SfN 2013—Schizophrenia Grab Bag
See Allison Curley's snapshots from the conference.
December 3, 2013. The morning of Monday, November 11, brought one of the few 2013 Society for Neuroscience meeting symposia dedicated to schizophrenia. Chaired by Akira Sawa, the session contained many flavors of schizophrenia research, including postmortem molecular studies, findings using a variety of neuroimaging techniques, and analyses of cultured skin cells derived from patients.
The first speaker was Vaidy Swaminathan of the University of Melbourne, Australia, who examined epidermal growth factor receptor (EGFR) mRNA and protein levels in the dorsolateral prefrontal cortex (DLPFC) of subjects with schizophrenia and controls. Although he did not find a change in EGFR mRNA, protein levels were significantly increased in cases. Further examination of the protein data revealed that EGFR protein levels were significantly higher in schizophrenia subjects who did not have a history of suicide attempts than in controls or in patients with a history of suicidal behavior. The group has previously demonstrated that clozapine, but not other antipsychotics, augments EGFR signaling (Pereira et al., 2012). Given that clozapine reduces suicidality in schizophrenia, the current findings suggest that EGFR signaling may underlie this effect, said Swaminathan.
Gianluca Ursini from the Lieber Institute for Brain Development in Baltimore, Maryland, discussed his work on brain-derived neurotrophic factor (BDNF), a protein that has previously been implicated in schizophrenia through genetic and postmortem findings in patients as well as data from animal models (see SRF related conference story). Using RNA sequencing, Ursini screened for variants of BDNF mRNA in the DLPFC of a large sample of schizophrenia subjects and controls. He uncovered several novel splicing events involving a truncated version of BDNF’s exon 1 and reported that expression of these transcripts was higher in schizophrenia cases. In addition, an imaging study demonstrated that a single nucleotide polymorphism that controls the expression of the novel transcripts predicted prefrontal activity in both schizophrenia subjects and siblings. Taken together, the findings provide further evidence for a role for BDNF in the illness.
Using RNA sequencing, Sarven Sabunciyan from Johns Hopkins University, also in Baltimore, examined the expression of repeat elements—stretches of DNA that are repeated in large numbers throughout the genome—in the orbitofrontal cortex of people with schizophrenia, bipolar disorder, and depression. He reported that repetitive element loci were abundantly transcribed in the healthy brain and differentially expressed in a combined group of subjects with schizophrenia or bipolar disorder. Sabunciyan and colleagues hypothesize that some repeat elements are being incorporated into transcripts as splice variants (a process recently described as "exonization"), and that this process is disrupted in neuropsychiatric disorders.
Chang-Gyu Hahn from the University of Pennsylvania in Philadelphia took aim at the NMDA receptor hypothesis of schizophrenia (see SRF Current Hypotheses by Bita Moghaddam and Daniel Javitt, and SRF related news story). Hahn and colleagues examined DLPFC tissue from matched pairs of schizophrenia subjects and controls and found that NMDA receptor complexes are increased in the postsynaptic densities of schizophrenia patients, but the cascade of post-receptor kinases is decreased. The activity of Src kinase, which phosphorylates the NR2 subunits of the NMDA receptor, was decreased in schizophrenia cases, as was Src’s binding capacity for its activators, leading the researchers to hypothesize that attenuation of Src activity is a pathogenic mechanism for NMDA receptor hypofunction in the illness.
Sotiris Posporelis from Johns Hopkins described a preliminary study examining the relationship between brain temperature and cognitive function in six recent-onset schizophrenia subjects and six healthy controls. Temperature in the anterior cingulate, measured using proton magnetic spectroscopy, was significantly correlated with verbal memory performance and negative symptoms. In addition, Posporelis reported that brain temperature was significantly different from core temperature in subjects with schizophrenia, but the two did not differ in control subjects. Brain temperature reflects brain metabolism, so the findings suggest a role for neuroinflammation and oxidative stress (which can alter metabolism) in the illness.
In the lone non-schizophrenia talk of the symposium, Robert Innis from the National Institute of Mental Health, Bethesda, Maryland, described work investigating a downregulation of the cyclic adenosine monophosphate (cAMP) cascade in major depression. The researchers used the radioligand (R)-11C-rolipram, an inhibitor of the phosphodiesterase PDE4 (a component of the cAMP cascade) to approximate cAMP function using positron emission tomography (PET). Consistent with the researchers’ hypothesis, rolipram binding was lower in unmedicated patients with MDD, indicating a downregulation of the cAMP cascade (Fujita et al., 2012). In preliminary results from an ongoing study, antidepressant treatment normalized rolipram binding, suggesting that PDE4 inhibitors could potentially be used to treat major depression (although increased rolipram binding was not associated with symptom improvement).
Next up was Guusje Collin of University Medical Center Utrecht in the Netherlands, who examined the connectivity of the “rich club”—a central collection of strongly interconnected hubs crucial for information integration—in the unaffected siblings of people with schizophrenia by using diffusion tensor imaging. Collin reported that the connections spanning the rich club are impaired in patients with schizophrenia (see SRF related news story), and that rich club connectivity in healthy siblings is intermediate between cases and controls. These findings suggest that impaired rich club connectivity in schizophrenia is genetic in origin.
Hengyi Cao of the University of Heidelberg in Mannheim, Germany, described work designed to clarify the contrasting findings of amygdala dysfunction during emotional processing in unaffected relatives of individuals with schizophrenia. In the current study, Cao and colleagues administered an emotional face-matching task to 160 healthy subjects (60 with a first-degree relative with schizophrenia and 100 without a family history of the illness) undergoing fMRI. Cao reported that there were no alterations in amygdala activation in either group (replicating the findings of a previous study using the same task), suggesting that amygdala activation is unlikely to be an emotion-related intermediate phenotype for schizophrenia. However, decreased connectivity in a limbic subnetwork was observed in the relatives of patients with schizophrenia, he said, pointing to a possible intermediate phenotype for the illness.
Toby Winton-Brown of the Institute of Psychiatry in London, United Kingdom, discussed his work examining salience processing—the way the brain distinguishes important stimuli from the myriad of sensory inputs it receives—which is thought to be disturbed in schizophrenia. Winton-Brown and colleagues developed a novel fMRI task to measure the brain’s response to the novelty, emotion, and monetary values of pictures and found that unmedicated subjects at high risk for developing psychosis showed elevated brain activation to the reward aspects of salience, as well as to images that combined reward and emotion. In addition, the researchers quantified dopamine levels using PET in order to test the predictions made by the methylazoxymethanol acetate (MAM) model of schizophrenia (see SRF related conference story) and found support for the hypothesis that overdrive of the ventral hippocampus results in elevated striatal dopamine in psychosis.
The t(1;11) balanced chromosomal translocation is strongly associated with psychiatric illnesses (see SRF related news story). Two of the affected genes, disrupted-in-schizophrenia (DISC1) and Boymaw, blend together as a consequence of the translocation, forming a DISC1-Boymaw fusion protein, said Kerin Higa of the University of California, San Diego (see SRF related conference story). She reported that expression of the fusion protein in vitro reduces intracellular oxidoreductase activity as well as ribosomal RNA synthesis. Mice with the human DISC1-Boymaw genes knocked in also showed these changes, as well as alterations reminiscent of mental illness such as decreased expression of GAD67, NMDAR1, and PSD95 proteins and several depressive-like behaviors. These results are consistent with the hypothesis that expression of the fusion protein in psychiatric illness may alter the expression of genes involved in GABA and glutamate neurotransmission through a reduction in ribosomal RNA synthesis, said Higa.
Margot Fournier of Lausanne University Hospital in Switzerland described her data suggesting a metabolic signature of reactivity to oxidative stress in early psychosis (see SRF related news story). Fournier and colleagues cultured skin-derived fibroblasts from individuals with early psychosis and performed metabolomic profiling after exposing the cells to oxidative stress. Compared to cells from controls, those from early psychosis patients exhibited alterations in extracellular matrix and collagen metabolism and arginine metabolism pathways that are known to regulate neuronal plasticity and activity. The findings suggest that intermediates of these pathways may represent useful biomarkers in the early phases of schizophrenia, Fournier concluded.
Prior work has suggested that plasma levels of the amino acid homocysteine are elevated in individuals with schizophrenia, said Akira Nishi of the University of Tokushima Graduate School in Japan, but the impacts of gender and genotype have not been conclusively established. Nishi and colleagues measured plasma homocysteine levels in patients with schizophrenia and controls and found that homocysteine levels were higher in schizophrenia subjects than in controls, higher in males than in females, and higher in some alleles of MTHFR, a schizophrenia risk gene involved in the metabolism of homocysteine (see SRF related news story).—Allison A. Curley.
Comments on Related News
Related News: Sweeping SchizophreniaGene Study Applies New Criteria to Finger SuspectsComment by: Stephen J. Glatt
Submitted 17 July 2008
Posted 21 July 2008
I recommend the Primary Papers
The paper by Allen et al. is a tremendously useful addition to the fields of schizophrenia research, psychiatric genetics, and medical genetics. By efficiently summarizing a tremendous amount of work, Allen et al. have endeavored to provide a "state-of-the-art" summary that most of us, as individuals, struggle to accomplish; they have largely succeeded in their attempt. This manuscript, and the continual availability of the SZGene database, should long serve as invaluable resources for the increasingly complex task of building polygenic models of risk for schizophrenia. Furthermore, these methods, which were initially implemented in the AlzGene database, have clearly generalized quite successfully to SZGene and thus, should be easy enough to scale up to cover many other psychiatric disorders as well. In this way, the contribution to psychiatric genetics, and possibly other disorders outside of psychiatry, is crystalline.
Aside from the database, the contribution of the recent manuscript to the field of schizophrenia research is also tremendous. As pointed out by the authors, several of the significantly associated genes identified by their meta-analyses were never before studied in this manner, so a whole new set of top candidate genes was identified. This work also served to confirm the results of prior meta-analyses from my group and others, which is always reassuring. Application of the HuGENet criteria to grading the detected associations is useful as a heuristic, but it must be kept in mind that that while these criteria reflect a consensus, they also reflect a moving target. One difficulty in implementing grades (especially the "overall" grade) is analogous to difficulties often encountered in meta-analyses when rating the quality of studies, and that is the ambiguity of ratings. Thus, on a seven-point quality scale (or a three-letter-grade scale), a score can be arrived at by a variety of combinations of flaws or strengths, but similar scores may not (often do not) reflect identical strengths and weaknesses of the graded studies. For example, I, for one, am not certain that having a relatively low number of minor alleles reflected in a meta-analytic result (especially if it is a rare variant) is as big a decrement as the pooled OR dropping from significance when the initial study is omitted.
Nevertheless, I reiterate that the use of this heuristic grading system is helpful, but should be taken with a grain of salt. Overall, the paper and its conclusions are a great contribution to this field and warrant mass attention. The ultimate question, not yet addressed here but apparently on the horizon, is how well the emerging GWASs detect these "positive control" associations, or we might say how well these hypothesis-driven results stack up against new candidates to emerge from the high-throughput generation of novel hypotheses....
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Related News: Boosting NMDA Receptors Improves Symptoms, Cognition in Schizophrenia
Comment by: Hugo Geerts
Submitted 20 October 2013
Posted 20 October 2013
I recommend the Primary Papers
The group around Dr. Hsien-Yuan Lane has published a number of papers on clinical trials in schizophrenia patients with agents that act on co-agonist sites of the NMDA-receptor. This time they report on the beneficial effects of augmentation therapy with high-dose benzoate, a D-amino acid oxidase inhibitor, on a number of clinical scales (about 25 subjects/treatment arm). The effect is substantial (effect sizes between 1.16 on the PANSS negative and 1.69 on the PANSS positive subscale). For instance, this effect size is about twice the value seen in clinical trials with bitopertin, a glycine transporter-1 inhibitor in a larger Phase II study (Umbricht et al., 2010). Only one dose of benzoate has been tested, so the issue of a possible inverse U-shape response that has been observed earlier for a similar target and supported by theoretical-mechanistic insights has not been addressed in this study. They took great care in balancing the treatment arms with regard to the type of basal antipsychotic medication and found that haldol and risperidone were particularly receptive for benzoate augmentation therapy.
Of interest is the observation that benzoate is a food additive (E210-E213) with an impressive record of safety, opening up the possibility of an easier treatment approach of lower levels of the drug be achieved using food strategies. It might therefore be of interest to test lower levels of benzoate as well.
Antipsychotics are often considered deleterious or neutral at best for cognitive improvement, so this augmentation study suggests that benzoate is able to reverse this trend of worsening. In addition, there were no correlations between changes in PANSS positive or EPS changes and changes in both PANSS negative or cognitive outcome. This suggests that the observed effect of the compound is unlikely to be indirectly due to an improvement in PANSS positive symptoms or motor side effects, suggesting a genuine impact on the negative or cognitive subscales.
With regard to cognition, from the MATRICS subscale, the authors only found speed of processing and visual learning and memory to be significantly improved with the active treatment. However, this is one of the few trials in which the global composite score increased more with treatment than the placebo, despite the possible practice effect. Nevertheless, it underscores the difficulty of improving all seven domains of the cognitive MATRICS scale.
With the caveat of low numbers in the treatment arm, this study has to be recommended because it once again suggests a path forward for glutamatergic strategies. The glutamatergic system is currently the focus of much research in psychiatric indications (such as ketamine in depression). However the major problem, unlike older dopaminergic and neuromodulatory strategies, is finding a balance between excitation and inhibition in the human brain, and the feedback mechanism that operates, that makes it sometimes difficult to find the best dose-range for any treatment paradigm. The authors of this paper, however, show that this is possible.
Umbricht D, Yoo K, Youssef E, Dorflinger E, Martin-Facklam M, Bausch A, Arrowsmith R, Alberati D, Marder S, Santarelli L. Glycine Transporter Type 1 (GLYT1) Inhibitor RG1678: Positive
Results of the Proof-of-Concept Study for the Treatment of Negative Symptoms in Schizophrenia. Neuropsychopharmacology. 2010; 35:S320-321.
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Related News: Boosting NMDA Receptors Improves Symptoms, Cognition in Schizophrenia
Comment by: Michael McFarland
Submitted 5 November 2013
Posted 11 November 2013
Sodium benzoate combined with ascorbic acid produces benzene, a known carcinogen. I hope that another D-amino acid oxidase inhibitor can be found easily.
View all comments by Michael McFarland
Related News: SfN 2013—Different Roads to Dopamine Dysfunction in Schizophrenia
Comment by: Melkaye Melka
Submitted 5 December 2013
Posted 9 December 2013
Atypical antipsychotics have been used to treat psychiatric disorders such as schizophrenia. However, the mechanisms of action of antipsychotics remain poorly understood. On the other hand, dopamine neurons form the focus of attention in the etiology and pathophysiology of schizophrenia. As noted by Michele Solis’ snapshot from the conference, the work of Grace and colleagues showed that prenatal injections of methylazoxymethanol acetate (MAM), a DNA-methylating agent, lead to hyperactive dopamine signaling (Moore et al., 2006). Focusing on the mechanisms of action, previous studies have suggested that antipsychotic drugs may cause promoter methylation of genes involved in psychosis (Dong et al., 2009). DNA methylation changes have also been associated with major psychosis (Mill et al., 2008).
In a recent in-vivo study, we have observed organ-specific (hippocampus, cerebellum, and liver) changes in DNA methylation following a therapeutic dose of a model antipsychotic drug (olanzapine) (Melka et al., 2013, in press). In particular, we noted that the dopamine signaling pathway was one of the most significant networks affected by olanzapine-induced DNA methylation changes. Specifically, the results showed that olanzapine significantly alters promoter DNA methylation of genes involved in dopamine synthesis, transport, receptors, and metabolism. These results support a dopamine hypothesis of psychosis and a role for epigenetic mechanisms in the development of psychosis, as well as its treatment with antipsychotic drugs. Given that some of the genes affected are tissue specific and affect a variety of networks, our results could also explain the delayed therapeutic response of antipsychotics as well as their patient-specific efficacy and side effects.
Dong E, Grayson DR, Guidotti A, Costa E. Antipsychotic subtypes can be characterized by differences in their ability to modify GABAergic promoter methylation: Epigenomics 2009; 1: 201-1. Abstract
Melka MG, Castellani CA, Laufer BI, Rajakumar N, O’Reilly R and Singh SM. Olanzapine induced DNA methylation changes support the dopamine hypothesis of psychosis. J Mol Psychiatry; 2013; 1:19. (In press)
Mill J, Tang T, Kaminsky Z, Khare T, Yazdanpanah S, Bouchard L, Jia P, Assadzadeh A, Flanagan J, Schumacher A, Wang SC, Petronis A. Epigenomic profiling reveals DNA-methylation changes associated with major psychosis. Am J Hum Genet . 2008 Mar ; 82(3):696-711. Abstract
Moore H, Jentsch JD, Ghajarnia M, Geyer MA, Grace AA. A neurobehavioral systems analysis of adult rats exposed to methylazoxymethanol acetate on E17: implications for the neuropathology of schizophrenia. Biol Psychiatry . 2006 Aug 1 ; 60(3):253-64. Abstract
View all comments by Melkaye Melka
Related News: SfN 2013—New Tools for Rational Drug Design
Comment by: Hugo Geerts
Submitted 29 January 2014
Posted 5 February 2014
Multi-target drug discovery has typically been neglected in the world of genetics and high-throughput screening because of the difficulty of rationally defining a pharmacological profile, but it has major advantages for treating complex disorders such as schizophrenia. It is no wonder that the currently approved antipsychotics do have a rich pharmacology and substantially improve the clinical phenotype. With so many different genotypes defining individual patients, focusing on only one target is likely to have small effects that might disappear in clinical trials with larger patient populations. Even over all indications (not only CNS), more than half of the first-in-class medicines approved in the last decade have been found by using phenotypic assays and have typically multi-target pharmacology (Swinney and Anthony, 2011).
The approach presented here suggests a rational way to identify 1) a set of targets and 2) chemical structures that might serve as hits for further medical chemistry development. It might therefore alleviate the concerns of many medical chemistry departments in pharmaceutical companies.
Changing the mindset from developing the next extremely specific and potent inhibitor to pursuing multi-target pharmacology is urgently needed to break the deadlock of unsuccessful new drug development in schizophrenia.
Swinney DC, Anthony J. How were new medicines discovered? Nat Rev Drug Discov . 2011 Jul ; 10(7):507-19. Abstract
View all comments by Hugo Geerts
Related News: Neural Progenitor Cells Model Aspects of Schizophrenia
Comment by: Nao Gamo, Akira Sawa (SRF Advisor)
Submitted 7 May 2014
Posted 7 May 2014
This study introduces a novel use of neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (hiPSCs) to address mechanisms that may possibly underlie a predisposition to schizophrenia. Brennand et al. (2014) generated hiPSC-derived NPCs from patients with schizophrenia and control subjects. These NPCs, as well as six-week-old neurons differentiated from them, showed gene expression profiles similar to those of the fetal forebrain. Thus, these cells were used to address early disease etiology, in particular, focusing on mechanisms related to disruptions in prefrontal cortical development. Interestingly, the researchers found overlap in gene signatures between the six-week-old neurons and NPCs from patients, raising the possibility that disease predisposition may already be established at the NPC stage.
Particularly striking is the reduced migration of schizophrenia NPCs relative to control NPCs as they differentiated into neurons. This reduced migration may be due to schizophrenia NPCs remaining in a proliferative state before differentiating, as suggested by previous work from our group (Ishizuka et al., 2011). The authors also proposed that this reduced migration might lead to reduced synaptic connectivity, which they previously reported in schizophrenia hiPSC-derived neurons (Brennand et al., 2011).
The study also found differential expression of various genes and proteins, including those involved in neuronal differentiation and migration, glutamate receptor signaling, and cellular adhesion. The schizophrenia NPCs showed smaller mitochondria with altered cellular distribution relative to control NPCs, as well as oxidative stress, although the effects of oxidative stress might be limited to a subset of schizophrenia NPCs. This is a telling observation, in light of recent human and animal studies that suggest a role for oxidative stress in schizophrenia (Emiliani et al., 2014).
While it is as yet unknown whether these observations truly reflect disease predisposition, this work is innovative in taking advantage of the tools at hand. It is understood in the field that hiPSC-derived neurons can take months to fully functionally mature, and it would be difficult to simulate experience-dependent shaping of neuronal networks in a dish. However, instead of tolerating such shortcomings, the authors have used them to their advantage by addressing mechanisms that may occur at the fetal stage. Furthermore, NPCs are proliferative and suitable for high-throughput assays. This point is particularly useful when studying a disease with such heterogeneous etiology.
The true value of this experimental system will be revealed when it can predict actual brain mechanisms and clinical characteristics of individuals as well as groups of patients. The authors acknowledge that the sample size is currently small, and that the effect sizes of their observations are insufficient to predict diagnosis. It would be interesting to observe neuronal phenotypes in cells from patients with similar clinical characteristics. In addition, cells from patients with similar genetic backgrounds should be tested to control for possible biases in genetic architecture, for example, in cells from family members, or known mutations that can be created in control cell lines. We are optimistic that hiPSCs will prove a useful tool to study biological mechanisms of schizophrenia (Gamo et al., 2014, in press).
Brennand KJ, Simone A, Jou J, Gelboin-Burkhart C, Tran N, Sangar S, Li Y, Mu Y, Chen G, Yu D, McCarthy S, Sebat J, Gage FH. Modelling schizophrenia using human induced pluripotent stem cells. Nature . 2011 May 12 ; 473(7346):221-5. Abstract
Emiliani FE, Sedlak TW, Sawa A. Oxidative stress and schizophrenia: recent breakthroughs from an old story. Curr Opin Psychiatry . 2014 May ; 27(3):185-90. Abstract
Gamo and Sawa (in press). Human Stem Cells and Surrogate Tissues for Basic and Translational Study of Mental Disorders. Biol. Psychiatry.
Ishizuka K, Kamiya A, Oh EC, Kanki H, Seshadri S, Robinson JF, Murdoch H, Dunlop AJ, Kubo K, Furukori K, Huang B, Zeledon M, Hayashi-Takagi A, Okano H, Nakajima K, Houslay MD, Katsanis N, Sawa A. DISC1-dependent switch from progenitor proliferation to migration in the developing cortex. Nature . 2011 May 5 ; 473(7345):92-6. Abstract
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Related News: Neural Progenitor Cells Model Aspects of Schizophrenia
Comment by: Bryan Mowry, Samuel Nayler
Submitted 29 May 2014
Posted 29 May 2014
In a recent follow-up to their 2011 paper, Brennand et al. report
considerable progress toward generation of a defined neuronal population
generated from patient-derived induced pluripotent stem (iPS) cells. The advent
of the iPS cell has been somewhat Promethean in that pluripotent stem
cells are now a commonly utilized laboratory tool for disease modeling.
While marked progress has occurred on a number of fronts, it is still not
known to what degree stem cell-derived neurons truly resemble mature
neurons that exist in the brain of a living human. Moreover, it is an open
question what these cells can tell us about the onset of a clinically
heterogeneous, polygenic disease such as schizophrenia.
Using gene expression analysis, Brennand et al. compare their samples to a developmental spectrum of samples from the Allen Brain Atlas to show that
their iPSC-derived neurons most closely resemble early fetal forebrain
neurons. This may provide precisely the model system that will allow
researchers to validate the neurodevelopmental theory of schizophrenia,
provided early molecular mechanisms can be identified that predispose to
schizophrenia in later life. Brennand and colleagues go on to show
functional phenotypic differences in schizophrenia patient-derived neurons
relating to elevated oxidative stress and extra-mitochondrial oxygen
consumption, as well as reduced migrational ability. It remains to be seen
how relatable these phenomena are to events which occur in vivo and
whether they may be informative in identifying and characterizing the
underlying molecular and cellular mechanisms in schizophrenia.
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