Prediction of susceptibility to major depression by a model of interactions of multiple functional genetic variants and environmental factors

Schizophrenia and Depression Co-Morbidity: What We have Learned from Animal Models

Patients with schizophrenia are at an increased risk for the development of depression. Overlap in the symptoms and genetic risk factors between the two disorders suggests a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. Understanding these shared mechanisms will be important in informing the development of new treatments. Rodent models are powerful tools for understanding gene function as it relates to behavior. Examining rodent models relevant to both schizophrenia and depression reveals a number of common mechanisms. Current models which demonstrate endophenotypes of both schizophrenia and depression are reviewed here, including models of CUB and SUSHI multiple domains 1, PDZ and LIM domain 5, glutamate Delta 1 receptor, diabetic db/db mice, neuropeptide Y, disrupted in schizophrenia 1, and its interacting partners, reelin, maternal immune activation, and social isolation. Neurotransmission, brain connectivity, the immune system, the environment, and metabolism emerge as potential common mechanisms linking these models and potentially explaining comorbid depression in schizophrenia.

Clinical outcomes and genome-wide association for a brain methylation site in an antidepressant pharmacogenetics study in Mexican Americans

OBJECTIVE

The authors compared the effectiveness of fluoxetine and desipramine treatment in a prospective double-blind pharmacogenetics study in first-generation Mexican Americans and examined the role of whole-exome functional gene variations in the patients' antidepressant response.

METHOD

A total of 232 Mexican Americans who met DSM-IV criteria for major depressive disorder were randomly assigned to receive 8 weeks of double-blind treatment with desipramine (50-200 mg/day) or fluoxetine (10-40 mg/day) after a 1-week placebo lead-in period. Outcome measures included the Hamilton Depression Rating Scale (HAM-D), the Hamilton Anxiety Rating Scale, and the Beck Depression Inventory. At week 8, whole-exome genotyping data were obtained for 36 participants who remitted and 29 who did not respond to treatment.

RESULTS

Compared with desipramine treatment, fluoxetine treatment was associated with a greater reduction in HAM-D score, higher response and remission rates, shorter time to response and remission, and lower incidences of anticholinergic and cardiovascular side effects. Pharmacogenetics analysis showed that exm-rs1321744 achieved exome-wide significance for treatment remission. This variant is located in a brain methylated DNA immunoprecipitation sequencing site, which suggests that it may be involved in epigenetic regulation of neuronal gene expression. This and two other common gene variants provided a highly accurate cross-validated predictive model for treatment remission of major depression (receiver operating characteristic integral=0.95).

CONCLUSIONS

Compared with desipramine, fluoxetine treatment showed a more rapid reduction of HAM-D score and a lower incidence of side effects in a population comprising primarily first-generation Mexican Americans with major depression. This study's pharmacogenetics approach strongly implicates the role of functional variants in antidepressant treatment response.

Dysbindin-associated proteome in the p2 synaptosome fraction of mouse brain

The gene DTNBP1 encodes the protein dysbindin and is among the most promising and highly investigated schizophrenia-risk genes. Accumulating evidence suggests that dysbindin plays an important role in the regulation of neuroplasticity. Dysbindin was reported to be a stable component of BLOC-1 complex in the cytosol. However, little is known about the endogenous dysbindin-containing complex in the brain synaptosome. In this study, we investigated the associated proteome of dysbindin in the P2 synaptosome fraction of mouse brain. Our data suggest that dysbindin has three isoforms associating with different complexes in the P2 fraction of mouse brain. To facilitate immunopurification, BAC transgenic mice expressing a tagged dysbindin were generated, and 47 putative dysbindin-associated proteins, including all components of BLOC-1, were identified by mass spectrometry in the dysbindin-containing complex purified from P2. The interactions of several selected candidates, including WDR11, FAM91A1, snapin, muted, pallidin, and two proteasome subunits, PSMD9 and PSMA4, were verified by coimmunoprecipitation. The specific proteasomal activity is significantly reduced in the P2 fraction of the brains of the dysbindin-null mutant (sandy) mice. Our data suggest that dysbindin is functionally interrelated to the ubiquitin-proteasome system and offer a molecular repertoire for future study of dysbindin functional networks in brain.

Nonsynonymous polymorphisms of the PDLIM5 gene association with the occurrence of both bipolar disorder and schizophrenia

Two single nucleotide polymorphisms of PDLIM5, rs7690296 and rs11097431, were genotyped using Mass-Array SNP genotyping by Sequenom technology in 244 bipolar disorder patients, 471 schizophrenia patients, and 601 control individuals who were Malay, Chinese, and Indian ethnic groups in the Malaysian population. A significant association was observed in allele frequency between the rs7690296 polymorphism and bipolar disorder in the Indian ethnic group [P=0.02, adjusted odds ratio (OR) 0.058, 95% confidence interval (CI) 0.36-0.93]. A significant association was also observed between the rs7690296 polymorphism and schizophrenia under the recessive model for both Malay (P=0.02, adjusted OR 1.86, 95% CI 1.12-3.10) and Indian (P=0.02, adjusted OR 1.92, 95% CI 1.10-3.37) ethnic groups. However, no association was detected between the rs11097431 polymorphism either with bipolar disorder or with schizophrenia. Therefore, it can be deduced that the nonsynonymous rs7690296 polymorphism could play an important role in the pathophysiology of both bipolar disorder and schizophrenia.

Impact of variation in the BDNF gene on social stress sensitivity and the buffering impact of positive emotions: replication and extension of a gene-environment interaction

A previous study reported that social stress sensitivity is moderated by the brain-derived-neurotrophic-factor(Val66Met) (BDNF rs6265) genotype. Additionally, positive emotions partially neutralize this moderating effect. The current study aimed to: (i) replicate in a new independent sample of subjects with residual depressive symptoms the moderating effect of BDNF(Val66Met) genotype on social stress sensitivity, (ii) replicate the neutralizing impact of positive emotions, (iii) extend these analyses to other variations in the BDNF gene in the new independent sample and the original sample of non-depressed individuals. Previous findings were replicated in an experience sampling method (ESM) study. Negative Affect (NA) responses to social stress were stronger in "Val/Met" carriers of BDNF(Val66Met) compared to "Val/Val" carriers. Positive emotions neutralized the moderating effect of BDNF(Val66Met) genotype on social stress sensitivity in a dose-response fashion. Finally, two of four additional BDNF SNPs (rs11030101, rs2049046) showed similar moderating effects on social stress-sensitivity across both samples. The neutralizing effect of positive emotions on the moderating effects of these two additional SNPs was found in one sample. In conclusion, ESM has important advantages in gene-environment (GxE) research and may attribute to more consistent findings in future GxE research. This study shows how the impact of BDNF genetic variation on depressive symptoms may be explained by its impact on subtle daily life responses to social stress. Further, it shows that the generation of positive affect (PA) can buffer social stress sensitivity and partially undo the genetic susceptibility.

The dynamic nature of depression: a new micro-level perspective of mental disorder that meets current challenges

The examination of moment-to-moment, 'micro-level' patterns of experience and behaviour using experience sampling methodology has contributed to our understanding of the 'macro-level' development of full-blown symptoms and disorders. This paper argues that the micro-level perspective can be used to identify the smallest building blocks underlying the onset and course of mental ill-health. Psychopathology may be the result of the continuous dynamic interplay between micro-level moment-to-moment experiences and behavioural patterns over time. Reinforcing loops between momentary states may alter the course of mental health towards either a more or less healthy state. An example with observed data, from a population of individuals with depressive symptoms, supports the validity of a dynamic network model of psychopathology and shows that together and over time, this continuous interplay between momentary states may result in the cluster of symptoms we call major depressive disorder. This approach may help conceptualize the nature of mental disorders, and generate individualized insights useful for diagnosis and treatment in psychiatry.

Monitoring candidate gene expression variations before, during and after a first major depressive episode in a 51-year-old man

BACKGROUND

Although psychiatric disorders are frequently characterized by clinical heterogeneity, high recurrence, and unpredictable prognosis, studies of mRNA expression variations in blood cells from psychiatric patients constitute a promising avenue to establish clinical biomarkers. We report here, to our knowledge, the first genetic monitoring of a major depressive episode (MDE).

CASE PRESENTATION

The subject is a 51-year-old male, who was healthy at baseline and whose blood mRNA was monitored over 67 weeks for expression variations of 9 candidate genes. At week 20 the subject experienced a mild to moderate unexpected MDE, and oral antidepressant treatment was initiated at week 29. At week 36, the patient recovered from his MDE. After 6 months, antidepressant treatment was discontinued and the subject remained free of depressive symptoms. Genetic monitoring revealed that mRNA expression of SLC6A4/5HTT increased with the emergence of a depressive state, which later returned to basal levels after antidepressant treatment and during MDE recovery. PDLIM5, S100A10 and TNF mRNA showed also an interesting pattern of expression with regards to MDE evolution.

CONCLUSION

This case demonstrated the applicability of peripheral mRNA expression as a way to monitor the natural history of MDE.

Genomewide interaction and enrichment analysis on antidepressant response

BACKGROUND

Genomewide association studies (GWASs) on antidepressant efficacy have yielded modest results. A possible reason is that response is influenced by other factors, which possibly interact with genetic variation. We used a GWAS model to predict antidepressant response, by including predictors previously known to affect response, such as quality of life (QoL). We also evaluated the association between genes, previously implicated in gene-environment (G × E) interactions, and response using an enrichment analysis.

METHOD

We examined a sample of 1426 depressed patients from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial: 774 responders, 652 non-responders and 418,865 single nucleotide polymorphisms (SNPs) were analysed. First, in a GWAS model, we investigated whether genetic variations interact with patients' levels of QoL to predict response, after controlling for demographic characteristics, severity and population stratification. Second, we conducted an enrichment analysis exploring whether candidate genes that have emerged from prior G × E interaction studies on depression are associated with treatment response.

RESULTS

The GWAS model, with QoL as a moderator, yielded one SNP (rs520210) associated with response in the NEDD4L gene (p = 3.64 × 10⁻⁸). In the Caucasian sample only, we observed a drop in significance for this SNP. The enrichment analysis showed that SNPs within serotonergic genes contained more significant markers that predicted response, compared with a random set of genes in the genome.

CONCLUSIONS

Our findings point to possible target genes, which are proposed for further independent replication. Our enrichment analysis provides further support, in a genomewide context, of the role of serotonergic genes in influencing antidepressant response.

Helminth infection alters mood and short-term memory as well as levels of neurotransmitters and cytokines in the mouse hippocampus

Helminthic infections are important causes of morbidity and mortality in many developing countries, where children bear the greatest health burden. The ability of parasites to cause behavioral changes in the host has been observed in a variety of host-parasite systems, including the Taenia crassiceps-mouse model. In murine cysticercosis, mice exhibit a disruption in the sexual, aggressive and avoidance predator behaviors.

OBJECTIVE

The present study was conducted to characterize short-term memory and depression-like behavior, as well as levels of neurotransmitters and cytokines in the hippocampus of cysticercotic male and female mice.

METHODS

Cytokines were detected by RT-PCR and neurotransmitters were quantified by HPLC.

RESULTS

Chronic cysticercosis infection induced a decrease in short-term memory in both male and female mice, having a more pronounced effect in females. Infected females showed a significant increase in forced swimming tests with a decrease in immobility. In contrast, male mice showed an increment in total activity and ambulation tests. Serotonin levels decreased by 30% in the hippocampus of infected females whereas noradrenaline levels significantly increased in infected males. The hippocampal expression of IL-4 increased in infected female mice, but decreased in infected male mice.

CONCLUSION

Our study suggests that intraperitoneal chronic infection with cysticerci in mice leads to persistent deficits in tasks dependent on the animal's hippocampal function. Our findings are a first approach to elucidating the role of the neuroimmune network in controlling short-term memory and mood in T. crassiceps-infected mice.

No influence of brain-derived neurotrophic factor (BDNF) polymorphisms on treatment response in a naturalistic sample of patients with major depression

The role of the brain-derived neurotrophic factor (BDNF) in the pathophysiology of major depressive disorder (MDD) remains to be elucidated. Recent post hoc analyses indicated a potential association of three polymorphisms in the BDNF gene with worse treatment outcome in patients with the subtype of melancholic depression. We aimed at replicating these findings in a German naturalistic multicenter follow-up. Three polymorphisms in the BDNF gene (rs7103411, rs6265 (Val66Met) and rs7124442) were genotyped in 324 patients with MDD and 470 healthy controls. We applied univariate tests and logistic regression models stratifying for depression subtype and gender. The three polymorphisms were not associated with MDD as diagnosis. Further, no associations were found in univariate tests. With logistic regression, we only found a tendency towards an association of the rs6265 (Val66Met) polymorphism with overall response to treatment (response rates: GG (val/val) < GA (val/met) < AA (met/met); p = 0.0129) and some gender differences for the rs6265 (Val66Met) and rs7103411 polymorphisms. Treatment outcome stratified for subtypes of depression did not differ significantly between the investigated polymorphisms or using haplotype analyses. However, results showed a tendency towards significance. At this stage, we cannot support an influence of these three polymorphisms. Further studies in larger patient samples to increase sample sizes of subgroups are warranted.

Metabolic and glutathione redox markers associated with brain-derived neurotrophic factor in depressed african men and women: evidence for counterregulation?

BACKGROUND

Major depression is associated with evidence for metabolic and redox imbalance and also with reports of lower serum levels of brain-derived neurotrophic factor (BDNF). However, the relationship between these factors has not been well studied.

METHODS

We studied the contribution of physiological risk factors to cardiometabolic health in 200 adult male and female black Africans, aged between 36 and 52 years, presenting with (n = 89) and without (n = 111) symptoms of depression. Specifically the association between serum BDNF and markers of basal metabolic and redox status in depressed versus nondepressed individuals were analyzed.

RESULTS

BDNF and markers of redox and metabolic status were not associated with the symptoms of depression. Waist circumference, a metabolic risk factor, was positively associated with BDNF and accounts for 49% of the variance in BDNF in depressed men. Reduced and oxidized glutathione were positively and negatively correlated with BDNF in depressed women, respectively, with glutathione redox status accounting for 36-42% of the variance in BDNF.

CONCLUSION

Selected metabolic and redox factors explained gender-specific variances in serum BDNF levels in depressed African men and women. Our findings suggest that changes in redox and metabolic status may represent counterregulation by BDNF or alternatively that BDNF may mediate undesirable redox and metabolic changes that are associated with the development of a mood disorder.

Experimental evidence for the involvement of PDLIM5 in mood disorders in hetero knockout mice

Background

Reports indicate that PDLIM5 is involved in mood disorders. The PDLIM5 (PDZ and LIM domain 5) gene has been genetically associated with mood disorders; it’s expression is upregulated in the postmortem brains of patients with bipolar disorder and downregulated in the peripheral lymphocytes of patients with major depression. Acute and chronic methamphetamine (METH) administration may model mania and the evolution of mania into psychotic mania or schizophrenia-like behavioral changes, respectively.

Methods

To address whether the downregulation of PDLIM5 protects against manic symptoms and cause susceptibility to depressive symptoms, we evaluated the effects of reduced Pdlim5 levels on acute and chronic METH-induced locomotor hyperactivity, prepulse inhibition, and forced swimming by using Pdlim5 hetero knockout (KO) mice.

Results

The homozygous KO of Pdlim5 is embryonic lethal. The effects of METH administration on locomotor hyperactivity and the impairment of prepulse inhibition were lower in Pdlim5 hetero KO mice than in wild-type mice. The transient inhibition of PDLIM5 (achieved by blocking the translocation of protein kinase C epsilon before the METH challenge) had a similar effect on behavior. Pdlim5 hetero KO mice showed increased immobility time in the forced swimming test, which was diminished after the chronic administration of imipramine. Chronic METH treatment increased, whereas chronic haloperidol treatment decreased, Pdlim5 mRNA levels in the prefrontal cortex. Imipramine increased Pdlim5 mRNA levels in the hippocampus.

Conclusion

These findings are partially compatible with reported observations in humans, indicating that PDLIM5 is involved in psychiatric disorders, including mood disorders.

Association of serotonin-1A and -2A receptor promoter polymorphisms with depressive symptoms, functional recovery, and pain in patients 6 months after lumbar disc surgery

Single nucleotide polymorphisms (SNPs) in the serotonergic (5HT) system seem to have modulatory effects on depression and physical function. Preliminary evidence suggests that gene×environment interactions play a role in the development of depression, with somatic complaints serving as environmental stressors. We hypothesized that pain intensity may serve as a stress factor that modulates the association between SNPs in the 5HT system and depression. We investigated symptoms of pain, depression, physical functioning, and disability in 224 patients 6months after lumbar disc surgery. Associations between these variables and functional promoter SNPs in the serotonin receptor genes 5HTR1A (rs6295) and 5HTR2A (rs6311) were analyzed. For 5HTR2A, we found a significant gene×environment×sex interaction, as female patients carrying at least one A allele of the -1438A/G promoter SNP had significantly higher depression scores when confronted with severe pain compared to women harboring the GG genotype (P=.005). For 5HTR1A, patients homozygous for the -1019 G allele presented higher Beck Depression Inventory scores relative to the CG/CC group, indicating a major effect of this SNP on depression. Furthermore, women homozygous for either the 5HTR1A G allele or the 5HTR2A A allele had lower levels of physical functioning than patients with the other genotypes. These results suggest that 5HTR1A and 5HTR2A promoter variations have gender-dependent modulatory effects on depression and physical function in patients with pain. Furthermore, this study demonstrates that pain after lumbar surgery modulates the association between 5HT gene polymorphisms and depression.

Neural expression of nicotine's antidepressant properties during tryptophan depletion: an EEG study in healthy volunteers at risk for depression

Nicotine amelioration of serotonergically mediated mood dysregulation may contribute to the comorbidity between cigarette smoking and depression, a disorder which is associated with aberrant activation and hemispheric asymmetry in frontal and posterior cortical regions. This randomized, double-blind study in 20 healthy volunteers with a positive family history of depression examined the effects of transdermal nicotine on mood and EEG changes accompanying transient reductions in serotonin induced by acute tryptophan depletion (ATD). Increased self-ratings of depressed mood and elevation in left frontal high alpha power (decreased activation) were evidenced with ATD (vs. balanced mixture) in participants treated with the placebo but not the nicotine treated group. Nicotine alone increased vigor and posterior high alpha bilaterally, and during ATD it prevented the reduction in left frontal high alpha that was evident in the placebo patch group. These findings indicate that in depression prone individuals, nicotine acts to stabilize the mood lowering and associated frontal functional asymmetry elicited by an acute decrease in brain serotonin.

Multigene interactions and the prediction of depression in the Wisconsin Longitudinal Study

OBJECTIVES

Single genetic loci offer little predictive power for the identification of depression. This study examined whether an analysis of gene-gene (G × G) interactions of 78 single nucleotide polymorphisms (SNPs) in genes associated with depression and age-related diseases would identify significant interactions with increased predictive power for depression.

DESIGN

A retrospective cohort study.

SETTING

A survey of participants in the Wisconsin Longitudinal Study.

PARTICIPANTS

A total of 4811 persons (2464 women and 2347 men) who provided saliva for genotyping; the group comes from a randomly selected sample of Wisconsin high school graduates from the class of 1957 as well as a randomly selected sibling, almost all of whom are non-Hispanic white.

PRIMARY OUTCOME MEASURE

Depression as determine by the Composite International Diagnostic Interview-Short-Form.

RESULTS

Using a classification tree approach (recursive partitioning (RP)), the authors identified a number of candidate G × G interactions associated with depression. The primary SNP splits revealed by RP (ANKK1 rs1800497 (also known as DRD2 Taq1A) in men and DRD2 rs224592 in women) were found to be significant as single factors by logistic regression (LR) after controlling for multiple testing (p=0.001 for both). Without considering interaction effects, only one of the five subsequent RP splits reached nominal significance in LR (FTO rs1421085 in women, p=0.008). However, after controlling for G × G interactions by running LR on RP-specific subsets, every split became significant and grew larger in magnitude (OR (before) → (after): men: GNRH1 novel SNP: (1.43 → 1.57); women: APOC3 rs2854116: (1.28 → 1.55), ACVR2B rs3749386: (1.11 → 2.17), FTO rs1421085: (1.32 → 1.65), IL6 rs1800795: (1.12 → 1.85)).

CONCLUSIONS

The results suggest that examining G × G interactions improves the identification of genetic associations predictive of depression. 4 of the SNPs identified in these interactions were located in two pathways well known to impact depression: neurotransmitter (ANKK1 and DRD2) and neuroendocrine (GNRH1 and ACVR2B) signalling. This study demonstrates the utility of RP analysis as an efficient and powerful exploratory analysis technique for uncovering genetic and molecular pathway interactions associated with disease aetiology.