Experimental Study About Morphology And Expression Of Matrix Metalloproteinases Of Aneurysm Induced By Ascending Aorta Banding

ObjectiveThe ascending aortic aneurysm, which is a large aneurysm and with a high death rate, is easy to turn into dissecting aneurysm and rupture. In order to study the pathogenesis of the clinic ascending aortic aneurysm and carrying out the treatment of the ascending aortic aneurysm better, we must establish a kind of pathological model which is similar to the clinic morbidity progress.In 1998, Brophy CM ever applied genetic induction X chromosomal mutation, which made the matrix dyssynthesis between collagen fibers and elastic fibers in the wall of artery, and shaped aneurysm, but this method has no specificity. At present, study models on aneurysm mostly concentrate on abdominal aortic aneurysm, and have no ideal study model of ascending aortic aneurysm. In our experiment the ascending aortic aneurysm was induced by ascending aorta banding of the young Wistar rat, Up to now, there are no reports about making the aneurysm model in this way. The formation of this kind of aneurysm model is a chronic process, which has a great similarity to the clinic aneurysm, So we can do a more precise investigation on the clinic aneurysm.In the experiment, we investigated the effects of matrix metalloproteinase -2, matrix metalloproteinase - 3 and matrix metalloproteinase - 9 ( MMP - 2, MMP - 3 , MMP - 9 ) on the ascending aortic aneurysm, and further understood the morphology and the formation reason of the ascending aortic aneurysm induced by ascending aorta banding, by observing the morphological feature of ascending aortic aneurysms. This provids data for experimental and clinical research of aortic aneurysm, which will have a great referred value for therapy ofbig aneurysm in the clinical practice.Materials and Methods1. Animal grouping and sample gathering40 young feminine Wistar rats weighting 100 ~ 120g were randomly divided into 2 groups (the rats were supplied by china medical university) : control group (n = 10) ^experiment group ( n = 30) . According to our breadboard method, we made the model of ascending aortic aneurysm. The aneurysm samples were obtained after evaluating the function of ascending aorta about 3 -5months.2. Observation index and detection method2. 1 After the operation of ascending aortic banding, the function of heart and ascending aorta was evaluated2. 2 Observating the gross morphology of ascending aortic aneurysm2. 3 HE staining ^Gomori staining ^Romeis staining ^VG staining ^Orange G staining2.4 Observating the ultrastructural changes of ascending aortic aneurysm by scanning electron microscope (JSM - T300 )2. 5 The expression of MMP -2NMMP -3^MMP -9 in the aneurysm tissue was detected by immuohistochemistry staining technique2. 6 Observing the changes of gelatinase activity by gelatin zymography2. 7 Observing the changes of gelatinase activity by film in situ zymogra-phy(FIZ).Results1. 1 The ascending aortic aneurysms were induced by ascending aorta banding of the young Wistar rats for 3 - 5 months after operation, the pathological changes of the aneurysm were familiar to those of human big aneurysm. The occurrence of the aneurysm is 63. 3% , and the occurrence of dissecting aneurysms is 36.7%.1. 2 With the growth of the rats after ascending aorta banding, ASP ( aor-tic systolic pressure) and ADP (aortic diastolic pressure) declined 43% and 42% respectively, which indicated the function of contraction and diastolic of the aorta was damaged.1. 3 Scanning electron microscope observation ( SEM) :The elastic lamellas of aneurysms appear hypertrophy and fragmentation;the walls of the ascending aorta aneurysms were infiltrated by the inflammatory cells;the elastic fibers among the elastic lamellas were widely destroyed;most of the smooth muscle cells atrophied or vanished;the endothelia of the ascending aorta aneurysm was seriously destroyed, the walls of some ascending aorta aneurysms were infiltrated by the erythrocytes.1.4 The expression of MMP - 2 and MMP - 3 is strong in the ascending aortic aneurysm;The expression of MMP -3^MMP -9 is stronger in the ascending aortic aneurysm and mural thrombus than that in the normal ascending aorta.1. 5 Gelatinolytic activity in aneurysm tissue homogenates was measured by gelatin zymography. The proform of MMP — 2 was demonstrated as a lytic band at 72 kDa, and the active form was present at 62 kDa;an MMP - 9 band was present at 92 kDa. Gelatinase activity of normal ascending aortic aorta is very weak and there is almost no lytic band. Scanning densitometry revealed a significant increase in MMP - 2 levels of ascending aortic aneurysm ( n = 19, median OD =0.296) compared with that of control group: (n = 10, median OD = 0.287 ). Gelatinase activity of ascending aortic aneurysm was significantly increased compared with that of normal ascending aortic aorta. Film in situ zymography ( FIZ) showed that gelatinase activity in the wall of the ascending aorta aneurysm obviously elevated, mainly in the media and the adventitia of the ascending aorta aneurysm.ConclusionsOur study shows:1. The occurrence of ascending aortic aneurysm induced by banding ascending aorta of the young Wistar rat is high;the model is referred to the investigation of ascending aortic aneurysm.2. The ascending aorta aneurysm has ultrastructural changes, which shows the significant pathologic basis for the ascending aorta aneurysm.3. MMP -2NMMP -3 and MMP -9 may play an evident role in the formation of the ascending aortic aneurysm.4. Elevation of gelatinase activity may be one of the key reasons in the formation of ascending aortic aneurysm.