Expression and localization of tumour necrosis factor-α and its converting enzyme in human abdominal aortic aneurysm

Abstract

Abdominal aortic aneurysm (AAA) is characterized by chronic aortic wall inflammation and loss of matrix components. Proinflammatory cytokines such as tumour necrosis factor-α (TNF-α) are thought to be involved in this inflammatory process and, therefore, to play an important role in the pathogenesis of human AAA. TNF-α-converting enzyme (TACE) has recently been purified and cloned as a disintegrin and metalloproteinase that converts TNF-α precursor into its mature form. The aim of the present study was to determine whether TNF-α and TACE were expressed and localized in aortic tissues in human AAA. Infrarenal aortic tissues were obtained from AAA patients (n=19) undergoing elective aneurysm reconstruction and from autopsy cases without cardiovascular disorders as normal controls (n=5). Internal thoracic artery samples were also obtained from patients with coronary artery disease undergoing coronary artery bypass grafting to represent biopsied conduit vessels (n=5). The AAA specimens were taken from the mid-portion of the aneurysm and from the longitudinal transition zone between the non-dilated aorta and the proximal aspect of the aneurysm. TNF-α and TACE mRNA levels were determined by real-time quantitative reverse transcriptase–PCR. Expression levels of both TNF-α mRNA and TACE mRNA were significantly greater in the transition zone than in the mid-portion (both P<0.05). Expression levels of both forms of mRNA were significantly higher in AAA samples than in control aortas or atherosclerotic arteries. There was a significant correlation between the expression of TNF-α mRNA with that of TACE mRNA in AAA (r=0.54, P<0.005). Immunostaining was positive for both TNF-α and TACE in CD68-positive macrophages in the media and adventitia obtained from the transition zone in AAA, whereas neither TNF-α nor TACE was expressed in control vessels. In conclusion, the concomitant activation and localization of TNF-α and TACE in the media and adventitia of the transition zone in human AAA underlines the importance of this system in the pathogenesis of this disorder.