MMP9 and abdominal aortic aneurysm: Therefore, LRP1 activity appears to play an important role in the pathogenesis of an abdominal aortic aneurysm, since LRP1 expressed in vascular smooth muscle cells may influence the concentration of MMP-9 in the extracellular matrix of the aortic wall, potentially controlling elastin proteolysis and aneurysm development [48].