title: Diminished GATA4 protein levels contribute to hyperglycemia-induced cardiomyocyte injury.
abstract: Hyperglycemia is an independent risk factor for diabetic heart failure. However, the mechanisms that mediate hyperglycemia-induced cardiac damage remain poorly understood. The transcription factor GATA4 is essential for cardiac homeostasis, and its protein levels are dramatically reduced in the heart in response to diverse pathologic stresses. In this study, we investigated if hyperglycemia affects GATA4 expression in cardiomyocytes and if enhancing GATA4 signaling could attenuate hyperglycemia-induced cardiomyocyte injury. In cultured rat cardiomyocytes, high glucose (HG, 25 or 40 mm) markedly reduced GATA4 protein levels as compared with normal glucose (NG, 5.5 mm). Equal amount of mannitol did not affect GATA4 protein expression (NG, 100 +/- 12%; mannitol, 97 +/- 8%, versus HG, 43 +/- 16%, p < 0.05). The GATA4 mRNA content, either steady-state or polysome-associated, remained unchanged. HG-induced GATA4 reduction was reversed by MG262, a specific proteasome inhibitor. HG did not activate the ubiquitin proteasome system (UPS) in cardiomyocytes as indicated by a UPS reporter, nor did it increase the peptidase activities or protein expression of the proteasomal subunits. However, the mRNA levels of ubiquitin-protein isopeptide ligase (E3) carboxyl terminus of Hsp70-interacting protein (CHIP) were markedly increased in HG-treated cardiomyocytes. CHIP overexpression promoted GATA4 protein degradation, whereas small interfering RNA-mediated CHIP knockdown prevented HG-induced GATA4 depletion. Moreover, overexpression of GATA4 blocked HG-induced cardiomyocyte death. Also, GATA4 protein levels were diminished in the hearts of streptozotocin and db/db diabetic mice (44 +/- 7% and 67 +/- 13% of control, p < 0.05), which correlated with increased CHIP mRNA abundance. In summary, increased GATA4 protein degradation may be an important mechanism that contributes to hyperglycemic cardiotoxicity.
authors.affiliation: Cardiovascular Research Institute, Sanford Research, University of South Dakota Sanford School of Medicine, Sioux Falls, SD 57105, USA.
authors.forename: Satoru
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Kai
authors.initials: K
authors.lastname: Mao
authors.forename: Hanqiao
authors.initials: H
authors.lastname: Zheng
authors.forename: Xuejun
authors.initials: X
authors.lastname: Wang
authors.forename: Cam
authors.initials: C
authors.lastname: Patterson
authors.forename: Timothy D
authors.initials: TD
authors.lastname: O'Connell
authors.forename: Qiangrong
authors.initials: Q
authors.lastname: Liang
mesh_terms: D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D050991:GATA4 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism; D006321:Heart / Q000502:physiology; D006706:Homeostasis; D006943:Hyperglycemia / Q000150:complications / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000473:pathology*; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D018076:DNA, Complementary; D050991:GATA4 Transcription Factor; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D005947:Glucose