Obesity is a medical condition in which excess body fat has been accumulated. It is most commonly caused by imbalance between energy intake and energy expenditure (lack of physical activity and lower metabolic rate, etc.). The control of energy metabolism involves multiple tissues and signalling pathways and there is a great need for further understanding of these different interactions. In this study, I use Caenorhabditis elegans to study these complex pathways at the level of a whole organism. The downstream target of mTOR, p70 S6 kinase (S6K), has been implicated in the phosphorylation of multiple substrates and the regulation of growth and metabolism. In this study the worm homolog of S6K, rsks-1, found to be important for fat metabolism. Previous work in our lab found that RSKS-1::GFP is expressed at high levels in a set of sensory neurons and upregulated in ASJ, ASE and BAG sensory neurons in starved worms or mutants with low insulin activity. In this study, I found that the upregulation of rsks-1 expression was affected by serotonin, but not by the other neurotransmitters. Combined with the result that rsks-1 is required for the expression of TGFβ and insulin in ASI, rsks-1 may control dietary sensing by affecting insulin and TGFβ signalling within nervous system. Quantification of fat accumulation by TLC/GC revealed that in comparison to wild type worms, rsks-1 mutants have more than two-fold higher levels of triglycerides. This was confirmed by FT-IR microspectroscopy analysis. rsks-1 mutants also contain disproportionately high levels of C16:1n9 and C18:1n9 lipids compared with wild type worms. Genetic analysis has shown that rsks-1 acts either downstream of, or in parallel to the insulin and TGFβ pathways to affect fat levels. My studies showed that rsks-1 affects fat metabolism by influencing mRNA levels of genes encoding proteins in the β-oxidation pathway. Combined with defects in dietary sensing, fatty acid absorption, fertility and mitochondria function, the loss of rsks-1 activity induced much more energy storage than wild type by making a profound metabolic shift. These results are consistent with the metabolomics data analysis. Tissue specific RNAi showed that rsks-1 was required in many different tissues to regulate fat metabolism. Taken together, it can be concluded that RSKS-1 activity is needed for co-ordination of metabolic states in C. elegans. In order to understand more about the physiology behind fat accumulation, I analysed a mutant, aex-5, that has significantly lowered lipid levels. I found that this defect is associated with a significant reduction in the rate at which dietary fatty acids are taken up from the intestinal lumen. The aex-5 gene, which encodes a Kex2/subtilisin-family, Ca2+-sensitive proprotein convertase, is required for a discrete step in an ultraradian rhythmic phenomenon called the defecation motor program (DMP). Combined with other results, we conclude that aex-5 and other defecation genes may affect fat uptake by promoting the correct distribution of acidity within the intestinal lumen. This dissertation also described how to use Fourier transform infrared (FT-IR) microspectroscopy to detect lipids, proteins and carbohydrates directly in single worm. In conclusion, in this thesis I have uncovered several components that play roles in dietary sensing, fatty acid synthesis, adiposity regulation and fatty acid absorption in C. elegans.

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Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Organisms are constantly balancing energy demand with an adequate supply of oxygen and substrates to sustain metabolic activity. Thermogenesis is an important metabolic process by which endotherms predominately burn lipids to regulate and maintain their body temperatures by balancing heat loss with heat production. Due to their high rates of heat loss, small winter-active mammals, like the North American deer mouse (Peromyscus maniculatus), are constantly challenged with thermogenesis. Deer mice are also native to high-altitude environments, conditions that further complicate the process of thermogenesis due to the inherent reduced oxygen availability. How metabolic substrates are used for fuelling and sustaining thermogenesis at high altitude remains unclear. The goal of my thesis was to examine how lipid metabolism has evolved to sustain heat production in animals living in high-altitude environments. This was achieved by using deer mice native to high- and low-altitudes acclimated to either standard lab conditions or simulated high altitude (cold hypoxia). I demonstrate that during thermogenic capacity (cold-induced V̇O2max), high-altitude deer mice have higher thermogenic lipid oxidation rates compared to their lowland counterparts, which is further increased after cold hypoxia acclimation. Interestingly, these high rates of lipid oxidation were associated with higher circulatory delivery rates of fatty acids and triglycerides to thermo-effector tissues. Specifically, I show that after a bout of cold-induced V̇O2max, fatty acid uptake occurs primarily in the skeletal muscle in control acclimated high-altitude deer mice, and then shifts to brown adipose tissue following acclimation to high altitude conditions. These findings clearly show that in high-altitude deer mice, maximal thermogenesis is reliant on elevated delivery of circulatory lipids to muscle and brown adipose tissue. This research further sheds light on the mechanistic underpinnings responsible for enhanced thermogenic capacity of high-altitude deer mice and capacity for the highest lipid oxidation rates observed in any mammal. / Thesis / Doctor of Philosophy (PhD) / Thermogenesis, the metabolic production of heat, allows endotherms to maintain stable body temperatures in cold environments. However, it was not yet understood how small mammals fuel and sustain heat production in the cold and low oxygen environment of high altitude. My thesis has uncovered how deer mice native to high altitudes have adapted to burning fats at high rates in hypoxia to sustain thermogenesis. My findings show that high delivery rates of fats to heat-generating tissues are responsible for the elevated rates of heat production in high altitude deer mice. My work contributes to our understanding of the inner workings of the fat pathways and how it has evolved to ensure survival in extreme environmental conditions.

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Acylation stimulating protein (ASP) is a plasma protein that significantly increases adipose tissue fat storage. In vivo and in vitro studies have suggested a role for plasma ASP in enhancing postprandial plasma triglyceride (TG) clearance. The primary objective of this study was to examine, for the first time, the postprandial response of plasma ASP and the fate of an exogenous fat source in 8 post-obese and 8 matched control women. This was done through following 13C-labeled high fat breakfast meal (1062 Cal, 67% fat) every 2 hours for 8 hours in 3 plasma pools and in expired breath CO2. The 3 plasma pools were: TG fraction in triglyceride rich lipoproteins (TRL) with sedimentation factor Sf > 400 (referred to as chylomicron-TG), TG fraction in TRL with Sf = 20--400 (referred to as VLDL-TG), and plasma free fatty acid (FFA). The secondary objective was to examine fasting and postprandial resting energy expenditure (REE), thermic effect of food (TEF), carbohydrate to fat oxidation rate and insulin sensitivity, which are factors that have been implicated in the tendency of post-obese women to regain weight. (Abstract shortened by UMI.)

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Obesity and obesity related diseases represent a leading cause of mortality in the United States and worldwide. Our research is oriented towards the role of lipid metabolism in longevity. Adipose triglyceride lipase, or ATGL, is a rate limiting enzyme in the lipolytic pathway. The nematode, C. elegans has many conserved biologic pathways to mammals, and the lipolytic pathway is one of them. The homologues include the insulin receptor (DAF-2), FoxO1 (DAF-16), and ATGL (ATGL-1). In this study, we use C. elegans as a model to study the role of lipolysis in longevity. It has been previously shown in our lab that overexpression of ATGL-1::GFP increases lifespan. To confirm that the increase in longevity was due to the overexpression of ATGL-1, we have used RNA interference to downregulate expression of ATGL-1::GFP. We have corroborated that ATGL-1::GFP worms have longer lifespans, than wildtype N2 worms. We have also found that RNAi control diet does not affect lifespan of ATGL-1::GFP strains. However, ATGL-1::GFP strains on an RNAi GFP diet demonstrate reduced levels of ATGL-1::GFP and have shorter lifespans compared to their control counterparts. Our findings confirm that overexpression of ATGL-1 increases lifespan of C. elegans probably due to its role in reducing fat content.