Post-transcriptional effects and interactions between chronic mild stress and acute sleep deprivation: regulation of translation factor and cytoplasmic polyadenylation element-binding protein phosphorylation.

Stress and restricted or disrupted sleep trigger adaptive responses in the brain at the level of gene transcription. We investigated the possible impact of chronic mild stress (CMS), acute sleep deprivation, and a combination of these in male rats on post-transcriptional mechanisms important for cognitive function and synaptic plasticity. Relationships between sleep architecture and translational regulators were also assessed. After four weeks of CMS, phosphorylation of two key translation factors, eukaryotic initiation factor 4E (eIF4E) and elongation factor 2 (eEF2), was enhanced in the prefrontal cortex, but unchanged in the hippocampus and dentate gyrus. Sleep deprivation decreased phosphorylated eIF4E in the dentate gyrus. In contrast, eEF2 phosphorylation was elevated in all brain regions after sleep deprivation. Thus, CMS and sleep deprivation, when given alone, have distinct region-specific effects. Furthermore, the combined treatment revealed striking interactions with eEF2 phosphorylation in which sleep deprivation counteracts the effect of CMS cortically and CMS modulates the effects of sleep deprivation in the hippocampus proper. Although CMS exposure alone had no effect in the hippocampus, it inhibited the sleep deprivation-induced eIF4E phosphorylation, while inducing phosphorylation of a major regulatory RNA-binding protein, cytoplasmic polyadenylation element-binding protein (CPEB) in the combined treatment. CMS had no effect on plasma corticosterone, but led to disruption of sleep. Sleep quality and sleep quantity in non-stressed animals showed predictive changes in eIF4E and eEF2 phosphorylation cortically. Prior exposure to CMS abolishes this relationship. We conclude that CMS and acute sleep deprivation have interactive and brain region-specific effects on translational regulators of relevance to mechanisms of stress responsiveness and sleep homeostasis.

Chronic fluoxetine treatment induces brain region-specific upregulation of genes associated with BDNF-induced long-term potentiation.

Several lines of evidence implicate BDNF in the pathogenesis of stress-induced depression and the delayed efficacy of antidepressant drugs. Antidepressant-induced upregulation of BDNF signaling is thought to promote adaptive neuronal plasticity through effects on gene expression, but the effector genes downstream of BDNF has not been identified. Local infusion of BDNF into the dentate gyrus induces a long-term potentiation (BDNF-LTP) of synaptic transmission that requires upregulation of the immediate early gene Arc. Recently, we identified five genes (neuritin, Narp, TIEG1, Carp, and Arl4d) that are coupregulated with Arc during BDNF-LTP. Here, we examined the expression of these genes in the dentate gyrus, hippocampus proper, and prefrontal cortex after antidepressant treatment. We show that chronic, but not acute, fluoxetine administration leads to upregulation of these BDNF-LTP-associated genes in a brain region-specific pattern. These findings link chronic effects of antidepressant treatment to molecular mechanisms underlying BDNF-induced synaptic plasticity.

Dual regulation of translation initiation and peptide chain elongation during BDNF-induced LTP in vivo: evidence for compartment-specific translation control.

Protein synthesis underlying activity-dependent synaptic plasticity is controlled at the level of mRNA translation. We examined the dynamics and spatial regulation of two key translation factors, eukaryotic initiation factor 4E (eIF4E) and elongation factor-2 (eEF2), during long-term potentiation (LTP) induced by local infusion of brain-derived neurotrophic factor (BDNF) into the dentate gyrus of anesthetized rats. BDNF-induced LTP led to rapid, transient phosphorylation of eIF4E and eEF2, and enhanced expression of eIF4E protein in dentate gyrus homogenates. Infusion of the extracellular signal-regulated kinase (ERK) inhibitor U0126 blocked BDNF-LTP and modulation of the translation factor activity and expression. Quantitative immunohistochemical analysis revealed enhanced staining of phospho-eIF4E and total eIF4E in dentate granule cells. The in vitro synaptodendrosome preparation was used to isolate the synaptic effects of BDNF in the dentate gyrus. BDNF treatment of synaptodendrosomes elicited rapid, transient phosphorylation of eIF4E paralleled by enhanced expression of alpha-calcium/calmodulin-dependent protein kinase II. In contrast, BDNF had no effect on eEF2 phosphorylation state in synaptodendrosomes. The results demonstrate rapid ERK-dependent regulation of the initiation and elongation steps of protein synthesis during BDNF-LTP in vivo. Furthermore, the results suggest a compartment-specific regulation in which initiation is selectively enhanced by BDNF at synapses, while both initiation and elongation are modulated at non-synaptic sites.

Chronic fluoxetine induces region-specific changes in translation factor eIF4E and eEF2 activity in the rat brain.

The delayed therapeutic onset observed in response to chronic antidepressant drug treatment is little understood. While current theories emphasize effects on gene transcription, possible effects of antidepressant drugs on translation control pathways have not been explored. We examined the effect of the selective serotonergic reuptake inhibitor fluoxetine on regulation of two major determinants of mRNA translation, eukaryotic initiation factor 4E (eIF4E) and eukaryotic elongation factor 2 (eEF2). Chronic fluoxetine treatment induced hyperphosphorylation of eEF2 (Thr56) in prefrontal cortex, hippocampus and dentate gyrus of rats. By contrast, phosphorylation of eIF4E (Ser209) was observed specifically in the dentate gyrus. Acute fluoxetine treatment had no effect on translational factor activity. These findings suggest that region-specific regulation of translation contributes to the delayed action of antidepressant drugs such as fluoxetine.