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Biomedical subjects

Q Hu

Publications and source records attributed to Q Hu.

At least 109 records · Page 6Linked to original sources
PubMed1997

Limits to the differential avidity model of T cell selection in the thymus.

It has been postulated that the critical feature that determines the developmental fate of an immature thymocyte is the avidity of interaction between thymocyte TCR and peptide/MHC molecules on thymic stromal cells. However, it is possible that certain innate properties of peptides predispose them to triggering only positive or negative selection irrespective of their density on thymic stromal cells. To distinguish between these hypotheses, we examined the ability of several different peptides to induce the positive and negative selection of TCR transgenic (P14) antilymphocytic choriomeningitis virus (LCMV) CTLs in fetal thymus organ cultures (FTOC) from TAP1+ and TAP1- mice. We found that only relatively weak agonist peptides could induce the positive selection of anti-LCMV CTLs. A nonagonist peptide could induce positive selection but not negative selection; however, a weak agonist peptide could induce the positive selection of anti-LCMV CTLs in P14 TAP1- FTOC and negative selection in P14 TAP1+ FTOC. These data imply that there are upper and lower limits for the affinity of a peptide in triggering positive or negative selection, but that for peptides of intermediate affinity the overall avidity of interaction with the P14 TCR is the critical parameter in determining the developmental fate of thymocytes. Our observations also suggest a prominent role for low affinity self peptides in selecting a function repertoire of CD8+ T cells.

Animals↗
PubMed1997

An Acanthamoeba polyubiquitin gene and application of its promoter to the establishment of a transient transfection system.

We have isolated and sequenced a 2388 bp polyubiquitin encoding genomic DNA from Acanthamoeba encompassing two complete and one incomplete ubiquitin units. Codon usage frequency shows extreme bias. The deduced amino acid sequences of each unit are identical to each other and the same as that deduced from a previously sequenced Acanthamoeba castellanii cDNA. The upstream region of this gene, which contained some putative regulatory modules, was recovered by PCR (polymerase chain reaction) amplification and subcloning. This upstream fragment was ligated to the CAT (chloramphenicol acetyltransferase) gene in a eukaryotic expression plasmid and successfully applied to the establishment of an Acanthamoeba transient transfection system. Transfection was performed by electroporation and the optimal voltage was 4500 volts/cm at capacitance 25 microF. DEAE-dextran (25 microg/ml) added into the electroporation buffer increased the transfection efficiency by about 45%. The CAT activity was proportional to the amount of DNA transfected and reached the peak level 48 h after transfection. CAT assays showed that the polyubiquitin gene upstream fragment contains a functional promoter which is about 2.5 times as strong as a viral RSV-LTR promoter when driving CAT expression in Acanthamoeba.

Acanthamoeba↗
PubMed1997

Inhibition of Toosendanin on the delayed rectifier potassium current in neuroblastoma x glioma NG108-15 cells.

The effect of Toosendanin (TSN), a presynaptic transmission blocker, on the outward delayed rectifier potassium current (IKD) of NG108-15 cells was studied by using the whole-cell voltage-clamp technique. It was observed that externally applying TSN not only reduced IKD amplitude in a dose-dependent and partial reversible manner but also accelerated its inactivation. The effect of internally applying TSN was also examined by including TSN in the electrode, and it was the same as that of externally applying TSN. Further, comparison observations with TEA, 4-AP, verapamil, nifedipine, and (+/-)-Bay K 8644 were also made, and the results were as follows. The time courses of TSN's inhibition effect as well as its recovery after washing were much slower than those of TEA and 4-AP. Externally applying TEA or 4-AP reduced IKD amplitude but did not accelerate its inactivation. Externally applying verapamil, nifedipine, or (+/-)-Bay K 8644, however, similarly to the effect of TSN, not only reduced IKD amplitude but also accelerated its inactivation. Thus, from the obtained results it is suggested that TSN might diffuse into the cell interior and act intracellularly, and the underlying mechanism might be different from that of TEA and 4-AP but similar to that of verapamil, nifedipine, and (+/-)-Bay K 8644 to some extent.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1997

Characterization of an inward-rectifying potassium current in NG108-15 neuroblastoma x glioma cells.

By using the whole-cell patch-clamp technique, an inwardly rectifying potassium current, which resembled the "classic" inward-rectifying potassium current (IKIR) of other cells in terms of electrophysiological and pharmacological properties, was identified in db-cAMP-differentiated NG108-15 cells. First, the current was dependent on voltage and time. It could be elicited by applying an initial depolarizing prepulse and a subsequent hyperpolarizing command pulse to the cell. The amplitude of the current depended on both the prepulse and the command pulse and increased with the hyperpolarization of the command pulse as well as the depolarization and the prolongation of the prepulse. The activation and inactivation of the current could be fitted well by single-exponential functions and increased with the hyperpolarization of the membrane. Second, the current was dependent on the extracellular potassium concentration ([K+]o). Elevation of [K+]o resulted in a marked increase in the current amplitude and a positive shift of the peak-current/voltage curve as well as the reversal potential. A tenfold increase of [K+]o introduced an approximately 43-mV shift of the reversal potential, indicating that the current was carried mainly by K+. The conductance (g/gMax) of the current was also dependent on the [K+]o and increased with increases in [K+]o in a manner approximately proportional to the square-root of [K+]o. Finally, the current was sensitive to Cs+ (1 mmol/l), Ba2+ (1 mmol/l) and quinidine (0.2 mmol/l); whereas, two typical potassium channel inhibitors, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), were weak blockers and reduced the current at high concentration (>10 mmol/l). It was also observed that the current was depressed by Cd2+ (1 mmol/l) and Co2+ (1 mmol/l) and increased by perfusing the cell with Ca2+-free solution. Thus, except for the sensitivity to Cd2+, Co2+ and Ca2+, the current displayed most of the hallmarks described for the "classic" IKIR. In conclusion, there appears to be a voltage-dependent IKIR-type inward rectifier in db-cAMP-differentiated NG108-15 cells.

4-Aminopyridine↗
PubMed1997

Specific recognition of thymic self-peptides induces the positive selection of cytotoxic T lymphocytes.

To understand how thymic selection gives rise to T cells that are capable of major histocompatibility complex (MHC)-restricted recognition of antigen but are tolerant of self, we directly examined how peptide/MHC ligands expressed on thymic epithelial cells trigger the positive selection of immature thymocytes. We demonstrate that abundant self-peptides, purified from the H-2D(b) molecules of thymic epithelial cells, are specifically recognized during the positive selection of CD8+ T cells, implying that positive selection generates a repertoire of T cells that is weakly self-reactive. We also found that this recognition is somewhat cross-reactive, thereby providing an explanation for how the specific recognition of a limited repertoire of thymic self-peptides can select a diverse repertoire of T cells.

Animals↗
PubMed1997

Heterogeneity of L-type calcium current density in coronary smooth muscle.

Heterogeneity of vascular responses to physiological and pharmacological stimuli has been demonstrated throughout the coronary circulation. Typically, this heterogeneity is based on vessel size. Although the cellular mechanisms for this heterogeneity are unknown, one plausible factor may be heterogeneous distribution of ion channels important in regulation of vascular tone. Because of the importance of voltage-gated Ca2+ channels in regulation of vascular tone, we hypothesized that these channels would be unequally distributed throughout the coronary arterial bed. To test this hypothesis, voltage-gated Ca2+ current was measured in smooth muscle from conduit arteries (>1.0 mm), small arteries (200-250 microm), and large arterioles (75-125 microm) of miniature swine using whole cell voltage-clamp techniques. With 2 mM Ca2+ or 10 mM Ba2+ as charge carrier, voltage-gated Ca2+ current density was inversely related to arterial diameter, i.e., large arterioles > small arteries > conduit. Peak inward currents (10 mM Ba2+) were increased approximately 2.5- and approximately 1.5-fold in large arterioles and small arteries, respectively, compared with conduit arteries (-5.58 +/- 0.53, -3.54 +/- 0.34, and -2.26 +/- 0.31 pA/pF, respectively). In physiological Ca2+ (2 mM), small arteries demonstrated increased inward current at membrane potentials within the physiological range for vascular smooth muscle (as negative as -40 mV) compared with conduit arteries. In addition, cells from large arterioles showed a negative shift in the membrane potential for half-maximal activation compared with small and conduit arteries (-13.23 +/- 0.88, -6.22 +/- 1.35, and -8.62 +/- 0.81 mV, respectively; P < 0.05). Voltage characteristics and dihydropyridine sensitivity identified this Ca2+ current as predominantly L-type current in all arterial sizes. We conclude that L-type Ca2+ current density is inversely related to arterial diameter within the coronary arterial vasculature. This heterogeneity of Ca2+ current density may provide, in part, the basis for functional heterogeneity within the coronary circulation.

Animals↗
PubMed1997

[Study on the best sampling time and the time distribution of atmospheric bacterial particle].

The changes of atmospheric bacterial particle concentrations in three areas--Beijing, Tianjin and Shenyang, were investigated in different seasons and period of one day. The samplers used in this study were MF-45 and HTK-201 air microbial samplers. The results showed that the concentrations of atmospheric bacterial particle in Beijing and Tianjin are higher in spring than those in other seasons. They are 2053/m3 and 2556/m3 respectively in spring, 995/m3 and 1064/m3 respectively in summer. The concentrations of atmospheric bacterial particle in Shenyang is higher in autumn (10108/m3) and lower in winter (1294/m3). The changes of atmospheric bacterial particle concentrations have two peak values during a day. The two high peak values are at 6:00 to 7:00 and 18:00, while the two low values are at 11:00 to 13:00 and 1:00 to 2:00. We sampled the atmospheric bacterial particles at 4 different combinations of sampling time in the three cities. They were 12, 8, 6 and 4 times a day. The sampling time combination was analyzed by mathematical statistics according to the results. The best sampling time was decided by the statistics results and time distribution character of atmospheric bacterial particle concentration in different seasons and period of one day. The concentration of atmospheric bacterial particle should be detected in the middle month of the four seasons: January, April, July and October. Sampling time at 7:00, 10:00, 13:00, 16:00, 19:00, 22:00, 1:00 and 4:00 could be selected for 8 times sampling a day. The sampling time sequence should be at 5:00, 11:00, 17:00 and 23:00 for 4 times sampling a day. The four times sampling at daytime in spring and fall should be at 6:00, 9:00, 12:00 and 19:00; 5:00, 9:00, 13:00 and 17:00 in summer; 7:00, 10:00, 13:00 and 16:00 in winter.

Air Microbiology↗
PubMed1997

[Preliminary determination of the properties of HX-I refractory die material].

The setting time, the setting expansion ratio and the compatibility with impression materials of the HX-I refractory die material were determined. The results showed: the setting time was 11 +/- 3 min: the setting expansion ratio was 0.23%; the compatibility with impression materials was excellent between HX-I die material and agar or silicone rubber respectively, but the compatibility was bad between HX-I die material and alginate. These properties of HX-I die material were close to the ones of Lamina die material.

Dental Materials↗
PubMed1997

Effects of thrombolytic therapy on recanalization in different starting time of treatment after acute myocardial infarction.

OBJECTIVE: To investigate the effects of thrombolytic therapy on recanalization in different starting time of treatment after acute myocardial infarction. METHODS: 172 cases with intravenous thrombolytic agents were divided into 4 groups: < or = 2 hours, > 2-4 hours, > 4-6 hours and > 6-12 hours, according to the different starting time of therapy after onset of symptoms. RESULTS: The recanalization rates were 78.6%, 74%, 39. 6% and 14.3% in < or = 2 hours, > 2-4 hours, > 4-6 hours and > 6-12 hours, respectively. The recanalization rate within 4 hours was significantly higher than those in the groups of > 4-6 hours AND > 6-12 hours. The time interval from the initiation of thrombolytic therapy to reperfusion was increased as the starting time of thrombolysis after onset of symptoms was delayed. CONCLUSIONS: Starting time of thrombolysis within 4 hours after onset of acute myocardial infarction is of the best effect on recanalization.

Aged↗
PubMed1996

Co-existence of serum-dependent and serum-independent mechanisms for liposome clearance and involvement of non-Kupffer cells in liposome uptake by mouse liver.

The effect of serum on liver uptake of liposomes with different compositions was investigated using a single-pass liver perfusion technique. Among the liposomes tested are those containing CL, PA, DPGS, PE or glycolipids such as PI, GD, GT1b and aGM1. Liposomes containing PA, CL and DPGS showed high level of liver uptake in the absence of serum. Presence of serum decreased the total liver uptake for liposomes containing CL and PA by 50% and did not affect the level of liver uptake for DPGS-containing liposomes. The presence of serum, however, significantly increased the liposome uptake by the perfused liver for PG, PE and aGM1 liposomes. Liposomes containing PI showed a minimal liver uptake regardless of serum presence. Fluorescence microscopic studies using a dual fluorescence label system in combination with Kupffer cell elimination technique showed that, in addition to the dominant role of Kupffer cells in taking up liposomes, non-Kupffer cells may also be involved in taking up CL and DCP-containing liposomes. Competition experiments using various liposome compositions indicated that liposome uptake by the liver cells may involve different receptors. Serum activity in enhancing the liver uptake for PE- and aGM1-containing liposomes can be blocked by treatment of serum with EDTA, EGTA/Mg2+ and high temperature (56 degrees C), suggesting the involvement of complement system. Results from this study support the conclusion that blood clearance of liposomes by the liver involves two independent mechanisms, one requires serum opsonins and the other does not.

Animals↗
PubMed1996

Amelioration of lupus-like autoimmune disease in NZB/WF1 mice after treatment with a blocking monoclonal antibody specific for complement component C5.

New Zealand black x New Zealand white (NZB/W) F1 mice spontaneously develop an autoimmune syndrome with notable similarities to human systemic lupus erythematosus. Female NZB/WF1 mice produce high titers of antinuclear antibodies and invariably succumb to severe glomerulonephritis by 12 months of age. Although the development of the immune-complex nephritis is accompanied by abundant local and systemic complement activation, the role of proinflammatory complement components in disease progression has not been established. In this study we have examined the contribution of activated terminal complement proteins to the pathogenesis of the lupus-like autoimmune disease. Female NZB/W F1 mice were treated with a monoclonal antibody (mAb) specific for the C5 component of complement that blocks the cleavage of C5 and thus prevents the generation of the potent proinflammatory factors C5a and C5b-9. Continuous therapy with anti-C5 mAb for 6 months resulted in significant amelioration of the course of glomerulonephritis and in markedly increased survival. These findings demonstrate an important role for the terminal complement cascade in the progression of renal disease in NZB/W F1 mice, and suggest that mAb-mediated C5 inhibition may be a useful approach to the therapy of immune-complex glomerulonephritis in humans.

Animals↗
PubMed1996

The antenna complexes of the purple non-sulfur photosynthetic bacterium Rhodocyclus tenuis. Structural and spectral characterization.

The photoreceptor complex (B885-RC) and the peripheral antenna complex (B800-860) were isolated from photosynthetic membranes of the purple non-sulfur bacterium Rhodocyclus tenuis DSM 109 using a detergent combination of Deriphate-160 and octyl glucoside and subsequent linear sucrose gradient centrifugation. The two complexes were characterized by room-temperature absorption, circular dichroism and fluorescence spectroscopy. The B800-860 complex has a more red-shifted B860 absorbance band. The alpha,beta-polypeptides were purified with a reverse-phase HPLC system and resolved at a ratio of 1:1 in the B800-860 complex and at an overall ratio of 1:1 for the B885-RC complex. The complete amino acid sequences of the alpha and beta polypeptides of the B800-860 and B885-RC complexes were determined by micro-sequencing analysis and mass spectrometry. The B800-860-alpha polypeptide possesses an identical N-terminal domain (the first 15 residues) to Rhodobacter sphaeroides B800-850-alpha polypeptide. The central hydrophobic and C-terminal domains of the B800-860-alpha,beta polypeptides show a number of B870/880-like structural elements in which, of special interest, is the WWSEF cluster in the C-terminal domain of the B800-860-alpha polypeptide which is very similar to the WWEF cluster in the same region of Rhodopseudomonas viridis B1015-alpha polypeptide. The more red-shifted absorption characteristic of the 860-nm bacteriochlorophylls could most probably be related to the B870/880-like polypeptide features in the central hydrophobic domains and the C-terminal domains of the B800-860-alpha,beta polypeptides. The hydropathy plot of the B800-860-alpha polypeptide exhibits an extended C-terminal hydrophobic segment indicative of a second membrane-contacting domain, which has not been found in the antenna polypeptides of the purple bacteria with intracytoplasmic membranes. Further sequence analysis revealed the existence of multiple forms of the B885-alpha,beta polypeptides, the B885-alpha 1,alpha 2 polypeptides, and the B885-beta 1,beta 2 polypeptides. The B885-Alpha 2 polypeptide shows an identical sequence to the B885-alpha 1 polypeptide, but it is 12 amino acid residues shorter than the B885-alpha 1 polypeptide at the C-terminal. The two species of the B885-beta polypeptides were identified as an identical sequence with only one amino acid residue variation at sequence position 34, where the B885-beta 1 has a valine residue and the B885-beta 2 polypeptide an isoleucine residue. The possible correlation between the intensity of the near-infrared circular dichroic signal and the specific structural features of the alpha and beta core antenna polypeptides is also discussed.

Amino Acid Sequence↗
PubMed1996

Altered expression and regulation of the alpha 5beta1 integrin-fibronectin receptor lead to reduced amounts of functional alpha5beta1 heterodimer on the plasma membrane of senescent human diploid fibroblasts.

Previously, we reported that fibronectin (FN) mRNA was overexpressed in normal late-passage (old) and pre- maturely senescent Werner syndrome (WS) fibroblasts when compared to normal early-passage (young) cells (Murano et al. Mol. Cell. Biol. 11, 3905-3914, 1991). Therefore, we investigated the expression and function of the alpha5 beta1 FN receptor (FNR), a member of the integrin family, in young and senescent normal and WS cells. Levels of the alpha5 polypeptide, a unique subunit of the alpha5 beta1 FNR, were reduced in old cells, so that old cells produced fewer alpha5 beta1 heterodimers on the plasma membrane. The reduced levels of alpha5 polypeptide might be due to deficient translation and/or nonfunctional alpha5 mRNA since increased mRNA levels and unchanged polypeptide turnover were found in these cells. Moreover, the alpha5 polypeptides on the senescent cell surface were less accessible to monoclonal antibody, suggesting sequestration of this subunit, which might affect receptor-ligand binding. In contrast, beta1 subunit, a common subunit for the beta1 integrin subfamily, showed relatively stable levels during cellular aging, but underwent slower intracellular processing. Old cells exhibited reduced attachment to FN, which might be in part mediated by the alpha5 beta1 FNR. More importantly, old cells were deficient in response to FN-induced DNA synthesis and cell proliferation. This induction was pronounced in young cells, however, and could be completely inhibited by alpha5-specific monoclonal antibody, indicating mediation by alpha5 beta1 FNR. WS cells behaved like normal old cells in the above assays. Our results indicate that reduction of alpha5 beta1 FNR expression and its mediated effects are associated with the senescent phenotype of fibroblasts. These findings provide new insight into the mechanism(s) of replicative senescence in human fibroblasts.

Antibodies, Monoclonal↗
PubMed1996

Strong induction of activin expression after injury suggests an important role of activin in wound repair.

Activins are members of the transforming growth factor beta (TGF beta) superfamily, which comprises a growing group of dimeric proteins. TGF beta and several other members of this superfamily are known to play an important role in wound healing. However, expression of activin during wound healing has not been demonstrated so far. In this study we have analyzed the expression pattern of activin and activin receptors in normal and wounded skin. We found a large induction of activin A and a minor induction of activin B mRNA expression 1 day after skin injury and high expression levels of activin A and B were found within the first 7 days after wounding. At 13 days after injury, expression of activin A mRNA had returned to the basal level, whereas high levels of activin B persisted. In situ hybridization studies revealed expression of activin A in the granulation tissue below the wound and activin B in the hyperproliferative epithelium at the wound edge and in the migrating epithelial tongue. All known types of activin receptors as well as the activin binding protein follistatin were expressed in normal and wounded skin. However, no significant induction of receptor gene expression was seen during the repair process. The distribution of activins and activin receptors in the wound suggests multiple autocrine and paracrine activities of the ligands during wound healing. Our data provide evidence for a novel function of activin and indicate that--besides TGF beta s themselves--other members of this superfamily might also play an important role in tissue repair.

Activin Receptors↗
PubMed1996

Dose-rate sparing for micronucleus induction in lymphocytes of controls and ataxia-telangiectasia heterozygotes exposed to 60Co gamma-irradiation in vitro.

We investigated the reproducibility of the cytochalasin B micronucleus (MN) assay in irradiated human lymphocytes to assess its suitability in predicting cancer predisposition and response to radiotherapy by virtue of defects in the processing of clastogenic lesions. G0 lymphocytes were exposed to 3.0 Gy 60Co gamma-rays at high (HDR) or low dose-rate (LDR). Six healthy donors were assayed three times each in nine experiments and compared with six ataxia-telangiectasia (A-T) heterozygotes. In controls, significant interexperiment variability in MN yields was observed at HDR and LDR, also in dose-rate sparing (i.e. reduction in MN yield at LDR compared with HDR). Significant inter-individual variability was seen at HDR, but not at LDR or for sparing. Average sparing was 66.4 +/- 4.8%. In spite of the experimental variability, a significant difference between controls and A-T heterozygotes was detected at LDR, and 5/6 heterozygotes had sparing values below the control range. This gives encouragement for the use of this assay in predictive testing if sources of experimental variability can be identified so as to improve discrimination between individuals. HDR and to a lesser extent LDR irradiation induced significant mitotic inhibition, seen as a reduction in binucleate cells after cytocholasin treatment. A positive correlation between mitotic inhibition and MN frequency suggests that similar lesions may be involved in these effects.

Adult↗
PubMed1996

cDNA cloning and chromosome mapping of the human Fe65 gene: interaction of the conserved cytoplasmic domains of the human beta-amyloid precursor protein and its homologues with the mouse Fe65 protein.

Using the yeast two hybrid system, a mouse embryo cDNA library was screened for proteins that interact with the C-terminus of the human beta-amyloid precursor protein (beta PP). A fusion protein was identified that interacts specifically with the cytoplasmic domain of beta PP and does not interact with the beta-amyloid region. The protein encoded by this partial mouse cDNA is identical to the C-terminus of the rat Fe65 protein. This mouse protein also interacts with the homologous C-terminal domains of the mouse amyloid precursor-like proteins, APLP1 and APLP2. These conserved cytoplasmic regions contain a common amino acid motif, Asn-Pro-Thr-Tyr, which has previously been shown to influence both the secretion and internalization of beta PP. Fe65 has been implicated in regulatory and cell signaling mechanisms because it contains two different motifs involved in protein binding, a WW domain (a variant of Src homology 3 domains) and a phosphotyrosine interaction domain (PID). Interestingly, the PID domain binds to the same motif present in the conserved cytoplasmic domains of the beta PP and beta PP-like proteins. RNA analyses reveal that Fe65 is predominantly expressed in brain and in the regions most affected by Alzheimer's disease (AD)-associated neuropathology. The human Fe65 mRNA was cloned from a fetal brain cDNA library. The message encodes a protein of 735 amino acids that is 95% identical to the rat Fe65 protein. The human Fe65 gene was mapped on human metaphase chromosomes to band 11p15 using fluorescence in situ hybridization.

Amino Acid Sequence↗
PubMed1996

Mouse thyroglobulin: conservation of sequence homology in C-terminal immunogenic regions of thyroglobulin.

cDNA encoding 287 amino acids of the C-terminus of mouse thyroglobulin was cloned and sequenced. The amino acid homology between mouse and rat thyroglobulin was 96%, and was 78% between mouse and human. It was found that mouse thyroglobulin completely shared homology with two thyroiditogenic peptides described by other investigators. These findings are consistent with our hypothesis that in murine experimental thyroiditis, the primary thyroiditogenic epitopes are encoded by mouse-specific regions of thyroglobulin.

Amino Acid Sequence↗