Effect of noradrenaline on triacylglycerol synthesis in rat brown adipocytes.
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ABSTRACT:
SUBMITTER: Baht HS
PROVIDER: S-EPMC1138371 | biostudies-other | 1989 Mar
REPOSITORIES: biostudies-other
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Project description:Adenosine deaminase (1 unit/ml) potentiated the lipolytic action of noradrenaline in adipocytes isolated from brown adipose tissue of 1- and 6-week-old rats by decreasing the EC50 (concn. giving 50% of maximal effect) for noradrenaline by 3-4-fold. With cells from neonatal rabbit tissue, adenosine deaminase only had a small, non-significant, effect on the EC50 for noradrenaline. Lipolysis in rat brown adipocytes was inhibited by low concentrations of N6-phenylisopropyladenosine (PIA). Rabbit cells were far less sensitive to PIA. PIA, prostaglandin E1 and nicotinate all inhibited noradrenaline-stimulated respiration in rat brown adipocytes. Hypothyroidism diminished the maximum response of respiration and lipolysis to noradrenaline in rat cells and increased the EC50 for noradrenaline. Responsiveness of lipolysis to noradrenaline was particularly decreased in hypothyroidism and was partially restored by addition of adenosine deaminase. Lipolysis in cells from hypothyroid rats was more sensitive to the anti-lipolytic action of PIA. Bordetella pertussis toxin increased lipolysis in the presence of PIA, suggesting an involvement of the Ni guanine-nucleotide-binding protein in the control of brown-adipocyte metabolism.
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Project description:Patatin-Like Phospholipase Domain Containing 2 (PNPLA2)/Adipose Triglyceride Lipase (ATGL) and PNPLA3/Adiponutrin are close paralogs that appear to have opposite functions on triacylglycerol (TAG) mobilization and storage. PNPLA2/ATGL is a major triglyceride lipase in adipose tissue and liver, whereas a common human variant of PNPLA3, I148M, greatly increases risk of hepatosteatosis. Nonetheless, the function of PNPLA3 and the mechanism by which the I148M variant promotes TAG accumulation are poorly understood. Here we demonstrate that PNPLA3 strongly interacts with ?/? hydrolase domain-containing 5 (ABHD5/CGI-58), an essential co-activator of PNPLA2/ATGL. Molecular imaging experiments demonstrate that PNPLA3 effectively competes with PNPLA2/ATGL for ABHD5, and that PNPLA3 I148M is more effective in this regard. Inducible overexpression of PNPLA3 I148M greatly suppressed PNPLA2/ATGL-dependent lipolysis and triggered massive TAG accumulation in brown adipocytes, and these effects were dependent on ABHD5. The interaction of PNPLA3 and ABHD5 can be regulated by fatty acid supplementation and synthetic ABHD5 ligands, raising the possibility that this interaction might be targeted for treatment of fatty liver disease.
| S-EPMC6730670 | biostudies-literature
Project description:1. Adipocytes were isolated from the interscapular brown fat and the epididymal white fat of normal, streptozotocin-diabetic and hypothyroid rats. 2. Measurements were made of the maximum rate of triacylglycerol synthesis by monitoring the incorporation of [U-14C]glucose into acylglycerol glycerol in the presence of palmitate (1 mM) and insulin (4 nM) and of the activities of the following triacylglycerol-synthesizing enzymes: fatty acyl-CoA synthetase (FAS), mitochondrial and microsomal forms of glycerolphosphate acyltransferase (GPAT), dihydroxyacetonephosphate acyltransferase (DHAPAT), monoacylglycerol phosphate acyltransferase (MGPAT), Mg2+-dependent phosphatidate phosphohydrolase (PPH) and diacylglycerol acyltransferase (DGAT). 3. FAS activity in brown adipocytes was predominantly localized in the mitochondrial fraction, whereas a microsomal localization of this enzyme predominated in white adipocytes. Subcellular distributions of the other enzyme activities in brown adipocytes were similar to those shown previously with white adipocytes [Saggerson, Carpenter, Cheng & Sooranna (1980) Biochem. J. 190, 183-189]. 4. Relative to cell DNA, brown adipocytes had lower activities of triacylglycerol-synthesizing enzymes and showed lower rates of metabolic flux into acylglycerols than did white adipocytes isolated from the same animals. 5. Diabetes decreased both metabolic flux into acylglycerols and the activities of triacylglycerol-synthesizing enzymes in white adipocytes. By contrast, although diabetes decreased metabolic flux into brown-adipocyte acylglycerols by 80%, there were no decreases in the activities of triacylglycerol-synthesizing enzymes, and the activity of PPH was significantly increased. 6. Hypothyroidism increased metabolic flux into acylglycerols in both cell types, and increased activities of all triacylglycerol-synthesizing enzymes in brown adipocytes. By contrast, in white adipocytes, although hypothyroidism increased the activities of FAS, microsomal GPAT and DGAT, this condition decreased the activities of mitochondrial GPAT and PPH. 7. It was calculated that the maximum capabilities for fatty acid oxidation and esterification are approximately equal in brown adipocytes. In white adipocytes esterification is predominant by approx. 100-fold. 8. Diabetes almost abolished incorporation of [U-14C]glucose into fatty acids in both adipocyte types. Hypothyroidism increased fatty acid synthesis in white and brown adipocytes by 50% and 1000% respectively.
| S-EPMC1148859 | biostudies-other
Project description:Murine embryonic fibroblasts were isolated from WT and DGAT1,DGAT2-KO (D1D2KO) animals. mRNA was isolated from cells untreated (UNDIFF) or treated (DIFF) according to standard differentiation protocol for adipocytes (Harris, C, et al. JLR 2011).
2011-01-31 | GSE26624 | GEO
Project description:Murine embryonic fibroblasts were isolated from WT and DGAT1,DGAT2-KO (D1D2KO) animals. mRNA was isolated from cells untreated (UNDIFF) or treated (DIFF) according to standard differentiation protocol for adipocytes (Harris, C, et al. JLR 2011). 12 Samples total: 3 biological replicates of 3 undifferentiated wild type and D1D2KO mice and 3 biological replicates of 3 differentiated wild type and D1D2KO mice.
2011-01-31 | E-GEOD-26624 | biostudies-arrayexpress
Project description:The total contribution of the acyl CoA:diacylglycerol acyltransferase (DGAT) enzymes, DGAT1 and DGAT2, to mammalian triacylglycerol (TG) synthesis has not been determined. Similarly, whether DGAT enzymes are required for lipid droplet (LD) formation is unknown. In this study, we examined the requirement for DGAT enzymes in TG synthesis and LDs in differentiated adipocytes with genetic deletions of DGAT1 and DGAT2. Adipocytes with a single deletion of either enzyme were capable of TG synthesis and LD formation. In contrast, adipocytes with deletions of both DGATs were severely lacking in TG and did not have LDs, indicating that DGAT1 and DGAT2 account for nearly all TG synthesis in adipocytes and appear to be required for LD formation during adipogenesis. DGAT enzymes were not absolutely required for LD formation in mammalian cells, however; macrophages deficient in both DGAT enzymes were able to form LDs when incubated with cholesterol-rich lipoproteins. Although adipocytes lacking both DGATs had no TG or LDs, they were fully differentiated by multiple criteria. Our findings show that DGAT1 and DGAT2 account for the vast majority of TG synthesis in mice, and DGAT function is required for LDs in adipocytes, but not in all cell types.
| S-EPMC3284159 | biostudies-literature
Project description:1. Brown adipocytes were isolated from the interscapular depot of male rats maintained at approx. 21 degrees C. In some experiments parallel studies were made with white adipocytes from the epididymal depot. 2. Insulin increased and noradrenaline decreased [U-14C]glucose incorporation into fatty acids by brown adipocytes. Brown adipocytes differed from white adipocytes in that exogenous fatty acid (palmitate) substantially decreased fatty acid synthesis from glucose. Both noradrenaline and insulin increased lactate + pyruvate formation by brown adipocytes. Brown adipocytes converted a greater proportion of metabolized glucose into lactate + pyruvate and a smaller proportion into fatty acids than did white adipocytes. 3. In brown adipocytes, when fatty acid synthesis from [U-14C]glucose was decreased by noradrenaline or palmitate, incorporation of 3H2O into fatty acids was also decreased to an extent which would not support proposals for extensive recycling into fatty acid synthesis of acetyl-CoA derived from fatty acid oxidation. 4. In the absence of glucose, [U-14C]lactate was a poor substrate for lipogenesis in brown adipocytes, but its use was facilitated by glucose. When brown adipocytes were incubated with 1 mM-lactate + 5 mM-glucose, lactate-derived carbon generally provided at least 50% of the precursor for fatty acid synthesis. 5. Both insulin and noradrenaline increased [U-14C]glucose conversion into CO2 by brown adipocytes (incubated in the presence of lactate) and, in combination, stimulation of glucose oxidation by these two agents showed synergism. Rates of 14CO2 formation from glucose by brown adipocytes were relatively small compared with maximum rates of oxygen consumption by these cells, suggesting that glucose is unlikely to be a major substrate for thermogenesis. 6. Brown adipocytes from 6-week-old rats had considerably lower maximum rates of fatty acid synthesis, relative to cell DNA content, than white adipocytes. By contrast, rates of fatty acid synthesis from 3H2O in vivo were similar in the interscapular and epididymal fat depots. Expressed relative to activities of fatty acid synthase or ATP citrate lyase, however, brown adipocytes synthesized fatty acids as effectively as did white adipocytes. It is suggested that the cells most active in fatty acid synthesis in the brown adipose tissue are not recovered fully in the adipocyte fraction during cell isolation. Differences in rates of fatty acid synthesis between brown and white adipocytes were less apparent at 10 weeks of age.
| S-EPMC1149061 | biostudies-other
Project description:The effect of human plasma lipoproteins on lipogenesis from glucose has been studied in isolated rat adipocytes. The very-low-density lipoproteins increased lipogenesis specifically, whereas low-density lipoproteins and high-density lipoproteins were without effect. Such stimulation could be reproduced with partially delipidated very-low-density lipoproteins. Nod-esterified fatty acids and glycerol were also without effect. Pretreatment of the adipocytes with trypsin did not alter the effect of very-low-density lipoprotein. The presence of Ca2+ was required for the full activation of lipogenesis. The synthesis of acylglycerol fatty acids and of acylglycerol glycerol were equally increased. The effect of very-low-density lipoprotein was not additive to that of insulin. It is suggested that very-low-density lipoprotein may directly stimulate lipogenesis in fat-cells, particularly in states when the lipoproteins are present at high concentration in the circulation.
| S-EPMC1186217 | biostudies-other
Project description:Aims/hypothesisIn mammals, the evolutionary conserved family of Mg(2+)-dependent phosphatidate phosphatases (PAP1), involved in phospholipid and triacylglycerol synthesis, consists of lipin-1, lipin-2 and lipin-3. While mutations in the murine Lpin1 gene cause lipodystrophy and its knockdown in mouse 3T3-L1 cells impairs adipogenesis, deleterious mutations of human LPIN1 do not affect adipose tissue distribution. However, reduced LPIN1 and PAP1 activity has been described in participants with type 2 diabetes. We aimed to characterise the roles of all lipin family members in human adipose tissue and adipogenesis.MethodsThe expression of the lipin family was analysed in adipose tissue in a cross-sectional study. Moreover, the effects of lipin small interfering RNA (siRNA)-mediated depletion on in vitro human adipogenesis were assessed.ResultsAdipose tissue gene expression of the lipin family is altered in type 2 diabetes. Depletion of every lipin family member in a human Simpson-Golabi-Behmel syndrome (SGBS) pre-adipocyte cell line, alters expression levels of adipogenic transcription factors and lipid biosynthesis genes in early stages of differentiation. Lipin-1 knockdown alone causes a 95% depletion of PAP1 activity. Despite the reduced PAP1 activity and alterations in early adipogenesis, lipin-silenced cells differentiate and accumulate neutral lipids. Even combinatorial knockdown of lipins shows mild effects on triacylglycerol accumulation in mature adipocytes.Conclusions/interpretationOverall, our data support the hypothesis of alternative pathways for triacylglycerol synthesis in human adipocytes under conditions of repressed lipin expression. We propose that induction of alternative lipid phosphate phosphatases, along with the inhibition of lipid hydrolysis, contributes to the maintenance of triacylglycerol content to near normal levels.
| S-EPMC4969345 | biostudies-literature
Project description:The metabolic utilization of 14C-labelled acetate, pyruvate, lactate and glucose by isolated epididymal fat-cells was compared in two groups of rats fed ad libitum, one group young and lean (150-200 g body wt.), the other older and spontaneously obese (500-650 g body wt.). The influence of unlabelled glucose (6 mM) and insulin on substrate utilization by adipocytes was also studied. (1) Pyruvate and lactate were found to be good precursors for fatty-acid synthesis in small fat-cells, but not in larger fat-cells. On the other hand, lactate conversion into CO2 and the glycerol moiety of acylglycerols proceeded activity in both types of cells, and in some cases, it even exceeded the rates of glucose utilization. (2) The addition of glucose or glucose plus insulin, but not insulin alone, enhanced the metabolism of acetate, pyruvate and lactate in both types of fat-cells. (3) Fatty-acid synthesis de novo in large fat-cells was markedly decreased regardless of the substrate utilized. These findings point to lactate as a significant precursor for triacylglycerol synthesis in adipocytes. Furthermore, decreased fatty-acid synthesis de novo appears to be an acquired metabolic deficiency of enlarging adipocytes, independent of precursor substrate availability.
| S-EPMC1162760 | biostudies-other