Plasma HDL levels are inversely associated with coronary, cerebral and peripheral arterial disease
(PAD), and also type 2 diabetes mellitus (T2DM). However, how HDL influences these conditions remains poorly
understood. We previously showed that HDL attenuates vascular inflammation and promotes neovascularization
via scavenger receptor class B type I (SR-BI) and its adaptor protein PDZK1 in endothelial cells (EC). We recently
identified Breakpoint Cluster Region (BCR) protein as a novel PDZK1 interacting protein in human EC. In other
contexts BCR has known functions modulating Rac1 and RhoA, and we discovered it to be a novel kinase for
Akt kinase activated by HDL in EC. Our studies in BCR null mice then revealed for the first time that BCR is
required for HDL-related atheroprotection, HDL-induced endothelial repair and angiogenesis, and normal
glucose homeostasis. The Overall Goal of the present project is to determine HOW BCR actions in EC contribute
to HDL-related atheroprotection and promotion of neovascularization and normal glucose homeostasis. Three
Aims are proposed in cultured EC and mice. Aim 1 will determine how endothelial BCR impacts atherosclerosis.
We recently discovered in culture that BCR is necessary for HDL attenuation of both the monocyte-EC adhesion
and the Rac1-dependent EC LDL transport that converge to drive atherogenesis. Using cultured EC, floxed BCR
mice, and nanoparticle-based EC cDNA delivery to reconstitute EC wild-type or mutant BCR expression in vivo,
we will test the hypothesis that HDL-related atheroprotection is mediated by EC BCR and its capacity to function
as a kinase or inhibitor of Rac1. In cultured EC we will also query how HDL subspecies with varying Apo-A1 and
Apo-A2 content and size impact BCR-dependent atheroprotective processes. Aim 2 will determine how EC BCR
impacts neovascularization, which is critical to PAD pathogenesis and resolution. We recently showed that EC
migration prompted by HDL is BCR-dependent. Using cultured EC, floxed BCR mice, reconstitution of EC BCR
in vivo, and mouse models of EC repair, angiogenesis and hindlimb ischemia, we will test the hypothesis that
EC BCR function as a kinase or an activator of RhoA underlies HDL-induced neovascularization. In culture, how
HDL subspecies impact EC neovascularization mechanisms will also be examined. Aim 3 will determine how
EC BCR impacts glucose control. Knowing that HDL has antidiabetic action and that EC insulin transport to
skeletal muscle drives processes underlying 80-90% of total body glucose disposal, we have discovered that
HDL stimulates EC insulin transport via BCR. Using cultured EC, floxed BCR mice, reconstitution of EC BCR
and glucose control phenotyping in vivo, we will test the hypothesis that EC BCR function as an Akt kinase
kinase underlies HDL promotion of normal glucose homeostasis. In culture, how HDL subspecies impact EC
insulin transport will also be studied. The proposed work providing new insights into how HDL affords
cardiometabolic protection has the potential to add clarity to why HDL has varying impact on individuals, and to
reveal new therapeutic targets to leverage against cardiovascular and metabolic disease.