CD137-CD137L Interaction Regulates Atherosclerosis Via Cyclophilin A In Apolipoprotein E-deficient Mice

ObjectiveTo investigate the effects of CD137-CD137L interaction on the formation and progression of atherosclerosis in apolipoprotein E knockout (ApoE-/-) mice via regulation of cyclophilin A (CyPA).MethodsA constrictive collar was placed around right carotid arterie of ApoE-/-mice with a high-fat diet to induce plaques formation. After that, the mice were intraperitoneally injected with anti-CD37or anti-CD137L in the presence or absence of recombinant LVTHM-CyPA or pGC-FU-CyPA, which were used to inhibit or overexpress CyPA respectively. Pathological morphological analysis was performed, CyPA mRNA in mice plaque, spleen lymphocytes, vascular smooth muscle cells (VSMC) was detected by RT-PCR, while immunohistochemistry, ELASA, Western Blot, flow cytometry was used to detect the protein levels of CyPA.Results(1) Compared to control group, Serum TC、TG and LDL-C contents in mice after Collar-treated Surgery were increased obviously, while the HDL-C content decreased.(2) Hematoxylin and eosin (HE) staining revealed that the structure of proximal carotid artery of ApoE-/-mice before collar insertion and Western-Type Diet Feeding were integrity, which the arrangement of VSMCs were in order and no stenosis or atherosclerotic lesion formation. The structure of proximal carotid artery were not integrity, elastic fiber were crooked and broken, and the arrangement of VSMCs were disorder in mice with collar insertion. Extensive intracellular and extracellular lipid deposits located in the plaques, with abundant of cholesterol crystal clefts. However the plaques surface area was significantly increased in anti-CD137treated group after Collar-implant Surgery. Contrary, the plaques surface area in anti-CD137L treated group were markly decreased that compare with simplely Collar-implant Surgerygroup and anti-CD137treated group.(3) On immunohistochemistry staining, compared to the negatively expression of control Mice, CyPA was a strong positive expressed in anti-CD137treated group while decreased after LVTHM-CyPA treatment, and CyPA was a weak positive in anti-CD137L treated group but increased by pGC-FU-CyPA injection after Collar-implant Surgery.(4) In vivo, intraperitoneal injection with anti-CD137mAb substantially elevated levels of CyPA in the lymphocytes in ApoE-/-mice compared with control. Contrary, intraperitoneal injection with anti-CD137L mAb markedly suppressed levels of CyPA compared with control.(5)The atherogenic plaques contained a marked increase in numbers of VSMCs and the distribution of VSMCs were closely overlapped with the areas of highest CyPA expression in plaque.(6) In vitro, after stimulating or blocking CD137-CD137L signal pathway, the expression of CyPA mRNA and protein in leukocytes and VSMCs of ApoE-/-mice were significantly increased or decreased respectively, which maximal effect occurs at20μg/ml and24h.Conclusions(1) Stimulating or blocking CD137-CD137L signal pathway could promote or inhibit the formation and progression of atherosclerosis in ApoE-/-mice.(2) CD137-CD137L signal positively regulated the expression of CyPA in ApoE-/mice in vivo and in vitro.(3) CD137-CD137L signal affected the formation and progression of atherosclerosis in ApoE-/-mice by regulation of CyPA.