Transcriptomic signatures of schizophrenia revealed by dopamine perturbation in an ex vivo model

Abstract

The dopaminergic hypothesis of schizophrenia (SZ) postulates that dopaminergic over activity causes psychosis, a central feature of SZ, based on the observation that blocking dopamine (DA) improves psychotic symptoms. DA is known to have both receptor- and non-receptor-mediated effects, including oxidative mechanisms that lead to apoptosis. The role of DA-mediated oxidative processes in SZ has been little studied. Here, we have used a cell perturbation approach and measured transcriptomic profiles by RNAseq to study the effect of DA exposure on transcription in B-cell transformed lymphoblastoid cell lines (LCLs) from 514 SZ cases and 690 controls. We found that DA had widespread effects on both cell growth and gene expression in LCLs. Overall, 1455 genes showed statistically significant differential DA response in SZ cases and controls. This set of differentially expressed genes is enriched for brain expression and for functions related to immune processes and apoptosis, suggesting that DA may play a role in SZ pathogenesis through modulating those systems. Moreover, we observed a non-significant enrichment of genes near genome-wide significant SZ loci and with genes spanned by SZ-associated copy number variants (CNVs), which suggests convergent pathogenic mechanisms detected by both genetic association and gene expression. The study suggests a novel role of DA in the biological processes of immune and apoptosis that may be relevant to SZ pathogenesis. Furthermore, our results show the utility of pathophysiologically relevant perturbation experiments to investigate the biology of complex mental disorders.

Fig. 1. Flow chart of the study design.

SZ schizophrenia, GWAS genome-wide association study, CNV copy number variation, DA dopamine, LCL lymphoblastoid cell line

Fig. 2. Dosage effect of dopamine (DA) on cell growth and genome-wide expression of 4 LCLs.

a DA effect on cell growth after 24 h of DA treatment (1 μM, 10 μM, 100 μM, and 1,000 μM). 100 μM DA started to show a significant inhibitory effect on cell growth, and most cells were dead at 1000 μM DA. Pre-treatment of the cells with the D1 receptor antagonist SCH23390 (200 nM) and/or the D2 receptor antagonist Spiperone (SP; 200 nM) for 6 h did not block the inhibitory effect of DA on cell growth. * P < 0.05 and ** P < 0.01 were derived from two-sided paired Student’s t-test. b Box plot of DA effect on genome-wide expression. 100 μM DA showed a substantially stronger effect than 1 μM DA, but pre-treatment of the cells with D1 or D2 receptor antagonists did not reverse the effect of DA. Plotted are 2999 genes that showed significant expression changes after DA stimulation (100 μM) (P < 0.05). Arrows point to the values for HMOX1

Fig. 3. DA-responsive genes in 1204 LCLs of MGS subjects.

a Distribution of expression fold change (FC) for all genes expressed in LCLs upon DA (100 μM) stimulation. An expressed gene was defined as having RPKM > 0 in at least 50% of baseline or DA-stimulated samples. Two-side paired Student’s t-test was used to test for DA response. The red dots show values for genes with log2 FC beyond the 1 SD cut off. b Gene expression before and after DA stimulation are highly correlated (Pearson R = 0.993). c GO-term enrichment analysis by DAVID. The enriched GO-terms were clustered and visualized by REVIGO. Scale bar = log(FDR), blue indicates the most significant enrichment

Fig. 4. Genes showing SZ-associated differential expression under different conditions and the enriched gene ontology terms.

a Venn diagram that shows the overlap of genes showing SZ-associated differential DA response, differentially expressed genes in baseline and under DA stimulation. b 229 genes that only showed SZ-associated differential response to DA are highly enriched for GO-terms related to cell death. c 541 genes that showed SZ-associated differential expression in all three analyses are highly enriched for GO-terms related to immune response and response to virus