Browsing by Subject "Fatty Acids"
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Item Discovering the controls of fatty acid oxidation and ketogenesis(2013-11-08) Foster, Daniel W.Item Ethnic Differences in Fatty Acid Oxidation(2014-02-04) Benjamin, Brian; Wada, Yasuyo; Vega, Gloria; Szuszkiewicz-Garcia, Magdalene; Grundy, ScottINTRODUCTION: Triglyceride levels of African Americans are significantly lower than those of Caucasians. This discrepancy complicates the recognition and diagnosis of metabolic disease in African Americans and represents a paradox in the metabolic health of African Americans. Many reasons for this difference have been explored including increased lipoprotein lipase activity, decreased hepatic lipase activity, and increased suppression of adipocyte lipolysis. Another possible explanation for this triglyceride discrepancy that has been sparsely explored is a difference in fatty acid oxidation between the two groups. The hypothesis of the present study is that the discrepancy in triglycerides can be explained, at least in part, by more efficient beta oxidation of fatty acids in the African American population. METHODS: A pilot study was initiated to examine whether a difference in beta oxidation of fatty acids between the two groups exists by examining the ratio of downstream metabolites of beta oxidation (beta hydroxybutyrate; BHB) to upstream metabolites (nonesterified fatty acids; NEFA). Healthy lean African American and Caucasian males were given a fat bolus (200 mg/kg Schepp's dairy heavy cream) hourly over a ten hour time period (fat tolerance test). BHB, NEFA, and plasma triglycerides were measured throughout the test. The data were plotted against time and area under the curve (AUC) was calculated for each plot using the trapezoid rule. The ratio of BHB to NEFA total AUC was calculated and compared between groups. One volunteer from the Caucasian group was excluded from analysis as an outlier based on fasting BHB levels (Grubb's test p<0.01). Groups were compared using 2 sample t-tests. RESULTS: Preliminary results (n=9 African Americans, n=8 Caucasians) demonstrate a trend, as predicted, for the ratio of BHB AUC to NEFA AUC to be higher in African Americans compared to Caucasians (p<0.05). Additionally, the BHB AUC is significantly higher in African Americans (p<0.05), further supporting the study hypothesis. CONCLUSIONS: Initial results suggest that healthy lean African American men may be more efficient oxidizers of fatty acids when compared to healthy lean Caucasian men. This difference could be a contributing factor to the triglyceride difference observed in African Americans and Caucasians. The study is still ongoing and further recruitment and analysis remains to be done.Item Fat: absorption and malabsorption(1992-04-09) Dietschy, John M.Item [News](1988-05-19) Bosler, Tommy JoyItem Nonalcoholic fatty liver disease (NAFLD) turns 38: what have we learned?(2018-10-05) Horton, Jay D.Item Protein Composition and Subcellular Localization of the De Novo Lipogenic Metabolon(2016-04-18) McKean, William Bennion, Jr.; DeBose-Boyd, Russell A.; Horton, Jay D.; Russell, David W.; Uyeda, KosakuFatty acids are the major components of triglycerides, phospholipids, and sphingolipids. Production of palmitate, the most abundant saturated fatty acid, involves the stepwise actions of three enzymes: ATP citrate lyase, acetyl-CoA carboxylase, and fatty acid synthase. Canonically each enzyme catalyzes discrete reactions, and it is thought that they localize diffusely in cellular cytoplasm separate from one another. If true, transfer of metabolic intermediates must occur through passive diffusion from one lipogenic enzyme to another. Such a model proposes an extremely inefficient and potentially hazardous method of palmitate production. We demonstrated that two related proteins - designated MIG12 and Spot 14 - modulate fatty acid synthesis and triglyceride production by regulating the polymerization and activity of acetyl-CoA carboxylase. To better characterize the relationship between these three proteins, biochemical properties of purified recombinant MIG12, Spot 14, and MIG12:Spot 14 heterodimer were assayed in combination with acetyl-CoA carboxylase. We found that Spot 14 abrogates the ability of MIG12 to polymerize and activate acetyl-CoA carboxylase. Co-immunoprecipitation studies using Spot 14 in rat liver revealed Spot 14 exists in a complex with fatty acid synthase and acetyl-CoA carboxylase. MIG12 and Spot 14 co-immunoprecipitation also revealed that ATP citrate lyase was in association with the complex, suggesting that these proteins can function as scaffolds for the three enzymes required for palmitate synthesis. Studies of the subcellular localization of these lipogenic proteins corroborated a functional interaction between these proteins. Confocal images of MIG12 and acetyl-CoA carboxylase in primary hepatocytes show filamentous structures that are immunofluorescent along junctions between the endoplasmic reticulum and mitochondria. Under high carbohydrate dietary conditions in which lipogenesis is stimulated, these structures expand to include fatty acid synthase, ATP citrate lyase, and Spot 14. They also co-localize around lipid droplets - storage organelles for excess triglycerides. Finally, the structural integrity of this lipogenic complex is shown to require microtubules. Blockade of microtubule formation inhibits proper formation of acetyl-CoA carboxylase structure and decreases total fatty acid synthesis in cells. Combined, these findings support the existence of a functional metabolon complex which facilitates the efficient channeling of fatty acid synthesis intermediates through an enzyme cascade that results in the production of palmitate at functionally relevant locations within the cell.Item The Role of Pyruvate Dehydrogenase in Cell Growth(2014-07-28) Rajagopalan, Kartik N.; Amatruda, James F.; DeBerardinis, Ralph J.; Brown, Michael S.; Lum, LawrenceOtto Warburg's observation that tumor cells have increased rates of glucose uptake and lactate secretion in comparison to normal cells spawned his notion that tumors have dysfunctional mitochondria. However, in addition to metabolizing glucose to lactate, tumors in vivo exhibit mitochondrial glucose oxidation, indicating activity of pyruvate dehydrognase (PDH), which gates entry of glucose derived carbon into the tricarboxylic acid (TCA) cycle. To test whether cells require glucose oxidation for proliferation, the work in this thesis establishes a model wherein PDH activity is suppressed using RNA interference. Small hairpin RNAs against the transcript encoding the PDHE1α protein were cloned into a retroviral vector which allowed doxycycline-inducible control of expression. Metabolism of cancer cells was studied in vitro using a combination of metabolomics and metabolic flux analysis. Growth in monolayer culture was performed in medium containing lipid-replete serum as well as serum in which lipids had been depleted. As expected, suppression of PDH activity reduced flow of carbon from glucose to the TCA cycle and to de novo fatty acid synthesis. Surprisingly, H460 lung cancer cells could tolerate a 60% reduction of PDH flux without any significant effect on proliferation rate, as long as lipids were present in the medium. Further examination of the effects of PDH silencing on the overall network of central carbon metabolism revealed enhanced channeling of carbon from glutamine to fatty acids and an increase in scavenging free fatty acids. Lipid depletion caused a reduction in growth rate of PDH deficient cells, and this defect was completely rescued by supplying free fatty acids to the medium. Together the data indicate that proliferating cells exhibit PDH activity that allows transfer of glucose carbon to citrate and the TCA cycle as well as ultimately into fatty acids. Importantly, suppression of PDH activity limits growth in conditions in which cancer cells do not have access to extracellular lipids. This work illustrates that compensatory pathways that sustain cell proliferation are activated during suppression of mitochondrial oxidation of glucose.Item A Study in SCAR20 Neurologic Disorder Reveals Defective Cellular Lipid Homeostasis(2020-11-23) Datta, Sanchari; Goodman, Joel M.; Henne, W. Mike; Schmid, Sandra; DeBose-Boyd, Russell A.Fatty acids (FAs) are important cellular metabolites that are utilized by the cells to perform important functions such as the generation of ATP, membrane biosynthesis, and cell signaling. Dysregulation in FA processing and storage causes toxic FA accumulation which alters membrane compositions and contributes to metabolic and neurological disorders. Excess lipids are stored as lipid droplets (LDs) which sequester toxic FAs and serve as metabolic buffers to maintain lipid and energy homeostasis. LDs emerge from the endoplasmic reticulum (ER) but how their formation is regulated is not completely understood. Recently, we identified sorting nexin family protein Snx14, implicated in cerebellar ataxia disease SCAR20, as a novel factor that enriches at ER-LD contacts following exogenous FA treatment independently of Seipin and promotes FA-induced LD growth. Loss of Snx14 perturbs LD morphology whereas Snx14 overexpression extends ER-LD contacts and promotes LD biogenesis. Proximity-based APEX2 labeling revealed the enrichment of Snx14 at ER-LD contacts during LD biogenesis. Capitalizing on this APEX technology, we also utilize Snx14-APEX2 localization to dissect the protein composition of ER-LD contact sites. We identify proteins involved in fatty acid activation, desaturation, and triacylglycerol synthesis as being enriched at ER-LD contacts, indicating these contact sites serve as lipogenic sub-domains of the ER network. Furthermore, we identify the major delta-9 FA desaturase SCD1 as a key interacting partner of Snx14. Consistent with this, Snx14-deficient cells are hypersensitive to saturated fatty acid (SFA)-mediated lipotoxic cell death that compromises ER integrity. We show that SCD1 is upregulated in SNX14-KO cells, and Snx14-associated SFA hypersensitivity can be rescued by ectopic SCD1 overexpression. The lipid-associated PXA domain of Snx14 and its interaction with SCD1 are required for Snx14-mediated SFA protection function. Snx14 loss mimics SCD1 inhibition and causes accumulation of free FAs and increased membrane lipid saturation. Altogether these mechanistic insights reveal a role for ER-LD contacts as lipogenic ER sub-domains, and Snx14 as an ER-LD tether with a key role in maintaining cellular FA homeostasis through a functional interaction with SCD1, defects of which may underlie the neuropathology of SCAR20.Item Trans fatty acids: is margarine really better than butter?(1995-03-23) Denke, Margo A.Item [UT News](1987-01-07) Bosler, Tommy JoyItem [UT Southwestern Medical Center News](2013-04-04) Wormser, Deborah