Time dependent expression of the blood biomarkers EIF2D and TOX in patients with schizophrenia.

BACKGROUND: During last years, there has been an intensive search for blood biomarkers in schizophrenia to assist in diagnosis, prognosis and clinical management of the disease. METHODS: In this study, we first conducted a weighted gene coexpression network analysis to address differentially expressed genes in peripheral blood from patients with chronic schizophrenia (n = 30) and healthy controls (n = 15). The discriminating performance of the candidate genes was further tested in an independent cohort of patients with first-episode schizophrenia (n = 124) and healthy controls (n = 54), and in postmortem brain samples (cingulate and prefrontal cortices) from patients with schizophrenia (n = 34) and healthy controls (n = 35). RESULTS: The expression of the Eukaryotic Translation Initiation Factor 2D (EIF2D) gene, which is involved in protein synthesis regulation, was increased in the chronic patients of schizophrenia. On the contrary, the expression of the Thymocyte Selection-Associated High Mobility Group Box (TOX) gene, involved in immune function, was reduced. EIF2D expression was also altered in first-episode schizophrenia patients, but showing reduced levels. Any of the postmortem brain areas studied did not show differences of expression of both genes. CONCLUSIONS: EIF2D and TOX are putative blood markers of chronic patients of schizophrenia, which expression change from the onset to the chronic disease, unraveling new biological pathways that can be used for the development of new intervention strategies in the diagnosis and prognosis of schizophrenia disease.

Drosophila melanogaster Models of Metal-Related Human Diseases and Metal Toxicity.

Iron, copper and zinc are transition metals essential for life because they are required in a multitude of biological processes. Organisms have evolved to acquire metals from nutrition and to maintain adequate levels of each metal to avoid damaging effects associated with its deficiency, excess or misplacement. Interestingly, the main components of metal homeostatic pathways are conserved, with many orthologues of the human metal-related genes having been identified and characterized in Drosophila melanogaster. Drosophila has gained appreciation as a useful model for studying human diseases, including those caused by mutations in pathways controlling cellular metal homeostasis. Flies have many advantages in the laboratory, such as a short life cycle, easy handling and inexpensive maintenance. Furthermore, they can be raised in a large number. In addition, flies are greatly appreciated because they offer a considerable number of genetic tools to address some of the unresolved questions concerning disease pathology, which in turn could contribute to our understanding of the metal metabolism and homeostasis. This review recapitulates the metabolism of the principal transition metals, namely iron, zinc and copper, in Drosophila and the utility of this organism as an experimental model to explore the role of metal dyshomeostasis in different human diseases. Finally, a summary of the contribution of Drosophila as a model for testing metal toxicity is provided.

Accelerated Cortical Thinning in Schizophrenia Is Associated With Rare and Common Predisposing Variation to Schizophrenia and Neurodevelopmental Disorders.

BACKGROUND: Schizophrenia is a highly heritable disorder characterized by increased cortical thinning throughout the life span. Studies have reported a shared genetic basis between schizophrenia and cortical thickness. However, no genes whose expression is related to abnormal cortical thinning in schizophrenia have been identified. METHODS: We conducted linear mixed models to estimate the rates of accelerated cortical thinning across 68 regions from the Desikan-Killiany atlas in individuals with schizophrenia compared with healthy control participants from a large longitudinal sample (ncases = 169 and ncontrols = 298, ages 16-70 years). We studied the correlation between gene expression data from the Allen Human Brain Atlas and accelerated thinning estimates across cortical regions. Finally, we explored the functional and genetic underpinnings of the genes that contribute most to accelerated thinning. RESULTS: We found a global pattern of accelerated cortical thinning in individuals with schizophrenia compared with healthy control participants. Genes underexpressed in cortical regions that exhibit this accelerated thinning were downregulated in several psychiatric disorders and were enriched for both common and rare disrupting variation for schizophrenia and neurodevelopmental disorders. In contrast, none of these enrichments were observed for baseline cross-sectional cortical thickness differences. CONCLUSIONS: Our findings suggest that accelerated cortical thinning, rather than cortical thickness alone, serves as an informative phenotype for neurodevelopmental disruptions in schizophrenia. We highlight the genetic and transcriptomic correlates of this accelerated cortical thinning, emphasizing the need for future longitudinal studies to elucidate the role of genetic variation and the temporal-spatial dynamics of gene expression in brain development and aging in schizophrenia.

A "double hit" murine model for schizophrenia shows alterations in the structure and neurochemistry of the medial prefrontal cortex and the hippocampus.

Both alterations in neurodevelopment and aversive experiences during childhood and adolescence seem important risk factors for schizophrenia. Animal models reproducing these alterations mimic some of the symptoms, constituting a valid approach to study the etiopathology of this disorder. Among these models, the perinatal injection of N-methyl-d-aspartate receptor antagonists and the postweaning social isolation rearing are among the most widely used. Our aim is to combine them in a "double hit" model, which should produce a wider spectrum of alterations. Lister Hooded rats have been subjected to a single injection of MK-801 at postnatal day 7 and socially isolated from postweaning to adulthood. These animals presented increased body weight gain and volume reductions in their medial prefrontal cortex (mPFC) and hippocampus. They also showed an increased number of activated pyramidal neurons and alterations in the numbers of parvalbumin and calbindin expressing interneurons in the mPFC. The expressions of the polysialylated form of the neural cell adhesion molecule and GAD67 are decreased in the mPFC. The mRNA level of calbindin was decreased, while that of calretinin was increased in the mPFC. The mRNA level of ERbB4, a gene associated to schizophrenia, was also altered in this region. All these structural and neurochemical alterations, specially in cortical inhibitory circuits, are similar to those found in schizophrenic patients and are more numerous than in each of the single models. Consequently, the present "double hit" model may be a better tool to study the neurobiological basis of schizophrenia and to explore new therapeutic approaches.

Common genetic variants contribute to heritability of age at onset of schizophrenia.

Schizophrenia (SCZ) is a complex disorder that typically arises in late adolescence or early adulthood. Age at onset (AAO) of SCZ is associated with long-term outcomes of the disease. We explored the genetic architecture of AAO with a genome-wide association study (GWAS), heritability, polygenic risk score (PRS), and copy number variant (CNV) analyses in 4 740 subjects of European ancestry. Although no genome-wide significant locus was identified, SNP-based heritability of AAO was estimated to be between 17 and 21%, indicating a moderate contribution of common variants. We also performed cross-trait PRS analyses with a set of mental disorders and identified a negative association between AAO and common variants for SCZ, childhood maltreatment and attention-deficit/hyperactivity disorder. We also investigated the role of copy number variants (CNVs) in AAO and found an association with the length and number of deletions (P-value = 0.03), whereas the presence of CNVs previously reported in SCZ was not associated with earlier onset. To our knowledge, this is the largest GWAS of AAO of SCZ to date in individuals from European ancestry, and the first study to determine the involvement of common variants in the heritability of AAO. Finally, we evidenced the role played by higher SCZ load in determining AAO but discarded the role of pathogenic CNVs. Altogether, these results shed light on the genetic architecture of AAO, which needs to be confirmed with larger studies.

Recent natural selection conferred protection against schizophrenia by non-antagonistic pleiotropy.

Schizophrenia is a debilitating psychiatric disorder associated with a reduced fertility and decreased life expectancy, yet common predisposing variation substantially contributes to the onset of the disorder, which poses an evolutionary paradox. Previous research has suggested balanced selection, a mechanism by which schizophrenia risk alleles could also provide advantages under certain environments, as a reliable explanation. However, recent studies have shown strong evidence against a positive selection of predisposing loci. Furthermore, evolutionary pressures on schizophrenia risk alleles could have changed throughout human history as new environments emerged. Here in this study, we used 1000 Genomes Project data to explore the relationship between schizophrenia predisposing loci and recent natural selection (RNS) signatures after the human diaspora out of Africa around 100,000 years ago on a genome-wide scale. We found evidence for significant enrichment of RNS markers in derived alleles arisen during human evolution conferring protection to schizophrenia. Moreover, both partitioned heritability and gene set enrichment analyses of mapped genes from schizophrenia predisposing loci subject to RNS revealed a lower involvement in brain and neuronal related functions compared to those not subject to RNS. Taken together, our results suggest non-antagonistic pleiotropy as a likely mechanism behind RNS that could explain the persistence of schizophrenia common predisposing variation in human populations due to its association to other non-psychiatric phenotypes.

Polygenic contribution to the relationship of loneliness and social isolation with schizophrenia.

Previous research suggests an association of loneliness and social isolation (LNL-ISO) with schizophrenia. Here, we demonstrate a LNL-ISO polygenic score contribution to schizophrenia risk in an independent case-control sample (N = 3,488). We then subset schizophrenia predisposing variation based on its effect on LNL-ISO. We find that genetic variation with concordant effects in both phenotypes shows significant SNP-based heritability enrichment, higher polygenic contribution in females, and positive covariance with mental disorders such as depression, anxiety, attention-deficit hyperactivity disorder, alcohol dependence, and autism. Conversely, genetic variation with discordant effects only contributes to schizophrenia risk in males and is negatively correlated with those disorders. Mendelian randomization analyses demonstrate a plausible bi-directional causal relationship between LNL-ISO and schizophrenia, with a greater effect of LNL-ISO liability on schizophrenia than vice versa. These results illustrate the genetic footprint of LNL-ISO on schizophrenia.

FOXP2 expression and gray matter density in the male brains of patients with schizophrenia.

Common genetic variants of FOXP2 may contribute to schizophrenia vulnerability, but controversial results have been reported for this proposal. Here we evaluated the potential impact of the common FOXP2 rs2396753 polymorphism in schizophrenia. It was previously reported to be part of a risk haplotype for this disease and to have significant effects on gray matter concentration in the patients. We undertook the first examination into whether rs2396753 affects the brain expression of FOXP2 and a replication study of earlier neuroimaging findings of the influence of this genetic variant on brain structure. FOXP2 expression levels were measured in postmortem prefrontal cortex samples of 84 male subjects (48 patients and 36 controls) from the CIBERSAM Brain and the Stanley Foundation Array Collections. High-resolution anatomical magnetic resonance imaging was performed on 79 male subjects (61 patients, 18 controls) using optimized voxel-based morphometry. We found differences in FOXP2 expression and brain morphometry depending on the rs2396753, relating low FOXP2 mRNA levels with reduction of gray matter density. We detected an interaction between rs2396753 and the clinical groups, showing that heterozygous patients for this polymorphism have gray matter density decrease and low FOXP2 expression comparing with the heterozygous controls. This study shows the importance of independent replication of neuroimaging genetic studies of FOXP2 as a candidate gene in schizophrenia. Furthermore, our results suggest that the FOXP2 rs2396753 affects mRNA levels, thus providing new knowledge about its significance as a potential susceptibility polymorphism in schizophrenia.

Antioxidant Therapies and Oxidative Stress in Friedreich´s Ataxia: The Right Path or Just a Diversion?

Friedreich´s ataxia is the commonest autosomal recessive ataxia among population of European descent. Despite the huge advances performed in the last decades, a cure still remains elusive. One of the most studied hallmarks of the disease is the increased production of oxidative stress markers in patients and models. This feature has been the motivation to develop treatments that aim to counteract such boost of free radicals and to enhance the production of antioxidant defenses. In this work, we present and critically review those "antioxidant" drugs that went beyond the disease´s models and were approved for its application in clinical trials. The evaluation of these trials highlights some crucial aspects of the FRDA research. On the one hand, the analysis contributes to elucidate whether oxidative stress plays a central role or whether it is only an epiphenomenon. On the other hand, it comments on some limitations in the current trials that complicate the analysis and interpretation of their outcome. We also include some suggestions that will be interesting to implement in future studies and clinical trials.

Friedreich ataxia: an update on animal models, frataxin function and therapies.

Friedreich ataxia (FRDA) is an autosomal recessive progressively debilitating degenerative disease that principally affects the nervous system and the heart. Although FRDA is considered a rare disease, is the most common inherited ataxia. It is caused by loss-of-function mutations in the FXN gene, mainly an expanded GAA triplet repeat in the intron 1. The genetic defect results in the reduction of frataxin levels, a protein targeted to the mitochondria. Frataxin deficiency leads to mitochondrial dysfunction, oxidative damage and iron accumulation. Studies of the yeast and animal models of the disease have led to propose several different roles for frataxin. Animal models have also been important for dissecting the steps of pathogenesis in FRDA and they are essential for the development of effective therapies. Currently, antioxidant and iron chelation therapies are under evaluation in clinical trials. Gene reactivation, gene therapy and protein replacement strategies for FRDA are promising approaches. This review focuses on the current models developed for FRDA, the different roles proposed for frataxin and the progress of potential treatment strategies for the disease.

Recent adaptive selection at MAOB and ancestral susceptibility to schizophrenia.

The ancestral susceptibility hypothesis has been proposed to explain the existence of susceptibility alleles to common diseases. Some ancestral alleles, reflecting ancient adaptations, may be poorly adapted to the more contemporary environmental conditions giving rise to an increased risk to suffer some common disorders. In order to test this hypothesis in schizophrenia, we focused on the monoamine oxidase B gene (MAOB). This gene is involved in deamination of several monoamines, including both xenobiotic amines present in several foods, as well as neurotransmitters such as dopamine. In addition, preliminary analysis based on phase I HapMap data suggested that recent natural selection has acted on this locus. We further explored the existence of this recent positive selection using a test based on extension of linkage disequilibrium (LD) to large distance at the specific selected haplotype taking data from HapMap phase II, and searched for association of the ancestral haplotypes with schizophrenia in a sample of 532 schizophrenic patients and 597 controls from Spain. Our analysis suggested the existence of a haplotype of MAOB subject to recent selection. In agreement with the ancestral susceptibility hypothesis, the ancestral haplotypes were significantly over-represented in patients (P = 0.047). These haplotypes conferred an increased risk to schizophrenia, restricted to males (P = 0.024, OR = 1.41, 95% CI 1.01-1.90). Thus, pending on replication studies, MAOB seems to fit the ancestral susceptibility model, validating a new strategy to search for common schizophrenia susceptibility genes by focusing in those functional candidate genes subject to recent positive selection.

The Role of Iron in Friedreich's Ataxia: Insights From Studies in Human Tissues and Cellular and Animal Models.

Friedreich's ataxia (FRDA) is a rare early-onset degenerative disease that affects both the central and peripheral nervous systems, and other extraneural tissues, mainly the heart and endocrine pancreas. This disorder progresses as a mixed sensory and cerebellar ataxia, primarily disturbing the proprioceptive pathways in the spinal cord, peripheral nerves and nuclei of the cerebellum. FRDA is an inherited disease with an autosomal recessive pattern caused by an insufficient amount of the nuclear-encoded mitochondrial protein frataxin, which is an essential and highly evolutionary conserved protein whose deficit results in iron metabolism dysregulation and mitochondrial dysfunction. The first experimental evidence connecting frataxin with iron homeostasis came from Saccharomyces cerevisiae; iron accumulates in the mitochondria of yeast with deletion of the frataxin ortholog gene. This finding was soon linked to previous observations of iron deposits in the hearts of FRDA patients and was later reported in animal models of the disease. Despite advances made in the understanding of FRDA pathophysiology, the role of iron in this disease has not yet been completely clarified. Some of the questions still unresolved include the molecular mechanisms responsible for the iron accumulation and iron-mediated toxicity. Here, we review the contribution of the cellular and animal models of FRDA and relevance of the studies using FRDA patient samples to gain knowledge about these issues. Mechanisms of mitochondrial iron overload are discussed considering the potential roles of frataxin in the major mitochondrial metabolic pathways that use iron. We also analyzed the effect of iron toxicity on neuronal degeneration in FRDA by reactive oxygen species (ROS)-dependent and ROS-independent mechanisms. Finally, therapeutic strategies based on the control of iron toxicity are considered.

Phosphodiesterase Inhibitors Revert Axonal Dystrophy in Friedreich's Ataxia Mouse Model.

Friedreich's ataxia (FRDA) is a neurodegenerative disorder caused by an unstable GAA repeat expansion within intron 1 of the FXN gene and characterized by peripheral neuropathy. A major feature of FRDA is frataxin deficiency with the loss of large sensory neurons of the dorsal root ganglia (DRG), namely proprioceptive neurons, undergoing dying-back neurodegeneration with progression to posterior columns of the spinal cord and cerebellar ataxia. We used isolated DRGs from a YG8R FRDA mouse model and C57BL/6J control mice for a proteomic study and a primary culture of sensory neurons from DRG to test novel pharmacological strategies. We found a decreased expression of electron transport chain (ETC) proteins, the oxidative phosphorylation (OXPHOS) system and antioxidant enzymes, confirming a clear impairment in mitochondrial function and an oxidative stress-prone phenotype. The proteomic profile also showed a decreased expression in Ca2+ signaling related proteins and G protein-coupled receptors (GPCRs). These receptors modulate intracellular cAMP/cGMP and Ca2+ levels. Treatment of frataxin-deficient sensory neurons with phosphodiesterase (PDE) inhibitors was able to restore improper cytosolic Ca2+ levels and revert the axonal dystrophy found in DRG neurons of YG8R mice. In conclusion, the present study shows the effectiveness of PDE inhibitors against axonal degeneration of sensory neurons in YG8R mice. Our findings indicate that PDE inhibitors may become a future FRDA pharmacological treatment.

Identification of potential therapeutic compounds for Parkinson's disease using Drosophila and human cell models.

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. It is caused by a loss of dopaminergic neurons in the substantia nigra pars compacta, leading to a decrease in dopamine levels in the striatum and thus producing movement impairment. Major physiological causes of neurodegeneration in PD are oxidative stress (OS) and mitochondrial dysfunction; these pathophysiological changes can be caused by both genetic and environmental factors. Although most PD cases are sporadic, it has been shown that 5-10% of them are familial forms caused by mutations in certain genes. One of these genes is the DJ-1 oncogene, which is involved in an early-onset recessive PD form. Currently, PD is an incurable disease for which existing therapies are not sufficiently effective to counteract or delay the progression of the disease. Therefore, the discovery of alternative drugs for the treatment of PD is essential. In this study we used a Drosophila PD model to identify candidate compounds with therapeutic potential for this disease. These flies carry a loss-of-function mutation in the DJ-1ß gene, the Drosophila ortholog of human DJ-1, and show locomotor defects reflected by a reduced climbing ability. A pilot modifier chemical screen was performed, and several candidate compounds were identified based on their ability to improve locomotor activity of PD model flies. We demonstrated that some of them were also able to reduce OS levels in these flies. To validate the compounds identified in the Drosophila screen, a human cell PD model was generated by knocking down DJ-1 function in SH-SY5Y neuroblastoma cells. Our results showed that some of the compounds were also able to increase the viability of the DJ-1-deficient cells subjected to OS, thus supporting the use of Drosophila for PD drug discovery. Interestingly, some of them have been previously proposed as alternative therapies for PD or tested in clinical trials and others are first suggested in this study as potential drugs for the treatment of this disease.

Early Social Isolation Stress and Perinatal NMDA Receptor Antagonist Treatment Induce Changes in the Structure and Neurochemistry of Inhibitory Neurons of the Adult Amygdala and Prefrontal Cortex.

The exposure to aversive experiences during early life influences brain development and leads to altered behavior. Moreover, the combination of these experiences with subtle alterations in neurodevelopment may contribute to the emergence of psychiatric disorders, such as schizophrenia. Recent hypotheses suggest that imbalances between excitatory and inhibitory (E/I) neurotransmission, especially in the prefrontal cortex and the amygdala, may underlie their etiopathology. In order to understand better the neurobiological bases of these alterations, we studied the impact of altered neurodevelopment and chronic early-life stress on these two brain regions. Transgenic mice displaying fluorescent excitatory and inhibitory neurons, received a single injection of MK801 (NMDAR antagonist) or vehicle solution at postnatal day 7 and/or were socially isolated from the age of weaning until adulthood (3 months old). We found that anxiety-related behavior, brain volume, neuronal structure, and the expression of molecules related to plasticity and E/I neurotransmission in adult mice were importantly affected by early-life stress. Interestingly, many of these effects were potentiated when the stress paradigm was applied to mice perinatally injected with MK801 ("double-hit" model). These results clearly show the impact of early-life stress on the adult brain, especially on the structure and plasticity of inhibitory networks, and highlight the double-hit model as a valuable tool to study the contribution of early-life stress in the emergence of neurodevelopmental psychiatric disorders, such as schizophrenia.

Association between FOXP2 polymorphisms and schizophrenia with auditory hallucinations.

OBJECTIVE: A mutation in the FOXP2 gene has been the first genetic association with a language disorder. Language disorder is considered as a core symptom of schizophrenia. Therefore, the FOXP2 gene could be considered a good candidate gene for the vulnerability to schizophrenia. METHODS: A set of single nucleotide polymorphisms mainly located in the 5' regulatory region of the FOXP2 gene was analysed in a sample of 186 DSM-IV schizophrenic patients with auditory hallucinations and in 160 healthy controls. RESULTS: Statistically significant differences in the genotype (P=0.007) and allele frequencies (P=0.0027) between schizophrenic patients with auditory hallucinations and controls were found in the single nucleotide polymorphism rs2396753. These P values changed to 0.07 and 0.0273, respectively, after Bonferroni sequential correction. The haplotype rs7803667T/rs10447760C/rs923875A/rs1358278A/rs2396753A (TCAAA) also showed a significant difference confirmed with a permutation test (P=0.009). CONCLUSIONS: These results suggested that the FOXP2 gene may confer vulnerability to schizophrenic patients with auditory hallucinations.

Metal Homeostasis Regulators Suppress FRDA Phenotypes in a Drosophila Model of the Disease.

Friedreich's ataxia (FRDA), the most commonly inherited ataxia in populations of European origin, is a neurodegenerative disorder caused by a decrease in frataxin levels. One of the hallmarks of the disease is the accumulation of iron in several tissues including the brain, and frataxin has been proposed to play a key role in iron homeostasis. We found that the levels of zinc, copper, manganese and aluminum were also increased in a Drosophila model of FRDA, and that copper and zinc chelation improve their impaired motor performance. By means of a candidate genetic screen, we identified that genes implicated in iron, zinc and copper transport and metal detoxification can restore frataxin deficiency-induced phenotypes. Taken together, these results demonstrate that the metal dysregulation in FRDA includes other metals besides iron, therefore providing a new set of potential therapeutic targets.

FOXP2 polymorphisms in patients with schizophrenia.

BACKGROUND: FOXP2 was described as the first gene involved in our ability to acquire spoken language. The main objective of this study was to compare the distribution of FOXP2 gene polymorphisms between patients with schizophrenia and healthy controls. METHODS: Two FOXP2 polymorphisms, Intron3a and SNP 923875, and the G-->A transition in exon 14 were analysed in 149 patients with schizophrenia and schizoaffective disorders according to DSM-IV, as well as in 137 controls. All the patients showed a history of auditory hallucinations. RESULTS: The transition G-->A at exon 14, detected in all the affected members in KE family, was not found in any of the analyzed samples from patients or controls. No significant differences were found between individual controls and patients for the two analysed polymorphisms. CONCLUSIONS: This study would not support a possible role of the two FOXP2 analyzed polymorphisms in the vulnerability to schizophrenia.