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Biomedical subjects

L X Liu

Publications and source records attributed to L X Liu.

At least 19 recordsLinked to original sources
PubMed2005

The role of noninvasive monitoring of cerebral electrical impedance in stroke.

OBJECTIVE: To explore the change regularity of cerebral electrical impedance (CEI) in the healthy people and patients with intracerebral hemorrhage (ICH) and ischemic stroke. METHODS: CEI of 100 healthy volunteers, 52 patients with ICH and 33 patients with ischemic stroke was measured by noninvasive Brain-Edema Monitor. The results of perturbative index (PI) converted from CEI were compared with the volume of infarction, hematoma and surrounding edema, which calculated by image analyzing system according to MRI or CT. RESULTS: In the normal groups, PI in the left and right sides of cerebral hemispheres was respectively 7.76 +/- 0.75 and 7.79 +/- 0.58, and there was no significant difference between the two sides (P > 0.05). In the patients with ICH, PI in the hematoma side decreased and was lower than the other side, and then increased gradually, finally exceeded that of the other side. The average "cross" time was (16.25 +/- 8.96) h. It showed that the volume of hematoma was no obvious change before and after the "cross" time [(31.25 +/- 21.59) vs (37.59 +/- 27.57)] (P > 0.05). However, the volume of peri-hematoma edema was significantly larger after the "cross" time than before the "cross" time [(26.35 +/- 13.96) vs (14.68 +/- 5.30)] (P < 0.05). There was a positive correlation between the PI of hematoma side and the volume of peri-hematoma edema (r = 0.8811, P < 0.01). In the patients with arterothrombotic cerebral infarction, PI in the infarct side had a positive correlation with the volume of infarction (r = 0.8496, P < 0.01). CONCLUSIONS: CEI is a stable physical parameter reflecting the electrical character of human brain tissue. It is useful for monitoring edema and hematoma in stroke.

Brain↗
PubMed2001

A reverse genetic analysis of components of the Toll signaling pathway in Caenorhabditis elegans.

BACKGROUND: Both animals and plants respond rapidly to pathogens by inducing the expression of defense-related genes. Whether such an inducible system of innate immunity is present in the model nematode Caenorhabditis elegans is currently an open question. Among conserved signaling pathways important for innate immunity, the Toll pathway is the best characterized. In Drosophila, this pathway also has an essential developmental role. C. elegans possesses structural homologs of components of this pathway, and this observation raises the possibility that a Toll pathway might also function in nematodes to trigger defense mechanisms or to control development. RESULTS: We have generated and characterized deletion mutants for four genes supposed to function in a nematode Toll signaling pathway. These genes are tol-1, trf-1, pik-1, and ikb-1 and are homologous to the Drosophila melanogaster Toll, dTraf, pelle, and cactus genes, respectively. Of these four genes, only tol-1 is required for nematode development. None of them are important for the resistance of C. elegans to a number of pathogens. On the other hand, C. elegans is capable of distinguishing different bacterial species and has a tendency to avoid certain pathogens, including Serratia marcescens. The tol-1 mutants are defective in their avoidance of pathogenic S. marcescens, although other chemosensory behaviors are wild type. CONCLUSIONS: In C. elegans, tol-1 is important for development and pathogen recognition, as is Toll in Drosophila, but remarkably for the latter rôle, it functions in the context of a behavioral mechanism that keeps worms away from potential danger.

Actinomycetales↗
PubMed2001

Regulation of DAF-2 receptor signaling by human insulin and ins-1, a member of the unusually large and diverse C. elegans insulin gene family.

The activity of the DAF-2 insulin-like receptor is required for Caenorhabditis elegans reproductive growth and normal adult life span. Informatic analysis identified 37 C. elegans genes predicted to encode insulin-like peptides. Many of these genes are divergent insulin superfamily members, and many are clustered, indicating recent diversification of the family. The ins genes are primarily expressed in neurons, including sensory neurons, a subset of which are required for reproductive development. Structural predictions and likely C-peptide cleavage sites typical of mammalian insulins suggest that ins-1 is most closely related to insulin. Overexpression of ins-1, or expression of human insulin under the control of ins-1 regulatory sequences, causes partially penetrant arrest at the dauer stage and enhances dauer arrest in weak daf-2 mutants, suggesting that INS-1 and human insulin antagonize DAF-2 insulin-like signaling. A deletion of the ins-1 coding region does not enhance or suppress dauer arrest, indicating a functional redundancy among the 37 ins genes. Of five other ins genes tested, the only other one bearing a predicted C peptide also antagonizes daf-2 signaling, whereas four ins genes without a C peptide do not, indicating functional diversity within the ins family.

Amino Acid Sequence↗
PubMed2001

Vancomycin resistance reversal in enterococci by flavonoids.

The development of clinical vancomycin-resistant strains of enterococci (VRE) is a major cause for concern. Here we show that a combination of galangin or 3,7-dihydroxyflavone with vancomycin may be used to sensitize resistant strains of Enterococcus faecalis and Enterococcus faecium to the level of vancomycin-sensitive strains. Minimum inhibitory concentrations (MICs) and viable counts were determined in Iso-sensitest broth using a microtitre method. MICs of vancomycin against 67% of resistant clinical isolates and a type strain of enterococci were lowered from > 250 microg mL(-1) to < 4 microg mL(-1) in the presence of galangin (12.5 microg mL(-1)) or 3,7-dihydroxyflavone (6.25 microg mL(-1)). Viable counts for type culture E. faecalis ATCC 51299 showed the flavonoids alone significantly lowered numbers of colony forming units (CFUs). CFUs were maintained at low levels (< 10(3) CFU mL(-1)) for 24 h by vancomycin/flavone combinations. This combinational action in reversing vancomycin resistance of enterococci highlights novel drug targets and has importance in the design of new therapeutic regimes against resistant pathogens.

Anti-Bacterial Agents↗
PubMed2000

Mutation of a conserved residue (D123) required for oligomerization of human immunodeficiency virus type 1 Nef protein abolishes interaction with human thioesterase and results in impairment of Nef biological functions.

Nef is a myristoylated protein of 27 to 35 kDa that is conserved in primate lentiviruses. In vivo, Nef is required for high viral load and full pathological effects. In vitro, Nef has at least four activities: induction of CD4 and major histocompatibility complex (MHC) class I downregulation, enhancement of viral infectivity, and alteration of T-cell activation pathways. We previously reported that the Nef protein from human immunodeficiency virus type 1 interacts with a novel human thioesterase (hTE). In the present study, by mutational analysis, we identified a region of the Nef core, extending from the residues D108 to W124, that is involved both in Nef-hTE interaction and in Nef-induced CD4 downregulation. This region of Nef is located on the oligomer interface and is in close proximity to the putative CD4 binding site. One of the mutants carrying a mutation in this region, targeted to the conserved residue D123, was also found to be defective in two other functions of Nef, MHC class I downmodulation and enhancement of viral infectivity. Furthermore, mutation of this residue affected the ability of Nef to form dimers, suggesting that the oligomerization of Nef may be critical for its multiple functions.

Amino Acid Sequence↗
PubMed2000

Therapeutic target discovery using Caenorhabditis elegans.

Use of the human genome sequence in disease therapy will require efficient identification of disease-causing and disease-associated genes with functions that are amenable to pharmacological manipulation. The validation and development of such genes as therapeutic targets requires information about both the genes' functions and the biochemical pathways in which they participate. One powerful means of obtaining such information is the study of homologous genes in model organisms amenable to laboratory manipulation. Among model organisms the nematode Caenorhabditis elegans offers several advantages, including well-established techniques for genetic and experimental manipulation and the first completed genome sequence for a multicellular organism. Molecular genetic experiments using C. elegans can contribute at several levels to drug discovery programs, from elucidation of genetic functions and pathways to the validation of candidate targets. Additionally, the ease of culture allows adaptation of the nematode for use in high-throughput chemical screens for the identification of lead compounds in drug development.

Animals↗
PubMed1999

Homo- and heterodimerization of peroxisomal ATP-binding cassette half-transporters.

Mammalian peroxisomal proteins adrenoleukodystrophy protein (ALDP), adrenoleukodystrophy-related protein (ALDRP), and 70-kDa peroxisomal protein (PMP70) belong to the superfamily of ATP-binding cassette (ABC) transporters. Unlike many ABC transporters that are single functional proteins with two related halves, ALDP, ALDRP, and PMP70 have the structure of ABC half-transporters. The dysfunction of ALDP is responsible for X-linked adrenoleukodystrophy (X-ALD), a neurodegenerative disorder in which saturated very long-chain fatty acids accumulate because of their impaired peroxisomal beta-oxidation. No disease has so far been associated with mutations of adrenoleukodystrophy-related or PMP70 genes. It has been proposed that peroxisomal ABC transporters need to dimerize to exert import functions. Using the yeast two-hybrid system, we show that homo- as well as heterodimerization occur between the carboxyl-terminal halves of ALDP, ALDRP, and PMP70. Two X-ALD disease mutations located in the carboxyl-terminal half of ALDP affect both homo- and heterodimerization of ALDP. Co-immunoprecipitation demonstrated the homodimerization of ALDP, the heterodimerization of ALDP with PMP70 or ALDRP, and the heterodimerization of ALDRP with PMP70. These results provide the first evidence of both homo- and heterodimerization of mammalian ABC half-transporters and suggest that the loss of ALDP dimerization plays a role in X-ALD pathogenesis.

ATP Binding Cassette Transporter, Subfamily D↗
PubMed1999

Regulation of the insulin-like developmental pathway of Caenorhabditis elegans by a homolog of the PTEN tumor suppressor gene.

The human PTEN tumor suppressor gene is mutated in a wide variety of sporadic tumors. To determine the function of PTEN in vivo we have studied a PTEN homolog in Caenorhabditis elegans. We have generated a strong loss-of-function allele of the PTEN homolog and shown that the deficient strain is unable to enter dauer diapause. An insulin-like phosphatidylinositol 3-OH kinase (PI3'K) signaling pathway regulates dauer-stage entry. Mutations in either the daf-2 insulin receptor-like (IRL) gene or the age-1 encoded PI3'K catalytic subunit homolog cause constitutive dauer formation and also affect the life span, brood size, and metabolism of nondauer animals. Strikingly, loss-of-function mutations in the age-1 PI3'K and daf-2 IRL genes are suppressed by loss-of-function mutations in the PTEN homolog. We establish that the PTEN homolog is encoded by daf-18, a previously uncloned gene that has been shown to interact genetically with the DAF-2 IRL AGE-1 PI3'K signaling pathway. This interaction provides clear genetic evidence that PTEN acts to antagonize PI3'K function in vivo. Given the conservation of the PI3'K signaling pathway between C. elegans and mammals, the analysis of daf-18 PTEN mutant nematodes should shed light on the role of human PTEN in the etiology of metabolic disease, aging, and cancer.

Alleles↗
PubMed1999

D2S, D2L, D3, and D4 dopamine receptors couple to a voltage-dependent potassium current in N18TG2 x mesencephalon hybrid cell (MES-23.5) via distinct G proteins.

We utilized the approach of stably expressing different dopamine (DA) receptors into identified cell lines in an attempt to better understand the coupling of these receptors to membrane ion channels via second messenger systems. Recently, we examined the N18TG2 x mesencephalon (MES-23.5) cell line that is phenotypically similar to mesencephalic dopamine-containing neurons. Whole-cell voltage-clamp methods were used to investigate a voltage-dependent K+ current present in these cells. Untransfected MES-23.5 cells displayed a voltage-dependent slow-onset, slowly inactivating outward current which was not altered by bath application of either the D2 DA receptor agonist quinpirole (QUIN; 10-100 microM) or the D1 DA receptor agonist SKF38393, indicating that these cells were devoid of DA receptors. The K+ current studied was activated upon depolarization from a holding potential of -60 mV to a level more positive than -20 mV and was observed to be sensitive to bath application of tetraethylammonium. When MES-23.5 cells were transfected to stably express the D2S, D2L, D3, and D4 receptors, the same current was observed. In cells expressing D2L, D2S, and D3 receptors, application of the DA receptor agonists QUIN (1-80 microM), 7-hydroxy-dipropylaminoteralin (7-OH-DPAT, 1-80 microM), and dopamine (DA, 1-80 microM), increased the peak outward current by 35-40%. In marked contrast, cells stably expressing the D4 receptor demonstrated a significant DA agonist-induced reduction of the peak K+ current by 40%. For all four receptor subtypes, the D2-like receptor antagonist sulpiride (SUL 5 microM), when coapplied with QUIN (10 microM), totally abolished the change in K+ current normally observed, while coapplication of the D1-like receptor antagonist SCH23390 was without effect. The modulation of K+ current by D2L, D3, and D4 receptor stimulation was prevented by pretreatment of the cells with pertussis toxin (PTX, 500 ng/ml for 4 h). In addition, the intracellular application of a polyclonal antibody which specifically recognizes Goalpha completely blocked the ability of D2L, D3, and D4 receptors to modulate outward K+ currents. In contrast, the intracellular application of an antibody directed against Goalpha was without effect, whereas intracellular application of an antibody recognizing Gsalpha abolished the ability of the D2S receptor to enhance K+ current. These findings demonstrate that different members of the D2 DA receptor family may couple in a given cell to a common effector in dramatically different ways.

Animals↗
PubMed1999

High-throughput isolation of Caenorhabditis elegans deletion mutants.

The nematode Caenorhabditis elegans is the first animal whose genome is completely sequenced, providing a rich source of gene information relevant to metazoan biology and human disease. This abundant sequence information permits a broad-based gene inactivation approach in C. elegans, in which chemically mutagenized nematode populations are screened by PCR for deletion mutations in a specific targeted gene. By handling mutagenized worm growth, genomic DNA templates, PCR screens, and mutant recovery all in 96-well microtiter plates, we have scaled up this approach to isolate deletion mutations in >100 genes to date. Four chemical mutagens, including ethyl methane sulfonate, ethlynitrosourea, diepoxyoctane, and ultraviolet-activated trimethylpsoralen, induced detectable deletions at comparable frequencies. The deletions averaged approximately 1400 bp in size when using a approximately 3 kb screening window. The vast majority of detected deletions removed portions of one or more exons, likely resulting in loss of gene function. This approach requires only the knowledge of a target gene sequence and a suitable mutagen, and thus provides a scalable systematic approach to gene inactivation for any organism that can be handled in high density arrays.

Algorithms↗
PubMed1999

Interaction with the p6 domain of the gag precursor mediates incorporation into virions of Vpr and Vpx proteins from primate lentiviruses.

Vpr and Vpx proteins from human and simian immunodeficiency viruses (HIV and SIV) are incorporated into virions in quantities equivalent to those of the viral Gag proteins. We demonstrate here that Vpr and Vpx proteins from distinct lineages of primate lentiviruses were able to bind to their respective Gag precursors. The capacity of HIV type 1 (HIV-1) Vpr mutants to bind to Pr55(Gag) was correlated with their incorporation into virions. Molecular analysis of these interactions revealed that they required the C-terminal p6 domain of the Gag precursors. While the signal for HIV-1 Vpr binding lies in the leucine triplet repeat region of the p6 domain reported to be essential for incorporation, SIVsm Gag lacking the equivalent region still bound to SIVsm Vpr and Vpx, indicating that the determinants for Gag binding are located upstream of this region of the p6 domain. Binding to Gag cleavage products showed that HIV-1 Vpr interacted directly with the nucleocapsid protein (NC), whereas SIVsm Vpr and Vpx did not interact with NC but with the p6 protein. These results (i) reveal differences between HIV-1 and SIVsm for the p6 determinants required for Vpr and Vpx binding to Gag and (ii) suggest that HIV-1 Vpr and SIVsm Vpr and Vpx interact with distinct cleavage products of the precursor following proteolytic processing in the virions.

Amino Acid Sequence↗
PubMed1998

Characterization of the myoglobin and its coding gene of the mollusc Biomphalaria glabrata.

A cDNA clone isolated from a Biomphalaria glabrata (Mollusca, Gastropoda) neural cDNA library was identified as encoding a myoglobin-like protein of 148 amino acids with a single domain and a calculated mass of 16,049.29. Alignment with globin sequences with known tertiary structure confirms its overall globin nature. The expressed myoglobin was identified in the radular muscle and isolated. Oxygen equilibrium measurements on the protein reveal a high oxygen affinity. Val-B10 and Gln-E7, important residues for the determination of the oxygen affinity, are strikingly different from the standard molluscan pattern (Conti, E., Moser, C., Rizzi, M., Mattevi, A., Lionetti, C., Coda, A., Ascenzi, P., Brunori, M., Bolognesi, M. (1993) J. Mol. Biol. 233, 498-508). The single gene encoding the globin chain is interrupted by three introns at positions A3.2, B12.2, and G7.0. Comparison with other nonvertebrate globin genes reveals on the one hand conservation (B12.2 and G7.0) and on the other hand variability of the insertion positions (A3.2). The Biomphalaria myoglobin sequence was used together with all other molluscan globin sequences available to assess the origin and phylogeny of the phylum. Our results confirm the doubts raised about monophyletic origin of the Mollusca, which was first observed using SSU rRNA as a molecular marker.

Amino Acid Sequence↗
PubMed1998

A molecular evolutionary framework for the phylum Nematoda.

Nematodes are important: parasitic nematodes threaten the health of plants, animals and humans on a global scale; interstitial nematodes pervade sediment and soil ecosystems in overwhelming numbers; and Caenorhabditis elegans is a favourite experimental model system. A lack of clearly homologous characters and the absence of an informative fossil record have prevented us from deriving a consistent evolutionary framework for the phylum. Here we present a phylogenetic analysis, using 53 small subunit ribosomal DNA sequences from a wide range of nematodes. With this analysis, we can compare animal-parasitic, plant-parasitic and free-living taxa using a common measurement. Our results indicate that convergent morphological evolution may be extensive and that present higher-level classification of the Nematoda will need revision. We identify five major clades within the phylum, all of which include parasitic species. We suggest that animal parasitism arose independently at least four times, and plant parasitism three times. We clarify the relationship of C. elegans to major parasitic groups; this will allow more effective exploitation of our genetic and biological knowledge of this model species.

Animals↗
PubMed1998

Large-scale taxonomic profiling of eukaryotic model organisms: a comparison of orthologous proteins encoded by the human, fly, nematode, and yeast genomes.

Comparisons of DNA and protein sequences between humans and model organisms, including the yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster, are a significant source of information about the function of human genes and proteins in both normal and disease states. Important questions regarding cross-species sequence comparison remain unanswered, including (1) the fraction of the metabolic, signaling, and regulatory pathways that is shared by humans and the various model organisms; and (2) the validity of functional inferences based on sequence homology. We addressed these questions by analyzing the available fractions of human, fly, nematode, and yeast genomes for orthologous protein-coding genes, applying strict criteria to distinguish between candidate orthologous and paralogous proteins. Forty-two quartets of proteins could be identified as candidate orthologs. Twenty-four Drosophila protein sequences were more similar to their human orthologs than the corresponding nematode proteins. Analysis of sequence substitutions and evolutionary distances in this data set revealed that most C. elegans genes are evolving more rapidly than Drosophila genes, suggesting that unequal evolutionary rates may contribute to the differences in similarity to human protein sequences. The available fraction of Drosophila proteins appears to lack representatives of many protein families and domains, reflecting the relative paucity of genomic data from this species.

Animals↗
PubMed1997

GPIIIa-(49-66) is a major pathophysiologically relevant antigenic determinant for anti-platelet GPIIIa of HIV-1-related immunologic thrombocytopenia.

High-affinity (Kd = 1 x 10(-9) M) anti-platelet GPIIIa has been isolated from serum immune complexes of immunologic thrombocytopenic HIV-1-infected patients (HIV-1-ITP). Affinity-purified anti-platelet antibody reacted with a recombinant GPIIIa-(1-200) and -(1-66) fusion peptide and with an 18-mer GPIIIa-(49-66) peptide but not with seven other GPIIIa peptides spanning the length of GPIIIa. Most of the anti-platelet antibody ( approximately 85%) could be adsorbed to and eluted from a GPIIIa-(49-66) affinity column. Binding of antibody to platelets could be inhibited by GPIIIa-(49-66) or an equimolar peptide-albumin conjugate (IC50 = 2 microM). Sera from 7 control subjects and 10 classic autoimmune thrombocytopenic patients gave background reactivity with GPIIIa-(49-66). HIV-1-ITP sera from 16 patients reacted with a mean OD 6-fold greater than background (range, 4- to 9-fold). Serum anti-GPIIIa-(49-66) concentration correlated inversely with platelet count, R2 = 0.51, n = 31, P < 0. 0001. Because mouse platelet GPIIIa-(49-66) has 83% homology with human GPIIIa and mouse monocytes contain Fc receptors for the human IgG1-kappa/lambda antibody, we determined the in vivo effect of human anti-GPIIIa on mouse platelets. Affinity-purified antibody, 25-50 microg given i.p., resulted in a precipitous drop in platelet count to 30% of baseline, with nadir at 4 hr and return to normal in 36 hr. No effect was noted with control IgG. Acute thrombocytopenia could be prevented or reversed by the injection of the GPIIIa-(49-66) albumin conjugate at zero time or 2 hr after antibody, respectively, but not with a scrambled peptide-albumin conjugate. Thus HIV-1-ITP patients have high-affinity anti-platelet GPIIIa against a major antigenic determinant, GPIIIa-(49-66), which correlates inversely with platelet count and induces thrombocytopenia in mice.

Animals↗
PubMed1997

Binding of HIV-1 Nef to a novel thioesterase enzyme correlates with Nef-mediated CD4 down-regulation.

Nef is a 27-kDa myristoylated protein conserved in primate lentiviruses. In vivo, simian immunodeficiency virus Nef is required in macaques to produce a high viral load and full pathological effects. Nef has at least three major effects in vitro, induction of CD4 down-regulation, alteration of T cell activation pathways, and enhancement of viral infectivity. We have used the yeast two-hybrid system to identify cellular proteins that interact with HIV-1Lai Nef and could mediate Nef function. A human cDNA was isolated that encodes a new type of thioesterase, an enzyme that cleaves thioester bonds. This novel thioesterase is unlike the animal types I and II thioesterases previously cloned but is homologous to the Escherichia coli thioesterase II. Nef and this thioesterase interact in vitro and are co-immunoprecipitated by anti-Nef antibodies in CEM cells expressing Nef. Nef alleles from human immunodeficiency virus-1 (HIV-1) isolates unable to down-regulate CD4 do not react or react poorly with thioesterase. An HIV-1 NefLai mutant selected for its lack of interaction with thioesterase was also unable to down-regulate CD4 cell-surface expression. These observations suggest that this human thioesterase is a cellular mediator of Nef-induced CD4 down-regulation.

Alleles↗
PubMed1997

Structure and expression of a novel filarial gene for glia maturation factor.

Factors that influence neural growth and development in parasitic nematodes have not yet been identified. We have isolated and sequenced a Brugia malayi nematode 3.4-kb genomic DNA fragment and its corresponding cDNA, which encode a predicted protein of 138 amino acids with 52% identity and 75% similarity to the mammalian neuroglial growth factor, glia maturation factor-beta (GMF). GMF promotes the differentiation of mammalian glia and neurons and stimulates axonal regeneration. The filarial nematode gene Bmgmf for Brugia malayi glia maturation factor contains six predicted exons, with the first exon encoding only the initiation methionine. Brugia malayi GMF (BmGMF) is also related to a large family of eukaryotic actin depolymerizing factors (ADFs). Although BmGMF does not contain the consensus actin-depolymerizing motif of ADFs, it does share a similar intron exon structure, including the unusual first exon, with the unc-60 ADF gene of the nematode Caenorhabditis elegans. RT-PCR experiments reveal that BmGMF is trans-spliced with the nematode spliced leader sequence SL1 and is expressed in microfilariae but not in third-stage larvae or adult worms. We speculate that BmGMF may function as a stage-specific neuroglial growth factor.

Actin Depolymerizing Factors↗