(provided by +applicant): The focal nature of atherosclerosis at the bifurcations and curved regions of arterial tree is correlated with the local flow patterns imposed on vascular endothelial cells (ECs). We hypothesize that disturbed flow provides a hemodynamic milieu to activate sterol regulatory element binding proteins (SREBPs) in ECs and modulate the expression and function of genes involved in lipid metabolism and trafficking. Synergistic with hyperlipidemia, disturbed flow causes the accumulation of LDL and its metabolites in the subendothelial space, vascular smooth muscle cells (VSMCs), and macrophages. In contrast, steady flow protects the endothelium by preventing SREBP activation, thus maintaining lipid homeostasis in straight parts of the arterial tree.
Four specific aims are proposed to test our hypotheses.
Specific Aim 1 is to apply flows with variations in magnitude of shear stress, temporal and spatial shear stress gradients, and amplitude and frequency of pulsatility to ECs cultured in flow channels. We will profile SREBP activation and transcriptional regulation of genes involved in lipid metabolism and trafficking in response to the various flow patterns.
Specific Aim 2 is to investigate the synergistic effect of flow activation of SREBPs and high levels of LDL in the subendothelial accumulation of lipids. Flow conditions that can cause sustained SREBP activation will be applied to EC-VSMC or EC-macrophage co-culture systems under high levels of LDL The lipid accumulation in the subendothelial space, VSMCs, and macrophages will be investigated accordingly.
Specific Aim 3 is to compare the topographic distribution of flow-activated SREBPs and atherosclerofic lesions in the arterial tree in rive. We will create transgenic mice possessing an EC-specific SRE-LacZ reporter system. The topographic expression of LacZ regulated by arterial flow will be compared with the distribution of atherosclerotic lesions in apoE -/- mice.
Specific Aim 4 is to explore the role of SREBPs in focal pattern of atherosclerosis. Transgenic lines with either EC-specific knockout of SREBP cleavage-activating protein (SCAP) or overexpression of the active form of SREBP2 [SREBP2(N)] will be created and crossed with apoE mice. We will examine whether atherosclerotic lesions in arterial branches can be attenuated in SCAP knockout animals (loss-of-function) and whether mice overexpressing SREBP2(N) show an enhancement of atherogenesis throughout the arterial tree (gain-of-function). By combining bioengineering, vascular biology, and transgenic approaches, this program will generate new insights into the molecular and mechanical bases of local flow patterns in atherogenesis.
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