Gene-microRNA interactions associated with antipsychotic mechanisms and the metabolic side effects of olanzapine

Abstract

Rationale: Changes in the cortical expression of small non-coding microRNA (miRNA) have been observed in postmortem analysis of psychotic disorders. Antipsychotic drugs (APDs) are the most effective treatment option for these disorders and have been associated with changes in gene expression. MicroRNA regulate numerous genes involved in brain development and function. It is therefore plausible to question whether miRNA expression is also altered and hence whether they take part in the neuroleptic mechanism of action.

Objectives: We sought to investigate whether treatment with APDs induces changes in miRNA expression and query the functional implications of such changes. Furthermore, we investigated the possible functional interplay of miRNA-gene regulatory interactions.

Method: High-throughput miRNA profiling of the whole brain of C57BL/6 mice treated with haloperidol, olanzapine or clozapine for 7 days was performed. Functional analysis was conducted on the putative targets of altered microRNA. Significant miRNA-gene regulatory interactions were evaluated by the integration of genome-wide mRNA expression analysis using the Bayesian networks with splitting-averaging strategy and functional analysis conducted.

Results: Small subsets of miRNA were altered with each treatment with potential neurologically relevant influence. Metabolic pathways were enriched in olanzapine and clozapine treatments, possibly associated with their weight gain side effects. Neurologically and metabolically relevant miRNA-gene interaction networks were identified in the olanzapine treatment group.

Conclusion: This study is the first to suggest a role for miRNA in the mechanism of APD action and the metabolic side effects of the atypical ADPs, and adds support for their consideration in pharmacogenomics.

Fig. 1

Changes in miRNA expression after treatment with APDs. a–c Hierarchical clustering of significantly dysregulated miRNA microarray expression in APD-treated mouse brain (log transformed, median centered and uncentered correlation, average linkage clustering; Cluster 3.0) (Eisen et al. 1998). Blue low expression, yellow high expression. Images produced with Java TreeView (version 1.1.1) (Saldanha 2004). a Haloperidol and saline treatment groups. b Olanzapine and saline treatment groups. c Clozapine and saline treatment groups. d Microarray expression and qPCR expression of selected miRNA from olanzapine and haloperidol treatment groups. Bars represent fold change in expression + SEM (APD treated vs. saline)

Fig. 2

Potential miRNA–mRNA regulatory networks identified in the olanzapine treatment group. Predicted miRNA target genes identified as significantly differentially expressed were identified. The strength of the potential miRNA–mRNA interactions was assessed in regard to correlation of miRNA to mRNA expression values using the BN-SA method. Those interactions reported with strong correlation with a high confidence comment are pictured here. a Negatively correlated interactions. b Positively correlated interactions. (pink upregulated miRNA, green downregulated miRNA, blue downregulated mRNA, yellow upregulated mRNA)

Fig. 3

The potential involvement of miRNA in the underlying mechanisms of APD therapeutic action or side effects. Neurotransmitters (orange balls) are released by presynaptic receptors (blue funnels) and bind to their postsynaptic receptors (purple tubes) to induce signalling cascades. Transcription factor activation of DNA (purple waves) leads to altered miRNA and gene expression, including miRNA biogenesis genes. Mature miRNA modulate gene expression leading to further upstream changes and ultimately to changes in neurobiological processes. In schizophrenia, neurotransmitter receptor binding and signalling cascades are enhanced (three plus signs), resulting in the presence of psychotic symptoms. Recent findings support enhancement of miRNA biogenesis, with miRNA dysregulation leading to changes in gene expression, which results in neurobiological disturbances. APDs (green cups) block postsynaptic neurotransmitter receptors, relieving psychotic symptoms. Signalling cascades are tuned down (two minus signs), and opposing changes in miRNA and gene expression occur. The end result is modulation of pathways and processes that are neuroprotective, as well as those that, when altered, may be involved in the manifestation of side effects