Biomedical subjects

S Xu

Publications and source records attributed to S Xu.

At least 19 recordsLinked to original sources

PubMed1998

Relative importance of cytotoxic T lymphocytes and nitric oxide-dependent cytotoxicity in contractile dysfunction of rejecting murine cardiac allografts.

BACKGROUND: Previous in vitro studies have suggested that both cytotoxic T lymphocyte (CTL)-mediated and non-CTL-mediated myocyte lysis occur during murine cardiac heterotopic allograft rejection, but the relative importance of these injury mechanisms on myocardial function is not established. We therefore compared the in vivo effects of depletion of CTL and inhibition of nitric oxide synthase (NOS) on contractility of the rejecting heart. METHODS: Syngeneic (BALB/c into BALB/c) and allogeneic (BALB/c into C57/B16) heterotopic abdominal cardiac transplants were performed. In some of the allogeneic transplants, CD8+ lymphocytes were depleted by intraperitoneal injection of anti-CD8 monoclonal antibody. NOS inhibition was accomplished by continuous infusion of NG-monomethyl-L-arginine via a subcutaneous osmotic pump. Five days after transplantation, the abdominal cavity was opened and the transplanted heart exposed. Base to apex developed force was measured during spontaneous beating at a diastolic stretch of 4 g by placing a suture through the apex of the heart and attaching it to a strain gauge. Effects of interventions on graft survival were determined by recording the days required for loss of palpable graft contractions. RESULTS: Allogeneic hearts showed a significant reduction in systolic force compared to non-rejecting syngeneic hearts. Depletion of CD8+ cells improved contractility significantly relative to non-depleted allogeneic hearts, but contractility remained significantly reduced relative to syngeneic hearts. Developed force in allogeneic hearts was also improved by NOS inhibition (P<0.01), and NG-monomethyl-L-arginine infusion slightly prolonged graft survival. CONCLUSION: Both CTL-mediated and NOS-dependent (possibly macrophage-mediated) mechanisms contribute to contractile dysfunction during early cardiac allograft rejection in this model. However, NOS inhibition combined with CTL depletion only slightly prolongs graft survival in this model.

Animals↗

PubMed1998

Apolipoprotein(a) binds to low-density lipoprotein at two distant sites in lipoprotein(a).

Lipoprotein(a) [Lp(a)] consists of low-density lipoprotein (LDL) and apolipoprotein(a) [apo(a)] linked with a disulfide bond. Scanning force microscopy (SFM) of Lp(a) showed, for the first time, a belt-like structure of apo(a) with both ends attached to a spherical LDL. The two ends of apo(a) were bound to the LDL sphere at two distant sites. Occasionally, the ends were attached to two touching spheres. Under the same imaging conditions, LDL appeared as individual spheres. Electron microscopy (EM) studies of Lp(a) by several groups over the past decade failed to reveal this belt-like structure of apo(a). Images of isolated apo(a) in air or in phosphate buffer showed apo(a) as individual belts, and these belts tended to crowd together. Lp(a) formed leaf-like aggregates; apo(a) aggregates were fishnet-like, whereas LDL aggregates were less characteristic. Quantitative analysis of Lp(a) showed the diameter of the LDL to be 24.8 +/- 8.7 nm (n = 46), which is close to the reported value of 24.2 +/- 4.2 nm found with EM. The length of the belts attached to the spheres was measured to be 173.5 +/- 6.6 nm (n = 15). I also found, by using a functionalized tip, that the interaction force between apo(a) and its ligand, lysine, was related to the ionic strength of the bulk solution. This force can be reduced by the presence of epsilon-aminocaproic acid.

Apolipoproteins A↗

PubMed1998

Study of relapsing remitting experimental allergic encephalomyelitis SJL mouse model using MION-46L enhanced in vivo MRI: early histopathological correlation.

MION-46L, a superparamagnetic iron oxide contrast agent, was investigated for its ability to increase the sensitivity of in vivo 3D MRI in the detection of brain lesions in a chronic experimental allergic encephalomyelitis (crEAE) mouse model. Lesion conspicuity on postcontrast 3D MRI was dramatically enhanced as compared to precontrast images corresponding to areas of inflammatory and demyelinating lesions. MION-46L could be detected on Prussian blue iron stain in the vascular endothelium, the perivascular space, and in macrophages within perivascular cuffs and areas of inflammation and demyelination. By taking advantage of the MION-46L induced macroscopic susceptibility effect, acute early lesions measuring only 100 microm in diameter could be detected. MION-46L enhanced MRI may be used to 1) provide a unique sensitivity in EAE lesion detection and correlate imaging to histopathology; 2) help to understand EAE lesion development and its underlying pathophysiology; and 3) eventually assist in preclinical screening of new experimental therapies directed at patients with multiple sclerosis (MS).

Animals↗

PubMed1998

Cloning genes encoding receptors related to chemoattractant receptors.

We report the cloning of a novel human gene (GPR32) encoding a putative G-protein-coupled receptor (GPCR) of 356 amino acids and a related pseudogene psi GPR32. The deduced amino acid sequence of GPR32 shares 35-39% identity with members of the chemoattractant receptor family. psi GPR32 shares 93% nucleotide identity with GPR32. We identified a mouse EST encoding a putative GPCR (GPR33) of 309 amino acids. The deduced amino acid sequence of GPR33 shares 30-35% identity with members of the chemoattractant receptor family and 36% identity with the receptor encoded by GPR32. The human orthologue of GPR33 contains a single basepair substitution with respect to the mouse, resulting in the presence of an in-frame stop codon within the predicted second intracellular loop, demonstrating that it is a pseudogene. Through fluorescence in situ hybridization and physical mapping of YACs, both GPR32 and psi GPR32 were mapped to chromosomal 19, region q13.3, while psi GPR33 was mapped to chromosome 14q12.

Amino Acid Sequence↗

PubMed1998

HTLV-I Tax protein binds to MEKK1 to stimulate IkappaB kinase activity and NF-kappaB activation.

NF-kappaB, a key regulator of the cellular inflammatory and immune response, is activated by the HTLV-I transforming and transactivating protein Tax. We show that Tax binds to the amino terminus of the protein kinase MEKK1, a component of an IkappaB kinase complex, and stimulates MEKK1 kinase activity. Tax expression increases the activity of IkappaB kinase beta (IKKbeta) to enhance phosphorylation of serine residues in IkappaB alpha that lead to its degradation. Dominant negative mutants of both IKKbeta and MEKK1 prevent Tax activation of the NF-kappaB pathway. Furthermore, recombinant MEKK1 stimulates IKKbeta phosphorylation of IkappaB alpha. Thus, Tax-mediated increases in NF-kappaB nuclear translocation result from direct interactions of Tax and MEKK1 leading to enhanced IKKbeta phosphorylation of IkappaB alpha.

Animals↗

PubMed1998

Different biochemical properties of nuclear and microsomal estrone-3-sulfatases: evidence for the presence of a nuclear isozyme.

In female rats, total estrone-3-sulfatase activity per liver in the nuclear fraction is comparable to the total activity per liver in the microsomal fraction. The combined estrone-3-sulfatase activity in the other fractions (lysosomal, mitochondrial, and cytosolic fractions) is negligible and only accounts for < 5% of the total nuclear or microsomal sulfatase activity. Nuclear and microsomal estrone-3-sulfatases have different pH optima (pH 8.0 and 7.2, respectively). The apparent Km values for the nuclear and microsomal estrone-3-sulfatases are 2.5 and 10.1 microM, respectively, suggesting that the nuclear sulfatase has a considerably higher affinity for estrone-3-sulfate than the microsomal sulfatase. Moreover, the nuclear estrone-3-sulfatase is more sensitive to inhibition by several steroids than the microsomal sulfatase. The results suggest that estrone-3-sulfatase in the nuclear fraction is a different isozyme than that in the microsomal fraction.

Animals↗

PubMed1998

Homozygosity mapping of autosomal recessive retinitis pigmentosa locus (RP22) on chromosome 16p12.1-p12.3.

Autosomal recessive retinitis pigmentosa (arRP) is a genetically and clinically heterogeneous and progressive degenerative disorder of the retina, leading usually to severe visual handicap in adulthood. To date, disease loci/genes have been mapped/identified only in a minority of cases. DNA samples were collected from 20 large consanguineous Indian families, in which arRP segregated and that were suitable for homozygosity mapping of the disease locus. After excluding linkage to all known arRP loci, a genome-wide scan was initiated. In two families, homozygosity mapping, haplotype analysis, and linkage data mapped the disease locus (RP22) in an approximately 16-cM region between D16S287 and D16S420 on the proximal short arm of chromosome 16. No mutation has been found by direct sequencing in the gene (CRYM) encoding micron crystallin, which maps in the critical region.

Chromosome Mapping↗

PubMed1998

Probing the ATP binding site of tubulin with thiotriphosphate analogues of ATP.

Tubulin assembly studies with GTP alpha S diastereoisomers have shown that there is stereoselectivity at the alpha-phosphate binding region of tubulin. GTP alpha S(Sp) bound tighter than GTP alpha S(Rp) and promoted nucleation and assembly better than GTP and GTP alpha S(Rp). ATP and dATP have been reported to bind weakly to tubulin and to be less effective than GTP and dGTP in promoting tubulin assembly. This study was done to learn if ATP alpha S(Sp) and dATP alpha S(Sp) are good promoters of tubulin assembly and to compare these ATP thiotriphosphate analogues to the corresponding GTP analogues in tubulin assembly. Studies were also done with ATP alpha S(Rp), GTP, ATP beta S(Sp) and ATP gamma S. At least three cycles of tubulin (25 microM) assembly-disassembly were found with 1 mM ATP alpha S(Sp) and dATP alpha S(Sp) and both nucleotides were incorporated and hydrolyzed in the polymers. Less dATP alpha S(Sp) (25 microM) than ATP alpha S(Sp) (100 microM) promoted assembly to 50% of the maximum value. The critical concentrations (Cc) for assembly with 1 mM nucleotide were low for ATP alpha S(Sp) (3 microM) and dATP alpha S(Sp) (2 microM) and compared favorably with GTP (5 microM), GTP alpha S(Sp) (2 microM) and dGTP alpha S(Sp) (1 microM). Both 1 mM ATP and dATP were poor promoters of tubulin assembly and were not detected in the polymers. The predominant structures induced by 1 mM (ATP alpha S(Sp) and dATP alpha S(Sp) were bundles of sheets and microtubules, which were more stable to the cold and to Ca(II) than microtubules assembled with GTP, ATP or dATP. ATP alpha S(Rp) (1 mM) did not promote assembly suggesting that there is stereoselectivity at the ATP alpha S alpha-phosphate binding region of tubulin as there is with GTP alpha S diastereoisomers. ATP alpha S(Sp) and dATP alpha S(Sp) mimic GTP alpha S(Sp) and dGTP alpha S(Sp) in tubulin assembly since all four nucleotides promote bundles of tubulin in buffer with glycerol, and the deoxy nucleotides have lower Cc, shorter lags and faster rates for tubulin assembly.

Adenosine Triphosphate↗

PubMed1998

Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans.

Experimental introduction of RNA into cells can be used in certain biological systems to interfere with the function of an endogenous gene. Such effects have been proposed to result from a simple antisense mechanism that depends on hybridization between the injected RNA and endogenous messenger RNA transcripts. RNA interference has been used in the nematode Caenorhabditis elegans to manipulate gene expression. Here we investigate the requirements for structure and delivery of the interfering RNA. To our surprise, we found that double-stranded RNA was substantially more effective at producing interference than was either strand individually. After injection into adult animals, purified single strands had at most a modest effect, whereas double-stranded mixtures caused potent and specific interference. The effects of this interference were evident in both the injected animals and their progeny. Only a few molecules of injected double-stranded RNA were required per affected cell, arguing against stochiometric interference with endogenous mRNA and suggesting that there could be a catalytic or amplification component in the interference process.

Animals↗

PubMed1998

Characterization of the human class Mu glutathione S-transferase gene cluster and the GSTM1 deletion.

A partial physical map has been constructed of the human class Mu glutathione S-transferase genes on chromosome 1p13.3. The glutathione S-transferase genes in this cluster are spaced about 20 kilobase pairs (kb) apart, and arranged as 5'-GSTM4-GSTM2-GSTM1-GSTM5-3'. This map has been used to localize the end points of the polymorphic GSTM1 deletion. The left repeated region is 5 kb downstream from the 3'-end of the GSTM2 gene and 5 kb upstream from the beginning of the GSTM1 gene; the right repeated region is 5 kb downstream from the 3'-end of the GSTM1 and 10 kb upstream from the 5'-end of the GSTM5 gene. The GSTM1-0 deletion produces a novel 7.4-kb HindIII fragment with the loss of 10.3- and 11.4-kb HindIII fragments. The same novel fragment was seen in 13 unrelated individuals (20 null alleles), suggesting that most GSTM1-0 deletions involve recombinations between the same two regions. We have cloned and sequenced the deletion junction that is produced at the GSTM1-null locus; the 5'- and 3'-flanking regions are more than 99% identical to each other and to the deletion junction sequence over 2.3 kb. Because of the high sequence identity between the left repeat, right repeat, and deletion junction regions, the crossing over cannot be localized within the 2.3-kb region. The 2.3-kb repeated region contains a reverse class IV Alu repetitive element near one end of the repeat.

Base Sequence↗

PubMed1998

The mitogen-activated protein kinase p38-2 is necessary for the inhibition of N-type calcium current by bradykinin.

Calcium influx via voltage-dependent calcium channels (ICa,V) links depolarization of excitable cells to critical cellular processes, such as secretion, contraction, and gene transcription. Fast regulation of ICa,V (<1 sec) by G-protein-coupled receptors is a relatively well-defined mechanism, whereas slow (30-60 sec) actions of transmitters and hormones on the same current remain poorly understood. In NG108-15 cells, the kinetically slow inhibition of N-type ICa,V by bradykinin (BK) requires the sequential activation of two G-proteins, heterotrimeric G13 and monomeric Rac1/Cdc42. We have now defined a role in this pathway for the relatively fast-acting p38 mitogen-activated protein kinase (MAPK). The slow inhibition of ICa,V by BK was suppressed specifically by SB203580, a compound that inhibits the p38 family of MAPKs. BK potently and selectively activated a newly discovered p38 family member, p38-2. These data provide the first evidence that a MAPK is involved in the regulation of ICa,V by a receptor-mediated process.

Animals↗

PubMed1998

Structure- and property-activity relationship models for prediction of microbial toxicity of organic chemicals to activated sludge.

Two quantitative structure-activity relationship (QSAR) and two quantitative property-activity relationship (QPAR) models reported in the literature for predicting toxicity of synthetic organic chemicals to activated sludge microorganisms are summarized and compared. The QSAR models were developed using solvatochromic parameters and molecular connectivity indices; the QPAR models, using octanol-water partition coefficient and aqueous solubility. Experimental data on 16 chemicals not used in developing the above models are used to compare and evaluate the predictive ability of these QSAR/QPAR models. Based on the quality of the original models, their predictions, ease of application, and availability of model parameters, molecular connectivity indices and log P appear to be the most suitable in toxicity predictions.

1-Octanol↗

PubMed1998

Behavior of N-phenylmaleimide-reacted muscle fibers in magnesium-free rigor solution.

Using x-ray diffraction and mechanical stiffness, the response of N-phenylmaleimide (NPM)-reacted cross-bridges to solutions containing different amounts of ATP and Mg2+ has been studied. In relaxing solution containing greater than millimolar amounts of ATP and Mg2+, NPM-treated muscle fibers give x-ray diffraction patterns and stiffness records, which are nearly indistinguishable from those of untreated relaxed fibers. In a solution devoid of added ATP, but with Mg2+ (rigor(+Mg) solution), the muscle fibers still give x-ray diffraction patterns and mechanical responses characteristic of relaxed muscle. The new finding reported here is that in a solution devoid of both ATP and Mg2+ (rigor(-Mg) solution containing EDTA with no added ATP), NPM-reacted cross-bridges do give rigor-like behavior. This is the first report that NPM-reacted cross-bridges, at least in the presence of EDTA, are capable of going into a strongly binding conformation.

Adenosine Triphosphate↗

PubMed1998

Characterizations of cross-bridges in the presence of saturating concentrations of MgAMP-PNP in rabbit permeabilized psoas muscle.

Several earlier studies have led to different conclusions about the complex of myosin with MgAMP-PNP. It has been suggested that subfragment 1 of myosin (S1)-MgAMP-PNP forms an S1-MgADP-like state, an intermediate between the myosin S1-MgATP and myosin S1-MgADP states or a mixture of cross-bridge states. We suggest that the different states observed result from the failure to saturate S1 with MgAMP-PNP. At saturating MgAMP-PNP, the interaction of myosin S1 with actin is very similar to that which occurs in the presence of MgATP. 1) At 1 degrees C and 170 mM ionic strength the equatorial x-ray diffraction intensity ratio I11/I10 decreased with an increasing MgAMP-PNP concentration and leveled off by approximately 20 mM MgAMP-PNP. The resulting ratio was the same for MgATP-relaxed fibers. 2) The two dimensional x-ray diffraction patterns from MgATP-relaxed and MgAMP-PNP-relaxed bundles are similar. 3) The affinity of S1-MgAMP-PNP for the actin-tropomyosin-troponin complex in solution in the absence of free calcium is comparable with that of S1-MgATP. 4) In the presence of calcium, I11/I10 decreased toward the relaxed value with increasing MgAMP-PNP, signifying that the affinity between cross-bridge and actin is weakened by MgAMP-PNP. 5) The degree to which the equatorial intensity ratio decreases as the ionic strength increases is similar in MgAMP-PNP and MgATP. Therefore, results from both fiber and solution studies suggest that MgAMP-PNP acts as a non hydrolyzable MgATP analogue for myosin.

Actins↗

PubMed1998

Long-term follow-up of Stargardt's disease and fundus flavimaculatus.

OBJECTIVE: To understand better the shared characteristics of Stargardt's macular dystrophy (SMD) and fundus flavimaculatus (FF) by reviewing the clinical morphologic and retinal function changes in a large group of affected patients. DESIGN: The study design was a retrospective case review. PARTICIPANTS: Fifty-two patients with SMD and 48 patients with FF were observed from 1 to 22 years. INTERVENTION: Visual acuity (VA), visual fields (VFs), fundus photographs (FPs), fluorescein angiography (FA), electro-oculography (EOG), and electroretinography (ERG) were studied at various intervals. MAIN OUTCOME MEASURES: Changes of VA, VF, FP, FA, EOG ratio, and ERG amplitudes and implicit time at different periods in patients with SMD and patients with FF were measured. RESULTS: Visual acuity decreased gradually in both the SMD and FF groups, and once the 20/200 level was reached, little further change occurred. The yellowish flecks associated with these entities faded with time, and areas of retinal pigment epithelial (RPE) and choriocapillary atrophy developed. In advanced longstanding disease, retinal vessel attenuation and peripheral pigmentary changes were noted. Ninety-four percent of patients with FF were noted to have macular dystrophy at their last visit. Patients who had only central lesions did not have peripheral lesions develop. Intrafamilial variation in the funduscopic pattern was shown in four families. The EOG ratio was abnormal in 2.6% of the patients with SMD and in 48.6% of the patients with FF. An abnormal scotopic ERG was noted in 21.1% of the patients with FF and in none of the patients with SMD. The photopic ERG was abnormal in 32.4% of the patients with FF and in 5.4% of the patients with SMD. In patients with FF, a statistical dependence was noted between the duration of the disease and the ERG results, but no such correlation was seen in the SMD group. CONCLUSIONS: Morphologic changes and retinal function deterioration are more severe in patients with FF than in patients with SMD. The duration of the disease has a greater effect on patients with FF than on patients with SMD. These clinical morphologic and physiologic data may be used to supplement laboratory molecular biologic studies and aid in the further classification of these entities.

Adolescent↗

PubMed1998

Multipoint genetic mapping of quantitative trait loci using a variable number of sibs per family.

We present a multipoint algorithm to map quantitative trait loci (QTLs) using families from outbred populations with a variable number of sibs. The algorithm uses information from all markers on a chromosome simultaneously to extract information of QTL segregation. A previous multipoint method (Kruglyak & Lander (1995) American Journal of Human Genetics 57, 439-454) extracts information using a hidden Markov model. However, this method is restricted to small families (< 10 sibs). We present an approximate hidden Markov model approach that can handle large sibships while retaining similar efficiency to the previous method. Computer simulations support the notion that data sampled from a small number of large families provide more power than data obtained from a large number of small families, under the constraint that the total number of individuals for the two schemes is the same. This is further reflected in simulations with variable family sizes, where variance in family size improves the statistical power of QTL detection relative to a constant size control.

Chromosome Mapping↗

PubMed1998

Further investigation on the regression method of mapping quantitative trait loci.

The simple regression method of mapping quantitative trait loci (QTL) is further investigated in comparison with the mixture model maximum likelihood method under high heritabilities, dominant and missing markers. No significant difference between the two methods is detected in terms of errors of parameter estimation and statistical powers, with the exception that the estimation of residual variance provided by the regression method is confounded with part of the QTL variance. The test statistic profiles show some difference between the two methods, but the difference is only detectable at the micro level. An alternative method, referred to as iteratively reweighted least squares, is proposed, which can correct the deficiency of parameter confounding in the regression method yet retains the properties of simplicity and rapidity of the ordinary regression method. Like the existing regression method, the weighted least squares method can be useful in QTL mapping in conjunction with the permutation tests and construction of confidence intervals by bootstrapping.

Chromosome Mapping↗

PubMed1998

Efficiency of multistage marker-assisted selection in the improvement of multiple quantitative traits.

The application of marker-assisted selection (MAS) to breeding programmes depends on its relative cost and the expected economic return compared to conventional phenotypic selection. The relative efficiency of MAS can be increased through a two-stage selection scheme or through marker-based, multiple-trait improvement. However, the effectiveness of these alternatives has not been quantified. In this study, we evaluate the efficiency of MAS relative to conventional phenotypic selection and marker-only selection in multistage selection for the improvement of multiple traits. We further incorporate the costs of obtaining measurements on phenotypic characters and marker loci into the objective function to evaluate the efficiency of MAS with respect to the gain per unit cost. Deterministic analyses indicate that excluding costs, multiple-trait MAS can be used to increase the aggregate breeding values in quantitative characters and is expected to be more effective than conventional selection or single-trait MAS. Two-stage MAS has a slightly reduced gain because of culling in the first stage. If the objective function is to maximize the gain per unit cost, multiple-trait MAS is inferior to phenotypic selection in most of the selection schemes investigated when the cost ratio (r) of obtaining measurements on phenotypic characters to scoring marker loci is less than unity (r < or = 1.0) and the heritability (h2) is greater than 0.3. The efficiency of MAS increases as r increases and h2 decreases. For MAS to be more effective, it is necessary to decrease further the cost associated with molecular marker assays.

Chromosome Mapping↗