Mitochondrial complex I as a novel target for intraneuronal DA: modulation of respiration in intact cells

Prenatal immune activation in mice induces long-term alterations in brain mitochondrial function

Prenatal exposure to infections is a risk factor for neurodevelopmental disorders in offspring, and alterations in mitochondrial function are discussed as a potential underlying factor. Here, using a mouse model of viral-like maternal immune activation (MIA) based on poly(I:C) (POL) treatment at gestational day (GD) 12, we show that adult offspring exhibit behavioral deficits, such as reduced levels of social interaction. In addition, we found increased nicotinamidadenindinucleotid (NADH)- and succinate-linked mitochondrial respiration and maximal electron transfer capacity in the prefrontal cortex (PFC) and in the amygdala (AMY) of males and females. The increase in respiratory capacity resulted from an increase in mitochondrial mass in neurons (as measured by complex IV activity and transcript expression), presumably to compensate for a reduction in mitochondrion-specific respiration. Moreover, in the PFC of control (CON) male offspring a higher excess capacity compared to females was observed, which was significantly reduced in the POL-exposed male offspring, and, along with a higher leak respiration, resulted in a lower mitochondrial coupling efficiency. Transcript expression of the uncoupling proteins (UCP4 and UCP5) showed a reduction in the PFC of POL male mice, suggesting mitochondrial dysfunction. In addition, in the PFC of CON females, a higher expression of the antioxidant enzyme superoxide dismutase (SOD1) was observed, suggesting a higher antioxidant capacity as compared to males. Finally, transcripts analysis of genes involved in mitochondrial biogenesis and dynamics showed reduced expression of fission/fusion transcripts in PFC of POL offspring of both sexes. In conclusion, we show that MIA causes alterations in neuronal mitochondrial function and mass in the PFC and AMY of adult offspring with some effects differing between males and females.

Network-based drug repurposing for schizophrenia

Despite recent progress, the challenges in drug discovery for schizophrenia persist. However, computational drug repurposing has gained popularity as it leverages the wealth of expanding biomedical databases. Network analyses provide a comprehensive understanding of transcription factor (TF) regulatory effects through gene regulatory networks, which capture the interactions between TFs and target genes by integrating various lines of evidence. Using the PANDA algorithm, we examined the topological variances in TF-gene regulatory networks between individuals with schizophrenia and healthy controls. This algorithm incorporates binding motifs, protein interactions, and gene co-expression data. To identify these differences, we subtracted the edge weights of the healthy control network from those of the schizophrenia network. The resulting differential network was then analysed using the CLUEreg tool in the GRAND database. This tool employs differential network signatures to identify drugs that potentially target the gene signature associated with the disease. Our analysis utilised a large RNA-seq dataset comprising 532 post-mortem brain samples from the CommonMind project. We constructed co-expression gene regulatory networks for both schizophrenia cases and healthy control subjects, incorporating 15,831 genes and 413 overlapping TFs. Through drug repurposing, we identified 18 promising candidates for repurposing as potential treatments for schizophrenia. The analysis of TF-gene regulatory networks revealed that the TFs in schizophrenia predominantly regulate pathways associated with energy metabolism, immune response, cell adhesion, and thyroid hormone signalling. These pathways represent significant targets for therapeutic intervention. The identified drug repurposing candidates likely act through TF-targeted pathways. These promising candidates, particularly those with preclinical evidence such as rimonabant and kaempferol, warrant further investigation into their potential mechanisms of action and efficacy in alleviating the symptoms of schizophrenia.

Mitochondria in the Central Nervous System in Health and Disease: The Puzzle of the Therapeutic Potential of Mitochondrial Transplantation

Mitochondria, the energy suppliers of the cells, play a central role in a variety of cellular processes essential for survival or leading to cell death. Consequently, mitochondrial dysfunction is implicated in numerous general and CNS disorders. The clinical manifestations of mitochondrial dysfunction include metabolic disorders, dysfunction of the immune system, tumorigenesis, and neuronal and behavioral abnormalities. In this review, we focus on the mitochondrial role in the CNS, which has unique characteristics and is therefore highly dependent on the mitochondria. First, we review the role of mitochondria in neuronal development, synaptogenesis, plasticity, and behavior as well as their adaptation to the intricate connections between the different cell types in the brain. Then, we review the sparse knowledge of the mechanisms of exogenous mitochondrial uptake and describe attempts to determine their half-life and transplantation long-term effects on neuronal sprouting, cellular proteome, and behavior. We further discuss the potential of mitochondrial transplantation to serve as a tool to study the causal link between mitochondria and neuronal activity and behavior. Next, we describe mitochondrial transplantation's therapeutic potential in various CNS disorders. Finally, we discuss the basic and reverse-translation challenges of this approach that currently hinder the clinical use of mitochondrial transplantation.

Mitochondria play an essential role in the trajectory of adolescent neurodevelopment and behavior in adulthood: evidence from a schizophrenia rat model

Ample evidence implicate mitochondria in early brain development. However, to the best of our knowledge, there is only circumstantial data for mitochondria involvement in late brain development occurring through adolescence, a critical period in the pathogenesis of various psychiatric disorders, specifically schizophrenia. In schizophrenia, neurodevelopmental abnormalities and mitochondrial dysfunction has been repeatedly reported. Here we show a causal link between mitochondrial transplantation in adolescence and brain functioning in adulthood. We show that transplantation of allogenic healthy mitochondria into the medial prefrontal cortex of adolescent rats was beneficial in a rat model of schizophrenia, while detrimental in healthy control rats. Specifically, disparate initial changes in mitochondrial function and inflammatory response were associated with opposite long-lasting changes in proteome, neurotransmitter turnover, neuronal sprouting and behavior in adulthood. A similar inverse shift in mitochondrial function was also observed in human lymphoblastoid cells deived from schizophrenia patients and healthy subjects due to the interference of the transplanted mitochondria with their intrinsic mitochondrial state. This study provides fundamental insights into the essential role of adolescent mitochondrial homeostasis in the development of normal functioning adult brain. In addition, it supports a therapeutic potential for mitochondria manipulation in adolescence in disorders with neurodevelopmental and bioenergetic deficits, such as schizophrenia, yet emphasizes the need to monitor individuals' state including their mitochondrial function and immune response, prior to intervention.

Schizophrenia as metabolic disease. What are the causes?

Schizophrenia (SZ) is a devastating neurodevelopmental disease with an accelerated ageing feature. The criteria of metabolic disease firmly fit with those of schizophrenia. Disturbances in energy and mitochondria are at the core of complex pathology. Genetic and environmental interaction creates changes in redox, inflammation, and apoptosis. All the factors behind schizophrenia interact in a cycle where it is difficult to discriminate between the cause and the effect. New technology and advances in the multi-dispensary fields could break this cycle in the future.

Analysis of Three-Dimensional Cell Migration in Dopamine-Modified Poly(aspartic acid)-Based Hydrogels

Several types of promising cell-based therapies for tissue regeneration have been developing worldwide. However, for successful therapeutical application of cells in this field, appropriate scaffolds are also required. Recently, the research for suitable scaffolds has been focusing on polymer hydrogels due to their similarity to the extracellular matrix. The main limitation regarding amino acid-based hydrogels is their difficult and expensive preparation, which can be avoided by using poly(aspartamide) (PASP)-based hydrogels. PASP-based materials can be chemically modified with various bioactive molecules for the final application purpose. In this study, dopamine containing PASP-based scaffolds is investigated, since dopamine influences several cell biological processes, such as adhesion, migration, proliferation, and differentiation, according to the literature. Periodontal ligament cells (PDLCs) of neuroectodermal origin and SH-SY5Y neuroblastoma cell line were used for the in vitro experiments. The chemical structure of the polymers and hydrogels was proved by ¹H-NMR and FTIR spectroscopy. Scanning electron microscopical (SEM) images confirmed the suitable pore size range of the hydrogels for cell migration. Cell viability assay was carried out according to a standardized protocol using the WST-1 reagent. To visualize three-dimensional cell distribution in the hydrogel matrix, two-photon microscopy was used. According to our results, dopamine containing PASP gels can facilitate vertical cell penetration from the top of the hydrogel in the depth of around 4 cell layers (~150 μm). To quantify these observations, a detailed image analysis process was developed and firstly introduced in this paper.

Dopamine signaling impairs ROS modulation by mitochondrial hexokinase in human neural progenitor cells

Dopamine signaling has numerous roles during brain development. In addition, alterations in dopamine signaling may be also involved in the pathophysiology of psychiatric disorders. Neurodevelopment is modulated in multiple steps by reactive oxygen species (ROS), byproducts of oxidative metabolism that are signaling factors involved in proliferation, differentiation, and migration. Hexokinase (HK), when associated with the mitochondria (mt-HK), is a potent modulator of the generation of mitochondrial ROS in the brain. In the present study, we investigated whether dopamine could affect both the activity and redox function of mt-HK in human neural progenitor cells (NPCs). We found that dopamine signaling via D₁R decreases mt-HK activity and impairs ROS modulation, which is followed by an expressive release of H₂O₂ and impairment in calcium handling by the mitochondria. Nevertheless, mitochondrial respiration is not affected, suggesting specificity for dopamine on mt-HK function. In neural stem cells (NSCs) derived from induced-pluripotent stem cells (iPSCs) of schizophrenia patients, mt-HK is unable to decrease mitochondrial ROS, in contrast with NSCs derived from healthy individuals. Our data point to mitochondrial hexokinase as a novel target of dopaminergic signaling, as well as a redox modulator in human neural progenitor cells, which may be relevant to the pathophysiology of neurodevelopmental disorders such as schizophrenia.

The role of mitochondria in the pathophysiology of schizophrenia: A critical review of the evidence focusing on mitochondrial complex one

There has been increasing interest in the role of mitochondrial dysfunction in the pathophysiology of schizophrenia. Mitochondrial complex one (MCI) dysfunction may represent a mechanism linking bioenergetic impairment with the alterations in dopamine signalling, glutamatergic dysfunction, and oxidative stress found in the disorder. New lines of evidence from novel approaches make it timely to review evidence for mitochondrial involvement in schizophrenia, with a specific focus on MCI. The most consistent findings in schizophrenia relative to controls are reductions in expression of MCI subunits in post-mortem brain tissue (Cohen's d> 0.8); reductions in MCI function in post-mortem brains (d> 0.7); and reductions in neural glucose utilisation (d= 0.3 to 0.6). Antipsychotics may affect glucose utilisation, and, at least in vitro, affect MC1. The findings overall are consistent with MCI dysfunction in schizophrenia, but also highlight the need for in vivo studies to determine the link between MCI dysfunction and symptoms in patients. If new imaging tools confirm MCI dysfunction in the disease, this could pave the way for new treatments targeting this enzyme.

Beneficial effects of combined administration of fluoxetine and mitochondria-targeted antioxidant at in behavioural and molecular studies in mice model of depression

Chronic or recurrent stress is associated with reactive oxygen species (ROS) overproduction and can lead to oxidative damage, which plays important roles in neurodegenerative diseases. Mito - TEMPO is an antioxidant targeted at mitochondria. The aim of the presented study was to assess antidepressant and antioxidant efficacy of Mito - TEMPO administered alone or with fluoxetine in mice exposed to chronic stress. The evaluation of the antidepressant-like activity was based on forced swimming test (FST) and tail suspension test (TST). In order to evaluate the antioxidant potential, the level of mRNA expression of Adora1, Ogg1, Msra, Nrf2 and Tfam in the hippocampus of mice was determined. Behavioural research data showed the antidepressant effect of fluoxetine and Mito - TEMPO administered to mice alone and in combination. The molecular research results indicate a significant impact of chronic stress on the oxidation-reduction balance and an antioxidant effect of Mito - TEMPO. The results obtained in the study suggest that Mito - TEMPO protects DNA against oxidative damage and may be beneficial in the way of cellular function improvement under the conditions of chronic stress. Adora1, Msra, Nrf2 and Tfam genes may be involved in mediating the antioxidant effect of the combined treatment with fluoxetine and Mito - TEMPO.

Mitochondrial function parameters as a tool for tailored drug treatment of an individual with psychosis: a proof of concept study

Pharmacological treatment of mental disorders is currently decided based on "trial and error" strategy. Mitochondrial multifaceted dysfunction is assumed to be a major factor in the pathophysiology and treatment of schizophrenia (SZ) and bipolar disorder (BD). This study aimed to explore the feasibility of using a profile of mitochondrial function parameters as a tool to predict the optimal drug for an individual patient (personalized medicine). Healthy controls (n = 40), SZ (n = 48) and BD (n = 27) patients were recruited. Mental and global state of the subjects, six mitochondrial respiration parameters and 14 mitochondrial function-related proteins were assessed in fresh lymphocytes following in-vitro or in-vivo treatment with five antipsychotic drugs and two mood-stabilizers. In healthy controls, hierarchal clustering shows a drug-specific effect profile on the different mitochondrial parameters following in-vitro exposure. Similar changes were observed in untreated SZ and BD patients with psychosis. Following a month of treatment of the latter patients, only responders showed a significant correlation between drug-induced in-vitro effect (prior to in-vivo treatment) and short-term in-vivo treatment effect for 45% of the parameters. Long- but not short-term psychotropic treatment normalized mitochondria-related parameters in patients with psychosis. Taken together, these data substantiate mitochondria as a target for psychotropic drugs and provide a proof of concept for selective mitochondrial function-related parameters as a predictive tool for an optimized psychotropic treatment in a given patient. This, however, needs to be repeated with an expanded sample size and additional mitochondria related parameters.

NDUFV2 pseudogene (NDUFV2P1) contributes to mitochondrial complex I deficits in schizophrenia

Mitochondria together with other cellular components maintain a constant crosstalk, modulating transcriptional and posttranslational processes. We and others demonstrated mitochondrial multifaceted dysfunction in schizophrenia, with aberrant complex I (CoI) as a major cause. Here we show deficits in CoI activity and homeostasis in schizophrenia-derived cell lines. Focusing on a core CoI subunit, NDUFV2, one of the most severely affected subunits in schizophrenia, we observed reduced protein level and functioning, with no change in mRNA transcripts. We further show that NDUFV2 pseudogene (NDUFV2P1) expression is increased in schizophrenia-derived cells and in postmortem brain specimens. In schizophrenia and controls pooled samples, NDUFV2P1 level demonstrated a significant inverse correlation with NDUFV2 pre- and matured protein level and with CoI-driven cellular respiration. Our data suggest a role for a pseudogene in its parent-gene regulation and possibly in CoI dysfunction in schizophrenia. The abnormal expression of the pseudogene may be one element of a vicious circle in which CoI deficits lead to mitochondrial dysfunction potentially affecting genome-wide regulation of gene expression, including the expression of pseudogenes.

Psychiatric drugs impact mitochondrial function in brain and other tissues

Mitochondria have been linked to the etiology of schizophrenia (SZ). However, studies of mitochondria in SZ might be confounded by the effects of pharmacological treatment with antipsychotic drugs (APDs) and other common medications. This review summarizes findings on relevant mitochondria mechanisms underlying SZ, and the potential impact of psychoactive drugs including primarily APDs, but also antidepressants and anxiolytics. The summarized data suggest that APDs impair mitochondria function by decreasing Complex I activity and ATP production and dissipation of the mitochondria membrane potential. At the same time, in the brains of patients with SZ, antipsychotic drug treatment normalizes gene expression modules enriched in mitochondrial genes that are decreased in SZ. This indicates that APDs may have both positive and negative effects on mitochondria. The available evidence suggests three conclusions i) alterations in mitochondria functions in SZ exist prior to APD treatment, ii) mitochondria alterations in SZ can be reversed by APD treatment, and iii) APDs directly cause impairment of mitochondria function. Overall, the mechanisms of action of psychiatric drugs on mitochondria are both direct and indirect; we conclude the effects of APDs on mitochondria may contribute to both their therapeutic and metabolic side effects. These studies support the hypothesis that neuronal mitochondria are an etiological factor in SZ. Moreover, APDs and other drugs must be considered in the evaluation of this pathophysiological role of mitochondria in SZ. Considering these effects, pharmacological actions on mitochondria may be a worthwhile target for further APD development.

The bimodal mechanism of interaction between dopamine and mitochondria as reflected in Parkinson's disease and in schizophrenia

Parkinson's disease (PD) and schizophrenia (SZ) are two CNS disorders in which dysfunctions in the dopaminergic system and mitochondria are major pathologies. The symptomology of both, PD a neurodegenerative disorder and SZ a neurodevelopmental disorder, is completely different. However, the pharmacological treatment of each of the diseases can cause a shift of symptoms into those characteristic of the other disease. In this review, I describe a pathological interaction between dopamine and mitochondria in both disorders, which due to differences in the extent of oxidative stress leads either to cell death and tissue degeneration as in PD substantia nigra pars compacta or to distorted neuronal activity, imbalanced neuronal circuitry and abnormal behavior and cognition in SZ. This review is in the honor of Moussa Youdim who introduced me to the secrets of research work. His enthusiasm, curiosity and novelty-seeking inspired me throughout my career. Thank you Moussa.

Impaired heme metabolism in schizophrenia-derived cell lines and in a rat model of the disorder: Possible involvement of mitochondrial complex I

Accumulating data point to heme involvement in neuropsychiatric disorders. Heme plays a role in major cellular processes such as signal transduction, protein complex assembly and regulation of transcription and translation. Its synthesis involves the mitochondria, which dysfunction, specifically that of the complex I (Co-I) of the electron transport chain is involved in the pathophysiology of schizophrenia (SZ). Here we aimed to demonstrate that deficits in Co-I affect heme metabolism. We show a significant decrease in heme levels in Co-I deficient SZ-derived EBV transformed lymphocytes (lymphoblastoid cell lines - LCLs) as compared to healthy subjects-derived cells (n = 9/cohort). Moreover, protein levels assessed by immunoblotting and mRNA levels assessed by qRT-PCR of heme catabolic enzyme, heme Oxygenase 1 (HO-1), and protein levels of heme downstream target phosphorylated eukaryotic initiation factor 2-alpha (Peif2a/eif2a) were significantly elevated in SZ-derived cells. In contrast, protein and mRNA levels of heme synthesis rate limiting enzyme aminolevulinic acid synthase-1 (ALAS1) were unchanged in SZ derived LCLs. In addition, inhibition of Co-I by rotenone in healthy subjects-derived LCLs (n = 4/cohort) exhibited an initial increase followed by a later decrease in heme levels. These findings were associated with opposite changes in heme's downstream target and HO-1 level, similar to our findings in SZ-derived cells. We also show a brain region specific pattern of impairment in Co-I subunits and in HO-1 and PeIF2α/eIF2α in the Poly-IC rat model of SZ (n = 6/cohort). Our results provide evidence for a link between CoI and heme metabolism both in-vitro and in-vivo suggesting its contribution to SZ pathophysiology.

Novel Complex Interactions between Mitochondrial and Nuclear DNA in Schizophrenia and Bipolar Disorder

Mitochondrial dysfunction has been associated with schizophrenia (SZ) and bipolar disorder (BD). This review examines recent publications and novel associations between mitochondrial genes and SZ and BD. Associations of nuclear-encoded mitochondrial variants with SZ were found using gene- and pathway-based approaches. Two control region mitochondrial DNA (mtDNA) SNPs, T16519C and T195C, both showed an association with SZ and BD. A review of 4 studies of A15218G located in the cytochrome B oxidase gene (CYTB, SZ = 11,311, control = 35,735) shows a moderate association with SZ (p = 2.15E-03). Another mtDNA allele A12308G was nominally associated with psychosis in BD type I subjects and SZ. The first published study testing the epistatic interaction between nuclear-encoded and mitochondria-encoded genes demonstrated evidence for potential interactions between mtDNA and the nuclear genome for BD. A similar analysis for the risk of SZ revealed significant joint effects (34 nuclear-mitochondria SNP pairs with joint effect p ≤ 5E-07) and significant enrichment of projection neurons. The mitochondria-encoded gene CYTB was found in both the epistatic interactions for SZ and BD and the single SNP association of SZ. Future efforts considering population stratification and polygenic risk scores will test the role of mitochondrial variants in psychiatric disorders.

FOXRED1 silencing in mice: a possible animal model for Leigh syndrome

Leigh syndrome (LS) is one of the most puzzling mitochondrial disorders, which is also known as subacute necrotizing encephalopathy. It has an incidence of 1 in 77,000 live births worldwide with poor prognosis. Currently, there is a poor understanding of the underlying pathophysiological mechanisms of the disease without any available effective treatment. Hence, the inevitability for developing suitable animal and cellular models needed for the development of successful new therapeutic modalities. In this short report, we blocked FOXRED1 gene with small interfering RNA (siRNA) using C57bl/6 mice. Results showed neurobehavioral changes in the injected mice along with parallel degeneration in corpus striatum and sparing of the substantia nigra similar to what happen in Leigh syndrome cases. FOXRED1 blockage could serve as a new animal model for Leigh syndrome due to defective CI, which echoes damage to corpus striatum and affection of the central dopaminergic system in this disease. Further preclinical studies are required to validate this model.

Animal Model for Leigh Syndrome

Leigh syndrome (LS) is a common neurodegenerative disease affecting neonates with devastating sequences. One of the characteristic features for LS is the phenotypic polymorphism, which-in part-can be dedicated to variety of genetic causes. A strong correlation with mitochondrial dysfunction has been assumed as the main cause of LS. This was based on the fact that most genetic causes are related to mitochondrial complex I genome. The first animal LS model was designed based on NDUFS4 knockdown. Interestingly, however, this one or others could not recapitulate the whole spectrum of manifestations encountered in different cases of LS. We show in this chapter a new animal model for LS based on silencing of one gene that is reported previously in clinical cases, FOXRED1. The new model carries some differences from previous models in the fact that more histopathological degeneration in dopaminergic system is seen and more behavioral changes can be recognized. FOXRED1 is an interesting gene that is related to complex I assembly, hence, plays important role in different neurodegenerative disorders leading to different clinical manifestations.

Mitochondrial Targeted Therapies: Where Do We Stand in Mental Disorders?

The neurobiology of psychiatric disorders is still unclear, although changes in multiple neuronal systems, specifically the dopaminergic, glutamatergic, and gamma-aminobutyric acidergic systems as well as abnormalities in synaptic plasticity and neural connectivity, are currently suggested to underlie their pathophysiology. A growing body of evidence suggests multifaceted mitochondrial dysfunction in mental disorders, which is in line with their role in neuronal activity, growth, development, and plasticity. In this review, we describe the main endeavors toward development of treatments that will enhance mitochondrial function and their transition into clinical use in congenital mitochondrial diseases and chronic disorders such as types 1 and 2 diabetes, cardiovascular disorders, and cancer. In addition, we discuss the relevance of mitochondrial targeted treatments to mental disorders and their potential to become a novel therapeutic strategy that will improve the efficiency of the current treatments.

Isolated Mitochondria Transfer Improves Neuronal Differentiation of Schizophrenia-Derived Induced Pluripotent Stem Cells and Rescues Deficits in a Rat Model of the Disorder

Dysfunction of mitochondria, key players in various essential cell processes, has been repeatedly reported in schizophrenia (SZ). Recently, several studies have reported functional recovery and cellular viability following mitochondrial transplantation, mostly in ischemia experimental models. Here, we aimed to demonstrate beneficial effects of isolated active normal mitochondria (IAN-MIT) transfer in vitro and in vivo, using SZ-derived induced pluripotent stem cells (iPSCs) differentiating into glutamatergic neuron, as well as a rodent model of SZ. First, we show that IAN-MIT enter various cell types without manipulation. Next, we show that IAN-MIT transfer into SZ-derived lymphoblasts induces long-lasting improvement in various mitochondrial functions including cellular oxygen consumption and mitochondrial membrane potential (Δ ψ m). We also demonstrate improved differentiation of SZ-derived iPSCs into neurons, by increased expression of neuronal and glutamatergic markers β3-tubulin, synapsin1, and Tbr1 and by an activation of the glutamate-glutamine cycle. In the animal model, we show that intra-prefrontal cortex injection of IAN-MIT in adolescent rats exposed prenatally to a viral mimic prevents mitochondrial Δ ψ m and attentional deficit at adulthood. Our results provide evidence for a direct link between mitochondrial function and SZ-related deficits both in vitro and in vivo and suggest a therapeutic potential for IAN-MIT transfer in diseases with bioenergetic and neurodevelopmental abnormalities such as SZ.

Mitochondrial Complex I Deficiency in Schizophrenia and Bipolar Disorder and Medication Influence

Subjects with schizophrenia (SZ) and bipolar disorder (BD) show decreased protein and transcript levels for mitochondrial complex I. In vitro results suggest antipsychotic and antidepressant drugs may be responsible. We measured complex I activity in BD, SZ, and controls and presence of antipsychotic and antidepressant medications, mitochondrial DNA (mtDNA) copy number, and the mtDNA "common deletion" in the brain. Complex I activity in the prefrontal cortex was decreased by 45% in SZ compared to controls (p = 0.02), while no significant difference was found in BD. Complex I activity was significantly decreased (p = 0.01) in pooled cases (SZ and BD) that had detectable psychotropic medications and drugs compared to pooled cases with no detectable levels. Subjects with age at onset in their teens and psychotropic medications showed decreased (p < 0.05) complex I activity compared to subjects with an adult age at onset. Both SZ and BD groups displayed significant increases (p < 0.05) in mtDNA copy number compared to controls; however, common deletion burden was not altered. Complex I deficiency is found in SZ brain tissue, and psychotropic medications may play a role in mitochondrial dysfunction. Studies of medication-free first-episode psychosis patients are needed to elucidate whether mitochondrial pathophysiology occurs independent of medication effects.

Chronic Variable Stress Is Responsible for Lipid and DNA Oxidative Disorders and Activation of Oxidative Stress Response Genes in the Brain of Rats

Chronic environmental stress is associated with reactive oxygen species (ROS) overproduction and the pathogenesis of depression. The purpose of this study was to evaluate biochemical and molecular changes associated with ROS generation in the brains of rats submitted to chronic variable stress. Male Wistar rats (50–55 days old, weighing 200–250 g) were divided in two groups (n = 10): control and stressed. Rats in the stressed group were exposed to stress conditions for 40 days. The animals were decapitated and the brain samples were collected. In prefrontal cortex, we measured the following biochemical parameters: lipid peroxidation and concentration of glutathione—GSH, GSSG, GSH/GSSG ratio, glutathione peroxidase, and glutathione reductase activities. In the hippocampus marker of DNA, oxidative damage and expression of DNA-repairing genes (Ogg1, MsrA) and gene-encoding antioxidative transcriptional factor (Nrf2) were determined. The results demonstrate indirect evidence of ROS overproduction and presence of oxidative stress. They also reveal disruption of oxidative defense systems (decreased GR activity, diminished GSH/GSSG ratio, and decreased Nrf2 expression) and activation of the oxidative DNA repair system (increased Ogg1 and MsrA expression). Together, the presented data suggest that independent activation of oxidative stress response genes occurs in chronic variable stress conditions.

Mitochondrial multifaceted dysfunction in schizophrenia; complex I as a possible pathological target

Mitochondria are key players in various essential cellular processes beyond being the main energy supplier of the cell. Accordingly, they are involved in neuronal synaptic transmission, neuronal growth and sprouting and consequently neuronal plasticity and connectivity. In addition, mitochondria participate in the modulation of gene transcription and inflammation as well in physiological responses in health and disease. Schizophrenia is currently regarded as a neurodevelopmental disorder associated with impaired immune system, aberrant neuronal differentiation and abnormalities in various neurotransmitter systems mainly the dopaminergic, glutaminergic and GABAergic. Ample evidence has been accumulated over the last decade indicating a multifaceted dysfunction of mitochondria in schizophrenia. Indeed, mitochondrial deficit can be of relevance for the majority of the pathologies observed in this disease. In the present article, we overview specific deficits of the mitochondria in schizophrenia, with a focus on the first complex (complex I) of the mitochondrial electron transport chain (ETC). We argue that complex I, being a major factor in the regulation of mitochondrial ETC, is a possible key modulator of various functions of the mitochondria. We review biochemical, molecular, cellular and functional evidence for mitochondrial impairments and their possible convergence to impact in-vitro neuronal differentiation efficiency in schizophrenia. Mitochondrial function in schizophrenia may advance our knowledge of the disease pathophysiology and open the road for new treatment targets for the benefit of the patients.

The Role of Nutrients in Protecting Mitochondrial Function and Neurotransmitter Signaling: Implications for the Treatment of Depression, PTSD, and Suicidal Behaviors

Numerous studies have linked severe stress to the development of major depressive disorder (MDD) and suicidal behaviors. Furthermore, recent preclinical studies from our laboratory and others have demonstrated that in rodents, chronic stress and the stress hormone cortisol cause oxidative damage to mitochondrial function and membrane lipids in the brain. Mitochondria play a key role in synaptic neurotransmitter signaling by providing adenosine triphosphate (ATP), mediating lipid and protein synthesis, buffering intracellular calcium, and regulating apoptotic and resilience pathways. Membrane lipids are similarly essential to central nervous system (CNS) function because cholesterol, polyunsaturated fatty acids, and sphingolipids form a lipid raft region, a special lipid region on the membrane that mediates neurotransmitter signaling through G-protein-coupled receptors and ion channels. Low serum cholesterol levels, low antioxidant capacity, and abnormal early morning cortisol levels are biomarkers consistently associated with both depression and suicidal behaviors. In this review, we summarize the manner in which nutrients can protect against oxidative damage to mitochondria and lipids in the neuronal circuits associated with cognitive and affective behaviors. These nutrients include ω3 fatty acids, antioxidants (vitamin C and zinc), members of the vitamin B family (Vitamin B12 and folic acid), and magnesium. Accumulating data have shown that these nutrients can enhance neurocognitive function, and may have therapeutic benefits for depression and suicidal behaviors. A growing body of studies suggests the intriguing possibility that regular consumption of these nutrients may help prevent the onset of mood disorders and suicidal behaviors in vulnerable individuals, or significantly augment the therapeutic effect of available antidepressants. These findings have important implications for the health of both military and civilian populations.

Mitochondrial Oxidative Phosphorylation System (OXPHOS) Deficits in Schizophrenia: Possible Interactions with Cellular Processes

Mitochondria are key players in the generation and regulation of cellular bioenergetics, producing the majority of adenosine triphosphate molecules by the oxidative phosphorylation system (OXPHOS). Linked to numerous signaling pathways and cellular functions, mitochondria, and OXPHOS in particular, are involved in neuronal development, connectivity, plasticity, and differentiation. Impairments in a variety of mitochondrial functions have been described in different general and psychiatric disorders, including schizophrenia (SCZ), a severe, chronic, debilitating illness that heavily affects the lives of patients and their families. This article reviews findings emphasizing the role of OXPHOS in the pathophysiology of SCZ. Evidence accumulated during the past few decades from imaging, transcriptomic, proteomic, and metabolomic studies points at OXPHOS deficit involvement in SCZ. Abnormalities have been reported in high-energy phosphates generated by the OXPHOS, in the activity of its complexes and gene expression, primarily of complex I (CoI). In addition, cellular signaling such as cAMP/protein kinase A (PKA) and Ca(+2), neuronal development, connectivity, and plasticity have been linked to OXPHOS function and are reported to be impaired in SCZ. Finally, CoI has been shown as a site of interaction for both dopamine (DA) and antipsychotic drugs, further substantiating its role in the pathology of SCZ. Understanding the role of mitochondria and the OXPHOS in particular may encourage new insights into the pathophysiology and etiology of this debilitating disorder.

Mitochondrial Dysfunction in Schizophrenia: Determination of Mitochondrial Respiratory Activity in a Two-Hit Mouse Model

Schizophrenia is a chronic mental illness in which mitochondrial dysfunction has been suggested. Our laboratory recently developed a juvenile murine two-hit model (THM) of schizophrenia based on the combination of gestational inflammation, followed by juvenile restraint stress. We previously reported that relevant behaviors and neurochemical disturbances, including oxidative stress, were reversed by the antioxidant lipoic acid (LA), thereby pointing to the central role played by oxidative abnormalities and prompting us to investigate mitochondrial function. Mitochondrial activity was determined with the MitoXpress® commercial kit in two schizophrenia-relevant regions (prefrontal cortex (PFC) and striatum). Measurements were performed in state 3, with substrates for complex I- and complex II-induced respiratory activity (IRA). We observed an increase in complex I IRA in the PFC and striatum in both sexes but an increase in complex II activity only in males. LA treatment prevented this increase only in complex II IRA in males. Expression levels of the different respiratory chain complexes, as well as fission/fusion proteins and protein carbonylation, were unchanged. In conclusion, our juvenile schizophrenia THM shows an increase in mitochondrial activity reversed by LA, specifically in complex II IRA in males. Further investigations are required to determine the mechanisms of these modifications.

Purinergic signaling and energy homeostasis in psychiatric disorders

Purinergic signaling regulates numerous vital biological processes in the central nervous system (CNS). The two principle purines, ATP and adenosine act as excitatory and inhibitory neurotransmitters, respectively. Compared to other classical neurotransmitters, the role of purinergic signaling in psychiatric disorders is not well understood or appreciated. Because ATP exerts its main effect on energy homeostasis, neuronal function of ATP has been underestimated. Similarly, adenosine is primarily appreciated as a precursor of nucleotide synthesis during active cell growth and division. However, recent findings suggest that purinergic signaling may explain how neuronal activity is associated neuronal energy charge and energy homeostasis, especially in mental disorders. In this review, we provide an overview of the synaptic function of mitochondria and purines in neuromodulation, synaptic plasticity, and neuron-glia interactions. We summarize how mitochondrial and purinergic dysfunction contribute to mental illnesses such as schizophrenia, bipolar disorder, autism spectrum disorder (ASD), depression, and addiction. Finally, we discuss future implications regarding the pharmacological targeting of mitochondrial and purinergic function for the treatment of psychiatric disorders.

Evidence of Mitochondrial Dysfunction within the Complex Genetic Etiology of Schizophrenia

Genetic evidence has supported the hypothesis that schizophrenia (SZ) is a polygenic disorder caused by the disruption in function of several or many genes. The most common and reproducible cellular phenotype associated with SZ is a reduction in dendritic spines within the neocortex, suggesting alterations in dendritic architecture may cause aberrant cortical circuitry and SZ symptoms. Here, we review evidence supporting a multifactorial model of mitochondrial dysfunction in SZ etiology and discuss how these multiple paths to mitochondrial dysfunction may contribute to dendritic spine loss and/or underdevelopment in some SZ subjects. The pathophysiological role of mitochondrial dysfunction in SZ is based upon genomic analyses of both the mitochondrial genome and nuclear genes involved in mitochondrial function. Previous studies and preliminary data suggest SZ is associated with specific alleles and haplogroups of the mitochondrial genome, and also correlates with a reduction in mitochondrial copy number and an increase in synonymous and nonsynonymous substitutions of mitochondrial DNA. Mitochondrial dysfunction has also been widely implicated in SZ by genome-wide association, exome sequencing, altered gene expression, proteomics, microscopy analyses, and induced pluripotent stem cell studies. Together, these data support the hypothesis that SZ is a polygenic disorder with an enrichment of mitochondrial targets.

Abnormal high-energy phosphate molecule metabolism during regional brain activation in patients with bipolar disorder

Converging evidence suggests bioenergetic abnormalities in bipolar disorder (BD). In the brain, phosphocreatine (PCr) acts a reservoir of high-energy phosphate (HEP) bonds, and creatine kinases (CK) catalyze the transfer of HEP from adenosine triphosphate (ATP) to PCr and from PCr back to ATP, at times of increased need. This study examined the activity of this mechanism in BD by measuring the levels of HEP molecules during a stimulus paradigm that increased local energy demand. Twenty-three patients diagnosed with BD-I and 22 healthy controls (HC) were included. Levels of phosphorus metabolites were measured at baseline and during visual stimulation in the occipital lobe using (31)P magnetic resonance spectroscopy at 4T. Changes in metabolite levels showed different patterns between the groups. During stimulation, HC had significant reductions in PCr but not in ATP, as expected. In contrast, BD patients had significant reductions in ATP but not in PCr. In addition, PCr/ATP ratio was lower at baseline in patients, and there was a higher change in this measure during stimulation. This pattern suggests a disease-related failure to replenish ATP from PCr through CK enzyme catalysis during tissue activation. Further studies measuring the CK flux in BD are required to confirm and extend this finding.

Maternal deprivation disrupts mitochondrial energy homeostasis in the brain of rats subjected to ketamine-induced schizophrenia

Maternal deprivation (MD) appears to be one of the environmental factors involved in the pathophysiology of schizophrenia. A widely used animal model of the schizophrenia involves the administration of ketamine, a dissociative anesthetic, NMDA receptors noncompetitive antagonist, that induce symptoms such as schizophrenia. To clarify the molecular mechanism of schizophrenia induced by MD, we investigated alterations in energetic metabolism, oxidative stress and neurotrophic factor levels in the brain of rats following MD and/or a single administration of ketamine during adulthood. Male Wistar rats were subjected to MD for 10 days. Additionally, these animals received acute ketamine (5, 15 or 25 mg/kg by intraperitoneal route, i.p.) during adulthood, and 30 min later, they were killed and the prefrontal cortex (PFC), the hippocampus and the striatum were removed for molecular analyses. Ketamine 25 mg/kg and/or MD and Ketamine 15 and 5 mg/kg with MD decreased the creatine kinase (CK) activity in the hippocampus. The enzyme activity of succinate dehydrogenase (SDH) in the Krebs cycle had increased in the striatum following the administration of ketamine 25 mg/kg, MD per se or MD plus ketamine 5 and 15 mg/kg. MD per se or MD combined with ketamine in different doses increased the activity of mitochondrial complexes. The PFC of animals subjected to MD and administered with ketamine 5 mg/kg exhibited increased protein carbonyl content. In the hippocampus, ketamine 15 mg/kg, ketamine 25 mg/kg and MD each increased the carbonyl content. In the striatum, the TBARS levels were increased by the administration of ketamine 25 mg/kg. Finally, in the hippocampus, MD alone or in combination with ketamine reduced the Nerve Growth Factor (NGF) levels; however, the Brain-derived Neurotrophic Factor (BDNF) levels were unaltered. In the present study, we suggest that MD increased the risk of psychotic symptoms in adulthood, altering different parameters of energy and oxidative stress. Our results suggest that adverse experiences occurring early in life may sensitize specific neurocircuits to subsequent stressors, inducing vulnerability, and may help us understand the pathophysiological mechanisms involved in this disorder.

The proteome of schizophrenia

On observing schizophrenia from a clinical point of view up to its molecular basis, one may conclude that this is likely to be one of the most complex human disorders to be characterized in all aspects. Such complexity is the reflex of an intricate combination of genetic and environmental components that influence brain functions since pre-natal neurodevelopment, passing by brain maturation, up to the onset of disease and disease establishment. The perfect function of tissues, organs, systems, and finally the organism depends heavily on the proper functioning of cells. Several lines of evidence, including genetics, genomics, transcriptomics, neuropathology, and pharmacology, have supported the idea that dysfunctional cells are causative to schizophrenia. Together with the above-mentioned techniques, proteomics have been contributing to understanding the biochemical basis of schizophrenia at the cellular and tissue level through the identification of differentially expressed proteins and consequently their biochemical pathways, mostly in the brain tissue but also in other cells. In addition, mass spectrometry-based proteomics have identified and precisely quantified proteins that may serve as biomarker candidates to prognosis, diagnosis, and medication monitoring in peripheral tissue. Here, we review all data produced by proteomic investigation in the last 5 years using tissue and/or cells from schizophrenic patients, focusing on postmortem brain tissue and peripheral blood serum and plasma. This information has provided integrated pictures of the biochemical systems involved in the pathobiology, and has suggested potential biomarkers, and warrant potential targets to alternative treatment therapies to schizophrenia.

Mitochondrial dysfunction in schizophrenia: an evolutionary perspective

Schizophrenia (SCZ) is a severe psychiatric illness with a lifetime prevalence of 0.4 %. A disturbance of energy metabolism has been suggested as part of the etiopathogenesis of the disorder. Several lines of evidence have proposed a connection between etiopathogenesis of SCZ and human brain evolution, which was characterized by an increase in the energy requirement, demanding a co-evolution of the mitochondrial system. Mitochondria are key players in brain energy homeostasis and multiple lines of evidence suggest that the system is disrupted in SCZ. In this review, we will describe the current knowledge on pathways/system involved in the human brain evolution as well as the main theories regarding the evolutionary origin of SCZ. We will furthermore discuss the role of mitochondria in the context of brain energy metabolism and its role in the etiopathogenesis of SCZ. Understanding SCZ in the context of human brain evolution opens a new perspective to elucidate pathophysiological mechanisms involved in the origin and/or portions of the complex symptomatology of this severe mental disorder.

Abnormal neuronal differentiation and mitochondrial dysfunction in hair follicle-derived induced pluripotent stem cells of schizophrenia patients

One of the prevailing hypotheses suggests schizophrenia as a neurodevelopmental disorder, involving dysfunction of dopaminergic and glutamatergic systems. Accumulating evidence suggests mitochondria as an additional pathological factor in schizophrenia. An attractive model to study processes related to neurodevelopment in schizophrenia is reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) and differentiating them into different neuronal lineages. iPSCs from three schizophrenia patients and from two controls were reprogrammed from hair follicle keratinocytes, because of their accessibility and common ectodermal origin with neurons. iPSCs were differentiated into Pax6(+)/Nestin(+) neural precursors and then further differentiated into β3-Tubulin(+)/tyrosine hydroxylase(+)/DAT(+) dopaminergic neurons. In addition, iPSCs were differentiated through embryonic bodies into β3-Tubulin(+)/Tbox brain1(+) glutamatergic neurons. Schizophrenia-derived dopaminergic cells showed severely impaired ability to differentiate, whereas glutamatergic cells were unable to maturate. Mitochondrial respiration and its sensitivity to dopamine-induced inhibition were impaired in schizophrenia-derived keratinocytes and iPSCs. Moreover, we observed dissipation of mitochondrial membrane potential (Δψm) and perturbations in mitochondrial network structure and connectivity in dopaminergic along the differentiation process and in glutamatergic cells. Our data unravel perturbations in neural differentiation and mitochondrial function, which may be interconnected, and of relevance to dysfunctional neurodevelopmental processes in schizophrenia.

Comment on "Impaired respiratory and body temperature control upon acute serotonergic neuron inhibition"

Ray et al. (Reports, 29 July 2011, p. 637) assume that clozapine-N4-oxide (CNO) represents a "biologically inert synthetic ligand" that selectively activates the M4 muscarinic receptor-based DREADD (designer receptor exclusively activated by a designer drug). In contrast, due to the redox cycling of CNO with clozapine and to their cell membrane permeability, CNO is biologically active and its conversion products are capable of undermining DREADD effects.

Molecular links between mitochondrial dysfunctions and schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with both neurochemical and neurodevelopmental components in the pathogenesis. Growing pieces of evidence indicate that schizophrenia has pathological components that can be attributable to the abnormalities of mitochondrial function, which is supported by the recent finding suggesting mitochondrial roles for Disrupted-in-Schizophrenia 1 (DISC1). In this minireview, we briefly summarize the current understanding of the molecular links between mitochondrial dysfunctions and the pathogenesis of schizophrenia, covering recent findings from human genetics, functional genomics, proteomics, and molecular and cell biological approaches.

Intrinsic bioenergetic properties and stress sensitivity of dopaminergic synaptosomes

Dopaminergic neurons of the substantia nigra pars compacta are defective in Parkinson's disease, but the specificity of this dysfunction is not understood. One hypothesis is that mitochondrial bioenergetic capacity is intrinsically lower in striatal dopaminergic presynaptic nerve varicosities, making them unusually susceptible to inhibition of electron transport by oxidative damage. To test this hypothesis, we separated isolated synaptosomes bearing dopamine transporters using immunomagnetic beads and compared their respiration with that of the residual nondopaminergic synaptosomes. As predicted, dopaminergic synaptosomes from striatum had lower respiratory rates. However, so did dopaminergic synaptosomes from cortex, indicating a lack of the predicted striatal specificity. We used fluorescent probes to analyze the bioenergetic competence of individual synaptosomes in the two fractions. The respiratory differences became nonsignificant when respiration rates were normalized to the number of respiration-competent synaptosomes, suggesting that differences reflected the quality of the different fractions. To circumvent damage induced by synaptosomal separation, we monitored membrane potentials in whole unseparated single synaptosomes using fluorescent imaging, and then identified the dopaminergic subpopulation using a fluorescent dopamine transporter substrate (ASP(+) [4-(4-diethylaminostyryl)-N-methylpyridinium iodide]). The capacity of dopaminergic and nondopaminergic synaptosomes to maintain plasma membrane and mitochondrial membrane potential under several stresses did not differ. In addition, this capacity did not decline in either subpopulation with age, a risk factor for Parkinson's disease. We conclude that the intrinsic bioenergetic capacities of dopaminergic and nondopaminergic presynaptic synaptosomes from mice do not differ.

Perturbation in mitochondrial network dynamics and in complex I dependent cellular respiration in schizophrenia

BACKGROUND

Mitochondria have been suggested to be involved in the pathology of bipolar disorder (BD) and schizophrenia. However, the mechanism underlying mitochondrial dysfunction is unclear. Mitochondrial network dynamics, which reflects cellular metabolic state, is important for embryonic development, synapse formation, and neurodegeneration. This study aimed to investigate mitochondrial network dynamics and its plausible association with abnormal cellular oxygen consumption in schizophrenia.

METHODS

Viable Epstein-Barr virus (EBV)-transformed lymphocytes (lymphoblastoids) from DSM-IV diagnosed patients with schizophrenia (n = 17), BD (n = 15), and healthy control subjects (n = 15) were assessed for mitochondrial respiration, mitochondrial dynamics, and relevant protein levels by oxygraph, confocal microscopy, and immunoblotting, respectively.

RESULTS

Respiration of schizophrenia-derived lymphoblastoids was significantly lower compared with control subjects, and was twice as sensitive to dopamine (DA)-induced inhibition. Unlike DA, haloperidol inhibited complex I-driven respiration to a similar extent in both schizophrenia and the control cells. Both drugs interact with complex I but at different sites. At the site of DA interaction, we found alterations in protein levels of three subunits of complex I in schizophrenia. In addition, we observed structural and connectivity perturbations in the mitochondrial network, associated with alterations in the profusion protein OPA1, which was similarly reduced in schizophrenia prefrontal cortex specimens. None of these alterations were observed in the BD cells, which were similar to control cells.

CONCLUSIONS

We show impaired mitochondrial network dynamics associated with reduced cellular respiration and complex I abnormalities in schizophrenia but not in BD. If these findings represent disease-specific alterations, they may become an endophenotype biomarker for schizophrenia.

Region-specific expression of mitochondrial complex I genes during murine brain development

Mutations in the nuclear encoded subunits of mitochondrial complex I (NADH:ubiquinone oxidoreductase) may cause circumscribed cerebral lesions ranging from degeneration of the striatal and brainstem gray matter (Leigh syndrome) to leukodystrophy. We hypothesized that such pattern of regional pathology might be due to local differences in the dependence on complex I function. Using in situ hybridization we investigated the relative expression of 33 nuclear encoded complex I subunits in different brain regions of the mouse at E11.5, E17.5, P1, P11, P28 and adult (12 weeks). With respect to timing and relative intensity of complex I gene expression we found a highly variant pattern in different regions during development. High average expression levels were detected in periods of intense neurogenesis. In cerebellar Purkinje and in hippocampal CA1/CA3 pyramidal neurons we found a second even higher peak during the period of synaptogenesis and maturation. The extraordinary dependence of these structures on complex I gene expression during synaptogenesis is in accord with our recent findings that gamma oscillations – known to be associated with higher cognitive functions of the mammalian brain – strongly depend on the complex I activity. However, with the exception of the mesencephalon, we detected only average complex I expression levels in the striatum and basal ganglia, which does not explain the exquisite vulnerability of these structures in mitochondrial disorders.

Mitochondrial dynamics, cell death and the pathogenesis of Parkinson's disease

The structure and function of the mitochondrial network is regulated by mitochondrial biogenesis, fission, fusion, transport and degradation. A well-maintained balance of these processes (mitochondrial dynamics) is essential for neuronal signaling, plasticity and transmitter release. Core proteins of the mitochondrial dynamics machinery play important roles in the regulation of apoptosis, and mutations or abnormal expression of these factors are associated with inherited and age-dependent neurodegenerative disorders. In Parkinson's disease (PD), oxidative stress and mitochondrial dysfunction underlie the development of neuropathology. The recessive Parkinsonism-linked genes PTEN-induced kinase 1 (PINK1) and Parkin maintain mitochondrial integrity by regulating diverse aspects of mitochondrial function, including membrane potential, calcium homeostasis, cristae structure, respiratory activity, and mtDNA integrity. In addition, Parkin is crucial for autophagy-dependent clearance of dysfunctional mitochondria. In the absence of PINK1 or Parkin, cells often develop fragmented mitochondria. Whereas excessive fission may cause apoptosis, coordinated induction of fission and autophagy is believed to facilitate the removal of damaged mitochondria through mitophagy, and has been observed in some types of cells. Compensatory mechanisms may also occur in mice lacking PINK1 that, in contrast to cells and Drosophila, have only mild mitochondrial dysfunction and lack dopaminergic neuron loss. A better understanding of the relationship between the specific changes in mitochondrial dynamics/turnover and cell death will be instrumental to identify potentially neuroprotective pathways steering PINK1-deficient cells towards survival. Such pathways may be manipulated in the future by specific drugs to treat PD and perhaps other neurodegenerative disorders characterized by abnormal mitochondrial function and dynamics.

Mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is a progressive, neurodegenerative condition that has increasingly been linked with mitochondrial dysfunction and inhibition of the electron transport chain. This inhibition leads to the generation of reactive oxygen species and depletion of cellular energy levels, which can consequently cause cellular damage and death mediated by oxidative stress and excitotoxicity. A number of genes that have been shown to have links with inherited forms of PD encode mitochondrial proteins or proteins implicated in mitochondrial dysfunction, supporting the central involvement of mitochondria in PD. This involvement is corroborated by reports that environmental toxins that inhibit the mitochondrial respiratory chain have been shown to be associated with PD. This paper aims to illustrate the considerable body of evidence linking mitochondrial dysfunction with neuronal cell death in the substantia nigra pars compacta (SNpc) of PD patients and to highlight the important need for further research in this area.

Mitochondrial dysfunction and pathology in bipolar disorder and schizophrenia

Bipolar disorder (BPD) and schizophrenia (SZ) are severe psychiatric illnesses with a combined prevalence of 4%. A disturbance of energy metabolism is frequently observed in these disorders. Several pieces of evidence point to an underlying dysfunction of mitochondria: (i) decreased mitochondrial respiration; (ii) changes in mitochondrial morphology; (iii) increases in mitochondrial DNA (mtDNA) polymorphisms and in levels of mtDNA mutations; (iv) downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration; (v) decreased high-energy phosphates and decreased pH in the brain; and (vi) psychotic and affective symptoms, and cognitive decline in mitochondrial disorders. Furthermore, transgenic mice with mutated mitochondrial DNA polymerase show mood disorder-like phenotypes. In this review, we will discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BPD and SZ. We will furthermore describe the role of mitochondria during brain development and the effect of current drugs for mental illness on mitochondrial function. Understanding the role of mitochondria, both developmentally as well as in the ailing brain, is of critical importance to elucidate pathophysiological mechanisms in psychiatric disorders.

Methylenedioxymethamphetamine inhibits mitochondrial complex I activity in mice: a possible mechanism underlying neurotoxicity

BACKGROUND AND PURPOSE

3,4-methylenedioxymethamphetamine (MDMA) causes a persistent loss of dopaminergic cell bodies in the substantia nigra of mice. Current evidence indicates that such neurotoxicity is due to oxidative stress but the source of free radicals remains unknown. Inhibition of mitochondrial electron transport chain complexes by MDMA was assessed as a possible source.

EXPERIMENTAL APPROACH

Activities of mitochondrial complexes after MDMA were evaluated spectrophotometrically. In situ visualization of superoxide production in the striatum was assessed by ethidium fluorescence and striatal dopamine levels were determined by HPLC as an index of dopaminergic toxicity.

KEY RESULTS

3,4-methylenedioxymethamphetamine decreased mitochondrial complex I activity in the striatum of mice, an effect accompanied by an increased production of superoxide radicals and the inhibition of endogenous aconitase. alpha-Lipoic acid prevented superoxide generation and long-term toxicity independent of any effect on complex I inhibition. These effects of alpha-lipoic acid were also associated with a significant increase of striatal glutathione levels. The relevance of glutathione was supported by reducing striatal glutathione content with L-buthionine-(S,R)-sulfoximine, which exacerbated MDMA-induced dopamine deficits, effects suppressed by alpha-lipoic acid. The nitric oxide synthase inhibitor, N(G)-nitro-L-arginine, partially prevented MDMA-induced dopamine depletions, an effect reversed by L-arginine but not D-arginine. Finally, a direct relationship between mitochondrial complex I inhibition and long-term dopamine depletions was found in animals treated with MDMA in combination with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

CONCLUSIONS AND IMPLICATIONS

Inhibition of mitochondrial complex I following MDMA could be the source of free radicals responsible for oxidative stress and the consequent neurotoxicity of this drug in mice.

The interplay between mitochondrial complex I, dopamine and Sp1 in schizophrenia

Schizophrenia is currently believed to result from variations in multiple genes, each contributing a subtle effect, which combines with each other and with environmental stimuli to impact both early and late brain development. At present, schizophrenia clinical heterogeneity as well as the difficulties in relating cognitive, emotional and behavioral functions to brain substrates hinders the identification of a disease-specific anatomical, physiological, molecular or genetic abnormality. Mitochondria play a pivotal role in many essential processes, such as energy production, intracellular calcium buffering, transmission of neurotransmitters, apoptosis and ROS production, all either leading to cell death or playing a role in synaptic plasticity. These processes have been well established as underlying altered neuronal activity and thereby abnormal neuronal circuitry and plasticity, ultimately affecting behavioral outcomes. The present article reviews evidence supporting a dysfunction of mitochondria in schizophrenia, including mitochondrial hypoplasia, impairments in the oxidative phosphorylation system (OXPHOS) as well as altered mitochondrial-related gene expression. Abnormalities in mitochondrial complex I, which plays a major role in controlling OXPHOS activity, are discussed. Among them are schizophrenia specific as well as disease-state-specific alterations in complex I activity in the peripheral tissue, which can be modulated by DA. In addition, CNS and peripheral abnormalities in the expression of three of complex I subunits, associated with parallel alterations in their transcription factor, specificity protein 1 (Sp1) are reviewed. Finally, this review discusses the question of disease specificity of mitochondrial pathologies and suggests that mitochondria dysfunction could cause or arise from anomalities in processes involved in brain connectivity.