Abdominal aortic aneurysms (AAA) are the third cause of cardiovascular mortality in industrialized countries. AAA consist in progressive dilatation of the aorta which can lead to spontaneous rupture. Aneurysm evolution depends on the balance between degradation and repair of elastin and collagens in the aortic extracellular matrix (ECM), due to inflammatory cells infiltration in parallel with loss of vascular smooth muscle cells (VSMC). The cross-linking enzymes, lysyl oxidase (LOX), lysyl oxidase-like protein 2 (LOXL2) and transglutaminase 2 (TG2) are involved in the maturation of ECM components and arterial remodeling, by covalently bonding elastin and collagens. These crosslinking enzymes are therefore good candidates for AAA stabilisation and prevention of rupture, through ECM remodeling.
We show that TG2 and LOXL2 are expressed in endothelial cells and VSMC, in addition to LOX, as they were detected in the intima and the media of healthy mouse aortic wall by immunofluorescence. In addition, these enzymes are all present in the ECM Triton-resistant fraction.
We used a murine CaCl2-induced aneurysm model, in which AAA progression is associated with a decrease in VSMC density, as demonstrated by smooth muscle alpha-actin immunostaining. Whereas LOX and TG2 expression was strongly decreased in parallel with the loss of VSMC, LOXL2 expression was less severely affected. The involvement of lysyl oxidases in AAA was investigated using the irreversible inhibitor, beta-aminopropionitrile (BAPN). After induction of AAA by CaCl2, BAPN-treated mice showed a greater increase of the internal aortic diameter in comparison with untreated controls, suggesting that activity from remaining lysyl oxidase partially prevents AAA progression. In parallel, fibrillar collagens content is determined by Sirius red staining and second harmonic generation imaging; and elastin fibers organisation by Orcein-staining. These ongoing experiments will characterize the involvement of crosslinking enzymes in ECM repair during the evolution of AAA. Altogether, this study will allow to determine whether LOXL2 and/or TG2 could be therapeutic targets for stabilizing AAA progression through ECM repair.Le texte complet de cet article est disponible en PDF.