College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item NPC1L1 knockout protects against colitis-associated tumorigenesis in mice(Springer Nature, 2015-03-27) He, Jianming; Shin, Hyunsu; Wei, Xing; Kadegowda, Anil Kumar G; Chen, Rui; Xie, Sandy KrystalColorectal cancer is strongly associated with lipid metabolism. NPC1L1, a sterol transporter, plays a key role in modulating lipid homeostasis in vivo. Its inhibitor, ezetimibe, began to be used clinically to lower cholesterol and this caused the great debate on its role in causing carcinogenesis. Here we explored the role of NPC1L1 in colorectal tumorigenesis. Wild-type mice and NPC1L1−/− (NPC1L1 knockout) mice were treated with azoxymethane (AOM)-dextran sodium sulfate (DSS) to induce colitis-associated colorectal tumorigenesis. Mice were sacrificed 10, 15, 18 or 20 weeks after AOM treatment, respectively. Colorectal tumors were counted and analyzed. Plasma lipid concentrations were measured using enzymatic reagent kit. Protein expression level was assayed by western blot. NPC1L1−/− mice significantly had fewer tumors than wild-type. The ratio of malignant/tumor in NPC1L1−/− mice was significantly lower than in wild-type 20 weeks after AOM-DSS treatment. NPC1L1 was highly expressed in the small intestine of wild-type mice but its expression was undetectable in colorectal mucous membranes or tumors in either group. NPC1L1 knockout decreased plasma total cholesterol and phospholipid. NPC1L1−/− mice had significant lower intestinal inflammation scores and expressed inflammatory markers p-c-Jun, p-ERK and Caspase-1 p20 lower than wild-type. NPC1L1 knockout also reduced lymphadenectasis what may be caused by inflammation. NPC1L1 knockout in mice decreased β-catenin in tumors and regulated TGF-β and p-gp in adjacent colons or tumors. There was not detectable change of p53 by NPC1L1 knockout. Our results provide the first evidence that NPC1L1 knockout protects against colitis-associated tumorigenesis. NPC1L1 knockout decreasing plasma lipid, especially cholesterol, to reduce inflammation and decreasing β-catenin, p-c-Jun and p-ERK may be involved in the mechanism.Item The Role of Adipocyte Lipid Droplet Lipolysis in Thermogenesis and Metabolic Health(2017) Shin, Hyunsu; Yu, Liqing; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)My thesis was focused on the role of Comparative Gene Identification-58 (CGI-58)-mediated adipocyte lipid droplet (LD) lipolysis in thermogenesis and metabolic health. LD lipolysis in energy-dissipating brown adipose tissue (BAT) was believed to play a central role in cold-induced non-shivering thermogenesis, but this concept has not been tested in whole animal in vivo. We created a mouse line that lacks BAT CGI-58, a coactivator of Adipose Triglyceride Lipase (ATGL) that initiates the first step of cytosolic LD lipolysis by cleaving a fatty acyl chain from a triglyceride (TG) molecule. We found that BAT-specific CGI-58 knockout (BAT-KO) mice defend against the cold normally when food is absent, despite a defect in BAT LD lipolysis. Interestingly, BAT-KO versus control mice display higher body temperature when food is present during cold exposure. This cold adaptation in BAT-KO mice is associated with increases in BAT glucose uptake, insulin sensitivity, white adipose tissue (WAT) browning, energy expenditure, and sympathetic innervation. To identify the sources of fuels for thermogenesis of BAT-KO mice in the fasted state, we hypothesized that WAT lipolysis is a major source of thermogenic fuels during fasting. To test this hypothesis, we genetically inactivated CGI-58 expression in the whole fat tissues (both BAT and WAT) of mice (FAT-KO mice). We observed that FAT-KO mice are cold sensitive when food is absent, but tolerate cold normally when food is present, demonstrating that WAT lipolysis is essential for cold-induced thermogenesis during fasting and that dietary nutrients can substitute WAT lipolysis for fueling whole-body thermogenesis. Intriguingly, FAT-KO mice display a dramatic increase in cardiac glucose uptake under both basal and insulin-stimulated conditions, which is associated with significant increases in glucose tolerance, insulin sensitivity, and cardiac expression levels of natriuretic peptides. In conclusion, our studies demonstrate that 1) BAT LD lipolysis is not essential for cold-induced whole-body thermogenesis due to increased BAT uptake of circulating fuels and WAT browning; 2) WAT lipolysis is required for fueling thermogenesis during fasting; and 3) Adipose lipolysis is critically implicated in whole-body energy metabolism and cardiac function.Item The Potential Role of Milk-Fat-Globule Membrane (MFGM) Proteins in Regulating the Size of Milk-Lipid Droplets(2012) Shin, Hyunsu; Mather, Ian H; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The aim of this thesis was to identify protein factors that may regulate the size of lipid droplets in milk. To address this hypothesis, the relative amounts of specific MFGM proteins on lipid droplets fractionated according to size were measured. Protein amounts were estimated by quantitative western blotting and confocal microscopy. By quantitative confocal microscopy, small lipid droplets (<1.26 um) contained more XOR, BTN, adipophilin (ADPH) and fatty acid binding protein (FABP) per surface area than medium (>1.26 to <2.8 um) or large (>2.8 um) sized droplets. Milk-fat-globule-EFG-8 (MFG-E8) protein was more evenly distributed on small, medium and large droplets. In contrast CD36, in both cow and mouse milk, was concentrated on small droplets and absent from large droplets. Based on these data, we postulate that CD36 possibly association with FABP may have a function in small lipid droplet secretion by localizing excessively on the small lipid droplets.