Studies On Effect Of Loss Of Tumor Necrosis Factor-α On Atherosclerosis In Mice Model

Objective: Cardiovascular diseases, especially coronary heart diseases, are responsible for the majority of deaths in the world. Therefore, it is very important to investigate the pathogenesis of atherosclerosis and find the methods to disturb it for preventing and treating coronary heart diseases. Growing data show that atherosclerosis is an inflammatory disease. In fact Inflammatory processes are involved with all phases of atherosclerotic lesion growth, even the plaques rupture and umerous cytokines participate in this process. One of the best-studied proinfiammatory cytokines is tumor necrosis factor-a (TNF-a), TNF-a in the pathogenesis of atherosclerosis is supported by clinical data showing its presence in human and rodent atherosclerotic plaques. The contribution of TNF-a to atherosclerosis is reinforced by numerous data underlining its stimulatory effects on the expression of proteins involved in the vascular cell dysfunction. But most studies were based on indirect ways, for example the in vitro systems. According to our researches upon atherosclerosis in TNF-a gene knockout mice, We employ ApoE and TNF-a double genes knockout mice model (A/T KO). We make studies of the direct effects of the less of TNF-a on atherosclerosis via the a novel mice models. Methods: In part 1, We used TNF-a knockout mice as experiment group and wild type C57B6J (WT) as the control. Furthermore, double knockouts lacking both apoE and TNF-a (A/T KO), were obtained by conventional crossbreeding of two single mutants. All mice were fed an "atherogenic diet" from the age of 3 weeks after being weaned. Biochemical indexes: total plasma cholesterol (TC) and triglycerides (TG) were tested at 0, 2,4, 8 and 12 weeks (W) during the experiment, and that of 3-week-old mice as the origin point. All data were statistically analysed using SPSS software. Aortas of experimental mice were taken out at 12 and 24W, fixed in 10% formaldehyde solution, washed by flowing water, then embedded in ice bag glue to slide under -20 and lesion areas were quantified by planimeter.Results: Compared with the control of WT, the serum lipid (TC and TG) level of T KO mice decreased significantly at initial stages (4W), P < 0.05, but at terminal stages the difference was not so remarkable. Frozen sections showed that intimal lesion area of T KO has a massive reduction (15-fold) compared with those in WT mice. Compared with the control of A KO, theserum lipid (TC and TG) level of A/T KO decreased significantly, P < 0.01 or P < 0.05. At initial stages (4W), the difference was remarkable especially. The vascular stenosis rate of A KO and A/T KO were (23 + 5)% and (14+3)%, (57?1)% and (39 + 8)% at 12W, 24W respectively, P <0.05.The atherosclerotic plaques of A/T KO mice were comprise of lipids, cholesterol crystal and calcified components basically. The vascular wall had no obvious fibrin cap with a better elastic structure. While the WT and A KO controls had typical cell and fibrin hyperplasia response, and their vascular wall were thinner and weaker with a worse elastic structure. Conclusion: It is proved that the deficiency of TNF-a can depress the serum lipid level, mitigate inflammation response, and reduce the development of atherosclerosis in wild type C57B6J mice and in pro-atherogenic gene knockout mice. This is consistent with the conclusion that TNF-a has an antiatherogenic effect on atherosclerosis in human and rodent.