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

Inhibitory synaptic transmission within the vestibular circuits plays an essential regulatory role in coordinating vestibular functions. The maturation profile of γ- aminobutyric acid (GABA) synapses in the vestibular system remains unknown. To address this, we first used double immunohistochemistry to document the postnatal expression profile of GABAA receptors in canal-related and saccule-related vestibular nuclear neurons of rats. The proportion of Fos / GABAA receptors α1 subunit doublelabeled neurons progressively increased with age. Whole-cell patch-clamp experiments on brainstem slice preparations were also employed to characterize the developmental properties of these synapses within the medial vestibular nucleus. The frequency of GABAA receptor-mediated miniature inhibitory postsynaptic currents (IPSC) progressively increased during the first two postnatal weeks and reached a plateau thereafter. This is in agreement with an increase in sensitivity to GABAA receptor α1 subunit agonist zolpidem during the same period. The rise time and decay time however decreased by 2-fold. These results suggest that change in the composition of GABAA receptor occurs during the functional maturation of medial vestibular neurons. To further investigate whether GABA receptors contribute to synaptic plasticity in the developing vestibular nucleus, two stimulus protocols were used. Repetitive depolarizing pulses induced long-lasting decrease in the frequency of GABAA receptormediated spontaneous IPSCs between P3 and P7. The probability of inducing such frequency decline of sIPSCs decreased after the first postnatal week. High frequency stimulation on the other hand, induced long-term depression (LTD) of GABAA receptormediated evoked IPSCs between P3 and P5. The probability of inducing LTD decreased after P14. These results indicate that LTD at GABAergic synapses could be easily induced in developing medial vestibular neurons before maturation of GABAergic synaptic transmission. To examine if GABAergic transmission within the vestibular nucleus is crucial for establishment of gravity-related spatial organization, an intervention approach was adopted to perturb GABAergic transmission within the postnatal vestibular nucleus. A slice of Elvax loaded with either GABAA receptor agonist muscimol or antagonist bicuculline was inserted into the fourth ventricle and covered the bilateral vestibular nuclei at different ages. Expression of Fos protein in functionally activated neurons was used to demarcate the topographic spatial map in the inferior olive. The spatial map in subnuclei IOβ and DMCC was disturbed in each adult rat that was implanted with bicuculline- or muscimol-loaded Elvax at P1. However, no change was observed in adult rats that were pretreated with bicuculline or muscimol at P14 or P21. Vestibularrelated behavior tests were also performed. The acquisition of negative geotaxis, an otolith-related orientation reflex, was delayed in postnatal rats pretreated with bicuculline but was advanced in those rats pretreated with muscimol. Furthermore, the acquisition of motor learning, evaluated by rotarod test, was impaired in adult rats treated with bicuculline or muscimol. Taken together, our results indicated that maturation of GABAergic transmission within the vestibular nucleus play important roles in development of spatial recognition and vestibular-related behavior. / published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

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Drug-induced liver injury (DILI) is the major cause of pharmaceutical withdrawal from the market and cholestasis is one of the most common DILI observed. Cholestasis stem from abnormalities in the activity of bile acid transporters, namely the sodium-dependent taurocholate co-transporting polypeptide, Ntcp (Slc10a1), and the bile salt export pump, Bsep (Abcb11). The nuclear receptors, pregnane X receptor (PXR) and farnesoid X receptor (FXR), have been implicated in the regulation of Ntcp and Bsep. The aim of this study was to establish the relative roles of FXR and PXR in the regulation of Ntcp and Bsep, in the rat liver and sandwich cultured rat hepatocytes (SCRH) to establish the usefulness of SCRH as a good model for bile acid transport studies. For this purpose, male Sprague Dawley rats were treated with FXR and PXR ligands and siRNAs. Intraperitoneal (IP) injection of FXR ligand, CDCA, resulted in induction in FXR mRNA levels whereas siRNA treatment knocked down FXR transcript levels. FXR induction decreased Ntcp transcript levels that were reversed in FXR knockdown animals. CDCA treatment resulted in greater than 2-fold increase in Bsep mRNA levels that was absent in FXR knockdown animals. The PXR ligand, PCN, showed an induction in PXR mRNA levels while siRNA treatment resulted in the knockdown in PXR transcript levels. PXR induction did not cause any change in Ntcp and Bsep transcript levels. Furthermore, sandwich cultured rat hepatocytes were used to ascertain if the above in vivo findings are reproducible in vitro. Treatment of hepatocytes with FXR ligand, CDCA, and PXR ligand, PCN, caused greater than 5-fold increase in the respective mRNA levels whereas respective siRNA treatment caused >79% knocked in their transcript levels. FXR induction decreased Ntcp mRNA levels that were ablated in FXR knockdown cultures. FXR induction resulted in a 6-fold increase in Bsep mRNA levels that disappeared in FXR knockdown cultures. On the contrary, PXR induction did not influence the expression levels of Ntcp and Bsep. Taken together these data demonstrate that both FXR and PXR are inducible at mRNA and protein levels in vivo and their expression can be knocked down in the rat liver. Moreover, FXR negatively regulate Ntcp and positively regulate Bsep while PXR does not influence Ntcp and Bsep expression. Finally, the data shows that these in vivo findings can be successfully reproduced in sandwich cultured rat hepatocytes. To conclude, sandwich cultured rat hepatocytes mimic the in vivo situation and provide a good model for bile acid transport studies.

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published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / abstract / Pharmacology / Master / Master of Philosophy

published_or_final_version / abstract / toc / Zoology / Master / Master of Philosophy