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A3952 - Inhibition of the SCFFBXO3 E3 Ligase as a Novel Anti-Inflammatory Therapy for Atherosclerosis
Author Block: D. Chandra1, J. D. Londino2, J. S. Bednash3, Y. Zhang4, T. Nyunoya5, F. C. Sciurba6, B. Chen7, R. K. Mallampalli8; 1Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA, United States, 2University of Pittsburgh, Pittsburgh, PA, United States, 3Internal Medicine, Pittsburgh, PA, United States, 4Univ of Pittsburgh, Pittsburgh, PA, United States, 5Medicine, University of Pittsburgh, Pittsburgh, PA, United States, 6Univ of Pittsburgh Med Ctr, Pittsburgh, PA, United States, 7Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, United States, 8PACCM, UPMC Montefiore, VAMC, Pittsburgh, PA, United States.
Abstract Rationale: Atherosclerosis is a chronic inflammatory disease highly prevalent in patients with COPD. Oxidatively modified low-density lipoproteins (OxLDL) are deposited in the subendothelial space of systemic arteries early in atherosclerosis. This OxLDL ligates the CD36 scavenger receptor on the surface of macrophages thereby activating the p65 subunit of NFkB with the help of TRAF6 resulting in the secretion of pro-inflammatory mediators central to atherosclerosis. The SCFFBXO3 E3 ubiquitin ligase governs the stability of TRAF proteins that link signaling from cell-surface receptors such as CD36 with NFkB. Therefore, we hypothesized that SCFFBXO3 modulates the inflammatory response to OxLDL in macrophages and impacts the risk of atherosclerosis. Methods: In 146 current and prior smokers enrolled in the Pittsburgh SCCOR cohort, FBXO3 genotyping was performed using DNA extracted from PBMCs, while severity of atherosclerosis was assessed by carotid sonography. Surgically excised carotid plaque tissue from an unrelated group of 9 individuals (5 with asymptomatic and 4 with symptomatic carotid atherosclerosis) was processed to perform immunoblotting for FBXO3. The role of FBXO3 in modulating OxLDL uptake and inflammation was examined in vitro using a monocytic cells line (THP-1). Results: 24 smokers who carried a hypofunctioning genetic variant of FBXO3 had fewer plaques and less thickening of the carotid intima-media compared with 122 individuals with wild type FBXO3. In adjusted analyses, those with the hypofunctioning variant were at 62% lower odds of being in a higher category of severity of carotid atherosclerosis compared to those with wide-type FBXO3 (odds ratio=0.38, 95% CI 1.02-6.49, p=0.04 adjusted for established cardiovascular risk factors). There was a close to 4-fold increase in FBXO3 protein levels in carotid plaque tissue from those with symptomatic rather than asymptomatic atherosclerosis. The phosphorylation of p65 induced by OxLDL was prevented by cellular depletion of FBXO3. Similarly, secretion of pro-inflammatory cytokines IL1β, IL8, and TNFα was reduced by depletion of FBXO3. Levels of FBXO3 protein were not altered by exposure of the cells to OxLDL. Conclusions: High-level expression of the FBXO3 E3 ligase subunit increases the risk of atherosclerosis in smokers, and FBXO3 protein levels in carotid plaques are increased in those with more severe atherosclerosis. Suppression of FBXO3 protein levels in macrophages abolished the inflammatory response to oxidized LDL. Thus, the SCFFBXO3 E3 ligase is a potential novel target for anti-inflammatory therapy in atherosclerosis.