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

Abstract

Cold exposure is associated with an increased prevalence for 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 Ca2+ derangement, fibrosis, ER stress and apoptosis. Echocardiographic, cardiomyocyte function and Masson trichrome staining were evaluated in friendly virus B (FVB) and cardiac-specific metallothionein transgenic mice following cold exposure (3 mo, 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 ROS production and apoptosis, and suppressed ER stress marker Bip, calregulin and phospho-eIF2α accompanied with 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 H2O2- but not TGF-β-induced cell proliferation in fibroblasts. In summary, our data suggested that metallothionein protects against cold exposure-induced cardiac anomalies possibly through attenuation of myocardial fibrosis.

Heavy metal scavenger metallothionein mitigates deep hypothermia-induced myocardial contractile anomalies: role of autophagy

“…Fluorescence was calibrated with InSpeck microspheres (Molecular Probes). An average of 100 cells was evaluated using the grid crossing method in 15 visual fields per isolation (34).…”

“…The precipitate was resuspended in 6 M guanidine solution and centrifuged for 3 min to remove any insoluble debris. The maximum absorbance (360 -390 nm) of supernatant was read against appropriate blanks (water, 2 M HCl), and carbonyl content was calculated using the molar absorption coefficient of 22,000 M/cm (34).…”

Inhibition of NADPH oxidase 2 (NOX2) prevents sepsis-induced cardiomyopathy by improving calcium handling and mitochondrial function

“…Mitochondrial dysfunction has been a consistent finding in sepsis models, with decreased mitochondrial oxidative phosphorylation and decreased transcription of mitochondrial genes (11)(12)(13). Abnormalities of intracellular calcium handling have also been observed in cardiomyocytes from animal models of sepsis (14)(15)(16)(17). Multiple stress-related kinases are activated in the heart during sepsis, including protein kinase C (PKC) and c-Jun N-terminal kinase (JNK) (18,19).…”

Is cold acclimation of benefit to hibernating rodents?

“…However, CA hamsters were adversely affected on acute cooling, displaying hypotension due to decreased systolic and diastolic pressures, coupled with reduced f H , leading to a lower cardiac output. As LV blood flow was preserved, implying that oxygen delivery to the myocardium was potentially better for the CA hamster than euthermic hamster on acute cooling, functional impairment was likely not perfusion-mediated (Zhang et al, 2012). One possible outcome of CA may also be the chronic β-adrenergic desensitisation of cardiac tissue, previously noted for CA rat hearts (Cheng and Hauton, 2008).…”

“…Hence, a reduction in the maximum oxygen diffusion distance for myocardium potentially increased the delivery of oxygen following CA. Cardiac fibrosis, noted following prolonged exposure to cold (Zhang et al, 2012), which would increase ventricle stiffness, was not observed. However, the changes to developed pressure and RPP following cooling directly support the thermal sensitivity of the LV.…”