Catechol O-methyltransferase (COMT) functional haplotype is associated with recurrence of affective symptoms: A prospective birth cohort study.

BACKGROUND: Catechol-O-methyltransferase (COMT) polymorphisms play an essential role in dopamine availability in the brain. However, there has been no study investigating whether a functional four-SNP (rs6269-rs4633-rs4818-rs4680) haplotype is associated with affective symptoms over the life course. METHODS: We tested this using 2093 members of the Medical Research Council National Survey of Health and Development (MRC NSHD), who had been followed up since birth in 1946, and had data for COMT genotypes, adolescent emotional problems (age 13-15) and at least one measure of adult affective symptoms at ages 36, 43, 53, or 60-64 years. First, differences in the levels of affective symptoms by the functional haplotype using SNPs rs6269, rs4818, and rs4680 were tested in a structural equation model framework. Second, interactions between affective symptoms by COMT haplotype were tested under an additive model. Finally, a quadratic regressor (haplotype2) was used in a curvilinear model, to test for a possible inverted-U trend in affective symptoms according to COMT-related dopamine availability. RESULTS: Women had a significant interaction between COMT haplotypes and adolescent emotional problem on affective symptoms at age 53. Post hoc analysis showed a significant positive association between adolescent emotional problems and affective symptoms at age 53 years in the middle dopamine availability group (valA/valB or met/met; β = .11, p = .007). For men, no significant interactions were observed. CONCLUSIONS: Combination of the COMT functional haplotype model and inverted-U model may shed light on the effect of dopaminergic regulation on the trajectory of affective symptoms over the life course

Disruptive mRNA folding increases translational efficiency of catechol-O-methyltransferase variant

Catechol-O-methyltransferase (COMT) is a major enzyme controlling catecholamine levels that plays a central role in cognition, affective mood and pain perception. There are three common COMT haplotypes in the human population reported to have functional effects, divergent in two synonymous and one nonsynonymous position. We demonstrate that one of the haplotypes, carrying the non-synonymous variation known to code for a less stable protein, exhibits increased protein expression in vitro. This increased protein expression, which would compensate for lower protein stability, is solely produced by a synonymous variation (C166T) situated within the haplotype and located in the 5′ region of the RNA transcript. Based on mRNA secondary structure predictions, we suggest that structural destabilization near the start codon caused by the T allele could be related to the observed increase in COMT expression. Our folding simulations of the tertiary mRNA structures demonstrate that destabilization by the T allele lowers the folding transition barrier, thus decreasing the probability of occupying its native state. These data suggest a novel structural mechanism whereby functional synonymous variations near the translation initiation codon affect the translation efficiency via entropy-driven changes in mRNA dynamics and present another example of stable compensatory genetic variations in the human population

Identifying molecular mechanisms of catechol o-methyltransferase activity and regulation

Catechol O-methyltransferase (COMT) is a regioselective enzyme that functions by metabolizing catecholamines such as neurotransmitters and hormones via methylation at a single hydroxyl of the catechol moiety. Two cofactors are necessary in order to catalyze the reaction: S-adenosyl-L-methionine (SAM) and a divalent metal cation. Through computational docking studies, we show that a reason metal cations may be necessary for catalysis is due to its role in aligning the donating methyl group of SAM with the nucleophile of the substrate. It is intriguing that an enzyme whose sole function is to degrade catecholamines contains highly conserved residues responsible for regioselective behavior at the catechol moiety, a function in which site-specific chemistry seems unnecessary. Our barrier height calculations for two different COMT ligands suggest that deprotonating the meta- hydroxyl leads to higher rates of methylation and consequently there is evolutionary pressure for selecting residues that can dock the ligand in an ideal conformation for efficient catalysis. Our group previously identified three major haplotypes of COMT, where two single nucleotide polymorphisms (SNPs) produce synonymous changes and an additional SNP that creates a low enzymatic activity variant (Val108Met). Here we show that the allelic variant encoding for the low activity protein shows the highest translational efficiency among the haplotypes, suggesting evolutionary selection of an RNA-structure destabilizing allele to compensate for the low activity mutation present within its protein structure. We provide a mechanism whereby destabilizing alleles may facilitate translation initiation via computational modeling of each mRNA haplotype. One of several biological factors that COMT influences is pain perception because of its role in degrading the neurotransmitters. Peripherally injected serotonin has been clinically shown to induce a hyperalgesic effect. Here we report that serotonin-induced hyperalgesia may be induced by inhibition of COMT. Our kinetic assays reveal serotonin as a non-competitive inhibitor with respect to catechol substrates. From computational modeling, we observe serotonin actively competing with the methyl donor S-adenosyl-L-methionine at the active site. Binding of COMT to serotonin inhibits the methyl donor from entering the active site, thus preventing methylation of COMT substrates

A review of molecular genetic studies of neurocognitive deficits in schizophrenia.

Schizophrenia is a complex and debilitating illness with strong genetic loading. In line with its heterogeneous symptomatology, evidence suggests genetic etiologies for the phenotypes in schizophrenia. A search across endophenotypes has pointed towards consistent findings in its neurocognitive deficits. Extensive literature has demonstrated impaired cognition including executive function, attention, and memory in schizophrenia patients when compared to healthy subjects. This review (1) provides an overview of recent studies and (2) develops an up-to-date conceptualization of genetic variations influencing neurocognitive functions in schizophrenia patients. Several neurotransmitter system genes have been examined given knowledge of their role in brain functions and their reported genetic associations with schizophrenia and cognition. Several genetic variations have emerged as having preliminary effects on neurocognitive deficits in schizophrenia. These include genes in the neurotrophic, serotonin, cell adhesion, and sodium channel systems. Limited evidence also suggests the dopaminergic system genes, with the most studied catechol-o-methytransferase (COMT) gene showing inconsistent findings. Further investigations with larger samples and replications are required to elucidate genetic risk for cognitive deficits in schizophrenia

Dosage effects of BDNF Val66Met polymorphism on cortical surface area and functional connectivity

The single nucleotide polymorphism (SNP) that leads to a valine-to-methionine substitution at codon 66 (Val66Met) in BDNF is correlated with differences in cognitive and memory functions, as well as with several neurological and psychiatric disorders.MRIstudies have already shown that this genetic variant contributes to changes in cortical thickness and volume, but whether the Val66Met polymorphism affects the cortical surface area of healthy subjects remains unclear. Here, we used multimodal MRI to study whether this polymorphism would affect the cortical morphology and resting-state functional connectivity of a large sample of healthy Han Chinese human subjects. An SNP-wise general linear model analysis revealed a "dosage effect" of the Met allele, specifically a stepwise increase in cortical surface area of the right anterior insular cortex with increasing numbers of the Met allele. Moreover, we found enhanced functional connectivity between the anterior insular and the dorsolateral prefrontal cortices that was linked with the dosage of the Met allele. In conclusion, these data demonstrated a "dosage effect" ofBDNFVal66Met on normal cortical structure and function, suggesting anewpath for exploring the mechanisms underlying the effects of genotype on cognition

Functional and molecular alterations of the enteric nervous system in murine models of gut neuropathy

The interaction between cellular constituents of gastrointestinal (GI) tract and commensal microflora is essential for the maintenance of mucosal barrier, promotion of the development of the GI system and modulation of enteric functions such as motility, secretion, mucosal immunity and visceral sensitivity. Alterations in the composition of the gut microflora have been associated to several GI disorders (e.g. inflammatory bowel disease, IBD, and irritable bowel syndrome, IBS) while changes in intestinal microbiota during infancy and adolescence, caused by infection or antibiotic therapy, appear to predispose to the onset of these diseases. Furthermore, dysfunctions of the enteric nervous system (ENS) such structural abnormalities and/or changes in the content of neurotransmitters, have been associated with the onset of IBD and IBS. In this context, a sophisticated system of proteins, so-called Toll-like receptors (TLRs), plays a key role in mediating the inflammatory response against pathogens and triggers beneficial signals to ensure tissue integrity under physiological and pathological conditions. Polymorphisms in genes encoding TLRs, including TLR2 or TLR4, have been associated with different phenotypes of disease extent and severity in patients with GI disorders. In this study we characterized structural and functional alterations of murine ENS induced by: i) anomalies in the composition of the microbiota, ii) changes in innate immunity response, mediated by TLR2 and/or TLR4 following recognition of gut commensal microflora, iii) alterations in the expression of the protein catechol-O-methyltransferase (COMT), involved in the turnover of several neurotransmitters present in both the ENS and the central nervous system, such as dopamine and other catecholamines. Functional and structural studies in male mice C57BL/6J WT and TLR2-/- (21 ± 5 days old) highlighted the presence of significant alterations of intestinal contractility and ENS architecture in ileal preparations of genetically modified mice. Once demonstrated that the deletion of the gene encoding for TLR2 determines ENS structural and functional abnormalities, it was examined whether TLR2-mediated functional anomalies were hematopoietic cell-independent. Therefore, bone marrow chimeric mice were generated and experimental transfers were as follows: WT donors into WT recipients (WT?WT), WT donors into TLR2-/- recipients (WT? TLR2-/-), TLR2-/- donors into TLR2-/- recipients (TLR2-/-? TLR2-/-), and TLR2-/- donors into WT recipients (TLR2-/-? WT). Contractility experiments conducted in bone marrow chimeric mice evidenced that the structure and function of ENS were similar in WT mice given either WT or TLR2?/? bone marrow, indicating that TLR2 signaling in nonhematopoietic cells is a main contributor to ENS health. To investigate the role of the TLR2-microbiota axis in the homeostasis of ENS and enteric smooth muscle we depleted gut microbiota by intragastric administration of a cocktail of broad spectrum antibiotics (50 mg/kg vancomycin, 100 mg/kg neomycin, 100 mg/kg metronidazol and 100 mg/kg ampicillin) twice a day for 14 days in adolescent mice (aged 21 ± 5, ABX). Mice resulted to be successfully depleted after antibiotic treatment and displayed significantly smaller spleens and enlarged ceca, macroscopically phenocopying germ-free mice. This condition, already highlighted in IBS subjects, appears to be due to a delayed emptying of feces from enlarged cecum, due to impaired motility. Functional studies in ABX mice revealed a significant decrease in gastrointestinal transit, accompanied by alterations in the rate of fecal pellet expulsion and stool water content, to suggest that continuous presence of microbial stimuli is required to control intestinal motility and potentially mucosal barrier permeability. Immunohistochemical analysis of ileal preparations from ABX mice showed abnormalities in the distribution and expression of the the pan-neuronal marker HuC/D, the glial structural protein GFAP (glial fibrillary acidic protein) and the cytoplasmatic and nuclear glial calcium-binding protein S100?. Overall these observations highlight the primary role of commensal microbiota in the preservation of the structural integrity of the enteric neuronal and glial network. Given the importance of proper composition of commensal microbiota in the maintenance of neuronal network and neurochemical coding of the ENS intestinal contractility was evaluated in isolated ileal segments from control and ABX mice. These analyses evidenced impaired neuromuscular function associated to antibiotic treatment to further underline that proper neuromuscular function relies on a correct composition of gut microbiota. The primary role of TLR2 signaling in controlling gut motor function was further confirmed by testing the effect of TLR2 engagement by Pam3-CSK4 (a TLR2/TLR1 agonist) in ABX mice. Intraperitoneal supplementation with Pam3CSK4, during the second week of antibiotic treatment, partially corrected these anomalies in ENS structure and intestinal contraction, supporting the presence of a dialogue between commensal microbiota and TLR2, essential for the modulation of neuromuscular function. To highlight the key role of gut microbiota?TLR2-ENS axis in maintaining intestinal function and development of the ENS, male C57Bl/6 mice (2 weeks old) were daily treated subcutaneously with OxPAPC (a TLR2 and TLR4 inhibitor) for 7 days. In vivo inhibition of both TLR2 and TLR4 determined a significant alteration of receptor and non-receptor-mediated neuromuscular responses, in a manner similar to that found in TLR2-deficient mice, providing evidence that TLR2 and TLR4 signaling is essential in ensuring the structural and functional integrity of the SNE during adolescence. Then, we investigate changes in gene expression of GluN1 subunit of N-Methyl-D-Aspartate (NMDA) receptor of the neurotransmitter glutamate in the myenteric plexus of ileal preparations from control and ABX mice. Antibiotic-mediated depletion of commensal microflora determined increased mRNA levels of GluN1, suggesting that commensal microbiota is involved in modulating visceral sensitivity. Finally, the role of brain-gut axis in ENS homeostasis was assessed in an animal model of psychiatric disease, characterized by the genetic reduction of catechol-o-methyltransferase (COMT), an enzyme responsible for the degradation of catecholamines. In female animals genetic-driven COMT defective activity determined increased levels of NO associated to altered ENS architecture, neurochemical coding and visceral sensitivity. We cannot exclude that such changes may be involved in the pathogenesis of IBS in female patients, underlining a potential link with psychiatric disorders

INVESTIGATING THE GENETICS OF MICROSTRUCTURE OF THE CORPUS CALLOSUM IN THE AGEING BRAIN

Abstract: Age-related atrophy of the corpus callosum (CC) has been associated with cognitive impairment and neurodegenerative disease. To date, there is limited knowledge about the role genetics plays in age-related microstructural changes of CC. The current study sought to examine the role of genetic factors on the microstructure of CC in older individuals. Heritability, genetic correlation analyses and a genome-wide search for SNPs associated with the microstructural integrity of CC were undertaken. Brain imaging scans were collected from two studies of community-dwelling older adults the Older Australian Twins Study (OATS) and the Sydney Memory and Ageing Study (MAS). Diffusion tensor imaging (DTI) measures were estimated for the whole CC as well as for five subregions. Parcellation of the CC was performed using Analyze® software. Heritability analyses for CC DTI measures were undertaken in 284 healthy older twins (66% female; 79 MZ and 63 DZ pairs) from OATS (mean age = 69.82, SD=4.76 years). Heritability and genetic correlation analyses were undertaken using the SOLAR software package. Genome-wide association studies (GWAS) for CC DTI measures were undertaken in MAS and replication performed in OATS. Heritability (h2) analysis for the whole CC, indicated significant h2 for fractional anisotropy (FA) (h2=0.56), mean diffusivity (MD) (h2=0.52), radial diffusivity (RD) (h2=0.49) and axial diffusivity (AD) (h2=0.37). Bivariate genetic correlation analyses were also performed between whole CC DTI measures. Across the DTI measures for the whole CC, MD and RD shared 84% of the common genetic variance, followed by MD- AD (77%), FA - RD (52%), RD- AD (37%) and FA MD (11%). The GWAS did not identify any significant SNPs nor were any of the suggestive SNPs replicated in OATS. In addition, candidate CC DTI SNPs were not associated with CC DTI measures. These findings suggest that the CC white matter microstructure in older adults is generally under moderate genetic control. There was also evidence of shared genetic factors between all four CC DTI measures. This study did not identify any significant SNPs associated with CC DTI measures in the GWAS analysis. This work suggests larger genetic association studies may be required to find CC-DTI associated SNPs