The prevalence of obesity and type 2 diabetes has increased at alarming rates in recent decades. These diseases are prominent components of the metabolic syndrome, which is characterized by marked dyslipidemia. Adipose tissue contributes to the development of obesity-related diabetes through increased release of hormones and non-esterified fatty acids. The development of sensitive analytical tools for the broad detection of lipid biomolecules, such as liquid chromatographymass spectrometry (LC-MS), has spurred interest in the molecular determinants of the metabolic syndrome. The development of mature adipocytes from precursor fibroblasts—adipogenesis—plays a crucial role in the expansion of adipose tissue in obesity. We profiled differentiating 3T3-L1 pre-adipocytes by LC-MS and found that a class of monoglyceride lipids, monoalkylglycerol ethers (MAGEs), was transiently elevated early in adipogenesis. Upon addition to differentiating cells, MAGE specifically promoted adipocyte maturation and expression of adipogenic gene markers, indicating that MAGEs may be signaling molecules during adipogenesis. The insulin-sensitive glucose transporter, GLUT4, is downregulated during obesity and diabetes. In collaboration with Prof. Barbara Kahn, we studied a transgenic mouse model that overexpressed GLUT4 specifically in adipose tissue (AG4OX) and was protected from developing diabetes. We used LC-MS-based metabolomics to discover a previously undescribed class of bioactive lipids that was highly upregulated in AG4OX adipose tissue. We structurally characterized these lipids as fatty acyl hydroxy fatty acids (FAHFAs) and several positional isomers were chemically synthesized to confirm structural assignments via coelution studies. We discovered that individual FAHFAs, such as 5-palmitoyl-hydroxystearic acid (5-PAHSA), were differentially regulated by the transcription factor ChREBP. Circulating 5-PAHSA levels in mice and humans correlated with ChREBP expression and insulin resistance. In order to explore the biochemical regulation of FAHFAs, we developed an LCMS-based assay to measure FAHFA hydrolysis activity. We identified one enzyme, carboxyl ester lipase (CEL), as the major FAHFA hydrolase in pancreas, where the activity was highest. We confirmed its relevance in vivo by feeding labeled FAHFA to CEL inhibitor-treated mice. In this work we used LC-MS-based metabolomics to discover two lipids, MAGE and FAHFA, along with the CEL pathway, that may help us to better understand the pathogenesis of obesity and diabetes. / Chemistry and Chemical Biology
| Identifer | oai:union.ndltd.org:harvard.edu/oai:dash.harvard.edu:1/10310131 |
| Date | January 2012 |
| Creators | Homan, Edwin |
| Contributors | Saghatelian, Alan |
| Publisher | Harvard University |
| Source Sets | Harvard University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Rights | closed access |
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