Gene Expression Study in Positron Emission Tomography–Positive Abdominal Aortic Aneurysms Identifies CCL18 as a Potential Biomarker for Rupture Risk

Rupture of abdominal aortic aneurysm (AAA) is a cause of significant mortality and morbidity in ageing populations. Uptake of 18-fluorodeoxyglucose (FDG) detected by positron emission tomography (PET) is observed in the wall of 12% of AAA (A+), most of them being symptomatic. We previously showed that the metabolically active areas displayed adventitial inflammation, medial degeneration and molecular alterations prefacing wall rupture. The aim of this study was to identify new factors predictive of rupture.Transcriptomic analyses were performed in the media and adventitia layers from three types of samples: AAA without (A0) and with FDG uptake (A+), both at the positive spot (A+Pos) and at a paired distant negative site (A+Neg) of the same aneurysm. Follow-up studies included RT-PCR, immunohistochemical staining and ELISA. A large number of genes, including matrix metalloproteinases, collagens and cytokines as well as genes involved in osteochondral development, were differentially expressed in the A+Pos as compared to A+Neg. Moreover, a series of genes, notably CCL18, was differentially expressed both in the A+Neg and A+Pos as compared to the A0. A significant increase of CCL18 was also found at the protein level in the aortic wall and in peripheral blood of A+ patients as compared to A0.In conclusion, new factors, including CCL18, involved in the progression of AAA and, potentially, in their rupture were identified by a genome-wide analysis of PET-positive and negative human aortic tissue samples. Further work is needed to study their role in AAA destabilization and weakening.