Jack Oram, PhD
Title:
Research Professor, Department of Medicine, Division of Metabolism, Endocrinology and Nutrition
Email Address:
Background:
Dr. Oram received his PhD from the Department of Physiology at the Hershey Medical Center, Pennsylvania State University, in 1972 and continued his postdoctoral training in the same department under the supervision of Dr. James Neely. He joined the Division of Metabolism, Endocrinology, and Nutrition in the Department of Medicine at the University of Washington in 1973 and is currently a member of the Diabetes and Obesity Center of Excellence. Dr. Oram has been continuously funded by federal and private grants to study the cell and molecular biology of cholesterol and other lipids and their involvement in cardiovascular disease. He has published extensively in these fields of research and is recognized as a world expert. Dr. Oram is the principle investigator of two NIH R01 grants and a project in a NIH Program Project grant and is a co-director of the Virus, Molecular Biology and Cell Core of the Diabetes Endocrinology Research Center.
Focus:
Dr. Oram's research focuses on high-density lipoprotein (HDL) metabolism and the cell and molecular biology of cholesterol transport and their roles in the cardiovascular complications of diabetes.
HDL and reverse cholesterol transport
Population studies have shown an inverse relationship between plasma HDL levels and cardiovascular disease (CVD), implying that factors associated with HDL metabolism are cardioprotective. One of the major functions of HDL is to transport cholesterol from peripheral tissues to the liver, where it can be eliminated from the body through biliary excretion. This pathway, called reverse cholesterol transport, involves multiple cellular and plasma transport proteins and enzymes.
We were one of the first to show that a major cardioprotective effect of HDL is its ability to remove excess cholesterol from arterial cells, and that this may involve the interaction of HDL with cell-surface proteins. HDL components can remove cellular cholesterol by multiple mechanisms. One of these processes is mediated by the major protein component of HDL, called apoA-I. We showed that patients with a genetic disorder that leads to very low levels of blood HDL and increased CVD have a cellular defect that impairs the ability of apoA-I to remove cholesterol. We and others then discovered that this defect involved mutations in a gene that encodes a membrane transporter called ATP-binding cassette transporter A1 (ABCA1). Subsequent studies of humans and mouse models showed that ABCA1 is a determinant of plasma HDL levels and risk for CVD. A major focus of our laboratory is to characterize the lipid transport and anti-inflammatory properties of ABCA1 and how impairment of its function may contribute to CVD, the most common cause of death among diabetic subjects.
Anti-inflammatory effects of ABCA1
There is evidence that ABCA1 also has an anti-inflammatory function, and that this could involve mechanisms that are dependent and independent of lipid transport. A major discovery in our laboratory is that the interaction of apoA-I with ABCA1 activates a tyrosine kinase signaling pathway involving Janis kinase 2 (JAK2). This kinase enhances the binding of apolipoproteins to ABCA1 required for cholesterol export. Importantly, it also activates a key transcription factor called STAT3. The JAK2/STAT3 pathway is well-known to have an anti-inflammatory function in macrophages and is the major mechanism by which the cytokine IL-10 exerts its anti-inflammatory effects.
We found that the interaction of apoA-I with ABCA1-expressing macrophages markedly suppresses expression of inflammatory molecules and that this involves activation of JAK2/STAT3. Thus, ABCA1 can directly function as an anti-inflammatory receptor independent of its lipid transport activity. ABCA1 therefore has the potential of reducing CVD by both exporting excess cholesterol from arterial cells and suppressing inflammation. The mechanisms and physiological relevance of the anti-inflammatory effects of ABCA1 are now major interests of our laboratory.
Regulation of ABCA1
Because ABCA1 is a major factor that raises HDL levels and protects against CVD, interest was generated in identifying biochemical processes that regulate its cell levels and activity. It was shown that cholesterol loading of macrophages and other cells enhances apoA-I-mediated lipid efflux and increases ABCA1 mRNA levels through oxysterol nuclear receptors termed LXRs. These findings were expected for a transporter that functions to rid cells of potentially damaging excess cholesterol. One study, however, revealed that there was a high level of discordance between ABCA1 protein and mRNA levels among different mouse tissue, suggesting that ABCA1 protein is highly regulated independent of mRNA transcription in vivo. We then investigated the possibility that common metabolic factors could regulate ABCA1 protein levels.
We found that incubating cultured cholesterol-loaded macrophages with common free fatty acids, such palmitate and oleate, reduced ABCA1 levels by increasing ABCA1 protein degradation. This occurred by activating a biochemical pathway that stimulates ABCA1 phosphorylation through a phospholipase D2 (PLD2) and protein kinase C (PKC) signaling pathway. In a collaborative study, Karin Bornfeldt’s laboratory showed that macrophages from mice genetically engineered to have a reduced ability to enzymatically activate oleate have higher levels of ABCA1. These finding suggest that the destabilizing effects of fatty acids on ABCA1 have physiologic relevance. Studies are ongoing to determine what cellular mechanisms are involved in the fatty acid-induced destabilization ABCA1 and how this may impair ABCA1 function in whole animals and humans.
Reactive carbonyls destabilize ABCA1
CVD is the major cause of morbidity and mortality in both types 1 and 2 diabetes and in the metabolic syndrome. The low HDL levels frequently associated with these disorders raised the possibility that impaired ABCA1 could contribute to the increased CVD. Two metabolic abnormalities of diabetes are elevated free fatty acids and glucose. We already showed that fatty acids can destabilize ABCA1. Another focus of our laboratory is to determine the effects of elevated glucose on this cholesterol export pathway.The oxidation of glucose generates small sugars called reactive carbonyls that can covalently attach to amino acids and damage proteins. These damaged proteins increase with diabetes and age. In collaboration with Jay Heinecke, we found that incubating macrophages with the carbonyls glyoxal and glycoaldehyde rapidly and severely impaired ABCA1 function, which was associated with a destabilization of ABCA1 protein. Thus, this could be another mechanism by which the diabetic state accelerates CVD.
Impaired ABCA1 in diabetic animal models
Another interest of our laboratory is to determine if ABCA1 is impaired by diabetes in whole animals and whether this could relate to human disease. Our cell culture studies suggested that ABCA1 protein levels should decrease in macrophages from animals when they are made diabetic. We found that inducing diabetes in fat-fed pigs increased the size of their atherosclerotic lesions but decreased the number of cholesterol-loaded macrophages having detectable levels of ABCA1 protein, consistent with impaired ABCA1-dependent cholesterol export contributing to the increased number and size of cholesterol-loaded macrophages.
In collaboration with Renee Leboeuf and Karin Bornfeldt, we tested the possibility that ABCA1 protein is reduced in macrophages and tissues in two mouse models of type 1 diabetes. After diabetes was induced in these mice, tissues and peritoneal macrophages were removed and immediately assayed for ABCA1 mRNA and protein levels. We found that diabetes had no effect on ABCA1 mRNA levels in isolated macrophages, liver, kidney, and brain from these mice, decreased ABCA1 protein levels in isolated macrophages and kidneys from both animal models by ~40 %, but had no effect on or slightly increased ABCA1 protein levels in the liver and brain. The reduced protein to mRNA ratio is consistent with our cell culture studies showing that diabetic factors destabilize ABCA1 protein, which in macrophages would accelerate CVD. The reduced ABCA1 in kidneys raises the interesting possibility that impaired lipid transport from renal cells contributes to the increased renal disease seen in diabetic patients. Studies are ongoing in our laboratory to determine the mechanisms by which diabetes reduces ABCA1, to evaluate its contribution to diabetes-accelerated CVD, and to determine if therapeutic interventions can reverse these effects.
Representative Publications:
Oram, J.F., Bennetch, S.L., and Neely, J.R.: Regulation of fatty acid utilization in isolated perfused rat hearts. J. Biol. Chem. 248:5299-5309, 1973.
Oram, J.F., Wenger, J.I., and Neely, J.R.: Regulation of long-chain fatty acid activation in heart muscle. J. Biol. Chem. 250:73-78, 1975.
Oram, J.F., Albers, J.J., and Bierman, E.L.: Rapid regulation of the activity of the low density lipoprotein receptor of cultured human fibroblast. J. Biol. Chem. 255:475-485, 1980.
Oram, J.F., Shafrir, E., and Bierman, E.L.: Triacylglycerol metabolism and triacylglycerol lipase activities of cultured human skin fibroblasts. Biochim. Biophys. Acta 619:214-227, 1980.
Oram, J.F., Cheung, M.C., Albers, J.J., and Bierman, E.L.: The effects of subfractions of high density lipoprotein on cholesterol efflux from cultured fibroblasts: regulation of low density lipoprotein receptor activity. J. Biol. Chem. 256:8348-8356, 1981.
Oram, J.F.: The effects of high density lipoprotein subfractions on cholesterol homeostasis in human fibroblasts and arterial smooth muscle cells. Arteriosclerosis 3:420-432, 1983.
Oram, J.F., Brinton, E.A., and Bierman, E.L.: Regulation of high density lipoprotein receptor activity in cultured human skin fibroblasts and human arterial smooth muscle cells, J. Clin. Inv. 72:1611-1621, 1983.
Oram, J.F., Johnson, C.J., and Brown, T.A.: Interaction of high density lipoprotein with its receptor on cultured fibroblasts in macrophages: Evidence for reversible binding at the cell surface without internalization. J. Biol. Chem. 262:2405-2410, 1987.
Graham, D.L., and Oram, J.F.: Identification and characterization of a high density lipoprotein binding protein in cell membranes by ligand blotting. J. Biol. Chem. 262:7439-7442, 1987.
Aviram, M., Bierman, E.L., and Oram, J.F.: High density lipoprotein stimulates sterol translocation between intracellular and plasma membrane pools in human monocyte-derived macrophages. J. Lipid Res. 30:65-76, 1989.
Duell, P.B., Oram, J.F., and Bierman, E.L.: Nonenzymatic glycosylation of HDL resulting in inhibition of high-affinity binding to cultured human fibroblasts. Diabetes 39:1257-1263, 1990.
Duell, P.B., Oram, J.F. and Bierman, E.L.: Nonenzymatic glycosylation of high density lipoprotein impairs HDL-receptor mediated cholesterol efflux. Diabetes 40:377-384, 1991.
Oram, J.F., Mendez, A.J., Slotte, J.P., and Johnson, T.F.: High-density lipoprotein apolipoproteins mediate removal of sterol from intracellular pools but not from plasma membranes of cholesterol-loaded fibroblasts. Arterioscler. Thromb. 11:403-414, 1991.
Mendez, A.J., Oram, J.F., and Bierman, E.L.: Protein kinase C as a mediator of high density lipoprotein receptor-dependent efflux of intracellular cholesterol. J. Biol. Chem. 266:10104-10111, 1991.
McKnight, G.L., Reasoner, J., Gilbert, T., Sundquist, K.O., Hokland, B.M., McKernan, P.A., Champagne, J., Johnson, C.J., Bailey, M.C., Holly, R., O'Hara, P.J., and Oram, J.F.: Cloning and expression of a cellular high density lipoprotein-binding protein that is up-regulated by cholesterol loading of cells. J. Biol. Chem. 267:12131-12141, 1992.
Hokland, B.M., Mendez, A.J., and Oram, J.F.: Cellular localization and characterization of proteins that bind high density lipoprotein. J. Lipid Res. 33:1335-1342, 1992.
Oikawa, S., Mendez, A.J., Oram, J.F., Bierman, E.L. and Cheung, M.C.: Effects of high-density lipoprotein particles containing apo A-I, with or without apo A-II, on intracellular cholesterol efflux. Biochim. Biophys. Acta 1165:327-334, 1993.
Xia, Y.-R., Klisak, I., Sparkes, R.S., Oram, J.F. and Lusis, A.J.: Localization of the gene for high-density lipoprotein binding protein to human chromosome 2q37. Genomics 16:524-525, 1993.
Hokland, B.M., Slotte, J.P., Bierman, E.L., and Oram, J.F.: Cyclic-AMP stimulates efflux of intracellular sterol from cholesterol-loaded cells. J. Biol. Chem. 268:5343-5349, 1993.
Mendez, A.J., Anatharamaiah, G.M., Segrest, J.P., and Oram, J.F.: Synthetic amphipathic helical peptides that mimic apolipoprotein A-I in clearing cellular cholesterol. J. Clin. Invest. 94:1698-1705, 1994.
Francis, G.A., Knopp, R.H., and Oram, J.F.: Defective removal of cellular cholesterol and phospholipids by apolipoprotein A-I in Tangier Disease. J. Clin. Invest. 96:78-87, 1995.
Oram, J.F.: Can insulin promote atherogenesis by altering cellular cholesterol metabolism? J. Lab. Clin. Med. 126:229-230, 1995.
Francis, G.A., Oram, J.F., Heinecke, J.W., and Bierman, E.L.: Oxidative tyrosylation of HDL enhances the depletion of cellular cholesteryl esters by a mechanism independent of passive sterol desorption. Biochemistry 35:15188-15197, 1996.
24. cellular cholesterol and phospolipids. J. Lipid Res. 37:2473-2491, 1996.25. Mendez, A.J. and Oram, J.F.: Limited proteolysis of high density lipoprotein abolishes its interaction with cell-surface binding sites that promote cholesterol efflux. Biochim. Biophys. Acta. 1346:285-299, 1997.
26. lipoproteins stimulate mitogen-activated protein kinases in human skin fibroblasts. Arterioscler. Thromb. Vasc. Biol. 17:1667-1674, 1997.
Garver, W.S., Deeg, M.A., Bowen, R.F., Bierman, E.L., and Oram, J.F.: Phosphoproteins regulated by the interaction of high density lipoprotein with human fibroblasts. Arterioscler. Thromb. Vasc. Biol. 17:2698-2706, 1997.
Chiu, D.S., Oram, J.F., Alpers, C.E., and O'Brien, K.D.: High density lipoprotein binding protein (HBP) is expressed in human atherosclerotic lesions and co-localizes with apolipoprotein E. Arterioscler. Thromb. Vasc. Biol. 17:2350-2358, 1997.
Marcil, M., Yu, L., Krimbou, L., Boucher, B., Oram, J.F., Cohn, J.S., and Genest Jr., J.: Cellular cholesterol transport and efflux in fibroblasts is abnormal in subjects with familial HDL deficiency. Arterioscler. Thromb. Vasc. Biol. 19:159-169, 1999.
Oram, J.F., Mendez, A.J., Lymp, J., Kavanagh, T.J., and Halbert, C.L.: Reduction in apolipoprotein-mediated removal of cellular lipids by immortalization of human fibroblasts and its reversion by cAMP: lack of effect with Tangier disease cells. J. Lipid Res. 40:1769-1781, 1999.
Lawn, R.M., Wade, D.P., Garvin, M.R., Wang, X., Schwartz, K., Porter, J.G., Seilhamer, J.J., Vaughan, A.M., and Oram, J.F.: The Tangier disease gene product ABC1 controls the cellular apolipoprotein-mediated lipid removal pathway. J. Clin. Invest. 104:R25-R31, 1999.
Lin, G., and Oram, J.F.: Apolipoprotein binding to protruding membrane domains during removal of excess cellular cholesterol. Atherosclerosis 149:359-370, 2000.
Oram, J.F., Lawn, R.M., Garvin, M.R., and Wade, D.P.: ABCA1 is the cAMP-inducible receptor that mediates cholesterol secretion from macrophages. J. Biol. Chem. 275:34508-34511, 2000.
Oram, J.F. and Vaughan, A.M.: ABCA1-mediated transport of cellular cholesterol and phospholipids to HDL apolipoproteins. Curr. Opin. Lipidol. 11:253-260, 2000.
Oram, J.F.: Tangier disease and ABCA1. Biochim. Biophys. Acta 1529:321-330, 2000.
Mendez, A.J., Lin, G., Wade, D.P., Lawn, R.M., and Oram, J.F.: Membrane lipid domains distinct from cholesterol/sphingomyelin-rich rafts are involved in the ABCA1-mediated lipid secretory pathway. J. Biol. Chem. 276:3158-3166, 2001.
Oram, J.F., Vaughan, A.M., and Stocker, R.: ABCA1 mediates cellular secretion of alpha-tocopherol. J. Biol. Chem. 276:39898-39902, 2001.
Huang, Z.H., Lin, C.-Y., Oram, J.F., and Mazzone, T.: Sterol efflux mediated by endogenous macrophage apoE expression is independent of ABCA1. Arterioscler Thromb Vasc Biol 21:2019-2025, 2001.
Oram, J.F. and Lawn, R.M.: ABCA1: the gatekeeper for eliminating excess tissue cholesterol. J. Lipid Res. 42:1173-1179, 2001.
Wang, Y., and Oram, J.F.: Unsaturated fatty acids inhibit cholesterol efflux from macrophages by increasing degradation of ATP-binding cassette transporter A1. J. Biol. Chem., 277:5692-5697, 2002.
Lee, J., Shirk, A., Oram, J.F., Lee, S.P., and Kuver, R.: Polarized cholesterol and phospholipid efflux in cultured gallbladder epithelial cells: Evidence for an ABCA1-mediated pathway. Biochem J 364:475-484, 2002.
Vaughan AM and Oram JF: ABCA1 redistributes membrane cholesterol independent of apolipoprotein interactions. J Lipid Res 44:1373-1380, 2003.
Oram JF, Wolfbauer G, Vaughan AM, Tang C, and Albers J: Phospholipid transfer protein interacts with and stabilizes ABCA1 and enhances cholesterol efflux from cells. J Biol Chem 278:552379-52385, 2003.
Oram, J.F.: HDL apolipoproteins and ABCA1: Partners in the removal of excess cellular cholesterol. Arterioscler Thromb Vasc Biol. 23:720-727, 2003.
Tang C, Vaughan AM, and Oram JF: Janus kinase 2 modulates the apolipoprotein interactions with ABCA1 required for removing cellular cholesterol. J Biol Chem, 279:7622-7628, 2004.
Wang Y, Kurdi-Haidar B, Oram JF.: LXR-mediated activation of macrophage stearoyl-CoA desaturase generates unsaturated fatty acids that destabilize ABCA1. J Lipid Res 45:972-980, 2004.
Oram JF, Bornfeldt KE.: Direct effects of long-chain non-esterified fatty acids on vascular cells and their relevance to macrovascular complications of diabetes. Front Biosci. 9:1240-1253, 2004.
Natarajan P, Forte TM, Chu B, Phillips MC, Oram JF, Bielicki JK.: Identification of an apolipoprotein A-I structural element that mediatescellular cholesterol efflux and stabilizes ABCA1. J Biol Chem 279:24044-24052, 2004.
Pennathur S, Bergt C, Shao B, Byun J, Kassim SY, Singh P, Green PS, McDonald TO, Brunzell J, Chait A, Oram JF, O'Brien K, Geary RL, Heinecke JW: Human atherosclerotic intima and blood of patients with established coronary artery disease contain high density lipoprotein damaged by reactive nitrogen species. J Biol Chem 279:42977-42983, 2004.
Bergt C, Pennathur S, Fu X, Byun J, O'Brien K, McDonald TO, Singh P, Anantharamaiah GM, Chait A, Brunzell J, Geary RL, Oram JF, Heinecke JW: The myeloperoxidase product hypochlorous acid oxidizes HDL in the human artery wall and impairs ABCA1-dependent cholesterol transport. Proc Natl Acad Sci USA 101:13032-13037, 2004.
Shao B, Bergt C, Fu X, Green P, Voss JC, Oda MN, Oram JF, Heinecke JW: Tyrosine 192 in apolipoprotein A-I is the major site of nitration and chlorination by myeloperoxidase, but only chlorination markedly impairs ABCA1-dependent cholesterol transport. J Biol Chem 280:5983-5993, 2005.
Vaughan AM, Oram JF: ABCG1 redistributes cell cholesterol to domains removable by high density lipoprotein but not by lipid-depleted apolipoproteins. J Biol Chem 280:30150-30157, 2005.
Shao B, O'brien KD, McDonald TO, Fu X, Oram JF, Uchida K, Heinecke JW. Acrolein modifies apolipoprotein A-I in the human artery wall. Ann N Y Acad Sci. 1043:396-403, 2005.
Passarelli M, Tang C, McDonald TO, O'Brien KD, Gerrity RG, Heinecke JW, Oram JF: Advanced glycation end product precursors impair ABCA1-dependent cholesterol removal from cells. Diabetes 54:2198-2205, 2005.
Wang Y, Oram JF: Unsaturated fatty acids phosphorylate and destabilize ABCA1 through a phospholipase D2 pathway. J Biol Chem 280:35896-35903, 2005.
Shao B, Fu X, McDonald TO, Green PS, Uchida K, O'Brien KD, Oram JF, Heinecke JW: Acrolein impairs ABCA1-dependent cholesterol export from cells through site-specific modification of apolipoprotein A-I. J Biol Chem 280:36386-36396, 2005.
Oram JF, Heinecke JW. ATP-binding cassette transporter A1: A cell cholesterol exporter that protects against cardiovascular disease. Physiol Rev 85:1343-1372, 2005.
Tang C, Vaughan AM, Anantharamaiah GM, Oram JF: Janus Kinase 2 modulates the lipid-removing but not protein-stabilizing interactions of amphipathic helices with ABCA1. J Lipid Res 47:107-114, 2006.
Shao B, Oda MN, Bergt C, Fu X, Green PS, Brot N, Oram JF, Heinecke JW: Myeloperoxidase impairs ABCA1-dependent cholesterol efflux through methionine oxidation and site-specific tyrosine chlorination of apolipoprotein A-I. J Biol Chem 281: 9001-9004, 2006.
Vaughan AM, Oram JF: ABCA1 and ABCG1 or ABCG4 act sequentially to remove cellular cholesterol and generate cholesterol-rich HDL. J Lipid Res 47:2433-43, 2006.
Oram JF, Vaughan AM: ATP-binding cassette cholesterol transporters and cardiovascular disease. Circ Res, 99:1031-1043, 2006.
Vaisar T, Pennathur S, Green PS, Gharib SA, Hoofnagle AN, Cheung MC, Byun J, Vuletic S, Kassim S Singh P, Chea H, Knopp RH, Brunzell J, Geary R, Chait A, Zhao XQ, Elkon K, Marcovina S, Ridker P Oram JF, Heinecke JW: Shotgun proeomics implicates protease inhibition and complement activation in the anti-inflammatory properties of HDL. J Clin Invest 117: 746-756, 2007.
Wang Y, Oram JF: Unsaturated fatty acids phosphorylate and destabilize ABCA1 through a protein kinase C delta pathway. J Lipid Res 48:1062-1068, 2007.
Oram JF, Wolfbauer G, Tang C, Davidson WS, Albers JJ. An amphipathic helical region of the N-terminal barrel of phospholipid transfer protein is critical for ABCA1-dependent cholesterol efflux. J Biol Chem: 283:11541-11549, 2008.
Vaughan AM, Tang C, Oram JF. ABCA1 mutants reveal an interdependency between lipid export function, apoA-I binding activity, and Janus kinase 2 activation. J Lipid Res: 2008 [Epub ahead of print].
Current Collaborations:
Within the Diabetes and Obesity Center of Excellence and its Affiliated Members
Jay Heinecke, MD
Renee LeBoeuf, PhD
Karin Bornfeldt, PhD
Alan Chait, MD
Lab Members:
Kimberly Edgel, PhD
Chongren Tang, PhD
Carl Storey
Peter Kessler, PhD
Yuhua Liu, PhD