Connexin40 messenger ribonucleic acid is positively regulated by thyroid hormone (TH) acting in cardiac atria via the TH receptor.
Thyroid hormone (TH) regulates many cardiac genes via nuclear thyroid receptors, and hyperthyroidism is frequently associated with atrial fibrillation. Electrical activity propagation in myocardium depends on the transfer of current at gap junctions, and connexins (Cxs) 40 and 43 are the predominant junction proteins. In mice, Cx40, the main Cx involved in atrial conduction, is restricted to the atria and fibers of the conduction system, which also express Cx43. We studied cardiac expression of Cx40 and Cx43 in conjunction with electrocardiogram studies in mice overexpressing the dominant negative mutant thyroid hormone receptor-beta Delta337T exclusively in cardiomyocytes [myosin heavy chain (MHC-mutant)]. These mice develop the cardiac hypothyroid phenotype in the presence of normal serum TH. Expression was also examined in wild-type mice rendered hypothyroid or hyperthyroid by pharmacological treatment. Atrial Cx40 mRNA and protein levels were decreased (85 and 55%, respectively; P < 0.001) in MHC-mt mice. Atrial and ventricular Cx43 mRNA levels were not significantly changed. Hypothyroid and hyperthyroid animals showed a 25% decrease and 40% increase, respectively, in Cx40 mRNA abundance. However, MHC-mt mice presented very low Cx40 mRNA expression regardless of whether they were made hypothyroid or hyperthyroid. Atrial depolarization velocity, as represented by P wave duration in electrocardiograms of unanesthetized mice, was extremely reduced in MHC-mt mice, and to a lesser extent also in hypothyroid mice (90 and 30% increase in P wave duration). In contrast, this measure was increased in hyperthyroid mice (19% decrease in P wave duration). Therefore, this study reveals for the first time that Cx40 mRNA is up-regulated by TH acting in cardiac atria via the TH receptor and that this may be one of the mechanisms contributing to atrial conduction alterations in thyroid dysfunctions.
Almeida
Norma A S
NA
Laboratório de Endocrinologia Molecular, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21949-900, Brazil.
Cordeiro
Aline
A
Machado
Danielle S
DS
Souza
Luana L
LL
Ortiga-Carvalho
Tânia M
TM
Campos-de-Carvalho
Antonio C
AC
Wondisford
Fredric E
FE
Pazos-Moura
Carmen C
CC
D000818:Animals; D018031:Connexin 43 / Q000235:genetics; D017630:Connexins / Q000235:genetics*; D017931:DNA Primers; D004562:Electrocardiography; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D018995:Myosin Heavy Chains / Q000235:genetics; D011486:Protein C / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics*; D011988:Receptors, Thyroid Hormone / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013963:Thyroid Hormones / Q000494:pharmacology*; D014284:Triiodothyronine / Q000097:blood; D000097003:Gap Junction alpha-5 Protein
D018031:Connexin 43; D017630:Connexins; D017931:DNA Primers; D018995:Myosin Heavy Chains; D011486:Protein C; D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D013963:Thyroid Hormones; D014284:Triiodothyronine; D000097003:Gap Junction alpha-5 Protein