Based on the incompleteness of our understanding of High Density Lipoprotein (HDL) metabolism the focus of this proposal is the identification of new genes involved in the metabolism of this lipoprotein through genome-wide expression screens. Mouse cDNA arrays containing >5000 mouse genes will be used to identify genes whose expression is altered in the liver and adrenals of several transgenic and knockout lines of mice chosen based on their characterized abnormalities in HDL metabolism. This will initially include transgenic and knockout mice for apolipoprotein A-I (apo A-I), Scavenger Receptor class b1 (sr- bi), Hepatic lipase (HL), and Lecithin Cholesterol Acyl Transferase (LCAT). A basic assumption in these studies is that alterations in the expression of genes known to be involved in HDL metabolism will affect the expression of other genes also participating in the metabolism of this lipoprotein. The novel genes identified from these studies will be prioritized for further biological characterization based on a variety of parameters including: level of expression change, clustering of expression patterns between mice of different HDL mutant genotypes, and sequence or expression pattern similarities to other genes known to participate in lipoprotein metabolism. The function of a limited number of novel "HDL candidate" genes (approximately 10) will be assessed each year through their over-expression in transgenic mice coupled with careful analysis of the consequence of transgene over-expression over-expression on lipoprotein metabolism. In these studies we will be utilizing a combination of new technologies and previously developed experimental substrates to address the fundamental question of what genes are directly or indirectly involved in the metabolism of HDL in vivo.