Differential expression of microRNA in peripheral blood mononuclear cells as specific biomarker for major depressive disorder patients

Highlights

• 26 miRNAs were identified by microarray profiling in MDD patients.

• 5 miRNAs were confirmed by qRT-PCR.

• A significant enrichment manifested in several pathways related to neuronal brain function.

Abstract

Currently, diagnosis and treatment of major depressive disorder (MDD) are based on the patients' description of symptoms, mental status examinations, and clinical behavioral observations, which increases the chance of misdiagnosis. There is a serious need to find a practical biomarker for the proper diagnosis of MDD. This study aimed to explore the possibility of microRNA (miRNA) in peripheral blood mononuclear cells (PBMCs) as specific blood-based biomarker for MDD patients. By using an Affymetrix array that covers 723 human miRNAs, we identified 26 miRNAs with significant changes in expression in PBMCs of MDD patients. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis in a larger cohort of 81 MDD patients and 46 healthy controls confirmed that the expression levels of 5 miRNAs (miRNA-26b, miRNA-1972, miRNA-4485, miRNA-4498, and miRNA-4743) were up-regulated. By receiver operating characteristic (ROC) curve analysis, the combining area under the ROC curve (AUC) of these five miRNAs was 0.636 [95% confidence interval (CI): 0.58–0.90]. MiRNA target gene prediction and functional annotation analysis showed that there was a significant enrichment in several pathways associated with nervous system and brain functions, supporting the hypothesis that differentially-regulated miRNAs may be involved in mechanism underlying development of MDD. We conclude that altered expression of miRNAs in PMBCs might be involved in multiple stages of MDD pathogenesis, and thus might be able to serve as specific biomarker for diagnosis of MDD.

Introduction

Major depressive disorder (MDD) is a common psychiatric illness with a high lifetime prevalence (2–14%) (Falagas et al., 2007), resulting in heavy social and economic burdens. Despite unremitting efforts of a few decades, the molecular and cellular mechanisms associated with MDD remain unclear. Currently, diagnosis and treatment of MDD are based on the patient's subjective description of symptoms, psychiatrists' subjective assessment of mental status with relevant scales and clinical behavioral observations. No objective biomarker is available for accurate diagnosis of MDD patients, and thus the chances of misdiagnosis and mistreatment are unavoidable. There is an urgent need for a sensitive and specific biomarker for the proper diagnosis of MDD. Due to the difficulty in fully understanding the pathophysiology of the disease, biomarker study in MDD proved difficult. Previous studies have identified a number of factors such as growth factor, cytokine, endocrine factor, or metabolic marker, but none of them could serve as a clinically useful biomarker for MDD due to limited sensitivity and specificity (Schmidt et al., 2011).

MicroRNAs (miRNAs) are a large family of single-stranded noncoding RNAs, regulating diverse biological processes by negatively regulating gene expression at the post-transcriptional level (Huntzinger and Izaurralde, 2011). Single miRNA could regulate up to hundreds of genes, and collectively may regulate 50%–60% of total transcriptomes (Baek et al., 2008, Krol et al., 2010), suggesting that miRNAs may have pleiotropic biological effects. Accumulating evidences have shown that miRNAs are implicated in multiple biological processes associating with central nervous system, including neurogenesis, neuronal proliferation, synaptic plasticity (Cheng et al., 2009, Liu et al., 2010, Zeng, 2009) and so on. Recent studies have demonstrated that specific miRNAs expression can be detected in peripheral blood in many diseases (Ajit, 2012, Wittmann and Jäck, 2010, Xu et al., 2012), including neuropsychiatric disorder (Gardiner et al., 2011, Katsuura et al., 2012, Lai et al., 2011, Rong et al., 2011). Given that gene expression profiling and certain mRNA in blood levels has shown to be correlated with brain levels (Gladkevich et al., 2004, Glatt et al., 2005, Marazziti et al., 2010, Vawter et al., 2001), a growing number of studies on psychiatric illness have focused on miRNAs in peripheral blood. In fact, since brain tissue is not readily accessible, blood-based miRNAs, being inexpensive, noninvasive and easy to collect, have become an increasingly important approach to identify clinically applicable biomarkers for MDD. Altered peripheral miRNA expression has been detected in some mental disorders such as schizophrenia, bipolar disorder, Alzheimer's disease (Lai et al., 2011, Rong et al., 2011, Song et al., 2014, Tan et al., 2014). Interestingly, the miRNA expression profiling correlates closely with the clinical symptoms (Lai et al., 2011), suggesting the lymphocyte might reflect the metabolism of brain cells.

Recent investigations have suggested that miRNAs have been involved in several pathways which may contribute to MDD pathomechanism (Meerson et al., 2010, Saus et al., 2010, Vreugdenhil et al., 2009). Saus et al. found that abnormal processing of pre-miR-182 in patients carrying the T allele of the rs76481776 polymorphism may contribute to the dysregulation of circadian rhythms in MDD patients with insomnia, which could influence expression levels of the mature form of miRNA-182, and might intensify downregulation in some of its target genes (Saus et al., 2010). Xu et al. conducted an association analyses in 1088 MDD patients and 1102 control subjects from the Han Chinese population and detected a statistically significant positive association between miRNA-30e ss178077483 and MDD (Xu et al., 2010). Szulwach et al. found that MeCP2, a DNA methyl-CpG–binding protein, can epigenetically regulate specific miRNA-137 in adult neural stem cells (aNSCs) (Szulwach et al., 2010). Kawashima et al. verified that U0126,an inhibitor of the MAPK/ERK pathway, suppressed the BDNF-increased miRNA-132, suggesting that BDNF upregulates miRNA-132 via the MAPK/ERK1/2 pathway (Kawashima et al., 2010).

So far, there has been few reports on miRNA profiling from PBMC in MDD. The present study aimed to analyze the miRNAs that might be involved in MDD pathomechanism, and evaluate the feasibility of using them as non-invasive biomarkers. Putative target genes of the differentially expressed miRNAs and their possible functions and biological mechanisms were investigated using bioinformatic tools.