PROJECT SUMMARY There is a critical need to stop atherosclerosis initiation and progression, rather than trying to treat its progression in an advanced state. It is widely recognized that entry and retention of low density lipoproteins (LDL) are key steps in atherogenesis. However, our data show high density lipoproteins (HDL) can compete with LDL to bind SR-BI and HDL can interact with LDL to decrease binding to proteoglycans. With the recent realization that lipoproteins, both LDL and HDL, exist a series of related but compositionally distinct subpopulations, new questions have arisen as to how lipoprotein subspeciation may affect these igniting steps of atherosclerosis. This work builds on data generated under PI Shah’s K award (K23HL118132) showing that 1) HDL and LDL exist as multiple subspecies, 2) specific HDL subspecies, their amount, composition (lipids, proteins) and function are altered in the plasma of individuals with type 2 diabetes, and 3) the amount of large HDL subspecies in plasma are inversely correlated with early markers of cardiovascular risk. This proposal also builds on our preliminary data that shows HDL modulates both LDL transcytosis and binding to proteoglycans, but this is disrupted in the context of type 2 diabetes. Our overarching hypothesis that that LDL and HDL subspecies differentially impact transcytosis and proteoglycan binding and disruption of their balance in type 2 diabetes contributes to the high risk of cardiovascular disease in this population. Using complementary approaches that include in-vitro cell based assays with animal models and patient samples in adolescents and adults, we aim to identify and characterize the LDL and HDL subspecies involved in endothelial cell transcytosis (Aim 1) and extracellular proteoglycan binding (Aim 2) and to understand the impact of type 2 diabetes on these lipoprotein subspecies (Aim 3). These results have the potential to inform future therapeutic strategies to use recombinant particles or mimetic peptides to prevent atherosclerosis initiation. The ability to block atherosclerosis initiation and progression will benefit both youth and adults, and particularly individuals with type 2 diabetes who are at increased risk for cardiovascular disease.