Synthesis of Fatty Acids in Animal Tissues

Immunometabolism and HIV-1 pathogenesis: food for thought

Antiretroviral therapies efficiently block HIV-1 replication but need to be maintained for life. Moreover, chronic inflammation is a hallmark of HIV-1 infection that persists despite treatment. There is, therefore, an urgent need to better understand the mechanisms driving HIV-1 pathogenesis and to identify new targets for therapeutic intervention. In the past few years, the decisive role of cellular metabolism in the fate and activity of immune cells has been uncovered, as well as its impact on the outcome of infectious diseases. Emerging evidence suggests that immunometabolism has a key role in HIV-1 pathogenesis. The metabolic pathways of CD4⁺ T cells and macrophages determine their susceptibility to infection, the persistence of infected cells and the establishment of latency. Immunometabolism also shapes immune responses against HIV-1, and cell metabolic products are key drivers of inflammation during infection. In this Review, we summarize current knowledge of the links between HIV-1 infection and immunometabolism, and we discuss the potential opportunities and challenges for therapeutic interventions.

General morphology and ultrastructure of the female reproductive apparatus of Trichomalopsis shirakii crawford (Hymenoptera, Pteromalidae)

The morphology and ultrastructure of the female reproductive system were examined for a larval-pupal parasitoid Trichomalopsis shirakii Crawford of Oulema oryzae Kuwayama using light and electron microscopes. The reproductive system includes two ovaries, two pairs of accessory glands, an unbranched venom gland, a large venom reservoir and a Dufour gland. Each ovariole contains follicles and oocytes at different stages of maturation. A fibrous layer covers the surface of mature egg. The accessory glands are made up of a layer of secretory cells surrounded by muscle fibers. In these secretory cells, numerous mitochondria, electron-dense secretory granules and vesicles filled with dense granular particles are present. These granular particles appear as virus-like particles (VLPs). The venom gland consists of a single layer of secretory cells which are organelle rich with abundant rough endoplasmic reticulum, mitochondria and vesicular organelles, a layer of duct cells and an inner intima. The reservoir consists of a muscular sheath, epidermal cells with few organelles and an intima layer. The Dufour gland has a relatively large lumen surrounded by a single layer of columnar epithelial cells which are characterized by clusters of smooth endoplasmic reticulum and lipid droplets. Aside from the venom, the fibrous layer coating the egg and the granular particles which may be VLPs have been discovered in our study. They may serve as one of the parasitoid-associated factors in their host-parasitoid relationship and play a role in host immune suppression. Microsc. Res. Tech. 79:625-636, 2016. © 2016 Wiley Periodicals, Inc.

Triomics Analysis of Imatinib-Treated Myeloma Cells Connects Kinase Inhibition to RNA Processing and Decreased Lipid Biosynthesis

The combination of metabolomics, lipidomics, and phosphoproteomics that incorporates triple stable isotope labeling by amino acids in cell culture (SILAC) protein labeling, as well as (13)C in vivo metabolite labeling, was demonstrated on BCR-ABL-positive H929 multiple myeloma cells. From 11 880 phosphorylation sites, we confirm that H929 cells are primarily signaling through the BCR-ABL-ERK pathway, and we show that imatinib treatment not only downregulates phosphosites in this pathway but also upregulates phosphosites on proteins involved in RNA expression. Metabolomics analyses reveal that BCR-ABL-ERK signaling in H929 cells drives the pentose phosphate pathway (PPP) and RNA biosynthesis, where pathway inhibition via imatinib results in marked PPP impairment and an accumulation of RNA nucleotides and negative regulation of mRNA. Lipidomics data also show an overall reduction in lipid biosynthesis and fatty acid incorporation with a significant decrease in lysophospholipids. RNA immunoprecipitation studies confirm that RNA degradation is inhibited with short imatinib treatment and transcription is inhibited upon long imatinib treatment, validating the triomics results. These data show the utility of combining mass spectrometry-based "-omics" technologies and reveals that kinase inhibitors may not only downregulate phosphorylation of their targets but also induce metabolic events via increased phosphorylation of other cellular components.

Deletion of ELOVL6 blocks the synthesis of oleic acid but does not prevent the development of fatty liver or insulin resistance

Elongation of very long chain fatty acid-like family member 6 (ELOVL6) is a fatty acyl elongase that performs the initial and rate-limiting condensing reaction required for microsomal elongation of long-chain fatty acids. Our previous in vitro studies suggested that ELOVL6 elongated long-chain saturated fatty acids and monounsaturated fatty acids with chain lengths of 12 to 16 carbons. Here, we describe the generation and phenotypic characterization of Elovl6^−/− mice. As predicted from the in vitro studies, livers from Elovl6^−/− mice accumulated palmitic (C16:0) and palmitoleic (C16:1, n-7) fatty acids and contained significantly less stearic (C18:0) and oleic (C18:1, n-9) acids, confirming that ELOVL6 is the only enzyme capable of elongating palmitate (C16:0). Unexpectedly, Elovl6^−/− mice produced vaccenic acid (C18:1, n-7), the elongated product of palmitoleate (C16:1, n-7), suggesting that palmitoleate (C16:1, n-7) to vaccenate (C18:1, n-7) elongation was not specific to ELOVL6. The only detected consequence of deleting Elovl6^−/− in mice was that their livers accumulated significantly more triglycerides than wild-type mice when fed a fat-free/high-carbohydrate diet. When mice were fed a high-fat diet or ELOVL6 was deleted in ob/ob mice, the absence of ELOVL6 did not alter the development of obesity, fatty liver, hyperglycemia, or hyperinsulinemia. Combined, these results suggest that palmitoleic (C16:1, n-7) and vaccenic (C18:1, n-7) acids can largely replace the roles of oleic acid (C18:1, n-9) in vivo and that the deletion of ELOVL6 does not protect mice from the development of hepatic steatosis or insulin resistance.

Characterization of two cotton cDNAs encoding trans-2-enoyl-CoA reductase reveals a putative novel NADPH-binding motif

Very long chain fatty acids are important components of plant lipids, suberins, and cuticular waxes. Trans-2-enoyl-CoA reductase (ECR) catalyses the fourth reaction of fatty acid elongation, which is NADPH dependent. In the present study, the expression of two cotton ECR (GhECR) genes revealed by quantitative RT-PCR analysis was up-regulated during cotton fibre elongation. GhECR1 and 2 each contain open reading frames of 933 bp in length, both encoding proteins consisting of 310 amino acid residues. GhECRs show 32% identity to Saccharomyces cerevisiae Tsc13p at the deduced amino acid level, and the GhECR genes were able to restore the viability of the S. cerevisiae haploid tsc13-deletion strain. A putative non-classical NADPH-binding site in GhECR was predicted by an empirical approach. Site-directed mutagenesis in combination with gas chromatography-mass spectrometry analysis suggests that G(5X)IPXG presents a putative novel NADPH-binding motif of the plant ECR family. The data suggest that both GhECR genes encode functional enzymes harbouring non-classical NADPH-binding sites at their C-termini, and are involved in fatty acid elongation during cotton fibre development.

Coupling of the de novo fatty acid biosynthesis and lipoylation pathways in mammalian mitochondria

The objective of this study was to identify the products and possible role of a putative pathway for de novo fatty acid synthesis in mammalian mitochondria. Bovine heart mitochondrial matrix preparations were prepared free from contamination by proteins from other subcellular components and, using a combination of radioisotopic labeling and mass spectrometry, were shown to contain all of the enzymes required for the extension of a 2-carbon precursor by malonyl moieties to saturated acyl-ACP thioesters containing up to 14 carbon atoms. A major product was octanoyl-ACP and, in the presence of the apo-H-protein of the glycine cleavage complex, the newly synthesized octanoyl moieties were translocated to the lipoylation site on the acceptor protein. These studies demonstrate that one of the functions of the de novo fatty acid biosynthetic pathway in mammalian mitochondria is to provide the octanoyl precursor required for the essential protein lipoylation pathway.

Impaired arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) acid synthesis by phenylalanine metabolites as etiological factors in the neuropathology of phenylketonuria

The recent literature on polyunsaturated fatty acid metabolism in phenylketonuria (PKU) is critically analyzed. The data suggest that developmental impairment of the accretion of brain arachidonic (20:4n-6) and docosahexaenoic (22:6n-3, DHA) acids is a major etiological factor in the microcephaly and mental retardation of uncontrolled PKU and maternal PKU. These fatty acids appear to be synthesized by the recently elucidated carnitine-dependent, channeled, mitochondrial fatty acid desaturases for which alpha-tocopherolquinone (alpha-TQ) is an essential enzyme cofactor. alpha-TQ can be synthesized either de novo or from alpha-tocopherol. The fetus and newborn would primarily rely on de novo alpha-TQ synthesis for these mitochondrial desaturases because of low maternal transfer of alpha-tocopherol. Homogentisate, a pivotal intermediate in the de novo pathway of alpha-TQ synthesis, is synthesized by 4-hydroxyphenylpyruvate dioxygenase. The major catabolic products of excess phenylalanine, viz. phenylpyruvate and phenyllactate, are proposed to inhibit alpha-TQ synthesis at the level of the dioxygenase reaction by competing with its 4-hydroxyphenylpyruvate substrate, thus leading to a developmental impairment of 20:4n-6 and 22:6n-3 synthesis in uncontrolled PKU and fetuses of PKU mothers. The data suggest that dietary supplementation with carnitine, 20:4n-6, and 22:6n-3 may have therapeutic value for PKU mothers and for PKU patients who have been shown to have a low plasma status of these essential metabolites.

The fatty acid chain elongation system of mammalian endoplasmic reticulum

Much has been learned about FACES of the endoplasmic reticulum since its discovery in the early 1960s. FACES consists of four component reactions, requires the fatty acid to be activated in the form of a CoA derivative, utilizes reducing equivalents in the form of NADH or NADPH, is induced by a fat-free diet, resides on the cytoplasmic surface of the endoplasmic reticulum, appears to function in concert with the desaturase system and appears to exist in multiple forms (either multiple condensing enzymes connected to a single pathway or multiple pathways). FACES has been found in all tissues investigated, namely, liver, brain, kidney, lung, adrenals, retina, testis, small intestine, blood cells (lymphocytes and neutrophils) and fibroblasts, with one exception--the heart has no measurable activity. Yet, much more needs to be learned. The critical, inducible and rate-limiting condensing enzyme has resisted solubilization and purification; the purification of the other components has met with limited success. We know nothing about the site of synthesis of each component of FACES. How is each component enzyme integrated into the endoplasmic reticulum membrane? Is there a single mRNA directing synthesis of all four components or are there four separate mRNAs? How are elongation and desaturation coordinated? What is (are) the physiological regulator(s) of FACES--ADP, AMP, IP3, G-proteins, phosphorylation, CoA, Ca2+, cAMP, none of these? The molecular biology of FACES is only in the fetal stage of development. We are only scratching the surface--it is an undiscovered country.

Induction of rat liver mitochondrial fatty acid elongation by the administration of peroxisome proliferator di-(2-ethylhexyl)phthalate: absence of elongation activity in peroxisomes

The administration of di-(2-ethylhexyl)phthalate (DEHP)3 to male Sprague-Dawley rats resulted in more than a threefold increase in activity of acetyl CoA-dependent hepatic mitochondrial fatty acid elongation. Peroxisomes obtained either from control or DEHP-treated rats were not capable of elongating any of the fatty acyl CoAs tested. Furthermore, the peroxisomes possessed no trans-2-enoyl CoA reductase activity. Therefore, the elongation activity in the 7500g fraction from both control and DEHP-fed animals can be attributed totally to the mitochondria. Maximal incorporation of acetyl CoA occurred in the presence of both NADH and NADPH, and octanoyl CoA (8:0) and decanoyl CoA (10:0) were found to be optimal primers for fatty acid elongation in both control and DEHP-treated animals. The apparent Km for 8:0 CoA was 17 microM in both animal groups while the Vmax was increased from 4.5 to 12.5 nmol/min/mg following treatment. The apparent Km for 10:0 CoA was 10 microM in both control and DEHP-treated groups while the apparent Vmax increased from 2.5 to 10 nmol/min/mg; palmitoyl-CoA (16:0) was a very poor primer for chain elongation. Although the acetyl CoA-dependent fatty acid elongation was stimulated by DEHP treatment, the mitochondrial trans-2-enoyl CoA reductase activity was unaffected. The mitochondrial total elongation activity following DEHP-treatment using 8:0 CoA as primer was about two times higher than enoyl CoA reductase activity using trans-2-decenoyl CoA (10:1). This was the result of accumulation of intermediates, which were identified as trans-2-10:1 (35%), beta-hydroxy 10:0 (25%), unidentified (15%), and elongated saturated product 10:0 (24%). Elongation by one acetate unit was found in both the control and DEHP-treated animals. The results are discussed in terms of physiological significance.

Metabolism of palmitaldehyde in human cardiac muscle-II. Fatty chain elongation and shortening

1. The metabolism of [1-14C[ palmitaldehyde has been studied in human heart homogenates. 2. Incorporation of the radioactivity into the individual acyl chains of nonpolar (NPL) and polar (PL) lipid fractions was assessed as well as changes in the weight percentage distribution of these chains. 3. Incorporation of the radioactivity into specific lipid fractions of free fatty acids (FFAcd), free fatty aldehydes (FFAld) and cholesterol esters were also studied. 4. A significant amount of incorporation into fatty chains of both fewer and more than 16 carbons was observed. 5. Chain shortening was found to be favored by NAD while the chain elongation required NADPH.

De novo fatty acid synthesis and fatty acid elongation catalyzed by subcellular fractions from hog and human aorta

De novo synthesis and mitochondrial elongation of fatty acids have been demonstrated in subcellular fractions from hog and human aorta. Microsomal fatty acid elongation has been shown in hog aorta. The activity catalyzing the formation of fatty acids from acetyl and malonyl CoA was associated with a high molecular weight complex in the 6 x 10(6) g x min supernatant fraction. The principal product was palmitic acid. Some myristic and stearic acids were also formed. One elongation system was associated with protein which sedimented between 4500 g x min and 150,000 g x min. It used acetyl CoA but not malonyl CoA, and NADH was the preferred reducing agent. Radioactivity from acetyl CoA was incorporated into many fatty acids. In hog aorta a second elongation system was found associated with protein which sedimented at 6 x 10(6) g x min. It used malonyl CoA preferentially as substrate and either NADH or NADPH as reducing agent.

Comparison of long term lipogenic effects of two different medium-chain triglycerides (tri C8: O and tri C12 : O) in the growing rat

During the growth (35 g-340 g), and as compared to results obtained with a lipid-free diet or a diet containing long-chain fatty acids, high levels of Tri C8 : O or Tri C12 : O did not change the quantitative aspects of proteinogenesis and lipogenesis balances. The incorporation of Tri C8 : O into the diet did not change the fatty acid composition of body lipid stores while the incorporation of Tri C12 : O induced a lipogenesis characterized by the disappearance of about 50% of the n-9 and n-7 unsaturated fatty acids, the emergence of an equivalent amount of saturated fatty acids in C12 and C14, and the decrease of hexadecanoic or palmitic acid concentration. Titers of saturated fatty acids with a melting point higher than 40 degrees C increased from 34% to 64%. Results suggested an efficient inhibition of fatty acid biosynthesis de novo by C12 : O, associated with an impossibility for microsomal enzymes to assume the elongation of a sufficient amount of C12 : O to maintain C16 : O concentration and to furnish an important amount of substrate (C18 : O) to delta-9-stearoyl coenzyme A desaturase for oleic acid synthesis. Introducing dodecanoic acid into the diet of growing animals appears to be the most efficient method for increasing the degree of saturation of body lipids without changing the concentrations of long-chain saturated fatty acids.

Effect of thyroid hormones on microsomal fatty acid chain elongation synthesis in rat liver

Evidence is presented that rat liver microsomal fatty acid chain elongation synthesis and desaturation, as well as acetyl-CoA carboxylase and fatty acid synthetase, are strongly influenced by thyroid hormone level. Conversely, the fatty acid chain elongation system in mitochondria, unlike the oxidative capacity of palmitate, NADH, succinate and malate, does not seem significantly affected by the thyrotoxic state. In triiodothyronine-induced or thyroxine-induced hyperthyroidism, rat liver acetyl-CoA carboxylase, fatty acid synthetase and microsomal chain elongation and desaturation reactions are not greatly affected after the first 10 days of treatment, while after longer intervals a respective increase in these activities is shown of up to 87, 116 and 65% after 22 days. In propylthiouracil-induced hypothyroidism, all the above synthetic activities are strongly reduced immediately after three days of drug administration and diminished no further following longer periods. Although the pattern of synthesized fatty acids in the thyrotoxic state is similar to that obtained from normal subcellular rat fractions, the esterification process of fatty acids in microsomal lipids appears to be slightly inhibited in hypothyroid rats and increased following triiodothyronine or thyroxine administration. Finally, a reduction in the hepatic cyclic AMP level of about 41% is reported after 19 days of triiodothyronine-administration to rats. On the basis of the observed insensitivity of the mitochondrial fatty acid chain elongation system to the thyrotoxic state, a tentative interpretation of its role in the hepatic cell is postulated.

Partial purification and properties of the fatty acid elongation systems in the outer and inner membranes of beef liver mitochondria

Purified outer membrane of beef liver mitochondria was found to elongate medium chain fatty acyl-CoA primer by the incorporation of [1-14C]acetyl-CoA. This enzymic activity, extracted by Triton X-100, was purified 8-fold by ammonium sulfate fractionation followed by chromatography on a Sephadex column. Purified inner membrane, when processed through an identical purification procedure, yielded a second enzyme system which incorporated [1-14C]acetyl-CoA into long chain fatty acids in the presence of medium chain fatty acyl-CoA primer. This enzyme preparation was about four times as active as the preparation from the outer membrane, and used NADH as the reductant for the synthesis. The molecular weights of the inner and the outer membrane enzyme systems, estimated by gel filtration as well as sucrose density gradient centrifugation, were approx. 57 000 and 126 000, respectively. The partially purified outer membrane enzyme system required NADH and a medium chain acyl-CoA primer for the incorporation of [1-14C]acetyl-CoA into long chain fatty acids. KNC stimulated the reaction. NADPH could substitute for NADH only to a limited extent. Malonyl-CoA was ineffective as a substrate in this reaction. The optimum pH of the reaction was 7.2-7.6 in 0.1 M potassium phosphate buffer. Dithiothreitol, beta-mercaptoethanol, N-ethylmaleimide and high concentrations of ATP and acyl-CoA primer inhibited the reaction. The specificity for the acyl-CoA primer in the reaction was very broad. All the primers tested, C8 to C16, incorporated acetyl-CoA significantly. However, maximum incorporation was observed with dodecanoyl-CoA. Decanoyl-CoA was the best primer for the enzyme system isolated from the inner membrane. About 42% of the radioactivity in the fatty acids synthesized by the outer membrane enzyme system, from myristoyl-CoA and [1-C14]acetyl-CoA, was in palmitic acid. Of the remaining activity, 41% was in stearic acid and about 38% in longer-chain acids. Hence, the elongation of the primer fatty acid by one C2 unit appeared to be the predominant process in this synthesis. In the elongation of myristoyl-C0A by the inner membrane enzyme system, palmitic acid which constituted nearly 78% of the fatty acids synthesized, was the primary product.

In vivo metabolism of labeled oleic and linoleic acids by the laying hen

Radioactive oleic and linoleic acids, labeled with 3H in the chain and 14C in the carbonyl group, were administered to white leghorn laying hens. Mixtures fed in separate experiments included: (1) 3H- and 14C-labeled oleic acid, (2) 3H- and 14C-labeled linoleic acid and (3) [3H]oleic aicd and [14C] linoleic acid. The 3H/14C ratios of both the neutral lipid and phospholipid fractions from the egg yolk and of the isolated acids from these lipid fractions were compared to that in the administered mixture. Agreement in the 3H/14C ratios for the neutral lipid fraction from each of the feeding experiments indicated that neither the 3H- and 14C labeled acids nor the oleic or linoleic acids were distinguishable during synthesis of the neutral lipid. Analysis of the phospholipid fractions showed that when dual-labeled mixtures of oleic acid were administered, 3H/14C ratios were elevated and, therefore, there was selective elimination of the 14C label. When dual-labeled mixtures of linoleic acid were administered, the 3H/14C ratios were in agreement; and when the two acids were administered simultaneously as a dual-labeled mixture, there was selective incorporation of linoleic acid. These findings indicate separate metabolic pathways for synthesis of neutral lipid and phospholipid in egg yolk as expected, as well as preferential use of the essential fatty acid in the phospholipid by the hen.

[Biosynthesis of fatty acids in mouse brain mitochondria in the presence of malonyl-CoA or acetyl-CoA]

Incorporation of malonyl-CoA or acetyl-CoA is studied in mouse brain mitochondrial fatty acids. Rupture of mitochondria is necessary ; Triton X-100 gives the best result. Other detergents or sonication are of lesser efficiency. Cofactor requirements have been studied : NADH and NADPH have been tested ; ATP increases biosynthesis and CoA causes an inhibition. Two systems of biosynthesis are involved : -- One is a de novo system using malonyl-CoA. Malonyl-CoA alone is incorporated and synthesizes mainly C16, indicating the existence of a malonly-CoA decarboxylase although elongation of short chain fatty acids cannot be excluded. Addition of acetyl-CoA increases the biosynthesis and palmityl-CoA when added causes an inhibition. -- The other system, using acetyl-CoA, elongates exogenous palmityl-CoA ; endogenous acyl-CoAs are not elongated by acetyl-CoA. All these results are confirmed by radiogas chromatographic studies of the reactions products.

Fatty acid synthesis from 2-14C-acetate in rat testis mitochondrial and cytosol fractions in vitro

An in vitro system for acetate incorporation into fatty acids by the mitochondrial and the cytosol fractions of rat testis is described. The rate of incorporation of acetate into fatty acids was twice as fast with the mitochondrial as with the cytosol fraction; both systems were stimulated in the presence of adenosine triphosphate, reduced nicotinamide adenine dinucleotide phosphate, coenzyme A, and MgC1(2). The optimum pH was between 7.0-7.5 for the mitochondrial fraction and between 6.5-8.0 for the cytosol fraction. Radio gas chromatography showed that palmitic acid was the most highly labeled acid, followed by stearic acid, in the mitochondrial fraction in accord with the pathway of de novo fatty acid synthesis. Some of the labeled acetate was also incorporated into the 16:1 and 18:1 fatty acids of this fraction. Distribution of radioactivity among the mitochondrial lipid classes was highest in the phospholipids and monoglycerides, followed by diglycerides and cholesterol; little radioactivity was present in the triglyceride fraction. These observations are in accord with studies of the incorporation of labeled metabolites into testicular lipids following intratesticular injection and indicate the validity of the in vitro system for studies of specific reactions occurring in vivo.

Studies in vitro of lipogenesis in rat testicular tissue

Testicular tissue was shown to contain the full complement of enzymes required for de novo synthesis of fatty acids. The enzymes capable of snythesizing palmitic acid from citrate, acetate, or acetyl CoA were found to be present in the soluble (cytoplasmic) fraction. These included fatty acid synthetase, acetyl CoA carboxylase, citrate-cleavage enzyme, malic enzyme, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase. Optimal conditions for assaying activities of fatty acid synthetase and acetyl CoA carboxylase in the soluble fraction from rat testes were established, and the activities of these two enzymes were determined to be 0.54 +/- 0.1 and 0.030 +/- 0.002 (nmoles of substrate incorporated into fatty acid per min per mg of soluble fraction protein), respectively. The activities of citrate-cleavage enzyme, malic enzyme, and the glucose-6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase pair were also measured. The activities were 6.0 +/- 0.7, 34.9 +/- 4.2, and 29.9 +/- 9.3 nmoles/min/mg, respectively.