Translational profiling of stress-induced neuroplasticity in the CA3 pyramidal neurons of BDNF Val66Met mice

Genetic susceptibility and environmental factors (such as stress) can interact to affect the likelihood of developing a mood disorder. Stress-induced changes in the hippocampus have been implicated in mood disorders and mutations in several genes have now been associated with increased risk, such as brain-derived neurotrophic factor (BDNF). The hippocampus has important anatomical subdivisions, and pyramidal neurons of the vulnerable CA3 region show significant remodeling after chronic stress, but the mechanisms underlying their unique plasticity remain unknown. This study characterizes stress-induced changes in the in vivo translating mRNA of this cell population using a CA3-specific EGFP reporter fused to the L10a large ribosomal subunit (EGFPL10a). RNA-sequencing after isolation of polysome-bound mRNAs allows for cell-type specific, genome-wide characterization of translational changes after stress. The data demonstrated that acute and chronic stress produced unique translational profiles and that the stress history of the animal can alter future reactivity of CA3 neurons. CA3-specific EGFPL10a mice were then crossed to the stress-susceptible BDNF Val66Met mouse line to characterize how a known genetic susceptibility alters both baseline translational profiles and the reactivity of CA3 neurons to stress. Not only did Met allele carriers exhibit distinct levels of baseline translation in genes implicated in ion channel function and cytoskeletal regulation, but also activated a stress response profile that was highly dissimilar from wild type mice. Closer examination of genes implicated in the mechanisms of neuroplasticity, such as the NMDA and AMPA subunits and the BDNF pathway, revealed how wild type mice were able to upregulate many of these genes in response to stress, but Met allele carriers failed to do so. These profiles provide a roadmap of stress-induced changes in a genetically homogenous population of hippocampal neurons and illustrate the profound effects of gene-environment interactions on the translational profile of these cells.