| Heat stress is not only a serious threat to human survival, but also restricts the development of animal husbandry in those regions where heat stress being an issue, expecially for development of dairy industry. Starting from the point of characterizing the index reflecting heat stress response, screening the heat stress response related genes, further exploring regulatory mechanism of heat stress response and making effective measures for resisting heat stress and selection strategy that is suitable for the practical operation, profound significance for reducing heat stress damage and economic losses caused by heat stress will be made, and the production efficiency will be improved. The disadvantages of using dairy cattle as experimental animals include uncontrolled experimental condition, large genetic variation existed among individuals, as well as the high cost. The objectives of current study were to treat SD rats as model for heat stress response, and gain knowledge about how heat stress related physiological and biochemical indexes changes and how genes expressed differently at transcriptome level under controlled heat stress condition. Then, indexes and genes which are sensitive to heat stress response would be researched in depth, and physiological pathways and stress response process participated regulation of heat stress response would be identified. Further discussion of the regulatory mechanism for heat stress in rat would lay the foundation for the research related to the heat stress response in dairy cattle.The experimental animals of current study were 28 eight-week virgin fema le rats, weighting 180-210g, randomly grouped to heat stress treatment group (HS group) (42℃,Relative humidity (RH) 50%) and control group (NC group) (25 "C, RH50%). HS group rats were treated at different duration of time under heat stress treatment, namely:HS30min, HS60min, and HS120min, to detect t he changes of biochemical indicators in tissues of blood, liver, adrenal gland, a nd leg muscle, respectively. Blood, liver, and adrenal gland tissues of HS120mi n and NC groups rats were used for the transcriptome sequencing, to screen th e differential expressed genes.The results showed that:1) under condition of the ambient temperature bei ng 42℃ and RH50%, the SD rats suffered from severe heat stress, however th ese condition was not lethel. When rats were maintained under HS30min, HS6 Omin, or HS120min condition, their body core temperature rised from 37.13℃ to 39.70℃,39.63’C, and 40.48℃ respectively, there after the continuing high c ore temperature status was revealed when heat stress persisted.2) For HS120m in group rats, their level of cortisol (CORT) in leg muscle was significantly hi gher than that in the NC, HS30min, and HS60min groups, and their CORT in adrenal gland tissue was significantly higher than that in the NC; however thei r CORT level in lung, heart, kidney and stomach were lower comparing to tha t in the NC, HS30min, and HS60min groups. As the heat stress time extended, the level of Dopamine (DA) in leg muscle increased gradually, and that of H S120min significantly higher than that of NC group. Sensitivity analysis for bi ochemical indicators in blood and leg muscle, Growth hormone (HG) and COR T were the most sensitive heat stress biochemical indicators in blood and leg muscle, respectively:3) Totally 98,3551, and 4484 differentially expressed gen es in blood, liver and adrenal gland tissues were identified. Functional enrichm ent and pathway analysis were performed using all aboved mentioned differenti ally expressed genes, the main enriched gene ontology (GO) terms included cel 1 metabolism, repairing damage of DNA and protein, and response to stimulus, et al. The main enriched pathways were Circadian rhythm, Steroid hormone bi osynthesis, MAPK signaling pathway, PPAR signaling pathway and Antigen pro cessing and presentation.The resulted heat stress response sensitive biomarkers and the differentially expressed genes under heat stress condition from current study revealed that, under heat stress, a high body core temperature was the most intuitive physical performance in rats. For maintaining homeostasis, the HPA axis would be activated, and the concentration of related hormone and protein would change accordingly. These activities were results of the interaction among pathways including pathways related to the response of heat stress, the repair of DNA damage and hormone synthesis which were stimulated by heat, reflecting the survivial mechanism of reducing damage due to heat stress.Thus, results of current study would provide references for establishing standards for assessing the heat stress response and revealing molecular mechanism behind regulation of heat stress, and provide basic data for selection of heat resistant breeds in livestock and poultry. |
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