The class type I scavenger receptor (SR-BI) is the high density lipoprotein (HDL) receptor that regulates HDL- cholesterol metabolism and is directly linked to the ability of HDL to be athero-protective. The long-term objective of our research is to understand the function of SR-BI in the delivery of cholesteryl ester (CE) from HDL to the liver for cholesterol disposal. New insight into how SR-BI mediates the efficiency of HDL-CE delivery is key to developing methods for prevention of cardiovascular disease. This proposal consists of three primary objectives that will evaluate how the structural organization of SR-BI at the plasma membrane and the proper alignment of SR-BI with HDL mediate enhanced cholesterol flux to the liver.
Aim 1 will determine the physiological organization and relevance of the SR-BI oligomer in vivo. Goal 1 will use bimolecular fluorescence complementation coupled with fluorescence resonance energy transfer spectroscopy to confirm the presence of SR-BI oligomers in live cells and monitor changes in oligomer formation upon ligand engagement. In Goal 2, the physiological relevance of SR-BI oligomerization in reverse cholesterol transport will be assessed following adenoviral-mediated expression of oligomerization-defective mutant SR-BI receptors in SR-BI knock-out mice.
Aim 2 is designed to examine the molecular determinants for "productive complex" formation (i.e. proper alignment) between HDL and SR-BI that promote selective uptake of HDL-CE. In Goal 1, a series of SR-BI/CD36 chimeras will be designed to identify regions within the extracellular domain of SR-BI that are crucial for HDL-CE selective uptake and vital for "productive complex" formation. In Goal 2, the combination of site-specific ligand-directed crosslinking and mass spectrometry will be used to map sites of interaction between SR-BI and HDL.
Aim 3 will explore how the conformation of the extracellular domain of SR-BI impacts lipid transfer from HDL to the plasma membrane. Goal 1 will use tryptophan quenching to test the hypothesis that hydrophobic regions of SR-BI are required to interact with the plasma membrane and/or ligand to facilitate efficient lipid transfer and cholesterol flux. Goal 2 will determine the role of extracellular cysteine residues in SR-BI function and experiments are designed to identify intra- and intermolecular disulfide bonding patterns. Together, these studies will improve our understanding of how SR-BI mediates the efficiency of HDL-CE selective uptake and will shed new insights into cholesterol metabolism and protection against atherosclerosis.

Public Health Relevance

Heart disease kills more Americans each year than all cancers combined. Our research is designed to understand how we can improve cholesterol removal from the body and lower plasma cholesterol levels. Our findings will help identify new strategies for treating heart disease and other related complications.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL058012-18
Application #
8625808
Study Section
Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
Program Officer
Liu, Lijuan
Project Start
1997-04-01
Project End
2015-02-28
Budget Start
2014-03-01
Budget End
2015-02-28
Support Year
18
Fiscal Year
2014
Total Cost
$707,256
Indirect Cost
$241,956
Name
Medical College of Wisconsin
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
937639060
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
Kartz, Gabriella A; Holme, Rebecca L; Nicholson, Kay et al. (2014) SR-BI/CD36 chimeric receptors define extracellular subdomains of SR-BI critical for cholesterol transport. Biochemistry 53:6173-82
Chadwick, Alexandra C; Sahoo, Daisy (2013) Functional genomics of the human high-density lipoprotein receptor scavenger receptor BI: an old dog with new tricks. Curr Opin Endocrinol Diabetes Obes 20:124-31
Saddar, Sonika; Carriere, Veronique; Lee, Wan-Ru et al. (2013) Scavenger receptor class B type I is a plasma membrane cholesterol sensor. Circ Res 112:140-51
Papale, Gabriella A; Hanson, Paul J; Sahoo, Daisy (2011) Extracellular disulfide bonds support scavenger receptor class B type I-mediated cholesterol transport. Biochemistry 50:6245-54
Papale, Gabriella A; Nicholson, Kay; Hanson, Paul J et al. (2010) Extracellular hydrophobic regions in scavenger receptor BI play a key role in mediating HDL-cholesterol transport. Arch Biochem Biophys 496:132-9
Sahoo, Daisy; Peng, Yinan; Smith, Jeffery R et al. (2007) Scavenger receptor class B, type I (SR-BI) homo-dimerizes via its C-terminal region: fluorescence resonance energy transfer analysis. Biochim Biophys Acta 1771:818-29
Sahoo, Daisy; Darlington, Yolanda F; Pop, Diana et al. (2007) Scavenger receptor class B Type I (SR-BI) assembles into detergent-sensitive dimers and tetramers. Biochim Biophys Acta 1771:807-17
Parathath, Saj; Darlington, Yolanda F; de la Llera Moya, Margarita et al. (2007) Effects of amino acid substitutions at glycine 420 on SR-BI cholesterol transport function. J Lipid Res 48:1386-95
Parathath, Saj; Sahoo, Daisy; Darlington, Yolanda F et al. (2004) Glycine 420 near the C-terminal transmembrane domain of SR-BI is critical for proper delivery and metabolism of high density lipoprotein cholesteryl ester. J Biol Chem 279:24976-85
Connelly, Margery A; Williams, David L (2004) SR-BI and HDL cholesteryl ester metabolism. Endocr Res 30:697-703

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