Animal & Avian Sciences Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2741
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Item Investigating Copper Acquisition And Delivery via Transporters and a Pharmacological Chaperone in Copper-Deficient Worms and Mice(2019) Yuan, Sai; Kim, Byung-Eun; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Copper (Cu) is a key micronutrient required for a variety of essential biochemical pathways. Systemic or tissue-specific Cu-deficiencies, caused by insufficient dietary Cu uptake or mutations in Cu transporting genes, result in impaired growth, neuropathy, ataxia, hypopigmentation, osteoporosis and anemia-like symptoms in mammals. How organisms regulate Cu homeostasis at the systemic levels in response to Cu deficiencies remain elusive. In this study, we use Caenorhabditis elegans (C. elegans), a genetically tractable, multi-tissue metazoan to explore Cu homeostasis and investigate these unknowns. The high-affinity Cu transporters encoded by CTR family genes are required for dietary Cu uptake and maintaining systemic Cu balance from yeast to mammals. However, little is known about Cu acquisition mechanisms in C. elegans. We identified ten CTR ortholog genes in C. elegans; of these, chca-1 was functionally characterized. Cu availability regulates transcription of chca-1 in both the intestine and hypodermis, and chca-1 is essential for normal growth, and reproduction in the worm. Additionally, altered Cu balance caused by the loss of CHCA-1 results in defects in Cu-responsive avoidance behavior. Identification of this CTR-like gene in C. elegans, which appears to be essential for normal Cu homeostasis in the worm, illustrates the importance of Cu delivery via CHCA-1 for normal metazoan development and behavioral phenotypes. In addition, we show that a Cu-binding pharmacological chaperone, elesclomol (ES), fully restores the developmental defects and Cu deficiencies in chca-1-depleted worms, as well as the lethality in worms lacking cua-1 expression (Cu exporter ATP7A ortholog), suggesting ES is able to efficiently deliver Cu from dietary sources to peripheral tissues through the intestine in C. elegans. Our study was further expanded to mammalian models such as cardiac-specific Ctr1-depleted (Ctr1hrt/hrt) mice. We found that ES administration fully restores the postnatal lethality, developmental defects and cardiac hypertrophy found in Ctr1hrt/hrt mice, as well as rescuing the secondary systemic Cu homeostasis responses, including aberrant ATP7A protein levels in the liver and intestine. Moreover, ES shows the potential ability to transport Cu across the blood-brain-barrier in in vitro studies. These results illustrate the capability of ES to rescue systemic Cu deficiency in worms and mice, independent of the presence of functional Cu transporters, and shed light on the therapeutic usage of ES in Cu-deficient human diseases.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 Denovo synthesized fatty acids as regulators of milk fat synthesis(2011) Vyas, Diwakar; Erdman, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objectives of the dissertation research were to determine the role of denovo synthesized fatty acids (DNFA) in the regulation of milk fat synthesis. Milk fat responses to increasing amounts of short- and medium-chain fatty acids (SMCFA), added in the proportion as synthesized denovo, were studied in lactating dairy cows. The results showed a significant linear increase in milk fat concentration with SMCFA supplementation. However, milk fat yield was similar for all treatments. A subsequent study was aimed at increasing the availability of SMCFA during trans-10, cis-12 CLA-induced milk fat depression (MFD) in lactating dairy cows to determine whether SMCFA can rescue part of CLA-induced MFD. Post-ruminal infusion of butterfat (BF) was used as a source of SMCFA. The BF treatment was compared to a mixture of fats containing only the long-chain FA (LCFA) with or without trans-10, cis-12 CLA infusion. Milk fat content and yield were significantly reduced with trans-10, cis-12 CLA. However, increased availability of SMCFA with BF infusion had no effects on milk fat yield and concentration. Trans-10, cis-12 CLA significantly reduced the mRNA expression of transcription factor SREBP-1c along with its downstream targets including ACC,FASN, LPL, SCD and AGPAT. The increased availability of SMCFA had no effect on either lipogenic gene or protein expression suggesting that nutritional manipulation was not sufficient to rescue trans-10, cis-12 CLA-induced MFD. Finally, the effects of combination of a Rosiglitazone (ROSI), a PPAR-γ agonist, and trans-10, cis-12 CLA were examined on mammary and hepatic lipogenesis in lactating mice. Mammary lipogenesis was significantly reduced with trans-10, cis-12 CLA, reducing the milk fat content and mRNA expression of lipogenic transcription factors SREBP1-c and PPAR- γ. Trans-10, cis-12 CLA significantly increased hepatic lipid accumulation, while the mRNA expression of SREBP1-c and PPAR- γ were not altered. On the contrary, ROSI had no effects on mammary lipogenesis. However, ROSI significantly rescued trans-10, cis-12 CLA-induced hepatic steatosis.