title: MuRF2 regulates PPARγ1 activity to protect against diabetic cardiomyopathy and enhance weight gain induced by a high fat diet.
abstract: BACKGROUND
  In diabetes mellitus the morbidity and mortality of cardiovascular disease is increased and represents an important independent mechanism by which heart disease is exacerbated. The pathogenesis of diabetic cardiomyopathy involves the enhanced activation of PPAR transcription factors, including PPARα, and to a lesser degree PPARβ and PPARγ1. How these transcription factors are regulated in the heart is largely unknown. Recent studies have described post-translational ubiquitination of PPARs as ways in which PPAR activity is inhibited in cancer. However, specific mechanisms in the heart have not previously been described. Recent studies have implicated the muscle-specific ubiquitin ligase muscle ring finger-2 (MuRF2) in inhibiting the nuclear transcription factor SRF. Initial studies of MuRF2-/- hearts revealed enhanced PPAR activity, leading to the hypothesis that MuRF2 regulates PPAR activity by post-translational ubiquitination.
  
  
  METHODS
  MuRF2-/- mice were challenged with a 26-week 60% fat diet designed to simulate obesity-mediated insulin resistance and diabetic cardiomyopathy. Mice were followed by conscious echocardiography, blood glucose, tissue triglyceride, glycogen levels, immunoblot analysis of intracellular signaling, heart and skeletal muscle morphometrics, and PPARα, PPARβ, and PPARγ1-regulated mRNA expression.
  
  
  RESULTS
  MuRF2 protein levels increase ~20% during the development of diabetic cardiomyopathy induced by high fat diet. Compared to littermate wildtype hearts, MuRF2-/- hearts exhibit an exaggerated diabetic cardiomyopathy, characterized by an early onset systolic dysfunction, larger left ventricular mass, and higher heart weight. MuRF2-/- hearts had significantly increased PPARα- and PPARγ1-regulated gene expression by RT-qPCR, consistent with MuRF2's regulation of these transcription factors in vivo. Mechanistically, MuRF2 mono-ubiquitinated PPARα and PPARγ1 in vitro, consistent with its non-degradatory role in diabetic cardiomyopathy. However, increasing MuRF2:PPARγ1 (>5:1) beyond physiological levels drove poly-ubiquitin-mediated degradation of PPARγ1 in vitro, indicating large MuRF2 increases may lead to PPAR degradation if found in other disease states.
  
  
  CONCLUSIONS
  Mutations in MuRF2 have been described to contribute to the severity of familial hypertrophic cardiomyopathy. The present study suggests that the lack of MuRF2, as found in these patients, can result in an exaggerated diabetic cardiomyopathy. These studies also identify MuRF2 as the first ubiquitin ligase to regulate cardiac PPARα and PPARγ1 activities in vivo via post-translational modification without degradation.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, 111 Mason Farm Road, MBRB 2340B, Chapel Hill, NC, USA. heju@email.unc.edu.|General Hospital of Ningxia Medical University, Yinchuan, Ningxia, People's Republic of China. heju@email.unc.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: He
authors.affiliation: Department of Surgery, University of North Carolina, Chapel Hill, NC, USA. MQuintan@unch.unc.edu.
authors.forename: Megan T
authors.initials: MT
authors.lastname: Quintana
authors.affiliation: Department of Biology, University of North Carolina, Chapel Hill, NC, USA. sullivj@live.unc.edu.
authors.forename: Jenyth
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authors.lastname: Sullivan
authors.affiliation: McAllister Heart Institute, University of North Carolina, 111 Mason Farm Road, MBRB 2340B, Chapel Hill, NC, USA. parry@med.unc.edu.
authors.forename: Traci
authors.initials: T
authors.lastname: L Parry
authors.affiliation: Department of Nutrition, University of North Carolina, Chapel Hill, NC, USA. tgreven@live.unc.edu.
authors.forename: Trisha
authors.initials: T
authors.lastname: J Grevengoed
authors.affiliation: McAllister Heart Institute, University of North Carolina, 111 Mason Farm Road, MBRB 2340B, Chapel Hill, NC, USA. schisler@med.unc.edu.|Department of Pharmacology, University of North Carolina, Chapel Hill, NC, USA. schisler@med.unc.edu.
authors.forename: Jonathan C
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authors.lastname: Schisler
authors.affiliation: Department of Internal Medicine (Cardiology), University of Texas Southwestern Medical Center, Dallas, TX, USA. joseph.hill@UTsouthwestern.edu.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Hill
authors.affiliation: Department of Health Promotions and Development, School of Nursing, University of Pittsburgh, Pittsburgh, PA, USA. CEY4@pitt.edu.
authors.forename: Cecelia C
authors.initials: CC
authors.lastname: Yates
authors.affiliation: Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch, 7600, South Africa. rfmapanga@sun.ac.za.
authors.forename: Rudo F
authors.initials: RF
authors.lastname: Mapanga
authors.affiliation: Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch, 7600, South Africa. mfessop@sun.ac.za.
authors.forename: M Faadiel
authors.initials: MF
authors.lastname: Essop
authors.affiliation: Department of Surgery, University of North Carolina, Chapel Hill, NC, USA. William.Stansfield@uhn.ca.
authors.forename: William E
authors.initials: WE
authors.lastname: Stansfield
authors.affiliation: Sarah W. Stedman Nutrition and Metabolism Center, Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC, USA. james.bain@duke.edu.|Division of Endocrinology, Metabolism, and Nutrition, Department of Medicine, Duke University Medical Center, Durham, NC, USA. james.bain@duke.edu.
authors.forename: James R
authors.initials: JR
authors.lastname: Bain
authors.affiliation: Sarah W. Stedman Nutrition and Metabolism Center, Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC, USA. chris.newgard@duke.edu.|Division of Endocrinology, Metabolism, and Nutrition, Department of Medicine, Duke University Medical Center, Durham, NC, USA. chris.newgard@duke.edu.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Newgard
authors.affiliation: Sarah W. Stedman Nutrition and Metabolism Center, Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC, USA. michael.muehlbauer@duke.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Muehlbauer
authors.affiliation: East Chapel Hill High School, Chapel Hill, NC, USA. yipinhan97@gmail.com.
authors.forename: Yipin
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authors.lastname: Han
authors.affiliation: Novartis, Novartis Institutes for BioMedical Research, Inc., 400 Technology Square, Boston, MA, 601-4214, USA. brian.clarke@novartis.com.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Clarke
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, 111 Mason Farm Road, MBRB 2340B, Chapel Hill, NC, USA. monte_willis@med.unc.edu.|McAllister Heart Institute, University of North Carolina, 111 Mason Farm Road, MBRB 2340B, Chapel Hill, NC, USA. monte_willis@med.unc.edu.
authors.forename: Monte S
authors.initials: MS
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mesh_terms: D000818:Animals; D009202:Cardiomyopathies / Q000201:enzymology / Q000209:etiology / Q000235:genetics / Q000517:prevention & control*; D059305:Diet, High-Fat; D004195:Disease Models, Animal; D005260:Female; D005786:Gene Expression Regulation; D005838:Genotype; D007333:Insulin Resistance; D008297:Male; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology*; D009765:Obesity / Q000201:enzymology / Q000209:etiology* / Q000235:genetics; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D054875:Ubiquitination; D015430:Weight Gain
chemical_list: D009124:Muscle Proteins; D047495:PPAR gamma; D012333:RNA, Messenger; C502755:muscle RING finger 2 protein, mouse