Objective To explore the mechanism by which CD137 signal regulates the aging of vas-cular smooth muscle cells(VSMCs).Methods Thirty 8-week-old male C57BL/6J mice were ran-domly divided into a young group(8 weeks old)and an aged group(80 weeks old),with 30 mice in each group.After corresponding periods of feeding,the mice were euthanized,and the plasma and aortic blood vessels were isolated.In the cell experiments,normal VSMCs were divided into a control group,bleomycin(BLM)group,combined agonist group,and combined inhibitor group.The cellular senescence level of VSMCs was assessed using a cellular senescence β-galactosidase staining kit.Western blotting and PCR were employed to examine the expression of senescence-related proteins in tissues and cells,while ELISA was utilized to measure the expression of senes-cence-related inflammatory factors.Results The expression of CD137 and γ-H2AX in the aorta was significantly higher,while that of PCNA was obviously lower in the aged group than the young group(P＜0.05).The plasma level of CD137 was notably higher in the aged group than the young group(154.0±4.1 pg/ml vs 98.0±2.3 pg/ml,P＜0.05).Compared with the normal control group,there were significantly more aged VSMCs in the BLM group(P＜0.05).While,treatment of combined agonist resulted in larger amount of aged VSMCs when compared with the BLM group(P＜0.05),which was reversed by combined inhibitor treatment(P＜0.05).The levels of TNF-α,IL-6 and IL-1β were significantly elevated in the BLM group than the normal control group(P＜0.05).The combined agonist group had even higher levels of TNF-α,IL-6,and IL-1βthan the BLM group(P＜0.05),but the levels were decreased in the combined inhibitor group(P＜0.05).Compared with the normal control group,the expression of Bcl-2,γ-H2AX,P53,and P21 were significantly increased in the BLM group,combined agonist group,and combined inhibi-tor group,while that of PCNA was significantly decreased(P＜0.05).Compared with the BLM group,the expression of P53 and P21 in the combined agonist group showed an increase(P＜0.05),and the expression of P53 was significantly decreased in the combined inhibitor group(P＜0.05).Conclusion CD137 signal regulates the P53/P21 pathway to promote VSMC aging.