Evidence implicating the candidate schizophrenia/bipolar disorder susceptibility gene G72 in mitochondrial function

Mitochondria dysfunction and bipolar disorder: From pathology to therapy

Bipolar disorder (BD) is one of the major psychiatric diseases in which the impairment of mitochondrial functions has been closely connected or associated with the disease pathologies. Different lines of evidence of the close connection between mitochondria dysfunction and BD were discussed with a particular focus on (1) dysregulation of energy metabolism, (2) effect of genetic variants, (3) oxidative stress, cell death and apoptosis, (4) dysregulated calcium homeostasis and electrophysiology, and (5) current as well as potential treatments targeting at restoring mitochondrial functions. Currently, pharmacological interventions generally provide limited efficacy in preventing relapses or recovery from mania or depression episodes. Thus, understanding mitochondrial pathology in BD will lead to novel agents targeting mitochondrial dysfunction and formulating new effective therapy for BD.

Schizophrenia Synaptic Pathology and Antipsychotic Treatment in the Framework of Oxidative and Mitochondrial Dysfunction: Translational Highlights for the Clinics and Treatment

Schizophrenia is a worldwide mental illness characterized by alterations at dopaminergic and glutamatergic synapses resulting in global dysconnectivity within and between brain networks. Impairments in inflammatory processes, mitochondrial functions, energy expenditure, and oxidative stress have been extensively associated with schizophrenia pathophysiology. Antipsychotics, the mainstay of schizophrenia pharmacological treatment and all sharing the common feature of dopamine D2 receptor occupancy, may affect antioxidant pathways as well as mitochondrial protein levels and gene expression. Here, we systematically reviewed the available evidence on antioxidants' mechanisms in antipsychotic action and the impact of first- and second-generation compounds on mitochondrial functions and oxidative stress. We further focused on clinical trials addressing the efficacy and tolerability of antioxidants as an augmentation strategy of antipsychotic treatment. EMBASE, Scopus, and Medline/PubMed databases were interrogated. The selection process was conducted in respect of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Several mitochondrial proteins involved in cell viability, energy metabolism, and regulation of oxidative systems were reported to be significantly modified by antipsychotic treatment with differences between first- and second-generation drugs. Finally, antioxidants may affect cognitive and psychotic symptoms in patients with schizophrenia, and although the evidence is only preliminary, the results indicate that further studies are warranted.

Emerging roles of brain metabolism in cognitive impairment and neuropsychiatric disorders

Here we discuss the role of diverse environmental manipulations affecting cognition with special regard to psychiatric conditions. We present evidence supporting a direct causal correlation between the valence of the environmental stimulation and some psychopathological traits and how the environment influences brain structure and function with special regard to oxidative stress and mitochondrial activity. Increasing experimental evidence supports a role for mitochondrial dysfunctions in neuropsychiatric disorders. Brain mitochondria are considered crucial mediators of allostasis, that is the capability to adapt to stress via a complex interaction between the autonomic, metabolic, and immune systems to maintain cellular homeostasis. In this process, mitochondria act as highly dynamic integrators by sensing and transducing stressors into adaptation mechanisms via metabolic stress mediators, such as glucocorticoids and catecholamines. Alterations in cellular homeostasis induced by chronic stress are thought to predispose to disease by triggering the so-called "mitochondrial allostatic load". This process is characterized by functional and structural changes of the mitochondria, ultimately leading to oxidative stress, inflammation, mitochondrial DNA damage and apoptosis. In this review we discuss the role of diverse environmental manipulations to affect cognition with special regard to psychiatric conditions. How the environment influences brain structure and function, and the interactions between rearing conditions, oxidative stress and mitochondrial activity are fundamental questions that are still poorly understood. As will be discussed, increasing experimental evidence supports a role for mitochondrial dysfunctions in neuropsychiatric disorders. Brain mitochondria are considered crucial mediators of allostasis, that is the capability to adapt to stress via a complex interaction between the autonomic, metabolic, and immune systems to maintain cellular homeostasis. In this process, mitochondria act as highly dynamic integrators by sensing and transducing stressors into adaptation mechanisms via metabolic stress mediators, such as glucocorticoids and catecholamines. Alterations in cellular homeostasis induced by chronic stress are thought to predispose to disease by triggering the so-called "mitochondrial allostatic load". This process is characterized by functional and structural changes of the mitochondria, ultimately leading to oxidative stress, inflammation, mitochondrial DNA damage and apoptosis. The brain requires considerable mitochondrial reserve not only to sustain basal neuronal needs but a also to provide increasing energy demands during stress. Consistently with these high energetic requirements, it is reasonable to hypothesise that the brain is particularly vulnerable to mitochondrial defects. Thus, even subtle metabolic alterations might have a substantial impact on cognitive functions. Over the last decade, several experimental evidence supported the hypothesis that a suboptimal mitochondrial function, which could be of genetic origin or acquired following adverse life events, is a key vulnerability factor for stress-related psychopathologies. Chronic psychological stress is a major promoter of anxiety as well as of oxidative damage, as shown in several studies. Recent evidence from mouse models harbouring mutations in mitochondrial genes demonstrated the role of mitochondria in modulating the response to acute psychological stress. However, it has yet to be determined whether mitochondrial dysfunctions are the cause or the consequence of anxiety. In this review, we discuss how adverse psychosocial environments can impact mitochondrial bioenergetics at the molecular level and we gather evidence from several studies linking energy metabolism and stress resilience/vulnerability. Moreover, we review recent findings supporting that metabolic dysfunction can underlie deficits in complex social behaviours. As will be discussed, aberrations in mitochondrial functionality have been found in the nucleus accumbens of highly anxious mice and mediate low social competitiveness. In addition, alterations in sociability can be reversed by enhancing mitochondrial functions. Recent evidence also demonstrated that a specific mutation in mitochondrial DNA, previously linked to autism spectrum disorder, produces autistic endophenotypes in mice by altering respiration chain and reactive oxygen species (ROS) production. Finally, we discuss a "Negative Enrichment" model that can explain some of the psychopathological conditions relevant to humans. Evidence of a direct causal correlation of valence of environmental stimulation and psychopathological traits will be presented, and possible molecular mechanisms that focus on oxidative stress. Collectively, the findings described here have been achieved with a wide set of behavioural and cognitive tasks with translational validity. Thus, they will be useful for future work aimed to elucidate the fine metabolic alterations in psychopathologies and devise novel approaches targeting mitochondria to alleviate these conditions.

Biochemical Properties and Physiological Functions of pLG72: Twenty Years of Investigations

In 2002, the novel human gene G72 was associated with schizophrenia susceptibility. This gene encodes a small protein of 153 amino acids, named pLG72, which represents a rare case of primate-specific protein. In particular, the rs2391191 single nucleotide polymorphism (resulting in in the R30K substitution) was robustly associated to schizophrenia and bipolar disorder. In this review, we aim to summarize the results of 20 years of biochemical investigations on pLG72. The main known role of pLG72 is related to its ability to bind and inactivate the flavoenzyme d-amino acid oxidase, i.e., the enzyme that controls the catabolism of d-serine, the main NMDA receptor coagonist in the brain. pLG72 was proposed to target the cytosolic form of d-amino acid oxidase for degradation, preserving d-serine and protecting the cell from oxidative stress generated by hydrogen peroxide produced by the flavoenzyme reaction. Anyway, pLG72 seems to play additional roles, such as affecting mitochondrial functions. The level of pLG72 in the human body is still a controversial issue because of its low expression and challenging detection. Anyway, the intriguing hypothesis that pLG72 level in blood could represent a suitable marker of Alzheimer’s disease progression (a suggestion not sufficiently established yet) merits further investigations.

Mitochondrial Damage of Lymphocytes in Patients with Acute Relapse of Schizophrenia: A Correlational Study with Efficacy and Clinical Symptoms

OBJECTIVE

Accumulating evidence has demonstrated that schizophrenia is associated with mitochondrial and immune abnormalities. In this pilot case-control study, we investigated the level of mitochondrial impairment in lymphocytes in patients with acute relapse of schizophrenia and explored the correlation between the level of mitochondrial damage and symptoms or treatment response.

METHODS

Lymphocytic mitochondrial damage was detected using mitochondrial fluorescence staining and flow cytometry in 37 patients (at admission and discharge) and 24 controls. Clinical symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS) and Clinical Global Impression Scale (CGI-S).

RESULTS

The levels of mitochondrial damage in CD3+ T, CD4+ T, and CD8+ T lymphocytes of the patients with schizophrenia at admission were significantly higher than those of the controls (p<0.05) and did not return to normal at discharge (p>0.05). The mitochondrial damage of T cells significantly improved at discharge for responsive patients only, as compared with that at admission (P<0.05). However, no significant difference was found in mitochondrial damage in CD19+ B cells between patients and healthy controls, or between admission and discharge (p>0.05). Furthermore, the reduction in mitochondrial damage of CD3, CD4, and CD8 lymphocytes was positively correlated with the reduction of the score of the PANSS positive scale at discharge (p<0.05), while no significant correlation was found between the level of mitochondrial damage in lymphocytes and the scores of PANSS and CGI-S.

CONCLUSION

Acute relapse of schizophrenia might be associated with higher levels of mitochondrial damage in peripheral blood T lymphocytes. The degree of recovery of mitochondrial impairment in the T cells may be used as a predictor of treatment response in schizophrenia. As this is a pilot study, the conclusion still needs further verification in large-scale studies.

d-Amino Acids and pLG72 in Alzheimer's Disease and Schizophrenia

Numerous studies over the last several years have shown that d-amino acids, especially d-serine, have been related to brain and neurological disorders. Acknowledged neurological functions of d-amino acids include neurotransmission and learning and memory functions through modulating N-methyl-d-aspartate type glutamate receptors (NMDARs). Aberrant d-amino acids level and polymorphisms of genes related to d-amino acids metabolism are associated with neurodegenerative brain conditions. This review summarizes the roles of d-amino acids and pLG72, also known as d-amino acid oxidase activator, on two neurodegenerative disorders, schizophrenia and Alzheimer’s disease (AD). The scope includes the changes in d-amino acids levels, gene polymorphisms of G72 genomics, and the role of pLG72 on NMDARs and mitochondria in schizophrenia and AD. The clinical diagnostic value of d-amino acids and pLG72 and the therapeutic importance are also reviewed.

Mitochondrial dysfunction in schizophrenia: With a focus on postmortem studies

Among the many brain abnormalities in schizophrenia are those related to mitochondrial functions such as oxidative stress, energy metabolism and synaptic efficacy. The aim of this paper is to provide a brief review of mitochondrial structure and function and then to present abnormalities in mitochondria in postmortem brain in schizophrenia with a focus on anatomy. Deficits in expression of various mitochondrial genes have been found in multiple schizophrenia cohorts. Decreased activity of complexes I and IV are prominent as well as abnormal levels of individual subunits that comprise the complexes of the electron transport chain. Ultrastructural studies have shown layer, input and cell specific decreases in mitochondria. In cortex, there are fewer mitochondria in axon terminals, neuronal somata of pyramidal neurons and oligodendrocytes in both grey and white matter. In the caudate and putamen mitochondrial number is linked with symptoms and symptom severity. While there is a decrease in the number of mitochondria in astrocytes, mitochondria are smaller in oligodendrocytes. In the nucleus accumbens and substantia nigra, mitochondria are similar in density, size and structural integrity in schizophrenia compared to controls. Mitochondrial production of ATP and calcium buffering are essential in maintaining synaptic strength and abnormalities in these processes could lead to decreased metabolism and defective synaptic activity. Abnormalities in mitochondria in oligodendrocytes might contribute to myelin pathology and underlie dysconnectivity in the brain. In schizophrenia, mitochondria are affected differentially depending on the brain region, cell type in which they reside, subcellular location, treatment status, treatment response and predominant symptoms.

Effect of DAOA genetic variation on white matter alteration in corpus callosum in patients with first-episode schizophrenia

D-amino acid oxidase activator (DAOA) gene, which plays a crucial role in the process of glutamatergic transmission and mitochondrial function, is frequently linked with the liability for schizophrenia. We aimed to investigate whether the variation of DAOA rs2391191 is associated with alterations in white matter integrity of first-episode schizophrenia (FES) patients; and whether it influences the association between white matter integrity, cognitive function and clinical symptoms of schizophrenia. Forty-six patients with FES and forty-nine healthy controls underwent DTI and were genotyped for DAOA rs2391191. Psychopathological assessments were performed by Brief Psychiatric Rating Scale (BPRS) and Scale for Assessment of Negative Symptoms (SANS). Cognitive function was assessed by MATRICS Consensus Cognitive Battery (MCCB). Schizophrenia patients presented lower fractional anisotropy (FA) and higher radial diffusivity (RD), mainly spreading over the corpus callosum and corona radiata compared with healthy controls. Compared with patients carrying G allele, patients with AA showed lower FA in the body of corpus callosum, and higher RD in the genu of corpus callosum, right superior and anterior corona radiata, and left posterior corona radiata. In patients carrying G allele, FA in body of corpus callosum was positively correlated with working memory, RD in genu of corpus callosum was negatively associated with the speed of processing, working memory, and the composite score of MCCB, while no significant correlations were found in AA homozygotes. In our study, patients with FES presented abnormal white matter integrity in corpus callosum and corona radiata. Furthermore, this abnormality was associated with the genetic variation of DAOA rs2391191, with AA homozygotes showing less white matter integrity in the corpus callosum. Our findings possibly provide further support to the evidence that DAOA regulates the process of glutamatergic neurotransmission and mitochondrial function in the pathophysiological mechanism of schizophrenia.

Is the primate-specific protein pLG72 affecting SOD1 functionality and superoxide formation?

pLG72 is a primate-specific protein of enigmatic function that was proposed to modulate mitochondria fragmentation and the activity of the peroxisomal enzyme D-amino acid oxidase (DAAO). DAAO is deputed to degradation of the NMDA receptor co-agonist D-serine in human brain and the R199W substitution in DAAO was identified in a familial case of amyotrophic lateral sclerosis (ALS). A recent work reported that U87 glioblastoma cells ectopically expressing pLG72 showed a lower proliferation, produced superoxide radicals, induced SOD1 aggregation and decreased its activity. Because of the role of SOD1 in eliminating ROS species and its relevance in ALS we evaluated the link between pLG72 and SOD1 using both wild-type pLG72 and its R30K variant related to schizophrenia susceptibility. In vitro studies on recombinant proteins excluded the establishment of a stable complex and that pLG72 could affect SOD1 activity and stability. At cellular level, ectopic expression of pLG72 in glioblastoma U87 cells did not affect cell viability and ROS/superoxide production: only caspase activity (a marker of apoptosis) was slightly increased in cells expressing the R30K pLG72 variant. SOD1 and pLG72 did not colocalize in transfected U87 glioblastoma cells: pLG72 largely localised to mitochondria and SOD1 was largely cytosolic. Moreover, the ectopic expression of pLG72 appeared not to alter the expression of SOD1 and its aggregation. Altogether, the combination of biochemical and cellular studies allow to exclude that pLG72 modulates SOD1 function and aggregation, thus that it could play a role in ALS susceptibility.

pLG72 levels increase in early phase of Alzheimer's disease but decrease in late phase

pLG72, named as D-amino acid oxidase activator (although it is not an activator of D-amino acid oxidase demonstrated by later studies), in mitochondria has been regarded as an important modulator of D-amino acid oxidase that can regulate the N-methyl-D-aspartate receptor (NMDAR). Both oxidative stress in mitochondria and NMDAR neurotransmission play essential roles in the process of neurodegenerative dementia. The aim of the study was to investigate whether pLG72 levels changed with the severity of neurodegenerative dementia. We enrolled 376 individuals as the overall cohort, consisting of five groups: healthy elderly, amnestic mild cognitive impairment [MCI], mild Alzheimer's disease [AD], moderate AD, and severe AD. pLG72 levels in plasma were measured using Western blotting. The severity of cognitive deficit was principally evaluated by Clinical Dementia Rating Scale. A gender- and age- matched cohort was selected to elucidate the effects of gender and age. pLG72 levels increased in the MCI and mild AD groups when compared to the healthy group. However, pLG72 levels in the moderate and severe AD groups were lower than those in the mild AD group. D-serine level and D- to total serine ratio were significantly different among the five groups. L-serine levels were correlated with the pLG72 levels. The results in the gender- and age- matched cohort were similar to those of the overall cohort. The finding supports the hypothesis of NMDAR hypofunction in early-phase dementia and NMDAR hyperfunction in late-phase dementia. Further studies are warranted to test whether pLG72 could reflect the function of NMDAR.

pLG72 induces superoxide radicals via interaction and aggregation with SOD1

G72 has been characterised as a susceptibility gene that can have wide-ranging effects in a number of neurodegenerative diseases, including schizophrenia and major depression. Indeed, its product, pLG72, is a potential serum biomarker for schizophrenia. Previous transcriptomic and biochemical studies have indicated that pLG72 may induce the production of mitochondrial reactive oxygen species (ROS), resulting in cell damage. Here, we investigated the mechanism of pLG72 by transfecting a human U87 glioblastoma cell line with a G72 construct. By employing ROS-specific scavengers, we discovered that superoxide radicals were specifically induced in the pLG72-expressing cells. We also found that pLG72 interacted and co-localised with superoxide dismutase 1 (SOD1), resulting in aggregation of SOD1 with a concomitant 23% or 74% reduction of total SOD activity, depending on the amount of G72 transfection plasmid. Finally, we found that transfection of U87 cells with the G72 construct caused a 29% decrease in cell proliferation. The observed loss of SOD1 function in pLG72-expressing cells may explain the elevated ROS levels and inhibition of U87 cell proliferation and has implications for understanding the onset of neurodegenerative diseases in humans.

The Complex Interaction of Mitochondrial Genetics and Mitochondrial Pathways in Psychiatric Disease

While accounting for only 2% of the body's weight, the brain utilizes up to 20% of the body's total energy. Not surprisingly, metabolic dysfunction and energy supply-and-demand mismatch have been implicated in a variety of neurological and psychiatric disorders. Mitochondria are responsible for providing the brain with most of its energetic demands, and the brain uses glucose as its exclusive energy source. Exploring the role of mitochondrial dysfunction in the etiology of psychiatric disease is a promising avenue to investigate further. Genetic analysis of mitochondrial activity is a cornerstone in understanding disease pathogenesis related to metabolic dysfunction. In concert with neuroimaging and pathological study, genetics provides an important bridge between biochemical findings and clinical correlates in psychiatric disease. Mitochondrial genetics has several unique aspects to its analysis, and corresponding special considerations. Here, we review the components of mitochondrial genetic analysis - nuclear DNA, mitochon-drial DNA, mitochondrial pathways, pseudogenes, nuclear-mitochondrial mismatch, and microRNAs - that could contribute to an observable clinical phenotype. Throughout, we highlight psychiatric diseases that can arise due to dysfunction in these processes, with a focus on schizophrenia and bipolar disorder.

Differential mitochondrial DNA copy number in three mood states of bipolar disorder

BACKGROUND

Accumulating evidences indicated that mitochondrial abnormalities were associated with bipolar disorder. As a sensitive index of mitochondrial function and biogenesis, Mitochondrial DNA copy number (mtDNAcn) may be involved in the pathophysiology of bipolar disorder.

METHODS

Leukocyte relative mtDNAcn was measured by quantitative polymerase chain reaction in subjects with BD (n = 131) in manic, depressive, and euthymic symptoms. Thirty-four healthy individuals were used as comparison control. BD clinical symptomatology was evaluated by Young Mania Rating Scale (YMRS), Hamilton Depression Scale (HAM-D), Clinical Global Impression-Bipolar Disorder-Severity of Illness Scale (CGI-BD-S), and the Positive and Negative Syndrome Scale (PANSS).

RESULTS

Compared to healthy controls, BD patients with manic and depressive symptoms presented significantly decreased mtDNAcn levels (p-value = 0.009 and 0.041, respectively). No significant differences were detected in mtDNAcn between euthymic patients and healthy controls. The mtDNAcn was negatively correlated with the number of relapses in manic patients (β = - 0.341, p = 0.044).

CONCLUSIONS

Our study described the first evidence of (1) a significant decline of mtDNAcn in manic BD patients, (2) a similar decreased level of mtDNAcn between manic and depressed BD patients, (3) a negative correlation of mtDNAcn with number of relapses in patients suffering from manic states. Alterations of mtDNAcn in manic and depressed patients, which may reflect disturbances of energy metabolism, supported the role of mitochondrial abnormalities in the pathophysiology of BD.

D-Amino Acid Oxidase-pLG72 Interaction and D-Serine Modulation

pLG72 is a small, primate-specific protein of 153 amino acids. It is the product of the G72 gene, expressed in testis, spinal cord, and brain. The presence of G72 transcript and pLG72 has recurrently been called into question, however G72 mRNA and pLG72 protein levels were higher in blood and brain of patients with schizophrenia than in healthy controls. On the one hand, the SNP rs2391191 corresponding to the R30K substitution in pLG72 was genetically linked to schizophrenia, reduced thickness of the brain cortex in schizophrenia-affected individuals, and altered memory function. Various lines of evidence indicated that pLG72 is a mitochondrial protein, specifically an extrinsic protein bound on the outer membrane. Over the years, pLG72 was proposed to be involved in different functions: (a) overexpression induces mitochondria fragmentation, increasing the numbers of shorter and more mobile ones which could be delivered faster to regions of intense growth and facilitating the dendritic complexity; (b) it might induce oxidative stress by interacting with methionine-R-sulfoxide reductase B2; and (c) it binds and modulates the activity of FMN-containing oxidoreductase of the respiratory complex I. The main role of this protein, however, is related to its binding to the human flavoenzyme D-amino acid oxidase (hDAAO), i.e., the main catabolic enzyme for D-enantiomer of serine. This D-amino acid is a main endogenous coagonist of the N-methyl-D-aspartate type glutamate receptor (NMDAR) involved in main functions such as synaptic plasticity, learning, memory, and excitotoxicity. For this work, we reviewed the recent literature concerning the hDAAO-pLG72 interaction, focusing on the molecular details of the interaction, the effect of hDAAO function and stability, and the cellular effects, especially on D-serine concentration. The main effects related to the pathological R30K substitution are also reported. We have highlighted the gaps in our knowledge of this human protein as well as the relevance of clarifying the molecular details of hDAAO-pLG72 interaction in order to design molecules to modulate hDAAO activity/stability and thus NMDAR function acting at the D-serine cellular level.

Combination of G72 Genetic Variation and G72 Protein Level to Detect Schizophrenia: Machine Learning Approaches

The D-amino acid oxidase activator (DAOA, also known as G72) gene is a strong schizophrenia susceptibility gene. Higher G72 protein levels have been implicated in patients with schizophrenia. The current study aimed to differentiate patients with schizophrenia from healthy individuals using G72 single nucleotide polymorphisms (SNPs) and G72 protein levels by leveraging computational artificial intelligence and machine learning tools. A total of 149 subjects with 89 patients with schizophrenia and 60 healthy controls were recruited. Two G72 genotypes (including rs1421292 and rs2391191) and G72 protein levels were measured with the peripheral blood. We utilized three machine learning algorithms (including logistic regression, naive Bayes, and C4.5 decision tree) to build the optimal predictive model for distinguishing schizophrenia patients from healthy controls. The naive Bayes model using two factors, including G72 rs1421292 and G72 protein, appeared to be the best model for disease susceptibility (sensitivity = 0.7969, specificity = 0.9372, area under the receiver operating characteristic curve (AUC) = 0.9356). However, a model integrating G72 rs1421292 only slightly increased the discriminative power than a model with G72 protein alone (sensitivity = 0.7941, specificity = 0.9503, AUC = 0.9324). Among the three models with G72 protein alone, the naive Bayes with G72 protein alone had the best specificity (0.9503), while logistic regression with G72 protein alone was the most sensitive (0.8765). The findings remained similar after adjusting for age and gender. This study suggests that G72 protein alone, without incorporating the two G72 SNPs, may have been suitable enough to identify schizophrenia patients. We also recommend applying both naive Bayes and logistic regression models for the best specificity and sensitivity, respectively. Larger-scale studies are warranted to confirm the findings.

Heterogeneity of D-Serine Distribution in the Human Central Nervous System

D-serine is an endogenous ligand for N-methyl-D-aspartate glutamate receptors. Accumulating evidence including genetic associations of D-serine metabolism with neurological or psychiatric diseases suggest that D-serine is crucial in human neurophysiology. However, distribution and regulation of D-serine in humans are not well understood. Here, we found that D-serine is heterogeneously distributed in the human central nervous system (CNS). The cerebrum contains the highest level of D-serine among the areas in the CNS. There is heterogeneity in its distribution in the cerebrum and even within the cerebral neocortex. The neocortical heterogeneity is associated with Brodmann or functional areas but is unrelated to basic patterns of cortical layer structure or regional expressional variation of metabolic enzymes for D-serine. Such D-serine distribution may reflect functional diversity of glutamatergic neurons in the human CNS, which may serve as a basis for clinical and pharmacological studies on D-serine modulation.

The association between gene variants and longitudinal structural brain changes in psychosis: a systematic review of longitudinal neuroimaging genetics studies

Evidence suggests that genetic variation might influence structural brain alterations in psychotic disorders. Longitudinal genetic neuroimaging (G-NI) studies are designed to assess the association between genetic variants, disease progression and brain changes. There is a paucity of reviews of longitudinal G-NI studies in psychotic disorders. A systematic search of PubMed from inception until November 2016 was conducted to identify longitudinal G-NI studies examining the link between Magnetic Resonance Imaging (MRI) and Diffusion Tensor Imaging (DTI)-based brain measurements and specific gene variants (SNPs, microsatellites, haplotypes) in patients with psychosis. Eleven studies examined seven genes: BDNF, COMT, NRG1, DISC1, CNR1, GAD1, and G72. Eight of these studies reported at least one association between a specific gene variant and longitudinal structural brain changes. Genetic variants associated with longitudinal brain volume or cortical thickness loss included a 4-marker haplotype in G72, a microsatellite and a SNP in NRG1, and individual SNPs in DISC1, CNR1, BDNF, COMT and GAD1. Associations between genotype and progressive brain changes were most frequently observed in frontal regions, with five studies reporting significant interactions. Effect sizes for significant associations were generally of small or intermediate magnitude (Cohen’s d < 0.8). Only two genes (BDNF and NRG1) were assessed in more than one study, with great heterogeneity of the results. Replication studies and studies exploring additional genetic variants identified by large-scale genetic analysis are warranted to further ascertain the role of genetic variants in longitudinal brain changes in psychosis.

Controversial Effects of D-Amino Acid Oxidase Activator (DAOA)/G72 on D-Amino Acid Oxidase (DAO) Activity in Human Neuronal, Astrocyte and Kidney Cell Lines: The N-methyl D-aspartate (NMDA) Receptor Hypofunction Point of View

Dysfunction of D-amino acid oxidase (DAO) and DAO activator (DAOA)/G72 genes have been linked to neuropsychiatric disorders. The glutamate hypothesis of schizophrenia has proposed that increased DAO activity leads to decreased D-serine, which subsequently may lead to N-methyl-D-aspartate (NMDA) receptor hypofunction. It has been shown that DAOA binds to DAO and increases its activity. However, there are also studies showing DAOA decreases DAO activity. Thus, the effect of DAOA on DAO is controversial. We aimed to understand the effect of DAOA on DAO activity in neuron-like (SH-SY5Y), astrocyte-like (1321N1) and kidney-like (HEK293) human cell lines. DAO activity was measured based on the release of hydrogen peroxide and its interaction with Amplex Red reagent. We found that DAOA increases DAO activity only in HEK293 cells, but has no effect on DAO activity in SH-SY5Y and 1321N1 cells. This might be because of different signaling pathways, or due to lower DAO and DAOA expression in SH-SY5Y and 1321N1 cells compared to HEK293 cells, but also due to different compartmentalization of the proteins. The lower DAO and DAOA expression in neuron-like SH-SY5Y and astrocyte-like 1321N1 cells might be due to tightly regulated expression, as previously reported in the human post-mortem brain. Our simulation experiments to demonstrate the interaction between DAOA and human DAO (hDAO) showed that hDAO holoenzyme [hDAO with flavine adenine dinucleotide (FAD)] becomes more flexible and misfolded in the presence of DAOA, whereas DAOA had no effect on hDAO apoprotein (hDAO without FAD), which indicate that DAOA inactivates hDAO holoenzyme. Furthermore, patch-clamp analysis demonstrated no effect of DAOA on NMDA receptor activity in NR1/NR2A HEK293 cells. In summary, the interaction between DAO and DAOA seems to be cell type and its biochemical characteristics dependent which still needs to be elucidated.

An emerging role for mitochondrial dynamics in schizophrenia

Abnormal brain development has long been thought to contribute to the pathophysiology of schizophrenia. Impaired dendritic arborization, synaptogenesis, and long term potentiation and memory have been demonstrated in animal models of schizophrenia. In addition to aberrant nervous system development, altered brain metabolism and mitochondrial function has long been observed in schizophrenic patients. Single nucleotide polymorphisms in the mitochondrial genome as well as impaired mitochondrial function have both been associated with increased risk for developing schizophrenia. Mitochondrial function in neurons is highly dependent on fission, fusion, and transport of the organelle, collectively referred to as mitochondrial dynamics. Indeed, there is mounting evidence that mitochondrial dynamics strongly influences neuron development and synaptic transmission. While there are a few studies describing altered mitochondrial shape in schizophrenic patients, as well as in animal and in vitro models of schizophrenia, the precise role of mitochondrial dynamics in the pathophysiology of schizophrenia is all but unexplored. Here we discuss the influence of mitochondrial dynamics and mitochondrial function on nervous system development, and highlight recent work suggesting a link between aberrant mitochondrial dynamics and schizophrenia.

Postmortem studies on mitochondria in schizophrenia

The aim of this paper is to provide a brief review of mitochondrial structure as it relates to function and then present abnormalities in mitochondria in postmortem schizophrenia with a focus on ultrastructure. Function, morphology, fusion, fission, motility, ΔΨmem, ATP production, mitochondrial derived vesicles, and mitochondria-associated ER membranes will be briefly covered. Pathology in mitochondria has long been implicated in schizophrenia, as shown by genetic, proteomic, enzymatic and anatomical abnormalities. The cortex and basal ganglia will be reviewed. In the anterior cingulate cortex, the number of mitochondria per neuronal somata in layers 5/6 in schizophrenia is decreased by 43%. There are also fewer mitochondria in terminals forming axospinous synapses. In the caudate and putamen the number of mitochondria is abnormal in both glial cells and neurons in schizophrenia subjects, the extent of which depends on treatment, response and predominant lifetime symptoms. Treatment-responsive schizophrenia subjects had about a 40% decrease in the number of mitochondria per synapse in the caudate nucleus and putamen, while treatment resistant cases had normal values. A decrease in mitochondrial density in the neuropil distinguishes paranoid from undifferentiated schizophrenia. The appearance, size and density of mitochondria were normal in the nucleus accumbens. In the substantia nigra, COX subunits were affected in rostral regions. Mitochondrial hyperplasia occurs within axon terminals that synapse onto dopamine neurons, but mitochondria in dopamine neuronal somata are similar in size and number. In schizophrenia, mitochondria are differentially affected depending on the brain region, cell type, subcellular location, treatment status, treatment response and symptoms.

A systematic meta-analysis of the association of Neuregulin 1 (NRG1), D-amino acid oxidase (DAO), and DAO activator (DAOA)/G72 polymorphisms with schizophrenia

The glutamate hypothesis of schizophrenia is related to the proposed dysregulation of D-amino acid oxidase (DAO), DAO activator (DAOA)/G72, and Neuregulin 1 (NRG1) genes. Genetic studies have shown significant associations between DAO, DAOA, NRG1 single-nucleotide polymorphisms (SNPs), and schizophrenia. The systematic literature search yielded 6, 5, and 18 new studies for DAO, DAOA, and NRG1 published after 2011 and not included in the previous SchizophreniaGene (SZGene) meta-analysis. We conducted meta-analyses of 20, 23, and 48 case-control studies, respectively, to comprehensively evaluate the association of 8 DAO, 12 DAOA, and 14 NRG1 SNPs with schizophrenia. The updated meta-analyses resulted in the following findings: the C-allele of DAO rs4623951 was associated with schizophrenia across all pooled studies [Odds ratio (OR) = 0.88, 95% confidence interval (CI) = 0.79-0.98, p = 0.02, N = 3143]; however, no new reports could be included. The G-allele of DAOA rs778293 was associated with schizophrenia in Asian patients (OR = 1.17, 95% CI = 1.08-1.27, p = 0.00008, N = 6117), and the T-allele of DAOA rs3916971 was associated with schizophrenia across all studies (OR = 0.84, 95% CI = 0.73-0.96, p = 0.01, N = 1765). Again, for both SNPs, no new eligible studies were available. After adding new reports, the T-allele of NRG1 SNP8NRG241930 (rs62510682) across all studies (OR = 0.95, 95% CI = 0.91-0.997, p = 0.04, N = 22,898) and in Caucasian samples (OR = 0.95, 95% CI = 0.90-0.99, p = 0.03, N = 16,014), and the C-allele of NRG1 rs10503929 across all studies (OR = 0.89, 95% CI = 0.81-0.97, p = 0.01, N = 6844) and in Caucasian samples (OR = 0.89, 95% CI = 0.81-0.98, p = 0.01, N = 6414) were protective against schizophrenia. Our systematic meta-analysis is the most updated one for the association of DAO, DAOA, and NRG1 SNPs with schizophrenia.

Plasma and cerebrospinal fluid G72 protein levels in schizophrenia and major depressive disorder

G72 is a modulator of D-amino acid oxidase, the enzyme that degrades D-serine, an amino acid that plays a critical role in glutamate neurotransmission, and has been implicated in psychiatric disorders. The aim of this study was to examine whether plasma or cerebrospinal fluid (CSF) G72 protein levels were altered in either schizophrenia or major depressive disorder (MDD) and whether any correlation between G72 levels and disease severity existed. Initially, 27 schizophrenic patients, 26 MDD patients, and 27 healthy controls matched for age, sex, and ethnicity were enrolled. Compared to those of controls, plasma or CSF G72 levels were not significantly different in patients with schizophrenia or MDD. Although we found a significant positive correlation between plasma G72 levels and a positive symptoms score on the positive and negative syndrome scale (PANSS), this was not replicated in the second study (40 schizophrenic patients). CSF G72 levels showed no significant correlation with PANSS scores. In MDD, neither plasma nor CSF G72 levels correlated significantly with depression severity. Since severity of our patients were relatively mild, further investigations in a large number of subjects including drug-free patients, younger patients, and more severely affected patients are warranted.

Structure models of G72, the product of a susceptibility gene to schizophrenia

The G72 gene is one of the most susceptible genes to schizophrenia and is contained exclusively in the genomes of primates. The product of the G72 gene modulates the activity of D-amino acid oxidase (DAO) and is a small protein prone to aggregate, which hampers its structural studies. In addition, lack of a known structure of a homologue makes it difficult to use the homology modelling method for the prediction of the structure. Thus, we first developed a hybrid ab initio approach for small proteins prior to the prediction of the structure of G72. The approach uses three known ab initio algorithms. To evaluate the hybrid approach, we tested our prediction of the structure of the amino acid sequences whose structures were already solved and compared the predicted structures with the experimentally solved structures. Based on these comparisons, the average accuracy of our approach was calculated to be ∼5 Å. We then applied the approach to the sequence of G72 and successfully predicted the structures of the N- and C-terminal domains (ND and CD, respectively) of G72. The predicted structures of ND and CD were similar to membrane-bound proteins and adaptor proteins, respectively.

Expression of D-Amino Acid Oxidase (DAO/DAAO) and D-Amino Acid Oxidase Activator (DAOA/G72) during Development and Aging in the Human Post-mortem Brain

In the brain, D-amino acid oxidase (DAO/DAAO) mainly oxidizes D-serine, a co-agonist of the N-methyl-D-aspartate (NMDA) receptors. Thus, DAO can regulate the function of NMDA receptors via D-serine breakdown. Furthermore, DAO activator (DAOA)/G72 has been reported as both DAOA and repressor. The co-expression of DAO and DAOA genes and proteins in the human brain is not yet elucidated. The aim of this study was to understand the regional and age span distribution of DAO and DAOA (mRNA and protein) in a concomitant manner. We determined DAO and DAOA mRNA and protein expression across six brain regions in normal human post-mortem brain samples (16 weeks of gestation to 91 years) using quantitative real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. We found higher expression of DAO mRNA in the cerebellum, whereas lower expression of DAO protein in the cerebellum compared to the other brain regions studied, which suggests post-transcriptional regulation. We detected DAOA protein but not DAOA mRNA in all brain regions studied, suggesting a tightly regulated expression. To understand this regulation at the transcriptional level, we analyzed DNA methylation levels at DAO and DAOA CpG sites in the cerebellum and frontal cortex of control human post-mortem brain obtained from Gene Expression Omnibus datasets. Indeed, DAO and DAOA CpG sites in the cerebellum were significantly more methylated than those in the frontal cortex. While investigating lifespan effects, we found that DAO mRNA levels were positively correlated with age <2 years in the cerebellum and amygdala. We also detected a significant positive correlation (controlled for age) between DAO and DAOA protein in all of the brain regions studied except for the frontal cortex. In summary, DAO and DAOA expression in the human brain are both age and brain region dependent.

Increased serum G72 protein levels in patients with schizophrenia: a potential candidate biomarker

OBJECTIVE

The product of the G72 gene is an activator of d-amino acid oxidase and has been suggested to play a role in the pathogenesis of schizophrenia. Increased G72 protein levels may be associated with disturbed glutamatergic transmission and increased reactive oxygen species. Only one pilot study by Lin et al. has investigated the potential role of serum G72 protein levels as a biomarker for schizophrenia. In this study, we aimed to compare serum G72 protein levels between patients with schizophrenia and healthy controls, and to retest the results of the previous pilot study. Materials and methods In total, 107 patients with a diagnosis of schizophrenia according to the inclusion and exclusion criteria and 60 age-sex-matched healthy controls were included in the study. The groups were compared regarding serum G72 protein levels.

RESULTS

The mean serum G72 protein values were 495.90±152.03 pg/ml in the schizophrenia group and 346.10±102.08 pg/ml in the healthy control group. The mean serum G72 protein level was significantly increased in the schizophrenia group compared with the healthy control group (t=-3.89, p<0.001). A receiver operating characteristics analysis was performed to compare the schizophrenia and healthy control groups. It was determined that the cut-off value was 141.51 pg/ml with a sensitivity of 0.991 and a specificity of 0.821.

CONCLUSION

We suggest that serum G72 protein levels may represent a candidate biomarker for schizophrenia and have confirmed the results of the previous preliminary study. Additional studies with larger sample sizes and the inclusion of first episode schizophrenia patients are required to clarify the reliability and validity of serum G72 protein levels as a biomarker for schizophrenia.

Elucidating the role of the pLG72 R30K substitution in schizophrenia susceptibility

In the human brain, pLG72 interacts with the flavoenzyme d-amino acid oxidase (hDAAO), which is involved in catabolism of d-serine, a co-agonist of N-methyl-d-aspartate receptors (NMDAR). Here, we investigated the wild-type pLG72, the R30K variant associated with schizophrenia susceptibility, and the K62E variant. The protein conformation, oligomeric state, ligand-, and hDAAO-binding properties are only slightly modified by the substitutions. All pLG72 variants inhibit hDAAO and lead to an increase in cellular (d/d+l)-serine. However, the R30K pLG72 is significantly more prone to degradation than the R30 and the K62E variants in a cell system, thus possessing a lower ability to interact/inhibit hDAAO. This links R30K pLG72 with the hyperactivity of hDAAO, the decreased d-serine level, and NMDAR hypofunction observed in schizophrenia-affected patients.

Decreased level of serum autoantibody against LG72 is a biosignature of amyotrophic lateral sclerosis

AIM

LG72 can increase mitochondrial ROSs and oxidative stress has been implicated in the pathophysiology of amyotrophic lateral sclerosis (ALS). The serum level of LG72 or LG72-related molecules might therefore be associated with ALS. Here, we aim to determine the serum autoantibody against LG72 has potential as a biomarker for the diagnosis of ALS.

MATERIALS

Seventy-eighty patients with ALS, 45 patients with AD, 43 patients with PD and 88 healthy adults were enrolled.

RESULTS

The concentration of serum autoantibody against LG72 was more than fourfold lower in ALS than other control groups (p < 0.001). The AUC was 0.9627 when the cut-off value for autoantibody concentration was 0.167 μg/ml.

CONCLUSION

This finding suggests that the autoantibody against LG72 might serve as a surrogate biomarker for ALS.

Upstream Pathways Controlling Mitochondrial Function in Major Psychosis: A Focus on Bipolar Disorder

Mitochondrial dysfunction is commonly observed in bipolar disorder (BD) and schizophrenia (SCZ) and may be a central feature of psychosis. These illnesses are complex and heterogeneous, which is reflected by the complexity of the processes regulating mitochondrial function. Mitochondria are typically associated with energy production; however, dysfunction of mitochondria affects not only energy production but also vital cellular processes, including the formation of reactive oxygen species, cell cycle and survival, intracellular Ca(2+) homeostasis, and neurotransmission. In this review, we characterize the upstream components controlling mitochondrial function, including 1) mutations in nuclear and mitochondrial DNA, 2) mitochondrial dynamics, and 3) intracellular Ca(2+) homeostasis. Characterizing and understanding the upstream factors that regulate mitochondrial function is essential to understand progression of these illnesses and develop biomarkers and therapeutics.

Mitochondrial dysfunction in bipolar disorder: Evidence, pathophysiology and translational implications

Bipolar disorder (BD) is a chronic psychiatric illness characterized by severe and biphasic changes in mood. Several pathophysiological mechanisms have been hypothesized to underpin the neurobiology of BD, including the presence of mitochondrial dysfunction. A confluence of evidence points to an underlying dysfunction of mitochondria, including decreases in mitochondrial respiration, high-energy phosphates and pH; changes in mitochondrial morphology; increases in mitochondrial DNA polymorphisms; and downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration. Mitochondria play a pivotal role in neuronal cell survival or death as regulators of both energy metabolism and cell survival and death pathways. Thus, in this review, we discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BD. The final part of this review discusses mitochondria as a potential target of therapeutic interventions in BD.

G72 primate-specific gene: a still enigmatic element in psychiatric disorders

Numerous studies have demonstrated a link between genetic markers on chromosome 13 and schizophrenia, bipolar affective disorder, and other psychiatric phenotypes. The G72/G30 genes (transcribed in opposite directions) are located on chromosome 13q33, a region demonstrating strong evidence for linkage with various neuropsychiatric disorders. G72/G30 was identified in 2002 as a schizophrenia susceptibility locus; however, subsequent association studies did not reach consensus on single SNPs within the locus. Simultaneously, a new vision for the genetic architecture of psychiatric disorders suggested that schizophrenia was a quantitative trait, therefore ascribable to potentially hundreds of genes and subjected to the vagaries of the environment. The main protein product of G72 gene is named pLG72 or D-amino acid oxidase activator DAOA (153 amino acids) and its function is still debated. Functional analyses, also showing controversial results, indicate that pLG72 contributes to N-methyl-D-aspartate receptor modulation by affecting activity of the flavoprotein D-amino acid oxidase, the enzyme responsible for degrading the neuromodulator D-serine. In this review we, for the first time, summarize findings from molecular genetic linkage and association studies concerning G72 gene, cellular and molecular studies on pLG72, and investigations performed on G72/G30 transgenic mice. This will help elucidate the role of psychosis susceptibility genes, which will have a major impact on our understanding of disease pathophysiology and thus change classification and treatment.

Synaptic and cellular changes induced by the schizophrenia susceptibility gene G72 are rescued by N-acetylcysteine treatment

Genetic studies have linked the primate-specific gene locus G72 to the development of schizophrenia and bipolar disorder. Transgenic mice carrying the entire gene locus express G72 mRNA in dentate gyrus (DG) and entorhinal cortex, causing altered electrophysiological properties of their connections. These transgenic mice exhibit behavioral alterations related to psychiatric diseases, including cognitive deficits that can be reversed by treatment with N-acetylcysteine, which was also found to be effective in human patients. Here, we show that G72 transgenic mice have larger excitatory synapses with an increased amount of N-methyl-d-aspartate (NMDA) receptors in the molecular layer of DG, compared with wild-type littermates. Furthermore, transgenic animals have lower number of dentate granule cells with a parallel, but an even stronger decrease in the number of excitatory synapses in the molecular layer. Importantly, we also show that treatment with N-acetylcysteine can effectively normalize all these changes in transgenic animals, resulting in a state similar to wild-type mice. Our results show that G72 transcripts induce robust alterations in the glutamatergic system at the synaptic level that can be rescued with N-acetylcysteine treatment.

Diseases caused by defects of energy level and loss of coherence in living cells

Human and animal diseases are brought about by pathological alterations of production, composition, and conformation of macromolecules and structures in cells. Additional contributing factors include changes in physiological states caused by disturbances of energy supply, energy transduction, energy dissipation in moving or oscillating parts, and parasitic energy consumption. Disturbances of energy states may endanger existence of the system. The cell-mediated immunity (CMI) response of T lymphocytes correlating with their adherence properties was examined using antigen prepared from the serum of inbred laboratory mice strain C3H H(2k) infected with lactate dehydrogenase elevating (LDH) virus. LDH virus is a parasite on the cellular energy system. Significant CMI response was elicited in T lymphocytes prepared from the blood of patients with cancer of different phenotypes, acute myocardial infarctions, schizophrenia, and recurrent spontaneous abortions in early pregnancy from unknown reasons. The CMI response is assumed to monitor transferred information about decreased levels of energy states and decoherence in the cells caused by mitochondrial malfunction, parasitic consumption, production of lactate, and possibly other disturbances. The LDH virus infection or similar pathological processes caused by different agents might be connected with the diseases and monitored by the examined CMI response. A large amount of mitoses with chromosome defects in aborted fetuses suggest increased mutability of genomes caused by defective energy states.

Identification of pLG72-Induced Oxidative Stress Using Systemic Approaches

G72 is a schizophrenia-susceptible gene encoding a polypeptide with 153 amino acids. In 2002, it was originally proposed as an activator of D-amino acid oxidase (DAOA) that could enhance the activity of DAAO and subsequently reduce the neurotransmission of N-methyl-D-aspartate receptors. However, several controversial findings have been reported recently. Due to a number of inconsistent descriptions of pLG72's biofunctions, this study aims to identify the cellular effects induced by pLG72 in U87 cells using systems biology approaches. The analyses of transcriptomics and biological networks showed that pLG72 might be involved in the induction of oxidative stress. To confirm the in silico prediction, we tested and discovered that overexpression of pLG72 effectively enhanced reactive oxygen species (ROS) in U87 cells and, furthermore, this induction can be quenched by Tempol, a general ROS scavenger. Therefore, G72-transgenic mice presenting some psychiatric symptoms, along with the pLG72 level being significantly increased in the serum of patients with schizophrenia, have led us to propose that the ROS enhancement in mental diseases may be from the overexpression of pLG72 in brain cells.

High-Throughput Screening Strategy Identifies Allosteric, Covalent Human D-Amino Acid Oxidase Inhibitor

Genome-wide association studies have linked polymorphisms in the gene G72 to schizophrenia risk in several human populations. Although controversial, biochemical experiments have suggested that the mechanistic link of G72 to schizophrenia is due to the G72 protein product, pLG72, exerting a regulatory effect on human D-amino acid oxidase (hDAAO) activity. In an effort to identify hDAAO inhibitors of novel mechanism of action, we designed a pLG72-directed hDAAO activity assay suitable for high-throughput screening (HTS). During assay development, we confirmed that pLG72 was an inhibitor of hDAAO. Thus, our assay employed an IC20 pLG72 concentration that was high enough to allow dynamic pLG72-hDAAO complexes to form but with sufficient remaining hDAAO activity to measure during an HTS. After conducting an approximately 150,000-compound HTS, we further characterized a class of compound hits that were less potent hDAAO inhibitors when pLG72 was present. Focusing primarily on compound 2 [2-(2,5-dimethylphenyl)-6-fluorobenzo[d]isothiazol-3(2H)-on], we demonstrated that these compounds inhibited hDAAO via an allosteric, covalent mechanism. Although there is significant interest in the therapeutic potential of compound 2 and its analogues, their sensitivity to reducing agents and their capacity to bind cysteines covalently would need to be addressed during therapeutic drug development.

Adaptive evolution and elucidating the potential inhibitor against schizophrenia to target DAOA (G72) isoforms

Schizophrenia (SZ), a chronic mental and heritable disorder characterized by neurophysiological impairment and neuropsychological abnormalities, is strongly associated with D-amino acid oxidase activator (DAOA, G72). Research studies emphasized that overexpression of DAOA may be responsible for improper functioning of neurotransmitters, resulting in neurological disorders like SZ. In the present study, a hybrid approach of comparative modeling and molecular docking followed by inhibitor identification and structure modeling was employed. Screening was performed by two-dimensional similarity search against selected inhibitor, keeping in view the physiochemical properties of the inhibitor. Here, we report an inhibitor compound which showed maximum binding affinity against four selected isoforms of DAOA. Docking studies revealed that Glu-53, Thr-54, Lys-58, Val-85, Ser-86, Tyr-87, Leu-88, Glu-90, Leu-95, Val-98, Ser-100, Glu-112, Tyr-116, Lys-120, Asp-121, and Arg-122 are critical residues for receptor–ligand interaction. The C-terminal of selected isoforms is conserved, and binding was observed on the conserved region of isoforms. We propose that selected inhibitor might be more potent on the basis of binding energy values. Further analysis of this inhibitor through site-directed mutagenesis could be helpful for exploring the details of ligand-binding pockets. Overall, the findings of this study may be helpful in designing novel therapeutic targets to cure SZ.

Genetic variation in the G72 gene is associated with increased frontotemporal fiber tract integrity

G72 (syn. DAOA, D-amino acid oxidase activator) is a susceptibility gene for both schizophrenia and bipolar disorder. Diffusion tensor imaging studies hint at changes in fiber tract integrity in both disorders. We aimed to investigate whether a G72 susceptibility haplotype causes changes in fiber tract integrity in young healthy subjects. We compared fractional anisotropy in 47 subjects that were either homozygous for the M23/M24 risk haplotype (n = 20) or homozygous for M23(rs3918342)/M24(rs1421292) wild type (n = 27) using diffusion tensor imaging with 3 T. Tract-based spatial statistics, a method especially developed for diffusion data analysis, was used to delineate the major fiber tracts. We found clusters of increased FA values in homozygous risk haplotype carriers in the right periinsular region and in the right inferior parietal lobe (IPL). We did not find clusters indicating decreased FA values. The insula and the IPL have been implicated in both schizophrenia and bipolar pathophysiology. Increased FA values might reflect changes in dendritic morphology as previously described by in vitro studies. These findings further corroborate the hypothesis that a shared gene pool between schizophrenia and bipolar disorder might lead to neuroanatomic changes that confer an unspecific vulnerability for both disorders.

Effects of sodium benzoate on pre-pulse inhibition deficits and hyperlocomotion in mice after administration of phencyclidine

OBJECTIVE

A recent clinical study demonstrated that sodium benzoate (SB), a prototype competitive d-amino acid oxidase inhibitor, was effective in the treatment of several symptoms, such as positive and negative symptoms, and cognitive impairment in medicated patients with schizophrenia. The objective of the study was to examine the effects of SB on behavioural abnormalities such as pre-pulse inhibition (PPI) deficits and hyperlocomotion in mice after a single administration of the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP).

METHODS

The effects of SB on behavioural abnormalities (PPI deficits and hyperlocomotion) in mice after PCP administration were examined. Furthermore, effects of SB on tissue levels of amino acids were also examined.

RESULTS

A single oral dose of SB (100, 300, or 1000 mg/kg) attenuated PPI deficits in mice after administration of PCP (3.0 mg/kg, s.c.) in a dose-dependent manner. In contrast, L-701,324 (10 mg/kg), an antagonist at the glycine site of the NMDA receptor, did not affect the effect of SB (1000 mg/kg) on PCP-induced PPI deficits. Furthermore, a single oral dose of SB (1000 mg/kg) significantly attenuated the hyperlocomotion in mice after administration of PCP (3.0 mg/kg, s.c.). However, a single oral dose of SB (1000 mg/kg) caused no changes to D-serine levels in plasma or in the frontal cortex, hippocampus, and striatum of these animals.

CONCLUSION

This study suggests that SB induced antipsychotic effects in the PCP model of schizophrenia, although it did not increase D-serine levels in the brain.

A primate-specific functional GTTT-repeat in the core promoter of CYTH4 is linked to bipolar disorder in human

Evidence of primate-specific genes and gene regulatory mechanisms linked to bipolar disorder (BD) lend support to evolutionary/adaptive processes in the pathogenesis of this disorder. Following a genome-scale analysis of the entire protein coding genes annotated in the GeneCards database, we have recently reported that cytohesin-4 (CYTH4) contains the longest tetra-nucleotide short tandem repeat (STR) identified in a human protein-coding gene core promoter, which may be of adaptive advantage to this species. In the current study, we analyzed the evolutionary trend of this STR across evolution. We also analyzed the functional implication and distribution of this STR in a group of patients with type 1 BD (n=233) and controls (n=262). We found that this STR is exceptionally expanded in primates (Fisher exact p<0.00003). Association was observed between type I BD and the 6-repeat allele of this STR, (GTTT)₆ (Yates corrected Χ(2)=12.68, p<0.0001, OR: 1.68). This allele is the shortest length of the GTTT-repeat identified in the human subjects studied. Consistent with that finding, excess homozygosity was observed for the shorter alleles, (GTTT)₆ and (GTTT)₇, vs. the longer alleles, (GTTT)₈ and (GTTT)₉ in the BD group (Yates corrected Χ(2)=5.18, p<0.01, 1 df, OR: 1.96). Using Dual Glo luciferase system in HEK-293 cells, a trend for gene expression repression was observed from the 6- to the 9-repeat allele (p<0.003), and the GTTT-repeat significantly down-regulated gene expression, per se (p<0.0006). This is the first evidence of a link between a primate-specific STR and a major psychiatric disorder in human. It may be speculated that the CYTH4 GTTT-repeat in primates may have conferred selective advantage to this order, reflected in neural function and neurophenotypes. The role of the CYTH4 gene in the pathogenesis of type I BD remains to be clarified in the future studies.

DISC1-TSNAX and DAOA genes in major depression and citalopram efficacy

BACKGROUND

Major depressive disorder (MDD) is a common disease with high morbidity and still unsatisfying treatment response. Both MDD pathogenesis and antidepressant effect are supposed to be strongly affected by genetic polymorphisms. Among promising candidate genes, distrupted in schizophrenia 1 (DISC1), translin-associated factor X (TSNAX) and D-amino acid oxidase activator (DAOA) were suggested since their regulator role in neurodevelopment, neuroplasticity and neurotransmission, and previous evidence of cross-involvement in major psychiatric diseases.

METHODS

The present paper investigated the role of 13 SNPs within the reported genes in MDD susceptibility through a case-control (n=320 and n=150, respectively) study and in citalopram efficacy (n=157). Measures of citalopram efficacy were response (4th week) and remission (12th week). Pharmacogenetic findings were tested in the STAR(⁎)D genome-wide dataset (n=1892) for replication.

RESULTS

Evidence of association among rs3738401 (DISC1), rs1615409 and rs766288 (TSNAX) and MDD was found (p=0.004, p=0.0019, and p=0.008, respectively). A trend of association between remission and DISC1 rs821616 and DAOA rs778294 was detected, and confirmation was found for rs778294 by repeated-measure ANOVA (p=0.0008). In the STAR(⁎)D a cluster of SNPs from 20 to 40Kbp from DISC1 findings in the original sample was associated with citalopram response, as well as rs778330 (12,325bp from rs778294).

LIMITATIONS

Relatively small size of the original sample and focus on only three candidate genes.

CONCLUSIONS

The present study supported a role of DISC1-TSNAX variants in MDD susceptibility. On the other hand, genetic regions around DAOA rs778294 and DISC1 rs6675281-rs1000731 may influence citalopram efficacy.

Targeting mitochondrially mediated plasticity to develop improved therapeutics for bipolar disorder

INTRODUCTION

Bipolar disorder (BPD) is a severe illness with few treatments available. Understanding BPD pathophysiology and identifying potential relevant targets could prove useful for developing new treatments. Remarkably, subtle impairments of mitochondrial function may play an important role in BPD pathophysiology.

AREAS COVERED

This article focuses on human studies and reviews evidence of mitochondrial dysfunction in BPD as a promising target for the development of new, improved treatments. Mitochondria are crucial for energy production, generated mainly through the electron transport chain (ETC) and play an important role in regulating apoptosis and calcium (Ca²⁺) signaling as well as synaptic plasticity. Mitochondria move throughout the neurons to provide energy for intracellular signaling. Studies showed polymorphisms of mitochondria-related genes as risk factors for BPD. Postmortem studies in BPD also show decreased ETC activity/expression and increased nitrosative and oxidative stress (OxS) in patient brains. BPD has been also associated with increased OxS, Ca²⁺ dysregulation and increased proapoptotic signaling in peripheral blood. Neuroimaging studies consistently show decreased energy levels and pH in brains of BPD patients.

EXPERT OPINION

Targeting mitochondrial function, and their role in energy metabolism, synaptic plasticity and cell survival, may be an important avenue for development of new mood-stabilizing agents.

Neuroprogression in schizophrenia: Pathways underpinning clinical staging and therapeutic corollaries

OBJECTIVE

Whilst dopaminergic dysfunction remains a necessary component involved in the pathogenesis of schizophrenia, our current pharmacological armoury of dopamine antagonists does little to control the negative symptoms of schizophrenia. This suggests other pathological processes must be implicated. This paper aims to elaborate on such theories.

METHODS

Data for this review were sourced from the electronic database PUBMED, and was not limited by language or date of publication.

RESULTS

It has been suggested that multiple 'hits' may be required to unveil the clinical syndrome in susceptible individuals. Such hits potentially first occur in utero, leading to neuronal disruption, epigenetic changes and the establishment of an abnormal inflammatory response. The development of schizophrenia may therefore potentially be viewed as a neuroprogressive response to these early stressors, driven on by changes in tryptophan catabolite (TRYCAT) metabolism, reactive oxygen species handling and N-methyl d-aspartate (NMDA) circuitry. Given the potential for such progression over time, it is prudent to explore the new treatment strategies which may be implemented before such changes become established.

CONCLUSIONS

Outside of the dopaminergic model, the potential pathogenesis of schizophrenia has yet to be fully elucidated, but common themes include neuropil shrinkage, the development of abnormal neuronal circuitry, and a chronic inflammatory state which further disrupts neuronal function. Whilst some early non-dopaminergic treatments show promise, none have yet to be fully studied in appropriately structured randomized controlled trials and they remain little more than potential attractive targets.

Chronic nicotine improves short-term memory selectively in a G72 mouse model of schizophrenia

BACKGROUND AND PURPOSE

The prevalence of smoking in schizophrenia patients is exceptionally high; it is not known why but many researchers suggest that smoking constitutes a form of self-medication. Among the symptoms of schizophrenia that may be improved by nicotine are cognitive deficits. Hence, we studied the effects of long-term nicotine administration on cognition in a genetic animal model of schizophrenia susceptibility, G72-transgenic (G72Tg) mice.

EXPERIMENTAL APPROACH

The effect of long-term nicotine or saline, administered by osmotic minipumps, on different cognitive domains was assessed in G72Tg mice and controls using a battery of behavioural tests. To investigate the mechanism underlying phenotypic differences, quantitative autoradiographic mapping of nACh receptor subtypes was performed in forebrain structures to explore effects of chronic nicotine exposure on nACh receptor density in wild-type (WT) and G72Tg mice.

KEY RESULTS

Genotype significantly affected the cognitive effects of chronic nicotine administration. Whereas chronic nicotine disrupted cognitive performance in WT mice, it was effective at restoring impaired prepulse inhibition, working memory and social recognition in G72Tg mice. However, long-term spatial learning was further impaired by nicotine in transgenic animals. In contrast, associative learning was protected by G72-expression against the adverse nicotine effects seen in WT animals. G72-expression did not decisively influence nicotine-induced up-regulation of the α4β2*subtype, whereas α7nACh receptor density was differentially altered by genotype or by a genotype·treatment interaction in specific brain areas, most notably hippocampal subregions.

CONCLUSIONS AND IMPLICATIONS

Our data support the hypothesis that nicotine self-medication of schizophrenics improves cognitive symptoms, possibly by facilitating nicotine-induced α7nACh receptor activation in the hippocampus.

Expression of the G72/G30 gene in transgenic mice induces behavioral changes

The G72/G30 gene complex is a candidate gene for schizophrenia and bipolar disorder. However, G72 and G30 mRNAs are expressed at very low levels in human brain, with only rare splicing forms observed. We report here G72/G30 expression profiles and behavioral changes in a G72/G30 transgenic mouse model. A human BAC clone containing the G72/G30 genomic region was used to establish the transgenic mouse model, on which gene expression studies, western blot and behavioral tests were performed. Relative to their minimal expression in humans, G72 and G30 mRNAs were highly expressed in the transgenic mice, and had a more complex splicing pattern. The highest G72 transcript levels were found in testis, followed by cerebral cortex, with very low or undetectable levels in other tissues. No LG72 (the long putative isoform of G72) protein was detected in the transgenic mice. Whole-genome expression profiling identified 361 genes differentially expressed in transgenic mice compared with wild-type, including genes previously implicated in neurological and psychological disorders. Relative to wild-type mice, the transgenic mice exhibited fewer stereotypic movements in the open field test, higher baseline startle responses in the course of the prepulse inhibition test, and lower hedonic responses in the sucrose preference test. The transcriptome profile changes and multiple mouse behavioral effects suggest that the G72 gene may play a role in modulating behaviors relevant to psychiatric disorders.

Pre-clinical models of neurodevelopmental disorders: focus on the cerebellum

Recent studies have advanced our understanding of the role of the cerebellum in non-motor behaviors. Abnormalities in the cerebellar structure have been demonstrated to produce changes in emotional, cognitive, and social behaviors resembling clinical manifestations observed in patients with autism spectrum disorders (ASD) and schizophrenia. Several animal models have been used to evaluate the effects of relevant environmental and genetic risk factors on the cerebellum development and function. However, very few models of ASD and schizophrenia selectively target the cerebellum and/or specific cell types within this structure. In this review, we critically evaluate the strength and weaknesses of these models. We will propose that the future progress in this field will require time- and cell type-specific manipulations of disease-relevant genes, not only selectively in the cerebellum, but also in frontal brain areas connected with the cerebellum. Such information can advance our knowledge of the cerebellar contribution to non-motor behaviors in mental health and disease.

Interaction between effects of genes coding for dopamine and glutamate transmission on striatal and parahippocampal function

The genes for the dopamine transporter (DAT) and the D-Amino acid oxidase activator (DAOA or G72) have been independently implicated in the risk for schizophrenia and in bipolar disorder and/or their related intermediate phenotypes. DAT and G72 respectively modulate central dopamine and glutamate transmission, the two systems most robustly implicated in these disorders. Contemporary studies have demonstrated that elevated dopamine function is associated with glutamatergic dysfunction in psychotic disorders. Using functional magnetic resonance imaging we examined whether there was an interaction between the effects of genes that influence dopamine and glutamate transmission (DAT and G72) on regional brain activation during verbal fluency, which is known to be abnormal in psychosis, in 80 healthy volunteers. Significant interactions between the effects of G72 and DAT polymorphisms on activation were evident in the striatum, parahippocampal gyrus, and supramarginal/angular gyri bilaterally, the right insula, in the right pre-/postcentral and the left posterior cingulate/retrosplenial gyri (P < 0.05, FDR-corrected across the whole brain). This provides evidence that interactions between the dopamine and the glutamate system, thought to be altered in psychosis, have an impact in executive processing which can be modulated by common genetic variation.

Neonatal disruption of serine racemase causes schizophrenia-like behavioral abnormalities in adulthood: clinical rescue by d-serine

BACKGROUND

D-Serine, an endogenous co-agonist of the N-methyl-D-aspartate (NMDA) receptor, is synthesized from L-serine by serine racemase (SRR). Given the role of D-serine in both neurodevelopment and the pathophysiology of schizophrenia, we examined whether neonatal disruption of D-serine synthesis by SRR inhibition could induce behavioral abnormalities relevant to schizophrenia, in later life.

METHODOLOGY/PRINCIPAL FINDINGS

Neonatal mice (7-9 days) were injected with vehicle or phenazine methosulfate (Met-Phen: 3 mg/kg/day), an SRR inhibitor. Behavioral evaluations, such as spontaneous locomotion, novel object recognition test (NORT), and prepulse inhibition (PPI) were performed at juvenile (5-6 weeks old) and adult (10-12 weeks old) stages. In addition, we tested the effects of D-serine on PPI deficits in adult mice after neonatal Met-Phen exposure. Finally, we assessed whether D-serine could prevent the onset of schizophrenia-like behavior in these mice. Neonatal Met-Phen treatment reduced D-serine levels in the brain, 24 hours after the final dose. Additionally, this treatment caused behavioral abnormalities relevant to prodromal symptoms in juveniles and to schizophrenia in adults. A single dose of D-serine improved PPI deficits in adult mice. Interestingly, chronic administration of D-serine (900 mg/kg/day from P35 to P70) significantly prevented the onset of PPI deficits after neonatal Met-Phen exposure.

CONCLUSIONS/SIGNIFICANCE

This study shows that disruption of D-serine synthesis during developmental stages leads to behavioral abnormalities relevant to prodromal symptoms and schizophrenia, in later life. Furthermore, early pharmacological intervention with D-serine may prevent the onset of psychosis in adult.