UBC Theses and Dissertations
The low-density lipoprotein receptor knock-out mouse : a model for the study of energy balance Ngai, Ying Fai Tiffany
The discovery of leptin and other humoral signals which regulate food intake and energy expenditure has greatly contributed to our understanding of molecular pathways controlling energy homeostasis. Leptin produced by adipocytes, insulin produced by the pancreas, and ghrelin produced by the stomach all contribute to the body’s energy balance. One question remaining is whether the lipid transport system also plays a role. Our hypothesis is that lipid clearance is important in the maintenance of energy homeostasis. The low-density lipoprotein receptor (Ldlr) is a key molecule involved with lipid clearance. The experiments presented in this thesis used the Ldlr-/- mouse to study the Ldlr’s role in energy balance. One aim of this thesis was to provide a detailed analysis of the energy balance phenotype of the Ldlr-/- mouse. Another aim of this thesis was to use the Ldlr-/- mouse to study the potential interaction between Ldlr and the leptin signaling pathway. Adult Ldlr-/- mice and Ldlr+/+ controls on a C57BL/6J background were fed either a chow or a high-fat, high-sucrose Western-type diet (WTD) for eight weeks. Physiological studies of food intake, energy expenditure, activity, heat production, insulin sensitivity, and leptin responsiveness were performed. As well, the effect of these diet interventions on circulating leptin and on leptin gene expression was examined. On the chow diet, Ldlr-/- mice had lower energy expenditure and higher activity levels relative to controls. On the WTD, Ldlr-/- mice gained less weight relative to Ldlr+/+ mice, specifically gaining less fat mass. Increased thermogenesis in Ldlr-/- mice fed the WTD was detected. Additionally, leptin responsiveness was blunted in chow-fed Ldlr-/- mice, suggesting a novel role for the Ldlr pathway that extends to leptin’s regulation of energy balance. In addition to its known role in lipid transport, these results from the Ldlr-/- mouse demonstrate the importance of the Ldlr in regulating energy homeostasis and suggest a direct physiological link between dyslipidemia and energy balance.
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