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Open Access Highly Accessed Original investigation

Diabetic cardiomyopathy is associated with defective myocellular copper regulation and both defects are rectified by divalent copper chelation

Shaoping Zhang12, Hong Liu1, Greeshma V Amarsingh1, Carlos C H Cheung1, Sebastian Hogl1, Umayal Narayanan1, Lin Zhang1, Selina McHarg3, Jingshu Xu12, Deming Gong1, John Kennedy4, Bernard Barry4, Yee Soon Choong1, Anthony R J Phillips12 and Garth J S Cooper1235*

Author Affiliations

1 The School of Biological Sciences, Faculty of Science, University of Auckland, Auckland, New Zealand

2 The Maurice Wilkins Centre for Molecular Biodiscovery, Faculty of Science, University of Auckland, Auckland, New Zealand

3 Centre for Advanced Discovery and Experimental Therapeutics, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, and the Centre for Diabetes and Endocrinology, Institute of Human Development, Faculty of Medical and Human Sciences, University of Manchester, Manchester M13 9WL, UK

4 National Isotope Centre, GNS Science, Gracefield, Wellington, New Zealand

5 Department of Pharmacology, Medical Sciences Division, University of Oxford, Oxford, UK

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Cardiovascular Diabetology 2014, 13:100  doi:10.1186/1475-2840-13-100

Published: 14 June 2014

Abstract

Background

Heart disease is the leading cause of death in diabetic patients, and defective copper metabolism may play important roles in the pathogenesis of diabetic cardiomyopathy (DCM). The present study sought to determine how myocardial copper status and key copper-proteins might become impaired by diabetes, and how they respond to treatment with the Cu (II)-selective chelator triethylenetetramine (TETA) in DCM.

Methods

Experiments were performed in Wistar rats with streptozotocin (STZ)-induced diabetes with or without TETA treatment. Cardiac function was analyzed in isolated-perfused working hearts, and myocardial total copper content measured by particle-induced x-ray emission spectroscopy (PIXE) coupled with Rutherford backscattering spectrometry (RBS). Quantitative expression (mRNA and protein) and/or activity of key proteins that mediate LV-tissue-copper binding and transport, were analyzed by combined RT-qPCR, western blotting, immunofluorescence microscopy, and enzyme activity assays. Statistical analysis was performed using Student’s t-tests or ANOVA and p-values of < 0.05 have been considered significant.

Results

Left-ventricular (LV) copper levels and function were severely depressed in rats following 16-weeks’ diabetes, but both were unexpectedly normalized 8-weeks after treatment with TETA was instituted. Localized myocardial copper deficiency was accompanied by decreased expression and increased polymerization of the copper-responsive transition-metal-binding metallothionein proteins (MT1/MT2), consistent with impaired anti-oxidant defences and elevated susceptibility to pro-oxidant stress. Levels of the high-affinity copper transporter-1 (CTR1) were depressed in diabetes, consistent with impaired membrane copper uptake, and were not modified by TETA which, contrastingly, renormalized myocardial copper and increased levels and cell-membrane localization of the low-affinity copper transporter-2 (CTR2). Diabetes also lowered indexes of intracellular (IC) copper delivery via the copper chaperone for superoxide dismutase (CCS) to its target cuproenzyme, superoxide dismutase-1 (SOD1): this pathway was rectified by TETA treatment, which normalized SOD1 activity with consequent bolstering of anti-oxidant defenses. Furthermore, diabetes depressed levels of additional intracellular copper-transporting proteins, including antioxidant-protein-1 (ATOX1) and copper-transporting-ATPase-2 (ATP7B), whereas TETA elevated copper-transporting-ATPase-1 (ATP7A).

Conclusions

Myocardial copper deficiency and defective cellular copper transport/trafficking are revealed as key molecular defects underlying LV impairment in diabetes, and TETA-mediated restoration of copper regulation provides a potential new class of therapeutic molecules for DCM.

Keywords:
Diabetic cardiomyopathy; Copper-deficiency cardiomyopathy; Left-ventricular dysfunction; Myocellular copper; Copper transporters; Superoxide dismutase 1; Copper chaperones; Cu (II)-chelation; Copper metalation; Heart failure