Replication of brain function effects of a genome-wide supported psychiatric risk variant in the CACNA1C gene and new multi-locus effects

Altered cortical synaptic lipid signaling leads to intermediate phenotypes of mental disorders

Excitation/inhibition (E/I) balance plays important roles in mental disorders. Bioactive phospholipids like lysophosphatidic acid (LPA) are synthesized by the enzyme autotaxin (ATX) at cortical synapses and modulate glutamatergic transmission, and eventually alter E/I balance of cortical networks. Here, we analyzed functional consequences of altered E/I balance in 25 human subjects induced by genetic disruption of the synaptic lipid signaling modifier PRG-1, which were compared to 25 age and sex matched control subjects. Furthermore, we tested therapeutic options targeting ATX in a related mouse line. Using EEG combined with TMS in an instructed fear paradigm, neuropsychological analysis and an fMRI based episodic memory task, we found intermediate phenotypes of mental disorders in human carriers of a loss-of-function single nucleotide polymorphism of PRG-1 (PRG-1R345T/WT). Prg-1R346T/WT animals phenocopied human carriers showing increased anxiety, a depressive phenotype and lower stress resilience. Network analysis revealed that coherence and phase-amplitude coupling were altered by PRG-1 deficiency in memory related circuits in humans and mice alike. Brain oscillation phenotypes were restored by inhibtion of ATX in Prg-1 deficient mice indicating an interventional potential for mental disorders.

Effect of rs1108580 of DBH and rs1006737 of CACNA1C on Cognition and Tardive Dyskinesia in a North Indian Schizophrenia Cohort

Genetic perturbations in dopamine neurotransmission and calcium signaling pathways are implicated in the etiology of schizophrenia. We aimed to test the association of a functional splice variant each in Dopamine β-Hydroxylase (DBH; rs1108580) and Calcium voltage-gated channel subunit alpha1 C (CACNA1C; rs1006737) genes in these pathways with schizophrenia (506 cases, 443 controls); Abnormal Involuntary Movement Scale (AIMS) scores in subjects assessed for tardive dyskinesia (76 TD-positive, 95 TD-negative) and Penn Computerized Neurocognitive Battery (PennCNB) scores (334 cases, 234 controls). The effect of smoking status and SNP genotypes on AIMS scores were assessed using ANOVA; health status and SNP genotypes on three performance functions of PennCNB cognitive domains were assessed by ANCOVA with age and sex as covariates. Association with Positive and Negative Syndrome Scale (PANSS) scores in the TD cohort and cognitive scores in healthy controls of the cognition cohort were tested by linear regression. None of the markers were associated with schizophrenia. Smoking status [F(2, 139) = 10.6; p = 5 × 10-5], rs1006737 [F(2, 139) = 7.1; p = 0.001], TD status*smoking [F(2, 139) = 8.0; p = 5.0 × 10-4] and smoking status*rs1006737 [F(4, 139) = 2.7; p = 0.03] had an effect on AIMS score. Furthermore, rs1006737 was associated with orofacial [F(2, 139) = 4.6; p = 0.01] and limb-truncal TD [(F(2, 139) = 3.8; p = 0.02]. Main effect of rs1108580 on working memoryprocessing speed [F(2, 544) = 3.8; p = 0.03] and rs1006737 on spatial abilityefficiency [F(1, 550) = 9.4; p = 0.02] was identified. Health status*rs1006737 interaction had an effect on spatial memoryprocessing speed [F(1, 550) = 6.9; p = 0.01]. Allelic/genotypic association (p = 0.01/0.03) of rs1006737 with disorganized/concrete factor and allelic association of rs1108580 (p = 0.04) with a depressive factor of PANSS was observed in the TD-negative subcohort. Allelic association of rs1006737 with sensorimotor dexterityaccuracy (p = 0.03), attentionefficiency (p = 0.05), and spatial abilityefficiency (p = 0.02); allelic association of rs1108580 with face memoryaccuracy (p = 0.05) and emotionefficiency (p = 0.05); and allelic/genotypic association with emotionaccuracy (p = 0.003/0.009) were observed in healthy controls of the cognition cohort. These association findings may have direct implications for personalized medicine and cognitive remediation.

A randomized controlled trial of Vitamin D supplementation in Iranian patients with schizophrenia: Effects on serum levels of glycogen synthase kinase-3β and symptom severity

BACKGROUND

Growing evidence has shown that hypovitaminosis D is a risk factor for developing schizophrenia and comorbid conditions. Therefore, this study aimed to examine the effect of vitamin D supplementation on serum levels of vitamin D, metabolic factors related to insulin resistance (IR) and the severity of the disorder in patients with schizophrenia.

METHODS

Forty-eight chronic male patients with schizophrenia with vitamin D deficiency (≤20 ng/mL= (≤50 nmol/l) were selected and randomly assigned to vitamin D treatment and placebo groups. Subjects were supplemented for 8 weeks with vitamin D (2000 IU/day) or placebo.

RESULTS

Within-group comparison revealed that the vitamin D group had a significant reduction in waist circumference, Positive and Negative Syndrome Scale - total score (PANSS-TS), and glycogen synthase kinase 3 beta (GSK-3β) levels (P = .022, P = <.001 and P = .013, respectively). On the other hand, the placebo group showed a significant increase in the level of fasting serum insulin and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) (P = .003 and P = .003). The between-group comparison showed a significant difference in terms of PANSS-TS, GSK-3β, fasting serum insulin (FSI), and HOMA-IR (P = .022, P = .048, P = .013 and P = .014 respectively).

CONCLUSIONS

Among vitamin D deficient patients with schizophrenia, vitamin D supplementation may affect GSK-3 β, an important biomarker in schizophrenia and insulin resistance. In addition, vitamin D supplementation in such patients may reduce the disorder's symptom severity.

Association between CACNA1C gene rs100737 polymorphism and glutamatergic neurometabolites in bipolar disorder

Abnormalities in Ca²⁺ homeostasis in Bipolar Disorders (BD) have been associated with impairments in glutamatergic receptors and voltage-gated calcium channels. Increased anterior cingulate cortex (ACC) glutamatergic neurometabolites have been consistently disclosed in BD by proton magnetic resonance spectroscopy (¹H-MRS). A single nucleotide polymorphism (SNP) in the CACNA1C gene (rs1006737), which encodes the alpha 1-C subunit of the L-type calcium channel, has been associated with BD and is reported to modulate intra-cellular Ca²⁺. Thus, this study aimed to explore the association of the CACNA1C genotype with ACC glutamatergic metabolites measured by ¹H-MRS in both BD and HC subjects. A total of 194 subjects (121 euthymic BD type I patients and 73 healthy controls (HC) were genotyped for CACNA1C rs1006737, underwent a 3-Tesla ¹H-MRS imaging examination and ACC glutamatergic metabolite were assessed. We found overall increased glutamatergic metabolites in AA carriers in BD. Specifically, higher Glx/Cr was observed in subjects with the AA genotype compared to both AG and GG in the overall sample (BD + HC). Also, female individuals in the BD group with AA genotype were found to have higher Glx/Cr compared to those with other genotypes. CACNA1C AA carriers in use of anticonvulsant medication had higher estimated Glutamine (Glx-Glu) than the other genotypes. Thus, this study suggest an association between calcium channel genetics and increased glutamatergic metabolites in BD, possibly playing a synergic role in intracellular Ca²⁺ overload and excitotoxicity.

Cav1.2 Activity and Downstream Signaling Pathways in the Hippocampus of An Animal Model of Depression

Functional and morphological modifications in the brain caused by major mood disorders involve many brain areas, including the hippocampus, leading to cognitive and mood alterations. Ca_v1.2 channel expression has been found to increase in animals with depressive-like behaviors. Calcium influx through these channels is associated with changes in excitation-transcriptional coupling by several intracellular signal pathways that are regulated by its C-terminus region. However, which of these signaling pathways is activated during the development of depressive-like behaviors is not known. Here, we evaluate the phosphorylation and expression levels of crucial kinases and transcription factors at the hippocampus of rats after 21 days of chronic restraint stress. Our results show that rats subjected to CRS protocol achieve less body weight, have heavier adrenal glands, and exhibit depression-like behaviors such as anhedonia, behavioral despair and decreased social interaction. Ca_v1.2 mRNA and protein expression levels, plus l-type calcium current amplitude, are also increased in treated rats when compared with control animals. Out of the three main signaling pathways activated by l-type currents, we only observed an increment of CaM-NFAT axis activity with the concomitant increment in Fas ligand expression. Thus, our results suggest that CRS activates specific pathways, and the increased expression of Ca_v1.2 could lead to neuronal death in the hippocampus.

Neurocan genome-wide psychiatric risk variant affects explicit memory performance and hippocampal function in healthy humans

Alterations of the brain extracellular matrix (ECM) can perturb the structure and function of brain networks like the hippocampus, a key region in human memory that is commonly affected in psychiatric disorders. Here, we investigated the potential effects of a genome-wide psychiatric risk variant in the NCAN gene encoding the ECM proteoglycan neurocan (rs1064395) on memory performance, hippocampal function and cortical morphology in young, healthy volunteers. We assessed verbal memory performance in two cohorts (N = 572, 302) and found reduced recall performance in risk allele (A) carriers across both cohorts. In 117 participants, we performed functional magnetic resonance imaging using a novelty-encoding task with visual scenes. Risk allele carriers showed higher false alarm rates during recognition, accompanied by inefficiently increased left hippocampal activation. To assess effects of rs1064395 on brain morphology, we performed voxel-based morphometry in 420 participants from four independent cohorts and found lower grey matter density in the ventrolateral and rostral prefrontal cortex of risk allele carriers. In silico eQTL analysis revealed that rs1064395 SNP is linked not only to increased prefrontal expression of the NCAN gene itself, but also of the neighbouring HAPLN4 gene, suggesting a more complex effect of the SNP on ECM composition. Our results suggest that the NCAN rs1064395 A allele is associated with lower hippocampus-dependent memory function, variation of prefrontal cortex structure and ECM composition. Considering the well-documented hippocampal and prefrontal dysfunction in bipolar disorder and schizophrenia, our results may reflect an intermediate phenotype by which NCAN rs1064395 contributes to disease risk.

Cacna1c haploinsufficiency lacks effects on adult hippocampal neurogenesis and volumetric properties of prefrontal cortex and hippocampus in female rats

The cross-disorder risk gene CACNA1C is strongly involved in the etiology of all major neuropsychiatric disorders, with women often being more affected by CACNA1C mutations than men. Human neuroimaging studies provided evidence that CACNA1C variants are associated with anatomical and functional brain alterations, such as decreased prefrontal volumes, microstructural changes in the hippocampus, and reduced hippocampal activity during memory tasks. In mouse models, Cacna1c alterations were repeatedly linked to disorder-like behavioral phenotypes and reduced adult hippocampal neurogenesis, which has been implicated in the pathology of neuropsychiatric disorders. Here, we applied a recently developed rat model and conducted two studies to investigate the effects of partial Cacna1c depletion on adult hippocampal neurogenesis and volumetric properties of the hippocampus and the prefrontal cortex in adult female constitutive heterozygous (Cacna1c^+/-) rats and wildtype (Cacna1c^+/+) littermate controls. In study 1, we analyzed proliferation versus survival of adult-born hippocampal cells based on a 5-bromodeoxyuridine assay ensuring neuronal cell-type specificity through applying an immunofluorescent multiple staining approach. In study 2, we performed a detailed volumetric analysis with high structural resolution of the dorsal hippocampus and the medial prefrontal cortex, including their major substructures. Our results indicate comparable levels of cell proliferation and neuronal survival in Cacna1c^+/- rats and Cacna1c^+/+ controls. Additionally, we found similar volumes of the dorsal hippocampus and the medial prefrontal cortex across major substructures irrespective of genotype, indicating that Cacna1c haploinsufficiency has no prominent effects on these brain features in female rats.

CACNA1C Risk Variant and Mood Stabilizers Effects in the Prefrontal Cortical Thickness of Mexican Patients with Bipolar Disorder

PURPOSE

Bipolar disorder (BD) is a condition associated with structural alterations in the prefrontal cortex (PFC); some genetic variants and mood stabilizer medications like lithium or valproate are associated with these changes. CACNA1C is a gene involved in BD pathology and brain function; carriers of the A allele of rs1006737 are reported to have increased risk for BD and increased cortical thickness (CT) in the PFC compared to non-carriers. Lithium is also associated with increased CT in the PFC of BD subjects compared to the ones on valproate. The influence of these treatments and gene variants over the PFC structure of Mexican subjects has not been explored. Therefore, we evaluate the effects of mood stabilizers and risk A allele of CACNA1C rs1006737 on the prefrontal cortical thickness of Mexican BD patients treated with lithium or valproate.

PATIENTS AND METHODS

A cross-sectional study of 40 BD type I euthymic adult outpatients (20 treated with lithium and 20 with valproate) who underwent a 3T T1-weighted 3D brain scan and genotyping for CACNA1C risk allele rs1006737 was conducted. We performed a cortical thickness analysis of the dorsolateral and orbitofrontal regions of the prefrontal cortex with BrainVoyager 20.6. The effects of treatment and gene variants were analyzed with a two-way multivariate analysis of covariance.

RESULTS

There was no association of CACNA1C risk allele rs1006737 with CT measures of both PFCs nor significant interaction between the genetic variant and treatment. Mood stabilizers reported the main effect on the CT measures of the right PFC of our sample. Patients on treatment with lithium showed higher mean CT on the right orbitofrontal cortex.

CONCLUSION

We did not find any association between the prefrontal CT and CACNA1C risk A allele rs1006737 in BD Mexican patients treated with lithium or valproate. Our results suggest that mood stabilizers had the main effect in the CT of the right PFC.

Interaction of the Psychiatric Risk Gene Cacna1c With Post-weaning Social Isolation or Environmental Enrichment Does Not Affect Brain Mitochondrial Bioenergetics in Rats

The pathophysiology of neuropsychiatric disorders involves complex interactions between genetic and environmental risk factors. Confirmed by several genome-wide association studies, Cacna1c represents one of the most robustly replicated psychiatric risk genes. Besides genetic predispositions, environmental stress such as childhood maltreatment also contributes to enhanced disease vulnerability. Both, Cacna1c gene variants and stressful life events are associated with morphological alterations in the prefrontal cortex and the hippocampus. Emerging evidence suggests impaired mitochondrial bioenergetics as a possible underlying mechanism of these regional brain abnormalities. In the present study, we simulated the interaction of psychiatric disease-relevant genetic and environmental factors in rodents to investigate their potential effect on brain mitochondrial function using a constitutive heterozygous Cacna1c rat model in combination with a four-week exposure to either post-weaning social isolation, standard housing, or social and physical environmental enrichment. Mitochondria were isolated from the prefrontal cortex and the hippocampus to evaluate their bioenergetics, membrane potential, reactive oxygen species production, and respiratory chain complex protein levels. None of these parameters were considerably affected in this particular gene-environment setting. These negative results were very robust in all tested conditions demonstrating that Cacna1c depletion did not significantly translate into altered bioenergetic characteristics. Thus, further investigations are required to determine the disease-related effects on brain mitochondria.

Genetic Variation in the Psychiatric Risk Gene CACNA1C Modulates Reversal Learning Across Species

Genetic variation in CACNA1C, which encodes the alpha-1 subunit of Cav1.2 L-type voltage-gated calcium channels (VGCCs), has been strongly linked to risk for psychiatric disorders including schizophrenia and bipolar disorder. How genetic variation in CACNA1C contributes to risk for these disorders is however not fully known. Both schizophrenia and bipolar disorder are associated with impairments in reversal learning (RL), which may contribute to symptoms seen in these conditions. We used a translational RL paradigm to investigate whether genetic variation in CACNA1C affects RL in both humans and transgenic rats. Associated changes in gene expression were explored using in situ hybridization and quantitative PCR in rats and the BRAINEAC online human database. Risk-associated genetic variation in CACNA1C in healthy human participants was associated with impairments in RL. Consistent with this finding, rats bearing a heterozygous deletion of Cacna1c were impaired in an analogous touchscreen RL task. We investigated the possible molecular mechanism underlying this impairment and found that Cacna1c +/- rats show decreased expression of Bdnf in prefrontal cortex. Examination of BRAINEAC data showed that human risk-associated genetic variation in CACNA1C is also associated with altered expression of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex in humans. These results indicate that genetic variation in CACNA1C may contribute to risk for schizophrenia and bipolar disorder by impacting behavioral flexibility, potentially through altered regulation of BDNF expression in the prefrontal cortex. Tests of RL may be useful for translational studies and in the development of therapies targeting VGCCs.

A Common CACNA1C Gene Risk Variant has Sex-Dependent Effects on Behavioral Traits and Brain Functional Activity

Genome-wide association studies have suggested that allelic variations in the CACNA1C gene confer susceptibility to schizophrenia and bipolar disorder only in women. Here we investigated the sex-specific effects of the CACNA1C variant rs1024582 on psychiatry-related traits, brain activity during tasks and rest, and brain volume in 1207 normal male and female subjects. After correcting for multiple comparisons, there were significant interaction effects between sex and the minor allele of this polymorphism on the hostile behavior subscale scores of the Coronary-Prone Type Scale mediated by higher scores in female carriers of the minor allele. Imaging analyses revealed significant interaction effects between sex and the minor allele on fractional amplitude of low-frequency fluctuations in the right dorsolateral prefrontal cortex and on brain activity during the 2-back task in areas of the right posterior cingulate cortex, right thalamus, and right hippocampus, which were all mediated by reduced activity in female carriers of the minor allele. Our results demonstrated that the rs1024582 risk variant of CACNA1C is associated with reduced activity in the frontolimbic regions at rest and during a working memory task as well as with greater hostility in females in the healthy population.

Identification of rare nonsynonymous variants in SYNE1/CPG2 in bipolar affective disorder

BACKGROUND

Bipolar affective disorder (BPD) is a severe mood disorder with a prevalence of ∼1.5% in the population. The pathogenesis of BPD is poorly understood; however, a strong heritable component has been identified. Previous genome-wide association studies have indicated a region on 6q25, coding for the SYNE1 gene, which increases disease susceptibility. SYNE1 encodes the synaptic nuclear envelope protein-1, nesprin-1. A brain-specific splice variant of SYNE1, CPG2 encoding candidate plasticity gene 2, has been identified. The intronic single-nucleotide polymorphism with the strongest genome-wide significant association in BPD, rs9371601, is present in both SYNE1 and CPG2.

METHODS

We screened 937 BPD samples for genetic variation in SYNE1 exons 14-33, which covers the CPG2 region, using high-resolution melt analysis. In addition, we screened two regions of increased transcriptional activity, one of them proposed to be the CPG2 promoter region.

RESULTS AND CONCLUSION

We identified six nonsynonymous and six synonymous variants. We genotyped three rare nonsynonymous variants, rs374866393, rs148346599 and rs200629713, in a total of 1099 BPD samples and 1056 controls. Burden analysis of these rare variants did not show a significant association with BPD. However, nine patients are compound heterozygotes for variants in SYNE1/CPG2, suggesting that rare coding variants may contribute significantly towards the complex genetic architecture underlying BPD. Imputation analysis in our own whole-genome sequencing sample of 99 BPD individuals identified an additional eight risk variants in the CPG2 region of SYNE1.

Downregulation of the psychiatric susceptibility gene Cacna1c promotes mitochondrial resilience to oxidative stress in neuronal cells

Affective disorders such as major depression and bipolar disorder are among the most prevalent forms of mental illness and their etiologies involve complex interactions between genetic and environmental risk factors. Over the past ten years, several genome wide association studies (GWAS) have identified CACNA1C as one of the strongest genetic risk factors for the development of affective disorders. However, its role in disease pathogenesis is still largely unknown. Vulnerability to affective disorders also involves diverse environmental risk factors such as perinatal insults, childhood maltreatment, and other adverse pathophysiological or psychosocial life events. At the cellular level, such environmental influences may activate oxidative stress pathways, thereby altering neuronal plasticity and function. Mitochondria are the key organelles of energy metabolism and, further, highly important for the adaptation to oxidative stress. Accordingly, multiple lines of evidence including post-mortem brain and neuro-imaging studies suggest that psychiatric disorders are accompanied by mitochondrial dysfunction. In this study, we investigated the effects of Cacna1c downregulation in combination with glutamate-induced oxidative stress on mitochondrial function, Ca²⁺ homeostasis, and cell viability in mouse hippocampal HT22 cells. We found that the siRNA-mediated knockdown of Cacna1c preserved mitochondrial morphology, mitochondrial membrane potential, and ATP levels after glutamate treatment. Further, Cacna1c silencing inhibited excessive mitochondrial reactive oxygen species formation and calcium influx, and protected the HT22 cells from oxidative cell death. Overall, our findings suggest that the GWAS-confirmed psychiatric risk gene CACNA1C plays a major role in oxidative stress pathways with particular impact on mitochondrial integrity and function.

Interactive effects of early life stress and CACNA1C genotype on cortisol awakening response

The rs1006737 (A/G) single nucleotide polymorphism within the gene encoding the Ca_v1.2 subunit of the L-type voltage-dependent calcium channel (CACNA1C) has been strongly implicated in psychiatric disorders. In addition, calcium channels are sensitive to the effects of glucocorticoids and functional variation may contribute to altered stress responsivity. This study aimed to investigate the role of early life stress (ELS) and its interaction with CACNA1C rs1006737 in affecting the cortisol awakening response (CAR), an indicator of HPA-axis function. Salivary cortisol was measured in 103 healthy adult males (aged 21-63) on two consecutive days at awakening and 30 min later. The ELS measure investigated self-reported adverse life events prior to age 17. The results revealed a marginally significant main effect of CACNA1C, a significant main effect of ELS, and a significant genotype-by-ELS interaction on the CAR, whereby non-risk allele carriers (GG) who had experienced early adversity showed higher CAR compared to the other groups. Further exploratory analyses showed that this interaction may have arisen from individuals who had experienced ELS before adolescence (prior to age 13). This study is the first to provide evidence that the effect of ELS on CAR may be partially moderated via CACNA1C rs1006737 genotype, whereby the heightened CAR in the GG-ELS group may be an indicator of mental health resilience in response to ELS.

Genomic and Imaging Biomarkers in Schizophrenia

Recent large-scale genomic studies have confirmed that schizophrenia is a polygenic syndrome and have implicated a number of biological pathways in its aetiology. Both common variants individually of small effect and rarer but more penetrant genetic variants have been shown to play a role in the pathogenesis of the disorder. No simple Mendelian forms of the condition have been identified, but progress has been made in stratifying risk on the basis of the polygenic burden of common variants individually of small effect, and the contribution of rarer variants of larger effect such as Copy Number Variants (CNVs). Pathway analysis of risk-associated variants has begun to identify specific biological processes implicated in risk for the disorder, including elements of the glutamatergic NMDA receptor complex and post synaptic density, voltage-gated calcium channels, targets of the Fragile X Mental Retardation Protein (FMRP targets) and immune pathways. Genetic studies have also been used to drive genomic imaging approaches to the investigation of brain markers associated with risk for the disorder. Genomic imaging approaches have been applied both to investigate the effect of polygenic risk and to study the impact of individual higher-penetrance variants such as CNVs. Both genomic and genomic imaging approaches offer potential for the stratification of patients and at-risk groups and the development of better biomarkers of risk and treatment response; however, further research is needed to integrate this work and realise the full potential of these approaches.

Genome-Wide Supported Risk Variants in MIR137, CACNA1C, CSMD1, DRD2, and GRM3 Contribute to Schizophrenia Susceptibility in Pakistani Population

OBJECTIVE

Schizophrenia is a chronic neuropsychiatric disease afflicting around 1.1% of the population worldwide. Recently, MIR137, CACNA1C, CSMD1, DRD2, and GRM3 have been reported as the most robustly emerging candidates involved in the etiology of schizophrenia. In this case control study, we performed an association analysis of rs1625579 (MIR137), rs1006737, rs4765905 (CACNA1C), rs10503253 (CSMD1), rs1076560 (DRD2), rs12704290, rs6465084, and rs148754219 (GRM3) in Pakistani population.

METHODS

Schizophrenia was diagnosed on the basis of the Diagnostic and Statistical Manual of Mental Disorders 4th ed (DSM-IV). Detailed clinical information, family history of all patients and healthy controls were collected. RFLP based case control association study was performed in a Pakistani cohort of 508 schizophrenia patients and 300 healthy control subjects. Alleles and genotype frequencies were calculated using SPSS.

RESULTS

A significant difference in the genotype and allele frequencies for rs4765905, rs1076560 and rs6465084 were found between the patients and controls (p=0.000).

CONCLUSION

This study provides substantial evidence supporting the role of CACNA1C, GRM3 and DRD2 as schizophrenia susceptibility genes in Pakistani population.

Rescue of impaired sociability and anxiety-like behavior in adult cacna1c-deficient mice by pharmacologically targeting eIF2α

CACNA1C, encoding the Ca_v1.2 subunit of L-type Ca²⁺ channels, has emerged as one of the most prominent and highly replicable susceptibility genes for several neuropsychiatric disorders. Ca_v1.2 channels play a crucial role in calcium-mediated processes involved in brain development and neuronal function. Within the CACNA1C gene, disease-associated single-nucleotide polymorphisms have been associated with impaired social and cognitive processing and altered prefrontal cortical (PFC) structure and activity. These findings suggest that aberrant Ca_v1.2 signaling may contribute to neuropsychiatric-related disease symptoms via impaired PFC function. Here, we show that mice harboring loss of cacna1c in excitatory glutamatergic neurons of the forebrain (fbKO) that we have previously reported to exhibit anxiety-like behavior, displayed a social behavioral deficit and impaired learning and memory. Furthermore, focal knockdown of cacna1c in the adult PFC recapitulated the social deficit and elevated anxiety-like behavior, but not the deficits in learning and memory. Electrophysiological and molecular studies in the PFC of cacna1c fbKO mice revealed higher E/I ratio in layer 5 pyramidal neurons and lower general protein synthesis. This was concurrent with reduced activity of mTORC1 and its downstream mRNA translation initiation factors eIF4B and 4EBP1, as well as elevated phosphorylation of eIF2α, an inhibitor of mRNA translation. Remarkably, systemic treatment with ISRIB, a small molecule inhibitor that suppresses the effects of phosphorylated eIF2α on mRNA translation, was sufficient to reverse the social deficit and elevated anxiety-like behavior in adult cacna1c fbKO mice. ISRIB additionally normalized the lower protein synthesis and higher E/I ratio in the PFC. Thus this study identifies a novel Ca_v1.2 mechanism in neuropsychiatric-related endophenotypes and a potential future therapeutic target to explore.

From Gene to Behavior: L-Type Calcium Channel Mechanisms Underlying Neuropsychiatric Symptoms

The L-type calcium channels (LTCCs) Cav1.2 and Cav1.3, encoded by the CACNA1C and CACNA1D genes, respectively, are important regulators of calcium influx into cells and are critical for normal brain development and plasticity. In humans, CACNA1C has emerged as one of the most widely reproduced and prominent candidate risk genes for a range of neuropsychiatric disorders, including bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. Separately, CACNA1D has been found to be associated with BD and autism spectrum disorder, as well as cocaine dependence, a comorbid feature associated with psychiatric disorders. Despite growing evidence of a significant link between CACNA1C and CACNA1D and psychiatric disorders, our understanding of the biological mechanisms by which these LTCCs mediate neuropsychiatric-associated endophenotypes, many of which are shared across the different disorders, remains rudimentary. Clinical studies with LTCC blockers testing their efficacy to alleviate symptoms associated with BD, SCZ, and drug dependence have provided mixed results, underscoring the importance of further exploring the neurobiological consequences of dysregulated Cav1.2 and Cav1.3. Here, we provide a review of clinical studies that have evaluated LTCC blockers for BD, SCZ, and drug dependence-associated symptoms, as well as rodent studies that have identified Cav1.2- and Cav1.3-specific molecular and cellular cascades that underlie mood (anxiety, depression), social behavior, cognition, and addiction.

Functional neuroimaging effects of recently discovered genetic risk loci for schizophrenia and polygenic risk profile in five RDoC subdomains

Recently, 125 loci with genome-wide support for association with schizophrenia were identified. We investigated the impact of these variants and their accumulated genetic risk on brain activation in five neurocognitive domains of the Research Domain Criteria (working memory, reward processing, episodic memory, social cognition and emotion processing). In 578 healthy subjects we tested for association (i) of a polygenic risk profile score (RPS) including all single-nucleotide polymorphisms (SNPs) reaching genome-wide significance in the recent genome-wide association studies (GWAS) meta-analysis and (ii) of all independent genome-wide significant loci separately that showed sufficient distribution of all allelic groups in our sample (105 SNPs). The RPS was nominally associated with perigenual anterior cingulate and posterior cingulate/precuneus activation during episodic memory (P_FWE(ROI)=0.047) and social cognition (P_FWE(ROI)=0.025), respectively. Single SNP analyses revealed that rs9607782, located near EP300, was significantly associated with amygdala recruitment during emotion processing (P_FWE(ROI)=1.63 × 10^-4, surpassing Bonferroni correction for the number of SNPs). Importantly, this association was replicable in an independent sample (N=150; P_FWE(ROI)<0.025). Other SNP effects previously associated with imaging phenotypes were nominally significant, but did not withstand correction for the number of SNPs tested. To assess whether there was true signal within our data, we repeated single SNP analyses with 105 randomly chosen non-schizophrenia-associated variants, observing fewer significant results and lower association probabilities. Applying stringent methodological procedures, we found preliminary evidence for the notion that genetic risk for schizophrenia conferred by rs9607782 may be mediated by amygdala function. We critically evaluate the potential caveats of the methodological approaches employed and offer suggestions for future studies.

L-type Ca2+ channels in mood, cognition and addiction: integrating human and rodent studies with a focus on behavioural endophenotypes

Brain Cav 1.2 and Cav 1.3 L-type Ca2+ channels play key physiological roles in various neuronal processes that contribute to brain function. Genetic studies have recently identified CACNA1C as a candidate risk gene for bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder (MDD) and autism spectrum disorder (ASD), and CACNA1D for BD and ASD, suggesting a contribution of Cav 1.2 and Cav 1.3 Ca2+ signalling to the pathophysiology of neuropsychiatric disorders. Once considered sole clinical entities, it is now clear that BD, SCZ, MDD and ASD share common phenotypic features, most likely due to overlapping neurocircuitry and common molecular mechanisms. A major future challenge lies in translating the human genetic findings to pathological mechanisms that are translatable back to the patient. One approach for tackling such a daunting scientific endeavour for complex behaviour-based neuropsychiatric disorders is to examine intermediate biological phenotypes in the context of endophenotypes within distinct behavioural domains. This will better allow us to integrate findings from genes to behaviour across species, and improve the chances of translating preclinical findings to clinical practice.

A systematic review of calcium channel antagonists in bipolar disorder and some considerations for their future development

l-type calcium channel (LTCC) antagonists have been used in bipolar disorder for over 30 years, without becoming an established therapeutic approach. Interest in this class of drugs has been rekindled by the discovery that LTCC genes are part of the genetic aetiology of bipolar disorder and related phenotypes. We have therefore conducted a systematic review of LTCC antagonists in the treatment and prophylaxis of bipolar disorder. We identified 23 eligible studies, with six randomised, double-blind, controlled clinical trials, all of which investigated verapamil in acute mania, and finding no evidence that it is effective. Data for other LTCC antagonists (diltiazem, nimodipine, nifedipine, methyoxyverapamil and isradipine) and for other phases of the illness are limited to observational studies, and therefore no robust conclusions can be drawn. Given the increasingly strong evidence for calcium signalling dysfunction in bipolar disorder, the therapeutic candidacy of this class of drugs has become stronger, and hence we also discuss issues relevant to their future development and evaluation. In particular, we consider how genetic, molecular and pharmacological data can be used to improve the selectivity, efficacy and tolerability of LTCC antagonists. We suggest that a renewed focus on LTCCs as targets, and the development of 'brain-selective' LTCC ligands, could be one fruitful approach to innovative pharmacotherapy for bipolar disorder and related phenotypes.

CACNA1C risk variant is associated with increased amygdala volume

Genome-wide association studies suggest that genetic variation within L-type calcium channel subunits confer risk to psychosis. The single nucleotide polymorphism at rs1006737 in CACNA1C has been associated with both schizophrenia and bipolar disorder and with several intermediate phenotypes that may serve as neurobiological antecedents, linking psychosis to genetic aetiology. Amongst others, it has been implicated in alterations in amygdala structure and function. In the present study, we show that the risk allele (A) is associated with increased amygdala volume in healthy individuals (n = 258). This observation reinforces a hypothesis that genetic variation may confer risk to psychosis via alterations in limbic structures. Further study of CACNA1C using intermediate phenotypes for psychosis will determine the mechanisms by which variation in this gene confers risk.

The impact of CACNA1C allelic variation on regional gray matter volume in Chinese population

The SNP rs1006737 in CACNA1C gene has been significantly associated with psychiatric disorders (e.g., schizophrenia and bipolar disorder) in European populations. In Han Chinese, rs1006737 is also strongly associated with schizophrenia, although the effects of the psychosis risk SNP on related brain functions and structures in this population remain unclear. Here, we examined the association of rs1006737 with gray matter volume in a sample of 278 healthy Han Chinese. A whole-brain voxel-based morphometry (VBM) analysis revealed a significant association in the region around right superior occipital gyrus (family-wise error corrected, P = 0.023). Our data provides initial evidence for the involvement of this psychosis genetic risk locus in brain structure variations in Chinese population, and calls for further investigations.

Charting the landscape of priority problems in psychiatry, part 2: pathogenesis and aetiology

This is the second of two companion papers proposing priority problems for research on mental disorders. Whereas the first paper focuses on questions of nosology and diagnosis, this Personal View concerns pathogenesis and aetiology of psychiatric diseases. We hope that this (non-exhaustive and subjective) list of problems, nominated by scientists and clinicians from different fields and institutions, provides guidance and perspectives for choosing future directions in psychiatric science.

Current state of biomarkers in bipolar disorder

Bipolar disorder (BD) is a chronic psychiatric illness of which the etiology remains unknown. Extensive research has provided some hypotheses for the pathophysiology of this disorder; however, there are no molecular tests available to help support the diagnosis obtained by self-report and behavioral observations. A major requirement is to identify potential biomarkers that could be used for early diagnosis in patients susceptible to the disease and for its treatment. The most recently published findings regarding alterations in BD were found to be related to oxidative stress, inflammatory and trophic factor deregulation, and also polymorphisms of genes that are associated with the development of BD. Many of these targets are potential biomarkers which could help to identify the BD subgroups and to advance treatment strategies, which would beneficiate the quality of life of these patients. Therefore, the main objective of this review is to examine the recent findings and critically evaluate their potential as biomarkers for BD.

New developments in the genetics of bipolar disorder

The last several years have been breakthrough ones in bipolar disorder (BPD) genetics, as the field has identified robust risk variants for the first time. Leading the way have been genome-wide association studies (GWAS) that have assessed common genetic markers across very large groups of patients and controls. These have resulted in findings in genes including ANK3, CACNA1C, SYNE1, ODZ4, and TRANK1. Additional studies have begun to examine the biology of these genes and how risk variants influence aspects of brain and behavior that underlie BPD. For example, carriers of the CACNA1C risk variant have been found to exhibit hippocampal and anterior cingulate dysfunction during episodic memory recall. This work has shed additional light on the relationship of bipolar susceptibility variants to other disorders, particularly schizophrenia. Even larger BPD GWAS are expected with samples now amassed of 21,035 cases and 28,758 controls. Studies have examined the pharmacogenomics of BPD with studies of lithium response, yielding high profile results that remain to be confirmed. The next frontier in the field is the identification of rare bipolar susceptibility variants through large-scale DNA sequencing. While only a couple of papers have been published to date, many studies are underway. The Bipolar Sequencing Consortium has been formed to bring together all of the groups working in this area, and to perform meta-analyses of the data generated. The consortium, with 13 member groups, now has exome data on ~3,500 cases and ~5,000 controls, and on ~162 families. The focus will likely shift within several years from exome data to whole genome data as costs of obtaining such data continue to drop. Gene-mapping studies are now providing clear results that provide insights into the pathophysiology of the disorder. Sequencing studies should extend this process further. Findings could eventually set the stage for rational therapeutic development.

CACNA1C risk variant affects reward responsiveness in healthy individuals

The variant at rs1006737 in the L-type voltage-gated calcium channel (alpha 1c subunit) CACNA1C gene is reliably associated with both bipolar disorder and schizophrenia. We investigated whether this risk variant affects reward responsiveness because reward processing is one of the central cognitive-motivational domains implicated in both disorders. In a sample of 164 young, healthy individuals, we show a dose-dependent response, where the rs1006737 risk genotype was associated with blunted reward responsiveness, whereas discriminability did not significantly differ between genotype groups. This finding suggests that the CACNA1C risk locus may have a role in neural pathways that facilitate value representation for rewarding stimuli. Impaired reward processing may be a transdiagnostic phenotype of variation in CACNA1C that could contribute to anhedonia and other clinical features common to both affective and psychotic disorders.