118 research outputs found
Chandra and FUSE spectroscopy of the hot bare stellar core H1504+65
H1504+65 is an extremely hot hydrogen-deficient white dwarf with an effective
temperature close to 200,000 K. We present new FUV and soft X-ray spectra
obtained with FUSE and Chandra, which confirm that H1504+65 has an atmosphere
primarily composed of carbon and oxygen. The Chandra LETG spectrum (60-160
Angstroem) shows a wealth of photospheric absorption lines from highly ionized
oxygen, neon, and - for the first time identified in this star - magnesium and
suggests relatively high Ne and Mg abundances. This corroborates an earlier
suggestion that H1504+65 represents a naked C/O stellar core or even the C/O
envelope of an O-Ne-Mg white dwarf.Comment: 15 pages, 10 figures, accepted for publication in A&
Milk fat globule epidermal growth factor-factor 8-derived peptide attenuates organ injury and improves survival in sepsis
INTRODUCTION: Sepsis involves overwhelming inflammatory responses with subsequent immune-suppression that can lead to multiple organ dysfunction and ultimately death. Milk fat globule epidermal growth factor-factor 8 (MFG-E8) is a secretory protein found to have multiple biological activities against autoimmune and inflammatory diseases. MFG-E8 contains an Arg-Gly-Asp (RGD) motif involved in cell-cell and cell-matrix interactions. In sepsis, excessive neutrophils migration through endothelial cells and matrix to sites of inflammation results in organ damage. We hypothesized that MFG-E8-derived short peptides (MSP) flanking its RGD motif could provide protection against organ injury in sepsis. METHODS: The differentiated human neutrophil-like HL-60 cells (dHL60) were incubated with a series of peptides flanking the RGD motif of human MFG-E8 for a cell adhesion assay to fibronectin or human pulmonary artery endothelial cells (PAECs). For the induction of sepsis, male C57BL/6 mice (20â25 g) were subjected to cecal ligation and puncture (CLP). Peptide MSP68 (1 mg/kg body weight) or normal saline (vehicle) was injected intravenously at 2 h after CLP. Blood and tissue samples were collected at 20 h after CLP for various measurements. RESULTS: After screening, peptide MSP68 (VRGDV) had the highest inhibition of dHL-60 cell adhesion to fibronectin by 55.8 % and to PAEC by 67.7 %. MSP68 treatment significantly decreased plasma levels of organ injury marker AST by 37.1 % and the proinflammatory cytokines IL-6 and TNF-α by 61.9 % and 22.1 %, respectively after CLP. MSP68 improved the integrity of microscopic architectures, decreased IL-6 levels in the lungs by 85.1 %, and reduced apoptosis. MSP68 treatment also significantly reduced the total number of neutrophil infiltration by 61.9 % and 48.3 % as well as MPO activity by 40.8 % and 47.3 % in the lungs and liver, respectively, after CLP. Moreover, the number of bacteria translocated to mesenteric lymph nodes was decreased by 57 % with MSP68 treatment. Finally, the 10-day survival rate was increased from 26 % in the vehicle group to 58 % in the MSP68-treated group. CONCLUSIONS: MSP68 effectively inhibits excessive neutrophils infiltrating to organs, leading to moderate attenuation of organ injury and significantly improved survival in septic mice. Thus, MSP68 may be a potential therapeutic agent for treating sepsis
High-resolution ultraviolet spectroscopy of PG1159-035 with HST and FUSE
PG1159-035 is the prototype of the PG1159 spectral class which consists of
extremely hot hydrogen-deficient (pre-) white dwarfs. It is also the prototype
of the GW Vir variables, which are non-radial g-mode pulsators. The study of
PG1159 stars reveals insight into stellar evolution and nucleosynthesis during
AGB and post-AGB phases. We perform a quantitative spectral analysis of
PG1159-035 focusing on the abundance determination of trace elements. We have
taken high-resolution ultraviolet spectra of PG1159-035 with the Hubble Space
Telescope and the Far Ultraviolet Spectroscopic Explorer. They are analysed
with non-LTE line blanketed model atmospheres. We confirm the high effective
temperature with high precision (Teff=140,000+/-5000 K) and the surface gravity
of logg=7. For the first time we assess the abundances of silicon, phosphorus,
sulfur, and iron. Silicon is about solar. For phosphorus we find an upper limit
of solar abundance. A surprisingly strong depletion of sulfur (2% solar) is
discovered. Iron is not detected, suggesting an upper limit of 30% solar. This
coincides with the Fe deficiency found in other PG1159 stars. We redetermine
the nitrogen abundance and find it to be lower by one dex compared to previous
analyses. The sulfur depletion is in contradiction with current models of AGB
star intershell nucleosynthesis. The iron deficiency confirms similar results
for other PG1159 stars and is explained by the conversion of iron into heavier
elements by n-capture in the s-processing environment of the precursor AGB
star. However, the extent of the iron depletion is stronger than predicted by
evolutionary models. The relatively low nitrogen abundance compared to other
pulsating PG1159 stars weakens the role of nitrogen as a distinctive feature of
pulsators and non-pulsators in the GW Vir instability strip.Comment: A&A accepted, 13 pages, 10 figure
Iron abundance in hot hydrogen-deficient central stars and white dwarfs from FUSE, HST, and IUE spectroscopy
We present a first systematic investigation of the iron abundance in very hot
(Teff>50,000K) hydrogen-deficient post-AGB stars. Our sample comprises 16
PG1159 stars and four DO white dwarfs. We use recent FUSE observations as well
as HST and IUE archival data to perform spectral analyses with line blanketed
NLTE model atmospheres. Iron is not detected in any PG1159 star. In most cases
this is compatible with a solar iron abundance due to limited quality of HST
and IUE data, although the tendency to an iron underabundance may be
recognized. However, the absence of iron lines in excellent FUSE spectra
suggests an underabundance by at least 1 dex in two objects (K1-16 NGC 7094). A
similar result has been reported recently in the [WC]-PG1159 transition object
Abell 78 (Werner et al. 2002). We discuss dust fractionation and s-process
neutron-captures as possible origins. We also announce the first identification
of sulfur in PG1159 stars.Comment: Accepted for publication in A&A, 10 pages, 9 figure
A fluorogenic cyclic peptide for imaging and quantification of drug-induced apoptosis
Programmed cell death or apoptosis is a central biological process that is dysregulated in many diseases, including inflammatory conditions and cancer. The detection and quantification of apoptotic cells in vivo is hampered by the need for fixatives or washing steps for non-fluorogenic reagents, and by the low levels of free calcium in diseased tissues that restrict the use of annexins. In this manuscript, we report the rational design of a highly stable fluorogenic peptide (termed Apo-15) that selectively stains apoptotic cells in vitro and in vivo in a calcium-independent manner and under wash-free conditions. Furthermore, using a combination of chemical and biophysical methods, we identify phosphatidylserine as a molecular target of Apo-15. We demonstrate that Apo-15 can be used for the quantification and imaging of drug-induced apoptosis in preclinical mouse models, thus creating opportunities for assessing the in vivo efficacy of anti-inflammatory and anti-cancer therapeutics
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PEGâpeptide conjugates
The remarkable diversity of the self-assembly behavior
of PEGâpeptides is reviewed, including self-assemblies formed by PEGâpeptides with ÎČ-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized
Bacterial size matters:Multiple mechanisms controlling septum cleavage and diplococcus formation are critical for the virulence of the opportunistic pathogen Enterococcus faecalis
Enterococcus faecalis is an opportunistic pathogen frequently isolated in clinical settings. This organism is intrinsically resistant to several clinically relevant antibiotics and can transfer resistance to other pathogens. Although E. faecalis has emerged as a major nosocomial pathogen, the mechanisms underlying the virulence of this organism remain elusive. We studied the regulation of daughter cell separation during growth and explored the impact of this process on pathogenesis. We demonstrate that the activity of the AtlA peptidoglycan hydrolase, an enzyme dedicated to septum cleavage, is controlled by several mechanisms, including glycosylation and recognition of the peptidoglycan substrate. We show that the long cell chains of E. faecalis mutants are more susceptible to phagocytosis and are no longer able to cause lethality in the zebrafish model of infection. Altogether, this work indicates that control of cell separation during division underpins the pathogenesis of E. faecalis infections and represents a novel enterococcal virulence factor. We propose that inhibition of septum cleavage during division represents an attractive therapeutic strategy to control infections
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