title: Molecular role of GATA binding protein 4 (GATA-4) in hyperglycemia-induced reduction of cardiac contractility.
abstract: BACKGROUND
  Diabetic cardiomyopathy, a diabetes-specific complication, refers to a disorder that eventually leads to left ventricular hypertrophy in addition to diastolic and systolic dysfunction. In recent studies, hyperglycemia-induced reactive oxygen species (ROS) in cardiomyocytes have been linked to diabetic cardiomyopathy. GATA binding protein 4 (GATA-4) regulates the expression of many cardio-structural genes including cardiac troponin-I (cTnI).
  
  
  METHODS
  Streptozotocin-induced diabetic rats and H9c2 embryonic rat cardiomyocytes treated with a high concentration of glucose (a D-glucose concentration of 30 mM was used and cells were cultured for 24 hr) were used to examine the effect of hyperglycemia on GATA-4 accumulation in the nucleus. cTnI expression was found to be linked to cardiac tonic dysfunction, and we evaluated the expression levels of cTnI and GATA-4 by Western blot analysis.
  
  
  RESULTS
  Cardiac output was lowered in STZ-induced diabetic rats. In addition, higher expressions of cardiac troponin I (cTnI) and phosphorylated GATA-4 were identified in these rats by Western blotting. The changes were reversed by treatment with insulin or phlorizin after correction of the blood sugar level. In H9c2 cells, ROS production owing to the high glucose concentration increased the expression of cTnI and GATA-4 phosphorylation. However, hyperglycemia failed to increase the expression of cTnI when GATA-4 was silenced by small interfering RNA (siRNA) in H9c2 cells. Otherwise, activation of ERK is known to be a signal for phosphorylation of serine105 in GATA-4 to increase the DNA binding ability of this transcription factor. Moreover, GSK3β could directly interact with GATA-4 to cause GATA-4 to be exported from the nucleus. GATA-4 nuclear translocation and GSK3β ser9 phosphorylation were both elevated by a high glucose concentration in H9c2 cells. These changes were reversed by tiron (ROS scavenger), PD98059 (MEK/ERK inhibitor), or siRNA of GATA-4. Cell contractility measurement also indicated that the high glucose concentration decreased the contractility of H9c2 cells, and this was reduced by siRNA of GATA-4.
  
  
  CONCLUSIONS
  Hyperglycemia can cause systolic dysfunction and a higher expression of cTnI in cardiomyocytes through ROS, enhancing MEK/ERK-induced GATA-4 phosphorylation and accumulation in the cell nucleus.
authors.affiliation: Department of Medical Research, Chi-Mei Medical Center, No, 901 Chon-Hwa Road, Yong Kang, Tainan City, Taiwan.
authors.forename: Po-Ming
authors.initials: PM
authors.lastname: Ku
authors.forename: Li-Jen
authors.initials: LJ
authors.lastname: Chen
authors.forename: Jia-ru
authors.initials: JR
authors.lastname: Liang
authors.forename: Kai-Chun
authors.initials: KC
authors.lastname: Cheng
authors.forename: Yin-Xiao
authors.initials: YX
authors.lastname: Li
authors.forename: Juei-Tang
authors.initials: JT
authors.lastname: Cheng
mesh_terms: D000818:Animals; D002302:Cardiac Output / Q000502:physiology*; D006332:Cardiomegaly / Q000209:etiology* / Q000378:metabolism* / Q000503:physiopathology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000150:complications* / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D050991:GATA4 Transcription Factor / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006943:Hyperglycemia / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D013311:Streptozocin / Q000009:adverse effects; D019210:Troponin I / Q000378:metabolism
chemical_list: D050991:GATA4 Transcription Factor; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D019210:Troponin I; D013311:Streptozocin; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases; D005947:Glucose