The enzyme hepatic lipase (HL) is central to cholesterol homeostasis. HL participates in the regulation of plasma cholesterol levels, a major risk factor for atherosclerosis. It also mediates steroid hormone production, by controlling access to exogenous cholesterol in steroid-producing tissues. In turn, increased production of the adrenal steroid cortisol (corticosterone in mice) as occurs in stress, depression and certain tumors of adrenal and pituitary origin, modulates the development of atherosclerosis: increased cortisol levels are linked to an increased risk for atherosclerosis. However, HL's precise role in atherosclerosis is unknown. HL exerts its role via at least two functions. Its catalytic function processes lipoproteins for both receptor-mediated endocytosis and selective cholesterol uptake. Its bridging function facilitates interactions between lipoproteins, receptors, and the plasma membrane, thereby modulating lipoprotein cholesterol flux. This proposal seeks to establish the respective contributions of the catalytic and bridging functions to the cellular uptake of lipoprotein cholesterol and atherosclerosis by generating transgenic mice that express wildtype HL and functional mutants of HL. These mice will be bred with mice deficient in endogenous HL(hl-/-) and with h1-/- mice that are also deficient in the low density lipoprotein (LDL) receptor to generate Ldlr-/-hl-/- mice. (The Ldlr-/- mice serves as a model for diet-induced atherosclerosis). Thus, we will determine the effect of the expression of wildtype and mutant HLs on plasma lipid and lipoprotein concentrations, composition and size, and lipoprotein turnover. The mechanisms of lipoprotein cholesterol uptake will be examined in primary hepatocyte cultures from the livers of these mice by determining the effects of wildtype and mutant HL on cellular binding and uptake of labeled lipoproteins in the presence of specific inhibitors of cellular receptors. The effect of expression of wildtype and mutant HL on atherosclerosis development will be established in high-fat diet fed wildtype and mutant HL expressing mice on the Ldlr-/-hl-/-background. In addition this proposal seeks to establish the role of HL in regulating the adrenal steroidogenic response to stress and to identify the contribution of the catalytic function of HL to the adrenal steroidogenic response to stress. This will be accomplished by determining plasma corticosterone response, adrenal cholesterol content and adrenal expression of receptors and enzymes involved in cholesterol metabolism, in response to chronic pharmacologic stimulation of corticosterone production in wildtype- and mutant HL-expressing mice and compared to nontransgenic mice.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL069775-03
Application #
6638846
Study Section
Special Emphasis Panel (ZRG1-SSS-T (01))
Program Officer
Applebaum-Bowden, Deborah
Project Start
2001-07-01
Project End
2006-05-31
Budget Start
2003-06-01
Budget End
2004-05-31
Support Year
3
Fiscal Year
2003
Total Cost
$304,000
Indirect Cost
Name
University of Washington
Department
Pediatrics
Type
Schools of Medicine
DUNS #
605799469
City
Seattle
State
WA
Country
United States
Zip Code
98195
Eacker, Stephen M; Agrawal, Nalini; Qian, Kun et al. (2008) Hormonal regulation of testicular steroid and cholesterol homeostasis. Mol Endocrinol 22:623-35
Qian, Kun; Agrawal, Nalini; Dichek, Helen L (2007) Reduced atherosclerosis in chow-fed mice expressing high levels of a catalytically inactive human hepatic lipase. Atherosclerosis 195:66-74
Dichek, Helen L; Agrawal, Nalini; El Andaloussi, Nazim et al. (2006) Attenuated corticosterone response to chronic ACTH stimulation in hepatic lipase-deficient mice: evidence for a role for hepatic lipase in adrenal physiology. Am J Physiol Endocrinol Metab 290:E908-15
Dichek, Helen L; Qian, Kun; Agrawal, Nalini (2004) The bridging function of hepatic lipase clears plasma cholesterol in LDL receptor-deficient ""apoB-48-only"" and ""apoB-100-only"" mice. J Lipid Res 45:551-60
Dichek, Helen L; Qian, Kun; Agrawal, Nalini (2004) Divergent effects of the catalytic and bridging functions of hepatic lipase on atherosclerosis. Arterioscler Thromb Vasc Biol 24:1696-702