Project 1. Diabetes, triglyceride-rich lipoproteins, and advanced atherosclerosis

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Both type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS; also known as pre-diabetes) increase the risk of atherosclerosis, the leading cause of cardiovascular disease (CVD) events and death in diabetic patients. Even with statin treatment to effectively lower LDL cholesterol, diabetes is associated with increased CVD risk linked to abnormal metabolism of triglyceride-rich lipoproteins (TRLs) and their remnant lipoprotein particles (RLPs). Novel strategies to enhance TRL clearance have therefore recently generated significant interest, especially in the setting of diabetes. This application uses three strategies to increase TRL and RLP clearance in diabetes; i) inhibition of apolipoprotein C3 (APOC3), ii) inhibition of angiopoietin-like 3 (ANGPTL3), and iii) hepatic expression of an active form of the transcription factor CREB-H (cAMP response element-binding protein H). The proposed studies build on strong preliminary data demonstrating that diabetes accelerates progression of advanced lesions and that normalizing circulating levels of TRLs prevents atherosclerosis in diabetic mice. Furthermore, diabetes causes increased macrophage death associated with accumulation of cellular cholesterol and caspase 11 activation, which we hypothesize contributes to the more advanced atherosclerotic lesion phenotype. Collectively, our observations support the following hypothesis: Diabetes accelerates advanced atherosclerosis by increasing APOC3 and associated TRLs and RLPs, which in turn induce macrophage lipid loading and exacerbate the death of macrophages by pyroptosis. Such a mechanism could help explain the increased CVD risk in subjects with diabetes. The first specific aim will address whether APOC3-enriched TRLs/RLPs are required for diabetes- mediated atherosclerosis progression. We propose to test this hypothesis and to clarify the role of APOC3 by normalizing plasma APOC3 and/or TRL/RLP levels in mouse models of T1DM and MetS/T2DM by three distinct approaches; the use of an Apoc3 antisense oligonucleotide (ASO), an Angptl3 ASO, which reduces TRLs and other lipoproteins independent of hepatic Apoc3 expression, and hepatic expression of CREB-H, which lowers TRLs without affecting total plasma levels of APOC3. Contrasting the effects of these treatments will provide new insights into the role of APOC3 versus TRL/RLP lowering. The second specific aim will determine whether pyroptosis mediated by APOC3-enriched TRLs/RLPs contributes to lesional macrophage death and advanced lesions in diabetes. We propose to mechanistically test the importance of this pathway by using mice deficient in caspase 11 and gasdermin D, its downstream effector, in myeloid cells. We also expect that pyroptosis will be prevented by TRL-lowering in diabetic mice. The in vivo studies will be complemented by mechanistic studies in macrophages to clarify the pathways responsible in diabetes-induced macrophage death, and by studies addressing mechanisms whereby reduced insulin receptor signalling leads to increased levels of APOC3 in models of T1DM and MetS/T2DM.