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Bjorkman SH, Marti A, Jena J, García-Peña LM, Weatherford ET, Kato K, Koneru J, Chen J, Sood A, Potthoff MJ, Adams CM, Abel ED, Pereira RO. ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms. Sci Rep 2024; 14:1563. [PMID: 38238383 PMCID: PMC10796914 DOI: 10.1038/s41598-024-52004-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 01/12/2024] [Indexed: 01/22/2024] Open
Abstract
In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.
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Affiliation(s)
- Sarah H Bjorkman
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
- Department of Obstetrics and Gynecology, Reproductive Endocrinology and Infertility, University of Iowa Hospital and Clinics, Iowa City, IA, USA
| | - Alex Marti
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Jayashree Jena
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Luis Miguel García-Peña
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Eric T Weatherford
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Kevin Kato
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Jivan Koneru
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Jason Chen
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Ayushi Sood
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
| | - Matthew J Potthoff
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
- Department of Neuroscience and Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Christopher M Adams
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
- Division of Endocrinology, Metabolism and Nutrition, Department of Medicine, Mayo Clinic, Rochester, MN, USA
| | - E Dale Abel
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Renata O Pereira
- Fraternal Order of Eagles Diabetes Research Center and Division of Endocrinology and Metabolism, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 169 Newton Road, 4338 PBDB, Iowa City, IA, 52242, USA.
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Bjorkman SH, Marti A, Jena J, Garcia Pena LM, Weatherford ET, Kato K, Koneru J, Chen J, Sood A, Potthoff MJ, Adams CM, Abel ED, Pereira RO. ATF4 Expression in Thermogenic Adipocytes is Required for Cold-Induced Thermogenesis in Mice via FGF21-Independent Mechanisms. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.09.531964. [PMID: 36945390 PMCID: PMC10028960 DOI: 10.1101/2023.03.09.531964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially via upregulation of FGF21. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis by generating mice selectively lacking either Atf4 ( ATF4 BKO ) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum -fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue (WAT). Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum -fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis by activating amino acid metabolism in BAT in a FGF21-independent manner.
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Abstract
Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.
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Affiliation(s)
- André C Carpentier
- Division of Endocrinology, Department of Medicine, Centre de recherche du Centre hospitalier universitaire de Sherbrooke, Université de Sherbrooke, Sherbrooke, Quebec, J1H 5N4, Canada
| | - Denis P Blondin
- Division of Neurology, Department of Medicine, Centre de recherche du Centre hospitalier universitaire de Sherbrooke, Université de Sherbrooke, Sherbrooke, Quebec, J1H 5N4, Canada
| | | | - Denis Richard
- Centre de recherche de l’Institut universitaire de cardiologie et de pneumologie de Québec, Université Laval, Quebec City, Quebec, G1V 4G5, Canada
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Colas C, Mouchiroud M, Al Dow M, Kolnohuz A, Gélinas Y, Caron A, Laplante M. DEPTOR loss impairs brown adipocyte development in vitro but has limited impacts in mice. Mol Metab 2022; 67:101660. [PMID: 36535626 PMCID: PMC9827061 DOI: 10.1016/j.molmet.2022.101660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 12/09/2022] [Accepted: 12/11/2022] [Indexed: 12/23/2022] Open
Abstract
OBJECTIVES The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that regulates growth and metabolism. In mice, activation of mTOR controls cold adaptation by promoting the recruitment and the activation of brown adipose tissue (BAT). DEP-domain containing mTOR-interacting protein (DEPTOR) interacts with mTOR to modulate its activity. Whether DEPTOR levels are modulated by cold in BAT and whether this protein regulates brown adipocyte development and thermogenic activation has never been tested. METHODS DEPTOR levels were measured in mouse tissues upon cold exposure and in brown preadipocytes following the induction of adipogenesis. Lentiviruses expressing short-hairpin RNA were used to repress DEPTOR expression in brown preadipocytes in vitro. Conditional deletion of DEPTOR in brown preadipocytes and in mature brown fat cells was achieved by crossing DEPTOR floxed mice with either Myf5-Cre or Ucp1-CreERT2 mice. These animals were exposed to cold and extensively phenotyped. RESULTS DEPTOR is highly expressed in BAT and its levels are induced by chronic cold exposure, a condition that triggers BAT expansion and activation. Supporting a role for DEPTOR in brown fat cell recruitment, we found that DEPTOR is induced during brown adipocyte development and that its depletion impairs adipogenesis in vitro. This adipogenic lesion was associated with defects in both Akt activation and the expression of key adipogenic regulators. Conditional deletion of DEPTOR in brown preadipocytes or mature brown fat cells did not impact BAT recruitment and thermogenesis in mice but slightly reduced the expression of adipogenic and lipogenic genes. CONCLUSIONS DEPTOR is highly expressed in BAT and its levels are dynamically regulated during brown fat cell development and upon cold exposure. Although DEPTOR depletion severely represses brown fat adipogenesis in vitro, its deletion is dispensable for BAT development, recruitment, and thermogenic activation in mice.
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Affiliation(s)
- Charles Colas
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Centre de recherche sur le cancer de l'Université Laval, Université Laval, 9 rue McMahon, Québec, QC, Canada, G1R 3S3
| | - Mathilde Mouchiroud
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Centre de recherche sur le cancer de l'Université Laval, Université Laval, 9 rue McMahon, Québec, QC, Canada, G1R 3S3
| | - Manal Al Dow
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Centre de recherche sur le cancer de l'Université Laval, Université Laval, 9 rue McMahon, Québec, QC, Canada, G1R 3S3
| | - Alona Kolnohuz
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Centre de recherche sur le cancer de l'Université Laval, Université Laval, 9 rue McMahon, Québec, QC, Canada, G1R 3S3
| | - Yves Gélinas
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Centre de recherche sur le cancer de l'Université Laval, Université Laval, 9 rue McMahon, Québec, QC, Canada, G1R 3S3
| | - Alexandre Caron
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Faculté de Pharmacie, Université Laval, 1050 avenue de la Médecine, Québec, QC, Canada, G1V0A6
| | - Mathieu Laplante
- Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval (CRIUCPQ), 2725 Chemin Ste-Foy, Québec, QC, Canada, G1V 4G5; Centre de recherche sur le cancer de l'Université Laval, Université Laval, 9 rue McMahon, Québec, QC, Canada, G1R 3S3; Département de Médecine, Université Laval, 1050 avenue de la Médecine, Québec, QC, Canada, G1V0A6.
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Saha B, Leite-Dellova DCA, Demko J, Sørensen MV, Takagi E, Gleason CE, Shabbir W, Pearce D. WNK1 is a chloride-stimulated scaffold that regulates mTORC2 activity and ion transport. J Cell Sci 2022; 135:jcs260313. [PMID: 36373794 PMCID: PMC9789407 DOI: 10.1242/jcs.260313] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 10/26/2022] [Indexed: 11/16/2022] Open
Abstract
Mammalian (or mechanistic) target of rapamycin complex 2 (mTORC2) is a kinase complex that targets predominantly Akt family proteins, SGK1 and protein kinase C (PKC), and has well-characterized roles in mediating hormone and growth factor effects on a wide array of cellular processes. Recent evidence suggests that mTORC2 is also directly stimulated in renal tubule cells by increased extracellular K+ concentration, leading to activation of the Na+ channel, ENaC, and increasing the electrical driving force for K+ secretion. We identify here a signaling mechanism for this local effect of K+. We show that an increase in extracellular [K+] leads to a rise in intracellular chloride (Cl-), which stimulates a previously unknown scaffolding activity of the protein 'with no lysine-1' (WNK1) kinase. WNK1 interacts selectively with SGK1 and recruits it to mTORC2, resulting in enhanced SGK1 phosphorylation and SGK1-dependent activation of ENaC. This scaffolding effect of WNK1 is independent of its own kinase activity and does not cause a generalized stimulation of mTORC2 kinase activity. These findings establish a novel WNK1-dependent regulatory mechanism that harnesses mTORC2 kinase activity selectively toward SGK1 to control epithelial ion transport and electrolyte homeostasis.
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Affiliation(s)
- Bidisha Saha
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Deise C. A. Leite-Dellova
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, Sao Paulo 13635-900, Brazil
| | - John Demko
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Mads Vaarby Sørensen
- Departments of Biomedicine and Physiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Enzo Takagi
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Catherine E. Gleason
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Waheed Shabbir
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - David Pearce
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
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6
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Eerola K, Longo F, Reinbothe TM, Richard JE, Shevchouk OT, López-Ferreras L, Mishra D, Asker M, Tolö J, Miranda C, Musovic S, Olofsson CS, Rorsman P, Skibicka KP. Hindbrain insulin controls feeding behavior. Mol Metab 2022; 66:101614. [PMID: 36244663 PMCID: PMC9637798 DOI: 10.1016/j.molmet.2022.101614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 10/10/2022] [Accepted: 10/11/2022] [Indexed: 11/08/2022] Open
Abstract
OBJECTIVE Pancreatic insulin was discovered a century ago, and this discovery led to the first lifesaving treatment for diabetes. While still controversial, nearly one hundred published reports suggest that insulin is also produced in the brain, with most focusing on hypothalamic or cortical insulin-producing cells. However, specific function for insulin produced within the brain remains poorly understood. Here we identify insulin expression in the hindbrain's dorsal vagal complex (DVC), and determine the role of this source of insulin in feeding and metabolism, as well as its response to diet-induced obesity in mice. METHODS To determine the contribution of Ins2-producing neurons to feeding behavior in mice, we used the cross of transgenic RipHER-cre mouse and channelrhodopsin-2 expressing animals, which allowed us to optogenetically stimulate neurons expressing Ins2 in vivo. To confirm the presence of insulin expression in Rip-labeled DVC cells, in situ hybridization was used. To ascertain the specific role of insulin in effects discovered via optogenetic stimulation a selective, CNS applied, insulin receptor antagonist was used. To understand the physiological contribution of insulin made in the hindbrain a virogenetic knockdown strategy was used. RESULTS Insulin gene expression and presence of insulin-promoter driven fluorescence in rat insulin promoter (Rip)-transgenic mice were detected in the hypothalamus, but also in the DVC. Insulin mRNA was present in nearly all fluorescently labeled cells in DVC. Diet-induced obesity in mice altered brain insulin gene expression, in a neuroanatomically divergent manner; while in the hypothalamus the expected obesity-induced reduction was found, in the DVC diet-induced obesity resulted in increased expression of the insulin gene. This led us to hypothesize a potentially divergent energy balance role of insulin in these two brain areas. To determine the acute impact of activating insulin-producing neurons in the DVC, optic stimulation of light-sensitive channelrhodopsin 2 in Rip-transgenic mice was utilized. Optogenetic photoactivation induced hyperphagia after acute activation of the DVC insulin neurons. This hyperphagia was blocked by central application of the insulin receptor antagonist S961, suggesting the feeding response was driven by insulin. To determine whether DVC insulin has a necessary contribution to feeding and metabolism, virogenetic insulin gene knockdown (KD) strategy, which allows for site-specific reduction of insulin gene expression in adult mice, was used. While chow-fed mice failed to reveal any changes of feeding or thermogenesis in response to the KD, mice challenged with a high-fat diet consumed less food. No changes in body weight were identified, possibly resulting from compensatory reduction in thermogenesis. CONCLUSIONS Together, our data suggest an important role for hindbrain insulin and insulin-producing cells in energy homeostasis.
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Affiliation(s)
- Kim Eerola
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden,Unit of Integrative Physiology and Pharmacology, Institute of Biomedicine, University of Turku, Finland
| | - Francesco Longo
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden
| | | | | | | | | | - Devesh Mishra
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden
| | - Mohammed Asker
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden
| | - Johan Tolö
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden
| | - Caroline Miranda
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden
| | - Saliha Musovic
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden
| | | | - Patrik Rorsman
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden,Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
| | - Karolina P. Skibicka
- Institute for Neuroscience and Physiology, University of Gothenburg, Sweden,Wallenberg Centre for Molecular and Translational Medicine, University of Gothenburg, Sweden,Department of Nutritional Sciences and The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA, USA,Corresponding author. Department of Physiology, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Medicinaregatan 11, PO Box 434, SE-405 30, Gothenburg, Sweden. Fax: +46 31 786 3512.
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Yu Z, Chen J, Takagi E, Wang F, Saha B, Liu X, Joubert LM, Gleason CE, Jin M, Li C, Nowotny C, Agard D, Cheng Y, Pearce D. Interactions between mTORC2 core subunits Rictor and mSin1 dictate selective and context-dependent phosphorylation of substrate kinases SGK1 and Akt. J Biol Chem 2022; 298:102288. [PMID: 35926713 PMCID: PMC9440446 DOI: 10.1016/j.jbc.2022.102288] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 07/04/2022] [Accepted: 07/05/2022] [Indexed: 12/02/2022] Open
Abstract
Mechanistic target of rapamycin complex 2 (mTORC2) is a multi-subunit kinase complex, central to multiple essential signaling pathways. Two core subunits, Rictor and mSin1, distinguish it from the related mTORC1 and support context-dependent phosphorylation of its substrates. mTORC2 structures have been determined previously; however, important questions remain, particularly regarding the structural determinants mediating substrate specificity and context-dependent activity. Here, we used cryo-EM to obtain high-resolution structures of the human mTORC2 apo-complex in the presence of substrates Akt and SGK1. Using functional assays, we then tested predictions suggested by substrate-induced structural changes in mTORC2. For the first time, we visualized in the apo-state the side chain interactions between Rictor and mTOR that sterically occlude recruitment of mTORC1 substrates and confer resistance to the mTORC1 inhibitor rapamycin. Also in the apo-state, we observed that mSin1 formed extensive contacts with Rictor via a pair of short α-helices nestled between two Rictor helical repeat clusters, as well as by an extended strand that makes multiple weak contacts with Rictor helical cluster 1. In co-complex structures, we found that SGK1, but not Akt, markedly altered the conformation of the mSin1 N-terminal extended strand, disrupting multiple weak interactions while inducing a large rotation of mSin1 residue Arg-83, which then interacts with a patch of negatively charged residues within Rictor. Finally, we demonstrate mutation of Arg-83 to Ala selectively disrupts mTORC2-dependent phosphorylation of SGK1, but not of Akt, supporting context-dependent substrate selection. These findings provide new structural and functional insights into mTORC2 specificity and context-dependent activity.
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Affiliation(s)
- Zanlin Yu
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Junliang Chen
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Enzo Takagi
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Feng Wang
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Bidisha Saha
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Xi Liu
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, USA
| | - Lydia-Marie Joubert
- Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California, USA
| | - Catherine E Gleason
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Mingliang Jin
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Chengmin Li
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Carlos Nowotny
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - David Agard
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Yifan Cheng
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA; Howard Hughes Medical Institute, University of California San Francisco, San Francisco, California, USA
| | - David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA.
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8
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Onogi Y, Ussar S. Regulatory networks determining substrate utilization in brown adipocytes. Trends Endocrinol Metab 2022; 33:493-506. [PMID: 35491296 DOI: 10.1016/j.tem.2022.04.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Revised: 03/25/2022] [Accepted: 04/05/2022] [Indexed: 11/16/2022]
Abstract
Brown adipose tissue (BAT) is often considered as a sink for nutrients to generate heat. However, when the complex hormonal and nervous inputs and intracellular signaling networks regulating substrate utilization are considered, BAT appears much more as a tightly controlled rheostat, regulating body temperature and balancing circulating nutrient levels. Here we provide an overview of key regulatory circuits, including the diurnal rhythm, determining glucose, fatty acid, and amino acid utilization and the interdependency of these nutrients in thermogenesis. Moreover, we discuss additional factors mediating sympathetic BAT activation beyond β-adrenergic signaling and the limitations of glucose-based BAT activity measurements to foster a better understanding and interpretation of BAT activity data.
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Affiliation(s)
- Yasuhiro Onogi
- RG Adipocytes & Metabolism, Institute for Diabetes & Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health GmbH, 85764 Neuherberg, Germany; German Center for Diabetes Research (DZD), 85764 Neuherberg, Germany.
| | - Siegfried Ussar
- RG Adipocytes & Metabolism, Institute for Diabetes & Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health GmbH, 85764 Neuherberg, Germany; German Center for Diabetes Research (DZD), 85764 Neuherberg, Germany; Department of Medicine, Technische Universität München, Munich, Germany.
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9
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Yang L, Zhang Z, Wang D, Jiang Y, Liu Y. Targeting mTOR Signaling in Type 2 Diabetes Mellitus and Diabetes Complications. Curr Drug Targets 2022; 23:692-710. [PMID: 35021971 DOI: 10.2174/1389450123666220111115528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 10/21/2021] [Accepted: 12/01/2021] [Indexed: 11/22/2022]
Abstract
The mechanistic target of rapamycin (mTOR) is a pivotal regulator of cell metabolism and growth. In the form of two different multi-protein complexes, mTORC1 and mTORC2, mTOR integrates cellular energy, nutrient and hormonal signals to regulate cellular metabolic homeostasis. In type 2 diabetes mellitus (T2DM) aberrant mTOR signaling underlies its pathological conditions and end-organ complications. Substantial evidence suggests that two mTOR-mediated signaling schemes, mTORC1-p70S6 kinase 1 (S6K1) and mTORC2-protein kinase B (AKT), play a critical role in insulin sensitivity and that their dysfunction contributes to development of T2DM. This review summaries our current understanding of the role of mTOR signaling in T2DM and its associated complications, as well as the potential use of mTOR inhibitors in treatment of T2DM.
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Affiliation(s)
- Lin Yang
- School of Life Sciences, Beijing University of Chinese Medicine, Beijing 102488, China
| | - Zhixin Zhang
- School of Life Sciences, Beijing University of Chinese Medicine, Beijing 102488, China
| | - Doudou Wang
- School of Life Sciences, Beijing University of Chinese Medicine, Beijing 102488, China
| | - Yu Jiang
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
| | - Ying Liu
- School of Life Sciences, Beijing University of Chinese Medicine, Beijing 102488, China
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