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Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 973 records · Page 54Linked to original sources
PubMed1996

Magnetic resonance imaging of experimental tracheal transplantation.

RATIONALE AND OBJECTIVES: We evaluated the feasibility of using contrast-enhanced magnetic resonance (MR) imaging for in vivo monitoring of tracheal transplants in rabbits. METHODS: Plain and gadolinium-enhanced, high-resolution MR images were obtained from six rabbits 4 weeks to 6 months after an orthotopic tracheal transplantation (after heterotopic revascularization). The animals were sacrificed after the MR examination, and comparisons were made among the MR images, macroscopic observations, and histologic sections. RESULTS: All transplants were clearly identifiable on the MR images; they produced slight-to-moderate narrowing of the airway diameter. Enhancement of the transplant tissues was clearly present. There was close correspondence between the MR morphology and the macroscopic and histologic sections. CONCLUSION: MR imaging can be used to monitor in vivo tracheal transplantation after heterotopic revascularization.

Anastomosis, Surgical↗
PubMed1996

Liquid chromatography--electrospray ionization mass spectrometric detection of an ethenodeoxyguanosine adduct and its hemiaminal precursors in DNA reacted with alpha-acetoxy-N-nitrosopiperidine and cis-4-Oxo-2-pentenal.

N-Nitrosopiperidine, a carcinogenic cyclic nitrosamine that occurs in the diet and may be formed endogenously, is believed to be metabolically activated by alpha-hydroxylation. The DNA reactive compounds that could be formed in this process have been studied using alpha-acetoxy-N-nitrosopiperidine as a model. Previous studies have shown that 4-oxo-2-pentenal is one product of the hydrolysis of alpha-acetoxyNPIP and that it reacts with deoxyguanosine to produce 7-(2-oxopropyl)-5,9-dihydro-9-oxo-3-beta-D-deoxyribofuranosylimidazo+ ++ [1,2-a]purine (7-(2-oxopropyl)-1,N2-ethenodG). Several other products were formed in that reaction, and these have now been identified as diastereomers of 7-(2-oxopropyl)-5-hydroxy-5,6,7,9-tetrahydro-9-oxo-3-beta-D- deoxyribofuranosylimidazo[1,2-a]purine, the hemiaminal precursors to 7-(2-oxopropyl-1,N2-ethenodG. Their structures were characterized by electrospray ionization mass spectrometry (ESI-MS), and by reduction with NaBH4 followed by hydrolysis to 7-(2-hydroxypropyl)-5,6,7,9-tetrahydro-9-oxoimidazol [1,2-a]purine, which was characterized by 1H-NMR, MS, and UV. The presence of 7-(2-oxopropyl)-1,N2-ethenodG and its hemiaminal precursors in DNA reacted with either alpha-acetoxy-N-nitrosopiperidine or cis-4-oxo-2-pentenal was confirmed by LC-ESI-MS/MS. The results of this study demonstrate that ethenodG adducts and their precursors are present in DNA reacted with alpha-acetoxy-N-nitrosopiperidine, which suggests a possible basis for the unique carcinogenic properties of nitrosamine.

Acrolein↗
PubMed1996

Cloning of mouse integrin alphaV cDNA and role of the alphaV-related matrix receptors in metanephric development.

Metanephrogenesis has been a long-standing model to study cell-matrix interactions. A number of adhesion molecules, including matrix receptors (i.e., integrins), are believed to be involved in such interactions. The integrins contain alpha and beta s ubunits and are present in various tissues in different heterodimeric forms. In this study, one of the members of the integrin superfamily, alphaV, was characterized, and its relevance in murine nephrogenesis was investigated. Mouse embryonic renal cDNA libraries were prepared and screened for alphaV, and multiple clones were isolated and sequenced. The deduced amino acid sequence of the alpha-v cDNA clones and hydropathic analysis revealed that it has a typical signal sequence and extracellular, transmembrane, and cytoplasmic domains, with multiple Ca2+ binding sites. No A(U)nA mRNA instability motifs were present. Conformational analysis revealed no rigid long-range-ordered structure in murine alphaV. The alphaV was expressed in the embryonic kidney at day 13 of the gestation, with a transcript size of approximately 7 kb. Its expression increased progressively during the later gestational stages and in the neonatal period. It was distributed in the epithelial elements of developing nephrons and was absent in the uninduced mesenchyme. In mature metanephroi, the expression was relatively high in the glomeruli and blood vessels, as compared to the tubules. Various heterodimeric associations of alphaV, i.e., with beta1, beta3, beta5, and beta6, were observed in metanephric tissues. Inclusion of alphaV-antisense-oligodeoxynucleotide or -antibody in metanephric culture induced dysmorphogenesis of the kidney with reduced population of the nephrons, disorganization of the ureteric bud branches, and reduction of mRNA and protein expressions of alphaV. The expressions of integrin beta3, beta5, and beta6 were unaltered. These findings suggest that the integrin alphaV is developmentally regulated, has a distinct spatio-temporal expression, and is relevant in the mammalian organogenesis.

Amino Acid Sequence↗
PubMed1996

Syntaxin 4 in 3T3-L1 adipocytes: regulation by insulin and participation in insulin-dependent glucose transport.

Syntaxins are thought to be membrane receptors that bind proteins of the synaptobrevin/vesicle-associated membrane protein (VAMP) family found on transport vesicles. Recently, we detected synaptobrevin II and cellubrevin on immunopurified vesicles containing the glucose transporter 4 (GLUT4) in insulin-responsive cells. In an effort to identify the plasma membrane receptors for these vesicles, we now examine the expression of syntaxins in the 3T3-L1 adipocyte cell line. Neither syntaxin 1A nor 1B was found, in keeping with the neuronal restriction of these isoforms. In contrast, syntaxins 2 and 4 were readily detectable. By subcellular fractionation and estimation of protein yields, 67% of syntaxin 4 was localized to the plasma membrane, 24% to the low-density microsomes, and 9% to the high-density microsomes. Interestingly, acute insulin treatment decreased the content of syntaxin 4 in low-density microsomes and caused a corresponding gain in the plasma membrane fraction, reminiscent of the recruitment of GLUT4 glucose transporters. In contrast, there was no change in the distribution of syntaxin 2, which was mostly associated in the plasma membrane. A fraction of the intracellular syntaxin 4 was recovered with immunopurified GLUT4-containing vesicles. Moreover, anti-syntaxin 4 antibodies introduced in permeabilized 3T3-L1 adipocytes significantly reduced the insulin-dependent stimulation of glucose transport, in contrast to the introduction of irrelevant immunoglobulin G, which was without consequence. We propose that either the plasma membrane and/or the vesicular syntaxin 4 are involved in docking and/or fusion of GLUT4 vesicles at the cell surface of 3T3-L1 adipocytes.

3T3 Cells↗
PubMed1996

Engagement of CD45 during in vitro priming enhances antigen-specific Th cell frequencies.

CD45 is a transmembrane protein tyrosine phosphatase expressed by all lymphoid cells including T cells. Substantial experimental data has shown that CD45 maintains a permissive state for TCR signaling. The highly glycosylated extracellular domain of CD45 may be the site of interaction with regulatory lectin-like counter-receptors on antigen-presenting cells. The mAb NDA5, recognizing a unique but broadly distributed epitope of CD45, was used to study the possible immunoregulatory role of CD45 during anti-CD3 and antigen-specific CD4+ T cell activation. In vitro priming of peripheral blood mononuclear cells with peptide antigens in the presence of mAb NDA5 results in a higher frequency of antigen-specific T cells. The responses of both naive and memory T cells to peptide antigens were sensitive to mAb NDA5-enhanced priming. Anti-CD3 activation of normal resting T cells, in the presence of mAb NDA5, resulted in enhancement of tyrosine phosphorylation of specific intracellular proteins associated with TCR signal transduction. In cultures without antigen, mAb NDA5 down-regulated the cell surface expression of both CD3 and CD4, yet did not stimulate proliferation of resting T cells. Together these results suggest that engagement of CD45 during in vitro priming has a significant effect on the development of antigen-specific T cell populations.

Animals↗
PubMed1996

Functional aromatase expression in porcine adrenal gland and testis.

The expression of aromatase cytochrome P450 (P450arom) in the adrenal glands, testes, and placentas of fetal and newborn pigs was investigated. Western immunoblot analysis detected a single 48-50-kDa protein band in these tissues as well as in other porcine tissues known to express P450arom including Day 12 tubular conceptuses, theca interna, and granulosa. Slight differences in migration suggested that the P450arom protein expressed in the testis was larger than that in the adrenal gland, which was, in turn, larger than that in placenta, theca, and granulosa. Consistent with P450arom expression in these tissues, a cDNA encoding porcine P450arom hybridized to a 2.3-kb transcripts in Northern analyses of porcine blastocysts, placentas, and fetal and newborn adrenal glands and testes, as well as in theca and granulosa tissues from preovulatory follicles. No differences in transcript size were detectable among tissues. The identity of P450arom transcripts was confirmed by sequence analysis of partial cDNA clones amplified from porcine fetal adrenal glands, testes, and placentas according to the RACE procedure. The sequences of the adrenal and testis clones were identical but differed from the placental sequence, which represented the first 85 amino acids of porcine P450arom. Specifically, the adrenal and testis clones expressed transcripts that resembled the ovarian isoform of porcine P450arom, rather than the porcine placental isoform, predicting a two-amino acid deletion and 12 predicted amino acid substitutions. P450arom activity was examined to further define expression in these tissues. Activity in adrenal, testis, and placental homogenates was inhibited by 4-hydroxyandrostenedione (4OH-A4) whereas inhibition by etomidate was demonstrated in the adrenal and testis homogenates but not in the placental homogenates. The sensitivity of activity in the newborn porcine adrenal glands and testes to inhibition by etomidate was similar to that of ovarian P450arom activity. The level of P450arom activity was highest in the placenta and lowest in the adrenal gland, and no effect of fetal sex was noted in either tissue. Immunocytochemical studies localized the expression of P450arom in the adrenal gland of newborns to cells at the corticomedullary junction and, with greater intensity, to cells around the developing medullary lobules. The same cells expressed cytochrome P450 17 alpha-hydroxylase, the expression of which also extended throughout the zona fasciculata. The interstitial cells were the site of P450arom expression in the testis, but no expression could be detected in any cells with the spermatic tubules. These data demonstrate that fetal and newborn porcine adrenal glands and testes express an active P450arom that resembles the isoform expressed in the ovary. The localization of adrenal expression suggests a possible role in medullary maturation and function in the fetal and newborn pig.

Adrenal Glands↗
PubMed1996

Mucociliary clearance following segmental tracheal reversal.

Ciliated tracheal epithelium is arranged in a polarized pattern oriented according to the inferior-superior axis of the trachea and is responsible for the transport of mucus toward the larynx. In this study, ciliary beat orientation and the influence of external factors on mucociliary clearance direction were studied in rabbit inverted cervical tracheas. The animals displayed normal respiration postoperatively. After 16 weeks, airway clearance was studied by observation of the movement of silicone particles placed in the inverted segment and in normal parts of the ciliated epithelium. Cilia exhibited unidirectional and coordinated movement within inverted tracheal segments. As shown by the direction of effective flow produced by beating cilia and by scanning electron microscopy, the cilia in the inverted segment beat in the opposite direction from the cilia in the remainder of the trachea. This study demonstrated that ciliary orientation is irreversibly determined, but the reversal of ciliary beating within the cervical trachea had no adverse effects on the survival of the animals.

Animals↗
PubMed1996

The highly inducible member of the 70 kDa family of heat shock proteins increases canine distemper virus polymerase activity.

The cellular stress response is characterized by the production of heat shock proteins (HSP) which serve important cytoprotective functions. Paradoxically, in vitro induction of the stress response promotes cytopathic effect mediated by infection with canine distemper virus (CDV). The stress-mediated increase in cytopathic effect is correlated to the formation of complexes between the viral nucleocapsid (NC) and the major inducible member of the approximately 70 kDa family of HSP (hsp72). The objective of the present study was to document the functional significance of CDV NC-HSP interaction. Cytoplasmic NC was purified from Vero cells lytically infected with the Onderstepoort strain of CDV. Both ultrastructural variants of CDV NC interacted with both hsp72 and the constitutively expressed member of the approximately 70 kDa family of HSP (hsp73) in a reversible and ATP-dependent manner. An effect of hsp72/73 on NC polymerase activity was demonstrated using cell-free assays derived from either Vero or HeLa cell lines. Antibody specific to hsp72 suppressed both basal and stress-enhanced polymerase activity whereas hsp73-specific antibody had no affect. Supplementation of purified hsp72/73, but not hsp73 alone, enhanced basal polymerase activity in a dosage-dependent manner. Using purified NC variants, polymerase activity was demonstrated in pre-formed hsp72/73-NC complexes but not in NC devoid of HSP. These results suggest that the stimulatory effect of the stress response upon CDV gene expression may, in part, be mediated by a reversible and direct interaction between hsp72 and the viral core particle.

Adenosine Triphosphate↗
PubMed1996

Identification of an Arabidopsis thaliana ribulose-1,5-bisphosphate carboxylase/oxygenase activase (RCA) minimal promoter regulated by light and the circadian clock.

Transcription of the Arabidopsis thaliana gene encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is organ-specific, light-responsive, and regulated by the circadian clock. RCA is transcribed throughout the green parts of the plant, but not in roots and petals. Responses elicited by short pulses of light indicate that the light response is mediated, at least in part, by phytochrome. Analysis of transgenic tobacco and Arabidopsis carrying RCA 5' untranscribed regions fused to reporter genes (uidA, encoding beta-glucuronidase, or cat, encoding chloramphenicol acetyltransferase) indicate that elements sufficient to confer organ-specific, light-responsive, and clock-regulated transcription are localized within 317 base pairs upstream of the site of transcription initiation. A clock-responsive element sufficient to confer a low-amplitude (approximately 2-fold) circadian oscillation lies within 317 base pairs of the trascription start, but other elements necessary for high-amplitude (approximately 10-fold) circadian oscillation lie upstream of -317 and are removed by deletion from -970 to -317.

Arabidopsis↗
PubMed1996

A novel subepidermal blistering disease with autoantibodies to a 200-kDa antigen of the basement membrane zone.

Several components of the basement membrane zone (BMZ) have been identified as antigenic targets in autoimmune bullous diseases. We report a novel disease with autoantibodies to a BMZ antigen that is different from the targets described so far. The patient suffering from this disorder showed tense bullae and severe mucous membrane involvement rapidly responding to oral tetracyclines and colchicine. Histopathologic findings resembled those of dermatitis herpetiformis. Direct immunofluorescence microscopy showed linear deposits of IgG and C3 at the BMZ. By indirect immunofluorescence studies on split human skin, using both 1 M NaCl and suction blistering for dermal-epidermal separation, IgG antibodies localized exclusively to the dermal side of the split. The antibodies were mainly of the IgG4 sub-class. By Western blot analysis of epidermal and dermal extracts, the patient's serum unequivocally reacted with a dermal antigen of 200 kDa. It did not recognize bullous pemphigoid antigens (the autoantigen of epidermolysis bullosa acquisita), purified preparations of laminin-1 and laminin-5, or the recently described 105-kDa BMZ antigen. By immunoblotting of concentrated conditioned SCC-25 medium, the patient's antibodies reacted with a band of 200 kDa and several bands of lower molecular weight. No reactivity was seen with extracts of cultured human fibroblasts. By indirect immunogold electron microscopy, immunoreactants localized to the lower lamina lucida. After clearance of skin lesions, both indirect immunofluorescence and Western blot analysis became negative. This patient suffers from a novel autoimmune bullous disease with autoantibodies to a 200-kDa antigen of the BMZ.

Animals↗
PubMed1996

A novel subepidermal blistering disease with autoantibodies to a 200-kDa antigen of the basement membrane zone.

Several components of the basement membrane zone (BMZ) have been identified as antigenic targets in autoimmune bullous diseases. We report a novel disease with autoantibodies to a BMZ antigen that is different from the targets described so far. The patient suffering from this disorder showed tense bullae and severe mucous membrane involvement rapidly responding to oral tetracyclines and colchicine. Histopathologic findings resembled those of dermatitis herpetiformis. Direct immunofluorescence microscopy showed linear deposits of IgG and C3 at the BMZ. By indirect immunofluorescence studies on split human skin, using both 1 M NaCl and suction blistering for dermal-epidermal separation, IgG antibodies localized exclusively to the dermal side of the split. The antibodies were mainly of the IgG4 subclass. By Western blot analysis of epidermal and dermal extracts, the patient's serum unequivocally reacted with a dermal antigen of 200 kDa. It did not recognize bullous pemphigoid antigens, the autoantigen of epidermolysis bullosa acquisita, purified preparations of laminin-1 and laminin-5, or the recently described 105-kDa BMZ antigen. By immunoblotting of concentrated conditioned SCC-25 medium, the patient's antibodies reacted with a band of 200 kDa and several hands of lower molecular weight. No reactivity was seen with extracts of cultured human fibroblasts. By indirect immunogold electron microscopy, immunoreactants localized to the lower lamina lucida. After clearance of skin lesions, both indirect immunofluorescence and Western blot analysis became negative. This patient suffers from a novel autoimmune bullous disease with autoantibodies to a 200-kDa antigen of the BMZ.

Autoantibodies↗
PubMed1996

Tumor necrosis factor alpha and interleukin-12 contribute to resistance to the intracellular bacterium Brucella abortus by different mechanisms.

Both interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-alpha) are produced early in intracellular bacterial infection. Depletion of either IL-12 or TNF-alpha by a single injection of specific antibody 4 h before the injection of Brucella abortus 19 led to the exacerbation of infection 2 weeks later. Whereas the effect of IL-12 depletion on resistance was persistent and exacerbation was still significant 6 weeks later, the bacterial numbers in mice depleted of TNF-alpha were similar to the bacterial numbers in control infected mice by 6 weeks postinfection. Massive splenomegaly, which is often seen in 2-week Brucella-infected mice, was not observed in IL-12- or TNF-alpha-depleted mice. Both IL-12- and TNF-alpha-depleted mice showed reduced cell accumulation in the spleen compared with the massive cell accumulation in control infected mice. Granuloma formation in livers was much reduced in IL-12-depleted mice but not in TNF-alpha-depleted mice. Gamma interferon (IFN-gamma) production by cells from TNF-alpha-depleted mice was not significantly different from that of cells from control infected mice. In contrast, the production of IFN-gamma by both CD4+ and CD8+ T cells from IL-12-depleted mice was greatly reduced, compared with that from control infected mice. This effect was still observed when the antibody injection was delayed for up to 7 days postinfection, but injections of anti-IL-12 antibody into mice with established Brucella infection had no significant effect on IFN-gamma production by T cells. Taken together, these results suggested that IL-12 contributed to resistance mainly via an IFN-gamma-dependent pathway and had a profound effect on the induction of acquired cellular resistance. In contrast, TNF-alpha was involved in resistance possibly via direct action on effector cells and may not be essential for the induction of acquired cellular resistance.

Animals↗
PubMed1996

Identification of domains in rubella virus genomic RNA and capsid protein necessary for specific interaction.

In rubella virus-infected cells, genomic 40S and subgenomic 24S RNAs are present in the cytoplasm of infected cells. However, encapsidation by rubella virus capsid protein is specific for 40S genomic RNA. As a first step toward understanding the assembly of rubella virus nucleocapsid at the molecular level, the interaction between capsid protein and genomic RNA was studied by Northwestern (RNA-protein) blot analysis. RNA probes prepared by in vitro transcription were used to localize the RNA sequence that participates in binding to the capsid protein. We have identified a 29-nucleotide RNA sequence (nucleotides 347 to 375) that is essential for the binding. By using overlapping synthetic peptides of capsid protein, a peptide domain (residues 28 to 56) that displays specific RNA-binding activity of capsid protein has been located. This result suggests that the specific recognition of viral RNA during rubella virus assembly involves, at least in part, the nucleocapsid protein.

Amino Acid Sequence↗
PubMed1996

Exercise increases the plasma membrane content of the Na+ -K+ pump and its mRNA in rat skeletal muscles.

Muscle fibers adapt to ionic challenges of exercise by increasing the plasma membrane Na+-K+ pump activity. Chronic exercise training has been shown to increase the total amount of Na+-K+ pumps present in skeletal muscle. However, the mechanism of adaptation of the Na+-K+ pump to an acute bout of exercise has not been determined, and it is not known whether it involves alterations in the content of plasma membrane pump subunits. Here we examine the effect of 1 h of treadmill running (20 m/min, 10% grade) on the subcellular distribution and expression of Na+-K+ pump subunits in rat skeletal muscles. Red type I and IIa (red-I/IIa) and white type IIa and IIb (white-IIa/IIb) hindlimb muscles from resting and exercised female Sprague-Dawley rats were removed for subcellular fractionation. By homogenization and gradient centrifugation, crude membranes and purified plasma membranes were isolated and subjected to gel electrophoresis and immunoblotting by using pump subunit-specific antibodies. Furthermore, mRNA was isolated from specific red type I (red-I) and white type IIb (white-IIb) muscles and subjected to Northern blotting by using subunit-specific probes. In both red-I/IIa and white-IIa/IIb muscles, exercise significantly raised the plasma membrane content of the alpha1-subunit of the pump by 64 +/- 24 and 55 +/- 22%, respectively (P < 0.05), and elevated the alpha2-polypeptide by 43 +/- 22 and 94 +/- 39%, respectively (P < 0.05). No significant effect of exercise could be detected on the amount of these subunits in an internal membrane fraction or in total membranes. In addition, exercise significantly increased the alpha1-subunit mRNA in red-I muscle (by 50 +/- 7%; P < 0.05) and the beta2-subunit mRNA in white-IIb muscles (by 64 +/- 19%; P < 0.01), but the alpha2- and beta1-mRNA levels were unaffected in this time period. We conclude that increased presence of alpha1- and alpha2-polypeptides at the plasma membrane and subsequent elevation of the alpha1- and beta2-subunit mRNAs may be mechanisms by which acute exercise regulates the Na+-K+ pump of skeletal muscle.

Animals↗
PubMed1996

Viewpoint dependency in object representation and recognition.

In order to recognize an object from a certain viewpoint, it is necessary for the object's image from this viewpoint to match the object's representation in memory. Clearly, both information from this image and the object representation in memory determine recognition performance. However, the current debate on the viewpoint dependency of internal representations focuses only on the viewpoint dependency of the performance, and equates it directly with viewpoint dependency of the representation, excluding the possibility that a viewpoint-independent representation can also give rise to a viewpoint-dependent performance. In the latter case, the performance will only depend on the image information from the viewpoint, which is determined by the three-dimensional (3D) shape of the object, irrespective of how the internal representation is learnt. A recognition performance that depends on the views from which the representation is learnt will provide strong evidence against any viewpoint-independent representations. Such an implication was supported from this study with 3D natural objects. In particular, performance from views that shared the same visible major object parts was systematically different a result which is not predicted by the Recognition-By-Components theory (Biederman, Psychol. Rev. 94. 115-147, 1987).

Humans↗