Objective: To investigate whether CD137-CD137L signaling could affect the secretion of mouse vascular smooth muscle cells (VSMCs) -derived exosomes through autophagy mediated Rab7 pathway. Methods: Primary thoracic aorta VSMCs from C57BL/6J mouse were obtained by tissue block adherence method. VSMCs between the third to fifth passages were used and VSMCs were divided into 4 groups: control group, CD137 agonist group, lentivirus control group, Rab7 lentiviral interference group. VSMCs in CD137 agonist group were treated with recombinant protein of CD137L (10 μg/ml), VSMCs in lentivirus control group were treated with lentiviral followed by recombinant protein of CD137L (10 μg/ml), VSMCs in Rab7 lentiviral interference group were treated with Rab7 lentiviral intervention followed by recombinant protein of CD137L (10 μg/ml). Western blot was used to detect the protein expression of LC3Ⅱ, p62, Rab7, CD9, CD81 and Hsc70. Fluorescence microscopy was used to track the changes of autophagy in cells infected with mRFP-GFP-LC3. Transmission electron microscope was used to observe the morphology and size of VSMCs-derived exosomes. The nanoparticle tracking analysis(NTA) was used to detect the concentration and size of exosomes in each group. Results: (1) The expressions of Rab7, LC3Ⅱ and p62 protein in VSMCs of CD137 activation group were significantly higher than those in control group (all P<0.05). The expressions of Rab7, LC3Ⅱ and p62 protein in Rab7 lentivirus interference group was lower than in CD137 activation group (all P<0.05), while the expressions were similar between the lentivirus control group and the CD137 activation group (all P>0.05). (2) The total number of fluorescent spots and yellow fluorescent spots in the VSMCs of the CD137 activation group were higher than those in the control group (all P<0.05), and the number of yellow fluorescent spots was higher than that of the red fluorescent spots in the VSMCs of the CD137 activation group ((50.3±0.9) vs. (10.3±1.5)/cell). The total numbers of fluorescent spots and yellow fluorescent spots in VSMCs of Rab7 lentivirus interference group were lower than those of CD137 activation group (both P<0.05), and the number of red fluorescent spots in VSMCs was higher than that of yellow fluorescent spots ((40.7±4.0) and (10.7±1.2)/cell) in the Rab7 lentiviral interference group. The total numbers of fluorescent spots and yellow fluorescent spots in the VSMCs were similar between the lentivirus control group and the CD137 activation group (all P>0.05). (3) Under transmission electron microscopy, the size of the VSMCs-derived exosomes was about 30-150 nm. The exosome markers (CD9, CD81) could be detected in vesicles by Western blot. NTA results showed that the concentration of VSMCs-derived exosomes was significantly higher in the CD137-activated group than in the control group (P<0.05), which was significantly lower in the Rab7 lentiviral interference group than in the CD137-activation group (P<0.05) and was similar between the lentivirus control group and the CD137 activation group (P>0.05). The expression of Hsc70 protein in exosomes secreted by CD137 activation group was higher than that in the control group (P<0.05). The expression of Hsc70 protein in exosomes was lower in Rab7 lentivirus interference group than in the CD137 activation group (P<0.05), which was similar between the lentivirus control group and the CD137 activation group (P>0.05). The expression of LC3Ⅱ protein in exosome was higher in CD137 activation group than in control group (P<0.05), which was lower in Rab7 lentivirus interference group than in CD137 activation group (P<0.05), which was similar between the lentivirus control group and the CD137 activation group (P>0.05). Conclusion The CD137-CD137L signaling may affect the secretion of mouse VSMCs-derived exosomes through modulating the Rab7 pathway mediated autophagy.

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.