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Title: The crosstalk between Toll-like receptor signalling and cholesterol homeostasis under inflammatory stress
Author: Li, L.
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2013
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It is proposed that dysregulated cholesterol homeostasis resulting from inflammation and the crosstalk that develops between these two factors are important mechanisms for the progression of both atherosclerosis and chronic kidney disease (CKD). This thesis emphasizes the identification of various pathways of inflammation, Toll-like receptors (TLRs) and dysregulated cholesterol homeostasis. These factors are inter-dependent and interact in initiating foam cell formation in the vascular wall and kidney. THP-1 and HK2 cells were used as in vitro cell models. The roles of myeloid differentiation factor 88 (MyD88), the adaptor protein for most TLRs, and nuclear factor kappa B (NFκB) in the regulation of LDL receptor (LDLr), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCoAR) (Chapter 3) and scavenger receptors, SR-A and CD36 (Chapter 6), were investigated in THP-1 macrophages. The roles of the cholesterol sensor and regulator, sterol regulatory element-binding protein (SREBP) and SREBP cleavage activating protein (SCAP), in the regulation of inflammatory responses in THP-1 and HK2 cells were studied in Chapter 4 and 5. Lipid accumulation in the mouse kidney and cells were visualised by Oil Red O staining. Intracellular cholesterol content was assessed by cholesterol measurement. The mRNA and protein expression were examined by real-time RT-PCR and Western blotting. The intracellular translocation of SCAP in the organelles was detected by immunofluorecence and confocal microscopy. The results showed that LPS/TLR4-associated inflammation disrupts cholesterol homeostasis by up-regulating LDLr, HMGCoAR, SR-A and CD36 in both mouse kidney and cell models. Inhibition of MyD88 and NFκB attenuated the up-regulatory effects of LPS on LDLr and HMGCoAR via SCAP/SREBP2 pathway, and also ameliorated the upregulation of CD36 in THP-1 macrophages. Furthermore, it was demonstrated in THP-1 and HK2 cells that SCAP mediated the inflammatory responses via the NFκB signalling pathway and independent of SREBP2 translocation. SCAP is not only a cholesterol sensor, but is also an important regulator of the inflammatory response. These studies improve our current understanding of the mechanisms of crosstalk between inflammation and lipid homeostasis and also suggest that SCAP could be a potential target in control of both inflammation and cholesterol homeostasis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available