Atherosclerosis in SLE - OGG-1 as a novel target for therapeutic intervention

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Systemic Lupus Erythematosus (SLE) is a chronic inflammatory autoimmune disease, which is associated with accelerated atherosclerosis. The overall risk of myocardial infarction (MI) with SLE is 10-fold higher than in the general population and a 50-fold higher risk in women aged 35-44 years. Why patients with SLE or other autoimmune diseases are at increased risk of atherosclerosis remains unclear, and biomarkers are needed to identify those at higher risk of adverse cardiovascular events. Inflammation is a key component of the atherogenic process. Recent studies strongly indicate a central role for the proinflammatory cytokine IL-1β in atherosclerosis, although the mechanism by which IL-1β is activated during atherogenesis is unknown. We have determined that immunologic danger signals induce mitochondrial dysfunction with generation of reactive oxygen species. The resulting oxidatively damaged mitochondrial DNA (mtDNA) is released into the cytoplasm where it binds to and activates the NLRP3 inflammasome, the machinery by which active IL-1β is made. We have shown that 8-oxoguanine-DNA glycosylase 1 (OGG1), an enzyme involved in repairing oxidized mtDNA, prevents NLRP3 inflammasome activation and IL-1β production. Importantly, unpublished work in the Arditi lab demonstrates that mice deficient in OGG1 are more prone to develop atherosclerosis, emphasizing the protective effect of this enzyme. It is well known that SLE patients develop mitochondrial oxidative DNA damage and accumulate very high concentrations of oxidative mtDNA products that in turn amplify inflammation. Moreover, inactivating polymorphisms in OGG1 have been associated with the development of nephritis in SLE. Given this background, we hypothesize that oxidative DNA damage leads to SLE- associated atherogenesis and that OGG1 is protective and hence a novel target for therapeutic intervention. To test this hypothesis, we will adopt a two-pronged approach, using SLE mouse models with hyperlipidemia, and ex vivo analysis of NLRP3 and OGG1 activity and function in immune cells derived from SLE patients with atherosclerosis vs. those without. We propose two Specific Aims: Aim 1-To investigate the role of mitochondrial OGG1 as a novel therapeutic target to prevent SLE-associated atherogenesis. Aim 2 – To determine the role of mtDNA in NLRP3 activation in SLE atherogenesis and the role of OGG1 in limiting mtDNA damage in immune cells from SLE patients with or without atherosclerosis. We will manipulate these systems via mitochondrial targeting of OGG1 or via novel microRNA that regulates OGG1 expression so as to evaluate the utility of targeting OGG1 as a potential therapeutic approach in SLE-associated atherosclerosis. Completion of these studies will significantly enhance our current understanding the pathogenic mechanisms of accelerated atherogenesis during SLE and uncover new therapeutic targets for this very important disease.