Convergent lines of evidence support CAMKK2 as a schizophrenia susceptibility gene

CaMKK2 as an emerging treatment target for bipolar disorder

Current pharmacological treatments for bipolar disorder are inadequate and based on serendipitously discovered drugs often with limited efficacy, burdensome side-effects, and unclear mechanisms of action. Advances in drug development for the treatment of bipolar disorder remain incremental and have come largely from repurposing drugs used for other psychiatric conditions, a strategy that has failed to find truly revolutionary therapies, as it does not target the mood instability that characterises the condition. The lack of therapeutic innovation in the bipolar disorder field is largely due to a poor understanding of the underlying disease mechanisms and the consequent absence of validated drug targets. A compelling new treatment target is the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme. CaMKK2 is highly enriched in brain neurons and regulates energy metabolism and neuronal processes that underpin higher order functions such as long-term memory, mood, and other affective functions. Loss-of-function polymorphisms and a rare missense mutation in human CAMKK2 are associated with bipolar disorder, and genetic deletion of Camkk2 in mice causes bipolar-like behaviours similar to those in patients. Furthermore, these behaviours are ameliorated by lithium, which increases CaMKK2 activity. In this review, we discuss multiple convergent lines of evidence that support targeting of CaMKK2 as a new treatment strategy for bipolar disorder.

Metabolic regulation to treat bipolar depression: mechanisms and targeting by trimetazidine

Bipolar disorder's core feature is the pathological disturbances in mood, often accompanied by disrupted thinking and behavior. Its complex and heterogeneous etiology implies that a range of inherited and environmental factors are involved. This heterogeneity and poorly understood neurobiology pose significant challenges to existing drug development paradigms, resulting in scarce treatment options, especially for bipolar depression. Therefore, novel approaches are needed to discover new treatment options. In this review, we first highlight the main molecular mechanisms known to be associated with bipolar depression-mitochondrial dysfunction, inflammation and oxidative stress. We then examine the available literature for the effects of trimetazidine in said alterations. Trimetazidine was identified without a priori hypothesis using a gene-expression signature for the effects of a combination of drugs used to treat bipolar disorder and screening a library of off-patent drugs in cultured human neuronal-like cells. Trimetazidine is used to treat angina pectoris for its cytoprotective and metabolic effects (improved glucose utilization for energy production). The preclinical and clinical literature strongly support trimetazidine's potential to treat bipolar depression, having anti-inflammatory and antioxidant properties while normalizing mitochondrial function only when it is compromised. Further, trimetazidine's demonstrated safety and tolerability provide a strong rationale for clinical trials to test its efficacy to treat bipolar depression that could fast-track its repurposing to address such an unmet need as bipolar depression.

SGC-CAMKK2-1: A Chemical Probe for CAMKK2

The serine/threonine protein kinase calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) plays critical roles in a range of biological processes. Despite its importance, only a handful of inhibitors of CAMKK2 have been disclosed. Having a selective small molecule tool to interrogate this kinase will help demonstrate that CAMKK2 inhibition can be therapeutically beneficial. Herein, we disclose SGC-CAMKK2-1, a selective chemical probe that targets CAMKK2.

Cold avoidance and heat pain hypersensitivity in neuronal nucleoredoxin knockout mice

Nucleoredoxin is a thioredoxin-like oxidoreductase that mainly acts as oxidase and thereby regulates calcium calmodulin kinase Camk2a, an effector of nitric oxide mediated synaptic potentiation and nociceptive sensitization. We asked here if and how NXN affects thermal sensation and nociception in mice using pan-neuronal NXN deletion driven by Nestin-Cre, and sensory neuron specific deletion driven by Advillin-Cre. In a thermal gradient ring, where mice can freely choose the temperature of well-being, Nestin-NXN^-/- mice avoided unpleasant cold temperatures. In neuropathic and inflammatory nociceptive models, Nestin-NXN^-/- and Advillin-NXN^-/- mice displayed subtle phenotypes of heightened heat nociception. Abnormal thermal in vivo responses were associated with heightened calcium influx upon stimulation of transient receptor channels, with heightened oxygen consumption upon disruption of the mitochondrial membrane potential and with higher density of neurite trees of primary sensory neurons of the dorsal root ganglia in cultures. The data suggest that loss of NXN's balancing redox functions leads to maladaptive changes in sensory neurons that manifest in vivo as polyneuropathy-like abnormal cold sensitivity and heat "pain".

Genetic similarities and differences among distinct definitions of depression

Depression is a common and complex psychiatric illness with considerable heritability. Genome-wide association studies (GWAS) have been conducted among different definitions of depression based on different diagnostic criteria. However, the heritability explained by different depression GWAS and the identified loci varied widely. To understand the genetic architectures of different definitions of depression, we conducted a series of genetic analyses including linkage disequilibrium score regression (LDSC), Mendelian randomization, and polygenic overlap quantification and identification. Different definitions of depression and other common psychiatric traits were included in this analysis. We found that although genetic correlations between different definitions of depression were relatively high, they showed substantially different genetic correlation and causality with other psychiatric traits. Using bivariate causal mixture mode (MiXeR) and conjunctional false discovery rate (conjFDR) approach, we observed both shared and unique risk loci across different definitions of depression. Further functional mapping with expression quantitative trait loci (eQTL) information from multiple brain tissues and single cell types indicated distinct genes underlying different definitions of depression, and pathways associated with synapses were significantly enriched in the illness. Our study showed that the genetic architectures of different definitions of depression were distinct and genetic studies of depression should be conducted more cautious.

Molecular Mechanisms Underlying Ca2+/Calmodulin-Dependent Protein Kinase Kinase Signal Transduction

Ca²⁺/calmodulin-dependent protein kinase kinase (CaMKK) is the activating kinase for multiple downstream kinases, including CaM-kinase I (CaMKI), CaM-kinase IV (CaMKIV), protein kinase B (PKB/Akt), and 5′AMP-kinase (AMPK), through the phosphorylation of their activation-loop Thr residues in response to increasing the intracellular Ca²⁺ concentration, as CaMKK itself is a Ca²⁺/CaM-dependent enzyme. The CaMKK-mediated kinase cascade plays important roles in a number of Ca²⁺-dependent pathways, such as neuronal morphogenesis and plasticity, transcriptional activation, autophagy, and metabolic regulation, as well as in pathophysiological pathways, including cancer progression, metabolic syndrome, and mental disorders. This review focuses on the molecular mechanism underlying CaMKK-mediated signal transduction in normal and pathophysiological conditions. We summarize the current knowledge of the structural, functional, and physiological properties of the regulatory kinase, CaMKK, and the development and application of its pharmacological inhibitors.

Treatment of cancer with antipsychotic medications: Pushing the boundaries of schizophrenia and cancer

Over a century ago, the phenothiazine dye, methylene blue, was discovered to have both antipsychotic and anti-cancer effects. In the 20th-century, the first phenothiazine antipsychotic, chlorpromazine, was found to inhibit cancer. During the years of elucidating the pharmacology of the phenothiazines, reserpine, an antipsychotic with a long historical background, was likewise discovered to have anti-cancer properties. Research on the effects of antipsychotics on cancer continued slowly until the 21st century when efforts to repurpose antipsychotics for cancer treatment accelerated. This review examines the history of these developments, and identifies which antipsychotics might treat cancer, and which cancers might be treated by antipsychotics. The review also describes the molecular mechanisms through which antipsychotics may inhibit cancer. Although the overlap of molecular pathways between schizophrenia and cancer have been known or suspected for many years, no comprehensive review of the subject has appeared in the psychiatric literature to assess the significance of these similarities. This review fills that gap and discusses what, if any, significance the similarities have regarding the etiology of schizophrenia.

Rare germline variants in individuals diagnosed with schizophrenia within multiplex families

An extensive catalog of common and rare genetic variants contributes to overall risk for schizophrenia and related disorders. As a complement to population genetics efforts, here we present whole genome sequences of multiple affected probands within individual families to search for possible high penetrance driver variants. From a total of 15 families diagnostically evaluated by a single research psychiatrist, we performed whole genome sequencing of a total of 61 affected individuals, called SNPs, indels, and copy number variants, and compared to reference genomes. In fourteen out of fifteen families, the schizophrenia polygenic risk score for each proband was within the control range defined by the Thousand Genomes cohort. In six families, each affected member carried a very rare or private, predicted-damaging, variant in at least one gene. Among these genes, variants in LRP1 and TENM2 suggest these are candidate disease-related genes when taken into context with existing population genetic studies and biological information. Results add to the number of pedigree sequences reported, suggest pathways for the investigation of biological mechanisms, and are consistent with the overall accumulating evidence that very rare damaging variants contribute to the heritability of schizophrenia.

Motor Stereotypic Behavior Was Associated With Immune Response in Macaques: Insight From Transcriptome and Gut Microbiota Analysis

Motor stereotypic behaviors (MSBs) are common in captive rhesus macaques (Macaca mulatta) and human with psychiatric diseases. However, large gaps remain in our understanding of the molecular mechanisms that mediate this behavior and whether there are similarities between human and non-human primates that exhibit this behavior, especially at gene expression and gut microbiota levels. The present study combined behavior, blood transcriptome, and gut microbiota data of two groups of captive macaques to explore this issue (i.e., MSB macaques with high MSB exhibition and those with low: control macaques). Observation data showed that MSB macaques spent the most time on MSB (33.95%), while the CONTROL macaques allocated more time to active (30.99%) and general behavior (30.0%), and only 0.97% of their time for MSB. Blood transcriptome analysis revealed 382 differentially expressed genes between the two groups, with 339 upregulated genes significantly enriched in inflammation/immune response-related pathway. We also identified upregulated pro-inflammatory genes TNFRSF1A, IL1R1, and IL6R. Protein–protein interaction network analysis screened nine hub genes that were all related to innate immune response, and our transcriptomic results were highly similar to findings in human psychiatric disorders. We found that there were significant differences in the beta-diversity of gut microbiota between MSB and CONTROL macaques. Of which Phascolarctobacterium, the producer of short chain fatty acids (SCFAs), was less abundant in MSB macaques. Meanwhile, PICRUSTs predicted that SCFAs intermediates biosynthesis and metabolic pathways were significantly downregulated in MSB macaques. Together, our study revealed that the behavioral, gene expression levels, and gut microbiota composition in MSB macaques was different to controls, and MSB was closely linked with inflammation and immune response. This work provides valuable information for future in-depth investigation of MSB and human psychiatric diseases.

Functional analysis of an R311C variant of Ca2+ -calmodulin-dependent protein kinase kinase-2 (CaMKK2) found as a de novo mutation in a patient with bipolar disorder

OBJECTIVES

Loss-of-function mutations in the gene encoding the calcium-calmodulin (Ca²⁺ -CaM)-dependent protein kinase kinase-2 (CaMKK2) enzyme are linked to bipolar disorder. Recently, a de novo arginine to cysteine (R311C) mutation in CaMKK2 was identified from a whole exome sequencing study of bipolar patients and their unaffected parents. The aim of the present study was to determine the functional consequences of the R311C mutation on CaMKK2 activity and regulation by Ca²⁺ -CaM.

METHODS

The effects of the R311C mutation on CaMKK2 activity and Ca²⁺ -CaM activation were examined using a radiolabeled adenosine triphosphate (ATP) kinase assay. We performed immunoblot analysis to determine whether the R311C mutation impacts threonine-85 (T85) autophosphorylation, an activating phosphorylation site on CaMKK2 that has also been implicated in bipolar disorder. We also expressed the R311C mutant in CaMKK2 knockout HAP1 cells and used immunoblot analysis and an MTS reduction assay to study its effects on Ca²⁺ -dependent downstream signaling and cell viability, respectively.

RESULTS

The R311C mutation maps to the conserved HRD motif within the catalytic loop of CaMKK2 and caused a marked reduction in kinase activity and Ca²⁺ -CaM activation. The R311C mutation virtually abolished T85 autophosphorylation in response to Ca²⁺ -CaM and exerted a dominant-negative effect in cells as it impaired the ability of wild-type CaMKK2 to initiate downstream signaling and maintain cell viability.

CONCLUSIONS

The highly disruptive, loss-of-function impact of the de novo R311C mutation in human CaMKK2 provides a compelling functional rationale for being considered a potential rare monogenic cause of bipolar disorder.

Calcium-binding proteins are altered in the cerebellum in schizophrenia

Alterations in the cortico-cerebellar-thalamic-cortical circuit might underlie the diversity of symptoms in schizophrenia. However, molecular changes in cerebellar neuronal circuits, part of this network, have not yet been fully determined. Using LC-MS/MS, we screened altered candidates in pooled grey matter of cerebellum from schizophrenia subjects who committed suicide (n = 4) and healthy individuals (n = 4). Further validation by immunoblotting of three selected candidates was performed in two cohorts comprising schizophrenia (n = 20), non-schizophrenia suicide (n = 6) and healthy controls (n = 21). We found 99 significantly altered proteins, 31 of them previously reported in other brain areas by proteomic studies. Transport function was the most enriched category, while cell communication was the most prevalent function. For validation, we selected the vacuolar proton pump subunit 1 (VPP1), from transport, and two EF-hand calcium-binding proteins, calmodulin and parvalbumin, from cell communication. All candidates showed significant changes in schizophrenia (n = 7) compared to controls (n = 7). VPP1 was altered in the non-schizophrenia suicide group and increased levels of parvalbumin were linked to antipsychotics. Further validation in an independent cohort of non-suicidal chronic schizophrenia subjects (n = 13) and non-psychiatric controls (n = 14) showed that parvalbumin was increased, while calmodulin was decreased in schizophrenia. Our findings provide evidence of calcium-binding protein dysregulation in the cerebellum in schizophrenia, suggesting an impact on normal calcium-dependent synaptic functioning of cerebellar circuits. Our study also links VPP1 to suicide behaviours, suggesting a possible impairment in vesicle neurotransmitter refilling and release in these phenotypes.

Neuronal Inactivity Co-opts LTP Machinery to Drive Potassium Channel Splicing and Homeostatic Spike Widening

Homeostasis of neural firing properties is important in stabilizing neuronal circuitry, but how such plasticity might depend on alternative splicing is not known. Here we report that chronic inactivity homeostatically increases action potential duration by changing alternative splicing of BK channels; this requires nuclear export of the splicing factor Nova-2. Inactivity and Nova-2 relocation were connected by a novel synapto-nuclear signaling pathway that surprisingly invoked mechanisms akin to Hebbian plasticity: Ca²⁺-permeable AMPA receptor upregulation, L-type Ca²⁺ channel activation, enhanced spine Ca²⁺ transients, nuclear translocation of a CaM shuttle, and nuclear CaMKIV activation. These findings not only uncover commonalities between homeostatic and Hebbian plasticity but also connect homeostatic regulation of synaptic transmission and neuronal excitability. The signaling cascade provides a full-loop mechanism for a classic autoregulatory feedback loop proposed ∼25 years ago. Each element of the loop has been implicated previously in neuropsychiatric disease.

Further evidence for the association between LRP8 and schizophrenia

Previous studies (including genome-wide association study (GWAS) and candidate gene studies) have revealed the important roles of genetic risk factors in schizophrenia, and RELN has been identified as a risk gene for this illness. We recently found that the low-density lipoprotein receptor-related protein 8 (LRP8), a receptor of Reelin (the protein encoded by RELN), was significantly associated with schizophrenia and bipolar disorder in European populations. To further enhance our understanding of its role in the risk of psychiatric illnesses, we conducted meta-analyses of a higher density of single nucleotide polymorphisms (SNPs, N=173) in LRP8 to understand their associations with schizophrenia in much larger samples (39,400 cases and 50,357 controls) from populations of European, Chinese and African American ancestries. The significant risk SNPs then underwent further analyses to understand their correlations with bipolar disorder and anxiety disorders, as well as LRP8 expression. We observed that rs5177 in the 3' untranslated region (3'UTR) of LRP8 was associated with schizophrenia and other psychiatric disorders, and rs5177 was also associated with LRP8 mRNA expression. These data further support LRP8 as a schizophrenia susceptibility gene, and suggest that this variant is likely a risk locus in general populations.

Systems-level analysis of risk genes reveals the modular nature of schizophrenia

Schizophrenia (SCZ) is a complex mental disorder with high heritability. Genetic studies (especially recent genome-wide association studies) have identified many risk genes for schizophrenia. However, the physical interactions among the proteins encoded by schizophrenia risk genes remain elusive and it is not known whether the identified risk genes converge on common molecular networks or pathways. Here we systematically investigated the network characteristics of schizophrenia risk genes using the high-confidence protein-protein interactions (PPI) from the human interactome. We found that schizophrenia risk genes encode a densely interconnected PPI network (P = 4.15 × 10^-31). Compared with the background genes, the schizophrenia risk genes in the interactome have significantly higher degree (P = 5.39 × 10^-11), closeness centrality (P = 7.56 × 10^-11), betweeness centrality (P = 1.29 × 10^-11), clustering coefficient (P = 2.22 × 10^-2), and shorter average shortest path length (P = 7.56 × 10^-11). Based on the densely interconnected PPI network, we identified 48 hub genes and 4 modules formed by highly interconnected schizophrenia genes. We showed that the proteins encoded by schizophrenia hub genes have significantly more direct physical interactions. Gene ontology (GO) analysis revealed that cell adhesion, cell cycle, immune system response, and GABR-receptor complex categories were enriched in the modules formed by highly interconnected schizophrenia risk genes. Our study reveals that schizophrenia risk genes encode a densely interconnected molecular network and demonstrates the modular nature of schizophrenia.

Common and Rare Genetic Risk Factors Converge in Protein Interaction Networks Underlying Schizophrenia

Hundreds of genomic loci have been identified with the recent advances of schizophrenia in genome-wide association studies (GWAS) and sequencing studies. However, the functional interactions among those genes remain largely unknown. We developed a network-based approach to integrate multiple genetic risk factors, which lead to the discovery of new susceptibility genes and causal sub-networks, or pathways in schizophrenia. We identified significantly and consistently over-represented pathways in the largest schizophrenia GWA studies, which are highly relevant to synaptic plasticity, neural development and signaling transduction, such as long-term potentiation, neurotrophin signaling pathway, and the ERBB signaling pathway. We also demonstrated that genes targeted by common SNPs are more likely to interact with genes harboring de novo mutations (DNMs) in the protein-protein interaction (PPI) network, suggesting a mutual interplay of both common and rare variants in schizophrenia. We further developed an edge-based search algorithm to identify the top-ranked gene modules associated with schizophrenia risk. Our results suggest that the N-methyl-D-aspartate receptor (NMDAR) interactome may play a leading role in the pathology of schizophrenia, as it is highly targeted by multiple types of genetic risk factors.

Genetic association and meta-analysis of a schizophrenia GWAS variant rs10489202 in East Asian populations

Previous genome-wide association studies (GWAS) suggest that rs10489202 in the intron of MPC2 (mitochondrial pyruvate carrier 2) is a risk locus for schizophrenia in Han Chinese populations. To validate this discovery, we conducted a replication analysis in an independent case-control sample of Han Chinese ancestry (437 cases and 2031 controls), followed by a meta-analytic investigation in multiple East Asian samples. In the replication analysis, rs10489202 showed marginal association with schizophrenia (two-tailed P = 0.071, OR = 1.192 for T allele); in the meta-analysis using a total of 14,340 cases and 20,349 controls from ten East Asian samples, rs10489202 was genome-wide significantly associated with schizophrenia (two-tailed P = 3.39 × 10^-10, OR = 1.161 for T allele, under the fixed-effect model). We then performed an explorative investigation of the association between this SNP and bipolar disorder, as well as a major depressive disorder, and the schizophrenia-predisposing allele was associated with an increased risk of major depressive disorder in East Asians (two-tailed P = 2.49 × 10^-2, OR = 1.103 for T allele). Furthermore, expression quantitative trait loci (eQTL) analysis in lymphoblastoid cell lines from East Asian donors (N = 85 subjects) revealed that rs10489202 was specifically and significantly associated with the expression of TIPRL gene (P = 5.67 × 10^-4). Taken together, our data add further support for the genetic involvement of this genomic locus in the susceptibility to schizophrenia in East Asian populations, and also provide preliminary evidence for the underlying molecular mechanisms.

Expression Analysis of CYFIP1 and CAMKK2 Genes in the Blood of Epileptic and Schizophrenic Patients

Schizophrenia and epilepsy are two prevalent neurological disorders with high global burden to the society. Genome-wide studies have identified potential underlying causes for these neurological diseases. In the present case-control study, we have assessed expression of CYFIP1 and CAMKK2 genes in the blood samples of epileptic and schizophrenic patients compared with healthy subjects. A total of 180 subjects including 40 epileptic patients, 50 schizophrenic patients, and 90 healthy individuals participated in the study. Expression of the mentioned genes was measured using TaqMan real-time PCR. The results demonstrated a significant upregulation of CYFIP1 gene expression in epileptic patients (P = 0.029). CAMKK2 was downregulated in female schizophrenic patients compared with female healthy individuals (P = 0.048). These results may provide new insight into the pathogenesis of epilepsy and schizophrenia and suggest these genes as potential therapeutic targets for these neurological disorders. Future studies should evaluate these results in larger cohorts of patients.

Integrated analysis supports ATXN1 as a schizophrenia risk gene

Protein-protein interaction (PPI) is informative in identifying hidden disease risk genes that tend to interact with known risk genes usually working together in the same disease module. With the use of an integrated approach combining PPI information with pathway and expression analysis as well as genome-wide association study (GWAS), we intended to find new risk genes for schizophrenia (SCZ). We showed that ATXN1 was the only direct PPI partner of the know SCZ risk gene ZNF804A, and it also had direct PPIs with other 18 known SCZ risk genes. ATXN1 serves as one of the hub genes in the PPI network containing many known SCZ risk genes, and this network is significantly enriched for the MAPK signaling pathway. Further gene expression analysis indicated that ATXN1 is highly expressed in prefrontal cortex, and SCZ patients had significantly decreased expression compared with healthy controls. Finally, the published GWAS data supports an association of ATXN1 with SCZ as well as other psychiatric disorders though not reaching genome-wide significance. These convergent evidences support ATXN1 as a promising risk gene for SCZ, and the integrated approach serves as a useful tool for dissecting the genetic basis of psychiatric disorders.

The Gene Encoding Protocadherin 9 (PCDH9), a Novel Risk Factor for Major Depressive Disorder

Genomic analyses have identified only a handful of robust risk loci for major depressive disorder (MDD). In addition to the published genome-wide significant genes, it is believed that there are undiscovered 'treasures' underlying the current MDD genome-wide association studies (GWASs) and gene expression data sets, and digging into these data will allow better understanding of the illness and development of new therapeutic approaches. For this purpose, we performed a meta-analytic study combining three MDD GWAS data sets (23andMe, CONVERGE, and PGC), and then conducted independent replications of significant loci in two additional samples. The genome-wide significant variants then underwent explorative analyses on MDD-related phenotypes, cognitive function alterations, and gene expression in brains. In the discovery meta-analysis, a previously unidentified single-nucleotide polymorphism (SNP) rs9540720 in the PCDH9 gene was genome-wide significantly associated with MDD (p=1.69 × 10^-8 in a total of 89 610 cases and 246 603 controls), and the association was further strengthened when additional replication samples were included (p=1.20 × 10^-8 in a total of 136 115 cases and 355 275 controls). The risk SNP was also associated with multiple MDD-related phenotypes and cognitive function impairment in diverse samples. Intriguingly, the risk allele of rs9540720 predicted lower PCDH9 expression, consistent with the diagnostic analysis results that PCDH9 mRNA expression levels in the brain and peripheral blood tissues were reduced in MDD patients compared with healthy controls. These convergent lines of evidence suggest that PCDH9 is likely a novel risk gene for MDD. Our study highlights the necessity and importance of excavating the public data sets to explore risk genes for MDD, and this approach is also applicable to other complex diseases.

Further evidence for the genetic association between CACNA1I and schizophrenia

Background

Recent large-scale genome-wide association studies (GWAS) have showed that the neuronal calcium signaling has pivotal roles in schizophrenia (SCZ) in populations of European of ancestry. However, it is not known if calcium signaling pathway genes are also associated with SCZ in Han Chinese population.

Methods

Here we investigated the association between genetic variants in three calcium signaling pathway genes (CACNB2, CACNA1C and CACNA1I) and SCZ in 1615 SCZ cases and 1597 controls.

Results

A single nucleotide polymorphism (SNP) (rs4522708) in CACNA1I is significantly associated with SCZ in our Chinese sample (OR_{A allele} = 1.19, corrected P = 0.042), suggesting that CACNA1I may also be a risk gene for SCZ in Chinese population. Of note, the risk allele (A allele) of SNP rs4522708 is same in European and Chinese populations. Meta-analysis of Chinese and European samples further strengthened the association of rs4522708 with SCZ (OR_{A allele} = 1.074, P = 6.26 × 10⁻¹¹). Expression analysis showed that CACNA1I was significantly up-regulated in hippocampus of SCZ cases compared with controls, implying that dysregulation of CACNA1I may have a role in schizophrenia pathogenesis.

Conclusions

Our study suggests that CACNA1I is a risk gene for SCZ in Chinese population and provides further evidence that supports the potential role of neuronal calcium signaling in schizophrenia.

Progress in genome-wide association studies of schizophrenia in Han Chinese populations

Since 2006, genome-wide association studies of schizophrenia have led to the identification of numerous novel risk loci for this disease. However, there remains a geographical imbalance in genome-wide association studies, which to date have primarily focused on Western populations. During the last 6 years, genome-wide association studies in Han Chinese populations have identified both the sharing of susceptible loci across ethnicities and genes unique to Han Chinese populations. Here, we review recent progress in genome-wide association studies of schizophrenia in Han Chinese populations. Researchers have identified and replicated the sharing of susceptible genes, such as within the major histocompatibility complex, microRNA 137 (MIR137), zinc finger protein 804A (ZNF804A), vaccinia related kinase 2 (VRK2), and arsenite methyltransferase (AS3MT), across both European and East Asian populations. Several copy number variations identified in European populations have also been validated in the Han Chinese, including duplications at 16p11.2, 15q11.2-13.1, 7q11.23, and VIPR2 and deletions at 22q11.2, 1q21.1-q21.2, and NRXN1. However, these studies have identified some potential confounding factors, such as genetic heterogeneity and the effects of natural selection on tetraspanin 18 (TSPAN18) or zinc finger protein 323 (ZNF323), which may explain the population differences in genome-wide association studies. In the future, genome-wide association studies in Han Chinese populations should include meta-analyzes or mega-analyses with enlarged sample sizes across populations, deep sequencing, precision medicine treatment, and functional exploration of the risk genes for schizophrenia.

The schizophrenia risk gene ZNF804A: clinical associations, biological mechanisms and neuronal functions

ZNF804A (zinc-finger protein 804A) has been recognized as a schizophrenia risk gene across multiple world populations. Its intronic single-nucleotide polymorphism (SNP) rs1344706 is among one of the strongest susceptibility variants that have achieved genome-wide significance in genome-wide association studies (GWAS) for schizophrenia and has been widely and intensively studied. To elucidate the biological mechanisms underlying the genetic risk conferred by rs1344706, we retrospectively analyzed the progresses in brain gene expression quantitative trait loci (eQTL) analyses, ZNF804A-induced pathway alterations in neural cells and changes in synaptic phenotypes associated with ZNF804A expression. Based on these data, we hypothesize a potential biological mechanism for a genetic risk allele of ZNF804A in schizophrenia pathogenesis. We also review the efforts being made to characterize the affected intermediate phenotypes using neuroimaging and neuropsychological approaches. We then discuss additional common and rare ZNF804A variants in schizophrenia susceptibility and the potential genetic heterogeneity of these genomic loci between Europeans and Asians. This review for we believe the first time systematically presents the evidence for ZNF804A, describing its discovery and likely roles in brain development and schizophrenia pathogenesis. We believe that this work has summarized this information with a systemic and broad assessment of recent findings.

Relationship between serum calcium and neuropsychological performance might indicate etiological heterogeneity underlying cognitive deficits in schizophrenia and depression

Cognitive dysfunction is a core feature of schizophrenia spectrum and depressive disorders. Influx of extracellular calcium is essential for neuronal processes such as pre-synaptic neurotransmitter release and NMDA receptor mediated neuroplasticity. Since serum and brain interstitial fluids maintain equilibrium for ion concentrations via passive diffusion, the amount of peripheral calcium could affect neuronal and hence cognitive function. Within the physiological norm-levels, we hypothesized higher serum-calcium would be associated with better neuropsychological performance in patients diagnosed with schizophrenia or depression. One-tailed Pearson's correlations were calculated between total serum-calcium levels and performance on an extensive computer-based neuropsychological test battery. Influence of covariates was assessed using linear regression. Serum calcium was significantly and positively correlated with neuropsychological composite, information processing speed, executive function and global assessment of functioning (GAF) in depression patients but not in schizophrenia patients. Amongst covariates, age associated significantly with serum calcium and neuropsychological functioning in depression but only with serum calcium in schizophrenia group. The study provides first evidence for a positive relationship between serum calcium and neuropsychological/daily-life function in depression. Absence of this correlation in schizophrenia could point to etiological heterogeneity concerning calcium-related processes underlying cognitive deficits in these disorders.

Impact of Genetic Variation on Human CaMKK2 Regulation by Ca2+-Calmodulin and Multisite Phosphorylation

The Ca²⁺-calmodulin dependent protein kinase kinase-2 (CaMKK2) is a key regulator of neuronal function and whole-body energy metabolism. Elevated CaMKK2 activity is strongly associated with prostate and hepatic cancers, whereas reduced CaMKK2 activity has been linked to schizophrenia and bipolar disease in humans. Here we report the functional effects of nine rare-variant point mutations that were detected in large-scale human genetic studies and cancer tissues, all of which occur close to two regulatory phosphorylation sites and the catalytic site on human CaMKK2. Four mutations (G87R, R139W, R142W and E268K) cause a marked decrease in Ca²⁺-independent autonomous activity, however S137L and P138S mutants displayed increased autonomous and Ca²⁺-CaM stimulated activities. Furthermore, the G87R mutant is defective in Thr85-autophosphorylation dependent autonomous activity, whereas the A329T mutation rendered CaMKK2 virtually insensitive to Ca²⁺-CaM stimulation. The G87R and R139W mutants behave as dominant-negative inhibitors of CaMKK2 signaling in cells as they block phosphorylation of the downstream substrate AMP-activated protein kinase (AMPK) in response to ionomycin. Our study provides insight into functionally disruptive, rare-variant mutations in human CaMKK2, which have the potential to influence risk and burden of disease associated with aberrant CaMKK2 activity in human populations carrying these variants.

Further evidence of VRK2 rs2312147 associated with schizophrenia

OBJECTIVES

Previous genome-wide association studies (GWAS) have reported that rs2312147 near the VRK2 gene was significantly associated with schizophrenia in populations of European descent, but negative results have also been observed.

METHODS

To perform a systematic meta-analysis, we collected statistical data of rs2312147 from both GWAS and individual replication samples in European and Asian populations, which finally included up to 30,867 schizophrenia patients and 59,863 healthy controls.

RESULTS

The VRK2 rs2312147 was genome-wide significantly associated with schizophrenia in combined populations (P = 1.31 × 10(-15), odds ratio, OR = 1.10) as well as in Europeans only (P = 2.35 × 10(-12), OR =1.09). In Asian samples, the SNP did not reach genome-wide level of statistical significance (P = 1.23 × 10 (-) (5), OR =1.19), which is likely due to the limited power of small sample size in this population (2,974 cases and 4,786 controls). However, the effect size of rs2312147 did not alter significantly between populations, and is also in agreement with the observed effect sizes of other genetic risk loci in large scale studies.

CONCLUSIONS

Our data provides further evidence for the genetic contributions of VRK2 rs2312147 to schizophrenia susceptibility especially in Europeans, while further replication analyses in Asian populations are still needed, and future studies, e.g., the underlying molecular mechanisms of genetic risk, are necessary.

Excitation-Transcription Coupling in Parvalbumin-Positive Interneurons Employs a Novel CaM Kinase-Dependent Pathway Distinct from Excitatory Neurons

Properly functional CNS circuits depend on inhibitory interneurons that in turn rely upon activity-dependent gene expression for morphological development, connectivity, and excitatory-inhibitory coordination. Despite its importance, excitation-transcription coupling in inhibitory interneurons is poorly understood. We report that PV+ interneurons employ a novel CaMK-dependent pathway to trigger CREB phosphorylation and gene expression. As in excitatory neurons, voltage-gated Ca(2+) influx through CaV1 channels triggers CaM nuclear translocation via local Ca(2+) signaling. However, PV+ interneurons are distinct in that nuclear signaling is mediated by γCaMKI, not γCaMKII. CREB phosphorylation also proceeds with slow, sigmoid kinetics, rate-limited by paucity of CaMKIV, protecting against saturation of phospho-CREB in the face of higher firing rates and bigger Ca(2+) transients. Our findings support the generality of CaM shuttling to drive nuclear CaMK activity, and they are relevant to disease pathophysiology, insofar as dysfunction of PV+ interneurons and molecules underpinning their excitation-transcription coupling both relate to neuropsychiatric disease.

Effect of rs1063843 in the CAMKK2 gene on the dorsolateral prefrontal cortex

Recently, a single nucleotide polymorphism (SNP) in the CAMKK2 gene (rs1063843) was found to be associated with lower expression of the gene in the dorsolateral prefrontal cortex (DLPFC) and with schizophrenia (SCZ) and deficits in working memory and executive function. However, the brain mechanism underlying this association is poorly understood. A functional magnetic resonance imaging (fMRI) study (N = 84 healthy volunteers) involving multiple cognitive tasks, including a Stroop task (to measure attentional executive control), an N-back task (to measure working memory), and a delay discounting task (to measure decision making) to identify the brain regions affected by rs1063843 was performed. Across all three tasks, it was found that carriers of the risk allele consistently exhibited increased activation of the left DLPFC. In addition, the risk allele carriers also exhibited increased activation of the right DLPFC and the left cerebellum during the Stroop task and of the left caudate nucleus during the N-back task. These findings helped to elucidate the role of CAMKK2 in cognitive functions and in the etiology of SCZ. Hum Brain Mapp 37:2398-2406, 2016. © 2016 Wiley Periodicals, Inc.

Genetic variants in Nogo receptor signaling pathways may be associated with early life adversity in schizophrenia susceptibility

Background

Schizophrenia is a severe neuropsychiatric disorder thought to result from abnormal brain development. Nogo, an oligodendrocyte bound molecule, signals by binding to the Nogo receptor (NgR) located on axonal membranes. The NgR co-receptors include p75 neurotrophin receptor or TNF receptor orphan Y (TROY). Nogo signaling is responsible for central nervous system myelin regulation and neurite outgrowth during neurodevelopment, and plasticity in the mature brain.

Methods

We examined single nucleotide polymorphisms (SNPs) in NgR, p75, and TROY receptor genes and downstream signaling partner With No Lysine (K) (WNK1) and Myelin transcription factor 1-like (Myt1l) genes in an Australian case–control schizophrenia cohort (n = 268/group). High-throughput SNP genotyping was performed using the MassARRAY® genotyping assay.

Results

Analysis revealed a significant association between the Myt1l SNP rs2304008 and female schizophrenia subjects. The WNK1 SNP rs1468326 and the Myt1l SNP rs3748988 showed significant associations with schizophrenia in subjects with a maternal mental history and in subjects who experienced childhood trauma respectively. Following Bonferroni correction, all significance was lost.

Conclusions

Despite the lack of positive findings in our population after correction for multiple testing, previous gene expression and association studies in schizophrenia suggest the implication of NgR signaling pathway genes in the etiology of schizophrenia remains topical and timely.

General significance

Further investigations will be necessary to fully assess the role of these genes in the pathophysiology of schizophrenia. However these genes may prove useful in further understanding the mechanism by which negative experiences early in life can affect myelin-related processes in the context of schizophrenia.

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NgR signaling polymorphisms were evaluated in schizophrenia patients and healthy controls.

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Prior to Bonferroni correction Myt1l rs2304008 had a significant association in female schizophrenia subjects.

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Prior to Bonferroni correction WNK1 rs1468326 and Myt1l rs3748988 were associated with schizophrenia in subjects who experienced early life adversities.

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Disruption to NgR signaling may be associated with early life adversity in schizophrenia.

Convergent Lines of Evidence Support LRP8 as a Susceptibility Gene for Psychosis

Reelin (RELN) is identified as a risk gene for major psychiatric disorders such as schizophrenia (SCZ) and bipolar disorder (BPD). However, the role of its downstream signaling molecule, the low-density lipoprotein receptor-related protein 8 (LRP8) in these illnesses is still unclear. To detect whether LRP8 is a susceptibility gene for SCZ and BPD, we analyzed the associations of single nucleotide polymorphisms (SNPs) in LRP8 in a total of 47,187 subjects (including 9379 SCZ patients; 6990 BPD patients; and 12,556 controls in a screening sample, and 1397 SCZ families, 3947 BPD patients, and 8387 controls in independent replications), and identified a non-synonymous SNP rs5174 in LRP8 significantly associated with SCZ and BPD as well as the combined psychosis phenotype (P _meta = 1.99 × 10^-5, odds ratio (OR) = 1.066, 95 % confidence interval (CI) = 1.035-1.098). The risk SNP rs5174 was also associated with LRP8 messenger RNA (mRNA) expression in multiple brain tissues across independent samples (lowest P = 0.00005). Further exploratory analysis revealed that LRP8 was preferentially expressed in fetal brain tissues. Protein-protein interaction (PPI) analysis demonstrated that LRP8 significantly participated in a highly interconnected PPI network build by top risk genes for SCZ and BPD (P = 7.0 × 10^-4). Collectively, we confirmed that LRP8 is a risk gene for psychosis, and our results provide useful information toward a better understanding of genetic mechanism involving LRP8 underlying risk of complex psychiatric disorders.

The NVL gene confers risk for both major depressive disorder and schizophrenia in the Han Chinese population

NVL (nuclear VCP (valosin containing protein)/p97-Like), a member of the AAA-ATPase (ATPases associated with various cellular activities) family, encodes a novel hTERT (human telomerase reverse transcriptase)-interacting protein NVL2 which is a telomerase component essential for holoenzyme assembly. Previous researches have reported the impacts of telomerase activity on mental illness and the potential association between NVL and major depressive disorder. To validate the susceptibility of NVL to major depressive disorder, and to investigate the overlapping risk conferred by NVL for both major depressive disorder and schizophrenia, we analyzed 9 tag single nucleotide polymorphisms (tag SNPs) using TaqMan® technology, in 1045 major depressive disorder patients, 1235 schizophrenia patients and 1235 normal controls of Han Chinese origin. We found that rs10916583 (P(allele) = 0.020, P(genotype) = 0.028, OR = 1.156) and rs16846649 (adjusted P(allele) = 0.014, P(genotype) = 0.007, OR = 0.718) were associated with major depressive disorder, while rs10916583 (adjusted P(allele) = 1.08E-02, OR = 1.213), rs16846649 (adjusted P(allele) = 7.40E-06, adjusted P(genotype) = 8.07E-05, OR = 0.598) and rs10799541 (adjusted P(allele) = 8.10E-03, adjusted P(genotype) = 0.049, OR= 0.826) showed statistically significant association with schizophrenia after Bonferroni correction. Furthermore, rs10916583 (adjusted P(allele) = 9.00E-03, adjusted P(genotype) = 3.15E-02, OR = 1.187) and rs16846649 (adjusted P(allele) = 8.92E-06, adjusted P(genotype) = 8.84E-05, OR = 0.653) remained strongly associated with the analysis of combined cases of major depressive disorder and schizophrenia after Bonferroni correction. Our results indicated that the NVL gene may contain overlapping common genetic risk factors for major depressive disorder and schizophrenia in the Han Chinese population. The roles of NVL in telomerase biogenesis were also highlighted in psychiatric pathogenesis. The study on variants conferring overlapping risk for multiple psychiatric disorders could be tangible pathogenesis support and clinical or diagnostic references.

Autophosphorylation of CaMKK2 generates autonomous activity that is disrupted by a T85S mutation linked to anxiety and bipolar disorder

Mutations that reduce expression or give rise to a Thr85Ser (T85S) mutation of Ca(2+)-CaM-dependent protein kinase kinase-2 (CaMKK2) have been implicated in behavioural disorders such as anxiety, bipolar and schizophrenia in humans. Here we report that Thr85 is an autophosphorylation site that endows CaMKK2 with a molecular memory that enables sustained autonomous activation following an initial, transient Ca(2+) signal. Conversely, autophosphorylation of Ser85 in the T85S mutant fails to generate autonomous activity but instead causes a partial loss of CaMKK2 activity. The loss of autonomous activity in the mutant can be rescued by blocking glycogen synthase kinase-3 (GSK3) phosphorylation of CaMKK2 with the anti-mania drug lithium. Furthermore, CaMKK2 null mice representing a loss of function model the human behavioural phenotypes, displaying anxiety and manic-like behavioural disturbances. Our data provide a novel insight into CaMKK2 regulation and its perturbation by a mutation associated with behavioural disorders.

A genetic variant in CAMKK2 gene is possibly associated with increased risk of bipolar disorder

A recent large-scale study have reported that rs1063843, a single nucleotide polymorphism located in the CAMKK2 gene is highly associated with schizophrenia in European and Han Chinese populations. Increasing evidences show that schizophrenia and bipolar disorder have some common genetic variance. Here, we evaluated the association of this variant with schizophrenia and bipolar disorder in Iranian population. Genomic DNA was extracted from peripheral blood of 500 schizophrenic patients, 500 bipolar patients and 500 normal controls and all were genotyped for the rs1063843 using a PCR-RFLP method. The allele frequency of rs1063843 was significantly different in both schizophrenia and bipolar patients comparing to control group. For the first time, we showed that rs1063843 is highly associated with bipolar disorder, although more replication studies are needed to confirm our findings. Our results also support the findings of previous studies suggesting a significant association between rs1063843 and schizophrenia.

Common variants of IRF3 conferring risk of schizophrenia

Schizophrenia is a brain disorder with high heritability. Recent studies have implicated genes involved in the immune response pathway in the pathogenesis of schizophrenia. Interferon regulatory factor 3 (IRF3), a virus-immune-related gene, activates the transcription of several interferon-induced genes, and functionally interacts with several schizophrenia susceptibility genes. To test whether IRF3 is a schizophrenia susceptibility gene, we analyzed the associations of its SNPs with schizophrenia in independent population samples as well as reported data from expression quantitative trait loci (eQTL) in healthy individuals. We observed multiple independent SNPs in IRF3 showing nominally significant associations with schizophrenia (P < 0.05); more intriguingly, a SNP (rs11880923), which is significantly correlated with IRF3 expression in independent samples (P < 0.05), is also consistently associated with schizophrenia across different cohorts and in combined samples (odds ratio = 1.075, Pmeta = 2.08 × 10(-5)), especially in Caucasians (odds ratio = 1.078, Pmeta = 2.46 × 10(-5)). These results suggested that IRF3 is likely a risk gene for schizophrenia, at least in Caucasians. Although the clinical associations of IRF3 with diagnosis did not achieve genome-wide level of statistical significance, the observed odds ratio is comparable with other susceptibility loci identified through large-scale genetic association studies on schizophrenia, which could be regarded simply as small but detectable effects.

Genetic studies of schizophrenia: an update

Schizophrenia (SCZ) is a complex and heterogeneous mental disorder that affects about 1% of global population. In recent years, considerable progress has been made in genetic studies of SCZ. A number of common variants with small effects and rare variants with relatively larger effects have been identified. These variants include risk loci identified by genome-wide association studies, rare copy-number variants identified by comparative genomic analyses, and de novo mutations identified by high-throughput DNA sequencing. Collectively, they contribute to the heterogeneity of the disease. In this review, we update recent discoveries in the field of SCZ genetics, and outline the perspectives of future directions.

Microglial intracellular Ca(2+) signaling as a target of antipsychotic actions for the treatment of schizophrenia

Microglia are resident innate immune cells which release many factors including proinflammatory cytokines, nitric oxide (NO) and neurotrophic factors when they are activated in response to immunological stimuli. Recent reports show that pathophysiology of schizophrenia is related to the inflammatory responses mediated by microglia. Intracellular Ca²⁺ signaling, which is mainly controlled by the endoplasmic reticulum (ER), is important for microglial functions such as release of NO and cytokines, migration, ramification and deramification. In addition, alteration of intracellular Ca²⁺ signaling underlies the pathophysiology of schizophrenia, while it remains unclear how typical or atypical antipsychotics affect intracellular Ca²⁺ mobilization in microglial cells. This mini-review article summarizes recent findings on cellular mechanisms underlying the characteristic differences in the actions of antipsychotics on microglial intracellular Ca²⁺ signaling and reinforces the importance of the ER of microglial cells as a target of antipsychotics for the treatment of schizophrenia.

An evaluation of association between a novel hippocampal biology related SNP (rs7294919) and schizophrenia

Recent genetic analyses have implicated several candidate susceptibility variants for schizophrenia. The single nucleotide polymorphism (SNP) rs7294919 is likely a schizophrenia-susceptibility variant according to its significant association with hippocampal volume, hippocampus function, and cognitive performance as well as the nominal association with schizophrenia. However, all previous analyses were conducted only in Europeans, and whether rs7294919 is associated with schizophrenia in other populations are yet to be tested. Here, we conducted a case-control analysis of rs7294919 with schizophrenia in six independent Chinese (N = 3) and Japanese (N = 3) samples, including a total of 7,352 cases and 10,824 controls. The results of our association analysis were not able to confirm the association of rs7294919 with schizophrenia (p = 0.51 in total samples, odds ratio = 1.02 for allele[C]). The absence of rs7294919's association in Chinese and Japanese suggest a potential genetic heterogeneity in the susceptibility of schizophrenia on this locus and also demonstrate the difficulties in replicating associations of schizophrenia across different ethnic populations.