UVA-Induced Immune Suppression Through an Oxidative Pathway

Although ultraviolet B (UVB) irradiation induces local immune or systemic immune suppression, depending on the dose, the immune suppression by ultraviolet A (UVA) has not been fully investigated. In this study, we investigated the effect of UVA on the immune response in vitro and in vivo. The effect of UVA on the antigen-presenting function of epidermal cells was measured in terms of antigen-specific T cell proliferation. A murine epidermal cell suspension was exposed to UVA in vitro, pulsed with trinitrobenzenesulfonic acid, and cultured with T cells prepared from syngeneic mice previously sensitized with trinitrochlorobenzene. UVA (5–20 J per cm2) suppressed the antigenpresenting function of epidermal cells in a dose-dependent manner, accompanied with suppression of the expression of costimulatory molecules on Langerhans cells. In order to investigate the effect of an antioxidant on the immune suppression, an epidermal cell suspension was irradiated with UVA in the presence or absence of glutathione. The suppressions of antigen-presenting function and ICAM-1 expression were significantly prevented by glutathione in a dose-dependent manner. Further, the effect of UVA on the immune response at the induction phase of contact hypersensitivity was evaluated in terms of lymph node cell proliferation ex vivo. UVA irradiation suppressed the endogenous proliferation of lymph node cells in trinitrochlorobenzene-painted mice, and this suppression was significantly reversed by the application of glutathione to the skin during irradiation. These results suggest that UVA-induced immune suppression may be mediated by reactive oxygen species, at least in part

Structural and functional studies on Ycf12 (Psb30) and PsbZ-deletion mutants from a thermophilic cyanobacterium

Ycf12 (Psb30) and PsbZ are two low molecular weight subunits of photosystem II (PSII), with one and two trans-membrane helices, respectively. In order to study the functions of these two subunits from a structural point of view, we constructed deletion mutants lacking either Ycf12 or PsbZ from Thermosynechococcus elongatus, and purified, crystallized and analyzed the structure of PSII dimer from the two mutants. Our results showed that Ycf12 is located in the periphery of PSII, close to PsbK, PsbZ and PsbJ, and corresponded to the unassigned helix X1 reported previously, in agreement with the recent structure at 2.9 Å resolution (A. Guskov, J. Kern, A. Gabdulkhakov, M. Broser, A. Zouni, W. Saenger, Cyanobacterial photosystem II at 2.9 Å resolution: role of quinones, lipids, channels and chloride, Nat. Struct. Mol. Biol. 16 (2009) 334–342). On the other hand, crystals of PsbZ-deleted PSII showed a remarkably different unit cell constants from those of wild-type PSII, indicating a role of PsbZ in the interactions between PSII dimers within the crystal. This is the first example for a different arrangement of PSII dimers within the cyanobacterial PSII crystals. PSII dimers had a lower oxygen-evolving activity from both mutants than that from the wild type. In consistent with this, the relative content of PSII in the thylakoid membranes was lower in the two mutants than that in the wild type. These results suggested that deletion of both subunits affected the PSII activity, thereby destabilized PSII, leading to a decrease in the PSII content in vivo. While PsbZ was present in PSII purified from the Ycf12-deletion mutant, Ycf12 was present in crude PSII but absent in the finally purified PSII from the PsbZ-deletion mutant, indicating a preferential, stabilizing role of PsbZ for the binding of Ycf12 to PSII. These results were discussed in terms of the PSII crystal structure currently availabl

Roles of PsbI and PsbM in photosystem II dimer formation and stability studied by deletion mutagenesis and X-ray crystallography

PsbM and PsbI are two low molecular weight subunits of photosystem II (PSII), with PsbM being located in the center, and PsbI in the periphery, of the PSII dimer. In order to study the functions of these two subunits from a structural point of view, we crystallized and analyzed the crystal structure of PSII dimers from two mutants lacking either PsbM or PsbI. Our results confirmed the location of these two subunits in the current crystal structure, as well as their absence in the respective mutants. The relative contents of PSII dimers were found to be decreased in both mutants, with a concomitant increase in the amount of PSII monomers, suggesting a destabilization of PSII dimers in both of the mutants. On the other hand, the accumulation level of the overall PSII complexes in the two mutants was similar to that in the wild-type strain. Treatment of purified PSII dimers with lauryldimethylamine N-oxide at an elevated temperature preferentially disintegrated the dimers from the PsbM deletion mutant into monomers and CP43-less monomers, whereas no significant degradation of the dimers was observed from the PsbI deletion mutant. These results indicate that although both PsbM and PsbI are required for the efficient formation and stability of PSII dimers in vivo, they have different roles, namely, PsbM is required directly for the formation of dimers and its absence led to the instability of the dimers accumulated. On the other hand, PsbI is required in the assembly process of PSII dimers in vivo; once the dimers are formed, PsbI was no longer required for its stability

Plasma chemistry of the chinstrap penguin Pygoscelis antarctica during fasting periods: A case of poor adaptation to food deprivation?

The chinstrap penguin (Pygoscelis antarctica) is the smallest penguin species to be used to study the physiology of fasting. We analysed body-mass change and plasma chemistry of five non-breeding chinstraps during an experimental fasting period in the breeding season. We also analysed the same parameters in six fasting birds under natural conditions (during an incubation shift, which lasts about 10 days). Both groups presented similar patterns of change, showing a rapid increase in urea and uric acid plasma concentrations. Urea surpassed 3 mmol/l after 5 fasting days, while uric acid reached 1 mmol/l after 9 days. Plasma glucose levels decreased after 11 days, whereas cholesterol also showed a clear reduction during fasting. These results as a whole suggest that chinstrap penguins reached phase III after a short period in comparison with other Pygoscelis species. Body size and ecological factors could explain these inter-specific differences.Peer Reviewe

Fission yeast Ags1 confers the essential septum strength needed for safe gradual cell abscission

[EN]Fungal cytokinesis requires the assembly of a dividing septum wall. In yeast, the septum has to be selectively digested during the critical cell separation process. Fission yeast cell wall alpha (1-3) glucan is essential, but nothing is known about its localization and function inthe cell wall or about cooperation between the alpha - and beta (1-3) glucan synthases Ags1 and Bgs for cell wall and septum assembly. Here, we generate a physiological Ags1-GFP variant and demonstrate a tight colocalization with Bgs1, suggesting a cooperation in the important early steps of septum construction. Moreover, we define the essential functions of alpha(1-3) glucan in septation and cell separation. We show that alpha (1-3) glucan is essential for both secondary septum formation and the primary septum structural strength needed to support the physical forces of the cell turgor pressure during cell separation. Consequently, the absence of Ags1 and therefore alpha(1-3)glucan generates a special and unique side-explosive cell separation due to an instantaneous primary septum tearing caused by the turgor pressure

Relative sea-level rise around East Antarctica during Oligocene glaciation

During the middle and late Eocene (∼48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarcticainduced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rosedespite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an icesheet grounding line

Eocene cooling linked to early flow across the Tasmanian Gateway

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO(2)). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO(2) forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling