Downregulation SMAD6 Leads To Aortic Remodeling In Mice And Increases Susceptibility To Thoracic Aortic Aneurysms

Objective:Thoracic aortic aneurysm(TAA)is a kind of macro vascular disease characterized by the expansion of thoracic aorta over 1.5 times the normal aorta.Current studies on TAA have found that the imbalance of the transforming growth factor ?(TGF-?)signaling pathway is an important factor in the formation of TAA.Therefore,this paper mainly studied the mechanism of SMAD6,an inhibitory regulator of TGF-signaling pathway,in the development of TAA.Methods:Mice(C57BL/6)were constructed with the CRISPR-Cas9 system.The aortic diameters of SMAD6 knockdown(smad6-kd)mice and wild type(WT)mice were measured by small animal ultrasound.The structure and expression of the elastic fiber in the aorta of mice were detected by Vehoeff-Van Gieson(VVG)staining.The expression of matrix metalloproteinases(MMPs)in aorta were analyzed by immunofluorescence.Meanwhile,we measured the weight,fasting blood glucose,Total cholesterol(TC),Triglyceride(TG),High density lipoprotein cholesterol(HDL-C)and low density lipoprotein cholesterol(LDL-C)of the SMAD6-KD and WT groups.Combined with clinical cases,we analyzed the metabolic levels of 78 patients with TAA who were admitted to The First Affiliated Hospital of Soochow University and 206 patients with non-TAA who underwent physical examination in The First Affiliated Hospital of Soochow University.Results:The results of small animal ultrasound showed that the thoracic aorta diameter of WT mice was 1.2±0.29 mm,and that of SMAD6-KD mice was 1.6±0.37 mm.The VVG staining results indicated that the elastic fibers of the aorta of SMAD6-KD mice had obvious degradation and fracture.Immunofluorescence results in tissue sections indicated that the expression of ?-SMA in aortic mice of smad6-kd was down-regulated,and the expression of MMP-2 and MMP-9 was not significantly changed.The weight of smad6-kd mice was 47.3±5.55 g,and that of WT mice was 25.6±0.70 g(p<0.05).The TC of smad6-kd mice was higher than that of normal mice,and there was no difference in the expression of TG,HDL-C and LDL-C.The results of clinical case analysis indicated that the age,fasting blood glucose,TC and TG of TAA patients were significantly higher than those of the control group,and the expression of HDL-C and LDL-C were significantly lower than those of the control group.Conclusion:1.The low expression of SMAD6 caused the widening of aortic,degradation and fracture of elastic fiber,down-regulated expression of ?-sma,induced aortic remodeling,and increased the susceptibility of thoracic aortic aneurysm in mice.2.TC/TG is an independent risk factor for TAA.The low expression of SMAD6 leads to an increase in total cholesterol in mice and increases the risk of thoracic aortic aneurysm.