Cardiac overexpression of metallothionein rescues cold exposure-induced myocardial contractile dysfunction through attenuation of cardiac fibrosis despite cardiomyocyte mechanical anomalies.

Cold exposure is associated with an increased prevalence of cardiovascular disease although the mechanism is unknown. Metallothionein, a heavy-metal-scavenging antioxidant, protects against cardiac anomalies. This study was designed to examine the impact of metallothionein on cold exposure-induced myocardial dysfunction, intracellular Ca(2+) derangement, fibrosis, endoplasmic reticulum (ER) stress, and apoptosis. Echocardiography, cardiomyocyte function, and Masson trichrome staining were evaluated in Friend virus B (FVB) and cardiac-specific metallothionein transgenic mice after cold exposure (3 months, 4 °C). Cold exposure increased plasma levels of norepinephrine, endothelin-1, and TGF-β; reduced plasma NO levels and cardiac antioxidant capacity; enlarged ventricular end-systolic diameter; compromised fractional shortening; promoted reactive oxygen species (ROS) production and apoptosis; and suppressed the ER stress markers Bip, calregulin, and phospho-eIF2α, accompanied by cardiac fibrosis and elevated levels of matrix metalloproteinases and Smad-2/3 in FVB mice. Cold exposure-induced echocardiographic, histological, ER stress, ROS, apoptotic, and fibrotic signaling changes (but not plasma markers) were greatly improved by metallothionein. In vitro metallothionein induction by zinc chloride ablated H(2)O(2)- but not TGF-β-induced cell proliferation in fibroblasts. In summary, our data suggest that metallothionein protects against cold exposure-induced cardiac anomalies possibly through attenuation of myocardial fibrosis.