Antidepressant actions of ketamine engage cell-specific translation via eIF4E

Effective pharmacotherapy for major depressive disorder remains a major challenge, as more than 30% of patients are resistant to the first line of treatment (selective serotonin reuptake inhibitors)(1). Sub-anaesthetic doses of ketamine, a non-competitive N-methyl-d-aspartate receptor antagonist(2,3), provide rapid and long-lasting antidepressant effects in these patients(4-6), but the molecular mechanism of these effects remains unclear(7,8). Ketamine has been proposed to exert its antidepressant effects through its metabolite (2R,6R)-hydroxynorketamine ((2R,6R)-HNK)(9). The antidepressant effects of ketamine and (2R,6R)-HNK in rodents require activation of the mTORC1 kinase(10,11). mTORC1 controls various neuronal functions(12), particularly through cap-dependent initiation of mRNA translation via the phosphorylation and inactivation of eukaryotic initiation factor 4E-binding proteins (4E-BPs)(13). Here we show that 4E-BP1 and 4E-BP2 are key effectors of the antidepressant activity of ketamine and (2R,6R)-HNK, and that ketamine-induced hippocampal synaptic plasticity depends on 4E-BP2 and, to a lesser extent, 4E-BP1. It has been hypothesized that ketamine activates mTORC1-4E-BP signalling in pyramidal excitatory cells of the cortex(8,14). To test this hypothesis, we studied the behavioural response to ketamine and (2R,6R)-HNK in mice lacking 4E-BPs in either excitatory or inhibitory neurons. The antidepressant activity of the drugs is mediated by 4E-BP2 in excitatory neurons, and 4E-BP1 and 4E-BP2 in inhibitory neurons. Notably, genetic deletion of 4E-BP2 in inhibitory neurons induced a reduction in baseline immobility in the forced swim test, mimicking an antidepressant effect. Deletion of 4E-BP2 specifically in inhibitory neurons also prevented the ketamine-induced increase in hippocampal excitatory neurotransmission, and this effect concurred with the inability of ketamine to induce a long-lasting decrease in inhibitory neurotransmission. Overall, our data show that 4E-BPs are central to the antidepressant activity of ketamine. The antidepressant-like effects of ketamine in mice depend on the expression of specific eIF4E-binding proteins in excitatory and inhibitory neurons.