Sabine Bahn

Oligodendrocyte dysfunction in schizophrenia and bipolar disorder

BACKGROUND Results of array studies have suggested abnormalities in expression of lipid and myelin-related genes in schizophrenia. Here, we investigated oligodendrocyte-specific and myelination-associated gene expression in schizophrenia and bipolar affective disorder. METHODS We used samples from the Stanley brain collection, consisting of 15 schizophrenia, 15 bipolar affective disorder, and 15 control brains. Indexing-based differential display PCR was done to screen for differences in gene expression in schizophrenia patients versus controls. Results were cross-validated with quantitative PCR, which was also used to investigate expression profiles of 16 other oligodendrocyte and myelin genes in schizophrenia and bipolar disorder. These genes were further investigated with an ongoing microarray analysis. FINDINGS Results of differential display and quantitative PCR analysis showed a reduction of key oligodendrocyte-related and myelin-related genes in schizophrenia and bipolar patients; expression changes for both disorders showed a high degree of overlap. Microarray results of the same genes investigated by quantitative PCR correlated well overall. INTERPRETATION Schizophrenia and bipolar brains showed downregulation of key oligodendrocyte and myelination genes, including transcription factors that regulate these genes, compared with control brains. These results lend support to and extend observations from other microarray investigations. Our study also showed similar expression changes to the schizophrenia group in bipolar brains, which thus lends support to the notion that the disorders share common causative and pathophysiological pathways.

Mitochondrial dysfunction in schizophrenia: evidence for compromised brain metabolism and oxidative stress.

The etiology and pathophysiology of schizophrenia remain unknown. A parallel transcriptomics, proteomics and metabolomics approach was employed on human brain tissue to explore the molecular disease signatures. Almost half the altered proteins identified by proteomics were associated with mitochondrial function and oxidative stress responses. This was mirrored by transcriptional and metabolite perturbations. Cluster analysis of transcriptional alterations showed that genes related to energy metabolism and oxidative stress differentiated almost 90% of schizophrenia patients from controls, while confounding drug effects could be ruled out. We propose that oxidative stress and the ensuing cellular adaptations are linked to the schizophrenia disease process and hope that this new disease concept may advance the approach to treatment, diagnosis and disease prevention of schizophrenia and related syndromes.

Kainate receptor gene expression in the developing rat brain

Kainate-preferring receptors are a subclass of ionotropic glutamate receptors that might play a role in brain development. The expression of the five known genes encoding kainate receptor subunits (GluR-5, -6, -7, KA-1, and KA-2) was studied by in situ hybridization during pre- and postnatal development of the rat brain. We compared the combined expression patterns of these genes with autoradiography using 3H- kainate in the developing brain from embryonic day 12 (E12) through to adult. Although mRNAs for the receptor subunits (except KA-1) can be detected at stage E12, 3H-kainic acid binding (as an index of receptor protein) is not found at this stage. However, by E14 high-affinity kainate sites are found throughout the gray matter, but particularly in spinal cord, primordial cerebellum, and ventral forebrain structures. All genes undergo a peak in their expression in the late embryonic/early postnatal period. GluR-5 expression during development shows the most interesting features because the changes are qualitative. The GluR-5 gene shows peaks of expression around the period of birth in the sensory cortex (layers II, III, and IV), in CA1 hippocampal interneurons in the stratum oriens, in the septum, and in the thalamus. GluR-6 shows a prenatal expression peak in the cingulate gyrus of the neocortex. KA-1 transcripts appear with the development of the hippocampus and remain largely confined to discrete areas such as the CA3 region, the dentate gyrus, and subiculum. KA-2 transcripts are found throughout the CNS from as early as E12 and remain constant until adulthood. The GluR-5 and GluR-6 genes are coexpressed in multiple peripheral ganglia (e.g., cranial nerve ganglia, dorsal root ganglia, and mural ganglia) at E14.

Metabolic profiling of CSF: evidence that early intervention may impact on disease progression and outcome in schizophrenia.

Background The identification of schizophrenia biomarkers is a crucial step towards improving current diagnosis, developing new presymptomatic treatments, identifying high-risk individuals and disease subgroups, and assessing the efficacy of preventative interventions at a rate that is not currently possible. Methods and Findings 1H nuclear magnetic resonance spectroscopy in conjunction with computerized pattern recognition analysis were employed to investigate metabolic profiles of a total of 152 cerebrospinal fluid (CSF) samples from drug-naïve or minimally treated patients with first-onset paranoid schizophrenia (referred to as “schizophrenia” in the following text) and healthy controls. Partial least square discriminant analysis showed a highly significant separation of patients with first-onset schizophrenia away from healthy controls. Short-term treatment with antipsychotic medication resulted in a normalization of the disease signature in over half the patients, well before overt clinical improvement. No normalization was observed in patients in which treatment had not been initiated at first presentation, providing the first molecular evidence for the importance of early intervention for psychotic disorders. Furthermore, the alterations identified in drug-naïve patients could be validated in a test sample set achieving a sensitivity and specificity of 82% and 85%, respectively. Conclusions Our findings suggest brain-specific alterations in glucoregulatory processes in the CSF of drug-naïve patients with first-onset schizophrenia, implying that these abnormalities are intrinsic to the disease, rather than a side effect of antipsychotic medication. Short-term treatment with atypical antipsychotic medication resulted in a normalization of the CSF disease signature in half the patients well before a clinical improvement would be expected. Furthermore, our results suggest that the initiation of antipsychotic treatment during a first psychotic episode may influence treatment response and/or outcome.

Transcriptional neoteny in the human brain

In development, timing is of the utmost importance, and the timing of developmental processes often changes as organisms evolve. In human evolution, developmental retardation, or neoteny, has been proposed as a possible mechanism that contributed to the rise of many human-specific features, including an increase in brain size and the emergence of human-specific cognitive traits. We analyzed mRNA expression in the prefrontal cortex of humans, chimpanzees, and rhesus macaques to determine whether human-specific neotenic changes are present at the gene expression level. We show that the brain transcriptome is dramatically remodeled during postnatal development and that developmental changes in the human brain are indeed delayed relative to other primates. This delay is not uniform across the human transcriptome but affects a specific subset of genes that play a potential role in neural development.

Individual differences in the peripheral immune system promote resilience versus susceptibility to social stress

Significance Depression and anxiety have been linked to increased inflammation. However, we do not know if inflammatory status predates onset of disease or whether it contributes to depression symptomatology. We report preexisting individual differences in the peripheral immune system that predict and promote stress susceptibility. Replacing a stress-naive animal’s peripheral immune system with that of a stressed animal increases susceptibility to social stress including repeated social defeat stress (RSDS) and witness defeat (a purely emotional form of social stress). Depleting the cytokine IL-6 from the whole body or just from leukocytes promotes resilience, as does sequestering IL-6 outside of the brain. These studies demonstrate that the emotional response to stress can be generated or blocked in the periphery, and offer a potential new form of treatment for stress disorders. Depression and anxiety disorders are associated with increased release of peripheral cytokines; however, their functional relevance remains unknown. Using a social stress model in mice, we find preexisting individual differences in the sensitivity of the peripheral immune system that predict and promote vulnerability to social stress. Cytokine profiles were obtained 20 min after the first social stress exposure. Of the cytokines regulated by stress, IL-6 was most highly up-regulated only in mice that ultimately developed a susceptible behavioral phenotype following a subsequent chronic stress, and levels remained elevated for at least 1 mo. We confirmed a similar elevation of serum IL-6 in two separate cohorts of patients with treatment-resistant major depressive disorder. Before any physical contact in mice, we observed individual differences in IL-6 levels from ex vivo stimulated leukocytes that predict susceptibility versus resilience to a subsequent stressor. To shift the sensitivity of the peripheral immune system to a pro- or antidepressant state, bone marrow (BM) chimeras were generated by transplanting hematopoietic progenitor cells from stress-susceptible mice releasing high IL-6 or from IL-6 knockout (IL-6−/−) mice. Stress-susceptible BM chimeras exhibited increased social avoidance behavior after exposure to either subthreshold repeated social defeat stress (RSDS) or a purely emotional stressor termed witness defeat. IL-6−/− BM chimeric and IL-6−/− mice, as well as those treated with a systemic IL-6 monoclonal antibody, were resilient to social stress. These data establish that preexisting differences in stress-responsive IL-6 release from BM-derived leukocytes functionally contribute to social stress-induced behavioral abnormalities.

Analysis of vertebrate SCL loci identifies conserved enhancers

The SCL gene encodes a highly conserved bHLH transcription factor with a pivotal role in hemopoiesis and vasculogenesis. We have sequenced and analyzed 320 kb of genomic DNA composing the SCL loci from human, mouse, and chicken. Long-range sequence comparisons demonstrated multiple peaks of human/mouse homology, a subset of which corresponded precisely with known SCL enhancers. Comparisons between mammalian and chicken sequences identified some, but not all, SCL enhancers. Moreover, one peak of human/mouse homology (+23 region), which did not correspond to a known enhancer, showed significant homology to an analogous region of the chicken SCL locus. A transgenic Xenopus reporter assay was established and demonstrated that the +23 region contained a new neural enhancer. This combination of long-range comparative sequence analysis with a high-throughput transgenic bioassay provides a powerful strategy for identifying and characterizing developmentally important enhancers.

Neuronal target genes of the neuron-restrictive silencer factor in neurospheres derived from fetuses with Down's syndrome: a gene expression study

BACKGROUND Identification of genes and characterisation of their function is an essential step towards understanding complex pathophysiological abnormalities in Downs syndrome. We did a study to investigate abnormalities in gene expression in human neuronal stem cells and progenitor cells from Downs syndrome and control post-mortem human fetal tissue. METHODS Indexing-based differential display PCR was done on neuronal precursor cells derived from the cortex of a fetus with Downs syndrome, and findings were compared with those of two control samples. Findings were validated against neurosphere preparations from three independent Downs syndrome fetuses and five independent controls by real-time quantitative PCR. FINDINGS Results of differential display PCR analysis showed that SCG10--a neuron--specific growth-associated protein regulated by the neuron-restrictive silencer factor REST-was almost undetectable in the Downs syndrome sample. This finding was validated by real-time PCR. We also found that other genes regulated by the REST transcription factor were selectively repressed, whereas non-REST-regulated genes with similar functions were unaffected. Changes in expression of several key developmental genes in the Downs syndrome stem-cell and progenitor-cell pool correlated with striking changes in neuron morphology after differentiation. INTERPRETATION Our findings suggest a link between dysregulation of the REST transcription factor and some of the neurological deficits seen in Downs syndrome. Experimental REST downregulation has been shown to trigger apoptosis, which could account for the striking and selective loss of neurons in the differentiated Downs syndrome cell preparations.

Identification of a biological signature for schizophrenia in serum

Biomarkers are now used in many areas of medicine but are still lacking for psychiatric conditions such as schizophrenia (SCZ). We have used a multiplex molecular profiling approach to measure serum concentrations of 181 proteins and small molecules in 250 first and recent onset SCZ, 35 major depressive disorder (MDD), 32 euthymic bipolar disorder (BPD), 45 Asperger syndrome and 280 control subjects. Preliminary analysis resulted in identification of a signature comprised of 34 analytes in a cohort of closely matched SCZ (n=71) and control (n=59) subjects. Partial least squares discriminant analysis using this signature gave a separation of 60–75% of SCZ subjects from controls across five independent cohorts. The same analysis also gave a separation of ∼50% of MDD patients and 10–20% of BPD and Asperger syndrome subjects from controls. These results demonstrate for the first time that a biological signature for SCZ can be identified in blood serum. This study lays the groundwork for development of a diagnostic test that can be used as an aid for distinguishing SCZ subjects from healthy controls and from those affected by related psychiatric illnesses with overlapping symptoms.

Gene expression analysis in schizophrenia: Reproducible up-regulation of several members of the apolipoprotein L family located in a high-susceptibility locus for schizophrenia on chromosome 22

We screened a custom-made candidate gene cDNA array comprising 300 genes. Genes chosen have either been implicated in schizophrenia, make conceptual sense in the light of the current understanding of the disease, or are located on high-susceptibility chromosome locations. The array screen using prefrontal cortex tissue from 10 schizophrenia and 10 control brains revealed robust up-regulation of apolipoprotein L1 (apo L1) by 2.6-fold. The finding was cross-validated in a blinded quantitative PCR study using prefrontal cortex tissue from the Stanley Foundation brain collection, Bethesda, MD. This collection consists of 15 schizophrenia, 15 bipolar disorder, 15 major depression, and 15 control individuals, all 60 brains being well-matched on conventional parameters, with antipsychotic drug exposure in the schizophrenia and bipolar disorder groups. Significant up-regulation of apo L1 gene expression in schizophrenia was confirmed. Using quantitative PCR, expression profiles of other members of the apo L family (apo L2–L6) were investigated, showing that apo L2 and L4 were highly significantly up-regulated in schizophrenia. Results were then confirmed in an independent set of 20 schizophrenia and 20 control brains from Japan and New Zealand. Apo L proteins belong to the group of high density lipoproteins, with all six apo L genes located in close proximity to each other on chromosome 22q12, a confirmed high-susceptibility locus for schizophrenia and close to the region associated with velocardiofacial syndrome that includes symptoms of schizophrenia.