Dysfunction of Microglial STAT3 Alleviates Depressive Behavior via Neuron-Microglia Interactions

Neuron-microglia interactions have a crucial role in maintaining the neuroimmune system. The balance of neuroimmune system has emerged as an important process in the pathophysiology of depression. However, how neuron-microglia interactions contribute to major depressive disorders has been poorly understood. Herein, we demonstrated that microglia-derived synaptic changes induced antidepressive-like behavior by using microglia-specific signal transducer and activator of transcription 3 (STAT3) knockout (KO) (STAT3(fl/fl); LysM-Cre(+/-)) mice. We found that microglia-specific STAT3 KO mice showed antidepressive-like behavior in the forced swim, tail suspension, sucrose preference, and open-field tests. Surprisingly, the secretion of macrophage colony-stimulating factor (M-CSF) was increased from neuronal cells in the brains of STAT3(fl/fl); LysM-Cre(+/-) mice. Moreover, the phosphorylation of antidepressant-targeting mediators and brain-derived neurotrophic factor expression were increased in the brains of STAT3(fl/fl); LysM-Cre(+/-) mice as well as in neuronal cells in response to M-CSF stimulation. Importantly, the miniature excitatory postsynaptic current frequency in the medial prefrontal cortex was increased in STAT3(fl/fl); LysM-Cre(+/-) mice and in the M-CSF treatment group. Collectively, microglial STAT3 regulates depression-related behaviors via neuronal M-CSF-mediated synaptic activity, suggesting that inhibition of microglial STAT3 might be a new therapeutic strategy for depression.