Exploring the evolutionary mechanism of hepatitis B and gastric cancer based on Mendelian randomization combined with bioinformatics analysis.

Chronic hepatitis B virus infection (HBV) infection appears to be associated with extrahepatic cancers. This study aims to evaluate the causality and evolutionary mechanism of chronic HBV infection and gastric cancer through Mendelian randomization (MR) analysis and bioinformatics analysis. We conducted 2-sample MR to investigate the causal relationship between chronic HBV infection and gastric cancer. We identified 5 independent genetic variants closely associated with exposure (chronic HBV infection) as instrumental variables in a sample of 1371 cases and 2938 controls of East Asian descent in Korea. The genome wide association study (GWAS) data for the outcome variable came from the Japanese Biobank. Bioinformatics analysis was used to explore the evolutionary mechanism of chronic HBV infection and gastric cancer. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed to identify key targets that are commonly associated with both diseases, and their biological functions were investigated. Multiple machine-learning models were employed to select hub genes. The MR analysis showed a positive causal relationship between chronic HBV infection and gastric cancer (IVW: OR = 1.165, 95% CI = 1.085-1.250, P < .001), and the result was robust in sensitivity analysis. According to the bioinformatics analysis, the 5 key targets were mainly enriched in Toll-like receptor signaling and PI3K-Akt signaling. Two hub genes, CXCL9 and COL6A2, were identified, and a high-performing predictive model was constructed. Chronic HBV infection is positively associated with gastric cancer, and the evolutionary mechanism may be related to Toll-like receptor signaling. Prospective studies are still needed to confirm these findings.

Quantitative Autoradiographic Method for Determination of Regional Rates of Cerebral Protein Synthesis In Vivo.

Protein synthesis is required for development and maintenance of neuronal function and is involved in adaptive changes in the nervous system. Moreover, it is thought that dysregulation of protein synthesis in the nervous system may be a core phenotype in some developmental disorders. Accurate measurement of rates of cerebral protein synthesis in animal models is important for understanding these disorders. The method that we have developed was designed to be applied to the study of awake, behaving animals. It is a quantitative autoradiographic method, so it can yield rates in all regions of the brain simultaneously. The method is based on the use of a tracer amino acid, L-[1-14C]-leucine, and a kinetic model of the behavior of L-leucine in the brain. We chose L-[1-14C]-leucine as the tracer because it does not lead to extraneous labeled metabolic products. It is either incorporated into protein or rapidly metabolized to yield 14CO2 which is diluted in a large pool of unlabeled CO2 in the brain. The method and the model also allow for the contribution of unlabeled leucine derived from tissue proteolysis to the tissue precursor pool for protein synthesis. The method has the spatial resolution to determine protein synthesis rates in cell and neuropil layers, as well as hypothalamic and cranial nerve nuclei. To obtain reliable and reproducible quantitative data, it is important to adhere to procedural details. Here we present the detailed procedures of the quantitative autoradiographic L-[1-14C]-leucine method for the determination of regional rates of protein synthesis in vivo.

Decreased rates of cerebral protein synthesis measured in vivo in a mouse model of Tuberous Sclerosis Complex: unexpected consequences of reduced tuberin.

Tuberous sclerosis complex (TSC) is an autosomal dominant neurogenetic disorder affecting about 1 in 6000 people and is caused by mutations in either TSC1 or TSC2. This disorder is characterized by increased activity of mammalian target of rapamycin complex 1 (mTORC1), which is involved in regulating ribosomal biogenesis and translation initiation. We measured the effects of Tsc2 haploinsufficiency (Tsc2+/- ) in 3-month-old male mice on regional rates of cerebral protein synthesis (rCPS) by means of the in vivo L-[1-14 C]leucine method. This quantitative autoradiographic method includes an estimate of the integrated specific activity of the tracer amino acid in brain tissue. The estimate accounts for recycling of unlabeled amino acids from tissue protein breakdown by means of a factor (λ) that was determined in control and Tsc2+/- mice. The value of λ was higher in Tsc2+/- mice, indicating that a greater fraction of leucine in the tissue precursor pool for protein synthesis is derived from the plasma compared to controls, consistent with reduced rates of protein degradation. We determined rCPS in freely moving, awake male Tsc2+/- and control mice, and we used the determined values of λ in the calculation of rCPS. Unexpectedly, we found that rCPS were significantly decreased in 16 of the 17 brain regions analyzed in Tsc2+/- mice compared to controls. Our results indicate a complex role of mTORC1 in the regulation of cerebral protein synthesis that has not been previously recognized.

R-Baclofen Reverses a Social Behavior Deficit and Elevated Protein Synthesis in a Mouse Model of Fragile X Syndrome.

BACKGROUND: Fragile X syndrome (FXS) is the most common known inherited form of intellectual disability and the single genomic cause of autism spectrum disorders. It is caused by the absence of a fragile X mental retardation gene (Fmr1) product, FMRP, an RNA-binding translation suppressor. Elevated rates of protein synthesis in the brain and an imbalance between synaptic signaling via glutamate and γ-aminobutyric acid (GABA) are both considered important in the pathogenesis of FXS. In a mouse model of FXS (Fmr1 knockout [KO]), treatment with R-baclofen reversed some behavioral and biochemical phenotypes. A remaining crucial question is whether R-baclofen is also able to reverse increased brain protein synthesis rates. METHODS: To answer this question, we measured regional rates of cerebral protein synthesis in vivo with the L-[1-(14)C]leucine method in vehicle- and R-baclofen-treated wildtype and Fmr1 KO mice. We further probed signaling pathways involved in the regulation of protein synthesis. RESULTS: Acute R-baclofen administration corrected elevated protein synthesis and reduced deficits on a test of social behavior in adult Fmr1 KO mice. It also suppressed activity of the mammalian target of rapamycin pathway, particularly in synaptosome-enriched fractions, but it had no effect on extracellular-regulated kinase 1/2 activity. Ninety min after R-baclofen treatment, we observed an increase in metabotropic glutamate receptor 5 expression in the frontal cortex, a finding that may shed light on the tolerance observed in human studies with this drug. CONCLUSIONS: Our results suggest that treatment via activation of the GABA (GABA receptor subtype B) system warrants further study in patients with FXS.

Cerebral protein synthesis in a knockin mouse model of the fragile X premutation.

The (CGG)n-repeat in the 5'-untranslated region of the fragile X mental retardation gene (FMR1) gene is polymorphic and may become unstable on transmission to the next generation. In fragile X syndrome, CGG repeat lengths exceed 200, resulting in silencing of FMR1 and absence of its protein product, fragile X mental retardation protein (FMRP). CGG repeat lengths between 55 and 200 occur in fragile X premutation (FXPM) carriers and have a high risk of expansion to a full mutation on maternal transmission. FXPM carriers have an increased risk for developing progressive neurodegenerative syndromes and neuropsychological symptoms. FMR1 mRNA levels are elevated in FXPM, and it is thought that clinical symptoms might be caused by a toxic gain of function due to elevated FMR1 mRNA. Paradoxically, FMRP levels decrease moderately with increasing CGG repeat length in FXPM. Lowered FMRP levels may also contribute to the appearance of clinical problems. We previously reported increases in regional rates of cerebral protein synthesis (rCPS) in the absence of FMRP in an Fmr1 knockout mouse model and in a FXPM knockin (KI) mouse model with 120 to 140 CGG repeats in which FMRP levels are profoundly reduced (80%-90%). To explore whether the concentration of FMRP contributes to the rCPS changes, we measured rCPS in another FXPM KI model with a similar CGG repeat length and a 50% reduction in FMRP. In all 24 brain regions examined, rCPS were unaffected. These results suggest that even with 50% reductions in FMRP, normal protein synthesis rates are maintained.

Voluntary exercise regionally augments rates of cerebral protein synthesis.

Exercise is a natural form of neurophysiologic stimulation that has known benefits for mental health, maintenance of cerebral function, and stress reduction. Exercise is known to induce an upregulation of brain-derived neurotrophic factor and this is thought to be involved in associated increases in neural plasticity. Protein synthesis is also an essential component of adaptive plasticity. We hypothesized that exercise may stimulate changes in brain protein synthesis as part of its effects on plasticity. Here, we applied the quantitative autoradiographic L-[1-(14)C]leucine method to the in vivo determination of regional rates of cerebral protein synthesis (rCPS) in adult rats following a seven day period of voluntary wheel-running and their sedentary counterparts. In four of 21 brain regions examined, the mean values of rCPS in the exercised rats were statistically significantly higher than in sedentary controls; regions affected were paraventricular hypothalamic nucleus, ventral hippocampus as a whole, CA1 pyramidal cell layer in ventral hippocampus, and frontal cortex. Increases in rCPS approached statistical significance in dentate gyrus of the ventral hippocampus. Our results affirm the value of exercise in encouraging hippocampal and possibly cortical neuroplasticity, and also suggest that exercise may modulate stimulation of stress-response pathways. Ultimately, our study indicates that measurement of rCPS with PET might be used as a marker of brain response to exercise in human subjects.

Lithium reverses increased rates of cerebral protein synthesis in a mouse model of fragile X syndrome.

Individuals with fragile X syndrome (FXS), an inherited form of cognitive disability, have a wide range of symptoms including hyperactivity, autistic behavior, seizures and learning deficits. FXS is caused by silencing of FMR1 and the consequent absence of fragile X mental retardation protein (FMRP). FMRP is an RNA-binding protein that associates with polyribosomes and negatively regulates translation. In a previous study of a mouse model of FXS (Fmr1 knockout (KO)) we demonstrated that in vivo rates of cerebral protein synthesis (rCPS) were elevated in selective brain regions suggesting that the absence of FMRP in FXS may result in dysregulation of cerebral protein synthesis. Lithium, a drug used clinically to treat bipolar disorder, has been used to improve mood dysregulation in individuals with FXS. We reported previously that in the Fmr1 KO mouse chronic dietary lithium treatment reversed or ameliorated both behavioral and morphological abnormalities. Herein we report that chronic dietary lithium treatment reversed the increased rCPS in Fmr1 KO mice with little effect on wild type mice. We also report our results of analyses of key signaling molecules involved in regulation of mRNA translation. Our analyses indicate that neither effects on the PI3K/Akt nor the MAPK/ERK 1/2 pathway fully account for the effects of lithium treatment on rCPS. Collectively our findings and those from other laboratories on the efficacy of lithium treatment in animal models support further studies in patients with FXS.

A mouse model of the fragile X premutation: effects on behavior, dendrite morphology, and regional rates of cerebral protein synthesis.

Carriers of FMR1 premutation alleles have 55-200 CGG repeats in the 5' untranslated region of the gene. These individuals are at risk for fragile X associated primary ovarian insufficiency (females) and, in late life, fragile X associated tremor and ataxia syndrome (males, and to a lesser extent, females). Premutation carrier status can also be associated with autism spectrum disorder, attention deficit hyperactivity disorder, and some cognitive deficits. In premutation carriers, FMR1 mRNA levels are often higher than those with normal sized alleles. In contrast, in subjects with full mutation alleles, (>200 repeats) the FMR1 gene is silenced and FMR1 mRNA and its product, FMRP, are absent. We have studied a male knock-in (KI) mouse model of the fragile X premutation (120-140 repeats) during young adulthood. In comparison to wild type, KI mice were hyperactive, exhibited less anxiety in both the open field and the elevated zero maze, were impaired on the passive avoidance test, and showed some subtle deficits on a test of social interaction. Motor learning as assessed by the rotarod test was normal. Dendritic arbors were less complex and spine densities and lengths increased in medial prefrontal cortex, basal lateral amygdala, and hippocampus compared with wild type. Regional rates of cerebral protein synthesis measured in vivo in KI mice were increased. KI mice also had elevated levels of Fmr1 mRNA and decreased levels of FMRP. Our results highlight similarities in phenotype between KI and Fmr1 knockout mice and suggest that the decreased concentration of FMRP contributes to the phenotype in young adult KI mice.

Effect of high-salt diet on vascular relaxation and oxidative stress in mesenteric resistance arteries.

This study tested the hypothesis that superoxide levels are elevated in isolated mesenteric resistance arteries (100-300 microm) from rats fed a short-term high-salt (HS) diet (4% NaCl for 3 days) compared to controls fed a low-salt (LS) diet (0.4% NaCl). Vascular relaxation induced by the superoxide dismutase mimetic tempol (4-hydroxytetramethylpiperidine-1-oxyl), the NADPH oxidase inhibitor apocynin and the xanthine/xanthine oxidase inhibitor oxypurinol was significantly larger in mesenteric arteries from animals fed HS diet compared to arteries from animals fed LS diet. Basal superoxide levels assessed via dihydroethidine (DHE) fluorescence were significantly elevated in arteries from rats fed HS diet, and were reduced by tempol, apocynin and oxypurinol, but not by L-NAME. Basal and methacholine-induced NO production (assessed by DAF-2T fluorescence) was significantly reduced in arteries from rats fed HS diet versus arteries from rats on LS diet. Impaired methacholine-induced NO release and vascular relaxation were restored by tempol and apocynin, but not by oxypurinol. These data suggest that the elevated production of superoxide by NADPH oxidase and xanthine/xanthine oxidase contribute to elevated basal superoxide levels, reduced NO release and impaired vascular relaxation in mesenteric resistance arteries of rats fed HS diet.

Salt-induced ANG II suppression impairs the response of cerebral artery smooth muscle cells to prostacyclin.

Recent studies have demonstrated that cerebral arteries from rats fed a high-salt (HS) diet exhibit impaired vasodilation and altered electrophysiological response to reduction in PO2. The present study examined whether an increase in salt intake alters the response of vascular smooth muscle cells (VSMC) to prostacyclin, a crucial mediator of hypoxic dilation in cerebral arteries. VSMC were isolated from cerebral arteries of male Sprague-Dawley rats maintained on an HS (4% NaCl) or a low-salt diet (0.4% NaCl) for 3 days. The stable prostacyclin analog iloprost (10 ng/ml) inhibited serotonin (0.1-10 microM)-induced contractions and the increase in intracellular Ca2+ concentration ([Ca2+]i) in VSMC isolated from arteries of animals fed the low-salt diet. In contrast, iloprost had no effect on serotonin-induced contractions and increases in [Ca2+]i in VSMC isolated from arteries of rats fed the HS diet. Preventing the fall in ANG in rats fed the HS diet by infusion of a low dose of ANG II (5 ng.kg(-1).min(-1) i.v.) restored the inhibitory effect of iloprost on serotonin-induced contractions and increases in [Ca2+]i in VSMC from animals fed the HS diet. These effects were reversed by AT1 receptor blockade with losartan. These results indicate that ANG II suppression secondary to elevated dietary salt intake impairs vascular relaxation and Ca2+ regulation by prostacyclin.

Effect of high-salt diet on NO release and superoxide production in rat aorta.

Sprague-Dawley rats were fed either a high-salt (HS) diet (4.0% NaCl) or a low-salt (LS) diet (0.4% NaCl) for 3 days. Nitric oxide (NO) and superoxide production were assessed in the thoracic aorta by evaluating the fluorescence signal intensity from 4,5-diaminofluorescein (DAF-2DA) and dihydroethidine, respectively. Methacholine caused increased NO release in the aortas from rats on a LS but not HS diet. The SOD mimetic tempol restored methacholine-induced NO release in aortas from rats on a HS diet. Methacholine also caused superoxide production in the aortas of rats on a HS diet but not in the aortas of rats on a LS diet. Tempol and N(G)-monomethyl-l-arginine eliminated methacholine-induced superoxide production in the aortas of rats on a HS diet. Aortic rings from rats on the HS diet showed impaired methacholine-induced relaxation, which was improved by tempol. Tempol alone caused a NO-dependent relaxation of norepinephrine-precontracted aortas that was significantly greater in the aortas of rats on the HS diet than in vessels from rats on the LS diet. These data suggest that a HS diet impairs endothelium-dependent relaxation via reduced NO levels and increased superoxide production.