Long-term Impact of Early-Life Stress on Hippocampal Apoptotic Gene Expression in Mice

Early-life stress (ELS) such as maternal separation has been associated with neuronal apoptosis and impaired hippocampal function in rodent models. This study investigated the long-term effects of early-life unpredictable maternal separation (MS) and MS combined with unpredictable maternal stress (MSUS) from postnatal days 1 to 14 on the mRNA expression levels of the proapoptotic genes Bax , Tp53 and Casp3 , and the prosurvival gene Bcl2 in the hippocampus of mice ( in vivo ). Additionally, total RNA from the MSUS hippocampus was nucleofected at different concentrations into healthy mouse hippocampal cells, followed by 3D neuronal cell culture using N-heptyl-D-galactonamide (GalC7) hydrogels as scaffolds for hippocampal cell growth and apoptotic gene expression studies ( in vitro ). Quantitative real-time PCR was conducted to assess the expression of target genes, which were subsequently analyzed using the comparative Ct method (2 ^-ΔΔCt ). Bax mRNA expression was significantly lower in the MS group than in the control group, whereas both the MS and MSUS groups presented significant increases in Bcl2 mRNA expression. In addition, the expression ratio of Bcl2 / Bax was significantly greater in the MS and MSUS groups. No significant differences in Tp53 or Casp3 mRNA expression levels were detected between the groups. Although the in vitro mRNA expression levels were not significantly different, the mRNA expression ratio of Bcl2/Bax reached equilibrium as the concentration of total RNA nucleofected increased. Our results suggested that, in response to ELS, hippocampal cells adapt to prioritize survival over apoptosis.