Abstract 350: Disruption Of Proprotein Convertase Subtilisin/Kexin 9 Suppresses Inflammation And Attenuates Abdominal Aortic Aneurysm Formation

Objective: Abdominal aortic aneurysm (AAA) is a degenerative inflammatory disease, with its rupture highly lethal. There have been no effective pharmacological medications. Proprotein convertase subtilisin/kexin 9 (PCSK9), which is known to modulate cholesterol metabolism, has recently been associated with AAA in human genome-wide association studies. However, its role in AAA pathogenesis is unknown. Approach and Results: Histology staining of mouse aortic aneurysmal tissue showed PCSK9 expression and its colocalization with macrophages. To investigate the role of PCSK9 in AAA formation, mice deficient in PCSK9 were crossed with ApoE SA/SA mice, which are hypercholesterolemic and inducible to develop angiotensin II-mediated hypertension upon doxycycline (Dox) administration. Deletion of PCSK9 reduced both incidence and severity of AAA and increased survival rate, without changing plasma cholesterol levels. This was associated with decreased aortic expression and activity of matrix metalloproteinase 9 (MMP9), less elastin breakdown, and reduced aortic expansion and aneurysm rupture. Additionally, PCSK9 deficiency suppressed systemic inflammatory response and macrophage infiltration into AAA lesions. In isolated macrophages stimulated with LPS, the upregulated expression of pro-inflammatory cytokines ( Tnfa, Il1b, Il6 ) was dramatically diminished in PCSK9-deficient macrophages. Furthermore, administration of PCSK9-specific siRNA in mice resulted in less macrophage accumulation in the aneurysmal aortic wall, decreased MMP9-mediated elastin degradation, and substantially constrained AAA formation. Conclusions: Endogenous PCSK9 promotes AAA formation, consistent with its novel action in mediating systemic and local inflammation, particularly, the macrophage-dependent MMP9 activity. Pharmacological inhibition of PCSK9 might be a promising strategy to curtail AAA. Key Words: aneurysm, PCSK9, elastin, inflammation, macrophages