Abstract 551: The Dual Effect of Cigarette Smoke on Macrophage Abca1-dependent Cholesterol Efflux and Protease Production Leads to Decreased Collagen and Increased Necrosis in Plaques of ApoE Deficient Mice

Abstract

Epidemiological evidence links smoking to an increase in the incidence and severity of cardiovascular disease. However, the molecular mechanisms responsible for susceptibility are unknown. The accumulation of lipids in macrophages induces an inflammatory response, with secretion of cytokines and proteases, and leads to necrosis and loss of collagen content within atherosclerotic lesions. Therefore, the effect of cigarette smoke on lipids in the atherosclerotic process and consequences was examined. Initial studies revealed that cigarette smoke attenuated cholesterol efflux. Subsequently, the end result of cigarette smoke exposure on atherosclerotic lesions in ApoE deficient mice demonstrated a significant increase in necrosis along with a dramatic decrease in the collagen content of lesions in ApoE deficient mice exposed to smoke for 20 weeks. Cigarette smoke extract (CSE) impaired the cholesterol efflux ability for ApoAI and correlated with ABCA1 loss and increased MMPs (9, 12, 13, in human THP-1 cells additionally MMP1 is increased), TLR4/Myd88 and TNFα expression in mouse bone marrow derived macrophages (BMdM) in vitro and in vivo in peritoneal macrophages elicited after 5 days of smoke exposure. Furthermore, by increasing ABCA1 expression with LXR agonist treatment the CSE-induced up regulation of MMPs (MMP-9 and 13) and TNFα was inhibited signifying a correlation between the cigarette smoke induced loss of ABC transporters and MMP induction. Moreover, BMDMs isolated from Cre-LysM-ABCA1 deficient mice displayed an increase in mRNA expression of MMPs (9, 12, 13) at a basal level, which was appreciably augmented with CSE as compared to control macrophages. The LXR induced decrease in MMPs and TNFα expression as well as decreased MMP-9 activity in macrophages was confirmed to be ABCA1-dependent since ABCA1 KO macrophages exposed to CSE did not exhibit this response. These findings establish that the effect of cigarette smoke on macrophage ABCA1-dependent cholesterol efflux impairment leads to both an increase in proteases and inflammatory cytokines and this combination of events is likely synergistic in ultimately generating a more vulnerable plaque through the increase in plaque necrosis and a decrease in collagen content.