Abstract 252: Elastin-derived Peptides Induce M1 Macrophage Polarization Promoting Abdominal Aortic Aneurysm Formation

Abstract

Objective: Abdominal aortic aneurysm (AAA) is a disease characterized by inflammatory cell infiltration and extracellular matrix (ECM) degradation. Damage to the ECM results in release of elastin-derived peptides (EDPs). EDPs recruit inflammatory cells and may influence macrophage polarization. BA4, a monoclonal antibody that specifically recognizes a six peptide sequence in EDPs, can block the EDP-mediated effect on macrophages. Our hypothesis is that EDPs induce M1 differentiation and that blocking the EDP-mediated M1 differentiation of macrophages will reduce aneurysm progression. Methods: Mice were given weekly intraperitoneal injections of BA4 (10 mg/kg) or IgG (10 mg/kg) after aneurysm induction via the calcium chloride (CaCl2) induced aneurysm model. Aortic tissue was then removed and subjected to Western blot, gelatin zymography, and histological analysis at various time points (3 days, 1, 2, 4, and 6 weeks) after aneurysm induction. Bone marrow-derived macrophages (BMMs) were isolated and treated with various doses of EDPs and their gene expression profiles were analyzed by qPCR. Additionally, BMMs were treated with IFN-γ to induce a pro-inflammatory M1 phenotype or IL-4 to induce an anti-inflammatory M2 phenotype. M1 or M2 BMMs were given intravenously to mice, which then underwent aneurysm induction. Results: BA4 treatment significantly reduced aortic dilation, ECM degradation, and macrophage infiltration. EDP treatment of naïve macrophages induced a response similar to IFN-γ resulting in M1 activation as seen by expression of M1 associated markers such as TNF-α and IL-1β. Additionally, administration of M1 polarized BMMs to CaCl2-treated mice significantly increased aortic dilation compared to administration of M2 polarized BMMs. Conclusions: EDPs cause a pro-inflammatory M1 response similar to that seen with IFN-γ treatment. Reducing the M1 response by inhibition of EDP-mediated signaling or administration of M2 polarized BMMs reduces aneurysm formation. Targeting the macrophage phenotype is a potential therapeutic target for AAA.