In the past few years we have clearly demonstrated in two large diabetic cohorts of type 1 and type 2 diabetes (DCCT/EDIC and VADT cohorts) that high levels of immune complexes (IC) containing oxidized LDL (oxLDL) and advanced glycated end-products-modified LDL (AGE-LDL) are associated with coronary artery disease (CAD)1-4 and can strongly predict the development and progression of CAD in the early stages of type 1 diabetes3. We have also shown in the VADT cohort, which includes many patients with advanced CAD, that high levels of malondialdehyde-modified (MDA)-LDL in IC are able to predict acute cardiovascular disease (CVD) events4. However, when circulating IC contain both high levels of MDA-LDL and high levels of oxLDL or AGE-LDL the risk to suffer an acute event is reduced4 leading us to conclude that the modified lipoproteins carried by IC play a differential modulating role in plaque progression/stability and plaque destabilization. Our mechanistic studies support the above hypothesis. OxLDL IC induce the transformation of macrophages into foam cells5-7, lead to upregulation of pro-survival genes8 and induce the release of pro-inflammatory cytokines10. OxLDL IC also induces increased collagen production by mesangial cells12.. In contrast, MDA-LDL IC induce macrophage apoptosis, stimulate the expression of matrix metalloproteinases (MMPs) by macrophages and by aortic endothelial cells, and reduce the expression of collagen genes in mesangial cells. Hypothesis and Specific Aims: Based on our clinical and in vitro preliminary data, we hypothesize that the type of predominant modifications of LDL in circulating IC (MDA-LDL, oxLDL or AGE-LDL) has a significant impact in plaque progression/destabilization. We postulate that, when MDA is the predominant modification of the LDL carried by IC, the uptake of those IC by macrophages induces cell apoptosis, increased release of MMPs, and increased collagenase activity, thus contributing to plaque destabilization. In contrast, when oxLDL is the predominant modification of LDL in IC, the uptake of these IC induce macrophage survival and stimulate the release of pro-inflammatory mediators and growth factors, thus contributing to plaque expansion/stability. Furthermore we postulate that a biomarker panel including MDA-LDL IC and MMPs will be more able to strongly predict patients at high risk to suffer acute CVD events than a panel of conventional CVD biomarkers. To test the above hypotheses we propose three aims.
The first aim will compare the activation patterns of macrophages exposed to IC (MDA-LD IC and oxLDL IC), the effect of these IC on the survival and apoptosis of macrophages, and the pathways involved. In the second aim we will measure novel biomarkers known to be associated with plaque instability in patient samples from the VADT cohort in which MDA-LDL IC and conventional CVD biomarkers have been previously measured. We will determine whether a panel including MDA-LDL IC, MMP-1 and MMP-9 will have a significantly higher predictive power to identify patients at high risk for acute MI. Finally in the third aim we will determine, on an animal mouse model of atherosclerosis and type 2 diabetes whether blocking/reducing engagement of Fc?Rs by oxLDL IC and MDA-LDL IC by treatment with mouse IgM anti-oxLDL and IgM anti-MDA-LDL will prevent plaque progression and instability. Methods: Cell isolation and culture, separation and modification of lipoproteins, isolation of antibodies, protein arrays, cell viability/apoptosis assays, rtPCR, western blots, enzyme-activity assays, immunohistochemical analysis of gene expression and histologic analysis of atherosclerotic lesions. Relevance to VA Health and Significance: The definition of mechanisms responsible for the differences in cell activation, survival and apoptosis induced by different modified LDL-IC may allow to define new therapeutic targets and new prevention strategies that will curtail the progression of cardiovascular complications and the occurrence of acute vascular events in patients with type 2 diabetes.
Our goal is to study the differential modulation of gene expression induced by immune complexes prepared with different forms of modified LDL on human macrophages and how that impacts the development of vascular complications in diabetes. We will combine in vitro studies of cell survival and apoptosis and gene modulation induced by modified LDL-IC with studies on a type 2 diabetes animal model assessing the impact of blocking modified LDL-IC in atherosclerosis development. Also, we will measure serum pro-inflammatory/pro-apoptotic biomarkers in type 2 diabetes to assess their predictive value for acute vascular events. These studies will result in a clearer and comprehensive picture of the mechanisms involved in the development of vascular complications in diabetes. The resulting data may uncover possible therapeutic approaches to prevent their development.