Effects of Long-term Incremental Exercise on Thymus Cell Apoptosis and Cell cycle Regulatory Proteins

Objective:To observe the variation characteristics of the thymus structure,the apoptosis proteins and the cell cycle regulatory proteins during long-term incremental exercise.Methods:80male SD rats divided into control group and exercise group randomly.The exercise group participated in six weeks incremental treadmill training.The thymus structure were observed by HE staining,the expression of bax and bcl-2,cyclinE,p21 and cyclinB1of thymus cell were detected by immunohistochemistry at 0week,after 2weeks exercise,4weeks exercise and 6weeks exercise.Results:1)The cells density of thymus decreased,the cortex and medulla of thymus lobule became fused,reticular formation in thymocytes were destructed,adipocytes and hemocytes occurred.2)Compared with WK0,bax/bcl-2increased significantly in WK2 and WK6(P<0.01).Compared with WK2,it decreased with a significant difference in WK4 and WK6(P<0.01).While the ratio increased again in WK6 than in WK4(P<0.01).3)Compared with WK0,CyclinE increased slightly in WK2(P>0.05).While it reduced significantly in WK4 compared with WK0 and WK2(P<0.01).Compared with WK4,WK6 increased with a statistical difference(P<0.05).Making the p21 expression in WK0 as a reference,p21 extremely increased in WK2(P<0.01).Compared with WK2,WK4 reduced drastically(P<0.01).The expression slightly increased in WK6,but still less.The expression of CyclinB1 in rat thymocytes in WK2 was higher than WK0,and it reduced in WK4.Compared with WK4,the expression in WK6 increased slightly.The expression of CyclinB1 changed smoothly among every week and there was no significant difference(P>0.05).Conclusion:During six-week incremental exercise,the structure of rat thymus was destructed gradually.Bax/bcl-2in thymus of rats shows a trend that increased firstly and then decreased,and finally increased again.The apoptosis of thymocytes increased and the changes of bcl-2led this thymocyte apoptosis.The effect of the expression of thymus cell cycle regulatory proteins in G1/S by incremental exercise is more obviously than that in G2/M.The block of thymus cell cycle due to long-term incremental exercise mainly because of the DNA replication disorder which caused by the regulation of G1/S phase.Cell cycle arrest may be one of the mechanisms of thymocyte apoptosis.