Proteome changes in rat hippocampus and pre-frontal/frontal cortex in Flinders rats after Escitalopram treatment.

Many of the commercially available antidepressants increase monoaminergic neurotransmitter concentration in synapses and their therapeutic efficacy most likely coincides with long-term molecular adaptations. GENDEP is an integrated project that combines large-scale clinical pharmacogenomic studies on depressed patients with preclinical research using animal models of disease, focussing on treatment with proserotonergic and pronoradrenergic antidepressants. In order to gain a better understanding of the molecular changes induced by chronic antidepressant treatment, we analysed, within GENDEP, proteomic changes in rat brain regions after a selective serotonin re-uptake inhibitor administration to gain more understanding about molecular changes induced by chronic antidepressant treatment. To this aim, a wide-scale analysis of protein expression was performed by 2D-electrophoresis on the Flinders Sensitive Line (FSL), a genetically selected rat model of depression displaying good face, predictive and construct validity. As a control, analyses were also carried out on the Flinders Resistant Line (FRL) rats, which do not show the depressive-like behaviour. Both FSL and FRL animals were split into groups receiving escitalopram (ESC) admixed to food pellets (25 mg/kg/day) or vehicle for 31 days. After sacrifice, proteins from pre-frontal/frontal cortex (PC) and hippocampus were extracted and separated by 2Delectrophoresis according to their isoelectric point and molecular mass. Protein spots were detected by fluorescent staining and image analysis was performed by PDQuest software (Bio-Rad). Comparisons were carried out between groups sharing the same genetic background but receiving vehicle or pharmacological treatment in order to detect ESC-induced changes. Protein level comparisons were performed with both univariate (Student’s t test) and multivariate (Partial Least Squares) statistical analysis methods. Spots displaying statistically significant differences were identified using peptide fingerprinting mass spectrometry. ESC treatment in hippocampus regulated 18 and 29 protein spots in FSL and FRL groups, respectively. In PC samples, 10 and 11 protein spots were modulated in FSL and FRL groups, respectively. DAVID Bioinformatics Resources 2007 were applied to obtain gene ontology (GO) term enrichment analysis to highlight the most relevant GO terms, associated with the modulated proteins resulting from the comparisons. Analysis highlighted several proteins with differential modulation upon ESC treatment in the different genetic backgrounds. In FRL, the treatment modulated expression of proteins mainly involved in cytoskeleton assembly and remodelling (tubulin-beta in both regions, actin-1 and alpha-internexin in hippocampus), in cell differentiation and nervous system development (a-internexin in hippocampus, dihydropyrimidinase-related protein-2 in both regions), in neurotransmitters secretion (synapsin-1 in hippocampus) and in cellular metabolism (e.g. a-enolase and isocitrate dehydrogenase in PC, glutamate dehydrogenase-1 and aldolase-C in hippocampus). In FSL, ESC modulated proteins involved in vesicle-mediated transport (alpha-SNAP in hippocampus), in cell differentiation (stathmin in hippocampus), in cytoskeleton organization (e.g. neurofilament-L, actin-1/2 and tubulin in hippocampus), in intracellular signalling cascade modulation (14−3-3-gamma in PC), in cellular calcium ion homeostasis (calreticulin in hippocampus) and in energy metabolism (e.g. ATP synthase-alpha/beta in the hippocampus and fumarate hydratase-1 in PC). These findings suggest new molecular correlates of vulnerability to depression and of response to antidepressant treatment.