published_or_final_version / Molecular Biology / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

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

published_or_final_version / Medicine / Master / Master of Philosophy

published_or_final_version / Molecular Biology / Doctoral / Doctor of Philosophy

Finally, two main extensions of this approach were considered - linkage approaches to examine more than two loci, and extending the method in this study to include a test of association.

Gao, Zhibo. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 147-157). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Liu, Xin. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 157-164). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Autoimmune diabetes is a disorder in which the (3-cells in the pancreatic islets of Langerhans are specifically destroyed resulting in absolute insulin deficiency; typically this is a childhood-onset disease, Type 1 Diabetes (T1D). Type 2 Diabetes (T2D) is a metabolic disorder usually developing in adults resulting from defects in insulin secretion and action. Latent Autoimmune Diabetes in Adults (LADA) is a form of diabetes that shares autoimmune disease pathology with T1D but a clinical presentation similar to T2D; LADA patients develop diabetes as adults (>25 years) and do not immediately require insulin treatment for survival. They are therefore often misdiagnosed with T2D. The aims of this work were to characterise immunological and genetic aspects of LADA using a large cohort collected from various patient repositories the United Kingdom to determine if it is a separate disease entity or an age-related extension of T1D. Both T1D and LADA are characterised by autoantibodies to the islet cell protein glutamic acid decarboxylase 65 (GADA) at diagnosis. The persistence and titre of GADA post-diagnosis in LADA was examined at 0.5, 3 and 6 years. GADA persisted in 93% of patients for 6 years; GADA litres decreased between 0.5 and 3 years post-diagnosis and either stabilised or increased again between 3 and 6 years. GADA titre was not associated with age at diagnosis, glycaemic control, β-cell function or other clinical features. GADA titre at 0.5 years was associated with a greater likelihood of requiring more intensive antihyperglycaemic therapy but did not predict therapy or insulin requirement at 3 and 6 years. Autoantibodies against IA-2 plus GADA compared to GADA alone at diagnosis predicted increased therapy requirement by 3 and 6 years and insulin requirement by 3 years postdiagnosis. Variants of the Human Leukocyte Antigen (HLA) genes DRB1 and DQB1, are associated with susceptibility for T1 D. An analysis of these variants in LADA (n = 378) revealed that the predisposing and protective variants in LADA are similar to those reported in T1D; DR3 (in linkage disequilibrium, LD with DQ2) and DR4 (in LD with DQ8) were the main predisposing variants whereas DR2 (in LD with DQ6) was most the protective against LADA. 85% of LADA patients possessed the DR3 and DR4 specificities, compared with 95% seen in T1D, suggesting a reduced predisposition in LADA compared with T1D. Synergistic effects of the DR3 and DR4 specificities occurred in LADA and the DRB1*0401 allele within the DR4 specificity was predisposing to disease, as seen in T1D. No other predisposing variants were identified in LADA. As reported for T1D, DR11, DR13, DQ5, DQ7 and DQ9 were protective against LADA; DQ6 was positively correlated with age at diagnosis. Association analysis of the insulin gene region in LADA (n = 400) showed that the variable number of tandem repeats (VNTR) locus primarily confers susceptibility to disease. Overall, the short Class I alleles predisposed to disease whereas longer Class III alleles conferred dominant protection, as reported in T1D. Fine-structure analysis showed that the Class I haplotypes 'IC+/ID+' and 'ID-' both conferred susceptibility for LADA - unlike in T1D, where the ID- haplotype has been reported to have protective effects. The Class III 'Protective' and Very Protective' haplotypes, conferred equal protection in LADA, as reported forTID. In conclusion; GADA persist post-diagnosis but are not markers for disease progression of LADA. Patterns of susceptibility at the HLA and insulin gene regions in LADA are similar to that reported for T1 D. LADA is likely to represent an age-related extension of T1D rather than a separate disease entity.

Thesis (MSc (Biomedical Technology))--Cape Peninsula University of Technology, 2016. / The early detection of individuals who are at risk of developing type 2 diabetes mellitus (T2DM) would decrease the morbidity and mortality associated with this disease. DNA methylation, the most widely studied epigenetic mechanism, offers unique opportunities in this regard. Aberrant DNA methylation is associated with disease pathogenesis and is observed during the asymptomatic stage of disease. DNA methylation has therefore attracted increasing attention as a potential biomarker for identifying individuals who have an increased risk of developing T2DM. The identification of high risk biomarkers for T2DM could facilitate risk stratification and lifestyle interventions, which could ultimately lead to better ways to prevent, manage and control the T2DM epidemic that is rampant worldwide. The aim of the study was to investigate global DNA methylation as a potential risk factor for T2DM by studying the association between the global DNA methylation levels and hyperglycaemic states. A cross-sectional, quantitative study design, involving 564 individuals of mixed ancestry descent, residing in Bellville South, South Africa was used. Participants were classified as normal, pre-diabetic (impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT)) or diabetic (screen detected diabetic and known diabetics) according to WHO criteria of 1998. DNA was extracted from whole blood using the salt extraction method. The percentage global DNA methylation was measured by an enzyme-linked immunosorbent assay (ELISA). The association between global DNA methylation and hyperglycaemia, as well as other biochemical markers of T2DM was tested in a robust linear regression analysis adjusted for age, gender and smoking.