acyl-CoA Synthetase Activity Research Articles

Expression of an acyl‐CoA synthetase, lipidosin, in astrocytes of the murine brain and its up‐regulation during remyelination following cuprizone‐induced demyelination

Lipidosin is an 80-kDa protein with long-chain acyl-CoA synthetase activity expressed in the brain, adrenal gland, testis, and ovary, which are selectively damaged in X-linked adrenoleukodystrophy (X-ALD). Western blot analysis of the cerebrum and cerebellum revealed a gradual increase in the expression of lipidosin postnatally. Light microscopic immunohistochemistry using a panel of specific monoclonal antibodies showed that the lipidosin-immunopositive cells were ubiquitously distributed in the brain and were denser in the gray matter than in the white matter. Lipidosin immunoreactivity was colocalized with GFAP immunoreactivity but not with ubiquitin C-terminal hydrolase 1 (= PGP9.5) immunoreactivity, a neuronal marker, and lipidosin-producing cells detected by an antisense probe specific for lipidosin mRNA were also GFAP immunopositive. These data together with Western blot analysis of primary cultured astrocytes indicate that lipidosin is expressed in astrocytes. Immunoelectron microscopic analysis revealed that lipidosin immunoreactivity was widely distributed from perivascular endfeet to perisynaptic processes without being limited to peroxisomes. Lipidosin immunoreactivity was greatly increased in astrocytes in the area of remyelination following experimental demyelination induced by the administration of cuprizone to mice. These data suggest that lipidosin was involved in fatty acid metabolism during reconstruction of the myelin sheath.

Fatty Acid Transport Protein 4 Is the Principal Very Long Chain Fatty Acyl-CoA Synthetase in Skin Fibroblasts

Fatty acid transport protein 4 (FATP4) is a fatty acyl-CoA synthetase that preferentially activates very long chain fatty acid substrates, such as C24:0, to their CoA derivatives. To gain better insight into the physiological functions of FATP4, we established dermal fibroblast cell lines from FATP4-deficient wrinkle-free mice and wild type (w.t.) mice. FATP4 -/- fibroblasts had no detectable FATP4 protein by Western blot. Compared with w.t. fibroblasts, cells lacking FATP4 had an 83% decrease in C24:0 activation. Peroxisomal degradation of C24:0 was reduced by 58%, and rates of C24:0 incorporation into major phospholipid species (54-64% decrease), triacylglycerol (64% decrease), and cholesterol esters (58% decrease) were significantly diminished. Because these lipid metabolic processes take place in different subcellular organelles, we used immunofluorescence and Western blotting of subcellular fractions to investigate the distribution of FATP4 protein and measured enzyme activity in fractions from w.t. and FATP4 -/- fibroblasts. FATP4 protein and acyl-CoA synthetase activity localized to multiple organelles, including mitochondria, peroxisomes, endoplasmic reticulum, and the mitochondria-associated membrane fraction. We conclude that in murine skin fibroblasts, FATP4 is the major enzyme producing very long chain fatty acid-CoA for lipid metabolic pathways. Although FATP4 deficiency primarily affected very long chain fatty acid metabolism, mutant fibroblasts also showed reduced uptake of a fluorescent long chain fatty acid and reduced levels of long chain polyunsaturated fatty acids. FATP4-deficient cells also contained abnormal neutral lipid droplets. These additional defects indicate that metabolic abnormalities in these cells are not limited to very long chain fatty acids.

The Fatty Acid Transport Protein (FATP) Family: Very Long Chain Acyl-CoA Synthetases or Solute Carriers?

Cellular fatty acids typically derive from uptake from the extracellular milieu and, to a lesser extent, de novo synthesis. Extracellular fatty acids must traverse the plasma membrane, after which they are activated to their CoA thioesters for subsequent metabolism. Both uptake and metabolism are rapid processes, and there has been considerable debate as to whether transport of fatty acids across the lipid bilayer of the plasma membrane proceeds by diffusion or requires transport proteins. One group of proteins proposed to translocate fatty acids is the six-member Fatty Acid Transport Protein (FATP) family. These proteins were designated as such because when overexpressed, host cells exhibited higher rates of accretion of radioactive or fluorescent fatty acids. However, one member of this family, FATP2, is identical to an enzyme with very long-chain acyl-CoA synthetase (ACSVL) activity. This enzyme (ACSVL1 or FATP2), was isolated using classical protein purification techniques. In fact, the six-member ACSVL protein family is identical to the six-member FATP family. We and others have established that all six proteins have acyl-CoA synthetase activity. It remains to be established whether they participate in the physical translocation process, or facilitate transport by trapping, as CoA derivatives, fatty acids that enter cells by diffusion. To characterize the biological functions of the ACSVLs, we are investigating the properties of the overexpressed proteins and the endogenous proteins. We observed that for many ACSVLs, the subcellular location of the overexpressed protein differs from that of the endogenous protein. Using RNA interference (siRNA), we knocked down expression of FATP4 (proposed name: ACSVL5) in Neuro2a cells. Activation of both long-chain (C16:0) and very long-chain fatty acids (C24:0) was decreased when FATP4 was depleted. Despite decreased enzyme activity, initial rates of uptake of [14C]C16:0 were not affected when FATP4 was depleted. In contrast, COS-1 cells overexpressing FATP4 showed enhanced [14C]C16:0 uptake. Neither endogenous (Neuro2a) nor overexpressed (COS-1) FATP4 was localized to plasma membrane under routine cell culture conditions, but rather were found in intracellular membrane compartments. We conclude that, in the cell lines studied, endogenous FATP4 does not function to translocate FA across the plasma membrane.

Fatty acid metabolism in adipocytes: functional analysis of fatty acid transport proteins 1 and 4

The role of fatty acid transport protein 1 (FATP1) and FATP4 in facilitating adipocyte fatty acid metabolism was investigated using stable FATP1 or FATP4 knockdown (kd) 3T3-L1 cell lines derived from retrovirus-delivered short hairpin RNA (shRNA). Decreased expression of FATP1 or FATP4 did not affect preadipocyte differentiation or the expression of FATP1 (in FATP4 kd), FATP4 (in FATP1 kd), fatty acid translocase, acyl-coenzyme A synthetase 1, and adipocyte fatty acid binding protein but did lead to increased levels of peroxisome proliferator-activated receptor gamma and CCAAT/enhancer binding protein alpha. Both FATP1 and FATP4 kd adipocytes exhibited reduced triacylglycerol deposition and corresponding reductions in diacylglycerol and monoacylglycerol levels compared with control cells. FATP1 kd adipocytes displayed an approximately 25% reduction in basal (3)H-labeled fatty acid uptake and a complete loss of insulin-stimulated (3)H-labeled fatty acid uptake compared with control adipocytes. In contrast, FATP4 kd adipocytes as well as HEK-293 cells overexpressing FATP4 did not display any changes in fatty acid influx. FATP4 kd cells exhibited increased basal lipolysis, whereas FATP1 kd cells exhibited no change in lipolytic capacity. Consistent with reduced triacylglycerol accumulation, FATP1 and FATP4 kd adipocytes exhibited enhanced 2-deoxyglucose uptake compared with control adipocytes. These findings define unique and distinct roles for FATP1 and FATP4 in adipose fatty acid metabolism.

Mechanisms and Regulation of Protein-Mediated Cellular Fatty Acid Uptake: Molecular, Biochemical, and Physiological Evidence

![Figure][1] Arend Bonen Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada abonen{at}uoguelph.ca ![Figure][1] Adrian Chabowski Department of Physiology, Medical University of Bialystok, Bialystok, Poland ![

Rosiglitazone Inhibits Acyl-CoA Synthetase Activity and Fatty Acid Partitioning to Diacylglycerol and Triacylglycerol via a Peroxisome Proliferator–Activated Receptor-γ–Independent Mechanism in Human Arterial Smooth Muscle Cells and Macrophages

Rosiglitazone is an insulin-sensitizing agent that has recently been shown to exert beneficial effects on atherosclerosis. In addition to peroxisome proliferator-activated receptor (PPAR)-gamma, rosiglitazone can affect other targets, such as directly inhibiting recombinant long-chain acyl-CoA synthetase (ACSL)-4 activity. Because it is unknown if ACSL4 is expressed in vascular cells involved in atherosclerosis, we investigated the ability of rosiglitazone to inhibit ACSL activity and fatty acid partitioning in human and murine arterial smooth muscle cells (SMCs) and macrophages. Human and murine SMCs and human macrophages expressed Acsl4, and rosiglitazone inhibited Acsl activity in these cells. Furthermore, rosiglitazone acutely inhibited partitioning of fatty acids into phospholipids in human SMCs and inhibited fatty acid partitioning into diacylglycerol and triacylglycerol in human SMCs and macrophages through a PPAR-gamma-independent mechanism. Conversely, murine macrophages did not express ACSL4, and rosiglitazone did not inhibit ACSL activity in these cells, nor did it affect acute fatty acid partitioning into cellular lipids. Thus, rosiglitazone inhibits ACSL activity and fatty acid partitioning in human and murine SMCs and in human macrophages through a PPAR-gamma-independent mechanism likely to be mediated by ACSL4 inhibition. Therefore, rosiglitazone might alter the biological effects of fatty acids in these cells and in atherosclerosis.

Ontogeny of mRNA expression and activity of long-chain acyl-CoA synthetase (ACSL) isoforms in Mus musculus heart

Ontogeny of mRNA expression and activity of long-chain acyl-CoA synthetase (ACSL) isoforms in Mus musculus heart

Rosiglitazone Inhibits Acyl-CoA Synthetase Activity and Fatty Acid Partitioning to Diacylglycerol and Triacylglycerol via a Peroxisome Proliferator-Activated Receptor- -Independent Mechanism in Human Arterial Smooth Muscle Cells and Macrophages

Rosiglitazone Inhibits Acyl-CoA Synthetase Activity and Fatty Acid Partitioning to Diacylglycerol and Triacylglycerol via a Peroxisome Proliferator-Activated Receptor- -Independent Mechanism in Human Arterial Smooth Muscle Cells and Macrophages

Ontogeny of mRNA expression and activity of long-chain acyl-CoA synthetase (ACSL) isoforms in Mus musculus heart

Long-chain acyl-CoA synthetases (ACSL) activate fatty acids (FA) and provide substrates for virtually every metabolic pathway that catabolizes FA or synthesizes complex lipids. We have hypothesized that each of the five cloned ACSL isoforms partitions FA towards specific downstream pathways. Adult heart expresses all five cloned ACSL isoforms, but their independent functional roles have not been elucidated. Studies implicate ACSL1 in both oxidative and lipid synthetic pathways. To clarify the functional role of ACSL1 and the other ACSL isoforms (3–6), we examined ACS specific activity and Acsl mRNA expression in the developing mouse heart which increases FA oxidative pathways for energy production after birth. Compared to the embryonic heart, ACS specific activity was 14-fold higher on post-natal day 1 (P1). On P1, as compared to the fetus, only Acsl1 mRNA increased, whereas transcripts for the other Acsl isoforms remained the same, suggesting that ACSL1 is the major isoform responsible for activating long-chain FA for myocardial oxidation after birth. In contrast, the mRNA abundance of Acsl3 was highest on E16, and decreased dramatically by P7, suggesting that ACSL3 may play a critical role during the development of the fetal heart. Our data support the hypothesis that each ACSL has a specific role in the channeling of FA towards distinct metabolic fates.

Catalytic Properties of Domain-Exchanged Chimeric Proteins between Firefly Luciferase andDrosophilaFatty Acyl-CoA Synthetase CG6178

Firefly luciferase and fatty acyl-CoA synthetase are members of the acyl-CoA synthetase super family, which consists of a large N-terminal domain and a small C-terminal domain. Previously we found that firefly luciferase has fatty acyl-CoA synthetic activity, and also identified that the homolog of firefly luciferase in Drosophila melanogaster (CG6178) is a fatty acyl-CoA synthetase and is not a luciferase. In this study, we constructed chimeric proteins by exchanging the domain between Photinus pyralis luciferase (PpLase) and Drosophila CG6178, and determined luminescence and fatty acyl-CoA synthetic activities. A chimeric protein with the N-terminal domain of PpLase and the C-terminal domain of CG6178 (Pp/Dm) had luminescence activity, showing approximately 4% of the activity of wild-type luciferase. The Pp/Dm protein also had fatty acyl-CoA synthetic activity and the substrate specificity was similar to PpLase. In contrast, a chimeric protein with the N-terminal domain of CG6178 and the C-terminal of PpLase (Dm/Pp) had only fatty acyl-CoA synthetase activity, and the substrate specificity was similar to CG6178. These results suggest that the N-terminal domain of firefly luciferase is essential for substrate recognition, and that the C-terminal domain is indispensable but not specialized for the luminescence reaction.

Rat long-chain acyl-CoA synthetase mRNA, protein, and activity vary in tissue distribution and in response to diet

Distinct isoforms of long-chain acyl-CoA synthetases (ACSLs) may partition fatty acids toward specific metabolic cellular pathways. For each of the five members of the rat ACSL family, we analyzed tissue mRNA distributions, and we correlated the mRNA, protein, and activity of ACSL1 and ACSL4 after fasting and refeeding a 69% sucrose diet. Not only did quantitative real-time PCR analyses reveal unique tissue expression patterns for each ACSL isoform, but expression varied markedly in different adipose depots. Fasting increased ACSL4 mRNA abundance in liver, muscle, and gonadal and inguinal adipose tissues, and refeeding decreased ACSL4 mRNA. A similar pattern was observed for ACSL1, but both fasting and refeeding decreased ACSL1 mRNA in gonadal adipose. Fasting also decreased ACSL3 and ACSL5 mRNAs in liver and ACSL6 mRNA in muscle. Surprisingly, in nearly every tissue measured, the effects of fasting and refeeding on the mRNA abundance of ACSL1 and ACSL4 were discordant with changes in protein abundance. These data suggest that the individual ACSL isoforms are distinctly regulated across tissues and show that mRNA expression may not provide useful information about isoform function. They further suggest that translational or posttranslational modifications are likely to contribute to the regulation of ACSL isoforms.

Molecular organization of peroxisomal enzymes: Protein–protein interactions in the membrane and in the matrix

The β-oxidation of fatty acids in peroxisomes produces hydrogen peroxide (H 2O 2), a toxic metabolite, as a bi-product. Fatty acids β-oxidation activity is deficient in X-linked adrenoleukodystrophy (X-ALD) because of mutation in ALD-gene resulting in loss of very long chain acyl-CoA synthetase (VLCS) activity. It is also affected in disease with catalase negative peroxisomes as a result of inactivation by H 2O 2. Therefore, the following studies were undertaken to delineate the molecular interactions between both the ALD-gene product (adrenoleukodystrophy protein, ALDP) and VLCS as well as H 2O 2 degrading enzyme catalase and proteins of peroxisomal β-oxidation. Studies using a yeast two hybrid system and surface plasmon resonance techniques indicate that ALDP, a peroxisomal membrane protein, physically interacts with VLCS. Loss of these interactions in X-ALD cells may result in a deficiency in VLCS activity. The yeast two-hybrid system studies also indicated that catalase physically interacts with l-bifunctional enzyme ( l-BFE). Interactions between catalase and l-BFE were further supported by affinity purification, using a catalase-linked resin. The affinity bound 74-kDa protein, was identified as l-BFE by Western blot with specific antibodies and by proteomic analysis. Additional support for their interaction comes from immunoprecipitation of l-BFE with antibodies against catalase as a catalase- l-BFE complex. siRNA for l-BFE decreased the specific activity and protein levels of catalase without changing its subcellular distribution. These observations indicate that l-BFE might help in oligomerization and possibly in the localization of catalase at the site of H 2O 2 production in the peroxisomal β-oxidation pathway.

Acyl-CoA Synthetase Activity Links Wild-Type but Not Mutant α-Synuclein to Brain Arachidonate Metabolism

Because alpha-synuclein (Snca) has a role in brain lipid metabolism, we determined the impact that the loss of alpha-synuclein had on brain arachidonic acid (20:4n-6) metabolism in vivo using Snca-/- mice. We measured [1-(14)C]20:4n-6 incorporation and turnover kinetics in brain phospholipids using an established steady-state kinetic model. Liver was used as a negative control, and no changes were observed between groups. In Snca-/- brains, there was a marked reduction in 20:4n-6-CoA mass and in microsomal acyl-CoA synthetase (Acsl) activity toward 20:4n-6. Microsomal Acsl activity was completely restored after the addition of exogenous wild-type mouse or human alpha-synuclein, but not by A30P, E46K, and A53T forms of alpha-synuclein. Acsl and acyl-CoA hydrolase expression was not different between groups. The incorporation and turnover of 20:4n-6 into brain phospholipid pools were markedly reduced. The dilution coefficient lambda, which indicates 20:4n-6 recycling between the acyl-CoA pool and brain phospholipids, was increased 3.3-fold, indicating more 20:4n-6 was entering the 20:4n-6-CoA pool from the plasma relative to that being recycled from the phospholipids. This is consistent with the reduction in Acsl activity observed in the Snca-/- mice. Using titration microcalorimetry, we determined that alpha-synuclein bound free 20:4n-6 (Kd = 3.7 microM) but did not bind 20:4n-6-CoA. These data suggest alpha-synuclein is involved in substrate presentation to Acsl rather than product removal. In summary, our data demonstrate that alpha-synuclein has a major role in brain 20:4n-6 metabolism through its modulation of endoplasmic reticulum-localized acyl-CoA synthetase activity, although mutant forms of alpha-synuclein fail to restore this activity.

A novel mammalian bubblegum-related acyl-CoA synthetase restricted to testes and possibly involved in spermatogenesis

We have characterized a new, membrane-associated acyl-CoA synthetase (ACS), termed bubblegum-related protein (BGR), which upon functional analysis demonstrated ACS activity capable of activating long- and very long-chain fatty acids. By multiple tissue RNA array and Northern blot analyses, human BGR mRNA was exclusively detected in testes. Murine Bgr mRNA was specifically expressed in pubertal and adult testes and was further demonstrated to be enriched in germ cells and Sertoli cells while present at a lower level in Leydig cells both by in situ hybridization and cell type fractionation. The complex 5′-end of the BGR mRNA appears to underlie translational control leading to differential utilization of alternative translation start sites. Thus, the BGR gene expands the bubblegum ACS family with a testes-specific, developmentally regulated member that may play a role in spermatogenesis.

Fatty acid transport protein chimeras define functional domains

Fatty acids are involved in essential metabolic processes including production of metabolic energy and providing precursors for membrane lipid biosynthesis. Several membrane proteins have been proposed to facilitate cellular fatty acid uptake. Amongst these is the fatty acid transport protein (FATPs) family, which consists of six isoforms (FATP1-6) that have distinct expression patterns and intrinsic acyl Co-A synthetase activity. The precise role(s) of the different FATP isoforms in mediating fatty acid transport and trafficking are not well defined. Our laboratory recently characterized the murine FATP family members expressed in yeast and showed that they have distinct transport and activation activities. We hypothesize regions adjacent to and within the highly conserved ATP/AMP and FATP/VLACS motifs found in the FATP isoforms distinguish their unique transport and activation activities. A series of protein chimeras using the mmFATP1, 4 and 6 isoforms were constructed to test the hypothesis. Results from these experiments showed the fatty acid transport and activation activities within these mmFATP isoforms were distinguishable and were consistent with the notion that elements within and adjacent to the FATP/VLACS motif are crucial for fatty acid transport. This work is supported by NIH grant R01GM56850.

Fatty acid transport protein 1 and long-chain acyl coenzyme A synthetase 1 interact in adipocytes

The fatty acid transport proteins (FATP) and long-chain acyl coenzyme A synthetase (ACSL) proteins have been shown to play a role in facilitating long-chain fatty acid (LCFA) transport in mammalian cells under physiologic conditions. The involvement of both FATP and ACSL proteins is consistent with the model of vectorial acylation, in which fatty acid transport is coupled to esterification. This study was undertaken to determine whether the functions of these proteins are coordinated through a protein-protein interaction that might serve as a point of regulation for cellular fatty acid transport. We demonstrate for the first time that FATP1 and ACSL1 coimmunoprecipitate in 3T3-L1 adipocytes, indicating that these proteins form an oligomeric complex. The efficiency of FATP1 and ACSL1 coimmunoprecipitation is unaltered by acute insulin treatment, which stimulates fatty acid uptake, or by treatment with isoproterenol, which decreases fatty acid uptake and stimulates lipolysis. Moreover, inhibition of ACSL1 activity in adipocytes impairs fatty acid uptake, suggesting that esterification is essential for fatty acid transport. Together, our findings suggest that a constitutive interaction between FATP1 and ACSL1 contributes to the efficient cellular uptake of LCFAs in adipocytes through vectorial acylation.

Perturbation of subcellular acyl‐CoA metabolism by methoxy acetic acid

Toxicity of ethylene glycol monomethyl ether is mediated by 2-methoxy acetic acid (MAA, 3-oxabutanoic acid). Impact of MAA on enzymes critical to normal lipid metabolism (acyl-CoA synthetase (ACS), acyl-CoA hydrolase (ACH), carnitine acyltransferase (CAT), diacylglycerol acyltransferase (DGAT), glycine N-acyltransferases, and UDP-glucuronosyltransferases) is evaluated with subcellular rat liver fractions. For ACS, MAA was compared with physiologic butanoic acid; mitochondrial ACS activity was 60% greater (376.9 nmol/min/mg vs 234.7) with MAA. For other assays, synthetic MAA-CoA and butanoyl-CoA were used. Peroxisomal ACH hydrolyzed MAA-CoA at 22% the rate of butanoyl-CoA (0.26 vs 1.16 nmol/min/mg). Reactivity of MAA-CoA with mitochondrial and peroxisomal CAT was 20% and 28% that of control. MAA-CoA was more reactive with UDP-glucuronosyltransferases compared to butanoyl-CoA (13.5 vs 8.90 nmol/min/mg). Decreased hydrolysis and membrane transport of MAA-CoA, compared with its facile synthesis, may sequester CoA in subcellular compartments. Decreased glycine conjugation of MAA-CoA suggests that MAA is not effectively eliminated by this route; thus MAA-CoA may accumulate in detrimental amounts and possibly interfere with other mitochondrial metabolic reactions. (Supported by Oakland University REF.)

Direct interaction of Saccharomyces cerevisiae Faa1p with the Omi/HtrA protease orthologue Ynm3p alters lipid homeostasis

In yeast, long chain acyl-CoA synthetase (ACSL) activity is required for fatty acid uptake, metabolism and fatty acid-dependent transcriptional control. The major ACSL contributing these functions is Faa1p. In a yeast two-hybrid screen, the Omi/HtrA serine protease family orthologue Ynm3p (YNL123w) was identified as a specific interactor with Faa1p. Interaction of Ynm3p and Faa1p was confirmed by co-immunoprecipitation. Disruption of the YNM3 gene encoding Ynm3p resulted in increased fatty acid uptake, triglyceride accumulation and reduced expression of the fatty acid-responsive OLE1 gene encoding the essential Delta(9)-acyl-CoA desaturase. These changes were linked with increased Faa1p and Faa4p ACSL activities. We propose that Ynm3p modulates fatty acid metabolism and gene regulation through negative regulation of ACSL activity. Additional strain-specific phenotypes associated with deletion of YNM3 included inability to grow on non-fermentable carbon sources and altered cellular morphology.

Rat long-chain acyl-CoA synthetase mRNA, protein, and activity vary in tissue distribution and in response to diet

Rat long-chain acyl-CoA synthetase mRNA, protein, and activity vary in tissue distribution and in response to diet

Rat Long Chain Acyl-CoA Synthetase 5 Increases Fatty Acid Uptake and Partitioning to Cellular Triacylglycerol in McArdle-RH7777 Cells

Long chain acyl-CoA synthetase (ACSL) catalyzes the initial step in long chain fatty acid metabolism. Of the five mammalian ACSL isoforms cloned and characterized, ACSL5 is the only isoform found to be located, in part, on mitochondria and thus was hypothesized to be involved in fatty acid oxidation. To elucidate the specific roles of ACSL5 in fatty acid metabolism, we used adenoviral-mediated overexpression of ACSL5 (Ad-ACSL5) in rat hepatoma McArdle-RH7777 cells. Confocal microscopy revealed that Ad-ACSL5 colocalized to both mitochondria and endoplasmic reticulum. When compared with cells infected with Ad-GFP, Ad-ACSL5-infected cells at 24 h after infection had 2-fold higher acyl-CoA synthetase activities and 30% higher rates of fatty acid uptake when incubated with 500 microM [1-(14)C]oleic acid. Metabolism of [1-(14)C]oleic acid to cellular triacylglycerol (TAG) increased 42% in Ad-ACSL5-infected cells, but when compared with control cells, metabolism to acid-soluble metabolites, phospholipids, and medium TAG did not differ substantially. The incorporation of [1-(14)C]oleate and [1,2,3-(3)H]glycerol into TAG was similar in Ad-ACSL5-infected cells, thus indicating that Ad-ACSL5 increased TAG synthesis through both de novo and reacylation pathways. However, [1-(14)C]acetic acid incorporation into cellular lipids showed that, when compared with control cells, Ad-ACSL5-infected cells did not increase the metabolism of fatty acids that were derived from de novo synthesis. These results suggest that uptake of fatty acids into cells is regulated by metabolism and that overexpressed ACSL5 partitions exogenously derived fatty acids toward TAG synthesis and storage.