Early life stress (ELS) increases the risk of depression later in life. Programmed cell death factor 4 (PDCD4), an apoptosis-related molecule, extensively participates in tumorigenesis and inflammatory diseases. However, its involvement in a person's susceptibility to ELS-related depression is unknown. To examine the effects and underlying mechanisms of PDCD4 on ELS vulnerability, we used a "two-hit" stress mouse model: an intraperitoneal injection of lipopolysaccharide (LPS) into neonatal mice was performed on postnatal days 7-9 (P7-P9) and inescapable foot shock (IFS) administration in adolescent was used as a later-life challenge. Our study shows that compared with mice that were only exposed to the LPS or IFS, the "two-hit" stress mice developed more severe depression/anxiety-like behaviors and social disability. We detected the levels of PDCD4 in the hippocampus of adolescent mice and found that they were significantly increased in "two-hit" stress mice. The results of immunohistochemical staining and Sholl analysis showed that the number of microglia in the hippocampus of "two-hit" stress mice significantly increased, with morphological changes, shortened branches, and decreased numbers. However, knocking down PDCD4 can prevent the number and morphological changes of microglia induced by ELS. In addition, we confirmed through the Golgi staining and immunohistochemical staining results that knocking down PDCD4 can ameliorate ELS-induced synaptic plasticity damage. Mechanically, the knockdown of PDCD4 exerts neuroprotective effects, possibly via the mediation of BDNF/AKT/CREB signaling. Combined, these results suggest that PDCD4 may play an important role in the ELS-induced susceptibility to depression and, thus, may become a therapeutic target for depressive disorders.
Keywords: Depression susceptibility; Early-life stress; PDCD4; Synaptic plasticity; “two-hit” stress.
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