Can Environmental Enrichment Modulate Epigenetic Processes in the Central Nervous System Under Adverse Environmental Conditions? A Systematic Review

The aim of this paper is to summarize the available evidence in the literature regarding the effects generated by exposure to an enriched environment (EE) on the modulation of epigenetic processes in the central nervous system under adverse environmental conditions. Searches were conducted in three databases: PubMed/Medline (1053 articles), Scopus (121 articles), and Embase (52 articles), which were subjected to eligibility criteria. Of the 1226 articles found, 173 duplicates were removed. After evaluating titles/abstracts, 904 studies were excluded, resulting in 49 articles, of which 14 were included in this systematic review. EE was performed using different inanimate objects. Adverse environmental conditions included CUMS, sepsis, nicotine exposure, PCP exposure, early stress, WAS, high fructose intake, TBI, and sevoflurane exposure. Regarding microRNA expression, after exposure to EE, an increase in the expression of miR-221 and miR-483 was observed in the prefrontal cortex, and a reduction in the expression of miR-92a-3p and miR-134 in the hippocampus. Regarding histone modifications, in the hippocampus, there was a reduction of HAT, HDAC/HDAC4, H3 (acetyl K14), H4 (acetyl K15), H3K4me3, K3k27me3, and HDAC2/3/5. In the cortex, there was a reduction of HDAC2, and in the prefrontal cortex, there was an increase in acetylated H3. Regarding DNA modifications, there was a reduction of DNMT in the hippocampus. This systematic review concludes that the benefits of EE on the brain and behavior of animals are directly related to different epigenetic mechanisms, reflecting in cell growth and neuroplasticity. EE may be a non-pharmacological and easy-to-apply alternative to prevent symptoms in disorders affecting brain tissue.