Gene-environment interaction in Alzheimer's disease: a potential role for cholesterol

Alzheimer's disease is probably a complex disease caused by an interaction of multiple environmental and genetic factors. Genetic defects include 'causative' genes which are rare and a 'susceptibility' gene (sigma4 allele of apolipoprotein E) which is more common in cases. Recent research suggests that environmental factors may interact with a genetic predisposition to modify the risk of Alzheimer's disease. An interaction between serum cholesterol levels and sigma4 genotype is proposed. The evidence for this gene-environment interaction is discussed.     

Genetically probing the regions of ribose-binding protein involved in permease interaction

The ribose-binding protein (RBP) of Escherichia coli, located in the periplasm, binds to ribose and mediates transport and chemotaxis. The regions on the tertiary structure of RBP that interact with the membrane permease, an ABC transporter, were genetically probed by screening a mutation using the chimeric receptor Trz. Trz is a hybrid protein between the periplasmic domain of chemoreceptor Trg and the cytoplasmic portion of osmosensor EnvZ, which provides a system for monitoring the chemotactic interaction of RBP on MacConkey agar plates when coupled with a reporter lacZ fused to an ompC gene. The expression of ompC can be increased by an interaction of ribose-bound RBP with Trz. A transport defect, either in the binding protein or in the membrane permease, causes a signalling-constitutive Lac+ phenotype of Trz even in the absence of ribose. This appears to be due to the presence of a small amount of ribose, which is normally taken up by the high-affinity transport system. By taking advantage of this, we have designed a system for genetic screening that permits a selection for mutations in the binding protein, causing specific defects in permease interaction but not in tactic interaction. Mutant RBPs that were isolated were unable to perform normal ribose uptake and to utilize ribose as a carbon source, while other functions such as taxis and sugar-binding properties were not substantially affected. The mutational changes were repeatedly found in several residues of RBP, concentrating on three surface regions and comprising two domains of the tertiary structure. We suggest that the two regions, including residues 52 and 166, are specifically involved in the permease interaction while the third region, including residues 72, 134, and others, recognizes both the permease and the chemosensory receptor.     

Cytochrome c peroxidase from a methylotrophic yeast: physiological role and isolation

Mutant strains of the methylotrophic yeast Hansenula polymorpha defective in catalase (cat) and in glucose repression of alcohol oxidase synthesis (gcr1) have been isolated following multiple UV mutagenesis steps. One representative gcr1 cat mutant C-105 grows during batch cultivation in a glucose/methanol medium. However, growth is preceded by a prolonged lag period. C-105 and other gcr1 cat mutants do not grow on methanol medium without an alternative carbon source. A large collection of second-site suppressor catalase-defective (scd) revertants were isolated with restored ability for methylotrophic growth (Mth+) in the absence of catalase activity. These Mth+ gcr1 cat scd strains utilize methanol as a sole source of carbon and energy, although biomass yields are reduced relative to the wild-type strain. In contrast to the parental C-105 strain, H2O2 does not accumulate in the methanol medium of the revertants. We show that restoration of methylotrophic growth in the suppressor strains is strongly correlated with increased levels of the alternative H2O2-destroying enzyme, cytochrome c peroxidase. Cytochrome c peroxidase from cell-free extracts of one of the scd revertants has been purified to homogeneity and crystallized.     

Amylin: physiological roles in the kidney and a hypothesis for its role in hypertension

1. There are high-affinity binding sites for amylin in the renal cortex associated with proximal tubules. These appear to represent seven transmembrane (heptatopic) receptors that are known to form ternary complexes with G-proteins and activate second messenger systems. 2. Amylin stimulates sodium/water reabsorption from the basolateral side of the proximal tubules and plays a role in sodium homeostasis. 3. The transient expression of amylin-like mRNA has been detected perinatally, using in situ hybridization, in the subnephrogenic zone of the metanephros and is associated with proximal tubules of the developing nephron. There it is thought to play a role as a growth factor for brush border epithelial cells in the developing kidney and in renal regrowth in the adult kidney. 4. In two models of hypertension, the spontaneously hypertensive rat (SHR) and one created surgically by subtotal nephrectomy, renal amylin receptors are activated. In the SHR, activation precedes the rise in blood pressure and suggests that activation of the amylin system may be an important event in the development of hypertension.     

Reduced positive feedback regulation between myosin crossbridge and cardiac troponin C in fast skeletal myofibrils

Several studies have shown that substitution of cardiac troponin C into fast skeletal muscle causes a marked reduction in cooperativity of Ca(2+)-activation of both myofibrillar ATPase and tension development. To clarify the underlying mechanisms, in the present study, Ca2+ binding to cardiac troponin C inserted into fast skeletal myofibrils was measured. Two classes of binding sites with different affinities (classes 1 and 2) were clearly identified, which were equivalent stoichiometrically to the two high-affinity sites (sites III and IV) and a single low-affinity site (site II) of troponin C, respectively. Ca2+ binding to class-2 sites and Ca(2+)-activation of myofibrillar ATPase occurred in roughly the same Ca2+ concentration range, indicating that site II is responsible for Ca2+ -regulation. Myosin crossbridge interactions with actin, both in the presence and absence of ATP, enhanced the Ca2+ binding affinity of only class-2 sites. These effects of myosin crossbridges, however, were much smaller than the effects on the Ca2+ binding to the low-affinity sites of fast skeletal troponin C, which are responsible for regulating fast skeletal myofibrillar ATPase. These findings provide strong evidence that the reduction in the cooperative response to Ca2+ upon substituting cardiac troponin C into fast skeletal myofibrils is due to a decrease in the positive feedback interaction between myosin crossbridge attachment and Ca2+ binding to the regulatory site of troponin C.     

Ca2+ activated myosin-ATPase in cardiac myofibrils of rainbow trout, freshwater turtle, and rat

The effects of natural variation in the number of copies of the growth hormone (GH) gene on growth parameters, plasma GH profiles, and the response to GHRH challenge were compared in Coopworth ram lambs from selection lines differing in body composition and GH levels. Different genotypes at the GH locus carried two, three, or four copies of the GH gene and GH secretion was studied under ad libitum feeding conditions and in the fasted state. There were no significant effects of GH genotype on any parameters of growth or body composition. Basal serum GH concentration, GH pulse frequency, and GH pulse amplitude differed significantly with selection line and fasting, but did not differ significantly between the GH genotypes. Significant differences of subtle nature were found between the GH genotypes in their responsiveness to GHRH. For the ad libitum-fed Lean selection line animals, the first GHRH challenge resulted in a higher mean maximum response for GH1/GH1 than GH2/GH2 (P < 0.05). Between the first and the second challenges there was a decrease in maximum response for the GH1/GH1 genotype and an increase for the GH2/GH2 genotype (P < 0.05 for GH genotype main effect). The differences between GH genotypes in response to GHRH challenge suggest that polymorphism in the number of GH gene copies in sheep may have physiological implications for the function of the GH axis, which may be manifested in growing lambs only under specific genotype-environment combinations.     

Promoting wellness in cardiac rehabilitation: exploring the role of altruism

Coronary artery disease continues to be the primary cause of mortality in the United States. Recent studies have significantly advanced the ability to improve outcomes in this disorder by demonstrating that intensive risk factor modification programs with diet, lipid-lowering drugs, exercise, and psychosocial interventions can reverse atherosclerosis and reduce events by 40% to 60%. Of all the interventional arms, psychosocial interventions have been the least studied despite research demonstrating that depression and social isolation are potent risk factors for events in patients with coronary artery disease. The few studies that have examined psychosocial interventions in patients with coronary artery disease have demonstrated a reduction in mortality and recurrent events, suggesting that this treatment strategy may be beneficial. Use of volunteer, patient-driven support groups may provide a cost-effective way to improve social support and enhance altruism in patients with coronary artery disease. Although the psychophysiology of altruism is not well defined, it is possible that altruistic activities might have positive health benefits in patients with coronary artery disease. Studies are needed to explore the roles of low-cost, patient-driven support programs in improving psychosocial functioning and outcomes in patients with coronary artery disease.     

Role of cardiac renin-angiotensin system in swimming induced physiological myocardial hypertrophy

To determine the contribution of cardiac renin-angiotensin system (RAS) to the physiological myocardial hypertrophy induced by swimming training and the relationship between locally produced and circulating RAS, both ventricular and plasma angiotensin (Ang) I and II contents, ventricular angiotensin converting enzyme (ACE) and plasma renin activity (PRA) were detected by means of radioimmunoassay and biochemical method. It was shown that after 5 weeks of swimming, the ventricular wet weight to body weight ratio (V/Bwt) and Ang II in both left and right ventricles and ACE activity increased markedly as compared with the controls (P < 0.05). Furthermore, significantly positive correlation was found between the ventricular Ang II and V/Bwt (r = 0.7721, P < 0.001), while the plasma Ang I and II and PRA remained at the control level. No correlation was found between plasma Ang II and V/Bwt. These above findings suggest that cardiac RAS may play an important role in physiological myocardial hypertrophy and to a large extent is in dependent on circulating RAS.     

Detecting gastrointestinal hypoperfusion during cardiac tamponade in pigs: a role for nitric oxide tonometry?

OBJECTIVE: To evaluate different techniques and regional approaches for detecting critical reductions in gastrointestinal (GI) perfusion. DESIGN: Laboratory, animal, controlled study. SETTING: University animal research laboratory. SUBJECTS: Thirteen anesthetized, ventilated, juvenile domestic pigs. INTERVENTIONS: Dextran was infused into the pericardial sac to achieve cardiac tamponade that reduced cardiac output to 25% of baseline value. Hemodynamics were invasively monitored, and blood gases were sampled in the systemic and portal circulations. Tonometers were placed in the corpus of the stomach and in the jejunum, 50 cm aboral to the ligament of Treitz. MEASUREMENTS AND MAIN RESULTS: We measured cardiac output, portal venous blood flow, mesenteric oxygen delivery and consumption, systemic and portal venous blood gases and acid-base balance, stomach and jejunal transepithelial potential difference, stomach and jejunal intramucosal pH, arterial plasma concentrations of asymmetric dimethylarginine, and jejunal, intraluminal nitric oxide. One hour of cardiac tamponade decreased mesenteric oxygen delivery and consumption in a linear fashion and resulted in mesenteric acidosis, as evidenced by decreases in pH, standard bicarbonate, oxygen saturation, and PO2 and increases in PCO2. The potential difference in the jejunum decreased earlier than in the stomach, whereas stomach intramucosal pH decreased before jejunal intramucosal pH. Intraluminal nitric oxide in the jejunum was markedly reduced soon after cardiac tamponade. This reduction was accompanied by an increase in arterial plasma concentrations of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine. Investigated variables were unchanged in control animals. CONCLUSIONS: Both intramucosal pH and potential difference measurements may be used to detect critical reduction in GI perfusion. Regional and temporal differences may reduce the accuracy of these methods. Jejunal tonometry can yield an early nitric oxide measurement that indicates mesenteric low-flow conditions. Jejunal tonometry also yields quantitative information about this modulator of hemodynamic and mucosal barrier function, information that is relevant to GI failure during shock.     

c-Src activation plays a role in endothelin-dependent hypertrophy of the cardiac myocyte

Activation of the atrial natriuretic peptide (ANP) gene is regarded as one of the earliest and most reliable markers of hypertrophy in the ventricular cardiac myocyte. We have examined the role of the nonreceptor tyrosine kinases in the signaling mechanism(s) leading to hypertrophy using human ANP gene promoter activity as a marker. Endothelin (ET), a well known hypertrophic agonist, increased activity of c-Src, c-Yes, and Fyn within minutes and promoted a selective redistribution of each of these kinases within the cell. Overexpression of c-Src effected a significant increase in activity of a cotransfected human ANP promoter-driven chloramphenicol acetyl transferase reporter, while expression of either c-Yes or Fyn was considerably less effective in this regard. ET-dependent stimulation of the human ANP gene promoter was partially inhibited by co-transfection with dominant negative Ras or dominant negative Src or Csk or by treatment with the potent Src family-selective tyrosine kinase inhibitor PP1, suggesting that the Src family kinases are involved in signaling ET-dependent activation of this promoter. Both ET- and Src-dependent activation of the ANP promoter required the presence of a CArG motif in a serum response element-like structure between -422 and -413 but did not appear to require assembly of a ternary complex for full activity. These findings support a role for Src in the activation of ANP gene expression and suggest that this kinase may contribute in an important way to the signaling mechanisms that activate hypertrophy in the cardiac myocyte.     

A physiological role of the adenosine A3 receptor: sustained cardioprotection

Adenosine released during cardiac ischemia exerts a potent, protective effect in the heart. A newly recognized adenosine receptor, the A3 subtype, is expressed on the cardiac ventricular cell, and its activation protects the ventricular heart cell against injury during a subsequent exposure to ischemia. A cultured chicken ventricular myocyte model was used to investigate the cardioprotective role of a novel adenosine A3 receptor. The protection mediated by prior activation of A3 receptors exhibits a significantly longer duration than that produced by activation of the adenosine A1 receptor. Prior exposure of the myocytes to brief ischemia also protected them against injury sustained during a subsequent exposure to prolonged ischemia. The adenosine A3 receptor-selective antagonist 3-ethyl 5-benzyl-2-methyl-6-phenyl-4-phenylethynyl-1, 4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS1191) caused a biphasic inhibition of the protective effect of the brief ischemia. The concomitant presence of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) converted the MRS1191-induced dose inhibition curve to a monophasic one. The combined presence of both antagonists abolished the protective effect induced by the brief ischemia. Thus, activation of both A1 and A3 receptors is required to mediate the cardioprotective effect of the brief ischemia. Cardiac atrial cells lack native A3 receptors and exhibit a shorter duration of cardioprotection than do ventricular cells. Transfection of atrial cells with cDNA encoding the human adenosine A3 receptor causes a sustained A3 agonist-mediated cardioprotection. The study indicates that cardiac adenosine A3 receptor mediates a sustained cardioprotective function and represents a new cardiac therapeutic target.     

The missing link: the role of interhemispheric interaction in attentional processing

Although interhemispheric interaction via the callosum is most often conceived as a mechanism for transferring sensory information and coordinating processing between the hemispheres, it will be argued here that the callosum also plays an important role in attentional processing. Experiments will be presented that support this viewpoint, both when attention is conceptualized as a resource and when it is conceptualized as a selective mechanism for gating sensory information. Interhemispheric interaction is posited to aid attentional processing because it allows for a division of labor across the hemispheres, and allows for parallel processing so that operations performed in one hemisphere can be insulated from those executed in the other. Given this additional role for interhemispheric processing, it is suggested that the corpus callosum should be considered a component in the network of neural structures that underlie attentional control.     

Evidence for hydrophobic interaction between galanin and the GalR1 galanin receptor and GalR1-mediated ligand internalization: fluorescent probing with a fluorescein-galanin

Galanin is a neuropeptide that activates specific receptors to modulate several physiological functions including food intake, nociception, and learning and memory. The molecular nature of the interaction between galanin and its receptors and the fate of the galanin/receptor complex after the binding event are not understood. A fluorescein-N-galanin (F-Gal) was generated to measure the interaction between galanin and rat GalR1 galanin receptor (rGalR1) and rGalR1-mediated ligand internalization using flow cytometry in transfected Chinese hamster ovary (CHO) cells. Like galanin, F-Gal bound rGalR1 with high affinity and stimulated intracellular signaling events. Fluorescence quenching by soluble KI of rGalR1-bound F-Gal revealed a highly protected environment around the fluorescein, suggesting that the N-terminal portion of galanin, which constitutes the binding site of galanin for the receptor, binds to a protected hydrophobic binding pocket within the receptor. Exposure to F-Gal stimulated rapid (t1/2 approximately 10 min) and extensive (78%) internalization of surface F-Gal into rGalR1/CHO cells at 37 degreesC but not at 0 degreesC. In addition, the internalization did not occur in parental CHO cells at either 0 or 37 degreesC and was inhibited by addition of 0.25 M sucrose in the medium, indicating a GalR1-mediated energy-requiring endocytic process. These results revealed a hydrophobic interaction between galanin and the GalR1 receptor, which is in contrast to those of other G protein-coupled receptors that mainly require hydrophilic interaction with their peptide ligands near or outside the plasma membrane surface, and illustrated that the initial binding interaction is followed by rapid cellular internalization of the agonist/GalR1 complex.