Biomedical subjects

Y Liu

Publications and source records attributed to Y Liu.

At least 55 records · Page 3Linked to original sources

PubMed2006

Enhancement of cell attachment and tissue integration by a IKVAV containing multi-domain peptide.

Laminin contains a number of cell binding motifs including IKVAV and some that bind heparin. We developed a multi-domain synthetic peptide, LA2, which combines IKVAV sequences with a heparin-binding domain with the goal of improving cell attachment to otherwise non-adherent substrates. LA2 was used to coat polystyrene, ethyl vinyl acetate (EVA), expanded polytetrafluoroethylene (ePTFE), polycarbonate, titanium and stainless steel. In cell attachment studies, LA2 dramatically increased cell attachment to polystyrene and EVA compared to uncoated counterparts or those coated with SIKVAV. Similar increases were observed on ePTFE and titanium. On polystyrene, LA2 enhanced the attachment of endothelial cells, smooth muscle cells, epithelial cells, myoblasts, and osteoblast progenitor cells. Following adhesion, the cells underwent proliferation to form confluent monolayers with phenotypic morphologies. Using osteoblast progenitor cells (MC3T3 cells) grown on LA2/polystyrene, the cells exhibited an increased production of a differentiation marker, alkaline phosphatase. In vivo, LA2 improved tissue integration into ePTFE when implanted subcutaneously in rats. After 2 weeks, cells had penetrated deep into the LA2 coated ePTFE implant whereas little cell penetration was found in uncoated grafts. The implant sites exhibited little inflammation or other untoward effects. The results indicated that the LA2 peptide improved cell adhesion and tissue integration and might be useful in a number of tissue engineering applications.

Animals↗

PubMed2006

Nonlinear absorption and Raman gain in helium-ion-implanted silicon waveguides.

We study whether helium ion implantation can reduce the carrier lifetime and thus reduce the density of two-photon-absorption-generated free carriers. Our experiments and theoretical model show that helium ion implantation into silicon waveguides can successfully reduce the free-carrier losses and allow net gain to be attained by cw-pumped stimulated Raman scattering without requiring reverse bias to remove the photogenerated free carriers.

Journal Article↗

PubMed2006

AFM colloidal forces measured between microscopic probes and flat substrates in nanoparticle suspensions.

Colloidal forces between atomic force microscopy probes of 0.12 and 0.58 N/m spring constant and flat substrates in nanoparticle suspensions were measured. Silicon nitride tips and glass spheres with a diameter of 5 and 15 mum were used as the probes whereas mica and silicon wafer were used as substrates. Aqueous suspensions were made of 5-80 nm alumina and 10 nm silica particles. Oscillatory force profiles were obtained using atomic force microscope. This finding indicates that the nanoparticles remain to be stratified in the intervening liquid films between the probe and substrate during the force measurements. Such structural effects were manifested for systems featuring attractive and weak repulsive interactions of nanoparticles with the probe and substrate. Oscillation of the structural forces shows a periodicity close to the size of nanoparticles in the suspension. When the nanoparticles are oppositely charged to the probes, they tend to coat the probes and hinder probe-substrate contact.

Journal Article↗

PubMed2006

Association of preconceptional health care utilization and early initiation of prenatal care.

OBJECTIVE: To assess whether women having preconceptional health care utilization were more likely to have early initiation of prenatal care than were women not having preconceptional health care utilization. STUDY DESIGN: In this cohort study, data were collected prospectively from a population-based Perinatal Health Care Surveillance System in China. The analysis included 195 796 women who delivered single live births in 13 cities/counties during 1997 to 2000. Mantel-Haenszel test was employed to calculate risk ratios and 95% confidence intervals (CI). Multivariate logistic regression was conducted to assess the association between preconceptional health care utilization and early initiation of prenatal care after controlling for maternal residence, age at delivery, educational attainment, occupation, parity, preconceptional medical disorders, and high-risk medical experiences during the first trimester. SPSS 11.5 (SPSS Inc.) was employed for data analysis. RESULTS: Women having preconceptional health care utilization were 2.6 times (95%CI: 2.5 to 2.6) more likely to have early initiation of prenatal care compared with women not having preconceptional health care utilization. When stratified by maternal residence, age at delivery, educational attainment, occupation, parity, preconceptional medical disorder, high-risk medical experiences during the first trimester, and preconceptional medical disorders, this association still existed. After controlling for stratification factors mentioned above and the interaction of maternal age, educational attainment, and parity, women having preconceptional health care utilization were 2.7 times (95%CI: 2.6 to 2.8) more likely to have early initiation of prenatal care than were women not having preconceptional health care utilization. CONCLUSION: Women who had preconceptional health care utilization were more likely to have early prenatal care than were women not having preconceptional health care utilization.

Adult↗

PubMed2006

Protein serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities.

We have previously demonstrated that the serine/threonine protein phosphatase-1 (PP-1) plays an important role in promoting cell survival. However, the molecular mechanisms by which PP-1 promotes survival remain largely unknown. In the present study, we provide evidence to show that PP-1 can directly dephosphorylate a master regulator of apoptosis, p53, to negatively modulate its transcriptional and apoptotic activities, and thus to promote cell survival. As a transcriptional factor, the function of p53 can be greatly regulated by phosphorylation and dephosphorylation. While the kinases responsible for phosphorylation of the 17 serine/threonine sites have been identified, the dephosphorylation of these sites remains largely unknown. In the present study, we demonstrate that PP-1 can dephosphorylate p53 at Ser-15 and Ser-37 through co-immunoprecipitation, in vitro and in vivo dephosphorylation assays, overexpression and silence of the gene encoding the catalytic subunit for PP-1. We further show that mutations mimicking constitutive dephosphorylation or phosphorylation of p53 at these sites attenuate or enhance its transcriptional activity, respectively. As a result of the changed p53 activity, expression of the downstream apoptosis-related genes such as bcl-2 and bax is accordingly altered and the apoptotic events are either largely abrogated or enhanced. Thus, our results demonstrate that PP-1 directly dephosphorylates p53, and dephosphorylation of p53 has as important impact on its functions as phosphorylation does. In addition, our results reveal that one of the molecular mechanisms by which PP-1 promotes cell survival is to dephosphorylate p53, and thus negatively regulate p53-dependent death pathway.

Amino Acid Substitution↗

PubMed2006

Cyclin-dependent kinase 2 is dispensable for normal centrosome duplication but required for oncogene-induced centrosome overduplication.

Cyclin-dependent kinase 2 (CDK2) has been proposed to function as a master regulator of centrosome duplication. Using mouse embryonic fibroblasts (MEFs) in which Cdk2 has been genetically deleted, we show here that CDK2 is not required for normal centrosome duplication, maturation and bipolar mitotic spindle formation. In contrast, Cdk2 deficiency completely abrogates aberrant centrosome duplication induced by a viral oncogene. Mechanistically, centrosome overduplication in MEFs wild-type for Cdk2 involves the formation of supernumerary immature centrosomes. These results indicate that normal and abnormal centrosome duplication have significantly different requirements for CDK2 activity and point to a role of CDK2 in licensing centrosomes for aberrant duplication. Furthermore, our findings suggest that CDK2 may be a suitable therapeutic target to inhibit centrosome-mediated chromosomal instability in tumor cells.

Animals↗

PubMed2006

Observation of strong quantum depletion in a gaseous Bose-Einstein condensate.

We studied quantum depletion in a gaseous Bose-Einstein condensate. An optical lattice enhanced the atomic interactions and modified the dispersion relation resulting in strong quantum depletion. The depleted fraction was directly observed as a diffuse background in the time-of-flight images. Bogoliubov theory provides a semiquantitative description for our observations of depleted fractions in excess of 50%.

Journal Article↗

PubMed2006

Fatty acid oxidation is a dominant bioenergetic pathway in prostate cancer.

Most malignancies have increased glycolysis for energy requirement of rapid cell proliferation, which is the basis for tumor imaging through glucose analog FDG (2-deoxy-2-fluoro-D-glucose) with positron emission tomography. One of significant characteristics of prostate cancer is slow glycolysis and low FDG avidity. Recent studies showed that prostate cancer is associated with changes of fatty acid metabolism. Several enzymes involved in the metabolism of fatty acids have been determined to be altered in prostate cancer relative to normal prostate, which is indicative of an enhanced beta-oxidation pathway in prostate cancer. Increased fatty acid utilization in prostate cancer provides both ATP and acetyl-coenzyme A (CoA); subsequently, increased availability of acetyl-CoA makes acceleration of citrate oxidation possible, which is an important energy source as well. Dominant fatty acid metabolism rather than glycolysis has the potential to be the basis for imaging diagnosis and targeted treatment of prostate cancer.

Carcinoma↗

PubMed2006

Oncolytic adenoviral vector carrying the cytosine deaminase gene for melanoma gene therapy.

We constructed an oncolytic adenoviral vector Ad.HE1HCD3, in which the adenoviral E1A promoter was replaced by a human tyrosinase enhancer (HTE)/promoter. The RGD-4C peptide was inserted into the HI loop of the fiber knob domain to increase the transduction efficiency of this vector for tumor cell lines. We also inserted the prodrug activating cytosine deaminase gene driven by the HTE/promoter into the E3 region of the Ad.HE1HCD3 vector. The in vitro cytotoxic effect of the Ad.HE1HCD3 vector with 5-fluorocytosine (5-FC) was greater than that of a wild-type adenovirus or that of the Ad.HE1HCD3 vector alone in tyrosinase-positive melanoma cell lines at low multiplicity of infection. Intratumoral injection of low doses of the Ad.HE1HCD3 vector into xenotransplanted human melanoma cell lines followed by the intraperitoneal injection of 5-FC led to a greater degree of tumor regression in vivo than did the intratumoral injection of the same dose of the Ad.HE1HCD3 vector alone. This oncolytic vector with a melanoma-specific prodrug activation therapeutic transcription unit and a RGD targeted fiber protein offers a potent therapeutic combination for the gene therapy of melanoma.

Adenoviridae↗

PubMed2006

Sub-38 nm resolution tabletop microscopy with 13 nm wavelength laser light.

We have acquired images with a spatial resolution better than 38 nm by using a tabletop microscope that combines 13 nm wavelength light from a high-brightness tabletop laser and Fresnel zone plate optics. These results open a gateway to the development of compact and widely available extreme-ultraviolet imaging tools capable of inspecting samples in a variety of environments with a 15-20 nm spatial resolution and a picosecond time resolution.

Journal Article↗

PubMed2006

Msh2 deficiency leads to chromosomal abnormalities, centrosome amplification, and telomere capping defect.

Msh2 is a key mammalian DNA mismatch repair (MMR) gene and mutations or deficiencies in mammalian Msh2 gene result in microsatellite instability (MSI+) and the development of cancer. Here, we report that primary mouse embryonic fibroblasts (MEFs) deficient in the murine MMR gene Msh2 (Msh2(-/-)) showed a significant increase in chromosome aneuploidy, centrosome amplification, and defective mitotic spindle organization and unequal chromosome segregation. Although Msh2(-/-) mouse tissues or primary MEFs had no apparent change in telomerase activity, telomere length, or recombination at telomeres, Msh2(-/-) MEFs showed an increase in chromosome end-to-end fusions or chromosome ends without detectable telomeric DNA. These data suggest that MSH2 helps to maintain genomic stability through the regulation of the centrosome and normal telomere capping in vivo and that defects in MMR can contribute to oncogenesis through multiple pathways.

Animals↗

PubMed2006

Prion protein gene (PRNP) polymorphisms in Xinjiang local sheep breeds in China.

Amino acid polymorphisms of the prion protein (PrP) gene (PRNP), particularly those occurring at codons 136, 154, and 171 have a significant influence on scrapie pathogenesis in many sheep breeds. We isolated blood samples from 222 sheep representing the eight main local sheep breeds in the Xinjiang Autonomous Region, the territory with the most abundant local sheep breeds in China, to identify the PRNP polymorphisms and to determine whether these breeds were at risk for developing scrapie. A new PRNP polymorphism encoding either glycine (G) or arginine (R) at codon 85 as well as eight previously reported polymorphisms at codons 101, 112, 127, 141, 146, 154, 171, and 189 in other sheep breeds were detected. Interestingly, the alanine (A)/V polymorphism at codon 136 was not observed in this study, all sheep being homozygous for A at this position. While the previously identified polymorphism of argine (R) or histidine (H) at codon 154 was detected, the H polymorphism was rare (2.25%). Four polymorphisms at codon 171 encoding glutamine (Q), R, H, or lysine (K) were detected. The predominant ARQ allele occurred at a high frequency of 77.48%, suggesting an increased risk of scrapie in Xinjiang Autonomous Region.

Alleles↗

PubMed2006

Proline oxidase activates both intrinsic and extrinsic pathways for apoptosis: the role of ROS/superoxides, NFAT and MEK/ERK signaling.

Proline oxidase (POX), often considered a 'housekeeping enzyme' might play an important role in apoptosis. We have shown that POX generated proline-dependent reactive oxygen species (ROS), specifically superoxide radicals, and induced apoptosis through the mitochondrial (intrinsic) pathway. In our current report, we used DLD-1 colorectal cancer cells stably transfected with the POX gene under the control of a tetracycline-inducible promoter and found POX-stimulated expression of tumor necrosis factor-related apoptosis inducing ligand (TRAIL), DR5 and cleavage of caspase-8. Importantly, apoptosis measured by flow cytometry was partially inhibited by Z-IETD-FMK, a specific inhibitor of caspase-8. These findings suggest that the extrinsic (death receptor) pathway also is activated by POX. Furthermore, the mechanism of this effect on the extrinsic pathway, specifically, the induction of TRAIL by POX, may be mediated by NFAT transcription factors. Additionally, POX expression also dramatically decreased phosphorylation of MEK and ERK, and the decrease was partially reversed by expression of manganese superoxide dismutase (MnSOD). Overexpression of constitutively active form of MEK, acMEK, partially blocked POX-induced apoptosis. These findings suggest the involvement of MEK/ERK signaling and further confirm the role of ROS/superoxides in POX-induced apoptosis. Combined with previously published data, we conclude that POX may induce apoptosis through both intrinsic and extrinsic pathways and is involved in nuclear factor of activated T cells (NFAT) signaling and regulation of the MEK/ERK pathway. It is suggested that, as a nutrition factor, POX may modulate apoptosis signals induced by p53 or other anti-cancer agents and enhance apoptosis in stress situations.

Apoptosis↗

PubMed2006

Tumor-specific therapeutic effect induced by an oncolytic adenoviral vector containing heat shock protein 70 and prodrug activation genes.

We constructed a melanoma-specific oncolytic adenoviral vector Ad.MCDIRESE1.71Hsp3, in which the cytosine deaminase and adenoviral E1A genes linked by the IRES sequence were under the control of a mouse tyrosinase enhancer/promoter transcriptional element in the E1 region of the vector. We also inserted the human heat shock protein 70 (Hsp70) gene driven by the cytomegalovirus promoter into the E3 region of this vector. The RGD-4C peptide was inserted into the HI loop of the fiber knob domain of the Ad.MCDIRESE1.71Hsp3 vector to increase the transduction efficiency of this vector to tumor cells. The Ad.MCDIRESE1.71Hsp3 vector replicates specifically in melanoma cells, and it has a melanoma-specific cytotoxic effect in the presence of 5-fluorocytosine in vitro and in vivo. Moreover, the in vivo killing of tumor cells associated with the overexpression of Hsp70 generated by the intratumoral injection of the Ad.MCDIRESE1.71Hsp3 vector into established subcutaneous tumors can lead to the suppression of tumor growth and potent melanoma-specific systemic immune responses.

Adenoviridae↗

PubMed2006

Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders.

This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders (n=8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group 2 ganders (n=8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August-March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season.

Animals↗

PubMed2006

Development of a multifunctional and efficient conjugal plasmid for use in Streptomyces spp.

A plasmid, pGB112, has recently been developed to transfer DNA from Escherichia coli to Streptomyces spp via conjugation. This technique made use of (A) E. coli replicon, (B) ampicillin (amp) resistance gene for selection in E. coli and thiostrepton (tsr) resistance gene for selection in Streptomyces, (C) a fragment of SCP2* replicon, (D) a 2.6 kb fragment of tra-cassette which consists of pIJ101 transfer gene (tra) and two ermE promoters, (E) a 0.8 kb fragment of oriT of (IncP) RK2. The results showed that this plasmid was able to transfer plasmid DNA from E. coli to Streptomyces coelicolor via conjugation, and that it could also transfer DNA between Streptomyces strains. Since this plasmid has both pBR322 and SCP2* replicons, it may provide a novel and useful method for genetic operation in E. coli and Streptomyces.

Conjugation, Genetic↗

PubMed2006

Surface free energy effect on bacterial retention.

Bacterial infection is one of the most frequent and severe complications in the long-term effectiveness of medical implants and devices, greatly increasing treatment cost and inconvenience to the patient. Surface physical and chemical properties are known to influence the extent and form of bacterial infection, although the exact correlation with specific properties is difficult due to the complexity of the system. One approach in the attempt to reduce the bacterial colonisation is to modify the surface energy and chemistry, so as to influence the interactions between the surface and the bacteria that come into contact with it. Five types of coatings were investigated in this study, together with silicone, and polished and non-polished stainless steel 316L. Surfaces were tested for retention of Pseudomonas aeruginosa AK1 after 1h. A good correlation (>90%) was found between P. aeruginosa AK1 retention and total surface free energy, as well as its polar and dispersive components. The minimum level of P. aeruginosa AK1 retention was found for a range of total surface free energy in the range 20-27 mN/m.

Bacterial Adhesion↗

PubMed2006

Comparison of haemodynamic responses to orotracheal intubation with GlideScope videolaryngoscope and fibreoptic bronchoscope.

BACKGROUND AND OBJECTIVE: The GlideScope videolaryngoscope is a newly developed laryngoscope for tracheal intubation recently introduced into clinical anaesthesia. In this randomised clinical study, we compared the haemodynamic responses to orotracheal intubation using a GlideScope videolaryngoscope and a fibreoptic bronchoscope. METHODS: Fifty-six adult patients, ASA I-II scheduled for elective plastic surgery under general anaesthesia requiring orotracheal intubation were randomly allocated to either the GlideScope videolaryngoscope group or the fibreoptic bronchoscope group. After a standard intravenous anaesthetic induction, orotracheal intubation was performed. Noninvasive blood pressure and heart rate were recorded before and after induction, at intubation and for 5 min after intubation at 1 min intervals. RESULTS: As compared with the post-induction values the orotracheal intubations using a fibreoptic bronchoscope and a GlideScope videolaryngoscope resulted in the significant increases in blood pressures which did not exceed their baseline values. In the two groups, heart rates at intubation and within 2 min after intubation were significantly higher than their baseline values. However, there were no significant differences in blood pressures and heart rates at all time points, their maximal values and maximal percent changes during the observation and the times required to reach their maximal values between the two groups. CONCLUSIONS: The orotracheal intubations using a fibreoptic bronchoscope and a GlideScope videolaryngoscope produce similar haemodynamic responses.

Adolescent↗