Agomelatine and fluoxetine treatments induce different and time-dependent modulation of rat hippocampal miRNome

Background: MicroRNAs (miRNAs) are small, non-coding RNAs that regulate target-gene expression by translation, inhibition or mRNA degradation. Each miRNA can regulate hundreds of target mRNAs, thus playing a crucial role into signaling and network modulation in almost every cellular process, including neuronal development and homeostasis [1]. Recent investigations suggested that dysregulation in miRNA expression may be critical for mental disorders pathophysiology, including major depression, and psychotropic drugs action [2]. Aim of this study was to verify whether hippocampal miRNome expression profile could be affected by treatment for 3 or 7 days with two different antidepressants: the SSRI fluoxetine and agomelatine, a MT1/MT2 receptor agonist and 5-HT2C receptor antagonist [3]. Methods: Rats (9 for group) were treated with vehicle, agomelatine (40mg/kg/day i.p.) or fluoxetine (10mg/kg/day i.p.) for 3 or 7 days. MiRNA expression analysis was conducted in total hippocampus by q-RT-PCR with TaqMan Array rodent MicroRNA A+B Cards Set v3.0 (Life Technologies). Statistical analysis was carried out with the SAM software, v. 4.0, with FDR for multiple testing at <5%. In order to identify miRNA putative target genes and molecular pathways potentially involved, bioinformatic analyses were performed by integrating and filtering the results of different miRNA target prediction algorithms, followed by annotation analyses with Gene Ontology subcategories and KEGG pathways (exact Fisher test with p<0.05; and multiple testing correction). Results: The expression analysis showed that hippocampal miRNome was significantly modulated by both drugs. After 3 days, while fluoxetine down-regulated the expression of 8 miRNAs, agomelatine induced a marked effect by modulating 34 miRNAs (6 up- and 28 down-regulated); interestingly, 2 miRNAs were similarly modulated by both antidepressants. A stronger effect of fluoxetine was found after 7 days of treatment, with 35 miRNAs modulated (28 up- and 7 down-regulated), while agomelatine modified the expression of 22 miRNAs (19 up- and 3 down-regulated), five of which were modulated also after 3 days of treatment. The bioinformatic analysis suggested that agomelatine, mainly after 3 days, could modulate pathways involved in epigenetic mechanisms, inflammation, and neuroplasticity among the others. The same analysis on miRNAs modulated by fluoxetine highlighted the possible involvement of mechanisms mainly related to neuronal and synaptic plasticity and neurotransmission. Interestingly, several target genes have been previously associated to both depression pathophysiology and antidepressant action. Experiments are in progress in order to validate some of the putative target genes, by means of mRNA/protein expression studies. Discussion: Our results show that fluoxetine and agomelatine can induce early and time-dependent modifications in rat hippocampal miRNome, although with different effects. Indeed, main effects of agomelatine were found after 3 days of treatment, whereas after 7 days of treatment with fluoxetine. The bioinformatic analyses revealed that pathways involved in epigenetic mechanisms, inflammation, neuroplasticity and neurotransmission could be affected by the modulated miRNAs. Although further work is needed to get further insight, these results suggest that miRNA might be involved in the effects of antidepressants and may explain the early improvement of some symptoms with agomelatine. 1. McNeill, E., Van Vactor, D., 2012. MicroRNAs shape the neuronal landscape. Neuron 75, 363–379. 2. Tardito, D., Mallei, A., Popoli, M., 2013. Lost in translation. New unexplored avenues for neuropsychopharmacology: epigenetics and microRNAs. Expert Opin Investig Drugs 22, 217–233. 3. Racagni, G., Riva, M.A., Molteni, R., Musazzi, L., Calabrese, F., Popoli, M., Tardito, D., 2011. Mode of action of agomelatine: synergy between melatonergic and 5-HT2C receptors. World J Biol Psychiatry 12, 574–587