Objective <p>To examine the impact of BRD4 on hippocampus injury in a murine model of depression via altering signaling pathways inside hippocampal cells.</p> Method <p>Sixty-four male C57BL/6 mice were randomly assigned to either a vector control group or a model group. A depression model was created via the use of solitary living and chronic unexpected mild stress (CUMS). Behavioral investigations demonstrated depressive-like behaviors in mice. Western blotting (WB) was used to determine the expression levels of signaling pathway proteins and brain-derived neurotrophic factor (BDNF) in hippocampus tissue. We used the ELISA method to find out how much 5-HT, Ach, DA, MDA, and SOD there was. Additionally, single-cell transcriptome analysis (GSE308075) was performed to explore cellular heterogeneity and astrocyte-related signaling in depression.</p> Results <p>Compared with the Control group, the model group exhibited reduced open field central activity and elevated plus maze open arm activity, along with upregulated hippocampal BRD4 and downregulated Notch-1, p-PI3K, p-CREB, and p-TrkB. After JQ-1 treatment, these behavioral deficits were reversed; nuclear BRD4 and JMJD3 decreased, while EZH2, Notch-1, p-PI3K, p-CREB, BDNF, p-TrkB, 5-HT, Ach, DA, and SOD increased, and MDA decreased. Single-cell transcriptomic data revealed reduced oxidative stress scores and altered cell–cell communication networks in hippocampal astrocytes, supporting the involvement of BRD4-modulated pathways in glial dysfunction.</p> Conclusion <p>This study demonstrates that BRD4 in the hippocampus serves as a key epigenetic regulator coupling oxidative stress with defective neurotrophic signaling. It drives depression progression by modulating the ROS/JMJD3/Notch-1/PI3K/BDNF/TrkB signaling network, suggesting that targeting BRD4 may represent a novel therapeutic strategy capable of simultaneously intervening in multiple pathological pathways.</p>