Dynamic MRI Research Of Mice Lumbar Intervertebral Disc Degeneration Caused By Mechanical Stress And Oxidative Stress

Objective:Combined MRI and pathology to monitor the changes of oxidative stress in the process of IDD of mice that was induced by mechanical stress.And use image to explore the indicators that evaluate the level of stress-oxidative stress and level of IDD.Methods:72 ICR male mice(3 months old,25-30 g)were randomly divided into 2 groups:IDD model group(n=60)and Control group(n=12).The IDD model group was divided into 5 subgroups:Id(A group),3d(B group),5d(C group),7d(D group)and 9d(E group),with 12 mice in each subgroup.Physical loading was used for modeling(8 hours per day),and conventional MRI monitoring was performed on the lumbar spine of mice at the corresponding time point,followed by immunohistochemistry to evaluate the level of ROS and the content of SOD.Result:MRI T2 imaging:The Control,A and B group,the intervertebral discs of all the mice showed high signal,the endplates showed uniform low signal,complete structure and clear boundary.The C group,the signal of intervertebral disc(3 mice)began to decrease slightly,the surface of endplates(5 mice)were uneven and rough,and the edge began to show spotty high signal.The D group,the signal of intervertebral discs(all mice)were mild to moderate decrease,endplates surface(10 mice)were uneven and fracture,its point-high signal was confluent.The E group,the discs(6 mice)show low signals and height decreasing,the endplate(all mice)showed low signal,fracture and collapse.Pathological manifestations:In the Control group and A group,the endplate chondrocytes were uniformly and arranged well,having clear boundaries.In B group,the chondrocytes in the endplate began to show swelling,enlargement and blurring of the mesenchyme.In C group,endplate cells begin to dissolve.In D group,the endplate cells were fuzzy and sparsely cellular.In E group,endplate cells were lysed and sparse with a reduced number,accompanied by structural disorder,collapse and blurring.Immunohistochemistry result:The content of SOD in end plate increased sharply in A group and B group.In contrast.ROS levels were inhibited in both A group and B group.After that,the content of SOD decreased gradually over time while the level of ROS continued to rise.There were statistically significant differences among them(p<0.05),excepting Control group VS A group and C group VS D group(p>0.05).Pearson correlation analysis:The stress level was highly positively correlated with ROS level and MRI T2 signal level(r Ros vs stress=0.94,rT2signal vs stress=0.94,p<0.05).The stress level was positively correlated with SOD content(r=0.37,p>0.05).The ROS level was highly positively correlated with MRI T2 signal level(r=0.92,p<0.05).Conclusions:MRI T2 signal and structural change were significantly correlated with temporal stress intensity and intervertebral disc ROS level(rROS vs strcss=0.94,rT2signal vs stress-0.94,p<0.05).These results suggest that MRI can be used to evaluate the level of stress-oxidative stress and IDD in clinical.