Overexpression of human acyl-CoA thioesterase upregulates peroxisome biogenesis

Hepatic conversion of acetyl-CoA to acetate plays crucial roles in energy stress

Accumulating evidence indicates that acetate is increased under energy stress conditions such as those that occur in diabetes mellitus and prolonged starvation. However, how and where acetate is produced and the nature of its biological significance are largely unknown. We observed overproduction of acetate to concentrations comparable to those of ketone bodies in patients and mice with diabetes or starvation. Mechanistically, ACOT12 and ACOT8 are dramatically upregulated in the liver to convert free fatty acid-derived acetyl-CoA to acetate and CoA. This conversion not only provides a large amount of acetate, which preferentially fuels the brain rather than muscle, but also recycles CoA, which is required for sustained fatty acid oxidation and ketogenesis. We suggest that acetate is an emerging novel 'ketone body' that may be used as a parameter to evaluate the progression of energy stress.

High Expression of ACOT2 Predicts Worse Overall Survival and Abnormal Lipid Metabolism: A Potential Target for Acute Myeloid Leukemia

Acyl-CoA thioesterase (ACOT) plays a considerable role in lipid metabolism, which is closely related to the occurrence and development of cancer, nevertheless, its role has not been fully elucidated in acute myeloid leukemia (AML). To explore the role of ACOT2 in AML and to provide a potential therapeutic target for AML, the expression pattern of ACOT was investigated based on the TNMplot, Gene Expression Profiling Interactive Analysis (GEPIA), and Cancer Cell Line Encyclopedia (CCLE) database, and diagnostic value, prognostic value, and clinical phenotype of ACOT were explored based on data from The Cancer Genome Atlas (TCGA). Functional annotation and enrichment analysis of the common targets between ACOT2 coexpressed and AML-related genes were further performed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) analyses. The protein-protein interaction (PPI) network of ACOT2 coexpressed genes and functional ACOT2-related metabolites association network were constructed based on GeneMANIA and Human Metabolome Database. Among ACOTs, ACOT2 was highly expressed in AML compared to normal control subjects according to TNMplot, GEPIA, and CCLE database, which was significantly associated with poor overall survival (OS) in AML ( $P=0.003$ ). Moreover, ACOT2 exhibited excellent diagnostic efficiency for AML (AUC: 1.000) and related to French-American-British (FAB) classification and cytogenetics. GO, KEGG, and GSEA analyses of 71 common targets between ACOT2 coexpressed and AML-related genes revealed that ACOT2 is closely related to ACOT1, ACOT4, enoyl-acyl carrier protein reductase, mitochondrial (MECR), puromycin-sensitive aminopeptidase (NPEPPS), SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1), and long-chain fatty acid-CoA ligase 1 (ACSL1) in PPI network, and plays a significant role in lipid metabolism, that is, involved in fatty acid elongation and biosynthesis of unsaturated fatty acids. Collectively, the increase of ACOT2 may be an important characteristic of worse OS and abnormal lipid metabolism, suggesting that ACOT2 may become a potential therapeutic target for AML.

Cloning of the gene encoding acyl-CoA thioesterase 11 and its functional characterization in hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂) under heat stress

Members of the ACOT (acyl-CoA thioesterase) family hydrolyze fatty acyl-CoA to form free fatty acids (FFAs) and coenzyme A (CoA). These enzymes play important roles in fatty acid metabolism. Here, we report the cloning and functional analysis of acot11β in hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × P. vachelli ♂). The open reading frame of acot11β was found to be 594 bp in length, encoding 198 amino acids. We determined the transcript levels of acot11β in ten tissues of hybrid yellow catfish by qRT-PCR and found that it was highly expressed in the liver, so we chose the liver for further analysis. We determined the transcript levels of acot11β in hybrid yellow catfish under heat stress conditions, and analyzed the changes in serum biochemical parameters, liver biochemical parameters, and transcript levels of lipid metabolism-related genes. Healthy yellow catfish were subjected to heat stress at 35 °C for 96 h, and the experimental results were compared with those from fish in a control group (28 °C). The levels of glucose (GLU), total cholesterol (TC), and triglyceride (TG) in serum were significantly increased in the heat-stressed group compared with the control group (P < 0.05). Acute heat stress led to decreased liver glycogen contents, but significantly increased TC and TG contents in the liver (P < 0.05). The transcript levels of acot11β, acc, and fas were significantly reduced, while that of pparα was significantly increased in hybrid yellow catfish exposed to heat stress (P < 0.05). Our results indicate that acot11β plays an important role in regulating lipid metabolism in hybrid yellow catfish, and this metabolic process is greatly affected by temperature. These results may be useful for developing effective strategies to prevent or reduce metabolic disorders of yellow catfish caused by high temperature.

Peroxisomes in Immune Response and Inflammation

The immune response is essential to protect organisms from infection and an altered self. An organism’s overall metabolic status is now recognized as an important and long-overlooked mediator of immunity and has spurred new explorations of immune-related metabolic abnormalities. Peroxisomes are essential metabolic organelles with a central role in the synthesis and turnover of complex lipids and reactive species. Peroxisomes have recently been identified as pivotal regulators of immune functions and inflammation in the development and during infection, defining a new branch of immunometabolism. This review summarizes the current evidence that has helped to identify peroxisomes as central regulators of immunity and highlights the peroxisomal proteins and metabolites that have acquired relevance in human pathologies for their link to the development of inflammation, neuropathies, aging and cancer. This review then describes how peroxisomes govern immune signaling strategies such as phagocytosis and cytokine production and their relevance in fighting bacterial and viral infections. The mechanisms by which peroxisomes either control the activation of the immune response or trigger cellular metabolic changes that activate and resolve immune responses are also described.

The role of acyl-CoA thioesterase ACOT8I in mediating intracellular lipid metabolism in oleaginous fungus Mortierella alpina

Thioesterases (TEs) play an essential role in the metabolism of fatty acids (FAs). To explore the role of TEs in mediating intracellular lipid metabolism in the oleaginous fungus Mortierella alpina, the acyl-CoA thioesterase ACOT8I was overexpressed. The contents of total fatty acids (TFAs) were the same in the recombinant strains as in the wild-type M. alpina, whilst the production of free fatty acids (FFAs) was enhanced from about 0.9% (wild-type) to 2.8% (recombinant), a roughly threefold increase. Linoleic acid content in FFA form constituted about 9% of the TFAs in the FFA fraction in the recombinant strains but only about 1.3% in the wild-type M. alpina. The gamma-linolenic acid and arachidonic acid contents in FFA form accounted for about 4 and 25%, respectively, of the TFAs in the FFA fraction in the recombinant strains, whilst neither of them in FFA form were detected in the wild-type M. alpina. Overexpression of the TE ACOT8I in the oleaginous fungus M. alpina reinforced the flux from acyl-CoAs to FFAs, improved the production of FFAs and tailored the FA profiles of the lipid species.

Deactivating Fatty Acids: Acyl-CoA Thioesterase-Mediated Control of Lipid Metabolism

The cellular uptake of free fatty acids (FFA) is followed by esterification to coenzyme A (CoA), generating fatty acyl-CoAs that are substrates for oxidation or incorporation into complex lipids. Acyl-CoA thioesterases (ACOTs) constitute a family of enzymes that hydrolyze fatty acyl-CoAs to form FFA and CoA. Although biochemically and biophysically well characterized, the metabolic functions of these enzymes remain incompletely understood. Existing evidence suggests regulatory roles in controlling rates of peroxisomal and mitochondrial fatty acyl-CoA oxidation, as well as in the subcellular trafficking of fatty acids. Emerging data implicate ACOTs in the pathogenesis of metabolic diseases, suggesting that better understanding their pathobiology could reveal unique targets in the management of obesity, diabetes, and nonalcoholic fatty liver disease.

Transcriptional profiling of leukocytes from rheumatoid arthritis patients before and after anti-tumor necrosis factor therapy: A comparison of anti-nuclear antibody positive and negative subsets

Anti-nuclear antibodies (ANAs) may be induced in patients with rheumatoid arthritis (RA) receiving anti-tumor necrosis factor (TNF) therapy with TNF inhibitors (TNFi), etanercept, infliximab or adalimumab. In the present study, 11 patients who were TNFi drug naive were started on TNFi at a time of high disease activity. Of these, all cases were positive for rheumatoid factor and 9 cases tested were positive for anti-citrullinated peptide (anti-CCP) antibodies prior to TNFi treatment. Peripheral blood mononuclear cells (PBMCs) and serum were collected from all patients before and after TNFi therapy. Serum was assayed for ANAs over time. Total cellular RNA was extracted from PBMCs and assessed using Illumina arrays. Gene expression profiles were examined for alterations in key effector pathways. After 3 or more months on TNFi, 6 patients converted to ANA-positivity. Analysis of transcripts from patients with RA who converted to ANA-positivity after 3 months on TNFi identified complex gene expression profiles that reflected a reduction in cell adhesion, cell stress and lipid metabolism transcripts. In summary, unique transcriptional profiles in PBMCs from patients with RA were observed after TNFi therapy. This pilot study suggests that transcriptional profiling is a precise method of measuring the impact of TNFi therapies and reveals novel pathways that likely influence the immune response.

Endogenous Protein Interactome of Human UDP-Glucuronosyltransferases Exposed by Untargeted Proteomics

The conjugative metabolism mediated by UDP-glucuronosyltransferase enzymes (UGTs) significantly influences the bioavailability and biological responses of endogenous molecule substrates and xenobiotics including drugs. UGTs participate in the regulation of cellular homeostasis by limiting stress induced by toxic molecules, and by controlling hormonal signaling networks. Glucuronidation is highly regulated at genomic, transcriptional, post-transcriptional and post-translational levels. However, the UGT protein interaction network, which is likely to influence glucuronidation, has received little attention. We investigated the endogenous protein interactome of human UGT1A enzymes in main drug metabolizing non-malignant tissues where UGT expression is most prevalent, using an unbiased proteomics approach. Mass spectrometry analysis of affinity-purified UGT1A enzymes and associated protein complexes in liver, kidney and intestine tissues revealed an intricate interactome linking UGT1A enzymes to multiple metabolic pathways. Several proteins of pharmacological importance such as transferases (including UGT2 enzymes), transporters and dehydrogenases were identified, upholding a potential coordinated cellular response to small lipophilic molecules and drugs. Furthermore, a significant cluster of functionally related enzymes involved in fatty acid β-oxidation, as well as in the glycolysis and glycogenolysis pathways were enriched in UGT1A enzymes complexes. Several partnerships were confirmed by co-immunoprecipitations and co-localization by confocal microscopy. An enhanced accumulation of lipid droplets in a kidney cell model overexpressing the UGT1A9 enzyme supported the presence of a functional interplay. Our work provides unprecedented evidence for a functional interaction between glucuronidation and bioenergetic metabolism.

Regulation of peroxisomal lipid metabolism: the role of acyl-CoA and coenzyme A metabolizing enzymes

Peroxisomes are nearly ubiquitous organelles involved in a number of metabolic pathways that vary between organisms and tissues. A common metabolic function in mammals is the partial degradation of various (di)carboxylic acids via α- and β-oxidation. While only a small number of enzymes catalyze the reactions of β-oxidation, numerous auxiliary enzymes have been identified to be involved in uptake of fatty acids and cofactors required for β-oxidation, regulation of β-oxidation and transport of metabolites across the membrane. These proteins include membrane transporters/channels, acyl-CoA thioesterases, acyl-CoA:amino acid N-acyltransferases, carnitine acyltransferases and nudix hydrolases. Here we review the current view of the role of these auxiliary enzymes in peroxisomal lipid metabolism and propose that they function in concert to provide a means to regulate fatty acid metabolism and transport of products across the peroxisomal membrane.

Peroxisomes take shape

Peroxisomes carry out various oxidative reactions that are tightly regulated to adapt to the changing needs of the cell and varying external environments. Accordingly, they are remarkably fluid and can change dramatically in abundance, size, shape and content in response to numerous cues. These dynamics are controlled by multiple aspects of peroxisome biogenesis that are coordinately regulated with each other and with other cellular processes. Ongoing studies are deciphering the diverse molecular mechanisms that underlie biogenesis and how they cooperate to dynamically control peroxisome utility. These important challenges should lead to an understanding of peroxisome dynamics that can be capitalized upon for bioengineering and the development of therapies to improve human health.

The emerging role of acyl-CoA thioesterases and acyltransferases in regulating peroxisomal lipid metabolism

The importance of peroxisomes in lipid metabolism is now well established and peroxisomes contain approximately 60 enzymes involved in these lipid metabolic pathways. Several acyl-CoA thioesterase enzymes (ACOTs) have been identified in peroxisomes that catalyze the hydrolysis of acyl-CoAs (short-, medium-, long- and very long-chain), bile acid-CoAs, and methyl branched-CoAs, to the free fatty acid and coenzyme A. A number of acyltransferase enzymes, which are structurally and functionally related to ACOTs, have also been identified in peroxisomes, which conjugate (or amidate) bile acid-CoAs and acyl-CoAs to amino acids, resulting in the production of amidated bile acids and fatty acids. The function of ACOTs is to act as auxiliary enzymes in the α- and β-oxidation of various lipids in peroxisomes. Human peroxisomes contain at least two ACOTs (ACOT4 and ACOT8) whereas mouse peroxisomes contain six ACOTs (ACOT3, 4, 5, 6, 8 and 12). Similarly, human peroxisomes contain one bile acid-CoA:amino acid N-acyltransferase (BAAT), whereas mouse peroxisomes contain three acyltransferases (BAAT and acyl-CoA:amino acid N-acyltransferases 1 and 2: ACNAT1 and ACNAT2). This review will focus on the human and mouse peroxisomal ACOT and acyltransferase enzymes identified to date and discuss their cellular localizations, emerging structural information and functions as auxiliary enzymes in peroxisomal metabolic pathways.

A model of redox kinetics implicates the thiol proteome in cellular hydrogen peroxide responses

Hydrogen peroxide is appreciated as a cellular signaling molecule with second-messenger properties, yet the mechanisms by which the cell protects against intracellular H(2)O(2) accumulation are not fully understood. We introduce a network model of H(2)O(2) clearance that includes the pseudo-enzymatic oxidative turnover of protein thiols, the enzymatic actions of catalase, glutathione peroxidase, peroxiredoxin, and glutaredoxin, and the redox reactions of thioredoxin and glutathione. Simulations reproduced experimental observations of the rapid and transient oxidation of glutathione and the rapid, sustained oxidation of thioredoxin on exposure to extracellular H(2)O(2). The model correctly predicted early oxidation profiles for the glutathione and thioredoxin redox couples across a range of initial extracellular [H(2)O(2)] and highlights the importance of cytoplasmic membrane permeability to the cellular defense against exogenous sources of H(2)O(2). The protein oxidation profile predicted by the model suggests that approximately 10% of intracellular protein thiols react with hydrogen peroxide at substantial rates, with a majority of these proteins forming protein disulfides as opposed to protein S-glutathionylated adducts. A steady-state flux analysis predicted an unequal distribution of the intracellular anti-oxidative burden between thioredoxin-dependent and glutathione-dependent antioxidant pathways, with the former contributing the majority of the cellular antioxidant defense due to peroxiredoxins and protein disulfides.

Functional and structural properties of mammalian acyl-coenzyme A thioesterases

Acyl-coenzyme A thioesterases (Acots) play important cellular roles in mammalian fatty acid metabolism through modulation of cellular concentrations of activated fatty acyl-CoAs. Acots catalyse the hydrolysis of the thioester bond present within acyl-CoA ester molecules to yield coenzyme A (CoASH) and the corresponding non-esterified fatty acid. Acyl-CoA thioesterases are expressed ubiquitously in both prokaryotes and eukaryotes and, in higher order organisms, the enzymes are expressed and localised in a tissue-dependent manner within the cytosol, mitochondria, peroxisomes and endoplasmic reticulum. Recent studies have led to advances in the functional and structural characterization of many mammalian Acot family members. These include the structure determination of both type-I and type-II Acot family members, structural elucidation of the START domain of ACOT11, identification of roles in arachidonic acid and inflammatory prostaglandin production by Acot7, and inclusion of a 13th Acot family member. Here, we review and analyse the current literature on mammalian Acots with respect to their characterization and summarize the current knowledge on the structure, function and regulation of this enzyme family.

The peroxisomal Acyl-CoA thioesterase Pte1p from Saccharomyces cerevisiae is required for efficient degradation of short straight chain and branched chain fatty acids

The role of the Saccharomyces cerevisae peroxisomal acyl-coenzyme A (acyl-CoA) thioesterase (Pte1p) in fatty acid beta-oxidation was studied by analyzing the in vitro kinetic activity of the purified protein as well as by measuring the carbon flux through the beta-oxidation cycle in vivo using the synthesis of peroxisomal polyhydroxyalkanoate (PHA) from the polymerization of the 3-hydroxyacyl-CoAs as a marker. The amount of PHA synthesized from the degradation of 10-cis-heptadecenoic, tridecanoic, undecanoic, or nonanoic acids was equivalent or slightly reduced in the pte1Delta strain compared with wild type. In contrast, a strong reduction in PHA synthesized from heptanoic acid and 8-methyl-nonanoic acid was observed for the pte1Delta strain compared with wild type. The poor catabolism of 8-methyl-nonanoic acid via beta-oxidation in pte1Delta negatively impacted the degradation of 10-cis-heptadecenoic acid and reduced the ability of the cells to efficiently grow in medium containing such fatty acids. An increase in the proportion of the short chain 3-hydroxyacid monomers was observed in PHA synthesized in pte1Delta cells grown on a variety of fatty acids, indicating a reduction in the metabolism of short chain acyl-CoAs in these cells. A purified histidine-tagged Pte1p showed high activity toward short and medium chain length acyl-CoAs, including butyryl-CoA, decanoyl-CoA and 8-methyl-nonanoyl-CoA. The kinetic parameters measured for the purified Pte1p fit well with the implication of this enzyme in the efficient metabolism of short straight and branched chain fatty acyl-CoAs by the beta-oxidation cycle.