Regulation of sarcoplasmic reticulum ca2+ atpase (serca2)
expression by thyroid hormone in cultured chick embryo
cardiomyocytes.
Fisher, David J, Sharon Phillips, Tim McQuinn.
Lillie Frank Abercrombie Section of Pediatric Cardiology,
Department of Pediatrics, Baylor College of Medicine and Texas
Children's Hospital, Houston, TX, 77030, and the Section of Pediatric
Cardiology, Department of Pediatrics, Ohio State University and
Children's Hospital, Columbus, OH, 43205
APStracts 2:0356H, 1995.
Previous studies have demonstrated that there is a physiological
perinatal increase in cardiac sarcoplasmic reticulum (SR) Ca2+ ATPase
expression, in a manner that was consistent with pretranslational,
possibly transcriptional regulation. The present study investigated
the potential role of thyroid hormone in this process. We isolated
cardiomyocytes from 11 day old White Leghorn chick embryos (term = 21
days) by enzymatic digestion and density gradient centrifugation. The
cardiomyocytes were cultured in 10-8 M triiodothyronine (T3) for 48
hours,, after which we measured SR Ca2+ ATPase mRNA and
immunodetectable protein contents, as well as SR dependent 45Ca2+
uptake rates. Actinomycin D was added to some of the cultures to
determine if the effect of T3 was mediated through regulation of
transcription. To further investigate the mechanism of action, we
also examined the effect of T3 on expression of the same gene in
monkey kidney CV-1 cells, which do not express thyroid hormone
receptors. T3 increased cardiomyocyte SR Ca2+ pump mRNA content by
289% +/- 35% (n=8; p<0.01) and immunodetectable SR Ca2+ pump protein
content by 255% +/- 44% (n=7; p<0.01). T3 also increased the oxalate
sensitive (i.e., SR Ca2+ pump specific) 45Ca2+ uptake rate by 189%
+/- 22% in digitonin permeabilized cultured cardiomyocytes (n=5;
p<0.01). In contrast, T3 had no significant effect on the total
cellular RNA or protein contents in the cardiomyocyte, and there was
no effect of T3 on Ca2+ ATPase mRNA content in the thyroid hormone
receptor-negative CV-1 cells. The stimulatory effects of T3 on SR
Ca2+ pump mRNA and immunodetectable protein contents were blocked
when transcription was inhibited with actinomycin D. These data
demonstrate that T3 increases expression of the cardiac SR Ca2+ pump,
that the effect can be localized to the cardiomyocyte, and that the
effect is dependent on thyroid hormone receptors. These data are
consistent with pre-translational, probably transcriptional
regulation of the cardiac SR Ca2+ pump gene (SERCA2) by thyroid
hormone. The physiological gestation-associated increase in thyroid
hormone may be at least partially responsible for the previously
demonstrated perinatal increase in cardiac SR Ca2+ pump expression.
Mammalian contractile function is less forceful and relaxation is
slower in the developing fetal and newborn heart compared to adults.
This is evident clinically as a significant mortality related to
diminished cardiovascular reserve in normally developed human
newborns when extreme stresses such as sepsis produce cardiac
failure.
Received 27 January 1995; accepted in final form 31 July 1995.
APS Manuscript Number H78-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.