The Role Of ADAMTS-4in Aortic Aneurysm And Aissection Formation

Aortic aneurysms and dissections cause more than10,500deaths in the United States every year.These diseases are characterized by the infiltration of inflammatory cells, progressive depletion of vascular smooth muscle cells (VSMC), and destruction of extracellular matrix (ECM) in the aorta.Proteinases that degrade ECM are known to play critical roles in the degradation of aortic ECM and in the formation of aortic aneurysms. These proteinases include matrix metalloproteinases, which are primarily produced by macrophages. A recently identified family of extracellular metalloproteinases known as ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) has been shown to be involved in ECM turnover.The ADAMTS family of proteins comprises20members; ADAMTS-1and ADAMTS-4are particularly wellstudied members of this family. ADAMTS-4promotes ECM turnover by digesting proteoglycans including aggrecan, versican, decorin, and biglycan and ECM proteins such as fibronectin. ADAMTS-1functions in ECM remodeling by digesting versican and tissue factor pathway inhibitor-2. Furthermore, it has been shown that ADAMTS-1inhibits cell proliferation by binding and sequestering growth factors, such as vascular endothelial growth factor and fibroblast growth factor. Similar to matrix metalloproteinases, ADAMTS-1and ADAMTS-4cause tissue destruction and have been implicated in vascular diseases, such as atherosclerosis. Therefore, we hypothesized that expression of these proteinases is increased in aneurysmal thoracic aortic tissue. The purpose of this study was to determine ADAMTS-4levels are elevated in aortic tissue obtained from patients with thoracic aortic aneurysms and dissections. In addition, we examined potential mechanisms by which the proteinases might contribute to disease progression.Part Ⅰ The expression of ADAMTS-1,4in aortic aneurysm and dissectionObjective ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) is a recently identified family of extracellular metalloproteinases that has been shown to participate in tissue destruction. We hypothesized that ADAMTS-1and ADAMTS-4expression is increased in aortic tissues from patients with thoracic aortic aneurysms and dissections. We aim to test ADAMTS-1and ADAMTS-4expression in human aortic aneurysms and dissection. Methods We examined ADAMTS-1and ADAMTS-4expression in human descending thoracic aortic aneurysms (n=14), chronic descending thoracic aortic dissections (n=16), and descending thoracic aortas from age-matched control organ donors (n=12). In these tissues, we also evaluated the degradation of versican, a proteoglycan substrate of ADAMTS-1and ADAMTS-4. Results ADAMTS-1and ADAMTS-4protein and mRNA expression was significantly higher in thoracic aortic aneurysm and dissection tissues than in control aortic tissues. Double immunofluorescence staining showed the expression of ADAMTS-1and ADAMTS-4in smooth muscle cells and macrophages. Consistent with the upregulation of ADAMTS-1and ADAMTS-4in thoracic aortic aneurysm and dissection tissues, versican was degraded significantly more in these tissues than in control aortic tissues. Conclusions Increased expression of ADAMTS proteins may promote thoracic aortic aneurysm progression by degrading versican and facilitating macrophage invasion. Part Ⅱ The role of ADAMTS-4in macrophage migration and VSMC apoptosisObjective We examined whether ADAMTS-4functions in macrophage infiltration and vascular smooth muscle cell(VSMC) apoptosis. Method In cultured macrophages, we examine the migration of human macrophage after transfected with ADAMTS-4siRNA by using a transwell assay. We culture macrophage and VSMC from ADAMTS4-/-mice, Invasion capacity of activated macrophages from ADAMTS4-/-mice was examined by using a transwell assay. VSMC from ADAMTS4-/-mice will be treated by palmitic acid (PA), TUNEL staining will examine the apoptosis of VSMC. Result In cultured macrophages, transforming growth factor-pincreased ADAMTS-4protein levels and induced macrophage invasion; knocking down ADAMTS-4reduced cell invasion. Invasion capacity was reduced in macrophages from ADAMTS4-/-mice compared to those from WT mice. The apoptosis was reduced in VSMC from ADAMTS4-/-mice compared to those from WT mice. Conclusions ADAMTS4deficiency attenuated macrophage migration and VSMC apoptosis. Our results suggest that ADAMTS4may play an important role in the formation of AAD by promoting inflammatory cell infiltration and VSMC apoptosis. Part Ⅲ ADAMTS4Deficiency Attenuates Aortic Aneurysm and Dissection Formation in MiceObjective ADAMTS4(a disintegrin and metalloproteinase with thrombospondin motifs4) is an extracellular metalloproteinase that has been shown to participate in extracellular matrix destruction and inflammation. We have observed increased expression of ADAMTS4in aortic tissues from patients with thoracic aortic aneurysms and dissections (AAD) and therefore hypothesized that ADAMTS4participates in the development of AAD. Methods Four-week-old male C57BL/6wild-type (WT) and ADAMTS4-deficient mice (ADAMTS4-/-) were fed high-fat diet (HFD) for8weeks and were infused with2000ng/min/kg angiotensin Ⅱ (AngⅡ) for4weeks. Four-week-old male Apoe-deficient mice (Apoe-/-) and Apoe Adamts4-double deficient (Apoe-/-Adamts4-/-)mice were fed high-fat diet (HFD) for8weeks and were infused with1000ng/min/kg angiotensin Ⅱ (AngⅡ) for4weeks., Aortas were evaluated for AAD formation, apoptosis, and inflammatory cell infiltration. Results The incidence of AAD was significantly lower in ADAMTS4-/-mice than in WT mice (P=0.041). Aortic tissue from ADAMTS4-/-mice exhibited significantly less apoptosis (P=0.02) and inflammatory cell infiltration (P=0.003) than WT mice. Moreover the destruction of versicam the activity of MMPs is less (P=0.009) in ADAMTS4-/-mice than WT mice. The incidence of AAD and the fatal rupture was significantly lower in Apoe-/-Adamts4-/-mice than in Apoe-/-mice (P=0.035, P=0.041). Survival curves were analyzed by log-rank test and a statistically significant difference between survival curves was found(P=0.023).There are no differences of plasma Levels of Total Cholesterol, LDL, Triglyceride, VLDL, Cholesterol/HDL between APOE-/-and Apoe-/-Adamts4-/-mice (P>0.05).Aortic tissue from ADAMTS4-/-mice exhibited significantly less apoptosis (P=0.001) and macrophage、 T lymphocyte cell infiltration (P<0.001、P=0.003) than Apoe-/-mice. Moreover, the destruction of versican、biglycan is less (P=0.002, P=0.005) in Apoe-/-Adamts4-/-mice than in Apoe-/-mice. Conclusions Under conditions that promote the formation of AAD in WT mice, ADAMTS4deficiency attenuated AAD formation. Our results suggest that ADAMTS4may play an important role in the formation of AAD by promoting inflammatory cell infiltration、cell apoptosis and aortic wall destruction. Future studies will examine whether the pharmacologic inhibition of ADAMTS4can prevent AAD progression.