Lipoproteins in Cardiovascular Biology and Pathology

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Linked publications & trials

Abstract

The HDL receptor, scavenger receptor class B type I (SR-BI), mediates cellular delivery of HDL cholesterol by[unreadable] selective lipid uptake, a mechanism distinct from classic receptor-mediated endocytosis. In addition, SR-BI can[unreadable] bind LDL and VLDL and can mediate both cellular uptake of non-lipoprotein cholesterol and stimulate cellular[unreadable] cholesterol efflux. Using in vivo studies with mice, we have shown that SR-BI plays a key role 1) in determining[unreadable] the structure of HDL and levels of both plasma HDL and biliary cholesterol, 2) in mediating the regulated delivery[unreadable] of HDL-cholesterol to steroidogenic tissues and the liver, and 3) in protecting against atherosclerosis. On a[unreadable] chow-fed apoE knockout (KO) genetic background (standard murine model of spontaneous atherosclerosis),[unreadable] homozygous null mutations in the SR-BI gene (SR-BI KO) cause dramatically accelerated atherosclerosis. In[unreadable] addition, these double KO mice ('dKO') express multiple characteristics commonly seen in human fatal coronary[unreadable] heart disease (CHD) and heart failure, including hypercholesterolemia, occlusive atherosclerosis, myocardial[unreadable] infarction (Ml), cardiac dysfunction and hypertrophy, pump failure and premature death (5-8 weeks of age,[unreadable] 50% mortality at 6 weeks). Crossing various transgenes or targeted gene deletions into dKO mice or treating[unreadable] them with pharmacologic agents is helping to elucidate the mechanisms underlying CHD and has provided[unreadable] additional evidence that this system may serve as a powerful model for human CHD. By crossing SR-BI single[unreadable] KO mice with mice carrying a hypomorphic apoE allele (ApoeR61-h/h), we generated SR-BI KO/ApoeR61-h/h mice[unreadable] that appear normal when fed a chow diet, but when fed an atherogenic ('Paigen') diet develop fatal occlusive[unreadable] CHD that is virtually identical to that in chow-fed dKO mice (50% mortality 32+/-6 days after initiation of the[unreadable] atherogenic diet). Withdrawal of the atherogenic diet can be used to study regression/recovery of disease[unreadable] (atherosclerosis, Ml, heart failure). Analysis of these two murine models of CHD should provide new[unreadable] mechanistic insights and a platform for preliminary analysis of new treatment or prevention strategies.[unreadable] The twin goals of this Project are I) to characterize the mechanisms underlying early onset CHD and death[unreadable] in dKO and SR-BI KO/ApoeR61-h/h mice and assess and improve the validity of these mice as models for[unreadable] human CHD, and II) to use somatic cell genetics to identify at the cellular level the gene products and[unreadable] functions that are required for SR-BI activity and underlie SR-BI's profound effects on the cardiovascular[unreadable] system. A wide array of molecular, cellular, physiologic, imaging, genetic, genomic and pharmacologic[unreadable] approaches will be used in close conjunction with the other Projects and Cores. For example, 1) with the[unreadable] Murine Genetics and Physiology Core we will continue to develop a system called HERMES to acquire, web[unreadable] broadcast and analyze in real time continuous EGG measurements from the very young (and thus small)[unreadable] dKO mice, which will allow us to correlate cardiac function with biochemistry, gene (including microRNA)[unreadable] expression and cardiac morphology. We will collaborate 2) with Projects II and V to evaluate the roles of[unreadable] adhesion molecules, platelets and hemostasis, and inflammation on CHD, 3) with Project III to explore the[unreadable] role of the key energy metabolism hormone adiponectin on CHD, and 4) with Project III in using retroviral[unreadable] technologies and somatic cell genetics to identify cellular genes required for SR-BI activity. As we identify[unreadable] additional genes by somatic cell genetics that are potentially significant contributors to cardiovascular[unreadable] pathophysiology, we will assess the contributions of genetic variation in these genes to clinical[unreadable] phenotypes. We will test the hypotheses that 1) our current and genetically improved SR-BI-based murine[unreadable] systems are valid models for human CHD and can be used to elucidate mechanisms underlying disease,[unreadable] and 2) identification of genes required for SR-BI function in cultured cells will help uncover both SR-BI-specific[unreadable] and globally important mechanisms of membrane protein processing and function. The proposed[unreadable] work should help elucidate key biological mechanisms underlying cardiovascular function and[unreadable] pathophysiology.