acclimation on Pacific bluefin tuna (Thunnus orientalis) cardiac transcriptome.
Am J Physiol Regul Integr Comp Physiol 305: R1010–R1020, 2013.
First published September 4, 2013; doi:10.1152/ajpregu.00254.2013.—
Little is known about the mechanisms underpinning thermal plasticity
of vertebrate hearts. Bluefin tuna hearts offer a unique model to
investigate processes underlying thermal acclimation. Their hearts,
while supporting an endothermic physiology, operate at ambient
temperature, and are presented with a thermal challenge when migrating
to different thermal regimes. Here, we examined the molecular
responses in atrial and ventricular tissues of Pacific bluefin tuna
acclimated to 14°C, 20°C, and 25°C. Quantitative PCR studies
showed an increase in sarcoplasmic reticulum Ca2 ATPase gene
expression with cold acclimation and an induction of Na/Ca2-
exchanger gene at both cold and warm temperatures. These data
provide evidence for thermal plasticity of excitation-contraction coupling
gene expression in bluefin tunas and indicate an increased
capacity for internal Ca2 storage in cardiac myocytes at 14°C.
Transcriptomic analysis showed profound changes in cardiac tissues
with acclimation. A principal component analysis revealed that temperature
effect was greatest on gene expression in warm-acclimated
atrium. Overall data showed an increase in cardiac energy metabolism
at 14°C, potentially compensating for cold temperature to optimize
bluefin tuna performance in colder oceans. In contrast, metabolic
enzyme activity and gene expression data suggest a decrease in ATP
production at 25°C. Expression of genes involved in protein turnover
and molecular chaperones was also decreased at 25°C. Expression of
genes involved in oxidative stress response and programmed cell
death suggest an increase in oxidative damage and apoptosis at 25°C,
particularly in the atrium. These findings provide insights into molecular
processes that may characterize cardiac phenotypes at upper
thermal limits of teleosts.