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ACOT7 in Brain 2013 Acyl Coenzyme A Thioesterase 7 Regulates Neuronal Fatty Acid Metabolism To Prevent Neurotoxicity Jessica M. Ellis,a G. William Wong,b Michael J. Wolfganga Departments of Biological Chemistrya and Physiology,b Johns Hopkins University School of Medicine, Center for Metabolism and Obesity Research, Baltimore, Maryland, USA Numerous neurological diseases are associated with dysregulated lipid metabolism; however, the basic metabolic control of fatty acid metabolism in neurons remains enigmatic. Here we have shown that neurons have abundant expression and activity of the long-chain cytoplasmic acyl coenzyme A (acyl-CoA) thioesterase 7 (ACOT7) to regulate lipid retention and metabolism. Unbi- ,ased and targeted metabolomic analysis of fasted mice with a conditional knockout of ACOT7 in the nervous system, Acot7N؊/؊ revealed increased fatty acid flux into multiple long-chain acyl-CoA-dependent pathways. The alterations in brain fatty acid me- tabolism were concomitant with a loss of lean mass, hypermetabolism, hepatic steatosis, dyslipidemia, and behavioral hyperex- -citability in Acot7N؊/؊ mice. These failures in adaptive energy metabolism are common in neurodegenerative diseases. In agree ment, Acot7N؊/؊ mice exhibit neurological dysfunction and neurodegeneration. These data show that ACOT7 counterregulates fatty acid metabolism in neurons and protects against neurotoxicity. eurons have a unique lipid composition that is critical for the terases has been proposed to play a regulatory role in the metab- Ndevelopment and function of the nervous system, and defects olism of fatty acids (22–25). Acyl-CoA thioesterases (ACOTs) are in lipid metabolism result in severe and debilitating neurological present in simple prokaryotes and conserved and expanded disease; however, there is a dearth of understanding about how through humans. Mammals express acyl-CoA thioesterases that neurons uniquely regulate intracellular fatty acid (FA) metabo- have various chain length specificities, cell type expression, and lism. There are numerous inborn errors of lipid metabolism that subcellular localizations (22). Although some of the basic enzy- have clear neuropathological outcomes. Apart from these inborn matic characteristics of ACOTs have been previously reported, errors of metabolism, it is becoming increasingly evident that little is known about the biochemical or physiologic significance many neurodegenerative diseases, including Alzheimer’s disease, of this enigmatic class of enzymes in a cellular or organismal con- Parkinson’s disease, and amyotrophic lateral sclerosis (ALS), have text. Neurons have a particularly high cytoplasmic long-chain underlying metabolic dysfunction that often involves dysregu- acyl-CoA hydrolase activity, which is thought to be mediated lated lipid metabolism (1–5). A better understanding of neuronal mainly by Acyl-CoA thioesterase 7 (ACOT7) (26). The high activ- metabolism is required to provide insight into neurological func- ity and cytoplasmic localization of an acyl-CoA hydrolase such as tion and pathology, since dysregulated neurometabolism may ACOT7 creates an apparently futile cycle because it is juxtaposed contribute to the progression of diabetes and obesity and hasten to the ATP-dependent Acyl-CoA synthetases. Given its biochem- neurodegeneration (6–8). ical activity, localization, and chain length specificity, ACOT7 Fatty acid metabolism in the nervous system has been shown to likely represents a major regulatory point in neural fatty acid me- directly and profoundly regulate multiple aspects of animal phys- tabolism by limiting the access of long-chain acyl-CoAs. Acyl- iology and behavior (9–14). Furthermore, ion channels that play a CoA hydrolysis provides neurons with a unique means to regulate role in neuronal activation have been shown to be regulated by fatty acid metabolism because neurons have a limited capacity for lipids either directly or indirectly (15–20). Fatty acids are precur- neutral lipid storage and mitochondrial fatty acid beta oxidation. sors for membrane biosynthesis, signaling lipids, posttransla- Here we have shown that ACOT7 is highly expressed in neu- tional modification (e.g., palmitoylation), energy storage, and en- rons and constitutes the main source of acyl-CoA thioesterase ergy production. Although most neurons are not thought to rely activity in the brain. Using a conditional knockout (KO) of on fatty acids to meet their cellular bioenergetic requirements, the ACOT7 in the nervous system, we have shown that ACOT7 regu- brain has a unique fatty acid composition and metabolism that are lates the metabolism of long-chain fatty acids into multiple acyl- critical for neural function. Due in part to the incredible hetero- CoA-dependent pathways. The biochemical consequences of a geneity of neurons themselves and the diversity of neuronal cell types in general, the means by which any neuronal population obtains or utilizes fatty acids is poorly understood. Received 14 November 2012 Returned for modification 7 December 2012 Fatty acids either made de novo or taken up from the diet re- Accepted 21 February 2013 quire ligation to coenzyme A (CoA) for their cellular retention Published ahead of print 4 March 2013 and activation by one of 26 known acyl-CoA synthetases (21). The Address correspondence to Michael J. Wolfgang, [email protected]. resulting acyl-CoAs, with their high-energy thioester linkage, are Supplemental material for this article may be found at http://dx.doi.org/10.1128 used as the substrate for almost all anabolic and catabolic bio- /MCB.01548-12 chemical reactions requiring fatty acids, with the noted exception Copyright © 2013, American Society for Microbiology. All Rights Reserved. of eicosanoid synthesis. The hydrolysis of acyl-CoAs to free fatty doi:10.1128/MCB.01548-12 acid (FFA) and free CoA by one of a family of acyl-CoA thioes- May 2013 Volume 33 Number 9 Molecular and Cellular Biology p. 1869–1882 mcb.asm.org 1869 Ellis et al. loss of ACOT7 are largely not apparent in fed mice and are greatly acclimatization period to a 70-dB background noise (continuous exacerbated by fasting, a time when circulating free fatty acids throughout the session), followed by the presentation of 10 40-ms 120-dB from lipolysis are elevated. ACOT7 brain-specific KO mice have white-noise stimuli at a 20-s interstimulus interval (the habituation ses- no alterations in food intake or body weight; however, KO mice sion). Upon completion of the habituation session, each mouse was left in have multiple alterations in behavior and physiology, including a the enclosure for 5 min without presentation of any startle stimuli. Im- loss of lean mass, hypermetabolism, hepatic steatosis, dyslipide- mediately after, the prepulse inhibition (PPI) session was begun. During each PPI session, a mouse was exposed to the following types of trials: mia, and behavioral hyperexcitability. These phenotypic changes pulse-alone trial (a 120-dB, 100-ms, broadband burst), the omission of are seen in models of neurodegeneration, and ACOT7 KO mice stimuli (no-stimulus trial), and five prepulse-pulse combinations (pre- exhibit neurodegeneration and neurological/behavioral deficits. pulse-pulse trials) consisting of a 20-ms broadband burst used as a pre- These data suggest that ACOT7 is required to maintain neuronal pulse and presented 80-ms before the pulse using one of the five prepulse fatty acid homeostasis, particularly during fasting, and dysregula- intensities: 74, 78, 82, 86, and 90 dB. Each session consists of six presen- tion of ACOT7 results in neural lipotoxicity. tations of each type of trial presented in a pseudorandom order. PPI is assessed as the percentage scores of PPI (%PPI): [1 Ϫ (average startle ϫ MATERIALS AND METHODS amplitude after prepulse/average startle amplitude after pulse only)] flox/flox 100 for each animal separately. Mice. Acot7 mice were generated by targeting loxP sequences to All procedures were performed in accordance with the National Insti- introns flanking exon 2 of the mouse acot7 gene by homologous recom- tutes of Health Guide for the Care and Use of Laboratory Animals and bination in C57BL/6 embryonic stem cells by standard methods. NϪ/Ϫ flox/flox under the approval of the Johns Hopkins Medical School Animal Care Acot7 and littermate Acot7 control mice were housed (12-h and Use Committee. light/dark cycle) with free access to water and a chow diet (13.5% kcal Metabolite analysis. Plasma triacylglycerol (TAG) (Sigma), ␤-hy- from fat; number 5001, LabDiet; PMI Nutrition International, St. Louis, droxybutyrate (Stanbio), cholesterol (BioAssay Systems), FFA (Wako), MO) or a high-fat diet (HFD) (60% kcal from fat, D12492; Research glucose (GlucometerX; BioAssay Systems), creatine kinase (Cayman), Diets). Body fat mass was assessed by magnetic resonance imaging analy- and free and total glycerol (Sigma) were measured colorimetrically. Brain sis (QNMR EchoMRI100; Echo Medical Systems, LLC). For thermogen- coenzyme A content was measured fluorometrically (Cayman Chemi- esis experiments, mice were fasted overnight or fed ad libitum and placed cals). Acyl-CoAs were measured by high-performance liquid chromatog- in a 4°C environment without food. Temperature was measured hourly raphy (HPLC) as detailed elsewhere (28). Unbiased metabolomics analy- with a rectal probe thermometer (BAT-12; Physitemp). sis was done as described previously (29). Brain and liver total lipids were Calorimetry and behavior. Locomotor activity, food intake, and extracted with chloroform-methanol via the Folch method
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