| 143641. |
- Li, X., et al.
(författare)
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Depot-specific messenger RNA expression of 11 beta-hydroxysteroid dehydrogenase type 1 and leptin in adipose tissue of children and adults
- 2007
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Ingår i: International Journal of Obesity. - London : Macmillan. - 0307-0565 .- 1476-5497. ; 31:5, s. 820-828
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To compare expression of messenger RNA (mRNA) coding for the cortisol regenerating enzyme 11-hydroxysteroid dehydrogenase type 1 (11-HSD1), and the adipocytokines leptin and resistin in paired biopsies of subcutaneous adipose tissue (SC) and omental adipose tissue (OM) from children. Design: Paired biopsies (SC and OM) were obtained from 54 children (age 0.17–16 years, body mass index (BMI) 12.5–28.3 kg/m2, BMI standard deviation score (SDS) -2.5–4.5) and 16 adults (age 27–79 years, BMI 19–46 kg/m2) undergoing open abdominal surgery. mRNA levels of 11-HSD1, leptin and resistin were measured using quantitative real-time polymerase chain reaction (PCR). Results: 11-HSD1 mRNA level was higher in OM than in SC (P<0.05), whereas leptin mRNA was higher in SC than in OM (P<0.001). There was no difference in the resistin mRNA level between SC and OM. These results were consistent in children and adults. In children, 11-HSD1 mRNA in SC was positively associated with BMI SDS (P<0.05), whereas in OM it was positively associated with age (P<0.05). The association between 11-HSD1 expression and age remained significant after adjustment for BMI SDS and gender. Leptin mRNA was positively associated with BMI SDS (SC:P<0.001, OM: P<0.001) but not with age in children. In multiple regression analyses, including anthropometric variables and age, BMI SDS was independently associated with mRNA levels of 11-HSD1 (P<0.05) and leptin (P<0.001) in SC. When normal weight and overweight children were analyzed separately, 11-HSD1 mRNA levels were positively associated with leptin in OM in the overweight group (P<0.05). Conclusion: There are depot-specific differences in mRNA levels of 11-HSD1 and leptin in children and adults. The positive association of 11-HSD1 mRNA in OM with age may reflect a causal role in visceral fat accumulation during growth. Increasing 11-HSD1 and leptin mRNA in SC with increasing BMI SDS could suggest that the risk of metabolic consequences of obesity may be established early in life.
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| 143642. |
- Li, Xin
(författare)
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Development of robust cyanobacterial strains for biotechnological applications : Stress tolerance and cell-specific expression in heterocyst-forming cyanobacteria
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthetic biology tools can be used to exploit potential applications of cyanobacteria, promising photosynthetic hosts for production of fuels and chemicals. Specific genetic tools are needed for the development of robust cyanobacterial strains for bioengineering. The key work presented in this thesis is a characterization and design of bioengineering tools for the heterocyst-forming cyanobacterium Nostoc punctiforme strain ATCC 29133. This multicellular cyanobacterium may express several oxidative stress-managing systems, including five Dps proteins. Two of these Dps proteins, NpDps2 and NpDps5, are involved in the tolerance against oxidative stress that induced by H2O2 or high light intensities. The capacity of NpDps2 and NpDps5 to further enhance oxidative stress tolerance, was confirmed by homologous overexpression and a constitutive strong promoter in N. punctiforme. The results show the potential of Dps proteins as tools to create robust cyanobacterial cells with improved stress tolerance. This work also establishes a Dps-mediated link among light tolerance, H2O2 scavenging, and iron homeostasis, and provides evidence on the non-redundant role of multiple Dps in multicellular cyanobacteria. To address the lack of well-defined promoters in cyanobacteria, a minimal synthetic promoter, SynDIF, was designed for heterocyst-specific expression. Promoters with 5’TCCGGA, the DIF motif, at the -35 region, have been identified to give heterocyst-specific transcription. To identify promoter elements, critical for cell-specificity, DIF promoter sequences from Anabaena PCC 7120 were used in a consensus sequence approach. The importance of the consensus regions for cell-specificity was investigated with promoter-eyfp reporters. This result provides new insights to the details of DIF promoters, which suggest that the DIF-motif, only together with the consensus or a native DIF promoter -10 region, are sufficient for heterocyst-specificity. Therefore, the DIF-35 region was (i) not independent of other promoter elements, and (ii) not sufficient for heterocyst-specific expression. Besides, the strength of the synthetic promoter was improved by including the upstream element from the native heterocyst specific promoter PNsiR1. Moreover, the SynDIF promoter is the shortest promoter ever reported to provide heterocyst-specific expression, indicating the potential of introducing this promoter in future biotechnological applications.
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| 143643. |
- Li, Xin, et al.
(författare)
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Differential transcriptional regulation of orthologous dps genes from two closely related heterocyst-forming cyanobacteria
- 2015
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Ingår i: FEMS Microbiology Letters. - : Oxford University Press (OUP). - 0378-1097 .- 1574-6968. ; 362:6
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Tidskriftsartikel (refereegranskat)abstract
- In cyanobacteria, DNA-binding proteins from starved cells (Dps) play an important role in the cellular response to oxidative and nutritional stresses. In this study, we have characterized the cell-type specificity and the promoter regions of two orthologous dps genes, Npun_R5799 in Nostoc punctiforme and alr3808 in Anabaena sp. PCC 7120. A transcriptional start site (TSS), identical in location to the previously identified proximal TSS of alr3808, was identified for Npun_R5799 under both combined nitrogen supplemented and N-2-fixing growth conditions. However, only alr3808 was also transcribed from a second distal TSS. Sequence homologies suggest that the promoter region containing the distal TSS is not conserved upstream of orthologous genes among heterocyst-forming cyanobacteria. The analysis of promoter GFP-reporter strains showed a different role in governing cell-type specificity between the proximal and distal promoter of alr3808. We here confirmed the heterocyst specificity of the distal promoter of alr3808 and described a very early induction of its expression during proheterocyst differentiation. In contrast, the complete promoters of both genes were active in all cells. Even though Npun_R5799 and alr3808 are orthologs, the regulation of their respective expression differs, indicating distinctions in the function of these cyanobacterial Dps proteins depending on the strain and cell type.
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| 143644. |
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| 143645. |
- Li, Xiaoqing, et al.
(författare)
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Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys
- 2020
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 189, s. 174-187
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a crack tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This crack-tip competition is evaluated for tensile loading and a totality of 15 crack configurations and slip systems. Our results predict that dislocation plasticity at the crack tip is generally unfavorable - although the competition is close for some crack orientations, suggesting intrinsic brittleness and low crack-tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant crack-tip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a crack on a {100} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred crack tip orientations, which are found to be alloy specific. Mixed-mode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on crack configuration and amplified by the effect of material anisotropy on crack tip stresses.
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| 143646. |
- Li, Xiaoze, et al.
(författare)
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Eight Nucleotide Substitutions Inhibit Splicing to HPV-16 3'-Splice Site SA3358 and Reduce the Efficiency by which HPV-16 Increases the Life Span of Primary Human Keratinocytes.
- 2013
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:9
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Tidskriftsartikel (refereegranskat)abstract
- The most commonly used 3'-splice site on the human papillomavirus type 16 (HPV-16) genome named SA3358 is used to produce HPV-16 early mRNAs encoding E4, E5, E6 and E7, and late mRNAs encoding L1 and L2. We have previously shown that SA3358 is suboptimal and is totally dependent on a downstream splicing enhancer containingmultiple potential ASF/SF2 binding sites. Here weshow that only one of the predicted ASF/SF2 sites accounts for the majority of the enhancer activity. We demonstrate that single nucleotide substitutions in this predicted ASF/SF2 site impair enhancer function and that this correlates with less efficient binding to ASF/SF2 in vitro. We provide evidence that HPV-16 mRNAs that arespliced to SA3358 interact with ASF/SF2 in living cells. In addition,mutational inactivation of the ASF/SF2 site weakened the enhancer at SA3358 in episomal forms of the HPV-16 genome, indicating that the enhancer is active in the context of the full HPV-16 genome.This resulted in induction of HPV-16 late gene expression as a result of competition from late splice site SA5639. Furthermore, inactivation of the ASF/SF2 site of the SA3358 splicing enhancer reduced the ability of E6- and E7-encoding HPV-16 plasmids to increase the life span of primary keratinocytes in vitro, demonstrating arequirement for an intact splicing enhancer of SA3358 forefficient production of the E6 and E7 mRNAs. These results link the strength of the HPV-16 SA3358 splicing enhancer to expression of E6 and E7 and to the pathogenic properties of HPV-16.
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| 143647. |
- Li, Xiaoqing, et al.
(författare)
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Elastic anharmonicity of bcc Fe and Fe-based random alloys from first-principles calculations
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:2
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Tidskriftsartikel (refereegranskat)abstract
- We systematically investigate elastic anharmonic behavior in ferromagnetic body-centered cubic (bcc) Fe and Fe1-xMx (M = Al, V, Cr, Co, or Ni) random alloys by means of density-functional simulations. To benchmark computational accuracy, three ab initio codes are used to obtain the complete set of second-and third-order elastic constants (TOECs) for bcc Fe. The TOECs of Fe1-xMx alloys are studied employing the first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. It is found that the alloying effects on C-111, C-112, and C-123, which are governed by normal strains only, are more pronounced than those on C-144, C-166, and C-456, which involve shear strains. Remarkably, the magnitudes of all TOECs but C-123 decrease upon alloying with Al, V, Cr, Co, or Ni. Using the computed TOECs, we study compositional effects on the pressure derivatives of the effective elastic constants (dB(ij)/dP), bulk (dK/dP), and shear moduli (dG/dP) and derive longitudinal acoustic nonlinearity parameters (beta). Our predictions show that the pressure derivatives of K and G decrease with x for all solute elements and reveal a strong correlation between the compositional trends on dK/dP and dG/dP arising from the fact that alloying predominantly altersdB(11)/dP. The sensitivity of dB(11)/dP to composition is attributed to intrinsic alloying effects as opposed to lattice parameter changes accompanying solute addition. For Fe and the considered Fe-based alloys, beta along high-symmetry directions orders as beta[111] > beta[100] > beta[110], and alloying increases the directional anisotropy of beta but reduces its magnitude.
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| 143648. |
- Li, Xiaoqing, et al.
(författare)
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Elastic properties of vanadium-based alloys from first-principles theory
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:1, s. 014105-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Cr and Ti on the fundamental mechanical properties of V-Cr-Ti alloys has been investigated using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The static lattice constant and elastic parameters have been calculated for the body-centered-cubic V1-x-yCrxTiy (0 <= x,y <= 0.1) random solid solution as a function of composition. Our theoretical predictions are in good agreement with the available experimental data. Alloys along the equicomposition region are found to exhibit the largest shear and Young's modulus as a result of the opposite alloying effects obtained for the two cubic shear elastic constants. The classical solid-solution hardening (SSH) model predicts larger strengthening effect in V1-yTiy than in V1-xCrx. By considering a phenomenological expression for the ductile-brittle transition temperature (DBTT) in terms of Peierls stress and SSH, it is shown that the present theoretical results can account for the variations of DBTT with composition.
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| 143649. |
- Li, Xiujuan, et al.
(författare)
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Embryonic stem cell models in vascular biology
- 2009
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Ingår i: Journal of Thrombosis and Haemostasis. - : Elsevier BV. - 1538-7933 .- 1538-7836. ; 7:Suppl. 1, s. 53-56
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Forskningsöversikt (refereegranskat)abstract
- Embryonic stem cells have become an established tool in vascular biology to study the details of vasculogenesis as well as angiogenesis. There is also a future potential in using embryonic stem cell-derived endothelial cells for therapeutic purposes. It is important to evaluate this model by comparing features of endothelial cells derived from differentiating stem cells and their responsiveness to external stimuli to those of primary endothelial cells and to in vivo models. Through culture of mouse embryonic stem cell we discovered that differentiating stem cells are highly amenable to analyzing biochemical and cell biologic processes that are independent of flow. Endothelial cell function can be studied in the context of mutations or deletions that are embryonically lethal in vivo. Many, if not all, of the features of sprouting angiogenesis in differentiating stem cells closely mimic the in vivo process.
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| 143650. |
- Li, Xiaoming, et al.
(författare)
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Evolutionary computation-based machine learning for Smart City high-dimensional Big Data Analytics
- 2023
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Ingår i: Applied Soft Computing. - : ELSEVIER. - 1568-4946 .- 1872-9681. ; 133
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Tidskriftsartikel (refereegranskat)abstract
- Science and technology development promotes Smart City Construction (SCC) as a most imminent problem. This work aims to improve the comprehensive performance of the Smart City-oriented high-dimensional Big Data Management (BDM) platform and promote the far-reaching development of SCC. It comprehensively optimizes the calculation process of the BDM platform through Machine Learning (ML), reduces the dimension of the data, and improves the calculation effect. To this end, this work first introduces the concept of SCC and the BDM platform application design. Then, it discusses the design concept of using ML technology to optimize the calculation effect of the BDM platform. Finally, the Tensor Train Support Vector Machine (TT-SVM) model is designed based on dimension reduction data processing. The proposed model can comprehensively optimize the BDM platform, and the model is compared with other models and evaluated. The research results show that the accuracy of the reduced dimension classification of the TT-SVM model is more than 95. The lowest average processing time for the model's reduced dimension classification is about 1ms. The model's highest data processing accuracy is about 98%, and the average processing time is between 1.0- 1.5ms. Compared with traditional models and BDM platforms, the proposed model has a breakthrough performance improvement, so it plays an important role in future SCC. This work has achieved a great breakthrough in big data processing, and innovatively improved the application mode of high-dimensional big data technology by integrating multiple technologies. Therefore, the finding provides targeted technical reference for algorithms in BDM platform and contributes to the construction and improvement of Smart City.& COPY; 2022 Elsevier B.V. All rights reserved.
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