The functional MAOA-uVNTR promoter polymorphism in patients with frontotemporal dementia

The Regulation of Monoamine Oxidase A Gene Expression by Distinct Variable Number Tandem Repeats

The monoamine oxidase A (MAOA) uVNTR (upstream variable number tandem repeat) is one of the most often cited examples of a gene by environment interaction (GxE) in relation to behavioral traits. However, MAOA possesses a second VNTR, 500 bp upstream of the uVNTR, which is termed d- or distal VNTR. Furthermore, genomic analysis indicates that there are a minimum of two transcriptional start sites (TSSs) for MAOA, one of which encompasses the uVNTR within the 5′ untranslated region of one of the isoforms. Through expression analysis in semi-haploid HAP1 cell lines genetically engineered in order to knockout (KO) either the uVNTR, dVNTR, or both VNTRs, we assessed the effect of the two MAOA VNTRs, either alone or in combination, on gene expression directed from the different TSSs. Complementing our functional analysis, we determined the haplotype variation of these VNTRs in the general population. The expression of the two MAOA isoforms was differentially modulated by the two VNTRs located in the promoter region. The most extensively studied uVNTR, previously considered a positive regulator of the MAOA gene, did not modulate the expression of what it is considered the canonical isoform, while we found that the dVNTR positively regulated this isoform in our model. In contrast, both the uVNTR and the dVNTR were found to act as negative regulators of the second less abundant MAOA isoform. The haplotype analysis for these two VNTRs demonstrated a bias against the presence of one of the potential variants. The uVNTR and dVNTR differentially affect expression of distinct MAOA isoforms, and thus, their combined profiling offers new insights into gene-regulation, GxE interaction, and ultimately MAOA-driven behavior.

Genetic variation in MAOA modulates prefrontal cortical regulation of approach-avoidance reactions

BACKGROUND

Regulation of automatic approach and avoidance behavior requires affective and cognitive control, which are both influenced by a genetic variation in the gene encoding Monoamine Oxidase A (termed MAOA-uVNTR).

METHODS

The current study investigated MAOA genotype as a moderator of prefrontal cortical activation measured with functional near-infrared spectroscopy (fNIRS) in 37 healthy young adults during performance of the approach-avoidance task with positive and negative pictures.

RESULTS

Carriers of the low- compared to the high-expressing genetic variant (MAOA-L vs. MAOA-H) showed increasing regulatory activity in the right dorsolateral prefrontal cortex (DLPFC) during incompatible conditions (approach negative, avoid positive). This might have been a compensatory mechanism for stronger emotional reactions as shown in previous studies and might have prevented any influence of incompatibility on behavior. In contrast, fewer errors but also lower activity in the right DLPFC during processing of negative compared to positive stimuli indicated MAOA-H carriers to have used other regulatory areas. This resulted in slower reaction times in incompatible conditions, but--in line with the known better cognitive regulation efficiency--allowed them to perform incompatible reactions without activating the DLPFC as the highest control instance. Carriers of one low- and one high-expressing allele lay as an intermediate group between the reactions of the low- and high-expressing groups.

CONCLUSIONS

The relatively small sample size and restriction to fNIRS for assessment of cortical activity limit our findings. Nevertheless, these first results suggest monoam-inergic mechanisms to contribute to interindividual differences in the two basic behavioral principles of approach and avoidance and their neuronal correlates.

Genetic susceptibility for individual cooperation preferences: the role of monoamine oxidase A gene (MAOA) in the voluntary provision of public goods

In the context of social dilemmas, previous research has shown that human cooperation is mainly based on the social norm of conditional cooperation. While in most cases individuals behave according to such a norm, deviant behavior is no exception. Recent research further suggests that heterogeneity in social behavior might be associated with varying genetic predispositions. In this study, we investigated the relationship between individuals' behavior in a public goods experiment and the promoter-region functional repeat polymorphism in the monoamine oxidase A gene (MAOA). In a dynamic setting of increasing information about others' contributions, we analyzed differences in two main components of conditional cooperation, namely the players' own contribution and their beliefs regarding the contribution of other players. We showed that there is a significant association between individuals' behavior in a repeated public goods game and MAOA. Our results suggest that male carriers of the low activity alleles cooperate significantly less than those carrying the high activity alleles given a situation where subjects had to rely on their innate beliefs about others' contributions. With increasing information about the others' cooperativeness, the genetic effect diminishes. Furthermore, significant opposing effects for female subjects carrying two low activity alleles were observed.

Type A monoamine oxidase regulates life and death of neurons in neurodegeneration and neuroprotection

In Parkinson's disease, type B monoamine oxidase (MAO-B) is proposed to play an important role in the pathogenesis through production of reactive oxygen species and neurotoxins from protoxicants, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. In addition, inhibitors of MAO-B protect neurons in the cellular and animal models of Parkinson's and Alzheimer's diseases. However, the role of type A MAO (MAO-A) in neuronal death and neuroprotection by MAO-B inhibitors has been scarcely elucidated. This chapter presents our recent results on the involvement of MAO-A in the activation of mitochondrial death signal pathway and in the induction of prosurvival genes to prevent cell death with MAO-B inhibitors. The roles of MAO-A in the regulation of neuronal survival and death are discussed in concern to find a novel strategy to protect neurons in age-associated neurodegenerative disorders and depression.