Abstract 66: TLR2 Signaling Protects Against Angiotensin II--Mediated AAA Formation in ApoE -/- Mice

Abstract

Abdominal aortic aneurysm (AAA) is a potentially life-threatening degenerative vascular disease that affects 6-9% of men over 65. Although Toll-like receptors (TLRs) mediate the innate immune response resulting in the recruitment of inflammatory cells to the site of a range of pathogen-associated molecular patterns, they have also been implicated in immune tolerance. To determine the role of TLR2 signaling in AAA formation we compared AAA formation in ApoE -/- and ApoE-/-TLR2 -/- DKO mice using a mouse model for angiotensin II (ANGII) mediated AAA formation. Treatment of ApoE -/- mice with Alzet pumps releasing 750 ng/kg/min ANG II resulted in formation of AAAs in 75% of mice (n=23) and a mean increase in aortic diameter from 1.0 mm in saline treated controls to 2.15±0.15 mm, p<0.001 with no effect on the thoracic aorta and the aortic arch. Although the incidence of AAAs in ApoE-/-TLR2 -/- DKO mice compared to ApoE -/- alone was unchanged, of the 12 ApoE-/-TLR2-/-DKO who developed AAAs, half demonstrated severe aneurismal involvement of the aortic arch and thoracic aorta compared to the ApoE -/- group consistent with a protective effect of TLR2. To test this hypothesis, mice were pretreated with PAM3, 50ug/ mouse/week. The incidence of AAA formation decreased to 32% in PAM 3 treated mice and aortic diameter decreased to 1.17±0.08 (n=18, p<0.001) compared to ANGII alone. PAM3 had no effect on blood pressure or lipid levels. Furthermore, treatment with PAM3 after a 7 day ANG II infusion decreased the incidence of AAA to 53%. ANG II stimulated expression of the cytokines RANTES and CXCl10 and the receptor CCR5 more than 8 fold as measured by ELISA and western blot respectively; PAM3 treatment of these ANG II infused mice decreased expression to control levels in association with decreased macrophage infiltration. Finally, while ANG II increased the ratio of M1/M2 macrophages in the abdominal aorta by 2 fold, PAM3 treatment reversed the effect of ANG II on M1/M2 in aortas of mice that did not develop AAAs. Thus TLR2 stimulation protected the abdominal aorta from ANG II mediated AAA at least in part by attenuating recruitment of macrophages and expression of chemokines and chemokine receptors.