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Y H Ma

Publications and source records attributed to Y H Ma.

At least 19 recordsLinked to original sources
PubMed2006

Neutron reflection study of a water-soluble biocompatible diblock copolymer adsorbed at the air/water interface: the effects of pH and polymer concentration.

The effect of varying both the solution pH and copolymer concentration on the structure of layers of poly[2-(methacryloyloxy)ethyl phosphorylcholine-block-2-(dimethylamino)ethyl methacrylate] copolymer (denoted as MPC(30)-DMA(60), M(n) = 18,000) adsorbed at the air/water interface is studied using surface tension and specular neutron reflection. The surface structure of the adsorbed diblock copolymer is represented by a dense layer of 10-15 A on the air side, accompanied by a loose layer of 20-30 A extending into the aqueous phase. Although the uniform layer model generally provided a reasonable description of the adsorbed copolymer chains, some deviations were observed. A more detailed analysis showed that the distribution of the copolymer across the interface required a minimum of three layers to take into account the structural inhomogeneities. Refinement of the structural distributions involved the combined fitting of partially deuterated copolymer in null reflecting water and D(2)O and the fully hydrogenated copolymer in D(2)O, leading to a substantial improvement in the reliability of the structural profiles obtained. The data analysis showed an increase in surface excess at higher copolymer concentrations and at more alkaline pH. However, the copolymer layer was fully immersed in water under all conditions studied. Because the surface excess showed a steady increase across the cmc over the high pH range, we speculate that copolymer adsorption above the cmc involves the formation of surface micellar aggregates under these conditions.

Adsorption↗
PubMed2001

Human xenoreactivity is reduced in mice bearing porcine antisense alpha(1,3) galactosyltransferase cDNA.

AIM: To explore the effect of antisense alpha(1,3) galactosyltransferase alpha(1,3) GT cDNA on production of Gal alpha(1,3) Gal (Gal epitope) xenoantigen in vivo. METHODS: Transgenic mice bearing the porcine antisense alpha(1,3) GT cDNA (nt 1alpha-640) were generated by pronuclei microinjection method. The integration of transgene was identified by PCR and Southern-blot analysis. The expression of murine alpha(1,3) GT was characterized by RT-PCR. Morphology of the spleen was examined by histological technique. Gal epitope was detected by immunofluorescent analysis. Binding of human natural xenoantibodies (IgM and IgG) and complement (C3c) to cells from mice was determined by flow cytometric assay. RESULTS: Transgenic mice bearing the porcine antisense alpha(1,3) GT cDNA were born healthy and developed normally. However, necrosis occurred in the spleen of some mice heterozygous for transgene. Cell surface Gal epitope in transgenic heterozygotes was evidently reduced. Substantially less (30 % - 60 %) xenoantibodies in human serum bound to cells from a variety of tissues of transgenic heterozygotes compared with wild-type controls. Consequentially, human complement activation on cells from these mice was reduced by 40 % - 50 %. CONCLUSION: Human xenoreactivity could be effectively reduced by inhibiting the expression of alpha(1,3) galactosyltransferase with an antisense gene.

Animals↗
PubMed2001

Transgenic mice ubiquitously expressing human Fas ligand develop a slight form of graft-versus-host-like disease.

AIM: To construct transgenic mice bearing human Fas ligand (FasL/CD95L) cDNA, and further explore the physiological effects of ubiquitous expression of FasL on such animals. METHODS: Transgenic mice were produced by pronuclei microinjection method. Integration and transmission of transgene were identified by nest-PCR and Southern-blot analysis. Level of FasL mRNA was evaluated by semi-quantitative RT-PCR analysis. FasL protein was detected by immunofluorescence analysis. Morphological alterations in tissues were analyzed by histological examination. The percentage of alphabetaT cells in the spleen was determined by flow cytometry analysis. RESULTS: Two independent founder mice bearing human FasL cDNA under the control of CMV promoter were generated healthily. Human FasL was moderately expressed in the majority of tissues examined in F1 heterozygotic mice. Although developing normally, adult transgenic mice exhibited a slight form of graft-versus-host (GVH)-like disease characterized by many morphological abnormalities occurring locally in the spleen, testis, lung and liver. In addition, the percentage of alphabetaT cells in the spleen was respectively decreased approximately by 32 % and 24 % in two independent transgenic lines, relative to wild-type mice. CONCLUSION: Ubiquitous expression of Fas ligand can lead to slight GVH-like disease

Animals↗
PubMed2001

Overexpression of gamma-aminobutyric acid transporter subtype I leads to cognitive deterioration in transgenic mice.

AIM: To explore the physiological role of gamma-aminobutyric acid transporter subtype I (GAT1) in cognition. METHODS: Transgenic mice were produced by pronuclei microinjection method. Integration of transgene was identified by Southern-blot and PCR analysis in various generations. Level of GAT1 mRNA in a variety of tissues was evaluated by semi-quantitative RT-PCR analysis. GAT1 protein was detected by immunofluorescence and histochemistry analysis. Associative learning capacity was analyzed by conditioned avoidance task. Memory retention was assessed by novel object recognition test. Morphology of synaptosomes was examined by electron microscope. RESULTS: Four independent founder mice bearing various copies of transgene were generated. GAT1 was evidently overexpressed at both mRNA and protein level in a variety of tissues from transgenic mice. In comparison with wild-type mice, transgenic mice exhibited significantly declined associative learning capacity (P < 0.01) and decreased memory retention (P < 0.01 in 1-h-retention, and P < 0.05 in 1-d-retention). In addition, the amount of asymmetric synapses in the brain of transgenic mice was reduced approximately by 24 %, relative to wild-type mice. CONCLUSION: Overexpression of GAT1 in mice results in cognitive deterioration, indicating that the alteration in the expression of gamma-aminobutyric acid transporters is involved in the pathophysiological mechanism underlying some cognitive deficiencies.

Animals↗
PubMed2000

Gamma-aminobutyric acid transporter (GAT1) overexpression in mouse affects the testicular morphology.

Gamma-aminobutyric acid and GABAergic receptors were previously reported to be distributed in reproductive systems besides CNS and predicted to participate in the modulation of testicular function. Gamma-aminobutyric acid transporter was implicated to be involved in this process. However, the potential role of gamma-aminobutyric transporter in testis has not been explored. In this study, we investigated the existence of mouse gamma-aminobutyric acid transporter subtype I (mGAT1) in testis. Wild-type and transgenic mice, which overexpressing mGAT1 in a variety of tissues, especially in testis, were primarily studied to approach the profile of mGAT1 in testis. Mice with overexpressed mGAT1 develop normally but with reduced mass and size of testis as compared with wild-type. Testicular morphology of transgenic mice exhibited overt abnormalities including focal damage of the spermatogenic epithelium accompanied by capillaries proliferation and increased diameter of seminiferous tubules lumen. Reduced number of spermatids was also found in some seminiferous tubules. Our results clearly demonstrate the presence of GAT1 in mouse testis and imply that GAT1 is possibly involved in testicular function.

Animals↗
PubMed2000

Transgenic mice overexpressing gamma-aminobutyric acid transporter subtype I develop obesity.

Transgenic mice ubiquitously overexpressing murine gamma-aminobutyric acid transporter subtype I were created. Unexpectedly, these mice markedly exhibited heritable obesity, which features significantly increased body weight and fat deposition. Behavioral examination revealed that transgenic mice have slightly reduced spontaneous locomotive capacity and altered feeding pattern. This preliminary finding indicates that the inappropriate level of gamma-aminobutyric acid transporters may be directly or indirectly involved in the pathogenic mechanism underlying certain types of obesity.

Animals↗
PubMed2000

Increased expression of GAD65 and GABA in pancreatic beta-cells impairs first-phase insulin secretion.

The functional role of glutamate decarboxylase (GAD) and its product GABA in pancreatic islets has remained elusive. Mouse beta-cells express the larger isoform GAD67, whereas human islets express only the smaller isoform GAD65. We have generated two lines of transgenic mice expressing human GAD65 in pancreatic beta-cells (RIP7-hGAD65, Lines 1 and 2) to study the effect that GABA generated by this isoform has on islet cell function. The ascending order of hGAD65 expression and/or activity in beta-cells was Line 1 heterozygotes < Line 2 heterozygotes < Line 1 homozygotes. Line 1 heterozygotes have normal glucose tolerance, whereas Line 1 homozygotes and Line 2 heterozygotes exhibit impaired glucose tolerance and inhibition of insulin secretion in vivo in response to glucose. In addition, fasting levels of blood glucose are elevated and insulin is decreased in Line 1 homozygotes. Pancreas perfusion experiments suggest that GABA generated by GAD65 may function as a negative regulator of first-phase insulin secretion in response to glucose by affecting a step proximal to or at the K(ATP)(+) channel.

Animals↗
PubMed1999

Mechanical strain increases PDGF-B and PDGF beta receptor expression in vascular smooth muscle cells.

Cyclic mechanical strain causes proliferation of vascular smooth muscle cells, mediated in part by platelet-derived growth factor (PDGF). We examined the effect of cyclic strain on expression of PDGF-B and the PDGF beta receptor. Neonatal rat vascular smooth muscle cells were exposed to 1 hertz cyclic strain on silicone elastomer plates. PDGF-B mRNA increased after 6 h of strain. In cells transfected with a PDGF-B promoter chloramphenicol acetyl transferase construct (psisCAT 6A), activity increased by 12-fold following 12 h of strain. Two neutralizing antibodies to the PDGF beta receptor both reduced strain-induced [(3)H]thymidine incorporation by 50%. Expression of the PDGF beta receptor protein increased 1.8-fold following 24 h of strain. During strain, PDGF beta receptor expression was not significantly altered by neutralizing antibodies to PDGF-B. Thus, both PDGF-B and the PDGF beta receptor are induced by cyclic mechanical strain and both contribute to cell proliferation in response to strain.

Animals↗
PubMed1999

Rapid induction and translocation of Egr-1 in response to mechanical strain in vascular smooth muscle cells.

The effect of mechanical strain on transcription and expression of the immediate-early genes, early growth response gene-1 (Egr-1), c-jun, and c-fos, was investigated in neonatal rat aortic vascular smooth muscle (VSM) cells. Cells grown on silicone elastomer plates were subjected to cyclic mechanical strain (1 Hz) at various durations and magnitudes. Egr-1 mRNA increased rapidly in response to cyclic strain, reached a maximum of 10-fold after 30 minutes, and returned to baseline after 4 hours. c-jun exhibited a similar pattern, whereas c-fos mRNA expression was unaffected by strain. Cycloheximide prolonged the increase in Egr-1 and c-jun mRNA and caused superinduction of both. The threshold level of continuous cyclic strain needed to induce expression was 5% for Egr-1 and c-jun. Even a single cycle of mechanical strain that lasted 1 second was sufficient to induce Egr-1 and c-jun mRNA. Strain also increased expression of a transiently transfected Egr-1 promoter-reporter construct. The effect of varying extracellular matrices on strain-induced Egr-1 and c-jun mRNA was examined. In contrast to collagen type 1- and pronectin-coated plates, strain did not significantly alter expression of Egr-1 and c-jun was less induced on laminin-coated plates. On collagen type 1, strain increased Egr-1 protein levels by 2.1-fold at 60 minutes. Immunofluorescence microscopy revealed translocation of Egr-1 to the nucleus in response to strain. These observations indicate that Egr-1 expression and translocation are sensitive to mechanical perturbation of the cell. c-jun is also induced by strain, but c-fos is not. The signal for this induction may involve specific cell-matrix interactions.

Animals↗
PubMed1999

Calcium-mediated mechanisms of eicosapentaenoic acid-induced relaxation in hypertensive rat aorta.

We have previously demonstrated the vasorelaxant properties of the omega-3 fatty acid, eicosapentaenoic acid (EPA), in normotensive and spontaneously hypertensive rat (SHR) aorta, although the mechanism(s) of action are not fully understood. Because endothelial dysfunction and increased intracellular free calcium concentration ([Ca2+]i) are seen in hypertensive rat aorta, we investigated the potential role of Ca2+ signaling, endothelium and derived factors, and the opening of potassium (K+) channels in EPA-induced relaxation. In the presence of extracellular Ca2+, EPA induced significant relaxations at >10 micromol/L (P<.01) in norepinephrine (NE) (10(-6) mol/L)-contracted aortic rings and at 30 micromol/L (P<.001) in high K+ (80 mmol/L)-contracted aortic rings. In the absence of extracellular Ca2+, EPA (10 to 30 micromol/L) inhibits the tonic component of NE-induced contraction (P<.0001). The relaxant properties of EPA in SHR aorta appear specific to Ca2+ release from an internal storage site associated with NE-induced tonic contraction. Further studies with the use of fura-2 to measure [Ca2+]i in cultured vascular smooth muscle (VSM) cells from SHR aorta indicated that EPA (30 micromol/ L)-pretreatment attenuated angiotensin II (50 nmol/ L)-induced Ca2+ transient by 95%, suggesting that an inhibitory effect on the Ca2+ signaling may underlie EPA-induced relaxation of the vessel preparation. In addition, EPA per se induced an increase in [Ca2+li with a duration of approximately 20 min in VSM cells, and the effect was not altered by removal of extracellular Ca2+. There was no increase in the level of inositol-1,4,5-trisphosphate in response to EPA (30 micromol/L). The actions of EPA are independent of endothelium-derived factors, cyclooxygenase metabolites, and activation of K+ channels since endothelium removal, N(omega)-nitro-L-arginine methyl ester hydrochloride, (L-NAME, 100 micromol/L), indomethacin (10 micromol/L), tetraethylammonium (1 mmol/L), and glibenclamide (10 micromol/L) did not affect EPA-induced vasodilation in NE-precontracted aortic rings. These results suggest that EPA directly modulates intracellular Ca2+ signaling in VSM cells, and that this may contribute to the vasorelaxant effect and, at least in part, the blood pressure-lowering effect of fish oil.

Angiotensin II↗
PubMed1999

Matrix-dependent gene expression of egr-1 and PDGF A regulate angiotensin II-induced proliferation in human vascular smooth muscle cells.

We have previously shown, in a neonatal rat cell line, that angiotensin II (Ang II)-induced proliferation in vascular smooth muscle cells is extracellular matrix (ECM) dependent. We hypothesized that such an effect might be mediated via differences in Ang II-induced increases in the transcriptional factor early growth response-1 (Egr-1) gene and, consequently, in platelet-derived growth factor (PDGF). Cultured human newborn aortic smooth muscle cells were studied on 4 different surfaces: (1) plastic, (2) laminin, (3) collagen, and (4) fibronectin. Ang II-induced increases in DNA synthesis were significantly greater on collagen (2.0+/-0.3-fold) and fibronectin (1.9+/-0.3-fold) than on laminin (1.0+/-0.2-fold) or plastic (1.4+/-0.2-fold). As with DNA synthesis, at 48 and 72 hours, Ang II-induced increases in cell numbers occurred only in cells grown on collagen and fibronectin culture plates and were blocked by an antagonist to the angiotensin type 1 (losartan, 10 micromol/L) but not the angiotensin type 2 (PD 123319, 10 micromol/L) receptor. Anti-PDGF AA antibody (6 microg/mL) blocked the increase in DNA synthesis by 60% to 64% in cells on collagen or fibronectin cultures but not on plastic cultures. When PDGF-AA (10 ng/mL) and Ang II were added together, DNA synthesis increased 2-fold and did not differ on the various ECM proteins. Increases in PDGF A-chain mRNA were observed only in cells grown on collagen (3.21+/-0.65-fold) and fibronectin (2.86+/-0.49-fold) plates 2 to 8 hours after the addition of Ang II and were blocked by losartan but not PD 123319. Expression of Egr-1, an early growth response gene, increased at 15 minutes, peaked at 30 minutes, and returned to normal after 2 hours with Ang II treatment. Ang II-induced increases in Egr-1 mRNA were greater on collagen (4. 82+/-0.66-fold at maximum) and fibronectin (4.01+/-0.56-fold) than on laminin (2.74+/-0.45-fold) or plastic (2.53+/-0.40-fold) and were blocked by losartan but not PD 123319. Thus, in human vascular smooth muscle cells in culture, Ang II-induced proliferation is mediated via the angiotensin type 1 receptor, dependent on ECM proteins, and regulated by differential gene expression of Egr-1 and PDGF-1.

Angiotensin II↗
PubMed1998

Reconstruction of three-dimensional digital teeth.

OBJECTIVE: Dental anatomy is one of the most important basic courses in the education of dentistry. The deep understanding of both the external and internal morphologic characteristics is very important to the teaching, research and clinical practice of dentistry. METHODS: In the present study, 32 permanent teeth from the skull specimen of a young man were individually embedded in black fluid resin, each in special containers. They were ground by a numerically-controlled grinding machine at intervals of 0.2 mm per layer. A distinct outline of the tooth could be seen on every section. Black and white photographs were taken and scanned into a computer by a film-scanner to obtain sequences of two-dimensional images of the tooth sections. After pattern recognition, all of the images of each tooth were piled up at intervals of 0.2 mm by the technique of computerized reconstruction. RESULTS: The three-dimensional stereo tooth models were built up from two-dimensional data. On the basis of those models, computer graphic techniques were used to highlight, smooth, and shade the teeth. These digital teeth and dentitions could function as a series of computerized teaching models. Their high resolution and accuracy could meet the basic demands of dentistry. CONCLUSIONS: The present study developed new techniques of model preparation, image input, and 3-D reconstruction. These digital teeth and dentitions provide an important foundation for the application of computer imaging, CAD/CAM, computer-assisted instruction, and virtual reality in dentistry.

Anatomy, Cross-Sectional↗
PubMed1997

Chronic sympathetic innervation of islets in transgenic mice results in differential desensitization of alpha-adrenergic inhibition of insulin secretion.

The effects of chronic sympathetic hyperinnervation on pancreatic beta-cell insulin secretion were investigated utilizing the in vitro perfused pancreas from transgenic mice. These mice exhibit islet hyperinnervation of sympathetic neurons resulting from overexpression of nerve growth factor in their beta-cells (1). The goal was to determine whether sympathetic hyperinnervation increased classic alpha-adrenergic inhibition of beta-cell insulin secretion or, in contrast, down-regulated beta-cell sensitivity to adrenergic input resulting in enhanced insulin secretion. Both fasting and fed blood sugars and pancreatic insulin content were normal in the transgenics. Response of the transgenic perfused pancreas to low glucose (7 mM) was primarily first phase and normal whereas high glucose (22 mM) caused enhanced, rather than reduced, insulin secretion of both first and second phases. The alpha-antagonist, phentolamine, caused a six-fold increase in glucose-stimulated insulin secretion from the control pancreas, an effect that was blunted for the transgenic pancreas. A similarly blunted response to phentolamine occurred when this agent was superimposed on a combined glucose-forskolin stimulus. (The positive effect on insulin secretion by phentolamine in normal beta-cell preparations has arguably been ascribed to non-specific ionic effects.) Therefore, as a test of possible changes in the ATP regulated K+ channel or the linked Ca++ channels, glyburide was perfused during glucose stimulation. Insulin secretion in response to glyburide was increased two fold in the control pancreas. However, with the transgenic pancreas, in contrast to the enhanced response to glucose, the effect of glyburide was almost completely inhibited. It is concluded that: 1) chronic adrenergic hyperinnervation results in enhanced glucose-stimulated insulin secretion by desensitization of a major alpha-adrenergic inhibitory site(s); and 2) adrenergic hyperinnervation acts directly or indirectly on ion flux to partially inhibit insulin release, an effect which is not desensitized. Since down-regulation of a single alpha-adrenergic receptor would be expected to desensitize both phenomena the observed differential desensitization indicates that different post receptor events or more than one adrenergic receptor are involved.

Adrenergic alpha-Antagonists↗
PubMed1997

Characterization of 5'-proximal sequence of mouse GABA transporter gene (GAT-1).

The cDNA molecule encoding the mouse GABA transporter gene (GAT-1) was used as probe for selecting GAT-1 gene from mouse genomic library. A positive clone, harboring the whole open reading frame of the GAT-1 protein and designated as MGABAT-G, was fished out from the library, the 5' proximal region and intron 1 were sequenced and analysed, and low homology was found in the above region between GAT-1 genes from mouse and human except some short conserved sequences. The DNA-protein interactions between DNA fragments containing the conserved sequences in the 5' proximal region and nuclear proteins from different tissues of mouse were studied by means of gel-shift assay, and Southern-Western blot. The results indicate a possible positive-negative regulation mode controlling the expression of the mouse GAT-1 gene.

Animals↗
PubMed1997

Growth hormone secretagogues stimulate the hypothalamic-pituitary-adrenal axis and are diabetogenic in the Zucker diabetic fatty rat.

Besides stimulating GH release, some GH secretagogues also release ACTH and adrenal steroids. Several novel classes of potent GH secretagogues have recently been described, and we have now tested their ability to release corticosterone in conscious normal rats. All analogs that released GH also stimulated corticosterone release to some degree, though the relative effects on GH and corticosterone varied somewhat. The corticosterone responses for some analogs were in the range of those obtained with CRF (2 microg, iv), whereas closely related analogs inactive for GH release failed to release corticosterone. Activation of the hypothalamic-pituitary-adrenal axis with GH release by GHRPs could be a highly diabetogenic combination in susceptible individuals. Therefore, a potent GHRP pentapeptide analog (G7039, 100 microg/day, sc, bid) was given to young obese male Zucker diabetic fatty rats (ZDF, n = 8/group) for 24 days. Other groups received hGH (500 microg/day, sc, bid), recombinant human insulin-like growth factor (rhIGF)-1 (750 microg/day, sc, infusion) or excipient, alone or in combination. Both G7039 and hGH increased weight gain, markedly raised serum glucose (G7039, 542 +/- 37; hGH, 725 +/- 30; excipient, 330 +/- 57 mg/dl) and doubled insulin levels but had opposite effects on serum triglycerides (G7039, 1412 +/- 44; hGH 501 +/- 46; excipient 1058 +/- 73 mg/dl) and fat depot weights. In contrast, treatment with IGF-1, alone or in combination with hGH or G7039, improved the diabetic state and stimulated growth. Thus, both G7039 and hGH treatment stimulated growth in ZDF rats, but greatly worsened diabetes, unless IGF-1 was coadministered. Some of the effects ofG7039 could be explained by GH release, but the effects on blood lipids and body fat were not seen with hGH and may reflect the additional activation of the hypothalamic-pituitary-adrenal axis by the secretagogue. The magnitude of these adverse effects in the ZDF animals suggest that chronic administration of GHRP analogs with cortisol-releasing activity to obese or diabetes-prone individuals warrants careful evaluation.

Animals↗
PubMed1996

Site-specific induction and repair of benzo[a]pyrene diol epoxide DNA damage in human H-ras protooncogene as revealed by restriction cleavage inhibition.

Most genotoxic DNA base modifications localized at key genomic sequences constitute the molecular alterations crucial or mutagenesis and tumorigenesis. We have utilized lesion-rendered inhibition of restriction endonuclease cleavage for the analysis of site-specific DNA damage induced by (+/-)-7,8-dihydroxy-anti-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (benzo[a]pyrene diol epoxide, anti-BPDE) in human genes. The H-ras protooncogene and insulin gene sequences were used as targets for modification in vitro and in vivo. Selective induction of individual facultative bands, resulting from covalent modification of the cognate recognition sites, was observed in modified plasmid DNA for a number of restriction nucleases. The ras gene-specific damage, at the PstI, BstYI, NotI and BstEII recognition sites, was visualized and quantitated in human genomic DNA adducted by anti-BPDE. Repair of lesions at hexanucleotide sequences and/or regions surrounding the restriction site, was assessed as a gradual disappearance of facultative bands in DNA from repair-proficient human fibroblasts exposed to the carcinogen in confluent culture. Efficiency of the PstI site-specific repair was compared at low and high levels of initial damage. Higher genotoxic dose caused a decrease in the extent of adduct removal from the bulk DNA, while the specific site of the ras gene was still subject to fast repair. No measurable PstI site-specific repair was detected in the insulin gene. These results show the region-selective induction of bulky anti-BPDE DNA damage in non-related genomic targets and suggest that repair of these lesions in human cells proceeds with the efficiency tightly controlled at different levels of initial genotoxic load.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗