Hippocampal semaphorin 3B improves depression‐like behaviours in mice by upregulating synaptic plasticity and inhibiting neuronal apoptosis

Depression is a global health problem, and there is a pressing need for a better understanding of its pathogenesis. Semaphorin 3B (Sema 3B) is an important axon guidance molecule that is primarily expressed in neurons and contributes to synaptic plasticity. Our previous studies using a high-throughput microarray assay suggested that Sema 3B expression was tremendously decreased during the development of depression, but the specific role and mechanisms of Sema 3B in depression are still unknown. Herein, we report that levels of Sema 3B protein are decreased in the hippocampus and serum of chronic mild stress (CMS)-treated mice. Increasing the levels of Sema 3B, either by injecting AAV-Sema 3B into the hippocampus or by injecting recombinant Sema 3B protein into the lateral ventricles, alleviated CMS-induced depression-like behaviours and enhanced the resistance to acute stress by increasing dendritic spine density in hippocampal neurons. In contrast, interfering with the function of Sema 3B by injecting anti-Sema 3B antibody into the lateral ventricles decreased the resistance to acute stress. In vitro, corticosterone (CORT) treatment decreased the survival rate and protein levels of Sema 3B and synapse-associated proteins in HT22 cells. Overexpression of Sema 3B improved the decreased survival rate caused by CORT by inhibiting apoptosis and increasing levels of synaptic-associated proteins, and knockdown of Sema 3B reduces the cellular resistance to CORT and the levels of synapse-associated proteins. These findings represent the first evidence for the neuroprotective mechanism of Sema 3B against stresses, suggesting that Sema 3B could be a promising novel target for the prevention and treatment of depression.