Hyperglycemia-Induced Changes in ZIP7 and ZnT7 Expression Cause Zn 2+ Release From the Sarco(endo)plasmic Reticulum and Mediate ER Stress in the Heart

• Published in: Diabetes (New York, N.Y.) Vol. 66; no. 5; p. 1346
• Main Authors: Tuncay, Erkan, Bitirim, Verda C, Durak, Aysegul, Carrat, Gaelle R J, Taylor, Kathryn M, Rutter, Guy A, Turan, Belma
• Format: Journal Article
• Language: English
• Published: United States 01.05.2017
• Subjects: Animals; Blotting, Western; Casein Kinase II - genetics; Cation Transport Proteins - genetics; Cation Transport Proteins - metabolism; Diabetes Mellitus, Experimental - genetics; Diabetes Mellitus, Experimental - metabolism; Diabetes Mellitus, Type 1 - genetics; Diabetes Mellitus, Type 1 - metabolism; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum Stress - genetics; Heart Ventricles - cytology; Hyperglycemia - genetics; Hyperglycemia - metabolism; Immunoprecipitation; Myocytes, Cardiac - metabolism; Phosphorylation; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - metabolism; Sarcoplasmic Reticulum - metabolism; Zinc - metabolism
• ISSN: 1939-327X

Changes in cellular free Zn concentration, including those in the sarco(endo)plasmic reticulum [S(E)R], are primarily coordinated by Zn transporters (ZnTs) whose identity and role in the heart are not well established. We hypothesized that ZIP7 and ZnT7 transport Zn in opposing directions across the S(E)R membrane in cardiomyocytes and that changes in their activity play an important role in the development of ER stress during hyperglycemia. The subcellular S(E)R localization of ZIP7 and ZnT7 was determined in cardiomyocytes and in isolated S(E)R preparations. Markedly increased mRNA and protein levels of ZIP7 were observed in ventricular cardiomyocytes from diabetic rats or high-glucose-treated H9c2 cells while ZnT7 expression was low. In addition, we observed increased ZIP7 phosphorylation in response to high glucose in vivo and in vitro. By using recombinant-targeted Förster resonance energy transfer sensors, we show that hyperglycemia induces a marked redistribution of cellular free Zn , increasing cytosolic free Zn and lowering free Zn in the S(E)R. These changes involve alterations in ZIP7 phosphorylation and were suppressed by small interfering RNA-mediated silencing of CK2α. Opposing changes in the expression of ZIP7 and ZnT7 were also observed in hyperglycemia. We conclude that subcellular free Zn redistribution in the hyperglycemic heart, resulting from altered ZIP7 and ZnT7 activity, contributes to cardiac dysfunction in diabetes.