Atherosclerosis is the most common cause of death in the United States. Elevated plasma levels of LDL are a major risk factor for the development of this disease. The major pathway by which LDL is catabolized is via the LDL-receptor (LDL-R). Therefore, factors that impede LDL-LDL-R interactions promote atherosclerosis. An unexplored question is whether platelet activation modulates LDL-R function. Whereas the role of platelets in the terminal thrombotic phase of this disease is well- established, it is less certain whether persistent platelet activation accelerates the pathogenesis of the atherosclerotic plaque. In view of the fact that certain clusters of positively charged residues on apolipoprotein Beta-100 are required for optimal binding of LDL to the LDL-R, the investigators tested the hypothesis that platelet factor 4 (PF4], an abundant lysine rich protein released upon platelet activation, can complete for receptor binding and thereby impede lipoprotein clearance and catabolism. Pilot data provided support for this hypothesis by demonstrating that PF4 binds to the LDL-R with nM affinity, inhibits the binding and degradation of LDL in vitro, and prolongs the plasma clearance of LDL in vivo. It is now proposed to study the biochemicals basis of the PF4-LDL-R interaction in greater detail and to develop models to elucidate the role of this platelet protein in the development of atherosclerosis through the following specific aims; 1) Specific Aim 1: Characterization of PF4 binding to the LDL-R and it's consequences in vitro. The binding kinetics of PF4 to cell lines that overexpress LDL-R as well as to recombinant soluble receptor will be measured using surface plasmon resonance. The effect of PF4 on the binding and cellular metabolism of LDL and apoE will be studied using cells that are genetically lacking or overexpress LDL-R and in which the level of proteoglycan expression has been controlled.
Specific Aim 2 : Effect of PF4 on lipoprotein metabolism and atherosclerosis in vivo. Adenoviral-mediated gene transfer of PF4 will be used to analyze changes in LDL clearance and endogenous lipoprotein levels in vivo. The propensity to develop hyperlipidemia and atherosclerosis will be examined in transgenic mice that overexpress human PF4. These studies are designed to gain insight into a novel mechanism by which persistent platelet activation may promote the development of atherothrombotic disease. An understanding of the structural basis of the PF4-LDL-R interaction may identify a potential locus for therapeutic intervention. This research proposal is part of comprehensive training program designed to prepare the applicant for a career as an independent investigator in the field of vascular biology.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Clinical Investigator Award (CIA) (K08)
Project #
5K08HL004245-04
Application #
6627307
Study Section
Special Emphasis Panel (ZHL1-CSR-K (O1))
Program Officer
Mondoro, Traci
Project Start
2000-01-15
Project End
2004-12-31
Budget Start
2003-01-01
Budget End
2003-12-31
Support Year
4
Fiscal Year
2003
Total Cost
$131,247
Indirect Cost
Name
University of Pennsylvania
Department
Pathology
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Sachais, Bruce S; Turrentine, Tiffany; Dawicki McKenna, Jennine M et al. (2007) Elimination of platelet factor 4 (PF4) from platelets reduces atherosclerosis in C57Bl/6 and apoE-/- mice. Thromb Haemost 98:1108-13
Rauova, Lubica; Poncz, Mortimer; McKenzie, Steven E et al. (2005) Ultralarge complexes of PF4 and heparin are central to the pathogenesis of heparin-induced thrombocytopenia. Blood 105:131-8
Yu, Guangyao; Rux, Ann H; Ma, Peihong et al. (2005) Endothelial expression of E-selectin is induced by the platelet-specific chemokine platelet factor 4 through LRP in an NF-kappaB-dependent manner. Blood 105:3545-51
Suvarna, Shayela; Rauova, Lubica; McCracken, Emily K E et al. (2005) PF4/heparin complexes are T cell-dependent antigens. Blood 106:929-31
Pitsilos, Stephanie; Hunt, Jennifer; Mohler, Emile R et al. (2003) Platelet factor 4 localization in carotid atherosclerotic plaques: correlation with clinical parameters. Thromb Haemost 90:1112-20
Sachais, Bruce S; Kuo, Alice; Nassar, Taher et al. (2002) Platelet factor 4 binds to low-density lipoprotein receptors and disrupts the endocytic machinery, resulting in retention of low-density lipoprotein on the cell surface. Blood 99:3613-22