Dynamic proteomics of nucleus accumbens in response to acute psychological stress in environmentally enriched and isolated rats

Abstract

Our prior research has shown that environmental enrichment (i.e. rats reared in an environment with novel objects, social contact with conspecifics) produces a protective antidepressant-like phenotype in rats and decreases neurobiological effects of acute psychological stress. Although CREB activity has been identified as a major player, the downstream molecular mechanisms remain largely unexplored. Thus, the current study investigates proteomic differences in the accumbens of rats raised in an enriched condition (EC) versus those raised in an isolated control condition (IC) under basal conditions and after 30 min of acute restraint stress. Results showed that under basal conditions, EC rats generally expressed less mitochondria-related proteins, particularly those involved in TCA cycle and electron transport compared to IC rats. After 30 min of acute stress, EC rats displayed increased expression of energy metabolism enzymes (among others) while IC rats exhibited decreased expression of similar proteins. Further, network and pathway analyses also identified links to AKT signaling proteins, 14-3-3 family proteins, heat-shock proteins, and ubiquitin-interacting proteins. The protein ENO1 showed marked differential expression and regulation; EC rats expressed higher levels under basal conditions that increased subsequent to stress, while the basal IC expression was lower and decreased further still after stress. The results of this study define differential protein expression in a protective rat model for major depression and additionally identify a dynamic and coordinated differential response to acute stress between the two groups. These results provide new avenues for exploration of the molecular determinants of depression and the response to acute stress.

Figure 1. The expression of significantly regulated proteins from cytosolic extracts of rat NAcc (P<0.05) comparing EC vs. IC basal expression (blue), IC stress (green), and EC stress (orange), which were analyzed by Progenesis SameSpots in CBB stained gels.

Figure 2. The expression of significantly regulated proteins from membrane extracts of rat NAcc (P<0.05) comparing EC vs. IC basal expression (blue), IC stress (green), and EC stress (orange), which were analyzed by Progenesis SameSpots in CBB stained gels.

Figure 3. Top ten major biological functionsof regulated proteins comparing EC and IC basal expression (a), IC stress (b), EC stress (c) via IPA analysis.

Y-axis represents the –log (P value).

Figure 4. Top ten major canonical pathways of regulated proteins comparing EC and IC basal expression (a), IC stress (b), EC stress (c) via IPA analysis.

Y-axis represents the –log (P value).

Figure 5. Significant networks identified via IPA analysis of (a) basal EC vs. IC protein expression, (b and c) IC stress, and (d) EC stress.

Red symbols represent upregulated and green denote downregulated proteins. Asterisks (*) denote multiple spots mapping to the same protein.

Figure 6. Functional assay of ATP synthase activity and ATP5B quantity.

Bars represent mean (± SEM) amount of ATP synthase activity in mM/min (a) and quantity in OD/min (b) of ATP synthase. Asterisk (*) represents statistically significant difference from control. Bottom panels depict correlation of activity and quantity as measured from the kit (c) and activity and quantity of ATP5C1 as measured from the 2D gel (d). Circles represent IC rats and triangles represent EC rats. Controls are white symbols and Stress groups are red. Solid line depicts a significant correlation for EC rats and dashed line depicts a lack of correlation in IC rats.

Figure 7. Regulated energy metabolism proteins are CREB targets.

The diagram depicts significantly regulated proteins in the glycolysis, TCA and electron transport pathways. The thirteen significantly regulated proteins are shown as large symbols. In addition, 12 of the 13 regulated proteins are from CREB target genes (shown as red symbols).