1
|
Shi Y, Pizzini J, Wang H, Das F, Abdul Azees PA, Ghosh Choudhury G, Barnes JL, Zang M, Weintraub ST, Yeh CK, Katz MS, Kamat A. β2-Adrenergic receptor agonist induced hepatic steatosis in mice: modeling nonalcoholic fatty liver disease in hyperadrenergic states. Am J Physiol Endocrinol Metab 2021; 321:E90-E104. [PMID: 34029162 PMCID: PMC8321826 DOI: 10.1152/ajpendo.00651.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Revised: 04/23/2021] [Accepted: 05/08/2021] [Indexed: 12/11/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disorders ranging from hepatic steatosis [excessive accumulation of triglycerides (TG)] to nonalcoholic steatohepatitis, which can progress to cirrhosis and hepatocellular carcinoma. The molecular pathogenesis of steatosis and progression to more severe NAFLD remains unclear. Obesity and aging, two principal risk factors for NAFLD, are associated with a hyperadrenergic state. β-Adrenergic responsiveness in liver increases in animal models of obesity and aging, and in both is linked to increased hepatic expression of β2-adrenergic receptors (β2-ARs). We previously showed that in aging rodents intracellular signaling from elevated hepatic levels of β2-ARs may contribute to liver steatosis. In this study we demonstrate that injection of formoterol, a highly selective β2-AR agonist, to mice acutely results in hepatic TG accumulation. Further, we have sought to define the intrahepatic mechanisms underlying β2-AR mediated steatosis by investigating changes in hepatic expression and cellular localization of enzymes, transcription factors, and coactivators involved in processes of lipid accrual and disposition-and also functional aspects thereof-in livers of formoterol-treated animals. Our results suggest that β2-AR activation by formoterol leads to increased hepatic TG synthesis and de novo lipogenesis, increased but incomplete β-oxidation of fatty acids with accumulation of potentially toxic long-chain acylcarnitine intermediates, and reduced TG secretion-all previously invoked as contributors to fatty liver disease. Experiments are ongoing to determine whether sustained activation of hepatic β2-AR signaling by formoterol might be utilized to model fatty liver changes occurring in hyperadrenergic states of obesity and aging, and thereby identify novel molecular targets for the prevention or treatment of NAFLD.NEW & NOTEWORTHY Results of our study suggest that β2-adrenergic receptor (β2-AR) activation by agonist formoterol leads to increased hepatic TG synthesis and de novo lipogenesis, incomplete β-oxidation of fatty acids with accumulation of long-chain acylcarnitine intermediates, and reduced TG secretion. These findings may, for the first time, implicate a role for β2-AR responsive dysregulation of hepatic lipid metabolism in the pathogenetic processes underlying NAFLD in hyperadrenergic states such as obesity and aging.
Collapse
Affiliation(s)
- Yun Shi
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Jason Pizzini
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Hanzhou Wang
- Department of Comprehensive Dentistry, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Falguni Das
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Parveez Ahamed Abdul Azees
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Department of Comprehensive Dentistry, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Goutam Ghosh Choudhury
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Jeffrey L Barnes
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Mengwei Zang
- Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, Texas
- Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Geriatric Research, Education and Clinical Center, Audie L. Murphy Division, South Texas Veterans Health Care System, San Antonio, Texas
| | - Susan T Weintraub
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
| | - Chih-Ko Yeh
- Department of Comprehensive Dentistry, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Geriatric Research, Education and Clinical Center, Audie L. Murphy Division, South Texas Veterans Health Care System, San Antonio, Texas
| | - Michael S Katz
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Geriatric Research, Education and Clinical Center, Audie L. Murphy Division, South Texas Veterans Health Care System, San Antonio, Texas
| | - Amrita Kamat
- Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas
- Geriatric Research, Education and Clinical Center, Audie L. Murphy Division, South Texas Veterans Health Care System, San Antonio, Texas
| |
Collapse
|
2
|
Eaton JM, Mullins GR, Brindley DN, Harris TE. Phosphorylation of lipin 1 and charge on the phosphatidic acid head group control its phosphatidic acid phosphatase activity and membrane association. J Biol Chem 2013; 288:9933-9945. [PMID: 23426360 DOI: 10.1074/jbc.m112.441493] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The lipin gene family encodes a class of Mg(2+)-dependent phosphatidic acid phosphatases involved in the de novo synthesis of phospholipids and triglycerides. Unlike other enzymes in the Kennedy pathway, lipins are not integral membrane proteins, and they need to translocate from the cytosol to intracellular membranes to participate in glycerolipid synthesis. The movement of lipin 1 within the cell is closely associated with its phosphorylation status. Although cellular analyses have demonstrated that highly phosphorylated lipin 1 is enriched in the cytosol and dephosphorylated lipin 1 is found on membranes, the effects of phosphorylation on lipin 1 activity and binding to membranes has not been recapitulated in vitro. Herein we describe a new biochemical assay for lipin 1 using mixtures of phosphatidic acid (PA) and phosphatidylethanolamine that reflects its physiological activity and membrane interaction. This depends on our observation that lipin 1 binding to PA in membranes is highly responsive to the electrostatic charge of PA. The studies presented here demonstrate that phosphorylation regulates the ability of the polybasic domain of lipin 1 to recognize di-anionic PA and identify mTOR as a crucial upstream signaling component regulating lipin 1 phosphorylation. These results demonstrate how phosphorylation of lipin 1 together with pH and membrane phospholipid composition play important roles in the membrane association of lipin 1 and thus the regulation of its enzymatic activity.
Collapse
Affiliation(s)
- James M Eaton
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
| | - Garrett R Mullins
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
| | - David N Brindley
- Signal Transduction Research Group, Department of Biochemistry, University of Alberta, Edmonton T6G 2S2, Canada
| | - Thurl E Harris
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908.
| |
Collapse
|
3
|
Haller JF, Krawczyk SA, Gostilovitch L, Corkey BE, Zoeller RA. Glucose-6-phosphate isomerase deficiency results in mTOR activation, failed translocation of lipin 1α to the nucleus and hypersensitivity to glucose: Implications for the inherited glycolytic disease. Biochim Biophys Acta Mol Basis Dis 2011; 1812:1393-402. [PMID: 21787864 DOI: 10.1016/j.bbadis.2011.07.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 07/10/2011] [Accepted: 07/12/2011] [Indexed: 11/30/2022]
Abstract
Inherited glucose-6-phosphate isomerase (GPI) deficiency is the second most frequent glycolytic erythroenzymopathy in humans. Patients present with non-spherocytic anemia of variable severity and with neuromuscular dysfunction. We previously described Chinese hamster (CHO) cell lines with mutations in GPI and loss of GPI activity. This resulted in a temperature sensitivity and severe reduction in the synthesis of glycerolipids due to a reduction in phosphatidate phosphatase (PAP). In the current article we attempt to describe the nature of this pleiotropic effect. We cloned and sequenced the CHO lipin 1 cDNA, a gene that codes for PAP activity. Overexpression of lipin 1 in the GPI-deficient cell line, GroD1 resulted in increased PAP activity, however it failed to restore glycerolipid biosynthesis. Fluorescence microscopy showed a failure of GPI-deficient cells to localize lipin 1α to the nucleus. We also found that glucose-6-phosphate levels in GroD1 cells were 10-fold over normal. Lowering glucose levels in the growth medium partially restored glycerolipid biosynthesis and nuclear localization of lipin 1α. Western blot analysis of the elements within the mTOR pathway, which influences lipin 1 activity, was consistent with an abnormal activation of this system. Combined, these data suggest that GPI deficiency results in an accumulation of glucose-6-phosphate, and possibly other glucose-derived metabolites, leading to activation of mTOR and sequestration of lipin 1 to the cytosol, preventing its proper functioning. These results shed light on the mechanism underlying the pathologies associated with inherited GPI deficiency and the variability in the severity of the symptoms observed in these patients.
Collapse
Affiliation(s)
- Jorge F Haller
- Department of Physiology and Biophysics, Boston University School of Medicine, USA
| | | | | | | | | |
Collapse
|
4
|
Suppression of cardiac phosphatidate phosphohydrolase 1 activity and lipin mRNA expression in Zucker diabetic fatty rats and humans with type 2 diabetes mellitus. Biochem Biophys Res Commun 2009; 390:165-70. [DOI: 10.1016/j.bbrc.2009.09.108] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2009] [Accepted: 09/24/2009] [Indexed: 11/20/2022]
|
5
|
Harris TE, Huffman TA, Chi A, Shabanowitz J, Hunt DF, Kumar A, Lawrence JC. Insulin controls subcellular localization and multisite phosphorylation of the phosphatidic acid phosphatase, lipin 1. J Biol Chem 2006; 282:277-86. [PMID: 17105729 DOI: 10.1074/jbc.m609537200] [Citation(s) in RCA: 178] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Brain, liver, kidney, heart, and skeletal muscle from fatty liver dystrophy (fld/fld) mice, which do not express lipin 1 (lipin), contained much less Mg(2+)-dependent phosphatidic acid phosphatase (PAP) activity than tissues from wild type mice. Lipin harboring the fld(2j) (Gly(84) --> Arg) mutation exhibited relatively little PAP activity. These results indicate that lipin is a major PAP in vivo and that the loss of PAP activity contributes to the fld phenotype. PAP activity was readily detected in immune complexes of lipin from 3T3-L1 adipocytes, where the protein was found both as a microsomal form and a soluble, more highly phosphorylated, form. Fifteen phosphorylation sites were identified by mass spectrometric analyses. Insulin increased the phosphorylation of multiple sites and promoted a gel shift that was due in part to phosphorylation of Ser(106). In contrast, epinephrine and oleic acid promoted dephosphorylation of lipin. The PAP-specific activity of lipin was not affected by the hormones or by dephosphorylation of lipin with protein phosphatase 1. However, the ratio of soluble to microsomal lipin was markedly increased in response to insulin and decreased in response to epinephrine and oleic acid. The results suggest that insulin and epinephrine control lipin primarily by changing localization rather than intrinsic PAP activity.
Collapse
Affiliation(s)
- Thurl E Harris
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908-0735, USA
| | | | | | | | | | | | | |
Collapse
|
6
|
Elabbadi N, Day CP, Gamouh A, Zyad A, Yeaman SJ. Relationship between the inhibition of phosphatidic acid phosphohydrolase-1 by oleate and oleoyl-CoA ester and its apparent translocation. Biochimie 2005; 87:437-43. [PMID: 15820750 DOI: 10.1016/j.biochi.2005.01.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Accepted: 01/04/2005] [Indexed: 11/29/2022]
Abstract
Phosphatidic acid phosphohydrolase-1 (PAP-1) activity is reversibly inhibited by fatty acids and their acyl-CoA esters and it appears paradoxical that these effectors have been reported to increase the liver's esterification capacity by translocating the rate-limiting enzyme PAP-1 from cytosol to the endoplasmic reticulum. Therefore, we have examined the effect of oleate, oleoyl-CoA, and spermine on the activation and translocation of PAP-1 of rat liver. PAP-1 activity is directly inhibited by oleic acid and oleoyl-CoA ester in an allosteric manner, resulting in the formation of inactive PAP-1-fatty acid (or -acyl-CoA) complex, even in the absence of any subcellular structures. Such association/aggregation of PAP-1 can be easily collected by centrifugation and may explain the apparent translocation phenomenon of this enzyme to a particular structure in the presence of fatty acids or acyl-CoA esters as reported in many works. Indeed, incubation of cytosol fraction alone with oleate or oleoyl-CoA at 37 degrees C, followed by centrifugation, induces a significant increase (sevenfold) in PAP-1 activity in the pellet fraction. This displacement is accompanied by an increase in the specific activity of PAP-1 in the pellet fraction. Spermine is less effective than oleate in inducing the displacement of PAP-1 activity from cytosol to the pellet fraction in the absence of any membrane structures. This apparent translocation of PAP-1 is also promoted when homogenate fraction was incubated with oleate prior to the preparation of cytosol and microsomal fraction. Thus, many of the announced factors, including fatty acids, would promote the in vitro association/aggregation of PAP-1 enzyme rather than its translocation, and therefore, re-evaluation of the reported effects on PAP-1 translocation phenomenon is required. It is proposed that fatty acids and their esters would favour beta-oxidation over esterification by promoting the forming of inactive associated PAP-1 in situations such as starvation and metabolic stress in which there is an increased supply of fatty acids to the liver.
Collapse
Affiliation(s)
- N Elabbadi
- Laboratoire d'Immunologie, Biochimie et Biologie Moléculaire, Faculté des Sciences et Techniques, Université Cadi Ayyad, B.P. 523 Beni-Mellal, Morocco.
| | | | | | | | | |
Collapse
|
7
|
Swanton EM, Saggerson ED. Effects of adrenaline on triacylglycerol synthesis and turnover in ventricular myocytes from adult rats. Biochem J 1997; 328 ( Pt 3):913-22. [PMID: 9396738 PMCID: PMC1219004 DOI: 10.1042/bj3280913] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Ca2+-tolerant myocytes were isolated with endogenous triacylglycerol (TAG) stores prelabelled with [3H]palmitate and subsequently incubated for a 1h chase period with [14C]palmitate, 2% albumin and 5mM glucose. Measurements were then made of [14C]palmitate conversion into TAG and phospholipids, of loss of [3H]TAG, of glycerol release and of change in the total TAG content. Rates of de novo synthesis of TAG were calculated by a balance method. With 0. 5mM palmitate present, 5 microM adrenaline increased de novo synthesis of TAG by 81% and incorporation of [14C]palmitate into phospholipids by 59%. Significant increases in these processes with adrenaline were also seen with 0.08, 0.14 and 0.26 mM palmitate. The beta-agonist isoprenaline had little effect on de novo synthesis of TAG and had no effect on [14C]palmitate conversion into phospholipids. The alpha1-agonist phenylephrine mimicked adrenaline in increasing [14C]palmitate conversion into phospholipids but had no effect on de novo synthesis of TAG. Adrenaline did not significantly alter the myocyte glycerol 3-phosphate content but caused a persistent 40% increase in the activity of the form of glycerolphosphate acyltransferase found predominantly in the sarcoplasmic reticulum. With 0.5 mM palmitate present, the value [14C]TAG formed -decrease in [3H]TAG consistently exceeded the enzymically measured change in cell TAG content. From this it was suggested that the specific radioactivity of [3H]TAG pool(s) mobilized during the chase period was lower than that of the overall cell TAG. In the basal state, complete mobilization of TAG measured as glycerol release was low, but cycling of TAG to diacylglycerol or monoacylglycerol and back to TAG appeared to be high. With adrenaline present, glycerol release was increased 5-6-fold but recycling of lower acylglycerols to TAG was abolished. Glycerol release was inhibited by increasing extracellular palmitate from 0.08 to 0.5 mM. Adrenaline partially over-rode this effect.
Collapse
Affiliation(s)
- E M Swanton
- Department of Biochemistry and Molecular Biology, University College London, Gower Street, London, WC1E 6BT, U.K
| | | |
Collapse
|
8
|
Swanton EM, Saggerson ED. Glycerolipid metabolizing enzymes in rat ventricle and in cardiac myocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1346:93-102. [PMID: 9187307 DOI: 10.1016/s0005-2760(97)00024-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
1. The properties and subcellular distribution of phosphatidate phosphohydrolase (PAP) were studied in rat heart. A Mg2(+)-activated activity (PAP1) which was inhibited by N-ethylmaleimide was found mainly in a 105,000 x g soluble fraction. Isolation of the membranes in a medium containing KCl increased the proportion of PAP1 that was associated. Translocation of PAP1 from these membranes occurred on subsequent incubation in a low-ionic strength medium from which KCI was omitted. Incubation of cardiac myocytes with palmitate promoted translocation of PAP activity to cellular membranes. A second activity which was insensitive to N-ethylmaleimide (PAP2) was found in the 105,000 x g membrane fraction. PAP2 was inhibited by concentrations of Mg2+ known to occur in ischaemia. Specific activities of PAP1 and PAP2 in ventricle muscle homogenates were similar. The specific activity of PAP2 in homogenates of cardiac myocytes was only 42% of that in homogenates of ventricle muscle. 2. A glycerolphosphate acyltransferase (GPAT) activity with properties similar to the GPAT found in microsomes from liver or adipose tissue was enriched in the sarcoplasmic reticulum fraction from ventricle muscle. This GPAT had a significantly higher K(m) for glycerol 3-phosphate than the GPAT found in adipose tissue microsomes. The possible physiological significance of this 'high K(m)' GPAT in heart, particularly in ischaemia, is discussed. 3. Comparisons were made of the specific activities of fatty acyl-CoA synthetase, monoacylglycerolphosphate acyltransferase, diacylglycerol acyltransferase and the mitochondrial and microsomal forms of GPAT in homogenates from cardiac myocytes and ventricle muscle.
Collapse
Affiliation(s)
- E M Swanton
- Department of Biochemistry and Molecular Biology, University College London, UK
| | | |
Collapse
|
9
|
Abstract
Phosphatidate phosphatase (EC 3.1.3.4) catalyzes the hydrolysis of phosphatidate to yield sn-1,2-diacylglycerol and inorganic phosphate. In mammalian systems, forms of phosphatidate phosphatase involved in glycerolipid synthesis and signal transduction have been identified. Forms of the enzyme involved in signal transduction have been purified and partially characterized. In yeast, phosphatidate phosphatases associated with the endoplasmic reticulum and mitochondria have also been purified and partially characterized. Information on phosphatidate phosphatases from mammals and yeast is useful in characterizing the enzyme from plant systems. This review examines progress on the characterization of phosphatidate phosphatases from mammals, yeast, and higher plants. The purification and characterization of the phosphatidate phosphatase involved in glycerolipid synthesis in developing oilseeds may lead to the identification of the encoding gene. Increasing our understanding of the enzymes of lipid synthesis in developing seeds will aid in the development of biotechnological strategies for seed oil modification.
Collapse
Affiliation(s)
- M G Kocsis
- Department of Chemistry, University of Lethbridge, Alberta, Canada
| | | |
Collapse
|
10
|
Fleming IN, Yeaman SJ. Subcellular distribution of N-ethylmaleimide-sensitive and -insensitive phosphatidic acid phosphohydrolase in rat brain. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1254:161-8. [PMID: 7827121 DOI: 10.1016/0005-2760(94)00179-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The dephosphorylation of phosphatidic acid by phosphatidic acid phosphohydrolase (PAP) is important in both cell-signalling and in glycerolipid metabolism. However, these roles are apparently performed by two different enzymes, which can be distinguished by their sensitivity in vitro to N-ethylmaleimide (NEM). Both of these enzymes are present in rat brain as well as a wide range of other rat tissues. However, the quantity and specific activity of each enzyme varies considerably between different tissues, as does the ratio of the two enzymes in each tissue. Tissues rich in glycerolipids are abundant in NEM-sensitive PAP, whereas there is no obvious pattern to the distribution of the NEM-insensitive enzyme in the different tissues tested. Studies on brain cortex, which is relatively rich in both forms of PAP, indicate that the NEM-insensitive PAP is located in the synaptosomes, and the NEM-sensitive enzyme present in the cytosol and microsomes. The NEM-sensitive PAP can also be translocated from the cytosol to the microsomes by oleate. When assayed against a range of phosphatidic acids, NEM-sensitive PAP showed a preference for phosphatidic acids with short acyl chains and for those containing arachidonate, whereas NEM-insensitive PAP had a preference for short and unsaturated acyl chains. The two isozymes also had different activity profiles against these substrates suggesting that they are in fact different enzymes. The implications for these results on the putative roles of the two forms of PAP are discussed.
Collapse
Affiliation(s)
- I N Fleming
- Department of Biochemistry and Genetics, Medical School, University of Newcastle-Upon-Tyne, UK
| | | |
Collapse
|
11
|
Höer A, Oberdisse E. Characterization of a phosphatidic acid phosphatase from rat brain cell membranes. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1994; 350:653-61. [PMID: 7708122 DOI: 10.1007/pl00004905] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have characterized a phosphatidic acid phosphatase (PAP, EC 3.1.3.4) that is associated with cell membranes from rat brain using [32P]phosphatidic acid as substrate in a simple assay. The enzyme could be activated by Triton X-100, cholic acid and Chaps and inhibited by Lubrol PX and sodium dodecyl sulfate. The optimal pH was between 6.0 and 7.0 Mg2+ was not essential for enzyme activity. The enzyme activity was decreased by about 50% by Ca2+ at concentrations of 0.1 to 1 mmol/l. Zn2+ inhibited the enzyme by 50% at concentrations of about 10 mumol/l in the absence of, and 100 nmol/l in the presence (3 mmol/l) of, Triton X-100. NaF decreased the activity by about 50% at concentrations between 0.3 and 1 mmol/l when Triton X-100 was added, but did not inhibit the enzyme if the detergent was not present. N-Ethylmaleimide (NEM) did not affect the enzyme. In the absence of Triton X-100, propranolol and metoprolol enhanced the PAP activity. In the presence of 3 mmol/l Triton X-100, the enzyme was inhibited by about 50% by propranolol at a concentration of 10 mmol/l, whereas metoprolol caused only a slight inhibition of PAP. The Km for phosphatidic acid was 150 mumol/l and was changed to 20 mumol/l by 3 mmol/l Triton X-100 without the Vmax being changed. Enzyme activity could be solubilized by 1-5% (w/v) Triton X-100. Gel filtration chromatography showed a M(r) of 320,000. This membrane-associated PAP from neuronal tissue probably belongs among the NEM-insensitive forms of PAP enzymes which have been proposed to play a role in transmembrane signal transduction via phospholipase D.
Collapse
Affiliation(s)
- A Höer
- Institut für Pharmakologie, Freien Universität Berlin, Germany
| | | |
Collapse
|
12
|
Palmer FB, Byers DM, Spence MW, Cook HW. Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake. Biochem J 1992; 286 ( Pt 2):505-12. [PMID: 1530583 PMCID: PMC1132926 DOI: 10.1042/bj2860505] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.
Collapse
Affiliation(s)
- F B Palmer
- Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia, Canada
| | | | | | | |
Collapse
|
13
|
Day CP, Yeaman SJ. Physical evidence for the presence of two forms of phosphatidate phosphohydrolase in rat liver. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1127:87-94. [PMID: 1627638 DOI: 10.1016/0005-2760(92)90205-a] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Phosphatidate phosphohydrolase (PAP)-catalysed dephosphorylation of phosphatidic acid to diacylglycerol is an important step in glycerolipid metabolism and cell-signalling. Gel filtration chromatography on Superose 6 and anion-exchange chromatography on Mono Q of rat liver subcellular fractions has provided physical evidence for the presence of two distinct forms of PAP activity. One form was sensitive to inhibition by N-ethylmaleimide (NEM), had an apparent M(r) of 540,000 and was eluted from the anion-exchange column by 0.35 M NaCl, while the other was insensitive to inhibition by NEM, had an apparent M(r) of 240,000 and was eluted from the anion-exchange column by 0.15 M NaCl. Studies on the subcellular distribution of these two enzymes, using 5'-nucleotidase as a plasma membrane marker, demonstrated that the NEM-sensitive form was predominantly cytosolic but translocated to the microsomal membranes in response to oleate. The NEM-insensitive form was predominantly located in the plasma membrane but a small proportion (approx. 10%) of total cell activity was present on the endoplasmic reticulum. The implications of these results for the likely roles of the two different forms of PAP in fatty acid esterification and cell-signalling are discussed.
Collapse
Affiliation(s)
- C P Day
- Department of Biochemistry, Medical School, University of Newcastle, Newcastle upon Tyne, UK
| | | |
Collapse
|
14
|
Mitchell JR, Saggerson ED. Activities of enzymes of glycerolipid synthesis in brown adipose tissue after treatment of rats with the adrenergic agonists BRL 26830A and phenylephrine, after exposure to cold and in streptozotocin-diabetes. Biochem J 1991; 277 ( Pt 3):665-9. [PMID: 1678597 PMCID: PMC1151294 DOI: 10.1042/bj2770665] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
1. Measurements were made, relative to tissue DNA, of the activities of enzymes of glycerolipid synthesis in homogenates of interscapular brown adipose tissue. These were: mitochondrial and microsomal forms of glycerolphosphate acyltransferase (GPAT), Mg(2+)-dependent phosphatidate phosphohydrolase (PPH) and fatty acyl-CoA synthetase (FAS). 2. In normal animals, 3 days of cold-exposure (4 degrees C) increased all activities. The increase in mitochondrial GPAT activity was particularly pronounced (5-fold). Administration of the beta-adrenergic agonist BRL 26830A mimicked the effect of cold on microsomal GPAT activity. Mitochondrial GPAT, PPH and FAS activities were unresponsive to BRL 26830A. The alpha-adrenergic agonist phenylephrine significantly decreased activities of GPAT and PPH. 3. Streptozotocin-diabetes decreased mitochondrial GPAT activity, but did not abolish the effect of cold to increase this activity or the activity of microsomal GPAT. Diabetes abolished the effect of cold on PPH and FAS activities. 4. The findings are relevant to signals that drive early events in mitochondriogenesis and cell proliferation in brown adipose tissue on exposure to cold.
Collapse
Affiliation(s)
- J R Mitchell
- Department of Biochemistry and Molecular Biology, University College London, U.K
| | | |
Collapse
|
15
|
Plasma membrane fractions from rat liver contain a phosphatidate phosphohydrolase distinct from that in the endoplasmic reticulum and cytosol. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)49945-0] [Citation(s) in RCA: 207] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
|
16
|
Schoonderwoerd K, Broekhoven-Schokker S, Hülsmann WC, Stam H. Properties of phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities in the isolated rat heart. Effect of glucagon, ischaemia and diabetes. Biochem J 1990; 268:487-92. [PMID: 2163615 PMCID: PMC1131459 DOI: 10.1042/bj2680487] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Myocardial triacylglycerol hydrolysis is subject to product inhibition. After hydrolysis of endogenous triacylglycerols, the main proportion of the liberated fatty acids is re-esterified to triacylglycerol, indicating the importance of fatty acid re-esterification in the regulation of myocardial triacylglycerol homoeostasis. Therefore, we characterized phosphatidate phosphohydrolase (PAP) and diacylglycerol acyltransferase (DGAT) activities, enzymes catalysing the final steps in the re-esterification of fatty acids to triacylglycerols in the isolated rat heart. The PAP activity was mainly recovered in the microsomal and soluble cell fractions, with an apparent Km of 0.14 mM for both the microsomal and the soluble enzyme. PAP was stimulated by Mg2+ and oleic acid. Oleic acid, like a high concentration of KCl, stimulated the translocation of PAP activity from the soluble to the particulate (microsomal) fraction. Myocardial DGAT had an apparent Km of 3.8 microM and was predominantly recovered in the particulate (microsomal) fraction. Both enzyme activities were significantly increased after acute streptozotocin-induced diabetes, PAP from 15.6 +/- 1.1 to 28.1 +/- 3.6 m-units/g wet wt. (P less than 0.01) and DGAT from 2.23 +/- 0.11 to 3.01 +/- 0.11 m-units/g wet wt. (P less than 0.01). In contrast with diabetes, low-flow ischaemia during 30 min did not affect PAP and DGAT activity in rat hearts. Perfusion with glucagon (0.1 microM) during 30 min did not affect total PAP activity, but changed the subcellular distribution. More PAP activity was recovered in the particulate fraction. DGAT activity was lowered by glucagon treatment from 0.37 +/- 0.03 to 0.23 +/- 0.02 m-unit/mg of microsomal protein (P less than 0.05). The role of PAP and DGAT activity and PAP distribution in the myocardial glucose/fatty acid cycle is discussed.
Collapse
Affiliation(s)
- K Schoonderwoerd
- Department of Biochemistry I, Medical Faculty, Erasmus University Rotterdam, The Netherlands
| | | | | | | |
Collapse
|
17
|
Vara E, Tamarit-Rodriguez J. Norepinephrine inhibits islet lipid metabolism, 45Ca2+ uptake, and insulin secretion. THE AMERICAN JOURNAL OF PHYSIOLOGY 1989; 257:E923-9. [PMID: 2514599 DOI: 10.1152/ajpendo.1989.257.6.e923] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We have previously shown that palmitate potentiates, in isolated islets, glucose-induced stimulation of insulin release, "de novo" lipid synthesis, and 45Ca2+ turnover in a correlative manner. Norepinephrine, a known inhibitor of the secretory response, has now been used to further investigate the relationships among the three phenomena. The amine decreased insulin secretion dose dependently in response to glucose and palmitate with alpha 2-adrenergic specificity. It also reduced similarly the oxidation of 1 mmol/l [U-14C]palmitate as well as the incorporation of 20 mmol/l D-[U-14C]glucose into islet phospholipids and neutral lipids through an alpha 2-adrenergic mechanism. These results indirectly suggest that alpha 2-adrenoceptor stimulation inhibits in islets both palmitate oxidation and esterification through an inactivation of long-chain acyl-CoA synthetase and other enzymes of glycerolipid synthesis. Islet uptake of 45Ca2+ was also decreased by norepinephrine with a similar sensitivity to that shown by insulin release and de novo lipid synthesis. Therefore, it is suggested that alpha 2-adrenoceptor-mediated reduction of the potentiation by palmitate of the secretory response to glucose depends on the inhibition of fatty acid metabolism and the resulting impairment of de novo lipid synthesis and 45Ca2+ turnover.
Collapse
Affiliation(s)
- E Vara
- Departmento de Bioquímica, Facultad de Medicina, Universidad Complutense, Madrid, Spain
| | | |
Collapse
|
18
|
Bonnel SI, Lin YP, Kelley MJ, Carman GM, Eichberg J. Interactions of thiophosphatidic acid with enzymes which metabolize phosphatidic acid. Inhibition of phosphatidic acid phosphatase and utilization by CDP-diacylglycerol synthase. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1005:289-95. [PMID: 2553100 DOI: 10.1016/0005-2760(89)90051-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Thiophosphatidic acid (1,2-diacyl-sn-glycero-3-phosphorothioate; thioPA) was chemically synthesized from egg phosphatidylcholine-derived 1,2-diacylglycerol and PSCl3 and tested for its effects on enzymes which utilize phosphatidic acid (PA) in phospholipid biosynthesis. The compound was not a substrate for rat liver cytosolic PA phosphatase and strongly inhibited this enzyme activity. ThioPA was also a potent inhibitor of purified membrane-associated PA phosphatase from Saccharomyces cerevisiae in a competitive manner and exhibited an apparent Ki = 60 microM. In contrast, purified CDPdiacylglycerol synthase (PA:CTP cytidylyltransferase) from this organism was able to convert thioPA to CDP-diacylglycerol. The apparent Vmax for thioPA was 7-fold lower than that for PA, whereas the apparent Km for thioPA (70 microM) was 4-fold lower than that for PA. Calculation of the specificity constant (Vmax/Km) demonstrated that PA was the preferred substrate. These properties of thioPA indicate that this substance may prove useful in studies of phospholipid metabolism and function.
Collapse
Affiliation(s)
- S I Bonnel
- Department of Biochemical and Biophysical Sciences, University of Houston 77204-5500
| | | | | | | | | |
Collapse
|
19
|
Mayorek N, Grinstein I, Bar-Tana J. Triacylglycerol synthesis in cultured rat hepatocytes. The rate-limiting role of diacylglycerol acyltransferase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1989; 182:395-400. [PMID: 2737209 DOI: 10.1111/j.1432-1033.1989.tb14844.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The limiting role of diacylglycerol acyltransferase with respect to triacylglycerol synthesis in cultured rat hepatocytes was evaluated by following the inhibition of the overall synthetic flux by 2-bromooctanoate acting as an inhibitor of the diacylglycerol acyltransferase step. The flux-control coefficient of diacylglycerol acyltransferase in intact cultured hepatocytes amounted to 0.76 in the presence of saturating glycerol and either palmitate or oleate as the fatty acyl substrates. The flux-control coefficient of diacylglycerol acyltransferase in lysolecithin-permeabilized cultured hepatocytes amounted to 0.80 and 0.99 in the presence of saturating glycerol 3-phosphate and either palmitate or oleate as the fatty acyl substrate, respectively. Hence, triacylglycerol synthesis in liver cells under the experimental conditions employed is rate-limited by the diacylglycerol acyltransferase.
Collapse
Affiliation(s)
- N Mayorek
- Department of Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel
| | | | | |
Collapse
|
20
|
Baht HS, Saggerson ED. Effect of noradrenaline on triacylglycerol synthesis in rat brown adipocytes. Biochem J 1989; 258:369-73. [PMID: 2650679 PMCID: PMC1138371 DOI: 10.1042/bj2580369] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Incubation of rat brown adipocytes with noradrenaline in the presence of insulin and palmitate caused a decrease in the rate of triacylglycerol synthesis as measured by [U-14C]glucose incorporation into acylglycerol glycerol. Concomitantly, the ratio of [1-14C]palmitate oxidized to CO2 to that esterified was increased. This alteration in the rate of triacylglycerol synthesis by noradrenaline was not observed when fatty acid oxidation was inhibited by etomoxir. Noradrenaline did not cause any acute inactivation of enzymes of the triacylglycerol-synthesis pathway. It is suggested that the decrease in triacylglycerol synthesis seen with noradrenaline is secondary to activation of fatty acid oxidation.
Collapse
Affiliation(s)
- H S Baht
- Department of Biochemistry, University College London, U.K
| | | |
Collapse
|
21
|
Pittner RA, Fain JN. Vasopressin transiently stimulates phospholipase C activity in cultured rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1010:227-32. [PMID: 2536285 DOI: 10.1016/0167-4889(89)90165-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Vasopressin stimulated phospholipase C activity in primary cultures of rat hepatocytes maintained for 18-24 h under serum free conditions. Soluble and membrane-associated phospholipase C activity was determined using exogenous [3H]phosphatidylinositol 4,5-bisphosphate ([3H]PIP2) in the presence of cholate, deoxycholate and NaCl. Exposure of hepatocytes for 5 s to vasopressin (100 nM) stimulated both membrane-associated and soluble phospholipase C activity by 30% and 40%, respectively. However, by 15 s this stimulation had disappeared. Addition of vasopressin to hepatocytes, previously labelled with [3H]inositol, stimulated inositol phosphate production within 5 s, but little further increase was seen over a 5-min incubation. These results indicate that vasopressin rapidly stimulates both soluble and membrane-associated phospholipase C activity.
Collapse
Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis 38163
| | | |
Collapse
|
22
|
Darnley AC, Carpenter CA, Saggerson ED. Changes in activities of some enzymes of glycerolipid synthesis in brown adipose tissue of cold-acclimated rats. Biochem J 1988; 253:351-5. [PMID: 3178717 PMCID: PMC1149305 DOI: 10.1042/bj2530351] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
1. Measurements were made of the activities of the following enzymes of glycerolipid synthesis in homogenates of interscapsular brown adipose tissue obtained from rats subjected to a 4 degrees C environment for time periods of 6 h up to 12 days: fatty acyl-CoA synthetase (FAS), mitochondrial and microsomal forms of glycerolphosphate acyltransferase (GPAT), monoacylglycerolphosphate acyltransferase (MGPAT) and Mg2+-dependent phosphatidate phosphohydrolase (PPH). 2. Relative to tissue DNA content, the activities of mitochondrial GPAT, MGPAT and Mg2+-dependent PPH were significantly increased after 1 day of exposure to cold, and continued to increase thereafter. By contrast, FAS and microsomal GPAT activities were unchanged relative to tissue DNA. 3. The time profile of the increase in MGPAT activity correlated well with a concomitant increase in the microsomal marker NADP+-cytochrome c reductase. Changes in mitochondrial GPAT and in Mg2+-dependent PPH activities were larger in amplitude than that of MGPAT. 4. It is proposed that these selective changes in enzyme activity may be associated with the onset of brown-adipose-tissue hyperplasia or possibly with an increase in triacylglycerol synthesis during cold-acclimation.
Collapse
Affiliation(s)
- A C Darnley
- Department of Biochemistry, University College London, U.K
| | | | | |
Collapse
|
23
|
Harper RD. The response of adipocyte glucose metabolism and fatty acid release to adenosine deaminase, insulin and perifusion. Investigation of intermediary metabolism by perifusion. Biochem J 1988; 251:733-7. [PMID: 3046601 PMCID: PMC1149065 DOI: 10.1042/bj2510733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Adipocytes incubated with adenosine deaminase (ADA) showed: (1) increased amounts of fatty acids in the medium; (2) increased glucose incorporation into acylglycerol glycerol; (3) decreased glucose incorporation into acylglycerol fatty acids; (4) a co-ordinate decrease in the sensitivity of lipolysis and glucose incorporation into acylglycerol to insulin; (5) similar effects on glucose incorporations in perifused and normal incubations. The decrease in fatty acid synthesis by perfusion was found to be dependent on the presence of insulin or fatty acids, and independent of the effects of ADA. The significance of the effects of perifusion, ADA and insulin are discussed in relation to effects of fatty acids.
Collapse
Affiliation(s)
- R D Harper
- Faculty of Applied Sciences, Luton College of Higher Education, Bedfordshire, U.K
| |
Collapse
|
24
|
Baht HS, Saggerson ED. Comparison of triacylglycerol synthesis in rat brown and white adipocytes. Effects of hypothyroidism and streptozotocin-diabetes on enzyme activities and metabolic fluxes. Biochem J 1988; 250:325-33. [PMID: 3355527 PMCID: PMC1148859 DOI: 10.1042/bj2500325] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
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.
Collapse
Affiliation(s)
- H S Baht
- Department of Biochemistry, University College London, U.K
| | | |
Collapse
|
25
|
Jamal Z, Saggerson ED. Factors influencing the altered thermogenic response of rat brown adipose tissue in streptozotocin-diabetes. Biochem J 1988; 249:415-21. [PMID: 3277624 PMCID: PMC1148719 DOI: 10.1042/bj2490415] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
1. Adipocytes were isolated from the interscapular brown fat of male rats maintained at 21 degrees C. These animals were controls, streptozotocin-diabetics or 2-day insulin-treated diabetics. 2. With adipocytes from diabetic animals, maximum rates of noradrenaline-stimulated O2 uptake were decreased by 58%, and the Bmax. of [3H]GDP binding to mitochondria was decreased by 55%. Insulin administration reversed both of these changes. 3. Streptozotocin-diabetes increased basal lipolysis in adipocytes incubated with adenosine deaminase (1 unit/ml), decreased the EC50 (concn. giving 50% of maximum effect) for noradrenaline, but did not change the maximum rate of noradrenaline-stimulated lipolysis. Except for some small differences at very low concentrations (10-100 pM), diabetes or insulin treatment did not alter the sensitivity of noradrenaline-stimulated lipolysis or O2 uptake to the inhibitory effect of N6-phenylisopropyladenosine. It is therefore concluded that the lesion(s) in thermogenesis in diabetes are not attributable to any changes in lipolysis. 4. Blood flow through interscapular brown fat, measured by accumulation of [14C]DDT [14C-labelled 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] was increased by 2.3-fold 70 min after a single administration of insulin to diabetic rats. This treatment decreased blood flow through epididymal white fat by 58%. 5. Propranolol treatment of diabetic rats muted the ability of insulin treatment to increase the maximum rate of noradrenaline-stimulated O2 uptake, suggesting that this action of insulin may be a secondary one rather than a direct effect of the hormone on the adipocytes.
Collapse
Affiliation(s)
- Z Jamal
- Department of Biochemistry, University College London, U.K
| | | |
Collapse
|
26
|
Martin A, Hales P, Brindley DN. A rapid assay for measuring the activity and the Mg2+ and Ca2+ requirements of phosphatidate phosphohydrolase in cytosolic and microsomal fractions of rat liver. Biochem J 1987; 245:347-55. [PMID: 2822021 PMCID: PMC1148128 DOI: 10.1042/bj2450347] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
1. A rapid extraction and purification scheme was designed for the recovery of [3H]diacylglycerol formed during the assay of phosphatidate phosphohydrolase. 2. The importance of removing polyvalent cations, particularly Ca2+, from the phosphatidate and other reagents used in the assay of the phosphohydrolase activity was demonstrated. This was achieved mainly by treating the phosphatidate with a chelating resin and by adding 1 mM-EGTA and 1 mM-EDTA to the assays. 3. The activity of the phosphohydrolase in dialysed samples of the soluble and microsomal fractions of rat liver was very low. 4. Addition of optimum concentrations of MgCl2 resulted in a 110-167-fold stimulation in activity. 5. CaCl2 was also able to stimulate phosphohydrolase activity, but to a much smaller extent than MgCl2. 6. Chlorpromazine, an amphiphilic cation, inhibited the reaction when it was measured in these experiments by using a mixed emulsion of phosphatidylcholine and phosphatidate at pH 7.4. 7. Microsomal fractions that were preincubated with albumin contained very low activities of the Mg2+-dependent phosphohydrolase. When these were then incubated with the soluble fraction in the presence of oleate, the soluble phosphohydrolase attached to the microsomal membranes, and it retained its high dependency on Mg2+.
Collapse
Affiliation(s)
- A Martin
- Department of Biochemistry, University of Nottingham Medical School, Queen's Medical Centre, U.K
| | | | | |
Collapse
|
27
|
Saggerson ED, Carpenter CA. Effects of streptozotocin-diabetes and insulin administration in vivo or in vitro on the activities of five enzymes in the adipose-tissue triacylglycerol-synthesis pathway. Biochem J 1987; 243:289-92. [PMID: 3300639 PMCID: PMC1147847 DOI: 10.1042/bj2430289] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
At 2 days after administration of streptozotocin (100 mg/kg), activities in rat epididymal fat-pads of the following enzymes were significantly decreased: fatty acyl-CoA synthetase (FAS), mitochondrial and microsomal forms of glycerolphosphate acyltransferase (GPAT), monoacylglycerolphosphate acyltransferase (MGPAT) and Mg2+-dependent phosphatidate phosphohydrolase (PPH). There were no significant changes in diacylglycerol acyltransferase or Mg2+-independent PPH. Insulin administration to diabetic rats over 2 days restored activities of FAS, both forms of GPAT, MGPAT and Mg2+-dependent PPH. Significant restoration of all five activities was also seen 2 h after a single administration of insulin, but was not observed 45 min after insulin treatment. Insulin significantly increased all five enzyme activities when adipocytes from diabetic rats were incubated for 2 h with a mixture of glucose, lactate, pyruvate and amino acids.
Collapse
|