Heavy metal scavenger metallothionein attenuates ER stress-induced myocardial contractile anomalies: role of autophagy.

Endoplasmic reticulum (ER) stress increases the risk of cardiovascular morbidity and mortality although the underlying mechanism remains elusive. This study was designed to examine the impact of cardiac over-expression of metallothionein, a cysteine-rich heavy metal scavenger, on ER stress-induced changes in myocardial function and underlying mechanism involved with a focus on autophagy. Wild-type friendly virus B (FVB) and metallothionein transgenic mice were subjected to the ER stress inducer tunicamycin (1 mg/kg). Our results showed that ER stress led to compromised echocardiographic and cardiomyocyte contractile function, intracellular Ca(2+) mishandling. Tunicamycin promoted ER stress and oxidative stress, increased left ventricular end systolic and diastolic diameter, as well as suppressed fractional shortening and whole heart contractility, the effects of which were significantly attenuated or ablated by metallothionein. Levels of the autophagy markers such as phosphorylated ULK1, Atg5, Atg7, LC3B and the autophagy adaptor p62 were significantly upregulated. These ER stress-induced changes in myocardial function, autophagy and autophagy signaling were distinctly mitigated or alleviated by metallothionein. Inhibition of autophagy using 3-methyladenine in vitro reversed ER stress-induced cardiomyocyte contractile defects. Meanwhile, ER stress-induced cardiomyocyte dysfunction was attenuated by the antioxidant N-acetylcysteine. Collectively, these findings suggested that metallothionein protects against ER stress-induced cardiac anomalies possibly through attenuation of cardiac autophagy.