Solar X-ray Flare Hazards on the Surface of Mars

Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to releases much larger than seen so far for the sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. We calculate the surficial reprocessed X-ray spectra using a Monte Carlo code we have developed. Biological doses from indirect genome damage are calculated for each parameterized flare spectrum by integration over the X-ray opacity of water. We estimate the mean waiting time for solar flares producing a given biological dose of ionizing radiation on Mars and compare with lethal dose data for a wide range of terrestrial organisms. These timescales range from decades for significant human health risk to 0.5 Myr for D. radiodurans lethality. Such doses require total flare energies of 10^33--10^38 erg, the lower range of which has been observed for other stars. Flares are intermittent bursts, so acute lethality will only occur on the sunward hemisphere during a sufficiently energetic flare, unlike low-dose-rate, extended damage by cosmic rays. We estimate the soil and CO_2 ice columns required to provide 1/e shielding as 4--9 g cm^-2, depending on flare mean energy and atmospheric column density. Topographic altitude variations give a factor of two variation in dose for a given flare. Life in ice layers that may exist ~ 100 g cm^-2 below the surface would be well protected.Comment: To be published in Planetary and Space Science; 33 pages, 3 figure

Protein crystals in adenovirus type 5-infected cells: requirements for intranuclear crystallogenesis, structural and functional analysis

Intranuclear crystalline inclusions have been observed in the nucleus of epithelial cells infected with Adenovirus serotype 5 (Ad5) at late steps of the virus life cycle. Using immuno-electron microscopy and confocal microscopy of cells infected with various Ad5 recombinants modified in their penton base or fiber domains, we found that these inclusions represented crystals of penton capsomers, the heteromeric capsid protein formed of penton base and fiber subunits. The occurrence of protein crystals within the nucleus of infected cells required the integrity of the fiber knob and part of the shaft domain. In the knob domain, the region overlapping residues 489–492 in the FG loop was found to be essential for crystal formation. In the shaft, a large deletion of repeats 4 to 16 had no detrimental effect on crystal inclusions, whereas deletion of repeats 8 to 21 abolished crystal formation without altering the level of fiber protein expression. This suggested a crucial role of the five penultimate repeats in the crystallisation process. Chimeric pentons made of Ad5 penton base and fiber domains from different serotypes were analyzed with respect to crystal formation. No crystal was found when fiber consisted of shaft (S) from Ad5 and knob (K) from Ad3 (heterotypic S5-K3 fiber), but occurred with homotypic S3K3 fiber. However, less regular crystals were observed with homotypic S35-K35 fiber. TB5, a monoclonal antibody directed against the Ad5 fiber knob was found by immunofluorescence microscopy to react with high efficiency with the intranuclear protein crystals in situ. Data obtained with Ad fiber mutants indicated that the absence of crystalline inclusions correlated with a lower infectivity and/or lower yields of virus progeny, suggesting that the protein crystals might be involved in virion assembly. Thus, we propose that TB5 staining of Ad-infected 293 cells can be used as a prognostic assay for the viability and productivity of fiber-modified Ad5 vectors

Risks due to X-ray Flares during Astronaut Extravehicular Activity

Solar hard X-ray flares can expose astronauts on lunar and deep space extravehicular activities (EVAs) to dangerous acute biological doses. We combine calculations of radiative transfer through shielding materials with subsequent transfer through tissue to show that hazardous doses, taken as >= 0.1 Gy, should occur with a probability of about 10% per 100 hours of accumulated EVA inside current spacesuits. The rapid onset and short duration of X-ray flares and the lack of viable precursor events require strategies for quick retreat, in contrast to solar proton events, which usually take hours to deliver significant fluence and can often be anticipated by flares or other light-speed precursors. Our results contrast with the view that only particle radiation poses dangers for human space exploration. Heavy-element shields provide the most efficient protection from X-ray flares, since X-rays produce no significant secondary radiation. We calculate doses due to X-ray flares behind aluminum shields and estimate the required shield masses to accompany EVA rovers.Comment: 8 pages, 2 figures; to be published in Space Weathe

Novel HIV-1 Knockdown Targets Identified by an Enriched Kinases/Phosphatases shRNA Library Using a Long-Term Iterative Screen in Jurkat T-Cells

HIV-1 is a complex retrovirus that uses host machinery to promote its replication. Understanding cellular proteins involved in the multistep process of HIV-1 infection may result in the discovery of more adapted and effective therapeutic targets. Kinases and phosphatases are a druggable class of proteins critically involved in regulation of signal pathways of eukaryotic cells. Here, we focused on the discovery of kinases and phosphatases that are essential for HIV-1 replication but dispensable for cell viability. We performed an iterative screen in Jurkat T-cells with a short-hairpin-RNA (shRNA) library highly enriched for human kinases and phosphatases. We identified 14 new proteins essential for HIV-1 replication that do not affect cell viability. These proteins are described to be involved in MAPK, JNK and ERK pathways, vesicular traffic and DNA repair. Moreover, we show that the proteins under study are important in an early step of HIV-1 infection before viral integration, whereas some of them affect viral transcription/translation. This study brings new insights for the complex interplay of HIV-1/host cell and opens new possibilities for antiviral strategies

Insights into household transmission of SARS-CoV-2 from a population-based serological survey

Understanding the risk of infection from household- and community-exposures and the transmissibility of asymptomatic infections is critical to SARS-CoV-2 control. Limited previous evidence is based primarily on virologic testing, which disproportionately misses mild and asymptomatic infections. Serologic measures are more likely to capture all previously infected individuals. We apply household transmission models to data from a cross-sectional, household-based population serosurvey of 4,534 people ≥5 years from 2,267 households enrolled April-June 2020 in Geneva, Switzerland. We found that the risk of infection from exposure to a single infected household member aged ≥5 years (17.3%,13.7-21.7) was more than three-times that of extra-household exposures over the first pandemic wave (5.1%,4.5-5.8). Young children had a lower risk of infection from household members. Working-age adults had the highest extra-household infection risk. Seropositive asymptomatic household members had 69.4% lower odds (95%CrI,31.8-88.8%) of infecting another household member compared to those reporting symptoms, accounting for 14.5% (95%CrI, 7.2-22.7%) of all household infections

Pharmacological Modulation of Platelet-derived Growth Factor Signalling with Imatinib Mesylate in a Murine Mod

Objective : Evidence for the importance of platelet-derived growth factor (PDGF) signalling in the fibrotic process is provided by 1) the fact that PDGF elicits direct fibrogenic action stimulating production of ECM 2) reports showing that a number of fibrogenic mediators such as TGFb, IL-1,TNF-α, bFGF and thrombin exhibit PDGF-dependent profibrotic activities. It has been suggested that the PDGF-PDGFR system might be a promising target for treating fibrotic diseases, thus we aimed at investigating whether the use of a tyrosin kinase inhibitor such as Imatinib mesylate (Glivec®) could reverse pulmonary fibrosis. Materials and methods: Lung fibrosis was induced in 15 pathogen-free 10-wk-old female C57/BL6 mice by IP injection of Bleomycin at 40 mg/kg body weight on Days 0, 2, 4, 6 and 8 and treated the mice with Glivec for 2 weeks with subcutaneous micro-osmotic pumps and sacrificed the 30th day. Mice were divided into 2 groups: controls treated with bleomycin alone and mice treated with bleomycin and Glivec at 50 mg/Kg. Mice follow-up was performed twice a week for the overall experimental period with check of weight. Tissue collection was performed at day 30. Fibrosis development was monitored by Hematoxilin Eosin Saffranin staining. Evolution of the molecular markers of fibrosis (CTGF, α-sm Actin, TGFβ) will be monitored by WB and Q-RT PCR. Results: In control mice treated with bleomycin alone, histopathological examination showed development of widespread fibrotic lesions with disruption of lung structure and accumulation of ECM in the sub-pleural areas. In mice treated with Glivec, lung fibrosis decreased. Inflammatory lesions persisted whereas fibrotic lesions became discontinuous and less dense. Conclusion: The present results showed that bleomycin-induced lung fibrosis can be improved by Glivec treatment. Experiments to quantify the reduction and the mechanism of reversion of fibrosis at the molecular level are currently ongoing. The next step it will be to combine Glivec with other anti-fibrotic agent (such as antioxidants or statins) to enhance the anti-fibrotic action

Expression, purification, crystallization and preliminary X-ray crystallographic studies of a psychrophilic cellulase from Pseudoalteromonas haloplanktis

peer reviewedThe Antarctic psychrophile Pseudoalteromonas haloplanktis produces a cold-active cellulase. To date, a three-dimensional structure of a psychrophilic cellulase has been lacking. Crystallographic studies of this cold-adapted enzyme have therefore been initiated in order to contribute to the understanding of the molecular basis of the cold adaptation and the high catalytic efficiency of the enzyme at low and moderate temperatures. The catalytic core domain of the psychrophilic cellulase CelG from P. haloplanktis has been expressed, purified and crystallized and a complete diffraction data set to 1.8 Angstrom has been collected. The space group was found to be P2(1)2(1)2(1), with unit-cell parameters a = 135.1, b = 78.4, c = 44.1 Angstrom. A molecular-replacement solution, using the structure of the mesophilic counterpart Cel5A from Erwinia chrysanthemi as a search model, has been found

Reversion Of Lung Fibrosis In C57BL6 Mice Using Statins

Objective: In radiation enteropathy models, activation of Rho/ROCK signalling pathway trigger radio-induced fibrosis and constitutes a new therapeutic target as Rho inhibition using anti-fibrotic properties of statins. In this study we investigate whether the pathological activation of the Rho/ROCK pathway was specific to the gut or could represent a more general pathogenic path. Therefore, anti-fibrotic properties of Rho/ROCK pharmacological inhibitors were tested in murine models of lung fibrosis. Materials and methods: Pulmonary fibrosis was induced in pathogen-free 10-wk-old female C57BL/6 mice by 1) IP injection of Bleomycin at 40 mg/kg body weight on Days 0, 2, 4, 6 and 8 and 2) Thorax irradiation (16 Gy, 17 Gy; RX 250 KeV). Mice follow-up was performed twice a week for the overall experimental period and tissue collection was performed at Day 15 and 30 and at week 15 and 26 respectively for bleomycin and irradiation model. Safron stain was used for collagen quantification after slide scanning (Nikon Scan) and analysis by Pixcyt program. Fibrosis development was monitored by HES staining. CTGF and α SM actin expression were studied by Western Blot and Q-RT-PCR. Curative effect of Rho and ROCK inhibition were studied in vivo using respectively pravastatin (40 mg/Kg/d) and simvastatin (20 mg/Kg/d) delivered over 14 days via osmotic pump implantation. Results: histopathological examinations show inflammatory lesions mixed up with fibrotic areas at Day 15 whereas fibrosis is fully established D30. The fibrotic lesions are located in the subpleural zones and within the large peripheral vessels. Quantification of the collagen deposition show progressive increase of collagen after D15. Curative administration of pravastatin increased the body weight of the animals by 25% as compared to the vehicle-treated group and significantly improved survival (83% vs 56%). In the same groups, HES analysis showed an almost complete regression of fibrosis in all animals. These results were less impressive in simvastatin group with a survival gain equal to 10%. Experiments on irradiation-induced lung fibrosis are currently ongoing. Conclusion: This study confirms and extends the anti-fibrotic therapeutic action of statins and shows that bleomycin-induced lung fibrosis can be modulated by Rho/ROCK pathway inhibition. However, further investigation are required to investigate the distinct action elicited by pravastatin versus simvastatin. As the Rho family is composed of several members, one hypothesis is that pravastatin and simvastatin could target different member of the Rho family