Epigenetic regulation of nociceptin/orphanin FQ and corticotropin-releasing factor system genes in frustration stress-induced binge-like palatable food consumption

Purpose of the study: Satisfactory treatments for eating disorders, such as binge eating disorder and bulimia nervosa, are not available at present. Using a well-characterized animal model of binge eating [1], we investigated the epigenetic regulation of the nociceptin/orphanin FQ (N/OFQ) and corticotropin-releasing factor (CRF) system genes. Understanding the nature of genetic and epigenetic (gene x environment) interactions in regulating individual risk of developing an eating disorder, binge eating included, might be helpful in search for new pharmacotherapeutic treatments. Methods: The animal model included four groups (rats fed normally, and then stressed or not, rats exposed to cycles of restriction/ refeeding, and then stressed or not). Biological materials (e.g., total RNA and DNA) were isolated from the amygdala complex, hypothalamus and ventral tegmental area (VTA). To assess mRNA abundances and to quantify gene promoters DNA methylation, Real-Time RT-PCR and Bisulfite pyrosequencing were used. Results: Rats subjected to cycles of food restriction and then exposed to frustration stress, showed binge eating behavior (F(3,69) = 3.75, p<0.05). Therefore, binge eating appears to be caused by a unique interaction between dieting and stress. Statistical analysis by two-way ANOVA showed that intermittent food restriction and frustration stress did not determine changes of pN/OFQ mRNA levels (F(1,36) = 0.01; p>0.05). Relevant changes were observed in N/OFQ receptor gene expression (F(1,36) = 4.55; p<0.05). No significant changes in gene expression were detected for CRF and CRF-1 receptor in the amygdala complex, however epigenetic changes were observed at CRF-1 receptor promoter region. Food restriction by itself might be responsible for the downregulation of N/OFQ (F(1,26) = 20.98; p<0.05) as well as of the N/OFQ receptor (F(1,27) = 11.99; p<0.05) and CRF-1 receptor (F(1,26) = 21.22; p<0.05) genes. Instead, CRF gene is upregulated (F(1,27) = 9.65; p<0.05) in the hypothalamus only when rats are food restricted and exposed to frustration stress, where an increase in DNA methylation at CRF-1 receptor gene promoter was also observed. Moreover, CRF system genes expression is also increased in the VTA: CRF (F(1,26) = 16.28; p<0.05) and CRF-1 receptor F(1,27) = 8.58; p<0.05), where these changes appear to be due to a reduction in DNA methylation at gene promoters. Conclusions: Overall, our findings suggest that stress associated with food restriction promotes alterations in critical genes for feeding and reward circuitry, that influences food intake and stressrelated behaviours. These changes seem to be partially driven by epigenetic mechanisms promoting increased sensitivity of stress pathways that alter reward circuitry. Our data add information on altered N/OFQ and CRF signaling in food restriction and under stressful conditions, and provide insight on the use of this model of binge eating for the study of epigenetic modifications in controlled genetic and environmental backgrounds. References [1] Cifani, C., Polidori, C., Melotto, S., Ciccocioppo, R., Massi, M., 2009. Preclinical model of binge-eating elicited by yo–yo dieting and stressful exposure to food: effect of sibutramine, fluoxetine, topiramate and midazolam. Psychopharmacology 204, 113–125.