Structural characteristics and chemical composition of birch (Betula pendula) leaves are modified by increasing CO2 and ozone

Impacts of ozone and CO₂ enrichment, alone and in combination, on leaf anatomical and ultrastructural characteristics, nutrient status and cell wall chemistry in two European silver birch (Betula pendula Roth) clones were studied. The young soil‐growing trees were exposed in open‐top chambers over three growing seasons to 2 × ambient CO₂ and/or ozone concentrations in central Finland. The trees were measured for changes in altogether 35 variables of leaf structure, nutrients and cell wall chemistry of green leaves, and 20 of the measured variables were affected by CO₂ and/or O₃. Elevated CO₂ increased the size of chloroplasts and starch grains, number of mitochondria, P : N ratio, and contents of cell wall hemicellulose. Elevated CO₂ decreased the total leaf thickness, specific leaf area, concentrations of N, K, Cu, S and Fe, and contents of cell wall α‐cellulose, uronic acids, acid‐soluble lignin and acetone‐soluble extractives. Elevated ozone led to thinner leaves, higher palisade to spongy ratio, increased number of peroxisomes and mitochondria, reduced content of Mn, Zn, Cu, hemicellulose and uronic acids, and lower Mn : N and Zn : N ratios. In the combined exposure, interactions were antagonistic. Ultrastructural changes became more evident towards the end of the exposure. Young leaves were tolerant against ozone‐caused oxidative stress, whereas oxidative H₂O₂ accumulation was found in older leaves. CO₂ enrichment improved ozone tolerance not only through increased photosynthesis rates, but also through changes in cell wall chemistry (hemicellulose, in particular). However, nutrient imbalances due to ozone and/or CO₂ may predispose the trees to other biotic and abiotic stresses. Down‐regulation and up‐regulation of photosynthesis under elevated CO₂ through anatomical changes is discussed.     

WW-domain-containing oxidoreductase is associated with low plasma HDL-C levels

Low serum HDL-cholesterol (HDL-C) is a major risk factor for coronary artery disease. We performed targeted genotyping of a 12.4 Mb linked region on 16q to test for association with low HDL-C by using a regional-tag SNP strategy. We identified one SNP, rs2548861, in the WW-domain-containing oxidoreductase (WWOX) gene with region-wide significance for low HDL-C in dyslipidemic families of Mexican and European descent and in low-HDL-C cases and controls of European descent (p = 6.9 × 10⁻⁷). We extended our investigation to the population level by using two independent unascertained population-based Finnish cohorts, the cross-sectional METSIM cohort of 4,463 males and the prospective Young Finns cohort of 2,265 subjects. The combined analysis provided p = 4 × 10⁻⁴ to 2 × 10⁻⁵. Importantly, in the prospective cohort, we observed a significant longitudinal association of rs2548861 with HDL-C levels obtained at four different time points over 21 years (p = 0.003), and the T risk allele explained 1.5% of the variance in HDL-C levels. The rs2548861 resides in a highly conserved region in intron 8 of WWOX. Results from our in vitro reporter assay and electrophoretic mobility-shift assay demonstrate that this region functions as a cis-regulatory element whose associated rs2548861 SNP has a specific allelic effect and that the region forms an allele-specific DNA-nuclear-factor complex. In conclusion, analyses of 9,798 subjects show significant association between HDL-C and a WWOX variant with an allele-specific cis-regulatory function.     

New evidence for cofactor's amino group function in thiamin catalysis by transketolase

Transketolase from Saccharomyces cerevisiae exhibits a rarely reported activity with a methylated analogue of the native cofactor, 4′-methylamino-thiamin diphosphate. We demonstrated the kinetic stability of the dihydroxyethyl carbanion/enamine intermediate to be dependent on the functionality of the 4′-aminopyrimidine moiety of thiamin diphosphate [R. Golbik, L.E. Meshalkina, T. Sandalova, K. Tittmann, E. Fiedler, H. Neef, S. König, R. Kluger, G.A. Kochetov, G. Schneider, G. Hübner, Effect of coenzyme modification on the structural and catalytic properties of wild-type transketolase and of the variant E418A from Saccharomyces cerevisae, FEBS J. (2005) 272 1326-1342]. This paper extends these investigations of the function of the coenzyme’s aminopyrimidine in transketolase catalysis exemplified for the 4′-monomethylamino-thiamin diphosphate analogue. Here, we report near UV circular dichroism data and NMR-based analysis of reaction intermediates that give evidence for a strong destabilisation of the carbanion/enamine of DHE-4’-monomethylamino-thiamin diphosphate on the enzyme. A new negative band in near UV circular dichroism arising during turnover is attributed to the conjugate acid of the carbanion/enamine intermediate, an assignment additionally corroborated by ¹H NMR-based intermediate analysis. As opposed to the kinetically stabilized carbanion/enamine intermediate in transketolase when reconstituted with the native cofactor, DHE-4′-monomethylamino-thiamin diphosphate is rapidly released from the active centers during turnover and accumulates in the medium on a preparative scale.     

ALDH-2 deficiency increases cardiovascular oxidative stress--evidence for indirect antioxidative properties

Mitochondrial aldehyde dehydrogenase (ALDH-2) reduces reactive oxygen species (ROS) formation related to toxic aldehydes; additionally, it provides a bioactivating pathway for nitroglycerin. Since acetaldehyde, nitroglycerin, and doxorubicin treatment provoke mitochondrial oxidative stress, we used ALDH-2^−/− mice and purified recombinant human ALDH-2 to test the hypothesis that ALDH-2 has an indirect antioxidant function in mitochondria. Antioxidant capacity of purified ALDH-2 was comparable to equimolar doses of glutathione, cysteine, and dithiothreitol; mitochondrial oxidative stress was comparable in C57Bl6 and ALDH-2^−/− mice after acute challenges with nitroglycerin or doxorubicin, whereas chronic acetaldehyde, nitroglycerin, and doxorubicin treatment dose-dependently increased mitochondrial ROS formation and impaired endothelial function to a greater extent in ALDH-2^−/− mice. Maximal nitroglycerin dose applied in vivo lead to a “super-desensitized” nitroglycerin response in isolated ALDH-2^−/− aortas, inaccessible in C57Bl6 mice. Our results suggest that ALDH-2 has an indirect antioxidative property independent of its thiol-moiety in disease states of cardiovascular oxidative stress.     

Cross-talk between integrins alpha1beta1 and alpha2beta1 in renal epithelial cells

The collagen-binding integrins α1β1 and α2β1 have profoundly different functions, yet they are often co-expressed in epithelial cells. When both integrins are expressed in the same cell, it has been suggested that α1β1 negatively regulates integrin α2β1-dependent functions. In this study we utilized murine ureteric bud (UB) epithelial cells, which express no functionally detectable levels of endogenous integrins α1β1 and α2β1, to determine the mechanism whereby this regulation occurs. We demonstrate that UB cells expressing integrin α2β1, but not α1β1 adhere, migrate and proliferate on collagen I as well as form cellular cords in 3D collagen I gels. Substitution of the transmembrane domain of the integrin α2 subunit with that of α1 results in decreased cell adhesion, migration and cord formation. In contrast, substitution of the integrin α2 cytoplasmic tail with that of α1, decreases cell migration and cord formation, but increases proliferation. When integrin α1 and α2 subunits are co-expressed in UB cells, the α1 subunit negatively regulates integrin α2β1-dependent cord formation, adhesion and migration and this inhibition requires expression of both α1 and α2 tails. Thus, we provide evidence that the transmembrane and cytoplasmic domains of the α2 integrin subunit, as well as the α1 integrin subunit, regulate integrin α2β1 cell function.     

MARINE‐DERIVED DINOFLAGELLATES IN ANTARCTIC SALINE LAKES: COMMUNITY COMPOSITION AND ANNUAL DYNAMICS1*[link]

The saline lakes of the Vestfold Hills in Antarctica offer a remarkable natural laboratory where the adaptation of planktonic protists to a range of evolving physiochemical conditions can be investigated. This study illustrates how an ancestral marine community has undergone radical simplification leaving a small number of well‐adapted species. Our objective was to investigate the species composition and annual dynamics of dinoflagellate communities in three saline Antarctic lakes. We observed that dinoflagellates occur year‐round despite extremely low PAR during the southern winter, which suggests significant mixotrophic or heterotrophic activity. Only a small number of dominant dinoflagellate species were found in each lake, in contrast to the species‐rich Southern Ocean from which the lake communities are believed to be derived. We verified that the lake species were representatives of the marine polar dinoflagellate community, and not freshwater species. Polarella glacialis Montresor, Procaccini et Stoecker, a bipolar marine species, was for the first time described in a lake habitat and was an important phototrophic component in the higher salinity lakes. In the brackish lakes, we found a new sibling species to the brackish‐water species Scrippsiella hangoei (J. Schiller) J. Larsen, previously observed only in the Baltic Sea.     

Folinic acid attenuates methotrexate chemotherapy-induced damages on bone growth mechanisms and pools of bone marrow stromal cells

Chemotherapy often induces bone growth defects in pediatric cancer patients; yet the underlying cellular mechanisms remain unclear and currently no preventative treatments are available. Using an acute chemotherapy model in young rats with the commonly used antimetabolite methotrexate (MTX), this study investigated damaging effects of five once-daily MTX injections and potential protective effects of supplementary treatment with antidote folinic acid (FA) on cellular activities in the tibial growth plate, metaphysis, and bone marrow. MTX suppressed proliferation and induced apoptosis of chondrocytes, and reduced collagen-II expression and growth plate thickness. It reduced production of primary spongiosa bone, volume of secondary spongiosa bone, and proliferation of metaphyseal osteoblasts, preosteoblasts and bone marrow stromal cells, with the cellular activities being most severely damaged on day 9 and returning to or towards near normal levels by day 14. On the other hand, proliferation of marrow pericytes was increased early after MTX treatment and during repair. FA supplementation significantly suppressed chondrocyte apoptosis, preserved chondrocyte proliferation and expression of collagen-II, and attenuated damaging effects on production of calcified cartilage and primary bone. The supplementation also significantly reduced MTX effects on proliferation of metaphyseal osteoblastic cells and of bone marrow stromal cells, and enhanced pericyte proliferation. These observations suggest that FA supplementation effectively attenuates MTX damage on cellular activities in producing calcified cartilage and primary trabecular bone and on pools of osteoblastic cells and marrow stromal cells, and that it enhances proliferation of mesenchymal progenitor cells during bone/bone marrow recovery.