Increased free Zn2+ correlates induction of sarco(endo)plasmic reticulum stress via altered expression levels of Zn2+-transporters in heart failure

Zn2+-homoeostasis including free Zn2+ ([Zn2+](i)) is regulated through Zn2+-transporters and their comprehensive understanding may be important due to their contributions to cardiac dysfunction. Herein, we aimed to examine a possible role of Zn2+-transporters in the development of heart failure (HF) via induction of ER stress. We first showed localizations of ZIP8, ZIP14 and ZnT8 to both sarcolemma and S(E)R in ventricular cardiomyocytes (H9c2 cells) using confocal together with calculated Pearson's coefficients. The expressions of ZIP14 and ZnT8 were significantly increased with decreased ZIP8 level in HF. Moreover, [Zn2+](i) was significantly high in doxorubicin-treated H9c2 cells compared to their controls. We found elevated levels of ER stress markers, GRP78 and CHOP/Gadd153, confirming the existence of ER stress. Furthermore, we measured markedly increased total PKC and PKC alpha expression and PKC alpha-phosphorylation in HF. A PKC inhibition induced significant decrease in expressions of these ER stress markers compared to controls. Interestingly, direct increase in [Zn2+](i) using zinc-ionophore induced significant increase in these markers. On the other hand, when we induced ER stress directly with tunicamycin, we could not observe any effect on expression levels of these Zn2+ transporters. Additionally, increased [Zn2+](i) could induce marked activation of PKC alpha. Moreover, we observed marked decrease in [Zn2+](i) under PKC inhibition in H9c2 cells. Overall, our present data suggest possible role of Zn2+ transporters on an intersection pathway with increased [Zn2+](i) and PKC alpha activation and induction of HF, most probably via development of ER stress. Therefore, our present data provide novel information how a well-controlled [Zn2+](i) via Zn2+ transporters and PKC alpha can be important therapeutic approach in prevention/treatment of HF.