# Early life stress-induced depression reveals distinct region-specific modulation of unfolded protein response genes in the prefrontal cortex and hippocampus of rats

## TL;DR

Early-life stress in rats leads to region-specific changes in genes related to cellular stress responses in the brain, which may contribute to depression.

## Contribution

This study identifies region-specific modulation of UPR genes in the hippocampus and prefrontal cortex due to early-life stress.

## Key findings

- Early-life stress significantly downregulates UPR genes in the hippocampus but not in the prefrontal cortex.
- Environmental enrichment does not fully reverse the UPR gene changes caused by early-life stress.
- The findings suggest a region-specific molecular signature linked to depression pathophysiology.

## Abstract

Early-life stress (ELS) has been implicated in the onset of major depressive disorder (MDD) in adulthood. Recent studies suggest that the unfolded protein response (UPR), a cellular response to stress, could be a precipitating factor in depressive symptoms.

The present study examined the expression of genes associated with UPR in the prefrontal cortex (PFC) and the hippocampus using a rodent model of ELS-induced depression, in which male pups experienced maternal separation (MS) with or without subsequent environmental enrichment (MS-E). Expression of UPR genes was determined by quantitative polymerase chain reaction using rat-specific primers.

Of the six key UPR genes (Xbp1, sXbp1, Atf4, Atf6, Grp94, and Chop) studied, four genes, including Xbp-1, sXbp-1, Chop, and Grp94, showed a trend toward downregulation in the PFC of MS group; however, none of them were significantly downregulated. On the other hand, significant downregulation in all six UPR genes was noted in the hippocampus when the control group was compared with the MS group. Under the enriched conditions, these genes did not improve, showing their ineffectiveness in reversing the changes induced by maternal separation.

In conclusion, our study indicates that ELS disrupts the UPR specifically in the hippocampus, suggesting a stress-induced, region-specific molecular signature linked to depression pathophysiology. On the other hand, changes in hippocampal and prefrontal UPR gene expression remain evident in the MS-enrichment group, suggesting that environmental enrichment can improve these changes but does not fully reverse them.