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1.  Early postnatal inhibition of serotonin synthesis results in long-term reductions of perseverative behaviors, but not aggression, in MAO A-deficient mice 
Neuropharmacology  2013;0:10.1016/j.neuropharm.2013.07.003.
Monoamine oxidase (MAO) A, the major enzyme catalyzing the oxidative degradation of serotonin (5-hydroxytryptamine, 5-HT), plays a key role in emotional regulation. In humans and mice, MAO-A deficiency results in high 5-HT levels, antisocial, aggressive, and perseverative behaviors. We previously showed that the elevation in brain 5-HT levels in MAO-A knockout (KO) mice is particularly marked during the first two weeks of postnatal life. Building on this finding, we hypothesized that the reduction of 5-HT levels during these early stages may lead to enduring attenuations of the aggression and other behavioral aberrances observed in MAO-A KO mice. To test this possibility, MAO-A KO mice were treated with daily injections of a 5-HT synthesis blocker, the tryptophan hydroxylase inhibitor p-chloro-phenylalanine (pCPA, 300 mg/kg/day, IP), from postnatal day 1 through 7. As expected, this regimen significantly reduced 5-HT forebrain levels in MAO-A KO pups. These neurochemical changes persisted throughout adulthood, and resulted in significant reductions in marble-burying behavior, as well as increases in spontaneous alternations within a T-maze. Conversely, pCPA-treated MAO-A KO mice did not exhibit significant changes in anxiety-like behaviors in a novel open-field and elevated plus-maze; furthermore, this regimen did not modify their social deficits, aggressive behaviors and impairments in tactile sensitivity. Treatment with pCPA from postnatal day 8 through 14 elicited similar, yet milder, behavioral effects on marble-burying behavior. These results suggest that early developmental enhancements in 5-HT levels have long-term effects on the modulation of behavioral flexibility associated with MAO-A deficiency.
doi:10.1016/j.neuropharm.2013.07.003
PMCID: PMC3849223  PMID: 23871843
2.  Monoamine Oxidase B Prompts Mitochondrial and Cardiac Dysfunction in Pressure Overloaded Hearts 
Antioxidants & Redox Signaling  2014;20(2):267-280.
Abstract
Aims: Monoamine oxidases (MAOs) are mitochondrial flavoenzymes responsible for neurotransmitter and biogenic amines catabolism. MAO-A contributes to heart failure progression via enhanced norepinephrine catabolism and oxidative stress. The potential pathogenetic role of the isoenzyme MAO-B in cardiac diseases is currently unknown. Moreover, it is has not been determined yet whether MAO activation can directly affect mitochondrial function. Results: In wild type mice, pressure overload induced by transverse aortic constriction (TAC) resulted in enhanced dopamine catabolism, left ventricular (LV) remodeling, and dysfunction. Conversely, mice lacking MAO-B (MAO-B−/−) subjected to TAC maintained concentric hypertrophy accompanied by extracellular signal regulated kinase (ERK)1/2 activation, and preserved LV function, both at early (3 weeks) and late stages (9 weeks). Enhanced MAO activation triggered oxidative stress, and dropped mitochondrial membrane potential in the presence of ATP synthase inhibitor oligomycin both in neonatal and adult cardiomyocytes. The MAO-B inhibitor pargyline completely offset this change, suggesting that MAO activation induces a latent mitochondrial dysfunction, causing these organelles to hydrolyze ATP. Moreover, MAO-dependent aldehyde formation due to inhibition of aldehyde dehydrogenase 2 activity also contributed to alter mitochondrial bioenergetics. Innovation: Our study unravels a novel role for MAO-B in the pathogenesis of heart failure, showing that both MAO-driven reactive oxygen species production and impaired aldehyde metabolism affect mitochondrial function. Conclusion: Under conditions of chronic hemodynamic stress, enhanced MAO-B activity is a major determinant of cardiac structural and functional disarrangement. Both increased oxidative stress and the accumulation of aldehyde intermediates are likely liable for these adverse morphological and mechanical changes by directly targeting mitochondria. Antioxid. Redox Signal. 20, 267–280.
doi:10.1089/ars.2012.4616
PMCID: PMC3887464  PMID: 23581564
3.  Monoamine oxidase A mediates prostate tumorigenesis and cancer metastasis 
The Journal of Clinical Investigation  2014;124(7):2891-2908.
Tumors from patients with high-grade aggressive prostate cancer (PCa) exhibit increased expression of monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines. Despite the association between MAOA and aggressive PCa, it is unclear how MAOA promotes PCa progression. Here, we found that MAOA functions to induce epithelial-to-mesenchymal transition (EMT) and stabilize the transcription factor HIF1α, which mediates hypoxia through an elevation of ROS, thus enhancing growth, invasiveness, and metastasis of PCa cells. Knockdown and overexpression of MAOA in human PCa cell lines indicated that MAOA induces EMT through activation of VEGF and its coreceptor neuropilin-1. MAOA-dependent activation of neuropilin-1 promoted AKT/FOXO1/TWIST1 signaling, allowing FOXO1 binding at the TWIST1 promoter. Importantly, the MAOA-dependent HIF1α/VEGF-A/FOXO1/TWIST1 pathway was activated in high-grade PCa specimens, and knockdown of MAOA reduced or even eliminated prostate tumor growth and metastasis in PCa xenograft mouse models. Pharmacological inhibition of MAOA activity also reduced PCa xenograft growth in mice. Moreover, high MAOA expression in PCa tissues correlated with worse clinical outcomes in PCa patients. These findings collectively characterize the contribution of MAOA in PCa pathogenesis and suggest that MAOA has potential as a therapeutic target in PCa.
doi:10.1172/JCI70982
PMCID: PMC4071401  PMID: 24865426
4.  Altered Cerebellar Organization and Function in Monoamine Oxidase A Hypomorphic Mice 
Neuropharmacology  2012;63(7):1208-1217.
Monoamine oxidase A (MAO-A) is the key enzyme for the degradation of brain serotonin (5-hydroxytryptamine, 5-HT), norepinephrine (NE) and dopamine (DA). We recently generated and characterized a novel line of MAO-A hypormorphic mice (MAO-ANeo), featuring elevated monoamine levels, social deficits and perseverative behaviors as well as morphological changes in the basolateral amygdala and orbitofrontal cortex. Here we showed that MAO-ANeo mice displayed deficits in motor control, manifested as subtle disturbances in gait, motor coordination, and balance. Furthermore, magnetic resonance imaging of the cerebellum revealed morphological changes and a moderate reduction in the cerebellar size of MAO- ANeo mice compared to wild type (WT) mice. Histological and immunohistochemical analyses using calbindin-D-28k (CB) expression of Purkinje cells revealed abnormal cerebellar foliation with vermal hypoplasia and decreased in Purkinje cell count and their dendritic density in MAO- ANeo mice compared to WT. Our current findings suggest that congenitally low MAO-A activity leads to abnormal development of the cerebellum.
doi:10.1016/j.neuropharm.2012.08.003
PMCID: PMC3442946  PMID: 22971542
Monoamine oxidase A; Hypomorphism; Serotonin; Cerebellum; Purkinje cells
5.  Cerebral cortical blood flow maps are reorganized in MAOB-deficient mice 
Brain research  1999;824(1):36-44.
Cerebral cortical blood flow (CBF) was measured autoradiographically in conscious mice without the monoamine oxidase B (MAOB) gene (KO, n = 11) and the corresponding wild-type animals (WILD, n = 11). Subgroups of animals of each genotype received a continuous intravenous infusion over 30 min of phenylethylamine (PEA), an endogenous substrate of MAOB, (8 nmol g−1 min−1 in normal saline at a volume rate of 0.11 μl g−1 min−1) or saline at the same volume rate. Maps of relative CBF distribution showed predominance of midline motor and sensory area CBF in KO mice over WILD mice that received saline. PEA enhanced CBF in lateral frontal and piriform cortex in both KO and WILD mice. These changes may reflect a differential activation due to chronic and acute PEA elevations on motor and olfactory function, as well as on the anxiogenic effects of this amine. In addition to its effects on regional CBF distribution, PEA decreased CBF globally in KO mice (range −31% to −41% decrease from control levels) with a lesser effect in WILD mice. It is concluded that MAOB may normally regulate CBF distribution and its response to blood PEA.
PMCID: PMC4075434  PMID: 10095040
Cerebral blood flow; Monoamine oxidase; Phenylethylamine; Autoradiography; Iodo-antipyrine; Mouse
6.  NMDARs Mediate the Role of Monoamine Oxidase A in Pathological Aggression 
Converging evidence shows that monoamine oxidase A (MAO A), the key enzyme catalyzing serotonin (5-hydroxytryptamine; 5-HT) and norepinephrine (NE) degradation, is a primary factor in the pathophysiology of antisocial and aggressive behavior. Accordingly, male MAO A-deficient humans and mice exhibit an extreme predisposition to aggressive outbursts in response to stress. As NMDARs regulate the emotional reactivity to social and environmental stimuli, we hypothesized their involvement in the modulation of aggression mediated by MAO A. In comparison with WT male mice, MAO A KO counterparts exhibited increases in 5-HT and NE levels across all brain regions, but no difference in glutamate concentrations and NMDAR binding. Notably, the prefrontal cortex (PFC) of MAO A KO mice exhibited higher expression of NR2A and NR2B, as well as lower levels of glycosylated NR1 subunits. In line with these changes, the current amplitude and decay time of NMDARs in PFC was significantly reduced. Furthermore, the currents of these receptors were hypersensitive to the action of the antagonists of the NMDAR complex (dizocilpine), as well as NR2A (PEAQX) and NR2B (Ro 25–6981) subunits. Notably, systemic administration of these agents selectively countered the enhanced aggression in MAO A KO mice, at doses that did not inherently affect motor activity. Our findings suggest that the role of MAO A in pathological aggression may be mediated by changes in NMDAR subunit composition in the PFC, and point to a critical function of this receptor in the molecular bases of antisocial personality.
doi:10.1523/JNEUROSCI.0225-12.2012
PMCID: PMC3417343  PMID: 22723698
7.  Novel monoamine oxidase A knock out mice with human-like spontaneous mutation 
Neuroreport  2008;19(7):739-743.
A novel line of mutant mice [monoamine oxidase A knockout (MAOAA863T KO)] harboring a spontaneous point nonsense mutation in exon 8 of the MAO A gene was serendipitously identified in a 129/SvEvTac colony. This mutation is analogous to the cause of a rare human disorder, Brunner syndrome, characterized by complete MAO A deficiency and impulsive aggressiveness. Concurrent with previous studies of MAO A KO mice generated by insertional mutagenesis (‘Tg8’), MAOAA863T KO lack MAO A enzyme activity and display enhanced aggression toward intruder mice. MAOAA863T KO, however, exhibited lower locomotor activity in a novel, inescapable open field and similar immobility during tail suspension compared with wild type, observations which differ from reports of Tg8. These findings consolidate evidence linking MAO A to aggression and highlight subtle yet distinctive phenotypical characteristics.
doi:10.1097/WNR.0b013e3282fd6e88
PMCID: PMC3435113  PMID: 18418249
Brunner syndrome; monoamine oxidase; nonsense mutation
8.  Monoamine Oxidases Regulate Telencephalic Neural Progenitors in Late Embryonic and Early Postnatal Development 
Monoamine neurotransmitters play major roles in regulating a range of brain functions in adults and increasing evidence suggests roles for monoamines in brain development. Here we show that mice lacking the monoamine metabolic enzymes MAO A and MAO B (MAO AB-deficient mice) exhibit diminished proliferation of neural stem cells (NSC) in the developing telencephalon beginning in late gestation [embryonic day (E) 17.5], a deficit that persists in neonatal and adult mice. These mice showed significantly increased monoamine levels and anxiety-like behaviors as adults. Assessments of markers of intermediate progenitor cells (IPC) and mitosis showed that NSC in the subventricular zone (SVZ), but not in the ventricular zone, are reduced in MAO AB-deficient mice. A developmental time course of monoamines in frontal cortical tissues revealed increased serotonin levels as early as E14.5, and a further large increase was found between E17.5 and postnatal day 2. Administration of an inhibitor of serotonin synthesis (parachlorophenylalanine) between E14.5 and E19.5 restored the IPC numbers and SVZ thickness, suggesting the role of serotonin in the suppression of IPC proliferation. Studies of neurosphere cultures prepared from the telencephalon at different embryonic and postnatal ages showed that serotonin stimulates proliferation in wild-type, but not in MAO AB-deficient, NSC. Together, these results suggest that a MAO-dependent long-lasting alteration in the proliferation capacity of NSC occurs late in embryonic development and is mediated by serotonin. Our findings reveal novel roles for MAOs and serotonin in the regulation of IPC proliferation in the developing brain.
doi:10.1523/JNEUROSCI.2037-10.2010
PMCID: PMC2967387  PMID: 20702706
9.  Behavioral disinhibition and reduced anxiety-like behaviors in monoamine oxidase B deficient mice 
Monoamine oxidase (MAO) B catalyzes the degradation of β-phenylethylamine (PEA), a trace amine neurotransmitter implicated in mood regulation. Although several studies have shown an association between low MAO B activity in platelets and behavioral disinhibition in humans, the nature of this relation remains undefined. To investigate the impact of MAO B deficiency on the emotional responses elicited by environmental cues, we tested MAO B knockout (KO) mice in a set of behavioral assays capturing different aspects of anxiety-related manifestations, such as the elevated plus maze, defensive withdrawal, marble burying and hole-board. Furthermore, MAO B KO mice were evaluated for their exploratory patterns in response to unfamiliar objects and risk-taking behaviors. In comparison to their wild-type (WT) littermates, MAO B KO mice exhibited significantly lower anxiety-like responses and shorter latency to engage in risk-taking behaviors and exploration of unfamiliar objects. To determine the neurobiological bases of the behavioral differences between WT and MAO B KO mice, we measured the brain-regional levels of PEA in both genotypes. Although PEA levels were significantly higher in all brain regions of MAO B KO in comparison to WT mice, the most remarkable increments were observed in striatum and prefrontal cortex, two key regions for the regulation of behavioral disinhibition. However, no significant differences in transcript levels of PEA’s selective receptor, trace amine-associated receptor 1 (TAAR1), were detected in either region. Taken together, these results suggest that MAO B deficiency may lead to behavioral disinhibition and decreased anxiety-like responses partially through regional increases of PEA levels.
doi:10.1038/npp.2009.118
PMCID: PMC2783894  PMID: 19710633
Monoamine Oxidase B; mice; behavioral disinhibition; anxiety; phenylethylamine
10.  Monoamine oxidase inactivation: from pathophysiology to therapeutics 
Advanced drug delivery reviews  2008;60(13-14):1527-1533.
Monoamine oxidases (MAOs) A and B are mitochondrial bound isoenzymes which catalyze the oxidative deamination of dietary amines and monoamine neurotransmitters, such as serotonin, norepinephrine, dopamine, β-phenylethylamine and other trace amines. The rapid degradation of these molecules ensures the proper functioning of synaptic neurotransmission and is critically important for the regulation of emotional behaviors and other brain functions. The byproducts of MAO-mediated reactions include several chemical species with neurotoxic potential, such as hydrogen peroxide, ammonia and aldehydes. As a consequence, it is widely speculated that prolonged excessive activity of these enzymes may be conducive to mitochondrial damages and neurodegenerative disturbances.
In keeping with these premises, the development of MAO inhibitors has led to important breakthroughs in the therapy of several neuropsychiatric disorders, ranging from mood disorders to Parkinson’s disease. Furthermore, the characterization of MAO knockout (KO) mice has revealed that the inactivation of this enzyme produces a number of functional and behavioral alterations, some of which may be harnessed for therapeutic aims. In this article, we discuss the intriguing hypothesis that the attenuation of the oxidative stress induced by the inactivation of either MAO isoform may contribute to both antidepressant and antiparkinsonian actions of MAO inhibitors. This possibility further highlights MAO inactivation as a rich source of novel avenues in the treatment of mental disorders.
doi:10.1016/j.addr.2008.06.002
PMCID: PMC2630537  PMID: 18652859
Monoamine oxidase; depression; Parkinson’s disease; oxidative stress
11.  Prenatal Exposure to Urban Air Nanoparticles in Mice Causes Altered Neuronal Differentiation and Depression-Like Responses 
PLoS ONE  2013;8(5):e64128.
Emerging evidence suggests that excessive exposure to traffic-derived air pollution during pregnancy may increase the vulnerability to neurodevelopmental alterations that underlie a broad array of neuropsychiatric disorders. We present a mouse model for prenatal exposure to urban freeway nanoparticulate matter (nPM). In prior studies, we developed a model for adult rodent exposure to re-aerosolized urban nPM which caused inflammatory brain responses with altered neuronal glutamatergic functions. nPMs are collected continuously for one month from a local freeway and stored as an aqueous suspension, prior to re-aerosolization for exposure of mice under controlled dose and duration. This paradigm was used for a pilot study of prenatal nPM impact on neonatal neurons and adult behaviors. Adult C57BL/6J female mice were exposed to re-aerosolized nPM (350 µg/m3) or control filtered ambient air for 10 weeks (3×5 hour exposures per week), encompassing gestation and oocyte maturation prior to mating. Prenatal nPM did not alter litter size, pup weight, or postnatal growth. Neonatal cerebral cortex neurons at 24 hours in vitro showed impaired differentiation, with 50% reduction of stage 3 neurons with long neurites and correspondingly more undifferentiated neurons at Stages 0 and 1. Neuron number after 24 hours of culture was not altered by prenatal nPM exposure. Addition of exogenous nPM (2 µg/ml) to the cultures impaired pyramidal neuron Stage 3 differentiation by 60%. Adult males showed increased depression-like responses in the tail-suspension test, but not anxiety-related behaviors. These pilot data suggest that prenatal exposure to nPM can alter neuronal differentiation with gender-specific behavioral sequelae that may be relevant to human prenatal exposure to urban vehicular aerosols.
doi:10.1371/journal.pone.0064128
PMCID: PMC3667185  PMID: 23734187
12.  Monoamine oxidase A and A/B knockout mice display autistic-like features 
Converging lines of evidence show that a sizable subset of autism-spectrum disorders (ASDs) is characterized by increased blood levels of serotonin (5-hydroxytryptamine, 5-HT), yet the mechanistic link between these two phenomena remains unclear. The enzymatic degradation of brain 5-HT is mainly mediated by monoamine oxidase (MAO)A and, in the absence of this enzyme, by its cognate isoenzyme MAOB. MAOA and A/B knockout (KO) mice display high 5-HT levels, particularly during early developmental stages. Here we show that both mutant lines exhibit numerous behavioural hallmarks of ASDs, such as social and communication impairments, perseverative and stereotypical responses, behavioural inflexibility, as well as subtle tactile and motor deficits. Furthermore, both MAOA and A/B KO mice displayed neuropathological alterations reminiscent of typical ASD features, including reduced thickness of the corpus callosum, increased dendritic arborization of pyramidal neurons in the prefrontal cortex and disrupted microarchitecture of the cerebellum. The severity of repetitive responses and neuropathological aberrances was generally greater in MAOA/B KO animals. These findings suggest that the neurochemical imbalances induced by MAOAdeficiency (either by itself or in conjunction with lack of MAOB) may result in an array of abnormalities similar to those observed in ASDs. Thus, MAOA and A/B KO mice may afford valuable models to help elucidate the neurobiological bases of these disorders and related neurodevelopmental problems.
doi:10.1017/S1461145712000715
PMCID: PMC3517692  PMID: 22850464
Animal models; autistic-spectrum disorders; monoamine oxidase
13.  Social Deficits and Perseverative Behaviors, but not Overt Aggression, in MAO-A Hypomorphic Mice 
Neuropsychopharmacology  2011;36(13):2674-2688.
Monoamine oxidase (MAO)-A is a key enzyme for the degradation of brain serotonin (5-hydroxytryptamine, 5-HT) and norepinephrine (NE). In humans and mice, total MAO-A deficiency results in high 5-HT and NE levels, as well as elevated reactive aggression. Here we report the generation of MAO-ANeo mice, a novel line of hypomorphic MAO-A mutants featuring the insertion of a floxed neomycin-resistance cassette in intron-12 of the Maoa gene. This construct resulted in a chimeric, non-functional variant of the Maoa-Neo transcript, with a truncated C-terminus, likely due to aberrant splicing; these deficits notwithstanding, small amounts of functional Maoa transcript were found in the brain of MAO-ANeo mice. In the prefrontal cortex and amygdala, MAO-ANeo mice showed low, yet detectable, MAO-A catalytic activity, as well as 5-HT levels equivalent to WT littermates; conversely, the hippocampus and midbrain of MAO-ANeo mice featured a neurochemical profile akin to MAO-A-knockout (KO) mice, with undetectable MAO-A activity and high 5-HT concentrations. MAO-ANeo mice showed significant increases in dendritic length in the pyramidal neurons of orbitofrontal cortex, but not basolateral amygdala, in comparison with WT littermates; by contrast, the orbitofrontal cortex of MAO-A KO mice showed significant reductions in basilar dendritic length, as well as a profound increase in apical dendritic length. MAO-ANeo mice showed a unique set of behavioral abnormalities, encompassing reduced open-field locomotion, perseverative responses, such as marble burying and water mist-induced grooming, and a lack of anxiety-like behaviors in the elevated plus-maze and light–dark box paradigms. Notably, whereas MAO-ANeo and KO mice showed significant reductions in social interaction, only the latter genotype showed increases in resident–intruder aggression. Taken together, our findings indicate that MAO A hypomorphism results in behavioral and morphological alterations distinct from those featured by MAO-A KO mice.
doi:10.1038/npp.2011.157
PMCID: PMC3230491  PMID: 21832987
monoamine oxidase-A; transgenic mice; social interaction; aggression; anxiety; repetitive behaviors; animal models; behavioral science; serotonin; neurochemistry; monoamine oxidase-A; aggression; anxiety; transgenic mice
14.  De novo microdeletion of Xp11.3 exclusively encompassing the monoamine oxidase A and B genes in a male infant with episodic hypotonia: A genomics approach to personalized medicine 
Monoamine oxidase A and B (MAOA and MAOB) play key roles in deaminating neurotransmitters and various other biogenic amines. Patients deficient in one or both enzymes have distinct metabolic and neurologic profiles. MAOB deficient patients exhibit normal clinical characteristics and behavior, while MAOA deficient patients have borderline intellectual deficiency and impaired impulse control. Patients who lack both MAOA and MAOB have the most extreme laboratory values (urine, blood, and CSF serotonin 4–6 times normal, with elevated O-methylated amine metabolites and reduced deaminated metabolites) in addition to severe intellectual deficiency and behavioral problems. Mice lacking maoa and moab exhibit decreased proliferation of neural stem cells beginning in late gestation and persisting into adulthood These mice show significantly increased monoamine levels, particularly serotonin, as well as anxiety-like behaviors as adults, suggesting that brain maturation in late embryonic development is adversely affected by elevated serotonin levels. We report the case of a male infant with a de novo Xp11.3 microdeletion exclusively encompassing the MAOA and MAOB genes. This newly recognized X-linked disorder is characterized by severe intellectual disability and unusual episodes of hypotonia, which resemble atonic seizures, but have no EEG correlate. A customized low dietary amine diet was implemented in an attempt to prevent the cardiovascular complications that can result from the excessive intake of these compounds. This is the second report of this deletion and the first attempt to maintain the patient’s cardiovascular health through dietary manipulation. Even though a diet low in tyramine, phenylethylamine, and dopa/dopamine is necessary for long-term management, it will not rescue the abnormal monoamine profile seen in combined MAOA and MAOB deficiency. Our patient displays markedly elevated levels of serotonin in blood, serum, urine, and CSF while on this diet. Serotonin biosynthesis inhibitors like para-chlorophenylalanine and p-ethynylphenylalanine may be needed to lower serotonin levels in patients with absent monoamine oxidase enzymes.
doi:10.1016/j.ejmg.2012.01.007
PMCID: PMC3468330  PMID: 22365943
Monoamine oxidase; Copy Number Variant; Xp11.3 deletion; Catacholamines; Serotonin; Tyramine; X-linked intellectual deficiency
15.  Altered Expression of Tyrosine Hydroxylase in the Locus Coeruleus Noradrenergic System in Citalopram Neonatally Exposed Rats and Monoamine Oxidase A Knock Out Mice 
In rodents, noradrenergic (NE) locus coeruleus (LC) neurons are well known to express tyrosine hydroxylase (TH) immunoreactivity. However, due to its very low enzyme activity, NE cortical fibers do not typically express TH immunoreactivity, thus dopamine-beta-hydroxylase (DBH) immunoreactivity is commonly utilized as a marker for NE cortical fibers. In this study, we performed double and/or triple immunofluorescent staining using antibodies against TH, DBH, and/or norepinephrine transporter (NET) to investigate the altered noradrenergic TH expression of cortical fibers in citalopram (CTM) exposed rats and monoamine oxidase (MAO) A knock out (KO) mice. We have noted the following novel findings: 1) neonatal exposure to the selective serotonin reuptake inhibitor (SSRI) CTM enhanced noradrenergic TH immunoreactive fibers throughout the entire neocortex, and a few of them appeared to be hypertrophic; 2) slightly enhanced noradrenergic cortical TH immunoreactive fibers were also noted in MAO A KO mice, and many of them revealed varicosities compared to the rather smooth noradrenergic cortical TH immunoreactive fibers in wild type (WT) mice; 3) LC dendrites of MAO A KO mice exhibited beaded morphology compared to the smooth LC dendrites in WT mice. Our findings suggest that both genetic and environmental factors during early development may play a critical role in the regulation and proper function of noradrenergic TH expression in the neocortex.
doi:10.1002/ar.21350
PMCID: PMC3177426  PMID: 21901841
norepinephrine; tyrosine hydroxylase; monoamine oxidase; neonates; antidepressants; knock out mice
16.  Monoamine oxidase A regulates neural differentiation of murine embryonic stem cells 
Monoamine oxidase (MAO) A is the major metabolizing enzyme of serotonin (5-hydroxytryptamine, 5-HT) which regulates early brain development. In this study, wild-type (WT) and MAO Aneo embryonic stem (ES) cell lines were established from the inner cell mass of murine blastocysts and their characteristics during ES and differentiating stages were studied. Our results show that the differentiation to neural cells in MAO Aneo ES cells was reduced compared to WT, suggesting MAO A played a regulatory role in stem cells neural differentiation.
doi:10.1007/s00702-011-0655-0
PMCID: PMC3435112  PMID: 21607742
Embryonic stem cells; Neural differentiation; Neurogenesis; Monoamine oxidase (MAO) A
17.  Maladaptive defensive behaviours in monoamine oxidase A-deficient mice 
Rich evidence indicates that monoamine oxidase (MAO) A, the major enzyme catalysing the degradation of monoamine neurotransmitters, plays a key role in emotional regulation. Although MAOA deficiency is associated with reactive aggression in humans and mice, the involvement of this enzyme in defensive behaviour remains controversial and poorly understood. To address this issue, we tested MAOA knockout (KO) mice in a spectrum of paradigms and settings associated with variable degrees of threat. The presentation of novel inanimate objects induced a significant reduction in exploratory approaches and increase in defensive behaviours, such as tail-rattling, biting and digging. These neophobic responses were context-dependent and particularly marked in the home cage. In the elevated plus- and T-mazes, MAOA KO mice and wild-type (WT) littermates displayed equivalent locomotor activity and time in closed and open arms; however, MAOA KO mice featured significant reductions in risk assessment, as well as unconditioned avoidance and escape. No differences between genotypes were observed in the defensive withdrawal and emergence test. Conversely, MAOA KO mice exhibited a dramatic reduction of defensive and fear-related behaviours in the presence of predator-related cues, such as predator urine or an anaesthetized rat, in comparison with those observed in their WT littermates. The behavioural abnormalities in MAOA KO mice were not paralleled by overt alterations in sensory and microvibrissal functions. Collectively, these results suggest that MAOA deficiency leads to a general inability to appropriately assess contextual risk and attune defensive and emotional responses to environmental cues.
doi:10.1017/S1461145710001483
PMCID: PMC3435117  PMID: 21156093
Anxiety; defensive behaviour; exploration; monoamine oxidase A; predator urine
18.  Transcriptional regulation and multiple functions of MAO genes 
Monoamine oxidase (MAO) A and MAO B are a crucial pair of isoenzymes, which oxidatively deaminate monoamine neurotransmitters and dietary amines with a production of hydrogen peroxide. These two isoenzymes have different but overlapping substrate and inhibitor specificities. MAO A and MAO B share 70% amino acid sequence identity and show different temporal and spatial expressions in both humans and mice. Abnormal MAO A or MAO B activity has been implicated in numerous neurological and psychiatric disorders. A better understanding of the transcriptional regulation of MAO A and MAO B genes may help explain the differential tissue-specific expression of these two isoenzymes and provide insights into the molecular basis of the disorders associated with MAO dysfunction. This review discusses the recent progress in the transcriptional regulation and multiple functions of MAO A and MAO B genes.
doi:10.1007/s00702-010-0562-9
PMCID: PMC3125068  PMID: 21359973
Monoamine oxidase; Promoter; Transcriptional regulation; Hormone; Sp1
19.  BEHAVIORAL OUTCOMES OF MONOAMINE OXIDASE DEFICIENCY: PRECLINICAL AND CLINICAL EVIDENCE 
Monoamine oxidase (MAO) isoenzymes A and B are mitochondrial-bound proteins, catalyzing the oxidative deamination of monoamine neurotransmitters as well as xenobiotic amines. Although they derive from a common ancestral progenitor gene, are located at X-chromosome and display 70% structural identity, their substrate preference, regional distribution, and physiological role are divergent. In fact, while MAO-A has high affinity for serotonin and norepinephrine, MAO-B primarily serves the catabolism of 2-phenylethylamine (PEA) and contributes to the degradation of other trace amines and dopamine. Convergent lines of preclinical and clinical evidence indicate that variations in MAO enzymatic activity—due to either genetic or environmental factors—can exert a profound influence on behavioral regulation and play a role in the pathophysiology of a large spectrum of mental and neurodegenerative disorders, ranging from antisocial personality disorder to Parkinson’s disease. Over the past few years, numerous advances have been made in our understanding of the phenotypical variations associated with genetic polymorphisms and mutations of the genes encoding for both isoenzymes. In particular, novel findings on the phenotypes of MAO-deficient mice are highlighting novel potential implications of both isoenzymes in a broad spectrum of mental disorders, ranging from autism and anxiety to impulse-control disorders and ADHD. These studies will lay the foundation for future research on the neurobiological and neurochemical bases of these pathological conditions, as well as the role of gene × environment interactions in the vulnerability to several mental disorders.
doi:10.1016/B978-0-12-386467-3.00002-9
PMCID: PMC3371272  PMID: 21971001
20.  Association of the Calcyon Neuron-Specific Vesicular Protein Gene (CALY) With Adolescent Smoking Initiation in China and California 
American Journal of Epidemiology  2011;173(9):1039-1048.
Although previous investigations have indicated a role for genetic factors in smoking initiation, the underlying genetic mechanisms are still unknown. In 2,339 adolescents from a Chinese Han population in the Wuhan Smoking Prevention Trial (Wuhan, China, 1998–1999), the authors explored the association of 57 genes in the dopamine pathway with smoking initiation. Using a conservative approach for declaring significance, positive findings were further examined in an independent sample of 603 Caucasian adolescents followed for up to 10 years as part of the Children's Health Study (Southern California, 1993–2009). The authors identified 1 single nucleotide polymorphism (rs2298122) in the calcyon neuron-specific vesicular protein gene (CALY) that was positively associated with smoking initiation in females (odds ratio = 2.21, 95% confidence interval: 1.49, 3.27; P = 8.4 × 10−5) in the Wuhan Smoking Prevention Trial cohort, and they replicated the association in females from the Children's Health Study cohort (hazard rate ratio = 2.05, 95% confidence interval: 1.27, 3.31; P = 0.003). These results suggest that the CALY gene may influence smoking initiation in adolescents, although the potential roles of underlying psychological characteristics that may be components of the smoking-initiation phenotype, such as impulsivity or novelty-seeking, remain to be explored.
doi:10.1093/aje/kwq471
PMCID: PMC3121219  PMID: 21415033
adolescent; dopamine; genetic association studies; smoking
21.  A transient placental source of serotonin for the fetal forebrain 
Nature  2011;472(7343):347-350.
Serotonin (5-hydroxytryptamine; 5-HT) is thought to regulate neurodevelopmental processes through maternal-fetal interactions that have long-term mental health implications. Dogma states that beyond fetal 5-HT neurons, there are significant maternal contributions to fetal 5-HT during pregnancy1,2, but this has not been tested empirically. To examine putative central and peripheral sources of embryonic brain 5-HT, we used the Pet-1−/− mice in which most dorsal raphe (DR) neurons lack 5-HT3. Measures of 5-HT revealed previously unknown differences in accumulation between the fore- and hindbrain during early and late fetal stages, through an exogenous source of 5-HT. We show that this source is not of maternal origin. Using additional genetic strategies, a new technology for studying placental biology ex vivo, and direct manipulation of placental neosynthesis, we investigated the nature of this exogenous source and uncovered a placental 5-HT synthetic pathway from a maternal tryptophan precursor, in both mice and humans. This study reveals a new, direct role for placental metabolic pathways in modulating fetal brain development and implicates novel maternal-placental-fetal interactions that could underlie the pronounced impact of 5-HT on long-lasting mental health outcomes.
doi:10.1038/nature09972
PMCID: PMC3084180  PMID: 21512572
22.  A novel role for GAPDH-MAO B cascade in ethanol-induced cellular damage 
Biological psychiatry  2009;67(9):855-863.
Background
Alcoholism is a major psychiatric condition at least partly associated with ethanol-induced cell damage. Although brain cell loss has been reported in subjects with alcoholism, the molecular mechanism is unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction under stressful conditions and may contribute to ethanol-induced cell damage.
Methods
Expression of GAPDH and MAO B protein was studied in human glioblastoma and neuroblastoma cell lines exposed to physiological concentrations of ethanol. Expression of these proteins was also examined in the prefrontal cortex from human subjects with alcohol dependence and in rats fed with an ethanol diet. Co-immunoprecipitation, subcellular fractionation, and luciferase assay were used to address nuclear GAPDH-mediated MAO B activation. To test the effects of inactivation, RNAi and pharmacological intervention were used, and cell damage was assessed by TUNEL and H2O2 measurements.
Results
Ethanol significantly increases levels of GAPDH, especially nuclear GAPDH, and MAO B in neuronal cells as well as in human and rat brains. Nuclear GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), and augments TIEG2-mediated MAO B transactivation, which results in cell damage in neuronal cells exposed to ethanol. Knockdown expression of GAPDH or treatment with MAO B inhibitors selegiline (Deprenyl) and rasagiline (Azilect) can block this cascade.
Conclusions
Ethanol-elicited nuclear GAPDH augments TIEG2-mediated MAO B, which may play a role in brain damage in subjects with alcoholism. Compounds that block this cascade are potential candidates for therapeutic strategies.
doi:10.1016/j.biopsych.2009.10.032
PMCID: PMC2854240  PMID: 20022592
alcoholism; human brain tissues; rats-fed with an ethanol diet; ethanol-induced brain cell dysfunction; monoamine oxidase B; glyceraldehyde-3-phosphate dehydrogenase
23.  Monoamine oxidase A mediated enhanced catabolism of norepinephrine contributes to adverse remodeling and pump failure in hearts with pressure overload 
Circulation research  2009;106(1):193-202.
Rationale
Monoamine oxidases (MAO) are mitochondrial enzymes that catabolize pro-hypertrophic neurotransmitters such as norepinephrine and serotonin, generating hydrogen peroxide. Since excess reactive oxygen species (ROS) and catecholamines are major contributors to the pathophysiology of congestive heart failure, MAO could play an important role in this process.
Objective
Here we investigated the role of MAO-A in maladaptive hypertrophy and heart failure.
Methods and results
We report that MAO-A activity is triggered in isolated neonatal and adult myocytes upon stimulation with NE, followed by increase in cell size, ROS production, and signs of maladaptive hypertrophy. All these in vitro changes occur in part independently from α- and β-adrenergic receptor-operated signaling and are inhibited by the specific MAO-A inhibitor clorgyline. In mice with left ventricular (LV) dilation and pump failure due to pressure overload, NE catabolism by MAO-A is increased accompanied by exacerbated oxidative stress. MAO-A inhibition prevents these changes, and also reverses fetal gene re-programming, metalloproteinase and caspase-3 activation as well as myocardial apoptosis. The specific role of MAO-A was further tested in mice expressing a dominant-negative MAO-A (MAO-Aneo), which were more protected against pressure overload than their wild type littermates.
Conclusions
In addition to adrenergic receptor-dependent mechanisms, enhanced MAO-A activity coupled with increased intramyocardial NE availability results in increased ROS generation, contributing to maladaptive remodeling and LV dysfunction in hearts subjected to chronic stress.
doi:10.1161/CIRCRESAHA.109.198366
PMCID: PMC2804073  PMID: 19910579
MAO-A; congestive heart failure; oxidative stress; catecholamines; serotonin; NET
24.  The VNTR 2 repeat in MAOA and delinquent behavior in adolescence and young adulthood: associations and MAOA promoter activity 
Genetic studies of delinquent and criminal behavior are rare in spite of the wide recognition that individuals may differ in their propensity for delinquency and criminality. Using 2524 participants in Add Health in the United States, the present study demonstrates a link between the rare 2 repeat of the 30-bp VNTR in the MAOA gene and much higher levels of self-reported serious and violent delinquency. The evidence is based on a statistical association analysis and a functional analysis of MAOA promoter activity using two human brain-derived cell lines: neuroblastoma SH-SY5Y and human glioblastoma 1242-MG. The association analysis shows that men with a 2R report a level of serious delinquency and violent delinquency in adolescence and young adulthood that were about twice (CI: (0.21, 3.24), P = 0.025; and CI: (0.37, 2.5), P = 0.008 for serious and violent delinquency, respectively) as high as those for participants with the other variants. The results for women are similar, but weaker. In the functional analysis, the 2 repeat exhibits much lower levels of promoter activity than the 3 or 4 repeat.
doi:10.1038/sj.ejhg.5201999
PMCID: PMC2922855  PMID: 18212819
delinquency; crime; violence; MAOA; genotype; antisocial behavior
25.  Down-regulated GABAergic expression in the olfactory bulb layers of the mouse deficient in monoamine oxidase B and administered with amphetamine 
This study explores primarily the role of the activity of monoamine oxidase B (MAOB) in the regulation of glutamic acid decarboxylase67 (GAD67) expression in distinct layers of main olfactory bulb (OlfB), which links the limbic system. Moreover, the response of GAD67 was investigated to amphetamine perturbation in the absence of MAOB activity. Immunocytochemical analysis was performed on OlfB sections prepared from the adult wild type (WT) and the MAOB gene-knockout (KO) mice after receiving repeated intraperitoneal injections (2 doses/day, total 7 doses) of saline or amphetamine, 5 mg/kg. The levels of the GAD67 immunoreactivity were approximate 25% and 38% lower in respective glomerular (GloL) and mitral cell layers (ML) of saline-treated KO mice than that of WT, whereas similar in the external plexiform or granule cell layers (GraL) of the KO and WT. In the GloL, the level of tyrosine hydroxylase was 39% lower in the KO mice than WT, implicating different dopamine content in the KO from WT. The amphetamine exposure down-regulated the levels of GAD67 in the WT layers by 46% to 52%, and in KO layers 65% to 71%, except ML. The GraL GAD67 level may be regulated by the activation of CREB, as the phosphorylated (p) CREB coexisted with GAD67, and the percentage of GAD67-expressing pCREB neurons was decreased by the amphetamine exposure. The data indicate that the activity of MAOB could modulate the regular and amphetamine-perturbed expression of GAD67 and pCREB. Thus, interactions are suggested among the MAOB activity, GABA content of OlfB and olfaction.
doi:10.1007/s10571-009-9475-2
PMCID: PMC2875355  PMID: 19902350
dopaminergic neurons; limbic system; neurotransmitter synthesizing enzymes; addiction

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