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Background The subependymal zone (SEZ) adjacent to the lateral ventricles represents the largest reservoir of postnatally-generated cortical and striatal inhibitory interneurons in the human brain. Expression of markers representing the generation of neuronal progenitors from neural stem cells is reduced in the adult SEZ in schizophrenia and bipolar disorder; however, underlying mechanisms and relationships to inhibitory interneuron dysfunction remain unknown. Stem cell maintenance, neuronal migration and cell survival are regulated by signaling of the CXC motif chemokine 12 (CXCL12) through CXC motif chemokine receptors 4 (CXCR4) and 7 (CXCR7), which are increasingly implicated in the pathophysiology of psychiatric disorders. Methods Post-mortem tissue was obtained from 33 schizophrenia, 32 bipolar disorder and 33 control cases from the Stanley Medical Research Institute. SEZ and caudate nucleus tissue was dissected from 60 µm sections for RNA isolation and cDNA synthesis. Gene expression of CXCL12, CXCR4 and CXCR7 were determined by quantitative polymerase chain reactions. Semi-partial correlations were performed to assess whether CXC chemokine family member mRNAs may correlate with markers of neural stem cells (PROM1, GFAPD), neuronal progenitors (SOX2, ASCL1) and inhibitory interneurons (CALB2, NPY) in the SEZ and caudate nucleus. Results In the SEZ, CXCL12 mRNA was decreased in schizophrenia compared to controls and bipolar disorder (14–24%, all p≤0.03). CXCR4 and CXCR7 mRNAs were both decreased in schizophrenia and bipolar disorder compared to controls (9–33%, all p≤0.05). CXCL12, CXCR4 and CXCR7 expression positively correlated with PROM1, GFAPD, SOX2 and ASCL1 mRNAs (0.28≥sr≤0.61). In the caudate nucleus, CXCL12 mRNA was decreased in schizophrenia and bipolar disorder compared to controls (19–26%, all p≤0.05). CXCR4 mRNA was decreased in schizophrenia compared to controls (20%, p=0.01), while CXCR7 expression did not significantly differ across diagnostic groups. CALB2 and NPY mRNAs were increased in bipolar disorder compared to controls (13–27%, all p≤0.05). CXCR4 expression positively correlated with CALB2 mRNA (sr=0.26), while CXCR7 expression negatively correlated with NPY mRNA (sr=0.26). Discussion These findings provide the first molecular evidence of decreased CXC chemokine family member expression in the SEZ and caudate nucleus in psychiatric disorders, with exacerbated deficits in schizophrenia compared to bipolar disorder. Dysregulated CXC chemokine family member expression may hamper neural stem cell maintenance and neuronal differentiation, which may contribute to inhibitory interneuron dysfunction in psychiatric disorders. Future work will determine the cellular localisation of CXCR4 and CXCR7 expression in the SEZ and caudate nucleus to disentangle the regulatory role of CXCL12 signalling in the generation, migration and survival of inhibitory interneurons in the human brain.

Background Inflammation is implicated in the pathogenesis of schizophrenia and bipolar disorder. Inflammation regulates neurogenesis, and markers for stem cells and neuronal progenitors are reduced in schizophrenia and bipolar disorder in the subependymal zone (SEZ) – the brain’s largest region of neurogenesis. This research aimed to discover core differences in gene expression and cellular composition in the SEZ in psychiatric disorders that may contribute to dysregulated neurogenesis. Methods We performed total RNA sequencing in the SEZ of 20 post-mortem schizophrenia and 21 control brains. Quantitative PCR (qPCR) and immunohistochemistry were performed in 32 schizophrenia and 32 control overlapping cases and 29 bipolar disorder cases. Immunohistochemistry was used for quantification and localisation of CD163+ macrophages. Cluster-analysis of IL6, IL6R, IL1R1 and SERPINA3 expression defined low and high inflammation subgroups, which were used to compare neurogenesis marker expression. Results Out of >60,000 genes, the most significantly differentially expressed gene in schizophrenia was CD163, a macrophage marker, which was increased 3.3 times compared to controls and confirmed by qPCR. Abundant CD163+ macrophages were located surrounding blood vessels, in the parenchyma and seem to infiltrate throughout the SEZ where neural stem and progenitor cells typically reside. Macrophage cell density was increased in schizophrenia compared to controls and bipolar disorder (by 29% and 61%; p = 0.017 and p = 0.002 respectively). CD163 expression positively correlated with the quiescent neural stem cell marker GFAPδ (r = 0.56, p = 0.001), and negatively correlated with neuronal progenitor marker ASCL1 (r = - 0.40, p = 0.032) in schizophrenia but not bipolar disorder. Cluster analysis of inflammatory gene expression revealed 40% of schizophrenia but only 10% of control cases were highly inflamed. The high inflammation schizophrenia subgroup had increased CD163 and GFAPδ expression but decreased ASCL1 expression (all p < 0.026). Discussion Increased macrophages in the SEZ is a key difference in schizophrenia pathology and potentially drives heightened inflammation in a subgroup. Inflammation has varied effects on different stages of neurogenesis in schizophrenia but not bipolar disorder, implicating divergent mechanisms leading to reduced neurogenesis in each psychiatric condition. In schizophrenia, macrophages and high inflammation seem to reduce neuronal differentiation and sustain neural stem cell quiescence, likely blunting stem cell proliferation. Therefore, reduced SEZ neurogenesis across the lifespan in schizophrenia may contribute to the widely reported inhibitory interneuron deficits.

Background Neuroinflammation and dopamine dysregulation contribute to psychosis and cognitive deficits in schizophrenia. Approximately 50% of people with schizophrenia have elevated gene expression of proinflammatory cytokines in the postmortem midbrain, the location of the dopamine neurons. Infiltration of macrophages into the cortex was identified in a subset of high inflammatory schizophrenia cases. It is not known whether molecular measures of macrophages and cell adhesion molecules are increased in the midbrain in schizophrenia. We hypothesised that gene expression of macrophage markers CD163 (cluster of differentiation 163; perivascular macrophages), Fn1 (fibronectin 1; expressed by peripheral macrophages, not brain microglia), CD64 (pro-inflammatory macrophage), MRC1 (anti-inflammatory macrophage) and intracellular cell adhesion molecule 1 (ICAM1; enabling recruitment of peripheral macrophages into the brain), will be elevated in the midbrain of schizophrenia cases compared to controls. Methods Gene expression was examined by qRT-PCR in the midbrain from 28 schizophrenia cases (13 high inflammation, 15 low inflammation) and 29 healthy controls (low inflammation). ANCOVA, with age, PMI and RIN as covariates when correlations detected, were used to detect differences between diagnostic or diagnostic/inflammatory groups. For schizophrenia cases, antipsychotic doses were converted to chlorpromazine (CPZ) equivalents. Correlations were used to determine relationships between illness duration, antipsychotics and gene expression. CD163+ cells were identified in fresh frozen midbrain (14µm) from schizophrenia and control cases by immunohistochemistry to qualitatively assess their location relative to dopamine neurons. Results We found abundant macrophages (CD163+ cells) in and around blood vessels and in the schizophrenia midbrain parenchyma in close proximity to dopamine neurons. CD163, Fn1 and ICAM mRNAs were increased 237.6%, 39.67% and 137.7% respectively, in schizophrenia cases compared to control cases [all F(1,50 >5.045, p0.5, p0.05, n=28). Fn1 mRNA did not correlate with illness duration or antipsychotics. Discussion Increased ICAM1 may lead to increased transmigration of monocytes into the midbrain parenchyma. The increase in CD64 and the positive relationship between Fn1, expressed by peripheral monocytes/macrophages but not brain microglia, and CD163 expression in schizophrenia cases provides support that there is an increase in pro-inflammatory bone marrow-derived immune cells in the psychotic midbrain. These peripheral immune cells may be a source of increased cytokines identified in the midbrain schizophrenia cases and thus may contribute to dopamine neuron pathophysiology. Although the role of antipsychotics in increased macrophage marker expression in the midbrain is suggested, increased antipsychotics in patients displaying higher expression of inflammatory transcripts may indicate a more symptomatic patient requiring higher treatment doses.

BACKGROUND: Schizophrenia is characterized by positive and negative symptoms and cognitive deficits related to functional disability. Approved treatments targeting small molecule neurotransmitter receptors are limited in their effectiveness and often leave residual symptoms and debilitating side effects. Psychotic symptoms, cognitive deficits, and treatment response are variable in schizophrenia, highlighting heterogeneity in the etiology and presentation of the illness. There is a critical need for novel treatments targeting subgroups related to underlying biology that can be identified by biomarkers. A substantial subgroup (40%) of people with schizophrenia can be distinguished by cytokines in both peripheral blood and in brain. The cytokine interleukin 1-beta (IL-1β) mRNA and protein levels are significantly increased in serum, plasma, white blood cells, cerebrospinal fluid and brain in chronically ill patients and in first episode psychosis. Canakinumab is an approved human anti-IL-1β monoclonal antibody that interferes with the bioactivity of IL-1β and interrupts excessive immune response. However, the extent to which IL-1β blockade by canakinumab can reduce peripheral markers of an overactive immune system (e.g., high sensitivity C-reactive protein: hsCRP) and reduce psychotic symptom severity in schizophrenia is unknown. METHODS: We conducted a randomized, placebo-controlled, double-blind, parallel group trial of the monoclonal antibody canakinumab to block IL-1β in schizophrenia. Twenty-seven chronically ill patients with schizophrenia or schizoaffective disorder who had elevated peripheral inflammation markers (IL-1β, IL-6, hsCRP and/or neutrophil to lymphocyte ratio) at baseline were randomized to a one-time subcutaneous injection of canakinumab (150 mg) or placebo (normal saline) as an adjunctive treatment to antipsychotics. Peripheral hsCRP levels were measured at baseline (prior to injection) and at 1, 4- and 8-weeks post treatment. Positive and Negative Syndrome Scale scores were assessed at baseline and at 4- and 8-weeks post treatment. RESULTS: Separate t-tests comparing canakinumab or placebo at weeks 1, 4, and 8 to baseline showed significant reductions in peripheral hsCRP levels at all time points (all p’s < .02) for canakinumab only. Separate t-tests also showed a significant reduction in positive symptom severity scores at week 8 (p = 0.05) for canakinumab and at week 4 (p = 0.02) for placebo. There was a trend for low peripheral hsCRP levels to be strongly correlated with low positive symptom severity scores (r = .57, p = .07) only at week 8 in the canakinumab group. There were no significant reductions in negative or general psychopathology symptom severity scores in either group. DISCUSSION: Blockade of the cytokine IL-1β by the monoclonal antibody canakinumab significantly reduces peripheral hsCRP serum levels and these reductions may be related to a reduction in positive symptom severity in chronically ill patients with schizophrenia. Importantly, only those patients who initially displayed elevated peripheral markers of inflammation were recruited. The effects of canakinumab on the reduction of peripheral hsCRP is potentially beneficial to general health. The relatively strong relationship between the effects of canakinumab on the biological marker hsCRP and positive symptom severity after 8 weeks of treatment supports the effect of canakinumab on positive symptom severity. Given that treatment with a monoclonal antibody is a novel and substantial advance in the potential treatment of psychotic symptom severity in schizophrenia, future studies should consider increased or top-up doses with longer follow-up to confirm the benefit of adjunctive canakinumab treatment in schizophrenia.

Background: The kynurenine pathway (KP) of tryptophan (TRP) catabolism is considered to link the immune and neurotransmitter systems. The KP metabolite kynurenic acid (KYNA) shows increases in the brain of patients with schizophrenia. Here, we tested whether changes in brain KP enzyme mRNAs and plasma KP metabolites are related to cytokine levels in schizophrenia. We expected Kynurenine Aminotransferase II (KATII) mRNA to be increased in brains of people with schizophrenia, particularly in patients displaying elevated cytokines. Furthermore, we expected that the kynurenine (KYN)–TRP ratio in the plasma of chronically ill patients to be associated with cognitive and brain volume abnormalities in schizophrenia with high inflammation.

Background Schizophrenia is a disabling and often unremitting mental illness with an unknown cause that is characterized by heterogeneity in psychotic symptom presentation, cognitive deficits and treatment response. There is accumulating evidence for the role of inflammation in the etiology of schizophrenia. Inflammatory markers have been identified in the brains and peripheral blood of chronically ill patients with schizophrenia and in first episode patients and these markers have been associated with structural and functional brain abnormalities and cognitive deficits. Intercellular adhesion molecule 1 (ICAM-1) is a transmembrane protein expressed on endothelial cells which binds to leukocyte receptors that promotes transmigration of white blood cells into tissue. While peripheral inflammatory markers are altered in people with schizophrenia relative to controls, the extent to which ICAM-1 is elevated in the brains of people with schizophrenia and peripheral levels of soluble ICAM-1 (sICAM-1) is increased in relation to cognitive impairment in schizophrenia is unknown. Methods In a post-mortem cohort, 8 mRNAs relating to BBB function and 3 immune cell markers were measured by qPCR in the prefrontal cortex of 37 people with schizophrenia and 37 matched controls. In an independent living cohort, sICAM-1 was measured with a Luminex immunoassay from the plasma of 78 chronically ill patients with schizophrenia (all receiving antipsychotic medication) and 73 healthy controls. All participants from the living cohort received the following cognitive assessments: Wechsler Adult Intelligence Scale – 3rd edition to assess current IQ, Controlled Oral Word Association Test verbal fluency and Wechsler Memory Scale-Revised to assess verbal memory. Pearson’s or Spearman’s correlations were performed between cognitive measures and sICAM1 levels as appropriate in schizophrenia patients and healthy controls. Results ICAM-1 was elevated in the brains of people with schizophrenia relative to controls and CD163+ perivascular macrophages were found in the parenchyma. Peripheral sICAM1 was elevated by 29.2% in people with schizophrenia compared to healthy controls, t(140) = -3.988, p < 0.01. In people with schizophrenia, sICAM1 was inversely correlated with immediate verbal memory (r=-0.30, p=0.01), delayed verbal memory (rho=-0.29, p=0.01), verbal abstract reasoning (r=-0.23, p=0.05), and processing speed (rho=-0.28, p=0.02). In healthy controls, sICAM1 levels were inversely correlated with verbal fluency (r=-0.27, p=0.03) and processing speed (rho=-0.26, p=0.03). Discussion The brain endothelium of people with schizophrenia can attract more immune cells via increased ICAM-1. sICAM-1, a cleavage product of ICAM which enables white blood cell migration into tissue (including brain) is significantly elevated in peripheral blood of patients with schizophrenia. sICAM-1 is associated with poor verbal memory, reasoning and processing speed in people with schizophrenia and accounts for variation in cognition of healthy controls. This suggests that increased inflammatory processes, measured in blood, may reflect brain related cognitive deficits that are the hallmark of schizophrenia. Anti-inflammatory treatments may reverse cognitive impairment in schizophrenia.

Background The predominant neurodevelopmental theory of schizophrenia posits that there is a failure of normal synaptic loss believed to occur during normal adolescence. However, the most consistent neuropathology in the cortex of people with schizophrenia is a deficit in the γ–aminobutyric acid (GABA) inhibitory interneurons, not a reduction in presynaptic and postsynaptic elements. Thus, disruption to the normal development of cortical interneurons may lead to interneuron deficiency in schizophrenia. However, to understand if pathological changes in the brain of an adult with schizophrenia would be consistent with aberrant development, the known neuropathology must be placed in the context of normal human cortical development. Methods We examined the molecular changes that occur in the synapses, interneurons and the neurotransmitter systems during normal development of the human prefrontal cortex of 68 brains from healthy individuals (1 month - 49 years). Results Contrary to the prevailing view that synaptic pruning predominates during adolescent brain development, we found presynaptic mRNA and protein levels generally peak between 5–12 years of age and then remain stable through adolescence and into adulthood. Likewise, markers for dendritic spines peak in infancy and while mRNA levels then decline, protein levels are maintained throughout development. The various interneuron markers show three very distinct patterns of expression over development. Parvalbumin and cholecystokinin increase from infancy, whereas somatostatin, calretinin and neuropeptide Y decrease from infancy. Calbindin and vasoactive intestinal peptide peak in the toddlers and then decrease in adults in an inverted U shaped-pattern. Levels of mRNA for the GABA synthesizing enzymes GAD65 (GAD2) and GAD67 (GAD1) peak around 1 year of age and stay consistent through to adulthood. The postsynaptic GABAA receptor α1, β2 and γ subunits increase over the postnatal period to peak in adolescent/young adulthood whereas the α2 subunit shows the inverse pattern and decreases over the postnatal period. The dopamine receptor, D1, increase expression throughout the postnatal period to peak in early adulthood, whereas D2 and D5 show a continual decline throughout life. The NMDA receptors are highest in the first year of life and while subunits GRIN 2B, 2D and 3A all decrease throughout life, GRIN1 remains stable and GRIN 2A decreases after childhood. More recently data supporting the neuroinflammatory hypothesis of schizophrenia has merged with the neurodevelopmental hypothesis and posits that the strongest signal from GWAS studies in schizophrenia is in the C4 gene, which is a component of the complement cascade involved in normal synaptic development. We have initiated an examination of the various components of the complement cascade to determine if/when they are expressed in the human cortex and how they could be impacting the developing circuitry. Preliminary data shows C4 mRNA expressed at very low, but constant levels throughout postnatal life. In contrast, C3 mRNA is expressed at higher levels than C4, peaks in infancy and remains stable into adulthood. MAC protein (CD-59) mRNA which protects cells from complement mediated damage, is expressed at very low levels at birth but then increases significantly with age and is highest in adulthood, suggesting that significant changes in complement may occur after brain maturation is complete. Discussion Together these findings show very dynamic and complex patterns of expression from birth to adulthood, with the most active growth phase and dynamic changes occurring in the early years before adolescence. Thus, an insult during these early years could profoundly affect the developmental trajectory.