miR-483-5p offsets functional and behavioural effects of stress in male mice through synapse-targeted repression of Pgap2 in the basolateral amygdala.

Severe psychological trauma triggers genetic, biochemical and morphological changes in amygdala neurons, which underpin the development of stress-induced behavioural abnormalities, such as high levels of anxiety. miRNAs are small, non-coding RNA fragments that orchestrate complex neuronal responses by simultaneous transcriptional/translational repression of multiple target genes. Here we show that miR-483-5p in the amygdala of male mice counterbalances the structural, functional and behavioural consequences of stress to promote a reduction in anxiety-like behaviour. Upon stress, miR-483-5p is upregulated in the synaptic compartment of amygdala neurons and directly represses three stress-associated genes: Pgap2, Gpx3 and Macf1. Upregulation of miR-483-5p leads to selective contraction of distal parts of the dendritic arbour and conversion of immature filopodia into mature, mushroom-like dendritic spines. Consistent with its role in reducing the stress response, upregulation of miR-483-5p in the basolateral amygdala produces a reduction in anxiety-like behaviour. Stress-induced neuromorphological and behavioural effects of miR-483-5p can be recapitulated by shRNA mediated suppression of Pgap2 and prevented by simultaneous overexpression of miR-483-5p-resistant Pgap2. Our results demonstrate that miR-483-5p is sufficient to confer a reduction in anxiety-like behaviour and point to miR-483-5p-mediated repression of Pgap2 as a critical cellular event offsetting the functional and behavioural consequences of psychological stress.

Increased neuroplasticity and hippocampal microglia activation in a mice model of rapid antidepressant treatment.

The search for biomarkers of antidepressant effects focused on pathways regulating synaptic plasticity, and on activated inflammatory markers. Repeated Sleep Deprivation (SD) provides a model treatment to reverse-translate antidepressant effects from in vivo clinical psychiatry to model organisms. We studied the effects of repeated SD alone (ASD) or combined with exercise on a slow spinning wheel (SSW), in 116 C57BL/6J male mice divided in three groups (ASD, SSW, untreated). Forced Swimming Test (FST) was used to detect antidepressant-like effects. Unbiased evaluation of the transcriptional responses were obtained in the hippocampus by Illumina Bead Chip Array system, then confirmed with real time PCR. Spine densities in granular neurons of the dentate gyrus (DG) were assayed by standard Golgi staining. Activation of Microglial/Macrophages cells was evaluated by immunufluorescence analysis for Iba1. Rates of cell proliferation was estimated pulsing mice with the S-phase tracer 5-Iodo-2'-deoxyuridine (IdU). All SD procedures caused a decreasing of floating time at FST, and increased expression of the immediate early gene Arc/Arg3.1. In addition, SSW also increased expression of the Microglia/Macrophages genes Iba-1 and chemokine receptors Cx3cR1 and CxcR4, of the canonical Wnt signaling gene Wnt7a, and of dendritic spines in CA4 neurons of the DG. SSW up-regulated both the number of Iba1+ cells and rates of cell proliferation in the subgranular region of the DG. The antidepressant-like effects of SD dissociated both, from hippocampal neuroplasticity in the DG (not occurring after ASD), and from microglial activation (not preventing behavioral response when occurring). The increase in dendritic spine density in the DG after SD and exercise was associated with an up-regulation of Wnt 7a, and with activation of the innate immune system of the brain. Increased Arc/Arg3.1 suggests however increased neuroplasticity, which could be common to all fast-acting antidepressants, and possibly occurring in other brain areas.