Influence Of Excessive Calorie Restriction On Expressions Of SIRT1 And SIRT3 In Rat's Myocardium

BackgroudCaloric restriction (CR) extends lifespan and increases resistance to age-related diseases inrodents and monkeys, and improves the health of overweight humans. Sirtuin1 (Sirt1) andsirtuin3 (Sirt3) have been reported to play a protective effect on cardiovascular disease. CR canincrease the expression of both SIRT1 and SIRT3. However, the relationship between extent ofCR and the level of SIRT expression is still unknown.ObjectiveTo investigate the influence of calorie restriction on expression of SIRT1 and SIRT3 in rat'smyocardium under different levels.MethodsSixty Sprague-Dawley rats, eight-weeks old, with an average body weight of 200±20g, wererandomly divided into four diet treatment groups: normal control (NC) group fed with standardrodent chow; 75% calorie restriction (CR) group fed with 75% of the food intake from the NCgroup；55% calorie restriction (CR) group fed with 55% of the food intake from the NC group；high-fat (HFa) group fed with a high-fat diet containing 2% cholesterol 20g, 0.5% sodiumcholate 5g,10% lard 100g, 0.2% propylthiouracil 2g,82.3% standard rodent chow 823g and5% white sugar 50%. Food intake and body weight of rats were recorded everyday, and thefood supply of the CR group was adjusted accordingly. Blood samples were collected from tailveins every two weeks after fasting for 16h. Sera were immediately isolated from bloodsamples by centrifugation and then stored at -20°C until analyzed for blood lipid. At the end ofstudy,blood was collected by heart puncture after anesthetization and the animal was sacrificedby decapitation. The hearts and viscera fat were harvested and weighed immediately.Expressions of SIRT1 and SIRT3 proteins in myocardium was analyzed by Western blotting. ResultesultsThe body weight of the NC and HF group both increased, but there is no significant differencebetween them, however, both the viscera fat and blood lipid levels were higher than NC group;the heart mass index and left ventricle mass index also were higher than NC group. The weightof 75% CR group had no significant change, but the viscera fat and blood lipid levels weredecreased compared with NC group, the heart mass index and left ventricle mass index weresimilar to NC group. The body weight, the viscera fat, the TRIG and LDL levels of the 55%CRwere the lowest, but their daily behavior were not so energetic, there heart mass index and leftventricle mass index were also the lowest. Treated with the 75% CR diet increased theexpression of both SIRT1 and SIRT3 in myocardium (p<0.05), while treatment with the 55%CR diet and the HF diet caused both decreased (p<0.05). And there was no significantdifference between them.ConclusionsWe concluded that a moderate CR can significantly improve the rats' ability of resistingmetabolism syndrome, and increase expressions of both SIRT1 and SIRT3 in rat's myocardium,while excessive CR can cause a decline of both SIRT1 and SIRT3.