BACKGROUND: Abdominal aortic aneurysm (AAA) is a complex and deadly vascular disorder. Hallmarks of AAA include chronic inflammation contributing to proteolytic destruction of extracellular matrix proteins within the elastic media and apoptosis of smooth muscle cells.Still, the exact mechanism behind AAA is not totally clear and the significance of tissues, such as perivascular adipose tissue (PVAT), surrounding the AAA has not been investigated. The purpose of this study is to clarify the impact of PVAT in the pathogenesis of AAA by investigating the content of leucocytes and proteases.
METHOD AND RESULTS: Aortic biopsies including PVAT were collected from aneurysmal patients undergoing elective surgery for AAA. Control infrarenal aortas were obtained from healthy organ donors. To evaluate vascular inflammation within the different layers of the vessel wall and PVAT, gene expression analysis and immunohistochemistry were performed. Compared with aneurysmal aortas, gene expression of mast cell chymase (P<0.01) and neutrophil marker CD66b (P>0.01) was found to be increased in PVAT mainly localized to necrotic adipocytes as demonstrated by immunohistochemical staining. In PVAT the mRNA expression of cathepsin K (P<0.05) and cathepsin S (P<0.05) were also increased as compared with non-aneurysmal control aortas, also pro-inflammatory IL-6 was increased in the PVAT (P<0.05) as compared to intima/media of aneurysmal aortas.
CONCLUSION: These results show that adipose tissue from the adventitial side of the aortic wall could take part in pathogenesis of AAA. By producing proteases inflammatory cells surrounding necrotic adipocytes facilitates degradation of the aortic wall from the outside of the aortic vessel wall causing weaken of the vascular wall of aneurysm. This study provides a wider understanding of the pathogenic mechanisms of AAA which can lead to better future treatment possibilities.