Epigenetic Adaptation: The Regulatory Mechanisms of Hypothalamic Plasticity that Determine Stress-Response Set Point

Abstract

Our hypothesis was that postnatal stress exposure or sensory input alters brain activity, which induces acetylation and/or methylation on lysine residues of histone 3 and alters methylation levels in the promoter regions of stress-related genes, ultimately resulting in long-lasting changes in the stress-response set point. Therefore, the objectives of the proposal were: 1. To identify the levels of total histone 3 acetylation and different levels of methylation on lysine 9 and/or 14 during both heat and feed stress and challenge. 2. To evaluate the methylation and acetylation levels of histone 3 lysine 9 and/or 14 at the Bdnfpromoter during both heat and feed stress and challenge. 3. To evaluate the levels of the relevant methyltransferases and transmethylases during infliction of stress. 4. To identify the specific localization of the cells which respond to both specific histone modification and the enzyme involved by applying each of the stressors in the hypothalamus. 5. To evaluate the physiological effects of antisense knockdown of Ezh2 on the stress responses. 6. To measure the level of CpG methylation in the promoter region of BDNF in thermal treatments and free-fed, 12-hour fasted, and re-fed chicks during post-natal day 3, which is the critical period for feed-control establishment, and 10 days later to evaluate longterm effects. 7. The phenotypic effect of antisense “knock down” of the transmethylaseDNMT 3a. Background: The growing demand for improvements in poultry production requires an understanding of the mechanisms governing stress responses. Two of the major stressors affecting animal welfare and hence, the poultry industry in both the U.S. and Israel, are feed intake and thermal responses. Recently, it has been shown that the regulation of energy intake and expenditure, including feed intake and thermal regulation, resides in the hypothalamus and develops during a critical post-hatch period. However, little is known about the regulatory steps involved. The hypothesis to be tested in this proposal is that epigenetic changes in the hypothalamus during post-hatch early development determine the stress-response set point for both feed and thermal stressors. The ambitious goals that were set for this proposal were met. It was established that both stressors i.e. feed and thermal stress, can be manipulated during the critical period of development at day 3 to induce resilience to stress later in life. Specifically it was established that unfavorable nutritional conditions during early developmental periods or heat exposure influences subsequent adaptability to those same stressful conditions. Furthermore it was demonstrated that epigenetic marks on the promoter of genes involved in stress memory are altered both during stress, and as a result, later in life. Specifically it was demonstrated that fasting and heat had an effect on methylation and acetylation of histone 3 at various lysine residues in the hypothalamus during exposure to stress on day 3 and during stress challenge on day 10. Furthermore, the enzymes that perform these modifications are altered both during stress conditioning and challenge. Finally, these modifications are both necessary and sufficient, since antisense "knockdown" of these enzymes affects histone modifications, and as a consequence stress resilience. DNA methylation was also demonstrated at the promoters of genes involved in heat stress regulation and long-term resilience. It should be noted that the only goal that we did not meet because of technical reasons was No. 7. In conclusion: The outcome of this research may provide information for the improvement of stress responses in high yield poultry breeds using epigenetic adaptation approaches during critical periods in the course of early development in order to improve animal welfare even under suboptimum environmental conditions.