Troponin I isoform expression in human and experimental atrial fibrillation.
BACKGROUND
Atrial fibrillation (AF) is accompanied by re-expression of fetal genes and activation of proteolytic enzymes. In this study both aspects were addressed with respect to troponin I (TnI) isoform expression.


RESULTS
Western blotting and real-time reverse transcription-polymerase chain reaction were used to study TnI isoform expression in patients with paroxysmal or chronic AF and in goats after 1, 2, 4, 8, and 16 weeks of AF. In addition to cardiac TnI (cTnI), low expression of slow-twitch skeletal TnI (ssTnI) protein was found in 60% of patients in sinus rhythm or paroxysmal AF and in 8% of patients with chronic AF. In adult goat atrium, ssTnI protein expression was undetectable. Calcium-dependent degradation of cTnI protein was found in 1 or 2 of 6 animals after 1 to 4 weeks of AF. Although always low, ssTnI mRNA levels were significantly higher in patients who expressed ssTnI protein than in those who did not. Relative ssTnI mRNA expression was significantly lower in patients with paroxysmal AF and chronic AF than in those in sinus rhythm. In goats there was a tendency toward higher relative levels of ssTnI at the onset of AF followed by a normalization when AF had become sustained.


CONCLUSIONS
Atrial re-expression of ssTnI during paroxysmal AF in patients and during the first 2 weeks of pacing-induced AF in goats does not seem to be part of the process of AF-associated cardiomyocyte dedifferentiation but seems to result from transient cardiomyocyte stress at the onset of AF.
Cardiovascular Research Institute Maastricht, University Maastricht, Maastricht, Netherlands. v.thijssen@path.unimaas.nl
Victor L J L
VL
Thijssen
Jannie
J
Ausma
Luisa
L
Gorza
Huub M W
HM
van der Velden
Maurits A
MA
Allessie
Isabelle C
IC
Van Gelder
Marcel
M
Borgers
Guillaume J J M
GJ
van Eys
D000208:Acute Disease; D000818:Animals; D001281:Atrial Fibrillation / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D002118:Calcium / Q000502:physiology; D002908:Chronic Disease; D005318:Fetal Heart / Q000378:metabolism; D005786:Gene Expression Regulation; D006041:Goats / Q000196:embryology; D006801:Humans; D008944:Mitral Valve Insufficiency / Q000235:genetics / Q000378:metabolism; D023421:Models, Animal; D008957:Models, Genetic; D032383:Myocytes, Cardiac / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D019210:Troponin I / Q000096:biosynthesis* / Q000235:genetics
D020033:Protein Isoforms; D012333:RNA, Messenger; D019210:Troponin I; D002118:Calcium