Role of ZIP7 in Regulation of Cytosolic Free Zn2+ Level in Mammalian Cardiomyocytes

Abstract

Zinc (as Zn2+), increasingly recognized as an important trace element, has physiological role in mammalian cell function. Resting intracellular free Zn2+ level ([Zn2+]i) can be greatly increased by thiol-reactive oxidants or high glucose that contributes to oxidant-induced alterations in EC-coupling of cardiomyocytes. Since Zn2+ is important in cellular physiology, very little is known how [Zn2+]i is controlled and stored intracellularly in cardiomyocytes. Therefore, in the present study we aimed to investigate the role of ZIP7 on regulation of [Zn2+]i in cardiomycoytes. We first used newly-developed genetically-encoded FRET-based sensors to monitor cytosolic (CYS), mitochondrial (MitC) and endoplasmic reticulum (ER) [Zn2+]. Our data showed that [Zn2+] levels in these compartments were about 0.5, 5.0 and 0.2 nM, respectively in isolated left ventricular cardiomyocytes. Since expression but not location of ZIP7 has been shown in the heart tissue, inhere, we tested whether Zn2+ transport from ER into cytosol by a transporter ZIP7 thereby responsible for cytosolic/S(E)R Zn2+ homeostasis in cardiomyocytes under pathological condition. Our data have shown that both protein level and expression of ZIP7 increased in either cardiomyocytes isolated from streptozotocin-induced diabetic rat heart or high glucose (25mM; 24-hours) incubated H9c2 cells. Our immunofluorescence analysis also demonstrated that ZIP7 is localised in ER but not in Golgi apparatus in these cells. Furthermore, ZIP7 knocked-down in cardiomycoytes induced a significant reduction of cytosolic [Zn2+]. All experimental data showed that ER is a Zn2+ pool and ZIP7 has a crucial role in regulation of cytosolic Zn2+ in mammalian cardiomyocytes (Supported by TUBITAK SBAG-113S466, COST Action TD1304, EFSD Fellowships).