Effect of variation in diacylglycerol kinase η (DGKH) gene on brain function in a cohort at familial risk of bipolar disorder

Molecular signature of excessive female aggression: study of stressed mice with genetic inactivation of neuronal serotonin synthesis

Aggression is a complex social behavior, critically involving brain serotonin (5-HT) function. The neurobiology of female aggression remains elusive, while the incidence of its manifestations has been increasing. Yet, animal models of female aggression are scarce. We previously proposed a paradigm of female aggression in the context of gene x environment interaction where mice with partial genetic inactivation of tryptophan hydroxylase-2 (Tph2+/- mice), a key enzyme of neuronal 5-HT synthesis, are subjected to predation stress resulting in pathological aggression. Using deep sequencing and the EBSeq method, we studied the transcriptomic signature of excessive aggression in the prefrontal cortex of female Tph2+/- mice subjected to rat exposure stress and food deprivation. Challenged mutants, but not other groups, displayed marked aggressive behaviors. We found 26 genes with altered expression in the opposite direction between stressed groups of both Tph2 genotypes. We identified several molecular markers, including Dgkh, Arfgef3, Kcnh7, Grin2a, Tenm1 and Epha6, implicated in neurodevelopmental deficits and psychiatric conditions featuring impaired cognition and emotional dysregulation. Moreover, while 17 regulons, including several relevant to neural plasticity and function, were significantly altered in stressed mutants, no alteration in regulons was detected in stressed wildtype mice. An interplay of the uncovered pathways likely mediates partial Tph2 inactivation in interaction with severe stress experience, thus resulting in excessive female aggression.

The preparation of Diacylglycerol-rich soybean oil by acetylated modification of arachin nanoparticles for W/O Pickering emulsion system

Pickering emulsion catalytic system (PEC) stabilized by nanoparticles is an efficient catalytic platform. Herein, a high-performance PEC was constructed by acetylated modification of arachin nanoparticles (AAPs). The results showed the pI of arachin was decreased from pH 5.5 to pH 3.5. The surface hydrophobicity index was significantly increased (from 56.28 ± 4.23 to 120.77 ± 0.79) after acetylated modification. The three-phase contact angle of AAPs was 91.20 ± 0.98°. AAPs were used as lipase immobilization carriers to increase the activity of free lipase fabricating lipase-AAPs. The immobilization efficiency and activity of lipase-AAPs were 12.95 ± 0.03% and 1.74 ± 0.07 U/mg, respectively. Enzymatic reaction kinetics showed that V_m of lipase-AAPs was twice of free lipase. K_m was 1/5 of free lipase. The catalytic efficiency of PEC to prepare DAG was 2.36 times of biphasic catalytic system (BCS). This work provided a promising way to promote the efficiency of DAG preparation.

Clinical, genetic, and brain imaging predictors of risk for bipolar disorder in high-risk individuals

Introduction: Early detection and intervention in bipolar disorder (BD) might reduce illness severity, slow its progression, and, in specific cases, even ward off the full-blown disorder. Therefore, identifying at-risk individuals and targeting them promptly before the illness onset is of the utmost importance. In the last decades, there has been a significant effort aimed at identifying genetic and molecular factors able to modulate risk and pharmacological outcomes.Areas covered: We performed a narrative review of articles aimed at identifying clinical, genetics, molecular, and brain imaging markers of BD specifically focusing on samples of individuals at high-risk for BD. Special emphasis was put on studies applying an integrative design, e.g. studies combining different markers such as genetic and brain imaging.Expert opinion: Findings from studies in risk individuals are still too sparse to allow drawing definite conclusions. However, the high potentiality of longitudinal studies in individuals considered at risk to develop BD supports the need for more efforts. Future investigations should focus on more homogeneous subpopulations and evaluate the cross-linking between clinical, genetic, and brain morphostructural/functional neuroimaging characteristics as predictors of risk for BD.

Unravelling the genetic basis of schizophrenia and bipolar disorder with GWAS: A systematic review

OBJECTIVES

To systematically review findings of GWAS in schizophrenia (SZ) and in bipolar disorder (BD); and to interpret findings, with a focus on identifying independent replications.

METHOD

PubMed search, selection and review of all independent GWAS in SZ or BD, published since March 2011, i.e. studies using non-overlapping samples within each article, between articles, and with those of the previous review (Li et al., 2012).

RESULTS

From the 22 GWAS included in this review, the genetic associations surviving standard GWAS-significance were for genetic markers in the regions of ACSL3/KCNE4, ADCY2, AMBRA1, ANK3, BRP44, DTL, FBLN1, HHAT, INTS7, LOC392301, LOC645434/NMBR, LOC729457, LRRFIP1, LSM1, MDM1, MHC, MIR2113/POU3F2, NDST3, NKAPL, ODZ4, PGBD1, RENBP, TRANK1, TSPAN18, TWIST2, UGT1A1/HJURP, WHSC1L1/FGFR1 and ZKSCAN4. All genes implicated across both reviews are discussed in terms of their function and implication in neuropsychiatry.

CONCLUSION

Taking all GWAS to date into account, AMBRA1, ANK3, ARNTL, CDH13, EFHD1 (albeit with different alleles), MHC, PLXNA2 and UGT1A1 have been implicated in either disorder in at least two reportedly non-overlapping samples. Additionally, evidence for a SZ/BD common genetic basis is most strongly supported by the implication of ANK3, NDST3, and PLXNA2.

Expressional profile of the diacylglycerol kinase eta gene DGKH

Bipolar disorder (BPD) is a genetically complex mental disorder, which is characterized by recurrent depressive and manic episodes, occurring with a typical cyclical course. In a recent study, we were able to identify a risk haplotype for BPD, as well as for unipolar depression and adult attention-deficit/hyperactivity disorder (ADHD), within the DGKH gene. DGKH codes for the eta (η) isoform of diacylglycerol kinase, which is involved in the phosphoinositol pathway. In the present study, we determined the expressional profile of Dgkh using quantitative real-time PCR (qPCR), in situ hybridization and immunohistological staining in the human and in the mouse brain. Expression studies showed that two different Dgkh transcripts exhibited distinct occurrence in a variety of murine tissues and also differed in their expression levels. The proteins encoded by those transcripts differ in functional protein domains suggesting distinct biochemical and cell biological properties and functions. qPCR analyses revealed an increase in Dgkh expression during mouse brain development indicating a possible role of this kinase in late developmental stages. Immunostainings revealed strong Dgkh expression in neurons of the hippocampus and the cerebellum of the murine brain, whereas highest expression levels of DGKH in the human brain were found in the striatum. Taken together, our studies revealed expressional changes during mouse brain development and occurrence of Dgkη in neurons of regions that have been linked to BPD as well as ADHD in humans providing evidence for the implication of DGKH in those disorders.

DGKH genetic risk variant influences gene expression in bipolar affective disorder

BACKGROUND

DGKH is a replicated risk gene of bipolar disorder (BD). However, the pathophysiological role of the coded protein, diacylglycerol kinase eta, remains elusive.

METHODS

In this proof-of-concept study we isolated mRNA from peripheral blood and fibroblasts of heterozygote DGKH risk variants carriers (risk haplotype rs994856/rs9525580/rs9525584 GAT) with bipolar disorder and non-risk variant carriers with and without bipolar disorder. Gene expression of DGKH1, DGKH2, INPP5E, PI4K2B, PIK4CA, PLCG2, PRKCA, PRKCD, PRKCE and PRKCH was analysed by qRT PCR.

RESULTS

DGKH1 expression was increased in peripheral blood of risk variant carriers (p=0.027). In fibroblast cells, PRKCD expression was significantly increased in DGKH GAT carriers (p=0.037). Patients with a current depressive episode had lower PRKCD levels and lithium treatment was associated with increased PRKCA expression (p=0.005, and p=0.033).

LIMITATIONS

No homozygote risk variant carriers and no healthy risk variant carriers were included due to their infrequency. Bipolar patients carrying the GAT haplotype were older with marginal significance, as age had also an influence on DGKH expression levels but not on PRKCD levels, replication with better age-matched samples and also bigger samples are needed.

CONCLUSIONS

The results add evidence for the role of fibroblast cells and peripheral blood as useful tools in the functional characterisation of risk gene variants. Also a combination of genotyping and peripheral gene expression analysis could proof useful in the search of biomarkers for endophenotypes. Furthermore, we could confirm the role of the inositol-1,4,5-triphosphate second messenger pathway and protein kinase C in the pathogenesis of BD.

Sex-Dependent Depression-Like Behavior Induced by Respiratory Administration of Aluminum Oxide Nanoparticles

Ultrafine aluminum oxide, which are abundant in ambient and involved occupational environments, are associated with neurobehavioral alterations. However, few studies have focused on the effect of sex differences following exposure to environmental Al₂O₃ ultrafine particles. In the present study, male and female mice were exposed to Al₂O₃ nanoparticles (NPs) through a respiratory route. Only the female mice showed depression-like behavior. Although no obvious pathological changes were observed in mice brain tissues, the neurotransmitter and voltage-gated ion channel related gene expression, as well as the small molecule metabolites in the cerebral cortex, were differentially modulated between male and female mice. Both mental disorder-involved gene expression levels and metabolomics analysis results strongly suggested that glutamate pathways were implicated in sex differentiation induced by Al₂O₃ NPs. Results demonstrated the potential mechanism of environmental ultrafine particle-induced depression-like behavior and the importance of sex dimorphism in the toxic research of environmental chemicals.

Bipolar disorder: Functional neuroimaging markers in relatives

Neural models of anatomical and functional alterations have been proposed for bipolar disorders (BD). However, studies in affected patients do not allow disentangling alterations linked to the liability to BD from those associated with the evolution, medication and comorbidities of BD. Explorations in high risk subjects allow the study of these risk markers. We reported and summarized all functional magnetic resonance imaging (fMRI) studies focusing on first-degree relatives of BD patients. We found 29 studies reporting neural correlates of working memory (WM), emotional processing, executive functions and resting state in relatives of BD patients, compared to healthy subjects. Overall, the same regions that have been involved in patients, such as the inferior frontal gyrus and limbic areas, seem to be functionally altered in high-risk subjects. We conclude that the same brain regions already implicated in the pathophysiology of the disease such as the amygdala are also associated with the risk of BD. However longitudinal studies are required to understand their implication in the transition to BD.

Cortical Thickness in Individuals at High Familial Risk of Mood Disorders as They Develop Major Depressive Disorder

BACKGROUND

Frontal and temporal cortical thickness abnormalities have been observed in mood disorders. However, it is unknown whether cortical thickness abnormalities reflect early adverse effects of genetic and environmental risk factors predisposing to mood disorders or emerge at illness onset.

METHODS

Magnetic resonance imaging was conducted at baseline and after a 2-year follow-up interval in 111 initially unaffected young adults at high familial risk of mood disorders and 93 healthy control subjects (HC). During the follow-up period, 20 high-risk subjects developed major depressive disorder (HR-MDD), with the remainder remaining well (HR-well). Cortical surface reconstruction was applied to measure cortical thickness of frontal and temporal regions of interest. Mixed-effects models were used to investigate differences and longitudinal changes in cortical thickness.

RESULTS

Reduced cortical thickness in the right parahippocampal and fusiform gyrus across both time points was found in both high-risk groups. HR-MDD also had thinner parahippocampi than HR-well individuals. Over time, HR-well and HC individuals had progressive thickness reductions in the left inferior frontal and precentral gyrus, which were greater in HR-well subjects. HR-MDD showed left inferior frontal gyrus thickening relative to HR-well subjects and left precentral gyrus thickening relative to HR-well and HC individuals.

CONCLUSIONS

Reduced right parahippocampal and fusiform gyrus thickness are familial trait markers for vulnerability to mood disorders. Increased risk for mood disorders is associated with progressive cortical thinning in the left inferior frontal and precentral gyri in subjects who remain well. In contrast, onset of depression is associated with increasing left inferior frontal and precentral thickness.

What is the impact of genome-wide supported risk variants for schizophrenia and bipolar disorder on brain structure and function? A systematic review

The powerful genome-wide association studies (GWAS) revealed common mutations that increase susceptibility for schizophrenia (SZ) and bipolar disorder (BD), but the vast majority were not known to be functional or associated with these illnesses. To help fill this gap, their impact on human brain structure and function has been examined. We systematically discuss this output to facilitate its timely integration in the psychosis research field; and encourage reflection for future research. Irrespective of imaging modality, studies addressing the effect of SZ/BD GWAS risk genes (ANK3, CACNA1C, MHC, TCF4, NRGN, DGKH, PBRM1, NCAN and ZNF804A) were included. Most GWAS risk variations were reported to affect neuroimaging phenotypes implicated in SZ/BD: white-matter integrity (ANK3 and ZNF804A), volume (CACNA1C and ZNF804A) and density (ZNF804A); grey-matter (CACNA1C, NRGN, TCF4 and ZNF804A) and ventricular (TCF4) volume; cortical folding (NCAN) and thickness (ZNF804A); regional activation during executive tasks (ANK3, CACNA1C, DGKH, NRGN and ZNF804A) and functional connectivity during executive tasks (CACNA1C and ZNF804A), facial affect recognition (CACNA1C and ZNF804A) and theory-of-mind (ZNF804A); but inconsistencies and non-replications also exist. Further efforts such as standardizing reporting and exploring complementary designs, are warranted to test the reproducibility of these early findings.

Influence of DGKH variants on amygdala volume in patients with bipolar affective disorder and schizophrenia

The diacylglycerol kinase eta (DGKH) gene, first identified in a genome-wide association study, is one of the few replicated risk genes of bipolar affective disorder (BD). Following initial positive studies, it not only was found to be associated with BD but also implicated in the etiology of other psychiatric disorders featuring affective symptoms, rendering DGKH a cross-disorder risk gene. However, the (patho-)physiological role of the encoded enzyme is still elusive. In the present study, we investigated primarily the influence of a risk haplotype on amygdala volume in patients suffering from schizophrenia or BD as well as healthy controls and four single nucleotide polymorphisms conveying risk. There was a significant association of the DGKH risk haplotype with increased amygdala volume in BD, but not in schizophrenia or healthy controls. These findings add to the notion of a role of DGKH in the pathogenesis of BD.

Candidate gene associations with mood disorder, cognitive vulnerability, and fronto-limbic volumes

BACKGROUND

Four of the most consistently replicated variants associated with mood disorder occur in genes important for synaptic function: ANK3 (rs10994336), BDNF (rs6265), CACNA1C (rs1006737), and DGKH (rs1170191).

AIMS

The present study examined associations between these candidates, mood disorder diagnoses, cognition, and fronto-limbic regions implicated in affect regulation.

METHODS AND MATERIALS

Participants included 128 individuals with bipolar disorder (33% male, Mean age = 38.5), 48 with major depressive disorder (29% male, Mean age = 40.4), and 149 healthy controls (35% male, Mean age = 36.5). Genotypes were determined by 5'-fluorogenic exonuclease assays (TaqMan®). Fronto-limbic volumes were obtained from high resolution brain images using Freesurfer. Chi-square analyses, bivariate correlations, and mediational models examined relationships between genetic variants, mood diagnoses, cognitive measures, and brain volumes.

RESULTS

Carriers of the minor BDNF and ANK3 alleles showed nonsignificant trends toward protective association in controls relative to mood disorder patients (P = 0.047). CACNA1C minor allele carriers had larger bilateral caudate, insula, globus pallidus, frontal pole, and nucleus accumbens volumes (smallest r = 0.13, P = 0.043), and increased IQ (r = 0.18, P < 0.001). CACNA1C associations with brain volumes and IQ were independent; larger fronto-limbic volumes did not mediate increased IQ. Other candidate variants were not significantly associated with diagnoses, cognition, or fronto-limbic volumes.

DISCUSSION AND CONCLUSIONS

CACNA1C may be associated with biological systems altered in mood disorder. Increases in fronto-limbic volumes and cognitive ability associated with CACNA1C minor allele genotypes are congruent with findings in healthy samples and may be a marker for increased risk for neuropsychiatric phenotypes. Even larger multimodal studies are needed to quantify the magnitude and specificity of genetic-imaging-cognition-symptom relationships.

Multivariate analysis reveals genetic associations of the resting default mode network in psychotic bipolar disorder and schizophrenia

The brain's default mode network (DMN) is highly heritable and is compromised in a variety of psychiatric disorders. However, genetic control over the DMN in schizophrenia (SZ) and psychotic bipolar disorder (PBP) is largely unknown. Study subjects (n = 1,305) underwent a resting-state functional MRI scan and were analyzed by a two-stage approach. The initial analysis used independent component analysis (ICA) in 324 healthy controls, 296 SZ probands, 300 PBP probands, 179 unaffected first-degree relatives of SZ probands (SZREL), and 206 unaffected first-degree relatives of PBP probands to identify DMNs and to test their biomarker and/or endophenotype status. A subset of controls and probands (n = 549) then was subjected to a parallel ICA (para-ICA) to identify imaging-genetic relationships. ICA identified three DMNs. Hypo-connectivity was observed in both patient groups in all DMNs. Similar patterns observed in SZREL were restricted to only one network. DMN connectivity also correlated with several symptom measures. Para-ICA identified five sub-DMNs that were significantly associated with five different genetic networks. Several top-ranking SNPs across these networks belonged to previously identified, well-known psychosis/mood disorder genes. Global enrichment analyses revealed processes including NMDA-related long-term potentiation, PKA, immune response signaling, axon guidance, and synaptogenesis that significantly influenced DMN modulation in psychoses. In summary, we observed both unique and shared impairments in functional connectivity across the SZ and PBP cohorts; these impairments were selectively familial only for SZREL. Genes regulating specific neurodevelopment/transmission processes primarily mediated DMN disconnectivity. The study thus identifies biological pathways related to a widely researched quantitative trait that might suggest novel, targeted drug treatments for these diseases.

White matter integrity as an intermediate phenotype: exploratory genome-wide association analysis in individuals at high risk of bipolar disorder

White matter integrity, as measured using diffusion tensor imaging (DTI), is reduced in individuals with bipolar disorder (BD), their unaffected relatives and carriers of specific risk-alleles. Fractional anisotropy (FA), an index of white matter integrity, is highly heritable but the genetic architecture of this trait has received little investigation. In this study we performed a genome-wide association study with FA as quantitative phenotype, in unaffected relatives of patients with BD (N=70) and a matched control group (N=80). Amongst our top results were SNPs located in genes involved in cell adhesion, white matter development and neuronal plasticity. Pathway analysis of the top associated polymorphisms and genes confirmed the enrichment of processes relevant to BD and white matter development, including axon guidance, ErbB-signalling neurotrophin signalling, phosphatidylinositol signalling, and cell adhesion. The majority of genes implicated in these pathways were differentially associated with FA in individuals at high familial risk, suggesting interactions with genetic background or environmental factors secondary to familial risk for BD. Although the present findings require independent replication, the results encourage the use of global FA as a quantitative phenotype in future large-scale studies which may help to identify the biological processes underlying reduced FA in BD and other psychiatric disorders.