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Blair MC, Neinast MD, Jang C, Chu Q, Jung JW, Axsom J, Bornstein MR, Thorsheim C, Li K, Hoshino A, Yang S, Roth Flach RJ, Zhang BB, Rabinowitz JD, Arany Z. Branched-chain amino acid catabolism in muscle affects systemic BCAA levels but not insulin resistance. Nat Metab 2023; 5:589-606. [PMID: 37100997 PMCID: PMC10278155 DOI: 10.1038/s42255-023-00794-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Accepted: 03/29/2023] [Indexed: 04/28/2023]
Abstract
Elevated levels of plasma branched-chain amino acids (BCAAs) have been associated with insulin resistance and type 2 diabetes since the 1960s. Pharmacological activation of branched-chain α-ketoacid dehydrogenase (BCKDH), the rate-limiting enzyme of BCAA oxidation, lowers plasma BCAAs and improves insulin sensitivity. Here we show that modulation of BCKDH in skeletal muscle, but not liver, affects fasting plasma BCAAs in male mice. However, despite lowering BCAAs, increased BCAA oxidation in skeletal muscle does not improve insulin sensitivity. Our data indicate that skeletal muscle controls plasma BCAAs, that lowering fasting plasma BCAAs is insufficient to improve insulin sensitivity and that neither skeletal muscle nor liver account for the improved insulin sensitivity seen with pharmacological activation of BCKDH. These findings suggest potential concerted contributions of multiple tissues in the modulation of BCAA metabolism to alter insulin sensitivity.
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Affiliation(s)
- Megan C Blair
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Michael D Neinast
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA
| | - Cholsoon Jang
- Department of Biological Chemistry, University of California Irvine, Irvine, CA, USA
| | - Qingwei Chu
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Jae Woo Jung
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Jessie Axsom
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Marc R Bornstein
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Chelsea Thorsheim
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Kristina Li
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Steven Yang
- Washington University School of Medicine, St Louis, MO, USA
| | | | | | - Joshua D Rabinowitz
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA
| | - Zoltan Arany
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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Whole-body metabolic fate of branched-chain amino acids. Biochem J 2021; 478:765-776. [PMID: 33626142 DOI: 10.1042/bcj20200686] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 02/01/2021] [Accepted: 02/03/2021] [Indexed: 12/12/2022]
Abstract
Oxidation of branched-chain amino acids (BCAAs) is tightly regulated in mammals. We review here the distribution and regulation of whole-body BCAA oxidation. Phosphorylation and dephosphorylation of the rate-limiting enzyme, branched-chain α-ketoacid dehydrogenase complex directly regulates BCAA oxidation, and various other indirect mechanisms of regulation also exist. Most tissues throughout the body are capable of BCAA oxidation, and the flux of oxidative BCAA disposal in each tissue is influenced by three key factors: 1. tissue-specific preference for BCAA oxidation relative to other fuels, 2. the overall oxidative activity of mitochondria within a tissue, and 3. total tissue mass. Perturbations in BCAA oxidation have been implicated in many disease contexts, underscoring the importance of BCAA homeostasis in overall health.
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Abstract
Branched chain amino acids (BCAAs) are building blocks for all life-forms. We review here the fundamentals of BCAA metabolism in mammalian physiology. Decades of studies have elicited a deep understanding of biochemical reactions involved in BCAA catabolism. In addition, BCAAs and various catabolic products act as signaling molecules, activating programs ranging from protein synthesis to insulin secretion. How these processes are integrated at an organismal level is less clear. Inborn errors of metabolism highlight the importance of organismal regulation of BCAA physiology. More recently, subtle alterations of BCAA metabolism have been suggested to contribute to numerous prevalent diseases, including diabetes, cancer, and heart failure. Understanding the mechanisms underlying altered BCAA metabolism and how they contribute to disease pathophysiology will keep researchers busy for the foreseeable future.
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Affiliation(s)
- Michael Neinast
- Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
| | - Danielle Murashige
- Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
| | - Zoltan Arany
- Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
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Abstract
PURPOSE OF REVIEW Elevations in circulating branched chain amino acids (BCAAs) have gained attention as potential contributors to the development of insulin resistance and diabetes. RECENT FINDINGS Epidemiological evidence strongly supports this conclusion. Suppression of BCAA catabolism in adipose and hepatic tissues appears to be the primary drivers of plasma BCAA elevations. BCAA catabolism may be shunted to skeletal muscle, where it indirectly leads to FA accumulation and insulin resistance, via a number of proposed mechanisms. BCAAs have an important role in the development of IR, but our understanding of how plasma BCAA elevations occur, and how these elevations lead to insulin resistance, is still limited.
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Affiliation(s)
- Zoltan Arany
- Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, TRC 11-106 3400 Civic Blvd, Philadelphia, PA, 19104, USA.
| | - Michael Neinast
- Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, TRC 11-106 3400 Civic Blvd, Philadelphia, PA, 19104, USA
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Lib M, Rodriguez-Mari A, Marusich MF, Capaldi RA. Immunocapture and microplate-based activity measurement of mammalian pyruvate dehydrogenase complex. Anal Biochem 2003; 314:121-7. [PMID: 12633610 DOI: 10.1016/s0003-2697(02)00645-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Altered pyruvate dehydrogenase (PDH) functioning occurs in primary PDH deficiencies and in diabetes, starvation, sepsis, and possibly Alzheimer's disease. Currently, the activity of the enzyme complex is difficult to measure in a rapid high-throughput format. Here we describe the use of a monoclonal antibody raised against the E2 subunit to immunocapture the intact PDH complex still active when bound to 96-well plates. Enzyme turnover was measured by following NADH production spectrophotometrically or by a fluorescence assay on mitochondrial protein preparations in the range of 0.4 to 5.0 micro g per well. Activity is sensitive to known PDH inhibitors and remains regulated by phosphorylation and dephosphorylation after immunopurification because of the presence of bound PDH kinase(s) and phosphatase(s). It is shown that the immunocapture assay can be used to detect PDH deficiency in cell extracts of cultured fibroblasts from patients, making it useful in patient screens, as well as in the high-throughput format for discovery of new modulators of PDH functioning.
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Affiliation(s)
- Margarita Lib
- Institute of Molecular Biology, University of Oregon, Eugene, Orgon 97403-1229, USA
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Popov KM, Shimomura Y, Hawes JW, Harris RA. Branched-chain alpha-keto acid dehydrogenase kinase. Methods Enzymol 2001; 324:162-78. [PMID: 10989428 DOI: 10.1016/s0076-6879(00)24229-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Affiliation(s)
- K M Popov
- Department of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City 64110, USA
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Huang Y, Chuang DT. Structural organization of the rat branched-chain 2-oxo-acid dehydrogenase kinase gene and partial characterization of the promoter-regulatory region. Biochem J 1996; 313 ( Pt 2):603-9. [PMID: 8573099 PMCID: PMC1216950 DOI: 10.1042/bj3130603] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The gene encoding the rat branched-chain 2-oxo-acid dehydrogenase kinase (EC 2.7.1.115) has been isolated and partially characterized. The entire gene, including the promoter-regulatory region, spans 6 kb and contains 11 exons. The 5'-untranslated region comprising 264 bp is interrupted by intron 1 which is 581 bp in size. The complete in-frame sequence of intron 7 encodes the 49 amino acid insert previously reported to be present in the larger isoform of the rat kinase (Harris, Popov, Shimomura, Zhao, Jaskiewicz, Nanaumi and Suzuki (1992) Adv. Enzyme Regul. 32, 267-284). Sequencing of the 679 bp of the 5'-flanking region showed the absence of a canonical TATA box, similar to other branched-chain 2-oxo-acid dehydrogenase-complex genes. Several candidate cis-acting elements are present. These include CAAT boxes, Sp-1-binding sites, GCN-4 sites, CCAAT enhancer binding-protein sites (C/EBP) and glucocorticoid-responsive element (GRE) sites. Also present are a pair of direct repeats of unknown function. The luciferase-reporter assay showed that promoter activity is markedly higher in normal rat kidney (NRK-52E) cells than in rat hepatoma (FTO-2B) cells, and that the 5'-flanking region between bases -449 and +264 is both necessary and sufficient for basal transcription of the kinase gene.
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Affiliation(s)
- Y Huang
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235, USA
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Harris RA, Popov KM, Zhao Y, Kedishvili NY, Shimomura Y, Crabb DW. A new family of protein kinases--the mitochondrial protein kinases. ADVANCES IN ENZYME REGULATION 1995; 35:147-62. [PMID: 7572341 DOI: 10.1016/0065-2571(94)00020-4] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Molecular cloning has provided evidence for a new family of protein kinases in eukaryotic cells. These kinases show no sequence similarity with other eukaryotic protein kinases, but are related by sequence to the histidine protein kinases found in prokaryotes. These protein kinases, responsible for phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase and pyruvate dehydrogenase complexes, are located exclusively in mitochondrial matrix space and have most likely evolved from genes originally present in respiration-dependent bacteria endocytosed by primitive eukaryotic cells. Long-term regulatory mechanisms involved in the control of the activities of these two kinases are of considerable interest. Dietary protein deficiency increases the activity of branched-chain alpha-ketoacid dehydrogenase kinase associated with the branched-chain alpha-ketoacid dehydrogenase complex. The amount of branched-chain alpha-ketoacid dehydrogenase kinase protein associated with the branched-chain alpha-ketoacid dehydrogenase complex and the message level for branched-chain alpha-ketoacid dehydrogenase kinase are both greatly increased in the liver of rats starved for protein, suggesting increased expression of the gene encoding branched-chain alpha-ketoacid dehydrogenase kinase. The increase in branched-chain alpha-ketoacid dehydrogenase kinase activity results in greater phosphorylation and lower activity of the branched-chain alpha-ketoacid dehydrogenase complex. The metabolic consequence is conservation of branched chain amino acids for protein synthesis during periods of dietary protein deficiency. Two isoforms of pyruvate dehydrogenase kinase have been identified and cloned. Pyruvate dehydrogenase kinase 1, the first isoform cloned, corresponds to the 48 kDa subunit of the pyruvate dehydrogenase kinase isolated from rat heart tissue. Pyruvate dehydrogenase kinase 2, the second isoform cloned, corresponds to the 45 kDa subunit of this enzyme. In addition, it also appears to correspond to a possibly free or soluble form of pyruvate dehydrogenase kinase that was originally named kinase activator protein. Assuming that differences in kinetic and/or regulatory properties of these isoforms exist, tissue specific expression of these enzymes and/or control of their association with the complex will probably prove to be important for the long term regulation of the activity of the pyruvate dehydrogenase complex. Starvation and the diabetic state are known to greatly increase activity of the pyruvate dehydrogenase kinase in the liver, heart and muscle of the rat. This contributes in these states to the phosphorylation and inactivation of the pyruvate dehydrogenase complex and conservation of pyruvate and lactate for gluconeogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- R A Harris
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202, USA
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Zhao Y, Hawes J, Popov K, Jaskiewicz J, Shimomura Y, Crabb D, Harris R. Site-directed mutagenesis of phosphorylation sites of the branched chain alpha-ketoacid dehydrogenase complex. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32349-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Harris RA, Popov KM, Kedishvili NY, Zhao Y, Shimomura Y, Robbins B, Crabb DW. Molecular cloning of the branched-chain alpha-keto acid dehydrogenase kinase and the CoA-dependent methylmalonate semialdehyde dehydrogenase. ADVANCES IN ENZYME REGULATION 1993; 33:255-65. [PMID: 8356911 DOI: 10.1016/0065-2571(93)90022-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The complete amino acid sequence of rat liver CoA-dependent methylmalonate semialdehyde dehydrogenase, the enzyme responsible for the oxidative decarboxylation of malonate- and methylmalonate semialdehydes to acetyl- and propionyl-CoA in the distal portions of the valine and pyrimidine catabolic pathways, has been deduced from overlapping cDNAs obtained by screening a lambda gt11 library with nondegenerate oligonucleotide probes synthesized according to PCR-amplified portions coding for the N-terminal amino acid sequence of the enzyme. Although unique because of its requirement for coenzyme A, the methylmalonate semialdehyde dehydrogenase clearly belongs to the aldehyde dehydrogenase superfamily of enzymes. Quantitation of mRNA and protein levels indicates tissue-specific expression of methylmalonate semialdehyde dehydrogenase. A large increase in expression of methylmalonate semialdehyde dehydrogenase occurs during 3T3-L1 preadipocyte differentiation into adipocytes. The complete amino acid sequence of rat liver branched-chain alpha-ketoacid dehydrogenase kinase, the enzyme responsible for phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase complex, was deduced from a cDNA cloned by a procedure similar to that described above for the methylmalonate semialdehyde dehydrogenase. Expression of the cDNA in E. coli yielded a protein that phosphorylated and inactivated the branched-chain alpha-ketoacid dehydrogenase complex. Very little sequence similarity between branched-chain alpha-ketoacid dehydrogenase kinase and other eukaryotic protein kinases could be identified. However, a high degree of similarity within subdomains characteristic of prokaryotic histidine protein kinases was apparent. Thus, this first mitochondrial protein kinase to be cloned appears closer, evolutionarily, to the prokaryotic histidine protein kinases than eukaryotic ser/thr protein kinases.
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Affiliation(s)
- R A Harris
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202
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