Lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) is a recently identified scavenger receptor expressed in endothelial cells and mediates the uptake of oxidized LDL (oxLDL). LOX-1 expression is increased in atherosclerotic lesions in animals and humans. Recent evidence has suggested that LOX-1 is involved in the development and progression of atherosclerosis. In addition to endothelial cells, it has also been reported that LOX-1 is also expressed by other cell types like macrophages. It is a multi-ligand class E scavenger receptor and cellular expression of LOX-1 can be induced by many of its ligands. The concentration of some of these ligands like oxLDL and advanced glycation end products (AGEs) are increased in the diabetic milieu. My hypothesis is that LOX-1 expression is increased in diabetes mellitus and LOX-1 activation may play a role in the development of micro- and/or macrovascular complications of diabetes. The objective of this thesis is to elucidate the role of LOX-1 in type 2 diabetes mellitus and its complications. The effect of modified LDL and AGEs on LOX-1 expression and the cellular response upon LOX-1 activation was investigated. In vitro studies have shown that both AGEs and oxLDL can activate and increase cellular expression of LOX-1 and the soluble form of LOX-1 (sLOX-1) in cultured endothelial cells. In addition, LDL modified by glycoxidation, is also a ligand of LOX-1 and glycoxidized LDL is even more potent than oxLDL in inducing LOX-1 expression. In patients with type 2 diabetes, serum level of sLOX-1 was significantly higher than non-diabetic normal control, indicating that LOX-1 expression was increased in diabetes. Serum levels of AGEs and glycoxidized LDL were important determinants of serum sLOX-1 level, and lowering serum AGEs led to a beneficial reduction in serum sLOX-1 concentration. Hence, AGEs was clearly an important ligand of LOX-1 in diabetes mellitus, and experiments were performed to further elucidate the underlying signaling pathway involved in the up-regulation of LOX-1 by AGEs. This was mediated by ligation of AGEs to the receptor for advanced glycation end products (RAGE) and activation of phosphoinositide 3-kinase. Mammalian target of rapamycin was a found to be a key downstream intermediary in AGEs-inducible LOX-1 expression in endothelial cells. I further demonstrated that LOX-1 was also expressed in human renal mesangial cells, and expression was at a low level at basal state but inducible by its ligands. Up-regulation of LOX-1 expression in activated mesangial cells resulted in increased oxidative stress, as well as increased production of proinflammatory cytokines, chemokines and growth factors. These experimental findings would suggest that LOX-1 might potentially be involved in renal inflammation and diabetic nephropathy. The above results collectively suggest that diabetes is associated with increased LOX-1 activation, and LOX-1 may play a role in the development of diabetic complications. Hence, LOX-1 might represent a suitable target for the future development of new strategies for treating and preventing diabetic vascular complications. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

Erratum final three leaves of thesis. / Includes bibliographical references (leaves 266-288). / xvi, 288, [3] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Demonstrates that fatty acids and antioxidants can regulate the low density lipoprotein (LDL) receptor at the level of gene transcription in cultured liver cells. EPA and linoleic acid (PUFAs) are specifically shown to downregulate the LDL receptor compared to saturated and monosaturated fatty acids in the presence or absence of cholesterol. The experiments lead to the discovery that antioxidants can upregulate the LDL receptor in the human HepG2 cells. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Science, 1996

published_or_final_version / Pathology / Master / Master of Philosophy

published_or_final_version / Pathology / Master / Master of Philosophy

[Truncated abstract] The low density lipoprotein receptor-related protein (LRP), a member of the low-density lipoprotein (LDL) receptor gene family is involved in numerous biological processes including lipoprotein metabolism. This thesis concerns investigations into some aspects of LRP metabolism/regulation and possible roles in coronary artery disease (CAD). Specific aims were: to investigate the association between polymorphisms in the LRP gene and in its associated protein, the lipoprotein receptor-associated protein (RAP), with the risk of CAD; to extensively examine the influence of the LRP exon 22 C200T polymorphism on lipid metabolism; to develop and characterise assays for the mRNA expression of LRP and 2 other genes relevant to lipid metabolism, the LDL receptor (LDLR), and HMG CoA reductase (HMGCR); and finally, to apply the latter techniques to studies on the influence of genetic variation in LRP, and dietary and drug interventions, on LRP, LDLR and HMGCR mRNA expression in nucleated blood cells from healthy human subjects. Six hundred CAD subjects and 700 similarly aged controls were genotyped for 8 LRP gene polymorphisms as well as for the RAP V311M polymorphism. ... In the final phase of my studies, I examined the influence of 4 weeks therapy with a cholesterol lowering drug, an HMGCR inhibitor, atorvastatin (20mg daily), on the mRNA expression of LDLR, LRP and HMGCR in human nucleated blood cells. Twelve normal Caucasian male subjects aged 49 ? 5 (SD) years were studied. Plasma total cholesterol and LDL-C decreased by averages of 29 % and 41 % after the 4 week period. This was accompanied by an elevation in LDLR mRNA expression by approximately 30 35 %. In contrast, there was no significant effect on LRP and HMGCR mRNA expression. In conclusion, the original findings in this thesis included: demonstration of a strong influence of the LRP exon 22 C200T polymorphism on coronary artery disease and LDLR expression, but without a clear effect on fasting or postprandial lipid levels; data on the biological variation in LDLR and LRP gene expression in nucleated blood cells from normal subjects; the influence of an oral fat load on the expression viii of these genes, finding that LDLR was significantly depressed; and finally, the observation that statin therapy upregulated LDLR in nucleated blood cells.