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Chen, Xi

Publications and source records attributed to Chen, Xi.

227 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

CCCP-Induced LC3 lipidation depends on Atg9 whereas FIP200/Atg13 and Beclin 1/Atg14 are dispensable

Highlights: ► CCCP-induced LC3 lipidation can be independent of initiation/nucleation molecules. ► Atg9-mediated trafficking is critically required for CCCP-induced LC3 lipidation. ► CCCP-induced mitophagy may thus be more dependent on Atg9-positive vesicles. -- Abstract: Treatment of cells with carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial proton gradient uncoupler, can result in mitochondrial damage and autophagy activation, which in turn eliminates the injured mitochondria in a Parkin-dependent way. How CCCP mobilizes the autophagy machinery is not fully understood. By analyzing a key autophagy step, LC3 lipidation, we examined the roles of two kinase complexes typically involved in the initiation and nucleation phases of autophagy, namely the ULK kinase complex (UKC) and the Beclin 1/Atg14 complex. We found that CCCP-induced LC3 lipidation could be independent of Beclin 1 and Atg14. In addition, deletion or knockdown of the UKC component FIP200 or Atg13 only led to a partial reduction in LC3 lipidation, indicating that UKC could be also dispensable for this step during CCCP treatment. In contrast, Atg9, which is important for transporting vesicles to early autophagosomal structure, was required for CCCP-induced LC3 lipidation. Taken together, these data suggest that CCCP-induced autophagy and mitophagy depends more critically on Atg9 vesicles than on UKC and Beclin 1/Atg14 complex.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Photoelectrochemical properties of electrostatically self-assembled multilayer films formed by three bipolar hemicyanines and H{sub 4}SiW{sub 12}O{sub 40}

Graphical abstract: Display Omitted Highlight: ► Three self-assembled films of hemicyanines of and H{sub 4}SiW{sub 12}O{sub 40}. ► Uniformly deposited multilayers with reversible electrochemical activity. ► Large cathodic photocurrent densities of 0.36–1.02 μA/cm{sup 2} with IPCE of 0.75–0.98%. -- Abstract: The electrostatically self-assembled multilayer films of three bipolar hemicyanines with varied alkyl chain lengths were prepared by alternating adsorption of H{sub 4}SiW{sub 12}O{sub 40} and these hemicyanines, and characterized by UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and cyclic voltammetry. The results showed that these inorganic–organic composite films were uniformly deposited with good electrochemical activity. Photoelectrochemical investigations showed that the films exhibited large cathodic photocurrent densities of 0.36–1.02 μA/cm{sup 2} with the monochromatic incident photon-to-electron conversion efficiency of 0.75–0.98% while irradiated with 100 mW/cm{sup 2} polychromatic light (730 nm > λ > 325 nm) at an applied potential of −0.2 V vs. saturated calomel electrode, being strongly dependent on the alkyl chain lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A SEARCH FOR 95 GHz CLASS I METHANOL MASERS IN MOLECULAR OUTFLOWS

We have observed a sample of 288 molecular outflow sources including 123 high-mass and 165 low-mass sources in order to search for class I methanol masers at the 95 GHz transition and to investigate the relationship between outflow characteristics and class I methanol maser emission with the Purple Mountain Observatory 13.7 m radio telescope. Our survey detected 62 sources with 95 GHz methanol masers above a 3{sigma} detection limit, which includes 47 high-mass sources and 15 low-mass sources. Therefore, the detection rate is 38% for high-mass outflow sources and 9% for low-mass outflow sources, suggesting that class I methanol masers are relatively easily excited in high-mass sources. There are 37 newly detected 95 GHz methanol masers (including 27 high-mass and 10 low-mass sources), 19 of which are newly identified (i.e., first identification) class I methanol masers (including 13 high-mass and 6 low-mass sources). A statistical analysis of the distributions of maser detections with the outflow parameters reveals that the maser detection efficiency increases with the outflow properties (e.g., mass, momentum, kinetic energy, mechanical luminosity of outflows, etc.). Systematic investigations of the relationships between the intrinsic luminosity of methanol masers and the outflow properties (including mass, momentum, kinetic energy, bolometric luminosity, and mass-loss rate of the central stellar sources) indicate a positive correlation. This further supports the theory that class I methanol masers are collisionally pumped and associated with shocks when outflows interact with the surrounding ambient medium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Phenylbutyric acid protects against carbon tetrachloride-induced hepatic fibrogenesis in mice

A recent report showed that the unfolded protein response (UPR) signaling was activated in the pathogenesis of carbon tetrachloride (CCl{sub 4})-induced hepatic fibrosis. Phenylbutyric acid (PBA) is a well-known chemical chaperone that inhibits endoplasmic reticulum (ER) stress and unfolded protein response (UPR) signaling. In the present study, we investigated the effects of PBA on CCl{sub 4}-induced hepatic fibrosis in mice. All mice were intraperitoneally (i.p.) injected with CCl{sub 4} (0.15 ml/kg BW, twice per week) for 8 weeks. In CCl{sub 4} + PBA group, mice were i.p. injected with PBA (150 mg/kg, twice per day) from the beginning of CCl{sub 4} injection to the end. As expected, PBA significantly attenuated CCl{sub 4}-induced hepatic ER stress and UPR activation. Although PBA alleviated, only to a less extent, hepatic necrosis, it obviously inhibited CCl{sub 4}-induced tumor necrosis factor alpha (TNF-α) and transforming growth factor beta (TGF-β). Moreover, PBA inhibited CCl{sub 4}-induced hepatic nuclear factor kappa B (NF-κB) p65 translocation and extracellular signal-regulated kinase (ERK) and c-Jun N-terminal Kinase (JNK) phosphorylation. Interestingly, CCl{sub 4}-induced α-smooth muscle actin (α-SMA), a marker for the initiation phase of HSC activation, was significantly attenuated in mice pretreated with PBA. Correspondingly, CCl{sub 4}-induced hepatic collagen (Col)1α1 and Col1α2, markers for the perpetuation phase of HSC activation, were inhibited in PBA-treated mice. Importantly, CCl{sub 4}-induced hepatic fibrosis, as determined using Sirius red staining, was obviously attenuated by PBA. In conclusion, PBA prevents CCl{sub 4}-induced hepatic fibrosis through inhibiting hepatic inflammatory response and HSC activation. Highlights: ► CCl{sub 4} induces hepatic ER stress, inflammation, HSC activation and hepatic fibrosis. ► PBA alleviates CCl{sub 4}-induced hepatic ER stress and UPR signaling activation. ► PBA inhibits CCl{sub 4}-induced hepatic NF-κB activation and ERK and JNK phosphorylation. ► PBA effectively protects against CCl{sub 4}-induced HSC activation and hepatic fibrosis. ► ER stress is involved in CCl{sub 4}-induced hepatic inflammation and fibrogenesis.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2013

Assessment of Evolving TRMM-Based Real-Time Precipitation Estimation Methods and Their Impacts on Hydrologic Prediction in a High-Latitude Basin

The real-time availability of satellite-derived precipitation estimates provides hydrologists an opportunity to improve current hydrologic prediction capability for medium to large river basins. Due to the availability of new satellite data and upgrades to the precipitation algorithms, the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis real-time estimates (TMPA-RT) have been undergoing several important revisions over the past ten years. In this study, the changes of the relative accuracy and hydrologic potential of TMPA-RT estimates over its three major evolving periods were evaluated and inter-compared at daily, monthly and seasonal scales in the high-latitude Laohahe basin in China. Assessment results show that the performance of TMPA-RT in terms of precipitation estimation and streamflow simulation was significantly improved after 3 February 2005. Overestimation during winter months was noteworthy and consistent, which is suggested to be a consequence from interference of snow cover to the passive microwave retrievals. Rainfall estimated by the new version 6 of TMPA-RT starting from 1 October 2008 to present has higher correlations with independent gauge observations and tends to perform better in detecting rain compared to the prior periods, although it suffers larger mean error and relative bias. After a simple bias correction, this latest dataset of TMPA-RT exhibited the best capability in capturing hydrologic response among the three tested periods. In summary, this study demonstrated that there is an increasing potential in the use of TMPA-RT in hydrologic streamflow simulations over its three algorithm upgrade periods, but still with significant challenges during the winter snowing events.

hydrologic prediction↗
DOE OSTI2012

Synthesis and characterization of negative thermal expansion HfW{sub 2-x}V{sub x}O{sub 8-x/2} solid solutions

Cubic HfW{sub 2-x}V{sub x}O{sub 8-x/2} (c-HfW{sub 2-x}V{sub x}O{sub 8-x/2}) solid solutions, where x is up to 0.34, were synthesized using a process of acidic steam hydrothermal (ASH)-thermal dehydrating precursors. The process is studied detailedly. The results reveal tetragonal HfW{sub 2-x}V{sub x}O{sub 7-x/2}(OH){sub 2}(H{sub 2}O){sub 2} precursors are synthesized after ASH treatment and they produce orthorhombic HfW{sub 2-x}V{sub x}O{sub 8-x/2} in dehydrating. Then c-HfW{sub 2-x}V{sub x}O{sub 8-x/2} are obtained at higher temperature. The crystal structures of c-HfW{sub 2-x}V{sub x}O{sub 8-x/2} are characterized as {alpha}-HfW{sub 2}O{sub 8} and {beta}-HfW{sub 2}O{sub 8} structure for 0{<=}x{<=}0.30 and x=0.34, respectively. All the c-HfW{sub 2-x}V{sub x}O{sub 8-x/2} show excellent negative thermal expansion property. The relationships between the properties, such as ordered degree parameter, crystal lattice parameter, phase transition temperature and linear average thermal expansion coefficient, and the V content are also discussed. - Graphical abstract: Novel c-HfW{sub 2-x}V{sub x}O{sub 8-x/2} solid solutions were synthesized and all of them still show excellent negative thermal expansion property. Highlights: Black-Right-Pointing-Pointer Novel cubic HfW{sub 2-x}V{sub x}O{sub 8-x/2} solid solutions and their precursors were synthesized. Black-Right-Pointing-Pointer Cubic HfW{sub 2-x}V{sub x}O{sub 8-x/2} solid solutions show excellent negative thermal expansion. Black-Right-Pointing-Pointer The relationship between the properties of the samples and the V content is revealed. Black-Right-Pointing-Pointer x up to 0.34, a rare large solid solubility in aliovalent substitution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

The Curie temperature distribution of FePt granular magnetic recording media

We present atomistic calculations of the magnetic phase transition behavior in an L1{sub 0} FePt system to study the effect of grain size distribution on the Curie temperature (T{sub c}) dispersion with relevance to heat assisted magnetic recording. Identifying the relation between the size and T{sub c} of a grain by means of finite size scaling analysis of the differentiated magnetization versus T data allows to show that a lognormal size distribution transforms into a lognormal T{sub c} distribution with moments dependent on the critical exponents. We also address the question of the universality class of FePt.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Early Low-Titer Neutralizing Antibodies Impede HIV-1 Replication and Select for Virus Escape

Single genome sequencing of early HIV-1 genomes provides a sensitive, dynamic assessment of virus evolution and insight into the earliest anti-viral immune responses in vivo. By using this approach, together with deep sequencing, site-directed mutagenesis, antibody adsorptions and virus-entry assays, we found evidence in three subjects of neutralizing antibody (Nab) responses as early as 2 weeks post-seroconversion, with Nab titers as low as 1:20 to 1:50 (IC50) selecting for virus escape. In each of the subjects, Nabs targeted different regions of the HIV-1 envelope (Env) in a strain-specific, conformationally sensitive manner. In subject CH40, virus escape was first mediated by mutations in the V1 region of the Env, followed by V3. HIV-1 specific monoclonal antibodies from this subject mapped to an immunodominant region at the base of V3 and exhibited neutralizing patterns indistinguishable from polyclonal antibody responses, indicating V1–V3 interactions within the Env trimer. In subject CH77, escape mutations mapped to the V2 region of Env, several of which selected for alterations of glycosylation. And in subject CH58, escape mutations mapped to the Env outer domain. In all three subjects, initial Nab recognition was followed by sequential rounds of virus escape and Nab elicitation, with Nab escape variants exhibiting variable costs to replication fitness. Although delayed in comparison with autologous CD8 T-cell responses, our findings show that Nabs appear earlier in HIV-1 infection than previously recognized, target diverse sites on HIV-1 Env, and impede virus replication at surprisingly low titers. The unexpected in vivo sensitivity of early transmitted/ founder virus to Nabs raises the possibility that similarly low concentrations of vaccine-induced Nabs could impair virus acquisition in natural HIV-1 transmission, where the risk of infection is low and the number of viruses responsible for transmission and productive clinical infection is typically one.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

Evaluating the SWAT Model for Hydrological Modeling in the Xixian Watershed and A Comparison with the XAJ Model

Already declining water availability in Huaihe River, the 6th largest river in China, is further stressed by climate change and intense human activities. There is a pressing need for a watershed model to better understand the interaction between land use activities and hydrologic processes and to support sustainable water use planning. In this study, we evaluated the performance of SWAT for hydrologic modeling in the Xixian River Basin, located at the headwaters of the Huaihe River, and compared its performance with the Xinanjiang (XAJ) model that has been widely used in China

54 ENVIRONMENTAL SCIENCES↗