Publications by authors named "Linhua Liu"

58 Publications

Discrete dipole approximation method for electromagnetic scattering by particles in an absorbing host medium.

Opt Express 2021 Mar;29(5):7690-7705

Electromagnetic (EM) scattering by particles in an absorbing host medium is frequently encountered in practical applications, which makes the conventional EM scattering theory controversial and most of the theoretical methods for EM scattering inapplicable. Most of the relevant works in literature are confined to spherical particles. In this work, we develop the discrete dipole approximation (DDA) method for EM scattering by an arbitrary particle immersed in an absorbing host medium. We elaborate how the near- and far-field scattering quantities can be calculated by DDA. The accuracy of DDA is validated by comparison with the apparent and inherent scattering quantities of spherical particles computed by exact Mie theory. Then EM extinction by non-absorbing spheroids in absorbing host medium is studied by DDA. We find that particles that are prolonged in the incident direction are more likely to produce a negative apparent extinction, which is also supported by the near-field electric field distribution. The DDA method we develop will be useful and flexible in the study of EM scattering by particles in absorbing host medium.
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http://dx.doi.org/10.1364/OE.418467DOI Listing
March 2021

Triphenyl phosphate disturbs the lipidome and induces endoplasmic reticulum stress and apoptosis in JEG-3 cells.

Chemosphere 2021 Feb 15;275:129978. Epub 2021 Feb 15.

School of Public Health, Dongguan Key Laboratory of Environmental Medicine, Guangdong Medical University, Guangdong, 523-808, China. Electronic address:

Triphenyl phosphate (TPP) is a frequently used aryl organophosphate flame retardant. Epidemiological studies have shown that TPP and its metabolite diphenyl phosphate (DPP) can accumulate in the placenta, and positively correlated with abnormal birth outcomes. TPP can disturb placental hormone secretion through the peroxisome proliferator-activated receptor γ (PPARγ) pathway. However, the extent and mechanism of placental toxicity mediation by TPP remains unknown. In this study, we used JEG-3 cells to investigate the role of PPARγ-regulated lipid metabolism in TPP-mediated placental toxicity. The results of lipidomic analysis showed that TPP increased the production of triglycerides (TG), fatty acids (FAs), and phosphatidic acid (PA), but decreased the levels of phosphatidylethanol (PE), phosphatidylserine (PS), and sphingomyelin (SM). TG accumulation was accompanied by increased levels of sterol regulatory element binding transcription factor 1 (SREBP1), acetyl-coA carboxylase (ACC), and fatty acid transport protein (CD36). Although PPARγ and its target CCAAT/enhancer binding proteins (C/EBPα) was decreased, the TG content and gene expression of SREBP1, ACC, and CD36 decreased when TPP was co-exposed to the PPARγ antagonist GW9662. TPP also induced inflammatory responses, endoplasmic reticulum stress (ERS), and cell apoptosis. Expression of genes related to ERS and apoptosis were attenuated by GW9662. Together, these results show that TPP can disturb lipid metabolism and cause lipid accumulation through PPARγ, induce ERS, and cell apoptosis. Our findings reveal that the developmental toxicity of TPP through placental toxicity should not be ignored.
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http://dx.doi.org/10.1016/j.chemosphere.2021.129978DOI Listing
February 2021

Preparing Viable Hippocampal Slices from Adult Mice for the Study of Sharp Wave-ripples.

Bio Protoc 2020 Oct 5;10(19):e3771. Epub 2020 Oct 5.

Department of Neuroscience, Georgetown University Medical center, Washington DC, 20007, USA.

We describe a protocol for preparing acute brain slices which can produce robust hippocampal sharp wave-ripples (SWRs) . The protocol is optimized for its simplicity and reliability for the preparation of solutions, slicing, and recovery incubation. Most slices in almost every mouse prepared though the protocol expressed vigorous spontaneous SWRs for ~24 h, compared to the 20-30% viability from "standard" low sodium slicing protocols. SWRs are spontaneous neuronal activity in the hippocampus and are essential for consolidation of episodic memory. Brain slices reliably expressing SWRs are useful for studying memory impairment and brain degeneration diseases in experiments. Spontaneous expression of SWRs is sensitive to conditions of slicing and perfusion/oxygenation during recording. The amplitude and abundance of SWRs are often used as a biomarker for viable slices. Key improvements include fast circulation, a long recovery period (3-6 h) after slicing, and allowing tissue to recover at 32 °C in a well perfused incubation chamber. Slices in our custom-made apparatus can express spontaneous SWRs for many hours, suggesting a long period with balanced excitation and inhibition in the local networks. Slices from older mice (~postnatal 180 days) show similar viability to younger (postnatal 21-30) mice.
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http://dx.doi.org/10.21769/BioProtoc.3771DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7842787PMC
October 2020

MiR-3138 deteriorates the insulin resistance of HUVECs via KSR2/AMPK/GLUT4 signaling pathway.

Cell Cycle 2021 Feb 28;20(4):353-368. Epub 2021 Jan 28.

Department of Endocrinology and Metabolism, Nanfang Hospital, Southern Medical University , Guangzhou, Guangdong Province, China.

Insulin resistance (IR) is a complex pathological condition resulting from the dysregulation of cellular response to insulin hormone in insulin-dependent cells and is recognized as a pathogenic hallmark and strong risk factor for metabolic syndrome. The present study aims to elucidate the molecular mechanism of the pathogenesis of IR. Here, we used human umbilical vein endothelial cells (HUVECs) to establish the IR cell model induced by 1 × 10 mmol/L insulin. After 48 h, reactive oxygen species (ROS) and glucose consumption were measured by DCFH-DA and GOD-POD methods, respectively. The results of Microarray analysis demonstrated that there were 10 differentially expressed miRNAs (DEMs) selected based on Fold change (FC) and P value in the IR cell model compared with HUVECs. The enriched gene ontology (GO) terms analysis showed that the target genes of these 10 DEMs were significantly enriched in biological process, cellular component and molecular function, and the significantly enriched Kyoto Encyclopedia of Genes or Genomes (KEGG) pathways mainly include AMPK signaling pathway and PI3K signaling pathway. Amongst all, the expression level of miR-3138 was highest in the IR cell model evaluated by qRT-PCR. Through Targetscan, KSR2 mRNA was predicted as a target of miR-3138. And mRNA and protein expression levels of miR-3138, KSR2, GLUT4, AMPK, PI3K, Akt were examined using qRT-PCR and Western blotting, respectively. The interaction between miR-3138 and KSR2 was evaluated by dual-luciferase reporter assay. Our results showed that miR-3138 significantly deteriorated the IR of HUVECs via KSR2/AMPK/GLUT4 signaling pathway.
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http://dx.doi.org/10.1080/15384101.2020.1870335DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7894458PMC
February 2021

Anharmonic phonon frequency and ultralow lattice thermal conductivity in β-CuSe liquid-like thermoelectrics.

Phys Chem Chem Phys 2020 Dec;22(48):28086-28092

School of Energy and Power Engineering, Shandong University, Jinan, Shandong 250061, China.

The prototype phonon-liquid electron-crystal β-Cu2Se has been ranked among the best thermoelectric material with its ultralow lattice thermal conductivity (κL). The atomic fluidity, harmonic approximation failure, and the existence of a large number of imaginary phonon modes hinder the atomistic analysis of phonon transport in β-Cu2Se. Thus, the atomistic origins of its ultralow κL remain elusive. In this study, we present a self-consistent phonon (SCPH) calculation of the lattice dynamical properties of β-Cu2Se by including quartic anharmonicity and stiffening imaginary phonon modes in the anharmonic phonon dispersion, aiming to unravel the atomistic origins of ultralow κL. Upon renormalizing harmonic phonon dispersion with quartic anharmonicity, those imaginary phonon modes arising from copper fluidity diminish as temperature increases and anharmonic phonon dispersions are obtained. By solving the Boltzmann transport equation within the relaxation time approximation (BTE-RTA), we predicted ultralow κL which demonstrated an overall agreement with previous experiments. After analyzing the harmonic as well as anharmonic phonon density of states, it was found that the inclusion of quartic anharmonicity induces the suppression of low-lying phonon modes, which coincides with the experimental observation of the selective breakdown of long-wave transverse acoustic phonons. However, for the propagative heat-carriers, the anharmonic scattering enhances and phonon relaxation lifetime decreases as temperature increases, leading to a further reduction of κL. This study provides an extra insight into the atomistic origins of ultralow κL in β-Cu2Se from first-principles anharmonic force constants and helps engineer the lattice dynamical properties for better thermoelectric performance.
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http://dx.doi.org/10.1039/d0cp04591hDOI Listing
December 2020

Electric Auxetic Effect in Piezoelectrics.

Phys Rev Lett 2020 Nov;125(19):197601

Optics and Thermal Radiation Research Center, Shandong University, Qingdao, Shandong 266237, China.

Auxetic materials are characterized by a negative Poisson's ratio that they expand laterally in the directions perpendicular to the applied stretching stress and vice versa. Piezoelectrics will change their dimensions when exposed to an external electric field. Here we introduce the concept of the "electric auxetic effect": electric auxetic materials will contract or expand in all dimensions in response to an electric field. Such unusual piezoelectric response driven by an electric field is a close analogy to the auxetic effect driven by a stress field. A key feature of electric auxetic materials is that their longitudinal and transverse piezoelectric coefficients are of the same sign. We demonstrate using first-principles calculations that the Pca2_{1} orthorhombic phase of ferroelectric HfO_{2} exhibits both the negative longitudinal piezoelectric effect and the electric auxetic effect. The unusual negative longitudinal piezoelectric effect arises unexpectedly from the domination of the negative internal-strain contribution over the positive clamped-ion contribution, a character often found in van der Waals solids. We confirm a few more electric auxetic materials with finite electric field calculations by screening through a first-principles-based database of piezoelectrics.
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http://dx.doi.org/10.1103/PhysRevLett.125.197601DOI Listing
November 2020

Polarized radiative transfer in dense dispersed media containing optically soft sticky particles.

Opt Express 2020 Sep;28(19):28252-28268

This paper focuses on polarized radiative transfer in dispersed layers composed of densely packed optically soft particles while considering the effects of dependent scattering and particle agglomeration. The radiative properties of the particles for different agglomeration degrees are calculated using the Lorenz-Mie theory combined with the Percus-Yevick sticky hard sphere model, and the vector radiative transfer equation is solved by using the spectral method. The normalized Stokes reflection matrix elements of the layers for different particle sizes, particle volume fractions and layer thicknesses are discussed. The results show that the effects of multiple scattering, dependent scattering and particle agglomeration have different degrees of influence on the polarized reflection characteristics of the layers. Due to the inhibition effect of far-field interference interaction on particle scattering, the dependent scattering weakens the depolarization caused by multiple scattering. However, as the particles form agglomerations, the scattering coefficients of the particles obviously increase with the agglomeration degree, which will lead to the significant enhancement of the multiple scattering and depolarization.
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http://dx.doi.org/10.1364/OE.404121DOI Listing
September 2020

Complex refractive indices measurements of polymers in visible and near-infrared bands.

Appl Opt 2020 Mar;59(8):2337-2344

The complex refractive indices of polymers have important applications in the analysis of their components and the study of radiation endothermic mechanisms. Since these materials have high transmittance in the visible to near-infrared ranges, it is difficult to accurately measure their complex refractive indices. At present, the data for complex refractive indices of polymers are seriously lacking, which greatly limits the applications of these materials in the field of thermal radiation. In this work, spectroscopic ellipsometry (SE) combined with the ray tracing method (RTM) is used to measure the complex refractive indices of five polymers, polydimethylsiloxane, poly(methyl methacrylate) (PMMA), polycarbonate, polystyrene, and polyethylene terephthalate, in the spectral range of 0.4-2 µm. The double optical pathlength transmission method (DOPTM) is used to measure the complex refractive indices of three polymers, PMMA, polyvinyl chloride, and polyetherimide, in the 0.4-2 µm range. The complex refractive index of PMMA measured by the DOPTM almost coincides with the data measured by SE combined with the RTM. The results show that the trends of the complex refractive indices spectra for the seven polymers in the 0.4-2 µm range are similar. This work makes up for the lack of complex refractive indices in the 0.4-2 µm range for these seven materials and points out the direction for accurate measurements of the complex refractive indices of polymers with weak absorption.
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http://dx.doi.org/10.1364/AO.383831DOI Listing
March 2020

Regulatory loop between lncRNA FAS-AS1 and DNMT3b controls FAS expression in hydroquinone-treated TK6 cells and benzene-exposed workers.

Environ Pollut 2020 Jun 11;261:114147. Epub 2020 Feb 11.

Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, 523808, PR China; Department of Environmental and Occupational Health, School of Public Health, Guangdong Medical University, Dongguan, 523808, PR China. Electronic address:

Hydroquinone (HQ), one of the main metabolites of benzene, is a well-known human leukemogen. However, the specific mechanism of how benzene or HQ contributes to the development of leukemia is unknown. In a previous study, we demonstrated the upregulation of DNA methyltransferase (DNMT) expression in HQ-induced malignant transformed TK6 (HQ-TK6) cells. Here, we investigated whether a regulatory loop between the long noncoding RNA FAS-AS1 and DNMT3b exists in HQ-TK6 cells and benzene-exposed workers. We found that the expression of FAS-AS1 was downregulated in HQ-TK6 cells and workers exposed to benzene longer than 1.5 years via histone acetylation, and FAS-AS1 expression was negatively correlated with the time of benzene exposure. Restoration of FAS-AS1 in HQ-TK6 cells promoted apoptosis and inhibited tumorigenicity in female nude mice. Interestingly, treatment with a DNMT inhibitor (5-aza-2-deoxycytidine), histone deacetylase inhibitor (trichostatin A), or DNMT3b knockout led to increased FAS-AS1 through increased H3K27ac protein expression in HQ-TK6 cells, and DNMT3b knockout decreased H3K27ac and DNMT3b enrichment to the FAS-AS1 promoter region, which suggested that DNMT3b and/or histone acetylation involve FAS-AS1 expression. Importantly, restoration of FAS-AS1 resulted in reduced expression of DNMT3b and SIRT1 and increased expression of FAS in both HQ-TK6 cells and xenograft tissues. Moreover, the average DNMT3b expression in 17 paired workers exposed to benzene within 1.5 years was decreased, but that of the remaining 103 paired workers with longer exposure times was increased. Conversely, DNMT3b was negatively correlated with FAS-AS1 expression. Both FAS-AS1 and DNMT3b influenced the enrichment of H3K27ac in the FAS promoter region by regulating the expression of SIRT1, consequently upregulating FAS expression. Taken together, these observations demonstrate crosstalk between FAS-AS1 and DNMT3b via a mutual inhibition loop and indicate a new mechanism by which FAS-AS1 regulates the expression of FAS in benzene-related carcinogenesis.
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http://dx.doi.org/10.1016/j.envpol.2020.114147DOI Listing
June 2020

Up-regulation of DNMT3b contributes to HOTAIRM1 silencing via DNA hypermethylation in cells transformed by long-term exposure to hydroquinone and workers exposed to benzene.

Toxicol Lett 2020 Apr 30;322:12-19. Epub 2019 Dec 30.

Department of Environmental and Occupational Health, School of Public Health, Guangdong Medical University, Dongguan, 523808, PR China; Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, 523808, PR China. Electronic address:

Benzene exposure is a risk factor of acute myeloid leukemia (AML), during such carcinogenesis long non-coding RNAs (lncRNAs) are important epigenetic regulators. HOTAIRM1 (HOXA transcript antisense RNA, myeloid-specific 1) plays an indispensable role in the development of AML. Hydroquinone (HQ) is one major metabolite of benzene and its ideal replacement in toxicology research. But the influence of benzene or HQ on HOTAIRM1 expression in AML associated pathway is still unclear. In the TK6 cells with short-term exposure to HQ (HQ-ST cells) or long term HQ exposure induced malignant transformed TK6 cells (HQ-MT cells), the relationship between DNMT3b and HOTAIRM1 was explored. Comparing to counterparts, HOTAIRM1 expression was increased firstly and then decreased in HQ-ST cells, and definitely decreased in HQ-MT cells; while the expression change tendency of DNMT3b was in contrast to that of HOTAIRM1. Moreover, the average HOTAIRM1 expression of 17 paired workers being exposed to benzene within 1.5 years was increased, but that of the remaining 92 paired workers with longer exposure time was decreased. Furthermore, in 5-AzaC (DNA methyltransferase inhibitor) or TSA (histone deacetylation inhibitor) treated HQ-MT cells, the expression of HOTAIRM1 was restored by reduced DNA promoter methylation levels. HQ-MT cells with DNMT3b knockout by CRISPR/Cas9 displayed the promoter hypomethylation and the increase of HOTAIRM1, also confirmed in benzene exposure workers. These suggest that long term exposure to HQ or benzene might induce the increase of DNMT3b expression and the promoter hypermethylation to silence the expression of HOTAIRM1, a possible tumor-suppressor in the AML associated carcinogenesis pathway.
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http://dx.doi.org/10.1016/j.toxlet.2019.12.028DOI Listing
April 2020

Extracting optical constants of solid materials with micro-rough surfaces from ellipsometry without using effective medium approximation.

Opt Express 2019 Jun;27(13):17667-17680

The effective medium approximation (EMA) model may cause a large deviation in the data analysis of spectroscopic ellipsometry (SE) for solid materials with randomly micro-rough surfaces since it ignores the influence of the lateral irregularities of the rough surfaces on the electromagnetic scattering. In this work, a novel inversion framework is developed to extract optical constants from the SE parameters for solid materials with randomly micro-rough surfaces. Our approach enables the integration of the Levenberg-Marquardt optimization algorithm and the first-principles calculations of electromagnetic scattering. In each iterative step, the electromagnetic interactions with rough surfaces are accurately obtained from first-principles calculations without using the EMA model for rough estimation, which significantly guarantees the precision and wide applicability of our method for actual surfaces without a perfectly Gaussian height distribution. Furthermore, a superior advantage of our approach is that its error can be feasibly evaluated from the instrumental errors of the surface morphology detectors and the SE.
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http://dx.doi.org/10.1364/OE.27.017667DOI Listing
June 2019

Dependent absorption property of nanoparticle clusters: an investigation of the competing effects in the near field.

Opt Express 2019 Apr;27(8):A280-A291

Noble metal nanoparticle clusters show unique light absorption and catalysis properties, which have been widely used in the application of photocatalysis, optoelectronics, biomedical optics and so on. The absorption cross section of densely packed nanoparticle clusters, which can be enhanced or restricted due to the near field effects needs to be studied thoroughly. In this work, focusing on Au nanoparticle at the localized plasmon resonance wavelength, the effects of monomer diameter D, monomer number N, particle volume fraction F and complex refractive index m on the nondimensional absorption cross section η = C/(N·C) (normalized by N and the absorption cross section C of a single particle) of densely packed nanoparticle clusters are studied by using the superposition T-matrix method. It is found that the enhancement (η > 1) and restriction (η < 1) mechanisms of the absorption cross section of nanoparticle clusters are determined by two competing factors (i.e. the multiple scattering and shielding effect), and the extent of these two mechanisms is mainly dependent on the monomer size parameter and the monomer number. The effect of the particle volume fraction on the nondimensional absorption cross section of nanoparticle clusters is totally different in different mechanisms. Specifically, the nondimensional absorption cross section peaks at the particle volume fraction of about 50% in the enhancement mechanism (in our calculation: D < 14 nm, N = 100), while in the restriction mechanism it decreases monotonously with increasing particle volume fraction. Moreover, the absorption efficiency of nanoparticle clusters with more absorptive monomer decreases more sharply with increasing particle volume fraction. The complex refractive index of particle shows significant effects on the nondimensional absorption cross section of nanoparticle clusters, and the largest nondimensional absorption cross section of nanoparticle clusters (N = 100) is larger than 8.
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http://dx.doi.org/10.1364/OE.27.00A280DOI Listing
April 2019

Chiral heteronanotubes: arrangement-dominated chiral interface states and conductivities.

Nanoscale 2019 May;11(18):8699-8705

Department of Physics, Harbin Institute of Technology, Harbin, 150001, P. R. China.

Structural analogue between pure carbonic nanostructures and their boron nitride counterparts provides possibilities for the fabrication of BCN hetero-nanomaterials, which have attracted widespread interest and been synthesized with stacked-layer, monolayer and tubular morphologies. In this work, the arrangement-dominated chiral interface states and conductivities of BCN heteronanotubes are investigated in detail by first principles calculations. The π-conjugated states can be driven by the high potential barrier of insulating BN domains to form chiral transport states along the interfaces. The emerging antiparallel and parallel chiral interface states play a dominant role for resonant transport and provide possibilities for the formation of chiral currents. Moreover, the unidirectional chiral currents have advantages to induce a magnetic field which can reach over 0.1 T. In contrast to the parallel-arranged chiral heteronanotubes, the antiparallel-arranged chiral heteronanotubes with the same stoichiometry have narrower band-gaps and stronger chiral conductivities. Such arrangement-dominated chiral transport interface states endow CHNTs with potential application in magneto-electronics.
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http://dx.doi.org/10.1039/c9nr01996kDOI Listing
May 2019

E4F1 silencing inhibits the cell growth through cell-cycle arrest in malignant transformed cells induced by hydroquinone.

J Biochem Mol Toxicol 2019 Apr 1;33(4):e22269. Epub 2018 Dec 1.

Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, China.

Hydroquinone (HQ), one of the most significant metabolic activation products of benzene in an organism, can cause hematological toxicity, such as acute myeloid leukemia. It is a clear carcinogen that can cause changes in the disorder of cell cycle and cell growth. However, its molecular mechanisms remain unclear. E4 transcription factor 1 (E4F1), an important transcription factor, participating in the regulation of cell cycle may be related to the occurrence of tumor. Here, we examined the HQ-induced malignant transformed TK6 cells (TK6-HT) to illustrate the role of E4F1 in carcinogenesis. The present study showed that both the expressions of E4F1 messenger RNA and protein increased obviously in TK6-HT, preliminarily indicating that E4F1 is associated with HQ-induced carcinogenesis. To further explore the role of E4F1, we established E4F1 silencing TK6-HT (pLVX-shE4F1) and its control cells (pLVX-shNC) using lentiviral short hairpin RNA (shRNA) interference expression plasmid vector pLVX-shRNA. Flow cytometry and cell counting kit-8 assay were used to determine the effects of E4F1 silencing on cell cycle and cell growth, respectively. E4F1 silencing inhibited cell growth in TK6-HT. The results from flow cytometry indicated that the inhibitory effect on cell growth may be the results of the E4F1 silencing-induced accumulation in G2/M compared with TK6-HT-shNC. Meanwhile, levels of DNA damage (γ-H2AX), proteins of Rb and phosphorylated Rb, and reactive oxygen species were increased in TK6-HT-shRNA2 cells, which is the critical reason of cell-cycle arrest. In conclusion, E4F1 silencing inhibits the cell growth through cell-cycle arrest in malignant transformed cells induced by HQ.
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http://dx.doi.org/10.1002/jbt.22269DOI Listing
April 2019

Poly(ADP-ribose) polymerase-1 promotes expression of miR-155 by the up-regulation of methyl-CpG binding domain protein 2 in TK6 cells exposed to hydroquinone.

Toxicol In Vitro 2019 Mar 15;55:51-57. Epub 2018 Nov 15.

Department of Environmental and Occupational Health, School of Public Health, Guangdong Medical University, Dongguan 523808, PR China; Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan 523808, PR China. Electronic address:

Hydroquinone (HQ), one of the major metabolites of benzene, can induce aberrant gene expression. MiR-155, a tumor activator, participates in various biological processes, including DNA damage response. However, the molecular mechanism of aberrant miR-155 expression is still not completely elucidated. Here, we investigated the mechanism of abnormal expression of miR-155 induced by poly(ADP-ribose)polymerase-1 (PARP-1) expression in HQ-treated TK6 lymphoblastoid cells. We examined the expression of genes related to abnormal expression of miR-155 to explore the reason for this phenomenon. The results of the present study showed that miR-155 was significantly increased and reactive oxygen species (ROS) were decreased in cells treated with HQ for 72 h compared with PBS-treated cells. Meanwhile, E4F1, PARP-1 and PARP-1 related co-regulators (NF-κB, HDAC1, and HDAC2), acetylated histone H3 (H3Ac) were increased in a concentration-dependent manner. Experiments for treatment with 5-AzaC (DNMTs inhibitor), TSA (HDACs inhibitor), DOX (to activate PARP-1) or MG132 (proteasome inhibitor) revealed that the MBDs and PARP-1 was positively associated with miR-155 expression. Moreover, in cells treated with HQ in conjunction with PARP-1 knockdown, expression of miR-155, H3Ac and MBD2 protein were decreased, compared with negative control. In conclusion, PARP-1 activates expression of miR-155 via acetylation by regulating MBD2 in TK6 cells exposed to HQ.
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http://dx.doi.org/10.1016/j.tiv.2018.11.007DOI Listing
March 2019

Applicability of the effective medium approximation in the ellipsometry of randomly micro-rough solid surfaces.

Opt Express 2018 Jun;26(13):16560-16571

The effective medium approximation (EMA) has been widely applied to model the effect of a solid sample with surface roughness in spectroscopic ellipsometry (SE). There are two specific cases to utilize the EMA model. One is utilizing the EMA model to perform the inversion of the optical constants of solid samples from the SE measurements. Another is utilizing the EMA model to estimate the thickness of the rough layer at solid surface from the SE measurements under the condition in which the optical constants of samples are known. For the first case, the thickness of the rough layer is usually assumed to be the root mean square (rms) roughness as measured by atomic force microscopy (AFM). We theoretically investigate the error of the EMA model to estimate optical constants for different surface morphologies and materials. Because the EMA model only accounts for the height irregularities of rough surfaces but neglects the effect of the lateral irregularities on electromagnetic scattering from rough surfaces, it is difficult to obtain high-precision results for optical constants. Moreover, the inversion error of optical constants by using the EMA model is difficult to evaluate. In the second case, the thickness of the rough layer is estimated by using the EMA model from the SE measurements, called the EMA model roughness. We show that the EMA model roughness generally has a deviation from the rms roughness as measured by AFM. Some correlated relationships are established between the EMA model roughness and the morphological parameters of rough surfaces. It is found that these relationships have similar forms but not identical coefficients for different materials. The results from this work may facilitate a better understanding and utilization for the EMA model in SE.
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http://dx.doi.org/10.1364/OE.26.016560DOI Listing
June 2018

The profiles and networks of miRNA, lncRNA, mRNA, and circRNA in benzo(a)pyrene-transformed bronchial epithelial cells.

J Toxicol Sci 2018 ;43(4):281-289

Our aim was to demonstrate the significance of miRNA, lncRNA, and circRNA in the transformation of human bronchial epithelial cells induced by benzo(a)pyrene (BaP), and to investigate their regulatory networks. Hierarchical clustering, gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and network regulation analysis were used to analyze the high-throughput sequencing results of human bronchial epithelial cell line BEAS-2B and BaP-transformed BEAS-2B cells (BEAS-2B-T). 76,191,786 and 3,431differentially-expressed miRNA, lncRNA, mRNA and circRNA were detected, respectively; 43 miRNA, 48 lncRNA, 438 mRNA and 2,079 circRNA were up-regulated; 33 miRNA, 143 lncRNA, 348 mRNA and 1,352 circRNA were down-regulated. Through GO analysis, 257 biological process (BP) terms, 12 cell composition (CC) terms and 49 molecular function (MF) terms were found in differentially-expressed lncRNA; 143 BP terms, 32 CC terms, and 48 MF terms were found in differentially-expressed circRNA. Pathways of KEGG analysis of lncRNA and circRNA could be classified into the categories "human diseases" and "organism systems". From miRNA-circRNA, circRNA-mRNA, and lncRNA-circRNA networks analysis, we found that mir-137, circ-RPS5, circ-ZNF292, circ-ERBB2IP, circ-SEMA3C, circ-IGF1R, circ-RTN4, APOC1, and CDKN2A may be of great significance for cell transformation. From the analysis of miRNA, lncRNA, mRNA, and circRNA networks, we found that PDGFRB, lncRNA RGMB-AS1, circ-ZNF292 are associated with miR-138-5p. Our study shows that miRNA, lncRNA, and circRNA have a significant regulatory role in the transformation of human bronchial epithelial cell induced by BaP.
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http://dx.doi.org/10.2131/jts.43.281DOI Listing
August 2018

miR-7-5p overexpression suppresses cell proliferation and promotes apoptosis through inhibiting the ability of DNA damage repair of PARP-1 and BRCA1 in TK6 cells exposed to hydroquinone.

Chem Biol Interact 2018 Mar 5;283:84-90. Epub 2018 Feb 5.

Department of Environmental and Occupational Health, Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, China. Electronic address:

Hydroquinone (HQ), one of the major metabolic products of benzene, is a carcinogen, which induces apoptosis and inhibit proliferation in lymphoma cells. microRNA-7-5p (miR-7-5p), a tumor suppressor, participates in various biological processes including cell proliferation and apoptosis regulation by repressing expression of specific oncogenic target genes. To explore whether miR-7-5p is involved in HQ-induced cell proliferation and apoptosis, we assessed the effect of miR-7-5p overexpression on induction of apoptosis analyzed by FACSCalibur flow cytometer in transfection of TK6 cells with miR-7-5p mimic (TK6- miR-7-5p). We observed an increased apoptosis by 25.43% and decreased proliferation by 28.30% in TK6-miR-7-5p cells compared to those negative control cells (TK6-shNC) in response to HQ treatment. Furthermore, HQ might active the apoptotic pathway via partly downregulation the expression of BRCA1 and PARP-1, followed by p53 activation, in TK6-miR-7-5p cells. In contrast, attenuated p53 and BRCA1 expression was observed in shPARP-1 cells than in NC cells after HQ treatment. Therefore, we conclude that HQ may activate apoptotic signals via inhibiting the tumor suppressive effects of miR-7-5p, which may be mediated partly by upregulating the expression of PARP-1 and BRCA1 in control cells. The increase of miR-7-5p expression further intensified downregulation of PARP-1 and BRCA1 in TK6-miR-7-5p cells, resulting in an increase of apoptosis and proliferation inhibited.
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http://dx.doi.org/10.1016/j.cbi.2018.01.019DOI Listing
March 2018

HMGA1 participates in MHCC97H cell proliferation and invasion through the ILK/Akt/GSK3β signaling pathway.

Mol Med Rep 2017 Dec 19;16(6):9287-9294. Epub 2017 Oct 19.

Department of Gastroenterology, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China.

Hepatocellular carcinoma (HCC) is one of the major causes of cancer‑related mortality, and the prognosis of HCC patients is unsatisfactory. It is known that the occurrence and development of HCC involves numerous genes, as well as various steps and stages in the pathological process. High mobility group AT‑hook 1 (HMGA1) and integrin‑linked kinase (ILK) may be overexpressed in HCC and may serve important roles in the development of cancer; however, the relationship between HMGA1 and ILK in HCC has not been examined. The present study demonstrated that inhibition of HMGA1 expression significantly decreased the levels of expression of ILK and the downstream elements phosphorylated (p)‑Akt, p‑glycogen synthase kinase 3β (GSK3β), matrix metalloproteinase (MMP)2, MMP9, CyclinD1 and c‑Myc. Transfection with an ILK expression vector was able to recover the decreased expression of these downstream genes, and affected cell proliferation and apoptosis. In addition, results from Transwell and wound‑healing experiments indicated that HMGA1 participates cell invasion and migration through the ILK/Akt/GSK3β pathway. The present study aimed to improve our understanding about the regulatory pathway involved in HCC and provides the basis for exploring HMGA1 inhibition as a therapy for patients with HCC and a new treatment strategy to prevent the development of HCC.
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http://dx.doi.org/10.3892/mmr.2017.7820DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779981PMC
December 2017

General design method of ultra-broadband perfect absorbers based on magnetic polaritons.

Opt Express 2017 Oct;25(20):A980-A989

Starting from one-dimensional gratings and the theory of magnetic polaritons (MPs), we propose a general design method of ultra-broadband perfect absorbers. Based on the proposed design method, the obtained absorber can keep the spectrum-average absorptance over 99% at normal incidence in a wide range of wavelengths; this work simultaneously reveals the robustness of the absorber to incident angles and polarization angles of incident light. Furthermore, this work shows that the spectral band of perfect absorption can be flexibly extended to near the infrared regime by adjusting the structure dimension. The findings of this work may facilitate the active design of ultra-broadband absorbers based on plasmonic nanostructures.
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http://dx.doi.org/10.1364/OE.25.00A980DOI Listing
October 2017

PARP‑1 may be involved in hydroquinone‑induced apoptosis by poly ADP‑ribosylation of ZO‑2.

Mol Med Rep 2017 Dec 27;16(6):8076-8084. Epub 2017 Sep 27.

Department of Environmental and Occupational Health, Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, Guangdong 523808, P.R. China.

Hydroquinone (HQ), a major reactive metabolite of benzene, contributes to benzene‑induced leukemia. The molecular mechanisms that underlie this activity remain to be elucidated. Poly ADP‑ribosylation (PARylation) is a type of reversible posttranslational modification that is performed by enzymes in the PAR polymerase (PARP) family and mediates different biological processes, including apoptosis. Zona occludens 2 (ZO‑2) is a tight junction scaffold protein, which is involved in cell proliferation and apoptosis. The present study investigated the activity and mechanisms regulated by PARP‑1 during HQ‑induced apoptosis using TK6 lymphoblastoid cells and PARP‑1‑silenced TK6 cells. The results revealed that exposure to 10 µM HQ for 72 h induced apoptosis in TK6 cells and that apoptosis was attenuated in PARP‑1‑silenced TK6 cells. In cells treated with HQ, inhibition of PARP‑1 increased the expression of B cell leukemia/lymphoma 2 (Bcl‑2), increased ATP production and reduced reactive oxygen species (ROS) production relative to the levels observed in cells treated with HQ alone. Co‑localization of ZO‑2 and PAR (or PARP‑1 protein) was determined using immunofluorescence confocal microscopy. The findings of the present study revealed that ZO‑2 was PARylated via an interaction with PARP‑1, which was consistent with an analysis of protein expression that was performed using western blot analysis, which determined that ZO‑2 protein expression was upregulated in HQ‑treated control cells and downregulated in HQ‑treated PARP‑1‑silenced TK6 cells. These findings indicated that prolonged exposure to a low dose of HQ induced TK6 cells to undergo apoptosis, whereas inhibiting PARP‑1 attenuates cellular apoptosis by activating Bcl‑2 and energy‑saving processes and reducing ROS. The present study determined that PARP‑1 was involved in HQ‑induced apoptosis by PARylation of ZO‑2.
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http://dx.doi.org/10.3892/mmr.2017.7643DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779892PMC
December 2017

Bcl-2 protects TK6 cells against hydroquinone-induced apoptosis through PARP-1 cytoplasm translocation and stabilizing mitochondrial membrane potential.

Environ Mol Mutagen 2018 01 26;59(1):49-59. Epub 2017 Aug 26.

Department of Environmental and Occupational Health, Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, 523808, China.

B cell leukemia/lymphoma-2 (Bcl-2) suppresses apoptosis by binding the BH3 domain of proapoptotic factors and thereby regulating mitochondrial membrane potential (MMP). This study aimed to investigate the role of Bcl-2 in controlling the mitochondrial pathway of apoptosis during hydroquinone (HQ)-induced TK6 cytotoxicity. In this study, HQ, one metabolite of benzene, decreased the MMP in a concentration-dependent manner and induced the generation of reactive oxygen species (ROS), the activation of the DNA damage marker γ-H2AX, and production of the DNA damage-responsive enzyme poly(ADP-ribose)polymerase-1 (PARP-1). Exposure of TK6 cells to HQ leads to an increase in Bcl-2 and co-localization with PARP-1 in the cytoplasm. Inhibition of Bcl-2 using the BH3 mimetic, ABT-737, suppressed the PARP-1 nuclear to cytoplasm translocation and sensitized TK6 cells to HQ-induced apoptosis through depolarization of the MMP. Western blot analysis indicated that ABT-737 combined with HQ increased the levels of cleaved PARP and γ-H2AX, but significantly decreased the level of P53. Thus, ABT-737 can influence PARP-1 translocation and induce apoptosis via mitochondria-mediated apoptotic pathway, independently of P53. In addition, we found that knockdown of PARP-1 attenuated the HQ-induced production of cleaved PARP and P53. These results identify Bcl-2 as a protective mediator of HQ-induced apoptosis and show that upregulation of Bcl-2 helps to localize PARP-1 to the cytoplasm and stabilize MMP. Environ. Mol. Mutagen. 59:49-59, 2018. © 2017 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/em.22126DOI Listing
January 2018

Down-regulation of miRNA-451a and miRNA-486-5p involved in benzene-induced inhibition on erythroid cell differentiation in vitro and in vivo.

Arch Toxicol 2018 Jan 21;92(1):259-272. Epub 2017 Jul 21.

Guangzhou Key Laboratory of Environmental Pollution and Health Risk Assessment, Department of Toxicology, School of Public Health, Sun Yat-sen University, Guangzhou, China.

Exposure to high-dose benzene leads to the inhibition of erythroid differentiation. However, whether lower doses of benzene exposure resemble high-dose effects in erythroid differentiation, as well as the underlying mechanisms, remains largely unknown. To identify the microRNAs (miRNAs) specifically responsible for benzene exposure and their regulatory role in erythroid differentiation, we performed miRNA microarray in CD34 hematopoietic progenitor cells isolated from human umbilical cord blood after treatment with hydroquinone (HQ), a metabolite of benzene at concentrations of 0, 1.0, 2.5, and 5.0 μM. As a result, HQ treatment inhibited erythroid differentiation in a dose-response manner. miRNA microarray analysis revealed that miRNA-451a, miRNA-486-5p and miRNA-126-3p expression were significantly lower in HQ-treated CD34 hematopoietic progenitor cells. In vitro studies showed that miRNA-451a and miRNA-486-5p were up-regulated during erythroid differentiation both in CD34 hematopoietic progenitor cells and K562 cells. The increase in the percentage of benzidine-positive cells and the expression of γ-globin in K562 cells transfected with either miRNA-451a or miRNA-486-5p mimic indicated that both miRNAs played a role in the promotion of erythroid cell differentiation. Overexpression of either miRNA-451a or miRNA-486-5p attenuated the inhibitory effects on erythroid differentiation in HQ-treated K562 cells. In vivo study showed a decreasing count of peripheral red blood cell (RBC) in C57BL/6J male mice treated with aerosol benzene at concentrations of 0, 1, 5, 25 ppm (time weight average, TWA). In addition, the expression of miRNA-451a or miRNA-486-5p was negatively correlated with the concentration of benzene inhalation on erythroid toxicity of C57BL/6J mice. Particularly, the decline in miRNA-451a and miRNA-486-5p expression appeared in male chronic benzene poisoning patients, and was correlated with a constant decrease in their RBC counts over the first 3 months after being diagnosed. These findings indicate that the suppression of miRNA-451a or miRNA-486-5p might be associated with the benzene-induced perturbation of erythroid cell differentiation.
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http://dx.doi.org/10.1007/s00204-017-2033-7DOI Listing
January 2018

Mechanism of mechanically induced optoelectronic and spintronic phase transitions in 1D graphene spirals: insight into the role of interlayer coupling.

Nanoscale 2017 Jul;9(27):9693-9700

Department of Physics, Harbin Institute of Technology, Harbin, 150001, P. R. China.

Graphene spirals (GSs), an emerging carbonic nano-material with a Riemann surface, demonstrate extraordinary topological electronic signatures: interlayer coupling similar to van der Waals (vdW) heterojunctions and intralayer coupling within the spiral conformation. Based on the state-of-the-art first-principles technique, the electronic properties of the periphery-modified GSs with geometry deformation are explored under axial strain. For all GSs, there emerges a remarkable phase transition from metal to semiconductor, due to the attenuation of interlayer "σ-bonds" reducing the interlayer tunneling probability for carriers. Analogous to graphene, GSs consist of bipartite sublattices with carbonic sp hybridization as well. Once the balance of the bipartite sublattices is lost, there will emerge intense edge (corner) states, contributed by the p orbitals. In contrast to isolated graphene nanoflakes, GSs realize the continuous spin-polarized edge (corner) state coupling with 1D morphology. However, the spin-polarization is blocked by the robust interlayer "σ-bonds" so that the spintronic transition takes place until this interlayer coupling is broken. More intriguingly, an indirect-direct bandgap transition is observed, revealing excellent optical on-off features. Their tunable properties provide great potential for their application in optoelectronics, spintronics and chemical or biological sensors.
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http://dx.doi.org/10.1039/c7nr03432fDOI Listing
July 2017

Hydroquinone induces TK6 cell growth arrest and apoptosis through PARP-1/p53 regulatory pathway.

Environ Toxicol 2017 Sep 26;32(9):2163-2171. Epub 2017 Apr 26.

Department of Environmental and Occupational Health, Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, China.

Hydroquinone (HQ), one of the most important metabolites derived from benzene, induces cell cycle arrest and apoptosis. Poly(ADP-ribose) polymerase-1 (PARP-1) participates in various biological processes, including DNA repair and cell cycle regulation. To explore whether PARP-1 regulatory pathway mediated HQ-induced cell cycle arrest and apoptosis, we assessed the effect of PARP-1 suppression on induction of apoptosis analyzed by FACSCalibur flow cytometer in PARP-1 deficientTK6 cells (TK6-shPARP-1). We observed an increase in the fraction of cells in G1 phase by 7.6% and increased apoptosis by 4.5% in PARP-1-deficient TK6 cells (TK6-shPARP-1) compared to those negative control cells (TK6-shNC cells) in response to HQ treatment. Furthermore, HQ might activate the extrinsic pathways of apoptosis via up-regulation of Fas expression, followed by caspase-3 activation, apoptotic body, and sub G1 accumulation. Enhanced p53 expression was observed in TK6-shPARP-1 cells than in TK6-shNC cells after HQ treatment. In contrast, Fas expression was lower in TK6-shPARP-1 cells than in TK6-shNC cells. Therefore, we conclude that HQ may activate apoptotic signals via Fas up-regulation and p53-mediated apoptosis in TK6-shNC cells. The reduction of PARP-1 expression further intensified up-regulation of p53 in TK6-shPARP-1 cells, resulting in an increased G1→S phase cell arrest and apoptosis in TK6-shPARP-1 cells compared to TK6-shNC cells.
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http://dx.doi.org/10.1002/tox.22429DOI Listing
September 2017

MGMT hypomethylation is associated with DNA damage in workers exposed to low-dose benzene.

Biomarkers 2017 Jul 12;22(5):470-475. Epub 2017 Jan 12.

a Guangzhou Key Laboratory of Environmental Pollution and Health Risk Assessment, Department of Toxicology, School of Public Health , Sun Yat-sen University , Guangzhou , China.

Objective: This study aims to assess the effects of low-dose benzene on DNA damage and O-methylguanine-DNA methyltransferase (MGMT) methylation in occupational workers.

Materials And Methods: We recruited 96 nonsmoking male petrochemical industry workers exposed to low-dose benzene and 100 matched control workers. Urinary S-phenylmercapturic acid (SPMA) and S-benzylmercapturic acid (SBMA) were measured for indicating internal exposure of benzene and toluene. The degree of DNA damage was determined by the Comet assay. The levels of MGMT methylation were detected quantitatively by bisulphite-PCR pyrosequencing assay.

Results: The benzene-exposed workers had significantly higher levels of urinary SPMA, degree of DNA damage but decreased MGMT methylation than the controls (all p < 0.05). In contrast, the level of urinary SBMA does not differ between benzene-exposed workers and the controls. In all participants, MGMT methylation was negatively associated with the urinary SPMA and the degree of DNA damage, indicating that epigenetic regulation might be involved in response to low-dose benzene exposure-induced genetic damage.

Discussion And Conclusion: MGMT methylation could be a potent biomarker associated with low-dose benzene exposure and benzene-induced DNA damage.
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http://dx.doi.org/10.1080/1354750X.2016.1274335DOI Listing
July 2017

Relationship between occupational stress and job burnout among rural-to-urban migrant workers in Dongguan, China: a cross-sectional study.

BMJ Open 2016 08 17;6(8):e012597. Epub 2016 Aug 17.

Department of Environmental and Occupational Health, Dongguan Key Laboratory of Environmental Medicine, School of Public Health, Guangdong Medical University, Dongguan, People's Republic of China.

Objectives: In China, there have been an increasing number of migrant workers from rural to urban areas, and migrant workers have the highest incidence of occupational diseases. However, few studies have examined the impact of occupational stress on job burnout in these migrant workers. This study aimed to investigate the relationship between occupational stress and job burnout among migrant workers.

Design: This study used a cross-sectional survey.

Setting: This investigation was conducted in Dongguan city, Guangdong Province, China.

Participants: 3806 migrant workers, aged 18-60 years, were randomly selected using multistage sampling procedures.

Primary And Secondary Outcome Measures: Multistage sampling procedures were used to examine demographic characteristics, behaviour customs and job-related data. Hierarchical linear regression and logistic regression models were constructed to explore the relationship between occupational stress and burnout.

Results: Demographics, behaviour customs and job-related characteristics significantly affected on burnout. After adjusting for the control variable, a high level of emotional exhaustion was associated with high role overload, high role insufficiency, high role boundary, high physical environment, high psychological strain, high physical strain, low role ambiguity, low responsibility and low vocational strain. A high level of depersonalisation was associated with high role overload, high role ambiguity, high role boundary, high interpersonal strain, high recreation, low physical environment and low social support. A low level of personal accomplishment was associated with high role boundary, high role insufficiency, low responsibility, low social support, low physical environment, low self-care and low interpersonal strain. Compared to the personal resources, the job strain and personal strain were more likely to explain the burnout of rural-to-urban migrant workers in our study.

Conclusions: The migrant workers have increased job burnouts in relation to occupational stress. Relieving occupational stress and maintaining an appropriate quantity and quality of work could be important measures for preventing job burnout among these workers.
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http://dx.doi.org/10.1136/bmjopen-2016-012597DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5013420PMC
August 2016

Rb silencing mediated by the down-regulation of MeCP2 is involved in cell transformation induced by long-term exposure to hydroquinone.

Mol Carcinog 2017 02 19;56(2):651-663. Epub 2016 Jul 19.

Department of Occupational Health and Occupational Medicine, Guangdong Provincial Key Laboratory of Tropical Disease Research, School of Public Health and Tropical Medicine, Southern Medical University, Guangzhou, PR China.

Hydroquinone (HQ), a metabolite of benzene, is a well-known human carcinogen; however, its molecular mechanisms of action remain unclear. MeCP2 has been traditionally described as a transcriptional repressor, though growing evidence indicates that it also activates gene expression. Here, we investigated whether some epigenetic machinery genes are aberrantly expressed as target tumor suppressor genes in HQ-transformed TK6 lymphoblastoid cells. Our results showed that treatment with 5-Aza-2'-deoxycytidine or trichostatin A enhanced the expression of Rb, resulting in cell arrest in G1-phase, and subsequently, an increase in apoptosis and a decrease in cell growth. Moreover, we hypothesised that Rb was silenced by the down-regulation of MeCP2 in HQ-transformed cells, resulting in the dynamic expression of Rb and epigenetic machinery proteins in HQ-transformed cells at different time points. The expression of Rb and MeCP2 in patients with B-cell non-Hodgkin's lymphoma (B-NHL) showed that positive staining for MeCP2 or Rb was significantly lower in B-NHL tumor tissues, and these changes were significantly and negatively correlated with the grade of B-NHL. The restoration of MeCP2 in HQ-transformed cells enhanced the expression of Rb, promoted cell apoptosis, and inhibited cell growth. The changes in the expression patterns of MeCP2 and Rb were inversely correlated with the degree of DNA methylation. A ChiP assay revealed that MeCP2 proteins were recruited to the Rb promoter with lower 5'-methylcytosine levels. In conclusion, we demonstrated that the down-regulation of MeCP2 silences Rb, a process involved in cell transformation resulting from long-term exposure to HQ. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/mc.22523DOI Listing
February 2017

A New Method for Determining the Optical Constants of Highly Transparent Solids.

Appl Spectrosc 2017 01 20;71(1):70-77. Epub 2016 Jul 20.

1 School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, China.

Highly transparent substrates are of interest for a variety of applications, but it is difficult to measure their optical constants precisely, especially the absorption index in the transparent spectral region. In this paper, a combination technique (DOPTM-EM) using both the double optical pathlength transmission method (DOPTM) and the ellipsometry method (EM) is presented to obtain the optical constants of highly transparent substrates, which overcomes the deficiencies of both the two methods. The EM cannot give accurate result of optical constants when the absorption index is very weak. The DOPTM is suitable to retrieve the weak absorption index; however, two sets of solutions exist for the retrieved refractive index and absorption index, and only one is the true value that needs to be identified. In the DOPTM-EM, the optical constants are measured first by using the EM and set as the initial value in the gradient-based inverse method used in the DOPTM, which ensures only the true optical constants are retrieved. The new method simultaneously obtains the refractive index and the absorption index of highly transparent substrate without relying on the Kramers-Kronig relation. The optical constants of three highly transparent substrates (polycrystalline BaF, CaF, and MgF) were experimentally determined within wavelength range from ultraviolet to infrared regions (0.2-14 µm). The presented method will facilitate the measurement of optical constants for highly transparent materials.
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http://dx.doi.org/10.1177/0003702816657568DOI Listing
January 2017

Implementation of Outstanding Electronic Transport in Polar Covalent Boron Nitride Atomic Chains: another Extraordinary Odd-Even Behaviour.

Sci Rep 2016 05 23;6:26389. Epub 2016 May 23.

College of Chemistry and Chemical Engineering, Chongqing University, Huxi Campus, Chongqing, 401331, P. R. China.

A theoretical investigation of the unique electronic transport properties of the junctions composed of boron nitride atomic chains bridging symmetric graphene electrodes with point-contacts is executed through non-equilibrium Green's function technique in combination with density functional theory. Compared with carbon atomic chains, the boron nitride atomic chains have an alternative arrangement of polar covalent B-N bonds and different contacts coupling electrodes, showing some unusual properties in functional atomic electronic devices. Remarkably, they have an extraordinary odd-even behavior of conductivity with the length increase. The rectification character and negative differential resistance of nonlinear current-voltage characteristics can be achieved by manipulating the type of contacts between boron nitride atomic chains bridges and electrodes. The junctions with asymmetric contacts have an intrinsic rectification, caused by stronger coupling in the C-N contact than the C-B contact. On the other hand, for symmetric contact junctions, it is confirmed that the transport properties of the junctions primarily depend on the nature of contacts. The junctions with symmetric C-N contacts have higher conductivity than their C-B contacts counterparts. Furthermore, the negative differential resistances of the junctions with only C-N contacts is very conspicuous and can be achieved at lower bias.
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http://dx.doi.org/10.1038/srep26389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4876473PMC
May 2016