Cholesteryl ester transfer protein (CETP) exchanges cholesteryl ester (CE) and triglyceride (TG) between lipoproteins and is well recognized as a regulator of plasma lipoprotein metabolism. CETP also resides inside cells where two isoforms exist: full-length (FL) and exon 9 (E9)-deleted CETP. The function of CETP inside cells is not understood, but it is clearly essential since inhibiting CETP biosynthesis in adipocytes impairs lipid storage. We postulate this occurs because intracellular CETP is required for CE and TG transport from their site of synthesis to their site of storage. To test this general hypothesis, we propose three specific aims.
Aim 1 - Determine the CETP isoform(s) that promote cellular lipid storage, and define the structural features of CETP that are essential to its intracellular function.
This aim tests the hypothesis that E9-deleted CETP facilitates intracellular lipid transport directly or by interacting with FL CETP, and also examines how this cellular activity depends on CETP structure.
Aim 2 - Define the role of CETP in cellular lipid metabolism. To unravel the mechanisms by which CETP deficiency disrupts cellular lipid metabolism, this aim quantifies metabolic alterations and defines changes in lipid droplet formation that occur when CETP isoform expression is altered.
Aim 3 - Define the role of CETP in the formation and utilization of lipid storage droplets in lipoprotein- synthesizing cells. Consistent with preliminary studies, we propose that in lipoprotein-synthesizing cells CETP assists in both lipid droplet formation and the reverse transport of stored lipids to microsomes for lipoprotein assembly. Genetic and adenoviral approaches will alter expression of FL and/or E9-deleted CETPs in SW872 adipocytes, Caco-2 intestinal enterocytes, and in hamster. The consequences of these molecular manipulations on lipid synthesis, interorganelle lipid transport, lipid droplet formation and lipoprotein assembly will be studied through biochemical and microscopy techniques. These studies will describe a novel function for CETP and advance our understanding of cellular lipid transport and storage mechanisms. Lipid storage in adipocytes is linked to their secretion of hormones that regulate glucose and lipid metabolism, which directly affect processes such as inflammation and atherogenesis.
PROJECT RELEVANCE This grant application focuses on cholesteryl ester transfer protein - a protein that may transport fat inside of cells so that these lipids can be efficiently stored and retrieved when needed. Fat storage is a key function of many cells, but especially in adipose tissue where the amount of fat stored alters the secretion of important hormones that influence the body's use of fat and sugar for energy, and effect the development of insulin resistance and heart disease.
|Morton, Richard E; Izem, Lahoucine (2014) Cholesteryl ester transfer proteins from different species do not have equivalent activities. J Lipid Res 55:258-65|
|Morton, Richard E; Greene, Diane J (2011) Conversion of lipid transfer inhibitor protein (apolipoprotein F) to its active form depends on LDL composition. J Lipid Res 52:2262-71|
|Izem, Lahoucine; Morton, Richard E (2009) Molecular cloning of hamster lipid transfer inhibitor protein (apolipoprotein F) and regulation of its expression by hyperlipidemia. J Lipid Res 50:676-84|
|He, Yubin; Greene, Diane J; Kinter, Michael et al. (2008) Control of cholesteryl ester transfer protein activity by sequestration of lipid transfer inhibitor protein in an inactive complex. J Lipid Res 49:1529-37|
|Morton, Richard E; Gnizak, Hannah M; Greene, Diane J et al. (2008) Lipid transfer inhibitor protein (apolipoprotein F) concentration in normolipidemic and hyperlipidemic subjects. J Lipid Res 49:127-35|
|Izem, Lahoucine; Morton, Richard E (2007) Possible role for intracellular cholesteryl ester transfer protein in adipocyte lipid metabolism and storage. J Biol Chem 282:21856-65|
|Morton, Richard E; Greene, Diane J (2007) Partial suppression of CETP activity beneficially modifies the lipid transfer profile of plasma. Atherosclerosis 192:100-7|
|Morton, Richard E; Greene, Diane J (2003) The surface cholesteryl ester content of donor and acceptor particles regulates CETP: a liposome-based approach to assess the substrate properties of lipoproteins. J Lipid Res 44:1364-72|
|Paromov, Viktor M; Morton, Richard E (2003) Lipid transfer inhibitor protein defines the participation of high density lipoprotein subfractions in lipid transfer reactions mediated by cholesterol ester transfer protein (CETP). J Biol Chem 278:40859-66|
|Morton, Richard E; Greene, Diane J (2003) CETP and lipid transfer inhibitor protein are uniquely affected by the negative charge density of the lipid and protein domains of LDL. J Lipid Res 44:2287-96|
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