic amines

The objective of this study was to enhance the activity of aniline dioxygenase (AtdA), a multi-component Rieske non-heme iron dioxygenase enzyme isolated from Acinetobacter sp. strain YAA, so as to create an enhanced biocatalyst for the bioremediation of aromatic amines. Previously, the mutation V205A was found to widen the substrate specificity of AtdA to accept 2-isopropylaniline (2IPA) for which the wild-type enzyme has no activity (Ang EL, Obbard JP, Zhao HM, FEBS J, 274:928–939, 2007). Using mutant V205A as the parent and applying one round of saturation mutagenesis followed by a round of random mutagenesis, the activity of the final mutant, 3-R21, was increased by 8.9-, 98.0-, and 2.0-fold for aniline, 2,4-dimethylaniline (24DMA), and 2-isopropylaniline (2IPA), respectively, over the mutant V205A. In particular, the activity of the mutant 3-R21 for 24DMA, which is a carcinogenic aromatic amine pollutant, was increased by 3.5-fold over the wild-type AtdA, while the AN activity was restored to the wild-type level, thus yielding a mutant aniline dioxygenase with enhanced activity and capable of hydroxylating a wider range of aromatic amines than the wild type. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of light on ascorbate formation and metabolism in apple fruits

To further understand the regulatory mechanism of light on the formation of ascorbic acid (AsA) in the sink organs of plants, a systematical investigation on AsA levels, activities of two key biosynthsis enzymes and their mRNA expression as well as the recycling was performed in the fruits of apple (Malus domestica Borkh), under different levels of shade. After the whole trees were shaded with the sun-light about 50–55% for 20 days, AsA levels were significantly decreased in fruit peel, flesh and leaves, while mRNA expression levels and activities of l-galactose dehydrogenase (l-GalDH, EC 1.1.1.117) and l-galactono-1,4-lactone dehydrogenase (l-GalLDH, EC 1.3.2.3) as well as activities of recycling enzymes was clearly declined in the leaf and peel but not in the flesh. By shading fruits only for 20 days, AsA levels, relative mRNA levels and activities of l-GalDH and l-GalLDH as well as activities of recycling enzymes all showed obvious decrease in the peel, but not in the flesh. However, their levels in the peel were markedly increased after the full shade was removed and re-exposed these fruits on natural light for 5 days. It is concluded that light affects AsA biosynthesis and recycling in the peel and leaf, but did not in the fresh. Results also suggest that apple fruit is potential to biosynthesize AsA via the l-galactose pathway, and AsA content in the fruits may depend partly on levels of AsA or other photochemistry controlled by light in the leaves.     

Evaluation of the toxicity of stress-related aldehydes to photosynthesis in chloroplasts

Aldehydes produced under various environmental stresses can cause cellular injury in plants, but their toxicology in photosynthesis has been scarcely investigated. We here evaluated their effects on photosynthetic reactions in chloroplasts isolated from Spinacia oleracea L. leaves. Aldehydes that are known to stem from lipid peroxides inactivated the CO₂ photoreduction to various extents, while their corresponding alcohols and carboxylic acids did not affect photosynthesis. α,β-Unsaturated aldehydes (2-alkenals) showed greater inactivation than the saturated aliphatic aldehydes. The oxygenated short aldehydes malondialdehyde, methylglyoxal, glycolaldehyde and glyceraldehyde showed only weak toxicity to photosynthesis. Among tested 2-alkenals, 2-propenal (acrolein) was the most toxic, and then followed 4-hydroxy-(E)-2-nonenal and (E)-2-hexenal. While the CO₂-photoreduction was inactivated, envelope intactness and photosynthetic electron transport activity (H₂O → ferredoxin) were only slightly affected. In the acrolein-treated chloroplasts, the Calvin cycle enzymes phosphoribulokinase, glyceraldehyde-3-phosphate dehydrogenase, fructose-1,6-bisphophatase, sedoheptulose-1,7-bisphosphatase, aldolase, and Rubisco were irreversibly inactivated. Acrolein treatment caused a rapid drop of the glutathione pool, prior to the inactivation of photosynthesis. GSH exogenously added to chloroplasts suppressed the acrolein-induced inactivation of photosynthesis, but ascorbic acid did not show such a protective effect. Thus, lipid peroxide-derived 2-alkenals can inhibit photosynthesis by depleting GSH in chloroplasts and then inactivating multiple enzymes in the Calvin cycle.     

Excitable Population Dynamics,Biological Control Failure,and Spatiotemporal Pattern Formation in a Model Ecosystem

Biological control has been attracting an increasing attention over the last two decades as an environmentally friendly alternative to the more traditional chemical-based control. In this paper, we address robustness of the biological control strategy with respect to fluctuations in the controlling species density. Specifically, we consider a pest being kept under control by its predator. The predator response is assumed to be of Holling type III, which makes the system’s kinetics “excitable.” The system is studied by means of mathematical modeling and extensive numerical simulations. We show that the system response to perturbations in the predator density can be completely different in spatial and non-spatial systems. In the nonspatial system, an overcritical perturbation of the population density results in a pest outbreak that will eventually decay with time, which can be regarded as a success of the biological control strategy. However, in the spatial system, a similar perturbation can drive the system into a self-sustained regime of spatiotemporal pattern formation with a high pest density, which is clearly a biological control failure. We then identify the parameter range where the biological control can still be successful and describe the corresponding regime of the system dynamics. Finally, we identify the main scenarios of the system response to the population density perturbations and reveal the corresponding structure of the parameter space of the system. A. Morozov is on leave from Shirshov Institute of Oceanology, Russian Academy of Science, Nakhimovsky Prosp. 36, Moscow 117218, Russia.