Transcriptomics of Environmental Enrichment Reveals a Role for Retinoic Acid Signaling in Addiction

Abstract

There exists much variability in susceptibility/resilience to addiction in humans. The environmental enrichment paradigm is a rat model of resilience to addiction-like behavior, and understanding the molecular mechanisms underlying this protective phenotype may lead to novel targets for pharmacotherapeutics to treat cocaine addiction. We investigated the differential regulation of transcript levels using RNA sequencing of the rat nucleus accumbens after environmental enrichment/isolation and cocaine/saline self-administration. Ingenuity Pathways Analysis and Gene Set Enrichment Analysis of 14,309 transcripts demonstrated that many biofunctions and pathways were differentially regulated. New functional pathways were also identified for cocaine modulation (e.g., Rho GTPase signaling) and environmental enrichment (e.g., signaling of EIF2, mTOR, ephrin). However, one novel pathway stood out above the others, the retinoic acid (RA) signaling pathway. The RA signaling pathway was identified as one likely mediator of the protective enrichment addiction phenotype, an interesting result given that nine RA signaling-related genes are expressed selectively and at high levels in the nucleus accumbens shell (NAcSh). Subsequent knockdown of Cyp26b1 (an RA degradation enzyme) in the NAcSh of rats confirmed this role by increasing cocaine self-administration as well as cocaine seeking. These results provide a comprehensive account of enrichment effects on the transcriptome and identify RA signaling as a contributing factor for cocaine addiction.

Cocaine Self-administration Alters Transcriptome-wide Responses in the Brain’s Reward Circuitry

“…HNF4A (NR2A1) was a predicted regulator in Patterns associated with a history of cocaine SA (Figure 3J–L; Patterns B and C) and genes associated with AI (Figure 5I). NRs have recently been identified as critical for CREB-regulated learning and memory in hippocampus (34) and important for aspects of cocaine SA in NAc (35). This, in combination with the prediction of CREB as an upstream regulator across all 3 Patterns and AI, raised the hypothesis that NRs may influence CREB transcriptional regulation in a context-dependent manner throughout the brain.…”

Convergent transcriptomics and proteomics of environmental enrichment and cocaine identifies novel therapeutic strategies for addiction

“…The primary analyses of tissue from NAc of enriched or isolated animals that self-administered cocaine or saline determined that environmental enrichment regulated 3393 of 14,309 transcripts ( p <0.05; (Zhang et al, 2016) and 117 of 1917 proteins (Lichti et al, 2014). Cocaine regulated 1274 transcripts and 52 proteins.…”

“…Detailed methods can be found in (Zhang et al, 2016). Briefly, RNA from the left NAc was purified with the RNeasy kit (Qiagen Valencia, CA, USA) and reverse transcribed into RNA.…”

“…To investigate the molecular mechanisms of the protective addiction phenotype, a transcriptomic study using high-throughput RNA sequencing and a proteomic study using high-performance liquid chromatography with tandem mass spectrometry (nanoLC–MS/MS) were conducted to explore the differential responses to cocaine in EC and IC rats at both the mRNA and protein level (Lichi et al, 2014; Zhang et al, 2016). More than 14,000 transcripts and 1900 proteins were identified and subsequently quantified in these studies.…”

Epigenetic rejuvenation of the hippocampus by environmental enrichment

“…With the exception of a few regulated genes 50, 51 , the molecular mechanisms underlying ENR-stimulated brain plasticity were, until now, mostly unknown. Our functional enrichment analyses of differentially methylated genes in the aged mouse dentate gyrus have exposed several pathways potentially underlying the neuroprotective effects of ENR during aging.…”