Biomedical subjects

Y Fu

Publications and source records attributed to Y Fu.

At least 127 records · Page 7Linked to original sources

PubMed1998

Response of the hypothalamo-pituitary-adrenal axis to nicotine.

Nicotine has been shown to be a potent stimulus for the secretion of the stress-responsive hormones, adrenocorticotropin (ACTH) and prolactin. This paper reviews the findings by our laboratory and others that demonstrate the polysynaptic pathways involved in the neuroendocrine responses to systemic nicotine. It will focus primarily on the hypothalamo-pituitary-adrenal (HPA) axis and the effect of nicotine on ACTH secretion, with supplementary information on prolactin secretion, where relevant. Data are presented demonstrating that nicotine acts via a central mechanism to stimulate indirectly the release of ACTH from the anterior pituitary corticotropes. Nicotine does not appear to act directly at the hypothalamic paraventricular nucleus (PVN), the site of the corticotropin-releasing hormone (CRH) neurons crucial to the regulation of ACTH. However, brainstem catecholaminergic regions projecting to the PVN showed a regionally selective and dose-dependent sensitivity to nicotine, particularly the noradrenergic/adrenergic nucleus tractus solitarius (NTS). A reduction in the modulatory effect of these catecholamines (by neurotoxic lesion, synthetic enzyme inhibitors or adrenergic receptor antagonists) resulted in an inhibition of nicotine-stimulated ACTH secretion. In addition, blockade of nicotinic cholinergic receptors (NAchRs) in the brainstem by the antagonist, mecamylamine, resulted in a dose-dependent reduction in norepinephrine (NE) release from terminals in the PVN, and a concomitant reduction in plasma ACTH. The differential sensitivity of these receptors to the nicotinic agonists, cytisine and nicotine, reflects the heterogeneity of the NAchR subtypes involved. The desensitization characteristics of the neuroendocrine responses to both acute and chronic nicotine exposure are indicative of an alteration in these NAchRs.

Animals↗

PubMed1998

Left ventricular geometric patterns and QT dispersion in borderline and mild hypertension: their evolution and regression.

To investigate whether QT dispersion increases in borderline and mild hypertension during a longitudinal observation of > 3 years and whether it is improved with medications, left ventricular geometric patterns and QT dispersion were studied with special regard to their longitudinal changes in 85 male borderline and mild hypertensive subjects with left ventricular mass index < 125 g/m2. These subjects were followed for > 3 years without medication. Thirty-two patients with a left ventricular mass index > 125 g/m2 at the end of follow-up period were further observed using antihypertensive drugs for an additional 3 years. Echocardiograms and electrocardiograms were obtained at the beginning and end of the follow-up period. At the end of the follow-up period, subjects were classified into four groups based on ventricular geometric patterns determined by left ventricular mass index and relative wall thickness in diastole. The QT dispersion was greater in patients with concentric hypertrophy (56+/-18 msec) than in patients with normal geometry (41+/-17 msec) (P < .05) and increased significantly in the former group during the follow-up period. After medication, the left ventricular mass index regressed and the QT dispersion decreased (from 55+/-21 to 50+/-26 msec, P < .01) in these patients. Thus, these findings suggest that changes in the QT dispersion reflect both concentric evolution and regression of left ventricular hypertrophy.

Adult↗

PubMed1998

No association between alpha-adducin 460 polymorphism and essential hypertension in a Japanese population.

Many unknown genetic factors are involved in the pathogenesis of hypertension. Recently, the reverse genetic approach revealed that some genetic variants, such as angiotensinogen, lipoprotein lipase, and alpha-adducin gene polymorphisms, increase the risk for hypertension. Both in rat and human, the genetic predisposition to hypertension was confirmed only for angiotensinogen and alpha-adducin genes. Adducin is a membrane cytoskeletal protein, which is thought to regulate sodium transport. Abnormalities of membrane sodium transport in the kidney play an important role in hypertension. A recent report by Cusi et al showed that the Trp allele of alpha-adducin polymorphism (Gly 460 Trp) is associated with an increased risk of hypertension in whites, which led us to carry out a case-control study to examine whether the same association is observed in the Japanese population. We recruited 170 hypertensive and 194 normotensive Japanese subjects and compared the genotype distribution of alpha-adducin 460 polymorphism between cases and controls and between whites and Japanese. Trp allele frequency of controls in the Japanese subjects was twice as high as in the whites. However, no association was observed between alpha-adducin polymorphism and hypertension. Furthermore, alpha-adducin 460 polymorphism was not associated with any clinical characteristics. Accordingly, we concluded that alpha-adducin 460 polymorphism is not a major genetic risk for hypertension in Japanese people.

Alleles↗

PubMed1998

Methylenetetrahydrofolate reductase gene polymorphism: relation to blood pressure and cerebrovascular disease.

Hyperhomocysteinemia is reported to be associated with an increase in the incidence of ischemic heart disease and cerebrovascular disease. Genetic aberrations in methylenetetrahydrofolate reductase (MTHFR) may account for reduced enzyme activity and elevated plasma homocysteine level. A recent report revealed that a common mutation (677C to T; Ala to Val) in the MTHFR gene is associated with decreased specific MTHFR activity and with increased risk for coronary artery disease in the homozygous state (Val/Val). In the present study, we investigated whether the MTHFR gene is a genetic risk factor for cerebrovascular disease (CVD). To undertake a case-control study, we selected the patients with cerebral infarction (n = 48) or cerebral hemorrhage (n = 35) and examined the association between MTHFR gene polymorphism and CVD. The genotype distribution of the MTHFR gene was not significantly different between cases and controls. Because the possibility of matching the morbidity of the effects of hypertension, the lack of association could not be excluded in the first study; however, we also examined whether the MTHFR mutation was associated with any clinical risk factor for CVD or with hypertension. It turned out that the subjects with the Val allele of the MTHFR gene had significantly lower blood pressure than the subjects with other genotypes in the general population (P = .02), and that the frequency of the Val/Val genotype in hypertensive subjects (n = 173) was significantly lower than in control subjects (n = 184) (P = .03). From these results, we conclude that the Val/Val homozygous state of the MTHFR gene increased the risk of thrombosis, but reduced the blood pressure, which resulted in the lack of increased risk for CVD.

Cerebrovascular Disorders↗

PubMed1998

Cytokine regulation of secondary lymphoid organ development.

Lymphotoxin and tumor necrosis factor provide essential signals for the formation of secondary lymphoid tissue structures. Lymphotoxin in its membrane form (LT alpha 1 beta 2 heterotrimer) is required for the development of lymph nodes and Peyer's patches and supports the development of normal spleen structure. In the spleen, lymphotoxin acts during embryonic development to support the formation of distinct B and T cell zones. Lymphotoxin also acts in a tonic fashion-supporting the formation and maintenance of the follicular dendritic cell network and of primary B cell follicle structure. The cells that deliver the tonic lymphotoxin signal supporting follicular dendritic cell structure are B cells; thus, B cells participate fundamentally in the development of the lymphoid tissue structure in which they subsequently mature.

Animals↗

PubMed1998

Viral sequences enable efficient and tissue-specific expression of transgenes in Xenopus.

Expression of transgenes within a single generation by direct DNA injection into vertebrate embryos has been plagued by inefficient and nonuniform gene expression. We report a novel strategy for efficient and stable expression of transgenes driven by both ubiquitous and tissue-specific promoters by direct DNA injection into developing Xenopus laevis embryos. This strategy involves flanking expression cassettes of interest with inverted terminal repeat sequences (ITRs) from adeno-associated virus. Our results suggest that the ITR strategy may be generally applicable to other systems, such as zebra fish and embryonic stem cells, and may enable tissue-specific expression of transgenes in problematic contexts.

Actins↗

PubMed1998

The Salmonella typhimurium tyrosine phosphatase SptP is translocated into host cells and disrupts the actin cytoskeleton.

The Salmonella typhimurium protein tyrosine phosphatase SptP is a target of the centisome 63 type III protein secrtion system. This system is essential for the interaction of these bacteria with host cells. We have shown here by a combination of biochemical and microscopy techniques that S. typhimurium directs the translocation of SptP into cultured epithelial cells. Translocation requires the function of the secreted proteins, SipB, SipC and SipD, as strains carrying mutations in any of the genes encoding these proteins fail to translocate SptP. Microinjection of purified GST-SptP into cultured cells results in the disruption of the actin cytoskeleton and the disappearance of stress fibres. These changes are reversible, as microinjected cells regain the normal appearance of their actin cytoskeleton upon prolonged incubation. Microinjection of the catalytically active GST-SptP(C481S) protein results in changes similar to those induced by the wild-type toxin. Furthermore, microinjection of a fusion protein between GST and the first 285 amino acids of SptP also leads to identical disruption of the host cell actin cytoskeleton, indicating that the amino-terminal half of SptP is sufficient to mediate this effect. However, microinjection of a fusion protein between GST and the last 259 amino acids of SptP also disrupted the normal appearance of the cytoskeleton. These results support the hypothesis that SptP is an effector protein arranged in modular domains that may co-operate with each other to exert relate functions.

Actins↗

PubMed1998

Treatment planning optimization by quasi-Newton and simulated annealing methods for gamma unit treatment system.

The gamma unit is used to irradiate a target within the brain. During such a treatment many parameters, including the number of shots, the coordinates, the collimator size and the weight associated with each shot, affect the amount of dose delivered to the target volume and to the surrounding normal tissues. Hence it is not easy to determine an appropriate set of these parameters by a trial and error method. For this reason, we present here an optimization method to determine mathematically those parameters. This method is composed of two steps: firstly, a quasi-Newton method is used to deal with the continuous variables such as position and weight of shots; the result obtained at the end of this step then serves as the initial configuration for the next step, in which a simulated annealing method is applied to optimize all the aforementioned parameters. Application of the proposed methods to two examples shows that our optimization algorithm runs in a satisfactory way.

Algorithms↗

PubMed1998

Mutagenesis of the glucose-1-phosphate-binding site of potato tuber ADP-glucose pyrophosphorylase

Lysine (Lys)-195 in the homotetrameric ADP-glucose pyrophosphorylase (ADPGlc PPase) from Escherichia coli was shown previously to be involved in the binding of the substrate glucose-1-phosphate (Glc-1-P). This residue is highly conserved in the ADPGlc PPase family. Site-directed mutagenesis was used to investigate the function of this conserved Lys residue in the large and small subunits of the heterotetrameric potato (Solanum tuberosum) tuber enzyme. The apparent affinity for Glc-1-P of the wild-type enzyme decreased 135- to 550-fold by changing Lys-198 of the small subunit to arginine, alanine, or glutamic acid, suggesting that both the charge and the size of this residue influence Glc-1-P binding. These mutations had little effect on the kinetic constants for the other substrates (ATP and Mg2+ or ADP-Glc and inorganic phosphate), activator (3-phosphoglycerate), inhibitor (inorganic phosphate), or on the thermal stability. Mutagenesis of the corresponding Lys (Lys-213) in the large subunit had no effect on the apparent affinity for Glc-1-P by substitution with arginine, alanine, or glutamic acid. A double mutant, SK198RLK213R, was also obtained that had a 100-fold reduction of the apparent affinity for Glc-1-P. The data indicate that Lys-198 in the small subunit is directly involved in the binding of Glc-1-P, whereas they appear to exclude a direct role of Lys-213 in the large subunit in the interaction with this substrate.

Journal Article↗

PubMed1998

ADP-Glucose pyrophosphorylase from potato tubers. Site-directed mutagenesis studies of the regulatory sites.

Several lysines (Lys) were determined to be involved in the regulation of the ADP-glucose (Glc) pyrophosphorylase from spinach leaf and the cyanobacterium Anabaena sp. PCC 7120 (K. Ball, J. Preiss [1994] J Biol Chem 269: 24706-24711; Y. Charng, A.A. Iglesias, J. Preiss [1994] J Biol Chem 269: 24107-24113). Site-directed mutagenesis was used to investigate the relative roles of the conserved Lys in the heterotetrameric enzyme from potato (Solanum tuberosum L.) tubers. Mutations to alanine of Lys-404 and Lys-441 on the small subunit decreased the apparent affinity for the activator, 3-phosphoglycerate, by 3090- and 54-fold, respectively. The apparent affinity for the inhibitor, phosphate, decreased greater than 400-fold. Mutation of Lys-441 to glutamic acid showed even larger effects. When Lys-417 and Lys-455 on the large subunit were mutated to alanine, the phosphate inhibition was not altered and the apparent affinity for the activator decreased only 9- and 3-fold, respectively. Mutations of these residues to glutamic acid only decreased the affinity for the activator 12- and 5-fold, respectively. No significant changes were observed on other kinetic constants for the substrates ADP-Glc, pyrophosphate, and Mg2+. These data indicate that Lys-404 and Lys-441 on the small subunit are more important for the regulation of the ADP-Glc pyrophosphorylase than their homologous residues in the large subunit.

Amino Acid Sequence↗

PubMed1998

Expression of the Candida albicans gene ALS1 in Saccharomyces cerevisiae induces adherence to endothelial and epithelial cells.

To identify genes encoding adhesins that mediate the binding of Candida albicans to endothelial cells, a genomic library from this organism was constructed and used to transform Saccharomyces cerevisiae. These transformed organisms were screened for adherence to endothelial cells, and a highly adherent clone was identified. The adherence of this clone to endothelial cells was over 100-fold greater than that of control S. cerevisiae transformed with the empty plasmid. This clone also exhibited enhanced adherence to epithelial cells. The C. albicans gene contained within this clone was found to be ALS1. These results indicate that ALS1 may encode a candidal adhesin.

Adhesiveness↗

PubMed1998

Cloning and characterization of CAD1/AAF1, a gene from Candida albicans that induces adherence to endothelial cells after expression in Saccharomyces cerevisiae.

Adherence to the endothelial cell lining of the vasculature is probably a critical step in the egress of Candida albicans from the intravascular compartment. To identify potential adhesins that mediate the attachment of this organism to endothelial cells, a genomic library from C. albicans was used to transform a nonadherent strain of Saccharomyces cerevisiae. The population of transformed yeasts was enriched for highly adherent clones by repeated passages over endothelial cells. One clone which exhibited a fivefold increase in endothelial cell adherence, compared with S. cerevisiae transformed with vector alone, was identified. This organism also flocculated. The candidal DNA fragment within this adherent/flocculent organism was found to contain a single 1.8-kb open reading frame, which was designated CAD1. It was found to be identical to AAF1. The predicted protein encoded by CAD1/AAF1 contained features suggestive of a regulatory factor. Consistent with this finding, immunoelectron microscopy revealed that CAD1/AAF1 localized to the cytoplasm and nucleus but not the cell wall or plasma membrane of the transformed yeasts. Because yeasts transformed with CAD1/AAF1 both flocculated and exhibited increased endothelial cell adherence, the relationship between adherence and flocculation was examined. S. cerevisiae expressing either of two flocculation phenotypes, Flo1 or NewFlo, adhered to endothelial cells as avidly as did yeasts expressing CAD1/AAF1. Inhibition studies revealed that the flocculation phenotype induced by CAD1/AAF1 was similar to Flo1. Thus, CAD1/AAF1 probably encodes a regulatory protein that stimulates endothelial cell adherence in S. cerevisiae by inducing a flocculation phenotype. Whether CAD1/AAF1 contributes to the adherence of C. albicans to endothelial cells remains to be determined.

Adhesiveness↗

PubMed1998

Identification of a specific chaperone for SptP, a substrate of the centisome 63 type III secretion system of Salmonella typhimurium.

Salmonella typhimurium uses of a type III protein secretion system encoded at centisome 63 of its chromosome to deliver effector molecule into the host cell. These proteins stimulate host cell responses such as reorganization of the actin cytoskeleton and activation of transcription factors. One of these effector proteins is SptP, a tyrosine phosphatase that causes disruption of the host cell actin cytoskeleton. A characteristic feature of many substrates of type III secretion systems is their association with specific cytoplasmic chaperones which appears to be required for secretion and/or translocation of these proteins into the host cell. We report here the identification of SicP, a 13-kDa acidic polypeptide that is encoded immediately upstream of sptP. A loss-of-function mutation in sicP resulted in drastically reduced levels of SptP but did not affect sptP expression, indicating that SicP exerts its effect posttranscriptionally. Pulse-chase experiments demonstrated that the loss of SicP leads to increased degradation of SptP. In addition, we show that SicP binds to SptP directly and that the binding site is located between residues 15 and 100 of the tyrosine phosphatase. Taken together, these results indicate that SicP acts as a specific chaperone for SptP.

Actins↗

PubMed1998

Endothelial nitric oxide synthase increases in left atria of dogs with pacing-induced heart failure.

In congestive heart failure (CHF) the alterations in cardiac NO synthase (NOS) isoforms activity and expression are incompletely documented and the chamber specificity of these changes is unknown. We studied plasma nitrate-nitrite (NO-x), atrial, and ventricular NOS activities and protein expression (Western blot and densitometric analysis) in nonpaced control dogs and in dogs paced for 2 or 21 days into CHF. Plasma NO-x rose significantly after 7 and 21 days of pacing, whereas creatinine levels remained unchanged. In control dogs Ca2+-dependent NOS activity in left atria was double that of right or left ventricular activity. In paced animals the activity increased only in the atria after 21 but not 2 days of pacing. Levels of endothelial NOS (eNOS) protein were enhanced in the left atria but not ventricles after 21 days of pacing because of a greater quantity of the 150-kDa but not the 135-kDa eNOS. Ca2+-independent NOS activity was undetectable in any cardiac tissue. The specific upregulation of eNOS in the left atria suggests that NO production may be enhanced to counterbalance hypertrophy that develops during pacing-induced CHF.

Animals↗

PubMed1998

Vertebrate tinman homologues XNkx2-3 and XNkx2-5 are required for heart formation in a functionally redundant manner.

Tinman is a Drosophila homeodomain protein that is required for formation of both visceral and cardiac mesoderm, including formation of the dorsal vessel, a heart-like organ. Although several vertebrate tinman homologues have been characterized, their requirement in earliest stages of heart formation has been an open question, perhaps complicated by potential functional redundancy of tinman homologues. We have utilized a novel approach to investigate functional redundancy within a gene family, by coinjecting DNA encoding dominantly acting repressor derivatives specific for each family member into developing Xenopus embryos. Our results provide the first evidence that vertebrate tinman homologues are required for earliest stages of heart formation, and that they are required in a functionally redundant manner. Coinjection of dominant repressor constructs for both XNkx2-3 and XNkx2-5 is synergistic, resulting in a much higher frequency of mutant phenotypes than that obtained with injection of either dominant repressor construct alone. Rescue of mutant phenotypes can be effected by coinjection of either wild-type tinman homologue. The most extreme mutant phenotype is a complete absence of expression of XNkx2-5 in cardiogenic mesoderm, an absence of markers of differentiated myocardium, and absence of morphologically distinguishable heart on the EnNkxHD-injected side of the embryo. This phenotype represents the most severe cardiac phenotype of any vertebrate mutant yet described, and underscores the importance of the tinman family for heart development. These results provide the first in vivo evidence that XNkx2-3 and XNkx2-5 are required as transcriptional activators for the earliest stages of heart formation. Furthermore, our results suggest an intriguing mechanism by which functional redundancy operates within a gene family during development. Our experiments have been performed utilizing a recently developed transgenic strategy, and attest to the efficacy of this strategy for enabling transgene expression in limited cell populations within the developing Xenopus embryo.

Amino Acid Sequence↗

PubMed1998

[A study on dose-effect of suppression to gap junctional intercellular communication function by 50-Hz magnetic fields].

OBJECTIVE: To study the relationship between dose of exposure to 50-Hz magnetic field (MF) and its effects of suppression to gap junctional intercellular communication (GJIC) function. METHODS: Lucifer yellow, a kind of fluorescent dye, was led into single CHL cell by iontophoretic injection. Number of dye-coupled cells (DCC) five minutes after injection was used as an indicator for GJIC function. The effects of different intensities and irradiation of MF on GJIC in CHL cells were studied. RESULTS: Suppression to GJIC by 50-Hz MF depended on its flux intensity. Irradiation with lower flux intensity (0.05, 0.2 and 0.4 mT) of the MF for 24 hours could not inhibit GJIC, but that with higher intensity (0.8 and 1.6 mT) could. No "amplitude window" effect was appeared by irradiation with MF at intensities of zero to 1.6 mT. Exposure to MF at a fixed intensity of 0.8 mT for five minutes had no effects, but that for one hour was more than enough to inhibit GJIC, with the most apparent effects for 24-hour exposure. In addition, it was showed that suppression to GJIC was caused by direct action of 50-Hz MF rather then induced electrical field. CONCLUSION: MF of 50-Hz had suppression to GJIC with a dose-effect relationship.

Animals↗

PubMed1998

Erythrocyte and plasma Ca2+, Mg2+ and cell membrane adenosine triphosphatase activity in patients with essential hypertension.

OBJECTIVE: To assess the relationships between plasma and intracellular Ca2+, Mg2+ and blood cell membrane adenosine triphosphatase (ATPase) activity in normotensive and hypertensive subjects. METHODS: Plasma and intracellular Ca2+, Mg2+ were measured with atomic absorption spectrophotometry, and red blood cell membrane Na(+)-K+ ATPase and Ca(2+)-ATPase activities were determined with colorimetric method in 55 patients with essential hypertension and 32 normotensive controls. RESULTS: The results showed that the hypertensive group consistently demonstrated a significant decreased activity of ATPase studied, with significantly lower plasma Ca2+ and higher cytosolic Ca2+ levels when compared with those in normotensive group (P < 0.01 or P < 0.05, respectively). No significant differences were found in either plasma Mg2+ or intracellular Mg2+ level between the two groups. CONCLUSIONS: This study suggests that patients with essential hypertension have widespread depression of cell membrane Na(+)-K(+)-ATPase and Ca(2+)-ATPase activities with plasma Ca2+ depletion and cytosolic Ca2+ overload, which may reflect an underlying membrane abnormality in essential hypertension. The cellular abnormalities may be related to the defective transport mechanisms that in turn may be aggravated by plasma Ca2+ depletion.

Adult↗

PubMed1998

Detection of the E7 transform gene of human papilloma virus type 16 in human oral squamous cell carcinoma.

OBJECTIVE: To determine, with the use of polymerase chain reaction, the prevalence of human papillomavirus (HPV) 16 in 30 patients with primary oral squamous cell carcinoma (OSCC) and 30 healthy control patients. MATERIALS AND METHODS: DNA was extracted from freshly frozen tumor tissues of 30 patients with primary oral squamous cell carcinoma and from the oral mucosa of 30 controls. A pair of specific primers of the E7 early gene of HPV 16 were designed. PCR products were run by 1.5% agarose gel and the results of electrophoresis were photographed. RESULTS: HPV 16 was detected in 36.7% (11/30) of oral squamous cell carcinoma patients and 11.1% (4/30) of controls. CONCLUSIONS: HPV 16 has a significant association with oral squamous cell carcinoma. However, the role HPV 16 plays in the tumorigenesis of oral cancer and its clinical significance remain to be investigated.

Adult↗