Thesis (M.A.) -- Boston University, 2013. / Increased free fatty acid (FFA) flux from adipocytes due to increased lipolysis, has a key contribution in the pathophysiology of metabolic disease. There is a lack of knowledge of the molecular components which determine the TG storing capacity and lipolysis in adipocytes. Studies from our lab and others have demonstrated the role of a lipid droplet associated protein, Fat Specific Protein 27 (FSP27, also called CIDEC), in regulating triglyceride accumulation and lipolysis in adipocytes, but its mechanism of action remains elusive. In the present study, we used cultured human primary adipocytes to define the role of FSP27 in regulating both basal and isoproterenol-stimulated lipolysis. Using a combination of RNAi and adenoviral mediated overexpression techniques, we have shown that FSP27 regulates ATGL-mediated lipolysis by down-regulating gene and protein expression of ATGL. Furthermore, our data shows that FSP27-mediated triglyceride accumulation is suppressed in the absence of ATGL. Our results support a model whereby FSP27 regulates ATGL-mediated lipolysis to accumulate triglycerides in human adipocytes

Fibroblast Growth Factor (FGF) 21 is a liver-derived endocrine factor with multiple metabolic effects on glucose and lipid homeostasis in animals. The adipose tissue has been proposed as a major target of FGF21, where it enhances glucose uptake and modulates lipolysis as well as thermogenesis. However, the molecular mechanisms underlying the pleiotropic effects of FGF21 in adipocytes and the physiological roles of FGF21 in regulating energy homeostasis remain poorly characterized. Therefore, the present study aimed to investigate: 1) the signal transduction pathway whereby FGF21 enhances glucose uptake in white adipocytes; 2) the role of FGF21 in lipolysis in both mouse and human white adipose tissues (WAT) and its underlying mechanisms involved; 3) the phenotypes of FGF21 knockout (KO) mice with respect to energy expenditure and adiposity under both standard chow and high fat diet. Key findings: 1. In vitro studies demonstrated that extracellular signal-regulated kinases (ERK1/2) play an obligatory role in mediating FGF21-induced upregulation of glucose transporter-1 (GLUT1) expression and hence elevation of glucose uptake in 3T3-L1 adipocytes. 2. Chromatin immunoprecipitation assay revealed that Serum Response Factor (SRF) and ETS-like protein-1 (Elk-1), the two transcription factors which are known as the downstream targets of ERK1/2, were recruited to the endogenous GLUT1 promoter in adipocytes. A conserved binding motif for these two transcription factors was also identified in the GLUT1 promoter responsive to FGF21 stimulation in 3T3-L1 adipocytes by site-directed mutagenesis and luciferase assay. 3. In WAT of diet-induced obese mice, FGF21-evoked downstream signaling events, including the phosphorylation of ERK1/2 and SRF/Elk-1, the upregulation of GLUT1, and the increased glucose uptake, were markedly blunted compared to lean controls, suggesting the existence of “FGF21 resistance” in obesity. 4. In vivo and ex vivo studies on fasted wild type and FGF21 KO mice demonstrated that FGF21 acutely suppressed basal and forskolin-stimulated lipolysis in WAT. 5. FGF21-inhibited lipolysis was mediated by Akt-dependent reduction of cyclic adenosine monophosphate (cAMP) levels in both mouse and human WAT. 6. FGF21 KO mice were resistant to diet- and aging-induced obesity, which was attributed to decreased fat mass. The increased lipolysis and fatty acid oxidation in FGF21 KO mice may explain in part the lean phenotype of FGF21 KO mice. Conclusions: These results collectively suggest FGF21 as a key modulator of glucose and lipid metabolism in WAT, by activation of ERK1/2 kinase and Akt respectively. FGF21 and its signaling components may represent potential targets for the future development of new strategies for treating obesity and its medical complications. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

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The present study has tested the hypothesis that leptin receptors are localized in caveolae and that caveolae are involved in the leptin-induced stimulation of lipolysis in 3T3-L1 adipocytes. Leptin, a peptide hormone, is secreted primarily by adipocytes and has been postulated to regulate food intake and energy expenditure via hypothalamic-mediated effects. Exposure to leptin increases the lipolytic activity in 3T3-L1 adipocytes. We isolated caveolae from 3T3-L1 adipocytes using a detergent free sucrose gradient centrifugation method. Leptin receptors were localized in the same gradient fraction as caveolin-1. Confocal microscopic studies demonstrated the colocalization of leptin receptors with caveolin-1 in the plasma membrane, indicating distribution of leptin receptors in the caveolae. We disrupted caveolae by treating cells with methyl--cyclodextrin and found that leptin induced lipolytic activity was reduced after caveolae disruption, indicating an important role of caveolae in the signaling mechanism of leptin.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains vii, 45 p. : ill. Includes abstract. Includes bibliographical references (p. 37-45).

This document only includes an excerpt of the corresponding thesis or dissertation. To request a digital scan of the full text, please contact the Ruth Lilly Medical Library's Interlibrary Loan Department (rlmlill@iu.edu).

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